Electric vehicle control device

Abstract

To provide a controller for an electric vehicle capable of preventing a motor from being locked.SOLUTION: An electric vehicle control unit (ECU) of a hybrid system comprises: a hill start determination unit (determination unit) that determines whether or not a drive motor may be locked; a first target torque instruction unit that instructs the drive motor to generate a first target torque; and a second target torque instruction unit that instructs the drive motor to generate a second target torque smaller than the first target torque when it is determined, after the first target torque instruction unit instructs the drive motor to generate the first target torque, that the drive motor may be locked. In addition, the first target torque instruction unit instructs the driver motor to generate a first target torque greater than the previous first target torque when it is determined, after the second target torque instruction unit instruct the driver motor to generate the second target torque, that the drive motor may be locked.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a control device for an electric vehicle. [Background technology]

[0002] Patent Document 1 discloses a control device for an electric vehicle using an electric motor as a drive source, which limits the drive force of the electric motor when it detects that the electric motor has locked. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2011-259601 Summary of the Invention [Problem to be solved by the invention]

[0004] The control device disclosed in Patent Document 1 has the problem that when it detects that the electric motor is locked, it performs control to limit the driving force of the electric motor, which places a burden on the locked electric motor.

[0005] An object of the present invention is to provide a control device for an electric vehicle that prevents the electric motor from locking up. [Means for solving the problem]

[0006] In order to achieve the above object, a control device for an electric vehicle according to the present invention is a control device for an electric vehicle having an electric motor as a drive source, and includes: a determination unit that determines whether there is a possibility that the electric motor will lock; When the determination unit determines that there is a possibility that the electric motor may lock up, a first target torque indicator that instructs the electric motor to generate a first target torque; and a second target torque indicator that instructs the electric motor to generate the first target torque after the first target torque indicator instructs the electric motor to generate the first target torque. The rotation speed is 0and a second target torque indicator that, when it is determined that the first target torque is greater than the first target torque, instructs the electric motor to generate a second target torque that is smaller than the first target torque, and the first target torque indicator instructs the electric motor to generate the second target torque after the second target torque indicator instructs the electric motor to generate the second target torque. The rotation speed is 0 If it is determined that there is a first target torque, the motor is instructed to generate a first target torque that is greater than the previous first target torque.

[0007] This configuration can prevent the electric motor from locking up.

[0008] Furthermore, in the control device for an electric vehicle according to the present invention, the first target torque instruction unit sets the amount and rate of change of torque when generating the first target torque to be larger than when the first target torque instruction unit instructed the generation of the first target torque the previous time.

[0009] This configuration allows the target torque to be output in a shorter time, making it possible to prevent the motor from locking up and to suppress temperature increases in the motor and its drive circuit.

[0010] Furthermore, the control device for an electric vehicle according to the present invention repeatedly executes the instruction to generate the first target torque by the first target torque instruction unit and the instruction to generate the second target torque by the second target torque instruction unit multiple times.

[0011] This configuration can reduce the load on the electric motor and some of the elements in the drive circuit for the electric motor. [Effects of the Invention]

[0012] According to the present invention, it is possible to prevent the electric motor from locking up. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is a block diagram showing an example of the overall configuration of an electric vehicle. [Figure 2]FIG. 2 is a block diagram showing an example of the overall configuration of a control device for an electric vehicle. [Figure 3] FIG. 3 is a functional block diagram showing an example of the functional configuration of a control device for an electric vehicle. [Figure 4] FIG. 4 is a time chart showing an example of torque control performed by the control device for an electric vehicle according to the first embodiment. [Figure 5] FIG. 5 is a flowchart showing an example of the flow of torque control performed by the control device for an electric vehicle according to the first embodiment. [Figure 6] FIG. 6 is a time chart showing an example of torque control performed by a control device for an electric vehicle of a comparative example. [Figure 7] FIG. 7 is a graph showing an example of the current flowing through each phase when the motor is locked. [Figure 8] FIG. 8 is a graph showing an example of the power saving function of the electric motor. [Figure 9] FIG. 9 is a time chart showing an example of torque control performed by the control device for an electric vehicle according to the second embodiment. [Figure 10] FIG. 10 is a flowchart showing an example of the flow of torque control performed by the control device for an electric vehicle according to the second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0014] (First embodiment) A first embodiment of the present invention will be described in detail below with reference to the accompanying drawings.

[0015] The configuration of a control device for an electric vehicle according to an embodiment of the present invention will be described with reference to Figures 1 and 2. Figure 1 is a block diagram showing an example of the overall configuration of an electric vehicle. Figure 2 is a block diagram showing an example of the overall configuration of a control device for an electric vehicle.

[0016] As shown in Fig. 1, vehicle 1 is equipped with a series hybrid system 10. Hybrid system 10 includes an engine 11, a generator motor (MG1) 12, a drive motor (MG2) 13, and a battery 14 (see Fig. 2), not shown in Fig. 1. Vehicle 1 is an example of an electric vehicle in the present disclosure.

[0017] The engine 11 is, for example, a gasoline engine.

[0018] The generator motor 12 is, for example, a permanent magnet synchronous motor. The rotating shaft of the generator motor 12 is mechanically connected to the crankshaft of the engine 11 via a gear (not shown) and a damper 40. For example, an output gear of the engine 11 is supported on the crankshaft of the engine 11 so as not to rotate relative to the crankshaft, and an output gear of the engine 11 is supported on the rotating shaft of the generator motor 12 so as not to rotate relative to the crankshaft, and the output gear of the engine 11 and the motor gear are meshed. The damper 40 absorbs torque fluctuations of the engine 11.

[0019] The drive motor 13 is, for example, a permanent magnet synchronous motor that is larger than the generator motor 12. The rotating shaft of the drive motor 13 is connected to a drive system 16 (see FIG. 2) of the vehicle 1. The drive system 16 includes a reduction gear 41 and a differential gear 42. The reduction gear 41 is a speed reducer that reduces the rotation speed of the drive motor 13. The differential gear 42 distributes the power of the drive motor 13 to drive wheels 17, which consist of left and right front or rear wheels. This causes the left and right drive wheels 17 to rotate, causing the vehicle 1 to move forward or backward. The drive motor 13 is an example of an electric motor in this disclosure.

[0020] (Overall configuration of the control device for electric vehicles) 2, the vehicle 1 is equipped with a series hybrid system 10. The hybrid system 10 includes an engine 11, a generator motor (MG1) 12, a drive motor (MG2) 13, a battery 14, and a PCU (Power Control Unit) 15.

[0021] The engine 11, the generator motor 12, and the drive motor 13 are as described above.

[0022] The battery 14 is a battery pack made up of a combination of a plurality of secondary batteries. The secondary batteries are, for example, lithium ion batteries. The battery 14 outputs, for example, DC power of approximately 200 to 350V.

[0023] The PCU 15 is a unit for controlling the driving of the generator motor 12 and the drive motor 13, and includes a first inverter 21, a second inverter 22, and a converter .

[0024] When starting the engine 11, the DC power output from the battery 14 is boosted by the converter 23, the boosted DC power is converted into AC power by the first inverter 21, and the AC power is supplied to the generator motor 12. This causes the generator motor 12 to perform power running, and the engine 11 is motored (cranked) by the generator motor 12. When the rotation speed of the crankshaft of the engine 11 has increased to the rotation speed required for starting due to motoring, the ignition plug of the engine 11 is sparked, and the engine 11 starts.

[0025] When the vehicle 1 is traveling, the drive motor 13 is powered and generates power.

[0026] When the output required of the drive motor 13 is smaller than the output of the battery 14, the vehicle 1 runs in EV mode. That is, the engine 11 is stopped, power generation by the generator motor 12 is not performed, and power is supplied from the battery 14 to the drive motor 13, which is then driven by the power.

[0027] Furthermore, when the remaining capacity of the battery 14 falls below a predetermined level, the generator motor 12 operates to generate electricity while the engine 11 is running, regardless of whether the drive motor 13 is running or stopped. At this time, AC power from the generator motor 12 is converted to DC power by the first inverter 21, and the DC power output from the first inverter 21 is stepped down by the converter 23. The stepped-down DC power is supplied to the battery 14, thereby charging the battery 14.

[0028] When the vehicle 1 decelerates, the drive motor 13 undergoes regenerative operation, and the power transmitted from the drive wheels 17 to the drive motor 13 is converted into AC power. At this time, the drive motor 13 acts as a resistor in the traveling drive system, and this resistance acts as a braking force (regenerative braking force) that brakes the vehicle 1. At this time, in the PCU 15, the AC power supplied from the drive motor 13 to the second inverter 22 is converted into DC power by the second inverter 22, and the DC power output from the second inverter 22 is stepped down by the converter 23. The stepped-down DC power is then supplied to the battery 14, thereby charging the battery 14.

[0029] Vehicle 1 is equipped with multiple ECUs (Electronic Control Units). Each ECU has a microcontroller unit (microcomputer), which incorporates, for example, a CPU, a non-volatile memory such as a flash memory, and a volatile memory such as a dynamic random access memory (DRAM). The multiple ECUs are connected to enable bidirectional communication using the CAN (Controller Area Network) communication protocol. Each ECU is connected to various sensors required for control, and receives detection signals from the connected sensors. In addition to the detection signals received from the various sensors, each ECU also receives information required for control from other ECUs.

[0030] FIG. 2 shows an ECU 31, one of the multiple ECUs, that controls the hybrid system 10. The ECU 31 is an example of a control device for an electric vehicle in the present disclosure. The ECU 31 is connected to an accelerator sensor 32, a vehicle speed sensor 33, a wheel speed sensor 34, and a G sensor 35. The accelerator sensor 32 outputs a detection signal corresponding to the amount of operation of an accelerator pedal operated by a driver (operator). The vehicle speed sensor 33 outputs, as a detection signal, a pulse signal synchronized with the rotation of a rotating body that rotates as the vehicle 1 travels. The wheel speed sensor 34 outputs, as a detection signal, a pulse signal synchronized with the rotation of each wheel (drive wheels 17 and non-drive wheels not shown) of the vehicle 1. The G sensor 35 detects the inclination of the vehicle 1.

[0031] The ECU 31 monitors the rotation speed of the drive motor 13. The ECU 31 also determines whether there is a possibility that the drive motor 13 will lock up. The ECU 31 also instructs the drive motor 13 to generate a first target torque. After instructing the drive motor 13 to generate the first target torque, the ECU 31 also The rotation speed is 0 If it is determined that there is a torque difference, the ECU 31 instructs the drive motor 13 to generate a second target torque that is smaller than the first target torque. After instructing the drive motor 13 to generate the second target torque, the ECU 31 The rotation speed is 0 If it is determined that there is a first target torque, the drive motor 13 is instructed to generate a first target torque that is greater than the previous first target torque.

[0032] (Functional configuration of the control device for electric vehicles) The functional configuration of the ECU 31 (control device for an electric vehicle) will be described with reference to Fig. 3. Fig. 3 is a functional block diagram showing an example of the functional configuration of the control device for an electric vehicle.

[0033] By executing a control program that operates the ECU 31, the ECU 31 realizes as functional units a hill start determination unit 51, a first target torque indication unit 52, a second target torque indication unit 53, an MG2 torque monitor unit 54, an MG2 rotation speed monitor unit 55, a tire rotation speed monitor unit 56, and a hill hold state monitor unit 57, all of which are shown in FIG. 3.

[0034] The slope start determination unit 51 determines whether the vehicle 1 is in a state to start on a slope, i.e., whether there is a possibility that the drive motor 13 will lock. The slope start determination unit 51 is an example of a determination unit in the present disclosure. More specifically, the slope start determination unit 51 determines that the vehicle 1 is in a state to start on a slope, for example, when the inclination of the vehicle 1 detected by the G sensor 35 is equal to or greater than a predetermined value and the vehicle speed of the vehicle 1 detected by the vehicle speed sensor 33 is 0.

[0035] The first target torque indicator 52 instructs the drive motor 13 to generate the first target torque. After the second target torque indicator 53 instructs the drive motor 13 to generate the second target torque, the first target torque indicator 52 MG2 RPM monitor 55 However, drive motor 13 The rotation speed is 0 If it is determined that there is a first target torque, the drive motor 13 is instructed to generate a first target torque that is larger than the previous first target torque. Furthermore, the first target torque instructing unit 52 sets the amount and rate of change of torque when generating the first target torque to be larger than when the first target torque instructing unit 52 instructed the generation of the first target torque one time previously.

[0036] After the first target torque specifying unit 52 specifies the generation of the first target torque to the drive motor 13, the second target torque specifying unit 53 specifies the generation of the first target torque to the drive motor 13. MG2 RPM monitor 55 However, drive motor 13 The rotation speed is 0 If it is determined that there is a second target torque, the drive motor 13 is instructed to generate a second target torque that is smaller than the first target torque.

[0037] The MG2 torque monitor unit 54 monitors the magnitude of the torque generated by the drive motor 13.

[0038] The MG2 rotation speed monitor 55 monitors the rotation speed and direction of the drive motor 13.

[0039] The tire rotation speed monitor unit 56 monitors the rotation speed and rotation direction of the drive wheels 17 .

[0040] The hill hold state monitor unit 57 monitors whether the hill hold function of the vehicle 1 is operating, that is, whether the brake is held when starting on a slope.

[0041] (Details of torque control performed by the control device of an electric vehicle) The details of the torque control performed by the ECU 31 (controller for an electric vehicle) will be described with reference to Fig. 4. Fig. 4 is a time chart showing an example of the torque control performed by the controller for an electric vehicle.

[0042] At time t=t0, the vehicle 1 is stopped on an uphill slope and is ready to start on the slope.

[0043] At time t=t0, the first target torque instruction unit 52 instructs the drive motor 13 to generate a first target torque T1. The value of the first target torque T1 may be set appropriately.

[0044] The drive motor 13 generates a first target torque T1 at time t=t1.

[0045] The MG2 rotation speed monitor 55 monitors the rotation speed and rotation direction of the drive motor 13 and detects that the rotation speed of the drive motor 13 has reached 0 at time t=t1. At this time, the rotation of the drive motor 13 reaches a plateau, and the rotational force of the drive motor 13 and the force acting on the vehicle 1 in the downhill direction are balanced. At this time, the rotational drive force of the drive motor 13 is transmitted to the drive wheels 17 via the power transmission shaft and various gears. However, the first target torque T1 output between time t=t0 and time t=t1 causes torsion of the power transmission shaft, and the various gears stop in a state where they have rotated by the amount of meshing play (backlash). The section from time t=t0 to time t=t1, during which the drive motor 13 is instructed to generate the first target torque T1, is referred to as section A.

[0046] At time t=t1, the second target torque instruction unit 53 instructs the drive motor 13 to generate a second target torque T2 that is smaller than the first target torque T1.

[0047] The drive motor 13 generates a second target torque T2 at time t=t2.

[0048] The MG2 rotation speed monitor 55 monitors the rotation speed and rotation direction of the drive motor 13 and detects that the rotation speed of the drive motor 13 has reached 0 at time t=t2. At this time, the drive motor 13 generates only the second target torque T2, which is smaller than the first target torque T1. Therefore, a force acts on the vehicle 1 in the direction of descending the slope, causing the rotation speed R of the drive motor 13 to assume a negative value from time t=t1 to time t=t2. That is, the drive motor 13 rotates slightly in a direction that moves the vehicle 1 backward. At this time, the torsion of the power transmission shaft generated by the first target torque T1 is released, and the various gears stop while rotating in the reverse direction by the amount of play in the reverse direction of their meshing. The section from time t=t1 to time t=t2, during which the drive motor 13 is instructed to generate the second target torque T2, is referred to as section B.

[0049] At time t=t2, the first target torque setting unit 52 instructs the drive motor 13 to generate a first target torque T3 that is greater than the previous first target torque T1.

[0050] The drive motor 13 generates a first target torque T3 at time t=t3. That is, in Figure 4, the slope of the torque T from time t=t2 to time t=t3 is greater than the slope of the torque T from time t=t0 to time t=t1.

[0051] The MG2 rotation speed monitor 55 monitors the rotation speed and rotation direction of the drive motor 13 and detects that the rotation speed of the drive motor 13 is positive at time t=t3. Although not shown in Fig. 4, the tire rotation speed monitor 56 detects that the drive wheels 17 are rotating in a direction that moves the vehicle 1 forward. The section from time t=t2 to time t=t3, during which the drive motor 13 is instructed to generate the first target torque T3, is referred to as section C.

[0052] Then, after time t=t3, the ECU 31 recognizes that the vehicle 1 has completed starting on a slope, and ends the control shown in FIG.

[0053] The vehicle 1 may be equipped with a hill-hold function. That is, the braking force may be maintained for a predetermined time (for example, two seconds) after the foot is released from the brake pedal. While the braking force is maintained, the vehicle 1 remains stopped on a slope even if the foot is released from the brake pedal. If the hill-hold function is released when the accelerator pedal is depressed, the vehicle 1 starts on a slope using the driving torque generated by depressing the accelerator pedal. For example, in FIG. 4, after issuing a command to generate the first target torque T3, the vehicle 1 may start on a slope after waiting for the hill-hold function to be released.

[0054] (Flow of processing performed by the control device of an electric vehicle) The flow of torque control performed by the ECU 31 (control device for an electric vehicle) will be described with reference to Fig. 5. Fig. 5 is a flowchart showing an example of the flow of torque control performed by the control device for an electric vehicle of the first embodiment.

[0055] The slope start determination unit 51 determines whether the vehicle 1 is in a state to start on a slope (step S11). If it is determined that the vehicle 1 is in a state to start on a slope (step S11: Yes), the process proceeds to step S12. On the other hand, if it is not determined that the vehicle 1 is in a state to start on a slope (step S11: No), the ECU 31 ends the process of FIG. 5.

[0056] When it is determined in step S11 that the vehicle 1 is in a state to start on a slope, the first target torque indicator 52 sets the first target torque to Ta (step S12). The first target torque Ta corresponds to the first target torque T1 in FIG.

[0057] Next, the first target torque setting unit 52 instructs the drive motor 13 to generate the first target torque Ta (step S13).

[0058] The hill hold state monitor unit 57 determines whether the hill hold is in the ON state (step S14). If it is determined that the hill hold is in the ON state (step S14: Yes), the process proceeds to step S15. On the other hand, if it is not determined that the hill hold is in the ON state (step S14: No), the process proceeds to step S16.

[0059] If it is determined in step S14 that the hill hold is ON, the MG2 rotation speed monitor unit 55 determines whether the rotation speed of the drive motor 13 is 0 (step S15). If it is determined that the rotation speed of the drive motor 13 is 0 (step S15: Yes), the process proceeds to step S17. On the other hand, if it is not determined that the rotation speed of the drive motor 13 is 0 (step S15: No), step S15 is repeated.

[0060] Returning to step S14, if it is not determined in step S14 that the hill hold is in the ON state, the tire rotation speed monitor unit 56 determines whether the rotation speed of the drive wheels 17 is positive, i.e., whether the drive wheels 17 are rotating in a direction that moves the vehicle 1 forward (step S16). If it is determined that the rotation speed of the drive wheels 17 is positive (step S16: Yes), the ECU 31 ends the processing of Fig. 5. On the other hand, if it is not determined that the rotation speed of the drive wheels 17 is positive (step S16: No), the ECU 31 proceeds to step S15.

[0061] If it is determined in step S15 that the rotation speed of the drive motor 13 is 0, the second target torque setting unit 53 sets the second target torque to (Ta-ΔT) (step S17). The second target torque (Ta-ΔT) corresponds to the second target torque T2 in FIG.

[0062] Next, the second target torque instruction unit 53 instructs the drive motor 13 to generate the second target torque (Ta-ΔT) (step S18).

[0063] The MG2 rotation speed monitor unit 55 determines whether the rotation speed of the drive motor 13 is 0 (step S19). If it is determined that the rotation speed of the drive motor 13 is 0 (step S19: Yes), the process proceeds to step S20. On the other hand, if it is not determined that the rotation speed of the drive motor 13 is 0 (step S19: No), step S19 is repeated.

[0064] If it is determined in step S19 that the rotation speed of the drive motor 13 is 0, the first target torque setting unit 52 sets the first target torque to Tmax (step S20). The first target torque Tmax corresponds to the first target torque T3 in Fig. 4. Then, the process returns to step S13.

[0065] (Torque control in comparative example) Torque control in a comparative example in which the control method described in this embodiment is not performed will be described using Figures 6, 7, and 8. Figure 6 is a time chart showing an example of torque control performed by a control device for an electric vehicle in the comparative example. Figure 7 is a graph showing an example of current flowing through each phase when the electric motor is locked. Figure 8 is a graph showing an example of a power saving function for the electric motor.

[0066] Assume that at time t=t0, the vehicle 1 starts to move on a slope. At this time, as shown in FIG. 6, in section D from time t=t1 to time t=t2, the drive motor 13 (MG2) is instructed to generate a target torque. Then, the torque of the drive motor 13 increases. In this torque increase section, heat is generated in the power control elements, such as IGBTs, that control the drive motor 13. This heat causes the temperature of the power control elements to increase.

[0067] As the torque of the drive motor 13 increases, the rotation speed R of the drive motor 13 reaches a plateau. Then, in section E from time t=t2 to time t=t3, the rotational force of the drive motor 13 and the force acting on the vehicle 1 in the downhill direction are balanced. The rotation speed R of the drive motor 13 becomes 0. Section E is a section in which the drive motor 13 is locked. In section E, the rotation speed R of the drive motor 13 is 0 even though rotation is instructed. Therefore, drive current continues to flow in each phase of the drive motor 13. As will be described later (see Figure 7), if a peak current flows in any of the U, V, or W phases at a position where the drive motor 13 is stopped, the temperature of the power control element that controls the current of that phase will rise. The longer the length of section E, the higher the temperature of the power control element. Therefore, it is desirable to make the length of section E as short as possible.

[0068] Then, after time t=t3, the torque of the drive motor 13 overcomes the force that is causing the vehicle 1 to move backward, and the vehicle 1 starts to climb the slope.

[0069] Note that the section F from the start of the slope start at time t = t0 until the vehicle 1 starts moving at time t = t3 is a section where the vehicle 1 is stationary.

[0070] Next, using FIG. 7, the current flowing in each phase when the drive motor 13 locks will be described. Note that FIG. 7 shows the magnitude of the current flowing in each phase when the drive motor 13, which is a three-phase AC motor, locks at the timing when the maximum current is flowing in the U phase.

[0071] As shown in FIG. 7, when the drive motor 13 locks at time t = ta, a peak current continues to flow in the U phase after time t = ta. Also, in the V phase and W phase, currents that are smaller than but approximately equal to the current flowing in the U phase continue to flow.

[0072] Thus, when the drive motor 13 locks, the temperature of the power control element that controls the current in each phase rises according to the continuously flowing current value.

[0073] To cope with such a temperature rise, generally, the control device of an electric vehicle has a function (power save function) to limit the torque of the drive motor 13 when the temperature of the power control element becomes high. FIG. 8 shows the characteristics of limiting the torque of the drive motor 13.

[0074] As shown in FIG. 8, the vehicle 1 changes the torque T of the drive motor 13 according to the temperature K of the power control element. That is, when the temperature K of the power control element is K < K1, the torque T of the drive motor 13 is generated at 100%. And when the temperature K of the power control element is K1 < K < K2, the torque T of the drive motor 13 is decreased according to the temperature K of the power control element. And when the temperature K of the power control element is K2 < K, the drive motor 13 does not generate the torque T. By performing such power saving, the power control element is protected.

[0075] Therefore, for example, if the drive motor 13 locks up as in section E shown in Fig. 6, if the power saving function described above is activated, the torque T will decrease, and the vehicle 1 may not be able to start uphill. Therefore, it is desirable to make the width of section E in which the drive motor 13 locks up as small as possible, and the ECU 31 (control device for an electric vehicle) of this embodiment described above can make section E in which the drive motor 13 locks up as short as possible, as shown in Fig. 4.

[0076] (Operation and effect of the first embodiment) As described above, the ECU 31 (controller for an electric vehicle) of the hybrid system 10 according to this embodiment is a controller for the vehicle 1 (electric vehicle) that has the drive motor 13 (electric motor) as a drive source, and includes a hill start determination unit 51 (determination unit) that determines whether there is a possibility that the drive motor 13 will lock; When the hill start determination unit 51 determines that there is a possibility that the drive motor 13 will lock, a first target torque indicator 52 that instructs the drive motor 13 to generate a first target torque T1; and a second target torque indicator 52 that instructs the drive motor 13 to generate the first target torque T1, and then The rotation speed is 0 and a second target torque indicator 53 that, when it is determined that there is a torque difference, instructs the drive motor 13 to generate a second target torque T2 that is smaller than the first target torque T1. After the second target torque indicator 53 instructs the drive motor 13 to generate the second target torque T2, the first target torque indicator 52 instructs the drive motor 13 to generate the second target torque T2. The rotation speed is 0 If it is determined that there is a first target torque T3, the drive motor 13 is instructed to generate a first target torque T3 that is greater than the previous first target torque T1. Therefore, the vehicle 1 can start on a slope without locking the drive motor 13.

[0077] Furthermore, in the ECU 31 (control device for an electric vehicle) of the hybrid system 10 according to this embodiment, the first target torque setting unit 52 sets the amount of change and rate of change of the torque T when generating the first target torque T3 to be larger than when the first target torque setting unit 52 instructed the generation of the first target torque T1 the previous time. Therefore, by shortening the time until the target torque is generated, it is possible to suppress a rise in temperature of the power control element that controls the drive motor 13.

[0078] (Second embodiment) A first embodiment of the present invention will be described in detail below with reference to the accompanying drawings.

[0079] (Details of torque control performed by the control device of an electric vehicle) Another torque control performed by the ECU 31 (controller for an electric vehicle) will be described with reference to Fig. 9. Fig. 9 is a time chart showing an example of torque control performed by the control device for an electric vehicle according to the second embodiment.

[0080] The hardware configuration and functional configuration of the hybrid system of the second embodiment are the same as those of the hybrid system 10 described in the first embodiment, and therefore the same reference numerals will be used in the description.

[0081] At time t=t0, the vehicle 1 is stopped on an uphill slope and is ready to start on the slope.

[0082] At time t=t0, the first target torque instruction unit 52 instructs the drive motor 13 to generate a first target torque T1. The value of the first target torque T1 may be set appropriately.

[0083] The drive motor 13 generates a first target torque T1 at time t=t1.

[0084] The MG2 rotation speed monitor unit 55 monitors the rotation speed and rotation direction of the drive motor 13 and detects that the rotation speed of the drive motor 13 has reached 0 at time t=t1. At this time, the rotation of the drive motor 13 has peaked out, and the rotational force of the drive motor 13 is balanced with the force acting on the vehicle 1 in the direction of descending the slope. At this time, the rotational drive force of the drive motor 13 is transmitted to the drive wheels 17 via the power transmission shaft and various gears, but the first target torque T1 output between time t=t0 and time t=t1 causes torsion of the power transmission shaft, and the various gears are stopped in a state where they have rotated by the amount of meshing play (backlash).

[0085] At time t=t1, the second target torque setting unit 53 instructs the drive motor 13 to generate a second target torque T2 that is smaller than the first target torque T1. The drive motor 13 generates the second target torque T2 at time t=t2.

[0086] The MG2 rotation speed monitor unit 55 monitors the rotation speed and rotation direction of the drive motor 13 and detects that the rotation speed of the drive motor 13 has reached 0 at time t=t2. At this time, the drive motor 13 generates only the second target torque T2, which is smaller than the first target torque T1, so a force acts on the vehicle 1 in the direction downhill, and the rotation speed R of the drive motor 13 assumes a negative value from time t=t1 to time t=t2. In other words, the drive motor 13 rotates slightly in a direction that moves the vehicle 1 backward. At this time, the torsion of the power transmission shaft generated by the first target torque T1 is released, and the various gears stop in a state where they have rotated in the reverse direction by the amount of play in the reverse direction of their meshing.

[0087] At time t=t2, the first target torque setting unit 52 instructs the drive motor 13 to generate a first target torque T3 that is greater than the previous first target torque T1. At this time, the first target torque setting unit 52 sets the amount and rate of change of the torque T to be the same as when the first target torque T1 was generated.

[0088] Thereafter, the same process is repeated to apply the torque T of the drive motor 13 in multiple stages. That is, after generating the first target torque T3, the second target torque T4, the first target torque T5, the second target torque T6, and the first target torque Tmax are applied in sequence. This allows a pseudo swaying start to be performed within the range of torsion of the power transmission shaft and play in the meshing of the various gears.

[0089] Since the hybrid system of this embodiment is equipped with a hill-hold function, even if the first target torque Tmax is generated at time t=t7, the vehicle 1 cannot start moving if the hill-hold function is activated.

[0090] In such a case, the second target torque setting unit 53 may generate the second target torque T7, and the first target torque setting unit 52 may generate the first target torque Tmax. If the hill hold function is released at time t=t10 while the first target torque Tmax is being generated, the tires will rotate and the vehicle 1 will start moving.

[0091] If the vehicle 1 does not start moving even when the first target torque Tmax is generated, it is possible to wait for the hill-hold function to be released at time t=t7. Since the hill-hold function is released after, for example, two seconds, if the hill-hold function is released while the first target torque Tmax is being generated, the tires will rotate as the hill-hold function is released, and the vehicle 1 will start moving.

[0092] (Flow of processing performed by the control device of an electric vehicle) The flow of torque control performed by the ECU 31 (control device for an electric vehicle) will be described with reference to Fig. 10. Fig. 10 is a flowchart showing an example of the flow of torque control performed by the control device for an electric vehicle according to the second embodiment.

[0093] The slope start determination unit 51 determines whether the vehicle 1 is in a state to start on a slope (step S31). If it is determined that the vehicle 1 is in a state to start on a slope (step S31: Yes), the process proceeds to step S32. On the other hand, if it is not determined that the vehicle 1 is in a state to start on a slope (step S31: No), the ECU 31 ends the process of FIG. 10.

[0094] When it is determined in step S31 that the vehicle 1 is in a state to start on a slope, the first target torque indicator 52 sets the first target torque to Ta (step S32). The first target torque Ta corresponds to the first target torque T1 in FIG.

[0095] Next, the first target torque setting unit 52 instructs the drive motor 13 to generate the first target torque Ta (step S33).

[0096] The hill hold state monitor unit 57 determines whether the hill hold is in the ON state (step S34). If it is determined that the hill hold is in the ON state (step S34: Yes), the process proceeds to step S35. On the other hand, if it is not determined that the hill hold is in the ON state (step S34: No), the process proceeds to step S36.

[0097] If it is determined in step S34 that the hill hold is ON, the MG2 rotation speed monitor unit 55 determines whether the rotation speed of the drive motor 13 is 0 (step S35). If it is determined that the rotation speed of the drive motor 13 is 0 (step S35: Yes), the process proceeds to step S37. On the other hand, if it is not determined that the rotation speed of the drive motor 13 is 0 (step S35: No), step S35 is repeated.

[0098] Returning to step S34, if it is not determined in step S34 that the hill hold is in the ON state, the tire rotation speed monitor unit 56 determines whether the rotation speed of the drive wheels 17 is positive, i.e., whether the drive wheels 17 are rotating in a direction that moves the vehicle 1 forward (step S36). If it is determined that the rotation speed of the drive wheels 17 is positive (step S36: Yes), the ECU 31 ends the processing of Fig. 10. On the other hand, if it is not determined that the rotation speed of the drive wheels 17 is positive (step S36: No), the ECU 31 proceeds to step S35.

[0099] If it is determined in step S35 that the rotation speed of the drive motor 13 is 0, the second target torque setting unit 53 sets the second target torque to (Ta-ΔTb) (step S37). The second target torque (Ta-ΔTb) corresponds to the second target torque T2 in FIG. 9.

[0100] Next, the second target torque instruction unit 53 instructs the drive motor 13 to generate the second target torque (Ta-ΔTb) (step S38).

[0101] The MG2 rotation speed monitor unit 55 determines whether the rotation speed of the drive motor 13 is 0 (step S39). If it is determined that the rotation speed of the drive motor 13 is 0 (step S39: Yes), the process proceeds to step S40. On the other hand, if it is not determined that the rotation speed of the drive motor 13 is 0 (step S39: No), step S39 is repeated.

[0102] If it is determined in step S39 that the rotation speed of the drive motor 13 is 0, the first target torque setting unit 52 sets the first target torque to Ta = Ta + ΔTa (step S40). The first target torque (Ta + ΔTa) corresponds to the first target torque T3 in Fig. 9. Then, the process returns to step S33.

[0103] (Operation and effect of the second embodiment) As described above, the ECU 31 (electric vehicle control device) of the hybrid system 10 according to this embodiment repeatedly issues a command to generate the first target torque (T1, T3, T5, max) from the first target torque setting unit 52 and a command to generate the second target torque (T2, T4, T6, T7) from the second target torque setting unit 53. Therefore, by increasing the time for which the drive motor 13 is rotated, it is possible to prevent the drive motor 13 from locking up. It is also possible to prevent a particular element of the multiple power control elements constituting the drive circuit of the drive motor 13 from being overloaded. Furthermore, it is possible to satisfy the hill-climbing performance of the vehicle 1 using a power control element with a smaller rating, thereby reducing the cost of the PCU 15.

[0104] In the first and second embodiments, an example has been described in which the ECU 31 (control device for an electric vehicle) controls the torque of the drive motor 13 when it detects that the vehicle 1 is in a state where it will start on a slope. However, situations in which such torque control of the drive motor 13 can be applied are not limited to starting on a slope. For example, a similar torque control can be applied when the drive motor 13 is locked, i.e., the number of rotations of the drive motor 13 is zero, even though the vehicle 1 has instructed the drive motor 13 to generate drive torque. For example, the above-described torque control can also be applied when the vehicle 1 starts from a stopped state by going over a curb.

[0105] Although the embodiments of the present invention have been described above, the above-described embodiments are presented as examples and are not intended to limit the scope of the present invention. This novel embodiment can be embodied in various other forms. Furthermore, various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. Furthermore, this embodiment is included within the scope and spirit of the invention, and is also included in the inventions and their equivalents as defined in the claims. [Explanation of symbols]

[0106] 1...vehicle (electric vehicle), 10...hybrid system, 11...engine, 12...generator motor, 13...drive motor (electric motor), 14...battery, 15...PCU, 16...drive system, 17...drive wheels, 21...first inverter, 22...second inverter, 23...converter, 31...ECU (controller for electric vehicle), 32...accelerator sensor, 33...vehicle speed sensor, 34...wheel speed sensor, 35...G sensor, 51...hill start determination unit (determination unit), 52...first target torque indication unit, 53...second target torque indication unit, 54...MG2 torque monitor unit, 55...MG2 rotation speed monitor unit, 56...tire rotation speed monitor unit, 57...hill hold state monitor unit, R...rotation speed, T...torque, T1, T3, T5, Tmax...first target torque, T2, T4, T6, T7...second target torque, t...time

Claims

1. A control device for an electric vehicle having an electric motor as a drive source, a determination unit that determines whether the electric motor is likely to lock; a first target torque instruction unit that instructs the electric motor to generate a first target torque when the determination unit determines that there is a possibility that the electric motor will lock; a second target torque instructing unit that, when it is determined that the number of revolutions of the electric motor is 0 after the first target torque instructing unit instructs the electric motor to generate the first target torque, instructs the electric motor to generate a second target torque that is smaller than the first target torque, the first target torque instruction unit instructs the electric motor to generate a first target torque greater than a previous first target torque when it is determined that the rotation speed of the electric motor is 0 after the second target torque instruction unit instructs the electric motor to generate the second target torque; Control device for electric vehicles.

2. The first target torque instruction unit The amount and rate of change of torque when generating the first target torque are set to be larger than when the first target torque instruction unit instructed generation of the first target torque one time previously. The control device for an electric vehicle according to claim 1.

3. the first target torque instruction unit instructs the second target torque unit to generate the first target torque and the second target torque instruction unit instructs the second target torque to generate the second target torque, the first target torque instruction unit instructs the second target torque unit to generate the second target torque, and the second target torque instruction unit instructs the first target torque instruction unit to generate the second target torque. The control device for an electric vehicle according to claim 1 or 2.

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