JPH0553672B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to an anti-skid device that controls the hydraulic pressure of a brake cylinder in order to prevent the slip ratio between the wheels and the road surface from becoming excessive when braking an automobile.

BACKGROUND TECHNOLOGY Brake devices for automobiles guide the brake fluid pressure generated in a master cylinder to the brake cylinder in response to the operation of a brake operating member, and operate a brake such as a drum brake or disc brake to rotate the wheels of the automobile. Hydraulic brake devices are commonly used to suppress this. and,
In this case, the coefficient of friction between the wheels and the road surface is maximum when the slip ratio of both is at a certain value, so in order to decelerate or stop the car most efficiently without compromising the running stability of the car, It is desirable to perform braking while controlling the hydraulic pressure in the brake cylinder so that the slip rate is maintained at the specified value.

Therefore, in recent years, anti-skid devices have come into use that control the hydraulic pressure of brake cylinders while monitoring the slip state of the wheels. this is,
An electromagnetic control valve is provided in the middle of the main fluid passage that connects the master cylinder and the brake cylinder, and this electromagnetic control valve is controlled by a controller that monitors the slip state of the wheels to adjust the hydraulic pressure of the brake cylinder to the friction of the road surface. This is to control the height to be appropriate in relation to the coefficient. Therefore, when the electromagnetic control valve lowers the hydraulic pressure in the brake cylinder, a portion of the brake fluid is released from the brake cylinder to the reservoir, and the brake fluid that has escaped to the reservoir is pumped up and pressurized.
The liquid is configured to be supplied to a portion of the main liquid passage connecting the electromagnetic control valve and the master cylinder via the pump passage. After the anti-skid control starts, the brake cylinder hydraulic pressure is controlled to an appropriate level by the electromagnetic control valve using the pump hydraulic pressure as the pressure source, regardless of the hydraulic pressure generated by the master cylinder. .

When such an anti-skid device is configured such that the pump and master cylinder are in communication with each other during operation, high-pressure brake fluid in the pump passage may flow into or out of the master cylinder depending on the control state of the electromagnetic control valve. This causes the brake operating member such as the brake pedal to be pushed back repeatedly, causing a jerking phenomenon that causes discomfort to the driver.

One way to solve this problem was published in Japanese Unexamined Patent Publication No. 56
-Disclosed in Publication No. 128251. A first check valve that blocks the flow of brake fluid from the solenoid control valve to the master cylinder is installed in the middle of the main fluid passage that connects the master cylinder and the solenoid control valve. A pump passage is connected between the valve and the electromagnetic control valve, and a second check valve is connected in parallel to the series circuit of the check valve and the electromagnetic control valve. The check valve bypasses the electromagnetic control valve and allows brake fluid to flow from the brake cylinder to the master cylinder when the master cylinder fluid pressure becomes lower than the brake cylinder fluid pressure. In such an anti-skid device, the brake fluid in the pump passage is prevented from flowing into the master cylinder during its operation, making it possible to avoid the above-mentioned skid back phenomenon. A problem arises.

Generally, in this type of anti-skid device, when increasing the brake cylinder hydraulic pressure during anti-skid control, the pump discharge pressure is within the expected range because the brake fluid on the pump side is pushed into the brake cylinder using the pressure difference. It is assumed that the pressure is always higher than the brake cylinder hydraulic pressure. and,
The pressure increase rate of the brake cylinder during operation of the anti-skid device is determined by the pressure difference between the pump discharge pressure and the brake cylinder hydraulic pressure. Therefore, when the pump discharge pressure is constant, the pressure increase rate changes depending on the level of the brake cylinder hydraulic pressure. In other words, when the brake cylinder fluid pressure is high, the pressure difference is small, and when it is low, the pressure difference is large, so the pressure increase speed is slow when the brake cylinder fluid pressure is high and fast when it is low, making fluid pressure control difficult. She is pregnant with .

As a means to improve this point, the above-mentioned publication provides a pressure regulating valve (a type of relief valve) that uses the master cylinder hydraulic pressure as the control hydraulic pressure, and the pressure difference between the pump discharge pressure and the master cylinder hydraulic pressure is reduced. An idea has been disclosed in which, when the pressure exceeds a predetermined value, the high-pressure liquid discharged from the pump is discharged into a reservoir to keep the pressure difference between the pump-side liquid pressure and the master cylinder liquid pressure substantially constant. In other words, after anti-skid control has started, it is considered normal for the driver not to press the brake pedal, etc. unnecessarily, so by controlling the pump discharge pressure to correspond to the high or low master cylinder hydraulic pressure. , which attempts to stabilize the pressure increase rate of the brake cylinder and perform accurate hydraulic pressure control.

However, during anti-skid control, the brake pedal etc. may be depressed strongly, and in that case, if the brake cylinder hydraulic pressure is low, a considerably high pump-side hydraulic pressure will be forced into the brake cylinder despite the low hydraulic pressure. Therefore, there remains the problem that the pressure increase rate is not stable.

OBJECT OF THE INVENTION The present invention has been made against the background of the above-mentioned circumstances, and its purpose is to prevent the occurrence of a jerking phenomenon in the brake operating member, and to prevent the brake cylinder from being damaged during anti-skid control. The aim is to provide an anti-skid device with a stable pressure increase rate.

Structure of the Invention In order to achieve the above object, an anti-skid device according to the present invention includes: (a) a brake cylinder installed in the middle of the main fluid passage, based on a command from a controller that monitors the slip state of the wheels; (b) an electromagnetic control valve that controls the hydraulic pressure of the
(c) a reservoir containing brake fluid that is released from the brake cylinder when the electromagnetic control valve lowers the hydraulic pressure in the brake cylinder; (d) a pump that supplies the liquid passage to a portion connecting the electromagnetic control valve and the master cylinder; and (d) a pump provided at the connection portion of the pump passage to the main liquid passage to select between the pump and the master cylinder. (e) connected to an intermediate portion of the pump passage or the main liquid passage connecting the switching valve and the electromagnetic control valve;
By receiving the hydraulic pressure of the brake cylinder as a control hydraulic pressure, when the hydraulic pressure on the pump side becomes higher than a set value due to the brake cylinder hydraulic pressure, the brake fluid is allowed to flow back from the intermediate part of the pump passage or the main liquid passage to the reservoir. It also includes a relief valve that keeps the pressure difference between the pump side hydraulic pressure and the brake cylinder hydraulic pressure almost constant.

Effects of the Invention In the anti-skid device configured as described above, when the anti-skid device is not in operation, only the master cylinder is communicated with the electromagnetic control valve via the switching valve,
When the anti-skid device is in operation, only the pump is communicated with the electromagnetic control valve by switching the switching valve, which prevents the brake fluid supplied from the pump from flowing into the master cylinder, thereby preventing the aforementioned kickback phenomenon. Avoided.

Furthermore, the relief valve receives the brake cylinder hydraulic pressure as a control hydraulic pressure, and the pump side hydraulic pressure is controlled in accordance with the actual brake cylinder hydraulic pressure. In other words, if the brake cylinder hydraulic pressure is high, the pump side hydraulic pressure is also high, and conversely, if it is low, it is lowered.
The pressure difference between the pump side hydraulic pressure and the brake cylinder hydraulic pressure is kept almost constant, and the pressure increase rate when increasing the brake cylinder hydraulic pressure by the pump side hydraulic pressure is stabilized. This makes it possible to control hydraulic pressure with high precision.

Embodiments Hereinafter, embodiments of the present invention will be described in detail based on the drawings.

In FIG. 1, 10 is a master cylinder,
Two mutually independent pressurizing chambers are provided, and the same level of hydraulic pressure is generated in each pressurizing chamber based on the depression operation of the brake pedal 12. The hydraulic pressure generated in one pressurizing chamber is supplied to rear wheel cylinders 18 and 20, which are brake cylinders of brakes provided on left and right rear wheels 14 and 16, respectively. Although not shown, the hydraulic pressure generated in the other pressurizing chamber is supplied to the front wheel cylinders of the brakes provided on the left and right front wheels, respectively, and the hydraulic brake system of this embodiment is It has two systems, front and rear.

A switching valve 22 and an electromagnetic control valve 24 are provided in the middle of the main fluid passage connecting the master cylinder 10 and the rear wheel cylinders (hereinafter simply referred to as wheel cylinders) 18 and 20. The liquid passage is master cylinder side passage 2
6, an intermediate passage 28 and a wheel cylinder side passage 30. Further, between the master cylinder side passage 26 and the wheel cylinder side passage 30, a switching valve 22 and an electromagnetic control valve 2 are provided.
A bypass passage 32 that bypasses 4 is provided,
This bypass passage 32 has a wheel cylinder 18
A check valve 34 whose forward direction is the direction from the 20 side to the master cylinder 10 side is provided.

A reservoir 38 is connected to the electromagnetic control valve 24 via a reservoir passage 36. This reservoir 38
A liquid chamber 44 having a variable volume is formed by disposing a piston 42 as a movable member in a housing 40 in a liquid-tight and slidable manner.
The piston 42 is always urged by a spring 46 in a direction to decrease the volume of the liquid chamber 44.
The brake fluid stored in the fluid chamber 44 is pumped up by a pump 48 and pressurized, and the brake fluid is pumped up and pressurized by a pump passage 50.
The liquid is supplied through the switching valve 22 to an intermediate passage 28 which is a part of the main liquid passage.

The electromagnetic control valve 24 is a switching valve that can be switched to three states: a pressure increase permissible state, a hydraulic pressure holding state, and a pressure drop permissible state. In the pressure increase permissible state, the intermediate passage 28 is connected to the wheel cylinder side passage 30 as shown in the figure.
This is a state in which the hydraulic pressure of the wheel cylinders 18 and 20 is allowed to increase due to the brake fluid supplied from the master cylinder 10 or the pump 48 to the intermediate passage 28. The passage 28, the wheel cylinder side passage 30, and the reservoir passage 36 are all shut off, and the hydraulic pressure in the wheel cylinders 18 and 20 is maintained constant. In addition, the pressure drop permissible state allows the wheel cylinder side passage 30 to communicate with the reservoir passage 36, and the wheel cylinders 18 and 2
This is a condition that allows brake fluid to flow from 0 to reservoir 38 and allows the hydraulic pressure in wheel cylinders 18 and 20 to fall.

The switching of this electromagnetic control valve 24 is performed by the controller 5.
This is done by a command signal from 6. The controller 56 is mainly composed of a microcomputer, and is equipped with a sensor 58 that detects the rotational speed of the left and right rear wheels 14 and 16.
Based on the signal from 8, the left and right rear wheels 14 and 16
The solenoid control valve 24 is switched to any of the three states by estimating the slip state of the solenoid and controlling the supply of current to the solenoid 60 of the solenoid control valve 24, which is a known method.
Further, detailed explanation will be omitted since it is not directly necessary for understanding the present invention.

The controller 56 is also adapted to control a motor 62 that drives the pump 48. That is, when the hydraulic pressure control of the wheel cylinders 18 and 20 by the anti-skid device is started, in other words, when the electromagnetic control valve 24 is switched for the first time from the pressure increase permissible state to the hydraulic pressure holding state or the pressure drop permissible state. The pump 48 is activated and continues to drive the pump 48 while the anti-skid device is in operation.

Brake fluid discharged from the pump 48 is guided to the switching valve 22 as described above. The housing 63 of this switching valve 22 is connected to the master cylinder side passage 2.
6. A valve chamber 64 formed at the connection between the intermediate passage 28 and the pump passage 50, and a piston chamber 66 formed in a portion of the pump passage 50 adjacent to the valve chamber 64.
A spherical valve element 68 is movably housed in the valve chamber 64, and a piston 6 is housed in the piston chamber 66.
9 is slidably fitted. A first valve seat 7 is provided at the opening through which the brake fluid pressure-fed from the master cylinder side passage 26 flows into the valve chamber 64.
0 is formed, and a second valve seat 72 is provided opposite the first valve seat 70, which is connected to the pump passage 50.
An opening is formed through which brake fluid pumped from the valve chamber 64 flows into the valve chamber 64. The valve element 68 is configured to be able to be seated alternatively on the first valve seat 70 and the second valve seat 72. It is biased in the direction of seating on the seat 72.

The piston chamber 66 is divided into a first chamber 80 and a second chamber 82 by a piston 69, and a communication passage 86 having a throttle 84 is formed in the piston 69 in the axial direction. This piston 69 is retracted by a spring 76 in the normal state when the pump 48 is not operating, allowing the valve element 68 to seat on the second valve seat 72, but the brake fluid does not flow from the pump 48. is pumped and flows from the first chamber 80 side through the communication path 86 to the second chamber 82 side, and when a fluid pressure difference is created between the first chamber 80 and the second chamber 82 by the throttle 84, the liquid The valve element 68 is moved forward toward the second chamber 82 by the pressure difference, and is seated on the first valve seat 70 against the biasing force of the spring 76.

On the other hand, a relief valve 9 is provided in the pump passage 50.
0 is connected in parallel to the pump 48, this relief passage has a relief valve 9
0 into an introduction passage 92 connected to the discharge side of the pump 48 and a drain passage 94 connected to the reservoir 38. Furthermore, the relief valve 90 is connected to the electromagnetic control valve 24 by a control passage 96.
It is connected to a wheel cylinder side passage 30 that connects the wheel cylinders 18 and 20 and communicates with the wheel cylinders 18 and 20.

A valve chamber 100 and a piston chamber 102 are continuously formed in the housing 98 of the relief valve 90, a first port 104 and a second port 106 are opened in the valve chamber 100, and a third Port 108 is open. 1st port 10
An introduction passage 92 is connected to the second port 106 to allow the brake fluid pumped from the pump 48 to flow in therein, a drain passage 94 communicating with the reservoir 38 is connected to the second port 106, and a third port 94 which opens into the piston chamber 102 is connected to the second port 106. The port 108 is connected to the wheel cylinder 18.
A control passage 96 communicating with and 20 is connected.

A valve seat 110 is formed at the opening of the first port 104 to the valve chamber 100.
A spherical relief valve element 112 that can be seated and removed from the valve chamber 100 is accommodated in the valve chamber 100. This relief valve element 112 prevents communication between the first port 104 and the second port 106 when seated on the valve seat 110, but the relief valve element 112 prevents communication between the first port 104 and the second port 106. When pushed up from above, the first port 104 and the second port 106 are communicated with each other, and the brake fluid in the pump passage 50 is allowed to flow back to the reservoir 38 via the introduction passage 92, the valve chamber 100, and the drain passage 94. It is.

Behind the relief valve element 112, a control piston 114 is slidably fitted into the piston chamber 102 and is constantly biased by a spring 116 in a direction to press the relief valve element 112 against the valve seat 110. The end surface (pressure receiving surface) of the control piston 114 on the third port 108 side and the piston chamber 1
02, a control chamber 118 is formed, and the hydraulic pressure of the wheel cylinders 18 and 20 is guided to this control chamber 118 via the control passage 96, and the wheel cylinder hydraulic pressure is applied to the pressure receiving surface of the control piston 114. By acting in the same direction as the biasing direction of the spring 116, the control piston 11
4 is adapted to press the relief valve element 112 against the valve seat 110 by the urging force of the spring 116 and the hydraulic pressure of the wheel cylinders 18 and 20. That is, this relief valve 90 receives the wheel cylinder hydraulic pressure as a control hydraulic pressure, so that when the wheel cylinder hydraulic pressure is high, the valve opening pressure (relief pressure) is high, and when the wheel cylinder hydraulic pressure is low, the valve opening pressure is also low. It is a relief valve that opens when the hydraulic pressure in the pump passage 50 (pump discharge pressure) becomes higher than the wheel cylinder hydraulic pressure by more than a set value. Note that the pressure receiving area Sp of the relief valve 112 when pressed against the valve seat 110 and the control piston 114
The pressure receiving areas Sw are made equal to each other.

In the hydraulic brake system with an anti-skid device configured as described above, the switching valve 22 is normally in a state in which the master cylinder side passage 26 is communicated with the intermediate passage 28, and the electromagnetic control valve 24 is in a state in which the master cylinder side passage 26 is communicated with the intermediate passage 28.
8 is in a state of communicating with the wheel cylinder side passage 30. Therefore, master cylinder 10 is communicated with wheel cylinders 18 and 20, but since brake pedal 12 is not depressed, wheel cylinders 18 and 20 are in an inactive state. Further, the piston 42 of the reservoir 38 is at the forward end position, the liquid chamber 44 is at its minimum volume, and the pump 48 is stopped.

When the brake pedal 12 is depressed from this state, the brake fluid from the master cylinder 10 passes through the master cylinder side passage 26, the switching valve 22, the intermediate passage 28, the electromagnetic control valve 24, and the wheel cylinder side passage 30, and then flows to the wheel cylinders 18 and 20.
is supplied to As a result, the brakes are activated, suppressing the rotation of the left and right rear wheels 14 and 16, and decelerating the car. In this case, if the friction coefficient of the road surface is high and the depression force of the brake pedal 12 is small, No problem slipping occurs on the left and right rear wheels 14 and 16, and the controller 56
Since the solenoid control valve 24 is not switched, the brake system operates as if there were no anti-skid system.

However, if the depression force of the brake pedal 12 is large relative to the coefficient of friction of the road surface, the slip ratios of the left and right rear wheels 14 and 16 increase beyond the appropriate range. Therefore, the controller 56 detects this fact via the sensor 58, switches the electromagnetic control valve 24 from the pressure increase permitting state to the hydraulic pressure holding state or the pressure drop permitting state, and simultaneously starts the motor 62.

When the electromagnetic control valve 24 is switched to the hydraulic pressure holding state, the hydraulic pressure in the wheel cylinders 18 and 20 is held constant, but when the electromagnetic control valve 24 is switched to the pressure drop allowing state, the hydraulic pressure in the wheel cylinders 18 and 20 is maintained constant.
Brake fluid escapes from 20 and 20 to reservoir 38, and the hydraulic pressure in wheel cylinders 18 and 20 decreases. At the same time, the brake fluid that has flowed into the reservoir 38 is pumped up by the pump 48,
Since the fluid is supplied to the switching valve 22, a fluid pressure difference is created between the first chamber 80 and the second chamber 82 based on the throttle 84,
The piston 69 moves forward to move the valve element 68 to the second valve seat 7.
2 and seated on the first valve seat 70.
This allows the pump passage 50 to communicate with the intermediate passage 28, but at the same time, the master cylinder side passage 26 is blocked, thereby preventing the brake fluid pumped from the pump 48 from flowing into the master cylinder 10. The occurrence of a jerking phenomenon in which the brake pedal 12 is pushed back is avoided.

After the pump 48 is activated, while the intermediate passage 28 is blocked by the electromagnetic control valve 24, the hydraulic pressure of the brake fluid pumped from the pump 48 rapidly increases. When the hydraulic pressure reaches the opening pressure of the relief valve 90, the relief valve element 112 is moved by the spring 116.
The control piston 114 is pushed back from the valve seat 110 by overcoming the urging force of
4, the brake fluid flows back to the reservoir 38 via the drain passage 94, thereby avoiding overload of the pump 48. In addition, since the hydraulic pressure in the pump passage 50 at this time is sufficiently higher than the hydraulic pressure in the master cylinder side passage 26,
The switching valve 22 maintains a state in which the master cylinder side passage 26 is blocked.

Wheel cylinders 18 and 20 as above
By reducing the hydraulic pressure of the left and right rear wheels 1
If the braking force on the left and right rear wheels 14 and 16 decreases, and the slip rate of the left and right rear wheels 14 and 16 decreases,
This fact is detected by the controller 56 via the sensor 58.
is detected, and the electromagnetic control valve 24 is switched to a hydraulic pressure holding state or a pressure increase allowing state. After the anti-skid device is activated in this way, if the electromagnetic control valve 24 is switched to the pressure increase permitting state and the intermediate passage 28 is made to communicate with the wheel cylinder side passage 30,
The brake fluid pumped from the pump 48 is transferred to the switching valve 2.
2. Wheel cylinder 1 via electromagnetic control valve 24 etc.
8 and 20 and their hydraulic pressures are increased.

The pressure increase rate at this time is determined by how much higher the hydraulic pressure in the pump passage 50 is than the hydraulic pressure in the wheel cylinders 18 and 20, that is, the pressure difference between the two. The wheel cylinder hydraulic pressure Pw fluctuates, for example, as shown by the broken line in the graph in Figure 2. Therefore, if the pump side hydraulic pressure Pp is constant, the pressure difference ΔP between the two is the fluctuation of the wheel cylinder hydraulic pressure Pw. It will vary considerably depending on the width.

However, the wheel cylinder hydraulic pressure Pw is introduced to the relief valve 90 through the control passage 96, and the relief valve element 112 is moved to the valve seat by the biasing force of the spring 116 and the wheel cylinder hydraulic pressure Pw applied to the control piston 114. 110, the wheel cylinder hydraulic pressure
If Pw is high, the relief valve 112 is replaced with the valve seat 110.
The force pressing on the relief valve 11 is correspondingly large, and conversely, if the wheel cylinder hydraulic pressure Pw is low, the relief valve 11
The pressing force acting on 2 also becomes smaller, and the relief pressure is determined by the pressing force. In other words, as shown in FIG.
The pump side hydraulic pressure Pp is controlled so that the pressure difference ΔP between the two is constant. Here, the pressure difference ΔP is determined by the biasing force F of the spring 116, the pressure receiving area Sw of the control piston 114, and the pressure receiving area Sp of the relief valve 112.ΔP=Pw{(Sw/Sp)−1}+F/Sp When Sw≠Sp, it changes according to the fluctuation of the wheel cylinder hydraulic pressure Pw.
Since the pressure receiving area Sw of No. 4 and the pressure receiving area Sp of the relief valve 112 are made equal, the pressure difference ΔP is constant.

By keeping the pressure difference ΔP between the two constant as described above, the rate of pressure increase when increasing the hydraulic pressure in the wheel cylinders 18 and 20 by the pump 48 is almost constant regardless of the level of the wheel cylinder hydraulic pressure Pw. becomes. One reason for this is that it prevents overshoot, which is likely to occur when the high hydraulic pressure on the pump side is pushed in even though the wheel cylinder hydraulic pressure Pw is low. Although it is desirable to push the pump-side hydraulic pressure Pp to a corresponding height, this will lead to an improvement in the problem that the pressure increase rate is slow due to the low pump-side hydraulic pressure Pp.

For example, in the slow increase mode in which the brake fluid from the pump 48 gradually increases the hydraulic pressure in the wheel cylinders 18 and 20, the electromagnetic control valve 24
This can be achieved by alternating between a pressure increase permissible state and a hydraulic pressure holding state for short periods of time. As the wheel cylinder hydraulic pressure increases, the pressure difference between the pump side hydraulic pressure and the wheel cylinder side hydraulic pressure becomes smaller, resulting in a lower pressure increase rate. Misalignment with the pressure increase pattern is likely to occur. On the other hand, in the case of this embodiment, since the pressure increase rate in the slow increase mode is kept almost constant, hydraulic pressure control that closely approximates a predetermined slow increase pattern is possible.

As described above, the brake fluid is supplied from the pump 48 to the wheel cylinders 18 and 20.
As a result of the increased hydraulic pressure on the left and right rear wheels 14 and 16, if the slip ratio between them and the road surface is about to exceed the appropriate range again, the controller 56 detects this fact via the sensor 58. It is detected and the electromagnetic control valve 24 is switched again to the hydraulic pressure holding state or the pressure drop allowing state. Thereafter, the same process is repeated, and the hydraulic pressure in the wheel cylinders 18 and 20 is controlled so that the slip ratio between the left and right rear wheels 14 and 16 and the road surface is maintained around the appropriate value, causing the vehicle to lose its running stability. This means that the vehicle can be slowed down or stopped in the most efficient manner without any problems.

When the vehicle is decelerated to a predetermined constant speed or below or when the brake pedal 12 is released, the controller 56 switches the electromagnetic control valve 24 to a pressure increase permissible state, and the anti-skid device becomes inactive. When the brake pedal 12 is released, the wheel cylinder 18
Brake fluid is returned to the master cylinder 10 from 20 and 20 via a bypass passage 32. Note that since the pump 48 continues to be driven for a certain period of time after that, if brake fluid remains in the reservoir 38, the brake fluid is transferred to the switching valve 22 and the intermediate passage 2.
8, is returned to the master cylinder 10 via the electromagnetic control valve 24, the bypass passage 32, the check valve 34, and the master cylinder side passage 26, and the reservoir 38 returns to its minimum volume state.

Then, when the pump 48 is stopped and the hydraulic pressure in the pump passage 50 decreases, the valve element 6 of the switching valve 22
8 is seated on the valve seat 72 while retracting the piston 69 according to the biasing force of the spring 76, and simultaneously returns to the state in which the master cylinder side passage 26 is communicated with the intermediate passage 28 while blocking the pump passage 50. At this time, the hydraulic pressure remaining in the wheel cylinder side passage 30 due to the opening pressure of the check valve 34 disappears as the brake fluid returns to the master cylinder 10 via this switching valve 22. This prevents brake dragging.

Although one embodiment of the present invention has been described in detail above,
These are literally examples, and the present invention is not limited by these specific descriptions.

For example, in the embodiment described above, the relief valve 90 was connected to the pump passage 50, but instead, as shown in FIG. 4, the switching valve 22 of the main liquid passage and the electromagnetic control valve 24 are connected. It is also possible to connect in the middle of the intermediate passage 28, which is the intermediate portion. The rest of the configuration is exactly the same as the previous embodiment, so some of the drawings are simplified and corresponding symbols are added, but even with this, there is a pressure difference between the pump side hydraulic pressure and the wheel cylinder hydraulic pressure. can be kept almost constant.

In addition, the switching valve 22 may be an electromagnetic switching valve that is switched by turning a solenoid ON or OFF, instead of using brake fluid pressure as the driving force.
In short, any structure that can selectively communicate the master cylinder side passage 26 and the pump passage 50 with the electromagnetic control valve 24 may be used.

Furthermore, regarding the solenoid control valve 24, it may be possible to take the three states mentioned above by combining a plurality of solenoid valves, and the state of maintaining the fluid pressure is not essential, and it is possible to increase the pressure. It can be omitted if it is obtained by a combination of a permissible state and a blood pressure lowering permissible state.

In addition, in the above embodiment, only the hydraulic pressure control of the rear wheel cylinders of the left and right rear wheels was explained, but in reality, the brake hydraulic pressure of the front wheel cylinders is usually also controlled by a similar anti-skid device. In that case, a dedicated anti-skid circuit may be provided for each wheel cylinder of the left and right front wheels, or a shared anti-skid circuit may be provided. This also applies to the respective wheel cylinders 18 and 20 of the left and right rear wheels 14 and 16.

In addition, it goes without saying that the present invention can be practiced with various modifications, improvements, etc. based on the knowledge of those skilled in the art, as long as they do not depart from the spirit of the present invention.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing a part of a hydraulic brake system for an automobile equipped with an anti-skid device, which is an embodiment of the present invention. FIG. 2 is a graph showing the characteristics of the pump-side hydraulic pressure and wheel cylinder hydraulic pressure of the anti-skid device, and FIG. 3 is a graph showing a gradual increase mode of the wheel cylinder hydraulic pressure in comparison with a conventional example. FIG. 4 is a circuit diagram showing a part of a hydraulic brake system for an automobile equipped with an anti-skid device according to another embodiment of the present invention. 10: Master cylinder, 18, 20: Rear wheel cylinder, 22: Switching valve, 24: Solenoid control valve, 26: Master cylinder side passage, 28: Intermediate passage, 30: Wheel cylinder side passage, 32: Bypass passage, 34: Check valve, 36: Reservoir passage,
38: Reservoir, 40: Housing, 48: Pump, 50: Pump passage, 56: Controller, 6
8: Valve, 69: Piston, 70: First valve seat,
72: Second valve seat, 84: Throttle, 86: Communication path,
90: relief valve, 92: introduction passage, 94: drain passage, 96: control passage, 104: first port,
106: Second port, 108: Third port, 11
0: Valve seat, 112: Relief valve element, 114: Control piston, 116: Spring.

Claims (1)

[Scope of Claims] 1. A vehicle comprising a master cylinder that generates brake fluid pressure in response to the operation of a brake operating member, and a brake cylinder that operates with the fluid pressure generated by the master cylinder to suppress rotation of the wheels of an automobile. In a hydraulic brake system for an automobile, the hydraulic brake system includes a brake that is connected to the brake cylinder, and a main fluid passage that connects the master cylinder and the brake cylinder. An anti-skid device for controlling hydraulic pressure, which is installed in the middle of the main liquid passage and controls the hydraulic pressure of the brake cylinder to an appropriate level based on a command from a controller that monitors the slip state of the wheels. a reservoir for accommodating brake fluid that is released from the brake cylinder when the solenoid control valve lowers the hydraulic pressure in the brake cylinder; and a reservoir for pumping and pressurizing brake fluid from the reservoir and pumping the brake fluid through a pump passage. a pump that supplies a portion of the main liquid passageway that connects the electromagnetic control valve and the master cylinder; and a pump that is provided at a connection portion of the pump passageway to the main liquid passageway that selectively connects the pump and the master cylinder. a switching valve that communicates with the electromagnetic control valve; and a switching valve that is connected to an intermediate portion of the pump passage or the main fluid passage that connects the switching valve and the electromagnetic control valve, and that controls the hydraulic pressure of the brake cylinder as a control hydraulic pressure. When the pump side hydraulic pressure becomes higher than the brake cylinder hydraulic pressure by more than a set value, the brake fluid is allowed to flow back from the pump passage or the middle part of the main liquid passage to the reservoir, and the pump side hydraulic pressure is increased. An anti-skid device characterized by comprising a relief valve that maintains a substantially constant difference between brake cylinder hydraulic pressure. 2. The relief valve includes: a first port through which brake fluid pumped from the pump can flow; a valve chamber in which a second port communicating with the drain passage to the reservoir opens; and a third valve chamber communicating with the brake cylinder. a piston chamber in which a port opens; a valve seat formed at a first port of the valve chamber; and the brake, which is normally seated on the valve seat to prevent communication between the first port and the second port. a relief valve that, when pushed up from the valve seat by the hydraulic pressure of the fluid, communicates the first port and the second port and allows the brake fluid to flow back to the reservoir via the drain passage; and the piston. It is slidably fitted into the chamber and receives the brake cylinder hydraulic pressure led from the third port, and is biased by a spring in the same direction as the brake cylinder hydraulic pressure, and the biasing force of these springs and the brake cylinder hydraulic pressure are 2. The anti-skid device according to claim 1, further comprising a piston for pressing said relief valve element against said valve seat. 3. A pressure increase permitting state in which the electromagnetic control valve communicates the brake cylinder with the master cylinder, a fluid pressure holding state in which communication with the master cylinder is cut off, and a pressure decreasing state in which the electromagnetic control valve cuts off communication with the master cylinder and communicates with the reservoir. Claim 1 or 2 which is switchable between the permissible state and the permissible state.
Anti-skid device as described in Section 1.