Vehicle control method and vehicle control device

Abstract

To suppress vehicle behavior unintended by a driver when starting a vehicle.SOLUTION: An electric vehicle comprises a front motor for driving front wheels and a rear motor for driving rear wheels. In a vehicle control method, a controller sets target first torque for the front motor and target second torque for the rear motor according to required torque and controls first torque, which is the torque of the front motor, and second torque, which is the torque of the rear motor, based on the target first torque and the target second torque. The controller prohibits setting the target first torque to negative torque, which is the torque in a direction opposite to a vehicle traveling direction when starting a vehicle. After detecting that the vehicle has started to move, the controller sets the target first torque to the negative torque and sets the target second torque such that, when combined with the target first torque, the same becomes the required torque, and then controls the first torque and the second torque based on the target first torque and the target second torque.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a vehicle control method and a vehicle control device.

Background Art

[0002] From the viewpoints of the ground contact performance of wheels and the comfort of passengers, it is desirable that the change in the behavior of the vehicle be small. In Patent Document 1, as a method for controlling the attitude of an electric vehicle in which the front wheels and the rear wheels are driven by different motors, by controlling the driving force distribution ratio between the front wheels and the rear wheels, the bouncing and pitching caused by the load change on the spring of the suspension device are suppressed. Specifically, the driving force distribution ratio is determined based on the instantaneous rotation center angle in the side view of the front wheel suspension means, the instantaneous rotation center angle in the side view of the front wheel suspension means, the height of the center of gravity of the vehicle, and the wheelbase between the front and rear wheels.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In a vehicle in which the driving force distribution between the front and rear wheels can be changed as described in the above document, when a driving force in the direction opposite to the traveling direction (hereinafter also referred to as the negative direction) is distributed to the front wheels and a driving force in the same direction as the traveling direction (hereinafter also referred to as the positive direction) is distributed to the rear wheels, it is known that pitching can be suppressed.

[0005] However, if the driving force is distributed as described above, there may be the following problems. For example, when starting (moving forward) from a stopped state where the front wheels are in contact with a dry road surface and the rear wheels are in contact with a frozen road surface, if the above driving force distribution is adopted, the rear wheels may slip, resulting in no traction for forward movement, and there is a risk of the vehicle moving backward due to the driving force of the front wheels. That is, although the driver intends to move forward, the vehicle may move backward.

[0006] Therefore, an object of the present invention is to suppress the behavior unintended by the driver as described above when starting.

Means for Solving the Problems

[0007] According to an aspect of the present invention, in an electric vehicle having a front motor that drives the front wheels and a rear motor that drives the rear wheels, a controller sets a target first torque for the front motor and a target second torque for the rear motor according to the required torque, and controls a first torque that is the torque of the front motor and a second torque that is the torque of the rear motor based on the target first torque and the target second torque. In this method, when the vehicle starts, the controller prohibits setting a negative torque, which is a torque in the direction opposite to the vehicle traveling direction, as the target first torque, and when it is detected that the vehicle has started moving, sets a target first torque that is a negative torque and a target second torque that, when combined with the target first torque, becomes the required torque, and controls the first torque and the second torque based on the target first torque and the target second torque.

Effects of the Invention

[0008] According to the above aspect, it is possible to suppress the behavior unintended by the driver when starting.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Embodiments for Carrying Out the Invention

[0010] Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[0011] [Configuration of the System] FIG. 1 is an explanatory diagram showing a schematic configuration of the electric vehicle 100. As shown in FIG. 1, the electric vehicle 100 is a four-wheel drive vehicle that drives the front wheels 22 by the front motor 21 and drives the rear wheels 32 by the rear motor 31.

[0012] The electric vehicle 100 includes a front drive system 11, a rear drive system 12, a battery 13, and a controller 14.

[0013] The front drive system 11 is a system that drives the front wheels 22 by the front motor 21. In addition to the front motor 21 and the front wheels 22, the front drive system 11 includes a front inverter 23, a rotation sensor 24, a current sensor 25, and the like.

[0014] The front motor 21 is, for example, a three-phase AC synchronous motor and is driven by AC power input from the front inverter 23. The output torque of the front motor 21 generates a driving force on the front wheels 22. Further, when the front motor 21 is rotated by being dragged by the front wheels 22, it generates a so-called regenerative torque. Thereby, the front motor 21 can recover the kinetic energy of the electric vehicle 100 as electrical energy.

[0015] The front wheels 22 are a pair of drive wheels arranged in front of the electric vehicle 100. The front wheels 22 are connected to the front motor 21 via the front gear box 26 and the drive shaft 27. In the present embodiment, the front wheels 22 consist of a right front wheel and a left front wheel. However, since the right front wheel and the left front wheel are connected by the drive shaft 27 and are driven integrally, in the present embodiment, the right front wheel and the left front wheel are not distinguished, and they are collectively referred to as the front wheels 22.

[0016] The rotation sensor 24 detects the rotor phase α f of the front motor 21. The rotor phase α f is a so-called electrical angle [rad]. The rotation sensor 24 is, for example, a resolver or an encoder. The detected rotor phase α f is input to the controller 14.

[0017] The current sensor 25 detects the current flowing through each phase of the front motor 21 (hereinafter referred to as the three-phase current) i uf , i vf , i wf . The three-phase current i uf , i vf , i wf of the front motor 21 is input to the controller 14.

[0018] The rear drive system 12 is a system that drives the rear wheels 32 by the rear motor 31, and is configured symmetrically with the front drive system 11. Therefore, in addition to the rear motor 31 and the rear wheels 32, the rear drive system 12 includes a rear inverter 33, a rotation sensor 34, a current sensor 35, a rear gear box 36, a drive shaft 37, etc. Each of these parts constituting the rear drive system 12 functions in the same manner as each part of the front drive system 11. That is, the rear wheels 32 are a pair of drive wheels arranged behind the electric vehicle 100. The rear wheels 32 consist of a right rear wheel and a left rear wheel, but in the present embodiment, these are not distinguished, and the right rear wheel and the left rear wheel are collectively referred to as the rear wheels 32. The rear wheels 32 are the second drive wheels in contrast to the front wheels 22 which are another pair of drive wheels. The rotor phase of the rear drive system 12 detected by the rotation sensor 34 is "α r". The currents flowing through each phase of the rear motor 31 detected by the current sensor 35 are "i ur , i vr , i wr ".

[0019] The battery 13 is provided in common to the front drive system 11 and the rear drive system 12, and supplies electric power for driving the front motor 21 and the rear motor 31. Further, during regenerative control, the battery 13 is charged by the regenerative power generated by the front motor 21 and the rear motor 31.

[0020] The controller 14 is a control device for the electric vehicle 100. The controller 14 is composed of one or more computers including, for example, a central processing unit (CPU), a read-only memory (ROM), a random access memory (RAM), and an input / output interface (I / O interface). Further, the controller 14 is programmed to control the front motor 21, the rear motor 31, etc. at a predetermined control cycle. For example, the controller 14 acquires various vehicle variables, and based on these vehicle variables, generates PWM signals for driving the front motor 21 and the rear motor 31, respectively. Then, the controller 14 drives the front motor 21 and the rear motor 31 according to the vehicle variables by inputting the generated PWM signals to the front inverter 23 and the rear inverter 33, respectively.

[0021] The vehicle variables are parameters representing the control state etc. of the electric vehicle 100. The controller 14 acquires, as vehicle variables, for example, the accelerator opening APO, the DC voltage V of the battery 13 dc , the rotational speed ω of the front motor 21 f (angular velocity), the rotational speed ω of the rear motor 31 r (angular velocity), and the pitch rate detection value λ det ′ etc. as vehicle variables. The accelerator opening APO is a parameter representing the operation amount of the accelerator pedal by the driver. The pitch rate detection value λ detλ' is the detected value of the pitch rate λ'. The pitch rate λ' is the time change rate of the pitch angle λ. Vehicle variables can be appropriately detected as needed using, for example, sensors (not shown). Also, vehicle variables can be obtained by calculation.

[0022] [Motor Control] FIG. 2 is a diagram showing the configuration of the controller 14 related to the control according to the present embodiment.

[0023] The controller 14 calculates a required torque based on vehicle variables (for example, the accelerator opening APO), and sets a target first torque, which is the target torque of the front motor 21, and a target second torque, which is the target torque of the rear motor 31, according to the required torque. Note that the controller 14 can calculate based on commands from an ADAS (Advanced Drive Assistance System) or an AD (Autonomous Driving) system, etc., instead of calculating the required torque based on the accelerator opening APO.

[0024] Then, the first torque, which is the torque of the front motor 21, and the second torque, which is the torque of the rear motor 31, are controlled based on the target first torque and the target second torque. For this control, the controller 14 includes a starting torque setting unit 14A, a movement determination unit 14B, a running torque setting unit 14C, and a torque control unit 14D.

[0025] The starting torque setting unit 14A sets the target first torque and the target second torque at the time of vehicle start based on vehicle variables. The movement determination unit 14B determines whether or not the electric vehicle 100 is moving based on the movement of the wheels. The movement of the wheels is detected by a wheel speed sensor (not shown). The running torque setting unit 14C sets the target first torque and the target second torque after the vehicle starts moving at the start. The torque control unit 14D controls the torque of the front motor 21 (hereinafter also referred to as the first torque) and the torque of the rear motor 12 (hereinafter also referred to as the second torque) based on the target first torque and the target second torque.

[0026] As described above, the electric vehicle 100 can perform four-wheel drive running using the front motor 21 and the rear motor 31, and can control the drive force distribution between the drive force of the front wheels 22 (i.e., the first torque) and the drive force of the rear wheels 32 (i.e., the second torque). Then, by utilizing this feature, control can be performed to suppress the pitching of the electric vehicle 100.

[0027] When suppressing pitching, the second torque may be made larger than the first torque. In particular, by setting the first torque as a negative torque and the second torque as a positive torque obtained by adding the torque corresponding to the first torque to the required torque, it is known that the effect of suppressing pitching becomes greater. In the following description, the control for distributing the drive force so that the front motor 21 generates a negative torque and the rear motor 31 generates a positive torque is also referred to as reverse-phase control.

[0028] If reverse-phase control is executed at the time of vehicle start, the comfort of the occupants and the ground contact performance can be improved. However, this is premised on the fact that neither the front wheels 22 nor the rear wheels 32 are slipping. When attempting to start moving forward, if only the front wheels 22 grip and the rear wheels 32 slip, the electric vehicle 100 will move backward contrary to the driver's intention due to the first torque which is a negative torque.

[0029] In order to suppress such behavior contrary to the driver's intention, the start control described below is executed in this embodiment.

[0030] FIG. 3 is a diagram for explaining the outline of the start control.

[0031] When the accelerator pedal is depressed at the timing 0 during parking, the target first torque and the target second torque for starting are set. At this time, the controller 14 prohibits reverse-phase control. That is, setting a negative torque as the target first torque is prohibited. In this embodiment, zero is set as the target first torque. At the timing T1 when the delay time required for calculation and the like has elapsed from the timing 0, the rear motor 31 starts rotating. At this time, since the target first torque is zero, the front motor 21 does not generate torque.

[0032] When the rear motor 31 starts to rotate, the play between the gears of the rear gearbox 36 interposed between the rear motor 31 and the rear wheels 32 begins to decrease. Then, at the timing T2 when the play of the rear gearbox 36 is jammed, the rear tire 32 starts to rotate and the electric vehicle 100 starts to move. At this time, of course, the front wheels 22 also start to rotate.

[0033] When the front wheels 22 start to rotate, the play between the gears of the front gearbox 26 interposed between the front wheels 22 and the front motor 21 begins to decrease. Then, at the timing T3 when the play of the front gearbox 26 is jammed, the front motor 21 starts to rotate.

[0034] Then, when it is detected that the front motor 21 is rotating at the timing T4, the prohibition of reverse-phase control is released. After the timing T4, reverse-phase control is started, the first torque of the front motor 21 is controlled toward the target first torque which is a negative torque, and the second torque of the rear motor 31 is controlled toward the target second torque. The target second torque at this time is set to a magnitude that becomes the required torque when combined with the target first torque. For example, if the target first torque is a negative torque of the magnitude of A[%] of the required torque, the target second torque becomes a positive torque of 100 + A[%.

[0035] By controlling as described above, even if the rear wheels 32 slip during starting, the electric vehicle 100 will not reverse. And by starting reverse-phase control after the electric vehicle 100 starts to move (after the timing T4 in FIG. 3), pitching can be suppressed.

[0036] FIG. 4 is an example of a flowchart showing the control routine of the above control. The control routine is executed during parking.

[0037] In step S100, the controller 14 determines whether the accelerator pedal is in the ON state. If it is ON, the process of step S110 is executed. If it is not ON, the determination is repeated.

[0038] In step S110, the controller 14 issues torque instructions to the front motor 21 and the rear motor 31 with a driving force distribution of 0[%] for the front wheels and 100[%] for the rear wheels.

[0039] In step S120, the controller 14 determines whether the rear motor 31 is rotating. If it is rotating, the process of step S130 is executed. If it is not rotating, the process of step S170 is executed. Note that this determination in this step is made after the delay time from when the torque instruction is issued until the motor starts to move has elapsed.

[0040] In step S130, the controller 14 determines whether the rotation of the front wheel 22 has been detected before a period 1 described later elapses. If it has been detected, the process of step S140 is executed. If the period 1 has elapsed without detection, the process of step S160 is executed. The period 1 is, for example, a period assumed to be required from when the rear motor 31 starts rotating until the rear wheel 32 and the front wheel 22 start rotating. Specifically, it is determined according to the second target torque for starting and the backlash of the gears of the rear gearbox 36. In FIG. 3, the rotation of the front wheel 22 is detected at the timing T2 when the play of the rear gearbox 36 jams, but a period longer than the period between the timings T1 and T2 may be set as the period 1.

[0041] In step S140, the controller 14 determines whether it has detected the rotation of the front motor 21 before the elapse of period 2, which will be described later. If it has detected the rotation, the process of step S150 is executed. If period 2 has elapsed without detecting the rotation, the process of step S160 is executed. Period 2 is a period that is assumed to be required, for example, from the start of rotation of the front wheels 22 until the play of the front gearbox 26 is taken up. Specifically, it is determined according to the second target torque for starting, the backlash of the gears of the front gearbox 26, and the like. In FIG. 3, although the rotation of the front motor 22 is detected at timing T4 after the front motor 22 starts rotating and before period 2 elapses, a period longer than the period between timings T2 to T4 may be set as period 2.

[0042] In step S150, the controller 14 permits reverse-phase control and starts controlling the front motor 21 with the target first torque as a negative torque. Then, the second target torque is increased by the amount of the negative torque distributed to the front motor 21. Details of the reverse-phase control will be described later.

[0043] In step S160, the controller 14 maintains the prohibition of reverse-phase control. If the rotation of the front wheels 22 is not detected before period 1 elapses in step S130, it means that the front wheels 22 are not rotating while the rear wheels 32 are rotating. That is, the rear wheels 32 are slipping and the electric vehicle 100 is not moving. If reverse-phase control is performed in this situation, the electric vehicle 100 will reverse due to the negative torque distributed to the front motor 21, so reverse-phase control is prohibited. Also, in a situation where the rotation of the front motor 21 is not detected in step S140, it can be estimated that the play of the front gearbox 26 has not been taken up. If reverse-phase control is started in this situation, there is a possibility that a meshing sound or vibration due to a collision between the gears in the front gearbox 26 will occur, so the prohibition of reverse-phase control is maintained. Further, if the rotation of the front motor 21 cannot be detected even after period 2 has elapsed, it is considered that there is some problem in the front drive mechanism 11. Therefore, in this case as well, the prohibition of reverse-phase control is maintained, and a fail-safe control routine different from this routine is executed.

[0044] In step S170, the controller 14 determines that the rear motor 31 has failed and ends this routine. If it is determined in step S170 that there is a failure, a fail-safe control routine different from this routine is executed.

[0045] Next, the reverse-phase control will be described with reference to FIGS. 5 and 6.

[0046] FIG. 5 is an example of a time chart when the above-described starting control is executed. The solid line in FIG. 5 indicates the starting control according to this embodiment, and the dashed line indicates the case where reverse-phase control is performed from the start of starting (hereinafter also referred to as a comparative example). Note that timings 0 to T4 in FIG. 5 correspond to timings 0 to T4 in FIG. 3. FIG. 6 is a diagram showing the relationship between the change rate of the first torque and the vehicle speed in the reverse-phase control.

[0047] In the control according to the comparative example, since the reverse-phase control is started at timing T1, for example, when the front wheels 22 do not rotate even after timing T2, that is, when the rear wheels 32 are slipping, the electric vehicle 100 will reverse.

[0048] On the other hand, in the starting control according to this embodiment, when the accelerator pedal is depressed at timing 0, the torque (second torque) of the rear motor 31 starts to increase from timing T1 after the elapse of the delay time. The play of the rear gearbox 26 occurs, that is, acceleration occurs from timing T2 when the front wheels 22 and the rear wheels 32 start to rotate. Then, the reverse-phase control is started from timing T4 when the rotation of the front motor 22 is detected. Thereby, even when the rear wheels 32 are slipping, the electric vehicle 100 does not reverse.

[0049] In the control according to this embodiment, after the start of reverse-phase control, the torque (first torque) of the front motor 22 increases in the negative direction, and the torque (second torque) of the rear motor 32 increases in the positive direction by the amount by which the first torque increases in the negative direction. The change rate of the first torque at this time is set to a magnitude such that even if the rear wheel 32 slips, the first torque at the timing of slipping is smaller than the inertial force of the electric vehicle 100 at the same timing. Thereby, even if the rear wheel 32 slips after the start of reverse-phase control, since the inertial force of the electric vehicle 100 is larger than the absolute value of the first torque, it is possible to prevent the electric vehicle 100 from retreating due to the first torque.

[0050] The controller 14 changes the change rate of the first torque according to the vehicle speed. This is because among the main parameters related to the magnitude of the inertial force of the electric vehicle 100, the vehicle weight is a fixed value according to the specifications of the electric vehicle 100, and what varies is the vehicle speed. Specifically, as shown in FIG. 6, the higher the vehicle speed, the faster the change rate. This is because the higher the vehicle speed, the greater the inertial force of the electric vehicle 100, and the greater the negative torque required to reduce the vehicle speed to zero or less.

[0051] As described above, in the present embodiment, in the electric vehicle 100 having the front motor 21 that drives the front wheels 22 and the rear motor 31 that drives the rear wheels 32, the controller 14 sets the target first torque for the front motor 21 and the target second torque for the rear motor 32 according to the required torque, and controls the first torque that is the torque of the front motor 21 and the second torque that is the torque of the rear motor 31 based on the target first torque and the target second torque. A vehicle control method is provided. In this method, the controller 14 prohibits setting a negative torque, which is a torque in the direction opposite to the vehicle traveling direction, as the target first torque when the vehicle starts, and when it is detected that the electric vehicle 100 has moved, sets the target first torque that is a negative torque and the target second torque that becomes the required torque by synthesizing with the target first torque, and controls the first torque and the second torque based on the target first torque and the target second torque. Thereby, even when the rear wheels 32 slip and only the front wheels 22 grip at the time of starting, the electric vehicle 100 does not start in a direction contrary to the driver's intention.

[0052] In the present embodiment, the controller 14 changes the first torque after the vehicle starts at a change rate such that the first torque at the timing when the rear wheels 32 slip is smaller than the inertial force of the electric vehicle 100 at the same timing even if the rear wheels 32 slip. Thereby, even if the rear wheels 32 slip after starting, it is possible to prevent the electric vehicle 100 from suddenly stopping or running in the opposite direction.

[0053] In the present embodiment, the controller 14 makes the change rate of the first torque faster as the vehicle speed is higher. Thereby, while preventing sudden stops and the like when the rear wheels 32 slip, it is possible to suppress the delay in acceleration.

[0054] Although the embodiments of the present invention have been described above, the above embodiments merely show a part of the application examples of the present invention, and are not intended to limit the technical scope of the present invention to the specific configurations of the above embodiments.

Description of Reference Numerals

[0055] 11: Front drive system, 12: Rear drive system, 13: Battery, 14: Controller, 21: Front motor, 22: Front wheel, 23: Front inverter, 24: Rotation sensor, 25: Current sensor, 26: Front gearbox, 27: Drive shaft, 31: Rear motor, 32: Rear wheel, 33: Rear inverter, 34: Rotation sensor, 35: Current sensor, 36: Rear gearbox, 37: Drive shaft, 100: Electric vehicle

Claims

1. In an electric vehicle having a front motor that drives the front wheels and a rear motor that drives the rear wheels, a controller sets a target first torque for the front motor and a target second torque for the rear motor according to a required torque, and controls a first torque that is the torque of the front motor and a second torque that is the torque of the rear motor based on the target first torque and the target second torque. In the vehicle control method, the controller, prohibits setting, as the target first torque, a negative torque that is a torque in a direction opposite to the vehicle traveling direction when the vehicle starts, when detecting that the vehicle has moved, sets the target first torque that is the negative torque and the target second torque that, when combined with the target first torque, becomes the required torque, A vehicle control method for controlling the first torque and the second torque based on the target first torque and the target second torque.

2. In the vehicle control method according to Claim 1, the controller, changes the first torque after the vehicle starts at a rate of change such that the first torque at the timing when the rear wheels slip is smaller than the inertial force of the vehicle at the same timing even if the rear wheels slip. A vehicle control method.

3. In the vehicle control method according to Claim 2, the controller, makes the rate of change of the first torque faster as the vehicle speed is higher. A vehicle control method.

4. In an electric vehicle having a front motor that drives the front wheels and a rear motor that drives the rear wheels, a controller sets a target first torque for the front motor and a target second torque for the rear motor according to a required torque, and controls a first torque that is the torque of the front motor and a second torque that is the torque of the rear motor based on the target first torque and the target second torque. In the vehicle control device, a starting torque setting unit that prohibits setting, as the target first torque at vehicle start, a negative torque that is a torque in a direction opposite to the vehicle traveling direction; a movement determination unit that determines whether the vehicle has moved; a traveling torque setting unit that, when determining that the vehicle has moved, sets the target first torque that is the negative torque and the target second torque that, when combined with the target first torque, becomes the required torque. A vehicle control device including: a torque control unit configured to control the first torque and the second torque based on the target first torque and the target second torque.

Images