BACKGROUND ART In the automotive sector, it is known to provide a double- clutch gear change of the type comprising two input shafts, which are mounted concentric with respect to one another and are designed to be connected selectively to a drive shaft of the vehicle via interposition of a double clutch, and each of which carries a respective plurality of first gears coupled, in an angularly fixed way, to the corresponding input shaft.

The gear change further comprises two output shafts, which are set parallel to the two input shafts, are connected to a differential for the transmission of motion to the driving wheels of the vehicle, and each carries a respective plurality of second gears, each of which is coupled in a rotatable way to the corresponding output shaft, is designed to be angularly locked on the corresponding output shaft itself, and is coupled to one aforesaid first gear according to a given transmission ratio corresponding to a given gear speed of the vehicle itself.

Known double-clutch gear changes of the type described above present some drawbacks mainly deriving from the fact that, on account of the large overall dimensions, said gear changes are suited to being mounted only on vehicles with a front-wheel drive and/or with a four-wheel drive with transversely mounted engine and gear change.

DISCLOSURE OF INVENTION The object of the present invention is to provide a double- clutch gear change which will be free from the drawbacks

described above and will enable its installation on vehicles with rear-wheel drive with longitudinally mounted engine and rear transversely mounted gear change.

According to the present invention, a double-clutch gear change is provided for vehicles with rear-wheel drive as claimed in Claim 1.

BRIEF DESCRIPTION OF THE DRAWINGS The present invention will now be described with reference to the annexed plate of drawings, which illustrate some non- limiting examples of embodiment thereof, and in which : Figures 1 to 7 are schematic illustrations, with parts removed for reasons of clarity, of seven variants of the double-clutch gear change according to the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION With reference to Figure 1, number 1 designates, as a whole, a double-clutch gear change for a vehicle (not illustrated) with rear-wheel drive with front or rear longitudinally mounted engine and with rear transversely mounted gear change.

The gear change 1 comprises a first drive shaft 2, which is mounted so as to rotate about a longitudinal axis 3 thereof transverse to a longitudinal axis of the vehicle (not illustrated), and is connected, via a pair of bevel gears 4, to a second drive shaft 5, which is in turn connected to an engine shaft (not illustrated) of the vehicle (not illustrated either).

The gear change 1 further comprises two input shafts 6,7, which are mounted so that they share the axis 3 and are concentric with respect to the shaft 2, are axially aligned to one another, are set on opposite sides of the shaft 5, and each carries a respective plurality of gears 8 (in the case in

point, four gears 8), which are coupled, in an angularly fixed way, to the corresponding shaft 6, 7.

The shafts 6,7 are coupled in a rotatable way to the shaft 2, and are selectively connected to the shaft 2 via respective clutches 9,10, in the case in point disk clutches in oil bath, mounted at the ends of the shaft 2 itself.

The gear change 1 further comprises a single output shaft 11, which is mounted so as to rotate about a longitudinal axis 12 thereof parallel to the axis 3, and supports a plurality of gears 13, which are equal in number to the number of the gears 8, are coupled to the shaft 11 in a rotatable way, and are angularly locked on the shaft 11 itself in a selective way, via synchronizer devices 14 (in the case in point four devices 14), each of which is common to two corresponding gears 13.

Each gear 13 is coupled to a gear 8 according to a given transmission ratio corresponding to a given gear speed of the vehicle (not illustrated). In this regard, it should be pointed out that each gear 8 is coupled directly to the corresponding gear 13 with the exception of the gear 8 (designated, in what follows, by 8a) of the reverse gear, which is coupled to the corresponding gear 13 (designated, in what follows, by 13a) via interposition of an idle wheel (of a known type and not illustrated), designed to reverse the direction of rotation of the shaft 11. It should moreover be pointed out that, in the case in point, the gears 8 corresponding to the odd gears are mounted on the shaft 6, and the gears 8 corresponding to the even gears and to the reverse gear are mounted on the shaft 7.

The shaft 11 moreover carries a gear 15, which is coupled, in an angularly fixed way, to the shaft 11 itself, and is further coupled to a gear 16 of a differential 17 designed to transmit motion to a pair of axle shafts (not illustrated), each of

which is fixed to a respective rear driving wheel (not illustrated either).

In use, once one of the input shafts 6,7 is connected to the drive shaft 2 via the corresponding clutch 9,10 and once one of the gears 13 is angularly locked on the output shaft 11 via the corresponding synchronizer device 14, the motion is transmitted from the selected input shaft 6,7 to the output shaft 11 and, hence, to the differential 17 via the gears 15 and 16.

The variant illustrated in Figure 2 relates to a gear change 18 which differs from the gear change 1 mainly in that, therein, the shafts 2,6, and 7 are mounted concentric with respect to one another and in that the two clutches 9,10 are replaced with a double clutch 19, which is mounted in a position corresponding to one end of the shafts 6 and 7 and is designed to connect selectively the shafts 6 and 7 themselves to the shaft 2.

The variant illustrated in Figure 3 relates to a gear change 20 which differs from the gear change 18 mainly in that, therein, the double clutch 19 is mounted in an area corresponding to an intermediate point of the shaft 6 so as to obtain a greater symmetry in the distribution of the gears 8 and 13 with respect to the gear change 18.

The variant illustrated in Figure 4 relates to a gear change 21 which differs from the gear change 18 mainly in that, therein, the shafts 2 and 5 are connected to one another via interposition of an intermediate shaft 22 mounted parallel to the shaft 5 and coupled to the shaft 2 via the pair of bevel gears 4 and to the shaft 5 via a pair of further gears 23, one of which is fixed to the shaft 5 and the other to the shaft 22.

The variant illustrated in Figure 5 relates to a gear change 24 which differs from the gear change 18 mainly in that, therein, the gears 8 of the odd gears are fixed to a first intermediate shaft 25, and the gears 8 of the even gears 8a and of the reverse gear are fixed to a second intermediate shaft 26. The shafts 25 and 26 are axially aligned to one another, are mounted so as to rotate about one and the same longitudinal axis 27 parallel to the axes 3 and 12, and are connected to the shafts 6 and 7, respectively, via respective pairs of gears 28 and 29.

The conformation of the gear change 24 bestows upon the gear change 24 itself relatively reduced overall dimensions in a direction parallel to the axis 3.

The variant illustrated in Figure 6 relates to a gear change 30 which differs from the gear change 18 mainly in that, therein, the output shaft 11 is replaced with two output shafts 31,32, which are mounted so as to rotate about respective longitudinal axes 33,34 parallel to the axis 3, and each of which carries, in the case in point, four respective gears 13 and one respective gear 15, and in that the shaft 7 supports only two gears 8, one of which is designed to actuate selectively the gears 13 of two even gears and the other is designed to actuate selectively the gear 13 of one even gear and the reverse gear 13a.

The variant illustrated in Figure 7 relates to a gear change 35 which differs from the gear change 18 mainly in that, therein, one of the gears 8 (designated, in what follows, by 8b) mounted on the shaft 6 is designed to actuate both the first gear and the third gear and the reverse gear.

The gear 8b is directly coupled to the gear 13 (designated, in what follows, by 13b) of the third gear, and is further coupled to the reverse gear 13a via interposition of one first

intermediate gear 36 fixed to one first intermediate shaft 37 mounted so as to rotate about a longitudinal axis 38 thereof parallel to the axes 3 and 12.

The gear 8b is moreover coupled to the gear 13 (designated, in what follows, by 13c) of the first gear via the gear 36 and via a second intermediate gear 39, which is fixed to a second shaft 40 mounted so as to rotate about a longitudinal axis 41 thereof parallel to the axis 38, is coupled to a gear 42 fitted on the shaft 37, and is moreover coupled to the gear 13c.

In use, when on the output shaft 11 the gear 13b is selected, the motion is transmitted directly from the shaft 6 to the shaft 11 via the gears 8b and 13b. When on the output shaft 11 the gear 13a is selected, the motion is transmitted in the first place from the shaft 6 to the shaft 37 via the gears 8b and 36 and, then, from the shaft 37 to the shaft 11 via the gears 36 and 13a. When on the output shaft 11 the gear 13c is selected, the motion is in the first place transmitted from the shaft 6 to the shaft 37 via the gears 8b and 36, then it is transmitted from the shaft 37 to the shaft 40 via the gears 42 and 39, and finally it is transmitted from the shaft 40 to the shaft 11 via the gears 39 and 13c.