Drive unit
By using a driving unit composed of an electric motor, a torque converter and a control unit in an electric vehicle, the problem of complex crawling torque output in the prior art is solved, and a simple and easy crawling torque output is achieved, ensuring smooth crawling driving.
Patent Information
- Application Number
- CN202421627744.1
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- Priority Date
- 2023-07-12
- Filing Date
- 2024-07-10
- Publication Date
- 2025-05-27
- Estimated Expiration
- 2034-07-10
AI Technical Summary
The existing motor torque control device has a complex structure when generating crawling torque, making it difficult to achieve simple and easy crawling torque output.
The driving unit consisting of an electric motor, a torque converter and a control unit is adopted to control the electric motor to rotate at a constant rotation speed, the torque is amplified by the torque converter, and the output of the crawling torque is realized through simple switching control.
It is realized that the driving unit easily generates crawling torque without performing complex torque calculations, ensuring smooth crawling driving under different load conditions.
Smart Images
Figure CN222905310U_ABST
Abstract
Description
Technical Field
[0001] The utility model relates to a drive unit. Background Art
[0002] An electric vehicle capable of crawling has been proposed. For example, the electric vehicle described in Patent Document 1 has a motor torque control device. This motor torque control device is configured to generate torque of the motor when neither the accelerator pedal nor the brake pedal is operated. Specifically, the motor torque control device gradually increases the crawling torque while controlling the gain according to the vehicle speed. In addition, the motor torque control device controls the increase ratio of the gain according to the road slope resistance. Thereby, the impact given to the occupant is suppressed and the riding comfort is improved.
[0003] Prior Art Documents
[0004] Patent Documents
[0005] Patent Document 1: Japanese Patent No. 3440757 Gazette Summary of the Utility Model
[0006] Technical Problem to be Solved by the Utility Model
[0007] The motor torque control device configured as described above performs complex torque calculations to generate crawling torque, and thus has a relatively complex structure. Therefore, the technical problem of the present utility model is to provide a drive unit that can easily generate crawling torque.
[0008] Solution for Solving the Technical Problem
[0009] The drive unit according to the first aspect includes an electric motor, a torque converter, and a control unit. The electric motor functions as a drive source of the drive unit. The torque converter is configured to amplify the torque output from the electric motor. The control unit controls the electric motor so that the electric motor rotates at a constant speed and outputs crawling torque.
[0010] According to this structure, when the control unit controls the electric motor to output crawling torque, the control unit only makes the electric motor rotate at a constant speed and does not perform complex controls such as torque calculations. Therefore, the above drive unit can easily generate crawling torque. In addition, since the drive unit outputs torque via the torque converter, when the load applied to the drive wheels is large, the torque output from the torque converter also becomes large, and when the load applied to the drive wheels is small, the torque output from the torque converter also becomes relatively small. Therefore, smooth crawling can be achieved.
[0011] For the drive unit related to the second mode, in the drive unit related to the first mode, there is also a first switch that can be operated by the driver. The control unit controls the electric motor so that when it is determined that the accelerator operation has not been performed and the first switch is in the ON state, the electric motor rotates at a first speed and outputs a creep torque.
[0012] For the drive unit related to the third mode, in the drive unit related to the second mode, it is configured as follows. The first speed is set so that the first torque is equal to or less than the rated torque of the electric motor, and the first torque is calculated based on the capacity coefficient of the torque converter and the first speed.
[0013] For the drive unit related to the fourth mode, in the drive unit related to the second or third mode, the first speed is below the base speed of the electric motor.
[0014] For the drive unit related to the fifth mode, in the drive unit related to any one of the second to fourth modes, there is also a second switch that can be operated by the driver. The control unit controls the electric motor so that when it is determined that the accelerator operation has not been performed, the first switch is in the ON state, and the second switch is in the ON state, the electric motor rotates at a second speed and outputs a creep torque.
[0015] For the drive unit related to the sixth mode, in the drive unit related to the fifth mode, the second speed is higher than the first speed.
[0016] For the drive unit related to the seventh mode, in the drive unit related to the fifth or sixth mode, it is configured as follows. The second speed is set so that the second torque is equal to or greater than the rated torque of the electric motor and equal to or less than the maximum torque, and the second torque is calculated based on the capacity coefficient of the torque converter and the second speed.
[0017] For the drive unit related to the eighth mode, based on the drive unit related to any one of the fifth to seventh modes, the second speed is below the base speed of the electric motor.
[0018] For the drive unit related to the ninth mode, in the drive unit related to any one of the fifth to eighth modes, it is configured as follows. When the control unit determines that the accelerator operation has not been performed and the first and second switches are in the ON state, when it is determined that the temperature of at least one of the electric motor and the working oil in the torque converter exceeds the threshold value, the speed of the electric motor is made equal to or less than the first speed. In addition, the temperature of the electric motor is a concept that includes not only the temperature of the electric motor itself but also the temperature of the inverter that controls the electric motor.
[0019] Effects of the utility model
[0020] According to the present utility model, it is possible to easily generate creep torque. BRIEF DESCRIPTION OF THE DRAWINGS
[0021] Figure 1 is a schematic diagram of the drive unit.
[0022] Figure 2 is a perspective view showing the shift lever.
[0023] Figure 3 is a graph showing the characteristics of the electric motor and the torque converter.
[0024] Figure 4 is a flowchart showing the control method based on the control unit. DETAILED DESCRIPTION OF THE EMBODIMENTS
[0025] Hereinafter, an embodiment of the drive unit will be described with reference to the drawings. Figure 1 is a schematic diagram of the drive unit according to the present embodiment. In the following description, the axial direction is the direction in which the rotation axis O of the electric motor 2 or the torque converter 3 extends. In addition, the circumferential direction is the circumferential direction of a circle centered on the rotation axis O, and the radial direction is the radial direction of a circle centered on the rotation axis O. In addition, forward rotation is the rotation when the vehicle moves forward, and reverse rotation is the rotation when the vehicle moves backward.
[0026] [DRIVE UNIT 100]
[0027] As Figure 1 shown, the drive unit 100 includes an electric motor 2, a torque converter 3, a first drive shaft body 4, a second drive shaft body 5, a speed reducer 6, and a control unit 7. The drive unit 100 is mounted on an electric vehicle, for example. The drive unit 100 is configured to drive the drive wheels 101.
[0028] <ELECTRIC MOTOR>
[0029] The electric motor 2 functions as a drive source of the drive unit 100. The electric motor 2 is an AC synchronous motor. In addition, the drive unit 100 has only the electric motor 2 as a drive source. That is, the drive unit 100 does not have an internal combustion engine as a drive source. In the present embodiment, the drive unit 100 does not have an internal combustion engine, but may have an internal combustion engine for power generation.
[0030] The electric motor 2 has a motor housing 21, a motor stator 22, and a rotor 23. The electric motor 2 of the present embodiment is a so-called inner rotor type motor. The electric motor 2 has an inverter (not shown) for controlling the rotational speed of the electric motor 2.
[0031] The motor housing 21 is fixed to the vehicle body frame or the like and cannot rotate. The motor stator 22 and the rotor 23 are housed in the motor housing 21.
[0032] The motor stator 22 is fixed to the inner circumferential surface of the motor housing 21. The motor stator 22 cannot rotate. The rotor 23 rotates about the rotation axis O. The rotor 23 is disposed radially inside the motor stator 22. The motor stator 22 is disposed at a radial interval from the rotor 23.
[0033] <Torque Converter>
[0034] The torque converter 3 is disposed at an axial interval from the electric motor 2. A speed reducer 6 is disposed between the torque converter 3 and the electric motor 2. Axially, they are arranged in the order of the electric motor 2, the speed reducer 6, and the torque converter 3.
[0035] The torque converter 3 is configured to be rotatable. The rotation axis O of the torque converter 3 substantially coincides with the rotation axis O of the electric motor 2. The torque converter 3 transmits the torque from the electric motor 2. The torque converter 3 is configured to amplify the torque output by the electric motor 2.
[0036] The torque converter 3 further includes a cover 31, an impeller 32, a turbine 33, a stator 34, a first one-way clutch 36, and a lock-up clutch 37. In the present embodiment, the housing of the torque converter 3 is constituted by the cover 31 and the impeller 32. A working fluid is supplied into the torque converter 3. The working fluid is, for example, working oil.
[0037] For the torque converter 3, the impeller 32 is disposed on the side of the electric motor 2 ( Figure 1 the left side), and the cover 31 is disposed on the side opposite to the electric motor 2 ( Figure 1 the right side). The torque converter 3 is housed in the torque converter housing 30.
[0038] The cover 31 is input with the torque from the electric motor 2. The cover 31 rotates by the torque from the electric motor 2. The cover 31 is fixed to the first drive shaft body 4. For example, the cover 31 has a spline hole, and the first drive shaft body 4 is spline-fitted with the spline hole of the cover 31. Therefore, the cover 31 and the first drive shaft body 4 rotate integrally. The cover 31 is disposed to cover the turbine 33.
[0039] The impeller 32 rotates integrally with the cover 31. The impeller 32 is input with the torque from the electric motor 2 via the cover 31. The impeller 32 is fixed to the cover 31. The impeller 32 is supported by the fixed shaft body 38 via a bearing member (not shown) so as to be rotatable. In addition, the fixed shaft body 38 is cylindrical. The space between the impeller 32 and the fixed shaft body 38 is hermetically sealed. Inside the fixed shaft body 38, the second drive shaft body 5 extends in the axial direction. Further, the fixed shaft body 38 extends from, for example, the speed reducer housing 62 or the torque converter housing 30. The fixed shaft body 38 cannot rotate.
[0040] The turbine 33 is disposed opposite to the impeller 32. Specifically, the turbine 33 is axially opposite to the impeller 32. The turbine 33 is transmitted with the torque from the impeller 32 via the working fluid.
[0041] A second drive shaft body 5 is installed on the turbine 33. Specifically, the second drive shaft body 5 is spline-fitted with the turbine 33. The turbine 33 rotates integrally with the second drive shaft body 5.
[0042] The stator 34 is configured to rectify the working oil returning from the turbine 33 to the impeller 32. The stator 34 can rotate about the rotation axis O. For example, the stator 34 is supported by the fixed shaft body 38 via the first one-way clutch 36. The stator 34 is axially disposed between the impeller 32 and the turbine 33.
[0043] The first one-way clutch 36 is disposed between the fixed shaft body 38 and the stator 34. The first one-way clutch 36 is configured to enable the stator 34 to rotate in the forward rotation direction. On the other hand, the first one-way clutch 36 prevents the stator 34 from rotating in the reverse rotation direction. Through this stator 34, the torque is amplified and transmitted from the impeller 32 to the turbine 33.
[0044] When the lock-up clutch 37 is in the clutch engaged state, the impeller 32 and the turbine 33 are directly connected. In addition, when the lock-up clutch 37 is in the clutch disengaged state, the direct connection between the impeller 32 and the turbine 33 is released.
[0045] In addition, in the present embodiment, the lock-up clutch 37 is installed on the turbine 33 or the second drive shaft body 5. The lock-up clutch 37 rotates integrally with the turbine 33. The lock-up clutch 37 is configured as a centrifugal clutch. That is, the lock-up clutch 37 is configured to connect the cover 31 and the turbine 33 by the centrifugal force generated by the rotation of the turbine 33. Specifically, the lock-up clutch 37 is configured to transmit torque from the cover 31 to the turbine 33 when the turbine 33 reaches a predetermined rotational speed or more.
[0046] The torque converter 3 is housed in the torque converter housing 30. The torque converter housing 30 is configured not to rotate. For example, the torque converter housing 30 is fixed to the vehicle body frame or the like.
[0047] <Reducer>
[0048] The reducer 6 is axially disposed between the electric motor 2 and the torque converter 3. The reducer 6 decelerates the rotation of the torque converter 3 and transmits it to the drive wheel 101 side. Specifically, the reducer 6 decelerates the rotation of the second drive shaft body 5 and transmits it to the drive wheel 101 side. In addition, the reducer 6 has a plurality of gears 61. The reducer 6 is housed in the reducer housing 62. In addition, one of the plurality of gears 61 meshes with the gear 51 fixed to the second drive shaft body 5.
[0049] <First drive shaft body>
[0050] The first drive shaft body 4 extends axially from the electric motor 2 towards the torque converter 3. Specifically, the first drive shaft body 4 extends from the rotor 23 of the electric motor 2. Additionally, when the electric motor 2 has an output shaft body, the first drive shaft body 4 is mounted on the output shaft body of the electric motor 2. The rotation axis of the first drive shaft body 4 is substantially on the same line as the rotation axis of the electric motor 2 and the rotation axis of the torque converter 3.
[0051] The first drive shaft body 4 transmits torque between the electric motor 2 and the torque converter 3. Specifically, the first drive shaft body 4 transmits the torque from the electric motor 2 to the torque converter 3. The first drive shaft body 4 is connected to the impeller 32 of the torque converter 3. Specifically, the first drive shaft body 4 is connected to the impeller 32 via the cover 31. The front end portion of the first drive shaft body 4 is mounted on the cover 31 of the torque converter 3.
[0052] <Second drive shaft body>
[0053] The second drive shaft body 5 transmits torque between the torque converter 3 and the speed reducer 6. The second drive shaft body 5 transmits the torque from the torque converter 3 towards the drive wheel 101 side. Specifically, the second drive shaft body 5 outputs the torque from the torque converter 3 to the speed reducer 6. The second drive shaft body 5 extends axially from the torque converter 3 towards the electric motor 2.
[0054] The second drive shaft body 5 is cylindrical. The first drive shaft body 4 extends within the second drive shaft body 5. Additionally, the first drive shaft body 4 is solid. One end portion ( Figure 1 the right end portion) of the second drive shaft body 5 is mounted on the turbine 33 of the torque converter 3. Further, a gear 51 is mounted on the other end portion ( Figure 1 the left end portion) of the second drive shaft body 5. The second drive shaft body 5 is rotatably supported, for example, via a bearing member or the like on the speed reducer housing 62 or the like.
[0055] <Second one-way clutch>
[0056] The drive unit 100 further includes a second one-way clutch 50. The second one-way clutch 50 is disposed between the first drive shaft body 4 and the second drive shaft body 5. Specifically, the second one-way clutch 50 is disposed between the cover 31 and the turbine 33. The second one-way clutch 50 enables the first drive shaft body 4 to rotate relative to the second drive shaft body 5 in the forward rotation direction. That is, the second one-way clutch 50 is configured such that when the electric motor 2 rotates forward to move the vehicle forward, the first drive shaft body 4 and the second drive shaft body 5 rotate relative to each other. Therefore, when the vehicle is moving forward, the second one-way clutch 50 does not transmit torque from the first drive shaft body 4 to the second drive shaft body 5.
[0057] On the other hand, the second one-way clutch 50 causes the first drive shaft body 4 to rotate integrally with the second drive shaft body 5 in the reverse direction. That is, the second one-way clutch 50 is configured such that when the electric motor 2 rotates in reverse to reverse the vehicle, the first drive shaft body 4 rotates integrally with the second drive shaft body 5. Therefore, when the vehicle reverses, the second one-way clutch 50 transmits torque from the first drive shaft body 4 to the second drive shaft body 5. That is, when the vehicle reverses, the torque of the electric motor 2 is transmitted from the first drive shaft body 4 to the second drive shaft body 5 via the second one-way clutch 50 rather than via the working fluid of the torque converter 3.
[0058] <Differential>
[0059] The drive unit 100 also includes a differential 103 and a pair of drive shafts 104. The differential 103 is configured to transmit the torque from the speed reducer 6 to the pair of drive wheels 101.
[0060] A pair of drive shafts 104 extend from the differential 103 to the pair of drive wheels 101. The drive shafts 104 extend in the axial direction. That is, the drive shafts 104 extend parallel to the first drive shaft body 4 and the second drive shaft body 5. In addition, the drive shafts 104 extend offset from the first drive shaft body 4 and the second drive shaft body 5.
[0061] <First and Second Switches>
[0062] As Figure 2 shown, the drive unit 100 has a first switch 105a and a second switch 105b. The first switch 105a is operated by the driver. The first switch 105a is, for example, a shift lever. Making the first switch 105a in the on state means that, for example, the driver moves the shift lever from a position other than the D (Drive) position (e.g., the N (Neutral) position) to the D position. Thus, in the present embodiment, making the first switch 105a in the on state means a state in which the vehicle can move forward if the accelerator is operated. In addition, by moving the shift lever from the D position to other positions, the first switch 105a becomes in the off state.
[0063] The second switch 105b is provided, for example, on the shift lever. The second switch 105b is operated by the driver. For example, the second switch 105b is a push-button switch. The second switch 105b can also be of the momentary type. That is, if the driver presses the second switch 105b, it becomes in the switch-on state, and if the driver releases the second switch 105b, it becomes in the switch-off state. In addition, the second switch 105b can also be of the toggle type. That is, if the driver presses the second switch 105b, it becomes in the switch-on state, and if the driver presses the second switch 105b again, it becomes in the switch-off state.
[0064] <Control Unit>
[0065] The control unit 7 is configured to control the electric motor 2 so that the electric motor 2 rotates at a constant speed and outputs a creep torque. By rotating the electric motor 2 at a constant speed and outputting a creep torque in this way, the vehicle equipped with the drive unit 100 creeps. The control unit 7 is constituted by a computer (e.g., a microcomputer) including a CPU (Central Processing Unit) and a ROM (Read Only Memory), etc. Programs for performing various operations are stored in the ROM. The CPU executes the programs stored in the ROM.
[0066] The control unit 7 is configured to execute a first creep mode and a second creep mode. The control unit 7 executes the first creep mode when it determines that no accelerator operation is performed and the first switch 105a is in the ON state. The control unit 7 controls the electric motor 2 in the first creep mode so that the electric motor 2 rotates at a first speed and outputs a creep torque.
[0067] Figure 3 is a graph showing the characteristics of the electric motor 2 and the characteristics of the torque converter 3. Figure 3 The solid line of is the characteristic line A showing the relationship between the rotational speed and the rated torque of the electric motor 2. Figure 3 The double-dot dash line of is the characteristic line B showing the relationship between the rotational speed and the maximum torque of the electric motor 2. Figure 3 The single-dot dash line of is the characteristic line C showing the relationship between the input rotational speed and the input torque based on the capacity coefficient of the torque converter 3. Here, since the electric motor 2 is connected to the input part (impeller 32) of the torque converter 3, the relationship between the rotational speed and the torque of the electric motor 2 also becomes the characteristic line C. Therefore, the torque of the electric motor 2 can be calculated from the characteristic line C and the rotational speed of the electric motor 2.
[0068] The first speed is set so that the first torque calculated based on the capacity coefficient of the torque converter 3 and the first speed is equal to or less than the rated torque of the electric motor 2. That is, the first speed is set so that the first torque calculated based on the characteristic line C and the first speed of the electric motor 2 is equal to or less than the rated torque of the electric motor 2. Specifically, as Figure 3 shown, according to the characteristic line C, the first torque t1 of the first speed r1 of the electric motor 2 is calculated. Then, the first speed r1 is set so that the first torque t1 is equal to or less than the rated torque t0 of the electric motor 2. That is, the first speed r1 is set to be equal to or less than the speed at the intersection of the characteristic line C and the characteristic line A. In addition, the first speed r1 is set to be equal to or less than the base speed r0 of the electric motor 2.
[0069] When the control unit 7 determines that no accelerator operation has been performed, the first switch 105a is in the ON state, and the second switch 105b is in the ON state, it executes the second creep mode. In the second creep mode, the control unit 7 controls the electric motor 2 so that the electric motor 2 rotates at a second rotational speed and outputs a creep torque. In addition, the second rotational speed r2 is higher than the first rotational speed r1. For example, on a slope or the like, the driver turns on the second switch 105b to execute the second creep mode.
[0070] The second rotational speed is set such that the second torque calculated based on the capacity coefficient of the torque converter 3 and the second rotational speed is equal to or greater than the rated torque of the electric motor 2 and equal to or less than the maximum torque. That is, the second rotational speed is set such that the second torque calculated based on the characteristic line C and the second rotational speed of the electric motor 2 is equal to or greater than the rated torque of the electric motor 2 and equal to or less than the maximum torque. Specifically, as Figure 3 shown, according to the characteristic line C, the second torque t2 of the second rotational speed r2 of the electric motor 2 is calculated. Then, the second rotational speed r2 is set such that the second torque t2 is equal to or greater than the rated torque t0 of the electric motor 2 and equal to or less than the maximum torque tmax. That is, the second rotational speed r2 is set to be equal to or higher than the rotational speed at the intersection of the characteristic line C and the characteristic line A and equal to or lower than the rotational speed at the intersection of the characteristic line C and the characteristic line B. In addition, the second rotational speed r2 is set to be equal to or lower than the base rotational speed r0 of the electric motor 2.
[0071] The control unit 7 determines whether at least one of the temperature of the electric motor 2 and the temperature of the working fluid of the torque converter 3 is equal to or lower than a threshold value. Specifically, the control unit 7 obtains the temperature of the electric motor 2 main body and the temperature of the inverter as the temperature of the electric motor 2 from the temperature sensor. In addition, the control unit 7 obtains the temperature of the working fluid of the torque converter 3 from the temperature sensor. Moreover, when the control unit 7 determines that at least one of the obtained temperature of the electric motor 2 and the temperature of the working fluid exceeds the threshold value, it sets the rotational speed of the electric motor 2 to be equal to or lower than the first rotational speed. In addition, the threshold value of the temperature of the electric motor 2 and the threshold value of the temperature of the working fluid may be the same as each other or different.
[0072] Figure 4 is a flowchart showing an example of the control method of the control unit 7. Hereinafter, with reference to Figure 4 the control method of the control unit 7 will be described.
[0073] The control unit 7 determines whether the first switch 105a is in the ON state (step S1). If the control unit 7 determines that the first switch 105a is in the ON state (Yes in step S1), it then determines whether an accelerator operation is being performed (step S2).
[0074] If the control unit 7 determines that an accelerator operation is being performed (Yes in step S2), it performs a torque current command (step S3). That is, the control unit 7 performs torque calculation based on the operation amount of the accelerator operation or the like, and instructs the current flowing through the electric motor 2 so as to output the torque. Thereby, the vehicle travels normally.
[0075] On the other hand, if the control unit 7 determines that no accelerator operation is being performed (No in step S2), it then determines whether the second switch 105b is in the ON state (step S4).
[0076] If the control unit 7 determines that the second switch 105b is not in the ON state (No in step S4), it executes the first creep mode (step S5). Thereby, the electric motor 2 rotates at the first rotational speed and outputs a creep torque. That is, the control unit 7 controls the electric motor 2 so that when it is determined that no accelerator operation is being performed and the first switch 105a is in the ON state, the electric motor 2 rotates at the first rotational speed and outputs a creep torque.
[0077] If the control unit 7 determines that the second switch 105b is in the ON state (Yes in step S4), it then determines whether at least one of the temperature of the electric motor 2 and the temperature of the working fluid of the torque converter 3 is below the threshold value (step S6). If the control unit 7 determines that the above temperature is higher than the threshold value, that is, the above temperature is not below the threshold value (No in step S6), it performs the process of step S5. That is, the control unit 7 executes the first creep mode.
[0078] On the other hand, if the control unit 7 determines that the above temperature is below the threshold value (Yes in step S6), it executes the second creep mode (step S7). Thereby, the electric motor 2 rotates at the second rotational speed and outputs a creep torque. That is, the control unit 7 controls the electric motor 2 so that when it is determined that no accelerator operation is being performed and the first switch 105a is in the ON state and the second switch 105b is in the ON state, the electric motor 2 rotates at the second rotational speed and outputs a creep torque.
[0079] [Modification Example]
[0080] The embodiments of the present invention have been described above, but the present invention is not limited to these, and various changes can be made as long as the gist of the present invention is not deviated from. In addition, the following modification examples can be basically applied simultaneously.
[0081] (a) In the above embodiment, the shift lever is illustrated as the first switch 105a, but the first switch 105a can also be a method other than the shift lever. For example, the first switch 105a can also be a push button switch or the like.
[0082] (b) The drive unit 100 may also not have the second switch 105b. In this case, the control unit 7 only executes the first creep mode and does not execute the second creep mode.
[0083] (c) Alternatively, the control unit 7 may control the electric motor 2 such that when at least one of the temperature of the electric motor 2 and the temperature of the working fluid exceeds a threshold value, the electric motor 2 rotates at a speed smaller than the first speed to output a creep torque.
[0084] Description of Reference Numerals
[0085] 2... Electric motor; 3... Torque converter; 7... Control unit; 100... Drive unit; 105a... First switch; 105b... Second switch.
Claims
1. A drive unit comprising: An electric motor functions as a drive source; a torque converter configured to amplify the torque output by the electric motor; and The control unit controls the electric motor so that the electric motor rotates at a constant rotation speed to output a creep torque.
2. The drive unit according to claim 1, wherein: The drive unit further includes a first switch operable by a driver, The control unit controls the electric motor so that the electric motor rotates at a first rotation speed to output a creep torque when it is determined that the accelerator operation is not performed and the first switch is in an on state.
3. The drive unit according to claim 2, wherein: The first rotation speed is set so that a first torque becomes equal to or less than a rated torque of the electric motor, the first torque being calculated based on a capacity factor of the torque converter and the first rotation speed.
4. The drive unit according to claim 2, wherein: The first speed is below a base speed of the electric motor.
5. The drive unit according to claim 2, wherein: The drive unit further includes a second switch operable by the driver, The control unit controls the electric motor so that the electric motor rotates at a second rotation speed to output a creep torque when it is determined that the accelerator operation is not performed, the first switch is in an on state, and the second switch is in an on state.
6. The drive unit according to claim 5, wherein: The second rotation speed is higher than the first rotation speed.
7. The drive unit according to claim 5, wherein: The second rotation speed is set so that a second torque becomes equal to or greater than a rated torque and equal to or less than a maximum torque of the electric motor, the second torque being calculated based on a capacity factor of the torque converter and the second rotation speed.
8. The drive unit according to claim 5, wherein: The second speed is below a base speed of the electric motor.
9. The drive unit according to claim 5, wherein: The control unit controls the rotation speed of the electric motor to be less than the first rotation speed when it is determined that the accelerator operation is not performed and the first and second switches are in the on state and when it is determined that the temperature of at least one of the electric motor and the working fluid in the torque converter exceeds a threshold value.