Hydraulic power steering apparatus

A hydraulic power steering apparatus having a pump for supplying an operational fluid, a power cylinder, a reservoir, and a control valve connected to said pump, said power cylinder and said reservoir and responsive to steering operation for controlling supply of the operational fluid to said power cylinder, said power steering apparatus comprising;

• a metering orifice disposed in the middle of a supply passage connecting said pump and said control valve;
• a flow control valve which is disposed in a bypass passage connected to the supply passage at the upstream side of said metering orifice and which comprises a valve spool and a spring disposed in a spring chamber formed at the back of the valve spool and connected to the supply passage at the downstream side of said metering orifice via a control orifice so as to open and close the bypass passage in accordance with a pressure drop across said metering orifice;
• and
• a bypass control valve disposed between the spring chamber of said flow control valve and said reservoir so as to increase the amount of bypassed fluid by controlling the pressure in the spring chamber,
• wherein said bypass control valve has a control spool, a load pressure introduction port connected to the upstream side of the control orifice for leading load pressure to a first end of said control spool, a pilot port connected to the downstream side of the control orifice for leading the pressure in the spring chamber of said flow control valve to a second end of said control spool, and a spring disposed in a chamber formed between said control spool and said pilot port, and wherein a pressure receiving area of the second end of the control spool is smaller than that of the first end of the control spool.