Mechanically and hydraulically operated brake actuator

Claim 2

An actuator assembly for a vehicle brake comprising a housing, a wedge member, two follower members slidably guided in said housing and formed with thrust receiving surfaces which are inclined to each other and between which said wedge member is disposed, and at least one roller interposed between each of said thrust receiving surfaces and said wedge member, said wedge member being displaceable from a retracted position into an advanced position to urge said follower members in opposite directions to apply friction members into braking engagement with a rotor, wherein one of said follower members comprises a pair of axially arranged innermost and outermost hydraulic pistons working in a common bore in said housing, said outermost piston having an outer face for engagement with one of said friction members and an inner face, and said innermost piston being provided with the said thrust receiving surface for the said one follower member and having an outer face for engagement with said inner face of said outermost piston, and a stop surface spaced axially from said outer face in an inward direction, and said housing is provided with a supply port communicating with a pressure space defined in said common bore between said inner face of said outermost piston and said outer face of said innermost piston, which said faces abut when said wedge member is displaced from said retracted position, and with an abutment face with which said stop surface on said innermost piston is engageable when said wedge member is in said retracted position whereby said pressure space can be pressurised through said supply port to urge said outermost piston away from said innermost piston which is relatively stationary to apply one of the friction members into braking engagement with the rotor.

Claim 3

An actuator assembly as claimed in claim 1, wherein said innermost piston has an inner end formed with two parallel projections forming said stop surface and which define a slot for guiding a cage assembly in which said roller is carried, and inner ends of said projections comprise stop faces engageable with said abutment face.

Claim 4

An internal shoe-drum brake for a vehicle comprising a rotatable drum, first and second arcuate shoes for engagement with said rotatable drum, and first and second actuator assemblies for separating said shoes located between each pair of shoe ends, said first actuator assembly comprising a housing, a wedge member, first and second follower members slidably guided in said housing and formed with thrust receiving surfaces which are inclined to each other and between which said wedge member is disposed, and at least one roller interposed between each of said thrust receiving surfaces and said wedge member, said wedge member being displaceable from a retracted position to urge said follower members in opposite directions to apply said shoes to said drum, wherein one of said follower members comprises a pair of axially arranged innermost and outermost hydraulic pistons working in a common bore in said housing, said outermost piston having an outer face for engagement with said first shoe and an inner face, and said innermost piston being provided with the said thrust receiving surface for the said one follower member and having an outer face for engagement with said inner face of said outermost piston, and a stop surface spaced axially from said outer face in an inward direction, and said housing is provided with a supply port communicating with a pressure space defined in said common bore between said inner face of said outermost piston and said outer face of said innermost piston, which said faces abut when said wedge member is displaced from said retracted position, and with an abutment face with which said stop surface of said innermost piston is engageable when said wedge member is in said retracted position whereby said pressure space can be pressurised through said supply port to urge said outermost piston away from said innermost piston which is relatively stationary to apply said first shoe to said drum, said second actuator including an hydraulic cylinder, and a piston working in said hydraulic cylinder and acting on the shoe end of said second shoe which is remote from said first actuator, the arrangement being such that when both actuators are operated hydraulically and simultaneously by pressurising said pressure space and said hydraulic cylinder simultaneously said brake operates as a brake of the two leading shoe type, at least for one direction of drum rotation.

Claim 5

An internal shoe-drum brake for a vehicle comprising a rotatable drum, first and second arcuate shoes for engagement with said rotatable drum, and first and second actuator assemblies for separating said shoes located between each pair of shoe ends, said first actuator assembly comprising a housing, a wedge member, first and second follower members slidably guided in said housing and formed with thrust receiving surfaces which are inclined to each other and between which said wedge member is disposed, and at least one roller interposed between each of said thrust receiving surfaces and said wedge member, said wedge member being displaceable from a retracted position to urge said follower members in opposite directions to apply said shoes to said drum, wherein one of said follower members comprises a pair of axially arranged innermost and outermost hydraulic pistons working in a common bore in said housing, said outermost piston having an outer face for engagement with said first shoe and an inner face, and said innermost piston being provided with the said thrust receiving surface for the said one follower member and having an outer face for engagement with said inner face of said outermost piston, and a stop surface spaced axially from said outer face in an inward direction, and said housing is provided with a supply port communicating with a pressure space defined in said common bore between said inner face of said outermost piston and said outer face of said innermost piston, which said faces abut when said wedge member is displaced from said retracted position, and with an abutment face with which said stop surface of said innermost piston is engageable when said wedge member is in said retracted position whereby said pressure space can be pressurised through said supply port to urge said outermost piston away from said innermost piston which is relatively stationary to apply said first shoe to said drum, said second actuator including an hydraulic cylinder, and a piston working in said hydraulic cylinder and acting on the shoe end of said second shoe which is remote from said first actuator, the arrangement being such that when both actuators are operated hydraulically and simultaneously by pressurising said pressure space and said hydraulic cylinder simultaneously said brake operates as a brake of the two leading shoe type, at least for one direction of drum rotation.

Claim 6

An internal shoe drum brake as claimed in claim 3, wherein said second actuator also includes a second hydraulic cylinder and a second piston working in an hydraulic cylinder and acting on the shoe end of said first shoe which is remote from said first actuator, the arrangement being such that when both actuators are operated hydraulically and simultaneously by pressurising said pressure space and both said hydraulic cylinders simultaneously said brake operates as a brake of the one-leading one-trailing shoe type at least for an opposite direction of drum rotation, and said outermost piston of said first actuator acts as a drag-taking abutment for said first shoe.