Combined hydraulic inlet and pressure relief valve

摘要

The timing-chain on an IC engine is tensioned by a shoe pushed against the chain by a hydraulic piston. The piston is hollow and is urged away from the bottom of the cylinder (36) by a coil spring (60) which presses against a flat end plate (70) which allows a slow escape of oil through a lubrication bore (40) to lubricate the cam face on the shoe. The pressure of the oil in the piston chamber assists the spring and is controlled by a combined inlet and overpressure relief valve (100), which contains a single ball (102). Oil supplied under pressure to the inlet chamber (127) pushes the ball off its seat (130,134) against a spring (104) and oil flows into the piston chamber. If the pressure in the piston chamber becomes excessive, the annular seat member is pushed back against a spring (128) to allow oil to flow back into the inlet chamber.