The present invention relates to a differential, in particular to a self-locking differential for use on both a driving axle and a non-driving axle of a vehicle.

A differential which has two output stages connected to each other by a central stage is known from the prior art. Each output stage has a first gear mounted on one axle shaft connected to a vehicle wheel, a second gear meshed with the first gear, and a worm. The worm is connected to the second gear so that the rotation of the second gear causes the corresponding rotation of the worm. The central stage includes a worm wheel meshed with the worms of the output stages.

In such a differential, the rotation of one axle shaft must equal the rotation of the other axle shaft, which in turn means that one vehicle wheel must cover the same distance as the other vehicle wheel through reverse movement of the wheel, because otherwise the differential will pinch. Such operation of the differential significantly reduces its strength.

One aim of the present invention is to provide a differential with increased strength and smooth operation.

Another aim of the present invention is to provide a differential which allows the drive to be always transferred to both wheels, regardless of whether any of the wheels loses contact with the ground, which in turn increases driving safety, regardless of the fact that when the differential is operating the rotational speed of the wheels on a given axle is constant.

A differential comprises: two output stages to be mounted on axle shafts for vehicle wheels and a central stage meshed with the output stages; wherein each output stage comprises a first gear to be mounted on an axle shaft and at least one worm sub-assembly comprising at least one second gear and a worm, wherein the at least one second gear is meshed with the first gear and is connected to the worm so that the rotation of the at least one second gear causes the corresponding rotation of the worm; the differential according to the invention is characterized in that the central stage comprises two main gears, each main gear comprising a worm wheel and a toothed portion, and at least one intermediate gear meshed with the toothed portions of the main gears; wherein the worm wheel of one main gear is meshed with the worm of each worm sub-assembly of one output stage, and the worm wheel of the other main gear is meshed with the worm of each worm subassembly of the second output stage.

Preferably, each output stage comprises three worm sub-assemblies, the worm subassemblies of each output stage being arranged so that their longitudinal axes form an equilateral triangle.

Preferably, the first gears are meshed with the second gears by means of intermediate gears, the number of the intermediate gears being equal to the number of the second gears.

Preferably, each worm sub-assembly comprises two second gears meshed with the corresponding first gear by means of two intermediate gears.

Preferably, the central stage comprises two intermediate gears.

In the differential of the present invention, the central stage allows one axle shaft to circulate around the other axle shaft, resulting in smooth operation. This means that one vehicle wheel may stand still and the other wheel may circle around the first wheel. Moreover, such an arrangement ensures smooth operation of the differential.

Even operation of the differential is ensured regardless of the ground, which helps to stably take turns.

The differential according to the invention allows the vehicle to start moving more smoothly on different types of road surfaces (e.g. wet or slippery). In addition, it is easier to drive off rough terrain or drive up a hill.

The differential according to the present invention does not contribute to excessive wear of tires during its operation.

The construction of the differential according to the present invention has a direct impact on driving safety. The impact of aquaplaning or changing the lane of a road with snow-covered surface is eliminated due to the fact that the wheels work evenly and there is no skidding effect.

It is possible to transfer 100% of the drive to the other wheel of a given axle, even in the case of full loss of traction with the ground, which makes it possible to continue driving or start with one active wheel. The differential according to the invention may be a central differential as used, for example, in 4x4 all-terrain vehicles. In addition, the differential according to the present application allows drive transmission from 0 to 100%, where 0% means that a given vehicle wheel is not rotating, whereas 100% means that a given wheel is rotating at the same rotational speed as the other wheel.

The object of the present invention is illustrated in its embodiments in the drawing, in which: fig. 1 shows schematically a partial cross-sectional view of a differential according to a first embodiment of the present invention; fig. 2 shows schematically an end view of a part of the first embodiment of fig. 1, with some components omitted for clarity; fig. 3 shows schematically a side view of one gear used in the differential according to the invention; fig. 4 shows schematically a top view of another gear used in the first embodiment of the present invention; fig. 5 shows schematically a partial cross-sectional view of the differential according to a second embodiment of the present invention; fig. 6 shows schematically an end view of a part of the second embodiment of fig. 5, with some components omitted for clarity; fig. 7 shows schematically a side view of one gear used in the second embodiment of the present invention; fig. 8 shows schematically a top view of another gear used in the second embodiment of the present invention.

Hereinafter, the embodiments of the present invention will be described with reference to the accompanying drawing. It should be noted that the present invention is shown schematically in the drawing. This means that various components may not be drawn to scale, for example, they may be smaller or larger in different figures to ensure the clarity of a given figure. Moreover, some components may be absent in some figures for the sake of clarity of representation.

Fig. 1 shows a differential 1 according to the first embodiment. The differential 1 has a housing 2 in which the components of the differential 1 are located. The differential 1 can be mounted on other subassemblies of a vehicle, such as a chassis, by means of bearings 18. If the differential 1 is to be used on a driving axle of the vehicle, a gear (not shown) may be provided on an outer surface of the housing 2 for connection to a drive shaft.

Three stages can be distinguished inside the differential 1 ; two output stages A and a central stage B located between and meshed with the output stages A. The output stages A are mounted on axle shafts 4 for vehicle wheels.

Each output stage A has a first gear 3 to be mounted on an axle shaft 4. The axle shafts 4 are further connected to the vehicle wheels. The connection between the first gear 3 and the axle shaft 4 is such that the rotation of the first gear 3 causes the same rotation of the axle shaft 4, i.e. one part cannot rotate relative to the other. This can be achieved, for example, by means of a sleeve 5 formed uniformly with the first gear 3. The sleeve 5 has an opening 6 therein, which has a plurality of projections 7 on its inner surface. The axle shaft 4 fits into the opening 6, on the surface of which axle shaft there are recesses into which the projections 7 fit. Obviously, the reverse arrangement of the projections and the recesses, i.e. the recesses on the inner surface of the opening 6 and the projections on the axle shaft 4, is also possible. The sleeve 5 may protrude or extend from the first gear 3 on its both sides.

Each output stage A further comprises at least one worm sub-assembly. Preferably, each output stage A comprises two or three (figures 2 and 6) worm sub-assemblies. As shown in figures 1 and 2, each worm sub-assembly comprises a second gear 8, which is perpendicular to and meshed with the first gear 3. As shown in the drawing, the first gear 3 and the second gears 8 may be bevel gears which mesh with each other at their circumferences. Each worm sub-assembly further comprises a worm 9.

Each worm sub-assembly also includes a pin 10 which is mounted at its ends in the housing 2. The worm 9 and the second gear 8 of a respective worm sub-assembly are mounted on this pin 10. The worm 9 and the second gear 8 can rotate together freely on the pin 10. The worm 9 is connected to the second gear 8 so that the rotation of the second gear 8 causes the corresponding rotation of the worm 9. This can be achieved by permanently connecting the second gear 8 to the worm 9, or by forming these two components as one unitary part.

Another way is to provide a sleeve 11 in the worm sub-assembly, which sleeve 11 is freely mounted on the pin 10. The second gear 8 and the worm 9 are permanently mounted on the sleeve 11, whereby the rotation of the second gear 8 causes the corresponding rotation of the sleeve 11 and, further, the worm 9. In order to reduce frictional resistance and maintain an appropriate distance, thrust bearings 12 are used on the pin 10 between the sleeve 11 and the housing 2.

Fig. 2 shows an arrangement of the differential 1 in which three worm subassemblies are used in each input stage A, each worm sub-assembly comprising one worm 9 and one second gear 8 both mounted on the pin 10 and the sleeve 11. Preferably, the worm sub-assemblies, and consequently their components, are arranged relative to each other so that the axes of rotation/longitudinal axes X of the worm sub-assemblies and their components form an equilateral triangle, i.e. the axes of rotation/longitudinal axes X of two adjacent worm sub-assemblies and their components form an angle of 60°. Such an arrangement significantly increases the strength of the differential 1 by distributing load evenly.

The first gear 3 and the second gears 8 may have hypoid teeth, which allows the axis of rotation of both gears to be positioned in two non-overlapping planes. Nevertheless, straight teeth can also be used if an offset of the axes of rotation of both gears is not needed.

The central stage B comprises two main gears 13 mounted, so that free rotation is possible, on the axle shaft 4 and the sleeve 5 (as shown in the figures) or on a separate pin (not shown), depending on the arrangement of the gears and the differential 1 itself. This means that the rotation of the axle shaft 4 and the sleeve 5 does not directly result in the rotation of the main gear 13, and vice versa.

Each main gear 13 has a worm wheel 13a and a toothed portion 13b (preferably conical), which are permanently connected to or integral with each other. The worm wheel 13a of one main gear 13 is meshed with the worm 9 of each worm sub-assembly of one output stage A, while the worm wheel 13a of the other main gear 13 is meshed with the worm 9 of each worm sub-assembly of the second output stage A. Two main gears 13 of the central stage B are meshed with each other by means of at least one, preferably two or three intermediate gears 14, preferably conical, of the central stage B. More specifically, each intermediate gear 14 is meshed with both toothed portions 13b of the main gears 13. The intermediate gears 14 and the toothed portions 13b may have hypoid teeth when an offset of their axes of rotation is necessary. Nevertheless, when an offset of the axes of rotation is not required, the intermediate gears 14 and the toothed parts 13b may have straight teeth. The intermediate gears 14 are mounted by means of a sleeve 16 on a pin 15, which is fixed at its ends in the housing 2. The intermediate gears 14 can rotate freely on the pin 15.

The second embodiment of the present invention is shown in fig. 5. This embodiment is very similar in construction to the first embodiment. Therefore, only the differences between both embodiments will be described below. In the second embodiment, the first gear 3 ’ of each output section A is a planar/cylindrical gear with teeth arranged circumferentially. In other respects, the first gear 3 ’ is the same as the first gear 3. The teeth of the first gear 3’ are straight teeth. In each output stage A, at least one worm sub-assembly is provided. Each worm sub-assembly in this embodiment comprises at least one, and preferably two second gears 8. The remaining components of each worm subassembly are the same as in the first embodiment.

Between the first gear 3’ and each second gear 8 of each output sub-assembly A is inserted an intermediate gear 17 of the output stage A, which is mounted on its pin. This means that the number of the intermediate gears 17 is equal to the number of the second gears 8. Each intermediate gear 17 has a cylindrical toothed part 17a, which is meshed with the first gear 3’, and a conical toothed part 17b, which is meshed with the corresponding second gear 8.

As shown in fig. 6, like in the first embodiment of fig. 2, preferably three worm sub-assemblies can be used in each output stage A. Preferably, three worm sub-assemblies are arranged relative to each other so that the axes of rotation/longitudinal axes X of the worm sub-assemblies and their components form an equilateral triangle.

The operation of the differential 1 according to the first embodiment is as follows. The operation of the differential 1 starts with the rotation of the housing 2 of the entire differential 1 mounted on the bearings 18. When driving straight ahead, the differential 1 is locked and functions like a typical differential at this stage. The intermediate gears 14 try to rotate the main gears 13, but the rotation of the vehicle wheels is uniform and the friction force on both vehicle wheels is the same - then the central stage B of the differential 1 remains motionless and the axle shafts 4 and the vehicle wheels rotate with the same speed.

In contrast to other differentials, when driving straight ahead, the central stage B of the differential 1 according to the present invention, in particular according to the first embodiment, is always locked - the intermediate gears 14 and the main gears 13 remain always fixed (i.e. motionless). The reason for this is the use of a self-locking worm gear, which includes the worms 9 and the worm wheels 13 b. The worms 9 arranged perpendicularly to the worm wheel 13a are able to rotate the worm wheels 13a, whereas the worm wheels 13a arranged along the differential 1 are not able to rotate the worms 9.

The central stage B of the differential 1 remains locked until there is a difference in the rotation between both axle shafts 4, which in turn causes a difference in the rotational speeds of the first gears 3, 3’ of both output stages A.

A given axle shaft 4 drives the first gear 3, 3’ which in turn causes the rotation of the second gears 8 (alternatively via the intermediate gears 17, if present) and further the worms 9, resulting in movement of the main gear 13 of the central stage B. The consequence of the operation of the main gear 13 is the rotation of the intermediate gears 14. The second output stage A operates in the same way.

Now let us consider a situation where one vehicle wheel on the first axle shaft 4 is in contact with the ground, while the other vehicle wheel on the second axle shaft 4 is not in contact with the ground, i.e. friction is equal to 0.

The axle shaft 4 of the vehicle wheel being in contact with the ground drives the first gear 3, 3', which in turn causes the rotation of the intermediate gears 17 (if present), the second gears 8 and the worms 9, resulting in the rotation of the main gear 13. The consequence of the operation of the main gear 13 is the rotation of the intermediate gears 14, which causes the rotation of the second main gear 13 meshed with the output stage A for the axle shaft 4, on which the wheel not having contact with the ground is mounted. This second main gear 13, however, cannot cause the rotation of the worms 9 of the output stage A, which is associated with the axle shaft 4 for the wheel not having contact with the ground due to the use of a self-locking transmission. At this point, differential 1 is locked on this side.

The result of the above is that both axle shafts 4 have the same rotational speed, which will subsequently cause the transfer of drive to the axle shaft 4 on which the vehicle wheel having contact with the ground is mounted.

Generally, the differential 1 according to the second embodiment of the present invention functions very similarly. Nevertheless, in the differential 1 according to the second embodiment, additional intermediate gears 17 are used. Due to the use of the intermediate gears 17 and the central stage B, the differential 1 can operate as smoothly as a conventional differential when one vehicle wheel is stationary and the other vehicle wheel circles around the first wheel. This is because when the respective axle shaft 4 and the associated first gear 3' are standing still, the rotation of the housing 2 also causes the intermediate gears 17 on the side of the standing still axle shaft 4 to rotate along the circumference of the associated first gear 3', which in turn causes the rotation of the associated second gear 8 and worm 9, which further cause the rotation of the second gear

13. In the meantime the intermediate gears 14 of the central stage B, which rotate freely on the pin 15, equalise differences in the rotation between the axle shafts 4, as it happens in a conventional differential, resulting in smooth operation.

In the differential 1 according to the second embodiment, the rotation of the housing 2 may cause the rotation of the second gear 8 and the worm 9 when the first gear 3' is standing still, due to the use of the intermediate gears 17.