JP2015196474A - Vehicular braking force control apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To balance between responsiveness and stability related to recovering braking force when the tendency of a wheel being locked is eliminated to recover the braking force.SOLUTION: An ECU 100 performs: starting to increase braking force only with motor regeneration when starting an ABS recovery control routine; subsequently (S11), computing a required increase amount of braking force on the basis of a slip ratio; increasing braking force only with the motor regeneration (S13 through S15) if the required increase amount of braking force is small or if an allowance of the motor-regenerative braking force is higher than a given level; or reducing the motor regeneration braking force while increasing frictional braking force, substituting the motor-regenerative braking force with the frictional braking force (S16), if the allowance of the motor-regenerative braking force is lower than the given level.

Description

  The present invention relates to an in-wheel motor drive type vehicle braking force control apparatus.

  As an embodiment of an electric vehicle, an in-wheel motor drive type vehicle has been developed in which a motor is disposed in or near a wheel of an unsprung wheel and the wheel is directly driven by this motor. In this in-wheel motor drive type vehicle, the driving force or braking force applied to each wheel can be controlled independently by independently driving (powering) control or regenerative control of the motor provided for each wheel. Can do.

  In such an in-wheel motor vehicle, the entire braking force can be generated by combining both the regenerative braking force by the regenerative control of the motor and the friction braking force by the hydraulic control of the hydraulic actuator. For example, in the braking force control device proposed in Patent Document 1, when a wheel locking tendency is detected, the regenerative braking force is controlled by the motor while the friction braking force is maintained at a constant value. Avoid the locking tendency.

JP-A-5-270387

  In general, the motor is superior to the hydraulic actuator in terms of control response. However, the regenerative braking force that can be generated by the motor varies depending on the situation, such as the motor rotation speed. For this reason, if only the regenerative braking force by the motor is controlled in a state where the friction braking force is maintained at a constant value as in the braking force control device proposed in Patent Document 1, the tendency of the wheels to be locked is eliminated and the braking force is reduced. When resetting, the braking force may be insufficient. For this reason, there is a possibility that the braking force cannot be stably returned. In addition, when a configuration in which the braking force is restored only by the friction braking force by the hydraulic control is used, the responsiveness is lowered as compared with the case where the regenerative braking force is controlled.

  The present invention has been made in order to solve the above-described problem, and aims to achieve both responsiveness and stability related to return of braking force when the tendency of wheel locking is resolved and braking force is restored. And

The feature of the present invention that solves the above problem is that an in-wheel motor (30) provided on a wheel and capable of generating a driving force and a regenerative braking force;
A friction brake mechanism (70) provided on the wheel and capable of generating a friction braking force by hydraulic pressure;
Controls the operation of the in-wheel motor and the friction brake mechanism, and reduces the total braking force that combines the regenerative braking force and the friction braking force when a tendency to lock the wheel is detected during wheel braking. And a control means (35, 75, 100) having an anti-lock brake control function for restoring the total braking force when the locking tendency is eliminated,
The control means includes
Regenerative braking force advance increasing means (S11) for increasing the regenerative braking force prior to the friction braking force when the locking tendency is resolved and the total braking force is restored;
After the regenerative braking force is increased prior to the friction braking force by the regenerative braking force advance increasing means, the friction braking force is increased while reducing the regenerative braking force, and at least a part of the regenerative braking force. And a braking force replacement means (S16) for replacing the friction braking force with the friction braking force.

  The vehicle braking force control apparatus of the present invention is applied to an in-wheel motor drive type vehicle. The braking force control apparatus includes an in-wheel motor capable of generating a driving force for driving a wheel and a regenerative braking force for braking the wheel, a friction brake mechanism capable of generating a friction braking force by hydraulic pressure, an in-wheel motor, and a friction brake. Control means for controlling the operation of the mechanism. The control means reduces the total braking force that combines the regenerative braking force and the friction braking force when a wheel locking tendency is detected during braking of the wheel, and returns the total braking force when the locking tendency is eliminated. The so-called anti-lock brake control is performed.

  The control means includes regenerative braking force advance increase means and braking force replacement means as means for restoring the total braking force after the locking tendency is eliminated. The regenerative braking force advance increasing means increases the regenerative braking force prior to the friction braking force when the locking tendency is eliminated and the total braking force is restored. That is, the regenerative braking force is preferentially increased without increasing the friction braking force. Therefore, the braking force can be increased with high responsiveness. After the regenerative braking force is increased prior to the friction braking force, the braking force replacement means increases the friction braking force while reducing the regenerative braking force to replace at least a part of the regenerative braking force with the friction braking force. For this reason, even if the control range of the regenerative braking force that can be generated by the in-wheel motor is small, the braking force applied to the wheel is frictionally controlled by replacing at least a part of the regenerative braking force with the friction braking force on the way. The regenerative braking force can be further increased and controlled from the state where the bottom is raised by the power. For this reason, it is possible to generate a large braking force with high responsiveness. As a result, according to the present invention, it is possible to achieve both responsiveness and stability related to braking force recovery.

  For example, the braking force replacement means obtains a margin that can increase the regenerative braking force during return of the braking force, and when this margin falls below a predetermined level, the regenerative braking force is converted into the friction braking force. It is good to change. Further, the total braking force may be increased while replacing the regenerative braking force with the friction braking force.

  In the above description, in order to help the understanding of the invention, the reference numerals used in the embodiments are attached to the configuration of the invention corresponding to the embodiments in parentheses, but each constituent element of the invention is described in the above reference numerals. It is not limited to the embodiment defined by.

1 is a schematic configuration diagram of a vehicle on which a vehicle braking force control device according to an embodiment is mounted. It is a flowchart showing an ABS return control routine. It is a graph showing transition of braking force etc. at the time of ABS return. It is a graph showing transition of the braking force at the time of ABS return concerning a comparative example.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 schematically shows the configuration of a vehicle 1 on which the vehicle braking force control apparatus of this embodiment is mounted.

  The vehicle 1 includes a left front wheel 10FL, a right front wheel 10FR, a left rear wheel 10RL, and a right rear wheel 10RR. The left front wheel 10FL, the right front wheel 10FR, the left rear wheel 10RL, and the right rear wheel 10RR are supported by the vehicle body via independent suspensions 20FL, 20FR, 20RL, and 20RR, respectively. Hereinafter, when it is not necessary to specify any of the wheels 10FL, 10FR, 10RL, and 10RR, they are collectively referred to as wheels 10. In addition, regarding the configuration provided corresponding to each wheel 10, “FL” is provided at the end of the reference symbol for the configuration provided corresponding to the left front wheel 10 FL, and “ “FR”, “RL” for the configuration provided corresponding to the left rear wheel 10RL, “RR” for the configuration provided corresponding to the right rear wheel 10RR, and identifying any of them for each wheel If there is no need to do this, the end sign is omitted.

  Motors 30FL, 30FR, 30RL, and 30RR are incorporated in the left front wheel 10FL, right front wheel 10FR, left rear wheel 10RL, and right rear wheel 10RR. Each motor 30 is a so-called in-wheel motor, and is fixed to the lower part of the spring together with the wheel 10 and is connected to each wheel 10 so that power can be transmitted. In the vehicle 1, the driving force and regenerative braking force generated at each wheel 10 can be controlled independently by controlling the torque of each motor 30 independently.

  Each motor 30 is connected to a motor driver 35. The motor driver 35 is, for example, an inverter, and four sets are provided so as to correspond to the motors 30. The motor driver 35 converts the DC power supplied from the battery 60 into AC power, and the AC power is independent of each motor 30. And supply. Thereby, each motor 30 is drive-controlled and gives a driving force to each wheel 10.

  Each motor 30 also functions as a generator, and can generate electric power by the rotational energy of the wheels 10 and regenerate the generated electric power to the battery 60 via the motor driver 35. The regenerative braking force generated by the power generation of the motor 30 gives a braking force to the wheel 10.

  The left front wheel 10FL, the right front wheel 10FR, the left rear wheel 10RL, and the right rear wheel 10RR are provided with friction brake mechanisms 70FL, 70FR, 70RL, and 70RR, respectively. Each friction brake mechanism 70 is a known braking device such as a disc brake or a drum brake. These brake mechanisms 70 are connected to a brake actuator 75, and a piston (not shown) of a wheel cylinder is operated by hydraulic pressure supplied from the brake actuator 75 to apply a braking force to each wheel 10.

  The brake actuator 75 is a power hydraulic pressure generator comprising a booster pump, an accumulator, etc., a pressure adjustment control valve that adjusts the pressure of the brake hydraulic oil and supplies it to the wheel cylinder of the friction brake mechanism 70, and the brake hydraulic oil to the friction brake mechanism 70. And an opening / closing control valve for opening / closing a hydraulic circuit for supplying the pressure (not shown).

  The motor driver 35 and the brake actuator 75 are connected to the electronic control unit 100, respectively. The electronic control unit 100 (hereinafter referred to as the ECU 100) includes a microcomputer including a CPU, a ROM, a RAM, and the like as main components, and executes various programs to independently operate the motors 30 and the friction brake mechanism 70. It is something to control. For this reason, the ECU 100 determines that the accelerator sensor 61 detects the accelerator operation amount from the accelerator pedal depression amount (or angle, pressure, etc.) and the driver from the brake pedal depression amount (or angle, pressure, etc.). A brake sensor 62 for detecting the brake operation amount of the vehicle and wheel speed sensors 63FL, 63FR, 63RL, 63RR for detecting the wheel speed of each wheel 10 are connected to each other, and a sensor representing the accelerator operation amount, the brake operation amount, and the wheel speed of the four wheels Input the signal. Further, the ECU 100 inputs sensor signals necessary for motor control, such as a signal representing a current value flowing from the motor driver 35 to each motor 30 and a signal representing a voltage value supplied to the motor driver 35 from the motor driver 35.

  Based on the signals input from the accelerator sensor 61 and the brake sensor 62, the ECU 100 requests the required driving force and the required braking force (target driving force and target braking force) according to the accelerator operation amount and the brake operation amount of the driver, that is, Then, the total required braking / driving force required for running or braking the vehicle 1 is calculated. Then, the total required braking / driving force is distributed to each wheel required braking / driving force generated by the motor 30 of each wheel 10 in accordance with a predetermined rule. When the value of the required braking / driving force is positive, the driving force is required, and when the required braking / driving force is negative, the braking force is required.

  The ECU 100 generates a control signal (for example, a PWM control signal) such that a current corresponding to each wheel required braking / driving force flows to the motor 30 and outputs the control signal to the motor driver 35. When each wheel requested braking / driving force is negative, ECU 100 regenerates each wheel requested braking / driving force according to a predetermined rule and friction braking force generated by motor 30 and friction brake mechanism 70. Distribute to power. ECU 100 outputs a control signal for generating a regenerative braking force to motor driver 35, and outputs a control signal for generating a friction braking force to brake actuator 75. As a result, the motor 30 generates a target regenerative braking force, and the friction brake mechanism 70 generates a target friction braking force.

  The ECU 100 includes a microcomputer in charge of control of the motor 30 (control of the motor driver 35) and a microcomputer in charge of control of the friction brake mechanism 70 (control of the brake actuator 75) so that they can communicate with each other. The braking force applied to the wheel is controlled by the cooperation of the microcomputer. Further, the control response of the motor 30 is superior to the control response of the brake actuator 75.

  In addition, the ECU 100 performs anti-lock brake control (referred to as ABS) that suppresses locking of wheels during braking and ensures vehicle stability.

  Here, ABS will be described. The ECU 100 compares the wheel speeds of the four wheels with the vehicle body speed and repeatedly calculates the slip ratio ((vehicle speed−wheel speed) / vehicle speed × 100%) of each wheel at a predetermined short calculation cycle. When the slip ratio of the wheel exceeds the ABS start determination threshold, it is determined that the wheel 10 is locked, and ABS is started for the wheel 10 for which the lock is determined. The vehicle body speed is calculated based on the wheel speeds of four wheels, for example.

When the ABS is started, the ECU 100 once resets the regenerative braking force generated by the motor 30 of the ABS target wheel to zero and the hydraulic pressure of the friction brake mechanism 70 of the ABS target wheel (the hydraulic pressure of a wheel cylinder (not shown)). Reduce. As a result, the friction braking force decreases and the slip ratio decreases. When the slip ratio falls below the depressurization end determination threshold, the ECU 100 ends the depressurization operation (the depressurization operation of a wheel cylinder (not shown)) of the friction brake mechanism 70 of the ABS target wheel, and starts a process of increasing the braking force. In the present embodiment, when the braking force is increased, the recovery of the braking force is accelerated by generating the regenerative braking force by preferentially using the motor 30 having high responsiveness.

  FIG. 2 shows an ABS return control routine executed by the ECU 100. When the ECU 100 detects that the slip ratio has fallen below the pressure reduction end determination threshold and ends the pressure reduction of the friction brake mechanism 70, the ECU 100 starts this ABS return control routine. First, in step S11, the ECU 100 starts increasing the braking force only by motor regeneration. At this time, the friction braking force by the friction brake mechanism 70 is maintained at a level immediately before the ABS return control routine is started (at the end of the pressure reducing operation). As a result, the braking force applied to the wheel is increased only by the motor regenerative braking force.

  Subsequently, in step S12, the ECU 100 reads the current slip rate and calculates a required increase amount of the braking force based on the slip rate. Subsequently, in step S13, the ECU 100 determines whether the required increase amount is smaller than the first threshold value (required increase amount: small), or greater than the first threshold value and smaller than the second threshold value (required increase amount: medium). ) And whether it is larger than the second threshold (request increase amount: large). The processing after step S12 is repeatedly performed, but when the determination processing of step S13 is performed first, the required increase amount based on the slip ratio that appears as a result of increasing the motor regenerative braking force by step S11 is increased. Calculated.

  When the braking force is reduced by ABS and then returned to the required braking / driving force for each wheel, it is necessary to prevent the wheels from locking again. Therefore, the ECU 100 calculates the required increase amount while confirming the slip ratio that appears as an increase result of the braking force. For example, when the slip ratio increases greatly as a result of an increase in braking force, the required increase amount is limited to a small value. Depending on the situation of the slip ratio, the required increase amount can be set to a negative value. Conversely, when the increase in the slip ratio is small, the required increase amount is set to a large value, and the return of the braking force is promoted.

  If the required increase amount is small, the ECU 100 increases the braking force only by motor regeneration in step S14. Therefore, the ECU 100 increases the motor regenerative braking force according to the required increase amount. If the required increase amount is medium, the ECU 100 determines in step S15 whether the margin of the motor regenerative braking force is equal to or less than a predetermined level. The margin of the motor regenerative braking force is, for example, the difference between the upper limit value of the regenerative braking force that can be generated by the motor 30 (regenerative braking force) and the currently generated regenerative braking force (regenerative braking force). It is represented by the size of the increaseable amount. Alternatively, it may be represented by the ratio of the above-described regeneration increaseable amount to the upper limit value. The ECU 100 calculates a margin based on the rotational speed of the motor, the state of charge of the battery 60, etc., and if the margin is higher than a predetermined level, the process proceeds to step S14 described above to increase the braking force. Is performed only by motor regeneration.

  On the other hand, if the margin is less than or equal to the predetermined level, the ECU 100 switches between the motor regenerative braking force and the friction braking force in step S16. In this case, the ECU 100 controls the hydraulic pressure supplied from the brake actuator 75 to the friction brake mechanism 70 to increase the friction braking force, while reducing the motor regenerative braking force, so that the total braking force (the motor regenerative braking force and the friction is increased). The sum of braking force). As a result, the total braking force can be increased while increasing the margin of the motor regenerative braking force. That is, the braking force applied to the wheel 10 can be raised by the friction braking force.

  The regenerative braking force that can be generated by the motor 30 varies depending on various conditions such as the motor rotation speed. For this reason, it is difficult to always keep the control range of the motor regenerative braking force at a relatively large value. Therefore, in this step S16, when the margin of the motor regenerative braking force is reduced, the braking force applied to the wheel 10 is raised by the friction braking force, and thereafter, the braking force increase request is made. On the other hand, the motor regenerative braking force can be sufficiently used. Thereby, braking force control can be continued with high responsiveness.

  Further, when the required increase amount is large, the ECU 100 increases the friction braking force in addition to the increase of the motor regenerative braking force in step S17. For example, when the traveling road surface of the vehicle is switched from a low μ road surface with a low friction coefficient μ to a high μ road surface with a high friction coefficient μ, a large braking force can be generated by the process of step S17.

  After executing any one of steps S14, S16, and S17, ECU 100 determines whether or not to end the braking force increasing process in step S18, that is, the braking force applied to wheel 10 is controlled by each wheel. It is determined whether or not the driving force has been reached. When the increased braking force has not reached each wheel required braking / driving force (S18: No), ECU 100 returns the processing to step S12 and repeats the above-described processing. Thereby, the required increase amount based on the slip ratio is calculated, and the form of the braking force applied to the wheel 10 is selected according to the magnitude of the required increase amount and the margin of the motor regenerative braking force.

  When such processing is repeated and the braking force reaches each wheel required braking / driving force, the ECU 100 ends the ABS return control routine and ends the antilock brake control.

  According to the braking force control apparatus of the present embodiment described above, when the ABS return control routine is started, the braking force increasing process using the motor regenerative braking force is performed prior to the friction braking force (S11). ). The motor control response is superior to the brake actuator control response. For this reason, the change of the slip ratio accompanying the increase in the braking force can be quickly reflected in the braking force control. Therefore, the braking force can be quickly returned without relocking the wheel 10.

  In addition, after the braking force increasing process using the motor regenerative braking force is performed, the braking force is increased only by the motor regenerative braking force when the required increase amount is small. Therefore, the braking force can be controlled with high responsiveness. The control range of the regenerative braking force that can be generated by motor regeneration is smaller than the control range of the frictional braking force that can be generated by hydraulic control. For this reason, the motor regenerative braking force may not be greatly increased. Therefore, in this embodiment, when the required increase amount is medium, if the margin of the motor regenerative braking force is low, the motor regenerative braking force and the friction braking force are switched.

  FIG. 3 shows a slip ratio (a) in the figure, the vehicle speed-wheel speed (b), a total braking force (c), and a motor regenerative braking force (d). ), The friction braking force (e in FIG. 4). The portions enclosed by the alternate long and short dash line in FIGS. 9D and 9E show the situation where the motor regenerative braking force and the friction braking force are switched. At the time of this replacement, the degree of increase in the friction braking force is set to be larger than the degree of decrease in the motor regenerative braking force so that the total braking force increases.

  By replacing the motor regenerative braking force with the friction braking force, the braking force applied to the wheel 10 is raised by the friction braking force. Thereafter, the motor regenerative braking force is used in response to a request to increase the braking force. It can respond sufficiently. Therefore, it is possible to achieve both responsiveness and stability related to braking force recovery. If the margin of the motor regenerative braking force is high, the braking force is increased only by the motor regenerative braking force. Therefore, the braking force control can be continued with high responsiveness.

  When the required increase amount is large, the friction braking force is increased in addition to the increase of the motor regenerative braking force. For this reason, even when the vehicle changes from a low μ road surface to a high μ road surface, the braking force can be appropriately increased.

  FIG. 4 shows, as a comparative example, the transition of the braking force (= total braking force) when only the friction braking force is increased by hydraulic control of the brake actuator, as a broken line. Since the hydraulic control is less responsive than the motor control, in order to increase the friction braking force while detecting the change in the slip ratio so that the wheel 10 does not re-lock, as shown by the broken line, the braking force (hydraulic pressure) Need to be gradually increased. For this reason, the return of the braking force is delayed as compared with the total braking force of the present embodiment.

  Although the vehicle braking force control apparatus according to the present embodiment has been described above, the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the object of the present invention.

  DESCRIPTION OF SYMBOLS 1 ... Vehicle, 10 ... Wheel, 30 ... Motor, 35 ... Motor driver, 60 ... Battery, 61 ... Accelerator sensor, 62 ... Brake sensor, 63 ... Wheel speed sensor, 70 ... Friction brake mechanism, 75 ... Brake actuator

Claims (1)

An in-wheel motor provided on the wheel and capable of generating a driving force and a regenerative braking force;
A friction brake mechanism provided on the wheel and capable of generating a friction braking force by hydraulic pressure;
Controls the operation of the in-wheel motor and the friction brake mechanism, and reduces the total braking force that combines the regenerative braking force and the friction braking force when a tendency to lock the wheel is detected during wheel braking. And a control means having an anti-lock brake control function for returning the total braking force when the locking tendency is eliminated,
The control means includes
Regenerative braking force advance increasing means for increasing the regenerative braking force prior to the friction braking force when the locking tendency is eliminated and the total braking force is restored;
After the regenerative braking force is increased prior to the friction braking force by the regenerative braking force advance increasing means, the friction braking force is increased while reducing the regenerative braking force, and at least a part of the regenerative braking force. A braking force control device for a vehicle, comprising: braking force replacement means for replacing the friction braking force with the braking force.

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