This invention is related to hybrid transmissions in general and to an apparatus and method for operating multi-mode variable speed transmissions in particular.

Hybrid variable speed transmissions operated under of the principle of power-split are known in prior art. In these transmissions, the input power from a primer mover, an engine for most cases, is split and transmitted through two paths, one mechanical path and one composite path. There are two additional movers often linked in series in the composite path. These two additional movers can be electric machines capable of being operated as motors and generators, in this case, the composite path is referred to as electro-mechanical path. The movers in composite path can also be hydraulic pumps and motors, In this case, the composite path is referred to as hydro-mechanical path. Thereafter, all movers whether being an engine, eieciric machines or hydraulic pumps or motors, are referred collectively to as the motive components of the transmission system.

An example of hybrid variable transmissions is Toyota Hybrid System (THS) where the hybrid transmission is configured to operate in a single power-split mode. THS is adequate for light-duty vehicle applications where the drive torque and required speed ratio spread are relatively low. To extend speed ratio range, concepts for multi-mode hybrid variable speed transmission were disclosed in prior art, see for example US 6,478,705, US 8,226,515 and US 8,602,938. These multi-mode variable speed transmissions were configured to operate under different power-split modes, each covering a specific speed ratio range. Switching between these modes of operation was accomplished through clutches, mostly hydraulic actuated frictiona! clutches. While these clutches can be engaged and disengaged under torque load, and have satisfactory shifting qualities to maintain adequate drivabiiity of the vehicle, they require a hydraulic system for actuation and have high parasitic power losses.

In US 9,005,076, a method and apparatus for controlling a shift in multi-mode powertrain system was disclosed. The apparatus included a multi-mode transmission configured to transfer torque among first and second torque machines (first and second motive components), an engine (a third motive component) and an output member in one of a plurality of transmission ranges or power-spilt operation modes. The disclosed method for mode shifting between two power-split i operation modes inciudes transitioning the transmission to operate with three speed degrees of freedom by "breaking" the gear-train of the transmission apart and controiiing speed of the second torque machine to synchronize speed of an incoming clutch associated with the target power split mode, and coincidentaliy controiiing speeds of the first torque machine and the engine to achieve a preferred speed of the output member of the transmission, and then controlling torque output from the first torque machine in response to an output torque request, and activating the incoming clutch upon synchronizing the speed of the incoming clutch. The disclosed method did not provide any measure to achieve high shift quality by reducing disturbance at drive wheels during the shifting while at the same time maintaining desired engine operation for minimized fuel consumption or emission reductions.

BRIEF SUMMARY OF INVENTION

An object of the present invention is to provide an apparatus and method for controlling a multi- mode hybrid variable speed transmission to achieve high quality mode shifting between different variable speed operations modes by reducing the torque and power disturbances at the drive wheels during the mode shifting while, at the same time, maintaining desired engine operation.

Another object of the present invention is to provide desirable mode shifting conditions through creation of a torque node point for the transmission by following a sequence of control steps; under these conditions positive engagement clutches can be used to achieve comparable or even superior shifting qualities as frictional dutches. Yet another object of the present invention is to provide various means for accomplishing aforementioned smooth and non-interruptive mode shifting.

The objects are achieved by a multi-mode hybrid variable speed transmission configured to operate under different variable speed operation modes, including an output system (Output), a first motive component (a first electric machine, EM1 ), a second motive component (a second electric machine, EM2) and a third motive component (an engine, Eng), a gear system having at least a p!anetary set that has multiple co-axia! rotatab!e gear components to which said motive components are directly or indirectly coupled, a dutch device (CL) having a linear or rotary actuator and multiple dutch components which can be engaged and disengaged by the actuator for shifting said transmission between an initial mode of operation and a target mode of operation, and a controller system for controiiing said transmission and clutch device; said control system including at least a controller and is configured to perform: a process for creating a torque node point in the vicinity of a speed ratio node point of said transmission (torque node point and speed ratio node point will be defined in invention description), the control system comprising a means for controlling torque of at least one of the motive components in accordance with the desired torque of the output system, a means for controlling power of at least one of the motive components in accordance with the desired power of the output system, a means for unloading the clutch device before disengaging the clutch device, a means for controlling speed of one of the motive components in accordance with a desired speed, a means for controlling the relative speed between the clutch components that are associated with the target mode of operation within a desirable range, a means for detecting and controlling the position of at least one clutch components, a means for reloading the dutch device after engaging the clutch device; the clutch device being a positive engagement clutch comprising: at least a first and a second co-axially arranged component, each having plural teeth for engaging another clutch component, the first clutch component is coupled to one of the motive components and the second clutch component is coupled to a gear component, a third clutch component co-axially arranged with the first and second clutch components, said third clutch component having plural teeth for engaging other clutch component or components, one of the said first, second and third clutch components has a neutral position and is selectively engage-able with the other two clutch components; in one embodiment, said first clutch component has a neutral position and is selectively engage-able with the second and/or the third clutch components.

The objects of the invention are also achieved by a method for operating the multi-mode hybrid variable speed transmission comprising the steps of: executing a transmission mode shift between the initial operating mode and the target operating mode, and operating said transmission in the target mode of operation, wherein the step of executing comprises; setting and adjusting the torque of at least one of the three motive components in accordance with the desired output torque at the output system, setting and controlling the speed of at least one of the three motive components unloading the clutch components of the clutch device associated with the initial mode of operation, disengaging the clutch components of said clutch device associated with the initial mode of operation, controlling the speed or torque of the second motive component to achieve a desired relative speed across the clutch components of the clutch device that are associated with the target mode of operation, engaging the clutch components of the clutch device that are associated with the target mode of operation, loading the clutch components of the clutch device that are associated with the target mode of operation, coincidentaily controlling the torque of the third motive component in accordance with the desired torque of the output system, and in one embodiment, controlling the torque of the first motive component in accordance with torque of the third motive component to achieve a preferred speed of the third motive component, or in another embodiment, controlling the speed of the first motive component in accordance with the speed of the output shaft to achieve a preferred speed of the third motive component.

BRIEF DESCRIPTION OF ACCOMPANYING DRAWINGS

In the accompany drawings which form part of the specification: Figure 1 is a schematic lever diagram of a preferred embodiment (embodiment 1 ) of a multi-mode electro-mechanical variable speed transmission of the present invention, showing a first dutch device in a first engagement position;

Figure 2 is a schematic lever diagram of the preferred embodiment (embodiment 1 ) of the multi- mode electro-mechanical variable speed transmission of the present invention, showing the first dutch device in a neutral position;

Figure 3 is a schematic lever diagram of the preferred embodiment (embodiment 1 ) of the multi- mode electro-mechanical variable speed transmission of the present invention, showing the first clutch device in a second engagement position;

Figure 4 is a component schematic diagram of the preferred embodiment (embodiment 1 ) of the multi-mode electro-mechanical variable speed transmission of the present invention: showing a second clutch device;

Figure 5 is a component schematic diagram of the first clutch device, showing the first engagement position;

Figure 6 is a component schematic diagram of the first clutch device, showing the neutral position;

Figure 7 is a component schematic diagram of the first clutch device, showing the second engagement position;

Figure 8 is a component schematic diagram of the first clutch device, showing a third engagement position;

Figure 9 is a close up sectional view of the first clutch device, showing the detailed component arrangements for an integrated clutch design and its four working positions;

Figure 10 is a close up section view showing the four positions of the sleeve ring (SL) associated with four operation modes from mode 1 , neutral mode, mode 2 to mode 4, respectively;

Figure 11 is another embodiment, the second embodiment in component schematic diagram; and

Figure 12 is a flowchart showing the procedure of mode shifting between two different power split operating modes for the multi-mode electro-mechanical variable speed transmission of the present invention. DETASLED DESCRIPTION

The present invention can have various embodiments, variants and configurations that incarnate the spirit of the present invention. Embodiments, variants and configurations disclosed thereafter in text and in illustrations are used for the purpose of explanation only and shall not be interpreted as limitation to the scope of the present invention. The following detailed description illustrates the invention by way of example and not by way of limitation.

Figures 1 to 3 show a preferred embodiment, i.e., an embodiment 1 of the present invention. The embodiment is i!lustrated in a lever diagram format. A lever diagram is a schematic representation of a planetary gear set wherein the co-axial rotatable components of the planetary gear set are each represented by a knot on the lever diagram. The lever diagram can be used to graphically describe rotation speeds among the co-axial rotatable components. Those having ordinary skill in the art will recognize that when referring to a knot on a lever diagram, it is equivalent to referring the corresponding co-axiai rotatable component of the planetary gear set which the lever diagram is representing and vice versa. Those having ordinary skill in the art will understand that a lever diagram can represent a series of planetary gear systems. It is also understood that the terms such as "couple", "connect" and "engage" are used to represent fixed mechanical connections or rotatable meshing engagements (through a pair of gears for example) between two or more mechanical components to transmit torque and mechanic power. These terms are also used to represent electric connections between two or more electric components to transmit electric power. Mechanical couplings or connections between the various members or components are illustrated by solid iines in the lever diagram.

Refer to Figures 1 to 3, the multi-mode electro-mechanical variable speed transmission is comprised of a gear system including a first planetary gear set (PG1 ) represented by a first lever and a second planetary gear set (PG2) represented by a second lever, an input shaft (Input) correctable to an engine (Eng), an output system (Output), a clutch device (CL), a first stationary member (FM1 ), and a first and second electric machines (EMI , EM2) along with their associated drives and controllers (not shown). The first planetary gear set (PG1 ) Is a three-branch planetary gear set, having a first co-axial rotatable gear component, a second co-axial rotatable gear component and a third co-axiai rotatable gear component each being represented by a first knot (KNii), a second knot (Kr½) and a third knot (Kr½) of the first lever, respectively. The second planetary gear set (PG2) is a four-branch planetary gear set, having a first, a second, a third and a fourth co-axial rotatable gear components that are represented by a first, a second, a third and a fourth knots (KN21 , KN22, KN23, and KIM24) of the second iever, respectively. The first knot (KN ) of the first lever (PG1 ) connects to the stationary member (FIVI1 ). The second knot (Kr½) of the first lever (PG1 ) connects to the second knot {KN22) of the second lever (PG2) such that the second knot (K ½) of the first lever (PG1) rotates at the same rational speed as the second knot {KN22) of the second lever (PG2). For sake of description, the first electric machine (EM1 ), the second electric machine (EM2) and the engine (Eng) are collectively referred to as motive components. As can be appreciated, motive components can take other forms such as hydraulic motors and pumps.

The first electric machine (EM1) includes a first rotor and a first stator. Referring to figures 1 to 3, the rotor of the first electric machine (EM1 ) directly couples to the first knot (KN21) of the second planetary gear set (PG2). The output system (Output) couples to the second knot (KN12) of the first planetary set (PG1 ) and to the second knot (KN22} of the second planetary gear set (PG2). The engine (Eng) couples, through the input shaft (Input), to the third knot (KN23) of the second planetary gear set (PG2).

The clutch device (CL) includes a neutral position, and first and second engagement positions. The second electric machine (EM2) includes a second rotor and a second stator. The rotor of the second electric machine (E 2) couples selectively through the first engagement position of said clutch device (CL) to the third knot (KN13) of the first planetary gear set (PG1 ) as shown in figure 1 or through the neutral position of said clutch (CL) to none of the knots of the planetary sets as shown in figure 2, or through the second engagement position of said clutch (CL) to the fourth knot (KN24) of the second planetary gear set (PG2), as shown in figure 3. Thus the second electric machine (E 2) selectively couples directly to the fourth knot (KN24) of the second planetary gear set (PG2) with a first constant speed ratio, or indirectly through the first planetary gear set (PG1) to the second knot (KN22) of the second planetary gear set (PG2) with a second constant speed ratio. The first and second electric machines (EM1 , E 2), along with their respective drives, are electrically connected to transmit power to and from each other. Said multi-mode electromechanical variable speed transmission may further include an energy storage device such as a battery pack (BT, not shown) to store and recapture energy. The energy storage device (BT) is connected to the first and second electric machines (EM1 , EM2) to receive power from or deliver power to one or both of the electric machines,

To facilitate the description, the ratio of the speed of the output system (Output) to the speed of the input shaft (input) is defined as the output-to-input speed ratio of the transmission and is simply referred to thereafter as the speed ratio denoted by SR. The speed ratio at which the speed of at least one of the electric machines is zero is defined as a speed ratio node point, or a speed ratio node, of the transmission. The speed ratio at which the torque of at least one of the electric machine is zero is defined as a torque node point, or torque node, of the transmission. The first embodiment (embodiment 1 ) is capable of providing a natural speed ratio node SRQ, and two regular speed ratio nodes SR1 and SR2. At the natural speed ratio node, the speeds of the first and second electric machines, and the speed of the output system are zero. At the first regular speed ratio node SR1, the speed of the first electric machine is zero. At the second regular speed ratio node SR2, the speed of the second electric machine is zero. The natural speed ratio node SRQ divides the entire speed ratio axis into a forward and a reverse ranges. Above the natural speed ratio node SRO is the forward speed ratio range; below the natural speed ratio node SRO is the reverse speed ratio range.

The first embodiment is also capable of providing at least two torque node points SR1 land SR2T. At the first speed ratio node SR† , the torque of the second electric machine (E 2) is zero if there is no net power exchange between the transmission and the energy storage device. Likewise, at the second speed ratio node SR2, the torque of the first electric machine (EM1 } is zero if there is no net power exchange between the transmission and the energy storage device, When torque of the second electric machine (EM2) is zero, the transmission is at its first torque node SR1T where the torque ratio of input shaft to output system is substantially equal to SR1. When torque of the first electric machine (EM1 ) is zero, the transmission is at its second torque node SR2T where the torque ratio of input shaft to output system is substantially equal to SR2. It should be pointed out that the first speed ratio node SR1 does not necessarily coincide with the first torque node (SR1T) if there exists net power exchange between the transmission and the energy storage device. Likewise, the second speed ratio node SR2 does not necessarily coincide with the second torque node (SR2T), if there is net power exchange between the transmission and the energy storage device. The positions of the first and second speed ratio nodes (SR1 and SR2) are fixed on the output-to-input speed ratio axis for a given transmission. The positions of the first and second torque nodes {SRITand SR2T), however, vary along the output-to-input speed ratio axis, depending on the amount of net power exchange between the transmission and the energy storage device. The distance between the first speed ratio node SR1 and the first torque node SR1T or between the second speed ratio node SR2 and the second torque node SR2T is a function of the amount of net power exchange between the transmission and the energy storage device. The first speed node SR1 further divides the forward speed ratio range into Sow-speed ratio range and a high-speed ratio range. In the low-speed ratio range below S 1 , the transmission preferably adopts a first power split configuration and operates in a first power split mode or a first variable speed mode. In the high-speed ratio range above SR1 , the transmission preferably adopts a second power split configuration and accordingly operates in a second power split mode or a second variable speed mode. The shift between the first and second power split modes is devised at the first torque node SR1 T, in vicinity of the first speed ratio node SR This creates a natural and the most desirable condition for a smooth and non-interruptive mode shifting event for positive engagement type of clutches. In the forward range, the transmission can be operated either pure electric drive mode, the first power split mode or the second power split mode to obtain the best efficiency, avoiding internal power circulation. In the reverse range, the transmission operates under pure electric drive mode. Thus, the power in each power path, whether the mechanical power path or the electromechanical power path, is always less than the power transmitted through the transmission from the input shaft to the output system. No internal power circulation exists in any speed ratio range for the multi-mode electro-mechanical variable speed transmission. The operable speed ratio range of the transmission is thus effectively extended.

When the second electric machine (E 2) couples to the second knot (KN22) of the second planetary gear set (PG2), the clutch device (CL) connects the second electric machine EIVS2 to the third knot (KN13) of the first planetary gear set (PG1 ) and disconnects the second electric machine (EM2) from the fourth knot (KN24) of the second planetary gear set (PG2) as shown in figure 1. The transmission is operated under the first power split mode. The input power from the engine is split into two power paths to transmit to the output system. One is the pure mechanical power path that goes from the input shaft (Input), through the second knots (KN12, KN22) of the first and second planetary gear sets (PG1 , PG2), to the output system (Output), The other is the electro-mechanical power path that goes from input shaft (Input), through the second planetary gear set (PG2), the first electric machine (EM1 ), the second electric machine (EM2), the clutch device (CL) and the first planetary gear set (PG1 ), to the output system (Output).

When the second electric machine (EM2) couples to the fourth knot ( N24) of the second planetary gear set (PG2), the clutch device (CL) disconnects the second electric machine (EM2) from the third knot (KN13) of the first planetary gear set (PG1 ) and connects it directly to the fourth knot (KN ₂₄ ) of the second planetary gear set (PG2) as shown in figure 3. The transmission is operated under the second power split mode. Similarly, the input power from the engine is split into two power paths to transmit to the output system (Output), The mechanical power path goes from the input shaft (Input) through the second planetary gear set (PG2) to the output system (Output); the electro-mechanical power path goes from the input shaft (Input), through the second planetary gear set (PG2), the first electric machine (EM1 ), the second electric machine (EM2), and the clutch device (CL) back to the second planetary gear set (PG2), and finally to the output system (Output).

The shifting between the first and second hybrid operation modes are carried out with the clutch device (CL) through a neutral position. Mode shifting criteria are developed. When shifting conditions are met, in accordance with a concrete procedure, mode shifting starts with generating a torque node (SR1 T) in the vicinity of the first speed ratio node (SRI) to unload the dutch device (CL) prior to disengagement by controlling torque of electric machines and the input torque from the engine in accordance with the desired wheel torque. When the torque load on said clutch device reduces below a predetermined level, said clutch device disengages from its current engagement position, disconnecting the second electric machine (EM2) from the knot if currently connects, and moves to the neutral position (see figure 1 ) where the second electric machine (EM2) is free from speed constraint imposed by the first and/or the second planetary gear set. The speed of the second electric machine (EM2) can be controlled independently. During disengagement, the position of the clutch device is determined and controlled through sensors and a feedback and/or feed-forward control loop. When the neutral position of the clutch is determined and confirmed, the second electronic machine (EM2) then commences to synchronize in rotational speed with the knot to be connected for target mode of operation. It is done to reduce the relative speed across the incoming clutch components. Upon synchronization, that is when the relative speed across the incoming clutch components is reduced within a predetermined range, the clutch device (CL) is controlled to engage the target engagement position by connecting the second electric machine to the knot associated with the target hybrid mode of operation. Mode shifting ends with ramping back the torque load of the clutch device (CL) to the normal torque value that is deemed appropriate for the clutch for the target mode of operation. To eliminate or reduce as much as possible the disturbance on drive torque and output power from the transmission, engine torque and/or power are adjusted during the entire shifting event which may include a pre-shifting phase. The amount of engine torque T _eng is adjusted to be substantially equal to the product of the output-to-input speed ratio at the first speed node point (SR1) and output torque Tveh delivered at output system of the transmission; the amount of engine power Peng is determined among others by the speed ratio node SR1, torque node SR17 and requested power Pve at the output system. That is to say, eng k SRI T, veh (1 )

SRI \

P (2)

smf)

where k is a proportional constant, substantially close to 1 ,

Figure 4 shows a variant of the performed embodiment of the present invention in component schematic diagram wherein the knots of the lever diagrams are represented by components of the corresponding planetary gear sets. The multi-mode electro-mechanical variable speed transmission is comprised of a first planetary gear set (PG1 ) including three co-axial rota able components, a second planetary gear set (PG2) including four-coaxial rotatable components, an input shaft (Input), an output system (Output), a first clutch device (CL), a second clutch device (OWC), a first stationary member (FM1 ), a first electric machine (EM1 ) and a second electric machine (EM2). The transmission may further include a torsional damper (DMP) to connect the input shaft (Input) to the engine output shaft (ENG) and a counter shaft system (CTS) to connect the first and second planetary gear sets to the output system (Output).

The first planetary gear set (PG1 ) includes a sun gear (S _s ), a ring gear (R _s ), a set of planet gears (P) supported on a planet carrier (CR _S ). The planet gears (P) are arranged around and in external mesh with the sun gear (S _s ). The planet gears (P) are in internal mesh with the ring gear (R ₃ ). The sun gear (S _s ), the planet carrier (CR _S ) and the ring gear (R _£ ) form the three co-axial rotatable gear components of the first planetary gear set (PG1 ). These three co-axial rotatable gear components are represented respectively as the first knot (KNn), the second knot (Kr½) and the third knot (KN13) on a three-knot lever diagram. The first planetary gear set (PG1 ) is characterized by the gear teeth ratio K _s of ring gear (R _s ) to the sun gear (S _s ) which is expressed as the inter-distance between the second and third knots on the three-knot lever diagram, with the inter-distance between the first and second knots being one unit in length.

where Zs _s and Z _Rs are the number of teeth for sun gear (S _s ) and ring gear (R _s ) of the first planetary gear set (PG1 ), respectively.

The second planetary gear set (PG2) is a Ravigneaux planetary gear-train, it includes a first sun gear (S1 ), a second sun gear (S2), a ring gear (R), a first set of planet gears (PS), a second set of planet gears (PL), and a planet carrier (CR) that hosts and supports the first and second sets of planet gears (PS, PL). The planet gears in the first set are short planet gears and the planet gears in the second set are long planet gears. Each of said long planet gears (PL) is in internal meshing engagement with the ring gear (R) and in external meshing engagement with the first sun gear (S1 ); each of said short planet gears (PS) is in external meshing engagement with a corresponding long planet gear (PL) and with the second sun gear (S2). The second sun gear (S2), the ring gear (R), the planet carrier (CR) and the first sun gear (S1 ) are the four co-axial rotatable gear components of the second planetary gear set (PG2), and are represented by the first knot (KN21), the second knot (KN22}, the third knot (KN23} and the fourth knot (KN ₂₄ ) on a four- knot lever diagram. The second planetary gear set is characterized by two gear teeth ratios K _a

^ ::: ^··· : K„ = ^ (4)

R S2

where Zsi , ZSJ and ZR are the tooth numbers of the first sun gear (81 ), the second sun gear (82) and the ring gear (R) of the second planetary gear set (PG2), respectively. On the four-knot lever diagram, K _a and Kb are denoted as the inter-distance between the second and third knots, and the inter-distance between the first and third knots, respectively. The first planetary gear set and the second planetary gear set are co-axially arranged and adjacent to each other in the axial direction. The ring gear (R _s ) of the first planetary gear set (PG1 ) is connected to the first stationary member (F 1 ). In this regard, the first planetary gear functions merely as a step-up gear with a constant gear ratio. The planet carrier (CR _S ) of the first planetary gear set is fixed with the ring gear (R) of the second planetary gear set (PG2) such that they have a same rotational speed.

The output system includes at least one drive shaft and an optional differential (DIP). The first clutch device (CL) has a neutral position and at least two engagement positions. It could be considered as an integrated unit of first and second clutches (C1 , C2) each having an engagement and a disengagement positions. The two clutches (CI , C2) could also be separate clutch units and operate independently. The first electric machine (EM1 ) includes a first rotor (RT1 ) and a first stator (ST1 ). The second electric machine (ESV12) includes a second rotor (RT2) and a second stator (ST2). The second clutch device includes a second stationary member (FM2) and a oneway clutch (OWC). The counter shaft system (CTS) includes a first pair of meshing gears (G1A, G1 B) and a second pair of meshing gears (G4A, G4B). Said multi-mode electro-mechanical variable speed transmission is configured to provide muitiple modes of operations through the unique connections of the gear system (PG1 , PG2) to the motive components (EM1 _« EM2 and Eng) as well as to the output system (Output). Referring to figure 4, the rotor (RT1 ) of the first electric machine (EM ) is connected to the second sun gear (S2) of the second planetary gear set (PG2). The output system (Output) is connected through the two pairs of meshing gears (G4B and G4A, and G1 B and G1A) of the counter shaft system (CTS) to the planet carrier (CR _S ) of the first planetary gear set (PG1 ) and the ring gear (R) of the second planetary gear set (PG2) wherein the differential (DIF) connects to the driven gear (G4B) of the second pair of meshing gears of the counter shaft system (CTS) and drive gear (G1 A) of the first pair of meshing gears of the counter shaft system (CTS) connects to the planet carrier (CR _S ) of the first planetary gear set (PG1 ) and the ring gear (R) of the second planetary gear set (PG2). The engine (Eng) drives the input shaft (Input) through the torsional damper (DMP). The input shaft (Input) in turn connects to the planet carrier (CR) of the second planetary gear set (PG2). The input shaft (Input) also couples to the second clutch device wherein the one-way clutch (OWC) directionaily engages the second stationary member (FM2) to prevent the input shaft from rotating in the opposite direction to the engine. The rotor (RT2) of the second electric machine (EM2) is selectively coupled through the first clutch device (CL) either to the sun gear (S _s ) of the first planetary gear set (PG1 ) wherein the first clutch (C1 ) engages and the second clutch (C2) disengages, or to the first sun gear (S1 ) of the second planetary gear set (PG2) wherein the first clutch (C1 ) disengages and the second clutch (C2) engages. Thus, the second electric machine (EM2) couples selectively to the first sun gear (S1 ) of the second planetary gear set (PG2) with a first constant speed ratio (a speed ratio of 1 :1 ) or through the first planetary gear set (PG1 ) to the ring gear (R) of the second planetary gear set (PG2) with a second speed ratio (a speed ratio of ( s+1 ):1 ). The first clutch (C1 ) and the second clutch (C2) can both disengage, leaving the rotor (RT2) of the second electric machine (EM2) in a free state where the speed of the rotor (RT2) can be independently controlled. When both of the first and second clutches (C1 and C2) are disengaged, the first clutch device (CL) is in the neutral position.

The first and second clutch devices (CL, OWC) are arranged on the same axial line of rotation as the first and second planetary gear sets, That is to say, the first planetary gear set (PG1 ), the second planetary gear set (PG2), the first clutch device (CL) and the second clutch device (OWC) all share the same axial line of rotation. In addition, the first and second planetary gear sets (PG1 , PG2) are co-axiaily arranged with and sandwiched between the first and second electric machines (EM1 ,EM2). This has a great advantage in reducing package size. The first clutch device (CL) may be further integrated with a brake (BR) and a third stationary member (FM3), and be modified to include a third engagement position. This makes the first clutch device (CL) to have total of four working positions as shown in figures 5 to 8. The integrated clutch device (CL) is comprised of a first clutch having a first clutch component (C1) at the first engagement position, a second dutch having a second clutch component (C2) at the second engagement position, a third clutch having a third clutch component (BR) at the third engagement position, and a sleeve ring component (SL). The first dutch component (C1 ) is fixed with the sun gear (S _s ) of the first planetary gear set (PG1 ), the second clutch component (C2) is fixed with the first sun gear (S1 ) of the second planetary gear set (PG2), and the third clutch component (BR) is fixed with the third stationary member (FM3). The sleeve ring component (SL) is connected to a rotor shaft (RTS) of the second electric machine (EM2) through a pair of mating splines (SPi, SPo). The male spline (SP ₀ ) of the mating pair is fixed to the rotor shaft (RTS) and the female spline (SP,) is fixed to the sleeve ring component (SL). The female spline (SPi) slides back-and- forth over the male spline (SP ₀ ) along the axial direction by an actuator under command. The actuator can be a simple linear actuator or rotatory actuator with a rotary motion to linear motion converting mechanism.

Figure 5 shows the first work position, namely the first engagement position, of the first clutch device (CL), wherein the sleeve ring component (SL) is engaged only with the first dutch component (C1 ). In this case, the rotor shaft (RTS) and thus the rotor (RT2) of the second electric machine (EM2) is coupled to the sun gear (S _s ) of the first planetary gear set (PG1 ). The transmission operates in the first power-split mode, also referred to as mode 1.

Figure 6 shows the second working position; that is the neutral position of the first clutch device (CL), wherein the sleeve ring component (SL) is moved to a neutral position (CO) disengaging from both of the first and second clutch components (C1 , C2). In this position, the rotor shaft (RTS) and thus the rotor (RT2) of the second electric machine (EM2) is not coupled to any gear component of the first planetary gear set (PG1) and the second planetary gear set (PG2), and thus the speed of the rotor (RT2) is not constrained by the speed of input shaft (input) and the output system (Output). The second electric machine (EM2) is in a free state, and can be operated independently at any desired speed to synchronize with the speed of clutch component (C1 ) or the speed of clutch component (C2). This reduces the relative speed across the sleeve ring component (SL) and the clutch component (C1), or across the sleeve ring component (SL) and the clutch component (C2). The neutral mode is also referred to as the mode 3. Figure 7 shows the third working position that is the second engagement position of the first c!utch device (CL), wherein the sleeve ring (SL) is engaged only with the second ciutch component (C2). In this position, the rotor shaft (RTS) and thus the rotor (RT2) of the second electric machine (EM2) is coupled to the first sun gear (S1 ) of the second planetary gear set (PG2). The transmission operates in a second power-split mode, also referred to as mode 2.

Figure 8 shows the fourth working position that is the third engagement position of the first ciutch device (CL), wherein the sieeve ring (SL) engages with both the second and the third clutch components (C2, BR), !n this position, the rotor shaft (RTS) and thus the rotor (RT2) of the second electric machine (EM2) is coupled to both the first sun gear (Si) of the second planetary gear set (PG2) and the third stationary member (FM3). The transmission operates in a fixed speed ratio mode, also referred to as mode 4,

Figures 9-10 are close up sectional views of the first clutch device (CL), showing as an example the detailed component arrangements for an integrated clutch design and its four working positions. The integrated clutch device (CL) includes a rotor hub which is also the rotor shaft (RTS), a sleeve ring component (SL), a first ciutch component C1 , a second clutch component (C2), a screw shaft assembly (SSH) having a screw shaft (SSFT), a screw hub assembly (SHB) having a screw nut (SNUT), a first and second bearings (BRG1 , BRG2), a braking component (BR, also referred to as the third clutch component) and the third stationary member (FM3). The integrated clutch device (CL) further includes at least a guide rail (GDR) extruded from the fixed member (FM3) in a direction parallel to the screw shaft, and an actuator (Actu) for driving the screw shaft (SSFT). The first ciutch component (C1 ) is coupled to the sun gear (S _s ) of the first planetary gear set (PG1 ), having plural radially extruded external dog teeth. The second dutch component (C2) is coupled to the first sun gear (S1 ) of the second planetary gear set (PG2), having the same number of outwardly extruded radial dog teeth. The third ciutch component (BR) is integrated with the fixed member of the transmission (FM3), and has plural outwardly extruded radial dog teeth. The sleeve ring component (SL) has a first set of inwardly extruded radial dog teeth at one end, and a second set of inwardly extruded radial dog-teeth at the other end. The first set of inwardly extruded dog-teeth of the sleeve ring (SL) is engage-able with the outwardly extruded dog-teeth of the first or the second clutch components (C1 , C2), and the second set of inwardly extruded dog-teeth of the sleeve ring (SL) is engage-able with the outwardly extruded dog-teeth of the third clutch component (BR). The sleeve ring component (SL) is coupled via splines to the rotor hub (RTS) and is slid-able along the axial direction inside the rotor hub (RTS). The sleeve ring component (SL) is also coupled to the screw hub assembly through the first ball bearing (BRG1 ) which allows relative rotation and restricts axial displacement between the sleeve ring component (SL) and the screw hub assembly (SHB). The screw shaft (SSFT) is coupled to the actuator (Actu) and supported through the second bearing (BRG2) on the fixed member (F 3). The screw hub assembly (SHB) is driven by screw shaft (SSFT) as it rotates, and guided by the at least guide rail (GDR) to prevent screw hub assembly (SHB) from rotating with the screw shaft (SSFT).

When the screw shaft (SSFT) is rotated by the rotary actuator (Actu) under command from a control unit (HCU), it drives the screw hub assembly via screw nut (SNUT) where the rotary motion is converted to a linear motion. The screw hub assembly moves back and forth along the axial direction of screw shaft (SSFT). Position sensors or displacement sensors are devised on the screw hub assemble (SHB) or on the at least guide rail (GDR) to detect and monitor the position of axial position of the screw hub assembly with respective to a predetermined reference point of the transmission. With this reference point and through a concrete calibration process, the position of the sleeve ring (SL) can be determined with respect to other clutch components and nominal of the four working positions of the clutch device can be established. Alternatively, the angular position sensors can also be used to determine the position of the sleeve ring and to establish the nominal values for the four working positions of the clutch device. The angular position sensor can be the internal angular displacement sensor of the actuator.

Figure 10 shows the four positions of the sieeve ring (SL) associated with four respective operation modes, namely mode 1 , neutral mode, mode 2 and mode 4. Detents are designed to arrest the motion of screw hub assembly (SHB). The detent mechanism include a blind hole (BH) opened on the outer surface of the sleeve ring component (SL) for hosting a compression spring (SPR) and a ball (BAL), and a set of grooves machined on the inner surface of the rotor hub (RTS). Each groove corresponds to a working position of the clutch device (CL). The compression spring urges the bail (BAL) outward against the inner surface of the rotor hub (RTS). When the sleeve ring component (SL) travels to a working position of the clutch device (CL), the ball drops to the corresponding detent groove arresting further movement of the sleeve ring component (SL).

As can be appreciated, the four working positions of the clutch device (CL) can be arranged adjacent to each other along the axial direction, leading to a very compact configuration. The existence of neutral position (CO) between the first and second engagement positions (C1 ) and (C2) allows the second electric machine (EM2) to rotate independently and to synchronize the rotation speed of its rotor (RT2) with the target engagement position (C1 , C2 or BR) before engagement is commenced. As those skilled in the art will appreciate, the operation of a hybrid vehicle is controlled by a centralized controller or distributed controllers, A hybrid control unit (HUC) in concert with an engine control unit (ECU) and a battery management system (BMS) controls the operation of the multi-mode electro-mechanic variable speed transmission, including the operation of the clutch device in the transmission.

Figure 1 1 shows another embodiment, the second embodiment, in component schematic diagram. The multi-mode electro-mechanical variable speed transmission is comprised of a planetary gear set (PG2) including four-coaxial rotatable gear components, a first pair of external meshing gears (G1 A and G1 B), a second pair of external meshing gears (G2A and G2B), a third pair of external meshing gears (G3A and G3B), an input shaft (Input), an output system (Output), a first clutch device (CL), a second device (OWC), a stationary member (F ), a first electric machine (EM 1 ) and a second electric machine (EM2). The transmission may further indude a torsional damper (DMP) to connect the input shaft (Input) to the engine output shaft (ENG) and a counter shaft system (CTS) to connect the planetary gear set (PG2) to the output system (Output). The planetary gear set (PG2) is a Ravigneaux planetary gear-train. It includes a first sun gear

(51 ) , a second sun gear (S2), a ring gear (R), a first set of planet gears (PS), a second set of planet gears (PL), and a planet carrier (CR) that hosts and supports the first and second sets of planet gears (PS, PL). The planet gears in the first set are short planet gears; the planet gears in the second set are long pfanet gears. Each of said long planet gears (PL) is in internal meshing engagement with the ring gear (R) and in external meshing engagement with the first sun gear (ST); each of said short planet gears (PS) is in external meshing engagement with a corresponding long planet gear (PL) and with the second sun gear (S2). The second sun gear

(52) , the ring gear (R), the planet carrier (CR) and the first sun gear (81 ) form the four co-axial rotatable gear components of the planetary gear set (PG2) and are represented respectively as the first knot (KN21 ), the second knot (KN22), the third knot (KN23) and the fourth knot (KN24) on a four-knot lever diagram. The planetary gear set is characterized by two gear teeth ratios K _a and

where Zsi , Zss and ZR are the tooth numbers of the first sun gear (S1 ), the second sun gear (S2) and the gear (R) of the planetary gear set (PG2), respectively. On the four-knot lever diagram, K ₃ and Kb are denoted as the inter-distance between the second and third knots and the inter- distance between the first and third knots, respectively. The first pair of meshing gears includes a drive gear (G1A) and a driven gear (G1 B). The gear teeth ratio of driven gear to drive gear for the first gear pair is GR1. The second pair of meshing gears includes a drive gear (G2A) and a driven gear (G2B). The gear teeth ratio of driven gear to drive gear for the second gear pair is GR2. The third pair of meshing gears includes a drive gear (G3A) and a driven gear (G3B). The gear teeth ratio of driven gear to drive gear for the third gear pair is GR3.

The first clutch device (CL) includes a neutral position (CO) and at least two engagement positions (C1 and C2). The first electric machine includes a first rotor (RT1 ) and a first stator (ST1 ), The first rotor (RT1 ) of the first electric machine connects the second sun gear (S2) of the planetary gear set (PG2). The output system (Output) couples to the ring gear (R) of the planetary gear set (PG2) through the first pair of meshing gears (G1A and G1 B). The input shaft (Input) couples to the crank shaft of the engine (Eng) through a damper (DMP) at one end and connects to planet carrier (CR) of the planetary gear set (PG2) at the other end.

The second electric machine (EM2) includes a second rotor (RT2) and a second stator (ST2). The second rotor (RT2) of the second electric machine (EM2) couples selectively via the at least two engagement positions (C1 , C2) of the first clutch device (CL) to the ring gear (R) of the planetary gear set (PG2) through the first and third pairs of meshing gears with a first speed ratio, or to the first sun gear (S1 ) of the planetary gear set through the second and third pairs of meshing gears with a second speed ratio. When the first clutch device (CL) is at the neutral position (CO), the second electric machine (EM2) is set to a freewheeling state where speed of rotor (RT2) can be independently controlled to facilitate mode shifting between different operating modes of the transmission. The second embodiment as shown in figure 11 provides that same functions and performance characteristics as the first embodiment. Both embodiments share essentially the same mode shifting procedure. In the second embodiment, the clutch device (CL) is installed on the counter shaft system (CTS) rather than on the main shaft of the transmission. The sleeve ring component (SL) is coupled to the rotor shaft (RTS) of the second electric machine (EM2) through a pair of meshing gears (G3A, G3B), linear actuator may be used to move the sleeve ring component (SL) along the counter shaft for different working positions. Figure 12 shows the procedure for mode shifting between the first power split mode of operation and the second power spiit mode of operation, It includes steps from (S1 ) to (S10). Some of these steps can be combined, or executed in parallel. Alternatively, the order of these steps can be changed to suit for a specific implementation. The procedure is executed by a centralized controller or by a group of distributed controilers. The procedure along with the controller or controilers and the associated software constitutes a means for creating a torque node in vicinity of the first speed ratio node point, a means for unloading clutch device (CL), a means for setting and adjusting engine power, a means for setting and adjusting engine speed and torque, a means for shifting one of the electric machines to freewheeling state, a means for setting and controlling the speed of one of the electric machines, a means for controlling the speed of at least one of the electric machines to reduce relative speed across incoming clutch components of the clutch device (CL), and a means for determining and controlling the position of clutch components to achieve desired engagement and disengagement status of the clutch device.

Referring to figure 12, the procedure for mode shifting between two power split modes of operation includes steps of:

(51 ) Check shifting criteria. If the speed ratio meets condition SR≥ SR1+ ASR. issue an upshifting signal; if the speed ratio SR≤ SR1- ASR, issue a downshifting signal. Here ASR can be a predetermined constant or a variable whose value may change in accordance with operation conditions. ASR may also assume different values for upshifting and downshifting, respectively;

(52) Calculate speed ratio deviation from nominal shifting point or the first speed ratio node SR1. The deviation OSR = SR-SR1 is evaluated on a relative scale and is expressed by a deviation factor

β = ^ (6)

^ SRI '

(S3) Create a torque node point SR1T, in vicinity of SR1, by setting and adjusting engine torque according to

Ten ⁼ k ' ' Tveh> ^anc ^

setting and adjusting the engine power according to

Above functions or relationships may also be obtained from calibration testing,

(S4) Set and control engine speed by adjusting torque of at least one of the electric machines. (55) Unioad the dutch device (CL) by adjusting torque of the electric machines, and prepare for disengagement. This is done in concert with adjustment of engine torque and/or power;

(56) Disengage the second electric machine (EIV12) from engagement position C1 for upshifting, or from engagement position C2 for downshifting, transition the second electric machine (EM2) to the freewheeling state by moving the dutch device (CL) to the neutral position CO;

(57) Determine and confirm the position of the dutch device (CL), namely, determine and confirm the position of the sleeve ring component (SL) of the clutch device (CL) with respect to its target position;

(58) Set a target speed for the second electric machine (EM2). The target speed can be a constant or a variable. The target speed determined by the speed of the component that is associated with the target engagement position, namely the engagement position C2 for upshifting or the engagement position C1 for downshifting. Control and synchronize the rotor speed of the second electric machine (EM2) with the target speed, such that the relative speed across the incoming clutch components for the target mode of operation is substantially reduced.

(59) Engage the second electric machine (EM2) with the component that is associated with engagement position C2 for upshifting, or with the component that is associated with engagement position C1 for downshifting.

(S10) Once the engagement is accomplished, and the position of the clutch device is determined and confirmed, the load on the clutch device will be ramped back to its normal value.

Using upshift as an example, the shifting procedures and various means for accomplishing such a shifting are further explained. To operate at high speed range and avoid internal power circulation, the transmission needs to be upshifted into the second power split mode. When the upshifting condition SR≥ SR1+&SR is met, an upshift signal is sent out, the hybrid control unit (HCU) commences to create a torque node SRTIT ^' vicinity of the first speed ratio node SR1 by setting torque commands to the electric machines to unload the clutch device (CL), and at the same time, setting and adjusting the engine power according to the calculated speed ratio deviation factor β such that drive torque and output power from the transmission remain substantially undisturbed. Alternatively, rather than setting and adjusting engine power, the HCU can set and adjust engine torque to be substantially in proportional to the product of the first speed ratio node SR1 and the requested output torque of the transmission to facilitate a smooth unloading process of the clutch device (CL), avoiding any undesirable disturbance at the drive wheels. Unloading the dutch device (CL) may be carried out via a ramping process. When the torque load on the clutch device (CL) is below a predetermined value, the control unit (HCU) then commands the clutch device (CL) to move to the neutral position (CO), disconnecting the second electric machine (EM2) from the third knot (KN13) of the first planetary set (PG1 ), and thus shifting the second electric machine (EM2) to a freewheeling state. During shifting event, the position of the clutch device (CL) is monitored by position sensors or displacement sensors, and precisely controlled by the hybrid control unit (HCU) via a linear or rotary actuator. In the freewheel state, the speed of the second electric machine (E5V12) can be independently controlled irrespective of the speed ratio of the transmission. Once the neutral position (CO) for the clutch device (CL) is determined and confirmed, the hybrid controller (HCU) sets and controls the speed of the second electric machine (EM2) in the freewheeling state, and synchronize the rotor (RT2) speed of the second electric machine (EM2) with the speed of the fourth knot (KN24) of the second planetary gear set (PG2) to which C2 is connected. Once the synchronization is confirmed, the clutch device (CL) is commanded to connect the second electric machine (E 2) to the fourth knot (KN24) of the second planetary gear set (PG2). Transmission is now operating under the second power split mode. The second power-split mode is maintained as long as the speed ratio of the transmission is above the downshifting point SRI-hSR.

Downshifting from the second power split mode of operation to the first power split mode of operation can be accomplished in a similar manner using aforementioned procedure and various means, including the means for determining and identifying the shift conditions, the means for creating a torque node point in vicinity of the first speed node point SR1, the means for determining and controlling position of the clutch device, the means for controliing the speed of the second electric machine (EM2) to reduce the relative speed across the clutch components of the clutch device associated with the target engagement position, and the means for moving the clutch device into and out from an engaged and disengaged position.

As can be appreciated, the above described means and procedure for mode shifting provide a smooth, continuous and non-interrupiive power shifting for the transmission irrespective of types of clutches. It allows for positive engagement type of clutches such as dog dutches to be used to achieve equivalent or even superior shifting quality as friction type of clutches. Positive engagement type of clutches are usually simple, compact and more efficient, and have higher torque transfer capacity.