Output torque control method
Readings of multiple sensors are utilized to estimate transmission output, which is used as a feedback signal to control the torque capacity of a transmission clutch. Some sensor readings, such as transmission output speed, are used to compute an input vector. Then, a current state vector is computed as a linear function of the previous state vector and the input vector. One of the values in the state vector is shaft twist, which is proportional to transmission output torque. Various other sensor readings, including wheel speed, are used to correct for noise. Wheel speed signals are received with a delay. To accommodate this delay, the state vector is expanded to include estimates of wheel speed at various past points in time. An accelerometer reading is used at very low speeds at which the wheel speed sensor and transmission output speed sensor are unreliable.
1. A controller comprising:
communication channels for receiving data from a plurality of sensors and for sending a command to adjust a torque capacity of a transmission clutch; and
a processor programmed to repeatedly:
compute an input vector comprising a plurality of input values based on the data from the sensors,
compute a current step state vector comprising a plurality of state values as a function of the input vector and a previous step state vector, the plurality of state values including a first state value that varies in proportion to transmission output torque, and
adjust the torque capacity of the clutch, based on the first state value, to deliver a target transmission output torque.
2. The controller of claim 1 wherein the first state value is an estimate of present shaft twist angle.
3. The controller of claim 2 wherein the plurality of state values further includes an estimate of present wheel speed.
4. The controller of claim 3 wherein the plurality of state values further includes an estimate of wheel speed at a time in the past.
5. The controller of claim 3 wherein the plurality of state values further includes an estimate of present vehicle speed.
6. The controller of claim 1 wherein the plurality of input values includes a transmission output speed measurement.
7. The controller of claim 6 wherein the plurality of input values further includes a wheel speed measurement.
8. The controller of claim 7 wherein the plurality of input values further includes a vehicle acceleration measurement.
9. A method of controlling a transmission clutch comprising, at regular intervals:
computing an input vector comprising a plurality of input values based on a plurality of measurements;
computing a current step state vector comprising a plurality of state values as a function of the input vector and a previous step state vector; and
adjusting a torque capacity of the transmission clutch based on one of the state values that is proportional to transmission output torque.
10. The method of claim 9 wherein the plurality of input values includes a transmission output speed measurement.
11. The method of claim 10 wherein the plurality of input values further includes a wheel speed measurement.
12. The method of claim 9 wherein the state value upon which the torque capacity of the transmission clutch is adjusted is an estimate of present shaft twist angle.
13. The method of claim 12 further comprising adjusting the estimate of present shaft twist angle based on a vehicle acceleration measurement.
14. The method of claim 12 wherein the plurality of state values further includes an estimate of present wheel speed.
15. The method of claim 14 wherein the plurality of state values further includes an estimate of wheel speed at a time in the past.
16. The method of claim 14 wherein the plurality of state values further includes an estimate of present vehicle speed.
17. The method of claim 9 wherein the transmission clutch is a launch clutch.