| 摘要 |
Fluid systems for controlling clutch engagement of a vehicle drive train normally have modulating pressure relief valves to aid in smooth clutch engagement. It is desired in such systems to ensure that the system pressure is reduced during a shift so that the load piston of the modulating pressure relief valve is fully reset prior to engagement of the vehicle drive train. In this arrangement, a fluid system is provided which has a plurality of clutches. In order to ensure that the load system is fully reset, a load piston reset control mechanism is provided which establishes a path to vent the pressurized fluid from a load piston pressure chamber of a modulating presure relief valve in response to the pressure of the fluid in one of the clutches being below a predetermined pressure level. The load piston reset control mechanism has a valve mechanism for controllably connecting pressurized fluid from the load piston pressure chamber to the reservoir in response to the pressure of the fluid directed to one of the clutches being below the predetermined value. The valve mechanism has a signal control valve therein to maintain the valve mechanism in the vented position for a predetermined period of time in order to ensure the load piston has moved to its full reset position even if the fill pressure to the clutches is to high. With the load piston in the full reset position, smooth engagement of the clutches is obtained. |
