Patent ID: 6960296

Claim:
An oil filter unit comprising: a filter housing comprising: a housing proper; and a lid member; a filter element received in the filter housing; a drain passage defined by the filter housing and connected with an interior of the filter housing; and a drain valve device that opens and closes the drain passage in response to detachment and attachment of the lid member from and to the housing proper, the drain valve device comprising: a valve seat provided in the drain passage and having a drain bore formed therethrough; a retainer installed in the drain passage and axially movable in the same, the retainer having an oil flow passage formed therethrough; a valve member installed in the retainer, the valve member being movable to contact with the valve seat to close the drain bore; a first biasing member that biases the retainer away from the valve seat; a structure that causes, upon attachment of the lid member to the housing proper, the retainer to move toward the valve seat thereby to induce a contact of the valve member with the valve seat due to an input force applied from the lid member against the biasing force of the first biasing member and causes, upon detachment of the lid member from the housing proper, the retainer to move away from the valve seat thereby to induce a separation of the valve member from the valve seat due to the biasing force of the first biasing member; and a second biasing member that biases the valve member toward the valve seat, wherein the second biasing member is arranged to produce a biasing force that is smaller than that produced by the first biasing member.