JPS6220932B2 - - 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 small-diameter cylinder chamber, and one reducing-diameter piston is engaged with each of the large-diameter cylinder chamber and the small-diameter cylinder chamber. The system is designed to shorten the stroke of the brake pedal by sending fluid from the large-diameter cylinder chamber to the small-diameter cylinder chamber until the fluid pressure in the large-diameter cylinder chamber reaches a 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, allowing the brake fluid in the large-diameter cylinder chamber to flow out into the reservoir tank. .

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.

Furthermore, in the brake master cylinder device described above, when the fluid pressure in the large diameter cylinder chamber reaches a predetermined value, the brake fluid pushes the relief valve open and flows into the brake reservoir, causing the valve element of the relief valve to vibrate. There is a risk that abnormal noise will occur.

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. 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 working together 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 fluid passage that communicates between the fluid reservoir and the large diameter cylinder chamber, and a fluid passage that communicates with the small diameter cylinder chamber only when the piston member is in the return position; It has an open fluid outlet, and is further provided with an accumulator chamber communicating with the large diameter cylinder chamber, and an accumulator chamber configured to respond to the fluid pressure of the large diameter cylinder chamber so that the fluid pressure is maintained at a predetermined level. an accumulator including a rod member that moves against the spring force of a return spring in response to an increase in fluid pressure when the fluid pressure rises above a certain value; a valve that is held in an open position until it moves by a first predetermined value or more against the spring force of the return spring from an initial position and communicates between the large diameter cylinder chamber and the small diameter cylinder chamber; and the rod member. When the rod member is selectively engaged and moves from the initial position by a second predetermined value greater than the first predetermined value against the spring force of the return spring, the large diameter cylinder chamber and the fluid reservoir are connected to each other. and a valve that communicates between the fluid reservoir and the large-diameter cylinder chamber only when fluid pressure in the large-diameter cylinder chamber is negative pressure. achieved by.

The accumulator may be incorporated inside the piston member.

According to the above configuration, the fluid pressure in the large-diameter cylinder chamber increases and the rod member moves by a first predetermined value or more in response, that is, in the initial stage of brake operation, the piston member moves. Then, the brake fluid in the large diameter cylinder chamber flows into the small diameter cylinder chamber, from which it is taken out from the fluid outlet along with the brake fluid in the small diameter cylinder chamber, so at this initial stage, the amount of fluid discharged is large relative to the amount of movement of the piston member. . When the rod member moves by more than a first predetermined value, the valve cuts off communication between the large diameter cylinder chamber and the small diameter cylinder chamber, and the accumulator is activated. When the increase in fluid pressure is suppressed and the fluid pressure further increases and the rod member moves by a second predetermined value or more in response, the relief valve is opened by the rod member and the large diameter cylinder chamber becomes a fluid reservoir. As a result, an increase in the fluid pressure in the large diameter cylinder chamber is suppressed, and at this time, only the brake fluid in the small diameter cylinder chamber is taken out from the fluid outlet. Therefore, at this time, if we look only at the master cylinder, only the fluid pressure in the small diameter cylinder chamber will substantially increase, and as a result, the master cylinder device will be able to apply high pressure to the small diameter cylinder chamber without requiring much pedal force. Fluid pressure will now be generated.

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 a predetermined value and the fluid pressure in the large-diameter cylinder chamber further increases due to depression of the brake pedal, the fluid pressure in the large-diameter cylinder chamber increases. The rod member moves against the spring force of the return spring, and this movement of the rod member provides an accumulator action, which suppresses the large diameter cylinder chamber further with the degree of suppression determined by the spring constant of the return spring. When the fluid pressure in the large-diameter cylinder chamber is suppressed from increasing, and the fluid pressure in the large-diameter cylinder chamber further increases and the amount of movement of the rod member increases accordingly, the relief valve is pushed open by the movement of the rod member. The brake fluid in the large-diameter cylinder chamber flows to the fluid reservoir, and the fluid pressure in the large-diameter cylinder chamber is prevented from increasing any further, so the rate of increase in output pressure relative to the pedal force changes in three stages, and the large-diameter cylinder Compared to the brake fluid in the large-diameter cylinder chamber that suddenly flows into the fluid reservoir when the fluid pressure in the chamber reaches a predetermined value, the degree of sudden change in the reaction force of the brake pedal during depression of the brake pedal is reduced. This achieves both the desired objective, namely, not increasing the stroke of the brake pedal so much and not requiring a very large depressing force especially in the high pressure generation region, and obtaining a desirable brake pedal depressing feeling. I come to do it. Since the relief valve does not respond to the fluid pressure in the large diameter cylinder chamber, but is pushed open and held in the open position by the movement of the rod member, the valve element vibrates when the relief valve opens. Therefore, problems such as abnormal noise do not occur.

When the accumulator is incorporated inside the piston member, the inside of the piston member is effectively utilized, and it is possible to avoid increasing the size of the brake master cylinder device due to the installation of the accumulator.

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 a tandem type master cylinder device in which a master cylinder device according to the present invention is implemented. In the figure,
1 indicates a cylinder member, and this cylinder member 1 has a mounting flange 2 near one end thereof. 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 smaller diameter than the large-diameter cylinder bore 3 and communicates with the large-diameter cylinder bore 3 at one end, on the same axis. has. Inside the cylinder member 1, first and second large-diameter piston lands 5 and 6 that engage with the large-diameter cylinder bore 3 and a small-diameter piston land 7 that engages with the small-diameter cylinder bore 4 are arranged axially with respect to each other. A first piston member 9 which is spaced apart and has a cylindrical portion 8 therebetween, and a second piston member 10 which has a small diameter piston land 11 that engages with the small diameter cylinder bore 4 are arranged along the axis thereof. It is provided so that it can be moved in the direction. The first piston member 9 is restricted from moving to the right in the figure by a snap spring 16 attached near one end of the cylinder member 1, and the movement between the first and second large diameter piston lands 5 and 6 is restricted. A first chamber 12 is defined between the first large-diameter piston land 5 and the small-diameter piston land 7, and a second chamber 13 is defined between the first large-diameter piston land 5 and the small-diameter piston land 7, respectively, in cooperation with the cylinder member 1. Moreover, the small diameter piston land 7 of the first piston member 9 and the small diameter piston land 11 of the second piston member 10 cooperate with the cylinder member 1 to open the third chamber 14 and the third chamber 14. The second piston member 10 is located in the third chamber 1.
On the side opposite to 4, a fourth chamber 15 is defined in cooperation with the cylinder member 1.

between the cup-shaped member 17 attached to the end of the first piston member 9 on the side of the small-diameter piston land 7 and the small-diameter piston land 11 of the second piston member 10 and the end inside the small-diameter cylinder bore 4; Compression coil springs 19 and 20 are provided between the cup-shaped member 18 provided in the section and the small-diameter piston land 11 of the second piston member 10, respectively.
is provided. When the first piston member 9 is not subjected to a force directed to the left in the figure, the first piston member 9 moves toward its second large diameter piston land 6 as shown.
The second piston member 10 is located at an intermediate position of the small diameter cylinder bore 4, and is in its return position.

The cylinder member 1 always has the first chamber 12
and a second port 22 that communicates with the second chamber 13 only when the first piston member 7 is near the return position as described above. . Further, a fluid reservoir 24 is attached to the cylinder member 1 by a nut member 23, and this fluid reservoir 24 is connected to the first and second ports 21, 22 through a hole 25 provided in the nut 23. are connected to each other. Further, the cylinder member 1 is provided with a first fluid outlet 26 that is always open toward the inside of the second chamber 14 regardless of the movement of the first and second piston members 9 and 10. This first fluid outlet 26 is connected via a conduit (not shown) to a brake system, for example a hydraulic actuator of a rear brake of a motor vehicle.

An annular seal member 27 made of a rubber-like elastic body is attached to the second large-diameter piston land 6 of the first piston member 9. Further, the second large-diameter piston land 5 of the first piston member 9 is provided with an annular seal member 29 made of a rubber-like elastic body and having an annular lip portion 28 . The annular seal member 29 passes from the first chamber 12 through a hole 30 provided in the large-diameter piston land 5 and a gap between the washer 31 and the first large-diameter piston land 5 and the cylinder member 1. It is designed to perform a one-way valve action that only allows fluid to flow toward the second chamber 13. Further, an annular seal member 33 made of a rubber-like elastic body and having an annular lip portion 32 is provided on the small diameter piston land 7 of the first piston member 9. The annular seal member 33
is a fluid flowing from the second chamber 13 toward the third chamber 14 through the hole 34 provided in the small diameter piston land 7, the gap between the washer 35, the small diameter piston land 7, and the cylinder member 1; It is designed to perform a one-way valve action that only allows the flow of water.

The first piston member 9 has a rod member 37 as an accumulator piston in a cylinder chamber 36 within the cylindrical portion 8 so as to be movable in its axial direction. The cylinder chamber 36 defines a valve chamber 36a that communicates with the first chamber 12 through a hole 38 on one side of the rod member 37, and a valve chamber 36a that communicates with the first chamber 12 on the other side of the rod member 37. A mulator chamber 36b is defined, and an accumulator chamber 3
6b communicates with the second chamber 13 through a hole 39 and with the third chamber 14 through a hole 40. As clearly shown in FIG. 2, the rod member 37 has a cross-shaped groove 41 at its tip.
It also has a groove 42 provided along one of its generatrix lines. Further, the rod member 37 has a first shaft portion 66 and a second shaft portion 67 having a smaller diameter than the first shaft portion 66 at one end, and the rod member 37 has a first shaft portion 66 and a second shaft portion 67 having a smaller diameter than the first shaft portion 66. The compression coil spring 45 as a return spring is provided between the spring receiving sleeve 68 and the screw plug 44 attached to the first piston member 9, which can be engaged with each other. Until the fluid pressure in the second chamber 13 reaches a predetermined value or more, it remains in the initial position of abutting against the end surface of the cylinder chamber 36 as shown in the figure.

A valve 46 for selectively opening and closing the hole 40 is provided within the cup-shaped member 17. The valve 46 has a valve rod 47.
passes through the hole 40 and comes into contact with the distal end surface of the rod member 37 at its distal end. When the rod member 37 is in the position shown, the valve 46 is pulled away from the end face of the first piston member 9 against the force of a spring 48 to open the hole 40; When the rod member 37 moves to the right in the figure by a first predetermined value _δ1 or more against the spring force of the compression coil spring 45, the seal member 49 follows this movement by the spring force of the spring 48. It is pressed against the end surface of the first piston member 9 to close the hole 40. Note that the cup-shaped member 17 has a hole 1.
7' is provided, and when the hole 40 is opened, the second chamber 13 and the third chamber 14 are connected to the hole 3.
9, groove 41, hole 40, and hole 17'.

Further, a relief valve 50 is provided within the valve chamber 36a. This relief valve 50 is slidably supported by the first shaft portion 66 of the rod member 37, and the rod member 37
The sealing member 52 is held by the spring force of the spring 51 until it moves by a second predetermined value _δ2 or more slightly larger than ₁ .
When the rod member 37 is pressed against the step surface in the cylinder chamber 36 to close the groove 42, and the rod member 37 moves by _more than the second predetermined value δ2,
The spring 51 comes into contact with the stepped portion of the rod member 37.
It moves to the right in the figure against the spring force, moves away from the step surface in the cylinder chamber 36, and opens the groove 42. Further, the first shaft portion 66 is provided with O.
A ring 43 is provided.

The screw plug 44 has a hemispherical engagement hole 53 on its end surface, and a plunger 54 that drives the first piston member 9 is engaged with this engagement hole 53.

Further, the cylinder member 1 is connected to the fourth chamber 15.
It has a third port 55 open at the end of the
Brake fluid is supplied to this third port 55 from a fluid reservoir 57 attached to the cylinder member 1 by a nut member 56. The third port 55 is selectively opened and closed by a valve 58 provided within the cup-shaped member 18. Said valve 5
8 is a valve rod 5 having a flange portion 60 at its tip.
9, and is attached to the second piston member 10 at the flange portion 60.
1 engages with the second piston member 10, and when the second piston member 10 is in the return position as shown, the force of the spring 62 is applied to the end face of the small diameter cylinder bore 4. When pulled apart, the third port 55 is opened, and at other times it is pressed against the end face of the small diameter cylinder bore 4 by the action of the spring 62, closing the third port 55. A seal member 63 made of a rubber-like elastic body is attached to the valve 58, and an O-ring 64 is attached to the second piston member 10.
The cylinder member 1 also has a second fluid outlet 65 that opens into the fourth chamber 15. This second fluid outlet 65 is connected via a conduit (not shown) to a brake system, a hydraulic actuator of a front brake of a motor vehicle.

As shown, when the first and second piston members 9, 10 are each in the return position, the valve 46
is in the open position and the first to third chambers 12, 13,
14 respectively communicate with a fluid reservoir 24 and are supplied with brake fluid from the fluid reservoir 24, and the fourth chamber 15 communicates with another fluid reservoir 57 and is supplied with brake fluid from this. The pressure of the brake fluid is approximately atmospheric pressure. When the brake pedal is depressed and the plunger 54 is driven to the left in the figure from the above-mentioned state, the first and second piston members 9 and 10 are moved by the compression coil springs 19 and 20, respectively.
It moves to the left in the figure against the spring force. Then, the annular seal member 29 attached to the first piston member 9 passes through the second port 22, and the second chamber 13 and the third chamber 14 are cut off from communicating with the fluid reservoir 24. ,
Further, when the valve 58 closes the third port 55, the fourth chamber 15 is connected to the fluid reservoir 57.
Communication is cut off. After this, the brake fluid in the second to fourth chambers 13, 14, 15 is transferred to the first and second piston members 9, 10.
In the figure, it is compressed as it moves to the left. As the first piston member 9 moves, the brake fluid in the second chamber 13 passes through the hole 39, the accumulator chamber 36b, and the holes 40 and 17' to the third chamber 1.
4 and is sent out together with the brake fluid in the third chamber 14 from the first fluid outlet 26 toward a hydraulic actuator (not shown). Therefore, at this time, the first piston member 9
A relatively large amount of brake fluid is discharged from the first fluid outlet 26 relative to the amount of movement. Further, as the second piston member 10 moves, the brake fluid in the fourth chamber 15 is sent out from the second fluid outlet 65 toward another hydraulic actuator (not shown). In this embodiment, the second fluid outlet 65
The amount of brake fluid discharged relative to the amount of movement of the piston member is substantially constant during the entire stroke of the second piston member 10.

When the first piston member 9 moves to the left in the figure as described above, brake fluid is discharged from the first fluid outlet 26 as described above, and the brake fluid is discharged into the second and third chambers 13 and 14. Fluid pressure at the pump also begins to rise. As the fluid pressure increases, the rod member 37 releases the compression coil spring 4.
The brake fluid in the second chamber 13 is accepted into the cylinder chamber 36 through the hole 39, and the valve 46 is moved to the right in the figure against the spring force of the valve 46. is moved to the right in the figure by the spring force of the spring 48, and when the amount of movement of the rod member 37 reaches a first predetermined value _δ1 , the valve 46 closes the hole 40. Therefore, from this point forward, brake fluid no longer flows from the second chamber 13 to the third chamber 14. When the brake fluid in the second chamber 13 is received into the accumulator chamber 36b as the first piston member 9 moves, the increase in fluid pressure in the second chamber 13 is suppressed by the accumulator action. However, as the spring load of the compression coil spring 45 increases with the movement of the rod member 37, the fluid pressure in the second chamber 13 decreases its rate of increase compared to before the accumulator action starts. However, the rod member 3 gradually rises.
7 continues to move to the right. Then, the relief valve 50 comes into contact with the stepped portion of the rod member 37, moves to the right in the figure against the spring force of the compression coil spring 51, and opens the groove 42. Therefore, the third chamber 13 has a hole 39 and an accumulator chamber 36.
b, groove 42, valve chamber 36a, hole 38, first chamber 1
2. It communicates with the fluid reservoir 24 through the first port 21 and hole 25, after which the brake fluid in the second chamber 13 flows towards the fluid reservoir 24, so that from now on, the piston movement is prevented. Even as the fluid pressure progresses, the fluid pressure in the second chamber 13 does not increase and remains at a substantially constant value, and only the fluid pressure in the third chamber 14 continues to rise. Therefore, at this time, the first piston member 9 moves without requiring much force.

Now, the force required to move the first piston member 9 to the left in the figure is F, the first piston member 9
The pressure receiving area of the first large diameter piston land 5 is
A ₁ , the pressure receiving area of the small diameter piston land 7 of the first piston member 9 is A ₂ , the fluid pressure in the second chamber 13 is P ₁ , the fluid pressure in the third chamber 14 is P ₂ , the compression coil spring 19, If the spring force of 20 is f, then
The force F is given by the following formula.

F=P ₁ (A ₁ −A ₂ )+P ₂ A ₂ +f Therefore, if the increase in the fluid pressure P ₁ in the second chamber 13 is suppressed compared to that in the third chamber 14,
The force F is lower than when the pressure in the second chamber 13 rises similarly to the fluid pressure in the third chamber 14.
becomes smaller. As a result, even if the movement of the first piston member 9 progresses as described above, the first piston member 9 moves without requiring a very large force.

As mentioned above, even after the valve 46 is closed, the fluid pressure _P1 in the second chamber 13 has an increase rate determined by the spring constant of the compression coil spring 45 as the rod member 37 moves to the right in the figure. Then, when the rod member 37 moves by a predetermined amount, the relief valve 50 is pushed open by the rod member 37 and the fluid pressure _P1 is prohibited from increasing any further. The degree to which the brake pedal depression reaction force changes rapidly is kept at a small value.

A predetermined fluid pressure is generated in the third chamber 14, and the fluid pressure is transmitted to a hydraulic actuator of a brake device (not shown) to perform a predetermined braking action, and then the braking action is released. When the brake pedal is released and the plunger 54 retreats to the right in the figure,
Accordingly, the first and second piston members 9, 10
are moved toward their respective return positions by the spring force of the compression coil springs 19 and 20, and accordingly, the brake fluid that was being applied to the hydraulic actuator of the brake device is transferred to the third and fourth chambers 14,
It will be returned within 15. Then, the fluid pressure in the second chamber 13 decreases and the rod member 37 returns to its original position, so the relief valve 50 closes the groove 42 and the valve 46 is separated from the end face of the first piston member 9. Then, the hole 40 is opened. Therefore, a portion of the brake fluid returned into the third chamber 14 flows into the second chamber 13 through the hole 40. Even if the brake fluid is returned to the second chamber 13 as described above, the brake fluid in this chamber is insufficient by the amount that flows out through the first chamber 12 and into the fluid reservoir 24 when the relief valve 50 is opened. Therefore, when the first piston member 9 further moves toward the return position, the fluid pressure in the second chamber 13 becomes a negative pressure state. Therefore, the brake fluid in the fluid reservoir 24 passes through the gap between the hole 25, the second port 21, the first chamber 12, the hole 30, the washer 31, the first large-diameter piston land 5, and the cylinder member 1. Furthermore, the annular lip portion 28 of the annular seal member 29 is elastically deformed in the diametrical direction while flowing into the second chamber 13, thereby replenishing the brake fluid.

FIG. 3 shows another embodiment of the master cylinder device according to the present invention. In FIG. 3, parts corresponding to those in FIG. 1 are designated by the same reference numerals as in FIG. Rod member 37
has a hole 42' passing through its center.
A cup-shaped member 71 having holes 69 and 70 is disposed within the accumulator chamber 36b. The cup-shaped member 71 is pressed against one end of the rod member 37 by a compression coil spring 72, so that it always moves in engagement with the rod member 37. The cup-shaped member 71 engages with the valve rod 47 of the valve 46 and holds the valve 46 in the open position until the rod member 37 moves to the right in the figure by more than a first predetermined value _δ1 . . Note that the valve rod 47 is connected to the hole 6.
It has a hole 47' connecting the holes 9 and 40. A relief valve 50 is provided in the cup-shaped member 71, and the relief valve 50 is connected to the rod member 3.
7 moves rightward in the figure by a second predetermined amount δ ₂ or more, the spring 51' presses against the end surface of the rod member 37 to close the hole 42'; When the rod moves to the right in the figure by a second predetermined amount _δ2 or more, it comes into contact with the rod 72 and is separated from the end surface of the rod member 37, opening the hole 42'.
Note that a seal member 52' is attached to the relief valve 50. Further, the rod member 37 is provided with an O-ring 43'.

Since the master cylinder arrangement shown in FIG. 3 operates substantially the same as that shown in FIG.
The explanation will be omitted.

In the above-described embodiments, the present invention was implemented in only 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.

In the above, the present invention has been described in detail with reference to specific embodiments, but it will be understood by those skilled in the art that the present invention is not limited to these embodiments, and that various embodiments can be made within the scope of the present invention. It should be obvious.

[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 FIG. 2 is a fragmentary perspective view showing the tip of the rod member incorporated in the master cylinder device shown in FIG. 3 are longitudinal sectional views showing another embodiment of the master cylinder device according to the present invention. 1... Cylinder member, 2... Mounting flange, 3...
Small diameter cylinder bore, 4...Large diameter cylinder bore, 5...
First large diameter piston land, 6... Second large diameter piston land, 8... Small diameter piston land, 9... First piston member, 10... Second piston member, 1
1... Small diameter piston land, 12... First chamber, 13
...Second chamber, 14...Third chamber, 15...Fourth chamber,
16... Snap ring, 17, 18... Cup-shaped member, 19, 20... Compression coil spring, 21... First port, 22... Second port, 23... Nut member, 24... Fluid reservoir, 25... Hole, 26...
first fluid outlet, 27... annular seal member,
28... Annular lip portion, 29... Annular seal member, 3
0... Hole, 31... Washer, 32... Annular lip part,
33... Annular seal member, 34... Hole, 35... Washer, 36... Cylinder chamber, 37... Rod member, 3
8,39,40...hole, 41,42...groove, 43,4
3'...O ring, 44...screw plug, 45...compression coil spring, 46...valve, 47...valve rod, 47'...
Hole, 48... Spring, 49... Seal member, 50, 5
0'... Relief valve, 51, 51'... Compression coil spring, 52, 52'... Seal member, 53... Engagement hole,
54...Plunger, 55...Third port, 56...
Nut member, 57... Fluid reservoir, 58...
Valve, 59... Valve rod, 60... Flange portion, 61...
Cover, 62... Spring, 63... Seal member, 64...
O-ring, 65...Second fluid outlet, 66...
First shaft part, 67... Second shaft part, 68... Spring receiving sleeve, 69, 70... Hole, 71... Cup-shaped member, 72... Rod.

Claims (1)

[Scope of Claims] 1. 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 cylinder 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. and the cylinder member has:
It has a fluid passage that communicates between the fluid reservoir and the large diameter cylinder chamber only when the piston member is in the return position, and a fluid outlet that opens toward the small diameter cylinder chamber, An accumulator chamber connected to a diameter cylinder chamber and an accumulator chamber provided in the accumulator chamber are responsive to the fluid pressure in the large diameter cylinder chamber, and when the fluid pressure rises beyond a predetermined value, the fluid pressure increases. an accumulator including a rod member that moves against the spring force of the return spring; and an accumulator that selectively engages the rod member so that the rod member moves from an initial position to a first position against the spring force of the return spring. A valve that communicates the large diameter cylinder chamber and the small diameter cylinder chamber is held at an open position until the valve moves by a predetermined value or more, and selectively engages with the rod member so that the rod member moves from the initial position to the return position. a relief valve that communicates the large-diameter cylinder chamber with the fluid reservoir when the movement exceeds a second predetermined value that is greater than the first predetermined value against the spring force of a spring; and a fluid pressure in the large-diameter cylinder chamber. A brake master cylinder device comprising a valve that communicates the fluid reservoir with the large diameter cylinder chamber only when the pressure is negative. 2. The brake master cylinder device according to claim 1, wherein the accumulator is incorporated inside the piston member.