Parallel shift transmission and method for controlling it

1. A parallel shift transmission for a motor vehicle having at least two partial transmissions, each of said at least two partial transmissions comprising a transmission input shaft that is coupleable to a drive shaft of a drive unit via a friction clutch and a plurality of gear ratio steps that are engageable between the transmission input shaft and an output shaft, wherein for each of said plurality of gear ratio steps a prescribable maximum speed of the transmission input shaft associated with said each of said plurality of gear ratio steps is set and in the case of gear ratio steps that have a higher and a lower gear ratio step and are to be simultaneously engaged in the two partial transmissions, the speed of the transmission input shaft having the gear ratio step with the higher ratio is limited.

2. The parallel shift transmission as described in claim 1 , wherein the speed of said transmission input shaft having the higher gear ratio step is limited to the maximum speed of the gear ratio step having the higher gear ratio.

3. The parallel shift transmission as described in one of claims 1 , wherein a selection for shifting a transmission step on the transmission shaft not associated with the transmission shaft having the gear ratio step with the higher gear ratio is limited as a function of the gear ratio of the higher gear ratio step.

4. The parallel shift transmission as described in claim 3 , wherein, before reaching the maximum speed, an engaged gear ratio step that would lead to an exceeding of the maximum speed of the gear ratio step having the higher gear ratio during engagement of the friction clutch assigned to this gear ratio step is disengaged.

5. The parallel shift transmission as described in claim 3 , wherein a gear ratio step to be shifted that would lead to an exceeding of the maximum speed of the gear ratio step having the higher gear ratio during engagement of the friction clutch assigned to this gear ratio step is not engaged.

6. The parallel shift transmission as described in claim 3 , wherein the gear ratio step to be engaged that would lead to an exceeding of the maximum speed of the gear ratio step having the higher gear ratio during engagement of the friction clutch assigned to this gear ratio step is engaged under the condition that a speed of the drive unit to be regulated by a controller is regulated in such a manner that the maximum speed of the gear ratio step having the higher speed is not exceeded.

7. The parallel shift transmission as described in claim 2 , wherein a selection for shifting a transmission step on the transmission shaft not associated with the transmission shaft having the gear ratio step with the higher gear ratio is limited as a function of the gear ratio of the higher gear ratio step.

8. The parallel shift transmission as described in claim 7 , wherein, before reaching the maximum speed, an engaged gear ratio step that would lead to an exceeding of the maximum speed of the gear ratio step having the higher gear ratio during engagement of the friction clutch assigned to this gear ratio step is disengaged.

9. The parallel shift transmission as described in claim 7 , wherein a gear ratio step to be shifted that would lead to an exceeding of the maximum speed of the gear ratio step having the higher gear ratio during engagement of the friction clutch assigned to this gear ratio step is not engaged.

10. The parallel shift transmission as described in claim 7 , wherein the gear ratio step to be engaged that would lead to an exceeding of the maximum speed of the gear ratio step having the higher gear ratio during engagement of the friction clutch assigned to this gear ratio step is engaged under the condition that a speed of the drive unit to be regulated by a controller is regulated in such a manner that the maximum speed of the gear ratio step having the higher speed is not exceeded.

11. A method for operating a parallel shift transmission in a motor vehicle having at least two partial transmissions, wherein each of said at least two partial transmissions comprises a transmission input shaft that is coupleable to a drive shaft of a drive unit via a friction clutch and a plurality of gear ratio steps that are engageable between the transmission input shaft and an output shaft comprising, setting for each gear ratio step a prescribable maximum speed of the transmission input shaft associated with this gear ratio step and, in the case of gear ratio steps that have a higher and a lower gear ratio step and are to be simultaneously shifted in the two partial transmissions, limiting the speed of the transmission input shaft having the gear ratio step with the higher ratio.

12. The method as described in claim 11 for use in an emergency operating mode, further comprising activating said emergency operating mode if said gear ratio step cannot be disengaged in at least one of said at least two partial transmissions.