阅读说明：本技术 双电动机电动变速器及控制方法 (Dual-motor electric transmission and control method ) 是由 J·范丁格恩 B·汉农 K·卡托尔 F·萨齐特 于 2021-06-08 设计创作，主要内容包括：本发明涉及一种用于电动车辆的双电动机电动变速器和一种用于双电动机电动变速器的控制方法。该变速器包括用于驱动车辆的第一电动机和第二电动机、第一齿轮布置、第二齿轮布置和汇总箱,其中,第一齿轮布置包括第一齿轮布置第一轴和至少一个第一齿轮和第二齿轮,其中,第一齿轮和第二齿轮中的每一个都可以经由第一离合器元件和第二离合器元件与第一齿轮布置第一轴选择性地接合和脱离,并且第一齿轮布置被构造成经由第一齿轮和第二齿轮中的一个将来自第一电动机的第一扭矩供应到汇总箱,第二齿轮布置包括第二齿轮布置第一轴和至少一个第二齿轮布置第一齿轮,其中,第二齿轮布置第一齿轮可以经由第二齿轮布置第一离合器元件与第二齿轮布置第一轴接合和脱离,并且第二齿轮布置被构造成将来自第二电动机的第二扭矩供应到汇总箱。(The present invention relates to a dual-motor electrically-variable transmission for an electric vehicle and a control method for the dual-motor electrically-variable transmission. The transmission comprises a first and a second electric motor for driving the vehicle, a first gear arrangement, a second gear arrangement and a junction box, wherein the first gear arrangement comprises a first gear arrangement first shaft and at least one first and second gear, wherein each of the first and second gear is selectively engageable and disengageable with the first gear arrangement first shaft via a first and second clutch element, and the first gear arrangement is configured to supply a first torque from the first electric motor to the junction box via one of the first and second gear, the second gear arrangement comprises a second gear arrangement first shaft and at least one second gear arrangement first gear, wherein the second gear arrangement first gear is engageable and disengageable with the second gear arrangement first shaft via a second gear arrangement first clutch element, and the second gear arrangement is configured to supply the second torque from the second electric motor to the junction box.)

1. A dual motor electrically variable transmission for an electric vehicle, the transmission comprising: a first motor and a second motor for driving the vehicle,

a first gear arrangement, a second gear arrangement, and a junction box, wherein

The first gear arrangement comprising a first gear arrangement first shaft and at least a first and a second gear, wherein each of the first and second gears is selectively engageable and disengageable with the first gear arrangement first shaft via a first and a second clutch element, and the first gear arrangement is configured to supply a first torque from the first electric motor to the junction box via one of the first and second gears,

the second gear arrangement comprises a second gear arrangement first shaft and at least a second gear arrangement first gear, wherein the second gear arrangement first gear is engageable with and disengageable from the second gear arrangement first shaft via a second gear arrangement first clutch element, and the second gear arrangement is configured to supply a second torque from the second electric motor to the junction box, and

the combiner box is configured to combine the first torque and the second torque and to output a combined output torque.

2. The dual-motor electrically variable transmission of the preceding claim, wherein the first gear arrangement further comprises a first gear arrangement second shaft and a first gear arrangement fixed gear set, wherein the first gear arrangement first shaft is coupled to the first gear arrangement second shaft via the first gear arrangement fixed gear set.

3. The dual-motor electrically variable transmission of any preceding claim, wherein the second gear arrangement further comprises a second gear arrangement second gear engageable with or disengageable from the second gear arrangement first shaft via a second gear arrangement second clutch element.

4. The dual-motor electrically variable transmission of any preceding claim, wherein the second gear arrangement further comprises a second gear arrangement second shaft and a second gear arrangement fixed gear set, wherein the second gear arrangement first shaft is coupled to the second gear arrangement second shaft via the second gear arrangement fixed gear set.

5. The dual-motor electrically variable transmission of claim 1 or 2, wherein the second gear arrangement further comprises a second gear arrangement second shaft and at least two additional gears fixedly engaged with the second gear arrangement second shaft, wherein one of the two additional gears is in mesh with the second gear arrangement first gear of the second gear arrangement first shaft and the other of the two additional gears is coupled to the junction box.

6. A dual-motor electrically variable transmission as claimed in any preceding claim, wherein the clutch elements are spring loaded and/or automatically disengaged in the event of loss of actuation.

7. A two-motor electrically variable transmission as claimed in any preceding claim, wherein the clutch elements comprise or consist of a dog clutch or a synchro-clutch.

8. The dual-motor electrically variable transmission of any preceding claim, wherein the second electric motor is connected to a power take-off and/or a charge pump.

9. The dual motor electrically variable transmission of any one of the preceding claims, further comprising a control unit adapted to control the second motor to provide an increased second torque during a gear shift of the first gear arrangement such that the combined output torque remains substantially constant during a gear shift.

10. A control method for controlling a dual motor electrically variable transmission according to one of the preceding claims to perform a gear shift from a first gear to a second gear in the first gear arrangement, the control method comprising:

controlling the second motor to synchronize with the second gearing arrangement first gear,

controlling the second gear arrangement first clutch element to engage with the second gear arrangement first shaft,

controlling the first motor to reduce the first torque to zero and simultaneously controlling the second motor to increase the second torque such that the combined output torque is substantially constant,

controlling the first clutch element to disengage from the first gear arrangement first shaft,

controlling the first motor to synchronize with the first gear arrangement second gear,

controlling the second clutch element to engage with the first gear arrangement first shaft,

controlling the second motor to decrease the second torque and simultaneously controlling the first motor to increase the first torque such that the combined output torque is substantially constant.

Technical Field

The present invention relates to a dual-motor electrically-variable transmission for an electric vehicle and a control method for controlling the dual-motor electrically-variable transmission.

Background

A major goal of improving the drive unit of an electric vehicle is to increase the efficiency of the electric transmission. In order for the electric motor to operate at optimum efficiency, multiple gear ratios to the transmission output are required. Power shifting (or "powershifting") is also required for optimum performance. The power switching enables gear switching (shifting) without reducing the output torque function. Design requiring power switching and functional safety, particularly in the off-highway market or other high performance applications

Disclosure of Invention

It is therefore an object of the present invention to provide a dual motor electrically variable transmission having a design with improved efficiency and functional safety.

This object is achieved by a dual-motor electrically variable transmission arrangement according to independent claim 1 and a control method for a dual-motor electrically variable transmission arrangement according to claim 10. Advantageous embodiments of the two-motor electrically variable transmission device are mentioned in the dependent claims.

The dual motor electric transmission for an electric vehicle according to the present invention includes: a first and a second electric motor for driving a motor vehicle, a first gear arrangement, a second gear arrangement, and a junction box, wherein the first gear arrangement comprises a first gear arrangement first shaft and at least one first and second gear, wherein each of the first and second gear is selectively engageable and disengageable with the first gear arrangement first shaft via a first or second clutch element, and the first gear arrangement is configured to supply a first torque from the first electric motor to the junction box via one of the first and second gear, the second gear arrangement comprises a second gear arrangement first shaft and at least one second gear arrangement first gear, wherein the second gear arrangement first gear is engageable and disengageable with the second gear arrangement first shaft via the second gear arrangement first clutch element, and the second gear arrangement is configured to supply the second torque from the second electric motor to the summing box, and the summing box is configured to combine the first torque and the second torque and to output the combined output torque.

By having two electric motors on the input side and a combined output torque on the output side of the transmission, the first and second electric motors can be driven substantially independently of each other and according to a separately connected gear arrangement, maximizing the efficiency of the two-motor electrically variable transmission. Furthermore, the transmission according to the invention is power shiftable, which means that the combined output torque can be maintained during gear shifting (shifting).

According to the simplest configuration of the invention, the second gear arrangement may be a direct drive or a single constant gear ratio.

According to an advantageous embodiment of the invention, the first gear arrangement may further comprise a first gear arrangement second shaft and a first gear arrangement fixed gear set, wherein the first gear arrangement first shaft is coupled to the first gear arrangement second shaft via the first gear arrangement fixed gear set.

According to a further advantageous embodiment, the second gear arrangement may further comprise a second gear arrangement second gear which is engageable with or disengageable from the second gear arrangement first shaft via the second gear arrangement second clutch element.

According to a further advantageous embodiment, the second gear arrangement may further comprise a second gear arrangement second shaft and a second gear arrangement fixed gear set, wherein the second gear arrangement first shaft is coupled to the second gear arrangement second shaft via the second gear arrangement fixed gear set.

According to a further advantageous embodiment, the second gear arrangement may further comprise a second gear arrangement second shaft and at least two further gears fixedly engaged with the second gear arrangement second shaft, wherein one of the two further gears is in mesh with the second gear arrangement first gear of the second gear arrangement first shaft and the other of the two further gears is coupled to the junction box.

According to a further advantageous embodiment, the clutch element may be spring-loaded and/or automatically disengaged in case of loss of actuation. This makes the mechanical system of the transmission functionally safe, meaning that no power can be transmitted from the electric motor to the wheels in case the clutches of the first and second gear arrangement are not hydraulically, electrically or otherwise activated.

According to a further advantageous embodiment, the clutch element may comprise or consist of a dog clutch or a synchromesh clutch.

According to a further advantageous embodiment, the second electric motor can be connected to the power take-off and/or the charge pump. In particular, the second motor may be selectively disengaged from the summing box to power only the power take-off and/or the charge pump.

According to a further advantageous embodiment, the combined output torque can be output to the front output yoke (fork) and/or the rear output yoke (fork).

According to a further advantageous embodiment, a third gear arrangement may be added between the summing box and the rear and front output yokes, wherein the third gear arrangement may comprise two gear sets which may be engaged and disengaged via the first and second clutch elements of the third gear arrangement. These clutch elements may consist of or consist of wet clutches. The wet clutch is capable of power switching.

According to a further advantageous embodiment, an inter-axle differential, optionally including a locking function, and/or a disconnect clutch may be arranged between the front and rear output yokes to disengage the front and rear output yokes or to disengage the rear output yoke from the front output yoke. Alternatively, the front and rear output yokes are rigidly connected or connected by other means.

According to a further advantageous embodiment, the dual motor electrically variable transmission may comprise a first control unit adapted to control the second motor to provide an increased second torque during a gear shift of the first gear arrangement such that the combined output torque remains substantially constant during the gear shift.

According to a further advantageous embodiment, the dual motor electrically variable transmission may comprise a second control unit adapted to control the first motor to provide an increased first torque during a gear shift of the second gear arrangement such that the combined output torque remains substantially constant during the gear shift.

The first control unit and the second control unit may be parts of one common control unit or may be separate components and/or may be connected to a main control unit. The first and second control units may be inverter control units and may be adapted to control the first and second electric motors, respectively, to achieve a speed-torque set point provided by the main control unit.

According to a further advantageous embodiment, the increased first or second torque may be a peak torque of the first or second motor, wherein the peak torque may be about twice a continuous torque of the first or second motor.

The present invention also includes a control method for controlling a dual motor electrically variable transmission as described above to perform a gear shift from a first gear to a second gear in a first gear arrangement, the control method comprising: controlling the second electric motor to be synchronized with the second gear arrangement first gear, controlling the second gear arrangement first clutch element to be engaged with the second gear arrangement first shaft, controlling the first electric motor to reduce the first torque to zero and simultaneously controlling the second electric motor to increase the second torque such that the combined output torque is substantially constant, controlling the first clutch element to be disengaged from the first gear arrangement first shaft, controlling the first electric motor to be synchronized with the first gear arrangement second gear, controlling the second clutch element to be engaged with the first gear arrangement first shaft, controlling the second electric motor to reduce the second torque and simultaneously controlling the first electric motor to increase the first torque such that the combined output torque is substantially constant.

According to an advantageous embodiment of the above-described control method, the gear change process in the first gear arrangement may be an upshift process if the first gear (gear) is lower than the second gear (gear).

According to another advantageous embodiment of the above-described control method, the gear shifting process in the first gear arrangement may be a downshift process if the first gear (gear) is higher than the second gear (gear).

The present invention also includes a dual motor electrically variable transmission for controlling a second gear arrangement comprising at least two gears as described above to perform a gear shift from a first gear to a second gear in the second gear arrangement, the control method comprising: controlling the first motor to synchronize with the first gear arrangement first gear, controlling the first clutch element to engage with the first gear arrangement first shaft, controlling the second motor to reduce the second torque to zero, and simultaneously controlling the first motor to increase the first torque such that the combined output torque is substantially constant, controlling the first clutch element to disengage from the second gear arrangement first shaft, controlling the second motor to synchronize with the second gear arrangement second gear, controlling the second gear arrangement second clutch element to engage with the second gear arrangement first shaft, controlling the first motor to reduce the first torque, and simultaneously controlling the second motor to increase the second torque such that the combined output torque is substantially constant.

According to an advantageous embodiment of the above-described control method, the gear change process in the second gear arrangement may be an upshift process if the second gear arrangement first gear (gear) is lower than the second gear (gear) of the second gear arrangement.

According to a further advantageous embodiment of the invention, the gear shifting process in the second gear arrangement may be a downshift process if the second gear arrangement first gear (gear) is higher than the second gear arrangement second gear (gear).

The advantage of the control method according to the invention is that the output torque is a continuous curve without a drop in the torque curve. Although the first gear arrangement is the simplest configuration, a two-speed gear arrangement with a dog clutch, the output torque will be maintained during the gear shift. This is achieved by increasing the torque of one motor while the other motor synchronizes the open dog clutch at zero power. For full power shifting, one can select a motor that has a peak power during the shift that is at least twice the continuous power. Power switching is required for many high performance applications, such as off-highway applications. However, electric power systems require high efficiency to reduce energy storage, such as battery size. Therefore, a high efficiency dog clutch is preferred.

Drawings

Hereinafter, some preferred embodiments of the two-motor electrically-variable transmission and the control method according to the present invention are described in more detail based on the following drawings. The described features are not only contemplated in combination in the disclosed embodiments, but may be implemented independently of the specific embodiments in various other combinations.

Figure 1 schematically shows a transmission layout according to a first embodiment of the invention,

figure 2 schematically shows a transmission layout according to a second embodiment of the invention,

figure 3 schematically shows a transmission layout according to a third embodiment of the invention,

FIG. 4 shows different transmission output torque curves as a function of transmission output speed, an

FIG. 5 shows different transmission output power curves as a function of transmission output speed.

Detailed Description

Fig. 1 schematically shows a transmission layout according to a first embodiment of the invention. According to the first embodiment, the dual-motor electric transmission apparatus for an electric vehicle includes the first motor 1, which is controlled by the first inverter controller la, and the second motor 2, which is controlled by the second inverter controller 2 a. The first and second electric motors 1, 2 are configured to drive an electric vehicle. The transmission further comprises a first gear arrangement 10, a second gear arrangement 20 and a summation (summation) box 30.

The first gear arrangement 10 comprises a first gear arrangement first shaft l0a, a first gear 11 and a second gear 12, wherein each of the first and second gears 11, 12 may be selectively engaged and disengaged with the first gear arrangement first shaft 10a via a first or second dog clutch (dog clutch)11a, 12 a. The first gear arrangement 10 further comprises a first gear arrangement second shaft 13 and a first gear arrangement fixed gear set with gears 14, 15. Gear 14 is in permanent engagement with the first gear arrangement second shaft, gear 15 is in permanent engagement with the first gear arrangement first shaft 10a, and gears 14, 15 mesh with each other such that the first gear arrangement first shaft 10a is coupled to the first gear arrangement second shaft 13 via the first gear arrangement fixed gear sets 14, 15.

The second gear arrangement 20 comprises a second gear arrangement first shaft 20a and a second gear arrangement first gear 22, wherein the second gear arrangement first gear 22 is engageable with and disengageable from the second gear arrangement first shaft 20a via a second gear arrangement first dog clutch 22 a. The second gear arrangement 20 further comprises a second gear arrangement second shaft 23 and two further gears 24, 25 fixedly engaged with the second gear arrangement second shaft 23, wherein one of the two further gears 24, 25 meshes with the second gear arrangement first gear 22 of the second gear arrangement first shaft 20a, while the other of the two further gears 24, 25 is coupled to the junction box 30. Furthermore, the second gear arrangement first shaft 20a is connected to a power take-off. In this case the dog clutch 22a is disengaged from the second gear arrangement first shaft 20a and only the power take-off is powered by the second electric motor 2.

The summing box comprises a shaft 30a, a summing box first gear 32 and a summing box second gear 31, the summing box first gear 32 and the summing box second gear 31 being permanently engaged with the shaft 30 a. The shaft 30a is also connected to a front output yoke 34 and a rear output yoke 33. The front and rear output yokes 33 and 34 are configured to deliver a combined output torque to the wheels of the vehicle.

The first gearwheel 11 of the first gearwheel arrangement 10 meshes with the first summing box gearwheel 32. Each of the second gear 12 of the first gear arrangement 10 and the gear 25 of the second gear arrangement 20 is in mesh with the summing box second gear 32.

The first gear arrangement 10 is configured to supply a first torque from the first electric motor 1 to the junction box 30 via one of the first and second gears 11, 12. The second gear arrangement 20 is configured to supply the second torque from the second electric motor 2 to the junction box 30. The junction box 30 is configured to combine the first torque and the second torque, and output the combined output torque to the front and rear output yokes 34 and 33.

In the present embodiment, the second gear 12 of the first gear arrangement 10 and the second gear arrangement first gear 22 have the same size and form the second gear of the transmission. The first gear 11 of the first gear arrangement 10 is smaller than the gears 12 and 22 and forms the first gear of the transmission. In other words, when the transmission is in first gear, only the electric motor 1 can be driven by engaging the first dog clutch 11 a. In the case of the second gear of the transmission, the motor 1 can be driven alone by engaging the clutch 12a or the motor 2 by engaging the clutch 22a, or both motors 1 and 2 can be driven together by engaging both clutches 12a and 22 a. Therefore, in the case of the second gear of the transmission, both the motors 1 and 2 can contribute to the output torque, and the load can be symmetrically distributed between both the motors 1 and 2 to improve the performance of the transmission.

Fig. 2 schematically shows a transmission layout according to a second embodiment of the invention. In the second embodiment, the first gear arrangement 10 and the summing box 30 are designed as in the first embodiment. The second embodiment differs from the first embodiment in the design of the second gear arrangement 20. The second gear arrangement 20 of the second embodiment is designed similarly to the first gear arrangement 10.

The second gear arrangement 20 comprises a second gear arrangement first shaft 20a and a second gear arrangement first gear 21, wherein the second gear arrangement first gear 21 can be engaged and disengaged with the second gear arrangement first shaft 20a via a second gear arrangement first dog clutch 21 a. The second gear arrangement 20 may further comprise a second gear arrangement second gear 22, which second gear arrangement second gear 22 may be engaged or disengaged with the second gear arrangement first shaft 20a via a second gear arrangement second tooth clutch 22 a. The second gear arrangement 20 further comprises a second gear arrangement second shaft 23 and a second gear arrangement fixed gear set with gears 26, 27. Gear 26 is in permanent engagement with the second shaft 23 and gear 27 is in permanent engagement with the first shaft 20 a. The gears 26 and 27 mesh with each other such that the second gear arrangement first shaft 20a is coupled to the second gear arrangement second shaft 23 via second gear arrangement fixed gear sets 26, 27.

Each of the first gear arrangement first gear 11 and the second gear arrangement first gear 21 meshes with the gear 32 of the summary tank 30. Further, each of the first gear-arrangement second gear 21 and the second gear-arrangement second gear 22 is meshed with the gear 31 of the summary tank 30.

In the present embodiment, the first gear 11 and the second gear arrangement first gear 21 of the first gear arrangement 10 have the same size and form the first gear of the transmission. The second gear 12 of the first gear arrangement 10 and the second gear arrangement first gear 22 have the same size, are larger than the gears 11 and 21, and form the second gear of the transmission. In other words, in the case of the first gear of the transmission, the electric motor 1 can be driven alone by engaging the clutch 11a or the electric motor 2 by engaging the clutch 21a, or both the electric motors 1 and 2 can be driven together by engaging both the clutches 11a and 21 a. Also, in the case of the second gear of the transmission, the motor 1 may be driven alone by engaging the clutch 12a or the motor 2 may be driven by engaging the clutch 22a, or both the motors 1 and 2 may be driven together by engaging both the clutches 12a and 22 a. Therefore, in the case of the first gear and the second gear of the transmission, both the motors 1 and 2 can contribute to the output torque, and the load can be symmetrically distributed between both the motors 1 and 2 to improve the efficiency of the transmission. In the case where both electric motors 1, 2 are configured to drive in the first gear, the maximum output torque of the transmission can be increased.

Fig. 3 schematically shows a transmission layout according to a third embodiment of the invention. The third embodiment is similar to the second embodiment. However, the third embodiment differs from the second embodiment in that it comprises a third gear arrangement 50 and an inter-axle differential 60, the third gear arrangement 50 being connected to the shaft 30a of the junction box 30.

Each of the first gear arrangement first gear 11 and the second gear arrangement first gear 21 meshes with the gear 32 of the summary tank 30. Further, each of the first gear arrangement second gear 12 and the second gear arrangement second gear 22 is meshed with the gear 31 of the summary tank 30. In the first to third embodiments, the collecting box gear 31 is smaller than the collecting box gear 32.

In the present embodiment, the first gear 11 and the second gear arrangement first gear 21 of the first gear arrangement 10 have the same size and form the first gear of the transmission. The second gear 12 of the first gear arrangement 10 and the second gear arrangement 22 have the same size, are larger than the gears 11 and 21, and form the second gear of the transmission. In other words, in the case of the first gear of the transmission, the electric motor 1 may be driven solely by engaging the clutch 11a and via the combiner box gear 32, or the electric motor 2 may be driven solely by engaging the clutch 21a and via the combiner box gear 32, or both the electric motors 1 and 2 may be driven by engaging the clutches 11a and 21a and via the combiner box gear 32. In the case of the second gear of the transmission, motor 1 may be driven solely by engaging clutch 12a and via summing box gear 31, or motor 2 may be driven solely by engaging clutch 22a and via summing box gear 31, or both motors 1 and 2 may be driven by engaging clutches 12a and 22a and via summing box gear 31. Therefore, both the two motors 1 and 2 can contribute to the output torque in the first gear and the second gear of the transmission. Since the coupling to different summing box gears is in the case of the first and second gears of the transmission, the load can be divided between both electric motors 1 and 2, which can improve the efficiency of the transmission.

The third gear arrangement is a two speed gear arrangement with a wet clutch. The other two gears 51, 52 can be selectively engaged and disengaged with the shaft 30a of the combiner box 30 via wet clutches 51a, 52 a. The gear ratios 51, 52 apply to both motors 1, 2. For some applications, these additional speed ratios may help to achieve higher speeds or torques. The wet clutches 51a, 52a allow power switching in the additional gears 51, 52. However, if the application allows some gear shifting to occur in the event of a drop in output torque, a dog clutch or synchronizer or other type of clutch may alternatively be used herein. As a further alternative, the third gear arrangement may be a single gear ratio without a clutch in a basic configuration.

Via the third gear arrangement 50, the combiner box is coupled to an inter-axle differential 60. The inter-axle differential 60 has a locking function provided by a wet clutch. Alternatively, other clutches, such as a dog clutch, may be selected.

Hereinafter, a control method for controlling the two-motor electric transmission according to the first embodiment to perform a shift change from the first gear 11 to the second gear 12 in the first gear arrangement 1 without a drop in output torque is described. The second gear arrangement 2 has only one gear ratio towards the output, whereas the first gear arrangement 1 has two gear ratios towards the output. This vehicle application allows one electric motor to be used in first gear and two electric motors to be used in second gear. In first gear, the first electric motor 1 is used to drive the vehicle, while the second electric motor 2 is switched off to supply power to the power take-off/charge pump at a sufficiently high speed. In the second gear, both the first electric motor 1 and the second electric motor 2 drive the vehicle. At the start of the gear shifting (range shifting) process, the first electric motor 1 is controlled to be driven via the first dog clutch 11 a. Next, the second motor 2 is controlled to be synchronized with the second gear arrangement first gear 22. Then, the second gear arrangement first dog clutch 22a is controlled to engage with the second gear arrangement first shaft 20 a. Then, the first electric motor 1 is controlled to reduce the first torque to zero, and simultaneously the second electric motor 2 is controlled to increase the second torque so that the combined output torque is substantially constant. Then, the first dog clutch 11a is controlled to disengage from the first gear arrangement first shaft 10 a. Next, the second motor 1 is controlled to be synchronized with the second gear arrangement first gear 12. Then, the second tooth clutch 12a is controlled to engage with the first gear arrangement first shaft 10 a. Next, the second motor 21 is controlled to decrease the second torque, and at the same time, the first motor 1 is controlled to increase the first torque so that the combined output torque is substantially constant.

FIG. 4 shows different transmission output torque curves as a function of transmission output speed. The continuous curves 71, 72 and 74 represent the continuous torque for one motor in second gear, two motors in second gear and one motor in first gear, respectively. Dashed curves 73, 75, 76 represent peak torque for one motor in second gear, two motors in second gear, and one motor in first gear, respectively. FIG. 5 shows different transmission output power curves as a function of transmission output speed. The continuous curves 81, 82 and 84 represent the continuous power of one motor in second gear, two motors in second gear and one motor in first gear, respectively. Dashed curves 83, 85 and 86 represent peak power for one motor in second gear, two motors in second gear, and one motor in first gear, respectively. The continuous torque for first gear is represented by continuous curve 74 and the continuous torque for second gear is represented by continuous curve 72. During a shift, the torque of one motor is increased to compensate for zero torque of the other motor. This is indicated by the dashed curve 73. Since the dashed curve 73 is above the curves 74 and 72 in the shift region, no torque drop is observed during the shift. Therefore, the output torque to the wheels is maintained over the entire vehicle speed range, without torque drop. In other words, the gear change is performed by power switching.

For functional safety reasons, it is necessary to automatically shift to neutral in the event that the vehicle is not safe. Although the dog clutch is preferably a normally open clutch for the first and second gear arrangements 10 and 20, other techniques may be used. One example is a spring-loaded synchronizer clutch. One advantage of using a synchronous clutch is that the synchronization of the electric motor may be less precise, which may simplify the control of the electric motor.