A DIFFERENTIAL DRIVE ASSEMBLY FOR A MOTORISED VEHICLE

FIELD OF INVENTION

This invention relates to a differential drive assembly for a motorized vehicle.

Any reference herein to a "chain" must be interpreted sufficiently broadly to include a reference to an elongate flexible continuous element such as a continuous belt.

Any reference herein to a "sprocket" must be interpreted sufficiently broadly to include a reference to a wheel which is engageable by a chain as defined hereinabove.

SUMMARY OF INVENTION

According to the invention there is provided a differential drive assembly for a motorized vehicle, comprising:

a first drive shaft connectable to a first driven wheel of the vehicle, the first drive shaft defining a longitudinal axis of rotation and having a first drive sprocket fixed thereto;

a second drive shaft connectable to a second driven wheel of the vehicle, the second drive shaft having a longitudinal axis of rotation, which is arranged co- axially with respect to the first drive shaft, the second drive shaft having a second drive sprocket fixed thereto; and

a differential including:

a) a rotatable planetary drive which is coupled, in use, to the motor of the vehicle for causing rotation the planetary drive, in use, the planetary drive defining an axis of rotation which is disposed co-axially with the axes of rotation of the first and second drive shafts;

b) a planetary sprocket arrangement which is fixed to the planetary drive, the planetary sprocket arrangement defining a planetary axis which is parallel to and spaced from the axes of rotation of the first and second drive shafts and which revolves around the drive shafts when the planetary drive rotates, in use; and

c) a chain drive system connecting the planetary sprocket arrangement to both the first drive sprocket and the second drive sprocket for driving the first drive shaft and the second drive shaft when the planetary drive rotates, in an arrangement allowing the first drive shaft and the second drive shaft to rotate at different speeds relative to one another, in use.

The chain drive system of the differential may comprise:

a first planetary sprocket rotatably mounted to the planetary shaft for rotation about the planetary axis;

a second planetary sprocket rotatably mounted to the planetary shaft for rotation about the planetary axis;

a first chain extending between the first planetary sprocket and the first drive sprocket in an arrangement wherein rotation of the planetary sprocket in a particular direction causes rotation of the first drive sprocket in the same direction; and

a second chain extending between the second planetary sprocket and the second drive sprocket in an arrangement wherein rotation of the second planetary sprocket in a particular direction causes rotation of the second sprocket in the opposite direction.

The differential drive assembly may include two idler shafts which are fixed to the planetary drive and which each define a longitudinal axis which is spaced from and disposed parallel to the axes of rotation of the drive shafts; and two idler sprockets which are each rotatably mounted to a different one of the idler shafts, along which the chain extending between the second planetary sprocket and the second drive sprocket runs in an arrangement wherein an inner side of the chain runs over the second planetary sprocket and the two idler sprockets and an outer side of the chain runs over the second drive sprocket.

The planetary drive may be in the form of a sprocket which is coupled to the motor of the vehicle by means of a chain.

One of the first drive shaft and the second drive shaft may be hollow, with part of the other of the first drive shaft and second drive shaft being received in the hollow drive shaft.

The differential drive assembly may include limited slip clutch means for causing frictional engagement between the first and second drive shafts thereby to limit the difference in speed of rotation of the first and second drive shafts.

The invention extends to a differential for a motorized vehicle, which is equivalent to the differential of the differential drive assembly as defined and described hereinabove.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features of the invention are described hereinafter by way of a non- limiting example of the invention, with reference to and as illustrated in the accompanying diagrammatic drawings. In the drawings:

Figure 1 shows a side view of a differential drive assembly for a vehicle, in accordance with the invention;

Figure 2 shows a perspective view of the differential drive assembly of Figure 1 ;

Figure 3 shows a sectional side view of the differential drive assembly of Figure 1 , the clutch mechanism being omitted for the sake of clarity;

Figure 4 shows a side view of the differential drive assembly of Figure 1 , coupled to the chain drive of a quad bike and mounted between the rear driven wheels thereof;

Figure 5 shows an end view of the differential drive assembly of Figure 1 as viewed along indicator line Z of Figure 3;

Figure 6 shows an end view of the differential drive assembly of Figure 1 as viewed along indicator line Y of Figure 3;

Figure 7 shows a schematic sectional end view of the differential drive assembly of Figure 1 , sectioned along section line VII - VII of Figure 3;

Figure 8 shows a schematic sectional end view of the differential drive assembly of Figure 1 , sectioned along section line VIII - VIII of Figure 3;

Figure 9 shows a sectional end view of the differential drive assembly of Figure 1 , sectioned along section line IX - IX of Figure 3;

Figure 10 shows a schematic sectional end view of the differential drive assembly of Figure 1 , sectioned along section line X - X of Figure 3;

Figure 1 1 shows a sectional end view of the differential drive assembly of Figure 1 , showing the clutch mechanism and sectioned along section line VII - VII;

Figure 12 shows an enlarged fragmentary sectional side view of the differential of the differential drive assembly of Figure 1 ;

Figure 13 shows a top view of a clutch mechanism mounted between the idler sprockets of the differential of the differential drive assembly;

Figure 14A shows a plan view of a fixed clutch plate of the clutch mechanism of Figure 13;

Figure 14B shows an end view of the fixed clutch plate of Figure 14A;

Figure 15A shows a plan view of a rotating clutch disc of the clutch mechanism of Figure 13;

Figure 15B shows an end view of the rotating clutch disc of Figure 13; and

Figure 16 shows an exploded top view of the clutch mechanism of Figure 13.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

With reference to Figures 1 to 13 of the drawings, a differential drive assembly in accordance with the invention is designated generally by reference numeral 10. The differential drive is adapted for use with a four-wheeled motorcycle 12 referred to herein as a "quad bike" for transferring power from the motor of the quad bike to the rear wheels thereof. The differential drive assembly 10 comprises, broadly, a first drive shaft 14, a second drive shaft 16, a differential 18 coupled to the first and second drive shafts 14, 16 and a carrier assembly.

The first drive shaft 14 is a solid shaft which is connected to a right rear wheel 22 of the quad bike. The drive shaft 14 has a left end 24 and a right end 26. A right wheel hub 28 is fixedly mounted by means of an annular clamping element 30 to the right end 26 of the drive shaft 14. The wheel hub 28 is retained on the end 26 of the drive shaft by means of a lock nut 32 and a retaining washer 34.

The second drive shaft 16 is in the form of a hollow shaft which extends between the differential 18 and a wheel mounting 36 to which the left rear wheel 23 of the quad bike is mounted. More particularly, the wheel mounting 36 includes a bearing carrier plate 38, an annular protrusion 40 in which a stepped end region 42 of the drive shaft 14 is located and an end cap 44 which closes off the hollow protrusion 40. A spherical roller bearing 46 is located on the stepped end section 42 of the drive shaft 14 within the cavity defined by the protrusion 40. A left end region of the solid drive shaft 14 is received within the hollow drive shaft 16. As such, the drive shafts 14, 16 define a common axis of rotation A.

The differential 18 includes a rotatable planetary drive including a sleeve 52 which is fixedly mounted to the drive shaft 14 in an arrangement wherein part of

the drive shaft 14 is rotatably received within the sleeve. The sleeve includes a shoulder formation 54 and terminates in a flange formation which defines an annular right side plate 56.

The planetary drive 50 further includes a toothed differential drive sprocket 58 which is driven by means of a chain 60 coupled to the engine of the quad bike. The sprocket 58 is fixed to the side plate 56 by means of four studs 62.

The differential 18 includes a first toothed drive sprocket 64 which is fixed to the drive shaft 14 and a second toothed drive sprocket 66 which is fixed to the second drive shaft 16. The differential further includes an annular left side plate 70 which is integral with and which extends perpendicularly to the drive shaft 16; and an annular cover plate 72 which is fitted to the cover plates 56 and 70 so as to define a closed cavity 74 which is filled with an oil lubricant.

The differential further includes a planetary socket arrangement 75 which comprises a planetary shaft 76 which is fixed to and which extends between the left and right side plates 70, 56 and a pair of toothed planetary sprockets 78.1 and 78.2 which are joined to and fixed relative to one another and rotatably mounted to the planetary shaft 76 so as to rotate in unison. The planetary shaft 76 defines a planetary axis B which is parallel to and spaced from the axis of rotation A. In use, the planetary shaft 76 revolves around the drive shafts 14, 16 when the differential drive sprocket 58 rotates. The sprockets 78.1 and 78.2 are mounted to a Vesconite bearing 77 with a thrust washer 79 located between the side plate 70 and the double planetary sprockets and an end of the bearing 77.

The differential also includes two idler shafts 80 which are fixedly connected between the left and right side plates 70, 56 and which define longitudinal axes which are spaced from and disposed parallel to the rotation axis A of the drive shafts. An idler sprocket 82 is rotatably mounted to each of the idler shafts.

The differential includes a first chain 84 which extends between and which engages the planetary socket 78.1 and the drive sprocket 64. More particularly, the chain 84 is arranged such that an inner side of the chain runs over the planetary sprocket 78.1 and the two idler sprockets 82 and an outer side of the chain runs over the drive sprocket 64. As such, rotation of the planetary sprocket

78.1 in a particular direction causes rotation of the drive sprocket 64 and thereby the drive shaft 14, in the opposite direction. The differential further includes a second chain 86 which extends between and engages the planetary sprocket

78.2 and the drive sprocket 66 in an arrangement wherein the chain 86 runs over the sprockets 78.2 and 66. As such, rotation of the planetary sprocket 78.2 in a particular direction causes rotation of the sprocket 66 and thereby the drive shaft 16, in the same direction. In use, forces transmitted via the drive shafts 14, 16 are transmitted to the planetary sprockets 78.1 and 78.2 which balance the forces thereby to effect rotation of both drive shafts clockwise when the sprocket 58 is driven in a clockwise direction and counter-clockwise when the sprocket 58 is driven in a counter-clockwise direction. In this manner, the differential 18 transmits power to the wheels 22 and 23 allowing the wheels 22 and 23 to rotate at different rotational speeds depending on the driving conditions. For example, when cornering the outer wheel is able to rotate faster than the inner wheel.

It will be appreciated that the differential drive sprocket 58 is fixed to the right side plate 56, the planetary shaft 76 and the left side plate 70 and as such, these components rotate as a unit when the sprocket 58 is driven by the chain 60.

The carrier assembly includes a central support structure 88 which is fitted on to the sleeve 52 in an arrangement wherein the support structure 88 is rotatably supported relative to the sleeve 52 by means of taper roller bearings 90. The support structure 88 is located against the shoulder formation 54 of the sleeve 52 and mounted to the coil spring suspension 92 of the quad bike. A disc brake mechanism 94 is fixedly mounted to the sleeve 52 by means of clamping element 96 to the right of the central support structure. In use, a braking force is applied

to the brake disc 97 by means of a brake caliper (not shown) causing braking of the rotation of the sleeve 52 and thereby both drive shafts 14, 16 via the differential 18. The braking force is thus transmitted to the drive shafts 14, 16 via the sleeve 52 and the side plate 56 to the planetary shaft 76 which is fixed to the plate 56.

The carrier assembly further includes a spacer sleeve 98 within which part of the drive shaft 14 is rotatably located. The carrier assembly includes a bearing carrier 100 in which a taper roller bearing 102 is located with an inner space of the bearing being mounted to the drive shaft 14. A bearing lock nut 104 is located adjacent the left side of the bearing carrier 100.

With reference to Figures 1 1 to 16, a clutch mechanism 106 in the form of two series clutch sets 108 is shown, which provides the differential with limited slip properties. Each clutch set 108 comprises two fixed clutch plates 1 10 and two rotating clutch discs 112 which are sandwiched between the fixed clutch plates. Each fixed clutch plate comprises a friction disc portion 1 14 and a torque arm portion 1 16. Each clutch plate is of metal which is lined on both sides of the disc portion 1 14 with a suitable friction material. The torque arm 1 16 defines a mounting aperture 1 18 at one end thereof and the disc portion defines a central aperture 120. Each rotating clutch disc is of metal and defines a central hexagonal aperture 122. Each idler sprocket has a hexagonal mounting formation 124 which extends to one side thereof and a shoulder formation 126. The idler sprocket is mounted on the idler shaft 80 with a Vesconite bush 128 acting as a bearing between the shaft and the sprocket.

The clutch mechanism further includes a number of compression springs 130 and a central locating pin 132. As can be seen in the drawings, each clutch set is assembled by fitting the fixed clutch plates and the rotating discs onto the mounting formation 124 of the relevant idler sprocket. The rotating discs are fitted onto the mounting formation 124 of the idler sprockets such that the rotating

discs are fixed to the idler sprockets and rotate therewith whereas the clutch plates are mounted to the mounting formation 124 via their apertures 120 so as to permit relative rotation between the clutch plates and the idler sprockets. The compression springs are located within recesses provided therefor in the side plate 70 so that the compression springs exert a force against each clutch set at one side thereof with the opposite side of the clutch set abutting against the shoulder formation 128 of the idler sprocket. In use, as the idler sprockets 82 rotate, a frictional force is exerted by the clutch sets on the idler sprockets. As the idler sprockets are coupled to the drive sprocket 64 via the chain 84, the frictional force is transmitted to the drive shaft 14. Further, as the chain 84 links the idler sprockets 82 with the planetary sprocket 78.2 the frictional force is transmitted simultaneously to the drive shaft 16 via the chain 86 as the sprockets 78.2 and 78.1 are fixed relative to one another and thus rotate in unison. The frictional engagement of the clutch mechanism with the idler sprockets resists the tendency of one of the rear wheels to rotate faster than the other.

In the embodiment of the differential described hereinabove, the planetary sprockets 78.1 and 78.2 and the drive sprockets 64 and 66 have the same diameters thereby providing a 1 :1 gear ratio. The Applicant envisages that the diameters of the planetary sprockets 78.1 and 78.2 relative to the diameters of the drive sprockets 64 and 66 may be altered so as to provide different gear ratios for each of the rear wheels thereby to allow the left and right rear wheels to be driven at different speeds of rotation which may render the quad bike suitable, for example, for use in oval track racing.