Hydraulic rotation control circuit

Claim 1

A hydraulic rotation control circuit operating below a maximum pressure for rotating a rotary body under a driving pressure, comprising a control valve assembly including a first, second, third and fourth port and first, second, third and fourth passages formed in said assembly wherein the cross sectional areas of said first and second passages are equal; a first pump connected to said first port communicating with said first passage and producing a maximum pressure; a first check valve communicating the second port with the second passage and allowing fluid flow from the first passage to the second port and passage; a second check valve communicating the third port with the third passage and allowing fluid flow from the first passage to the third port and passage; a third check valve allowing fluid flow from the third passage to the fourth passage; a fourth check valve communicating the fourth port with the fourth passage and allowing fluid flow from the second passage to the fourth port and passage wherein said fourth check valve is substantially the same structurally and dimensionally as said second check valve such that said driving pressure may be maintained at a substantially constant predetermined level; a first variable reducing valve communicating with said second and fourth check valves and including means for producing a variable pressure less than said maximum pressure by controlling blocking force of said second and fourth check valves against said first and second passages, respectively; a second variable reducing valve communicating with said first and third check valves and including means for producing a variable pressure less than said maximum pressure by controlling a blocking force of said first and third check valves against said first and third passages, respectively; and a second pump for delivering a pressurized fluid to said first and second variable reducing valves; a rotary actuator connected to said second and third ports and operable to rotate said rotary body; a fifth passage formed in said control valve assembly, said control circuit further comprising a fluid storage tank and a fifth check valve, said fifth check valve being disposed in said fifth passage communicating with said fourth port, biased closed by means, and having an opening facing said fourth port such that said fluid flows from said fourth port through said fifth check valve and into said tank; and a first auxiliary passage connecting said third port with said fourth passage, a check valve provided in said first auxiliary passage and having an opening facing said fourth passage, a second auxiliary passage means connecting said fourth port with said second port, and a check valve provided in said second auxiliary passage and having an opening facing said fourth port.