TECHNICAL FIELD

The invention relates to a differential unit for a vehicle, to an axle comprising such a differential unit and to a vehicle comprising such an axle.

The invention can be applied in heavy-duty vehicles, such as trucks, buses and construction equipment or vehicle.

BACKGROUND

A vehicle such as a truck is generally equipped with one or several differential units on its driven axles.

A differential unit (or differential) typically comprises a differential housing which is made of a first portion assembled with a second portion. A crown wheel, driven by an input or propeller shaft, is attached to the differential housing and is arranged around the differential housing. The differential housing contains the differential mechanism that includes side pinions and side gears in a meshing engagement. A first (longitudinal) end of the two drive shafts is respectively secured to a side gear of the differential. Also, each drive shaft is connected to a drive wheel of the vehicle at its second (longitudinal) end. The differential side pinions, which are for example four, are fitted on a“joint cross” that is rotationally fixedly arranged with the crown wheel (i.e. rotates with the crown wheel). The “joint cross” is also known as a“spider”. Each differential side gear meshes with at least one differential pinion and is fastened to the first (longitudinal) end of one of the drive shafts. In a conventional arrangement, such as disclosed in CN711779229U, the first differential housing portion and the second differential housing portion are attached together by a first set of screws arranged along a first circle and the crown wheel is secured to the first differential housing portion via a second set of screws arranged along a second circle. The second circle is of a diameter that is higher than that of the first circle. Such an arrangement negatively impacts the compactness of the differential unit and of the axle. Indeed, such a conventional arrangement imposes having overall diameters of the differential unit and of the axle that are quite large. From a vehicle perspective, such an arrangement results in a lower ground clearance that can be detrimental when the vehicle, especially a construction vehicle, has to cross over a high obstacle on the ground.

SUMMARY

An object of the invention is to provide an improved differential unit for a vehicle.

More specifically, an object of the invention is to provide a differential unit for a vehicle which is advantageous compared with conventional arrangement of the state of the art. Precisely, one objective of the invention is to provide a differential unit that is more compact than conventional arrangements and that is also more favourable in term of assembling process.

To that end, and according to a first aspect, the invention concerns a differential unit for a vehicle, the differential unit comprising a main axis, a differential housing comprising a first portion and a second portion, a crown wheel that is ring shaped and that is secured to the differential housing, wherein the crown wheel is arranged around the differential housing, and centred on the main axis, at least three differential pinions and two differential side gears, arranged inside the differential housing, wherein each differential side gear meshes with at least one differential pinion and wherein the two differential side gears are arranged on the main axis and a joint cross on which are fitted the differential pinions. According to the invention, the crown wheel, the first portion and the second portion of the differential housing are fastened together by one and the same set of fixing screws.

In the present invention, the main axis of the differential housing also corresponds to the axis of rotation of the crown wheel and of the differential side gears. When the differential unit is assembled in an axle, the main axis of the differential housing also corresponds to the axis of rotation of the drive shafts and is parallel to a transverse direction of the vehicle. In conventional arrangement first and second differential housing portions are assembled with a first set of screws and the crown wheel is secured to the differential housing by a second set of screws distributed along a second circle of larger diameter than the first set of screws. In the present invention, the crown wheel, the first differential housing portion and the second differential housing portion are fastened together by the same fixing screws.

The fact that, in the present invention, only one set of screws is used to fasten together the crown wheel, the first differential housing portion and the second differential housing portion instead of two set of screws reduces the number of screws compared to a conventional arrangement. In addition, according to the present invention the crown wheel , the first differential housing portion and the second differential housing portion can be assembled in the same work circle during the assembling process.

It results from the arrangement according to the invention that there is no need to accommodate a second set of screws arranged along a second circle of a larger diameter. Consequently, the differential unit according to the invention has a more compact footprint than a conventional differential unit, while being able to transmit the same torque to the wheels. The arrangement according to the invention is positively impacting footprint, especially the overall diameter of the differential unit that is to say according to radial direction that is perpendicular to the main axis of the differential housing.

For an improved compactness, all the fixing screws are advantageously arranged in a single circle. This single circle can be, for instance, equivalent to the circle along which first set of screws of conventional arrangement are conventionally located.

To regularly distributes stress and strain resulting from the tightening of the fixing screws on the crown wheel, the first differential housing portion and on the second differential housing portion, the fixing screws are regularly distributed along said single circle. In other words, the fixing screws are equally angularly spaced about the main axis of the differential unit. Preferably, at least one of the fixing screws, preferably each fixing screw, is engaged in three aligned holes, respectively provided in the first housing portion, in the second housing portion and in the crown wheel.

Advantageously, at least one of the fixing screws is engaged in four aligned holes, respectively provided in the first housing portion, in the joint cross, in the second housing portion and in the crown wheel, so that the joint cross is rotationally coupled with the crown wheel.

Advantageously, the joint cross is axially arranged between the first portion and the second portion of the differential housing.

Advantageously, the crown wheel is axially in contact with at least one side surface of the first differential housing portion, preferably an annular surface of the first differential housing portion that is opposite to the second differential housing portion.

Preferably, the crown wheel is axially arranged between the first differential housing portion and the second differential housing portion.

Preferably, the joint cross is centred on the main axis and comprises at least three legs extending radially from the main axis.

Preferably, each leg rotatably supports a differential pinion, wherein the free end of each leg comprises an axial hole and wherein the axial holes are passed through by fixing screws.

Preferably, some fixing screws are passed through the axial holes of the joint cross and some other fixing screws are not passing through the axial holes of the joint cross.

Such an arrangement allows using more fixing screws to fasten together the crown wheel, the first differential housing portion and the second differential housing portion. With more fixing screws the attachment of together the crown wheel, the first differential housing portion and the second differential housing portion is more robust and allows the differential units to accommodate higher torque than an equivalent differential unit with less screws. The additional number of screws that can be added with respect to conventional arrangements is dependent on the number of legs of the joint cross. For instance, if the joint cross comprises four legs rotatably supporting four differential side pinions, four holes can be formed at the free end of the legs this means that four additional fixing screws can be provided to fasten together the crown wheel, the first differential housing portion and the second differential housing portion.

Typically, some fixing screws are passed through holes of the crown wheel, holes of the first differential housing portion, the axial holes of the joint cross and are screwed in tapped holes of the second differential housing portion.

Owing to this arrangement, it is made possible to maximise the number of fixing screws arranged in a single circle while maintaining the fixing screws regularly distributed along said single circle.

Also, some other fixing screws are passed through holes of the crown wheel, holes of the first differential housing portion and are screwed in tapped holes of the second differential housing portion.

Advantageously, when the crown wheel is axially in contact with a side surface of the first differential housing portion, preferably an annular surface of the first differential housing portion, and that is opposite to the second differential housing portion or when the crown wheel is axially arranged between the first differential housing portion and the second differential housing portion some fixing screws.

The latter arrangement provides a very simple and robust way to fasten together the crown wheel, the first differential housing portion and the second differential housing portion.

Typically, the first portion and the second portion of the differential housing are two distinct parts.

The invention also concerns an axle comprising a differential unit as described above, an axle housing which contains two drive shafts, wherein one end of each drive shaft is connected to one differential side gear of the differential unit, the axle further comprising at least one wheel connected to the other end of each drive shaft. Eventually, the invention relates to a vehicle comprising such an axle.

Further advantages and advantageous features of the invention are disclosed in the following description and in the dependent claims.

BRIEF DESCRIPTION OF THE DRAWINGS

With reference to the appended drawings, below follows a more detailed description of embodiments of the invention cited as examples. In the drawings:

Fig. 1 is a schematic drawing of an underside of a vehicle showing two driven rear axles;

Fig. 2 is a longitudinal cross section of driven rear axle according to claim 1 including a differential unit according to an embodiment of the invention;

Fig. 3 is a view of the differential unit of Fig. 2 which includes a main axis of the differential unit; Fig. 4 is a side view of the differential unit of Fig. 3;

Fig. 5 is an enlarged view of figure 2 centred on the differential unit and showing the crownwheel and inside of the differential unit. Fig. 6 shows a perspective view of the joint cross represented on figure 5.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS OF THE INVENTION

Figure 1 shows a vehicle 1 that comprises an engine 2, preferably an Internal Combustion Engine (ICE). Nevertheless, the engine 2 could obviously be replaced by an electric motor or a combination of an ICE and an electric motor (hybrid motorization).

In the example, the engine 2 is configured to power a drive shaft 3. Preferably, the drive shaft 3 is a propeller shaft, meaning that the vehicle 1 is a propulsion vehicle, in which power is transmitted to the rear axle. Nevertheless, the invention obviously applies to a traction vehicle, in which power is transmitted to the front axle or to an all-wheel drive vehicle, in which power is transmitted both to a front axle and a rear axle.

The drive shaft 3 has a longitudinal axis 13, which is also the axis of rotation of the drive shaft 3.

A front axle 4 connects to front wheels 5. In the example of the figures, the front axle 4 is not driven by the engine.

The vehicle 1 has a longitudinal direction Y and a transverse direction X that is perpendicular to the longitudinal direction Y. The drive shaft 3 extends substantially according to the longitudinal direction Y of the vehicle.

Moreover, direction Z is defined as the vertical direction when the vehicle 1 is on a horizontal surface. Direction Z is perpendicular to the ground surface.

The vehicle 1 also comprises at least one rear axle 6. Each rear axle 6 extends along the transverse direction X. The or each rear axle 6 comprises an axle housing 7 that is not rotating (fixed) and whose larger central portion is conventionally identified as a differential carrier housing 71. A differential unit 10 (see figure 2) is arranged inside the different carrier housing 71.

In the illustrated embodiment of figure 1 , the vehicle 1 comprises a first driven rear axle 6a and a second driven rear axle 6b located rearwards from the first driven rear axle 6a.

Preferably, each rear axle 6a, 6b comprising two wheels 8 on each longitudinal side. Nevertheless, the invention obviously applies to a vehicle wherein each rear axle comprise only one wheel on each longitudinal side.

An additional shaft 9 connects the propeller shaft 3 to a differential unit (not shown )of the second driven rear axle 6b, through the differential unit 10 of the first driven rear axle 6a. This additional shaft 9 is the input shaft for the differential unit of the second driven rear axle 6b. Typically, the differential unit of the second driven rear axle 6b can be the same than the differential unit 10 of the first driven rear axle 6a. The two differential units may also be different.

In the example, a drive shaft 1 1 is arranged inside the axle housing 7, on each side of the differential unit 10. The drive shafts 11 have each a first end connected to the differential unit 10 and a second end connected to at least one wheel 8.

Preferably, each drive shaft 11 is connected to said at least one wheel 8 via a hub gear reduction 12, such as the one represented on figure 2.

With reference to figures 2, 3, 4 and 5, the differential unit 10 comprises a differential housing 14.

The differential housing 14 is made of a first portion 14a (shown in Figures 2, 3 and 4), and a second portion 14b (shown in Figures 2 and 3) that are assembled together. The first portion 14a and the second portion 14b are then distinct from each other (not in one piece).

The differential unit 10 also comprises a crown wheel 15 that is conventionally a ring- shaped conical gear . Typically, the crown wheel 5 is secured to the differential housing 14. The crown wheel 15 is arranged around the differential housing 4 and centred on a main axis X10 of the differential unit 10.

As shown in figures 1 and 2, in the operating position, i.e. when the differential unit 10 is mounted on the vehicle 1 , the main axis X10 of the differential unit 10 is oriented according to the transverse direction X of the vehicle 1. The main axis X10 can also be defined as the central axis of the differential unit 10 and is the axis of rotation of the drive shafts 1 1.

Advantageously, the crown wheel 15 is driven in rotation around said main axis X10 by the propeller shaft 3, by the meshing engagement of teeth 311 arranged on a frustoconical pinion 31 (see figure 5) connected to said propeller shaft 3 and teeth 152 arranged on the crown wheel 15 (The teeth 152 are illustrated on figure 5 but not on figure 3). The pinion 31 is arranged at one (longitudinal) end of the propeller shaft 3, the other end being connected to the engine 2. The crown wheel 15 and the differential housing 14 are rotating parts inside the differential carrier housing 71 and with respect to the differential carrier housing 71. The differential housing 14 is guided (or supported) in its rotational motion on the inner side of the differential carrier housing 71 by means of one, preferably two supporting devices 30.

Typically, each supporting device 30 carries a bearing 50, for example a ball bearing or a roller bearing, having an inner ring 51 that is mounted on the differential housing 14, 14a, 14b and an outer ring 52 mounted on the supporting device 30. Each bearing 50 further comprises rolling elements 53 (see figure 6 for example). In the example, the rolling elements are rollers that are incline with respect to a central axis of the bearing, which means that the bearing 50 is a tapered roller bearing. Nevertheless, any other type of roller bearing would be obviously suitable.

Preferably, the two supporting devices 30 are respectively located on both sides of the crown wheel 22, along the main axis X10. In the example, the differential unit 10 further comprises at least three differential pinions 16, preferably four, and two differential side gears 17 arranged inside the differential housing 14. Each differential side gear 17 meshes with at least one differential pinion 16. The two differential side gears 17 are arranged on the main axis X10. Each differential side gear 17 is fastened to a first end of each drive shaft 11.

The differential unit 10 also comprises a joint cross 18, represented on figures 5 and 6 and also known as a“spider”, on which are fitted the differential pinions 16. The joint cross 18 is axially arranged, i.e. according to the main axis X10 of the differential unit 10, between the first differential housing portion 14a and the second differential housing portion 14b. The joint cross 18 comprises at least three, preferably four legs 181 extending radially from the main axis X10.

Typically, the four legs 181 are perpendicular two by two. Each leg 181 rotatably supports a differential pinion 16. Preferably, the differential pinions 16 are each arranged substantially at the free end of each leg 181.

In the embodiment of figures 2, 5 and 6 the joint cross 18 comprises four legs 181 which respectively support four differential pinions 16.

According to the present invention, the crown wheel 15, the first differential housing portion 14a and the second differential housing portion 14b are fastened together by one and the same set of fixing screws 19. This means that, in comparison with differential units of prior art, and in particular the one disclosed in CN71 1779229U, the parts 15, 14a and 14b are not attached two by two but attached all the three together.

In other words, at least one of the fixing screws 19 is engaged in three aligned holes, respectively provided in the housing portion 14a, in the housing portion 14b and in the crown wheel 15.

Preferably, the axes X19 of the fixing screws 19 are parallel to the main axis X10 of the differential unit 10. The fixing screws 19 are advantageously arranged in a single circle 20 (see figure 4) that is centred on the main axis 10.

Also, the fixing screws 19 are preferably regularly distributed along said single circle 20 in order to regularly distributes stress and strain resulting from the tightening of the fixing screws 19 and that applies on the crown wheel 15, the first differential housing portion 14a and the second differential housing portion 14b.

Such as represented on figures 2 and 5, the crown wheel 15, the first differential housing portion 14a and the second differential housing portion 14b are arranged such that the crown wheel 15 is axially in contact with at least one side surface 141 of the first differential housing portion 14a that is opposite to the second differential housing portion 14b. Such as represented on figure 5, said side surface can be an annular surface 141 of the first differential housing portion 14a that is opposite to the second differential housing portion 14b. In other variants (not represented) the crown wheel 15 might be in contact with several flat surfaces of the first differential housing portion 14a. In another variant (not represented), the crown wheel 15, the first differential housing portion 14a, the second differential housing portion 14b and the joint cross are arranged such that the crown wheel 15 is axially arranged between the first differential housing portion 14a and the second differential housing portion 14b. In such a case an annular flange of the crown wheel 15 is sandwiched and axially pressed between a first annular surface of the first differential housing portion 14a and a second annular surface of the second differential housing portion 14b wherein the first and the second annular surfaces are facing each other. This alternative arrangement of the differential unit 10 reduces stress and strain resulting from the tightening of the fixing screws 19 and that may apply on the crown wheel 15. Another benefit resulting from this alternative arrangement is that the crown wheel 15 can be located in a more central position along the main axis X10 of the differential unit 10. In turn, a more central position of the crown wheel 15 results, for instance, in a better repartition of the load on the bearings 50 supporting in rotation the differential housing 14.

In an advantageous embodiment represented on figures 5 and 6, the end of each leg 181 of the joint cross 18 comprises one axial hole 182 and the axial holes 182 are passed through by fixing screws 19. Preferably, and in order to rotationally couple the crown wheel 15 with the joint cross 18, some fixing screws 19a are passed through the axial holes 182 of the joint cross 18.

Preferably, some other fixing screws 19b are not passing through the axial holes 182 of the joint cross 18.

In other words, some fixing screws 19a of the differential unit are passed through four aligned holes, respectively through a hole 151 of the crown wheel 15, a hole 141 of the first differential housing portion 14a, an axial hole 182 of the joint cross 18 and a tapped hole 142 of the second differential housing portion 14b (see figure 5).

Also, some other fixing screws 19b are passed only through three holes, respectively a hole 151 of the crown wheel 15, a hole 141 of the first differential housing portion 14a and a tapped hole 142 of the second differential housing portion 14b without passing through one axial hole of the joint cross 18. Such an arrangement allows using more fixing screws 19 to fasten together the crown wheel 15, the first differential housing portion 14a and the second differential housing portion 14b. With more fixing screws 19, the attachment of the crown wheel 15, the first differential housing portion 14a and the second differential housing portion 14b together is more robust and allows the differential unit 10 to accommodate higher torque than an equivalent differential unit with less fixing screws 19. The additional number of fixing screws 19a that can be used is dependent on the number of legs 181 of the joint cross 18. For instance, if the joint cross 18 comprises four legs rotatably supporting four differential pinions 16 (such as represented on figures 2 and 5), four holes 182 can be formed at the end of the legs 181. It results that four additional fixing screws 19a can be provided to fasten together the crown wheel 15, the first differential housing portion 14a and the second differential housing portion 14b.

According to a second aspect, the invention concerns an axle 6, 6a, 6b that comprises a differential unit 10 such as previously described, an axle housing 7 which contains two drive shafts 11. One end of each drive shaft 1 1 is connected to one differential side gear 17 of the differential unit 10. The axle 6, that is preferably a rear axle, 6a, 6b, further comprises at least one wheel 8 connected to the other end of each drive shaft 11. Such as represented on figure 1 the rear axle may, for instance, comprises two left wheels 8 and two right wheels per axle 6a, 6b. Such as represented on figures 2, the wheels 8 might be connected to the end of each drive shaft 11 via hug gear reductions 12, a left one and a right one.

According to a third aspect, the invention concerns a vehicle 1 that comprises at least one axle 6, 6a or 6b such as previously described. The vehicle represented on figure 1 comprises two rear axles 6a, 6b according to the invention. The vehicle 1 is preferably a heavy-duty vehicle, such as a truck, a bus or a construction equipment.

Therefore, the invention provides an improved differential unit in terms of assembling process, reliability and robustness.

It is to be understood that the present invention is not limited to the embodiments described above and illustrated in the drawings; rather, the skilled person will recognize that many changes and modifications may be made within the scope of the appended claims.