Limiting branch pressure to a solenoid valve in a fluid circuit

1. A vehicle comprising:

a transmission having a clutch;

a pump in fluid communication with the clutch through a branch of a fluid circuit;

a flow control variable force solenoid (QFVS) positioned in the branch;

a pressure control variable force solenoid (PVFS) valve positioned in the branch upstream of the QVFS, wherein the PVFS valve supplies oil from the pump to the QVFS valve; and

a controller in electrical communication with the clutch, the pump, the PVFS valve;

wherein the controller:

calculates an area of a variable orifice of the QVFS valve at the start of a clutch shift event;

records the calculated area as a maximum area;

calculates, in a calibrated loop during the shift event, a maximum allowable branch pressure in the branch as a function of the calculated maximum area; and

limits actual branch pressure in the branch during the shift event to the calculated maximum allowable branch pressure.

2. The vehicle of claim 1 , wherein the transmission is a dual-clutch transmission (DCT) and the clutch is one of a pair of input clutches to the DCT.

3. The vehicle of claim 1 , wherein the controller calculates the maximum area of the orifice as a function of a commanded branch pressure.

4. The vehicle of claim 1 , further comprising a temperature sensor positioned in the fluid circuit in electrical communication with the controller, wherein the temperature sensor measures a temperature of the oil, and wherein the controller calculates the maximum area of the orifice as a function of the measured oil temperature.

5. The vehicle of claim 4 , further comprising a lookup table containing a modeled clutch pressure, wherein the controller extracts the modeled clutch pressure from the lookup table and calculates the maximum area of the orifice as a function of the modeled clutch pressure.

6. The vehicle of claim 1 , wherein the clutch is an oncoming clutch, further comprising an offgoing clutch in another branch of the fluid circuit, wherein the controller limits pressure to the offgoing clutch by selecting a pressure value from a clutch torque-based lookup table.

7. The vehicle of claim 1 , wherein the controller filters the maximum branch pressure using one of a Kalman filter, a weighted average, a rolling average, and a lag filter.

8. A control system for a transmission having a clutch, a pump in fluid communication with the clutch through a branch of a fluid circuit, a pressure control variable force solenoid (PVFS), and a flow control variable force solenoid (QVFS) valve, wherein the PVFS and QVFS valves are positioned in the branch upstream of the clutch, the system comprising:

a host machine in electrical communication with the clutch, the pump, and the PVFS and QVFS valves;

a temperature sensor positioned in the fluid circuit in electrical communication with the host machine, wherein the temperature sensor measures a temperature of the oil; and

a tangible, non-transitory computer-readable medium on which is recorded instructions for limiting branch pressure, wherein the host machine executes the instructions from the computer-readable medium to thereby:

calculate an area of a variable orifice of the QVFS valve at the start of a clutch shift event as a function of a commanded branch pressure and a measured oil temperature;

record the calculated area as a maximum area;

calculate, in a calibrated loop during the shift event, a maximum branch pressure in the branch as a function of the calculated maximum area; and

limit actual branch pressure in the branch during the shift event to the calculated maximum branch pressure.

9. The control system of claim 8 , wherein the controller is configured to limit the branch pressure by transmitting a current command to the PVFS valve.

10. The control system of claim 8 , further comprising a lookup table containing a modeled clutch pressure, wherein the host machine extracts the modeled clutch pressure from the lookup table and calculates the maximum area of the orifice as a function of the modeled clutch pressure.

11. The control system of claim 8 , wherein the host machine is configured to filter the maximum branch pressure using one of a Kalman filter, a weighted average, a rolling average, and a lag filter.

12. A method comprising:

calculating an area of a variable orifice of a flow control variable force solenoid (QVFS) valve at the start of a clutch shift event in a vehicle, wherein the vehicle includes a pump that is in fluid communication with a clutch through a pressure control variable force solenoid (PVFS) valve and the QVFS valve in a branch of a fluid circuit;

recording the calculated area as a maximum area;

calculating, in a calibrated loop during the shift event, a maximum branch pressure in the branch as a function of the calculated maximum area; and

limiting, via a controller, fluid pressure in the branch during the shift event to the calculated maximum branch pressure.

13. The method of claim 12 , further comprising:

measuring a temperature of the oil; and

calculating the maximum area of the orifice as a function of the oil temperature.

14. The method of claim 12 , further comprising:

extracting a modeled clutch pressure from a lookup table using the controller; and

calculating the maximum area of the orifice as a function of the modeled clutch pressure.

15. The method of claim 12 , wherein the clutch is an oncoming clutch in the shift event, further comprising:

limiting pressure to an off-going clutch to a pressure value selected from a clutch torque-based lookup table.

16. The method of claim 12 , further comprising filtering the calculated maximum branch pressure using one of a Kalman filter, a weighted average, a rolling average, and a lag filter.