PERMANENT FOUR-WHEEL-DRIVE TRANSMISSION FOR A VEHICLE WITH A TRANSVERSE ENGINE

Abstract: A device for converting a front-wheel-drive transmission of a motor vehicle with a transverse engine into a permanent four-wheel-drive transmission, comprising a Ferguson-type fluid coupling (14) carried by a hollow shaft (13) coaxial with one of the front half-shafts (11) and fixed for rotation with the housing (7) of the front differential (9). In the event of slippage of the front axle, the Ferguson coupling (14) is arranged to cause rotation of a tubular hub (17) coaxially rotatably mounted on the hollow shaft (13) and carrying a ring gear (25) which, through a transmission unit (26-30, 33), drives a rear differential (34) for transmitting the torque to the half-shafts (35, 36) of the rear wheels of the vehicle.

Description: The present invention relates in general to motor vehicles with a transverse engine and a front-wheel-drive transmission including a gearbox having an output member which drives an epicyclic front differential driving the half-shafts of the front wheels of the vehicles. The object of the present invention is to produce a relatively simple and compact device of reduced size for automatically converting a front-wheel-drive transmission of the type defined above into a permanent four-wheel-drive transmission. The device according to the invention is characterised in that it includes a FERGUSON-type fluid coupling carried by a hollow shaft coaxial with one of the half-shafts and fixed for rotation with the housing of the front differential, the FERGUSON coupling being arranged to cause rotation of a tubular hub coaxially and rotatably mounted on the hollow shaft and carrying a ring gear, and a rear differential for transmitting the torque to the half-shafts of the rear wheels of the vehicle and driven by the ring gear through a transmission unit. Compared to known devices designed to carry out a similar function by means of torque-divider systems applied directly to the transmission shaft or between the latter and the rear differential, the device according to the invention has the advantage of appreciably reducing the bulk and the weight bearing on the transmission, as well as being structurally simpler and thus more economical. Conveniently, the transmission unit of the device includes a countershaft adjacent and parallel to the front half-shaft and carrying a gear which meshes with the ring gear, and an output unit including a pair of bevel gears of which one is fast with the countershaft and the other is kinematically connected to the rear differential. The front differential, the FERGUSON coupling, and the transmission unit are contained in a common casing fixed to the gearbox. The invention will now be described in detail with reference to the appended drawings, provided purely by way of non-limiting example, in which: Figure 1 is a schematic perspective view of a front-wheel-drive transmission of a motor vehicle incorporating a conversion device according to the invention and Figure 2 is a partially sectioned view of a detail of the transmission system of Figure 1, on an enlarged scale. In Figure 1, an internal combustion engine, schematically indicated 1, is intended to be mounted in the front part of a motor vehicle with its axis arranged transverse the longitudinal axis of the vehicle, indicated A in Figure 2. The engine 1 is provided with a gearbox 2, normally of the type with permanently engaged gear, having a main shaft, not illustrated, and a driven shaft 2a also arranged transverse the longitudinal axis A of the vehicle. A gear, indicated 3, is carried by the driven shaft 2a of the gearbox and meshes with a ring gear 4 supported for rotation by a casing, generally indicated 5, fixed to the gearbox. The ring gear 4 is joined by means of bolts 6 to the housing 7 of an epicyclic bevel-gear-type front differential 9 for transmitting the torque to the front wheels of the motor vehicle by means of two half-shafts 10, 11 in the manner explained below. The housing 7 of the differential 9 has on one side a tubular appendage 8 of reduced length coaxial with the half-shaft 10, and on the opposite side a tubular appendage 12 coaxial with the other half-shaft 11. The tubular appendage 12 is coupled for rotation with a hollow shaft 13 extending coaxially on the half-shaft 11 by means of a splined sleeve 19. A FERGUSON-type fluid coupling of known type, generally indicated 14, is housed within the casing 5. In conventional manner, the coupling 14 consists of a cylinder 15 carried by the tubular shaft 13 and coupled for rotation with a tubular hub 17 coaxially rotatably mounted on the outer end of the hollow shaft 13 by means of a toothed coupling 16. In known manner, the cylinder 15 contains two series of transmission discs, schematically indicated 18, 20, of which the first is coupled for rotation with the cylinder 15 and the second is coupled for rotation with a splined portion 21 of the hollow shaft 13. The tubular hub 17 carries a ring gear 25 which meshes with a gear 26 carried by one end of a countershaft 27 which is also supported for rotation by the casing 5. The shaft 27 is adjacent and parallel to the half-shaft 11 and carries on its opposite end a bevel gear 28 which meshes with a bevel pinion 29 on the inner end of a shaft 30 supported rotatably within a cylinder appendage 31 of the casing 5, arranged along the longitudinal axis A of the vehicle. The end of the shaft 30 opposite the bevel pinion 29 is connected, by means of a constant-velocity universal joint, generally indicated 32 in Figure 1, to a transmission shaft 33 for transmitting the torque to a conventional rear differential 34. The differential 34 transmits the torque to the half-shafts 35, 36 of the rear wheels of the vehicle. In operation, the torque imparted by the output gear 3 to the housing 7 of the front differential 9 is transmitted through the splined sleeve 19 to the hollow shaft 13 on which the FERGUSON fluid coupling 14 is mounted. When the vehicle is running under conditions of normal grip of the front wheels, the transmission shaft 33 remains disconnected from the hollow shaft 13. If slippage of the front axle occurs in slippery road conditions, the FERGUSON coupling automatically comes into operation to transmit torque to the rear axle by means of the toothed coupling 16, the gears 25 and 26, the shaft 27, the bevel gears 28, 31, the shafts 30 and 33, and the rear differential 34.

Claims: 1. A device for converting a front-wheel-drive transmission of a motor vehicle with a transverse engine into a permanent four-wheel-drive transmission, in which the front-wheel-drive transmission includes a gearbox having an output member which drives an epicyclic front differential driving the half-shafts of the front wheels of the vehicle, characterised in that it comprises a FERGUSON-type fluid coupling (14) carried by a hollow shaft (13) coaxial with one of the half-shafts (11) and fixed for rotation with the housing (7) of the front differential (9), the FERGUSON coupling (14) being arranged to cause rotation of a tubular hub (17) coaxially rotatably mounted on the hollow shaft (13) and carrying a ring gear (25), and a rear differential (34) for transmitting the torque to the half-shafts (35, 36) of the rear wheels of the vehicle and driven by the ring gear (25) through a transmission unit (26, 27, 28, 29, 30, 33). 2. A device according to Claim 1, characterised in that the transmission unit comprises a countershaft (27) adjacent and parallel to the front half-shaft (11) and carrying a gear (26) which meshes with the ring gear (25), and an output unit including a pair of bevel gears (28, 29) of which one is fast with the countershaft (27) and the other is kinematically connected to the rear differential (34). 3. A device according to Claim 1 or Claim 2, characterised in that the front differential (9), the FERGUSON coupling (14) and the transmission unit (26, 27, 28, 29, 30) are contained in a common casing fixed to the gearbox (5).

Inventors: CORDERO, FEDERICO, FALZONI, GIAN LUIGI
Applicants: FIAT AUTO S.P.A.
Application year: 1987
Main classification: B60K23
IPC codes: B60K17