Gearbox with six or more forward gears for single-clutch or twin-clutch motor-vehicle transmissions

The gearbox comprises a pair of coaxial input shafts, that is, an inner input shaft and an outer input shaft, a first, upper output shaft, a second, lower output shaft, and an intermediate shaft. A driven gearwheel for a fourth gear and a driven gearwheel for a reverse gear are idly mounted on the opposite ends of the upper output shaft, the driven gearwheel meshing with an intermediate gearwheel idly mounted on the intermediate shaft. A driven gearwheel for a sixth gear and a driven gearwheel for a first gear are idly mounted on opposite ends of the lower output shaft. A first driving gearwheel is drivingly connected for rotation with the outer input shaft at an end thereof and meshes both with the driven gearwheel for the fourth gear and with the third driven gearwheel for the sixth gear. A second driving gearwheel meshing with the driven gearwheel for the first gear and a third driving gearwheel meshing with the intermediate gearwheel are drivingly connected for rotation with the inner input shaft at the opposite end thereof. The third driving gearwheel, the driven gearwheel for the reverse gear and the intermediate gearwheel are straight gearwheels.

BACKGROUND OF THE INVENTION

The present invention relates to a gearbox with six or more forward gears for single-clutch or twin-clutch motor-vehicle transmissions.

A six-gear gearbox of the type specified above is known from European patent application EP-A-1589257 in the Applicant's name. This known gearbox comprises:a pair of coaxial input shafts, that is, an inner input shaft and an outer input shaft, each of which can be coupled for rotation with a drive shaft by means of a respective clutch,a pair of output shafts, that is, an upper output shaft and a lower output shaft, which are parallel to the input shafts and are disposed above and below those shafts, respectively,a first set of driving gearwheels associated with the odd gears (first, third and fifth) and with the reverse gear and carried by the inner input shaft,a second set of driving gearwheels associated with the even gears (second, fourth and sixth) and carried by the outer input shaft,a first set of driven gearwheels associated with the second, fourth and reverse gears, which gearwheels are idly mounted on the upper output shaft and can be coupled selectively for rotation with that shaft by means of sliding engagement sleeves, anda second set of driven gearwheels associated with the first, third, fifth and sixth gears, which gearwheels are idly mounted on the lower output shaft and can be coupled selectively for rotation with that shaft by means of sliding engagement sleeves.

More specifically, to limit the overall axial length of the transmission, in the gearbox that is known from the above-mentioned patent application, a driving gearwheels which is common to the first and reverse gears is provided on the inner input shaft and a driving gearwheel which is common to the fourth and sixth gears is provided on the outer input shaft. These two shared driving gearwheels are disposed at opposite ends of the gearbox. Moreover, the driven gearwheel for the first gear that is idly mounted on the lower output shaft is used as the idle gear of the reverse gear train.

A problem of the known gearbox described above is the considerable length of the upper output shaft which hinders a forward transverse arrangement of the gearbox, particularly with a twin-clutch transmission which itself leads to a greater axial length owing to the presence of a second clutch.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a gearbox with six or more gears for single-clutch or twin-clutch motor-vehicle transmissions which has a shorter upper output shaft.

A further object of the present invention is to provide a gearbox with six or more gears for single-clutch or twin-clutch motor-vehicle transmissions having a design such as to ensure maximum synergy between the single-clutch and twin-clutch versions, that is, such that it is possible to change from one version to the other with the minimum number of modifications in terms of number, structure and arrangement of the components.

These and other objects are achieved in full according to the present invention by virtue of a gearbox having the characteristics specified in claim1.

Advantageous embodiments of the invention are defined in the dependent claims.

As will become clear from the following description, a gearbox according to the invention enables the length of the upper output shaft to be limited, thus enabling the gearbox to be installed easily in a forward position and with a transverse orientation, even in the twin-clutch version. Moreover, a gearbox according to the invention enables the number of components that are common to the single-clutch version, be it manual or robotized, and to the corresponding twin-clutch version, to be maximized and the number of modifications that are required to change from one version to the other to be minimized. The single- and twin-clutch versions of the same gearbox can thus be manufactured in the same production line with clear advantages in terms of costs.

In the drawings, the gear trains corresponding to the various forward gears of the transmission are indicated by the Roman numerals I, II, III, IV, V and VI, for first, second, third, fourth, fifth and sixth gears, respectively, and the reverse gear train is indicated by the letter R.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

With reference initially toFIG. 1, a six-gear gearbox for a twin-clutch motor-vehicle transmission according to a preferred embodiment of the invention comprises:a pair of coaxial input shafts, that is, an inner input shaft10and an outer input shaft12, each of which can be coupled with a drive shaft (not shown) by means of a respective clutch (also not shown),an upper output shaft14which is parallel to and disposed at a higher level than the two input shafts10and12,a lower output shaft16which is parallel to and disposed at a lower level than the two input shafts10and12,an intermediate reverse-gear shaft18parallel to the two input shafts10and12, anda housing19in which the two input shafts10,12and the two output shafts14,16are supported.

The outer input shaft12is formed as a hollow shaft which partially houses the inner input shaft10. The inner input shaft10projects from the outer input shaft12at the end remote from that facing the clutches and hence the engine.

The inner input shaft10carries, in order from left to right as seen inFIG. 1, that is, towards the clutch unit, a driving gearwheel21for the first gear, a driving gearwheel28for the reverse gear, a driving gearwheel23for the third gear, and a driving gearwheel25for the fifth gear. The outer input shaft12carries, in order from left to right, a driving gearwheel22for the second gear and a driving gearwheel24for the fourth and sixth gears. The driving gearwheels21,22,23,24,25and28are drivingly connected for rotation with the respective input shafts10and12on which they are mounted and may either be produced integrally with the shafts or be formed as separate components from the shaft and fixed thereto by suitable mechanical fastening means.

The upper output shaft14carries, in order from left to right, a driven gearwheel38for the reverse gear, a driven gearwheel35for the fifth gear, a driven gearwheel32for the second gear, a driven gearwheel34for the fourth gear and a final reduction pinion15. The lower output shaft16carries, in order from left to right, a driven gearwheel31for the first gear, a driven gearwheel33for the third gear, a driven gearwheel36for the sixth gear, and a final reduction pinion17.

The driven gearwheels31,32,33,34,35,36and38are formed as freely rotatable gears and can be coupled selectively for rotation with the respective output shafts by means of sliding engagement sleeves40,42,44and46. More specifically, a first engagement sleeve40is mounted on the upper output shaft14between the driven gearwheels38and34for the reverse gear and for the fifth gear, respectively, and is movable selectively to the left or to the right to couple the gearwheel38or the gearwheel35, respectively, for rotation with the output shaft14. A second engagement sleeve42is mounted on the upper output shaft14between the driven gearwheels32and34for the second and fourth gears, respectively, and is movable selectively to the left or to the right to couple the gearwheel32or the gearwheel34, respectively, for rotation with the output shaft14. A third engagement sleeve44is mounted on the lower output shaft16between the driven gearwheels31and33for the first and third gears, respectively, and is movable selectively to the left or to the right in order to couple the gearwheel31or the gearwheel33, respectively, for rotation with the output shaft16. A fourth engagement sleeve46is mounted on the lower output shaft16beside the driven gearwheel36for the sixth gear and is movable to the right in order to couple the gearwheel36for rotation with the output shaft16.

The intermediate reverse-gear shaft18carries a freely rotatable gearwheel39meshing with the driven gearwheel38for the reverse gear carried by the upper output shaft14.

Proceeding in order from left to right, the driving gearwheel21on the inner input shaft10meshes with the driven gearwheel31on the lower output shaft16to implement the first gear ratio (I). The driving gearwheel28on the inner input shaft10meshes with the freely rotatable gearwheel39on the intermediate, reverse-gear shaft18and rotates the driven gearwheel38on the upper output shaft14by means of the gearwheel39to implement the reverse gear (R). The driving gearwheel23on the inner input shaft10meshes with the driven gearwheel33on the lower output shaft16to implement the third gear (III). The driving gearwheel25on the inner input shaft10meshes with the driven gearwheel35on the upper output shaft14to implement the fifth gear (V). The driving gearwheel22on the outer input shaft12meshes with the driven gearwheel32on the upper output shaft14to implement the second gear (II). Finally, the driving gearwheel24on the outer input shaft12meshes both with the driven gearwheel34on the upper output shaft14to implement the fourth gear (IV), and with the driven gearwheel36on the lower output shaft16to implement the sixth gear (VI).

Given the free space that exists on the lower output shaft16between the driven gearwheel33and the engagement sleeve46, it would be possible to mount on that shaft a further freely rotatable gear meshing with the driving gearwheel25on the inner input shaft10to implement a seventh gear. In that case, the engagement of the seventh gear would be controlled by the engagement sleeve46which, in the six-gear version, is associated solely with the sixth gear. As can be seen fromFIG. 1, the addition of the seventh gear would not lead to an increase in the axial size of the gearbox.

The gearbox further comprises, in per-se-known manner, a pair of guide rods each associated with a respective output shaft. Two shift forks for operating each a respective engagement sleeve are mounted on each of the guide rods. In particular, a guide rod48associated with the upper output shaft14is shown inFIGS. 2 and 3. A first shift fork50for operating the first engagement sleeve40and a second shift fork52for operating the second engagement sleeve42are mounted on the guide rod48.

With reference now also toFIG. 5which shows, on an enlarged scale, a detail ofFIG. 1relating to the region of the gearbox in which the intermediate reverse-gear shaft18is mounted, that shaft is supported, at one end, in a special support seat53formed by the gearbox housing19and, at the opposite end, by a support bracket54. The support bracket54is located and fixed to the housing19by means of a screw56and also forms an appendage58(FIGS. 2 and 3) having a locating hole60in which an end portion of the guide rod48remote from the clutch unit is fitted.

As can be seen fromFIG. 1in particular, by virtue of the particular arrangement of the gearwheels relating to the various gears, the gearbox according to the invention has a short upper output shaft, considerably shorter than the lower output shaft. This thus prevents problems of bulkiness in case of a forward, transverse arrangement of the gearbox.

A further advantage is that the reverse gear train uses a dedicated driving gearwheel, that is, a gear which is not shared with the gearwheel of another gear and straight gearwheels can therefore be used for that gear train. It is thus possible to prevent the transmission of axial forces and bending moments to the idle gearwheel mounted on the intermediate reverse-gear shaft.

Moreover, by virtue of the fact that the gear trains of the fourth and sixth gears, which share the same driving gearwheel, are arranged at the end of the gearbox facing the clutches, whereas the gear trains of the first and reverse gears are arranged at the axially opposite end, the above-described version of the gearbox, which is intended for a twin-clutch transmission, can easily be changed into a corresponding version for a single-clutch transmission, be it robotized or manual.

In this connection, a six-ratio gearbox for a manual, single-clutch motor-vehicle transmission that can be obtained from the gearbox shown inFIG. 1will now be described with reference toFIG. 4. InFIG. 4, parts and elements that are identical or correspond to those of the six-ratio gearbox for a twin-clutch transmission ofFIGS. 1 to 3have been attributed the same reference numerals as were used in those drawings.

The gearbox ofFIG. 4comprises:an input shaft10which can be coupled to a drive shaft (not shown) by means of a clutch (also not shown),an upper output shaft14which is parallel to and disposed at a higher level than the input shaft10,a lower output shaft16which is parallel to and disposed at a lower level than the input shaft10,an intermediate reverse-gear shaft18parallel to the input shaft10, anda housing19in which the input shaft10and the two output shafts14,16are supported.

The input shaft10carries, in order from left to right as seen inFIG. 4, that is, towards the clutch, a driving gearwheel21for the first gear, a driving gearwheel28for the reverse gear, a driving gearwheel22for the second gear, a driving gearwheel25for the fifth gear, a driving gearwheel23for the third gear, and a driving gearwheel24for the fourth and sixth gears. The driving gearwheels21,22,23,24,25and28are drivingly connected for rotation with the input shaft10on which they are mounted and may be produced integrally with that shaft or formed as separate components from the shaft and fixed thereto by suitable mechanical fastening means.

The upper output shaft14carries, in order from left to right, a driven gearwheel38for the reverse gear, a driven gearwheel33for the third gear, a driven gearwheel34for the fourth gear, and a final reduction pinion15. The lower output shaft16carries, in order from left to right, a driven gearwheel31for the first gear, a driven gearwheel32for the second gear, a driven gearwheel35for the fifth gear, a driven gearwheel36for the sixth gear, and a final reduction pinion17.

The driven gearwheels31,32,33,34,35,36and38are formed as freely rotatable gears and can be coupled selectively for rotation with the respective output shafts by means of sliding engagement sleeves40,42,44and46. More specifically, a first engagement sleeve40is mounted on the upper output shaft14beside the driven gearwheel38for the reverse gear and is movable to the left to couple the gearwheel38for rotation with the output shaft14. A second engagement sleeve42is mounted on the upper output shaft14between the driven gearwheels33and34for the third and fourth gears, respectively, and is movable selectively to the left or to the right to couple the gearwheel33or the gearwheel34, respectively, for rotation with the output shaft14. A third engagement sleeve44is mounted on the lower output shaft16between the driven gearwheels31and32for the first and second gears, respectively, and is movable selectively to the left or to the right in order to couple the gearwheel31or the gearwheel32, respectively, for rotation with the output shaft16. A fourth engagement sleeve46is mounted on the lower output shaft16between the driven gearwheels35and36for the fifth and sixth gears, respectively, and is movable selectively to the left or to the right in order to couple the gearwheel35or the gearwheel36, respectively, for rotation with the output shaft16.

The intermediate reverse-gear shaft18carries a freely-rotatable gearwheel39meshing with the driven reverse gearwheel38carried by the upper output shaft14.

Proceeding in order from left to right, the driving gearwheel21on the input shaft10meshes with the driven gearwheel31on the lower output shaft16to implement the first gear (I). The driving gearwheel28on the input shaft10meshes with the freely rotatable gearwheel39on the intermediate reverse-gear shaft18and rotates the driven gearwheel38on the upper output shaft14by means of the gearwheel39to implement the reverse gear (R). The driving gearwheel22on the input shaft10meshes with the driven gearwheel32on the lower output shaft16to implement the second gear (II). The driving gearwheel25on the input shaft10meshes with the driven gearwheel35on the lower output shaft16to implement the fifth gear (V). The driving gearwheel23on the input shaft10meshes with the driven gearwheel33on the upper output shaft14to implement the third gear (III). Finally, the driving gearwheel24on the input shaft10meshes both with the driven gearwheel34on the upper output shaft3to implement the fourth gear (IV), and with the driven gearwheel36on the lower output shaft16to implement the sixth gear (VI).

With regard to the support of the intermediate reverse-gear shaft18, the description given above with reference to the version of the gearbox for a twin-clutch transmission shown inFIGS. 1 to 3applies.

As is clear from a comparison betweenFIGS. 1 and 4, the gearbox for a single-clutch, manual transmission shown inFIG. 4can be obtained from the gearbox for a twin-clutch transmission shown inFIG. 1by replacing the two input shafts10,12with the single input shaft10, exchanging the positions of the driving gearwheels22and23for the second and third gears, respectively, moving the driven gearwheel32for the second gear from the upper output shaft14to the lower output shaft16, moving the driven gearwheel33for the third gear from the lower output shaft16to the upper output shaft14, and moving the driven gearwheel35for the fifth gear from the upper output shaft14to the lower output shaft16.

It is also possible to change from the gearbox for a twin-clutch transmission shown inFIG. 1to a gearbox for a single-clutch robotized transmission (not shown), simply by replacing the two input shafts with a single input shaft but keeping the same arrangement of the gearwheels.

It will therefore be understood that the architecture proposed herein permits a high degree of synergy between the different versions of the gearbox and hence considerable savings in manufacturing costs.

Naturally, the principle of the invention remaining the same, the embodiments and details of construction may be varied widely with respect to those described and illustrated purely by way of non-limiting example.