Field

This invention relates to transmission systems, particularly but not exclusively to vehicle transmission systems. Another aspect of the present invention relates to a vehicle incorporating such a transmission system. A novel variator that can be employed in the transmission system herein disclosed is also described.

This application claims priority from UK patent application GB1212367.5; and the content of this prior UK patent application is incorporated herein by reference as though it were reproduced in this document in full. Applicant's intention is that information should be freely transferrable between these applications.

A supplement accompanies this application, and that supplement provides further technical details of some of the arrangements described in this document. The accompanying supplement forms an integral part of this application, and information may be freely transferred between this application and the supplement, and vice versa.

Background

It appears likely that future engines in vehicles will probably need to be downsized (made to have fewer cylinders and smaller volumetric capacity) in order to reduce the internal frictional and pumping losses. Supercharging and/or turbocharging of downsized engines can enable them to provide the power of larger engines, and thereby meet the performance expectations of the customer whilst saving energy. Another method (which can be used simultaneously) is to provide a so-called "hybrid" system; an auxiliary propulsion system for the vehicle that can operate in conjunction with the engine or on its own to enable reduction in energy consumption and emissions by various methods (such as regenerative braking) and also the potential to increase vehicle performance.

Electric hybrid powertrains (using electrochemical batteries, power electronics and motor-generators) have previously been proposed, but such arrangements tend to be relatively expensive compared to traditional internal combustion engine powertrains. It is also the case that inefficiencies associated with the multiple conversions of energy into different forms that take place in such systems (particularly during regenerative braking) reduces the net amount of energy that can be saved with such a system as compared with a conventional vehicle. It is also the case that electric systems are typically relatively heavy and therefore extra energy is spent transporting this extra mass. Even though fully-electric vehicles will have zero "at the wheel" emissions, it is the case that manufacturing and subsequent end-of-life processing of electrochemical batteries for this application has significant environmental impact. In the light of this, it would be beneficial to provide hybrid systems that reduce the total energy consumption and emissions, that are fully- recyclable and that come at a price point that is affordable for manufacturer and customer alike. Previously proposed electric hybrids do not (at present) meet all of these criteria.

It has previously been proposed to use a flywheel as a kinetic energy storage device to provide a mechanical alternative to electrical systems. Previously proposed high-speed flywheel hybrid systems (such as those of Flybrid Automotive Ltd) generally have a higher power-to-weight ratio than equivalent electric hybrid systems and are able to capture and return more of a vehicle's kinetic energy when performing regenerative braking. This is mostly because energy form conversions are avoided, especially during regenerative braking; kinetic energy is simply transferred from one inertia to another (the vehicle and the energy storage flywheel). Mechanical transmissions are usually recyclable since they are constructed almost entirely from steel and aluminium (apart from the seals and lubricants and a carbon fibre wrap for the high-speed flywheel). The abundance of these materials means that the cost of the raw material is relatively low, and mass-manufacturing techniques allow relatively low-cost manufacture.

Previously proposed flywheel hybrid systems (such as those of Flybrid Automotive Ltd) are designed to interface with conventional vehicle architecture, comprising a clutch, discrete gearbox and differential. This is to provide a low-cost system that can be readily accepted by vehicle manufacturers mindful of financial risk, since it does not fundamentally change the layout and overall concept of the vehicle. Flybrid Automotive Ltd's current advertised systems are able to accomplish regenerative braking, function in engine stop-start mode (e.g. in a mode wherethe engine can be turned off while waiting at traffic lights) and drive the vehicle under flywheel power alone. In addition to these useful modes of operation, the flywheel can be used to allow the engine to operate in a more efficient regime than is normally possible with a discrete gearbox transmission alone. This is achieved by either subtracting surplus engine torque by charging the flywheel, or adding to insufficient engine torque by discharging the flywheel. Whilst these arrangements work well, it would be beneficial to provide flywheel technology that better unifies the engine and the flywheel so that additional useful modes of operation can be provided that enable further energy savings and reduce emissions.

Aspects of the present invention have been conceived with the foregoing in mind.

Summary

A presently preferred implementation of the teachings of the invention provides a transmission system, comprising first and second variators; first, second and third source/sink couplings; and reconfigurable mechanical linkage coupling the first and second variators to the first, second and third source/sink couplings; wherein the mechanical linkage is configurable for power transfer between at least two of said source/sink couplings via one of said first and second variators or via both of said first and second variators.

Preferably the mechanical linkage is configurable for simultaneous power transfer via both of said first and second variators.

In a particularly preferred arrangement, power transfer via both of said variators can occur without power transfer though one said variator followed by the other said variator.

In one arrangement one or both of said variators may be torque controlled. In another arrangement, one or both of said variators may be ratio controlled.

In one implementation said variators may have the same torque/power capacity. In another implementation, said variators may be of different torque/power capacity.

In one arrangement, said first source/sink coupling is connectable to a prime mover, said second source/sink coupling is connectable to a vehicle drive, and said third source/sink coupling is connectable to a secondary mover.

The prime mover may comprise an engine (for example, an internal combustion engine) and said secondary mover may comprise an energy storage unit. In one arrangement the energy storage unit may comprise a flywheel. In another arrangement, the energy storage unit may comprise a store for electrical power and an electric motor-generator. For example, the store for electrical power may comprise one or more electrochemical batteries or a capacitor or bank of capacitors. In one arrangement the mechanical linkage may be configurable to enable power transfer from said prime mover to said secondary mover via one of said variators.

In one arrangement the mechanical linkage may be configurable to enable power transfer from said vehicle drive to said secondary mover via one of said variators.

In one arrangement the mechanical linkage may be configurable to enable power transfer from said secondary mover to said vehicle drive via one or both of said variators.

In one arrangement the mechanical linkage may be configurable to enable power transfer from said prime mover to said vehicle drive via one of or both of said variators.

In one arrangement the mechanical linkage may be configurable to enable power transfer from said prime mover to said vehicle drive via one of said variators, and power transfer from said prime mover to said secondary mover via the other of said variators.

In one arrangement the mechanical linkage may be configurable to enable power transfer from said prime mover to said vehicle drive via one of said variators, and to enable power transfer from said secondary mover to said vehicle drive via the other of said variators..

In one arrangement the mechanical linkage may be configurable to enable power transfer from said prime mover to said secondary mover via one of said variators, and to enable power transfer from said vehicle drive to said secondary mover via the other of said variators.

In another implementation, the transmission system may comprise a fourth sink/source coupling. The fourth sink/source coupling may be connectable to a second vehicle drive.

In this arrangement the mechanical linkage may be selectively configurable to provide power transfer from said prime mover and/or said secondary mover to said vehicle drive and/or said secondary vehicle drive.

In a preferred arrangement, the mechanical linkage may be selectively configurable to provide power transfer from said prime mover to one of said vehicle drive or said second vehicle drive, and to provide power transfer from second secondary mover to the other of said vehicle drive or said second vehicle drive. Preferably the mechanical linkage includes a plurality of clutches.

In another arrangement implementing the teachings of the invention, there is provided a transmission system for a vehicle comprising first and second variators arranged in parallel with one another.

Another arrangement implementing the teachings of the invention provides a vehicle comprising a transmission system as herein described, a prime mover connectable to said first sink/source coupling, and a secondary mover connectable to said third sink/source coupling.

One illustrative implementation of the teachings of this invention provides a mechanical CVT for the engine (or other prime mover) as well as a mechanical CVT for controlling energy storage and recovery of a flywheel (or other energy storage device). One illustrative advantage of the arrangements disclosed herein is that power flow in any particular transmission configuration only passes through one traction drive (CVT), rather than through two traction drives in series, thereby substantially increasing mechanical efficiency.

Another illustrative advantage of the mechanical CVTs disclosed herein - as compared with electric CVT systems - is that energy form conversions are avoided; once fuel has been converted into mechanical energy at the engine crank (or energy stored in an electrochemical battery has been converted into mechanical energy at the motor-generator shaft), it remains in this state throughout the transmission. Additionally, the mechanical systems proposed herein will likely be less expensive and more recyclable than their electric alternatives.

In one aspect the teachings of the invention provide a continuously variable transmission that includes any combination of features disclosed in this application alone, or in combination with any features disclosed in the aforementioned priority application or the accompanying supplement.

Other aspects of the invention relate to: a variator for such a transmission, a propulsion system for a vehicle that includes such a transmission, and to a vehicle that includes such a propulsion system.

Further embodiments, features and advantages of aspects of the invention will be apparent from the following detailed description.

Brief Description of the Drawings

Embodiments of the present invention are described hereafter with reference to the accompanying drawings, in which: Fig. 1 is a schematic representation of an illustrative multi-input variator;

Fig. 2 is a three-dimensional cut-away view of the variator depicted in Fig. 1 ;

Fig. 3 is a schematic representation of a transmission employing a variator of the type depicted in Figs. 1 and 2;

Fig. 3 is a schematic representation of another transmission that employs a variator of the type depicted in Figs. 1 and 2;

Figs. 5(a) to 5(c) are illustrative transmission arrangements that implement the teachings of the invention, and which may (but do not have to) employ the variator of Figs. 1 and 2;

Fig. 6 is a schematic representation of another transmission arrangement that implements the teachings of the invention;

Figs. 7(a) to 7(k) are schematic representations of different operating modes for the transmission arrangement depicted in Fig. 6; and

Fig. 8 is a schematic representation of another transmission arrangement that implements the teachings of the invention.

Detailed Description

Various arrangements are described below by way of illustrative example. Whilst the arrangements described below are presented in headed sections, this is merely for convenience and should not be construed as meaning that each arrangement is discrete from the others. Rather, it is the applicant's intention that subject matter from these arrangements should be freely combinable (both with other arrangements disclosed in this application and/or with material contained in the supplement and/or the priority application).

Multi-Continuouslv Variable Planetary (MCVP) hybrid transmission (CVT/IVT)

The arrangement depicted in Fig. 1 employs a novel multiple-input variator with two independent ratio control mechanisms. The variator is a planetary transmission with multiple planets that are double conical surfaces whose rotational axes are inclined relative to the main variator rotational axis - in a preferred arrangement at an angle equal to the half cone angle, as shown in Fig. 2. This arrangement provides two surfaces that are parallel to the main axis. Axial shifting of a central disc 20 along the inside surface provides a sun branch with variable speed ratio to control the flywheel; and axial shifting of an outer annulus along the outside surface provides a branch with IVT functionality for example for the vehicle final drive.

Fig. 2 is a possible layout of the MCVP configured as in Fig. 1 where the constant annulus branch is fixed to ground. The final drive of the vehicle is connected to the variable annulus shaft, which gives IVT potential (including reverse, with the bias of the ratio spread being chosen to suit the application by suitable design selection of the MCVP radii shown in Fig. 1).

The MCVP shown in Error! Reference source not found, uses planets where the cones face base to base on the planet shaft. The two cones may also be arranged such that they may face tip to tip or in the same direction. The former arrangement would allow the diameter of the constant annulus to be reduced (which reduces the rotational stresses for the same shaft angular speed), the latter would mean that either both of the sun branches or both of the annuli branches would be variable.

Generation of normal forces in the traction fluid contact patches required for efficient torque transfer is not so straight forward in this arrangement, since the carrier is rotating. Planets may be inclined at an angle that is deliberately greater or smaller than the half cone angle so that an increasing interference as the contact disc/annulus moves in a direction of increasing (steady state) torque (i.e. reduction in speed output shaft speed, and hence increase in torque for the same power). This is a passive system; meaning it does not require any external control. Another passive method would be elastically straining the disc/annulus that make traction contact with the conical planets, where this strain creates further interference and hence generates normal pressure on the fluid which increases with applied torque. The system may be bi-directional so that two similar mechanisms are used to act in opposite directions to create pressure from reversing torque. There would be backlash in this system as one mechanism relaxes whilst the other tenses when the direction of torque reverses.

In more detail, a prime mover is connected to the constant sun shaft 1 , to which is attached a bevel gear 2 (the constant sun gear) which meshes with a set of planet bevel gears 3 which are located in this embodiment at the axial centre of the planet 4 (one for each planet). Also on each planet 4 is another bevel gear 5 which meshes with an internal bevel gear 6, which is the constant annulus shaft (non- rotational in this embodiment since this branch is fixed to the casing 7). It will be appreciated by those experienced in the art that the bevel gears on the planets can be positioned in various places along the planet axis, such as between the cones 8 as shown or either side to achieve the same functionality and that the choice will ultimately be made by the constraints of the assembly. The planets are supported in a planet carrier 9 using bearings 10, said carrier being free to rotate in thisarrangement, but may be used as an input/output shaft in anotherarrangement.

The input to the MCVP from the flywheel is connected to the variable sun shaft 11 which is supported by bearings 12,13 in the carrier 9 and constant sun shaft 1 respectively. The constant sun shaft 1 may be supported by bearings 14 in the carrier 9 which is in turn supported by bearings 15 in the hollow variable annulus shaft 16. The variable annulus shaft 16 is geared to the final drive of the vehicle. The variable annulus shaft 16 is supported by bearings 17 in the casing 7.

A beneficial feature of this arrangement is that all input/output shafts and the carrier rotate in the same direction, and so the bearings only run at the difference between the shaft speeds. A consequence of this is that the speed rating requirement for the bearings is not especially high despite the fact that the shafts may be running at high speed (absolute). This reduces the machining precision required for these bearings and hence the cost.

The variable annulus shaft 16 requires a mechanism allowing axial shifting of the annulus 19 making traction contact with the planet cone 7 in order to change the speed ratio between the prime mover and the vehicle. The variable sun shaft 11 also requires a mechanism to axially shift the variable sun disc 20 in order to change the speed of the flywheel relative to the prime mover/vehicle. These two variable branches may utilise methods employed in the so-called "Turbo Trac" variator (see patent nos. US6001042 & US7856902) to facilitate this ratio control.

The bevel gears 2,3,5,6 may be spiral bevel gears to reduce noise and vibration and provide smooth torque transfer and increased fatigue life for the gear teeth and surfaces. Klingelnberg spiral bevel gears (where the teeth are not tapered) in particular may be used which can be generated with a hobbing process much like automotive gearboxes and hence benefit from low cost in volume production despite their seemingly complex geometry. Palloid tooth form may also be produced by hobbing but has greater bending strength since the teeth are tapered.

All of the bevel gears mentioned (2,3,5,6) may also be replaced by traction- drive surfaces (sometimes referred to as friction gears).

The variable annulus shaft 16 is hollow, allowing the constant sun shaft 1 to pass through coaxially on the same side of the MCVP 28, being connected to the prime mover 29 via a gearbox 30 and a clutch 31. This arrangement conveniently allows the differential 32 to be placed in the middle of the vehicle's powered axle, between the prime mover 29 and the MCVP 28, since this is permitted by the relative sizing of the prime mover, MCVP and flywheel. The prime mover 29, gearbox 30 and clutch 31 may be a standard automotive or motorbike engine and gearbox arrangement 34 with the included clutch 31. The flywheel 33 is connected to the variable sun shaft 11 via a clutch 35 and a gear box 36; order of said clutch and gearbox in the torque path is chosen for ease of component design/selection. Said gearbox 36 may be a single fixed ratio, or a plurality of selectable ratios in order to behave as a ratio range extender for the flywheel branch of the MCVP, which can be appreciated by those skilled in the art. Said range extender may have capability to change gear without torque interruption (such as, but not limited to, dual- or multiple-clutch gearboxes) so as to allow continuous charging and discharging of the flywheel over a large range of vehicle/prime mover speeds.

In the layout proposed in Fig. 3, all shafts are parallel to the axle of the vehicle (they run transverse/across the vehicle). If the flywheel gearbox 36 does not reverse the rotational direction relative to the variable sun shaft 11 , the flywheel 33 rotates in the same plane as the wheels 37 but in the opposite direction. This causes the reaction to the flywheel gyroscopic moments acting on the vehicle during cornering to counteract vehicle roll which adds stability to the vehicle and also reduces the net loss of tyre traction due to lateral load transfer. This feature is of particular benefit to racing applications, but also to road cars. If the flywheel gearbox does reverse the direction of rotation, then this can be counteracted by first ensuring the flywheel is in the correct orientation to rotate oppositely to the wheels, then selecting a gearing arrangement that will ensure the correct direction of shaft rotation at the vehicle wheels, whilst ensuring the drive from the prime mover is also in the correct rotational direction.

Mechanical brakes 38 can bring the vehicle safely to rest in event of failure of any control critical components in the transmission. The flywheel and prime mover clutches 35,31 are simply disengaged in order to stop supply of power to the vehicle. Modified MCVP hybrid transmission (CVT/IVT)

The functionality and intents of the arrangement depicted in Fig. 4 are identical to those of the first embodiment. Here, however, there is no constant sun branch and the prime mover is instead connected to the carrier branch. This does not change the functionality, since there is a constant speed ratio between the constant sun branch and the carrier in the MCVP. This arrangement potentially reduces the cost of the transmission, since an entire set of bevel gears (or traction surfaces) on the planet can be eliminated.

Torque-controlled MCVP hybrid transmission

The MCVP described above is a dual ratio-controlled planetary variator that can also operate in a (quasi-)torque-controlled mode. This mode is achieved by virtue of its similarities with the conventional planetary gear set (comprising a sun gear and shaft, an annulus internal gear and shaft, both of said gears mesh with a set of planet gears located in the planet gear carrier connected to a carrier shaft), which is known to be used as a torque-splitting device in transmissions. When all of the three branches are free to rotate, it is a mechanism with "two degrees of freedom"; two of the shaft speeds must be known to determine the third shaft speed. There is a linear relationship between all three speeds that is a function of the planetary ratio. In contrast, the torque at all branches is known if the torque at any single branch is known, and these are again related by the planetary ratio. Additionally, it is well known that the sign of torque on the carrier branch is opposite to that on the other two branches (sun and annulus/ring).

In this envisaged arrangement three branches of the MCVP are used: the carrier, one of the annuli/rings and one of the suns. These three branches make up a conventional planetary arrangement, but here the planetary (or epicyclic) ratio is continuously variable. The flywheel, the prime mover and the vehicle final drive are each connected to a different branch. Clutches are used to vary which of the branches the prime mover, flywheel and vehicle are connected to, depending on the mode of operation.

Actuation of one (or both) of the ratio control mechanisms can change the planetary ratio and thus adjust the torque split. Each branch will accelerate depending on the torque applied to it (whilst obeying the linear speed relationship), thus facilitating torque control. The transmission system is controlled by controlling the engine torque in conjunction with the planetary ratio, in response to driver inputs or road conditions. In this mode, the vehicle speed depends on both the engine and flywheel speeds.

In this particular arrangement, any planetary variator may be employed to form this torque-controlled transmission (including but not limited to the NuVinci CVP, the Kopp variator and the Milner CVT). An advantage of using the MCVP of this arrangement as compared with the other variators is that a given planetary ratio can be achieved in a variety of actuator positions (if both ratio control mechanisms are changed simultaneously).

Integrated Toroidal Hybrid Transmission (ΙΤΉΤ)

This embodiment of the teachings of the invention makes use of two CVTs and a set of clutches that change the positions of these CVTs within the transmission to provide the arrangements depicted in Figs. 5(a) to 5(c), for example. In these arrangements power flow only passes through one CVT in all modes of operation (rather than two in series) and thereby provide relatively high transmission efficiency. Furthermore, the following embodiments provide a torque-controlled transmission.

In Fig. 5(a) power is supplied to the wheels of the vehicle (in this particular example) from both the prime mover (for example an internal combustion engine) and an energy storage unit, such as a flywheel. In Fig. 5(b) the prime mover drives the vehicle wheels, and excess power passes to the energy storage unit. In Fig. 5(c) power from the vehicle wheels (for example, from regenerative braking) and power from the prime mover pass to the energy storage unit.

Schematic transmission diagrams of various possible embodiments are shown in Figs 6 and 8 below and these arrangements will now be described with reference to these drawings. Such arrangements enable the power flow arrangements depicted in Figs. 5(a) to 5(c), and others.

The benefits of the previously proposed Torotrak toroidal variator are principally that it has high power density and that it is torque-controlled (unlike other CVTs, which are ratio-controlled). The former means it is a relatively compact and low mass system. The latter means that the desired torque to be applied is signalled by hydraulic pressure at the roller pistons and reaction torques are exerted either side of the variator; causing the ratio of the variator to change automatically. For this application, this means the variator ratio adjusts itself as the clutches are closed (as the operating mode is changed and during operation) and therefore the parasitic losses in the hydraulic actuation and computational system are lower. Of particular importance is the fact that direct control of torque allows effective management of the power flow arrangements depicted in Fig. 5a,5b,5c and also enables modes of operation of the embodiments depicted in Fig.6&7 where the vehicle is being driven by either flywheel power or prime mover power alone (described below). In such modes of operation, two torque-controlled variators are used in parallel and the speed ratios across each torque-controlled variator will automatically adjust as necessary. It would be very difficult to achieve this functionality with ratio-controlled variators.

Ratio-controlled variators, in contrast, have to calculate and control the precise ratio (and rate of change of ratio) in order to exert the correct torque on the flywheel, prime mover and final drive. The disclosed arrangements can be implemented with a ratio-controlled variator, but there will be higher parasitic losses and control will be more complex.

It may be appreciated by those skilled in the art that there are numerous permutations to the disclosed embodiments that can be made without altering the basic functionality of the system. Some of these are given by way of illustrative example. It will also be appreciated that certain components may be omitted to remove certain modes of operation that may not be required in certain applications. The embodiments disclosed are given by way of example and should not be viewed as limiting the scope of the invention. In one embodiment depicted schematically in Fig. 6, a prime mover 100 is connected to a first variator 101 via a clutch 102. A gear 103 can be rotationally coupled to the input shaft 104 to the first variator 101 via a clutch 105. Said gear 103 is in mesh with a gear 106 rotationally coupled to the output of a second variator 107. Another gear 108 can also be rotationally coupled to said input shaft 104 by another clutch 109. Said gear 108 is in mesh with idler gear 123. Said idler gear is in mesh with another gear 110. Said gear 110 is rotationally coupled to the input of said second variator 107. Said input of said second variator 107 is also rotationally coupled to the vehicle final drive 111 via a clutch 112. Between said clutch 112 and said final drive 111 is another gear 113 which can be rotationally coupled to said clutch 112 and said final drive 111 via a clutch 114. Said gear 113 is in mesh with another gear 115 which is rotationally coupled to the output of said first variator 101. Said gear 113 is also in mesh with another gear 1 16. Said gear 116 can be rotationally coupled to a shaft 117 via a clutch 118. Another gear 119 can be rotationally coupled to said shaft 117 via another clutch 120. Said gear 119 is in mesh with an idler gear 121. Said idler gear 121 is also in mesh with said gear 106, rotationally coupled to the said output of the second variator 107. An energy storage flywheel unit 122 is rotationally coupled to said shaft 1 17. Said flywheel unit 122 may also include step-up gearing to enable the use of a high-speed flywheel. Such step-up gearing may be traction drive technology.

As will be appreciated, a flywheel is merely one type of energy storage unit that may be employed in this and other embodiments. Other types of energy storage unit known to persons skilled in the art may instead be employed. For example, one or more electrochemical batteries (or a capacitor or bank of capacitors) connected to an electric motor-generator would serve the same purpose as a flywheel.

Operating modes

(i) Initial charging of the flywheel

If desired, the flywheel 122 can be charged by the prime mover 100 whilst the vehicle is stationary (or not being powered) via the first variator 101 when clutches 105,109,112,114,120 are open and clutches 102,118 are closed. Similarly, the flywheel 122 can also be charged by the prime mover 100 whilst the vehicle is stationary (or not being powered) via the second variator 107 when clutches 105,1 12,114,118 are open and clutches 102,109,120 are closed. The flywheel 122 can also be charged by the prime mover 100 whilst the vehicle is stationary (or not being powered) via both the first and the second variators 101 ,107 when clutches 105,1 12,114 are open and clutches 102,109,1 18,120 are closed.

(ii) Driving under flywheel power alone

When the prime mover 100 is disconnected by opening clutch 102, the vehicle final drive 111 can be powered by discharging the flywheel 122, via either the first variator 101 or the second variator 107 or via both said variators 101 ,107 simultaneously. When clutches 102,105,114,120 are open and clutches 109,112,118 are closed, the flywheel can be discharged via the first variator 101. When clutches 102,105,109,114,118 are open and clutches 1 12,120 are closed, the flywheel can be discharged via the second variator 107. When clutches 102,105,109,114,1 18 are open and clutches 109,1 12,118,120 are closed, the flywheel can be discharged via both the first and second variators 101 , 107.

(iii) Driving using the prime mover alone

When the flywheel stored energy is low (or if the flywheel fails) the vehicle final drive 111 can be powered by the prime mover alone through either or both of the variators 101 ,107. The flywheel 122 can be disconnected from the transmission by opening clutches 118,120. When clutches 102,114 are closed and the remaining clutches 105,109,1 12,118,120 are open, then the prime mover 100 is transmitting power to the vehicle final drive 111 via the first variator 101. When clutches 102,105,112 are closed and the remaining clutches 109,114,118,120 are open, then the prime mover 100 is transmitting power to the vehicle final drive 111 via the second variator 107. When clutches 102,105,112,114 are closed and the remaining clutches 109,118,120 are open, then the prime mover 100 is transmitting power to the vehicle final drive 111 via both the first and second variators 101 ,107.

(iv) Excess prime mover power

I f a control decision is made (for example if it is more energy/fuel efficient to do so), the prime mover 100 may supply more power than the vehicle needs at any instant in time. In this mode, the flywheel 122 can be charged with this excess power via the first variator 101 whilst required prime mover power is transmitted to the final drive 111 via the second variator 107. This is mode can occur when clutches 102,105,112,118 are closed and clutches 109,114,120 are open. Alternatively, the flywheel 122 can be charged with excess prime mover power via the second variator 107 whilst the required prime mover power is transmitted to the final drive 111 via the first variator 101. This mode can occur when clutches 102,109,1 14,120 are closed and clutches 105,112,118 are open.

(v) Insufficient prime mover power

If a control decision is made (for example if it is more energy/fuel efficient to do so), the prime mover 100 may supply less power than the vehicle needs at any instant in time. In this mode, in order to provide the shortfall in power, the flywheel 122 can be discharged via the second variator 107 whilst prime mover power is transmitted to the final drive 1 11 via the first variator 101. This mode can occur when clutches 102,112,114,120 are closed and clutches 105,109,118 are open.

(vi) Pure regenerative braking using the flywheel

When the prime mover 100 is disconnected by opening clutch 102, the vehicle final drive 1 1 1 can be retarded by charging the flywheel 122, via either the first variator 101 or the second variator 107 or via both said variators 101 ,107 simultaneously. When clutches 102,105,114,120 are open and clutches 109,112,118 are closed, the flywheel can be charged via the first variator 101. When clutches 102,105,109,114,1 18 are open and clutches 112,120 are closed, the flywheel can be charged via the second variator 107. When clutches 102,105,109,114,118 are open and clutches 109,112,1 18,120 are closed, the flywheel can be charged via both the first and second variators 101 ,107.

(vii) Regenerative braking and simultaneous prime mover charging of flywheel If it is desired to avoid engine transience, when the vehicle is retarding, power that is still being generated by the prime mover can be stored in the flywheel 122 even whilst regenerative braking is taking place. The torque supplied by the prime move is exerted on the flywheel using the first variator 101 , whilst the second variator 107 is exerting negative torque on the final drive 111 to retard the vehicle and an opposite (positive) reaction torque on the flywheel. Again, torque control of the variators means the variator ratio changes automatically, taking account of both actions of the transmission system. This mode can occur when clutches 102,112,118,120 are closed and clutches 105,109,114 are open.

Referring now to Figs. 7(a) to 7(k), the transmission depicted in Fig. 6 can provide the following operating modes:

• charging of flywheel by prime mover (Fig. 7a)

• flywheel powering final drive via variator V2 (Fig. 7b)

• flywheel powering final drive via variator V1 (Fig. 7c)

• flywheel powering final drive via variators V1 and V2 (Fig. 7d)

• prime mover powering final drive via variator V1 (Fig. 7e)

• prime mover powering final drive via variator V2 (Fig. 7f))

• prime mover powering final drive via variators V1 & V2 (Fig. 7g)

• prime mover powering final drive via variator V2, and charging flywheel via variator V1 (Fig. 7h)

• prime mover powering final drive via variator V1 , and charging flywheel via variator V2 (Fig. 7i)

• prime mover powering final drive via variator V1 , flywheel powering final drive via variator V2 (Fig. 7j)

• Regenerative braking of final drive charging flywheel via variator V2, and prime mover charging flywheel via variator V1

Four-Wheeled Drive (4WD) embodiment - extra modes of operation and functionality In another embodiment depicted schematically in Fig. 8, a 4WD transmission system has been devised. The arrangement depicted is a slight modification of the previous embodiment which includes a second final drive 125 rotationally coupled to said gear 110. A clutch 124 is also inserted between said gear 110 and input to said second variator 107. This arrangement can provide most of the modes of operation disclosed above, but also allows independent control of first and second final drives 126,125 during driving and regenerative braking.

This arrangement provides for vehicle kinetic energy to be taken from both front and rear axles simultaneously, allowing 100% of the braking force to be provided by the mechanical KERS, thus being able to capture more energy that would normally be wasted. The appropriate braking proportion can be applied to each axle by controlling the torque exerted by each torque-controlled variator. Both variators serve to accelerate the single flywheel, and the torque control feature means that both variator ratios adjust themselves automatically. If ratio-controlled variators were used, this would be much more difficult to control in synchrony.

In such an arrangement, the two variators 101 ,107 are able to serve the function of a conventional differential in 4WD vehicles that connects the differentials on the front and rear axles; however the mechanical efficiency will likely be higher (for example, similar to a conventional continuously variable transmission passing only through one differential). Previously proposed high-speed flywheel mechanical hybrid transmissions do not provide a means for four wheel drive kinetic energy recovery, partly due to the lower "round-trip" efficiency normally associated with passing through two bevel-geared differentials in series.

It will appreciated by those skilled in the art (and from the foregoing description) that the embodiments described above allow either one of the variators 101 ,107 to be used to transmit power to the vehicle on their own, or both can be used simultaneously to provide a parallel path. This allows load and associated wear on the variator surfaces to be shared or allocated to a specific variator and so prolong the life of the transmission. This also has the useful feature of providing a transmission with CVT characteristics that has variable torque capacity. It is known that traction drives reduce in efficiency at low input torque. Thus at very modest power levels (for example, small vehicles travelling at low speed in urban areas) the transmission efficiency can be increased by directing power through a single variator. Equally, when high power is required, both variators can be used.

Since, in the embodiments herein presented, either variator can be chosen to transmit the power to the vehicle (when using one source of motive power, be it prime mover or flywheel), the two variators can have different torque capacity. At very low power requirement, power can be transmitted through a smaller variator; at medium power requirement, power can be transmitted through a larger variator; at high power requirement, power can be transmitted through both larger and smaller variators simultaneously. This increases system efficiency and effectiveness. This applies to both driving (under flywheel or prime mover power, either in isolation or both combined) and regenerative braking using the flywheel. When the flywheel is accepting surplus engine torque (or supplementing insufficient engine torque), the power flow through the variator to the flywheel may well be low and so a lower torque capacity variator facilitates higher transmission efficiency.

Operating modes of 4WD system:

(i) Initial charging of flywheel

This mode can now only take place through the first variator 101 (described previously).

(ii) Driving with flywheel alone & 4WD regenerative braking

Each final drive 125,126 can be connected to the flywheel with a different variator 101 ,107. The clutch arrangements are the same for driving and braking under flywheel power alone. Controlling the torque in each variator provides control of brake balance front to rear during regenerative braking.

If the first final drive 126 is connected to the flywheel via the first variator 101 and the second final drive 125 is connected to the flywheel via the second variator 107, then clutches 102,109,112,118 are open and clutches 105,114,120,124 are closed.

If the second final drive 125 is connected to the flywheel via the first variator 101 and the first final drive 126 is connected to the flywheel via the second variator 107, then clutches 102,105,114,124 are open and clutches 109,112,118,120 are closed.

(iii) Driving with prime mover alone

The prime mover 100 can be connected to the first final drive 126 via the first variator 101 and to the second final drive 125 via the second variator 107. In this arrangement, the two variators provide the differential function between the two final drives 126,125. This mode of operation is achieved when clutches 109,112,118,120 are and open and clutches 102,105,114,124 are closed.

It is also possible to drive the vehicle through both variators 101 ,107 and the first final drive 126 only, when clutches 109,118,120,124 are open and clutches 102,105,112,114 are closed.

(iv) Excess prime mover power If a control decision is made (for example if it is more energy/fuel efficient to do so), the prime mover 100 may supply more power than the vehicle needs at any instant in time. In this mode, the flywheel 122 can be charged with this excess power via the first variator 101 whilst required prime mover power is transmitted to either (or both) final drive(s) 126,125 via the second variator 107. This is mode can occur when clutches 102,105,118 are closed, clutches 109,114,120 are open, and at least one of clutches 112,124 are closed. Clutch 112 allows drive to the first final drive 126 and clutch 124 allows drive to the second final drive 125.

(v) Insufficient prime mover power

The prime mover 100 can power the first final drive 126 via the first variator 101. Clutches 102,114 are closed and clutches 105,109,118 are all open. The flywheel 122can power the second final drive 125 via the second variator 107 when clutches 120,124 are closed and clutch 112 is open. Alternatively, the flywheel 122 can also power the first final drive 126 when clutches 112,120 are closed and clutch 124 is open. Finally, both final drives can be rigidly locked together by closing clutches 112,120,124, allowing both the prime mover 100 and the flywheel 122 to power the vehicle together.

(vi) Regenerative braking and prime mover charging of flywheel

The prime mover 100 charges the flywheel via the first variator 101 and one of the final drives provides a source of kinetic energy to be recovered via the flywheel 122 and second variator 107. This requires clutches 102,1 18,120 to be closed and clutches 105,109,114 to be open. If regenerative braking is to be carried out at the first final drive 126, then clutch 112 must also be closed. If regenerative braking is to be carried out at the second final drive then clutch 124 must also be closed.

It will be appreciated that whilst various aspects and embodiments of the present invention have heretofore been described, the scope of the present invention is not limited to the particular arrangements set out herein and instead extends to encompass all arrangements, and modifications and alterations thereto, which fall within the spirit or scope of the invention.

It should also be noted that whilst particular combinations of features have been set out herein, the scope of the present invention is not limited to those particular combinations, but instead extends to encompass any combination of features disclosed in this application, in the application from which this application claims priority and/or the accompanying supplement; and to encompass any of these features in isolation.

It should also be noted that protection is claimed for the use of two variators to mediate power flow between a prime mover, a flywheel (or other energy storage device) and one or more driven axles, where clutches engage and disengage to provide various different modes of operation wherein power flow avoids passing through two variators in series (thereby avoiding loss of efficiency). Protection is also claimed for arrangements particularly (but not exclusively) when these variators are torque-controlled rather than ratio-controlled. Protection is also claimed for using two variators of different torque/power capacity.

Finally, it should be noted that whilst the embodiments described above may be implemented using variators of the type depicted in Figs. 1 and 2 of the accompanying drawings, this is not an essential feature of the invention. Rather, any types of variator (torque or ratio controlled or a mix of torque and ratio controlled) may be utilised. It is the case, however, that particular functional benefit is to be found when using at least one torque controlled variator.

SUPPLEMENT 20

TRANSMISSION SYSTEM

Field

This invention relates to transmission systems, particularly but not exclusively to transmission systems for vehicles. Another aspect of the invention relates to a variator for such a transmission system.

Particular reference is made hereafter to the use of such systems in a road vehicle, but it will be appreciated by persons of ordinary skill in the art that the system disclosed herein has many other applications, and as a consequence the following description should not be read as being a limitation of the scope of the present invention.

Background

Many conventional road vehicles have internal combustion engines that are large and powerful enough to maintain a cruising speed on a motorway, for example, that is much higher than is permitted by the speed limits in the United Kingdom, and such engines are in this respect at least much more powerful than is strictly necessary. This effectively surplus power capability tends to be provided by manufacturers so that the vehicle is better able to accelerate by having sufficient power (after overcoming resistance forces) to change the kinetic energy of the vehicle. However, such larger engines tend to consume a relatively large amount of fuel (compared, for example, to smaller more frugal engines) and since fuel is both expensive and environmentally damaging (both in terms of its extraction and its combustion) it would be beneficial for the capacity of such engines to be reduced.

A further concern is that the amount and nature of engine emissions tend to vary considerably over the range of operating conditions experienced by the engine. Larger trucks, buses, lorries and off-highway vehicles tend to have larger diesel engines that typically produce peak emissions when under transient operating conditions, and as a consequence the performance of new engines of this type tends to be compromised in the design stage in order to meet increasingly stringent emissions regulations.

One proposal for tackling this issue of engine transience is to use a so-called "series" hybrid powertrain in which an electric transmission is used. In this proposed arrangement, the engine runs efficiently in a more or less constant condition and is used to power a generator that delivers electrical power to motor-generators at the wheels/final drive of the vehicle - which wheels/final drive can also accomplish regenerative braking. Braking energy and any surplus engine power generated while the vehicle is moving is sent to a storage device, such as an electrochemical battery, SUPPLEMENT 21

and the engine can also be switched off when the vehicle is temporarily stationary (for example, at traffic lights) - responsive vehicle behaviour when pulling away from standstill being provided by the motor-generators.

Whilst series hybrids of the type described above generally do not add power capability, they can improve efficiency (under the right conditions). However, series hybrids tend to be expensive to produce due to the significant added cost of the electric motors and batteries, and the additional weight that such devices add to a typical vehicle also impacts upon performance and efficiency. The batteries themselves are also an environmental concern and are costly even in mass production, due to the materials and processes required in manufacture. Another important drawback of such systems is that power flow through the powertrain requires multiple energy conversions (between chemical, potential, mechanical, kinetic and electrical forms) and resultant energy losses.

An alternative proposal is the so-called "parallel hybrid" in whcih two means are provided for propelling a vehicle. Such an arrangement offers an increase in power capability (by providing two means of propelling the vehicle), and those means can be used independently or in combination to offer more efficient operating conditions for the engine. However, electric parallel hybrids still add significantly to the cost of the vehicle, and still exhibit the deficiencies outlined above for series hybrid powertrains.

A further proposal is the so-called mechanical hybrid, such as those incorporating lightweight high-speed flywheels (such as those by Hybrid Systems, see www.flvbrid.co.uk ^' ). The Hybrid systems are effectively "bolt on" devices that provide for kinetic energy recovery (regenerative braking), and are designed to interface with conventional powertrain architecture that comprises a clutch, a discrete gearbox and a differential. The hybrid component of the Flybrid system comprises a flywheel, a fixed gear stage, a clutch and a continuously variable transmission (CVT).

Hybrid Systems have also demonstrated a so-called clutched flywheel transmission (CFT) that comprises two sets of three constantly meshed gears and a clutch per pair of gears (one designated from each set), and which uses controlled clutch slip to move between the fixed ratios. This CFT system behaves in a similar way to the aforementioned CVT system but is less expensive to produce and more suitable for low power applications.

Both of the aforementioned systems are so-called "parallel hybrid" systems that are capable of propelling the vehicle by means of a prime mover (such as an internal combustion engine) or the flywheel or a combination of both. The aforementioned systems also have "full hybrid" capability in that they can accept a proportion of surplus SUPPLEMENT 22

engine torque during ordinary driving, thereby enabling the engine to operate in a more efficient regime than in conventional powertrains over a range of conditions.

However, whilst the systems proposed by Flybrid offer advantages over previously proposed systems, they still do not allow the engine to operate fully independently from the instantaneous requirements of a vehicle, principally because the engine is accelerated through discrete gears in a gearbox. If a system were to be devised that enabled the engine to be fully isolated from the vehicle, then the efficiency of the engine could further be improved.

The present invention has been devised with the foregoing problems in mind.

Summary

In accordance with a presently preferred embodiment of the present invention, there is provided a variator (otherwise referred to as an MCVP) comprising a first and a second cone, said cones being rotatable about a common axis that is inclined relative to a main axis so that said first and second cones each provide a side that is substantially parallel to said main axis.

Protection is also claimed for a cone substantially as herein described, an MCVP as herein described, a vehicle transmission, and a vehicle incorporating an MCVP.

Particular note should be taken of the fact that the scope of the present invention includes any combination of features herein described.

Brief Description of Drawings

Illustrative embodiments of the present invention are described hereafter by way of illustrative example with reference to the accompanying drawings, in which:

Fig. 1 is a schematic representation of two truncated cones arranged along a common axis in a first configuration;

Fig. 2 is a schematic representation of alternative cone configurations;

Fig. 3 is another schematic representation of another cone configuration;

Fig. 4 is a schematic planetary analogy of an illustrative variator;

Fig. 5 is a schematic representation of an illustrative vehicle transmission;

Fig. 6 is a schematic representation of an arrangement that is functionally equivalent to the arrangement depicted in Fig. 5; and

Figs. 7(a) to 7(h) are schematic representations of several possible power paths.

Fig. 8 is a schematic representation of an illustrative variator configuration;

Fig. 9 is a cut-away schematic representation of the variator depicted in Fig. 8; SUPPLEMENT 23

and

Fig. 10 is a diagrammatic representation of a transmission system that incorporates the variator depicted in Figs. 8 or 9; and

Fig. 11 is a rendered image of the variator depicted in Figs. 8 and 9 in use with a prime mover and a flywheel.

Detailed Description

As will later be described in detail, the system described herein offers all the capabilities of previously proposed mechanical flywheel hybrid systems, whilst also offering further significant functional benefits thereover.

For example, rather than being a bolt-on system (such as that proposed by Flybrid), the system disclosed herein entirely replaces a conventional stepped (discrete gearbox) transmission. The system disclosed herein embodies the benefits of both series and parallel hybrid powertrains, in particular: increased power capability beyond that of the prime mover alone (parallel hybrid), and permitting the engine to operate entirely independently of the instantaneous vehicle requirements and thus achieve greater efficiency (series hybrid).

In a preferred arrangement, the transmission system disclosed herein is used in conjunction with a prime mover (for example an internal combustion (IC) engine) and a flywheel. As will be described in more detail below, the flywheel can be used to supply kinetic energy whilst also simultaneously accepting power from the prime.

The flywheel thus acts as a buffer by being able to accept surplus engine power (even during regenerative braking) and by being able to supply extra power to the vehicle when needed, thus aiding engine downsizing.

The system disclosed provides numerous additional useful modes of operation that are beneficial in a wide variety of ground vehicle applications. For example, the system provides infinitely variable transmission (IVT) functionality (with reverse gear) for the final drive, with the flywheel being able to be charged with the prime mover power even whilst the wheels are in a powered neutral mode (where this energy is normally wasted as heat in power recirculation). It is also possible to start the engine with the flywheel if desired. Furthermore, a variety of control strategies are also possible, which can be optimised for energy efficiency.

All this is potentially achieved at a much lower cost to current electric alternatives. This is largely due to keeping energy in the mechanical kinetic domain using flywheels, which also addresses the aforementioned issues associated with energy conversion losses. A vehicle with an electric transmission must have "X" SUPPLEMENT 24

kilowatts' worth of electrical machines (e.g. motor-generators) to deliver "X" kilowatts of power at the wheels, whereas a mechanical system using flywheels (such as the arrangement disclosed herein) can deliver more power than the prime mover (which could still be an electric machine) since more power effectively means more torque in the mechanical components, which just need to be designed to be able to withstand the increased loads. Mechanical systems reduce in cost in mass production and allow widely available and fully recyclable materials to be used, and are thus potentially a more sustainable and environmentally friendly solution than using expensive, heavy and less environmentally friendly electrochemical batteries.

The advantages outlined above derive from the use of a novel continuously variable transmission (CVT) that has up to five usable inputs/outputs ("branches") with two independent ratio control mechanisms, each of which is operable to change the speed ratio of one particular branch relative to all the others.

Whilst the majority of previously proposed CVTs tend to have just one input and one output ("branches"), two other GVTs (the so-called Milner CVT and the NuVinci CVP (continuously variable planetary)) have previously been proposed that have more than two branches. The developers of these systems have acknowledged the potential for use of their CVTs in hybrid vehicles, where more than one means of propelling the vehicle needs to be matched to the vehicle requirements. Both also share some similarity with a planetary gear set and so have power-split capabilities. However, both these multiple-input CVTs have only one ratio control mechanism, which upon actuation alters the speed ratios between all branches (i.e. any pair of branches), which imposes limitations on functionality. The ability to actuate two distinct mechanisms as provided in the system disclosed herein is equivalent to having two independent CVTs within one component, allowing the ability to independently choose an appropriate speed ratio for two different means of propelling a vehicle. This is useful in a multitude of applications, but is especially important for flywheel hybrids. The speed of the flywheel inherently changes during energy transfer (control of the flywheel speed controls the energy storage and recovery), since for a given flywheel inertia, the energy stored is purely a function of rotational speed; thus independent control of flywheel speed from the engine and the wheels is important.

The novel CVT described herein (one illustrative planetary analogy of which is shown schematically in Fig. 4 below) may be referred to as a Multi- Continuously Variable Planetary (or CVP) due to its similarities to a planetary gear set and the aforementioned NuVinci CVP. The MCVP differs, however, from the NuVinci CVP by having more than one actuation mechanism. Providing more than one actuation SUPPLEMENT 25

mechanism is equivalent to having two CVTs but since all the branches contact the same set of idling planet elements, all possible power paths cross only a maximum of two traction contacts (effectively a single CVT). Therefore, assuming efficient elasto- hydrodynamic conditions are generated at each of these contacts, the MCVP disclosed herein provides significantly higher transmission efficiencies than two CVTs in which some power paths involve crossing two CVTs (equating to 4 traction contacts in series).

In general, traction contacts in parallel add linearly to the torque capacity of a CVT, but traction contacts in series reduce efficiency With a multiplicative relationship. The MCVP benefits from both of these facts. There is also the benefit of reduced mass and component count (and hence cost) owing to the same components contributing to both CVT mechanisms.

As aforementioned, the transmissions disclosed herein are not limited to use in vehicles. Furthermore, the transmissions disclosed herein are not limited to vehicles or machinery where the primary source of power is an internal combustion engine. Indeed, most motor devices (whether combustion engines, electric machines, hydraulic motors etc) have regimes of operation where they are most efficient, and benefit from the properties gained from using the system disclosed herein. Thus the term "prime mover" is used here to not restrict the invention to IC engines, since the system is equally suited to any motor device.

The MCVP disclosed herein comprises a novel planetary traction drive (depicted schematically in Fig. 1 below) that employs planets which are double truncated cones inclined at an angle to the main shaft axis that is equal to half of the cone angle, thereby producing two effective straight edges aligned parallel to the main axis. Two independent actuator mechanisms control the axial position of a disc and a ring (green contact patches) that make contact with the inner and outer effective edges of the planet, which changes the contact radius on the planet and thus the linear speed, thereby changing the rotational speed of the said disc and ring. The ring and the disc rotate about the main rotational axis. Thus there are two independently controllable ratio mechanisms. One other "disc" and one other "ring" (red contact patches) also make contact and provide a means of clamping the planet on all sides and a means for supplying pressure (for example, hydraulic/sprung etc) to induce elasto-hyrdrodynamic conditions in the contact fluid for efficient torque transfer. The planets themselves are mounted via bearings seated on the cylindrical parts of the truncated cones into a carrier which can also rotate about the main axis. The red contact points which are constrained from moving axially can be replaced with toothed gears (depicted schematically in Fig. 3 below) in between the two cones in order to increase mechanical efficiency (although SUPPLEMENT 26

bevel teeth are required) at the expense of compactness.

Although the cones are shown in Fig. 1 as facing away from one another, in alternative arrangements (depicted schematically in Fig. 2) they may also face towards one another (or in the same direction, although this is less preferred as it will cause the bearings to react higher loads). SUPPLEMENT 27

— Main rotational axis (of all input/output shafts)

Fia. 3

Fia. 4

In accordance with convention, only one set of conical rotors are shown in the figures above, but it will be appreciated by persons of ordinary skill in the art that in reality a plurality of conical rotor pairs will be symmetrically arranged around the main axis.

The abovedeseribed MCVP may be employed in a vehicle transmission that couples two at least two sources of motive power to one or more driven elements (such as a pair of wheels on an axle). Fig. 5 below is a schematic representation of one such SUPPLEMENT 28

arrangement in which the abovedescribed MCVP is coupled between first and second sources of motive power (in this illustrative example, a flywheel (labelled "FW"); a prime mover (labelled "PM") such as, inter alia, a combustion engine, an electric machine or a hydraulic machine)), and a differential (labelled "Diff") that is coupled to a pair of driven wheels on a braked axle.

As shown in Fig. 5 below, in this embodiment the flywheel is connected to the variable "sun" branch of the MCVP, the prime mover is connected to the constant "sun" branch, the final drive is connected to the variable "ring" branch and the constant ring branch is fixed to ground (no rotation). The carrier is necessarily free to rotate. The flywheel and the prime mover are connected to their respective branches by means of a clutch (as shown) and a fixed ratio gear stage (not shown) may also be provided before or after the clutch in order to be at the right speed in the transmission.

As will be appreciated by persons of ordinary skill in the art, the prime mover can be switched on and the prime mover clutch can be engaged and fully closed which causes the constant sun branch to rotate and also defines the speed of the carrier branch, since the constant ring branch is fixed to ground. There is a constant speed ratio SUPPLEMENT 29

between the prime mover and the carrier branch.

When the diameter of the variable planet gear in contact/mesh with the variable speed output ring is the same as the diameter of the constant planet gear in contact/mesh with the grounded ring, the final drive is in a powered neutral condition. The prime mover is rotating and supplying power, but the final drive is locked stationary. Thus this device is capable of operating as an IVT (Infinitely Variable Transmission).

In common with all lVTs, in a powered neutral mode, any external torque exerted at the vehicle wheels will not cause the vehicle to move, such as in the case of being stationary on an inclined surface. Additionally, this means there is no need for a pulling- away clutch, reducing the number of components required. The final drive direction of rotation reverses either side of the powered neutral condition, providing the means for a reverse gear. The ratio spread either side of powered neutral can be adjusted to favour forward motion if desired by changing the diameter of the constant ring and planet gears.

A key function offered in this mode is that other branches of the system remain rotational, and actuation of the other ratio control mechanism provides continued functionality for that respective branch independent of the powered neutral condition of the final drive. This allows the flywheel to be charged with the engine power by actuating the other ratio mechanism so as to increase the flywheel speed.

In the powered neutral mode of conventional IVT systems, the power is just recirculated and ultimately dissipated (wasted) as heat in the transmission. An advantage of the arrangement described herein is that in this instance the power that would otherwise be wasted in a conventional IVT may be stored for later use, thus increasing system efficiency. As the vehicle pulls away, the torque subtracted from the transmission by increasing the flywheel speed is controllably reduced.

Since the prime mover may well be producing sufficient power (if operating in a constant condition) to cause the wheels to slip at low speed, the flywheel can conveniently continue to subtract torque to prevent this from happening (traction control system increases flywheel torque if wheels begin to slip) .

In order to accomplish kinetic energy recovery, both variator mechanisms require actuation, in order to slow down the final drive and simultaneously speed up the flywheel. SUPPLEMENT 30

Fia. 6

The arrangement shown schematically in Fig. 6 is functionally equivalent to the arrangement depicted in Fig. 5, and from this it is perhaps easier to visualise how simultaneous regenerative braking and engine charging of the flywheel is possible.

It has previously been proposed that changing the ratio of a CVT will apply a torque to two inertias connected either side of the CVT and cause one to speed up and one to slow down (this is how kinetic energy recovery is achieved with flywheels). Simultaneous kinetic energy recovery (regenerative braking) and engine charging of the flywheel is accomplished by changing the IVT ratio to apply a negative torque at the wheels whilst changing the CVT ratio such that the flywheel speeds up; the positive torque exerted on the transmission side of the CVT by changing the flywheel speed must equal the sum of the torque supplied by the engine and the positive torque on the transmission side of the IVT. This cannot be achieved as easily and efficiently with the aforementioned previously proposed flywheel systems that bolt-on to conventional stepped transmissions, which would require slipping of the engine clutch and thus not be very efficient.

Fig. 6 also shows two variators (the CVT and IVT) in the box that represents the MCVP in preferred configuration. If, instead of the aforementioned MCVP, two separate CVTs were used, a regenerative braking path would have to cross two CVTs per one way trip, and as such "round trip" power would have to cross four CVTs - an arrangement that is not particularly efficient. The arrangement described herein only effectively crosses one CVT per one-way trip (hence only two per round trip) and as a consequence is more efficient.

As has briefly been explained above, the MVCP disclosed in the application has several operating modes, and schematic representations of the respective power paths SUPPLEMENT 31

for each of these modes are shown in Figs. 7(a) to 7(h), in which the following symbols have the following meaning:

Variable radius Variable radius Open clutch Closed clutch Power flow gear not being gear in possible

actuated actuation

SUPPLEMENT 32

l

Fia. 7(a) SUPPLEMENT 33

l

Fie. Tfbi SUPPLEMEIMT 34

Surplus prime mover power (inch traction- limited acceleration)

SUPPLEMENT 35

Insufficient prime mover power (Inch power- limited acceleration)

SUPPLEMENT 36

SUPPLEMENT 37

Regenerative braking and simultaneous prime mover charging of flywheel (SP- KERS)

SUPPLEMENT 38

SUPPLEMENT 39

SUPPLEMENT 40

With reference to Figs. 8 to 10, one illustrative implementation of the teachings of the invention will now be described in more detail.

C P

Fia. 8

Fig. 9 SUPPLEMENT 41

Fia. 10

Fig. 9 is an illustration of a variator configured as shown schematically in Fig. 8 where the constant annulus branch is fixed to ground. The final drive of the vehicle is connected to the variable annulus shaft, which gives IVT potential (including reverse, with the bias of the ratio spread being chosen to suit the application by suitable design selection of the variator radii shown in Figure 8).

The particur implementation shown in Figure 9 employs planets where the cones face base to base on the planet shaft. The two cones may, in another envisaged implementation, be arranged such that they may face tip to tip or in the same direction. The former arrangement would allow the diameter of the constant annulus to be reduced (which reduces the rotational stresses for the same shaft angular speed), the latter would mean that either both of the sun branches or both of the annuli branches would be variable.

Generation of the normal forces in the traction fluid contact patches required for efficient torque transfer is not so straight forward in this present embodiment of the invention, since the carrier is rotating. Planets may be inclined at an angle that is deliberately greater or smaller than the half cone angle so that an increasing interference as the contact disc/annulus moves in a direction of increasing (steady state) torque (i.e. SUPPLEMENT 42

reduction in speed output shaft speed, and hence increase in torque for the same power). This is a passive system, meaning it does not require any external control. Another passive method would be elastically straining the disc/annulus that make traction contact with the conical planets, where this strain creates further interference and hence generates normal pressure on the fluid which increases wit applied torque. The system may be bi-directional so that two similar mechanisms are used to act in opposite directions to create pressure from reversing torque. There would be backlash in this system as one mechanism relaxes whilst the other tenses when the direction of torque reverses.

The prime mover is connected to the constant sun shaft 1 , to which is attached a bevel gear 2 (the constant sun gear) which meshes with a set of planet bevel gears 3 which are located in this embodiment at the axial centre of the planet 4 (one for each planet). Also on each planet 4 is another bevel gear 5 which meshes with an internal bevel gear 6, which is the constant annulus shaft (non-rotational in this embodiment since this branch is fixed to the casing 7). It will be appreciated by those experienced in the art that the bevel gears on the planets can be positioned in various places along the planet axis, such as between the cones 8 as shown or either side to achieve the same functionality and that the choice will ultimately be made by the constraints of the assembly. The planets are supported in a planet carrier 9 using bearings 10. The carrier is free to rotate in this particular implementation, but may be used as an input/output shaft in other implementations.

The input to the variator from the flywheel is connected to the variable sun shaft 11 which is supported by bearings 12, 13 in the carrier 9 and constant sun shaft 1 respectively. The constant sun shaft 1 may be supported by bearings 4 in the carrier 9 which is in turn supported by bearings 15 in the hollow variable annulu shaft 16. The variable annulus shaft 16 is geared to the final drive of the vehicle. The variable annulus shaft 16 is supported by bearings 17 in the casing 7. A beneficial feature of this arrangement is that all input/output shafts and the carrier rotate in the same direction and so the bearings only run at the difference between the shaft speeds, so the speed rating requirement for the bearings is not especially high despite the fact that the shafts may be running at high speed (absolute). This reduces the machining precision required for these bearings and hence the cost.

The variable annulus shaft 16 requires a mechanism allowing axial shifting of the annulus 19 making traction contact with the planet cone 7 in order to change the speed ratio between the prime mover and the vehicle. The variable sun shaft 11 also requires a mechanism to axially shift the variable sun disc 20 in order to change the speed of the SUPPLEMENT 43

flywheel relative to the prime mover/vehicle. These two variable branches may utilise techniques such as those employed in the Turbo Trac variator (see patent nos. US6001042 & US7856902) to facilitate this ratio control.

The bevel gears 2, 3, 5 and 6 may be spiral bevel gears to reduce noise and vibration and provide smooth torque transfer and increased fatigue life for the gear teeth and surfaces. Klingelnberg spiral bevel gears (where the teeth are not tapered) in particular may be used which can be generated with a nobbing process much like automotive gearboxes and hence benefit from low cost in volume production despite their seemingly complex geometry. Palloid tooth form may also be produced by nobbing but has greater bending strength since the teeth are tapered.

Figure 10 is a schematic representation of a transmission that incorporates the variator of Figs. 8 and 9. The variable annulus shaft 16 is hollow, allowing the constant sun shaft 1 to pass through coaxially on the same side of the variator 28, being connected to the prime mover 29 via a gearbox 30 and a clutch 31. This arrangement conveniently allows the differential 32 to be placed in the middle of the vehicle's powered axle, between the prime mover 29 and the variator 28, since this is permitted by the relative sizing of the prime mover, variator and flywheel. The prime mover 29, gearbox 30 and clutch 31 may be a standard automotive or motorbike engine and gearbox arrangement 34 with the included clutch 31. The flywheel 33 is connected to the variable sun shaft 11 via a clutch 35 and a gear box 36; order of said clutch and gearbox in the torque path is chosen for ease of component design/selection. The gearbox 36 may be a single fixed ratio, or a plurality of selectable ratios in order to behave as a ratio range extender for the flywheel branch of the variator, which can be appreciated by those skilled in the art. The range extender may have the capability to change gear without torque interruption (such as, but not limited to, dual or multiple clutch gearboxes) so as to allow continuous charging and discharging of the flywheel over a large range of vehicle/prime mover speeds.

In the arrangemend depicted in Figure 10, all shafts are parallel to the axle of the vehicle (they run transverse/across the vehicle). If the flywheel gearbox 36 does not reverse the rotational direction relative to the variable sun shaft 11 , the flywheel 33 rotates in the same plane as the wheels 37 but in the opposite direction. This causes the reaction to the flywheel gyroscopic moments acting on the vehicle during cornering to counteract vehicle roll which adds stability to the vehicle and also reduces the net loss of tyre traction due to lateral load transfer. This feature is of particular benefit to racing applications, but also to road cars. If the flywheel gearbox does reverse the direction of rotation, then this can be counteracted by first ensuring the flywheel is in the correct SUPPLEMENT 44

orientation to rotate oppositely to the wheels, then selecting a gearing arrangement that will ensure the correct direction of shaft rotation at the vehicle wheels, whilst ensuring the drive from the prime mover is also in the correct rotational direction.

Mechanical brakes 37 can bring the vehicle safely to rest in event of failure of any control critical components in the transmission. The flywheel and prime mover clutches 35, 31 are simply disengaged in order to stop supply of power to the vehicle.

Fig. 1 1 is a schematic representation of a variator of the type disclosed herein mated with a 4-stroke 250CC prime mover and a flywheel.

Further details of the arrangements described herein may be found in the attached "appendix", which appendix is intended to be an integral part of this description so that subject matter disclosed therein may be freely combined with subject matter disclosed in the description provided above, and vice versa.

In very general terms, the various arrangements disclosed herein provide the following benefits.

New variator (MCVP):

• Provides Iwo independent ratio control mechanisms whilst all power paths SUPPLEMENT 45

effectively only cross a single CVT, thereby providing improved flexibility and increased transmission efficiency.

• Mass savings may be made by effectively providing two CVTs in one assembly with common components shared between them.

• Planetary gear set similarities provide improved functionality as compared to existing planetary multiple input CVTs by adding at least one extra "branch" (5 in total), with two suns and two rings. Providing two similar type of branches e.g. suns is very useful and provides an improved choice of ratios and configurations (even in conventional one input / one output form) and by having independent ratio control.

• Simple (hence less expensive) geometry to manufacture Transmission:

• Improved control strategy and operating mode flexibility than current flywheel hybrid systems (at a potentially lower or similar cost by obviating the need for a normal gearbox; and flywheel CVT combined with the main vehicle transmission)

• Ability to isolate the engine from road conditions and instantaneous power required by vehicle, thus can run constantly (and efficiently) like a series hybrid. Thus providing the possibility of reducing transient engine emissions thereby allowing diesels to meet emissions regulations without compromising performance.

• Reduces the effective mass of the vehicle (inertia of rotating components, especially of the engine) and therefore increases acceleration response per unit engine size.

• Increases possible deliverable power like an electric parallel hybrid by using flywheel, but less expensive and recyclable.

• IVT powered neutral possible with other shafts than engine remaining active and other ratio mechanism operational, so another component can be powered or a flywheel charged rather than wasting energy in power recirculation.

• Useful in cars, buses, vans, off-highway vehicles (such as tractors, diggers etc)

• Particularly good for vehicles with heavily transient power requirements (such as city buses that repeatedly stop and start, and racing vehicles) allowing flywheel to buffer constant power supplied by prime mover.

It will be appreciated that whilst various aspects and embodiments of the present invention have heretofore been described, the scope of the present invention is not SUPPLEMENT 46

limited to the particular arrangements set out herein and instead extends to encompass all arrangements, and modifications and alterations thereto apparent to a person of ordinary skill in the art. For example, whilst a flywheel has been employed in the arrangements described above it will be apparent that other motive power sources may instead be employed without departing from the scope of the present invention.

It should also be noted that the applicant specifically claims protection for any combination or permutation of features herein disclosed.

SUPPLEMENT

APPENDIX

TRANSMISSION SYSTEM

The following academic paper provides further details of the various different arrangements that are disclosed in United Kingdom Patent Application No. 1209265.5 (filed on 25 May 2012), the entire contents of which are incorporated herein by reference.

ABSTRACT system (KERS) is an excellent way of increasing the overall efficiency of the vehicle. It must be remembered

A patent-pending multiple-input continuously variable that during braking a small portion of the vehicle's kinetic planetary traction drive wit two independent ratio energy is lost to resistance forces and therefore cannot control mechanisms has been presented. A particular be recovered.

configuration suitable for use in hybrid vehicles has been

identified and discussed. This configuration is shown to —— Vehicle Speed

yield novel functionality and provide the full range ——— Cummulative Spent Energy

in Brakes benefits associated with series and parallel electric

hybrids, but with a fully mechanical system using

flywheel energy storage.

Like many new vehicle technologies, the proposed

transmission has arisen from design work for a racing

application but the key features of the system make it

suitable for a wide range of ground vehicle applications.

This includes large off-highway diesel-powered vehicles,

which would benefit from the elimination of unfavourable

transient diesel emissions offered by the proposed

system. Time [s]

Figure 1: Drive cycle of an endurance lap shewing cumulative braking

INTRODUCTION energy and returnable KERS energy for mechanical system installed at rear axle

RACING REQUIREMENTS

The drive cycle of a typical lap of the endurance race is

shown in Figure 1. It is notable that the vehicle is always

accelerating or decelerating, never travelling at a

constant speed, which is to be expected of a racing

vehicle negotiating a winding track. On this drive cycle,

around 70% of the total energy spent at the wheels is

ultimately dissipated (wasted) as heat in the vehicle

brakes. Therefore an effective kinetic energy recovery SUPPLEMENT the NuVinci CVP (continuously variable planetary) and the Milner CVT. Both of these variators use spherical planets and are able to connect more than the conventional two branches (one input, one output), with a continuously variable ratio existing between all branches. The Milner CVT is the closest to the conventional PGS, since it has one sun, one annulus and one planet carrier branch.

Since actuation of the Milner CVT ratio alters the contact radius of the sun, the planets and the annulus simultaneously, it achieves a wider ratio range compared to the NuVinci CVP, where only the contact radii on the planet are altered. The NuVinci CVP typically has a ratio

Figure 2: Energy saving relative to a 240kg baseline conventional range from 0.5 to 2.0 whereas the Milner CVT can have vehicle (with 70kg driver)

a ratio range from around 0.6 to 3.8 [4][6],

Figure 2 shows the energy saving on the endurance

drive cycle resulting from a KERS installation and/or

increasing/decreasing mass of the vehicle. This graph

was produced following similar calculation methods to

Sovran [1],

Carrier

EXISTING FLYWHEEL HYBRID SYSTEMS

The most mature flywheel- based hybrid systems with a

mechanical transmission currently under development

are apparently those of Flybrid Systems LLP. Their

products advertised to date are systems designed to

interface with a conventional road vehicle transmission Figure 3: Milner CVT equivalent planetary schematic

(comprising a clutch, discrete gearbox and differential)

without significant change to the transmission or general The NuVinci CVP has two effective annuli branches, a packaging of the vehicle. sun and a planet carrier.

Flybrid's original system was developed for Formula

One, and has since appeared in a form optimized for

road car applications. The system uses a high-speed

flywheel connected to the vehicle transmission via a

planetary gear set, a clutch, a torque-controlled Torotrak

full-toroidal variator (CVT) and a second clutch [2].

A more recent product called the CFT (clutched flywheel

transmission) approximates the CVT system by using a

set of constantly meshed gear ratios and controlled slip

of clutches to move between these fixed ratios in order

to control flywheel energy storage and recovery. The

CFT hybrid system is inserted between the clutch and

the gearbox of a standard vehicle transmission, which

multiplies the overall number of ratios available between Figure 4: NuVinci CVP equivalent planetary schematic

the flywheel and the wheels, minimizing clutch slip and

associated losses. This system was designed with Due to their similarities with the PGS, both the NuVinci smaller, low-powered vehicles in mind, where a CVT CVP and Milner CVT have the potential to be used as a system would potentially be less efficient at such low power-splitting device. The developers of both variators power levels [8]. have acknowledged their potential for use in hybrid vehicles where more than one means of propelling a

MULTIPLE-INPUT PLANETARY VARIATORS vehicle must be connected to a vehicle final drive.

However, the focus has been only on electric hybrids

There are two known prior art variators that possess and on the Toyota Hybrid System (THS) in particular, some of the useful features of planetary gear set (PGS); where both developers propose replacing the SUPPLEMENT conventional PGS with their power-splitting variator

[4][5]. It seems from published literature that the use of

multiple input variators has not been considered

specifically for flywheel applications.

One reason for this may be the fact that actuation of the

ratio control mechanisms of both the NuVinci CVP and

the ilner CVT changes the ratio between all branches.

The variable gear radii shown in Figures 3 and 4 all

change simultaneously in varying degrees according to

the respective geometrical relationships. Thus, when

directly connecting two sources of motive power via

either of these multiple input variators, simultaneous

optimisation of the operating conditions of both sources

is not easily achieved.

The ability to actuate two distinct mechanisms would be Figure 5: MCVP planets being double truncated cones

equivalent to having two independent variators within

one component, providing the ability to independently Precision manufacture of the conical surfaces is choose the optimum speed ratio for two different means expected to be relatively inexpensive due to the of propelling a vehicle. This would be useful in a relatively simple geometry compared to other existing multitude of applications, but is especially important for variators. Mass and cost savings may be potentially flywheel hybrids. The speed of the flywheel inherently made due to the fact that components are shared changes during energy transfer (control of the flywheel between the two effective variators. The fact that all speed controls the energy storage and recovery), since branches (shaft inputs/outputs) of the MCVP are coaxial for a given flywheel inertia, the energy stored is purely a greatly aids producing a compact and torque/power- function of rotational speed; thus independent and dense package.

continuously variable control of flywheel speed from the

engine and the wheels is fundamental.

The ability of the present variator to provide independent MCVP EQUIVALENT SCHEMATIC

ratio control of two branches within a single planetary

arrangement has led to name of MCVP, meaning Multi- The analogous planetary representation of the MCVP is Continuously Variable Planetary. shown below, with the relevant gear pitch radii that appear in the equations.

MCVP VARIATOR

MCVP GEOMETRY MCVP

The MCVP is a new planetary traction drive using R, a I Planet, ω _ρ

planets that are double truncated cones inclined at an

angle to the main shaft axis equal to half of the cone ^" Tr, 7* ^r ca 7*

angle (Figure 5). This produces two effective straight

edges aligned parallel to the main axis of the variator. 7 fcs ~ ^r T?

Two independent actuator mechanisms control the axial

position of a disc and an annulus/ring (green contact

patches) that make contact with the inner and outer

effective edges of the planet. This changes the contact

radius on the planet and thus the linear speed, changing

the rotational speed of the said disc and annulus. The

annulus and the disc rotate about the main rotational

axis. Thus there are two independently controllable ratio

mechanisms, which, as mentioned, is equivalent to

having two independent variators. J T_

Figure 6: Equivalent compound planetary schematic for the MCVP SUPPLEMENT

With regard to the equivalence of the MCVP to using two These equations are ideal since they assume no slip separate variators, higher transmission efficiency is occurs in the traction contact patches.

expected here for certain power paths, which would

otherwise involve crossing two separate CVTs and Variable sun branch

therefore be subject to the square of the efficiency of a

single variator (see Figure 9 below).

∑£i ₊ ∑JL

ω

Of fundamental importance, (in common with the Milner ω ₅

CVT and the NuVinci CVP) all the branches contact the s

same set of idling planet elements, therefore all possible

power paths through the CVT cross a maximum of two Variable annulus branch

traction contacts in series (effectively passing through a

single CVT). Therefore, assuming efficient elasto- hydrodynamic conditions are generated at each of these 6> _a

contacts, higher transmission efficiency is expected

compared to using two CVTs, where some power paths

involve crossing two CVTs (which usually equates to 4

traction contacts in series). In general, traction contacts

in parallel add linearly to the torque capacity of a CVT, Planet carrier

but traction contacts in series reduce efficiency with a

multiplicative relationship. The MCVP and the two prior

art devices mentioned are advantageous in both of these

regards. ω ₅

Rs R&

SUPPLEMENT

However, this is when the engine is kept running in a proposed system. There is no need for a pulling away constant condition. If the engine speed reduces, the device such as a clutch or a torque converter. Any flywheel will not be able to reach its design speed of 25 external torque applied at the vehicle wheels will not 000 rev/min. A range extending gearbox could be cause the vehicle to move, whic provides an effective provided for the flywheel and or other branches. This is parking brake when the vehicle is stationary on an effectively a discrete gearbox with a number of speed inclined road.

ratios that can be used in conjunction with the

continuously variable ratio. A system like Flybrid's There is, however, a novel feature of this IVT system aforementioned CFT could be used for this purpose. that is very important, which is that all other branches of This would allow all the benefits of the proposed system the system remain rotational, and actuation of the other to be maintained but the ratio range for the flywheel ratio control mechanism provides full continued would be Increased. The same could be done for the functionality for that respective branch independent of final drive if necessary, to allow finer control of the the geared-neutral condition of the final drive. This vehicle speed. The use of the CFT system would mean allows the flywheel to be charged with prime mover that there would be no torque interruption when the power by actuating the other ratio mechanism so as to range extending ratios are changed. This would also be increase the flywheel speed. In conventional IVT the case with a dual clutch transmission used as a range systems in geared-neutral mode, the power is just extending gearbox. recirculated and ultimately dissipated (wasted) as heat in the transmission. In the present system it may be stared

The fact that these relations are linear makes for easier for later use, thus increasing system efficiency. As the control of the system. vehicle pulls away, the torque subtracted from the transmission by increasing the flywheel speed is

I T FUNCTIONALITY controllably reduced.

By examining the speed ratio equation for the variable OPERATING REGIMES

ratio annulus branch, it is clear that this branch has a

possible geared-neutral condition. This is when there is The most important operating regimes for the system are zero output speed for any finite input speed. This shown with the aid of power flow diagrams in the condition is achieved when the term in square brackets Appendix, in Figures A1 to A8. A key to the symbols is equal to zero, which occurs when the following two used is presented in Figure AO

quotients are equal:

The proposed system has exactly the same functionality as the transmission shown in Figure 9 below, and

Ra Ra reference shall be made to this figure in explaining how the proposed system is able to accomplish simultaneous

Either side of this geared-neutral condition, the direction regenerative braking (kinetic energy recovery) whilst of rotation of the variable annulus branch reverses, simultaneously charging the flywheel with surplus engine providing the potential for reverse gear (if desired): power. This feature is required if the engine is to run in a constant condition as the vehicle operates.

s, e o ow ng ene s are us ga ne y e such that the vehicle speed reduces, the kinetic energy SUPPLEMENT and momentum are exchanged between the vehicle and A scaling analysis of the variator is currently being the flywheel. If the engine is also supplying torque undertaken to assess what the optimum design (positive) and the CVT ratio is changed such that this parameters are for a given application. More detailed torque is also consumed by the changing the flywheel dynamic simulation is intended along with accurate speed, then the flywheel is being used to accept the mathematical models for the elasto-hydrodynamic (EHL) vehicle kinetic energy and the engine power at the same loss mechanisms within the variator.

time.

The system behaves like an electric series hybrid, in that

the engine can run in an efficient regime, but without the REFERENCES

associated energy conversion losses from mechanical to

electrical to chemical potential and back again. It also 1. Sovran, G., 'The Impact of Regenerative Braking on behaves like a parallel hybrid in that the flywheel can the Powertrain-Delivered Energy Required for add power to the transmission such that more power is Vehicle Propulsion" SAE Technical Paper, 2011-01- being supplied than that by the engine alone (Figure A4). 0891 , 2011 , doi: 10.4271/2011-01-0891

2. Cross, D., Brockbanck, C, "Mechanical Hybrid

When the engine is running in a constant condition, the System Comprising a Flywheel and CVT for flywheel can accept surplus engine torque to prevent the Motorsport and Mainstream Automotive wheels from slipping at low speed (Figure A3).

Applications" SAE Technical Paper, 2009-01-1312, 2009, doi: 10.4271/2009-01-1312

3. Genta, G., "Kinetic Energy Storage: Theory and

CONCLUSION

Practice of Advanced Flywheel Systems", Butterworths, London, ISBN 0408013966, 978-

A novel multiple-input variator with two independent ratio

0408013963, 1985

control mechanisms has been presented. A mechanical

hybrid transmission using flywheel energy storage 4. Moyers, J., Akehurst, S., Parker, DA, Schaaf, S., centred around this variator has been proposed. The "The Application of the Milner CVT as a Novel Power system provides the operational flexibility associated Splitting Transmission for Hybrid Vehicles", SAE with using two separate CVTs for the prime mover and Technical Paper, 2011-01 -0890, 2011 , doi: the flywheel, but achieved with a single variator. This 10.4271/2011-01-0890

provides a wide range of potential control strategies and 5. Pohl, B., Simister, M., Smithson, R., Miller, D., effectively provides a mechanical equivalent to electric "Configuration Analysis of a Spherical Traction Drive series and parallel hybrids. However, since the energy is CVT/IVT", SAE Conference Paper, 04CVT-9 not converted to different forms, the proposed solution 6. Smithson, R., Miller, D., and Allen, D., "Scalability for has the potential to be more efficient. Furthermore, an Alternative Rolling Traction CVT," SAE Technical power flow between any two branches effectively only Paper 2004-01-0355, 2004, doi:10.4271/2004-01- crosses a single CVT per one way trip and therefore 0355

relatively high mechanical transmission efficiency may 7. Carter, J. and Miller, D., 'The Design and Analysis of result. an Alternative Traction Drive CVT," SAE Technical

Paper 2003-01-0970, 2003, doi:10.4271/2003-01-

Being a fully mechanical solution, added value to the 0970

cost of materials in mass production is relatively high. 8. Cross, D., UK patent GB2476676B, published 7 ^th Tthe cost per unit should reduce significantly relative to Dec 2011

battery electric hybrids when produced in reasonable

volumes, since it only requires the use of widely

available and recyclable materials (such as steel and

aluminium) and can make use of mass production

forming processes (such as casting for the casings). At

the end of life, the system can be melted down and the

materials fully reused for another purpose.

Thus the proposed system potentially provides a more

sustainable and low cost alternative to electric hybrids

whilst retaining all the beneficial features, such as

efficient combustion engine operation, power assistance,

potential for engine stop-start and kinetic energy

recovery. SUPPLEMENT

DEFINITIONS, ACRONYMS, ABBREVIATIONS f _c : Contact radius on planet (perpendicular distance from planet axis) that can be varied by actuating ratio control

MAIN SMYBOLS: mechanism

ai: Angular speed

SUBSCRIPTS:

R: Perpendicular distance of centre of traction contact

from main rotational axis of MCVP or pitch radius of a: Constant ratio annulus branch

constant sun/annulus teeth a Variable ratio annulus branch

s: Constant ratio sun branch

r: Perpendicular distance of centre of traction contact s: Variable ratio sun branch

from planet rotational axis or pitch radius of planet teeth

APPENDIX: OPERATING REGIMES & POWER PATHS

Variable radius Variable radius Open clutch Closed clutch Power flow gear not being gear in possible

actuated actuation

Figure AO: Key to symbols

Figure A1 : Conventional geared-neutral mode (power recirculated & dissipated as heat) SUPPLEMENT

Fi ure A2: Charging of flywheel in geared-neutral mode

Figure A3: Surplus prime mover power (including traction-limited acceleration)

SUPPLEMENT

Figure A5: Pure regenerative braking

SUPPLEMENT

Figure A7: Driving with prime mover power alone

SUPPLEMENT

Figure A8: Driving with flywheel power alone