Vehicle control device and vehicle control method

Abstract

A vehicle control device and a vehicle control method according to one embodiment of the present invention are provided with: a first slip control mode for controlling a regenerative braking device so as to generate a regenerative braking force that reduces a difference in wheel speed with respect to a first target wheel speed; and a second slip control mode for controlling a friction braking device so as to generate a friction braking force that reduces a difference in wheel speed with respect to a second target wheel speed that is higher than the first target wheel speed. This makes it possible to perform slip convergence control while suppressing a decrease in the amount of regenerative energy associated with slip control.

Description

Vehicle control device and vehicle control method

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

[0002] In the vehicle control method of Patent Document 1, when a slip state is detected in which the wheel speed of a regenerative braking wheel performing regenerative braking is lower than a slip determination threshold value located between the vehicle body speed of the vehicle and the operating threshold value of anti-lock brake control, a regenerative braking force that reduces the deviation of the wheel speed of the regenerative braking wheel with respect to the slip determination threshold value is generated. A regenerative control process for controlling the regenerative braking device is executed. Then, during the execution of the regenerative control process, in order to satisfy the required vehicle braking force, a frictional braking force of a non-regenerative braking wheel is generated. When the required vehicle braking force increases during braking while the regenerative control process is being performed, after the frictional braking force of the non-regenerative braking wheel reaches a threshold value, the regenerative braking force is switched to the frictional braking force of the regenerative braking wheel.

[0003] Japanese Patent Application Laid-Open No. 2023-108761

[0004] By the way, when the vehicle decelerates using both frictional braking force and regenerative braking force, if the regenerative braking force is preferentially reduced as the slip of the driving wheel occurs, the amount of regenerative energy in the slip occurrence state decreases. Therefore, there has been concern about a reduction in electricity costs when the vehicle travels in an environment where slips are likely to occur, such as in cold regions or on rough roads.

[0005] Therefore, an object of the present invention is to provide a vehicle control device and a vehicle control method that can suppress a decrease in the amount of regenerative energy associated with slip control and converge the slip.

[0006] Therefore, according to the vehicle control device according to the present invention, in one aspect, a first slip control mode for controlling the regenerative braking device so as to generate a regenerative braking force that reduces the difference between the wheel speed and the first target wheel speed set as a wheel speed that is lower than the vehicle body speed of the vehicle by a predetermined first speed, and a second slip control mode for controlling the friction braking device so as to generate a friction braking force that reduces the difference between the wheel speed and the second target wheel speed set as a wheel speed that is lower than the vehicle body speed of the vehicle by a predetermined second speed smaller than the first speed.

[0007] Furthermore, according to the vehicle control method of the present invention, in one embodiment, when a vehicle slips, the vehicle is controlled using both a method of controlling the regenerative braking device to converge to a first target wheel speed of the vehicle, and a method of controlling the friction braking device to converge to a second target wheel speed set higher than the first target wheel speed.

[0008] According to the present invention, it is possible to converge slip while suppressing the decrease in regenerative energy associated with slip control.

[0009] This is an overall configuration diagram showing one aspect of a vehicle control system. This is an architecture diagram showing the coordinated operation of slip control based on target wheel speed. This is a time chart showing the change in braking force in slip control. This is a time chart showing the change in braking force when the target wheel speed is increased or decreased. This is a block diagram showing the target wheel speed setting process and slip control. This is an architecture diagram showing the coordinated operation of slip control based on target slip ratio. This is a time chart showing the switching of the target slip ratio. This is a block diagram showing the subtraction process function for the regenerative braking force request value (threshold) after distribution. This is a time chart showing how the regenerative braking force request value (threshold) after distribution gradually decreases.

[0010] Hereinafter, embodiments of the vehicle control device and vehicle control method according to the present invention will be described with reference to the drawings. Figure 1 is an overall configuration diagram showing one aspect of a vehicle control system. Vehicle 1 is a four-wheeled vehicle equipped with a pair of left and right front wheels 1FL, 1FR and a pair of left and right rear wheels 1RL, 1RR.

[0011] Furthermore, Vehicle 1 is a four-wheel drive electric vehicle having a front motor 10 that provides driving torque to the front wheels 1FL and 1FR, and a rear motor 20 that provides driving torque to the rear wheels 1RL and 1RR. Vehicle 1 may also be a front-wheel drive vehicle equipped only with the front motor 10, or a rear-wheel drive vehicle equipped only with the rear motor 20.

[0012] Power is transmitted between the front motor 10 and the front wheels 1FL and 1FR via a reduction gear 11, a differential gear 12, and the front axles 13FL and 13FR. Power is also transmitted between the rear motor 20 and the rear wheels 1RL and 1RR via a reduction gear 21, a clutch 22, a differential gear 23, and the axles 24RL and 24RR.

[0013] When the clutch 22 is engaged, power is transmitted between the rear motor 20 and the rear wheels 1RL and 1RR. On the other hand, when the clutch 22 is disengaged, no power is transmitted between the rear motor 20 and the rear wheels 1RL and 1RR.

[0014] Each of the four wheels 1FL, 1FR, 1RL, and 1RR has a wheel speed sensor 2FL, 2FR, 2RL, and 2RR, respectively, for detecting the wheel speed. The front motor 10 also has a front wheel resolver 14 for detecting the rotational speed of the front motor 10, and the rear motor 20 has a rear wheel resolver 25 for detecting the rotational speed of the rear motor 20.

[0015] Vehicle 1 has a low-voltage battery 31 and a high-voltage battery 32. The low-voltage battery 31 is, for example, a lead-acid battery. The high-voltage battery 32 is, for example, a lithium-ion battery or a nickel-metal hydride battery, and is charged by power boosted by a DC-DC converter 33.

[0016] Furthermore, vehicle 1 has friction braking devices 40FL, 40FR, 40RL, and 40RR provided on each wheel 1FL, 1FR, 1RL, and 1RR, which apply friction braking force to each wheel 1FL, 1FR, 1RL, and 1RR. The friction braking devices 40FL, 40FR, 40RL, and 40RR generate friction braking force by, for example, pressing brake pads against brake rotors using brake fluid pressure or an electric motor. The generation of friction braking force by each friction braking device 40FL, 40FR, 40RL, and 40RR is controlled by a brake controller 55.

[0017] Furthermore, vehicle 1 includes a drive force controller 51, a front motor controller 52, a rear motor controller 53, a battery controller 54, and a brake controller 55. The controllers 51, 52, 53, 54, and 55, which are control units, share information with each other via a bus 56 that constitutes an in-vehicle network such as a CAN (Controller Area Network).

[0018] The drive force controller 51 acquires information from various sensors, including an accelerator pedal sensor 61 that detects the amount of accelerator pedal operation by the driver, a transmission shift position sensor 62, a front wheel resolver 14, and a rear wheel resolver 25. The drive force controller 51 then calculates the required torque according to the amount of accelerator pedal operation by the driver, and further calculates the front required torque that the front motor 10 should output and the rear required torque that the rear motor 20 should output according to the required torque distribution. The required torque distribution is the required value of the torque distribution ratio between the front wheels 1FL, 1FR and the rear wheels 1RL, 1RR, and is set appropriately according to the driving conditions.

[0019] The front motor controller 52 controls the power supplied to the front motor 10 based on the front torque requirement. The rear motor controller 53 controls the power supplied to the rear motor 20 based on the rear torque requirement. The front motor controller 52 and the rear motor controller 53 control the power supplied to each motor 10 and 20 using an inverter.

[0020] The battery controller 54 monitors the charge and discharge state of the high-voltage battery 32, as well as the individual cell units that make up the high-voltage battery 32. Based on the charge and discharge state of the high-voltage battery 32, the battery controller 54 calculates an upper limit for the required torque. The upper limit for the required torque is the maximum torque allowed for the front motor 10 and the rear motor 20. When the charge level of the high-voltage battery 32 is low, the battery controller 54 changes the upper limit for the required torque to a value smaller than normal.

[0021] The brake controller 55 acquires information from various sensors, such as the brake pedal sensor 63 which detects the amount of brake pedal operation by the driver. The brake controller 55 then calculates the required braking force according to the amount of brake pedal operation by the driver and controls the friction braking force generated by the friction braking devices 40FL, 40FR, 40RL, and 40RR.

[0022] Furthermore, by rotating motors 10 and 20 with the rotational force of the wheels, it is possible to recover kinetic energy as electricity, and the rotational resistance of motors 10 and 20 at this time can be used as a braking force. In this application, the use of the rotational resistance of motors 10 and 20 as a braking force is called regenerative braking, and the braking force due to the rotational resistance of motors 10 and 20 is called regenerative braking force.

[0023] In the control system of vehicle 1 shown in Figure 1, coordinated braking force control (hereinafter referred to as regenerative coordinated braking) is performed to decelerate vehicle 1 by using in combination the friction braking force from the friction brakes 40FL, 40FR, 40RL, and 40RR and the regenerative braking force generated by the motors 10 and 20 (regenerative braking devices). In regenerative coordinated braking, the drive force controller 51 distributes the required braking force between the friction braking force and the regenerative braking force, sets the command values ​​for the friction braking force generated by the friction brakes 40FL, 40FR, 40RL, and 40RR, and the command values ​​for the regenerative braking force generated by the motors 10 and 20, so that the required braking force is satisfied by the friction braking force and the regenerative braking force, and outputs each braking force command to the motor controllers 52 and 53 and the brake controller 55. In other words, regenerative braking is controlled by a vehicle control system including a drive force controller 51, motor controllers 52 and 53, and a brake controller 55.

[0024] Furthermore, in regenerative cooperative braking, slip control is performed to adjust the braking force so as to reduce the difference between the target wheel speed and the actual wheel speed, or the difference between the target slip ratio and the actual slip ratio. This slip control has a regenerative slip control mode (first slip control mode) in which the control target is the regenerative braking force generated by motors 10 and 20, and a friction slip control mode (second slip control mode) in which the control target is the friction braking force generated by friction brake devices 40FL, 40FR, 40RL, and 40RR. Wheel slip is controlled by using these two slip control modes in combination.

[0025] In the regenerative slip control mode, motors 10 and 20 are controlled to generate a regenerative braking force that reduces the difference between the actual wheel speed and the first target wheel speed ωrtg. In the friction slip control mode, friction brakes 40FL, 40FR, 40RL, and 40RR are controlled to generate a friction braking force that reduces the difference between the actual wheel speed and the second target wheel speed ωftg.

[0026] In other words, the vehicle control device (control unit), including the drive force controller 51, motor controllers 52 and 53, and brake controller 55, controls wheel slippage using both a vehicle control method that controls the motors 10 and 20 to converge to a first target wheel speed ωrtg when the wheels of the vehicle 1 slip, and a vehicle control method that controls the friction brakes 40FL, 40FR, 40RL, and 40RR to converge to a second target wheel speed ωftg, which is set higher than the first target wheel speed ωrtg.

[0027] On the other hand, in the regenerative slip control mode based on the target slip ratio, motors 10 and 20 are controlled to generate a regenerative braking force that reduces the difference between the actual slip ratio and the target slip ratio SRrtg (first target slip ratio). Also, in the friction slip control mode based on the target slip ratio, friction brakes 40FL, 40FR, 40RL, and 40RR are controlled to generate a friction braking force that reduces the difference between the actual slip ratio and the target slip ratio SRftg (second target slip ratio).

[0028] Figure 2 is an architecture diagram showing the coordinated operation of slip control based on the target wheel speed. The drive force controller 51 transmits the motor torque command value (command value for drive force or regenerative braking force) and the friction braking force command value, which are necessary for accelerating and decelerating the vehicle 1, to the motor controllers 52, 53 and the brake controller 55, respectively, via the bus 56 that constitutes the in-vehicle network. During deceleration, regenerative coordinated braking is performed by using both friction braking force and regenerative braking force. In other words, in regenerative coordinated braking, the drive force controller 51 distributes the required braking force between regenerative braking and friction braking, and sets the required regenerative braking force value and the required friction braking force value after distribution.

[0029] Meanwhile, the drive force controller 51 acquires information on the vehicle speed VS estimated by the brake controller 55, and further receives information on the regenerative braking force command value after regenerative slip control, that is, information on the regenerative braking force command value after the regenerative braking force request value after distribution has been corrected by regenerative slip control, from the motor controllers 52 and 53. Here, the drive force controller 51 sets the first target wheel speed ωrtg in regenerative slip control and the second target wheel speed ωftg in friction slip control based on the vehicle speed VS, the regenerative braking force command value after regenerative slip control, the friction braking force request value after distribution, and the regenerative braking force request value after distribution.

[0030] The drive force controller 51 then transmits information on the first target wheel speed ωrtg to the motor controllers 52 and 53, and information on the second target wheel speed ωftg to the brake controller 55. Meanwhile, the brake controller 55 estimates the vehicle speed VS from the wheel speeds of each of the four wheels detected by the wheel speed sensors 2FL, 2FR, 2RL, and 2RR, and transmits the estimated vehicle speed VS information to the drive force controller 51.

[0031] Furthermore, the brake controller 55 obtains information on the second target wheel speed ωftg and the requested friction braking force after distribution from the drive force controller 51, and also obtains information on the regenerative braking force command value after regenerative slip control from the motor controllers 52 and 53. The brake controller 55 then performs friction slip control to converge the actual wheel speed to the second target wheel speed ωftg by changing the friction braking force generated by the friction brake devices 40FL, 40FR, 40RL, and 40RR within a range from zero to the requested friction braking force after distribution, in other words, within the control range of regenerative coordinated braking.

[0032] The motor controllers 52 and 53 obtain the first target wheel speed ωrtg and the regenerative braking force request value after distribution from the drive force controller 51. The motor controllers 52 and 53 then perform regenerative slip control to converge the actual wheel speed to the first target wheel speed ωrtg by changing the regenerative braking force generated by the motors 10 and 20 within a range from zero to the regenerative braking force request value after distribution, in other words, within the control range of regenerative coordinated braking. The motor controllers 52 and 53 also transmit information of the regenerative braking force command value after regenerative slip control to the drive force controller 51.

[0033] The following describes in detail the setting processes for the first target wheel speed ωrtg and the second target wheel speed ωftg performed by the drive force controller 51. In the regenerative slip control mode, the drive force controller 51 sets the first target wheel speed ωrtg as a wheel speed that is lower by a predetermined first speed Δω1 relative to the vehicle speed VS. In the friction slip control mode, the drive force controller 51 also sets the second target wheel speed ωftg as a wheel speed that is lower by a predetermined second speed Δω2 relative to the vehicle speed VS.

[0034] Here, the second speed Δω2 is set to be less than the first speed Δω1 (Δω2 < Δω1). Also, the first target wheel speed ωrtg and the second target wheel speed ωftg are lower than the equivalent vehicle speed, indicating the target values ​​for the slip ratio in a wheel slip state.

[0035] In other words, the drive force controller 51 sets the first target wheel speed ωrtg in the regenerative slip control mode as "first target wheel speed ωrtg = wheel speed equivalent to vehicle speed VS - first speed Δω1", and sets the second target wheel speed ωftg in the friction slip control mode as "second target wheel speed ωftg = wheel speed equivalent to vehicle speed VS - second speed Δω2". To put it another way, the drive force controller 51 sets the second target wheel speed ωftg for friction slip control and the first target wheel speed ωrtg for regenerative slip control to speeds lower than the wheel speed equivalent to vehicle speed VS, and sets the second target wheel speed ωftg for friction slip control to a wheel speed higher than the first target wheel speed ωrtg for regenerative slip control. Therefore, the first target wheel speed ωrtg and the second target wheel speed ωftg satisfy the condition "wheel speed equivalent to vehicle speed VS" > second target wheel speed ωftg > first target wheel speed ωrtg.

[0036] Thus, by setting the second target wheel speed ωftg for friction slip control higher than the first target wheel speed ωrtg for regenerative slip control, the frictional braking force will be preferentially reduced in response to wheel slip, thereby suppressing the reduction in regenerative energy associated with regenerative slip control. Furthermore, if the wheel slip does not converge even after reducing the frictional braking force, and the wheel speed falls below the second target wheel speed ωrtg, regenerative slip control can intervene to converge the wheel slip.

[0037] Figure 3 is a time chart showing an example of the changes in regenerative braking force and frictional braking force when regenerative slip control and frictional slip control are used in combination, with the second target wheel speed ωftg set higher than the first target wheel speed ωrtg. In Figure 3, as the vehicle 1 decelerates and the wheel speed begins to decrease from the equivalent of the vehicle speed VS, frictional slip control is implemented to adjust the frictional braking force so that the wheel speed converges to the second target wheel speed ωftg.

[0038] Here, if the wheel speed can be brought to a second target wheel speed ωftg by friction slip control, regenerative slip control will not operate, and the regenerative braking force will be maintained near the required regenerative braking force after distribution. In other words, by preventing a reduction in regenerative braking force, the decrease in the amount of regenerative energy associated with slip control is suppressed, and the energy efficiency of vehicle 1 is improved when it is running in an environment prone to slipping.

[0039] Furthermore, the drive force controller 51 increases or decreases the second target wheel speed ωftg and the first target wheel speed ωrtg while maintaining their relative magnitudes, depending on whether the regenerative braking force controlled by regenerative slip control, that is, the regenerative braking force command value after regenerative slip control, has reached a predetermined value set within the control range of regenerative cooperative braking, which is less than or equal to the regenerative braking force request value after distribution. For example, the drive force controller 51 determines whether the regenerative braking force command value after regenerative slip control has reached a predetermined value set within the control range of regenerative cooperative braking by comparing the regenerative braking force request value after distribution, in other words, the maximum value of the control range of regenerative cooperative braking, with the regenerative braking force command value after regenerative slip control.

[0040] Then, if the regenerative braking force request value after distribution (a predetermined value set within the control range of regenerative coordinated braking) matches the regenerative braking force command value after regenerative slip control, and the regenerative braking force has not been reduced by regenerative slip control, the drive force controller 51 sets the second target wheel speed ωftg and the first target wheel speed ωrtg, in other words, the first speed Δω1 and the second speed Δω2, to their default values ​​(initial values). On the other hand, if the regenerative braking force is reduced by regenerative slip control, and the regenerative braking force command value after regenerative slip control becomes smaller than the regenerative braking force request value after distribution (a predetermined value set within the control range of regenerative coordinated braking), the drive force controller 51 increases the second target wheel speed ωftg and the first target wheel speed ωrtg while maintaining their relative magnitudes to bring them closer to the vehicle speed VS. In other words, when the regenerative braking force command value after regenerative slip control becomes smaller than the regenerative braking force request value after distribution, the drive force controller 51 reduces the first speed Δω1 and the second speed Δω2 to less than their default values ​​while maintaining their relative magnitudes.

[0041] The driving force controller 51 sets, for example, the default value of the second target wheel speed ωftg in the friction slip control to the target wheel speed corresponding to the standard target slip ratio in the ABS (Anti-lock Brake System). Then, when the regenerative braking force command value after the regenerative slip control becomes smaller than the required regenerative braking force after distribution, the driving force controller 51 shifts the second target wheel speed ωftg and the first target wheel speed ωrtg in the direction of approaching the vehicle body speed so that the first target wheel speed ωrtg in the regenerative slip control becomes the target wheel speed corresponding to the standard target slip ratio in the ABS.

[0042] That is, the default value of the second target wheel speed ωftg and the first target wheel speed ωrtg that has been increased and shifted from the default value are set to values of the same degree. The standard target slip ratio in the ABS is set, for example, near the slip ratio at which the braking force is maximum. By setting the default value of the second target wheel speed ωftg and the first target wheel speed ωrtg that has been increased and shifted from the default value to values of the same degree, a desired deceleration and vehicle stability can be achieved.

[0043] Figure 4 is a time chart showing an example of changes in the regenerative braking force and the frictional braking force when the increase and decrease processes of the second target wheel speed ωftg and the first target wheel speed ωrtg are performed. In Figure 4, before time t1, the vehicle 1 is traveling on a road surface with a relatively high friction coefficient, and similar to the case of Figure 3, the wheel speed can be converged near the second target wheel speed ωftg (the slip ratio at which the braking force is maximum) by slip control mainly based on friction slip control.

[0044] On the other hand, after time t1, the friction coefficient of the road surface decreases, changing to an environment where slipping is more likely. At this time, even if the frictional braking force is reduced to the maximum, the increase in slip cannot be suppressed, and when the wheel speed becomes lower than the second target wheel speed ωftg, the control transitions to slip control mainly based on regenerative slip control, and the regenerative braking force command value after the regenerative slip control becomes smaller than the required regenerative braking force after distribution (a predetermined value set within the control range of regenerative cooperative braking).

[0045] Based on the transition of the slip control mode, a shift process is executed to increase the second target wheel speed ωftg and the first target wheel speed ωrtg while maintaining their relative magnitudes. After the shift process, the first target wheel speed ωrtg switches to the same level as the second target wheel speed ωftg before the shift process. As a result, if the slip does not converge even when the frictional braking force is reduced by frictional slip control, regenerative slip control automatically takes over, allowing the slip ratio to converge to the slip ratio at which the braking force is maximized. Therefore, the reduction in the amount of regenerative energy associated with slip control can be suppressed while stably achieving convergence to the optimal slip ratio.

[0046] Figure 5 is a block diagram showing the setting process for the second target wheel speed ωftg and the first target wheel speed ωrtg in the drive force controller 51, regenerative slip control in the motor controllers 52 and 53, and friction slip control in the brake controller 55. The drive force controller 51 has the following functional units: a target slip ratio calculation unit 51A, a comparison unit 51B, a first switching unit 51C, a second switching unit 51D, a first target wheel speed calculation unit 51E, and a second target wheel speed calculation unit 51F.

[0047] The target slip ratio calculation unit 51A sets default values ​​for the target slip ratio SRrtg and target slip ratio SRftg, that is, the target slip ratio in slip control mainly based on friction slip control, based on the vehicle speed VS. The target slip ratio calculation unit 51A also calculates the target slip ratio SRrtg and target slip ratio SRftg, that is, the target slip ratio in slip control mainly based on regenerative slip control, which are shifted downwards from the default values, based on the vehicle speed VS. The target slip ratio calculation unit 51A sets the default values ​​for the target slip ratio SRrtg and target slip ratio SRftg, and the target slip ratio SRrtg and target slip ratio SRftg, which are shifted downwards from the default values, so that the relationship "target slip ratio SRrtg > target slip ratio SRftg" is maintained.

[0048] The comparison unit 51B determines whether the regenerative braking force command value after the regenerative slip control is smaller than the regenerative braking force required value after distribution (in other words, the maximum regenerative braking force in regenerative cooperative braking or a predetermined value set within the control range of regenerative cooperative braking), and outputs a switching command signal for switching the target slip ratio. Note that the predetermined value set within the control range of regenerative cooperative braking, which is used for determining the output of the switching command signal, is not limited to the regenerative braking force required value after distribution. For example, it can be a regenerative braking force that is smaller than the regenerative braking force required value after distribution by a predetermined value.

[0049] Here, if the regenerative braking force required value after distribution is the same as the regenerative braking force command value after the regenerative slip control, the comparison unit 51B outputs a switching command signal that selects the default value as the target slip ratio. On the other hand, when the regenerative braking force command value after the regenerative slip control is smaller than the regenerative braking force required value after distribution, the comparison unit 51B outputs a switching command signal that selects, as the target slip ratio, a target slip ratio obtained by decreasing and shifting from the default value, that is, a target slip in which the target wheel speed increases.

[0050] The first switching unit 51C outputs either the default value of the target slip ratio SRrtg or the target slip ratio SRrtg after the decreasing shift according to the switching command signal output by the comparison unit 51B. That is, if the regenerative braking force required value after distribution is the same as the regenerative braking force command value after the regenerative slip control, the first switching unit 51C outputs the default value of the target slip ratio SRrtg, in other words, the target slip ratio SRrtg in slip control mainly based on friction slip control. On the other hand, when the regenerative braking force command value after the regenerative slip control is smaller than the regenerative braking force required value after distribution, the first switching unit 51C outputs the target slip ratio SRrtg after the decreasing shift, in other words, the target slip ratio SRrtg in slip control mainly based on regenerative slip control.

[0051] Furthermore, the second switching unit 51D outputs either the default value of the target slip ratio SRftg or the target slip ratio SRftg after the reduction shift, in accordance with the switching command signal output by the comparison unit 51B. In other words, if the regenerative braking force request value after distribution and the regenerative braking force command value after regenerative slip control are the same, the second switching unit 51D outputs the default value of the target slip ratio SRftg, or in other words, the target slip ratio SRftg in slip control mainly based on friction slip control. On the other hand, if the regenerative braking force command value after regenerative slip control is smaller than the regenerative braking force request value after distribution, the second switching unit 51D outputs the target slip ratio SRftg after the reduction shift, or in other words, the target slip ratio SRftg in slip control mainly based on regenerative slip control.

[0052] The first target wheel speed calculation unit 51E calculates the first target wheel speed ωrtg from the target slip ratio SRrtg obtained from the first switching unit 51C and the vehicle speed VS, and outputs information on the first target wheel speed ωrtg (in other words, the target value of the output shaft speed of motors 10 and 20) to the motor controllers 52 and 53. Similarly, the second target wheel speed calculation unit 51F calculates the second target wheel speed ωftg from the target slip ratio SRftg obtained from the second switching unit 51D and the vehicle speed VS, and outputs information on the second target wheel speed ωftg to the brake controller 55.

[0053] The motor controllers 52 and 53 have a start-determination speed calculation unit 52A and a wheel speed control unit 52B as functional units for performing regenerative slip control. The start-determination speed calculation unit 52A calculates a threshold speed ωrth, which is a threshold wheel speed for determining the start timing of regenerative slip control, based on information of the first target wheel speed ωrtg.

[0054] The wheel speed control unit 52B acquires information on the regenerative braking force request value after distribution, the threshold speed ωrth, and the first target wheel speed ωrtg. Then, when the wheel speed control unit 52B determines to start regenerative slip control based on a comparison between the actual wheel speed and the threshold speed ωrth, it adjusts the command value of the regenerative braking force generated by the motors 10 and 20 to minimize the difference between the actual wheel speed and the first target wheel speed ωrtg, within a control range where the regenerative braking force request value after distribution is the maximum value, and outputs this as the regenerative braking force command value after regenerative slip control.

[0055] On the other hand, the brake controller 55, along with an estimated vehicle speed calculation unit 55A that estimates the vehicle speed VS from the wheel speed, has a start judgment speed calculation unit 55B and a wheel speed control unit 55C as functional units for executing friction slip control. The start judgment speed calculation unit 55B calculates a threshold speed ωfth, which is a threshold wheel speed for determining the start timing of friction slip control, based on information of the second target wheel speed ωftg. Then, when the wheel speed control unit 55C determines the start of friction slip control based on a comparison between the actual wheel speed and the threshold speed ωfth, it adjusts the command values ​​of the friction braking force generated by the friction braking devices 40FL, 40FR, 40RL, and 40RR so as to reduce the difference between the actual wheel speed and the second target wheel speed ωftg, within a control range where the distributed friction braking force request value is the maximum value, and outputs the command value as the friction braking force command value after friction slip control.

[0056] Figure 6 is an architectural diagram showing the coordinated operation of slip control when the drive force controller 51 is configured to output information on the target slip ratio SRrtg and the target slip ratio SRftg. The drive force controller 51 acquires information on the vehicle speed VS estimated by the brake controller 55, and further receives information on the regenerative braking force command value after regenerative slip control from the motor controllers 52 and 53.

[0057] The drive force controller 51 then sets the target slip ratio SRrtg (first target slip ratio) for regenerative slip control and the target slip ratio SRftg (second target slip ratio) for friction slip control based on the vehicle speed VS, the regenerative braking force command value after regenerative slip control, the friction braking force request value after distribution, and the regenerative braking force request value after distribution. The target slip ratio SRftg (second target slip ratio) is set to be smaller than the target slip ratio SRrtg (first target slip ratio).

[0058] Next, the drive force controller 51 transmits information on the target slip ratio SRrtg and target slip ratio SRftg to the brake controller 55. The brake controller 55 converts the information on the target slip ratio SRrtg and target slip ratio SRftg into information on the first target wheel speed ωrtg and second target wheel speed ωftg based on the vehicle speed VS information.

[0059] Then, the brake controller 55 performs friction slip control (second slip control mode) based on the information of the second target wheel speed ωftg. In other words, the brake controller 55 controls the friction brake devices 40FL, 40FR, 40RL, and 40RR to generate a friction braking force that reduces the difference between the actual slip ratio and the target slip ratio SRftg.

[0060] Furthermore, the brake controller 55 outputs information on the first target wheel speed ωrtg to the motor controllers 52 and 53. Based on the information on the first target wheel speed ωrtg obtained from the brake controller 55, the motor controllers 52 and 53 perform regenerative slip control (first slip control mode). In other words, the motor controllers 52 and 53 control the motors 10 and 20 to generate a frictional braking force that reduces the difference between the actual slip ratio and the target slip ratio SRrtg.

[0061] Figure 7 is a time chart showing the switching settings (in other words, increase / decrease settings) of the target slip ratio SRrtg and target slip ratio SRftg. The drive force controller 51 compares the regenerative braking force request value after distribution, in other words, the maximum value of the control range of regenerative cooperative braking, with the regenerative braking force command value after regenerative slip control to determine whether the regenerative braking force command value after regenerative slip control has reached a predetermined value set within the control range of regenerative cooperative braking.

[0062] Then, the drive force controller 51 sets the target slip ratio SRrtg and target slip ratio SRftg to their default values ​​(initial values) if the regenerative braking force request value after distribution matches the regenerative braking force command value after regenerative slip control, and the regenerative braking force has not been reduced by regenerative slip control. Here, the default value of the target slip ratio SRrtg is set to a value greater than the default value of the target slip ratio SRftg.

[0063] Furthermore, when the regenerative braking force is reduced by regenerative slip control, and the regenerative braking force command value after regenerative slip control becomes smaller than the regenerative braking force request value after distribution, the drive force controller 51 reduces the target slip ratio SRrtg and target slip ratio SRftg while maintaining their relative magnitudes. Here, it is preferable that the default value of the target slip ratio SRftg is set to a value near the slip ratio at which the braking force is maximized in response to a change in slip ratio. It is also preferable that the target slip ratio SRrtg is reduced from its default value to a value near the slip ratio at which the braking force is maximized in response to a change in slip ratio, that is, a value approximately the same as the default value of the target slip ratio SRftg.

[0064] Incidentally, if the operation of simultaneously reducing braking force by friction slip control and regenerative slip control occurs frequently, the convergence of wheel speed (slip ratio) deteriorates. Therefore, in a system that controls the regenerative braking force controlled by the regenerative slip control mode within the control range of the regenerative braking force set in cooperative control, the drive force controller 51 can reduce the regenerative braking force request value after distribution by a predetermined amount if the regenerative braking force controlled by the regenerative slip control mode within the control range of the regenerative braking force falls below the regenerative braking force request value (threshold) after distribution again after returning to the regenerative braking force request value after distribution (in other words, after reaching the threshold value set within the control range).

[0065] Figure 8 is a block diagram showing the drive force controller 51 equipped with a function to subtract the regenerative braking force request value after distribution, as described above. In Figure 8, the same reference numerals are used for functional parts that are the same as those shown in the block diagram of Figure 5, and detailed explanations are omitted.

[0066] The switching determination unit 51G determines whether the determination result from the comparison unit 51B regarding whether the regenerative braking force command value after regenerative slip control is smaller than the regenerative braking force request value after distribution is different or the same for the previous and current times. The logical AND unit 51H obtains the determination result from the comparison unit 51B and the determination result from the switching determination unit 51G, and outputs a signal of "1" when it is the first time that the determination has switched to the case where the regenerative braking force command value after regenerative slip control is smaller than the regenerative braking force request value after distribution.

[0067] In other words, the comparison unit 51B determines that the regenerative braking force command value after regenerative slip control is smaller than the regenerative braking force request value after distribution, and the switching determination unit 51G determines that the determination result of whether or not the regenerative braking force command value after regenerative slip control is smaller than the regenerative braking force request value after distribution is different between the previous and current determinations, and this determination is also represented by "1". At this time, the logical AND unit 51H outputs a signal of "1" when the comparison unit 51B outputs a signal of "1" and the switching determination unit 51G outputs a signal of "1".

[0068] The third switching unit 51K outputs "0" when the output of the logical AND unit 51H is "0", and outputs a predetermined unit reduction amount when the output of the logical AND unit 51H is "1". The adder unit 51L adds the output of the third switching unit 51K to the accumulated reduction amount up to the previous time and outputs the result. The fourth switching unit 51M, based on the signal from the brake pedal switch which detects whether the brake pedal is pressed (in other words, whether or not the driver is performing a braking operation), outputs the accumulated reduction amount output by the adder unit 51L when a braking operation is performed, and outputs the initial value of "0" as the accumulated reduction amount when no braking operation is performed.

[0069] The subtraction unit 51N acquires the cumulative reduction amount output by the fourth switching unit 51M and the regenerative braking force request value after distribution (the maximum value of regenerative braking force in regenerative slip control), subtracts the cumulative reduction amount from the regenerative braking force request value after distribution, and outputs the final regenerative braking force request value after distribution to the motor controllers 52, 53 and the comparison unit 51B. In other words, each time the regenerative braking force command value after regenerative slip control becomes smaller than the regenerative braking force request value after distribution, the cumulative reduction amount increases by a unit reduction amount, and with each increase in the cumulative reduction amount, the regenerative braking force request value after distribution (in other words, the maximum value of regenerative braking force in regenerative slip control) gradually decreases.

[0070] Figure 9 is a time chart showing how the regenerative braking force requirement gradually decreases after distribution. Before time t1 in Figure 9, slip does not converge even when the friction braking force is reduced, so slip control is mainly performed using regenerative slip control.

[0071] Subsequently, between time t1 and t2, the slip becomes small, and the regenerative braking force is returned to the regenerative braking force request value after distribution. However, after time t2, the slip ratio increases sharply, and the system transitions again to slip control primarily based on regenerative slip control. Based on this transition to slip control, the cumulative decrease amount increases from "0", and the regenerative braking force request value after distribution is corrected to decrease. In other words, the base regenerative braking force is corrected to be smaller, regardless of regenerative slip control.

[0072] Then, from time t3, the system returns to slip control primarily based on friction slip control, but at time t4, it transitions again to slip control primarily based on regenerative slip control, further increasing the cumulative reduction and correcting the required regenerative braking force after distribution to a smaller value. This gradual reduction correction of the required regenerative braking force after distribution leads to a state where the slip converges with slip control primarily based on friction slip control. In other words, each time the drive force controller 51 transitions to slip control primarily based on regenerative slip control, it gradually reduces the required regenerative braking force after distribution (in other words, the maximum value of regenerative braking force in regenerative slip control, or the threshold value in regenerative slip control), thereby suppressing frequent simultaneous intervention of the two slip control systems and ensuring convergence.

[0073] The technical ideas described in the above embodiments can be used in appropriate combinations, provided that no contradictions arise. Furthermore, although the content of the present invention has been specifically described with reference to preferred embodiments, it will be obvious to those skilled in the art that various modifications can be taken based on the basic technical ideas and teachings of the present invention.

[0074] For example, a controller higher than the drive force controller 51, brake controller 55, and motor controllers 52 and 53 can be configured to set a target wheel speed or target slip ratio, and then output information about the target wheel speed or target slip ratio from the higher-level controller to the brake controller 55 and motor controllers 52 and 53.

[0075] Furthermore, the brake controller 55 is not limited to a system that has a function to estimate vehicle speed from wheel speed. Onboard controllers other than the drive force controller 51, brake controller 55, and motor controllers 52, 53 may have a function to calculate vehicle speed, or the drive force controller 51 or motor controllers 52, 53 may have a function to calculate vehicle speed.

[0076] 1...Vehicle, 1FL, 1FR...Front wheels, 1RL, 1RR...Rear wheels, 10, 20...Motor (Regenerative braking system), 40FL, 40FR, 40RL, 40RR...Friction braking system, 51...Drive force controller (Vehicle control system), 52, 53...Motor controller (Vehicle control system), 55...Brake controller (Vehicle control system)

Claims

1. A vehicle control device provided in a vehicle equipped with a friction braking device for applying frictional braking force to wheels and a regenerative braking device for applying regenerative braking force to the wheels, the vehicle control device comprising a control unit for coordinating control of the friction braking device and the regenerative braking device, wherein the control unit comprises: a first slip control mode for controlling the regenerative braking device to generate the regenerative braking force that reduces the difference between the speed of the wheels and a first target wheel speed, which is set to be a wheel speed lower by a predetermined first speed with respect to the vehicle's body speed; and a second slip control mode for controlling the friction braking device to generate the friction braking force that reduces the difference between the speed of the wheels and a second target wheel speed, which is set to be a wheel speed lower by a predetermined second speed less than the first speed with respect to the vehicle's body speed.

2. A vehicle control device according to claim 1, wherein the control unit controls the regenerative braking force controlled by the first slip control mode within the control range of the regenerative braking force set in the cooperative control, and increases or decreases the first target wheel speed and the second target wheel speed while maintaining the relative magnitude relationship between the first target wheel speed and the second target wheel speed, depending on whether the regenerative braking force controlled by the first slip control mode has reached a predetermined value set within the control range.

3. A vehicle control device according to claim 1, wherein the control unit controls the regenerative braking force controlled by the first slip control mode within the control range of the regenerative braking force set in the cooperative control, and if the regenerative braking force controlled by the first slip control mode within the control range of the regenerative braking force falls below the threshold again after reaching the threshold set within the control range, the setting of the threshold is reduced by a predetermined amount.

4. A vehicle control device provided in a vehicle equipped with a friction braking device for applying frictional braking force to a wheel and a regenerative braking device for applying regenerative braking force to the wheel, the vehicle control device comprising a control unit for coordinating control of the friction braking device and the regenerative braking device, wherein the control unit comprises: a first slip control mode for controlling the regenerative braking device to generate the regenerative braking force that reduces the difference between the slip ratio of the wheel and a predetermined first target slip ratio; and a second slip control mode for controlling the friction braking device to generate the friction braking force that reduces the difference between the slip ratio of the wheel and a predetermined second target slip ratio that is smaller than the first target slip ratio.

5. A vehicle control method performed by a control unit provided in a vehicle equipped with a friction brake and a regenerative brake, wherein, when the wheels of the vehicle slip, the vehicle controls the slip of the wheels by using both a method of controlling the regenerative brake so that the wheels converge to a first target wheel speed, and a method of controlling the friction brake so that the wheels converge to a second target wheel speed set higher than the first target wheel speed.

Images