Spring brake system with a constant force single stroke pumping means

Claim 1

In a braking system for a vehicle having a hydraulically operated spring parking brake, manually controllable pumping means for continually supplying fluid at a constant pressure to release said spring parking brake in a first mode of operation and for eliminating said constant pressure to activate said spring brakes in a second mode of operation, said manually controllable pumping means comprising: a first housing having an internal cavity therein; wall means including a flexible portion for dividing said cavity into a front chamber and a rear chamber, said front chamber being connected to a first source of fluid under pressure, said rear chamber being connected to a second source of fluid under pressure higher than said first pressure, said flexible portion being adapted to move in response to expansion of said fluid with changes in temperature in said first mode to maintain the constant hydraulic fluid pressure on the spring brake within a predetermined range; a cylinder having an internal bore with an inlet port and an outlet port, said inlet port being connected to a reservoir containing hydraulic fluid, said outlet port being connected by a conduit to said spring brake means; piston means connected to said wall means and extending into the internal bore of said cylinder; poppet means attached to said piston means for preventing communication between said reservoir and said bore during said first mode of operation and for allowing cOmmunication therebetween during said second mode of operation; resilient means located in said front chamber for urging said wall means toward said rear chamber during said second mode of operation; a second housing having a first chamber connected to said front chamber, a second chamber connected to said rear chamber and a control chamber interconnected to said first and second chambers; valve means located in said control chamber having a tubular shaft surrounded by a diaphragm for separating the second chamber fron the control chamber and a tubular valve stem extending through the second housing from the first chamber into the control chamber, said tubular housing having a resiliently positioned closure member on the end thereof adjacent said tubular shaft; sensing means located in said second housing and connected to said second chamber for visually indicating a differential pressure capable of being produced across said wall means in said first mode of operation; flow control means connected to said second chamber of the second housing and the front chamber of the first housing for maintaining said first source of fluid under pressure communicated thereto at a constant pressure during both the first and second modes of operation; means responsive to the hydraulic fluid pressure being supplied to said spring brake means during said first mode of operation for transmitting a first signal to an indicator device to inform the operator that the spring brakes are released and for transmitting a second signal during said second mode of operation to inform the operator that the spring brakes are applied and need to be released before movement of the vehicle; and manual control means connected to said tubular valve stem for selectively engaging said closure member with said tubular shaft in response to an operator for sequentially communicating said first and second chambers with said control chamber to develop a corresponding pressure differential across said wall means to move said piston means in the internal bore of the cylinder and sufficiently pressurize the hydraulic fluid therein by a single stroke to establish said first mode of operation.