Patent ID: 8573249

Claim:
A relief valve for an oil pump comprising: a housing defining a relief space therein; a plunger that is slidably disposed in the relief space of the housing and divides the relief space into a housing chamber fluid-communicating with a main gallery of an engine and a plunger chamber fluid-communicating with an outlet of the oil pump discharging oil to the main gallery and selectively bypassing a portion of oil discharged from the main gallery; an elastic member that elastically supports the plunger and is compressed by oil pressure of the main gallery supplied in the plunger chamber, wherein the oil pressure of the main gallery is relatively lower than an oil pressure under a warm-up state of the engine; a locator that is disposed under the plunger in the housing and supports the elastic member; a plug that is coupled to a lower portion of the housing under the relief space and supports the locator such that a modulus of elasticity in the elastic member is changed by a change in seat position of the elastic member; and a negative pressure supplier that is fluid-connected to the plug and selectively generates negative vacuum pressure in the locator such that a height of the locator changes; wherein the negative pressure supplier includes: a switch that is selectively turned on/off; a vacuum tank that generates the negative vacuum pressure in the locator through an axial hole formed through the plug; and a valve that makes the negative vacuum pressure of the vacuum tank transmitted in one direction.