Torque converter lockup control

1. A method of performing shift recovery in an off-road machine having an engine coupled to a torque converter with a lockup clutch and a transmission coupled to the torque converter, the method comprising:

engaging the lockup clutch of the off-road machine when the off-road machine reaches a minimum threshold speed;

maintaining the engagement of the lockup clutch during operation of the off-road machine including normal shifting between gears of the transmission;

sensing a missed shift between gears in the transmission;

disengaging the lockup clutch responsive to sensing the missed shift;

sensing a completed shift of the gears of the transmission;

calculating an engine speed corresponding to a desired torque converter output speed;

setting a speed limit for the engine corresponding to the calculated engine speed; and

reengaging the lockup clutch following a delay time.

2. The method of claim 1 , wherein engaging the lockup clutch occurs while the transmission of the off-road machine is in a gear above a first gear.

3. The method of claim 1 , wherein sensing the missed shift comprises sensing a change in revolutions per minute of a transmission shaft at a transmission controller.

4. The method of claim 1 , wherein disengaging the lockup clutch comprises receiving a signal from a transmission controller that causes the lockup clutch to disengage.

5. The method of claim 1 , wherein calculating the engine speed corresponding to the desired torque converter output speed comprises:

determining a gear that is engaged at the transmission following sensing the completed shift;

calculating from a current transmission shaft speed the desired torque converter output speed;

calculating a desired torque converter input speed based on the desired torque converter output speed; and

calculating the speed limit for the engine to provide the desired torque converter input speed.

6. The method of claim 5 , further comprising:

calculating the delay time corresponding to a known revolutions per minute decay time for the engine.

7. The method of claim 6 , wherein the missed shift occurs when the engine is under a load and the delay time is a range of 250-300 milliseconds.

8. A method of recovering from a missed shift in an off-road machine, the off-road machine including an engine and a transmission that are coupled by a torque converter having a lockup clutch, the method comprising:

disengaging the lockup clutch responsive to sensing the missed shift between gears of the transmission;

sensing a completed shift between gears of the transmission;

calculating a desired torque converter output speed corresponding to a transmission gear ratio for the completed shift;

calculating a desired engine speed necessary to reach the desired torque converter output speed;

setting an engine speed limit corresponding to the desired engine speed; and

reengaging the lockup clutch of the torque converter to mechanically couple the engine to the transmission following a delay time.

9. The method of claim 8 , further comprising engaging the lockup clutch after the off-road machine reaches an initial minimum speed from a full stop.

10. The method of claim 8 , wherein reengaging the lockup clutch of the torque converter to mechanically couple the engine to the transmission comprises reengaging the lockup clutch absent feedback related to engine speed.

11. The method of claim 8 , wherein setting the engine speed limit comprises sending a signal from a transmission controller to an engine controller, the signal containing the desired engine speed.

12. The method of claim 11 , wherein the engine speed limit is set for a duration in a range of 250 milliseconds to 350 milliseconds.

13. The method of claim 11 , wherein calculating the desired torque converter output speed comprises determining a gear setting for the transmission, determining a drive shaft speed and calculating a transmission input speed from the gear setting and the drive shaft speed.

14. The method of claim 8 , wherein reengaging the lockup clutch comprises receiving a signal at the torque converter from a transmission controller to reengage the lockup clutch.

15. A system for managing a lockup clutch for shift recovery in an off-road truck, the system comprising:

an engine;

a transmission;

a torque converter coupled between the engine and the transmission, the torque converter having the lockup clutch that when engaged directly couples the engine to the transmission;

a transmission controller that disengages the lockup clutch responsive to sensing a missed shift in the transmission, senses a subsequent completed shift, sets an engine speed limit corresponding to a gear associated with the completed shift, and reengages the lockup clutch.

16. The system of claim 15 , further comprising a sensor coupled to the transmission controller that reports a transmission input speed, a transmission output speed, and the engaged gear, the engaged gear defining a speed ratio between the transmission input speed and the transmission output speed.

17. The system of claim 15 , further comprising a communication bus between the transmission controller and an engine controller.

18. The system of claim 17 , wherein the communication bus is an SAE J1939 compliant bus.

19. The system of claim 15 , wherein the transmission controller reengages the lockup clutch after a delay time.

20. The system of claim 19 , wherein the transmission controller selects the delay time according to a known engine speed decay profile and a lockup clutch engagement time.