Power control device for electric vehicles

Abstract

To provide a driving force control device for an electric vehicle that allows smooth starting after executing single-phase lock avoidance control that suppresses excessive temperature rise in either of driving force sources provided in a pair of left and right drive wheels.SOLUTION: A driving force control device for an electric vehicle includes a first motor for driving a left drive wheel, a second motor for driving a right drive wheel, and a stopping maintenance device for maintaining the state where the electric vehicle is stopped. When the electric vehicle is stopped by outputting driving torque from the first motor and the second motor, the device determines whether one motor has exceeded a predetermined temperature (Step S2). When it is determined that one motor has exceeded a predetermined temperature, the device executes single-phase lock avoidance control that activates the stopping maintenance device and reduces the driving torque of each motor (Steps S3, S4).SELECTED DRAWING: Figure 6

Description

Technical Field

[0001] The present invention relates to a driving force control device for an electric vehicle provided with motors as driving force sources for a pair of left and right driving wheels respectively.

Background Art

[0002] Patent Document 1 describes a driving force control device for a hybrid vehicle provided with an engine and a first motor as driving force sources for a pair of front wheels, and a second motor as a driving force source for a pair of rear wheels. This driving force control device is configured to maintain the driving force of the entire vehicle by increasing the operation of the first motor when the operation of the second motor is restricted. Further, when the operation of the first motor is restricted, the output of the second motor is reduced in order to make the torque distribution ratio between the front and rear wheels the target distribution ratio.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] When the operation of the second motor that drives the rear wheels is restricted, the driving force control device described in Patent Document 1 increases the operation of the first motor that drives the front wheels so that the total driving force generated by the front and rear wheels satisfies the required driving force. On the other hand, in an electric vehicle provided with motors as driving force sources for a pair of left and right wheels respectively, if the torque ratio between the left and right wheels is different from the target torque ratio, an unintended deviation may occur.

[0005] Furthermore, in electric vehicles equipped with motors as driving forces for each of the left and right wheels, when the vehicle stops on an uphill road or when generating a driving force to counteract the load acting on the vehicle and maintain a stopped state, the motors do not rotate, and therefore a specific phase remains energized. In such cases, one of the motors may be energized with a relatively large current depending on the rotation angle at the time of stopping, potentially causing an excessive temperature rise. Conventionally, single-phase lock avoidance control is performed to suppress the excessive temperature rise of the motor by reducing the output of that motor and locking the drive wheel connected to that motor. On the other hand, when single-phase lock avoidance control is performed on one motor as described above, the lock on the drive wheel is released and the reduced motor torque is increased to generate enough driving force to start the vehicle. In contrast, the motor on which single-phase lock avoidance control is not performed can generate enough driving force to start the vehicle by further increasing the torque it is generating. In other words, the left and right drive systems will differ in whether or not the lock is released at the time of starting and the amount of torque increase, which can complicate the control.

[0006] The present invention has been made in view of the above technical problems, and aims to provide a drive force control device for an electric vehicle that can start smoothly after performing single-phase lock avoidance control to suppress excessive temperature rise in either of the drive force sources provided on each of the left and right drive wheels. [Means for solving the problem]

[0007] To achieve the above objective, the present invention provides a drive force control device for an electric vehicle, comprising a first motor for driving the left drive wheel and a second motor for driving the right drive wheel, wherein the first motor and the second motor can be controlled independently, and further comprising a stop-maintaining device capable of generating a drive torque or braking torque to maintain the electric vehicle in a stopped state, and a controller for controlling the first motor and the second motor, wherein the controller comprises a single-phase lock determination unit that determines that when the electric vehicle is stopped by outputting drive torque from the first motor and the second motor, either the first motor or the second motor has risen to a predetermined temperature or higher, and a single-phase lock avoidance control unit that, when the single-phase lock determination unit determines that one of the motors has risen to a predetermined temperature or higher, generates the drive torque or braking torque using the stop-maintaining device and reduces the drive torque of the first motor and the second motor. [Effects of the Invention]

[0008] According to the present invention, when an electric vehicle is stopped by outputting drive torque from a first motor that drives the left drive wheel and a second motor that drives the right drive wheel, if one of the motors heats up to a predetermined temperature, the stop maintenance device generates drive torque or braking torque and reduces the drive torque of both the first and second motors. Therefore, the drive torque of the motor that has reached a predetermined temperature and the other motor are similarly reduced. In other words, the drive torque of both the first and second motors is reduced. As a result, by reducing the drive torque or braking torque by the stop maintenance device while increasing the drive torque of both the first and second motors, the electric vehicle can be started smoothly. In other words, differences in the timing of increasing the drive torque of the first and second motors, and differences in the amount of increase, can be suppressed, and the control can be simplified while maintaining the stability of the electric vehicle's behavior when it starts. [Brief explanation of the drawing]

[0009] [Figure 1] This is a schematic block diagram showing an example of an electric vehicle according to an embodiment of the present invention. [Figure 2] This is a skeleton diagram showing an example of a drive unit on the rear wheel side. [Figure 3] This is a skeleton diagram showing an example of the drive unit on the front wheel side. [Figure 4] This figure shows an example of a driving force map. [Figure 5] This is a block diagram illustrating the functional configuration of the controller. [Figure 6] This is a flowchart illustrating an example of control performed in an embodiment of the present invention. [Figure 7] This is a time chart showing the changes in inverter temperature, brake signal, and current value when the control example shown in Figure 6 is executed. [Modes for carrying out the invention]

[0010] Next, embodiments of the present invention will be described with reference to the accompanying drawings. Note that the embodiments described below are merely examples of how the present invention may be implemented and do not limit the invention.

[0011] An example of an electric vehicle according to an embodiment of the present invention is schematically shown in Figure 1. The electric vehicle Ve shown in Figure 1 (hereinafter simply referred to as "vehicle") comprises a front drive unit Pf for driving a pair of front wheels 1r and 1l, and a rear drive unit Pr for driving a pair of rear wheels 2r and 2l. These drive units Pf and Pr are mainly composed of a motor and a gear reduction mechanism (transmission mechanism), respectively.

[0012] Figure 2 shows a skeleton diagram of an example of the rear drive unit Pr. This drive unit Pr is composed of a pair of drive systems that independently control the left and right rear wheels 2r and 2l. Since these drive systems are symmetrically configured, they will be described together without specifically designating them as "right" or "left". In the following description, if the subscript (suffix) of the reference numeral is one letter, "f" indicates the front wheel, "l" indicates the left wheel, and "r" indicates the right wheel or rear wheel. If there are two letters, the first letter "f" indicates the front wheel, "r" indicates the rear wheel, the second letter "r" indicates the right wheel, and "l" indicates the left wheel. Therefore, a motor with the subscript "l" corresponds to the first motor in the embodiment of the present invention, and a motor without the subscript "l" corresponds to the second motor in the embodiment of the present invention.

[0013] The rear drive unit Pr is mounted with motors Mrr and Mrl oriented in the longitudinal direction of the vehicle Ve. Drive gears 3rr and 3rl are attached to the rotor shafts of these motors, and these drive gears 3rr and 3rl mesh with counter-driven gears 4rr and 4rl. The counter-driven gears 4rr and 4rl have a larger diameter than the drive gears 3rr and 3rl, and therefore these gear pairs constitute a reduction mechanism.

[0014] The counter-driven gears 4rr and 4rl are mounted on the same axis as the bevel gears, counter-drive gears 5rr and 5rl, which rotate together. These counter-drive gears 5rr and 5rl mesh with the driven gears 7rr and 7rl, which are bevel gears integrated with the drive shafts 6rr and 6rl connected to the rear wheels 2r and 2l. By making the driven gears 7rr and 7rl larger in diameter than the counter-drive gears 5rr and 5rl, these gear pairs can be used as a reduction gear mechanism.

[0015] Figure 3 shows a skeleton diagram of an example of the front drive unit Pf. Since this drive unit Pf has a symmetrical configuration, it will be described collectively without specifically designating it as "right" or "left". Motors Mfr and Mfl are mounted with their rotational axis oriented in the width direction (lateral direction) of the vehicle Ve, and drive gears 12fr and 12fl are attached to their rotor shafts, and these drive gears 12fr and 12fl mesh with idler gears 13r and 13l. Counter shafts 14r and 14l are provided parallel to the rotational axis of these idler gears 13r and 13l, and the idler gears 13r and 13l mesh with counter driven gears 15fr and 15fl attached to these counter shafts 14r and 14l. Because the counter driven gears 15fr and 15fl have a larger diameter than the drive gears 12fr and 12fl attached to the motors Mfr and Mrl, these gear pairs constitute a reduction mechanism.

[0016] Counter drive gears 16fr and 16fl are attached to counter shafts 14r and 14l. These counter drive gears 16fr and 16fl mesh with driven gears 18fr and 18fl, which are integrated with drive shafts 17fr and 17fl connected to the front wheels 1r and 1l. Because the driven gears 18fr and 18fl have a larger diameter than the counter drive gears 16fr and 16fl, these gear pairs constitute a reduction mechanism.

[0017] The motors Mrl, Mrr, Mfl, and Mfr described above are configured similarly to motors used as power sources in conventional electric vehicles and hybrid vehicles. That is, in addition to functioning as motors that generate driving torque by receiving power from the energy storage device (Bat) 20 mounted on the vehicle Ve, they also function as generators that convert power into electricity and charge the energy storage device 20 by rotating the output shaft (rotor shaft). Specifically, they can be configured as synchronous motors equipped with permanent magnets in the rotor.

[0018] The motors Mrl, Mrr, Mfl, and Mfr configured as described above convert the DC voltage of the power storage device 20 into an AC voltage and apply it to the coils (phases) provided on the stator, thereby generating driving torque. The voltage applied to the coils (phases) increases and decreases according to the rotation angle of the rotor. In order to convert the DC voltage of the power storage device 20 into an AC voltage and apply it to the coils, and to convert the AC voltage generated when the motors Mrl, Mrr, Mfl, and Mfr are rotated into a DC voltage to charge the power storage device 20, power control units PCf and PCr mainly composed of inverters are provided between the front drive unit Pf and the power storage device 20, and between the rear drive unit Pr and the power storage device 20, respectively.

[0019] In addition, parking lock mechanisms (not shown) for locking the drive shafts 6rr, 6rl, 17fr, and 17fl are provided on the respective drive shafts 6rr, 6rl, 17fr, and 17fl described above. Also, brake mechanisms (not shown) for applying braking torque to the drive wheels 1r, 1l, 2r, and 2l are provided on the respective drive wheels 1r, 1l, 2r, and 2l.

[0020] An electronic control unit (hereinafter referred to as ECU) 31 for controlling each of the motors Mrl, Mrr, Mfl, and Mfr (that is, the power control units PCf and PCr) is provided. This ECU 31 is mainly composed of a microcomputer, similar to the ECU mounted on a conventional vehicle, and is configured to obtain output signals for controlling each of the motors Mrl, Mrr, Mfl, and Mfr based on the input signals and maps and arithmetic expressions stored in advance.

[0021] Specifically, the required drive torque is determined based on the accelerator pedal input, vehicle speed, and a drive force map pre-stored in the ECU31. This required drive torque is the total value of the drive torque transmitted to each drive wheel 1r, 1l, 2r, and 2l, and the required drive torque for each motor is determined based on the front-to-rear distribution ratio determined according to the magnitude of the required drive torque. Figure 4 shows an example of a drive force map, which is configured such that the required drive torque decreases as the vehicle speed increases, and increases as the accelerator pedal input increases.

[0022] Vehicle Ve, configured in this way, can maintain a stationary state on uphill roads by operating only the accelerator, without the driver having to operate the brakes. Specifically, when the load acting to reverse the vehicle Ve according to the gradient angle of the road and the required driving torque (required driving force), which is determined based on the amount of accelerator operation by the driver and the driving force map, are balanced, the vehicle Ve will maintain a stationary state.

[0023] On the other hand, the motors Mrl, Mrr, Mfl, and Mfr described above have currents that increase or decrease sinusoidally in the coils (phases) that make up the motor, depending on their rotation angle (or electrical angle). For example, at a given rotation angle, the same current is supplied to the U-phase coil and the V-phase coil, while at other rotation angles, the current supplied to the U-phase coil increases and the current supplied to the V-phase coil decreases.

[0024] Therefore, when driving torque is generated from each motor Mrl, Mrr, Mfl, and Mfr as described above to maintain the vehicle Ve in a stopped state, a single-phase lock may occur in one of the motors, in which a large current is continuously supplied to a predetermined coil (phase) constituting that motor. For this reason, the drive force control device of the present invention is configured to reduce the current supplied to the motor in which the single-phase lock occurred, and to the motor paired with that motor, when a single-phase lock occurs.

[0025] Figure 5 shows a block diagram illustrating the function of an ECU 31 (corresponding to the controller in this invention) configured to reduce the current supplied to a pair of motors when a single-phase lock occurs. The ECU 31 shown in Figure 5 receives signals from a vehicle speed sensor that detects vehicle speed, an accelerator opening sensor that detects accelerator operation amount, a shift sensor that detects shift position, a brake sensor that detects brake operation amount, a gradient angle sensor that detects the gradient angle of the road (or the inclination angle of the vehicle Ve), a temperature sensor that detects the temperature of each motor Mrl, Mrr, Mfl, Mfr or each power control unit PCf, PCr, and a resolver that detects the rotation angle of each motor Mrl, Mrr, Mfl, Mfr.

[0026] The ECU 31 also includes a gradient angle calculation unit 32, a single-phase lock determination unit 33, and a single-phase lock avoidance control unit 34. The gradient angle calculation unit 32 calculates the inclination angle of the vehicle Ve based on the signal input from the gradient angle sensor. The single-phase lock determination unit 33 determines that a single-phase lock has occurred if the temperature of a predetermined phase among the coils wound around the stator, or the temperature of the inverter for controlling the power supplied to that predetermined phase, is above a predetermined temperature. Such a phenomenon occurs, for example, when the vehicle is stopped on an uphill road with the accelerator pedal operated to generate driving torque, and power is continuously supplied to one of the phases depending on the rotation angle of the motor.

[0027] The single-phase lock avoidance control unit 34 is configured to perform control to reduce the current of the motor in which a single-phase lock has occurred and the motor paired with that motor. For example, if a single-phase lock occurs in motor Mrr, the current between motor Mrr and motor Mrl is reduced, the driving torque of the other pair of motors Mfr and Mfl required to maintain the stationary state of vehicle Ve is determined, and command signals are output to each motor Mrl, Mrr, Mfl, and Mfr. Alternatively, if a single-phase lock occurs in motor Mrr, the current between motor Mrr and motor Mrl is reduced, and command signals are output to the parking lock mechanism to lock each drive shaft 6rr and 6rl in order to maintain the stationary state of vehicle Ve, or the braking torque required to maintain the stationary state of vehicle Ve is determined and command signals are output to each brake mechanism.

[0028] Figure 6 shows a flowchart illustrating an example of control performed by the ECU 31. In the control example shown in Figure 6, first, it is determined whether or not the vehicle is stopped on an uphill road (step S1). In this step S1, the gradient angle calculation unit 32 detects the inclination angle of the vehicle Ve, and the ECU 31 can determine whether or not the vehicle is stopped based on the signal input from the vehicle speed sensor.

[0029] If step S1 is negatively determined due to the road being flat or downhill, or because the vehicle is in motion, this routine is terminated. Conversely, if step S1 is positively determined due to the vehicle being stopped on an uphill road, it is determined whether or not a single-phase lock has occurred (step S2). This step S2 is performed by the single-phase lock determination unit 33 and can be determined based on whether or not the temperature of each motor, specifically the temperature of any coil (phase) constituting each motor, is above a predetermined temperature. This step S2 may also be determined by estimating the coil temperature based on the voltage value applied to the coil, the current value flowing through the coil, the electrical resistance of the coil, the energizing time, etc. The predetermined temperature is set to a temperature lower than the single-phase lock temperature determined considering the durability of the motor and inverter.

[0030] If step S2 is negatively determined because no single-phase lock has occurred, this routine is terminated. Conversely, if step S2 is positively determined because a single-phase lock has occurred, single-phase lock avoidance control is executed. Specifically, the drive torque of the motor where the single-phase lock occurred, and the other motor that forms a pair with it (step S3), and the drive shaft to which these motors are connected is fixed (step S4), and this routine is terminated. In this case, it is preferable that the amount of reduction in the drive torque of the pair of motors is the same. Note that if step S4 is executed, the drive shaft will be fixed even if the driver is not operating the brakes, so the driver may be notified of this.

[0031] To explain with a specific example, if a single-phase lock occurs in motor Mrr, in step S3, the driving torque of motor Mrr and the motor Mrl that is paired with motor Mrr on the left and right sides is reduced. Then, a braking torque is applied to the drive shafts 6rr and 6rl by a parking mechanism or brake mechanism to lock them. This parking mechanism or brake mechanism corresponds to the "stopping and maintaining device" in the embodiment of the present invention.

[0032] Figure 7 shows a time chart illustrating the changes in inverter temperature, brake signal, and coil current when the above control example is executed. At time t0 in the example shown in Figure 7, the inverter temperature is below a predetermined temperature, causing each motor to output drive torque according to the accelerator operation. Therefore, the brake signal is kept off, and the coil current is kept relatively high.

[0033] As the motor is continuously energized from time t0, the inverter temperature gradually increases. As a result, when the inverter temperature reaches a predetermined temperature at time t1, a positive judgment is made in step S2, and the motor's driving torque is reduced and the drive shaft is fixed. That is, at time t1, the brake signal is switched on and the coil current value decreases. Therefore, the inverter temperature gradually decreases from time t1.

[0034] As described above, by reducing the drive torque of the motor experiencing single-phase lock and fixing the drive shaft with a parking lock mechanism and brake mechanism that maintain the vehicle Ve in a stationary state, it is possible to prevent the electric vehicle from moving unintentionally while suppressing the decrease in durability due to excessive temperature rise of the motor (including coils and inverter). Furthermore, by reducing the drive torque of the other motor, which is paired with the motor experiencing single-phase lock, in the same way as the motor experiencing single-phase lock, the vehicle Ve can be smoothly started by releasing the lock by the parking lock mechanism and brake mechanism and simultaneously increasing the drive torque of the pair of motors to the same extent. In other words, it is possible to suppress differences in the timing of increasing the drive torque of the pair of motors and the amount of increase being equal, thereby simplifying the control while maintaining the stability of the vehicle Ve's behavior when starting.

[0035] Furthermore, the stop-maintaining device in the embodiments of the present invention is not limited to those that apply braking torque, such as the parking lock mechanism and brake mechanism described above. It may also be configured to maintain the vehicle in a stopped state by outputting driving torque from a pair of motors on the opposite side in the front-rear direction of the vehicle from the pair of motors that have experienced a single-phase lock. In other words, if a single-phase lock occurs in either of the front motors, the pair of motors on the rear side corresponds to the stop-maintaining device, and if a single-phase lock occurs in either of the rear motors, the pair of motors on the front side corresponds to the stop-maintaining device.

[0036] Furthermore, the electric vehicle in the embodiment of the present invention is not limited to a vehicle equipped with only a motor as a driving force source, but may also be a hybrid vehicle equipped with both an engine and a motor as driving force sources. Specifically, it may be a vehicle in which an engine is connected to either the front or rear drive wheel, and a motor is connected to each of the other drive wheels on the front and rear sides. [Explanation of Symbols]

[0037] 1r,1l front wheel 2r,2l rear wheel 6rr, 6rl, 17fr, 17fl drive shaft 31 Electronic Control Unit (ECU) 32. Gradient Angle Calculation Unit 33 Single-phase lock determination unit 34 Single-phase lock avoidance control unit Mrl, Mrr, Mfl, Mfr motor PCf, PCr Power Control Unit Ve electric vehicle

Claims

[Claim 1] A drive force control device for an electric vehicle comprising a first motor for driving the left drive wheel and a second motor for driving the right drive wheel, wherein the first motor and the second motor can be controlled independently, A stop-maintaining device capable of generating driving torque or braking torque to maintain the electric vehicle in a stopped state, The system includes a controller that controls the first motor and the second motor, The aforementioned controller, When the electric vehicle is stopped by outputting drive torque from the first motor and the second motor, a single-phase lock determination unit determines that either the first motor or the second motor has risen to a predetermined temperature or higher, The system includes a single-phase lock avoidance control unit that, when the single-phase lock determination unit determines that one of the motors has risen to a predetermined temperature or higher, generates the drive torque or braking torque using the stop maintenance device and reduces the drive torque between the first motor and the second motor. A drive force control device for electric vehicles, characterized by the following features.

Images