Patent ID: 8667983

Claim:
A relief valve for an oil pump, comprising: a plunger that divides a relief space defined within a housing into a housing chamber communicating with a main gallery of an engine and a plunger chamber communicating with an outlet of an oil pump discharging oil to the main gallery and bypassing some of oil discharged from the main gallery to return; a coil spring that has a modulus of elasticity that is compressed under oil pressure of the main gallery which is relatively low in comparison to a warm-up state of the engine, and which elastically supports the plunger; and a locator that supports the coil spring such that the modulus of elasticity is changed by a change in a seat position of the coil spring; wherein the locator makes the seat position of the coil spring higher while expanded by supplied current; and wherein the locator includes a heater that is heated by current and an expandable substance that makes the seat position of the coil spring higher while expanded by heat from the heater.