PRIORART:
Conventional agricultural Tractor (fig - l) use block chassis with both the rear axle
halves attached to either side of centre housing which houses the differential unit.
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The axle shafts are guided inside the axle housings. The clearance under tractor belly and axle belly decide the ground clearance. Higher ground clearance on the same chassis is achieved by a portal rear axle arrangement that may have a gear pair or sprocket pair to enable create required offset between centre lines of differential gears and rear wheel shafts. These arrangements are complex, expensive, noisy and not easily adoptable on standard chassis. The typical schematic arrangements are shown in figures 2,3 and 4.
OBJECT QF THE INVENTION:
1. The object of the invention is to achieve higher ground clearance by means of creating vertical offset between differential gear and rear wheel axle shaft.
2. The another object of the invention is to achieve wheel base alteration by
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creating horizontal offset between differential gear and rear wheel axle shaft.
3. The another object of the invention is to achieve higher ground clearance and also eliminating the gear drives and chain drives.
4. The another object of the invention is to achieve a mechanism for higher
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ground clearance, which is easy to manufacture.
5. The another object of the invention is to achieve a mechanism for higher ground clearance, which is easy to be assembled into vehicle.
6. The another object of the invention is to achieve a mechanism for higher
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ground clearance, which is easy to be replaceable.
7. The another object of the invention is to achieve a mechanism for higher ground clearance, which is easily maintainable.
8. The another object of the invention is to achieve a mechanism for higher
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ground clearance, which is retrofit to the conventional vehicle. DESCRIPTION OF THE DRAWING:
Fig.i illustrates rear end view of conventional rear axle arrangement as in prior art.
Fig. 2 illustrates rear end view of gear drive at central housing end as in prior art.
Fig.3 illustrates rear end view of gear drive at wheel end as in prior art.
Fig.4 illustrates rear end view with bevel gear drive as known in prior art.
Fig.5 illustrates rear end of the vehicle with the cardan shaft drive as per invention.
Fig.6 illustrates the level difference between the engine and rear axle.
Fig.7 illustrates the cardan shaft between engine and rear axle as in prior art.
Fig.8 illustrate the solid rear shaft as in prior art.
Fig.9 illustrate the cardan shaft arrangement as in the invention.
Fig. 10 illustrate the various arrangements for maintaining level difference between engine and wheel.
Fig.il illustrates the offset in longitudinal direction.
Reference numerals in the enclosed drawings are as follows:-
1. Gear Shaft 14. Differential input shaft
2. Universal joints 15. Frame
3. Cardan shaft 16. Double cradan shaft drive for longer wheel base
4. Wheel Shaft 17. Wheel Base
5. Pseudo Housing 18. Rear Drive
6. Vertical offset "X" 19. Centre housing
7. Horizontals offset "X" 20. Normal clearance
8. Engine 21. Front engine support
9. Gear Box 22. Transmission Case
10. Gear box shaft 23. Normal Clearance + "X" mm
11. Rear axle differential Unit 24. Cardan shaft drive for rear axle
12. Rear Axle 25. New wheel base
13. Suspension Spring 26. chassis wheel base
DESCRIPTION OF INVENTION:
As per the Invention design does away with the additional gear drives or chain drives or belt drives and bevel drives, maintain 1:1 ratio between differential gear and axle shaft, readily interchangeable with conventional axles. The schematic layout of which is shown in figure 5 and described hereunder.
The differential gear shaft is coupled to a cardan shaft and in turn to wheel shaft through universal joints. The rear axle pseudo housing is bolted on one side to the centre housing and incorporates the wheel shaft hub / housing at the other end. It can be seen that by changing the shape of the pseudo housing and length of the cardan shaft, the offset 'X' can be altered to result in the desired ground clearance. The value "X" can be positive or negative. This can be adopted for any wheel track width. The offset 'X' can be in logitudinal direction of the tractor enabling alteration of wheel base as shown in fig.li. The offset 'X' could be in both directions also. General usage of cardan shaft:
Cardan shaft is being used in commercial vehicles to transmit the power from front to the rear end of the vehicle & vice versa. The commercial vehicle (generally a suspended vehicle) has chassis frame (two longitudinal frames with cross members) on which the engine is mounted. The gear box is attached with the engine and is also mounted on the cross member of the frame. The drive from gear box is transmitted by a cardan shaft arrangement (Otherwise called propeller shaft with universal joint) to the final drive (Differential unit). Then the drive is transmitted to the wheel by rear axle shaft. In this application, there is a level between rear axle because of layout constraint as shown in fig.6. This is another reason for using cardan shaft arrangement to transmit the power by maintaining the level difference.
The chassis frame of the vehicle is suspended by the spring and the spring is attached with the respective axles (front and rear). So, whenever the engine and gear box is lifted up, the frame also goes up and the inclination of cardan shaft get increased to accommodate the change.
Double cardan shaft is also used in many vehicles where the vehicle base is considerably longer as shown in fig.7. Very long shaft will cause vibration, noise, etc and therefore split into two shaft arrangement. In both the construction, the rear axial shaft is a solid straight shaft which transmit the drive from differential unit to the wheel.
SUMMARY OF THE INVENTION :
Tractor is a non-suspended (rigid body) vehicle widely used for agricultural field and
it is slow moving off highway vehicle. Here there is no frame, suspension spring, etc.
The engine, gear box and rear drive unit itself form a structure and are arranged in
line with each other. The engine is supported by Front Engine Support (FES) which
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in turn supported by front axle through pivot pin. The front axle is attached with the smaller front wheel by kingpin arrangement.
The rear drive unit is bolted with the rear axle housing. The bigger rear wheel axis is in line with the rear drive unit and is taking drive through solid rear shaft. The construction is shown in figure.8.
With the basic construction as above, the ground clearance can be increased by raising the level of engine, gear box and rear axle together. Now, after raising, there is level difference between wheel axis and the rear drive unit and that can be made inline only by increasing the wheel diameter. Therefore, the cardan shaft arrangement is used here to maintain the level difference without increasing the wheel diameter, i.e. Here the carden shaft is transmitting the power from rear drive to right & left side of the vehicle. The arrangement shown in fig 9.
Generally in normal tractors, the level difference is maintained by any of the following arrangement which is shown in figures 2,3 & 4.
The cardan shaft arrangement which has been attempted as per the invention in rear axle of the tractor does not exist in any prior art.
The merits of the invention includes:-
A tractor rear axle design which does not add any gear train, sproket chain drive to achieve alteration of ground clearance and wheel base for a given wheel / tire diameter (or) a smaller rear wheel can be used to retain the ground clearance as in conventional tractors.
A design which could be readily added on to a conventional drive line of tractors without having to modify driveline ratios.
A design which does not require any direction change for differential unit to achieve ground clearance and wheel base alterations.
The cardan shaft is easily replaceable. The differential gear shaft have very low over hang, thereby the life is longer.

WE CLAIM:
1. A four wheeled Agricultural tractor comprising an engine(8), a gear box(9), differential gear shafts(i) and wheel shafts(4) all together form a frame(is), characterized with a variable vertical offset(6) between center lines of differential gear shafts(i) and rear wheel shaft(4), to achieve variable desired ground clearances and also variable longitudinal offset(7) to achieve variable wheel base(i7), said differential unit mounted within a center housing(i9) with left differential gear axle shaft extending towards left, a right differential gear axle shaft extending towards right, comprising of:-
a. a cardan shaft(3), coupling the axle shaft to wheel shaft(4) by means of coupling joints(2),
b. a rear axle housing(n) bolted at one end to the center housing(i9) and the other end forming the rear wheel hub comprising atleast the wheel axle shaft & bearings, and
c. a front axle mounting bracket adapted to accommodate the vertical offset(6).
2. The four wheeled agricultural tractor as claimed in claim l, wherein the rear axles shaft is such that the rear axle shaft is not a solid straight shaft transmitting drive from differential unit to the wheel.
3. The four wheeled agricultural tractor as claimed in claim 1, wherein the differential gear shaft is such that the differential gear shaft centerline is at a different ground level with respect to centerline of rear wheel shafts to form a vertical offset 'X'.
4. The four wheeled agricultural tractor as claimed in claim 1, wherein the differential gear shaft is such that the differential gear shaft centerline is in front or behind the centerline of the rear wheel shaft along the length of the tractor to form a horizontal offset 'X'.
5. The four wheeled agricultural tractor as claimed in claim 1, wherein the offset is such that the vertical offset is positive or negative.
6. The four wheeled agricultural tractor as claimed in claim 1, wherein the differential gear shaft is such that the differential gear axle shaft have very low over hang by 60% thereby achieving longer life by 30%.
7. The four wheeled agricultural tractor as claimed in claim 1, wherein the cardan shaft is such that the cardan shaft is modular.