Driving force control device for electric vehicle

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 having electric motors as driving force sources for a pair of left and right drive wheels. [Background technology]

[0002] Patent Document 1 describes a driving force control device for a hybrid vehicle that includes an engine and a first motor as a driving force source 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. In addition, when the operation of the first motor is restricted, the output of the second motor is reduced in order to set the torque distribution ratio of the front and rear wheels to a target distribution ratio. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2001-112114 A Summary of the Invention [Problem to be solved by the invention]

[0004] 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 at the front and rear wheels satisfies the required driving force when the operation of the second motor that drives the rear wheels is restricted. On the other hand, in an electric vehicle equipped with a motor as a driving force source for each of a pair of left and right wheels, if the torque ratio of the left and right wheels differs from the target torque ratio, unintended deviation may occur.

[0005] In addition, in an electric vehicle having a pair of motors as driving force sources for the left and right wheels, when the vehicle stops on an uphill road, for example, and generates a driving force against the load acting on the vehicle to maintain the stopped state, the motor does not rotate, so a specific phase continues to be energized. In such a case, a relatively large current may be passed through one of the motors depending on the rotation angle at the time of stopping, causing an excessive temperature rise. Conventionally, therefore, single-phase lock avoidance control is performed to suppress an excessive temperature rise of the motor by reducing the output of the motor and locking the driving wheels connected to the motor. On the other hand, when the single-phase lock avoidance control is performed for one of the motors as described above, the driving force capable of starting can be generated by unlocking the driving wheels and increasing the torque of the reduced motor, whereas the motor for which the single-phase lock avoidance control is not performed can generate a driving force capable of starting by further increasing the generated torque. In other words, the left and right drive devices differ in whether or not the lock is released when starting, and in the amount of increase in torque, so that the control may become complicated.

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

[0007] In order to achieve the above-mentioned object, the present invention provides a driving force control device for an electric vehicle comprising a first motor for driving a left drive wheel and a second motor for driving a right drive wheel, and capable of independently controlling the first motor and the second motor, the driving force control device comprising: a stop maintaining device capable of generating a driving torque or a braking torque for maintaining a stopped state of the electric vehicle; and a controller for controlling the first motor and the second motor, the controller comprising: a single-phase lock determination unit for determining that one of the first motor and the second motor has risen in temperature to or above a predetermined temperature when the electric vehicle is stopped by outputting driving torque from the first motor and the second motor; and a single-phase lock avoidance control unit for generating the driving torque or the braking torque by the stop maintaining device and reducing the driving torque of the first motor and the second motor when the single-phase lock determination unit determines that the one of the motors has risen in temperature to or above the predetermined temperature. Effect of the Invention

[0008] According to the present invention, when an electric vehicle is stopped by outputting a driving torque from a first motor driving a left drive wheel and a second motor driving a right drive wheel, if one of the motors rises to a predetermined temperature or higher, a driving torque or a braking torque is generated by the stop maintaining device, and the driving torque of the first motor and the second motor is reduced. Therefore, the driving torque of the one motor that has reached a predetermined temperature or higher and the driving torque of the other motor are reduced in the same manner. That is, the driving torque of the first motor and the second motor are reduced. Therefore, the electric vehicle can be started smoothly by increasing the driving torque of the first motor and the second motor while reducing the driving torque and the braking torque by the stop maintaining device. In other words, it is possible to suppress differences in the timing of increasing the driving torque of the first motor and the second motor, differences in the amount of increase, etc., and to simplify the control while maintaining the stability of the behavior of the electric vehicle when it starts. [Brief description of the drawings]

[0009] [Figure 1] 1 is a block diagram illustrating an example of an electric vehicle according to an embodiment of the present invention. [Diagram 2] FIG. 2 is a skeleton diagram showing an example of a rear wheel side drive unit. [Diagram 3] FIG. 2 is a skeleton diagram showing an example of a front wheel drive unit. [Figure 4] FIG. 4 is a diagram showing an example of a driving force map. [Diagram 5] FIG. 2 is a block diagram illustrating an example of a functional configuration of a controller. [Figure 6] 4 is a flowchart illustrating an example of control executed in the embodiment of the present invention. [Figure 7] 7 is a time chart showing changes in inverter temperature, brake signal, and current value when the control example shown in FIG. 6 is executed. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Next, an embodiment of the present invention will be described with reference to the accompanying drawings. Note that the embodiment described below is merely an example of the case where the present invention is implemented, and is not intended to limit the present invention.

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

[0012] FIG. 2 shows a skeleton diagram of an example of a 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, 2l. Since these drive systems are symmetrical, they will be described together without being specifically designated as "right" or "left". In the following description, when the suffix (suffix) of the reference symbol is one letter, "f" indicates the front wheel, "l" indicates the left wheel, and "r" indicates the right wheel or the rear wheel, and when it is two letters, the first letter "f" indicates the front wheel, "r" indicates the rear wheel, and the second letter "r" indicates the right wheel, and "l" indicates the left wheel. Therefore, a motor with "l" in the suffix corresponds to a first motor in the embodiment of the present invention, and a motor without "l" in the suffix corresponds to a second motor in the embodiment of the present invention.

[0013] The rear drive unit Pr is equipped with motors Mrr, Mrl with their central axis of rotation directed in the front-rear direction of the vehicle Ve, and drive gears 3rr, 3rl are attached to the rotor shafts thereof, which mesh with counter driven gears 4rr, 4rl. The counter driven gears 4rr, 4rl have a larger diameter than the drive gears 3rr, 3rl, and therefore these gear pairs constitute a reduction mechanism.

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

[0015] FIG. 3 shows an example of the front drive unit Pf in a skeleton diagram. Since the drive unit Pf has a left-right symmetrical configuration, it will be described together without specifying "right" and "left". The motors Mfr, Mfl are mounted with their rotational center axis facing the width direction (lateral direction) of the vehicle Ve, and drive gears 12fr, 12fl are attached to the rotor shafts, and the drive gears 12fr, 12fl mesh with the idle gears 13r, 13l. Countershafts 14r, 14l are provided parallel to the rotational center axis of the idle gears 13r, 13l, and the idle gears 13r, 13l mesh with the counter driven gears 15fr, 15fl attached to the countershafts 14r, 14l. The counter driven gears 15fr, 15fl have a larger diameter than the drive gears 12fr, 12fl attached to the motors Mfr, Mrl, and the gear pairs form a reduction mechanism.

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

[0017] Each of the above-mentioned motors Mrl, Mrr, Mfl, and Mfr is configured in the same manner as a motor provided as a driving force source for a conventional electric vehicle or hybrid vehicle. That is, in addition to the function as a motor that generates driving torque by receiving electric power from the battery device (Bat) 20 mounted on the vehicle Ve, it also has the function as a generator that converts motive power into electric power and charges the battery device 20 by rotating the output shaft (rotor shaft). Specifically, it can be configured by a synchronous motor with a permanent magnet in the rotor.

[0018] The motors Mrl, Mrr, Mfl, Mfr thus configured generate drive torque by converting the DC voltage of the power storage device 20 into an AC voltage and applying it to the coils (phases) provided in the stators, and the voltage applied to the coils (phases) increases or decreases according to the rotation angle of the rotor. Power control units PCf, PCr mainly composed of inverters for converting the DC voltage of the power storage device 20 into an AC voltage and applying it to the coils, and for converting the AC voltage generated by the motors Mrl, Mrr, Mfl, Mfr being rotated into a DC voltage and charging the power storage device 20, 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] Each of the above-mentioned drive shafts 6rr, 6rl, 17fr, and 17fl is provided with a parking lock mechanism (not shown) for locking the drive shafts 6rr, 6rl, 17fr, and 17fl, and each of the drive wheels 1r, 1l, 2r, and 2l is provided with a brake mechanism (not shown) for applying a braking torque to the drive wheels 1r, 1l, 2r, and 2l.

[0020] The vehicle is equipped with an electronic control unit (hereinafter, referred to as ECU) 31 for controlling the motors Mrl, Mrr, Mfl, Mfr (i.e., power control units PCf, PCr). Like ECUs mounted on conventional vehicles, this ECU 31 is mainly composed of a microcomputer and is configured to obtain output signals for controlling the motors Mrl, Mrr, Mfl, Mfr based on input signals and pre-stored maps and arithmetic expressions.

[0021] Specifically, the required drive torque is determined based on the accelerator operation amount, the vehicle speed, and a drive force map stored in advance in the ECU 31. This required drive torque is the total value of the drive torque transmitted to each drive wheel 1r, 1l, 2r, 2l, and the drive torque required for each motor is determined based on a front / rear distribution ratio determined according to the magnitude of the required drive torque. An example of the drive force map is shown in Fig. 4, which is configured so that the higher the vehicle speed, the smaller the required drive torque that is set, and the larger the accelerator operation amount, the larger the required drive torque that is set.

[0022] The vehicle Ve configured in this way can be kept stopped on an uphill road by the driver operating only the accelerator without braking. Specifically, the vehicle Ve will keep stopped when the load acting in a direction to move the vehicle Ve backwards according to the gradient angle of the road is balanced with the accelerator operation amount by the driver and the required driving torque (required driving force) determined based on the driving force map.

[0023] On the other hand, in the above-mentioned motors Mrl, Mrr, Mfl, and Mfr, the current flowing through the coils (phases) constituting the motor increases and decreases like a sine wave according to the rotation angle (or electrical angle) of the motor. For example, at a certain rotation angle, the same current flows through the U-phase coil and the V-phase coil, and at other rotation angles, the current value flowing through the U-phase coil increases and the current value flowing through the V-phase coil decreases.

[0024] Therefore, when the vehicle Ve is maintained in a stopped state by generating drive torque from each of the motors Mrl, Mrr, Mfl, Mfr as described above, a single-phase lock may occur in any of the motors, in which a large current continues to flow through a specific coil (phase) constituting the motor. Therefore, the driving force control device of the present invention is configured to reduce the current flowing through the motor in which the single-phase lock has occurred and the motor paired with that motor when the single-phase lock occurs.

[0025] Fig. 5 is a block diagram for explaining the function of ECU 31 (corresponding to the controller in the present invention) configured to reduce the current flowing to the pair of motors when a single-phase lock occurs. ECU 31 shown in Fig. 5 receives signals from a vehicle speed sensor that detects the vehicle speed, an accelerator opening sensor that detects the accelerator operation amount, a shift sensor that detects the shift position, a brake sensor that detects the 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 of the motors Mrl, Mrr, Mfl, Mfr or each of the power control units PCf, PCr, a resolver that detects the rotation angle of each of the motors Mrl, Mrr, Mfl, Mfr, etc.

[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 a signal input from the gradient angle sensor. The single-phase lock determination unit 33 determines that a single-phase lock has occurred when the temperature of a specific phase of the coil wound around the stator, or the temperature of an inverter for controlling the power supplied to the specific phase, is equal to or higher than a predetermined temperature. This phenomenon occurs, for example, when the vehicle is stopped on an uphill road while the accelerator is operated to generate driving torque and current is continuously supplied to one of the phases according to the rotation angle of the motor.

[0027] The single-phase lock avoidance control unit 34 is configured to execute control to reduce the current of the motor in which the single-phase lock has occurred and the motor paired with the motor. For example, when the single-phase lock has occurred in the motor Mrr, the current of the motor Mrr and the motor Mrl is reduced, and the drive torque of the other pair of motors Mfr and Mfl required to maintain the vehicle Ve in a stopped state is calculated, and a command signal is output to each of the motors Mrl, Mrr, Mfl, and Mfr. Alternatively, when the single-phase lock has occurred in the motor Mrr, the current of the motor Mrr and the motor Mrl is reduced, and a command signal for locking each of the drive shafts 6rr and 6rl in order to maintain the vehicle Ve in a stopped state is output to the parking lock mechanism, or a braking torque required to maintain the vehicle Ve in a stopped state is calculated, and the command signal is output to each of the brake mechanisms.

[0028] Fig. 6 shows a flowchart for explaining an example of control executed by the ECU 31. In the control example shown in Fig. 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 it is possible to determine whether or not the vehicle is stopped based on a signal input from a vehicle speed sensor to the ECU 31.

[0029] If the road is flat or a downhill road, or the vehicle is traveling and the result of the negative determination in step S1 is negative, the routine is terminated. On the other hand, if the vehicle is stopped on an uphill road and the result of the positive determination in step S1 is positive, it is determined whether or not a single-phase lock has occurred (step S2). This step S2 is executed 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 of the coils (phases) constituting each motor, is equal to or higher than a predetermined temperature. This step S2 may 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 energization time, etc. The predetermined temperature is set to a temperature lower than the single-phase lock temperature, which is determined in consideration of the durability of the motor and the inverter.

[0030] If the result of step S2 is negative because the single-phase lock has not occurred, the routine is terminated. On the other hand, if the result of step S2 is positive because the single-phase lock has occurred, single-phase lock avoidance control is executed. Specifically, the drive torque of the motor in which the single-phase lock has occurred and the other motor paired with the motor on the left and right are reduced (step S3), the drive shafts to which the motors are connected are fixed (step S4), and the routine is terminated. In this case, it is preferable that the reduction amounts of the drive torque of the pair of motors are the same. Note that when step S4 is executed, the drive shaft is fixed even though the driver is not braking, and the driver may be notified of this fact.

[0031] To explain this with a specific example, when a single-phase lock occurs in the motor Mrr, in step S3, the drive torque of the motor Mrr and the motor Mrl paired with the motor Mrr on the left and right are reduced. Then, the drive shafts 6rr and 6rl are locked by applying a braking torque to them using a parking mechanism or a brake mechanism. The parking mechanism or the brake mechanism corresponds to the "stop 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 value 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, so that each motor outputs a drive torque according to the accelerator operation amount. Therefore, the brake signal is kept off and the coil current value is kept relatively high.

[0033] By continuously supplying power to the motor from time t0, the inverter temperature gradually increases. As a result, when the inverter temperature increases to a predetermined temperature at time t1, the above step S2 is judged as positive, so that the drive torque of the motor is reduced and the drive shaft is fixed. That is, at time t1, the brake signal is switched on and the current value of the coil is reduced. Therefore, the inverter temperature gradually decreases from time t1.

[0034] As described above, by reducing the drive torque of the motor in which the single-phase lock has occurred and fixing the drive shaft by the parking lock mechanism and the brake mechanism that maintain the vehicle Ve in a stopped state, it is possible to prevent the electric vehicle from moving unintentionally while suppressing a decrease in durability due to an excessive increase in temperature of the motor (including the coil and the inverter). In addition, since the drive torque of the other motor that is paired with the motor in which the single-phase lock has occurred is reduced in the same manner as the motor in which the single-phase lock has occurred, the vehicle Ve can be smoothly started by releasing the lock by the parking lock mechanism and the brake mechanism and increasing the drive torque of the pair of motors simultaneously and to the same extent when starting. In other words, it is possible to suppress differences in the timing of increasing the drive torque of the pair of motors and the increase amounts from being mutually exclusive, and it is possible to simplify the control while maintaining the stability of the behavior of the vehicle Ve when starting.

[0035] The stop maintaining device in the embodiment of the present invention is not limited to one that applies a braking torque like the parking lock mechanism or brake mechanism described above, but may be configured to output a drive torque from a pair of motors on the opposite side in the front-to-rear direction of the vehicle to the pair of motors including the motor in which single-phase lock has occurred to maintain the vehicle stopped. In other words, when a single-phase lock has occurred in one of the front motors, the pair of motors on the rear side corresponds to the stop maintaining device, and when a single-phase lock has occurred in one 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 having only a motor as a driving force source, but may be a hybrid vehicle having an engine and a motor as driving force sources. Specifically, the electric vehicle may be a vehicle in which an engine is connected to one of the front and rear drive wheels, and a motor is connected to the other of the front and rear drive wheels. [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 section 33 Single-phase lock determination unit 34 Single-phase lock avoidance control unit Mrl, Mrr, Mfl, Mfr motors PCf, PCr Power control unit Ve Electric Vehicle

Claims

[Claim 1] A driving force control device for an electric vehicle including a first motor for driving a left drive wheel and a second motor for driving a right drive wheel, the first motor and the second motor being independently controllable, a stop maintaining device capable of generating a driving torque or a braking torque for maintaining a stopped state of the electric vehicle; a controller that controls the first motor and the second motor, The controller: a single-phase lock determination unit that determines, when the electric vehicle is stopped by outputting drive torque from the first motor and the second motor, that one of the first motor and the second motor has risen in temperature to or above a predetermined temperature; a single-phase lock-up avoidance control unit that, when it is determined by the single-phase lock-up determination unit that the temperature of one of the motors has risen to or above a predetermined temperature, causes the stop maintaining device to generate the driving torque or the braking torque and reduces the driving torque of the first motor and the second motor. A driving force control device for an electric vehicle.

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