A disengageable four-wheel-drive transmission system for motor vehicles

Claim 2

A disengageable four-wheel-drive transmission system for a motor vehicle with a transverse gearbox, including a toothed input member meshed with a toothed output member of the gearbox, a front differential which drives the drive shafts of the front wheels of the vehicle, a rear differential which drives the drive shafts of the rear wheels of the vehicle, and means for distributing the torque between the front and rear differentials, characterised in that the means for distributing the torque are constituted by a hydraulic clutch (22) which can be engaged and disengaged gradually and which is operatively associated with an electronic control unit (43) arranged to pilot the gradual engagement of the hydraulic clutch (22) automatically in dependence on operating parameters of the transmission system, starting from a disengaged condition in which the drive is transmitted from the gearbox (2) to only the front (4) or the rear (32) differential in order to control the distribution of the torque between the front and rear axles.

Claim 3

A transmission system according to Claim 1, in which the front differential (4) includes a box (5) and the drive shafts (8, 9) of the wheels project from opposite sides thereof, characterised in that one side (6) of the box (5) of the front differential (4) is coupled permanently to the toothed input member (11) of the transmission system, in that the hydraulic clutch (22) includes, in known manner, first and second coaxial entrainment members (21, 23) and friction discs (35, 36) coupled alternately to the two entrainment members, and in that the first entrainment member (21) is coupled permanently for rotation with the other side (7) of the box (5) of the front differential (4) and toothed output member (26) for transmitting the drive to the rear differential (32) is coupled permanently for rotation with the second entrainment member (23) so that, when the hydraulic clutch (22) is disengaged, the drive is transmitted from the gearbox (2) to the front differential (4) only.

Claim 4

A transmission system according to Claim 1, in which the front differential (4) includes a box (5) and the drive shafts (8, 9) of the front wheels project from opposite sides thereof, characterised in that the hydraulic clutch (22) includes, in known manner, first and second coaxial entrainment members (21, 23) and friction discs (35, 36) coupled alternately to the entrainment members, and in that the first entrainment member (21) is coupled permanently for rotation with the casing (5) of the front differential (4) and the second entrainment member (23) is coupled permanently for rotation with the toothed input member (11) of the transmission system by means of a hollow element (25) which surrounds the front differential (4) coaxially, a toothed output member (26) for transmitting the drive to the rear differential (32) being coupled permanently for rotation with the second entrainment member (23) so that, when the hydraulic clutch (22) is in the disengaged condition, the drive is transmitted from the gearbox (2) to the rear differential (32) only.

Claim 5

A transmission system according to Claim 1, in which the front differential (4) includes a box (5) and the drive shafts (8, 9) of the front wheels project from opposite sides thereof, characterised in that the box (5) of the front differential (4) is coupled permanently for rotation with the toothed input member (11) of the transmission system as well as with a toothed output member (26) for transmitting the drive to the rear differential (32) by means of a longitudinal propeller shaft (31) having a first portion (50) which is driven by the toothed output member (26) and a second portion (51) for driving the rear differential (32), in that the hydraulic clutch (22) includes, in known manner, first and second coaxial entrainment members (21, 23) and friction discs (35, 36) coupled alternately to the two entrainment members (21, 23), the two entrainment members (21, 23) being coupled permanently for rotation with the first (50) and second (51) portions of the longitudinal shaft (31) respectively, so that, when the hydraulic clutch (22) is in the disengaged condition, the drive is transmitted from the gearbox (2) to the front differential (4) only.

Claim 6

A transmission system according to Claim 2, Claim 3 or Claim 4, characterised in that the electronic control unit (43) is arranged to pilot the operation of the hydraulic clutch (22) in dependence on the instantaneous torque delivered by the engine (1) of the vehicle.

Claim 7

A transmission system according to Claim 5, characterised in that the toothed input member (11) of the transmission system and the toothed output member (10) of the gearbox (2) each have helical teeth, and in that the input member (11) is supported rotatably by the housing (3) of the gearbox (2) by means of an axial rolling bearing (15) with a portion (152) which is resiliently deformable in dependence on the axial load transmitted by the helical teeth (10, 11) and which has an associated deformation transducer (53) operatively connected to the electronic control unit (43) and adapted to supply thereto electrical signals indicative of the deformation of the deformable portion (152) of the axial bearing (15).

Claim 8

A transmission system according to Claim 6, characterised in that the axial bearing (15) has an outer race (48) which is mounted with clearance relative to the housing (3) of the gearbox (2) and has at least one external annular projection (49) clamped axially relative to the housing and defining the resiliently deformable portion (152).

Claim 9

A transmission system according to Claim 6 or Claim 7, characterised in that the deformation transducer is constituted by extensometers (53).

Claim 10

A transmission system according to Claim 7, or Claim 8, characterised in that there is a single annular projection (49).

Claim 11

A transmission system according to Claim 7 or Claim 8, characterised in that there are two annular projections (55).

Claim 12

A transmission system according to any one of Claims 7 to 10, characterised in that the annular projection has rounded sides (54).