Flow Control
- The oil pump controls the delivery rate per rotation by changing the eccentricity of the cam ring.
- During low speed operation, the pressure difference between before and after the variable orifice is small. So the control valve is pressed toward the left by action of the control valve spring, and the tank pressure led to pressure chamber A. The pressure led to pressure chamber B is the pressure that has passed through the variable orifice. It is a higher pressure than that applied to pressure chamber A. The cam ring is pressed toward the left by the pressure difference between pressure chambers A and B and action of the cam ring spring, so the eccentricity of the cam ring reaches a maximum. When the eccentricity of the cam ring is maximized, the delivery rate per rotation is maximized.
Pump speed range A to B
- During medium speed operation, the delivery rate increases. So the pressure before passing through the variable orifice increases because of action of the variable orifice. When the pressure before passing through the variable orifice increases, the control valve is moved to the right against action of the control valve spring. When the control valve is moved to the right, the pressure before passing through the variable orifice is led to pressure chamber A, and the pressure is higher than that applied to pressure chamber B. Because of the pressure difference between pressure chambers A and B, the cam ring is moved to the right against action of the cam ring spring. When the cam ring is moved to the right, the eccentricity of the cam ring is reduced, and the delivery rate per rotation decreases. Therefore, the delivery rate is decreased even if the pump speed increases.
Pump speed range B to C
- During high speed operation, the cam ring moves further to the right to close the variable orifice and reduce the opening area of the variable orifice. When the opening area of the variable orifice is reduced, the pressure before passing through the variable orifice increases, and the pressure difference between pressure chambers A and B increases, and the cam ring moves further to the right. Movement of the cam ring further to the right further reduces the delivery rate per rotation. Therefore, the delivery rate is decreased even if the pump speed increases.
Pump speed range C to D
- When the delivery rate exceeds a preset value, the relief valve opens to let the hydraulic fluid to escape toward the upstream side of the pump, thereby controlling the maximum pressure.