High performance intermediate servo assembly

#The present invention relates to the field of automatic transmissions and, more particularly, to a high performance intermediate servo assembly for use in General Motors 200 4R transmissions (hereinafter “GM transmissions”).

#Automatic transmission systems of the prior art have a hydraulic circuit sub-system which includes at least a hydraulic pump, a valve body having fluid conducting passages or circuits, input and exhaust ports formed within the fluid circuits, and a plurality of valves comprised of generally cylindrical pistons having control lands formed thereon, which alternately open and close the ports to the fluid circuits to regulate the flow and pressure of automatic transmission fluid (hereinafter “ATF”) to hydraulically actuate various components of the transmission. It will be understood that in describing hydraulic circuits, ATF usually changes names when it passes through an orifice or control valve in a specific fluid circuit.

#In the GM transmissions the intermediate servo assembly is applied in 2nd gear and is used as an accumulator in 3rd gear. An accumulator is a spring-loaded device that absorbs a certain amount of apply fluid pressure to cushion the application of a clutch band against fluid shock to control shift feel and to prevent damage to these components.

#The novel features of the present invention are set forth in the appended claims. The invention itself, however, as well as other features and advantages thereof will be best understood by reference to the following detailed description of an illustrative embodiment when read in conjunction with the accompanying figures, wherein:

#FIG. 1 is an exploded view of an intermediate servo for the GM transmissions labeled Prior Art;

#FIG. 2 is a perspective view of an intermediate servo assembly shown in its functional position engaging a clutch band labeled Prior Art;

#Prior to describing the present invention in detail it may be beneficial to briefly review the structure and function of an intermediate servo assembly of the GM transmissions. With reference to FIG. 1 there is shown an exploded view of the OEM intermediate servo assembly, indicated generally at 100. The OEM servo assembly 100 is comprised of a servo cover 105, O-ring 106, retaining ring 107, piston 110, inner lip seal 111, outer lip seal 112, accumulator piston 115, Teflon seal 117, accumulator spring 118, retaining clip 119, spring retainer 120, band apply pin 122, cushion spring 124, and O-rings 125 arranged coaxially for installation in the transmission case 135 (FIG. 2).

#The OEM intermediate servo assembly 100 functions to apply the intermediate clutch band 130 in 2nd gear as shown in FIG. 2 and is used as an accumulator in 3rd gear. An accumulator is a spring-loaded device that absorbs a certain amount of apply fluid pressure to cushion the application of a clutch band against fluid shock and also improves shift feel.

#In 2nd gear the intermediate band 130 is applied by servo 100. The intermediate band 130 is compressed around the direct clutch drum (not shown) with its distal end 130a mechanically anchored to the transmission case 135. The other end of the intermediate band 130 is hydraulically actuated by the intermediate servo 100. When the intermediate band 130 is applied, the rotation of the direct clutch drum (not shown) is prevented, which places the transaxle in 2nd gear.