JPH04244470A - Brake device for automobile - Google Patents

Abstract

PURPOSE:To reduce the size of a boosting device for a hydraulic brake. CONSTITUTION:A piston 23 of a master cylinder M on which the press force of a brake pedal 41 is exerted is pressed by means of a piezoelectric element 34 for boosting. An operation amount of the brake pedal 41 is fetched as the detecting voltage of a different piezoelectric element 35 and a voltage responding to the detecting voltage is applied on the piezoelectric element 34 for boosting.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a braking system for a motor vehicle.

0002

2. Description of the Related Art Automobile brakes or braking devices for decelerating or stopping an automobile are generally of the hydraulic type. That is, when the driver presses the brake pedal with his/her foot, brake fluid pressure is generated in the master cylinder as a brake fluid pressure generation source, and this brake fluid pressure is applied to each wheel. Braking force is transmitted to wheel cylinders such as disc brakes and drum brakes, and applies braking force to each wheel. Such a hydraulic brake is not only convenient for obtaining sufficient braking force, but is also advantageous in terms of reliability, brake feeling, etc.

On the other hand, recently, it has been proposed to use piezoelectric elements instead of hydraulic brakes, especially from the viewpoint of performing ABS control and traction control with good response (Japanese Patent Laid-Open No. 63-266266). (see official bulletin). The system described in this publication incorporates a piezoelectric element into the caliper of a disc brake, and controls the duty of this piezoelectric element to generate a force corresponding to the mechanical displacement of the piezoelectric element, which is obtained according to the duty ratio. This presses the friction pad. In other words, all the brakes used to slow down or stop the car are electronically controlled, and when the driver depresses the brake pedal, an electrical signal corresponding to this depressing is extracted as a brake request signal. Accordingly, a control signal (duty ratio) for the piezoelectric element is determined so that a braking force corresponding to the brake request signal can be obtained. This piezoelectric element is extremely excellent in that its mechanical displacement changes extremely quickly with respect to voltage changes and satisfies responsiveness.

However, in the above publication,
Since the brake pedal and the friction pad are only electrically coupled via a piezoelectric element, this poses a major problem in terms of reliability. In particular, since the brake is an important safety component, if it is electronically controlled as described above, there is no fail-safe function.
However, it is difficult to set it up. In addition to this, not only during slip control but also during normal braking.
The braking force when braking is also obtained using a piezoelectric element, but the braking force is also obtained by using a piezoelectric element.
It is difficult to obtain a braking force, and it is also difficult to apply a braking reaction force to the driver. Even if this point could be satisfied, the overall control would be extremely complicated.

[0005]

By the way, in hydraulic brakes, a booster is often used to reduce the brake operation force by the driver. Most of these boosters are so-called vacuum boosters that utilize the differential pressure between the engine's intake negative pressure and atmospheric pressure. In this case, in order to utilize the above-mentioned differential pressure, a diaphragm with a considerably large diameter must be used, resulting in an increase in size. SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a brake system for an automobile in which a booster in a hydraulic brake system can be extremely downsized.

[0006]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention has the following configuration. That is, the depression force of the brake pedal is transmitted to the piston of the master cylinder, and the brake is activated within the master cylinder. The braking device for an automobile is configured to generate brake hydraulic pressure, and includes operation state detection means for detecting the operation state of the brake pedal, and a piezoelectric element as a drive source, and an auxiliary device for generating brake fluid pressure on the piston. The brake pedal is configured to include boosting means for applying force, and control means for controlling the voltage applied to the piezoelectric element in accordance with the operating state of the brake pedal detected by the operating state detecting means.

[0007]

[Effect of the invention] As described above, in the present invention, the brake
According to the operation state of the brake pedal, that is, the amount or force of operation of the brake pedal, a boosting effect is obtained by the piezoelectric element. Furthermore, since the piezoelectric element used for boosting can be extremely small, the booster as a whole can be significantly downsized. Furthermore, since a piezoelectric element is used, the boosting response is also excellent. Furthermore, when performing ABS control or traction control, there is an advantage that the boosting piezoelectric element can be used as is, that is, by adjusting the degree of boosting. Of course, the above-mentioned advantages can be obtained without sacrificing any of the advantages of hydraulic brakes. Note that when the ignition switch is turned off, it is recommended to prohibit the application of voltage to the piezoelectric element to reduce power consumption (no boosting effect), but the car may move slightly immediately after the ignition switch is turned off. It is preferable to allow the voltage to be applied to the piezoelectric element until a predetermined period of time has elapsed after the ignition switch is turned off (with boosting effect).

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Examples of the present invention will be described below with reference to the accompanying drawings. In FIG. 1, M is a master cylinder as a brake hydraulic pressure generation source. This master cylinder M is of a tandem type, and two pistons 2 and 3 are fitted into the cylinder 1 in series with each other. A liquid chamber 6 is defined in front of the piston 2 (left side in the figure), and both pistons 2
A liquid chamber 7 is defined between and 3. The piston 2 is biased by a spring 4, and the rear piston 3 is biased by a spring 5 in the right direction in the figure, that is, in the direction of releasing the brake fluid pressure. In the figure, reference numerals 10 and 11 indicate reservoir tanks. Near the position where the pistons 2 and 3 are most retracted, the reservoir tank 10 communicates with the liquid chamber 6 through the connection port 12, and the reservoir tank 11 communicates with the liquid chamber 6 through the connection port 13. It communicates with the liquid chamber 7 via.

Reference numeral 21 is a front wheel, and 22 is a rear wheel, each of which is equipped with a disk brake. These disc brakes 21 and 22 consist of a caliper 22 or 26 and a wheel cylinder 2 formed on the caliper.
3 or 27. The wheel cylinder 23 is connected via a brake pipe 24 to a connection port 8 that is always open to the liquid chamber 6. Moreover, the wheel cylinder 27 is
It is connected via a brake pipe 28 to a connection port 9 that is always open to the liquid chamber 7. In addition, brake piping 2 on the rear wheel side
8 is connected to a known proportioning valve 29.

In the figure, BB is a booster. This booster BB has a case 31 fixed to the vehicle body.
The rear end of the master cylinder M is bolted to the front surface of the housing 31. A pressing rod 32 is disposed within the case 31 so as to be movable in the left and right directions in the figure. The tip of the pressing rod 32 faces the rear end surface of the rear piston 3 so as to be able to come into contact with it. Further, the rear end portion of the pressing rod 32 is connected to a brake pedal 41 via an intermediate rod 42.

A pressure receiving plate 33 is fixed to the pressing rod 32 at an axially intermediate portion thereof. This pressure receiving plate 3
A first piezoelectric element 34, which serves as a boosting drive source, is interposed between the rear surface of the case 31 and the rear surface of the case 31. In addition, the pressure receiving plate 33
A second piezoelectric element 35, which is biased backward by a spring 36, is in contact with the front surface of the second piezoelectric element 35. Both piezoelectric elements 3
4 and 35 are actually made by laminating a plurality of piezoelectric elements, but the number of laminated elements is increased because the first piezoelectric element 34 serves as a drive source for boosting power. Note that each piezoelectric element 34 or 35 may be of an annular integral type,
Alternatively, the pressure rod 32 may be configured as divided pieces arranged at equal intervals in the circumferential direction.

Reference numeral U in FIG. 1 is a control unit configured using a microcomputer, and this control unit U receives a voltage signal from the second piezoelectric element 35 and an ON/OFF signal of the ignition switch IG. is input, while the control unit U outputs the signal to the first piezoelectric element 34.

Next, the operation of the above configuration will be explained. Now, when the driver depresses the brake pedal 41, a mechanical displacement corresponding to the amount of depression of the brake pedal 41 is generated via the intermediate rod 42 and the pressing rod 32.
It is transmitted to the rear piston 3 of the master cylinder M. As a result, the rear piston 3 is pushed forward and the front piston 2 is also pushed forward. During the forward displacement of both the pistons 3 and 2, the communication with the reservoir tanks 10 and 11 is cut off, and due to the further forward pressing displacement of both the pistons 3 and 2 after this cutoff, Brake hydraulic pressure is generated at 7 and 7. And liquid chamber 7
Alternatively, the brake fluid pressure generated at step 8 is transmitted to the wheel cylinder 23 or 27 to apply braking force to the wheels.

The amount of forward displacement of the pressing rod 32 is
This appears as the magnitude of the output voltage of the piezoelectric element 35. The control unit U that receives the voltage signal from the second piezoelectric element 35 applies a voltage corresponding to the voltage signal to the first piezoelectric element 34 . As a result, the first piezoelectric element 34 expands (expands), and the pressing rod 32 is pressed forward by the first piezoelectric element 34 . In this way, the boosting action by the first piezoelectric element 34 is performed.

FIG. 2 is a flowchart showing the contents of control by the control unit U described above. That is,
At P (step - the same below) 1, the second piezoelectric element 35
After the output voltage VO is read, at P2, the applied voltage VA corresponding to the voltage VO is determined with reference to the map shown in FIG. 3, and at P3, the voltage VA is output to the first piezoelectric element 34. .

[0016] At P4, the evening switch is OFF.
It is determined whether or not F is applied. With this P4 determination, N
If it is O, it is returned as is. P4 judgment: YES
In the case of S, it is determined in P5 whether a predetermined period of time has elapsed since the ignition switch was turned off. If the determination at P5 is NO, the process returns, but when the determination at P5 is YES, the control ends. Processing of P4 and P5 is performed when the ignition switch is OFF.
Immediately after F is applied, the boosting effect is obtained considering that the car is not completely stopped, and after this, there is no boosting effect from the perspective of preventing power consumption. It is.

Although the embodiment has been described above, the voltage applied to the first piezoelectric element 34 may be determined in accordance with the depression force of the brake pedal 41. Further, when performing slip control, it can be achieved by, for example, duty control of the voltage applied to the second piezoelectric element 34.

[Brief explanation of the drawing]

FIG. 1 is an overall system diagram showing one embodiment of the present invention.

FIG. 2 is a flowchart showing a control example of the present invention.

FIG. 3 is a diagram showing a map used in a control example of the present invention.

[Explanation of symbols]

U Control unit M Master cylinder BB Booster 1 Cylinder 2 Piston 3 Piston 6 Liquid chamber 7 Liquid chamber 23 Wheel cylinder 27 Wheel cylinder 31 Case 32 Pressing rod 33 Pressure receiving plate 34 First piezoelectric element (drive source) 35 Second piezoelectric element (brake operation amount detection) 41
Brake pedal 42 intermediate rod

Claims (2)

[Claims] 1. A braking device for an automobile, which transmits the depression force of a brake pedal to a piston of a master cylinder to generate brake fluid pressure within the master cylinder, wherein the operating state of the brake pedal is an operation state detection means for detecting an operation state; a booster means for applying an auxiliary force to the piston for generating brake hydraulic pressure using a piezoelectric element as a drive source;
A braking device for an automobile, comprising: control means for controlling a voltage applied to the piezoelectric element according to the operating state of the brake pedal detected by the operating state detecting means. 2. The piezoelectric element according to claim 1, wherein voltage application to the piezoelectric element is allowed until a predetermined time has elapsed after the ignition switch is turned off, and voltage application is prohibited after the predetermined time has elapsed.