JP4346001B2 - Electric vehicle braking system - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a braking technique for an electric vehicle including a driving wheel driven by an electric motor among a plurality of wheels that support a vehicle body. In particular, the braking is performed by regeneration of an electric motor to brake the driving wheel. The present invention relates to a braking technique that uses both regenerative braking means and hydraulic brake means that uses hydraulic pressure of hydraulic fluid generated by a master cylinder when a brake pedal is depressed.
[0002]
BACKGROUND OF THE INVENTION
2. Description of the Related Art Generally, as a braking device for an automobile, hydraulic brake means that mechanically brakes by supplying hydraulic pressure of hydraulic fluid generated by a master cylinder to a wheel cylinder when a brake pedal is depressed is used. In an electric vehicle, in addition to such mechanical hydraulic brake means, electromagnetic regenerative brake means using an electric motor (drive motor) can also be used. The required brake torque required for the electric vehicle is obtained as the sum of the regenerative brake torque by the regenerative brake means and the mechanical brake torque by the conventional general hydraulic brake means. Therefore, a braking device for an electric vehicle requires a hydraulic pressure control device for generating a mechanical brake torque corresponding to the difference between the required brake torque and the regenerative brake torque.
[0003]
As this hydraulic pressure control device, it is conceivable to utilize a brake optimization control mechanism that appropriately controls the mechanical brake torque by the hydraulic brake means for the traveling electric vehicle such as anti-lock control and vehicle attitude control. These brake optimization control mechanisms are intended for safe and comfortable driving of the automobile, and are necessary not only for ordinary automobiles that use an internal combustion engine as a power source but also for electric automobiles. In addition, the brake optimization control mechanism can perform pressure reduction control for releasing the hydraulic pressure of the wheel cylinder to the reservoir and pressure increase control for increasing the hydraulic pressure of the wheel cylinder. Therefore, by using the brake optimization control mechanism provided in the electric vehicle, it is possible to provide a relatively low-cost electric vehicle braking device without adding a new hydraulic pressure control device. In this regard, for example, Japanese Patent Application Laid-Open No. 7-336805 is an example in which an antilock control mechanism is used as a hydraulic pressure control device for an electric vehicle.
[0004]
Problems to be Solved by the Invention
By the way, such a brake optimization control mechanism includes a pump for returning the hydraulic fluid released from the wheel cylinder to the reservoir to the master cylinder side. The anti-lock control is a control with a small number of times of operation according to the lock tendency, whereas the normal brake operation is a natural operation with a large number of times. During frequent braking operations compared to anti-lock control, the pump will cause the brake pedal to kick back with each braking operation. Also, when considering cooperation with regenerative braking means that shows a gradual change in brake torque, the brake torque change due to the brake optimization control mechanism (or hydraulic pressure change accompanying pressure reduction control or pressure increase control) Smooth and gentle fluid pressure control is required.
[0005]
An object of the present invention is to provide a braking device for an electric vehicle capable of improving both pedal feeling and brake feeling while effectively utilizing a brake optimization control mechanism attached to the vehicle.
Another object of the present invention is to provide a technique capable of obtaining a good depression feeling of a brake pedal without providing a pedal simulator.
Other objects of the present invention will become apparent from the following description.
[0006]
[Means for Solving the Invention]
According to the present invention, the solenoid valve included in the brake optimization control mechanism is controlled by PWM (duty control) to limit both pressure increase and pressure reduction, and the pump motor is also PWM controlled (duty control). ) To facilitate pedal reaction during decompression control.
[0007]
In addition, in order to suppress the sudden movement of the hydraulic fluid and the sudden brake torque change accompanying the control, the brake fluid pressure control for the wheel cylinders of some of the wheels arranged in the front and rear, and the remaining The brake fluid pressure control for the wheel cylinder of the wheel is alternately performed with a predetermined time difference. From the standpoint of reducing the vehicle's yamment, it is preferable to alternately perform the brake fluid pressure control for the front wheel wheel cylinder and the hydraulic pressure control for the rear wheel wheel cylinder for a short time. By separately performing the brake fluid pressure control for a plurality of wheels in this way, the rapid movement of the hydraulic fluid accompanying the control is suppressed, and the overall brake torque change accompanying the control of pressure increase and pressure reduction can be made smooth. Also, pedal reaction during control is smooth.
[0008]
Further, when the pressure reduction control, instead of returning the hydraulic fluid in the reservoir to the master cylinder side each time the control, only when the working fluid volume in the reservoir exceeds a predetermined value Q _1, the hydraulic fluid in the reservoir by a pump It is better to return to the master cylinder side. When the pressure reduction control, when hydraulic fluid volume in the reservoir is below a predetermined value Q _1, the time of your next pressure increasing after the pressure reduction control, the hydraulic fluid in the reservoir back to the master cylinder side by the pump To do. Accordingly, the return amount of the brake pedal generated during the pressure reduction control can be reduced, and the extension amount of the brake pedal accompanying the subsequent pressure increase control can be reduced. As a result, the pedal stroke characteristics can be improved.
[0009]
Regarding braking of an electric vehicle, in general, at a stage that can be covered by a regenerative brake torque by regeneration of an electric motor (that is, a stage where the regenerative brake is fully applied and the regenerative brake torque reaches a maximum), The concept of obtaining the required brake torque required only by regenerative braking is adopted. However, even in a stage where the required brake torque can be provided by the regenerative brake means, another concept of securing the required brake torque by both the regenerative brake torque and the hydraulic brake torque can be adopted. Thereby, it is possible to obtain a good depression feeling of the brake pedal without providing a pedal simulator.
[0010]
【Example】
FIG. 1 clarifies the overall piping and the connection relationship of main control commands showing an embodiment of the braking system for an electric vehicle according to the present invention. In the figure, the piping system is indicated by a solid line, and the electrical control command is indicated by a broken line.
The electric vehicle to be braked is a front-wheel drive four-wheel vehicle. Of the four wheels, two front wheels, that is, the left front wheel FL and the right front wheel FR are drive wheels driven by the electric motor 10. The remaining two rear wheels, that is, the right rear wheel RR and the left rear wheel RL are driven wheels having no driving source. Each of the four wheels includes a wheel cylinder, and each wheel cylinder produces a mechanical brake torque for each wheel.
[0011]
The electric motor 10 that is a drive source for the front wheels is driven and controlled based on a control command from a motor controller 12 mainly composed of a microcomputer, for example, using a rechargeable battery as an energy source. On the other hand, the electric motor 10 also functions as a generator, and generates a brake torque of the regenerative brake. Therefore, the motor controller 12 is electrically connected to a brake controller 14 mainly composed of a microcomputer. The brake controller 14 gives a regenerative brake command to the motor controller 12, and the motor controller 12 gives the brake controller 14 the maximum regenerative brake signal corresponding to the brake torque of the regenerative brake that can be output at the present time, and / or the present time. Gives the actual value of the regenerative braking torque. The brake controller 14 is also given a signal from the hydraulic pressure sensor P / S for detecting the master cylinder hydraulic pressure and signals from the wheel speed sensors 161 to 164 of each wheel, and based on them, a predetermined value is given. As will be described later, a control command based on the calculation result is sent to the solenoid valve and the pump motor.
[0012]
Next, let's look at the piping for the hydraulic brake. There is a master cylinder 18 as a source of hydraulic pressure. The master cylinder 18 generates hydraulic pressure inside the cylinder through the booster 22 as the brake pedal 20 is depressed. The master cylinder 18 is a tandem type, and independent brake lines 31 and 32 extend from the primary and secondary hydraulic ports 24p and 24s to reach the wheel cylinders of the respective wheels. The brake lines 31 and 32 are components for anti-lock control, that is, a pump 34 driven by a motor M, a normally open first electromagnetic valve 36, and a normally closed second electromagnetic valve 38. And a reservoir 40 for relaxation. Here, two-port two-position valves (two two-port two-position valves corresponding to each wheel cylinder) are used as the first and second electromagnetic valves 36 and 38, respectively. Of course, it is possible to use the three-port, three-position solenoid valve, or other solenoid valve configurations. Each of the brake pipes 31 and 32 further includes a first position where the first electromagnetic valve 36 communicates with the master cylinder 18 side, and a hydraulic pressure upstream of the first electromagnetic valve 36 is applied to the master cylinder 18 side. A two-position type third solenoid valve 43 having a second position that produces a relief function when higher than a predetermined level, a two-position type that communicates and blocks between the master cylinder 18 side and the suction side of the pump 34. The fourth solenoid valve 44 is provided. The third solenoid valve 43 is used to balance the hydraulic pressure in the same system or to balance the hydraulic pressure between different systems, and the fourth solenoid valve 44 is opened during sudden braking. It can be used to increase the response of braking.
[0013]
[Example of processing in the brake controller]
FIG. 2 is a flowchart showing an example of processing performed in the brake controller 14 in order to distribute the required brake torque required for the electric vehicle to the regenerative brake torque and the hydraulic brake torque.
First, in order to know the required brake torque required, the hydraulic pressure Pm of the master cylinder 18 by the hydraulic pressure sensor P / S is sampled as shown in step S1. Next, based on the sampled hydraulic pressure Pm, in step S2, a predetermined calculation (for example, TB = α · Pm, α: proportional constant) is performed to calculate a required brake torque TB. In the next step S3, the regenerative brake torque Trb is calculated from the required brake torque TB calculated in step S2. For this calculation, the TB-Trb relationship is preset in the ROM in the brake controller 14. Regarding the TB-Trb relationship, for example, even if the characteristic C1 as shown in FIG. It is preferable to set so that the hydraulic brake torque can be provided. In this regard, in the normal regenerative brake priority concept, before the regenerative brake torque reaches the maximum, as long as the regenerative brake torque can provide, all the required brake torques are provided by the regenerative brake torque. According to the characteristic C1, when the brake pedal 20 is operated, a part of the hydraulic fluid accompanying the stepping flows from the master cylinder 18 side toward the wheel cylinder, so that a feeling of stepping on the plate, which is a problem in braking of an electric vehicle, is felt. Can be relaxed. Therefore, a good feeling of depression of the brake pedal 20 can be obtained without providing a pedal simulator mainly composed of a reservoir.
In the characteristic C1 of FIG. 3, the hydraulic brake torque is increased at a constant ratio until the regenerative brake torque reaches the maximum from zero. However, even if the interval is increased in a quadratic function, for example. good. If it does so, the break point of the characteristic C1 can be made small and the better depression feeling of the brake pedal 20 can be obtained.
[0014]
Next, in step S4, the maximum regenerative braking torque Trbmax is obtained from the motor controller 12. The motor controller 12 determines Trbmax based on the motor speed and the state of charge of the battery. In step S5, it is determined whether Trb is larger than Trbmax. If Trb> Trbmax is “YES”, Trb = Trbmax is set (step S6), and “NO” is set. For example, Trb itself is output to the motor controller 12 (step S7).
[0015]
The motor controller 12 calculates a hydraulic brake torque Thb based on Thb = TB−Trb (step 8), then obtains a hydraulic pressure P for obtaining the calculated Thb (step 9), A difference ΔP (= P−Po) between the hydraulic pressure P and the current estimated brake hydraulic pressure Po is obtained (step 10). The estimated brake fluid pressure Po can be obtained by inputting the current master cylinder fluid pressure, the operating state of each solenoid valve, and the like into a hydraulic model provided in a microcomputer in the brake controller 14. In the following steps, it is determined whether the ΔP is positive or negative. If ΔP> 0 is “YES”, the pressure increasing control is performed, and ΔP> 0 is “NO”. If ΔP <0 is “YES”, pressure reduction control is performed, and furthermore, ΔP> 0 is “NO”, and if ΔP <0 is “NO”, holding control is performed.
[0016]
[Other examples of processing in the brake controller]
In the process shown in the flowchart of FIG. 2, a regenerative brake signal is transmitted from the motor controller 12 to the brake controller 14, but such regenerative brake signal transmission can be eliminated. FIG. 4 is a flowchart showing processing in which transmission of the regenerative brake signal is eliminated.
First, in step S41, the hydraulic pressure Pm of the master cylinder 18 by the hydraulic pressure sensor P / S is sampled. Next, based on the sampled hydraulic pressure Pm, in step S42, the required deceleration Am is calculated instead of the brake torque. In the following step S43, the estimated vehicle speed Vc is calculated based on the outputs of the wheel speed sensors 161 to 164. In step S44, the estimated vehicle speed Vc is differentiated to calculate the estimated vehicle deceleration (that is, the actual vehicle speed Vc). The vehicle deceleration) Ac is calculated.
[0017]
A difference ΔA between the calculated required deceleration Am and the estimated vehicle deceleration Ac is obtained (step S45), and a difference ΔP as a hydraulic pressure is obtained by multiplying ΔA as the deceleration by a pressure conversion coefficient α. (Step S46). Thereafter, as described above, the pressure increase control, the pressure reduction control, and the holding control are performed based on the positive / negative of ΔP. It is also possible to incorporate both the regenerative brake signal and the wheel speed sensor signal and use them for control correction and inconsistency checking.
[0018]
[Pressure increase control]
FIG. 5 is a flowchart showing an example of pressure increase control.
In the pressure increase control, the second electromagnetic valve (AV) 38 is closed (step S51), and the first electromagnetic valve (EV) 36 is subjected to PWM control (duty control) (step S57). Therefore, the PWM duty ratio DEV of the first solenoid valve 36 is calculated from the above-described ΔP (step S52). The duty ratio DEV increases as ΔP increases (that is, the energization time increases). The motor of the pump 34 is subjected to PWM control (duty control) when it is estimated that hydraulic fluid is contained in the reservoir 40. Therefore, it is determined whether the reservoir fluid amount Qr is larger than Q ₀ (Q ₀ = 0) (step S53). If Qr> Q ₀ is “YES”, the PWM duty of the first solenoid valve 36 is determined. The pump drive duty ratio Dp is calculated from the ratio DEV (step S54), and the pump 34 is driven at the duty ratio Dp (step S55). The duty ratio Dp for driving the pump increases as the PWM duty ratio DEV of the first solenoid valve 36 increases (that is, the energization time increases). The reservoir fluid amount Qr is calculated using the estimated wheel cylinder fluid pressure Pw, the valve opening time of the second electromagnetic valve 38 during the pressure reduction control, and the motor drive time of the pump 34 as parameters. Therefore, in the series of processing, there are estimation of the reservoir fluid amount Qr (step S56) and estimation of the wheel cylinder fluid pressure Pw (step S58). In such pressure increase control, the first electromagnetic valve 36 is subjected to PWM control, so that the change in the brake fluid pressure accompanying the control is smooth and gradual, and there is no sudden fluctuation in the vehicle deceleration. Further, since the motor of the pump 34 is also subjected to PWM control, the liquid source at the time of pressure increase is present other than the master cylinder, and there is an effect of suppressing the extension of the pedal stroke.
[0019]
[Decompression control]
FIG. 6 is a flowchart showing an example of pressure reduction control.
In the pressure reduction control, the first electromagnetic valve (EV) 36 is closed (step S61), and the second electromagnetic valve (AV) 38 is controlled to open for a minimum time (step S62, instead of the minimum time valve opening control). PWM control can also be performed). At that time, estimated fluid amount Qr in the reservoir 40 is determined whether larger than the predetermined value _{Q 1} (step S65), when Qr> _{Q 1} is "YES", the motor of the PWM control of the pump 34 (duty Control) (step S66). The predetermined value Q ₁ is set to Q ₁ > Q ₀ and is a value that does not hinder even if the antilock control is started during the pressure reduction control. The anti-lock control is a control that takes precedence over the regenerative brake control, and it is necessary to always ensure that the reservoir 40 has a capacity enough to receive the hydraulic pressure of the hydraulic fluid on the wheel cylinder side so that the wheel is not locked. It is. Also in this case, estimation of the wheel cylinder hydraulic pressure Pw (step S63), estimation of the reservoir fluid amount Qr (step S64), and estimation of the reservoir fluid amount Qr after driving the pump (step S67) are performed in a series of processes. is there. In such pressure reduction control, since the second electromagnetic valve 38 is subjected to valve opening control or PWM control for a minimum time, the pressure can be gradually reduced, and no rapid fluctuation is observed in the vehicle deceleration. Moreover, the reaction force to the brake pedal 20 is smooth by controlling the motor of the pump 34 by PWM . Further, in the reservoir fluid amount Qr is a predetermined value or less Q ₁ is therefore not drive the motor of the pump 34, the return amount of the brake pedal 20 is reduced, it is possible to more effectively improve brake feeling.
[0020]
[Retention control]
FIG. 7 is a flowchart showing an example of holding control.
During the transition from the pressure increase control to the pressure decrease control and during the transition from the pressure decrease control to the pressure increase control, both the first solenoid valve (EV) 36 and the second solenoid valve (AV) 38 are closed to reduce the hydraulic pressure. Control to keep constant. However, when the master cylinder hydraulic pressure Pm = the wheel cylinder hydraulic pressure Pw or the regenerative brake torque Trb is zero, this holding control is not performed and the electromagnetic valves 36 and 38 are moved to their normal positions (the first electromagnetic valve 36 is opened). The second solenoid valve 38 is switched to the closed state.
[0021]
In the above control, the electromagnetic valves 36 and 38 for each wheel cylinder of a plurality of wheels can be controlled simultaneously. However, in the control for causing movement of the hydraulic fluid, that is, in the case of pressure increase control and pressure reduction control, the front wheels It is preferable to alternately control the side and the rear wheel side with a time difference. Thereby, the rapid movement of the hydraulic fluid can be avoided, the change of the stroke of the brake pedal 20 can be made smoother, and the reaction force to the brake pedal 20 can be made gentle, The feeling of the brake pedal 20 can be improved.
[0022]
In the embodiment described above, the predetermined value Q ₀ of the reservoir fluid amount is set to zero, but the predetermined value Q ₀ is set to be larger than zero and smaller than Q ₁ (0 <Q ₀ <Q ₁ ) to increase the pressure. time control only when the reservoir fluid amount Qr of Qr> _{Q 0,} the motor of the pump 34 may be PWM controlled (duty control).
[0023]
The present invention can be applied not only to an electric vehicle (so-called pure electric vehicle) that is driven entirely by electric energy, but also to a hybrid vehicle that is driven by a combination of electric energy and other energy. Furthermore, the present invention can be applied not only to a four-wheeled vehicle but also to a multi-axis vehicle such as a front uniaxial vehicle and a rear biaxial vehicle.
[0024]
Note that the motor of the pump 34 is PWM-controlled during hydraulic pressure control for cooperation between the regenerative brake and the hydraulic brake. However, during anti-lock control, the motor of the pump 34 is continuously driven as usual without PWM control. Or increase the duty ratio to drive.
[Brief description of the drawings]
FIG. 1 is a connection diagram of piping and the like showing an embodiment of a braking device of the present invention.
FIG. 2 is a flowchart showing an example of processing in a brake controller.
FIG. 3 is a characteristic diagram showing a TB-Trb relationship.
FIG. 4 is a flowchart showing another example of processing in the brake controller.
FIG. 5 is a flowchart showing an example of pressure increase control.
FIG. 6 is a flowchart showing an example of pressure reduction control.
FIG. 7 is a flowchart showing an example of holding control.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 Electric motor 12 Motor controller 14 Brake controllers 161-164 Wheel speed sensor 18 Master cylinder 34 Pump 36 1st solenoid valve 38 2nd solenoid valve 40 Reservoir

Claims (5)

Regenerative brake means for electromagnetically braking by regeneration of the electric motor, and hydraulic brake means for mechanically braking by supplying hydraulic pressure of the hydraulic fluid generated by the master cylinder to the wheel cylinder when the brake pedal is depressed. A braking device for an electric vehicle, which obtains a required brake torque required for the electric vehicle from a regenerative brake torque by the regenerative brake means and a mechanical brake torque by the hydraulic brake means, wherein the anti-lock control or the attitude of the car And further including a brake optimization control mechanism for appropriately controlling a mechanical brake torque by the hydraulic brake means for the electric vehicle traveling such as control, and using the brake optimization control mechanism, the required brake torque and the regeneration Obtain mechanical brake torque equivalent to the difference from brake torque In the braking device for an electric vehicle, the brake optimization control mechanism communicates between the master cylinder and the wheel cylinder, and blocks and communicates between the first solenoid valve capable of being disconnected and the wheel cylinder and the reservoir. A possible second solenoid valve and a pump for returning the hydraulic fluid in the reservoir to the master cylinder side by driving a motor, and communicating the second solenoid valve to release the hydraulic pressure of the wheel cylinder to the reservoir The pressure reducing control for controlling the pressure and the pressure increasing control for increasing the hydraulic pressure of the wheel cylinder by communicating the first electromagnetic valve are possible, respectively, and the control is performed by PWM controlling the first and second electromagnetic valves. limit both control of pressure and vacuum, moreover, the motor of the pump by PWM control, a configuration that facilitates the pedal reaction during pressure reduction control Ri, further,
When the pressure reduction control, the hydraulic fluid amount in the reservoir only when exceeding a predetermined value Q _1, return the hydraulic fluid in the reservoir to the master cylinder side by the pump, yet also when the decompression control, in the reservoir when hydraulic fluid amount is below the predetermined value Q _1, the time of your next pressure increasing after the pressure reduction control, return the hydraulic fluid in the reservoir to the master cylinder side by the pump, the electric vehicle braking apparatus. Regenerative brake means for electromagnetically braking by regeneration of the electric motor, and hydraulic brake means for mechanically braking by supplying hydraulic pressure of the hydraulic fluid generated by the master cylinder to the wheel cylinder when the brake pedal is depressed. A braking device for an electric vehicle, which obtains a required brake torque required for the electric vehicle from a regenerative brake torque by the regenerative brake means and a mechanical brake torque by the hydraulic brake means, wherein the anti-lock control or the attitude of the car And further including a brake optimization control mechanism for appropriately controlling a mechanical brake torque by the hydraulic brake means for the electric vehicle traveling such as control, and using the brake optimization control mechanism, the required brake torque and the regeneration Obtain mechanical brake torque equivalent to the difference from brake torque In the braking device for an electric vehicle, the brake optimization control mechanism communicates between the master cylinder and the wheel cylinder, and blocks and communicates between the first solenoid valve capable of being disconnected and the wheel cylinder and the reservoir. A possible second solenoid valve and a pump for returning the hydraulic fluid in the reservoir to the master cylinder side by driving a motor, and communicating the second solenoid valve to release the hydraulic pressure of the wheel cylinder to the reservoir The pressure reducing control for controlling the pressure and the pressure increasing control for increasing the hydraulic pressure of the wheel cylinder by communicating the first electromagnetic valve are possible, respectively, and the control is performed by PWM controlling the first and second electromagnetic valves. limit both control of pressure and vacuum, moreover, the motor of the pump by PWM control, a configuration that facilitates the pedal reaction during pressure reduction control Ri, further,
Even in the step of providing the required brake torque by the regenerative brake means, the required brake torque is ensured by both the regenerative brake torque and the hydraulic brake torque, thereby enabling the brake pedal of the brake pedal to be provided without providing a pedal simulator. A braking device for an electric vehicle that achieves a good depression feeling. The electric vehicle includes a plurality of wheels arranged in front and rear, and brake fluid pressure control for wheel cylinders of some of the wheels and brake fluid pressure control for wheel cylinders of the remaining wheels are predetermined. The braking device according to any one of claims 1 and 2, wherein the braking device is alternately performed with a time difference of. The braking device according to claim 3 , wherein the some wheels are either front wheels or rear wheels, and the remaining wheels are the other of the front wheels or the rear wheels. The braking device according to claim 1, wherein the required brake torque is regarded as a required deceleration.

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