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Title: Actuator assemblies for vehicle brakes
Claims: We claim: 1. An actuator assembly for a vehicle brake comprising a housing provided with an inlet for connection to a supply of hydraulic fluid under pressure, first and second actuating members working in said housing, said first actuating member being adapted to apply a mechanical force to said brake and being bounded by a pressure space communicating with said inlet whereby said mechanical force is responsive to changes in hydraulic pressure in said pressure space, resilient means biassing said second actuating member to engage said first actuating member to apply an actuating force to said brake, means for subjecting said second actuating member to fluid pressure in opposition to said resilient means to hold said second member out of engagement with said first member, and modulating means for modulating the pressure of fluid in said pressure space, said modulating means comprising an inlet valve controlling communication between said inlet and said pressure space, a modulator piston assembly movable in said housing between a first position in which said inlet valve is open and a second position in which said inlet valve is closed, means for subjecting said modulator piston assembly to fluid pressure to urge it into the first position, and means for subjecting said modulator piston to fluid pressure to urge it into the second position. 2. An actuator assembly as in claim 1 wherein said modulator piston assembly includes a piston having a stepped through bore in which works a stepped piston forming said second actuating member, a chamber being defined between the two pistons, the arrangement being such that pressure fluid introduced into said chamber urges said modulator piston into the first position and said second actuating piston away from said first actuating member to compress said resilient means. 3. An actuator assembly as in claim 2 including means for connecting said chamber to a second chamber in the housing on the opposite side of said modulator piston, whereby, in a vehicle, a control valve responsive to the deceleration of a braked wheel of the vehicle controls the connection between said chambers. 4. An actuator assembly as in claim 3 including a control valve controlling said fluid connection between said first and second chambers. 5. An actuator assembly as in claim 3 wherein said pressure space is connected to a cylinder bore in which said modulator piston assembly is movable, movement of said piston assembly to the second position increasing the effective volume of said pressure space to relieve the braking pressure. 6. An actuator assembly as in claim 5 wherein said modulator piston assembly comprises a first modulator piston which defines said first chamber, which is movable in a bore in communication with said second chamber, and which acts on a second modulator piston movable in the bore communicating with said pressure space. 7. An actuator assembly as in claim 6 wherein said first actuating member is also a piston axially aligned with said first modulator piston and said second actuating piston. 8. An actuator assembly as in claim 7 wherein said second modulator piston works in a bore parallel to said first modulator piston, a radial extension from said first modulator piston engaging said second modulator piston, and said housing being provided with a passage communicating between said bore and said pressure space. 9. An actuator assembly as in claim 8 wherein there are two second modulator pistons angularly spaced around said first modulator piston. 10. An actuator assembly as in claim 9 wherein said housing is provided with an outlet communicating with said pressure space. 11. An actuator assembly as in claim 8 wherein said housing is in two parts, a first part and a second part, and said stepped second actuating piston has a smaller diameter portion terminating at its step, the first part defining a bore for said first actuating piston and a bore for the smaller diameter portion of said second actuating piston, the second part defining bores for said first and second modulator pistons, the two housing parts being held together by bolts locating a plurality of springs acting on said second actuating piston. 12. An actuator assembly as in claim 7 wherein said second modulator piston works in a bore coaxial with the bore of said first modulator piston. 13. An actuator assembly as in claim 12 wherein said first and second modulator pistons are combined in a stepped piston, said second chamber being formed at the step in diameter, and said third chamber being defined between the end of said second modulator piston and said first actuating piston. 14. An actuator assembly as in claim 13 wherein said fluid inlet to said first chamber comprises a passage through the larger diameter portion of said second actuating piston. 15. An actuator assembly as in claim 12 wherein said resilient means acts between said housing and a cage secured to said second actuating piston, said cage being slidable on a bearing surface provided on said housing. 16. An actuator assembly as in claim 1 wherein said resilient means is a single spring. 17. An actuator assembly as in claim 1 wherein said resilient means is a plurality of angularly spaced springs. 18. An actuator assembly as in claim 1 wherein said resilient means acts on a member having an adjustable connection with said second actuating member. 19. An actuator assembly as in claim 1 in which said means subjecting said second actuating member to fluid pressure in opposition to said resilient means comprises said means subjecting said modulator piston assembly to fluid pressure to hold said modulator piston in the first position. Other info: Inventors: Ingram, Brian (Balsall Common, EN) Harries, David Anthony (Shirley, EN) Application Number: 395557 Filing Date: 1973-09-10 Publication_date: 1976-05-04 Assignee: Girling Limited (Birmingham, EN) Primary Class(es): 303/115.5 188/170, 303/10, 303/13, 303/122.02 Other Classes: US Patent Ref:
Other Refs: Primary Examiner: Blix, Trygve M. Assistant Examiner: Butler, Douglas C. Attorney: Scrivener Parker Scrivener and Clarke |
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