GB1345951A - Hydraulic boosters for vehicle braking systems - Google Patents

Abstract

1345951 Hydraulic boosters GIRLING Ltd 4 Oct 1972 [14 Oct 1971 29 March 1972] 47811/71 and 14632/72 Headings F2E and F2F An hydraulic booster for a vehicle braking system comprises a housing 1 having a stepped bore 2 in which works an intermediate piston 7 located between an input rod controlling a piston 13 and an output piston 18, a first pressure space 41, 16, 49 within the bore 2 to which the output piston 18 is exposed, a second pressure space 26, 34 within the bore for selective communication with the first pressure space, and a valve assembly operable upon movement of the input rod to actuate a valve of the assembly to establish communication between the pressure spaces whereby fluid pressure is applied to the output piston 18; further movement of the input rod is transmitted by a mechanical connection to the intermediate piston 7 which is advanced in the bore 2 to increase the pressure of the fluid within the pressure spaces which is applied to the output piston 18. In the embodiment of Fig. 1 the output piston 18 receives an output rod 20 adapted to actuate a master cylinder, and is itself received in a recess 17 in the intermediate piston 7. The valve assembly comprises a ball 29 biased into en gagement with a shoulder 28 in a passage 25 in the intermediate piston 7 and operable by means of a valve member 52 which has a bore normally providing communication between the first pressure space and a third pressure space 63. The first pressure space is connected via a radial port 43 to an hydraulic actuator, conveniently a rear wheel hydraulic actuator, or to a pressure indicator. The second pressure space is connected via a union 37 and a one-way ball valve 38, 39 with a high pressure source, i.e. a pump or accumulator. The third pressure space is connected via a radial port 48 with a reservoir for the high pressure source, and the first and third pressure spaces are normally in communication. When piston 13 and its integral rod 14 are moved a head 54 of valve member 52 engages with a seating member 50 to isolate the first pressure space from the third pressure space. Further movement of the rod 14 opens valve 28, 29 to communicate the second pressure space with the first pressure space and operate output piston 18. The intermediate piston 7 is held in a balanced condition by pressures on its faces after the piston 7 has been advanced by Belleville washers 61. Further movement of the rod 14 causes a thimble 59 to engage an abutment plate 55 where subsequently the piston 7 is advanced in the bore 2 to pressurize the first and second pressure spaces and augment the force applied to the intermediate piston 7. The increase in pressure acts on piston 18 to provide a boost ratio greater than 1 : 1, which continues until piston 7 engages piston 18 whereupon "feel" is lost on the rod 14. In the event of failure of the high pressure supply the fluid in first and second pressure spaces is pressurized by advance of piston 7 in bore 2. In the embodiment of Fig. 6 (not shown) the piston 18 works in bore 2 and piston 7 works entirely in bore 2 instead of partly in plug 3. In the embodiment of Fig. 7 there is no output rod 20 and piston 18 directly pressurizes fluid in a space 78 which is connected to front wheel brakes, while port 43 is connected to rear wheel brakes. In the embodiment of Fig. 8 the valve assembly comprises a spool 80 formed as an extension of rod 14 and movable in a sleeve 81 in a recess 82 in piston 7 the spool 80 having passages 88, 89 which control communication between the first and third, and first and second pressure spaces in co-operation with passages 91, 92 in sleeve 81 upon movement of rod 14. Further movement of rod 14 causes the end thereof to engage sleeve 81 to define a mechanical connection. Spool 80 and rod 14 have a resilient bush 97 therebetween which is deformable axially to allow relative movement between rod 14 and spool 80.