JPS6220937B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a master cylinder device that converts force applied to a brake pedal into hydraulic pressure in a hydraulic brake system installed in a vehicle such as an automobile.

The force applied to the brake pedal, so-called pedal force, is converted into hydraulic pressure by the master cylinder device, and the hydraulic pressure is transmitted to the hydraulic actuator of the brake device, thereby controlling friction members such as the brake shoe and brake pads. A so-called hydraulic brake system, which is configured to perform a braking action by pressing against a rotating member such as a brake drum or a brake disc, is used in many automobiles and the like.

In the above-mentioned hydraulic brake system, if the piston diameter of the master cylinder device is large, the amount of fluid discharged relative to the amount of piston movement is large, so the stroke of the brake pedal required to obtain the desired braking action is short. However, a large amount of pedal force is required, especially in areas where high pressure is generated. On the other hand, if the piston diameter of the master cylinder device is small, it does not require a very large pedal force even in the high pressure region, but since the amount of fluid discharged is small relative to the amount of piston movement, it is difficult to obtain the desired braking action. The required brake pedal stroke becomes longer. By the way, the amount of fluid required to be discharged from the master cylinder device is large in the initial stage when the friction member moves from the position where it is separated from the rotating member to the position where it engages with the rotating member; This is not so great in the later stages, which require an increase in the fluid pressure supplied to the hydraulic actuator. In particular, recently there has been a trend to increase the clearance between the friction member and the rotating member in order to prevent or reduce brake dragging due to the need for lower fuel consumption. The amount of brake fluid discharged from the master cylinder device in the initial stage must be large. In order to increase the amount of fluid discharged from the master cylinder device while keeping the depression stroke of the brake pedal constant from the viewpoint of operational feeling, it is necessary to increase the piston diameter. However, if the piston diameter is large, as described above, the necessary pedal force in the high pressure generation region becomes large, which impairs the operation feeling of the brake pedal and also requires a large brake booster.

In view of the above-mentioned drawbacks, in the early stages of brake operation, the amount of fluid discharged is large relative to the amount of piston movement, and in the later stages, the amount of fluid discharged relative to the amount of piston movement is reduced, making it possible to avoid increasing the stroke of the brake pedal so much. In addition, a so-called quick-take-up type brake master cylinder device that does not require a very large pedal force particularly in a high pressure generation region has been proposed, and this is shown in, for example, US Pat. No. 4,133,178.

The quick-take-up type brake master cylinder device as described above has a large-diameter cylinder chamber and a large-diameter cylinder chamber, and one reducing-diameter piston that engages with the large-diameter cylinder chamber and the small-diameter cylinder chamber, respectively. is provided, and until the fluid pressure in the large-diameter cylinder chamber reaches a predetermined value, fluid is sent from the large-diameter cylinder chamber to the small-diameter cylinder chamber to shorten the stroke of the brake pedal, and the fluid pressure in the large-diameter cylinder chamber reaches the predetermined value. In order to prevent the fluid pressure in the large diameter cylinder chamber from increasing any further, the brake fluid pressure in the large diameter cylinder chamber opens the relief valve and the brake fluid in the large diameter cylinder chamber flows out into the reservoir tank. There is.

In the brake master cylinder device having the structure described above, the fluid pressure in the large diameter cylinder chamber does not rise at all after the relief valve opens, which is good for reducing the pedal effort, but the relief valve does not increase at all. The brake pedal depression reaction force changes drastically between before and after the valve opens, making it impossible to obtain a good brake pedal depression feeling.

In the present invention, at the initial stage of brake operation, the amount of fluid discharged is large relative to the amount of movement of the piston, and at the later stage, the amount of fluid discharged is reduced relative to the amount of movement of the piston, so that the stroke of the brake pedal does not become so large and particularly high pressure is generated. The purpose of the present invention is to provide a new brake master cylinder device of a variable discharge amount type that does not require a very large pedal force in the range and can provide good brake pedal feeling.

According to the present invention, the present invention provides a fluid reservoir for storing brake fluid, a cylinder member having a large-diameter cylinder bore and a small-diameter cylinder bore, and a large-diameter piston that engages with the large-diameter cylinder bore and the small-diameter cylinder bore, respectively. a piston member having a land and a small-diameter piston land and cooperating with the cylinder member to define a large-diameter cylinder chamber and a small-diameter cylinder chamber; and a piston member that is flexible to a return position on the side of the large-diameter cylinder chamber. The cylinder member has a valve chamber that communicates with the fluid reservoir, a first port that always communicates and connects the valve chamber and the large diameter cylinder chamber, and the piston member that It has a second port that communicates and connects the valve chamber and the small-diameter cylinder chamber only when the valve chamber is in the return position, and a fluid outlet that opens toward the small-diameter cylinder chamber, and further includes a fluid outlet that is open toward the small-diameter cylinder chamber. a one-way valve that only allows fluid to flow from the chamber toward the small-diameter cylinder chamber; an orifice passage that always connects the valve chamber and the fluid reservoir; and an orifice passage that communicates with the large-diameter cylinder chamber to allow fluid in the large-diameter cylinder chamber an accumulator that receives brake fluid from the large-diameter cylinder chamber and suppresses a rise in fluid pressure in the large-diameter cylinder chamber when the pressure is equal to or higher than a first predetermined value; a relief valve that communicates and connects the valve chamber and the fluid reservoir only when the fluid pressure in the large diameter cylinder chamber is equal to or higher than a second predetermined value that is greater than the first predetermined value; A negative pressure valve is provided in the chamber and responds to the fluid pressure in the large diameter cylinder chamber to communicate and connect the fluid reservoir and the valve chamber only when the fluid pressure in the large diameter cylinder chamber is negative pressure. This is achieved by a brake master cylinder device characterized by the following.

According to the above configuration, the brake fluid in the large diameter cylinder chamber is drained as the piston member moves until the fluid pressure in the large diameter cylinder chamber exceeds the first predetermined value, that is, in the initial stage of brake operation. The fluid flows through the one-way valve to the small-diameter cylinder chamber, and is taken out from the fluid outlet together with the brake fluid in the small-diameter cylinder chamber, so at this initial stage, the amount of fluid discharged relative to the amount of movement of the piston member is large. When the fluid pressure in the large-diameter cylinder chamber reaches a first predetermined value or more, the brake fluid in the large-diameter cylinder chamber is taken into the accumulator, thereby suppressing the increase in fluid pressure in the large-diameter cylinder chamber. Also, only the brake fluid in the small diameter cylinder chamber is discharged from the fluid outlet.

As a result, the master cylinder device can generate high fluid pressure in its small diameter cylinder chamber without requiring a very large pedal force.

When the accumulator becomes saturated and the fluid pressure in the large-diameter cylinder chamber exceeds a second predetermined value, the relief valve opens with a predetermined degree of restriction, and the brake fluid in the large-diameter cylinder chamber flows through the valve. The fluid flows through the fluid reservoir to the fluid reservoir, thereby preventing the fluid pressure in the large diameter cylinder chamber from increasing any further. In this way, after the fluid pressure in the large-diameter cylinder chamber rises above the first predetermined value, the brake fluid in the large-diameter cylinder chamber is received by the accumulator, and after the accumulator reaches the saturated state. The brake fluid in the large-diameter cylinder chamber flows out to the fluid reservoir while its flow rate is restricted, so the amount of brake fluid flowing into the small-diameter cylinder chamber is more stable than the large-diameter cylinder chamber relative to the moving speed of the piston member, and the piston member does not suddenly move. Even if the fluid pressure in the large-diameter cylinder chamber increases rapidly due to movement, a sufficient amount of fluid flows from the large-diameter cylinder chamber to the small-diameter cylinder chamber.

As described above, in the brake master cylinder device according to the present invention, when the fluid pressure in the large diameter cylinder chamber reaches the first predetermined value, the fluid pressure in the large diameter cylinder chamber is further increased by the accumulator. The relief valve opens only when the fluid pressure in the large diameter cylinder chamber reaches a second predetermined value. The brake fluid then flows out to the fluid reservoir, and the fluid pressure in the large diameter cylinder chamber is prevented from increasing beyond the second predetermined value, so the rate of increase in output pressure relative to the pedal force changes in three stages, and the large diameter Compared to the brake fluid in the large diameter cylinder chamber that suddenly flows into the fluid reservoir when the fluid pressure in the cylinder chamber reaches a predetermined value or higher, the brake pedal depression reaction force changes rapidly during the brake pedal depression process. As a result, the intended purpose is achieved without increasing the stroke of the brake pedal and not requiring a large pedal force especially in the high pressure region, and achieving a favorable brake pedal depression feeling. Things will become compatible.

Furthermore, according to the above-mentioned configuration, since the valve chamber, in other words, the large diameter cylinder chamber, and furthermore the accumulator are always in communication with the fluid reservoir through the orifice passage, the brake pedal can be depressed at an intermediate position. When stopped, the brake fluid received by the accumulator flows through the orifice passage into the fluid reservoir, thereby restoring the accumulator and allowing it to operate effectively again when the brake pedal is depressed again. become.

Furthermore, in the brake master cylinder device according to the present invention, since the relief valve is provided in addition to the accumulator, the capacity of the accumulator will not be insufficient during the entire brake operation, and even if the accumulator is Even if the multor becomes inoperable due to a sticking phenomenon, etc., when the fluid pressure in the large diameter cylinder chamber reaches the second predetermined value, the relief valve opens and the brake fluid in the large diameter cylinder chamber escapes to the fluid reservoir. This prevents the required pedal effort from becoming significantly large in the high pressure generation region, thereby providing a so-called fail-safe.

During the return stroke of the piston member, the large diameter cylinder chamber lacks an amount of brake fluid equivalent to the amount that has flowed from the large diameter cylinder chamber through the valve to the fluid reservoir. It becomes a negative pressure state. This opens the valve and replenishes brake fluid from the fluid reservoir to the large diameter cylinder chamber. At this time,
The valve may be constructed so as not to perform a substantial throttling action, and the valve opening setting pressure may be set to a relatively small value, thereby minimizing the generation of negative pressure as described above and ensuring smooth return of the piston member. movement can be realized.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to the accompanying drawings.

FIG. 1 is a longitudinal sectional view showing one embodiment of the master cylinder device according to the present invention applied to a tandem type master cylinder device, and FIGS. 2 and 3 are longitudinal sectional views showing enlarged main parts thereof. It is. In the figure, 1 indicates a cylinder member, and this cylinder member 1 has a mounting flange 2 near one end thereof.
have. The cylinder member 1 has a large-diameter cylinder bore 3 on one side thereof, and a small-diameter cylinder bore 4 on the other side, which has a larger diameter than the large-diameter cylinder bore 3 and communicates with the large-diameter cylinder bore 3 at one end, on the same axis. Have it on the line. Inside the cylinder member 1, a large diameter piston land 5 that engages with the large diameter cylinder bore 3 and a small diameter piston land 6 that engages with the small diameter cylinder bore 4 are spaced apart from each other in the axial direction. a second piston member 11 having a first piston member 7 and a first small-diameter piston land 9 and a second small-diameter piston land 10 that engage with the small-diameter cylinder bore 4 and are spaced apart in the axial direction; are each provided movably in its axial direction. The first piston member 7 is restricted from moving to the right in the figure by a snap spring 8 attached near one end of the cylinder member 1, and is located between the large diameter piston land 5 and the small diameter piston land 6. It cooperates with the cylinder member 1 to define a first chamber 12. Moreover, the small diameter piston land 6 of the first piston member 7 and the first small diameter piston land 9 of the second piston member 11 cooperate with the cylinder member 1 to open the second chamber 13. Further, the second piston member 11 has a third chamber 14 between the first and second small-diameter piston lands 9 and 10, and also has a third chamber 14 with the cylinder member 1 on the opposite side from the third chamber 14. working to define the fourth chamber 15.

Between the first piston member 7 and the second piston member 11 and the small diameter cylinder bore 4
Compression coil springs 17 and 18 are provided between the inner ends and the second piston member 9, respectively. When the first piston member 7 is not subjected to a force directed to the left in the figure, the first piston member 7 moves in its large diameter piston land 5 as shown in the figure. The second piston member 11 is located at an intermediate position in the small diameter cylinder bore 4, and is in its return position.

The cylinder member 1 is provided with a cylindrical mounting seat 21, and a fluid reservoir 23 is mounted on the mounting seat 21 through a seal member 22 in a liquid-tight manner. The mounting seat 21 defines a valve chamber 56 inside thereof, and the valve chamber 56 communicates with the fluid reservoir 23 . Further, the cylinder member 1 is provided with a first port 19 that always communicates and connects the valve chamber 56 and the first chamber 12, and the valve chamber 56 is connected only when the first piston member 7 is near the return position as described above. A second port 20 is provided to communicate and connect the second chamber 13 and the second chamber 13 . As clearly shown in FIGS. 2 and 3, the mounting seat 2
1 is provided with an annular relief valve 24. The relief valve 24 is connected to this and the mounting seat 21.
A compression coil spring 27 provided between the retainer 26 and the retainer 26, which is locked by a snap spring 25, applies a spring force directed downward in the figure. 21'. When the relief valve 24 is in the open position as shown in FIG. 3, it cooperates with the cylindrical portion 26' of the retainer 26 to define an annular throttle passage 36. . Further, a seal member 28 is attached to the outer periphery of the relief valve 24. The relief valve 24 defines a valve port 29 in its center and has an annular seal member 30 around the valve port 29.
The annular seal member 30 includes a disc-shaped negative pressure valve 31.
is adapted to engage selectively, and this valve 3
1 is supported by a rod 32 and directed upward in the figure by a relatively weak compression coil spring 34 provided between a spring receiving plate 33 attached to one end of the rod 32 and the retainer 26. It is provided with a spring force and normally engages with the annular seal member 30 to close the valve port 29. Further, an orifice 35 is formed in the valve 31. The relief valve 24 and the negative pressure valve 31 are assembled with each other and moved upward in the figure until the valve 31 abuts the end of the retainer 26, and acts as an accumulator piston.

Further, the cylinder member 1 is provided with a first fluid outlet 38 that is always open toward the inside of the second chamber 13 regardless of the movement of the first and second piston members 7 and 11. . This first fluid outlet 38 is connected via a conduit (not shown) to a brake device, for example, a hydraulic actuator of a rear brake of an automobile.

An annular seal member 39 made of a rubber-like elastic body is attached to the large diameter piston land 5 of the first piston member 7. Further, the small diameter piston land 6 of the first piston member 7 is made of a rubber-like elastic body and has an annular lip portion 40.
An annular seal member 41 having a diameter is provided.
The annular seal member 41 performs a one-way valve action that only allows fluid to flow from the first chamber 12 through the hole 42 provided in the small-diameter piston land 6 toward the second chamber 13. It's summery.

Further, the cylinder member 1 is connected to the third port 43 that always communicates with the third chamber 14, and the third port 43 is connected to the fourth chamber 15 only when the second piston member 11 is near the return position as described above. It has a fourth port 44 that communicates with it. Further, the cylinder member 1 has a cylindrical mounting seat portion 45 that communicates with the third and fourth ports 43 and 44, and this mounting seat portion 45 is provided with fluid extending from the fluid reservoir 23. The end of the passage 47 is the sealing member 46
connected via.

Further, the cylinder member 1 has the fourth chamber 15.
A second fluid outlet 53 that opens inward is provided. This second fluid outlet 53 is connected to the brake device through a conduit (not shown).
For example, it is connected to the hydraulic actuator of the front brake of a car.

Annular seal members 48 and 49 made of a rubber-like elastic body are attached to the first small-diameter piston land 9 of the second piston member 11. Further, an annular seal member 51 made of a rubber-like elastic body and having an annular lip portion 50 is attached to the second small-diameter piston land 10 of the second piston member 11. The annular seal member 51 passes from the third chamber 14 to the fourth chamber 1 through a hole 52 provided in the second small-diameter piston land 10.
The one-way valve function is such that only the flow of fluid is allowed to flow toward the valve.

Further, a hemispherical engagement hole 5 is provided at the end of the first piston member 7 on the side of the large diameter piston land 5.
4 is formed, and a plunger 55 that drives the first piston member 7 is engaged with this engagement hole 54 .

As shown, when the first and second piston members 7, 11 are each in the return position, each valve is in the position as shown, and the first and second chambers 12, 13 are each in the position shown. The first and second chambers 12 and 13 are supplied with brake fluid from the fluid reservoir 23 through an orifice 35, and the third and fourth chambers 14 and 15 are connected to a fluid trajectory 47. The chambers are connected to a fluid reservoir 23 through which brake fluid is supplied, and the pressure of the brake fluid in each chamber is approximately atmospheric pressure. When the brake pedal is depressed in the above-mentioned state and the plunger 55 is driven to the left in the figure, the first and second piston members 7 and 11 each move against the compression coil spring 1.
It moves to the left in the figure against the spring force of 718.
Then, the fluid pressure in the first and second chambers 12, 13 increases, and the annular seal member 41 attached to the first piston member 7 passes through the second port 20, so that the fluid pressure in the first and second chambers 12, 13 increases. The chamber 13 is cut off from communication with the fluid reservoir 23. At this time, the annular seal member 51 attached to the second piston member 11 passes through the fourth port 44, thereby cutting off communication between the fourth chamber 15 and the fluid reservoir 23. At this time, a part of the brake fluid in the large diameter cylinder chamber 12 flows through the orifice 35 to the fluid reservoir 23, but the flow rate is very small, and most of the brake fluid in the first chamber 12 flows into the fluid reservoir 23 through the orifice 35. As the first piston member 7 moves, the annular lip portion 40 of the annular seal member 41 is elastically deformed in the diametrical direction through the hole 42, gets over it, flows into the second chamber 13, and flows into the second chamber 13. Together with the brake fluid in the chamber 13, the fluid is sent out from the first fluid outlet 38 toward a hydraulic actuator (not shown). Therefore, at this time, a relatively large amount of brake fluid is discharged from the first fluid outlet 38 relative to the amount of movement of the first piston member 7. Further, the brake fluid in the fourth chamber 15 is transferred to the second piston member 11.
As the fluid moves, the fluid is sent out from the second fluid outlet 53 toward another hydraulic actuator (not shown). In this embodiment, the amount of brake fluid discharged from the second fluid outlet 53 relative to the amount of movement of the piston member is substantially constant during the entire stroke of the second piston member 11.

When the first piston member 7 moves to the left in the figure as described above, brake fluid is discharged from the first fluid outlet 38 and the brake fluid is discharged from the first and second chambers 12 and 13. Fluid pressure will also begin to rise. When the fluid pressure in the first chamber 12 reaches a first predetermined value, the fluid pressure causes the relief valve 24 and the negative pressure valve 31 to engage with each other against the action of the compression coil spring 27 as shown in the figure. As a result, the brake fluid in the first chamber 12 flows out from the relief valve 24 and the negative pressure valve 31 into the valve chamber 56 below. This creates an accumulator effect,
After this, even if the first piston member 7 continues to move to the left, the fluid pressure in the first chamber 12 does not increase much, and only the fluid pressure in the second chamber 13 continues to increase. Become. Therefore, at this time, the first piston member 7 moves without requiring much force.

When the valve 31 rises until it comes into contact with the end of the retainer 26, the valve 31 cannot rise any further.
As a result, the movement of the first piston member 7 further advances, and when the fluid pressure increases in the first chamber and reaches a second predetermined value, as shown in FIG. rises against the spring force of the compression coil spring 27, opening the valve port 29. At this time, the relief valve 24 cooperates with the cylindrical portion 26' of the retainer 26 to define the throttle passage 36, so that the brake fluid in the first chamber 12 passes through the throttle passage 36 to the fluid reservoir 23. The fluid pressure in the first chamber 12 is maintained at a value close to the second predetermined value.

Now, the force required to move the first piston member 7 to the left in the figure is F, the first piston member 7
The pressure receiving area of the large diameter piston land 5 of is A ₁ , the pressure receiving area of the small diameter piston land 6 of the first piston member 7 is A ₂ , the fluid pressure of the first chamber 12 is P ₁ ,
When the fluid pressure in the second chamber 13 is P ₂ and the spring force of the compression coil spring 17 is f, the force F is given by the following equation.

F=P ₁ (A ₁ −A ₂ )+P ₂ A ₂ +f Therefore, if the increase in the fluid pressure P ₁ in the first chamber 12 is suppressed compared to that in the second chamber 13, The pressure in the first chamber 12 is lower than the pressure in the second chamber 1.
The force F becomes smaller than when the fluid pressure in 3 increases as well. As a result, even if the movement of the first piston member 7 progresses as described above, the first piston member 7 moves without requiring much force.

As mentioned above, even after the fluid pressure P ₁ in the second chamber 13 reaches the first predetermined value, the pressure of the compression coil spring 27 increases as the relief valve 24 and the negative pressure valve 31 move upward in the figure. The fluid pressure increases gradually with a rate of increase determined by a constant.
Only when P ₁ reaches the second predetermined value does the relief valve 24 open and the fluid pressure P ₁ is prohibited from increasing any further, so that the reaction force of the brake pedal is reduced during depression of the brake pedal. The degree to which the value changes rapidly is kept to a small value.

When the movement of the first piston member 7 stops, the brake fluid continues to flow from the first chamber 12 through the throttle passage 36 to the fluid reservoir 23, so that the fluid pressure in the first chamber 12 decreases, and the valve 24 descends and closes the valve port 29, and thereafter, brake fluid continues to flow from the first chamber 12 through the orifice 35 and into the fluid reservoir 2.
3, the fluid pressure in the first chamber 12 further decreases, the relief valve 24 and the negative pressure valve 31 both drop, and the accumulator is regenerated. As a result, an effective accumulator action can be obtained when the brake pedal is depressed again.

A predetermined fluid pressure is generated in the second chamber 13, and the fluid pressure is transmitted to a hydraulic actuator of a brake device (not shown in the figure) to perform a predetermined braking action, and then the braking action is released. When the brake pedal is released and the plunger 55 retreats to the right in the figure, the first and second piston members 7 and 11 are returned to their original positions by the spring force of the compression coil springs 17 and 18, respectively. Accordingly, the brake fluid that had been applied to the hydraulic actuator of the brake device is returned to the second and fourth chambers 13 and 15. At this time, the relief valve 24
has returned to the valve closed position, and the fluid pressure in the first chamber 12 becomes negative. This negative pressure is applied to the negative pressure valve 31
The negative pressure valve 31 is pulled down against the spring force of the compression coil spring 34. Therefore, the negative pressure valve 31 separates from the annular seal member 30, opens the valve port 29, and the first chamber 12 is replenished with brake fluid from the fluid reservoir 23 as the first piston member 7 moves back. When the first piston 7 returns to the vicinity of the return position as shown in the figure, the second port 20 again communicates with the second chamber 13 and the first chamber 1
The amount of brake fluid corresponding to the amount that has flowed from 2 to the second chamber 13 is returned to the fluid reservoir 23 through the second port 19 and the orifice 35. In the above-described embodiments, the present invention was implemented only in one system of the tandem type master cylinder device, but the present invention may be incorporated into both systems of the tandem type master cylinder device as necessary. It goes without saying that the present invention can also be applied to a single-type master cylinder device.

FIG. 4 is a longitudinal sectional view showing the main parts of another embodiment of the brake master cylinder device according to the present invention. In FIG. 4, parts corresponding to those in FIGS. 1 to 3 are designated by the same reference numerals as those in FIGS. 1 to 3. In such an embodiment, the relief valve 24 is connected to the cylindrical portion 2 of the retainer 26.
It has a cylindrical part 24' that engages with the outer periphery of 6' with a predetermined small gap, and a hole 37 is bored in this cylindrical part 24'.

In this embodiment as well, the relief valve 24 is moved up to the position where the negative pressure valve 31 abuts the end of the retainer 26.
The bore 37 is aligned with the outer circumferential surface of the cylindrical portion 26' of the retainer 26, and the cylindrical portion 24' is disposed between the valve port 29 and the fluid reservoir 23. The constriction passage is defined in cooperation with the aperture passage.

Further, FIG. 5 is a longitudinal cross-sectional view showing essential parts of a modified example of the brake master cylinder device shown in FIG. 4. In this embodiment, a compression coil spring 34 is provided between the negative pressure valve 31 and the bottom of the mounting seat 21.

The valve shown in FIG. 5 operates in the same manner as the valve shown in FIG. 4, so a description thereof will be omitted.

Although the present invention has been described in detail with respect to specific embodiments in the above, it will be appreciated by those skilled in the art that the present invention is not limited thereto and that various embodiments can be made within the scope of the present invention. It would be obvious to

[Brief explanation of the drawing]

FIG. 1 is a longitudinal sectional view showing one embodiment of the master cylinder device according to the present invention, and FIGS. 2 and 3 are enlarged longitudinal sectional views showing essential parts of the master cylinder device shown in FIG. 1. Of these, FIG. 2 shows the valve in the closed state, and FIG. 3 shows the valve in the open state. 4 and 5 are enlarged longitudinal cross-sectional views showing essential parts of other embodiments of the brake master cylinder device according to the present invention. 1... Cylinder member, 2... Mounting flange, 3...
Large diameter cylinder bore, 4...Small diameter cylinder bore, 5...
Large diameter piston land, 6...Small diameter piston land,
7...First piston member, 8...Snat spring,
9...First small diameter piston land, 10...Second small diameter piston land, 11...Second piston member,
12... first chamber, 13... second chamber, 14... third chamber, 15... fourth chamber, 17, 18... compression coil spring, 19... first port, 20... second port,
21... Mounting seat, 21'... Annular shoulder, 22... Seal member, 23... Fluid reservoir, 24... Relief valve, 25... Snap ring, 26... Retainer,
26'...Cylindrical part, 27...Compression coil spring, 28...
Seal member, 29... Valve port, 30... Annular seal member, 31... Negative pressure valve, 32... Rod, 33... Spring receiving plate, 34... Compression coil spring, 35... Orifice, 36... Throttle passage, 37... Hole, 38... First fluid outlet, 39... Annular seal member, 40... Annular lip portion, 41... Annular seal member, 42... Hole,
43...Third port, 44...Fourth port, 45
... Mounting seat, 46... Seal member, 47... Fluid passage, 48, 49... Annular seal member, 50... Annular lip portion, 51... Annular seal member, 52... Hole, 5
3...Second fluid outlet, 54...Engagement hole, 55
...Plunger, 56...Valve chamber.

Claims (1)

[Claims] 1. The cylinder has a fluid reservoir for storing brake fluid, a cylinder member having a large diameter cylinder bore and a small diameter cylinder bore, and a large diameter piston land and a small diameter piston land that engage with the large diameter cylinder bore and the small diameter cylinder bore, respectively. a piston member that cooperates with the member to define a large-diameter cylinder chamber and a small-diameter cylinder chamber; and a spring that flexibly biases the piston member to a return position on the side of the large-diameter cylinder chamber; The cylinder member has a valve chamber that communicates with the fluid reservoir, a first port that always communicates and connects the valve chamber and the large-diameter cylinder chamber, and a first port that communicates with the valve chamber only when the piston member is in the return position. It has a second port that communicates with the small diameter cylinder chamber, and a fluid outlet that is open toward the small diameter cylinder chamber, and further has a fluid outlet that is open toward the small diameter cylinder chamber and allows fluid to flow from the large diameter cylinder chamber to the small diameter cylinder chamber. an orifice passage that always connects the valve chamber and the fluid reservoir; and an orifice passageway that always connects the valve chamber and the fluid reservoir; an accumulator that receives brake fluid from a large-diameter cylinder chamber and suppresses an increase in fluid pressure in the large-diameter cylinder chamber;
The valve chamber is provided in the valve chamber and responds to the fluid pressure in the large diameter cylinder chamber, and only when the fluid pressure in the large diameter cylinder chamber is equal to or higher than a second predetermined value that is greater than the first predetermined value, the valve chamber and the fluid a relief valve that communicates with the reservoir; and a relief valve that is provided in the valve chamber and responds to the fluid pressure in the large diameter cylinder chamber to connect the fluid reservoir and the valve chamber only when the fluid pressure in the large diameter cylinder chamber is negative pressure. A brake master cylinder device characterized in that it has a negative pressure valve that is connected in communication with the brake master cylinder device.