Transmission gear shift control

A method for controlling pressure applied to a displaceable piston in a cylinder, piston displacement actuating a control element of an automatic transmission during a gearshift, comprising the steps of:

• (a) determining the displacement of the piston, and controlling the pressure based at least in part on a calculated piston displacement;
• (b) determining whether piston displacement exceeds at least one of:
• a free length of an isolation spring located between the piston and a friction plate of the control element, and a free length of a return spring located between the piston and a non-axial moving member;
• (c) calculating estimated pressure using A, a cross-sectional area of the piston;
• K, a coefficient of a return spring extending between the piston and a reference position in the cylinder;
• x, the piston displacement;
• F0 a pre-load of the return spring;
• xfree the length of the isolation spring;
• xmax, this maximum displacement of the piston, and Kis a coefficient of the isolation spring;
• (d) applying the estimated pressure to the piston.