1. Field of the Invention
This invention relates to the field of automatic transmission hydraulic control circuits that supply regulated line pressure to a hydraulic clutch of the transmission. In particular, the invention relates to a control valve operating in such a circuit on the basis of a pressure signal representing engine throttle position.
2. Description of the Prior Art
A control valve of this type is known from German Offenlegungsschrift DE-PS 34 17 784. A bypass line leading to the control valve includes a first connecting line having a flow orifice and is connected to a control pressure line that supplies a clutch actuated in all forward gears of the transmission. The control pressure line is directed through a branch of the bypass line to a chamber of the control valve. Regulated line pressure is directed through an aperture stop of a second connecting line of the control valve to a control pressure line leading to the clutch. Line pressure is supplied to the clutch when one control surface or collar of the valve spool has cleared the second connecting line against the force of a control spring and as a function of throttle pressure and line pressure downstream of the orifice in the first connecting line. The control valve is located in a valve bore that contains also a 1-2 shift valve and a 2-3 damper valve, loaded also with throttle pressure and interconnected to the individual gear shift valves of a control device, in which a shift pressure line is branched from the control pressure of the clutch. The branch is located at a point downstream of the flow orifice so that an aperture stop is connected through to the gear shift valves only after clearance of the second connecting line by one control surface of the valve spool.
U.S. Pat. No. 4,265,346 describes a control valve system for controlling the capacity of a hydraulic clutch in a power transmission wherein the clutch torque is nearly equal to engine torque resulting in a smooth clutch engagement as a torque transmitting path is established between the engine and a driven member.