TRANSMISSION SYSTEM FOR MOTOR VEHICLES

Abstract: Transmission system for four-wheel drive motor vehi­ cles includes a front differential (21) for distributing torque between the front wheels of the motor vehicle, a rear dif­ ferential (22) for distributing torque between the rear wheels, and an intermediate differential (23) for distributing torque between the front differential (21) and the rear differen­ tial (22), and is also provided with a speed variator de­ vice (31) between the intermediate differential (23) and the front differential (21).

Description: Transmission system for motor vehicles The present invention relates to motor vehicle transmission systems of the type comprising: a gearbox including a main shaft and a driven shaft carrying a number of meshed pairs of gears, one gear of each pair being permanently connected for rotation with one of the two shafts and the other being connectible for rotation with the other shaft by synchronising means, and means for transmitting torque from the gearbox to the front and rear wheels of the motor vehicle, these means including: a front differential for distributing torque between the front wheels of the motor vehicle, a rear differential for distributing torque between the rear wheels of the motor vehicle, and an intermediate differential for taking torque from the driven shaft of the gearbox and distributing it between the front differential and the rear differential. The object of present invention is to provide a transmission system of the type specified above, which enables an optimum distribution of torque between the various wheels of the motor vehicle as a function of the loads acting thereon and of the road-holding conditions. The main characteristic of the invention lies in the fact that a speed variator device is interposed between the intermediate differential and the front differential. In a first embodiment, the speed variator device comprises two parallel and spaced-apart shafts connected to the front differential and the intermediate differential respectively, and at least two meshed pairs of gears, one gear of each pair being permanently connected for rotation with one of the shafts, and the other being connectible for rotation with the other shaft by synchronising means. in a second embodiment, the speed variator device comprises two parallel and spaced-apart shafts connected to the front differential and the intermediate differential respectively, and an automatic speed variator of the expansible pulley and belt type connecting these shafts. By virtue of this characteristic, the intermediate differential and the front differential of the motor vehicle can be connected in accordance with various transmission ratios, enabling torque to be distributed between the front axle and the rear axle of the motor vehicle in the optimum manner as a function of the load and road-holding conditions. Further characteristics and advantages of the present invention will be apparent from the description which follows with reference to the appended drawings, supplied purely by way of non-limiting example. in which: Figures 1 and 2 show diagrammatically two different embodiments of the transmission system according to the invention. With reference to Figure 1, there is shown a transmission system 1 for four-wheel drive motor vehicles. The transmission system 1 includes a gearbox 2 having a main shaft 3 connectible to the engine of the motor vehicle by means of a conventional clutch, and a driven shaft 4. The shafts 3, 4 of the gearbox 2 carry a number of pairs of gears 5, 6; 7; 8; 9, 10; 11, 12; 13, 14. The gears 5, 7, 9, 11, 13 are permanently connected for rotation with the main shaft 3, while the gears 6, 8, 10, 12, 14 can be selectively connected for rotation with the driven shaft 4 by means of synchronising clutches 15, 16, 17. These pairs of gears correspond respectively to the first, second, third, fourth and fifth speed ratios obtainable through the gearbox. The synchroizing device 15 also controls the intervention of gears 18, 19 and 20 when reverse gear is selected. Transmission system 1 comprises a front differential 21 of known type for distributing torque between the front wheels of the motor vehicle, and a rear differential 22, also of known type, for distributing torque between the rear wheels. The two differentials 21, 22 are connected to an intermediate differential 23 for distributing torque between the front differential and the rear differential. The intermediate differential 23 is formed by an epicyclic train consisting of a sun wheel 24, a number of planets wheels 25, and an annulus 26. In the example shown, the annul us 26 is connected to the rear differential 22, while the cage of the epicyclic train (indicated 27) is connected to a shaft 29 by means of a known type of releasable connection device 28 (shown only in diagrammatic form in Figure 1). The axis of the shaft 29 is parallel to and spaced from the axis of a shaft 30 connected to the front differential 21. According to the invention, the shafts 29, 30 are connected together by means of a speed variator device 31 which, in the example shown in Figure 1, comprises two pairs of gears 32, 33 and 34, 35 capable of producing two different ratios of torque transmission from the shaft 29 to the shaft 30. The gears 33, 35 are permanently connected for rotation with the shaft 30, while the gears 32, 34 can be selectively connected for rotation with the shaft 29 by means of a synchronising clutch 36. In the example shown, the shaft 30 is also connected to the front differential 21 by means of a pair of constant-velocity universal joints 37. In Figure 2 the parts common to Figure 1 are given the same reference numeral. The embodiment shown in Figure 2 differs from that of Figure 1 in that the speed variator device 31 is constituted by an automatic belttype speed variator of known type, comprising a pair of expansible pulleys 38 connected by a belt 39. Naturally, while the principle of the invention remains the same, the details of construction and forms of embodiment may be widely varied from that described and illustrated purely by way of example, without thereby departing from the scope of the present invention.

Claims: CLAIMS 1. Transmission system for motor vehicles, comprising: a gearbox (2) including a main shaft (3) and a driven shaft (4) carrying a number of meshed pairs of gears (5, 6; 7, 8; 9, 10; 11, 12; 13, 141 r one gear of each pair being permanently connected for rotation with one of the shafts and the other being connectible for rotation with the other shaft by synchronising means (15, 16, 17), means for transmitting torque from the gearbox (2) to the front wheels and rear wheels of the motor vehicle, these means including: a front differential (21) for distributing torque between the front wheels of the motor vehicle, a rear differential (22) for distributing torque between the rear wheels of the motor vehicle, and an intermediate differential (23) for taking up the torque from the driven shaft (4) of the gearbox (2) and distributing it between the front differential (21) and the rear differential (22), characterised in that a speed variator device (31) is interposed between the intermediate differential (23) and the front differential (21). 2. Transmission system according to Claim 1, characterised in that the speed variator device 131r comprises two parallel and spaced-apart shafts (29, 30) connected to the intermediate differential (23) and the front differential (21) respectively, and at least two meshed pairs of gears (32, 33; 34, 35), one gear of each pair being permanently connected for rotation with one of the two shafts and the other being connectible for rotation with the other shaft by synchronising means. 3. Transmission system according to Claim 1, characterised in that the speed variator device (31) comprises two parallel and spacedapart shafts (29, 30) connected to thë intermediate differential (23) and the front differential (21) respectively, and an automatic speed variator of the expansible pulley and belt type connecting these shafts. 4. Transmission system according to any of Claims 1 and 3, characterised in that the intermediate differential (23) comprises an epicyclic train the cage (27) of which is driven by the driven shaft (4) of the gearbox (2). 5. Transmission system according to Claim 4 characterised in that the intermediate differential (23) is provided with a releasable coupling device (28) for connecting it to the front differential (21).

Inventors: BERTINO, GIUSEPPE, LOMBARDI, CLAUDIO, MESSORI, PIER PAOLO
Applicants: FIAT AUTO S.P.A.
Application year: 1985
Main classification: B60K17
IPC codes: B60K17