Patent ID: 6902043

Claim:
A driveline vehicle parking brake actuator, comprising: a housing defining an enclosed chamber adjacent a proximal end of said housing; a reciprocable piston within said chamber including a proximal end having a head portion engaging an internal surface of said chamber in sealed relation and a distal end receiving a cable; a source of fluid under pressure within said chamber normally biasing said piston in a first direction away from said proximal end of said housing; a spring guide within said chamber including a distal tubular portion surrounding and telescopically received in bearing relation on said piston and a proximal radial portion; a first coil spring surrounding said tubular portion of said spring guide compressed between said housing and said proximal radial portion of said spring guide; and a second coil spring having a greater spring rate than said first coil spring within said tubular portion of said spring guide surrounding said piston and compressed between said spring guide and said head portion of said piston; wherein said first and second coil springs function in series having a substantially constant spring rate within a stroke of said piston, urging said piston in a second direction toward said proximal end of said housing and tensioning said cable and actuate a vehicle parking brake.