Fluid-pressure and analogous brake systems – Releasing – Motor
Reexamination Certificate
2000-02-01
2001-08-07
Oberleitner, Robert J. (Department: 3613)
Fluid-pressure and analogous brake systems
Releasing
Motor
C303S009000, C303S081000, C303S007000
Reexamination Certificate
active
06270168
ABSTRACT:
This invention relates to pneumatically-operated braking systems for vehicles and in particular to systems of the kind for use in tractor-trailer combinations.
Known pneumatically-operated braking systems for tractor-trailer combinations embody a safety feature, typically called a “supply dump valve”, that is operative to limit the loss of air pressure stored in an air reservoir of the vehicle should a pneumatic control line between the tractor and the trailer become ruptured or otherwise damaged. By restricting the loss of supply air the operation of the trailer emergency relay valve is brought about.
The supply dump valve itself can usually be integrated into the trailer control valve which is fitted to the tractor. A trailer control valve for controlling operation of the brakes on the trailer under the control of an electronic braking system (EBS) is usually connected to the trailer through flexible couplings otherwise known as “suzies”. The supply dump valve acts substantially to bring about the operation of the trailer emergency relay valve, and hence the application of the trailer brakes.
Conventionally the supply dump valve comprises a differential pressure actuated valve. Thus when the pressures acting on opposite sides of the valve are in equilibrium, the valve remains in a fully open position supported or biased by a lightly loaded spring. Should a leak occur in the control coupling or other associated trailer pipe work, it can then be arranged such that the leak lowers the pressure on one side of the supply dump valve, thereby causing the valve to move into a restricting position.
Typically the pressures supplied to both sides of the supply dump valve are taken from the air supply line or port of the trailer valve through internal valve passages, This arrangement is satisfactory when the leak generated by a rupture down stream of the trailer valve is large, since a pressure differential is rapidly built up across the supply dump valve, generated by the internal impedance within the trailer control valve, causing the supply dump valve to actuate.
It has been found, however, that if the leak rate is throttled, for example if the rupture is remote from the trailer control valve, then the internal impedance's within the valve is substantially masked and the pressures, on both sides of the supply dump valve fall at approximately equal rates. Thus the supply dump valve does not actuate.
We are aware of FR-A-2 310 250 which comprises the pre-characterising portion of claim 1.
According to our invention in a pneumatically-operated braking system for a tractor-trailer combination, a trailer control valve for providing braking pressure for a trailer is adapted to be actuated by a pressure differential acting across it to limit the flow of air to a trailer supply line when a leak is present in a trailer control line, and the pressure differential being generated between the pressure in the trailer control line and pressure supply from another independent source, and the independent source comprises the trailer/park pressure supply tank which is always unaffected by a leak downstream of the trailer control valve.
This ensures that should a leak occur in the trailer control line, sufficient pressure differential is generated across the supply dump valve always to ensure that it operates satisfactory since the supply dump valve will always, during non-park operation, have full tank pressure acting upon it.
During a park operation the vehicle is at rest and the air supplied to the actuators is removed. This causes brake actuators of the spring-actuating type, to clamp the wheels of the vehicle. In this condition the supply dump valve is not being fed with tank pressure since the respective line has been exhausted. This is of no consequence since the vehicle is in a parked condition. Once the park brake is removed, the supply dump valve is again provided with full trailerlpark tank pressure on one side, and full tractor supply line pressure on the other side. The supply dump valve is therefore held fully open until such time as a leak occurs in the trailer system.
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International Search Report dated May 19, 1998.
Carlson Gaskey & Olds P.C.
Kramer Devon
Meritor Heavy Vehicle Systems L.L.C.
Oberleitner Robert J.
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