JPH048656A - Brake circuit provided with antilock device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a brake circuit equipped with an anti-lock device, and more specifically to a brake circuit equipped with an anti-lock device, which discharges hydraulic fluid from a wheel brake into a recirculation path during an anti-lock operation, and a brake circuit provided in the recirculation path. In a recirculation type anti-lock device in which the pump causes the flow to flow back to the master cylinder, this device prevents the pump pulsation from being transmitted to the master cylinder when the pump is in operation.

BACKGROUND OF THE INVENTION Conventionally, in this type of recirculation type anti-lock device, a) a main flow path is branched from the main flow path connecting the master cylinder and the wheel brake, and the flow path is connected to the main flow path on the upstream side of this branch point (i.e., on the master cylinder side). a recirculation path that returns the hydraulic fluid to a certain return point; b) a pump installed in the recirculation path that recirculates the hydraulic fluid; and C) braking of the wheel brakes by discharging the hydraulic fluid from the branch point to the recirculation path. Adopts a system that has a pressure regulating means that reduces the pressure and also supplies hydraulic fluid from the main flow path downstream of the return point to the wheel brakes via the branch point to increase the brake pressure of the wheel brakes. are doing.

In the device that employs the above-mentioned reflux type, for example, as the pressure regulating means, an electromagnetically operated normally open liquid pressure supply valve is provided in the main flow path between the return point and the branch point, and A normally closed hydraulic pressure discharge valve operated by electromagnetism is installed in the return path between the pump and the brake hydraulic pressure during anti-lock operation. is under control.

However, in the above-mentioned recirculation type anti-lock device, the hydraulic fluid discharged from the wheel brake when the anti-lock pressure is reduced is returned to the master cylinder side by the pump, so it is susceptible to brake pedal vibration and piping system vibration due to pump pulsation. Problems such as noise are occurring.

Various methods have been proposed to reduce the transmission of the pump pulsation to the master cylinder side. For example, a method of providing a throttle between the pump discharge port and the return point, and providing a buffer chamber having a large area between the throttle and the pump discharge port (
West German patent application N.

No. 2643860), a method in which a check valve means is provided between the return point and the master cylinder with the side from the master cylinder toward the return point being the forward direction, and the pump discharge pressure is not transmitted to the master cylinder side (Japanese Patent Publication No. 56-142733 (Japanese Patent Publication No. 61-16656) and a piston that receives the pump discharge pressure, the piston is moved during pump operation to communicate between the master cylinder and the return point via a throttle, and the pump pulsation is mastered. A device (Japanese Utility Model Application No. 63-98869) has been proposed in which the signal is not transmitted to the cylinder side.

Problems to be Solved by the Invention However, the previously proposed methods for preventing transmission of pump pulsation described above have various problems.

In other words, in the method of the above-mentioned West German patent, the entire amount of pump discharge passes through the throttle, which increases the pump discharge pressure before the throttle, increasing the load on the pump. There are problems such as the oxidation and the need for end plugs, etc. Furthermore, the method disclosed in Japanese Patent Publication No. 56-142733 requires an accumulator between the pump discharge pressure and the check valve, resulting in problems such as increased size and cost.

Furthermore, the method disclosed in Japanese Utility Model Application No. 63-68869 has the disadvantage that the piston moves during normal braking, increasing the stroke of the brake pedal, and the structure is complicated, resulting in high cost.

The present invention aims to solve the above-mentioned problems by providing a device that effectively suppresses the pulsation of the pump from being transmitted to the master cylinder. This prevents an increase in the pedal stroke, an increase in the size of the device, and an increase in cost.

Means for Solving the Problems Accordingly, the present invention separates the master cylinder from the main flow path connecting the wheel brake, and connects the main flow path from a first return point upstream of this branch point (i.e., on the master cylinder side). a reflux path for refluxing the working fluid; a pump provided in the reflux path for refluxing the working fluid; In a brake circuit equipped with an anti-lock device having a pressure regulating means for increasing the brake pressure of the wheel brakes by supplying hydraulic fluid from the road to the wheel brakes, there is a brake circuit between the master cylinder side of the main flow path and the return point. A first port that is interposed and communicates with the master cylinder side of the main flow path; a second port that communicates with the reflux path on the pump discharge side and the main flow path; and a second port that communicates with the first port. Also, a first liquid chamber equipped with a check valve whose forward direction is from the master cylinder side toward the first return point, and a first liquid chamber communicated with the first liquid chamber via a connecting flow path, and the second liquid chamber is connected to the first liquid chamber through a connecting passage. a second liquid chamber that communicates with the port; a throttle bypass flow path having a constriction portion that bypasses the first liquid chamber and communicates the first port with the second liquid chamber; A valve body is provided that is freely housed and is locked in one direction by spring pressure, and an actuation rod protruding from one end surface of the valve body allows the valve inside the first liquid chamber to be held in place by the spring force. At the same time as opening the check valve, when the brake pressure of the wheel brake is reduced (that is, when the anti-lock pressure is reduced), the pressure of the pump discharge fluid flowing from the second port is used to move the valve body against the spring force. A flow path area switching valve configured to move to close the check valve and cause the pump discharge liquid to flow out to the first port side through the throttle bypass flow path to reduce the area of the main flow path. The present invention provides a brake circuit equipped with an anti-lock device.

Note that the second port described above may be connected upstream of the return point, or the second liquid chamber may be configured as the return point.

Further, the second liquid chamber is communicated with a third port that communicates with the main flow path downstream of the flow rate control valve of the pressure regulating means and a fourth port that is connected to the wheel brake. It is preferable to communicate with the port through a housing for a spring that biases the valve body, so that spring pressure and hydraulic pressure act on the valve body during normal brake operation.

Function As mentioned above, when the anti-lock pressure is reduced, the pressure of the pump discharge fluid flowing in from the second port moves the valve body against the spring force and closes the check valve. flows out to the first port side through the throttle bypass flow path, so it is possible to reduce the pulsation of the pump transmitted to the brake pedal via the master cylinder.

Next, the present invention will be described in detail based on embodiments shown in the drawings.

In Fig. 1, ■ is a brake pedal, 2 is a master cylinder that operates according to the pressing force of brake pedal l, 3 is a wheel brake, Ll is a main flow path connecting the master cylinder 2 and wheel brake 3, and L2 is a main flow path. A return flow path that branches from L1 at a branch point Pi and joins the main flow path Ll at a first return point P2 on the upstream side of the branch point P1 (i.e., on the master turn cylinder 2 side), and L3 is a branch point of the main flow path Ll. A bypass flow path 4 branches from downstream of PI (i.e., on the wheel brake 3 side) and joins the main flow path Ll at a second return point P3 upstream of the first return point P2 of the main flow path L1; A flow rate control valve provided at the branch point P1 of the path Ll, 5 a solenoid valve provided in the recirculation path L2, 6 a pump for hydraulic fluid recirculation provided between the solenoid valve 5 and the first return point P2 in the recirculation path L2; 7 is the main flow path L
This is a flow path area switching valve provided at 1.

The flow path area switching valve 7 is interposed between the second return point P3 and the first return point P2 of the main flow path Ll.

As shown in detail in FIG. 2(A), the structure of the flow path area switching valve 7 includes a housing 8 having a liquid chamber 9 consisting of a first liquid chamber 9a with a small volume and a second liquid chamber 9b with a large volume. The first of these
The second liquid chambers 9a and 9b are communicated with each other by a connecting channel 9C. A first port 8a communicating with the main flow path Ll on the master turn cylinder 3 side is provided on the upper end surface of the housing 8 in the figure.
The first port 8a communicates with the first liquid chamber 9a on the opposite side of the connection channel 9C. Further, the housing 8 has a first port 8a connected to the second port by bypassing the first liquid chamber 9a.
A throttle bypass channel 13 connected to the liquid chamber 9b is provided, and the cross-sectional area of the throttle section 13a of the throttle bypass channel 13 is 0.1 to 0.3 mm with respect to the main flow channel L (the main flow channel Ll is φ3 mm,
The aperture part 13a has a diameter of 0.8 to 0.5 mm and a ratio of 1:0.
17 to 0.26).

The first liquid chamber 9a has a cylindrical shape, and the side connected to the connection flow path 9C is conically tapered to form a valve seat 9d, and a ball forming a check valve is placed inside the first liquid chamber 9a. The valve seat 9d is opened and closed by the ball IO. The ball 10
is one end of the actuating rod 11 which is biased in a direction to close the valve seat 9d by a first spring 12 disposed on the first port 8a side and is fixed to a valve body 15 housed in a second liquid chamber 9b, which will be described later. When the actuating rod 11 rises in the figure, the valve seat 9d opens against the force of the first spring 12.

The second liquid chamber 9b has a substantially cylindrical shape, and has a second port 8b opened in a side wall portion on the upper end side in the figure that communicates with the connecting flow path 9c, and a third port 8c in one side wall portion on the lower end side. A fourth port 8d is opened in the side wall. Said second port 8b
is connected to the upstream side of the first return point P2 of the main flow path Ll, the third port 8c is connected to the downstream side of the flow rate control valve 4 of the main flow path Ll, and the fourth port 8d is connected to the downstream side of the first return point P2 of the main flow path Ll. It is connected to the wheel brake 3 side, and the third port 8c and the fourth port 8d are arranged opposite to each other on both side walls of the upper end of the second liquid chamber 9b.

A valve body 15 is slidably fitted into the second liquid chamber 9b, and an O-ring 16 attached to the side surface of the valve body 15 allows
Inside the second liquid chamber 9b, the second port 8b side and the third and fourth ports 8c and 8d sides are isolated in a normal state. Valve body 15
, a first outer circumferential groove 15a is provided by notching the outer circumferential surface of the upper end on the second port 8b side, and a recess 15b is formed in the center of the upper end surface, and the recess 15b and the first outer circumferential groove 1 are formed in the center of the upper end surface.
5a through a radial flow path 15c.

The actuating rod 11 is vertically fixed to the bottom of the recess 15b, and the actuating rod 11 is inserted into the connecting channel 9c with a gap and protrudes into the first liquid chamber 9a, as described above. A ball 10 is fixed to its tip. On the other hand, the third and fourth ports 8c of the valve body 15.

On the 8d side, a second outer circumferential groove portion 15d is formed by cutting out the outer circumferential portion of the lower end.
In addition, the spring receiver is provided with a recess 15e in the center of the lower end surface. A second spring 17 is inserted into the spring receiver between the recess 15e and the bottom of the second liquid chamber, and the second spring 17 urges the valve body 15 upward in the drawing. The spring force of the second spring 17 is set to be greater than the spring force of the first spring 12, and the lower part of the second liquid chamber 9b housing the second spring 17 is connected to the third port 8c and the fourth port 8d. Since the hydraulic fluid is allowed to flow through the valve body 15 , the sum of the biasing force by the second spring 17 and the pressure of the hydraulic fluid is applied to the valve body 15 in opposition to the first spring 12 . Therefore, except during anti-lock when the pump discharge hydraulic pressure flowing in from the second port 8b acts on the valve body 15,
The upper end surface of the valve body 15 is locked to the earthen wall of the second liquid chamber 9b, the ball IO opens the valve seat 9d, and the large flow path passing through the first liquid chamber 9a is connected to the master cylinder side and the first return side. The main flow path Ll is formed between the points P2. On the other hand, when the pump discharge pressure flowing from the second port 8b is large during anti-lock pressure reduction, from the first outer circumferential groove 15a to the flow path 15.
The valve body 15 is pushed down by the hydraulic pressure flowing into the recess 15b through the valve 15, the ball 10 closes the valve seat 9d, the second port 8b communicates with the first port 8a through the throttle bypass channel 13, and the master cylinder A small-area flow path is formed between the main flow path L1 between the side and the return point P2.

The solenoid valve 5 installed in the recirculation path L2 is normally closed, and is automatically opened by electromagnetic operation when the anti-lock pressure is reduced, and the hydraulic fluid is recirculated from the wheel brake 3 via the flow path area switching valve 7 and the flow rate control valve 4. Road L2. The pressure of the wheel brakes 3 is reduced.

On the other hand, when the brake pressure is reapplied, the solenoid valve 5 closes.
While blocking discharge to the reflux path L2, hydraulic fluid is supplied from the main path L1 to the wheel brakes 3 via the flow path area switching valve 7 and the flow rate control valve 4 to pressurize the wheel brakes 3, The flow rate control valve 4 and the solenoid valve 5 constitute a hydraulic fluid pressure regulating means.

A reservoir 20 is provided downstream of the electromagnetic valve 5 in the reflux path L2.
is installed, and the above-mentioned pump 6 driven by a motor 21 is installed downstream of the reservoir 20. Second and third check valves 22 and 23 are provided between the pump 6 and the reservoir 20 and between the pump 6 and the first return point P2, respectively, and the working fluid discharged into the return path L2 is diverted from the branch point PI to the first return point P2. The water is circulated only in the direction of the return point P2.

Upper Mc! The flow rate control valve 4 constituting the pressure regulating means is shown in FIG.
), a hole 3 drilled in the housing 30.
A spool 31 is fitted into the spool 0a so as to be slidable in the axial direction. The second port 1-8 of the flow path area switching valve 7 is connected to the side surface of the hanging 30 via the main flow path L1 on the side of the first return point P2.
b, the flow paths 30c and 30d branch from the inlet 30b and communicate with the hole 30a, the first outlet 30e connects to the third port 8c of the flow path area switching valve 7, and the first outlet 30e connects to the reflux path L2. A second outlet 30f is provided, and flow paths 30g and 30h branched from the second outlet 30f and connected to the hole 30a.

The spool 31 is provided with an outer circumferential groove 31a on its side surface, and holes opened at both end surfaces along the axis through an orifice 32, thereby forming a pressurizing chamber 31b and a depressurizing chamber 31c. The decompression chamber 31c has a spring 3
3 is compressed to urge the spool 31 upward in the figure.

Since the flow rate control valve 4 has the above-described configuration, the spool 33 is in the position shown in FIG. 31a1, a large flow path is formed to be sent to the wheel brake 3 side via the first outlet 30e.

In addition, a first check valve I9 whose forward direction is in the direction of the master cylinder 2 is interposed in the bypass passage L3, so that the working fluid flows only from the wheel brake 3 side to the master cylinder 2 side. .

Next, the operation of the above embodiment will be explained.

First, during normal brake operation, that is, when anti-lock is not applied, in the flow passage area switching valve 7, the valve body 15 is attached to the first spring I2 and the second spring 17, as shown in FIG. 2(A). Due to the difference in force, the valve is locked to the earthen wall of the second liquid chamber 9b as shown in the figure, the pole IO opens the valve seat 9d, and the first liquid chamber 9a and the second liquid chamber 9b are in communication. . Therefore, a large flow path from the first port 8a to the first liquid chamber 9a to the connecting flow path 9c to the recessed portion 15b to the flow path 15c to the first outer periphery PT portion 15a to the second port 8b is secured, and the depression force of the brake pedal I is Hydraulic fluid corresponding to
From there, it is sent to the flow rate control valve 4 through the flow path area switching valve 7. Further, on the second liquid chamber 9b side, a large flow path connecting the third port 8c and the fourth port 8d is secured, and the hydraulic fluid is sent from the first outlet 30e of the flow control valve 4 to the third port 8c. is sent to the wheel brake 3 via the fourth port 30d. At this time, the pressure of the hydraulic fluid acts to push the valve body I5 upward in the figure, similar to the second spring 17 described above.

On the other hand, in the flow rate control valve 4, a large flow path is ensured as shown in FIG.
The hydraulic fluid sent from b flows into the inlet 30b, flows out from the first outlet 30e, and enters the third port 8 of the flow path area switching valve 7.
Sent to c.

As described above, during normal brake operation, a large flow path is ensured in the flow path area switching valve 7, so problems such as delay in brake effectiveness and delay in brake return do not occur.

During anti-lock pressure reduction, the solenoid valve 5 is opened, and the hydraulic fluid in the pressure reduction chamber 31c of the flow control valve 4 flows through the flow path 30g to the second
It is discharged from the outlet 30f to the reflux path L2 side, and flows into the reservoir 20 via the solenoid valve 5.

In the flow rate control valve 4, due to the outflow of the working fluid from the pressure reducing chamber 31c, a pressure difference is generated between the two ends of the spool 31 with the orifice 32 as a boundary, and the spool 31 is moved as shown in FIG. 3(B). Move downward. Therefore, the outer circumferential groove portion 31a
The edge 31d blocks communication between the outer circumferential groove 31a and the inlet 30b, and closes the large flow path. Furthermore, spool 3
1 moves downward in the figure as shown in Figure 3 (C),
A depressurizing flow path is formed from the first outlet 30e to the outer circumferential groove 31a to the flow path 30h to the second outlet 30f. In the reduced pressure channel,
The flow rate is controlled according to the open state of the flow path 30h by the edge 31e, and the hydraulic fluid is discharged from the wheel brake 3 to the recirculation path L2. The working fluid discharged into the reflux path L2 is stored in the reservoir 20, and is then refluxed from the reflux path L2 to the first return point P2 as pump discharge liquid by the pump 6 driven by the motor 21, and then flows from the return point P2. Road area switching valve 7
side and the flow control valve 4 side.

At this time, in the flow path area switching valve 7, since the inlet 30b of the flow rate control valve 4 is closed as described above, the pump discharge liquid discharged from the pump 6 flows into the second liquid chamber 9b from the second port 8b. , the pressure on the second port side of the second liquid chamber 9b increases. In the second liquid chamber 9b, first, the liquid flows from the first outer circumferential groove 15a through the flow path 15c and into the recess 15b, and the valve body 15 is lowered against the biasing force of the second spring 17. Due to the lowering, further: As shown in FIG. 2(B), the second port 8b flows between the upper end surface of the valve body 15 and the upper wall of the second liquid chamber, and further pushes the valve body 15 down. Due to the lowering of the valve body 15, the actuating rod 11
The ball 10 connected thereto is biased by the first spring 12 and lowers to close the valve seat 9d. Further, due to the lowering of the valve body 15, the third port 8c and the fourth port 8d are connected only through the second outer circumferential groove portion 15d. Therefore, the pump discharge liquid discharged from the pump 6 and flowing into the second port 8b side of the second liquid chamber 9b through the reflux line L2 is refluxed to the master cylinder 2 side through the throttle bypass channel 13. In addition, since the hydraulic fluid flowing back from the wheel brake 3 flows only through the second outer circumferential groove 15d,
The hydraulic pressure acting on the valve body 15 is limited.

As described above, the working fluid discharged from the pump is returned to the master cylinder 2 side through the throttle bypass passage 13, and passes through the throttle part 13a of the throttle bypass passage 13 through the first liquid chamber 9a. Since the cross-sectional area of the flow path is sufficiently narrowed compared to the above, the transmission of the pulsation of the pump 6 to the master cylinder 2 is sufficiently reduced.

At the time of repressurization after anti-lock, the electromagnetic valve 5 is de-energized, and the outflow of the working fluid from the second outlet 30f of the flow control valve 4 is stopped. In this state, as shown in FIG. 3(C), the flow rate control valve 4 moves from the population 30b to the flow path 30c to the pressurizing chamber 31b.
-Silver 32-Decompression chamber 31c→Flow path 30g→Flow path 3
A small flow path is formed from 0h to the outer circumferential groove 31a and the first outlet 30e. The working fluid from the master cylinder 2 is transferred from the throttle bypass passage 13 of the passage area switching valve 7 to the second liquid chamber 9.
From the second liquid chamber 9b, it is sent to the wheel brakes 3 through the main flow path Ll and the small flow path of the flow control valve 4, thereby gradually increasing the pressure of the brakes 3. When the differential pressure between the population 30b and the first outlet 30e becomes smaller, the spool 31 of the flow control valve 4 returns to the position shown in FIG. be done.

Further, during the repressurization, a part of the hydraulic fluid discharged from the pump 6 is supplied to the wheel brakes 3 from the first return point P2 via the flow control valve 4.

In this manner, all of the working fluid discharged by the pump 6 does not pass through the throttle bypass channel 13, so there is no problem of increased load on the pump.

When the hydraulic pressure of the hydraulic fluid discharged from the pump 6 decreases, the valve body 15 is urged by the second spring 17 and rises, and the ball lO opens the valve seat 9d, and the large flow path is again established in the main flow path Ll. It is formed.

The present invention is not limited to the above embodiments, and various changes can be made.

For example, FIG. 4 shows a first modification of the present invention, in which the second port 8b' of the flow path area switching valve 7' is connected to the second return point P2.

Further, in the second embodiment of the present invention shown in FIG. 5, the second return point P2'' is directly connected to the second liquid chamber 9b' of the flow path area switching valve 7''. ” constitutes the second return point.

In addition, in the first and second modified examples, the configurations other than those described above are the same as those in the embodiment, so the same reference numerals are given and the explanation is omitted.

As is clear from the above description, the brake circuit equipped with the anti-lock device according to the present invention maintains a large flow path connecting the master turn cylinder and the flow control valve in an open state during normal brake pressurization, while By simply installing a single flow path area switching valve that includes a check valve that closes when the anti-lock pressure is reduced and a bypass flow path for throttling, the pulsation that occurs when the pump is activated is routed through the master cylinder to the brake pedal. In addition, it is possible to prevent problems such as a delay in brake effectiveness and a delay in brake return during normal brake operation.

In addition, as mentioned above, since it has a simple configuration that only requires one flow path area switching valve, it has various advantages such as not increasing the size of the device or increasing costs. .

[Brief explanation of the drawing]

FIG. 1 is an overall configuration diagram showing an embodiment of a brake circuit equipped with an anti-lock device according to the present invention, FIG.
Figure (B) is a cross-sectional view showing the operation of the flow path area switching valve, Figures 3 (A) to 3 (C) are cross-sectional views showing the operation of the flow rate control valve, and Figures 4 and 5 are cross-sectional views showing the operation of the flow rate control valve. It is a sectional view showing a modification of the invention. ■...Brake pedal, 2...Master cylinder, 3
・Wheel brake, 4 flow control valve, 5... solenoid valve,
6. Pump, 7... Flow path area switching valve, 8a.
1st port, 8b-2nd port, 8c-3rd port, 8d...4th port, 9...liquid chamber, 9a...
1st liquid chamber, 9b... 2nd liquid chamber, 9c... connection flow path, 15 - valve body, Ll... main flow path,
L2...reflux path, L3...bypass flow path, Pl...
- Branching point, P2 - First return point, P3... Second return point. Patent applicant Sumitomo Electric Industries Co., Ltd. Patent attorney Aoyama Ao and two others @Figure 2 (A) Figure 2 + 8) Figure 3 (A) Figure 3 (8) Figure 3 fcl Figure 4

Claims (1)

[Scope of Claims] 1. A return passage that is separated from the main passage connecting the master cylinder and the wheel brakes and returns the working fluid from a return point upstream of this branch point (i.e., on the master cylinder side) to the main passage. a pump disposed in the recirculation path to recirculate the hydraulic fluid; and a pump for reducing the brake pressure of the wheel brakes by discharging the hydraulic fluid from the wheel brakes to the recirculation path, and for discharging the hydraulic fluid from the main flow path to the wheel brakes. In a brake circuit equipped with an anti-lock device having a pressure regulating means for increasing the brake pressure of a wheel brake by supplying a first port that communicates with the return flow path on the discharge side of the pump; a second port that communicates with the return flow path on the discharge side of the pump and also communicates with the main flow path; and a second port that communicates with the first port and communicates with the return point from the master cylinder side. a first liquid chamber provided with a check valve whose forward direction is toward the side; and a second liquid chamber communicated with the first liquid chamber via a connecting channel and with the second port. , a throttle bypass flow path having a throttle section that bypasses the first liquid chamber and communicates the first port with the second liquid chamber; A valve body is provided that is locked to the first liquid chamber, and an operating rod protruding from one end surface of the valve body opens the check valve in the first liquid chamber while being locked by the spring force. When the brake pressure of the brake is reduced (i.e.
When the anti-lock pressure is reduced), the pressure of the pump discharge fluid flowing in from the second port moves the valve body against the spring force to close the check valve, and the pump discharge fluid is used for the throttle. The anti-lock device is characterized by being provided with a passage area switching means configured to cause the flow to flow through the bypass passage to the first port side and reduce the passage area of the main passage between the master cylinder and the return point. Brake circuit with device. 2. The second port communicates with the main flow path upstream from the return point, communicates with the return flow path on the discharge side of the pump, and is connected to the inlet side of the flow rate control valve of the pressure regulating means provided in the main flow path. 2. The brake circuit according to claim 1, wherein the brake circuit is connected to the brake circuit. 3. The brake circuit according to claim 1, wherein the second fluid chamber is configured as the return point. 4. The second liquid chamber communicates with a third port that communicates with the main flow path downstream of the flow control valve of the pressure regulating means, and a fourth port that is connected to the wheel brake. 4. The brake circuit according to claim 1, wherein the brake circuit communicates with the four ports through the spring housing.