Patent ID: 6827562
Filing Date: 2004-12-07
Classification: F03C,F04C

Abstract:
A method of controlling the shifting of a multiple-speed ratio fluid pressure operated device between a first speed ratio and a second speed ratio, said device including a fluid pressure displacement mechanism defining a plurality of expanding and contracting fluid volume chambers; a motor valve operable to provide fluid communication to and from said fluid volume chambers in said first speed ratio; a shift valve operable, in a first condition, to achieve said first speed ratio, and in a second condition, to achieve said second speed ratio by interconnecting a plurality of said volume chambers as recirculating volume chambers; said method comprising the step of shifting said shift valve between said first and second conditions in response to changes in a pilot pressure signal between a first pressure and a second pressure; said method being characterized by:(a) providing a pressure control valve in fluid communication with a source of pressurized fluid, said pressure control valve being operable to communicate said pilot pressure signal to said shift valve in response to changes in an electrical command signal between a first signal and a second signal; (b) when a shift to said second condition is commanded, changing said electrical command signal from said first signal to said second signal over a first time period (T1); and (c) when a shift to said first condition is commanded, changing said electrical command signal from said second signal to said first signal over a second time period (T2), wherein T2 is greater than T1.