Fluid pressure control of braking system

Abstract: In a fluid pressure control apparatus for vehicle including: a main body (2) in which an input opening (4) is formed in communication with a master cylinder side (3) and an output opening (5) is formed in communication with a wheel cylinder side; a stepped bore made in the main body, in communication with the input opening and output opening; a piston (11) slidably fitted into the stepped bore; a throttle means (S) for limiting fluid flowing from the side of the output opening towards the side of the input opening in response to a predetermined length movement of said piston; a path (26) for connecting the input opening side of the piston with the output opening side of the piston; a valve means (T) for closing the path in response to a movement longer than the predetermined length; and an urging apparatus for urging the piston in a direction to open the valve, the urging apparatus comprises a first spring (36) for always urging the piston in a direction to open the valve means, and a second spring (13) for urging said piston in a direction to open the valve means in response to a movement longer than the predetermined length.

Description: This invention relates to a fluid pressure control apparatus which is used in a brake system for vehicle, and more particularly to a fluid pressure control apparatus which is used in a brake system provided with an anti-skid control apparatus. US-A-4 778 222 discloses a brake system for vehicle which includes an anti-skid control apparatus which automatically controls brake fluid pressures on the basis of the rotational conditions of the wheels into order to prevent the wheels from locking on braking, and a proportioning control valve which reduces the increasing rate of the fluid pressure of the wheel cylinder when the fluid pressure of the master cylinder is over a predetermined value. For example, EP-A-366 278 discloses a kind of the above described proportioning control valve. However, the pulsating pressure of the fluid pressure pump is transmitted to the master cylinder side during the anti-skid control in the above-described brake system with anti-skid control apparatus. Accordingly, it is advantageous to arrange a pulsating pressure absorbing apparatus which is disclosed, for example, in EP-A-360 378, and in which throttle means is changed over between the operative position and the inoperative position. However, when a proportioning control valve and a pulsating pressure absorbing apparatus are arranged merely independently and in serial with each other, in the above described brake system with anti-skid control apparatus and proportioning control valve, their conduit-connections are complicated. Since the proportioning control valve includes a stepped piston to open and close a valve, and the pulsating-pressure absorbing apparatus includes a control piston to change over the throttling means between the operative position and the inoperative position, there is further a problem that the entire apparatus is much large-sized. It is considered that the stepped piston of the proportioning control valve is used also as the control piston for the pulsating-pressure absorbing apparatus, and the throttling means is changed over between the operative position and the inoperative position with its movement. In that case, it is necessary that the diameter of the stepped piston, the effective pressure-receiving area of the stepped piston and accordingly the diameter of the stepped hole for inserting the stepped piston are altered for altering a pressure to change over the throttling means into the operative position. Such a consideration is not contributed so much to the reduction of the large-sizing of the apparatus. Further, parts cannot be used in common between systems which are different from each other in a fluid pressure to change over the throttling means into the operative position. Accordingly, this invention is concerned with attempting to provide a fluid pressure control apparatus which is compact in construction, in which respective parts can be used in common between different systems and further function both as a proportioning control valve and a pulsating-pressure absorbing apparatus. In accordance with the present invention there is provided a fluid pressure control apparatus for a vehicle including: (A) a main body in which an input opening is formed for communication with a master cylinder side and an output opening is formed for communication with a wheel cylinder side via an anti-skid apparatus having a fluid pressure pump; (B) a stepped bore made in said main body, in communication with said input opening and output opening; (C) a piston slidably fitted into said stepped bore; (D) a path for connecting the input opening side of said piston with the output opening side of said piston; (E) valve means for closing said path in response to a movement of the piston longer than a predetermined length; and (F) a first spring for always urging said piston in a direction to open said valve means; characterised by: (G) throttle means which is operable to limit fluid flowing from the side of said output opening towards the side of said input opening in response to the predetermined length of movement of said piston against the first spring so as to prevent pulsation of said fluid pressure pump from being transmitted to said master cylinder; and (H) a second spring for urging said piston in a direction to open said valve means in response to a movement of the piston longer than said predetermined length. Specific embodiments of the present invention will now be described by way of example with reference to the accompanying drawings in which: Fig. 1 is a cross-sectional view of a fluid pressure control apparatus according to one embodiment of this invention; Fig. 2 is a cross-sectional view of an important part of a fluid pressures control apparatus according to another embodiment of this invention; and Fig. 3 is a cross-sectional view taken along the line III-III in Fig. 1. Next, a fluid pressure control apparatus according to one embodiment of this invention will be described with reference to the drawings. In Fig. 1, a reference numeral 1 represents generally the whole of the fluid pressure control apparatus according to this embodiment. In this fluid pressure control apparatus for a vehicle, a main body 2 is screwed to a master cylinder 3, as shown by dashed lines. The cylindrical main body 2 consists of a first body portion 2 a and a second body portion 2 b which are screwed to each other as one body. A cup seal 48 is interposed between the first body portion 2 a and the second body portion 2 b . The first body portion 2 a has an input opening 4 to which the master cylinder 3 is connected. A coupling member 7 is screwed to the second body portion 2 b . The coupling member 7 has an outlet opening 5. Screw 7 a is made in an inside surface of the coupling member 7. A not-shown conduit is screwed into the female screw 7 a of the coupling member 7. Another end of the conduit is connected to a not-shown anti-skid apparatus with a fluid pressure pump, which in turn is connected to a not-shown wheel cylinder of a rear brake apparatus. A screw 8 is made on the peripheral surface of the end portion of the first body portion 2 a . A seal ring 10 interposed between the screw 8 and a side wall portion 9 of the first body portion 2 a . A stepped piston 11 is slidably fitted into the stepped bore 6 formed between the first body portion 2 a and the second body portion 2 b . A through axial path 26 is made in the piston 11. A larger-diameter portion 21 of the piston 11 provided with a seal ring 22 is slidably fitted to a bore portion 39 of the second body portion 2 b . The seal ring 24 is fitted into the annular groove formed in the larger-diameter portion 21 of the piston 11. The smaller-diameter portion 23 of the piston 11 is slidably fitted into the central hole of the first body portion 2 a in which a seal ring 24 is fitted. A cup-shaped contact member 19 is fitted to one end portion of the piston 11 at the side of the outlet opening 5. There is some clearance for fluid path between the cup shaped contact member 19 and the end surface of the piston 11. A cylindrical member 28 is securely fitted into a bore portion 27 made in the right end portion of the first body portion 2 a . A poppet-type valve body 29 is arranged in the cylindrical member 28. A top end of the poppet-type valve body 29 is facing into a not-shown fluid pressure generating chamber of the master cylinder 3. A through path 29 a is made in a bottom portion of the poppet-type valve body 29. A central round projection 30 is facing to a valve seat 31 formed on the top end of the piston 11. Thus, a valve V is constituted by the poppet-type valve body 29 and the valve seat 31. The poppet-type valve body 29 is urged towards the valve seat 31 by a valve spring 33. A cover member 32 is fitted into the cylindrical member 28. The valve spring 33 is compressedly extended between the cover member 32 and the bottom portion of the poppet-type valve body 29. The cover member 32 is engaged with an annular groove made in the opening end portion of the first body portion 2 a . A first spring 36 for urging always piston 11 in a direction to open the valve V and a second spring 13 for urging the piston 11 to the direction to open the valve V at the time when the piston 11 is moved more than a predetermined length, are arranged in a larger-diameter portion 6 a of the stepped bore 6 of the main body 2. Thus, an urging apparatus P is constituted by the first spring 36 and second spring 13. One end of the first spring 36 is received by a stepped portion 37 of the piston 11 and another end thereof is received by a stepped portion 38 of the first body portion 2 a . One end of the second spring 13 is received by a cup-shaped spring retainer 12 which has a central opening, and another end thereof is received by the stepped portion 38 of the first body portion 2 a . The spring retainer 12 is freely received by the stepped portion 37 of the piston 11. It can move towards the side of the input opening 4 from the shown position. A conduit member 42 is arranged in an output chamber 51 formed in the second body portion 2 b and it is prevented from falling off, by the coupling member 7. A cylindrical portion of the conduit member 42 is fitted firmly into the bore portion 14 of the second body portion 2 b . A valve-seat forming member 44 is arranged in the bore portion 14. A seal ring 40 is interposed between the valve-seat forming member 44 and the conduit member 42. In the assembling step of the apparatus, the conduit member 42 is first inserted into the bore portion 14 and then the coupling member 7 is screwed into the second body portion 2 b . Thus, the valve-seat forming member 44 is positioned through the conduit member 42. A opening 44 a is formed in the central portion of the valve-seat forming member 44 as shown in Fig. 3. The peripheral edge thereof functions as a valve seat. A cut-out 44 b is further formed in the opening 44 a . The cut-out 44 b constitutes a path for throttling. A poppet-type movable valve body 50 is arranged in a recess 42 a of the conduit member 42 and it is urged towards the side of the inlet opening 4 by a valve spring 43 which is compressedly extended in the recess 42 a of the conduit member 42. A rod portion 50 a of the movable valve body 50 passes through the opening 44 a of the valve-seat forming member 44 and a top end of the rod portion 50 a contacts with the contact member 19. Accordingly, the movable valve body 50 is regulated for its forward stop position. Further a clearance (valve lift) is made between the valve-seat forming member 44 and the movable valve body 50. The outlet port 5 formed in the coupling member 7 and the recess 42 a of the conduit member 42 communicate with each other through a path 16 formed in the conduit member 42. When the poppet-type valve body 50 contacts with the valve-seat forming member 44, the cut-out 44 b formed in the valve-seat member 44 functions as throttle S for throttling the fluid flow in a direction towards the side of the inlet opening 4 from the side of the outlet opening 5. In the shown condition , a spherical portion 50 b of the movable body 50 is separated from the valve-seat forming member 44 and so the throttle S becomes inoperative. In the fluid pressure control apparatus 1 provided with the above-mentioned throttle means S and valve V, a distance A from the bottom portion of the spring retainer 12 to the flange portion 11 a of the piston 11 is smaller than another distance B from the flange portion of the spring retainer 12 to the stepped portion 45 of the first body portion 2 a . Further, the distance that the piston 11 can be moved in the stepped bore 6, namely the distance A plus the distance B is larger than a further distance C from the valve seat 31 of the piston 11 to the round projection 30 of the poppet-type valve body 29. A further distance D that the movable valve body 50 move to close the opening 44 a of the valve-seat forming member 44 by the spherical portion 50 b , is smaller than the distance A. According to this embodiment, under the above conditions, the following ratios are employed : A=0.8, B=1.0, C=1.49 and D=0.5. Next, there will be described operations of the above described fluid pressure control apparatus 1. When the not-shown brake pedal is not yet trodden by the driver, the respective parts are located at the shown positions. In the urging apparatus P, the valve V is opened by the urging force of the first spring 36. The second spring 13 does not act on the piston 11. Thus, the flange portion 11 a of the piston 11 contacts with the stepped portion of the second body portion 2 b . And the rod portion 50 a of the movable valve body 50 contacts with the contact member 19 and it is prevented from moving rightwards. Thus, the throttle S is in inoperative condition. In the shown condition, when the driver depresses the brake pedal, a fluid pressure is generated in the fluid pressure generating chamber of the master cylinder 3. The fluid pressure from the master cylinder 3 is supplied through the inlet opening 4, the axial path 20 of the piston 11 and the opening 44 a of the valve-seat forming member 44 into the outlet opening 5. With a further depression of the brake pedal by the driver, pressure difference between the receiving areas of the inlet side and outlet side of the piston 11 is so increased that the fluid pressure force overcomes the spring force of the first spring 36. The piston 11 is moved rightwards compressing the first spring 36 and so the flange portion 11a of the piston 11 is separated from the stepped portion of the second body portion 2 b . With the increase of the fluid pressure of the brake fluid, the piston 11 is moved further so that the movable valve body 50 contacts with the valve-seat forming member 44. The movable valve body 50 follows the piston 11 with the urging force of the valve spring 43. Accordingly, the spherical portion 50 b of the movable body 50 come to contact with the peripheral edge of the opening 44 a of the valve-seat forming member 44. Thus, the throttle S becomes operative. When the piston 11 has moved by the distance A, the flange portion 11 a of the piston 11 contacts with the bottom portion of the spring retainer 12. After that, the piston 11 is urged leftwards both by the first spring 36 and by the second spring 13. With the increase of the fluid pressure, the piston 11 is moved rightwards against the spring forces of the first and second springs 36 and 13. In some cases, while the piston 11 is moving, or before the fluid pressure does not yet rise up to the knee point pressure or control-start pressure, the wheel tends to lock. The not-shown fluid pressure pump starts to be driven in the anti-skid apparatus, and the brake fluid is returned to the master cylinder 3 through the output opening 5 and the throttle S. According to this embodiment, even when the fluid pressure is lower than the knee-point pressure, or even before the fluid pressure control is started, the throttle S is operative. Accordingly, the pulsation of the fluid pressure pump is not transmitted through the brake pedal to the driver. With the further increase of the brake fluid pressure, the movement length of the piston 11 reaches the distance C, and so the valve seat 31 contacts with the round projection 30 of the poppet-type valve body 29. Thus, the valve V is closed. The fluid pressure control starts. At that time, the flange portion of the spring retainer 12 is separated by a little distance from the stepped portion 45 of the first body portion 2 a . The movable valve body 50 is separated from the contact member 19, and the throttle S is operative. Accordingly, also in the case that the wheel tends to lock after the fluid pressure control start, the pressurized brake fluid from the fluid pressure pump of the anti-skid apparatus is returned through the throttle S into the master cylinder 3. Thus, the pulsation of the fluid pressure pump is attenuated and so pedal-kick force is not transmitted to the driver. When the driver releases the brake pedal from treading, the fluid pressure in the interior of the master cylinder 3 becomes instantaneously negative (or very low), the piston 11 is moved rapidly to the side of the outlet opening 5 by the urging apparatus P. The contact member 19 comes to contact with the rod portion 50 a of the movable valve body 50. The rod portion 50 a of the movable valve body 50 is separated from the valve-seat forming member 44, and it is returned to the shown position. The throttle S becomes inoperative. Accordingly, the brake fluid from the rear wheel brake apparatus is freely returned through a large space between the movable valve body 50 and the valve-seat forming member 44 into the master cylinder 3. Before the throttle S is changed over from the inoperative condition into the operative condition, the piston 11 is urged only by the spring 36. When the operative condition of the throttle S will be started at a lower fluid pressure, the first spring 36 for urging always the piston 11 may be substituted with a spring of smaller spring force. Thus, the fluid pressure that the piston 11 starts to move rightwards, can be lower, and so the effective fluid pressure for throttling can be lower. Or when the operative condition of the throttle S will be started at a higher pressure, the first spring 36 for urging always the piston 11 may be substituted with a spring of larger spring force. Thus, the fluid pressure that the piston 11 starts to move rightwards, can be higher, and so the effective fluid pressure for throttling can be higher. According to this embodiment, the effective fluid pressure for throttling can be easily altered by substituting the first spring 36. It is unnecessary to change the design of the main body and the related parts. The apparatus is not large-sized. Fig. 2 shows an important part of a fluid pressure control apparatus according to a second embodiment of this invention. Parts in Fig. 2 which correspond to those in Fig. 1, are denoted by the same reference numerals, the description of which will be omitted. In Fig. 2 a spring retainer 72 is different from the spring retainer of the first embodiment in shape. A flange portion 72e of the spring retainer 72 contacts with the end of the second body portion 2 b . A piston 61 passes through a central opening 72a of the spring retainer 72. A tapered surface 72c is formed on a left peripheral edge of the central opening 72a. A tapered surface 47 is formed on a first flange portion 46 of the piston 61. The tapered surface 47 is substantially in parallel with the tapered surface 72 c on the left peripheral edge 72 b of the spring retainer 72. They are facing to each other. The distance between the tapered surfaces 47 and 72 c is equal to the distance A. When the piston 61 is moved rightwards by the distance A, the tapered surface 72 c of the spring retainer 72 comes to contact with the tapered surface 47 of the first flange portion 46 of the piston 61. A positioning means T is formed by the tapered surfaces 47 and 72 c . Thus, the spring retainer 72 is positioned relative to the piston 61, when the tapered surfaces 47 and 72 c contact with each other. The whole of the spring retainer 72 can be freely moved between the first flange portion 46 of the piston 61 and a second flange portion 37 thereof. However, the spring retainer 72 is prevented from deflecting in the radial direction by the positioning means T. Accordingly, the good braking performance can be obtained. Axial grooves 69 are formed on a top of the left end portion of the piston 61. Thus, a fluid path is formed between the rod portion 50 a of the movable valve body 50 and the top end portion of the piston 61. While the preferred embodiments have been described, variations thereto will occur to those skilled in the art within the scope of the present inventive concepts which are delineated by the following claims. For example, in the above embodiment, the cut-out 44 b is formed for throttling at the peripheral edge of the opening 44 a of the valve-seat member 44. Instead of the cut-out 44 b , a smaller groove may be formed on the spherical surface 50 b of the movable body 50. When the spherical surface of the movable valve body 50 contact with the peripheral edge of the central opening 44 a of the valve-seat forming member 44, the throttle means S is formed.

Claims: A fluid pressure control apparatus for a vehicle including: (A) a main body (2) in which an input opening (4) is formed for communication with a master cylinder (3) side and an output opening (5) is formed for communication with a wheel cylinder side via an anti-skid apparatus having a fluid pressure pump; (B) a stepped bore made in said main body, in communication with said input opening and output opening; (C) a piston (11) slidably fitted into said stepped bore; (D) a path (26) for connecting the input opening side of said piston with the output opening side of said piston; (E) valve means (V) for closing said path in response to a movement of the piston longer than a predetermined length; and (F) a first spring (36) for always urging said piston in a direction to open said valve means; characterised by: (G) throttle means (S) which is operable to limit fluid flowing from the side of said output opening towards the side of said input opening in response to the predetermined length of movement of said piston against the first spring so as to prevent pulsation of said fluid pressure pump from being transmitted to said master cylinder; and (H) a second spring (13) for urging said piston in a direction to open said valve means in response to a movement of the piston longer than said predetermined length. A fluid pressure control apparatus according to claim 1, in which said second spring is received by a spring retainer (12, 72) and when said piston is moved by longer than said predetermined length movement, said spring retainer is engaged with said piston for urging said piston in said direction, and said apparatus comprises positioning means for positioning said spring retainer to said piston in engagement with said piston. A fluid pressure control apparatus according to claim 2, in which said positioning means comprises a tapered flange portion (47) of said piston and a tapered edge (72c) of a central opening of said spring retainer, said tapered flange portion coming to contact with said tapered edge with said longer movement than the predetermined length. A fluid pressure control apparatus according to any preceding claim, in which spring force of said first spring is smaller than that of said second spring, and said first spring is so designed as to make said throttle means being inoperative to the initial condition. A fluid pressure control apparatus according to any preceding claim, in which said throttle means comprises a poppet-type valve body (50) arranged at the output opening side of said piston, a spring (43) for urging said poppet-type valve body towards said piston, a valve seat member (44) fixed to said main body, and a cut-out (44b) formed in a spherical portion of said valve body or in a peripheral edge of a central opening of said valve seat member. A fluid pressure control apparatus according to any preceding claim, in which said path is a through axial hole (26) made in said piston. A fluid pressure control apparatus according to any preceding claim, in which said valve means comprises a poppet-type valve body (29), a valve spring (33) for urging said poppet-type valve body towards one end of said piston and a valve seat (31) formed at one end of the piston.

Inventors: IHARA YOSHIFUMI, IHARA, YOSHIFUMI
Applicants: NIPPON AIR BRAKE CO, NIPPON AIR BRAKE CO., LTD.
Application year: 1991
Main classification: B60T8
IPC codes: B60T8, B60T11