Method and system for gear engagement

1. A method for motion control of a shift sleeve in a stepped gear transmission during a synchronisation and gear engagement sequence for avoiding gear teeth interference, wherein the stepped gear transmission comprises an axially displaceable shift sleeve arranged on and rotationally secured to a shaft, and a constant mesh gear wheel arranged on and rotatable relative to said shaft, the method comprising:

receiving a gear shift command,

determining a target relative displacement between sleeve teeth and gear teeth for a state when a gear wheel rotational speed reaches a shift sleeve rotational speed at an end of a synchronisation phase, the target relative displacement is determined for avoiding impact between the sleeve teeth and the gear teeth during a following gear engagement phase,

determining a first phase plane trajectory defining a relationship between a rotational speed difference between the shift sleeve and the gear wheel and a relative displacement between the sleeve teeth and the gear teeth, wherein the relative displacement according to the first phase plane trajectory equals the target relative displacement when said rotational speed difference becomes zero at the end of the synchronisation phase,

determining a second phase plane trajectory defining the relationship between the rotational speed difference between the shift sleeve and the gear wheel and the relative displacement between the shift teeth and the gear teeth, wherein the relative displacement according to the second phase plane trajectory equals the target relative displacement when said rotational speed difference becomes zero at the end of the synchronisation phase,

applying a synchronisation torque,

controlling said synchronisation torque for keeping a detected real relative displacement between the sleeve teeth and the gear teeth within boundaries of the first and second phase plane trajectories for any rotational speed difference, such that the real relative displacement between the sleeve teeth and the gear teeth reaches said target relative displacement simultaneously with said rotational speed difference becomes zero at the end of the synchronisation phase.

2. The method according to claim 1 , comprising controlling said synchronisation torque by a closed loop controller for keeping the real relative displacement between the sleeve teeth and the gear teeth within the boundaries of the first and second phase plane trajectories.

3. The method according to claim 2 , wherein the relative displacement according to the second phase plane trajectory is smaller or equal to the relative displacement of the first phase plane trajectory minus a maximal relative displacement at the rotational speed difference when the closed loop controller is configured to start.

4. The method according to claim 2 , comprising

determining a starting relative displacement between the sleeve teeth and gear teeth that causes the shift sleeve and gear wheel to reach said target relative displacement simultaneously with said rotational speed difference becomes zero at the end of the synchronisation phase when applying a synchronisation torque from the start to the end of the synchronisation phase, and

starting to apply said synchronisation torque when the real relative displacement reaches said starting relative displacement.

5. The method according to claim 1 ,

wherein the step of determining the first phase plane trajectory is based on application of a first angular acceleration, and

wherein the step of determining the second phase plane trajectory is based on application of a second reduced angular acceleration that is lower than the first angular acceleration, or based on deriving the second phase plane trajectory from the first phase plane trajectory and an offset.

6. The method according to claim 5 , wherein the step of determining the first angular acceleration involves taking into account a rotational speed dependent drag torque.

7. The method according to claim 1 , comprising determining said first and second phase plane trajectories by performing one or more backward in time calculations starting from the time point when said rotational speed difference becomes zero at the end of the synchronisation phase and ending at a predetermined rotational speed difference, in particular based on a predetermined gear shift map, wherein the phase plane trajectories are stored in lookup tables in a computer memory for enabling prompt access by an electronic transmission controller.

8. The method according to claim 1 , wherein each of the first and second phase plane trajectories extends between a rotational speed difference corresponding to the start of the synchronisation phase to the state when said rotational speed difference becomes zero at the end of the synchronisation phase, and the method comprising operating said closed loop controller from the beginning to the end of the first and second phase plane trajectories.

9. The method according to claim 1 , wherein when the real relative displacement between the sleeve teeth and gear teeth at the rotational speed difference when the closed loop controller is configured to start controlling said synchronisation torque is larger than the relative displacement of the first trajectory at said rotational speed difference, shifting said first and second trajectories with an integer times a maximal relative displacement, such that the real relative displacement becomes located between an offset first trajectory and an offset second trajectory.

10. The method according to claim 1 , comprising operation of two sequential controllers: an initial open loop controller and subsequently a closed loop controller,

wherein operation of the open loop controller involves keeping the synchronisation torque zero or at a compensation torque level for as long as real relative displacement is different from a starting relative displacement, and applying the synchronisation torque as soon as the real relative displacement is equal to the starting relative displacement, and

wherein operation of the closed loop controller involves controlling the synchronisation torque for keeping the real keeping real relative displacement within the boundaries of the first and second phase plane trajectories.

11. The method according to claim 1 , wherein the closed loop controller for the purpose of keeping the real relative displacement within the boundaries of the first and second phase plane trajectories comprises:

applying synchronisation torque and monitoring the real relative displacement and the rotational speed difference,

if the real relative displacement falls below the second trajectory for any given rotational speed difference, stop applying the synchronisation torque, or start applying only a compensation torque in a direction opposite to drag torque,

monitoring the real relative displacement, and start applying the synchronisation torque again when the real relative displacement is equal to the first trajectory for any given rotational speed difference, and

reiterating above steps in same order until rotational speed difference becomes zero at the end of the synchronisation phase.

12. The method according to claim 1 , comprising starting to apply said synchronisation torque substantially directly upon receiving the gear shift command and independent of current relative displacement between the sleeve teeth and gear teeth.

13. The method according to claim 1 , comprising initiating the closed loop control first after one of at least 5%, at least 25%, or at least 50%, of the total rotational speed difference between the shift sleeve and the gear wheel, from the start to the end of the synchronisation phase, has passed.

14. The method according to claim 1 , comprising determining the target relative displacement, a compensation torque applied on the gear wheel in a direction opposite to a drag torque and a shift sleeve axial engagement speed, for any specific sleeve teeth and gear teeth geometry, such that the sleeve teeth is determined to enter in the space between neighbouring gear teeth to a maximal engagement depth substantially without mutual contact, and preferably with a sleeve teeth side surface near or in side contact with an opposite gear teeth side surface.

15. The method according to claim 1 , wherein when the real relative displacement between the sleeve teeth and gear teeth at the rotational speed difference when the closed loop controller is configured to start controlling said synchronisation torque is smaller than the relative displacement of the second trajectory at said rotational speed difference, shifting said first and second trajectories with an integer times the maximal relative displacement, such that real relative displacement becomes located between an offset first trajectory and an offset second trajectory.

16. A method for motion control of a shift sleeve in a stepped gear transmission during a synchronisation and gear engagement sequence for avoiding gear teeth interference, wherein the stepped gear transmission comprises an axially displaceable shift sleeve arranged on and rotationally secured to a shaft, and a constant mesh gear wheel arranged on and rotatable relative to said shaft, the method comprising:

receiving a gear shift command,

determining a target relative displacement between the sleeve teeth and gear teeth for a state when a gear wheel rotational speed reaches a shift sleeve rotational speed at the end of a synchronisation phase, which target relative displacement is determined for avoiding impact between sleeve teeth and gear teeth during a following gear engagement phase,

determining a starting relative displacement between the sleeve teeth and gear teeth that causes the shift sleeve and gear wheel to reach said target relative displacement simultaneously with said rotational speed difference becomes zero at the end of the synchronisation phase when applying a synchronisation torque from the start to the end of the synchronisation phase,

starting to apply said synchronisation torque when the real relative displacement reaches said starting relative displacement.

17. A control system for motion control of a shift sleeve in a stepped gear transmission during a synchronisation and gear engagement sequence for avoiding gear teeth interference, wherein the stepped gear transmission comprises an axially displaceable shift sleeve arranged on and rotationally secured to a shaft, and a constant mesh gear wheel arranged on and rotatable relative to said shaft, the control system being configured for performing the following steps:

receiving a gear shift command,

determining a target relative displacement between the sleeve teeth and gear teeth for a state when a gear wheel rotational speed reaches a shift sleeve rotational speed at an end of a synchronisation phase, which target relative displacement is determined for avoiding impact between sleeve teeth and gear teeth during a following gear engagement phase,

determining a first phase plane trajectory defining a relationship between a rotational speed difference between the shift sleeve and the gear wheel and a relative displacement between the sleeve teeth and gear teeth, wherein the relative displacement according to the first phase plane trajectory equals the target relative displacement when said rotational speed difference becomes zero at the end of the synchronisation phase,

determining a second phase plane trajectory defining the relationship between the rotational speed difference between the shift sleeve and the gear wheel and the relative displacement between the sleeve teeth and gear teeth, wherein the relative displacement according to the second phase plane trajectory equals the target relative displacement when said rotational speed difference becomes zero at the end of the synchronisation phase,

applying a synchronisation torque,

controlling said synchronisation torque for keeping a real relative displacement between the sleeve teeth and gear teeth within boundaries of the first and second phase plane trajectories for any rotational speed difference, such that the real relative displacement between the sleeve teeth and gear teeth reaches said target relative displacement simultaneously with said rotational speed difference becomes zero at the end of the synchronisation phase.