Twin-clutch transmission

1. A twin clutch transmission for a motor vehicle with

a) at least seven forward gears which are shiftable under load and at least one reverse gear, comprising:

b) two concentric intermediate shafts ( 14 , 15 ) which are arranged co-axially with a transmission axis (X-X) and which can be engaged selectively with an input shaft ( 11 ) via a twin clutch ( 13 ) including first and second clutches K 1 , K 2 , one of the intermediate shafts ( 15 ) being a hollow shaft connected to the first clutch K 1 and, the other ( 14 ) extending through the hollow shaft ( 15 ) and being connected to the second clutch (K 2 ),

c) first and second countershafts ( 16 , 26 ) arranged parallel to the transmission axis (X-X),

d) the input shaft ( 11 ) extending coaxially with the transmission axis (X-X),

e) a transmission output shaft ( 12 ) extending coaxially with the transmission axis (X-X),

f) the transmission including four interim transmission stages for establishing at least a lowest forward gear between the input shaft ( 11 ) and the output shaft ( 12 ) and

g) for establishing at least a second lowest forward gear only two transmission stages being disposed between the input shaft ( 11 ) and the output shaft ( 12 ), and

h) for at least the lowest forward gear and the second lowest forward gear the power being transmitted via at least one identical gear ( 28 , 38 ), the lowest forward gear in the power path between the transmission input shaft ( 11 ) and the transmission output shaft ( 12 ) including two interconnected gears ( 34 , 35 ) which are rotatable together about the transmission axis (X-X), in the lowest forward gear one ( 35 ) of the interconnected gears ( 34 , 35 ) receiving the drive torque from one counter shaft ( 16 ) and the other gear ( 34 ) transmitting the drive torque to the other countershaft ( 26 ), and in another forward gear at least one of the interconnected gears ( 34 , 35 ) transmitting the drive torque between a countershaft ( 16 , 26 ) and the transmission output shaft ( 12 ) which extends co-axially with the transmission axis (X-X).

2. A twin clutch transmission according to Claim 1 , wherein the interconnected, gears ( 34 , 35 ) are interconnected for joined rotation by a hollow shaft ( 33 ) through which the transmission output shaft ( 12 ) extends.

3. A twin clutch transmission according to claim 1 , wherein one of the forward gears is a direct drive gear.

4. A twin clutch transmission according to claim 1 , wherein an input gear structure ( 17 ) assigned to the lowest forward gear and connected to the first clutch (K 1 ) has a longer transmission gear ratio than another input gear structure ( 25 ) connected to the second clutch (K 2 ) and assigned to the second lowest forward gear.

5. A twin clutch transmission according to claim 1 , wherein at least one of the, interconnected gears ( 34 , 35 ) is a helical gear with a tooth angle α and the other is a helical gear with a tooth angle β, wherein both angles α and β have the same sign arid are so dimensioned that the axial forces effective on the two gears in the first forward speed are about the same and oppositely directed so that they cancel each other.

6. A twin clutch transmission according to claim 1 , wherein an additional intermediate gear ( 39 ) is provided for reverse operation.

7. A twin clutch transmission according to claim 1 , wherein an additional countershaft ( 50 ) is provided for reverse operation.

8. A twin clutch transmission according to claim 1 , wherein the stage jump 1 -> 2 and 3 -> 4 are identical.

9. A twin clutch transmission according to claim 1 , wherein the gears 1 to 4 are spaced geometrically and the gears 4 to to 7 are progressively spaced.

10. A twin clutch transmission according to claim 1 , wherein the two interconnected gears ( 34 , 35 ) are included in gear stages for the third and fourth forward gears.

11. A twin clutch transmission according to claim 1 , wherein the at least seven forward gears are shiftable by four shifting elements ( 21 , 29 , 32 , 36 ).