Hydraulic elevator pressure relief valve

#This invention relates to a hydraulic elevator and, more particularly, to a relief valve used with the hydraulic elevator valving control system.

#Hydraulic elevators are comprised of a cab, a plunger attached to the cab either directly or by means of a roping configuration, and a cylinder housing the plunger. Hydraulic fluid is impelled into the cylinder to drive the plunger and the cab attached thereto, upwardly. The fluid is typically impelled into the cylinder by means of a constant speed motor which drives the fixed displacement pump.

#This type of hydraulic elevator requires valves to control the cab speed during acceleration, leveling, and lowering of the elevator. The valves waste energy while controlling the motion of the elevator by discharging excess fluid flow. Valves may also be noisy and provide relatively poor control.

#FIG. 1 is a schematic diagram, partly in section, of an embodiment of a relief valve used with a variable speed motor, pump, and a check valve in a hydraulic elevator; and

#FIG. 2 is a schematic diagram, partly in section, of the relief valve of FIG. 1.

#The elevator system 10 is comprised of an elevator car 12, a plunger 14, a hydraulic cylinder 16, a check valve 18, a relief valve 19, and a conventional variable speed reversible motor 20 and pump 22. The pump and motor are disposed within a tank 24 which is filled with hydraulic fluid 26. As is known in the art, the motor powers the pump to provide a variable fluid pressure force (FPF) to raise and lower the elevator.

#A first FPF F1 of the pump is communicated between the valve 18 and the pump 22 via line 28. A second FPF F2 is communicated between the valve 18 and the hydraulic cylinder 16 via line 30. A drain pressure line 32 is provided between the check valve 18 and the tank 24.

#When the cab 12 is at rest at a landing (not shown) a frustoconical portion 36 of the check valve 18 is seated against a circumference 38 to prevent hydraulic fluid from flowing through the valve 18 from the cylinder 16 to the tank 24 via lines 30 and 28, thereby maintaining the cab at the landing.