Hydraulic booster

Abstract: A hydraulic booster for vehicle, includes: a cylinder body (2) having a cylindrical bore; a piston (19) slidably fitted into the cylindrical bore; a pressure-servo chamber (29) formed at one side of the cylindrical bore by the piston; a valve hole (64) made in the side of the pressure-servo chamber in the piston; a pressure supply path extending into the valve hole and communicating with a fluid pressure source; a pressure discharge path extending into the valve hole and communicating with a pressure-relieving source; an input member (9) passing through the pressure-servo chamber and entering the valve hole; a pressure-supply valve (E) arranged in the valve hole for opening and closing the path between the pressure supply path and the pressure-servo chamber in response to the movement of the input member; a valve (G) arranged in the valve hole for opening and closing the path between the pressure discharge path and the pressure-servo chamber in response to the movement of the input member; a reaction chamber (88) in which the input member is able to receive the pressure-servo chamber side pressure of the pressure-supply valve in a direction against the input direction of the input member; and a valve apparatus (A) arranged in a path to the reaction chamber and preventing fluid pressure from transmitting into the reaction chamber at a lower pressure than a predetermined pressure. In the hydraulic booster, a by-pass path is arranged for connecting the pressure-servo chamber with the pressure-discharge valve without passing through the reaction chamber.

Description: This invention relates to a hydraulic booster for a vehicle which assists the driver with the operation of the master cylinder. Patent application JP-A-2-68258 discloses pressure-discharge valves which are closed and opened in response to the movement of the input member, and which are provided for a pressure chamber and for a reaction chamber, respectively. When brake is relieved, the discharge valve for the reaction chamber is opened sooner than that for the pressure servo-chamber. Accordingly, the pressure fluid from the pressure servo-chamber opens a valve apparatus (check valve), which is provided for obtaining jump-up phenomenon, and flows into a pressure relieving source through the reaction chamber until the opening of the discharge valve for servo-chamber, after the opening of the discharge valve for reaction chamber. Flow amount of the pressurized fluid is increased in the single discharge path. Accordingly, abnormal noise is made from the check valve, and the brake relieving action lags. Patent application DE-A-3912936 describes a discharge valve which is provided for a servo-chamber. One valve (check valve) is arranged between the servo-chamber and a reaction chamber, which prevents pressure fluid from flowing into the reaction chamber below a predetermined pressure. Another valve (check valve) is arranged between the servo-chamber and the reaction chamber, by which pressure fluid is permitted to flow into the servo-chamber from the reaction chamber when the fluid pressure of the servo-chamber becomes lower than that of the reaction chamber. When the brake is relieved, all of the pressure fluid from the reaction chamber is discharged through the servo-chamber. Accordingly, flow amount in the single path is increased in the above prior art JP-A-2-68258, and the brake-relieving action lags. Patent Application GB-A-2207205 describes a reaction piston which is mechanically engageable with an output rod for obtaining a reaction mechanism. The reaction chamber communicates always with an oil tank which is at atmospheric pressure. In accordance with the present invention there is provided a hydraulic booster for a vehicle, comprising: a cylinder body having a cylindrical bore; a piston slidably fitted into said cylindrical bore; a pressure-servo chamber formed at one side of said cylindrical bore by said piston; a valve hole made in a side of said pressure-servo chamber in said piston; pressure supply path means extending into said valve hole and communicating with a fluid pressure source; pressure discharge path means extending into said valve hole and communicating with a pressure-relieving source; an input member passing through said pressure-servo chamber and entering said valve hole for movement thereinto when input pressure is applied to said input member; pressure-supply valve means arranged in said valve hole for opening and closing the path between said fluid pressure source and said pressure-servo chamber in response to the movement of said input member; pressure-discharge valve means arranged in said valve hole for opening and closing the path between said pressure discharge means and said pressure-servo chamber in response to the movement of said input member; a reaction chamber in which said input member is able to receive the pressure-servo chamber side pressure of said pressure-supply valve means in a direction against the input direction of said input member; and valve apparatus arranged in a path to said reaction chamber and preventing fluid pressure from transmitting into said reaction chamber at a lower fluid pressure than a predetermined pressure; said path to the reaction chamber being formed as an axial path in a sleeve member, securely fitted into said piston, communicating with said pressure supply path means and said valve apparatus being a check valve arranged in said path; characterised in that: by-pass means is arranged for connecting said pressure-servo chamber with said pressure-discharge valve means without passing through said reaction chamber. By providing such an independent flow path, the brake relieving action can be improved and noise reduced. A specific embodiment of the invention will now be described by way of example with reference to the accompanying drawings in which: Figure 1 is a partially-broken side view of a hydraulic booster according to one embodiment of this invention; Fig. 2 is an enlarged cross-sectional view of an important part of the hydraulic booster of Fig. 1; Fig. 3 is an enlarged cross-sectional view taken along the line III-III in Fig. 2; Fig. 4 is an enlarged front view of a seal member in the hydraulic booster in Fig. 2; Fig. 5 is a cross-sectional view taken along the line V-V in Fig. 4; Fig. 6 a graph for comparing the operations of this invention and prior art; Fig. 7 is a conduit diagram of a brake control system to which the hydraulic booster of Fig. 1 is applied; and Fig. 8 is an enlarged cross-sectional view of the details of an important part of the brake control system shown in Fig. 7. In the drawings, the whole apparatus of this embodiment is represented generally by a reference numeral 1. A stepped bore 5 is made in a cylinder body 2. The rear end opening of the cylinder body 2 is covered with a cover member 6. The cover member 6 provided with an O-ring 16 is fixed to the cylinder body 2 by screws. The wall apparatus is fixed to a not-shown toe-board. A rod-like input member 9 through a cup-seal 11 is slidably fitted into a central through hole 8 of the cover member 6. In this description, "forward" means "leftward" and "backward" means "rightward". The cylinder bore 5 of the body 2 consists of a larger-diameter bore portion 17 to which the cover member 6 is fitted, and a smaller-diameter portion 18 as a major part. A piston 19 is slidably fitted through into the larger-diameter bore portion 17 and the smaller-diameter bore portion 18. The piston 19 has a first larger-diameter portion 25 at its rear end and a second larger-diameter portion 26 at its front end. Seal rings 20 a and 20 b are fitted into the first and second larger-diameter portions 20 a and 20 b respectively. Rings 26 a and 26 b of synthetic resin such as Teflon are further fitted on the peripheries of the seal rings 26 a and 26 b so that the sliding resistance of the piston 19 is reduced so much. Thus, an accumulator pressure chamber 28 is made between the first larger-diameter portion 25 and the second larger-diameter portion 26, and a pressure-servo chamber 29 is made between the first larger-diameter portion 25 and the cover member 6. On the other hand, a rod member 12 through a cup seal 10 is slidably fitted into a hole 2 c made in a bottom wall portion 2 b of the cylinder body 2. A bolt 45 is screwed to a head portion of the rod member 12, and it contacts with a not-shown piston of a master cylinder. Thus, a non-pressure chamber 27 is made between the second larger-diameter portion 26 of the piston 19 and the bottom wall portion 2 b of the cylinder body 2. Cup-shaped and annular spring receivers 46 and 47 are arranged at the front end of the piston 19 and at the bottom wall 2 b of the cylinder body 2, respectively. A spring 48 is extended under compressed condition between the spring receivers 46 and 47 . A boss portion 55 is made at the upper wall portion of the front part of the cylinder body 2. A fluid connecting port 56 of the boss portion 55 always communicates through a drain hole made in the wall portion of the cylinder body 2, with the non-pressure chamber 27. A "Grommet" seal 57 is compressedly fitted into the fluid connecting port 56. A nipple 58 for connection to a not-shown reservoir is combined with the "Grommet" seal 57. The piston 19 is a main constituent of the hydraulic booster 1. A boss portion 62 is made above the accumulator pressure chamber 28 in the cylinder body 2. A conduit is connected to the boss portion 62. Another end of the conduit is connected to a not-shown accumulator. Pressurized fluid is stored in the not-shown accumulator always under the predetermined range of pressure. A not-shown check valve consisting of a ball and a spring is arranged in the boss portion 62. It permits fluid to flow in the direction from the top towards the bottom in Fig. 2. It can communicate through a path 62a with the accumulator pressure chamber 28. A stepped axial valve hole 64 is made in the rear side of the piston 19. A movable valve body 67 is slidably fitted through into a smaller-diameter hole portion 65 and intermediate-diameter hole portion 66 of the valve hole 64. The front end portion through a seal member 99 is slidably fitted into the smaller-diameter hole portion 65. The smaller-diameter hole portion 65 of the valve hole 64 communicates through an axial hole 12 a of the rod member 12 and a radial path 39 with the non-pressure chamber 27. A ring of synthetic resin such as Teflon is overlapped on the seal ring 99 of rubber, so as to reduce the slide resistance of the movable body 67. Through hole 67 c is made in the movable valve body 67 and it communicates with the non-pressure chamber 27. A spring receiver ring 59 is arranged at the step between smaller-diameter hole portion 65 of the valve hole 64 and the intermediate-diameter hole portion 66 thereof so as to contact with the seal ring 99. A valve spring 68 is compressedly extended between the spring receiver ring 59 and an annular projecting portion 67 a formed on the peripheral portion of the movable valve body 67. Thus, the movable valve body 67 is urged backwards. A valve guide member 75 provided with a seal ring 74 is securely fitted into the rear opening portion of the valve hole 64 of the piston 19, and a sleeve member 80 is closely fitted into the valve guide member 75 as one body. The sleeve member 80 is prevented from falling off, by a stopper member 76 screwed to the rear end opening of the piston 19. The intermediate portion of the movable valve body 67 is slidably into the central hole of the valve guide member 75. The rear end of the movable valve body 67 is facing to a tapered recess 78 of the valve seat member 81 which is fitted into the front end portion of the input member 9. The annular projecting portion 67 a of the movable valve body 67 contacts with the front end 75 a of a valve guide member 75, so that the relative backward position of the movable valve body 67 to the piston 19 is regulated. An input chamber a is formed around the intermediate portion of the movable valve body 67, in the valve hole 64 of piston 19. It always communicates through a path 69 made in the peripheral wall portion of the piston 19, with the accumulator pressure chamber 28. A communicating chamber b is formed between the valve guide member 75 and the sleeve member 80. A supply valve E is constituted by the annular projecting portion 67 a of the movable valve body 67 and the front end portion 75 a of the guide member 75. It is closed in the normal condition as shown in Figures 2 and 3. When it is opened, the fluid pressure transmitted into the input chamber a from the accumulator as a fluid pressure source is transmitted through a pressure leading path C to the supply valve E into the recess 77 of the valve guide member 75. It is further supplied through a slant hole 79 of the valve guide member 75 into the pressure-servo chamber 29. A discharge valve G is formed by the rear end of the movable valve body 67 and a valve seat 78 a which is formed by a tapered surface of the recess 78 of the valve seat member 81. It closes in the normal condition as shown in Figures 2 and 3. As shown in Fig. 3 taken along the line III-III of Fig. 2, radial paths 94 are formed in the peripheral wall of the sleeve member 80. Further axial grooves 84 are formed in the peripheral wall of the sleeve member 80. They communicate with the radial paths 94. Right ends of the axial paths 84 communicate with an annular groove 82 formed in the rear end portion of the sleeve member 80. Thus, a chamber 95 including a head portion of the valve seat member 81 and the discharge valve G communicates always through the path 94, the axial groove 84, the annular groove 82 and radial paths 83 formed in the rear end portion of the piston 19 with the pressure-servo chamber 29. Accordingly, the fluid pressure from the pressure-servo chamber 29 is transmitted into the chamber 95. When the discharge valve G is opened, the fluid pressure through the discharge valve G is introduced into a discharging path B communicating with the fluid pressure relieving source. The valve seat member 81 provided with a seal ring 85 is slidably fitted into the front end portion of the input member 9. A spring 86 is extended under the compressed condition between the valve seat member 81 and the valve guide member 75. Thus, the valve seat member 81 is urged backwards. Axial recesses 96 and 87 are formed in the peripheral wall portion of the sleeve member 80 as shown in Fig. 2 and further axial paths 96 a and 87 a are formed in recesses 96 and 87. An annular reaction chamber 88 is formed between the input member 9 and the sleeve member 80. The rear ends of the paths 96 a and 87 a communicates with the reaction chamber 88. Thus, the reaction chamber 88 communicates through the paths 96 a and 87 a with recesses 96 and 87. In the recess 96, a valve body 89 and a spring 90 urging the valve body 89 are arranged and the former seats on a valve seat 63 in the non-operating condition. A check valve H is constituted by the valve body 89 and valve seat 63, and it permits fluid to flow from the reaction chamber 88 towards the communicating chamber b . On the other hand, a valve body 91 and a spring 92 are arranged in the recess 87. The valve body 91 is made to contact with a valve seat 93 by a spring 92 in the non-operating condition. Thus, a check valve A is constituted by the valve body 91, the valve seat 93 and the valve spring 92. A pressure fluid is prevented from transmitting to the reacting chamber 88 from the communicating chamber b under a lower pressure than a predetermined value. On the other hand, an annular groove 80 a is formed in inside wall of the intermediate portion of the sleeve member 80 and a seal member 97 is fitted into the annular groove 80 a . Further, an annular groove 9 b is formed in the top end portion of the input member 9. A seal member 98 is fitted into the groove 9 b . The seal members 97 and 98 are shown in Fig. 4, and Fig. 5 in the natural condition. They have four projecting portions 97 a and 98 a respectively, which work as elastic elements when they are pressed into the annular grooves 80 a . The seal members 97 and 98 are fitted into the annular grooves of the sleeve member 80 and input member 9 in opposite manners. The diameter of the seal member 98 is larger than that of the seal member 97. A communicated chamber made between the reaction chamber 88 and pressure-servo chamber 29, and it is sealed from the reaction chamber 88 while it communicates with the pressure-servo chamber 29. Next, there will be described operations and effects of the hydraulic booster 1 as above described. In the non-operating condition, the respective parts are located at the shown positions. The flange portion 9 c of the input member 9 is made to contact with the stopper 76. In the shown condition, when the driver depresses the brake pedal, the input member 9 is moved forwards at once and so the movable valve body 67 is pushed forwards through the valve seat member 81 by the front end of the input member 9, since the valve lift between the valve seat member 81 and the movable valve member 67 is zero. When the input member 9 is moved forwards, the movable valve body 67 is moved leftwards relative to the piston 19 against the spring force of the valve spring 68. Thus, the annular projecting portion 67 a is separated from the front end 75 a of the valve guide member 75. Thus, the supply valve E is opened and accordingly, the pressurized fluid from the input chamber a is led through the recess 77 and the port 79 into the pressure-servo chamber 29. Thus, the right end surface of the piston 19 receives the fluid pressure and a leftward force is applied to the piston 19. "Jump-up" phenomeon is prepared in the hydraulic booster 1. When the supply valve E is opened and so a pressure of the pressure-servo chamber 29 reaches the opening valve pressure of the valve A, the fluid pressure is introduced into the reaction chamber 88 and thus the "jump-up" phenomenon is completed in the hydraulic booster 1. Then, the "jump-up" phenomenon occurs also in the master cylinder side in accordance with the input transmitted from the hydraulic booster 1. When the check valve A is opened, the following fluid pressure F is applied to the input member 9. If D₁=D₂ , F=(D₂-D₃) × (P₁-P₂) + (D₃-D₄) × P₁ or if D₁<D₂, F=(D₂-D₃) × (P₁-P₂) + {(D₃-D₄) - (D₂-D₁)} × P₁, where D₁ is equal to the sealing area of the input member 9 by the cup seal 11, D₂ the sealing area of the input member 9 by the seal member 98, and D₃ the sealing area of the input member 9 by the seal member 97, D₄ the sealing area of the top end portion of the movable valve body 67 to the valve seat member 81, D₅ the sealing area of the input member 9 by the seal member 85, P₁ the pressure of the pressure-servo chamber 29, P₂ the opening pressure of the check valve A, and D₄ is so predetermined as to be nearly equal to D₅. As above described, in the hydraulic booster 1 according to this embodiment, when the input to the input member 9 reaches f₁, the master cylinder pressure steeply rises up to J as shown by the solid line in Fig. 6. Thus, "jump-up" phenomenon occurs at the input f₁. After the "jump-up" phenomenon ends, the master cylinder pressure rises linearly in proportion to the input in the same manner as the prior art hydraulic booster. The height of the "jump-up" J corresponds to the sum of the different resistant forces as described below. Some sliding resistance is imparted to the piston 19 by the rings 26 a and 26 b of synthetic resin which are arranged in the annular grooves in the first and second larger-diameter portions 25 and 26 of the piston 19. Also the spring force of the spring 68 urging the movable valve body 67 is resistive to the forward movement of the piston 19. The sliding resistance of the synthetic resin rings overlapping the seal ring 99 fitted to the movable valve body 67 and that of the seal ring 11 fitted into the input member 9 function as resistance to the forward movement of the piston 19. The "jump-up" J corresponds to the sum of the above sliding resistances of the respective seal members and all of the spring forces of the respective springs. When the hydraulic booster 1 is in the balanced condition, both the supply valve E and the discharge valve G close. On the other hand, when the driver releases his foot from the brake pedal to relieve the brake, the input member 9 is moved rightwards or backwards with the fluid pressure of the pressure-servo chamber 29 and reaction chamber 88, and the spring force of the spring 86. Accordingly, the discharge valve G is opened. Thus, the fluid pressure from the pressure-servo chamber 29 is returned to the reservoir side as the fluid pressure relieving source, through the communicating chamber b , the hole 94, the chamber 95 and the discharging path B. When the fluid pressure from the pressure-servo chamber 29 is returned through the discharging path B into the reservoir side, the pressure difference between the pressure-servo chamber 29 and the reaction chamber 88 is increased, and when it reaches the opening valve pressure of the check valve H, the check valve H is opened and the pressurized fluid from the reaction chamber 88 is led into the communicating chamber b through the check valve H. It is returned through the discharging path B into the reservoir side. Thus, the fluid pressure in the reaction chamber 119 becomes zero and the piston 19 and the input member 9 are moved back to the shown conditions and so the brake is relieved. Next, a brake conduit system using the above described hydraulic booster will be described with reference to Fig. 7. Hydraulic reservoirs 13 and 53 are arranged for the tandem master cylinder 12 and a hydraulic booster part 50. The reservoirs 13 and 53 are made to communicate with each other through a connecting path 14. The connecting path 14 is so arranged as to be levelled at the height of the inside partition wall 13 a of the reservoir 13 of the tandem master cylinder 4. In consideration of the fact that the fluid is supplied and discharged between the master cylinder 12 and the hydraulic booster part 50, it is arranged for preventing over-flow of the fluid. Accordingly, when the reservoir 53 for the hydraulic booster and the reservoir 13 for the master cylinder are formed as one body, the central connecting path 14 can be omitted. In this embodiment, the oil pressure source for the hydraulic booster part 50 is used also for the ASR control operation. The oil pressure source includes a fluid pressure pump 52 for pressurizing fluid, an electric motor 51 driving the fluid pressure pump 52 and a hydraulic accumulator 54. The accumulator 54 consists of a membrane type accumulator 54 a , a piston type accumulator 54 b and a check valve 54 c . The conduit type of this embodiment is of the front-rear separation type. An outlet port 4 a of the tandem master cylinder 4 is connected to one conduit 21 and the conduit 21 is divided into conduits 21 a and 21 b . They communicate with the wheel cylinders of brake apparatus 23 a and 23 b of front wheels. Another outlet port of the tandem master cylinder 4 is connected to a fluid pressure control valve 60 (a proportional control valve ) for control of the fluid pressure. A brake conduit 22 is connected to the proportional control valve 60. The brake conduit 22 is divided into conduits 22 a and 22 b and they communicate with the wheel cylinders of brake apparatus 24 a and 24 b for rear wheels. In this embodiment, the rear wheels are driven wheels. Thus, in the conduits 21, 22 and 24 a , 22 b , an electro-magnetic valve appratus 40 for an ASR control and an oil pressure control unit 30 for an ABS control are arranged. The oil pressure control unit 30 for ABS control is common for the brake apparatus 23 a , 23 b , 24 a , 24 b for the front and rear wheels. And they are located at the divided conduits 21 a , 21 b , 22 a and 22b. The oil pressure control unit 30 further includes three-position three-port electro-magnetic change-over valves 35 and check valves 36 connected in parallel with the electro-magnetic change-over valves 35 and low pressure hydraulic reservoirs 37 restoring brake fluid descharged from the wheel cylinders. Brake fluid discharged into the hydraulic reservoir 37 is pressurized by two fluid pressure pumps 321 and 322 which are driven by one common electric motor 31, and the brake fluid is returned to the brake conduits 21 and 22. A check valve device 33 and a damping valve unit 34 are arranged between the output ports of the master cylinder 4 and the fluid pressure pumps 321, 322 to prevent the pulsation of the fluid pressure pumps 321, 322 transmiting to the master cylinder side. When the pressure of the master cylinder 4 becomes higher than a predetermined pressure, the check valve device 33 is changed over to the position 33 a in which the side of the pump 321 and the side of the master cylinder 4 are cut off from each other and the pulsation of the pump 321 is prevented from transmitting to the master cylinder side. The check valve device 33 perfectly cuts the fluid flowing into the master cylinder side. Accordingly, a high-pressure hydraulic reservoir 38 is arranged in the conduit 21. The pressurized fluid from the fluid pressure pump 321 is stored in the high-pressure hydraulic reservoir 38. The damping valve unit 34 includes throttle 34 a connected in parallel with a check valve. The pulsation of the fluid pressure pump 322 is prevented from transmiting to the master cylinder side. The electro-magnetic change-over valve 35 in the oil pressure control unit 30 for the ABS control operation is of the current control type. Control signals from a not-shown electronic control unit are supplied to the change-over valves 35. It is changed over into a brake holding condition, a brake relieving condition or brake applying condition in accordance with a current level of the control signal from the electronic control unit. The electro-magnetic change-over valves 35 are in the communicating conditions as shown in Fig. 7. On the other hand, the electro-magnetic change-over valve apparatus 40 for the ASR control operation includes a first change-over valve 41 arranged in the brake conduit 22 for the rear wheels as the driven wheels and a second change-over valve 42 arranged in a conduit connecting the side of the brake apparatus 24a, 24b and further the side of the valve 41 with the oil pressure source for the hydraulic booster part 50. In the above-described manner, the brake fluid is discharged into the pressure relieving source from the pressure-servo chamber 29 and the reaction chamber 88. However, in contrast to the prior art, no abnormal sound is made, and the brake relieving operation is rapid. The input member 9 is moved rightwards relative to the piston 19 and movable valve body 67 by the pressure of the reaction chamber 88 and spring force of the spring 86. Accordingly, the valve seat member 81 is separated from the rear end of the movable valve body 67. Thus, the discharge valve G is opened. When the discharge valve G is opened, the pressurized fluid from the pressure-servo chamber 29 is discharged through the axial groove 28, the communicating chamber b and the through hole 65 into the reservoir side. The piston 19 is moved rightwards by spring action of the spring 48. The input member 9 is moved further rightwards, and the flange portion 9 c of the input member 9 comes to contact with the retainer r for stop. After the input member 9 stops at the retainer r , the piston 9 still moves rightwards and it contacts with the retainer r . With the movement of the piston 19, the spring 86 is compressed and the movable valve body 67 approaches the valve seat member 81. At last, it seats on the valve seat member 81. Thus, the discharge valve G closes as shown in Fig. 2 and Fig. 3. Also the supply valve E closes as shown in Fig. 2. Before the discharge valve G closes, the pressure of the reaction chamber 88 becomes higher by more than the opening valve pressure of the valve H than that of the communicating chamber b , and so the valve H is opened. From that time, the brake fluid is discharged into the brake relieving source also from the reaction chamber 88. However, the dischargeing amount of brake fluid flowing through the check valve H corresponding to the second valve apparatus of the hydraulic booster of the prior art is smaller than that of the prior art. Accordingly, no abnormal sound is made, and the brake relieving operation is smoothed. Next, there will be described the details of the electro-magnetic valve apparatus 40 for the ASR control operation and of the damping unit 34 with reference to Fig.8. A wall portion 501 is a part of the cylinder body 2 of the hydraulic booster 1. A reference numeral 502 represents a part of the cylinder bore 5. The master cylinder 4 is combined at a stepped portion 503 of the cylinder body portion 502 with the hydraulic booster part. Axial paths 505 and 506 are formed in parallel with the cylinder bore portion 502, in the wall portion 501. Ends of the paths 505 and 506 are blocked with a ball 507 and a screw element 508, respectively. Mounting holes 509, 510, 511 and 512 for mounting the damping valve unit 34, the first change-over valve 41, the relief valve 43 and the second change-over valve 42 are formed in parallel with each other, and in intersection with the axial paths 505 and 506, respectively. In the damping valve 34, a stepped plunger 344 is slidably fitted into a main body 341. A poppet-type valve body 345 is arranged at the lower end of the stepped plunger 344, urged by a valve spring 346. An output side of the proportioning valve 60 is connected through a steel conduit to a connecting port 343 a of a cover member 343 screwed to the main body 342. A cut-out 345 a is formed as the throttle 34 a in the valve body 345. The pressurized fluid from the master cylinder side pushes up the valve body 345 and so it can freely flow towards the axial path 505. Accordingly, the cut-out 345 a does not function as throttle. However, the cut-out 345 a functions as a throttle for the pressurized flow from the oil pressure control unit 30. Accordingly, the pulsation of the fluid pressure pump 322 can be effectively damped. When the pressure of the master cylinder is decreased to relieve the brake, the stepped plunger 344 is moved towards the cover member 343 by the pressure difference between the end surfaces. The valve body 345 is separated from a valve seat member 347. The throttle action of the cut-out 345 is released, and the pressurized fluid can be rapidly returned into the master cylinder side. In the first change-over valve 41, a stator block is fixedly fitted into the mounting hole 510, and vertical paths 416 and 417 are formed therein. A valve ball 418 is fixed on the top of a magnetic plunger 415 which is driven by a solenoid 413. The first change-over valve 41 is normally open. When the solenoid 413 is energized by an ASR control signal from a control unit, the plunger 415 is moved upwards, and the ball 418 comes to seat on a valve seat 416 a . An opening 416 b of the vertical path 416 communicates through the axial path 505 with the side of the damping valve 34. On the other hand, an opening 417 b of the vertical path 417 communicates through the second axial path 506 with the side of the second change-over valve 42. In the relief valve 43, a plug member 432 is fixedly fitted into the mounting hole 511. A T-shaped path 432 a is formed in the plug member 432, A ball 436 normally seats on a top end of a vertical portion of the T-shaped path 432 a , urged by a valve spring 435. The T-shaped path 432 a communicates with the side of the oil pressure control unit 30. When the pressure of the side of the oil pressure control unit 30 is excessively increased, the ball 436 is separated from the valve seat 433 a , and high pressurized fluid is relieved into the axial path 505. In the second change-over valve 42 and the check valve 54 c , a stator block 421 is fixedly fitted into the mounting hole 512, and a body for the check valve 54 c is arranged above the stator block 421. Vertical paths 426 and 427 are formed in the stator block 421. A ball 428 fixed on a magnetic plunger 425 seats normally on the lower end of the vertical path 426. Accordingly, the paths 426 and 427 are cut off from each other. A top end opening 426 b of the vertical path 426 communicates with the piston type accumulator 54 b , while a top end opening of the vertical path 427 communicates with the axial path 506. A path 501 a above the check valve 54 c communicates with the side of the accumulator 54 a . When the solenoid 423 is energized by an ASR control signal, the plunger 425 is moved downwards and the ball 428 is separated from the lower end of the vertical paths 426. The paths 426 and 427 are made to communicate with each other. While the preferred embodiment has been described, variations thereto will occur to those skilled in the art. For example, in the above embodiment the discharge valve G is constituted by the conical valve seat 78 formed on the valve seat member 81, and the rear end of the movable valve body 67. However, a well-known valve construction may be used as the discharge valve G instead of the illustrated construction. Further, this invention may be applied to a prior art hydraulic booster including a reaction chamber, not limited to the illustrated hydraulic booster 1. In the above embodiment, the valve lift between the rear end of the movable valve body 67and the valve seat 78 of the valve seat member 81, or the valve lift of the discharge valve G is zero. Thus, the rear end of the movable valve body 67 contacts with the valve seat 78 of the valve seat member 81 in the non-operating condition. However, the valve lift of the discharge valve G does not always need to be zero. In other words, the rear end of the movable valve body 67 may be separated by a certain value ℓ from the valve seat 78 of the valve seat member 81. In that case, the chamber 95 communicating with the pressure-servo chamber 29 may communicate with the reaction chamber 88, through the annular groove 80 a to which the seal member 97 is fitted. For example, an annular groove is made in the peripheral wall of the input member 9, facing to the annular groove 80 a , and a space ℓ₁ smaller than ℓ is made between the valve member 97 and the backward inside wall portions of the annular grooves of the input member 9 and the sleeve member 80 in the non-operating condition. When the driver depresses the brake pedal, the reaction chamber 88 is first cut off from the chamber 95, and then the valve seat 78 a is made to contact with the rear end of the movable valve body 67.

Claims: A hydraulic booster (1) for a vehicle, comprising: a cylinder body (2) having a cylindrical bore (5); a piston (19) slidably fitted into said cylindrical bore (5); a pressure-servo chamber (29) formed at one side of said cylindrical bore (5) by said piston (19); a valve hole (64) made in a side of said pressure-servo chamber (29) in said piston (19); pressure supply path means (62, 28, 69) extending into said valve hole (64) and communicating with a fluid pressure source (52, 54); pressure discharge path means (65, 27, 56) extending into said valve hole (64) and communicating with a pressure-relieving source (53); an input member (9) passing through said pressure-servo chamber (29) and entering said valve hole (64) for movement thereinto when input pressure is applied to said input member (9); pressure-supply valve means (E) arranged in said valve hole (64) for opening and closing the path between said fluid pressure source (52, 54) and said pressure-servo chamber (29) in response to the movement of said input member (9); pressure-discharge valve means (G) arranged in said valve hole (64) for opening and closing the path between said pressure discharge means (65, 27, 56) and said pressure-servo chamber (29) in response to the movement of said input member (9); a reaction chamber (88) in which said input member (9) is able to receive the pressure-servo chamber (29) side pressure of said pressure-supply valve means (E) in a direction against the input direction of said input member (9); and valve apparatus (A) arranged in a path to said reaction chamber (88) and preventing fluid pressure from transmitting into said reaction chamber (88) at a lower fluid pressure than a predetermined pressure; said path to the reaction chamber (88) being formed as an axial path (87) in a sleeve member (80), securely fitted into said piston (19), communicating with said pressure supply path means (62, 28, 69) and said valve apparatus (A) being a check valve arranged in said path; characterised in that: by-pass means (82, 84, 94) is arranged for connecting said pressure-servo chamber (29) with said pressure-discharge valve means (G) without passing through said reaction chamber (88). A hydraulic booster according to claim 1, in which said pressure-supply valve means (E) includes a movable valve body (67), a valve guide member (75) securely fitted into said piston (19), one end portion of said movable valve body being slidably fitted through the axial hole of said valve guide member, a valve seat (75a) formed at one end of said axial hole of the valve guide member and an annular projection (67a) formed on said movable valve body being able to seat on said valve seat. A hydraulic booster according to claim 2, in which said pressure-discharge valve means (G) includes said movable valve body (67), a through axial hole made in said movable valve body, a valve seat member (81) facing to a top end of said movable valve body and slidably fitted into a top end portion of said input member (9) and a spring (86) urging said valve seat member to said input member. A hydraulic booster according to claim 3, in which said top end of the movable valve body (67) seats on said valve seat member (81) in the inoperative condition. A hydraulic booster according to any preceding claim, in which a second axial path (96) is formed in said sleeve member (80) so as to make said reaction chamber (88) communicating with said pressure supply path means (62, 28, 69), and a second check valve (H) arranged in said second axial path, permitting fluid to flow from said reaction chamber towards said pressure-supply path means. A hydraulic booster according to any preceding claim, in which said by-pass means (83, 84, 94) comprises a radial hole (94) made in said sleeve member (80), an axial groove (84) made therein and another hole (83) made in one end portion of said piston (19) communicating with said axial groove.

Inventors: ISHIWATA ICHIRO, ISHIWATA, ICHIRO
Applicants: NIPPON AIR BRAKE CO, NIPPON AIR BRAKE CO., LTD.
Application year: 1991
Main classification: B60T13
IPC codes: B60T13