Patent ID: 7997505

Claim:
A bypass valve for a cooler connected downstream from a hydraulic aggregate, the bypass valve comprising a valve housing ( 2 ) with at least first and second connection ports ( 8 , 12 , 18 ) for respective connection to the hydraulic aggregate and to the cooler, a closure element ( 22 ) being arranged in the valve housing for closing and opening a bypass, a valve spring ( 32 ) biasing the closure element ( 22 ) into a closed position, and a thermo-sensitive means causing the closure element to open if a temperature of hydraulic fluid is below a threshold temperature, the thermo-sensitive means comprising a valve spring ( 32 , 42 ) made from a memory-metal alloy having a transition point close to the threshold temperature such that, below the threshold temperature, the valve spring ( 32 , 42 ) does not exert any force on the closure element ( 22 ) and allows the closure element ( 22 ) to open under action of hydraulic fluid pressure, a substantially cylindrical control piston ( 20 ) having an outer diameter smaller than an inside diameter of a cylindrical chamber ( 4 ), which holds the control piston ( 20 ), the control piston ( 20 ) being guided in an end area of the cylindrical chamber ( 4 ) facing the closure element ( 22 ) by a guiding flange ( 30 ) in contact with a cylinder wall, and the control piston ( 20 ) being guided in an end area of the cylindrical chamber ( 4 ) facing away from the closure element ( 22 ), and the control piston ( 20 ) being guided in a receiving opening ( 28 ) of a plug ( 26 ) that closes the cylindrical chamber ( 4 ), and the valve spring ( 32 ) surrounds the control piston ( 20 ) and is supported, on one side, against the guiding flange ( 30 ) and, on an opposite side, against the plug ( 26 ).