Brakes – Operators – Spring
Patent
1982-07-12
1984-07-10
Butler, Douglas C.
Brakes
Operators
Spring
60413, 60486, 303 71, 303 10, B60T 1322
Patent
active
044587910
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
1. Technical Field
This invention relates generally to a brake control system for a spring applied, pressure released brake on a winch and more particularly to a device for reducing the normal outlet pressure of a metering pump at low operating speeds of the winch.
2. Background Art
The winches used on pipelayers and the like commonly have a hydraulically disengaged brake operative to control the lowering of a supported load by controlling rotation of a cable drum of the winch. The brake control system sometimes has an accumulator connected between the pump and the control valve for providing an auxiliary source of pressurized hydraulic fluid for disengaging the brake to lower a suspended load when the pump is inoperative. The accumulator is charged to a predetermined pressure determined by a relief valve. To achieve steady lowering of the suspended load, the fluid pressure in the actuating chamber of the brake must be maintained constant. This is sometimes accomplished by a metering pump driven by the winch drum to pump fluid from the actuating chamber at a rate proportional to the rotational speed of the drum and at a rate essentially the same as the rate of flow through the control valve. Thus a constant pressure is maintained at a given position of the control valve. To conserve fluid when the accumulator is used as the source of fluid pressure, and to maintain accumulator pressure in normal operation, the metering pump directs the fluid back to the inlet of the control valve in a regenerative manner and must thereby pump the fluid against at least the pressure established by the relief valve which is substantially higher than the pressure required for initial reduction of braking force.
Some examples of such brake control systems are disclosed in U.S. Pat. No. 4,048,799 issued to Golan et al. on Sept. 20, 1977 and U.S. Pat. No. 4,278,155 issued to Golan et al. on July 14, 1981.
One of the problems associated with such brake control system is that of internal leakage between the inlet and outlet ports of the metering pump resulting from the pressure differential between the inlet and outlet ports. At very slow lowering speeds and relatively high pressures, the internal leakage within the metering pump reduces its efficiency so that the amount of fluid pumped from the actuating chamber is less than the amount of fluid directed to the actuating chamber by the control valve. Thus, the fluid pressure in the actuating chamber continues to increase for a given setting of the control valve thereby causing greater than desired disengagement of the brake and unexpected faster lowering of the load. Thus the control system does not provide the precision slow speed control required for lowering heavy loads. The internal leakage does not cause any problems at moderate or fast lowering speeds wherein the fluid flow necessary to maintain constant pressure in the actuating chamber is greater than the internal leakage of the metering pump.
The present invention is directed to overcoming one or more of the problems as set forth above.
DISCLOSURE OF THE INVENTION
In one aspect of the present invention a brake control system for actuation of a spring applied pressure released brake between engaged and disengaged conditions for respectively stopping and allowing rotation of a rotatable member includes a pump, a control valve having an inlet connected to the pump and an outlet connected to an actuating chamber of the brake, said control valve being movable between a first position at which the inlet port is blocked from the outlet port and a plurality of operative positions at which communication between the inlet and outlet ports is controllably modulated, a metering pump drivingly connected to the rotatable member and having inlet and outlet ports with the inlet port being connected to the outlet of the control valve, a conduit connecting the outlet port of the metering pump with the inlet port of the control valve, means for normally maintaining the pressure in the conduit at a predetermined operating lev
REFERENCES:
patent: 3762777 (1973-10-01), Jacob
patent: 3871714 (1975-03-01), Behrend
patent: 4048799 (1977-09-01), Golan et al.
patent: 4256350 (1981-03-01), Hoefer
patent: 4262969 (1981-04-01), Chatterjea
patent: 4278155 (1981-07-01), Golan et al.
patent: 4337926 (1982-07-01), Dehaan
Golan Kenneth F.
Schneider Marvin L.
Butler Douglas C.
Caterpillar Tractor Co.
Grant John W.
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