Field of the invention

The present invention relates to a hybrid system for vehicles, and in particular to a method for determining a fuel

consumption of a hybrid vehicle according to the preamble of claim 1. The invention relates also to a system and a

vehicle.

Background to the invention

Growing official concern about pollutants and air quality, especially in urban areas, has lead to the adoption of

emission standards and rules in many jurisdictions.

Such emission standards often set requirements which define acceptable limits for exhaust discharges from vehicles

equipped with combustion engines. These standards often regulate, for example, levels of discharge of nitrogen oxides (NO _x ) , hydrocarbons (HC) , carbon monoxide (CO) and particles from most types of vehicles.

The endeavour to meet such emission standards has led to ongoing research in many fields, one such field being post- treatment (cleaning) of the exhaust gases which arise from combustion in a combustion engine.

Another field, also stimulated by constantly rising fuel costs, is research into and development of hybrid vehicles.

The use in urban areas of vehicles in general, and heavy vehicles in particular, often involves frequent starts and stops during a journey, with consequent accelerations which consume fuel and, within the scope of fuel consumption

behaviour, retardations which release kinetic energy. The

RECORD COPY-TRANSLATION

(Rule 12.4 result is that a large amount of energy is put into accelerating the vehicle, only to be cancelled out, often after only a relatively short time, by braking action. Such scenarios are particularly common in areas where there is high traffic density and/or frequent traffic lights or, in the case of urban buses, stopping points at short intervals.

Hybrid vehicle is a vehicle which uses two or more sources of power and/or fuel. A common type of hybrid vehicle comprises electric hybrid vehicles, which have a first power-generating source, e.g. a combustion engine, and one or more electrical machines, the latter being used to generate driving force which is conveyed to the vehicle's powered wheels.

Using an electrical machine as prime mover affords the

advantage that in certain operating conditions, as when using the electrical machine for braking, e.g. to retard the vehicle or to maintain a constant vehicle speed downhill, the

electrical machine can regenerate electrical energy for feeding back to the vehicle's electrical system. This regenerative braking affords the advantage that the energy generated can be used to charge up an energy store for storage of electrical energy. Energy stored in the energy store can be utilised by the electrical machine on the occasion of a subsequent acceleration and thereby reduce the load upon the combustion engine, with consequent reduction in fuel

consumption.

This "cooperation" between electrical machine and combustion engine in electric hybrid vehicles often works so well that the vehicle's driver does in principle notice no difference between driving a hybrid vehicle and driving a similar conventional vehicle. As the purchase cost of an electric hybrid vehicle is usually higher than that of a conventional vehicle, it is important for the vehicle's owner to be able to have confirmation that investing in a hybrid vehicle is also economically profitable. Summary of the invention

An object of the present invention is to propose a method which solves the above problem. This object is achieved by a method according to claim 1.

The present invention relates to a method for comparing a fuel consumption of a first vehicle with a second vehicle, which first vehicle has a first energy converter in the form of a combustion engine to generate a first driving force for propulsion of said first vehicle, and at least a second energy converter in the form of a first electrical machine to

generate a second driving force for propulsion of said

vehicle, which method comprises, at a first point in time, where said first and second vehicles are driven in the same way:

- using determination means to determine a difference in fuel consumption between said first vehicle and said second

vehicle, said second vehicle having only one energy converter to generate driving force for its propulsion, in the form of a combustion engine which is substantially identical with said first combustion engine. The fuel consumption of the hybrid vehicle is thus compared with the fuel consumption which would have resulted from propulsion of the same vehicle, i.e. a vehicle equipped with a substantially identical combustion engine, and a preferably also identical gearbox, when driven along the same stretch of road. By determining the difference in fuel consumption of a vehicle which apart from the hybrid portion is in principle identical, i.e. a vehicle with otherwise substantially identical

essential power train components, i.e. combustion engine and gearbox, and preferably the same power train transmission ratio, it is possible to arrive at a very exact measure of amounts of fuel saved, and hence of cost of fuel saved, resulting in a simple way of presenting to the vehicle' s driver and/or owner the profitability of investing in a hybrid vehicle.

The fuel saving may be presented graphically on a display to the vehicle's driver, thereby providing him/her with

information about the fuel saving continually or when so desired. The fuel saving may for example be expressed in terms of total cumulative savings since the vehicle was first put into operation, or in terms of saving during a particular journey or period of time, e.g. a current month. The fuel saving may be presented as an amount of fuel and/or be

combined with fuel cost in order to provide also an economic measurement of the saving. The fuel saving may also be divided into savings in different situations.

As well as the driver being presented with fuel saving data, data may also be sent to the vehicle's owner, e.g. via an RTI (Road Traffic Informatics) system. In an embodiment, the method comprises comparing a driving force delivered by the electrical machine with a driving force delivered by the combustion engine and thereby determining a difference in fuel consumption based on said driving forces delivered respectively by said electrical machine and

combustion engine. Said driving force may take the form of torque delivered or power output delivered. Further characteristics of the present invention and advantages thereof are indicated by the detailed description of embodiment examples set out below and the attached

drawings . Brief description of the drawings

Fig. la depicts a power train in a vehicle with which the present invention may with advantage be used.

Fig. lb depicts an example of a control unit in a vehicle control system. Fig. 2 is a diagram of the fuel consumption of a combustion engine as a function of engine speed and torque.

Fig. 3 depicts a method example according to the present invention.

Detailed description of preferred enbodiments The power train in a hybrid vehicle comprises not only the components pertaining to a conventional vehicle but also a hybrid portion in the form of various further components, e.g. electrical machine, power electronics unit for running the electrical machine, energy store etc. These components are relatively expensive, with the natural consequence that the procurement cost of the hybrid vehicle is higher than that of a similar vehicle with no hybrid portion.

The combustion engine and the electrical machine are

controlled by the vehicle's control system, and the

cooperation between combustion engine and electrical machine often works so well that the vehicle driver's experience of driving a hybrid vehicle does in principle not differ at all from that of driving a conventional vehicle. He/she thus has no sensation of the fuel saving which the hybrid system does in fact contribute. The present invention resolves this by determining the hybrid vehicle's fuel saving relative to a conventional vehicle which apart from the hybrid portion is identical, when the conventional vehicle is driven along the same stretch of road as the hybrid vehicle.

This is exemplified below with reference to the depiction in Fig. la of a power train in a vehicle 100 according to a first embodiment example of the present invention. There are various types of hybrid vehicle, that depicted being a

parallel hybrid vehicle.

The power train of the parallel hybrid vehicle in Fig. la comprises a combustion engine 101. The combustion engine 101 is connected to a gearbox 103 in a conventional way, via an output shaft 102 from the engine 101. Gearboxes in heavy vehicles often take the form, as in the embodiment depicted, of a "manual" gearbox 103 in which gear changing is effected automatically (by means of the vehicle's control system).

This is partly because manual gearboxes are substantially less expensive to make, but also because of their greater

efficiency. For this reason, the vehicle 100 comprises also a clutch 106 for selectively connecting the output shaft 102 of the engine 101 to the gearbox 103.

In the present example, the clutch 106 is automatically controlled by the vehicle's control system, but it might also be manually controlled, since control systems in vehicles with a clutch which is controlled manually (by the driver) can in a known way effect gear changes with the clutch closed, i.e. without using the clutch. The automatically controlled clutch 106 is controlled by means of a clutch actuator (not depicted) on the basis of control signals from a control unit 116. The vehicle further comprises drive shafts 104, 105 which are connected to its powered wheels 113, 114 and which, as in a conventional combustion engine system, are powered by a gearbox output shaft 107 via an axle gear which may for example take the form of a conventional differential 108. The vehicle has also a pair of front wheels 111, 112.

Unlike a conventional vehicle, the vehicle depicted in Fig. la has also an electrical machine 110 connected to the input shaft 109 of the gearbox 103, "downstream" of the clutch 106, which means that the gearbox input shaft 109 can be driven by the electrical machine 110 even when the clutch 106 is open. Parallel hybrid vehicles can thus transmit power to powered wheels 113, 114 from two separate power sources

simultaneously, viz. both from the combustion engine 101 and from the electrical machine 110. Alternatively, the vehicle may be propelled by either power source individually, i.e. either by the combustion engine 101 or by the electrical machine 110. In an alternative embodiment, the electrical machine is situated upstream of the clutch or downstream of the gearbox. Depending on the location of the electrical machine, not all of the characteristics described below need be applicable. For example, the vehicle cannot be run on electric drive alone if the electrical machine is situated upstream of the clutch. The vehicle may also be of a type with conventional automatic gearbox, with the electrical machine situated upstream or downstream of the gearbox.

As specialists will appreciate, there are various types of electrical machines suitable for use in hybrid vehicles, so the electrical machine 110 may be of any suitable type. In the example described below, however, the electrical machine is a three-phase motor, so the power supply to the electrical machine 110 will be a three-phase power supply. Three-phase motors may be of both asynchronous and synchronous types, and a synchronous motor affords the advantage that exact

determination of its speed is possible. In vehicle

applications it is for obvious reasons desirable for it to be possible for the rotation speed of the powered wheels, and hence of the electrical machine, to be varied in addition to the variation achievable by conventional gear changes via the gearbox, so it is usually also necessary for it to be possible to control the speed of the electrical machine. The speed of an electrical machine is generally controlled by the frequency of the supply voltage by which the motor is powered, the speed of the electrical machine being directly proportional to that frequency. Speed control of an electrical machine thus entails being able to vary the voltage supplied to the motor. In the case of an alternating-current motor, this means that it has to be possible to vary the frequency of the AC supply voltage . The motor 110 depicted in Fig. 1 is therefore provided with by a three-phase power supply with variable frequency, generated by means of a power electronics unit 117. The power

electronics unit 117 works against an energy store 118, e.g. one or more batteries, supercapacitors etc. The energy store may be adapted to being charged in various different ways, e.g. by regenerative braking by means of the electrical machine 110 and/or by being plugged into an external power source, e.g. a conventional electricity network.

The power electronics unit 117 depicted may be of a type commonly used in hybrid vehicles and therefore not described in more detail here. Generally speaking, however, the power electronics unit 117, in the case of an AC motor, converts the DC voltage of the energy store 118 to an AC voltage. The conversion is effected by means of a converter device which may for example comprise a number of IGBTs (insulated gate bipolar transistors) which can, by means of suitable

switching, provide three-phase voltage of desired and variable amplitude and frequency to power the electrical machine 110 and hence the vehicle's powered wheels 113, 114.

The electrical machine 110 can thus be used to propel the vehicle 100 at vehicle speeds ranging from zero to maximum speed, or a lower speed, depending on the size of the

electrical machine, by control of the frequency supplied to the motor 106 from 0 Hz to a frequency which results in the top speed of the vehicle (or, in cooperation with the

combustion engine, the top speed of the engine) . In the case of heavy vehicles, however, a very large battery capacity and hence a very heavy battery is at present required to enable the vehicle to be powered for substantial distances by an electrical machine alone. For this reason, the electrical machine 110 is usually only used for propulsion in certain situations, some of which are described below.

Control systems in modern vehicles usually further comprise a communication bus system consisting of one or more

communication buses for connecting together a number of electronic control units (ECUs) , or controllers, and various components located on the vehicle. Such a control system may comprise a large a number of control units, and the

responsibility for a specific function may be divided among two or more of them.

For the sake of simplicity, Fig. la only depicts, apart from the previously mentioned control unit 116, four further electronic control units 115, 119, 126, 127. In this embodiment, the control unit 119 controls the engine 101, while the control unit 116 controls the clutch 106 and the gearbox 103 (two or more from among engine, gearbox and clutch may alternatively be arranged to be controlled by one and same control unit or by undepicted other control units) . The control unit 115 controls electrical machine/power electronics unit/energy store. The control units 115, 116, 119 can communicate with one another via said communication bus system, as illustrated by lines drawn between them in the diagram.

The control unit 126 controls the vehicle's RTI (Road

Transport Informatics) system, which covers functions such as traffic information and vehicle navigation. In the present example, the control unit 126 is also responsible for

presenting to the vehicle's owner in the present embodiment example the fuel saving of the hybrid portion. The RTI control unit is normally responsible for the vehicle's communication with, for example, a fleet management portal, making it possible for data to be transmitted to said portal for evaluation by the vehicle's owner.

The control unit 127 controls data display on the instruments provided in the driving cab, which often comprise not only conventional indicating instruments but also one or more displays. By means of the control unit 127 it is possible for fuel consumption data to be presented on these one or more displays, or a display specifically intended for presentation of fuel consumption data to the vehicle's driver.

Control units of the type referred to are normally adapted to receiving sensor signals from various parts of the vehicle, e.g. gearbox, engine, electrical machine, clutch and/or other control units or components of the vehicle. The control signals generated by control units normally depend both on signals from other control units and on signals from

components. For example, the control exercised by the control unit 115 over the electrical machine 110/power electronics 117 etc. will depend on, for example, information received from, for example, the control units 119, 126, 127 and/or 116.

The control units are further arranged to deliver control signals to various parts and components of the vehicle, e.g. to the electrical machine 110 and the power electronics unit 117, in order to control them. The present invention may be implemented in any of the above control units, or in some other suitable control unit in the vehicle's control system. The functions of the invention may also be divided among two or more of said or other control units. The control is often governed by programmed instructions.

These programmed instructions take typically the form of a computer programme which, when executed in a computer or control unit, causes the computer/control unit to effect desired forms of control action, e.g. method steps according to the present invention. The computer programme usually takes the form of a computer programme product 109 which is stored on a digital storage medium 121 (see Fig. lb), e.g. ROM (read-only memory) , PROM (programmable read-only memory) , EPROM (erasable PROM) , flash memory, EEPROM (electrically erasable PROM), a hard disc unit etc., in combination with or in the control unit, and which is executed by the control unit. The vehicle's behaviour in a specific situation can thus be adapted by altering the computer programme's

instructions. An example of a control unit (the control unit 127) is

depicted schematically in Fig. lb and the control unit 115 may in turn comprise a calculation unit 120 which may take the form of substantially any suitable type of processor or microcomputer, e.g. a circuit for digital signal processing (Digital Signal Processor, DSP) , or a circuit with a

predetermined specific function (Application Specific

Integrated Circuit, ASIC) . The calculation unit 120 is connected to a memory unit 121 which provides it with, for example, the stored programme code 109 and/or the stored data which the calculation unit 120 needs in order to be able to perform calculations. The calculation unit 120 is also arranged to store partial or final results of calculations in the memory unit 121.

The control unit 115 is further provided with respective devices 122, 123, 124, 125 for receiving and sending input and output signals. These input and output signals may comprise waveforms, pulses or other attributes which the input signal receiving devices 122, 125 can detect as information and which can be converted to signals processable by the calculation unit 120. These signals are thereafter conveyed to the calculation unit 120. The output signal sending devices 123, 124 are arranged to convert signals received from the

calculation unit 120 in order, e.g. by modulating them, to create output signals which can be transferred to other parts of the vehicle's control system and/or the

component/components for which the signals are intended. Each of the connections to the respective devices for receiving and sending input and output signals may take the form of one or more from among a cable, a data bus, e.g. a CAN (Controller Area Network) bus, a MOST (Media Orientated Systems Transport) bus or some other bus configuration, or a wireless connection.

A method example 300 according to the present invention is depicted in Fig. 3. As indicated above, the basic concept of the present invention is to compare the fuel consumption of the hybrid vehicle with the fuel consumption which would arise from driving the same vehicle with no hybrid portion along the same stretch of road. The method 300 begins at step 301, which determines whether the fuel consumption difference is to be determined. The fuel consumption difference may for example be arranged to be determined at equal intervals of time, e.g. every second, every fifth second or some other suitable interval. The interval may also be arranged to be varied when the vehicle is in motion. For example, the fuel consumption difference may be determined at shorter intervals in situations such as powerful accelerations which involve rapid changes in the operating point of the engine and/or the electrical machine. The method moves on from step 301 to 302, which determines the current fuel consumption of the hybrid vehicle 100, followed by step 303, which determines fuel consumption of a

corresponding conventional vehicle. When fuel consumption has been determined for both vehicles, the difference in fuel consumption is determined at step 304 and is presented to the driver and/or the vehicle owner at step 305. The method may then go back to 301 for the next determination (at a point in time or over a period of time) . Instead of determining consumption explicitly for both types of vehicle, and

thereafter the difference, as in steps 302-304, steps 302-304 may be combined in a single step, as exemplified by the equations below.

By determining the difference in fuel consumption of a vehicle which apart from the hybrid portion is in principle identical, i.e. a vehicle with otherwise substantially identical

essential power train components, i.e. combustion engine and preferably also gearbox, it is possible to arrive at a very exact measure of amounts of fuel saved, and hence also, by means of information concerning fuel prices, a very exact measure of fuel costs saved. Thus the vehicle's driver, and perhaps especially its owner, can as above have concrete proof that it is in fact not only environmentally friendly but also profitable to invest in a hybrid vehicle.

There are various possible ways of determining the difference in fuel consumption, and a specific calculation example is described below in the case of an engine in the form of a diesel engine, although the invention is applicable to any combustion engine.

As well as the possibility of fuel saving being calculated in various different ways, fuel may be saved by means of the hybrid system in various different situations. Examples of such situations are described below. It should however be appreciated that fuel savings may vary greatly from situation to situation. It should also be noted that at the same time as there being advantage in presenting the composite fuel saving for all of the fuel-saving situations, there may also be advantage in presenting fuel savings for only one or a limited number of the situations described below. One

embodiment example determines only the fuel saving achieved in situations where the engine's torque exceeds a predetermined value, since only this determination can provide a good indication of fuel saved. An alternative embodiment uses a combination of, for example, all of the calculation approaches exemplified below.

As previously mentioned, the electrical machine is situated on the gearbox input shaft, making it possible for the combustion engine and the electrical machine either individually or in conjunction to drive the vehicle's powered wheels. The electrical machine helping the engine to propel the vehicle reduces the engine's fuel requirement.

Fig. 2 is a diagram illustrating an example of how fuel consumption of an engine example may vary with its speed and torque delivered T. The fuel consumption is depicted as fuel flow in litres per hour. As may be seen in the diagram, the distance between the fuel flow curves is constant or

substantially constant throughout much of the diagram, particularly with respect to power output changes at a certain engine speed. This means that in principle the engine's fuel consumption varies in a linear manner with power output delivered (and hence also in a linear manner with torque changes). Thus the engine's efficiency is (substantially) constant over large parts of its operating range. Assume for example that the engine is operating at point a, i.e. is delivering a power output (torque is referred to below but power output might equally well be used, since torque and power output are linked by simple and well-known mathematical relationships. The claims set out below use the term driving force to denote torque delivered or power output delivered) T _a at engine speed ηχ. If the electrical machine now contributes a torque T _b , the torque delivered by the engine will drop to T _a -T _b =T _c (point c) (if the same driving force is to be obtained as would be the case without any hybrid portion) . As the engine's fuel consumption is linear with respect to power output, i.e. the efficiency at point c is the same as at point a (the fuel flow per kilowatt power/newtonmetre developed is the same) the fuel saving due to the help from the electrical machine will be directly proportional (linear) to the torque (the power output) contributed by the electrical machine. In other words, so long as the efficiency is the same, the amount of fuel injected will be linear to torque delivered. If the torque generated by the engine's combustion decreases by half, it means that fuel injected likewise decreases by half. The efficiency of a combustion engine is usually substantially constant at a given engine speed, in which case the fuel saved by means of the hybrid portion can be estimated at

FuelSaved =Y FuelRate{n)« ElMotorTorque(n) _χ ^ _{(/) eq ( 1 )}

EngineTorque(n)

This equation is written in the form of a sum whereby

calculations are made for various measuring points/measurement periods (n) of duration At , where At may as above vary in length depending on the particular driving situation.

In equation (1) the notations are as follows:

FuelSaved = fuel saved, expressed in litres, cumulatively over the period t covered by the calculation.

FuelR tein) = current fuel consumption at the time of measurement, e.g. expressed in litres per second. Fuel consumption may for example be determined by means of a model of the engine, which may be stored in the vehicle's control system as a

mathematical expression or in tabular form, making it possible to use current engine control parameters to determine

FuelRate(n) .

EngineTorque(n) is the engine's torque for a specific measuring point/measurement period (n) .

El Motor Torque(ri) is the electrical machine's torque for a

specific measuring point/measuring period (n) . The equation may of course also be written in the form of an integral, and torque may be replaced by power output delivered or some other suitable unit which represents driving force delivered. Equation (1) might thus also be written

FuelSaved =Y FuelRate(n)x — —x At (/)

Engine Pr opelPow(ri) in which PropelPow (propelling power) represents driving force.

As the engine's fuel consumption is, or may with good accuracy be assumed to be, linear to current torque in situations as above, the saving over the period Δ will be similar to the electrical machine's contribution relative to the engine's contribution. If the electrical machine delivers the same torque as the engine, the saving will thus be equal to the engine's current fuel consumption. If for example the

electrical machine's contribution is 25% of the torque which the engine would have had with no electrical machine, the fuel

0,25 saving thus becomes one-third of current consumption ( ).

(1 -0,25)

The method expressed in equation (1) for calculating fuel saving may be used so long as the engine' s torque is the same, or substantially the same, at the operating point at which the engine would operate with no contribution from the electrical machine, e.g. point a above, as at the operating point at which the engine operates with contribution from the

electrical machine (e.g. point c above). Depending on how accurate a determination is desired, the difference in the engine's efficiency between points a and c may for example be allowed to deviate by some value which depends on desired accuracy, e.g. 1%, i.e. the fuel consumption need not be completely linear to the engine's power output. The diagram in Fig. 2 may for example be stored in vehicle's control system in a suitable way, e.g. in the form of values for different (power output) torque/engine speed combinations, to make it possible on each occasion (n) to determine by means of said stored data whether equation (1) is applicable for use in the calculation in order to achieve the desired accuracy. For example, there may be certain parts of the engine's operating range in which it is not appropriate to employ equation (1) . Moreover, only positive electrical machine torque is included in the calculation when using equation (1) . In the case of negative electrical machine torque, ElMotorTorque =0. Moreover, calculation according to equation (1) is preferably only employed when the engine delivers positive power train torque. Even if the engine's combustion delivers positive torque, this may still mean, owing to engine friction and other losses, that the torque contribution to the power train is negative, i.e. there is engine braking, in which case saving according to equation (1) is not relevant. Moreover, equation (1) may be arranged to be applicable only when the engine's torque, EngineTorque , or the torque delivered by its flywheel, is greater than a predetermined threshold value. This depends for example on the possibility of the engine's efficiency at low torque being comparatively low, so further compensation as below may be required.

Points where EngineTorque is below the threshold value are set to 0. At the same time, other modes of calculation may therefore be used in such situations, some of which are exemplified below. In an embodiment, the mode of calculation described is also applicable when the vehicle runs on electric drive alone, but since power output is then used because the engine and the electrical machine will run at different speeds, no torque comparison can be applied.

In this case the engine usually also idles, often at an operating point with impaired efficiency. Depending on the operating point at which the engine would have run with no contribution from the electrical machine, the accuracy may therefore be impaired in this situation. If the engine would have run at an operating point with higher efficiency, the equation will not fit exactly (i.e. there is a difference in engine efficiency between the operating points), so a

compensation factor may be applied where necessary. For

vekn.gfad example, the calculated value may be compensated by - — verkn.grad _e to cater for the fuel saving not being exactly the value arrived at by the equation. Other types of recalculation factors may of course also be used.

The vehicle may also be propelled entirely electrically without the engine being run, in which case the saving will be the fuel which the engine would have consumed at the

respective engine speed and electrical machine power

output/torque .

The result of the sum in equation (1) may be summarised in a parameter which is preferably not zeroed during the truck's service life. This means that the total fuel saved to date can be presented to the driver and/or the vehicle owner. The result may also be saved in the form of a parameter

representing, for example, an ongoing journey in order to be able to compare savings on various consecutive journeys along the same route.

The vehicle may also be provided with current propellant costs, e.g. input of current propellant prices by its driver when refuelling. Knowing the propellant price makes it possible to present not only savings in terras of litres of fuel but also savings in economic terms. Instead of input by the driver, the fuel price may for example be obtained via some suitable wireless link, e.g. by means of the RTI system. A further example of a situation in which the hybrid portion of the power train may cause a fuel saving is when the vehicle is set in motion from stationary.

When setting off from stationary, as compared with a

conventional vehicle, a fuel saving arises from two factors. The first is the elimination of energy losses due to clutch slip. When the vehicle is being set in motion, the clutch normally closes enough to transmit the maximum torque which the engine can deliver at idling speed. This clutch position is then maintained until the gearbox input shaft reaches the engine's idling speed, whereupon the clutch closes completely. This clutch slip results in energy losses in the form of friction heat. The other factor is the fact that the

electrical machine can be used by itself to set the vehicle in motion without the engine having to be started. The saving achieved by less clutch slip can then be calculated as

SlipLossin) = *¾*» ⁽ n ^{) ~} ElMotorSpeedin) _{χ m χ mMotorTorqm n) {W)}

eq. (2) This value is then used in the equation

FuelSaved = _n SlipLoss(n)x Ergy2FuelFactx t (/) eq. (3) in which Ergy2FuelFact is a conversion factor to make it possible to correctly compare what energy drawn from the battery represents in terms of fuel. The calculation procedure described becomes somewhat generalised, since the engine does not have the same efficiency at every operating point and starting the engine may take place at different operating points. However, practical experiments have shown that despite the generalisation very good accuracy is achieved over time .

A further situation in which substantial saving is possible is when the engine is switched off at a halt.

In this case it is quite simple to determine the sum of the engine' s normal idling fuel consumption FuelRateldle for the periods of time when it would normally have been running, viz. FuelSavedldle = FuelRateldle x At (I) .

It may be advantageous to cater for this value separately, since an economically minded driver of a conventional vehicle may actually switch the engine off spontaneously on the occasion of shorter and/or longer halts, in which the actual saving may be less than calculated.

A further situation resulting in fuel saving, albeit in relatively small amounts, e.g. 5 Wh per start, is where the engine is started by the electrical machine. In a parallel hybrid the electrical machine may be used instead of a

conventional starter motor to start the engine. This means that a saving occurs when braked-in energy is drawn upon, and there is no need for generator load upon the engine to charge an ordinary starting battery.

Only fuel-saving measures are referred to in the foregoing, but there are also situations where the hybrid portion of the power train causes energy losses. The greatest loss occurs when the batteries are charged from positive engine torque. For the energy store to achieve long service life, it is for example usable only within a certain range of its total capacity, e.g. between 40 and 60% of battery full charge.

This means that if the charge becomes too low, e.g. drops to 35%, the battery has to be charged by the engine. This is effected by imposing electrical machine load upon the engine, with consequently increased fuel consumption.

This increased fuel consumption may be calculated as

„ ng ne orque n

There are also further factors which may cause the hybrid vehicle to suffer energy losses.

For example, fan and pump functions may be required for the hybrid portion of the power train (e.g. for cooling of electrical machine/energy store) , leading to electrical losses from the vehicle's conventional electrical system (usually a 24V system in heavy vehicles) .

This energy loss may be compensated for when there is positive engine torque (when "negative" engine torque is required, charging may be effected at no cost by using the electrical machine for braking) . The power consumed in operating such ancillaries can be calculated in conventional and known ways. The total power consumption arising due to these ancillaries can then be converted to a corresponding engine torque by dividing by 2*n* EngineSpeed . The fuel losses can then be calculated by means of equation (1) above, in which

ElMotorTorque(n) is replaced by the calculated torque.

The extra rolling resistance due to the increased weight of the hybrid vehicle has also to be taken into account. The rolling resistance may likewise be converted in a known way to a power output and be aggregated with the above ancillary losses when using equation (1) above.

The increased weight due to the hybrid portion of the power train (which varies from vehicle to vehicle and depends on energy store capacity, but may in an example represent about 200 kg) also causes increased energy expenditure during acceleration and when driving uphill. So long as no active braking takes place, however, this energy is stored as extra kinetic energy which can be utilised on, for example, downhill runs to accelerate the vehicle, or to charge the energy store by means of the electrical machine. If however the stored kinetic energy is braked away, these losses have also to be taken into account. A further aspect to be catered for in the calculation is that in hybrid vehicles the electrical machine can be used to move the engine's operating point in order to improve emission characteristics. In certain cases, this saves fuel as

compared with applying traditional methods. An example is that diesel fuel is often used to burn particle filters clean. By moving the engine's operating point it is possible to raise exhaust temperatures without having to use diesel fuel to burn the particle filter clean. In this case the amount of diesel fuel which would normally have been used to burn the filter clean is added to the above. Each individual emission strategy requires a calculation algorithm of its own for saved fuel.

All in all, a very good estimate of total fuel saving by the hybrid vehicle can thus be determined and be presented to the vehicle's driver in a suitable way, e.g. via a display as above .

For example, fuel saving may be expressed as fuel saved during the particular journey, average fuel saving per hour or distance, or total fuel saved since zero reset. The driver may preferably do a trip data reset in a conventional way. In the control unit, however, there is no zeroing of the

parameters, as the vehicle's journey computer determines only new reference points at zero reset.

As above, calculated parameters may likewise be sent to, for example, a fleet management portal, making it possible for the vehicle's owner to follow up saved fuel. Statistics may also be calculated about the routes, the driver/drivers or the type of driving for which the hybrid system is most advantageous and therefore most quickly saves against the increased purchase cost.

The invention is described above in relation to a parallel hybrid system. The invention is nevertheless applicable to other types of hybrid system, provided that they incorporate a combustion engine and provided that fuel consumption is compared with a vehicle provided with a substantially

identical combustion engine.

As previously mentioned, it should be noted that a combustion engine which is provided with starter motor/generator and is otherwise similar to the engine of the hybrid vehicle is regarded in this context as identical with the engine of the hybrid vehicle. The same applies to such other small changes as may be required by the hybrid system. The engine may nevertheless be similar with regard to cylinder volume etc. for the purposes of being regarded as similar according to the present invention.