Latching clutch valve control system

1. A valve assembly in a transmission, the valve assembly comprising:

a valve body having an input in selective communication with an output;

a latching piston disposed within the valve body;

a balance spring disposed between the latching piston and the valve body;

a valve piston disposed within the valve body, wherein the input communicates with the output when the valve piston is in a first position and wherein the input does not communicate with the output when the valve piston is in a second position;

a diaphragm spring disposed between the latching piston and the valve piston; and

a holding spring disposed between the valve piston and the valve body.

2. The valve assembly of claim 1 wherein the latch piston includes a first side in communication with the input and a second side in selective communication with the input.

3. The valve assembly of claim 2 further comprising a pressure relief valve disposed within the valve body, wherein the pressure relief valve allows selective communication between the input and the second side of the latching piston.

4. The valve assembly of claim 3 further comprising an inner housing disposed within the valve body, and wherein the latching piston is disposed within the inner housing.

5. The valve assembly of claim 4 wherein the inner housing includes a first port in communication with the first side of the latching piston, a second port in communication with the pressure relief valve, and a third port in communication with a sump.

6. The valve assembly of claim 5 wherein the valve piston is sealingly engaged to the valve body and the valve piston includes a stem that is disposed through an opening in the inner housing.

7. The valve assembly of claim 6 wherein the diaphragm spring contacts the second side of the latching piston and the stem of the valve piston.

8. The valve assembly of claim 7 wherein the balance spring contacts the second side of the latching piston and the inner housing.

9. The valve assembly of claim 1 wherein the valve body defines a fluid passage that communicates from the input to the output.

10. The valve assembly of claim 1 wherein the valve piston covers the output when the valve piston is in the second position.

11. A hydraulic control system for a transmission in a motor vehicle, the hydraulic control system comprising:

a pressure regulator subsystem that provides hydraulic fluid at variable pressures;

a clutch actuator subsystem;

a valve assembly including:

a valve body having an input in selective communication with an output, wherein the input is in communication with the pressure regulator subsystem and the output is in communication with the clutch actuator subsystem;

a latching piston disposed within the valve body and moveable between a first position and a second position;

a balance spring disposed between the latching piston and the valve body;

a valve piston disposed within the valve body, wherein the input communicates with the output when the valve piston is in a first position and wherein the input does not communicate with the output when the valve piston is in a second position;

a diaphragm spring disposed between the latching piston and the valve piston wherein the diaphragm spring has a normal state that exerts force between the latching piston and the valve piston and an inverted state that does not exert a substantial force on the latching piston and the valve piston; and

a holding spring disposed between the valve piston and the valve body,

wherein when a pressure of the hydraulic fluid is less than a first threshold the diaphragm spring is in a normal state and moves the valve piston to the first position against the bias of the holding spring,

wherein when a pressure of the hydraulic fluid is greater than the first threshold the latching piston moves to the second position and inverts the diaphragm spring;

wherein when a pressure of the hydraulic fluid is less than the first threshold and the diaphragm spring is inverted the holding spring moves the valve piston to the second position, and

wherein when a pressure of the hydraulic fluid is greater than a second threshold after the diaphragm spring is inverted and the valve piston is moved to the second position the diaphragm spring is returned to the normal state.

12. The valve assembly of claim 11 wherein the latching piston includes a first side in communication with the input and a second side in selective communication with the input.

13. The valve assembly of claim 12 further comprising a pressure relief valve disposed within the valve body, wherein the pressure relief valve allows selective communication between the input and the second side of the latching piston when a pressure of the hydraulic fluid is greater than a third threshold.

14. The valve assembly of claim 13 wherein the first threshold is greater than the second threshold and the third threshold is greater than the first threshold.

15. The valve assembly of claim 14 wherein the third threshold is associated with a pressure required to provide a reverse gear state.

16. The valve assembly of claim 13 further comprising an inner housing disposed within the valve body, and wherein the latching piston is disposed within the inner housing.

17. The valve assembly of claim 16 wherein the valve piston is sealingly engaged to the valve body and the valve piston includes a stem that is disposed through an opening in the inner housing, and wherein the diaphragm spring contacts the second side of the latching piston and the stem of the valve piston.

18. The valve assembly of claim 17 wherein the valve body defines a fluid passage that communicates from the input to the output.

19. The valve assembly of claim 18 wherein the valve piston covers the output when the valve piston is in the second position to keep hydraulic fluid within the clutch actuator subsystem during and an engine stop/start event.

20. A powertrain in a motor vehicle comprising:

an engine;

a pump driven by the engine for providing hydraulic fluid at variable pressures;

a transmission that receives power from the engine, the transmission having at least one clutch;

a valve assembly including:

a valve body having an input in selective communication with an output, wherein the input is in communication with the pump and the output is in communication with the clutch;

a latching piston disposed within the valve body and moveable between a first position and a second position;

a balance spring disposed between the latching piston and the valve body;

a valve piston disposed within the valve body, wherein the input communicates with the output when the valve piston is in a first position and wherein the input does not communicate with the output when the valve piston is in a second position;

a diaphragm spring disposed between the latching piston and the valve piston wherein the diaphragm spring has a normal state that exerts force between the latching piston and the valve piston and an inverted state that does not exert a substantial force on the latching piston and the valve piston; and

a holding spring disposed between the valve piston and the valve body,

wherein when a pressure of the hydraulic fluid is less than a first threshold the diaphragm spring is in a normal state and biases the valve piston to the first position against the bias of the holding spring and the latching piston is in the first position,

wherein when a pressure of the hydraulic fluid is greater than the first threshold the latching piston moves to the second position and inverts the diaphragm spring;

wherein when a pressure of the hydraulic fluid is less than the first threshold when the engine begins a stop/start event and the diaphragm spring is in the inverted state, the balance spring biases the latching piston to the first position and the holding spring biases the valve piston to the second position, and

wherein when a pressure of the hydraulic fluid is greater than a second threshold after the diaphragm spring is inverted and the valve piston is moved to the second position the diaphragm spring is returned to the normal state.