Flow rate control device of hydraulic pump in power steering system
A flow rate control device of a hydraulic pump in a power steering system, may include an upper cam ring having a cam profile, which is fixedly installed, a lower cam ring having a cam profile, which is engaged with the upper cam ring to be relatively rotatable about the upper cam ring, and a rotor including a plurality of vanes and engaged with the upper and lower cam rings to form an inner space therebetween to pressurize oil by protruding the vanes in the inner space by centrifugal force while rotating.
1. A flow rate control device of a hydraulic pump in a power steering system, comprising:
an upper cam ring having a cam profile, which is fixedly installed;
a lower cam ring having a cam profile, which is engaged with the upper cam ring to be relatively rotatable about the upper cam ring; and
a rotor including a plurality of vanes and engaged with the upper and lower cam rings to form an inner space therebetween to pressurize oil by protruding the vanes in the inner space by centrifugal force while rotating,
wherein a rotational displacement of the low cam ring is controlled by a control portion,
wherein the control portion is connected to the hydraulic pump and controls a rotational displacement of the low cam ring by oil pressure supplied from the hydraulic pump,
wherein the control portion includes a hydraulic cylinder actuated by the oil pressure,
wherein the control portion further includes a gear formed on an outer peripheral surface of the lower cam ring,
wherein the hydraulic cylinder includes:
a piston rod slidably received in a housing and having a rack gear engaging with the gear of the lower cam ring;
a spring seat having a hole and disposed in the housing to form an inner chamber Therein;
a hydraulic piston disposed in the inner chamber and integrally connected to the piston rod through the hole of the spring seat so as to move forwards and backwards in the inner chamber according to the oil pressure supplied from the hydraulic pump; and
a spring disposed between the spring seat and the hydraulic piston in the inner chamber and elastically supporting the hydraulic piston, and
wherein at least two bypass paths are formed at one side of the hydraulic cylinder between the spring seat and one end portion of the housing with a predetermined interval therebetween in a longitudinal direction of the housing to drain oil in the inner chamber, and an influx hole are formed at the one end portion of the hydraulic cylinder to receive the oil pressure supplied from the hydraulic pump.
2. The flow rate control device as defined in claim 1 , wherein the predetermined interval of the at least two bypass paths is equal to or larger than a thickness of the hydraulic piston.
3. The flow rate control device as defined in claim 1 , wherein the cam profiles of the upper cam ring and the lower cam ring are the same.