Automatic transmission synchronous gear shift

1. A method of commanding a synchronous gear shift in a vehicle powertrain that includes an engine and a transmission having a plurality of ordered gears, the method comprising:

receiving a request to shift from a third gear to a first gear, and skipping a second gear having a gear ratio between the gear ratio of the first gear and the gear ratio of the third gear;

reducing a torque command to a predetermined value;

opening a clutch disposed on an input shaft of the transmission to decouple the transmission from the engine;

transitioning the engine from a torque-control mode into a speed-control mode;

commanding the engine, while in the speed-control mode, to rotate at a speed dictated by the motion of the vehicle and the gear ratio of the first gear;

closing the clutch to couple the transmission and the engine; and

transitioning the engine back into the torque-control mode.

2. The method of claim 1 , wherein the engine operates in response to a driver torque request while in the torque-control mode; and

wherein closing the clutch to couple the transmission and the engine includes closing the clutch over a period of time such that a torque of the input shaft of the transmission is blended to match the driver torque request.

3. The method of claim 2 , further comprising receiving the driver torque request continuously throughout the synchronous gear shift.

4. The method of claim 3 , further comprising arbitrating between the driver torque request and a transmission input shaft speed request.

5. The method of claim 1 , wherein the torque command saturates at an immediate torque maximum during the speed-control mode, and wherein the immediate torque maximum includes a maximum amount of torque capable of being produced by the engine at a fixed airflow.

6. The method of claim 1 , wherein the torque command approaches zero prior to the closing of the clutch to couple the transmission and the engine.

7. The method of claim 1 , wherein the torque command and the engine rotation speed are independently controllable through the adjustment of a spark timing, a fuel supply, and an airflow supply.

8. The method of claim 1 , further comprising disregarding an axle torque request while in the speed-control mode.

9. The method of claim 1 , wherein transitioning the engine back into the torque-control mode includes gradually transitioning the engine back into the torque-control mode over a period of time.

10. The method of claim 1 , wherein the torque command is a function of a driver acceleration request when the engine is in the torque-control mode.

11. A method of commanding a synchronous gear shift in a vehicle powertrain that includes an engine and a transmission having a plurality of ordered gears, the method comprising:

receiving a request to shift from a third gear to a first gear, and skipping a second gear having a gear ratio between the gear ratio of the first gear and the gear ratio of the third gear;

reducing a torque command to approximately zero via an immediate torque request;

opening a clutch disposed on an input shaft of the transmission to decouple the transmission from the engine;

transitioning the engine from a torque-control mode into a speed-control mode;

disregarding an axle torque request while in the speed-control mode.

commanding the engine, while in the speed-control mode, to rotate at a speed dictated by the motion of the vehicle and the gear ratio of the first gear;

closing the clutch to couple the transmission and the engine; and

transitioning the engine back into the torque-control mode.

12. The method of claim 11 , wherein an immediate torque request effectuates a modification to at least one of a spark timing and an amount of fuel supplied to a cylinder.

13. The method of claim 11 , wherein the torque command saturates at an immediate torque maximum during the speed-control mode, and wherein the immediate torque maximum includes a maximum amount of torque capable of being produced by the engine at a fixed airflow.

14. The method of claim 11 , wherein the torque command approaches zero prior to the closing of the clutch to couple the transmission and the engine.

15. The method of claim 11 , wherein the torque command and the engine rotation speed are independently controllable through the adjustment of a spark timing, a fuel supply, and an airflow supply.

16. The method of claim 11 , wherein transitioning the engine back into the torque-control mode includes gradually transitioning the engine back into the torque-control mode over a period of time.

17. The method of claim 11 , wherein the torque command is a function of a driver acceleration request when the engine is in the torque-control mode.