Electro-hydraulic pulse motor

Claim 1

An electro-hydraulic pulse motor comprising an electric pulse motor, a rotary pilot valve including a sleeve and a spool, said spool disposed in said sleeve for rotary and slidable movement, an hydraulic motor having an output shaft, hydraulic path means including an oil supply path for supplying pressurized oil to said rotary pilot valve, an oil return path for exhausting return oil from said rotary pilot valve, a pair of hydraulic circuits for leading said pressurized oil from said oil supply path to said hydraulic motor through said rotary pilot valve and for leading said return oil from said hydraulic motor to said oil return path through said rotary pilot valve, the oil pressure in said hydraulic circuits being normally lower than that in said oil supply path, feedback means coupled between said output shaft and said spool for feeding back an axial displacement of said spool when said displacement is produced by said electric pulse motor by rotation of said output shaft, and a first and a second safety valve disposed within said sleeve, said first safety valve being connected between a first of said pair of hydraulic circuits and said oil supply path, said second safety valve being connected between a second of said pair of hydraulic circuits and said oil supply path, each of said safety valves including a cylinder provided with a cylinder bore having a wall, one end of each said cylinder bore connected to said oil supply path, the other end of each said cylinder bore connected to a respective hydraulic circuit, for each said safety valve an oil-type piston slidably fitted in said cylinder bore and having first and second end surfaces respectively facing said one end and said other end of said cylinder bore whereby said pressurized oil is applied to said first end surface and the normally lower pressure of the oil in a respective hydraulic circuit is applied to said second end surface, a spring disposed in each said cylinder bore for applying a spring force to said piston first end surface thereby providing a biasing force in addition to the pressure of said pressurized oil for biasing said piston toward said other end of said cylinder bore to a normal initial position, an hydraulic bypass circuit for each cylinder having an inlet and an outlet both formed in said wall of said cylinder bore for fluidly connecting a respective hydraulic circuit to said oil supply path only when said piston is displaced from said initial position by a predetermined rise in the oil pressure in the respective hydraulic circuit.