Hydraulic system for producing a pilot pressure to actuate a transmission component
A hydraulic system for producing a pilot pressure to actuate at least one transmission component of an automatic transmission of a vehicle. A pilot system is connected via an inlet orifice or flow restriction to a supply conduit that is under a predetermined input pressure and that includes a pressure limiting valve for setting a predetermined pilot pressure. At least one inlet orifice or flow restriction is provided in such a way that the resulting flow resistance compensates for a rise in residual pilot pressure at low temperatures.
1 . A hydraulic system for producing a pilot pressure to actuate at least one transmission component of an automatic transmission of a vehicle, said hydraulic system comprising: a pilot pressure system that is connected via an inlet flow restriction to a supply conduit that is at a predetermined input pressure, a pressure limiting valve in communication with the inlet flow restriction for setting a predetermined pilot pressure, wherein the flow restriction is formed so that a resulting inlet flow resistance compensates for a rise in residual pilot pressure at low temperatures.
2 . A hydraulic system in accordance with claim 1 , wherein the inlet flow restriction has a flow-through length sufficient to reduce the residual pilot pressure at low temperatures.
3 . A hydraulic system in accordance with claim 1 , wherein the inlet flow restriction is included in a housing containing the pressure pilot system and is a bore having a predetermined length.
4 . A hydraulic system in accordance with claim 3 , wherein the bore has an axis that is oriented transversely to a longitudinal axis of the pressure limiting valve.
5 . A hydraulic system in accordance with claim 3 , wherein the bore has an axis that is oriented coaxially to a longitudinal axis of the pressure limiting valve.
6 . A hydraulic system in accordance with claim 3 , wherein the housing is made of cast iron.
7 . A hydraulic system in accordance with claim 1 , wherein the flow restriction includes a plurality of inlet orifices connected in series for increasing flow-through length of the pilot pressure system.
8 . A hydraulic system in accordance with claim 7 , wherein the inlet flow restriction includes at least two orifices that are formed by stamping an intermediate plate that is connected to the housing.
9 . A hydraulic system in accordance with claim 1 , wherein the pressure limiting valve is a proportional solenoid valve.
10 . A hydraulic system in accordance with claim 1 , wherein the hydraulic system is a pilot pressure system of a CVT transmission.
11 . A hydraulic system in accordance with claim 9 , including a screen positioned upstream of the proportional solenoid valve.