JPH10236300A - Braking device for electric vehicle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To simplify braking control at a very slow speed and provide natural operation feeling in an electric car with a mechanical braking mechanism and electric braking mechanism. SOLUTION: When required braking force is smaller than a specified value, braking force (initial friction braking force) is generated only by a friction brake mechanism, i.e., a mechanical braking mechanism. That is, a proportioning valve is provided. This proportioning valve has such properties that when the pressure of a master cylinder(M/C) is smaller than a specified value P1 , M/C pressure and the pressure of a wheel cylinder(W/C) are made same as each other, and when it exceeds the specified value, W/C pressure is not increased or slightly increased compared with an increase in M/C pressure. The specified value P1 of this M/C pressure is determined based on the upper limit of the range of the braking force used when the vehicle runs at a very slow speed. Therefore, while the vehicle runs at a very slow speed, braking force is controlled not by an electric braking mechanism, but by the mechanical mechanism, providing simple control.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a braking device for an electric vehicle having an electric braking mechanism such as a regenerative braking mechanism and a braking mechanism by friction, and more particularly to a braking force intended by a driver or the like. Control when the braking force is small).

[0002]

2. Description of the Related Art An electric vehicle includes a regenerative braking mechanism that converts kinetic energy of a vehicle into electric energy and stores the electric energy during braking, and a friction braking mechanism that converts kinetic energy into thermal energy by friction and dissipates it into the atmosphere. It is common. Regenerative braking is a type of electrical braking in which kinetic energy is converted into electrical energy to perform braking, and the converted electrical energy can be reused, thereby increasing the efficiency of the vehicle. . Further, friction braking is the most common braking method in all fields, not limited to vehicles. When used in automobiles, a mechanism that transmits the driver's braking operation via fluid pressure is generally used,
There is a feature that fine control of the braking force is possible by adjusting the fluid pressure.

As described above, the electric vehicle is provided with two different braking mechanisms, and the distribution of the braking force generated by the two types of braking mechanisms is controlled under predetermined conditions. Japanese Patent Application Laid-Open No. 8-149607 discloses an example of control of a braking device of an electric vehicle having such two types of braking mechanisms. The braking device disclosed in this publication generates regenerative braking force with priority, and when the required braking force cannot be achieved even when the regenerative braking force is generated to the maximum, this shortage is reduced by friction braking. To be generated. In the device described in the above publication, the reason why the fluid pressure as the friction braking transmission means is increased when the operation amount of the braking device is extremely small is to eliminate play of the mechanical braking mechanism. Therefore, at this time, almost no mechanical braking force is generated.

[0004]

In the braking device described in the above publication, when the required braking force is relatively small, the braking force is obtained only by regenerative braking. On the other hand, the rotation of the motor serving as the generator at the time of regenerative braking corresponds to the rotation of the wheels one-to-one, and when the vehicle speed is low, the rotation of the motor is also low, and there is a problem that the braking force tends to fluctuate. . This fluctuation of the braking force leads to deterioration of the operational feeling. In order to cancel the fluctuation of the braking force, that is, it is conceivable to perform a control for supplementing the braking force reduced by the fluctuation with a mechanical braking force. However, the control becomes complicated, and a good operation feeling is given to a driver or the like. The fluctuation cannot be eliminated sufficiently. Further, when controlling the fluid pressure for controlling the mechanical braking force, noise may be generated due to the vibration caused by the solenoid valve or the variation of the fluid pressure.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and it is an object of the present invention to provide a driver with a good braking operation feeling even when the required braking force is low and the motor speed is low. It is an object of the present invention to provide a braking device for an electric vehicle that can be used.

[0006]

SUMMARY OF THE INVENTION In order to achieve the above object, a braking device for an electric vehicle according to the present invention is a braking device for an electric vehicle having an electric braking mechanism and a mechanical braking mechanism. Request braking force determination means for determining whether the braking force is less than a threshold value, and initial braking force generation means for generating an initial braking force only by a mechanical braking mechanism when the required braking force is less than the threshold value. Have.

According to this configuration, when the required braking force is low, the braking force is generated only by the mechanical braking mechanism, so that it is possible to prevent the operational feeling from being deteriorated due to the variation in the electrical braking force. Particularly, just before the vehicle stops, where delicate braking force control is required, a mechanical braking force that is easy to control, that is, has a good response, is used, so that a good operational feeling can be given to the driver and the like. .

[0008]

Embodiments of the present invention (hereinafter, referred to as embodiments) will be described below with reference to the drawings. FIG.
1 is a system outline diagram of the present embodiment. The brake pedal 10 is provided in the vehicle interior, and the driver controls the braking force based on the operation amount of the pedal 10. The operation amount of the brake pedal is converted into a liquid pressure, preferably a hydraulic pressure, by a master cylinder (M / C) 12 mechanically connected to the brake pedal, and the hydraulic pressure is detected by a master cylinder pressure sensor 14. In the present embodiment, the braking force required by the driver is determined based on the detected hydraulic pressure of the master cylinder 12. Hydraulic pressure generated in the master cylinder 12 is transmitted to the drive wheel 18 and the driven wheel 20 via the cooperative control unit 16 by drive wheel wheel cylinders (drive wheels W / C).
22 and a driven wheel wheel cylinder (driven wheel W / C) 24. In these wheel cylinders 22, 24, brake pads are operated by hydraulic pressure, and the wheels 22,
A frictional force is generated between the brake disk 24 and the brake disk that rotates together with the brake disk 24, and this frictional force becomes a braking force.

The driving wheels 18 are driven by a traveling motor 26. At the time of driving, electric power is supplied from a battery 30 to the traveling motor 26 via a motor control unit 28 including an inverter and a motor ECU (motor electronic control unit). Further, at the time of regenerative braking, the running motor 26 functions as a generator under the control of the motor control unit 28, and the generated power is charged in the battery 30.

FIG. 2 shows a specific configuration of the hydraulic circuit of the cooperative control unit 16. The upper end in the figure is connected to the master cylinder 12, and the lower end is connected to the wheel cylinders 22 and 24. As shown in the figure, the hydraulic circuit 32 has a solenoid valve 3 having two phases of communication and cutoff.
4. A proportioning valve (P / V) 36 and a differential pressure valve 38 are connected in parallel. The solenoid valve 34 is shut off when performing regenerative braking.
Further, when only the friction braking is performed without performing the regenerative braking, such as when the charged amount of the battery 30 is the upper limit value, the communication state is controlled. The proportioning valve 36 has a function of transmitting the master cylinder pressure directly to the wheel cylinder until the master cylinder pressure reaches a predetermined pressure, and transmitting no more pressure to the wheel cylinder if the pressure exceeds the predetermined pressure, or transmitting only a very small pressure. Have. This characteristic is shown in FIG. The pressure upstream of the proportioning valve is P
When less than _1, the pressure upstream and downstream of the valve are equal, at a pressure on the upstream side is the value P ₁ or more, an increase in pressure on the downstream side than the increase in pressure on the upstream side becomes small To slight ing. When the pressure difference between the master cylinder 12 and the wheel cylinders 22 and 24 reaches a predetermined pressure, the differential pressure valve 38 has a function of transmitting a pressure exceeding the predetermined pressure to the wheel cylinder. This characteristic is shown in FIG. 3. When the pressure difference between the upstream side and the downstream side is less than P ₂ ′, the pressure on the downstream side is 0, and when the pressure difference becomes more than P ₂ ′, the upstream pressure increases. And the increase in downstream pressure becomes equal.

FIG. 4 shows characteristics relating to the braking force of the present embodiment, particularly the distribution of the mechanical braking force and the electric braking force. Under the condition that regenerative braking is possible, the solenoid valve 34 is in the shut-off state, and the transmission of pressure from the master cylinder 12 to the wheel cylinders 22 and 24 is performed via at least one of the proportioning valve 36 and the differential pressure valve 38. Will be If the pressure in the master cylinder is less than P _1, the transmission of the pressure is made over proportioning valve 36, the frictional braking force corresponding to this pressure is generated. The braking force generated based on the operation of the proportioning valve 36 is hereinafter referred to as an initial friction braking force. Further, the threshold (first threshold value) P ₁ for performing the determination of the pressure P ₁ of the proportioning valve 36 is actuated to generate an initial frictional braking force. On the other hand, at this time, the motor control unit 28 performs control so that regenerative braking is not performed. Accordingly, the braking force the master cylinder pressure is generated when the first less than the threshold P ₁ is generated only by the friction braking force.

When the master cylinder pressure becomes equal to or higher than the first threshold value P ₁ , the proportioning valve 36 hardly transmits the pressure equal to or higher than the first threshold value P ₁ to the wheel cylinders 22 and 24. Therefore, the friction braking force hardly increases any more. Braking force corresponding to the first threshold value P ₁ or the master cylinder pressure is generated by the regenerative braking by the control of the motor controller 28. Therefore, the master cylinder pressure is the first threshold value P ₁ or more, the braking force when it is smaller than the second threshold value P _2, which will be described later, the initial frictional braking force increase and decrease control of the sum and becomes braking force of the regenerative braking force Is performed by increasing or decreasing the regenerative braking force.

[0013] The master cylinder pressure, working pressure P ₂ of the hydraulic pressure P ₁ and the differential pressure valve 38 of the proportioning valve 36
When the difference is equal to or greater than the second threshold value P ₂ (= P ₁ + P ₂ ′), the differential pressure valve 38 is opened, and the pressure is transmitted through this valve. Regenerative braking force at this time is maintained at a value at a second threshold P _2. Therefore, the braking force at this time is the initial friction braking force, the regenerative braking force, and the differential pressure valve 38 due to the action of the proportioning valve 36.
Is the sum of the friction braking forces. In this region, since the initial friction braking force and the regenerative braking force are constant, the braking force increase / decrease control is performed by increasing / decreasing the friction braking force controlled via the differential pressure valve 38.

As described above, in the present embodiment, the cooperative control unit 16 functions as required braking force determination means for determining whether the required braking force is less than the threshold value. The mechanism functions as initial braking force generating means for generating an initial braking force only by the mechanical braking mechanism when the above determination is made. Specifically, the threshold value P ₁ is determined by the proportioning valve 36.
If it is less than the set value, the pressure of the master cylinder 12 is directly transmitted to the wheel cylinders 22, 24, and a braking force is generated only by the friction braking mechanism.

According to the braking force control as described above, under a condition where the vehicle speed is very low, such as immediately before the vehicle stops, etc.
This is an area where the braking force is generated only by the initial friction braking force. In other words, under the above conditions, the first threshold value P _{1 is set} so that the braking force is generated only by the friction braking.
Is set. At extremely low speeds as described above,
Normally, the driver gradually reduces the braking force just before the vehicle stops,
Strict control is performed so as to stop smoothly so as not to cause the so-called Kakkun brake. In the present embodiment, since only the friction braking force acts in this region, sufficient responsiveness to the driver's operation is ensured. Therefore, a good and natural braking feeling can be given to the driver. The master cylinder 12 and the wheel cylinder 2
Since the solenoid valves 2 and 24 are directly connected without the intervention of a solenoid valve or the like and do not perform control of the solenoid valve or the like, there is no generation of operating noise or the like.

The second threshold value P ₂ is a regenerative braking force that can be generated, that is, a master cylinder pressure corresponding to a time when the regenerative braking force reaches a maximum value. By setting as described above, the relationship between the master cylinder pressure and the braking force becomes linear as shown in FIG. 4, and a natural feeling of braking can be achieved.

FIG. 5 shows a specific configuration of the hydraulic circuit of the cooperative control unit 16. The upper end in the figure is connected to the master cylinder 12, and the lower end is connected to the wheel cylinders 22 and 24. As shown, the hydraulic circuit 4
0 is constituted by a variable differential pressure valve 42. By changing the operating pressure of the variable differential pressure valve 42, it is possible to obtain the same characteristics as those of the hydraulic circuit 32 shown in FIG.

Under conditions where regenerative braking is not performed,
If the operating pressure of the variable differential pressure valve 42 is controlled to 0, the pressure of the master cylinder 12 is directly
And a braking force is generated only by the friction braking force.
Further, when the regenerative braking is interrupted when the master cylinder pressure is in the case of the first less than the threshold P ₁ which controls the variable differential pressure valve 42 in an open state, it exceeds the first threshold value P ₁ State. Further, when the master cylinder pressure is equal to the second threshold value P
_{In the case of 2} or more, the cylinder is opened again due to the pressure difference between the master cylinder 12 and the wheel cylinders 22, 24.

In the embodiment having the hydraulic circuit 40 shown in FIG. 5, the cooperative control unit also functions as required braking force determining means for determining whether the required braking force is less than the threshold value. The friction braking mechanism functions as an initial braking force generation unit that generates an initial braking force by only the mechanical braking mechanism when the above determination is made. Specifically, the threshold value is determined by a control set value of the variable differential pressure valve 42. If the control value is less than the set value, the pressure of the master cylinder 12 is directly reduced to the wheel cylinders 22, 24.
And a braking force is generated only by the friction braking mechanism. Therefore, the same effect as in the case of the hydraulic circuit 32 can be obtained.

[Brief description of the drawings]

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

FIG. 2 is a diagram illustrating an example of a hydraulic circuit of a cooperative control unit in FIG. 1;

FIG. 3 is a diagram showing characteristics of a proportioning valve and a differential pressure valve of the hydraulic circuit shown in FIG. 2;

FIG. 4 is a diagram showing a braking force distribution according to the embodiment.

FIG. 5 is a diagram illustrating another example of the hydraulic circuit of the coordination control unit in FIG. 1;

[Explanation of symbols]

10 Brake pedal, 12 Master cylinder, 14
Master cylinder pressure sensor, 16 cooperative control unit (required braking force determination means, control means), 22, 24 wheel cylinder, 26 running motor, 28 motor control unit, 30
Battery.

Claims (1)

[Claims] 1. A braking device for an electric vehicle, comprising: an electric braking mechanism and a mechanical braking mechanism, wherein a braking force distribution of the two kinds of braking mechanisms is determined under predetermined conditions to generate a braking force, Request braking force determining means for determining whether the required braking force is less than a threshold value, and initial braking force generating means for generating an initial braking force only by a mechanical braking mechanism when the required braking force is less than the threshold value ,
A braking device for an electric vehicle having the same.