Hydraulic temperature compensated cooler bypass control for an automatic transmission

A system for controlling fluid flow in an hydraulic circuit of an automatic transmission, comprising:

• a source of fluid having variable temperature;
• a cooler communicating with the fluid source, adapted to transfer heat between fluid from the fluid source to a second fluid;
• a circuit:
• a bypass valve for apportioning fluid from the fluid source to the circuit and cooler in accordance with the temperature of said fluid, wherein the bypass valve comprises:
• a fluid sump;
• a spool moveable in a chamber, the chamber communicating with the fluid source, cooler and circuit;
• a first land formed on the spool, fluid source pressure on said first land urging the spool to open a connection between the fluid source and circuit;
• a spring urging the spool to close a connection between the fluid source and circuit;
• a first orifice adapted to produce a flow rate of fluid therethrough that is relatively independent of temperature of said fluid;
• a second orifice adapted to produce a flow rate of fluid therethrough that is relatively dependent on temperature of said fluid, arranged in series with the first orifice between the chamber and sump;
• and
• a second land spaced from the first land along the spool, fluid pressure between the first orifice and second orifice applied to the second land urging the spool to close said connection.