GB2075933A - Driving system for four-wheel driven vehicle - Google Patents

Abstract

A vehicle driving system for a vehicle having a pair of front road wheels (12, 12') and a pair of rear road wheels (23,23'), comprising a power unit (1) having an output (1a) in a lateral direction of the vehicle; a transaxle mechanism (2) comprising a power transmission gear unit (4) having input and outputs shafts (4a, 4b) parallel with an extension of the output shaft of the power unit, and a first final reduction gear unit (5) for transmitting the driving power from the transmission output shaft to, for example, the front road wheels, a branch-off gear (27) driven by the first final reduction gear unit for rotation about an axis parallel with the transmission input and output shafts, a driveline (34, 36) including at least one propeller shaft extending in a fore-and- aft direction of the vehicle and a second final reduction gear unit (25) for transmitting the driving power from the driveline to, for example, the rear road wheels, and right-angle power transfer means (30,32) positioned between the branch-off gear and the driveline and operative to convert the rotation of the branch-off gear into rotation about an axis perpendicular to the axis of rotation of the branch-off gear for driving the propeller shaft for rotation about the axis thereof. Drive-wheel shift clutch means (28,29,31) may be provided between the branch-off gear and the right-angle power transfer means. <IMAGE>

Description

SPECIFICATION Driving system for four-wheel-driven vehicle The present invention relates to a vehicle driving system for a vehicle having at least two pairs of road wheels consisting of a pair of front road wheels and a pair of rear rod wheels and, more particularly, to a four-wheel drive system for such a wheeled vehicle.

A known four-wheel-driven vehicle uses a driveline including an engine and a power transmission gear unit which are arranged in series in a fore-andaft direction of the vehicle. The driving power delivered from the engine is split by means of a power transfer mechanism into two component drives one of which is transmitted through a front wheel propeller shaft to the wheels axles for the front road wheels and the other of which is transmitted through a rear wheel propeller shaft to the wheel axles for the rear road wheels.

Such a series arrangement of the engine and the power transmission gear unit requires an elongated vehicle chasis and, for this reason, results in deterioration of the stability of steering due to extended overhanging of the vehicle body. Furthermore, the transmission gear unit in the series engine and transmission arrangement occupies a portion of the spaces which could otherwise be utilized as the passenger and baggage spaces, thereby reducing the availability of the passenger and baggage spaces of the vehicle.

Additionally, provision of the propeller shafts for the front and rear wheel axles and the power transfer mechanism in the driveline using the series engine and transmission arrangement ordinarily causes an increase in the production cost and an increase in the overall weight of the vehicle.

The present invention contemplates overcoming these problems of a conventional four-wheel-driven vehicle by eliminating one of the propeller shafts for the front and rear wheel axles of a known fourwheel-driven vehicle and slightly modifying the driving system for an ordinary two-wheel-driven vehicle.

In accordance with the present invention, there is provided a vehicle driving system for a vehicle having at least two pairs of road wheels consisting of a pair of front road wheels and a pair of rear road wheels, comprising a power unit having an output shaft which is rotatable about an axis in a lateral direction of the vehicle, a transaxle mechanism comprising a power transmission gear unit and a first final reduction gear unit, the transmission gear unit including transmission input and output shafts each having an axis of rotation which is substantially parallel with an extension of the axis of rotation of the output shaft of the power unit and gears mounted on the transmission input and output shafts and arranged to be capable of selectively producing a plurality of ratios between the speeds of rotation of the transmission input and output shafts, the first final reduction gear unit including gears arranged in such a manner as to split the driving power from the transmission output shaft into two component drives to be respectively transmitted to one of the above mentioned two pairs of road wheels, a branch-off gear engaging the first final reduction gear unit for being driven by the final reduction gear unit for rotation about an axis which is substantially parallel with the axis of rotation of each of the transmission input and output shafts, a driveline including at least one propeller shaft extending in a fore-and-aft direction of the vehicle and a second final reduction gear unit including gears arranged in such a manner as to split the driving power from the driveline into two component drives to be transmitted to the other of the aforesaid two pairs of road wheels, and right-angle power transfer means operatively positioned between the branch-off gear and the driveline and operative to convert the rotation of the branch-off gear into rotation about an axis which is substantially perpendicular to the axis of rotation of the branch-off gear.

In the vehicle driving system basically constructed and arranged as above described, the transaxle mechanism may further comprises a transaxle casing structure enclosing the power transmission gear unit and the first final reduction gear unit and formed with an opening through which the final reduction gear unit is held in engagement with the above mentioned branch-off gear.

The features and advantages of the vehicle driving system according to the present invention will be more clearly understood from the following description in which like reference numerals and characters designate corresponding or similar members and structures throughout the figures of the drawings and in which: Figure 1A is a schematic view showing the general construction of a first preferred embodiment of the vehicle driving system according to the present invention; Figure 1B is a fragmentary sectional view showin part of the detailed construction and arrangement of the embodiment illustrated in Figure 1A; Figure 2A is a view similar to Figure 1A but showing the general construction of a second preferred embodiment of the vehicle driving system according to the present invention; and Figure 2B is a view similar to Figure 1 B but showing part of the detailed construction and arrangement of the embodiment illustrated in Figure 2A.

Referring to Figures 1A and 1 B of the drawings, the vehicle driving system embodying the present invention comprises a power unit which is shown constituted by an internal combustion engine 1 having an output shaft la. The vehicle driving system features a crosswise-positioned engine arrangement and, thus, the engine 1 is installed on the chassis of a wheeled vehicle in such a manner that the output shaft la extends horizontally in a lateral direction of the chassis. Furthermore, the vehicle driving system is assumed, by way of example, as being of the front-engine design and, thus, the engine 1 is positioned at the front of the chassis of the vehicle. When the engine 1 is of the reciprocating-piston type, the output shaft la thereof is constituted by the crankshaft of the engine.

The vehicle driving system further comprises a manually operated transmission-front-axle or, briefly, transaxle mechanism 2 which consists largely of a mechanical clutch unit 3, a manually-operated power transmission gear unit 4, and a front final reduction gear unit 5. The mechanical clutch unit 3 comprises a driving member connected to the output shaft 1a of the engine 1 and a driven member engageable with the driving member and connected to a transmission input shaft 4a forming part of the transmission gear unit 4. The clutch unit 3 further comprises a pressure member axially movable on the transmission input shaft 4a and adapted to force the driven member into engagementwth the driving member when actuated for axial movement on the shaft 4a.The pressure member is biased by means of a spring (not shown) for connecting the driven member of the driven member, as is well known in the art.

The transmission input shaft 4a axially extends in alignment with the output shaft la of the internal combustion engine 1 and is journalled in bearings supported on a transaxle casing structure 6. The transmission gear unit 4 is assumed, by way of example, as being of the five-forward-speed and one-reverse-speed type and comprises a total of six drive gears fixedly mounted on, or integral with, the transmission input shaft 4a and axially spaced from each other on then shaft 4a. The drive gear consist of a first-speed forward drive gear 7a, a second-speed forward drive gear 7b, a third-speed forward drive gear 7c, a fourth-speed forward drive gear 7d, a fifth-speed forward drive gear 7e, and a reverse drive gear7f.

The transaxle casing structure 6 has further supported thereon a transmission output shaft 4b which axially extends in parallel with the transmission input shaft 4a and which has opposite axial end portions respectively journaled in bearings mounted on the casing structure 6. The transmission output shaft 4b has coaxially mounted thereon a total of six driven gears which are axially spaced from each other on the shaft 4b and which are freely rotatable independently of one another on the shaft 4b about the center axis of the shaft 4b. The driven gears on the transmission output shaft 4b consist of a firstspeed forward driven gear 8a, a second-speed forward driven gear Bb, a third-speed forward driven gear 8c, a fourth-speed forward driven gear 8d, a fifth-speed forward driven gear 8e, and a reverse driven gear 8f.The first-speed to fifth-speed driven gears 8a to 8e on the transmission output shaft 4b are paired and held in mesh with the first-speed to fifth-speed drive gears 7a to 7e, respectively, on the transmission input shaft 4a. On the other hand, the reverse driven gear 8f on the output shaft 4b is engageable with the reverse drive gear 7f on the input shaft 4a through the intermediary of a reverse idler gear 9 axially movable and coaxially rotatable on an idler gear shaft 4c. The idler gear shaft 4c also extends axially in parallel with the transmission input shaft 4a and is secured to the transaxle casing structure 6.

The power transmission gear unit 4 is assumed, by way of example, as being of the fully synchronized type and, thus, further comprises three synchronizing clutch assemblies each of which is coaxially mounted on, and rotatable with, the transmission output shaft 4b. The synchronizing clutch assemblies are shown consisting of a first-second-speed synchronizing clutch assembly 10a, a third-fourthspeed syrchronizing clutch assembly 10b, and a fifth-speed synchronizing clutch assembly 10c.The first-second-speed synchronizing clutch assembly 10a is axially positioned between the first-speed and second-speed forward driven gears 8a and Bb and is selectively engageable with these gears 8a and Bb and, likewise, the third-fourth-speed synchronizing clutch assembly lOb is axially positioned between the third-speed and fourth-speed forward driven gears 8c and 8d and is selectively engageable with these gears 8c and 8d. The fifth-speed synchronizing clutch assembly 1 0c is provided in association with the fifth-speed forward driven gear 8e and is engageable with the gear 8e.

As is well known in the art and will be seen from the illustration of Figure 1 B, each of the synchronizing clutch assemblies 10a and lOb is largely composed of an externallytoothed clutch hub keyed or splined on the transmission output shaft 4b between the gears 8a and Bb or gears 8c and 8d, a pair of externally toothed synchronizing or blocking rings positioned adjacent to the opposite axial ends of the clutch hub and engageable with the clutch hub, and an internally toothed annular coupling sleeve held in mesh with, and axially movable on, the clutch hub.

The synchronizing rings of each of the clutch assemblies 10a and 10b are rotatable with the gears 8a and Bb or the gears 8c and 8d, respectivly. The synchronizing clutch assembly 10c is constructed similarly to each of the clutch assemblies 10a and 10b but has only one synchronizing ring rotatable with the gear 8e. Each of the gears 8a to 8e has, or is formed with, a coupling gear section adjacent to the associated synchronizing ring.The coupling sleeve of each of the clutch assemblies 10a, lob, and 10e is axially movable into engagement with the coupling gear section of one or the other of the gears 8a and Bb or gears 8c and 8d of the gear 8e past the associated synchronizing ring so as to establish synchronized coupling between the transmission output shaft 4b and the gear engaged by the coupling sleeve. The coupling sleeve of each clutch assembly is formed with a circumferential groove through which a gear shifter fork (not shown) is held in circumferentially slidable engagement with the sleeve. The shifter forks thus engaging the respec-.

tive coupling sleeves of the individual clutch assemblies 10a, 10b and 10c are, in turn, respectively carried on gearshift control rods or rails which are operatively connected to, or engaged by, a manually operated gearshift lever through gearshift control linkages, though not shown in the drawings.

The reverse driven gear 8fits constituted as part of the coupling sleeve of the first-second-speed synchronizing clutch assembly 1 Oa. The reverse idler gear 9 is engaged by a gear shifter fork (not shown) carried on the gearshift control rod or rail carrying the shifter fork engaging the coupling sleeve of the fifth-speed synchronizing clutch assembly 10c. The shafts 4a to 4c and all the gears and clutch assemblies mounted on these shafts are enclosed within the transaxle casing structure 6.

The construction and arrangement of the transmission gear unit 4 as hereinbefore described and shown in Figures 1Aand 1B ispersesimplyforthe purpose of illustration and may therefore be changed and/or modified in numerous ways as desired.

The output shaft 4b of the transmission gear unit 4 has fixedly mounted thereon a transmission output gear 11 which is rotatable about the center axis of the shaft 4b. The transmission output gear 11 is adapted to drive the previously mentioned front final reduction gear unit 5 forming part of the transaxle mechanism 2. The front final reduction gear unit 5 is also enclosed within the transaxle casing structure 6 and is adapted to provide a transfer of power from the transmission gear unit 4 to front road wheels which are schematically shown at 12 and 12' in Figure 1A.

The front final reduction gear unit 5 consists of a differential gear assembly and comprises a ring gear 13 which is rotatable about an axis parallel with the axis of rotation of the transmission output shaft 4b.

The ring gear 13 is secured to, or integral with, a differential gear casing 14 (Figure 1 B) which is rotatable with the ring gear 13 about the axis of rotation of the gear 13 with respect to the rearward extension 6a of the transaxle casing structure 6 and which has opposite axial end portions respectively journaled in bearings supported by a rearward extension 6a of the transaxle casing structure 6. The differential gear casing 14 has carried therein two pairs of differential bevel pinions 15 which are rotatably mounted on two pinion cross shafts 16 (Figure 1 B) secured to the gear casing 14 and extending at right angles to each other and to the axis of rotation of the gear casing 14, as will be seen from Figure 1 B in which only two of the four bevel pinions 15 are shown mounted on one of the cross shafts 16.The individual bevel pinions 15 are, thus, rotatable not only together with the gear casing 14 and cross shafts 16 about the axis of rotation of the gear casing 14 but also independently of one another about the center axes of the cross shafts 16, viz., axes perpendicular to the axis of rotation of the gear casing 14.

The four differential bevel pinions 15 are positioned between and held in mesh with a pair of differential side bevel gears 17 and 17' which are rotatable about the axis of rotation of the differential gear casing 14 and which are also carried in the gear casing 14. The side bevel gears 17 and 17' are keyed or splined to inner end portions of a pair of side gear shafts 18 and 18', respectively, extending from the rearward extension 6a of the transaxle casing structure 6 in a lateral direction of the chassis of the vehicle through openings formed in opposite side wall portions of the extension 6a. The side gear shafts 18 and 18' form part of front axle assemblies which further comprise front wheel drive shafts 19 and 19' connected to the side gear shafts 18 and 18' through couplinge means such as constant-velocity joints 20 and 20', respectively.The front wheel drive shafts 19 and 19' in turn extend outwardly from the constant-velocity joints 20 and 20' in a lateral direction of the vehicle chasis and are connected at their outer axial ends to front wheel axles 21 and 21' for the front road wheels 12 and 12' through coupling means such as constant-velocity joints 22 and 22', respectively.

The construction and arrangement of the front final reduction gear unit 5 as hereinbefore described and shown in Figures 1A and 1B isperse simply for the purpose of illustration and may thus be changed and/or modified in numerous manners as desired.

The rearward extension 6a of the transaxle casing structure 6 has at its rear end an opening 6b through which the rotation of the ring gear 13 of the front final reduction gear unit 5 can be further transmitted to rear road wheels 23 and 23' of the vehicle through a drive-wheel shift and right-angle power transfer unit 24 and a rear final reduction gear unit 25 as schematically illustrated in Figure 1A.

As shown in Figures 1A and 1 B, the drive-wheel shift and right-angle power transfer unit 24 comprises a hollow casing structure 26 detachably connected to the rearward extension 6a of the transaxle casing structure 6 by fastening means such as bolts and nuts. The hollow casing structure 26 is formed with an opening contiguous to the above mentioned opening 6b in the rearward extension 6a of the transaxle casing structure 6. The casing structure 26 has provided therein a branch-off gear 27, twowheel-drive and four-wheel-drive shift clutch means, and right-angle power transfer gear means. The branch-off gear 27 has opposite axial extensions or bosses respectively journaled in bearings supported on the casing structure 26 and which is rotatable about an axis substantially parallel with the axis of rotation of the abovementioned ring gear 13.The branch-off gear is held in mesh with the ring gear 13 an is securely connected to, or integrally formed with, an externally serrated first coupling gear 28 which is coaxially rotatable with the branch-off gear 27. In Figure 1 B, the first coupling gear 28 is shown splined to one of the axial extension or boss of the branch-off gear 27 and axially held in position on the particular extension or boss by means of an annular retainer element which is secured to the extension or boss. The first coupling gear 28 forms part of the above mentioned two-wheel-drive and four-wheel drive shift clutch means which further comprises an externally serrated second coupling gear 29.

In line with the branch-off gear 27 is provided a driving bevel gear 30 which forms part of the above mentioned right-angle power transfer means. The driving bevel gear 30 has an axial extension journaled in bearings supported on the casing structure 26 and is rotatable about an axis substantially aligned with the axis of rotation of the branch-off gear 27. The axial extension of the driving bevel gear 30 extends toward the branch-off gear 27 and has securely mounted, or formed thereon, the above mentioned second coupling gear 29 which is thus coaxially rotatable with the driving bevel gear 30.

The second coupling gear 29 is axially spaced from the first coupling gear 28 and is equal in diameter and pitches of gear teeth to the first coupling gear 28. In Figure 1 B, the second coupling gear 29 is shown splined to a reduced end portion of the axial extension of the driving bevel gear 30 and is axially held in position on the end portion of the extension by means of an annular retainer element secured to the end portion of the extension.

The first and second coupling gears 28 and 29 are coupled with, or uncoupled from, each other by means of an internally serrated coupling sleeve 31 which forms part of the above mentioned twowheel-drive and four-wheel-drive shift clutch means.

The coupling sleeve 31 is constantly held in mesh with one of the coupling gears 28 and 29 and is axially movable on the particular one of the gears into and out of mesh with the other of the coupling gears 28 and 29. In Figures 1A and 1 B, the coupling sleeve 31 is assumed, by way of example, as being held in mesh with the second coupling gear 29 and is axially movable on the coupling gear 29 into and out of mesh with the first coupling gear 28. The coupling sleeve 31 is formed with a circumferential groove through which a shifting fork (not shown) is held in circumferentially slidable engagement with the coupling sleeve 1. The shifting forkthus engaging the coupling sleeve 31 is, in turn, connected through a mechanical linkage to manually or otherwise operated two-wheel-drive and four-wheel drive shift control means, though not shown in the drawins.

The first and second coupling gears 28 and 29 and the coupling sleeve 31 constructed and arranged as above described constitute, in combination, the above mentioned two-wheel-drive and four-wheeldrive shift clutch means and are adapted for selectively coupling the branch-off gear 27 to the driving bevel gear 30.

The driving bevel gear 30 is held in mesh with a driven bevel gear 32 which has an axial extension journaled in bearings supported on a rearward extension 26a (Figure 1 B) of the hollow casing structure 26. The driven bevel gear 32 is rotatable about an axis extending at right angles to the axis of rotation of the driving bevel gear 29, viz., in a fore-and-aft direction of the chassis of the vehicle.

The combination of the driving and driven bevel gears 30 and 32 thus arranged constitutes the above mentioned right-angle power transfer means and is adapted to convert the rotation of the branch-off gear 27 about the axis of rotation thereof into rotation about an axis perpendicular to the axis of rotation of the branch-off gear 27. It may be herein mentioned that the relationship between the axis of rotation of the branch-off gear 27 and the axis of rotation of the driven bevel gear 31 is such that the particular two axes of rotation are substantially at right angles to each other but are not necessarily in perpendicularly intersecting relationship to each other.

The axial extension of the driven bevel gear 32 projects rearwardly from the rearward extension 26a of the casing structure 26 through an opening formed in the rearward extension 26a an is connected through coupling means such as a universal joint 33 to a first propeller shaft 34 extending rearwardly from the universal joint 33 in a fore-andaft direction of the vehicle chassis as schematically shown in Figure 1A.

The first propeller shaft 34 forms part of a driveline for the rear road wheels 23 and 23' an is connected through coupling means such as a universal joint 35 to a second propeller shaft 36 extending rearwardly from the universal joint 35 also in a fore-and-aft direction of the vehicle chassis. The second propeller shaft 36 in turn is rearwardly connected through coupling means such as a universal joint 37 to the rear final reduction gear unit 25.

As shown schematically in Figure 1A, the rear final reduction gear unit 25 comprises a driving bevel pinion 38 connected to the above mentioned second propeller shaft 36 through the universal joint 37 and having an axis of rotation in a fore-and-aft direction of the vehicle chassis. The driving bevel pinion 28 is held in mesh with a bevel ring gear 39 having an axis of rotation at right angles to the axis of rotation of the driving bevel pinion 38. The driving bevel piniot 38 and the bevel ring gear 39 constitute, in combination, right-angle power transfer means adapted to convert the rotation of the propeller shaft 36 about the axis of rotation thereof into rotation of the bevel ring gear 39 about an axis perpendicular, in intersecting or non-intersecting relationship, to the axis of rotation of the propeller shaft 36.Such bevel gears 38 and 39 are housed in a stationary gear casing 40 and are each journaled in bearings (not shown) supported on the gear casing 40.

Similarly to the previously described front final reduction gear unit 5, the rearfinal reduction gear unit 25 consists of a differential gear assembly and, thus, further comprises a rotatable gear casing (not shown) which is secured to, or integral with, the above mentioned bevel ring gear 39. The gear casing is rotatable with the ring gear 39 about the center axis thereof with respect to the above mentioned stationary gear casing 40 and has carried therein two pairs of differential bevel pinions 41 which are rotatable mounted on two pinion cross shafts (not shown) secured to the rotatable gear casing.The bevel pinions 41 are thus rotatable not only together with the cross shafts and the rotatable gear casing about the axis of rotation of the ring gear 39, but also independently of one another about the center axes of the cross shafts, viz., axes perpendicular to the axis of rotation of the ring gear 39.

The differential bevel pinions 41 are positioned between and held in mesh with a pair of differential side bevel gears 42 and 42' which are rotatable about the axis of rotation of the ring gear 39 and are also carried in the above mentioned rotatable gear; casing. The side bevel gears 42 and 42' are keyed or splined to inner end portions of a pair of side gear shafts 43 and 43', respectively, which extend from the stationary gear casing 40 in a lateral direction of the vehicle chassis through openings in opposite side wall portions of the gear casing 40. The side gear shafts 43 and 43' form part of rear axle assemblies which further comprise rear wheel drive shafts 44 and 44' connected to the side gear shafts 43 and 43' through coupling means such as constant-velocity joints 45 and 45', respectively. The rear wheel drive shafts 44 and 44' in turn extend outwardly from the constant-velocity joints 45 and 45' in a lateral direction of the vehicle chassis and are connected at their outer axial ends to rear wheel axles 46 and 46' of the rear road wheels 23 and 23' through coupling means such as constant-velocity joints 47 and 47', respectively.

The construction and arrangement of the rear final reduction gear unit 25 as hereinbefore described and shown in Figure 1A is per se simply by way of example and may therefore bs changed and/or modified in numerous manners as desired.

Description will be hereinafter made regarding the operation of the vehicle driving system constructed and arranged as hereinbefore described with reference to Figures 1A and 1 B.

When the engine 1 is in operation and the clutch unit 3 is coupled, the driving power delivered from the output shaft la of the engine 1 is transmitted through the clutch unit 3 to the input shaft 4a of the power transmission unit 4. Before the clutch unit 3 is actuated into the coupled condition, the transmission gearshift lever (not shown) is manually operated to select the gearshift control rod or rail carrying the shifter fork engaging the synchronizing clutch assembly 10a, 10b or lotto be put into motion on the transmission output shaft 4b if it is desired to select one of the forward-drive gear ratios.

Further manipulation of the gear-shift lever causes the particular gearshift control rod or rail to move axially with the shifter fork carried thereon and causes the associated synchronizing clutch assem- bly to axially move on the transmission output shaft 4b in a direction to produce synchronized coupling between the transmission output shaft 4b and the selected one of the gears 8a to 8e on the shaft 4b. If, on the other hand, it is desired to select the reverse-drive gear ratio, the reverse idler gear 9 is actuated to axially move on the idler gear shaft 4c into the position meshing with the reverse drive gear 7f and the reverse driven gear by on the shafts 4a and 4b, respectively.

When one of the gears 8a to 8e on the transmission output shaft 4b is coupled to the shaft 4b through the associated synchronizing clutch 10a, 1 Ob or 1 Oc or the reverse idler gear 9 is moved into mesh with the gears 7f and 8f, the driving power carried through the clutch unit 3 to the transmission input shaft 4a is transmitted to the transmission output shaft 4b through the selected pair of gears on the shafts 4a and 4b or through the gears 7f, 8f and 9.

The rotation of the transmission output shaft 4b thus driven for rotation at a speed proportioned in the selected ratio to the rotational speed of the transmission input shaft 4a is transmitted through the transmission output gear 11 on the shaft 4b to the ring gear 13 of the front final reduction gear unit 5.

The driving power delivered from the power transmission gear unit 4 is thus reduced in speed ratio by means of the final reduction gear unit 5 and is transmitted through the side gear shafts 18 and 18', constant-velocity joints 20 and 20', front wheel drive shafts 19 and 19', constant-velocity joints 22 and 22' and front wheel axles 21 and 21' to the front road wheels 12 and 12', respectively.

The driving power thus delivered to the ring gear 13 of the front final reduction gear unit 5 is split into three components two of which are distributed to the front road wheels 12 and 12' and the other of which is transmitted to the branch-off gear 27 of the drive-wheel shift and right-angle power transfer unit 24 and through the branch-off gear 27 to the first coupling gear 28 of the two-wheel-drive and fourwheel-drive shift clutch means of the unit 24. If, in this instance, the coupling sleeve 31 on the second coupling gear 29 of the clutch means is held in an axial position disengaged from the first coupling gear 28, the first and second coupling gears 28 and 29 are disengaged from each other so that the driveline for the rear road wheels 23 and 23' is disconnected from the branch-off gear 27.Under these conditions, only the front road wheels 12 and 12' are driven by the engine 1.

If, however, the coupling sleeve 31 is held in an axial position in mesh with both the first and second coupling gears 28 and 29, the driving power transmitted to the branch-off gear 27 is further transmitted through the first coupling gear 28, coupling sleeve 31 and second coupling gear 29 to the driving bevel gear 30 of the right-angle power transfer means and causes the driven bevel gear 32 to turn about its axis of rotation in a fore-and-aft direction of the vehicle chassis. The rotation of the driven bevel gear 32 is transmitted by way of the universal joint 33, first propeller shaft 34, universal joint 35, second propeller shaft 36 and universal joint 37 to the driving bevel pinion 38 and further through the bevel pinion 38 to the bevel ring gear 39 of the rear final reduction gear unit 25.The driving power delivered from the power transmission unit 4 to the driveline for the rear road wheels 23 and 23' is thus finally reduced in speed ratio by means of the rear final reduction gear unit 25 and is transmitted through the side gear shafts 43 and 43', constant-velocity joints 45,45' rear wheel drive shafts 44 and 44', constantvelocity joints 47 and 47' and rear wheel axles 46 and 46' to the rear road wheels 23 and 23', respectively.

Under these conditions, not only the front road wheels 12 and 12' but also the rear road wheels 23 and 23' are driven by the engine 1.

The embodiment of the vehicle driving system hereinbefore described with reference to Figures 1 A and 1 B is of the type using a manually-operated power transmission. Such an embodiment of the present invention can however be readily modified to use an automatic power transmission. Figures 2A and 2B of the drawings show an embodiment using an automatically operated transaxle mechanism 48 in lieu of the manually operated transmission-frontaxle or, briefly, transaxle mechanism 2.

As shown in Figures 2A and 2B, the automatically operated transaxle mechanism 48 largely consists of a hydrodynamic clutch unit 49, an automatically operated power transmission gear unit 50, and a front final reduction gear unit 51. The clutch unit 49, transmission gear unit 50 and front final reduction gear unit 51 are enclosed within a transaxle casing structure 52 juxtaposed with respect to the internal combustion engine 1 which is positioned in such a manner that the output shaft 1a thereof axially extends in a lateral direction of the chassis of a vehicle as schematically shown in Figure 2A.

The hydrodynamic clutch unit 49 is herein assumed, by way of example, as consisting of a three-member torque converter and is thus shown comprising a driving member constituted by a pump impeller 49a, a driven member constituted by a turbine runner 49b, and a reaction memberconsti- tuted by a stator 49c. The pump impeller 49a is connected by a converter driving plate 49dto the output shaft 1a of the engine 1 and is thus rotatable with the engine output shaft la about an axis substantially aligned with the axis of rotation of the shaft 1 a. The turbine runner 49b is connected to, and rotatable with, a hollow input shaft 50a of the transmission gear unit 50.The hollow transmission input shaft 50a is rotatable about an axis which is also substantially aligned with the axis of rotation of the engine output shaft la. The stator 49c is positioned between the pump impeller 49a and the turbine runner 49b and is connected to the transaxle casing structure 52 through a torque converter one-way clutch assembly 53. The general construction and arrangement of the torque converter 49 as above described is peruse well known in the art and will not be described for further details thereof.

The power transmission gear unit 50 is assumed, by way of example, as being of the three-forward- speed and one-reverse-speed type and is shown comprising two planetary gear assemblies which are arranged in series with each other coaxially on a hollow output shaft 50b of the transmission gear unit 50. The hollow transmission output shaft SOb is arranged in coaxially surrounding relationship to an intermediate portion of the transmission input shaft 50a which extends partly through the transmission output shaft 50b from the above mentioned turbinee runner 49b.

The planetary gear assemblies of the transmission gear unit 50 consist of a first planetary gear assembly 54 and a second planetary gear assembly 55. The first planetary gear assembly 54 comprises an externally toothed sun gear 54a coaxially rotatable on the transmission output shaft sob, an internally toothed ring gear 54b coaxially surrounding the sun gear 54a, and at least two planet pinions 54c each held in mesh with the sun gear 54a and ring gear 54b and rotatable about an axis parallel with a common axis if rotation of the sun gear 54a and ring gear 54b.

Similarly, the second planetary gear assembly 55 comprises an externally toothed sun gear 55 coaxially rotatable on the transmission output shaft 50b, an internally toothed ring gear 55b coaxially surrounding the sun gear 55a, and at least two planet pinions 55c each held in mesh with the sun gear 55a and ring gear 55b and rotatable about an axis parallel with a common axis of rotation of the sun gear 55a and ring gear55b. The planet pinions 54e of the fi rst planetary gear assembly 54 are jointly connected to a first pinion carrier 56 and, likewise, the planet pinions 55c of the second planetary gear assembly 55 are jointly connected to a second pinion carrier 57.The planet pinions of each planetary gear assembly are, thus, not only rotatable about their respective axes of rotation but also revolvable about the common axis of rotation of the sun and ring gears of the gear assembly while rolling round the sun gear or the ring gear of the assembly.

The power transmission gear unit 50 further comprises two transmission clutch assemblies which are positioned in series with each other in the direction in which the transmission output shaft 50b axially extends. The transmission clutch assemblies consist of a forward-drive clutch assembly 58 to be actuated for the selection of any of the first, second and third forward drive gear ratios, and a high-andreverse clutch assembly 59 to be actuated for the selection of the third forward drive gear ratio or the reverse drive gear ratio. The forward-drive clutch assembly 58 has input members constituted by clutch plates connected to, and coaxially rotatable with, the transmission input shaft 50a, and output members constituted by clutch discs connected to, and rotatable with, the ring gear 54b of the first planetary gear assembly 54.On the other hand, the high-and-reverse clutch assembly 59 has input members constituted by clutch discs connected to, and rotatable with, the transmission input shaft 50a, and output members or clutch plates connected to, and rotatable with, the respective sun gears 54a and 55a of the first and second planetary gear assemblies 54 and 55 through a clutch drum 60 and a drum-shaped connecting shell 61. The clutch drum 60 is coaxially surrounded by a second-speed brake band 62 which is actuated to brake the drum 60 and accordingly the sun gears 54a and 55a for the selection of the second forward drive gear ratio.

The transmission gear unit 50 further comprises a low-and-reverse brake assembly 63 having stationary members constituted by, for example, brake plates secured to the transaxle casing structure 52, and rotatable members constituted by, for example, brake discs connected to, and coaxially rotatable with, the pinion carrier 57 for the second planetary gear assembly 55. The low-and-reverse brake assembly 63 thus constructed and arranged is adapted to select the first forward drive gear ratio or the reverse drive gear ratio.The low-and-reverse brake assembly 63 is operatively associated with a transmission one-way clutch assembly 64 which comprises a stationary member constituted by, for example, an outer race member fixedly connected to the transaxle casing structure 52, and a rotatable member constituted by, for example, an inner race member connected to, and rotatable with, the pinion carrier 57 of the second planetary gear assembly 55 and the rotatable members of brake discs of the low-and-reverse brake assembly 63. The transmission one-way clutch assembly 64 further comprises a series of spring loaded coupling elements such as sprag segments (not shown) annularly disposed between the inner and outer race members of the clutch assembly 64. The coupling elements are arranged in such a manner as to permit the rotation of the inner race member about the axis of rotation of the transmission input shaft 4a only in a "forward" direction identical with the direction of rotation of the input shaft 4a.

The pinion carrier 56 for the first planetary gear assembly 54 and the ring gear 55b of the second planetary gear assembly 55 are jointly connected to, and coaxially rotatable with, the transmission output shaft 50b.

Each of the friction devices such as the clutch assemblies 58 and 59, brake band 62 and brake assembly 63 of the transmission gear unit 50 thus constructed and arranged is actuated by hydraulically operated actuating or servo means such as a fluid-operated piston for each of the clutch assemblies 58 and 59, a fluid-operated servo unit for the brake band 62, or a fluid-operated piston for the brake assembly 63. These actuating and servo means are selectively put into operation by the fluid pressure selectively distributed to the actuating and servo means through and under the control of a hydraulic control system (not shown). Thus, any of the three forward drive gear ratios and one reverse drive gear ratio is achieved between the transmission input and output shafts 50a and 50b when any two of the friction units including the one-way clutch assembly 64 are brought into operation.When all of these friction devices are held inoperative, the transmission gear unit 50 assumes a neutral condition with no driving torque transmitted from the input shaft 50a to the output shaft sob.

The hydraulic fluid to be distributed to the fluidoperated actuating and servo means for such friction devices through the hydraulic control system is supplied from a transmission oil pump assembly 65 mechanically connected to and driven by the output shaft 1a of the engine 1 through a pump drive shaft 50c axially extending through the hollow transmission input shaft 50a as shown. The pressurized fluid delivered from the oil pump assembly 65 is not only fed as a control fluid to the respective actuating and servo means for the friction devices of the transmission gear unit 50 but is also supplied as a working fluid to the torque converter 49.

The construction and arrangement of each of the torque converter 49 and the transmission gear unit 50 as hereinbefore descrbed is per se simply by way of example and may thus be modified and/or changed in numerous manners as desired.

The output shaft 50b of the transmission gear unit 50 has fixedly mounted thereon a transmission output gear 66 which is rotatable about the center axis of the shaft 50b and which is shown located, by way of example, axially intermediate the torque converter 49 and the planetary gear assemblies 54 and 55. The transmission output gear 66 has opposite axial extensions of boses respectively journaled in bearings supported on the transaxle casing structure 52. The gear 66 is held in mesh with an intermediate idler gear 67 rotatable through bearings on an idler shaft 68 extending in parallel with the transmission output shaft SOb.

The front final reduction gear unit 51 of the transaxle mechanism 48 of the embodiment shown in Figures 2A and 2B is provided in a rearward extension 52a of the transaxle casing structure 52.

The gear unit 51 is constructed and arranged similarly to the front final reduction gear unit 5 in the embodiment of Figures 1A and 1 B except in that the ring gear 13 rotatable with the differential gear casing 14 of the gear unit 51 is held in engagement with the transmission output gear 66 through the intermediate idle gear 67 as compared with the ring gear 13 of the final reduction gear unit 5 in which the ring gear 3 is held in direct mesh with the transmission output gear 11.

The rearward extension 52a of the transaxle casing structure 2 has at its rear end an opening 52b through which the rotation of the ring gear 13 is transmitted to a drive-wheel shift and right-angle power transfer unit which is constructed and arranged similarly to the unit 24 in the embodiment of Figures 1A and 1B and thus including a branch-off gear 27 held in mesh with the ring gear 13. The casing structure 26 of the drive-wheel shift and right-angle power transfer unit 24 in the embodiment of Figures 2A and 2B is, thus, also detachably connected to the rearward extension 52a of the transaxle casing structure 52 by fastening means such as bolts and nuts and is formed with an opening contiguous to the opening 52b in the rearward extension 52a of the casing structure 52.

The front axle assemblies for the front road wheels 12 and 12' and the driveline for the rear rod wheels 23 and 23' in the vehicle driving system shown in Figures 2A and 2B are also similar to those of the embodiment of Figures 1A and 1B and, for this reason, detailed description regarding the construction and arrangement thereof will not be repeated.

When, now, the engine 1 in the arrangement shown in Figure 2A is in operation, the driving power delivered from the output shaft 1a of the engine 1 is transmitted upon multiplication in torque by the torque converter 49 to the input shaft 50a of the power transmission gear unit 50. If, under these conditions, the manually operated gearshift lever is held in the neutral gear position thereof, none of the friction devices of the gear unit 50 is held in an inoperative condition so that the transmission input shaft 50a is rotated without imparting driving power to the transmission output shaft 50b. The transmission output shaft 50b is therefore held at rest and no driving power is transmitted to the front final reduction gear unit 51 for the front road wheels 12 and 12' as well as the driveline for the rear road wheels 23 and 23'.

If, however, any two of the friction devices of the transmission gear unit 50 are held in operative conditions by the fluid pressure applied to the respective fluid-operated actuating or servo means thereof, any one of the first, second and third forward drive gear ratios or the reverse drive gear ratio is established in the transmission gear unit 50.

The driving power delivered from the torque converter 49 to the transmission input shaft 50a is therefore transmitted through the combination of some of the component gears of the two planetary gear assemblies 54 and 55 to the transmission output shaft Sob.

The transmission output shaft 50b is thus driven for rotation at a speed proportioned with the selected gear ratio to the transmission input shaft 50a. The rotation of the transmission output shaft 50b is transmitted through the transmission output gear 66 to the intermediate idler gear 67 and further through the idler gear 67 to the ring gear 13 of the front final reduction gear unit 51. The driving power thus transmitted to the front final reduction gear unit 51 is reduced in speed ratio by means of the gear unit 51 and is split into three components, two of which are transmitted through the side gear shafts 18 and 18' of the gear unit 51 to the front road wheels 12 and 12' by way of the constant-velocity joints 20 and 20', front wheel drive shafts 19 and 19', constant-velocity joints 22 and 22' and front wheel axles 21 and 21', respectively.The remaining one of the above mentioned three components of the driving power transmitted to the final reduction gear unit 51 is transmitted from the ring gear 13 of the gear unit 51 to the branch-off gear 27 of the drive-wheel shift and right-angle power transfer unit 24.

If the coupling sleeve 31 of the clutch means forming part of the drive-wheel shift and right-angle power transfer unit 24 is held in mesh with only one of the first and second coupling gears 28 and 29 such as the second coupling gear 29 as shown, the branch-off gear 27 and the first coupling gear 29 thereon are permitted to simply idle so that the driveline for the rear road wheels 23 and 23' is disconnected from the engine 1. If, however, the coupling sleeve 31 is held in the axial position bridging the first and second coupling gears 28 and 29, the driving power transmitted to the branch-off gear 27 is further transmitted through the coupling gear 28, sleeve 31 and coupling gear 29 of the clutch means to thg driving and driven bevel gears 30 and 32 of the right-angle power transfer means.The rotation of the driven bevel gear 32 is, in turn, transmitted to the rear road wheels 23 and 23' in a manner previously described in connection with the embodiment of Figures 1A and 1B.

In each of the embodiments hereinbefore described, the ratio between the respective numbers of teeth of the ring gear 13 and the branch-off gear 27, the ratio between the respective numbers of teeth of the driving and driven bevel gears 30 and 32, and the ratio between the respective numbers of teeth of the driving bevel pinion 38 and the bevel ring gear 39 of the rear final reduction gear unit 25 are selected so that the front road wheels 12 and 12' and the rear road wheels 23 and 23' are driven for rotation at speeds reduced in equal reduction ratios from the speed of rotation of the output shaft la of the engine 1.

From the above description, it will have been appreciated that the vehicle driving system according to the present invention is characterized, inter alia, in the following respects.

(1) The power unit constituted by, for example, the internal combustion engine 1 is positioned with respect to the vehicle chassis in such a manner that the output shaft 1a of the power unit axially extends in a lateral direction of the vehicle chassis.

(2) The power transmission gear unit 4 or 50 forming part of the transaxle mechanism 2 or 48 is positioned with respect to the vehicle chassis in such a manner that the input and output shafts 4a and 4b or 50a and 50b thereof axially extend substantially in parallel with an extension of the axis of rotation of the output shaft 1a of the power unit such as the internal combustion engine 1.

(3) The front final reduction gear unit 5 or 51 is used not only for reducing the speed of the driving power delivered thereto and splitting the driving power into two components to be distributed to the front road wheels but for relaying the driving power to the drive line for the rear road wheels 23 and 23' if and when the drive-wheel shift clutch means positioned between the final reduction gear unit 5 or 51 and the drive line for the rear road wheels 23 and 23' is in a coupled condition.

By virtue of these outstanding features of the vehicle driving system according to the present invention, the availability of the passenger and baggage spaces in a conventional four-wheel-driven vehicle can be significantly improved.

In addition to the above mentioned principal features of the vehicle driving system according to the present invention, each of the embodiments of the system hereinbefore described has a feature that the system can be used selectively as a two wheel drive system or a four-wheel drive system through the provision of the clutch means provided as partbf the drive-wheel shift and right-angle power transfer unit 24. Since, in this instance, such a unit 24 is provided between the front final reduction gear unit 5 or 51 and the driveline for the rear road wheels 23 and 23', the vehicle driving system embodying the present invention can be readily modified into a front-wheel driving system simply by removing from the four-wheel driving system the drive-wheel shift and right-angle power transfer unit 24 and the whole driveline for the rear road wheels 23 and 23'. When the system shown in Figures 1A and 1B or the system shown in Figures 2A and 2B is thus used as the front-wheel driving system, the opening 6b of the rearward extension 6a ofthetransaxlecasing structure 6 of the system of Figures 1A and 1 B or the opening 52b of the rearward extension 52a of the transaxle casing structure 52 of the system of Figures 2A and 2B may be closed by a closure plate (not shown) attached to the extension 6a or 52.

Claims (6)

1. A vehicle driving system for a vehicle having at least two pairs of road wheels consisting of a pair of front road wheels and a pair of rear road wheels, comprising a power unit having an output shaft rotatable about an axis in a lateral direction of the vehicle, atransaxle mechanism comprising a powertransmission gear unit and a first final reduction gear unlit, the transmission gear unit including transmission input and output shafts each having an axis of rotation substantially parallel with an extension of the axis of rotation of the output shaft of the power unit and gears mounted on said transmission input and output shafts and arranged to be capable of selectively producing a plurality of ratios between the speeds of rotation of the transmission input and output shafts, said first final reduction gear unit including gears arranged to split the driving power from the transmission output shaft into two component drives to be respectively transmitted to one of said two pairs of road wheels, a branch-off gear engaging said first final reduction gear unit for being driven by the final reduction gear unit for rotation about an axis substantially parallel with the axis of rotation of each of said transmission input and output shafts, a driveline including at least one propeller shaft extending in a fore-and-aft direction of the vehicle and a second final reduction gear unit including gears arranged to split the driving power from the driveline into two component drives to be transmitted to the other of said two pairs of road wheels, and right-angle power transfer means operatively positioned between said branch-off gear and said driveline and operative to convert the rotation of the branch-off gear into rotation about an axis substantially perpendicular to the axis of rotation of the branch-off gear.

2. A vehicle driving system as set forth in claim 1, further comprising clutch means positioned between said branch-off gear and said right-angle power transfer means and operative to provide a driving connection and interrupt the driving connection between the branch-off gear and the power transfer means.

3. A vehicle driving system as set forth in claim 2, in which said clutch means comprises an externally serrated first coupling gear coaxially rotatable with said branch-off gear, an externally serrated second coupling gear drivingly connected to said right-angle power transfer means, and an internally serrated coupling member held in mesh with, and axially slidable on, one of the first and second coupling gears and axially movable into and out of mesh with the other of the coupling gears.

4. A vehicle driving system as set forth in claim 1, 2 or 3, in which said transaxle mechanism further comprises a transaxle casing structure enclosing said power transmission gear unit and said first final reduction gear unit and formed with an opening through which said first final reduction gear unit is in engagement with said branch-off gear.

5. A vehicle driving system as set forth in claim 3, in which said right-angle power transfer means comprises a driving bevel gear engageable with said branch-off gear and rotatable about an axis substantially aligned with the axis of rotation of the branchoff gear, and a driven bevel gear held in mesh with said driving bevel gear and rotatable about an axis substantially perpendicular to the axis of rotation of the driving bevel gear, the driven bevel gear being connected to said propeller shaft and the axis of rotation of the driven bevel gear being substantially aligned with the axis of rotation of said propeller shaft.

6. A vehicle driving system substantially as described with reference to, and as illustrated in, Figures 1A and 1 B, or Figures 2A and 2B, of the accompanying drawings.