Fluid-pressure and analogous brake systems – Locks
Reexamination Certificate
1999-06-01
2001-05-22
Schwartz, Christopher P. (Department: 3613)
Fluid-pressure and analogous brake systems
Locks
Reexamination Certificate
active
06234586
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a parking brake lock-in key switch system for a truck or bus brake system. One type of vehicle on which an embodiment of this invention may be used is a school bus with an air brake system with a driver area operated parking brake actuator. The parking brake actuator is a push pull double check valve. Following a driver manually engaging the parking brake actuator, the parking brake lock-in key switch system will lock the parking brake in the engaged position upon the driver turning the ignition key to the ‘off’ position. This effectively disables the parking brake actuator preventing inadvertent release of the parking brake. This system will not cause an inadvertent initiation of the parking brake should a driver turn the ignition key to the ‘off’ position while the vehicle is moving down the road. The driver must first consciously operate the parking brake actuator for the parking brake lock-in key switch system of this invention to be functional. One embodiment of the invention for vehicles with automatic transmissions will include an automatic apply-automatic release parking brake system which operates in parallel with the parking brake lock-in key switch system. The automatic apply-automatic release parking brake system has a valve that acts to operate and engage the parking brake when the automatic transmission is placed in the “Park” position. The valve of the automatic apply-automatic release parking brake system in this embodiment will deactivate and release the parking brake when the transmission shifter is moved out of the “Park” position and the engine of the vehicle is running. The automatic apply-release parking brake system may be used alone in a vehicle without the Park Brake Lock-In System.
PRIOR ART
Heretofore, parking brakes on vehicles with air brake systems have been operable by use of air from either a primary air tank or a secondary air tank. In prior art air brake systems used on International® truck and bus chassis, manufactured by Navistar International Transportation Corp., separate air lines run from the primary air tank and the secondary air tank to a parking brake actuator. The parking brake actuator is a push pull double check valve. The double check valve portion of the actuator will align the tank with the highest pressure to supply the brake chambers for individual wheel brakes. When pulled out or actuated to an ‘Engaged’ position, the push pull portion of the actuator closes off the air supply passageway from the air tanks and vents the single downstream air line. A single air line runs from the push pull double check valve through an inversion valve to spring brake chambers which act in a parking brake mode. The spring or park brake chambers are part of the individual brake assemblies for each wheel subject to park braking. Typically, the vehicle's rear wheels have the brake assemblies which act as parking brakes in addition to having a service brake function. The springs in the spring brake chambers act to lock the individual wheels when there is no air applied to counter the spring force. Operation of the push pull knob of the parking brake actuator with its resulting venting of the down stream air piping to the brake chambers allows the spring brakes to lock the individual wheels associated with the park braking. The spring brake chambers will only continue to lock the individual wheels so long as the parking brake actuator is in the ‘Engaged’ or pulled out position.
Vehicles with hydraulically operated service brakes have had air assisted drive line parking brakes in the prior art. While the hydraulic service brakes act directly on the wheels of the vehicle, the drive line parking brakes act to lock the drive line prop shaft of the vehicle. An air brake cylinder is engaged to the drum in the driveline which locks the shaft. The air brake cylinder allows the shaft to rotate when air is supplied to the cylinder. The air is provided from a single air reservoir through a parking spring brake control through a one way check valve to the air brake cylinder. When the driver operates the parking spring brake control to the engaged position, the air supply to the cylinder is stopped and the downstream piping is vented. Upon the venting of the piping between the spring brake central and the air brake cylinder, the air brake cylinder will cause the drum brake to lock the drive line prop shaft. Similar to the above described air brake system, the drum brake will only continue to lock the prop shaft so long as the parking spring brake control is in the ‘Engaged’ position.
Automatic parking brake systems exist in the prior art and will automatically vent downstream air lines supplying brake chambers or cylinders associated with park braking upon the operator turning the ignition key to an ‘off’ position. Hence the parking brakes will automatically engage. There is a real danger to vehicle, driver and passengers with these automatic parking braking engagement systems. A driver may inadvertently engage the parking brakes while the vehicle is operating at highway speeds by merely turning the ignition key to a non-operate or ‘off’ position. This involuntary automatic braking could result in a loss of control of the vehicle.
SUMMARY OF THE INVENTION
Accordingly, it is a primary object of the invention to provide a parking brake lock-in system for air brake systems and air assisted drive line parking brakes which will lock the parking brakes in an engaged position following manual engagement of the parking brakes and the driver subsequently turning the vehicle ignition key to the ‘off’ position. A second object of the invention is that the parking brake lock-in system must not cause an inadvertent engagement of the parking brake by the driver merely turning the ignition key to the ‘off’ position while the vehicle is moving. A third objective of the invention is to provide an embodiment that may be used for vehicles with automatic transmissions whereby the shifting of the automatic transmission to the “Park” position will automatically apply the parking brake.
The parking brake lock-in key switch system of this invention satisfies the primary object and has two parking brake lock-in valves. One parking brake lock-in valve is installed in the air line piping between the primary air tank and the push pull double check valve and the second parking brake lock-in valve is in the air line piping between the secondary air tank and the push pull double check valve. The parking brake lock-in valves are air operated valves which when closed will not allow system air pressure to the push pull double check valve. The parking brake lock-in valves are operated by a pneumatic pilot signal from an electric solenoid valve. With the ignition in the ‘off’ position, the solenoid valve will be closed and not send a pilot signal to the parking brake lock-in valves and therefore the lock-in valves will be closed. If the push pull double check valve, also known as the parking brake actuator is in the ‘engaged’ or pulled out position, the actuated parking brake will be locked in because new air from the respective tanks will be prevented from flowing to the push pull double check valve and hence the brake chambers. The springs in the brake chambers will maintain the wheels locked in position. When the ignition is moved to a ‘run’ or ‘accessory’ position, the solenoid valve opens to supply a pilot signal to open the parking brake lock-in valves.
The second objective that the system must not cause an automatic engagement of the parking brake by the driver merely turning the ignition key to the ‘off’ position is accomplished by having a parking brake lock-in valve design which does not vent off downstream air when it closes. Should the ignition be repositioned to the ‘off’ position with the vehicle in motion and the parking brake actuator not engaged in the park position, air will be locked in the air line piping between the parking brake lock-in valves and the individual brake chambers including the piping in which the
Davis Richard B.
Douglas Robert L.
Hively Brad A.
Hively Terry E.
Lehman Michael J.
Calfa Jeffrey P.
Hernandez Gilberto
Navistar International Transportation Corp.
Schwartz Christopher P.
Sullivan Dennis Kelly
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