Self-adjusting control valve for elevators

Abstract

The invention discloses an automated hydraulic valve, for use in an elevator propulsion system. The elevator includes a car which is powered by a piston which moves within a cylinder. The automated valve controls the flow of hydraulic fluid into and out of the cylinder. The valve insures that the acceleration and deceleration of the elevator car will be uniform, and that the acceleration or deceleration will occur over a constant, predetermined interval, regardless of the load in the car. The control valve allows fluid to flow from a reservoir, and into the cylinder or back to the reservoir, with varying rates of flow. When fluid is directed into the cylinder, the elevator ascends. When fluid is allowed out of the cylinder, the elevator descends. The operation of the control valve is governed by a bypass piston assembly which is moved in response to the sensed pressure in the cylinder and the pressure in the valve. The rate at which the bypass piston assembly is moved is precisely controlled, preferably by a microprocessor. The rate of movement of the bypass piston assembly compensates for changes in the weight of the elevator car. The invention therefore also includes a method of controlling a hydraulic valve for an elevator, which method insures that the operation of the elevator will be substantially independent of changing load conditions.