Method for controlling a motor vehicle powertrain

1. A method of controlling a motor vehicle powertrain comprising an engine which provides a controllable engine torque and acts through a continuously variable transmission comprising a torque-controlled variator to apply wheel torque to driven wheel(s) of the motor vehicle, the transmission being of the torque-controlled type, and the method comprising:

determining a reaction torque requirement, the reaction torque being generated in the torque-controlled variator, and an engine torque requirement suitable to create a desired wheel torque and a desired engine acceleration; and

setting the engine torque and reaction torque accordingly, the engine torque and reaction torque being independently controllable, and being characterised in that the aforementioned calculation involves estimating and allowing for vehicle acceleration.

2. A method as claimed in claim 1 wherein the estimation of vehicle acceleration is based upon the desired wheel torque.

3. A method as claimed in claim 1 wherein the estimation of vehicle acceleration is carried out using an adaptive model whose adjustable parameters include vehicle mass and road gradient.

4. A method as claimed in claim 1 wherein the estimation of vehicle acceleration involves estimation of braking force applied by the vehicle brakes.

5. A method as claimed in claim 1 wherein the desired engine acceleration is determined on the basis of current engine speed and a target engine speed.

6. A method as claimed in claim 5 wherein the target engine speed is determined on the basis of driver input.

7. A method as claimed in claim 1 wherein the desired wheel torque is determined on the basis of driver input.

8. A method as claimed in claim 1 wherein the engine torque requirement is the sum of (i) the engine torque needed to accelerate moments of inertia of the engine and transmission, taking account of desired engine acceleration and estimated vehicle acceleration and (ii) the engine torque needed to provide the desired wheel torque, acting through the transmission.

9. A method as claimed in claim 8 wherein a model of the transmission, taking account of both current transmission ratio and transmission efficiency, is used in determining the engine torque needed to provide the desired wheel torque.

10. A method as claimed in claim 8 wherein, in calculating the engine torque needed to accelerate moments of inertia of the engine and transmission, allowance is made for (a) an engine-side inertia, contributed by those rotary engine and transmission components whose speed is proportional to engine speed, and (b) a free inertia, contributed by those transmission components whose speed is dependent upon speed of both the engine and the driven wheel(s) of the motor vehicle.

11. A method as claimed in claim 10 wherein acceleration of the free inertia is estimated based upon the desired engine acceleration and the estimated vehicle acceleration.

12. A method as claimed in claim 1 wherein the engine torque requirement is the sum of (i) the engine torque needed to accelerate an engine-side inertia, contributed by those rotary engine and transmission components whose speed is proportional to engine speed, (ii) the engine torque needed to accelerate a free inertia, contributed by those components of the transmission whose speed is dependent upon speed of both the engine and the driven wheels, and (iii) the engine torque needed to accelerate the vehicle.

13. A method as claimed in claim 12 wherein the reaction torque requirement is the sum of (a) the reaction torque required to cause acceleration of the free inertia, and (b) the reaction torque required to cause acceleration of the vehicle.

14. A method as claimed in claim 1 further comprising determining, taking account of lag in the engine's response, an estimated instantaneous engine torque, and taking account of this in setting the reaction torque.