JP2000050409A - Braking equipment of vehicle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain braking equipment of a vehicle in which turning at braking is not deteriorated in the case of low μroad. SOLUTION: This braking equipment of a vehicle can control friction braking and regenerative braking. The braking equipment judges whether a condition of VSO-max (VWFR, VWFL)>a is satisfied when regenerative braking is operated (steps S110, S120). When the condition is satisfied, the regenerative braking is interrupted, and braking using the friction braking and the regenerative braking is transferred to the braking due to only the friction braking (step S150).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vehicle braking device capable of controlling friction braking and regenerative braking. The braking device of the present invention is applicable to both electric vehicles (EV) and hybrid vehicles (HEV).

[0002]

2. Description of the Related Art As a braking device for a vehicle, a friction braking device for transmitting hydraulic pressure (generally, hydraulic pressure) generated in response to a driver's braking operation to a wheel side to perform braking is generally used. In an electric vehicle or a hybrid car, the vehicle can also be braked by regenerating electric power by a motor for driving the vehicle. In electric vehicles and hybrid cars, friction braking and regenerative braking can be used together.

Conventionally, when regenerative braking is operated in a front-wheel-drive or four-wheel-drive electric vehicle or a hybrid car, a braking device is controlled so that the braking force distribution is closer to the front wheels. Such control aims at improving fuel efficiency.

[0004]

However, when the braking force distribution is closer to the front wheels as described above, a low μ road (for example,
On snowy roads and icy roads, the turning performance during braking is reduced and the vehicle tends to understeer. Therefore, there is a problem that it is difficult to turn the vehicle as intended by the driver.

SUMMARY OF THE INVENTION In view of the above problems, an object of the present invention is to provide a braking device for a vehicle in which the turning performance during braking does not decrease even on a low μ road.

[0006]

A vehicle braking device according to the present invention is a vehicle braking device capable of controlling frictional braking and regenerative braking, wherein a VS0-max is provided when regenerative braking is activated.
Determining means for determining whether or not a first condition (VWFR, VWFL)> a is satisfied; and, when the first condition is satisfied, stopping regenerative braking to provide friction braking and regenerative braking. Control means for shifting the braking by the friction braking to the braking by only the friction braking, whereby the above object is achieved. Here, VS0 indicates the estimated vehicle speed, VWFR indicates the wheel speed of the front right wheel, VWFL indicates the wheel speed of the front left wheel, and max (VWFR, VWF
L) indicates the maximum value of VWFR and VWFL, and a indicates a predetermined value.

[0007] The above-mentioned judging means satisfies ΔVS0-max (VW
FR, VWFL)｝ / VS0 × 100> b, and further determines whether or not a second condition is satisfied. If the first condition and the second condition are satisfied, the control unit performs a regeneration operation. Braking may be stopped. Here, b indicates a predetermined value. The determining means further determines whether a braking request value from the driver is equal to or less than a predetermined value, and whether a third condition that a stop switch is on is satisfied. The regenerative braking may be stopped when the first condition, the second condition, and the third condition are satisfied.

[0008] The control means may stop the regenerative braking by gradually reducing the braking force by the regenerative braking.

[0009]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows a braking device 1 according to an embodiment of the present invention.
Is shown. The braking device 1 can be applied to any type of vehicle having a vehicle driving motor. For example, the braking device 1 can be applied to both an electric vehicle (EV) and a hybrid car (HEV). Hereinafter, a case where the braking device 1 is applied to an electric vehicle will be described as an example.

A motor 32 is provided as a motor for driving the vehicle. The output shaft of the motor 32 includes front wheels 54a, 5
4b is connected to the drive shaft 58 connected to 4b. The motor 32 is driven to rotate in response to a control signal from the EV ECU 30. Power to the motor 32 is typically provided by a battery (not shown).

In this embodiment, the rear wheels 64a, 6a
No motor is connected to the drive shaft 68 of 4b. Therefore, the rear wheels 64a and 64b are braked only by the braking force by friction braking.

The master cylinder (M / C) 12a generates a hydraulic pressure according to the amount of depression of the brake pedal 10. The regulator (Reg) 12b is a master cylinder 12a
Generates the same oil pressure. The hydraulic pressure (master cylinder pressure) generated by the master cylinder 12a is
6a, 16b.

The brake ECU 20 includes a hydraulic sensor 16
A braking request value is calculated according to the master cylinder pressure detected by a and 16b. The braking request value indicates a target braking force to be achieved by friction braking and regenerative braking. The braking request value is sent to the EV ECU 30.

The EV ECU 30 performs regenerative braking according to the required braking value. The regenerative braking is performed by regenerating electric power by the motor 32. EV ECU
30 returns the regenerative braking execution value to the brake ECU 20. The regenerative braking execution value indicates the amount by which regenerative braking was actually performed.

For example, if the braking request value is 100 and the regenerative braking execution value is 80, the value 20 (= 100-
Insufficient braking force corresponding to (80). Brake EC
U20 outputs to the hydraulic actuator 18 a hydraulic target value corresponding to the shortage of the braking force.

The hydraulic sensors 16c and 16d are feedback type hydraulic sensors. Oil pressure sensors 16c, 16d
The feedback control is performed so that the actual oil pressure detected by the control unit matches the target oil pressure value.

As described above, the brake ECU 20 controls the hydraulic actuator 18 so as to compensate for the insufficient braking force by regenerative braking by frictional braking.

The hydraulic actuator 18 includes front wheels 54a,
54b, the pressure in the wheel cylinders 52a, 52b;
Wheel cylinders 62a, 62b of rear wheels 64a, 64b
The internal pressure can be increased or decreased.
Wheel cylinder 52 by hydraulic actuator 18
When the pressures of a, 52b, 62a, and 62b are increased, the braking force by friction braking increases. Wheel cylinders 52a, 52b, 62a, 62b
Is reduced, the braking force due to friction braking decreases.

A stroke simulator 14 is provided between the master cylinder 12a and the hydraulic actuator 18. The stroke simulator 14 adjusts the oil amount so that the pedal stroke of the brake pedal 10 becomes natural in a state where the oil passage from the master cylinder 12a to the wheel cylinders 52a, 52b, 62a, 62b is blocked by the hydraulic actuator 18. Consume.

As described above, the brake ECU 20
It controls friction braking and regenerative braking. In this embodiment, the wheel cylinders 52a, 52b, 6
2a, 62b, but the wheel cylinders 52a, 52b, 62a,
The pressure in 62b may be controlled. That is, the brake ECU 20 can control the friction braking and the regenerative braking.

FIG. 2 shows the distribution of the braking force of the front wheels and the braking force of the rear wheels when the regenerative braking is activated. When the regenerative braking is activated, the braking force is distributed closer to the front wheels than when the regenerative braking is not activated (that is, when only the friction braking is activated). The reason why the braking force is distributed closer to the front wheels is to improve fuel efficiency. In FIG. 2, a curve A indicates a braking force distribution when regenerative braking operates, and a curve B indicates a braking force distribution when regenerative braking does not operate.

FIG. 3 shows the procedure of the regenerative braking process. The regenerative braking process is executed by the brake ECU 20.

In step S110, it is determined whether regenerative braking is in operation. Such a determination is made, for example, by referring to the regenerative braking flag 22 held in the brake ECU 20. The brake ECU 20
If the regenerative braking execution value is not “0”, a value indicating that regenerative braking is in operation (for example, “1”) is set in the regenerative braking flag 22, and the regenerative braking execution value is “0” Has a value indicating that regenerative braking is not operating (for example,
“0”) is set in the regenerative braking flag 22.

If the determination in step S110 is "Yes", the process proceeds to step S120, and "No"
If so, the process ends.

In step S120, it is determined whether the condition of (Equation 1) is satisfied.

[0027]

VS0-max (VWFR, VWFL)> a Here, VS0 indicates the estimated vehicle speed. VWFR indicates the wheel speed of the front right wheel 54b. VWFL indicates the wheel speed of the front left wheel 54a. max (VWFR, VWFL) is VW
The maximum values of FR and VWFL are shown. a is a predetermined value (k
m / h).

The estimated vehicle speed VS0 is obtained as the maximum value of the four wheel speeds. That is, the estimated vehicle speed VS
0 is obtained by (Equation 2).

[0029]

VS0 = max (VWFR, VWFL, VWR
R, VWRL) Here, VWRR indicates the wheel speed of the rear right wheel 64b. V
WRL indicates the wheel speed of the rear left wheel 64a.

The wheel speed VWFL of the front left wheel 54a is detected by a wheel speed sensor 56a. The wheel speed VWFR of the front right wheel 54b is detected by a wheel speed sensor 56b. The wheel speed VWRL of the rear left wheel 64a is detected by a wheel speed sensor 66a. The wheel speed VWRR of the rear right wheel 64b is detected by a wheel speed sensor 66b.

Although not shown in FIG. 1 for simplicity, outputs from the wheel speed sensors 56a, 56b, 66a, 66b are supplied to the brake ECU 20. Therefore, the brake ECU 20 controls the wheel speed sensors 56a, 56b, 6
Based on the outputs from 6a and 66b, it can be determined whether or not the condition of (Equation 1) is satisfied.

Note that the estimated vehicle speed VS0 can also be obtained by the above-described method and other methods. For example, the estimated vehicle speed VS0 may be obtained based on the output of a vehicle speed sensor (not shown).

If the determination in step S120 is "Yes", the process proceeds to step S130, and "No"
If so, the process proceeds to step S160.

In step S130, it is determined whether the condition of (Equation 3) is satisfied.

[0035]

[Equation 3] {VS0-max (VWFR, VWFL)} /
VS0 × 100> b Here, b indicates a predetermined value (%).

If the determination in step S130 is "Yes", the process proceeds to step S140, and "No"
If so, the process proceeds to step S160.

In step S140, it is determined whether the condition of (Equation 4) is satisfied.

[0038]

## EQU4 ## Braking demand value ≦ c and stop switch 11
Is in an on state. Here, c is a predetermined value. As described above, the braking request value indicates a target braking force to be achieved by friction braking and regenerative braking. The braking request value is, for example, based on the output of the oil pressure sensors 16a, 16b.
It is calculated by 0. The stop switch 11 is turned on when the brake pedal 10 is depressed, and is turned off otherwise. Stop switch 11
Is supplied to the brake ECU 20.

That is, the condition of (Equation 4) is designed to be satisfied at the time of gentle braking and not at the time of sudden braking.

If the determination in step S140 is "Yes", the process proceeds to step S150, and "No"
If so, the process proceeds to step S160.

In step S150, the regenerative braking is stopped. Thereby, the braking by the friction braking and the regenerative braking is shifted to the braking by only the friction braking. When stopping regenerative braking, it is preferable to gradually reduce the braking force due to regenerative braking. This is to prevent a sudden feeling of regenerative braking from causing an uncomfortable feeling in the brake feeling.

For example, the brake ECU 20 outputs a control signal to the EV ECU 30 to gradually reduce the regenerative braking execution value together with the braking request value, so that the braking force due to the regenerative braking can be gradually reduced. . Alternatively, the brake ECU 20 may reduce the target execution value by the regenerative braking instead of the braking request value while gradually decreasing the target execution value.
By outputting to U30, the braking force due to regenerative braking can be gradually reduced.

In step S160, regenerative braking is continued.

Thus, steps S110 to S140
When all the conditions in are satisfied, the regenerative braking is stopped. As a result, the braking force distribution is returned from the distribution closer to the front wheels (curve A in FIG. 2) to the normal distribution (curve B in FIG. 2). As a result, a decrease in turning performance during braking on a low μ road (for example, a snowy road or an icy road) is prevented.

It should be noted that the determination of whether or not the conditions of steps S130 and S140 are satisfied can be omitted. That is, when the conditions in steps S110 and S120 are satisfied, the regenerative braking may be stopped.
Alternatively, steps S110, S120 and S130
When the condition in is satisfied, the regenerative braking may be stopped. Even in these cases, step S110
As compared with the case where all the conditions of S140 are satisfied,
Although the accuracy of the control is somewhat reduced, it is effective in preventing the turning performance during braking from being reduced.

In the determination of step S130, b
Is a predetermined value, but b may be a variable that changes according to the estimated vehicle speed VS0. In this case, it is preferable to change the value of the variable b so that the variable b decreases as the estimated vehicle speed VS0 increases.

FIG. 4 shows the relationship between the time from the start of the brake operation and the wheel speed. When regenerative braking is in operation, the braking force distribution is closer to the front wheels, so the front wheels are decelerated faster than the rear wheels.

FIG. 5 shows a change in distribution between the braking force by friction braking and the braking force by regenerative braking. For example, it is assumed that all of the conditions in steps S110 to S140 are satisfied at time T in FIG. In this case, FIG.
At time T, the braking force due to regenerative braking is gradually reduced. The braking force by the regenerative braking may be reduced linearly as shown in FIG. 5, or may be reduced stepwise. The braking force due to regenerative braking can be reduced along any curve.

[0049]

According to the present invention, it is determined whether or not the condition of VS0-max (VWFR, VWFL)> a is satisfied when the regenerative braking is operating. When the above condition is satisfied, the regenerative braking is stopped, and the friction braking and the braking by the regenerative braking are shifted to the braking only by the friction braking. Thereby, the distribution of the braking force is returned from the distribution closer to the front wheels to the normal distribution. As a result, a decrease in turning performance during braking on a low μ road (for example, a snowy road or an icy road) is prevented.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a braking device 1 according to an embodiment of the present invention.

FIG. 2 is a diagram showing distribution of a braking force of a front wheel and a braking force of a rear wheel when regenerative braking is activated.

FIG. 3 is a flowchart illustrating a procedure of a regenerative braking process.

FIG. 4 is a diagram showing a relationship between a time from a start of a brake operation and a wheel speed.

FIG. 5 is a diagram showing a change in distribution of a braking force by friction braking and a braking force by regenerative braking.

[Explanation of symbols]

 Reference Signs List 10 brake pedal 11 stop switch 12a master cylinder (M / C) 12b regulator (Reg) 14 stroke simulator 16a to 16d hydraulic sensor 18 hydraulic actuator 20 brake ECU 22 regenerative braking flag 30 EV ECU 32 motor 40 P / V 52a, 52b , 62a, 62b Wheel cylinders 56a, 56b, 66a, 66b Wheel speed sensor 54a Front left wheel 54b Front right wheel 58 Drive shaft 64a Rear left wheel 64b Rear right wheel 68 Drive shaft

Claims (4)

[Claims] 1. A vehicle braking device capable of controlling frictional braking and regenerative braking, wherein when regenerative braking is activated, VS0-max (VWF
R, VWFL)> a, a determining unit for determining whether or not a first condition is satisfied; and, when the first condition is satisfied, stopping regenerative braking to thereby reduce friction braking and regenerative braking. Control means for shifting the braking to braking only by friction braking; VS0 indicates the estimated vehicle speed; VWFR indicates the wheel speed of the front right wheel; VWFL indicates the wheel speed of the front left wheel;
x (VWFR, VWFL) indicates the maximum value of VWFR and VWFL, and a indicates a predetermined value. 2. The method according to claim 1, wherein the determining unit determines that ΔVS0−max (V
WFR, VWFL)｝ / VS0 × 100> b
It is further determined whether or not the condition is satisfied, and the control means stops regenerative braking when the first condition and the second condition are satisfied, and b indicates a predetermined value. Item 1
A vehicle braking device according to claim 1. 3. The determining means further determines whether a third condition that a braking request value from a driver is equal to or less than a predetermined value and a stop switch is on is satisfied. The vehicle braking device according to claim 1, wherein the control unit stops regenerative braking when the first condition, the second condition, and the third condition are satisfied. 4. The braking device for a vehicle according to claim 1, wherein the control unit stops the regenerative braking by gradually reducing a braking force by the regenerative braking.