Axle system for a vehicle and mounting process

An axle system (150) for a vehicle comprises: —a differential unit (10) including a first housing (24) and a second housing (20) which rotationally receives at least part of said first housing; —at least one drive shaft (11) having one end configured to be connected to a wheel of the vehicle and one end connected to the differential unit (10) and rotationally received in the first housing (24), the drive shaft (11) including at least one joint (110) connecting two portions (114a, 114d) of the drive shaft (11) to transmit rotary motion between said portions; —a first bearing (30) secured around the drive shaft (11), placed between the drive shaft and the first housing (24), having an outer diameter (D30) smaller than the radial dimension (D) of the joint (110); —a second bearing (40) placed between the first housing (24) and the second housing (20); —at least one tightening member (50) to axially lock the first bearing outer ring (32) relative to the first housing (24). The tightening member comprises at least one manoeuvring portion (51) which is arranged in an offset relation relative to the joint (110), when looking axially towards the differential unit (10), so that the tightening member manoeuvring portion (51) is visible and accessible, at least during a tightening phase of an axle system mounting process.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a U.S. National Stage application of PCT/EP2018/076585, filed Oct. 1, 2018, and published on Apr. 9, 2020, as WO 2020/069714 A1, all of which is hereby incorporated by reference in its entirety.

TECHNICAL FIELD

The invention relates to an axle system for a vehicle. The invention also relates to a drive shaft sub assembly for such an axle system, to a driven wheel system comprising such an axle system and to a vehicle comprising at least one such driven wheel system. The invention further relates to a process for mounting such an axle system.

BACKGROUND

A vehicle such as a truck is generally equipped with one or several differential units on its driven axles, to allow the left and right wheels of said axle to have different speeds when turning/manoeuvring.

As the transverse width of a vehicle, in particular a truck, is limited to a maximum value given by regulatory requirements, other vehicle components need to be fairly compact, which in particular applies to the powertrain system, especially the differential unit.

Such a space constraint is even more significant in some vehicle configurations:for electric vehicles, as they require significant space for batteries;for vehicles not comprising a mechanical differential, but implementing a torque vectoring solution. This creates packaging issues since the left and right wheels need to be independently driven, duplicating the transmission from the motor(s) to the wheel(s);for vehicles having an independent wheel suspension configuration, to which the invention more particularly applies.

A trend in transport industry, in particular in heavy duty transport industry, is to move from rigid axles to independent wheel suspension configurations, to improve several features (dynamic behavior, volume capacity for battery/fuel, wheel alignment, comfort, etc.). To get maximized battery/fuel efficiency from an independent wheel suspension driveline, wheel reduction (hub reduction) should be avoided. Without such a wheel reduction, the drive shafts have to be bigger. Moreover, these drive shafts must have a minimum length to support driveline torque and keep acceptable working angles, in order not to compromise the suspension stroke and consequently the comfort.

The width of vehicle being legally constrained, and a minimum length being needed for the drive shaft for torque and angle constraints, there is a need for an as much as possible compact differential unit in the vehicle transverse direction.

Other constraints derive from the independent wheel suspension configuration, such as the need for a stronger support of the drive shafts both in the differential unit area and in the wheel area, or the need to secure each drive shaft in translation, in both directions along the vehicle transverse direction and without play, in the differential unit, to avoid a greatly limit wear.

All these requirements have to be taken into account, bearing in mind that the mounting process of the whole vehicle driven wheel system must preferably not be significantly complicated nor take much longer. The same applies to maintenance operations.

SUMMARY

An object of the invention is to provide an improved axle system for a vehicle which solves at least one of the problems of the prior art.

In particular, the invention aims at improving compactness, and at making the mounting process and/or the maintenance operations easier.

To that end, and according to a first aspect, the invention concerns an axle system for a vehicle, having an axis and comprising:a differential unit including a first housing and a second housing which is at least partially arranged around the first housing and which rotationally receives at least part of said first housing;at least one drive shaft having one end configured to be connected to a wheel of the vehicle and one end connected to the differential unit and rotationally received in the first housing, the drive shaft including at least one joint connecting two portions of the drive shaft to transmit rotary motion between said portions, the joint having a radial dimension;a first bearing secured around the drive shaft, placed between the drive shaft and the first housing;a second bearing placed between the first housing and the second housing;

wherein:the outer diameter of the first bearing is smaller than the radial dimension of the joint;and the axle system comprises at least one tightening member configured to axially lock the first bearing outer ring relative to the first housing, said tightening member comprising at least one manoeuvring portion which is arranged in an offset relation relative to the joint, when looking axially towards the differential unit, so that the tightening member manoeuvring portion is visible and accessible, at least during a tightening phase of an axle system mounting process.

Providing an axle system including a first bearing, in addition to the second bearing, makes it possible to better support and guide the drive shaft in rotation inside the differential. Owing to the invention, this advantage is not obtained to the detriment of compactness, as explained below.

Indeed, by providing a first bearing having a smaller outer diameter than the radial dimension of the joint, the invention greatly improves the compactness. As a result, the differential unit is more compact in the radial direction but also as a whole. Indeed, a small first bearing can more easily be housed in a limited space and, in some embodiments, can be appropriately and efficiently arranged relative to the surrounding components to further limit compactness, including in other directions than the radial direction. Besides, as the first bearing has a fairly small outer diameter, it does not require other components of the differential unit to be sized as large and/or resistant parts. Therefore, the overall size, weight and cost of the differential unit are reduced.

However, with such a configuration, due to its small outer diameter, the first bearing can be hidden by the joint or another component of the axle system, when looking axially towards the differential unit. As a consequence, the first bearing cannot be accessed nor easily axially blocked by conventional tightening means.

This is the reason why the invention further provides a specific tightening member having a specifically designed manoeuvring portion for allowing a user to easily and efficiently tighten said tightening member. In concrete terms, the terms “arranged in an offset relation relative to the joint” mean that the manoeuvring portion and the joint are not superimposed, or at least partially not superimposed, when looking axially towards the differential unit.

The tightening member is used to axially lock the first bearing outer ring relative to the first housing, i.e. to axially maintain the first bearing outer ring relative to the first housing, in both directions, without play. This prevents or greatly limits wear on the components due to high axial forces, in both directions and at high frequency.

The invention thus makes it possible to improve compactness without negative effects on the assembly and structure quality of the axle system nor on the ease of the mounting process.

“Axle system” has to be understood as the set of pieces that joins two wheels, and is not limited to a rigid axle. In the present invention, the axle system is not rigid as the drive shafts include joints. In practice, the axle system comprises two drive shafts, one on each side of the differential unit. The joint can be a universal joint, a homocinetic joint, a Rzeppa joint, or any other kind of joint capable of coupling connecting rigid rods whose axes are inclined to each other and to transmit rotary motion between said rigid rods.

“Differential unit” refers to a unit providing a differential effect, in order to allow the outer drive wheel to rotate faster than the inner drive wheel during a turn. Such a differential unit can include a mechanical differential. Alternatively, the differential effect can be achieved by the fact that the wheels are driven independently by a dedicated motor, preferably but not exclusively an electric motor, and corresponding transmission system, in a so-called torque vectoring technology.

In concrete terms, the radial dimension of the joint is the diameter of the smallest cylinder which has its centre on the axis, and which fully contains the joint, when the drive shaft is in a straight configuration (also called “enveloping cylinder”). The joint is not necessarily a rotationally symmetric piece; it can have at least a first radial dimension along one direction, and a second radial dimension different from the first radial dimension along another direction. The largest dimension among the first and the second radial dimensions is then the joint radial dimension.

In practice, the second housing can be an outer part that does not rotate relative to the vehicle chassis, while the first housing can be an inner rotating part relative to the vehicle chassis.

According to an embodiment, the first bearing outer diameter can be smaller than the second bearing inner diameter. Such a configuration allows reducing the space required in the radial direction.

In addition, advantageously, the first bearing and the second bearing may have median planes which are orthogonal to the axis and which are substantially coincident. In other words, with this configuration, the first bearing is arranged inside the second bearing. This further reduces the space required in the transverse direction. The term “coincident” includes a configuration in which the median planes are offset by less than 50% of the axial length of the first bearing, preferably less than 30%, more preferably less than 20%.

The first housing may comprise a radial wall, the tightening member being configured to axially tighten the first bearing outer ring against said radial wall. Said radial wall may be a piece distinct from the first housing but secured to the first housing. Said radial wall—which extends in a plane orthogonal to the axis—thus forms an axial abutment.

The tightening member manoeuvring portion can comprise at least one hole, recess or the like, configured to receive a tool capable of moving the tightening member axially relative to the first housing.

The tightening member can comprise several manoeuvring portions which are all arranged in an offset relation relative to the joint, and which are preferably arranged substantially on one and the same circle.

The axle system can comprise several tightening members, each tightening member comprising at least one manoeuvring portion which is arranged in an offset relation relative to the joint, the tightening members preferably being arranged substantially on one and the same circle.

The term “circle” is not limited to a line but includes an annular zone having a small radial dimension.

The axle system may further comprise a seal arranged between the drive shaft—or a part secured to the drive shaft—and the second housing—or a part secured to the second35housing, the seal preferably having an annular shape.

The axle system may further comprise a cover having an opening for receiving the drive shaft, the cover being configured to be removably mounted on and/or fastened to the second housing after the tightening phase of the axle system mounting process. In an embodiment, the cover may cover the manoeuvring portion. However, other implementations may be envisaged. The cover can have an annular shape, the opening being then centrally arranged in the cover.

The seal may be mounted in the cover opening. In an embodiment, the annular seal is mounted in the central opening of the annular cover.

In an implementation, the axle system comprises a left drive shaft connected to the differential unit and configured to be connected to at least one left wheel, and a right drive shaft connected to the differential unit and configured to be connected to at least one right wheel, the differential unit further comprising a differential which mechanically links the two drive shafts. At least one of the drive shafts is made to rotate:by a crown wheel of the axle system which is connected to the differential and configured to be connected to an input shaft driven by a vehicle engine or by a vehicle electric motor;or by at least one motor (electric motor, hydraulic motor, etc.), through a transmission system.

The differential may further comprise a blocking system for blocking the differential operation.

In another implementation, the differential effect is not achieved by means of a differential but through torque vectoring technology. Then, the axle system comprises a left drive shaft connected to the differential unit and configured to be connected to at least one left wheel, and a right drive shaft connected to the differential unit and configured to be connected to at least one right wheel. The differential unit further comprises at least one motor (electric motor, hydraulic motor, etc.) capable of rotating the left drive shaft through a transmission system, and at least one motor (electric motor, hydraulic motor, etc.) capable of rotating the right drive shaft through a transmission system, independently from the left drive shaft.

According to a first embodiment of the invention, the manoeuvring portion of the tightening35member is located in an area of the tightening member which is radially outside from the joint enveloping cylinder—i.e. the smallest cylinder which has its centre on the axis, and which fully contains the joint—when looking axially towards the differential unit. In other words, said area of the tightening member is radially outwardly offset from the joint. For example, said manoeuvring portion can be located in an annular area having a diameter that is larger than the radial dimension of the joint.

The manoeuvring portion of the tightening member can be located in a peripheral area of the tightening member.

For example, the tightening member can comprise a nut having:a tightening portion, such as a sleeve coaxial with the drive shaft, configured for abutting against the outer ring of the first bearing;and an outer annular flange comprising at least one notch which opens outwardly and which forms the manoeuvring portion.

The annular seal may have an inner diameter that is larger than the radial dimension of the joint. This disposition is advantageous in that the annular seal may be replaced when needed without disassembling the drive shaft. The maintenance is thus significantly improved.

The axle system may comprise a contact piece secured around the drive shaft and having:a blocking portion, such as a sleeve coaxial with the drive shaft, configured for abutting against the inner ring of the first bearing;a contact portion, such as a cylindrical contact portion coaxial with the drive shaft, with which the annular seal is radially in contact, wherein, preferably, the contact portion is radially inwardly offset relative to the tightening member manoeuvring portion.

By providing a contact portion which is radially inwardly offset relative to the tightening member manoeuvring portion, the invention ensures that access to the manoeuvring portion is not impeded by the contact piece. In other words, the contact piece can be mounted before the tightening phase. For example, there may be provided several manoeuvring portions arranged substantially on one and the same circle (or annular area) having a larger diameter than the contact portion.

In use, the contact portion of the contact piece can turn inside and against the annular seal; the annular seal and the annular cover can hide the tightening member manoeuvring portion.

According to a second embodiment of the invention, when looking axially towards the differential unit, the manoeuvring portion of the tightening member is located in an area at least partially included in the joint enveloping cylinder—i.e. the smallest cylinder which has its centre on the axis, and which fully contains the joint—and the manoeuvring portion of the tightening member is circumferentially offset from the joint or each portion of the joint. As the manoeuvring portion is located in an area at least partially included in the joint enveloping cylinder, it would not be accessible for being tightened if not circumferentially offset from the joint or each portion of the joint.

The tightening member can comprise at least one plate configured for abutting against the outer ring of the first bearing, the plate being preferably substantially flat, and preferably having a transverse dimension less than the inner diameter of the first bearing. The “transverse dimension” means the dimension in a transverse plane, i.e. a plane orthogonal to the axis. In concrete terms, the plate can be disc-shaped, its transverse dimension then being its diameter.

In other words, the plate is preferably a localized and separate piece. For example, the plate can be disc shaped. It can comprise at least one hole—for example two holes—for receiving a screw or another fastener. There may preferably be provided several distinct plates (for example four plates) regularly arranged around the axis.

The annular cover can comprise at least one aperture substantially axially facing the tightening member, so as to allow access to the manoeuvring portion. For example, the plate can have the same shape and dimensions that the aperture, so that it can be engaged through the aperture.

The annular seal may have an inner diameter that is smaller than the radial dimension of the joint. With such a configuration, the annular seal cannot be removed after the mounting process has been completed. However, a smaller seal is more energy efficient and accepts higher rotational speeds.

The drive shaft can comprise a stepped portion including a transverse face which forms an axial abutment for the first bearing, and a cylindrical face which forms a contact portion with which the annular seal is in contact, the diameter of the cylindrical face being equal or larger than the first bearing inner diameter. Preferably, the outer diameter of the annular seal is smaller than the first bearing outer diameter. The first bearing is thus hidden by the joint, the annular seal and the annular cover.

In use, the contact portion of the drive shaft stepped portion turns inside and against the annular seal.

According to a second aspect, the invention relates to a drive shaft sub assembly for an axle system as previously described, wherein the drive shaft has one end configured to be connected to a vehicle wheel and one end connected to a differential unit of the axle system, the drive shaft including at least one joint connecting two portions of the drive shaft to transmit rotary motion between said portions, the joint having a radial dimension.

According to an embodiment, the drive shaft sub assembly comprises:a first bearing having an inner ring secured around the drive shaft, the outer diameter of the first bearing being smaller than the radial dimension of the joint;a tightening member, such as a nut, having a tightening portion which is configured for abutting against the outer ring of the first bearing and a manoeuvring portion which is radially outwardly offset from the joint, when looking axially towards the differential unit;and a contact piece secured around the drive shaft, having a blocking portion which is configured for abutting against the inner ring of the first bearing, and a contact portion for an annular seal, said contact portion being cylindrical, radially inwardly offset relative to the tightening member manoeuvring portion, and preferably having a diameter larger than the radial dimension of the joint.

Both the tightening member and the contact piece can be located between the first bearing and the joint; a nut can be provided on the side of the ring that is opposite the contact piece, in the axial direction.

According to another embodiment, the drive shaft sub assembly comprises:a first bearing having an inner ring secured around the drive shaft, the outer diameter of the first bearing being smaller than the radial dimension of the joint;an annular cover having a central opening in which the drive shaft is received, an annular seal being mounted between the drive shaft and said central opening, the annular cover being located between the first bearing and the joint and comprising at least one aperture which, when looking axially towards the differential unit, is located in an area at least partially included in the joint enveloping cylinder—i.e. the smallest cylinder which has its centre on the axis, and which fully contains the joint—and can be placed in a circumferentially offset position from the joint or each portion of the joint, the aperture being configured to allow a tightening member to be inserted through it until it abuts against the outer ring of the first bearing.

According to a third aspect, the invention concerns a driven wheel system for a vehicle, comprising an axle system as previously described, at least one left wheel and at least one right wheel, the axle system comprising a left drive shaft connected to the differential unit and to the left wheel(s), and a right drive shaft connected to the differential unit and to the right wheel(s), each wheel being further connected to the differential unit by at least one lower arm articulated at both ends and preferably at least one upper arm articulated at both ends.

According to a fourth aspect, the invention concerns a vehicle comprising at least one driven wheel system as previously described.

According to a fifth aspect, the invention relates to a process for mounting an axle system as previously described, the process comprising the following steps:a) providing a differential unit with a second bearing placed between the first housing and the second housing;b) providing a drive shaft sub-assembly comprising a drive shaft including at least one joint connecting two portions of the drive shaft to transmit rotary motion between said portions, the joint having a radial dimension, the drive shaft sub-assembly further comprising a first bearing having an inner ring secured around the drive shaft, the outer diameter of the first bearing being smaller than the radial dimension of the joint;c) providing a tightening member;d) after steps a), b) and c), engaging the drive shaft sub-assembly in the first housing so that the first bearing is placed between the drive shaft and the first housing, and connecting the drive shaft to the differential unit;e) after step d), tightening the tightening member in order to axially lock the first bearing outer ring relative to the first housing in the mounted position.

Owing to the invention, the drive shaft can be mounted at a late step of the mounting process, which makes said process significantly easier. Indeed, the number of subsequent mounting steps to be performed with the drive shaft already assembled, i.e. to be performed with a heavy and cumbersome system, are limited. The invention thus meets the strong demand to have the drive shaft kept as pre-assembled units (as these drive shafts need to be dynamically equilibrated) without significant negative impact on the mounting process.

According to an embodiment, in step c), the tightening member is provided as a piece mounted on the drive shaft, before the drive shaft sub-assembly is engaged in the first housing.

According to another embodiment, in step c), the tightening member is provided as a separate piece, and in that the tightening member is assembled to the axle system once the drive shaft sub-assembly has been engaged in the first housing. By “separate piece” is meant that the tightening member is not fastened to another piece (of the differential unit or of the drive shaft sub-assembly).

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

As shown inFIG.1, a vehicle1comprises at least one driven wheel system6. In the illustrated embodiment, the vehicle1comprises a first driven rear wheel system6aand a second driven rear wheel system6blocated rearwards from the first driven rear wheel system6a. The vehicle1further includes a front axle4connected to front wheels5.

Although the invention is described for a rear driven wheel system, it can be used in another driven wheel system, especially in a front driven wheel system.

The or each driven wheel system6has an axis12, and comprises a differential unit10, i.e. a unit providing a differential effect, in order to allow the outer drive wheel to rotate faster than the inner drive wheel during a turn.

The driven wheel system6further comprises two drive shafts11, namely a left drive shaft connected to the differential unit10and to at least one left wheel8, and a right drive shaft connected to the differential unit10and to at least one right wheel8. Each rear wheel system6a,6bcan comprise two wheels8on either side, thus forming a dual mounted tires arrangement. However, this should not be considered as limitative.

In the embodiment illustrated inFIG.1, the vehicle1comprises an engine2that drives an input shaft3having an axis13. The differential unit10includes a differential15which is driven by the input shaft3and which transmits the appropriate torque to the left and right drive shafts11. An additional shaft9connects the input shaft3to the differential unit10of the second driven rear wheel system6b, through the differential unit10of the first driven rear wheel system6a, and is the input shaft for the differential unit10of the second driven rear wheel system6b.

Alternatively, as will be described with reference toFIG.9, the invention can be applied to an electric vehicle. Such a vehicle does not include an engine2nor the corresponding driveline, but rather at least one electric motor. Either one motor (or more) is used to drive a corresponding drive shaft11, the drive shafts thus being independently driven by one or more dedicated motors, with the appropriate torque (seeFIG.9); or one motor (or more) is used to drive a mechanical differential rotating the drive shafts11with the appropriate torques (variant not illustrated).

The invention concerns a vehicle1having an independent wheel configuration, as schematically illustrated inFIG.2. In such a configuration, the left wheel(s)8and the right wheel(s)8are each connected to the differential unit10by means of the corresponding driveshaft11, at least one joint110(such as a universal i.e. a cardan joint, or another kind of joint), at least one lower arm14barticulated at both ends, and preferably at least one upper arm14aarticulated at both ends. Although inFIG.2the differential unit10is shown as including a differential15, other implementations are possible.

As shown inFIG.3, the drive shaft11comprises a first end111configured to be connected to the differential unit10and a second end112configured to be connected to a wheel8of the vehicle1. The first end111and the second end112may be provided with splines113or another system providing a rotationally blocked connection with the differential unit10/the wheel8.

The drive shaft11is made of several rigid portions114. In the embodiment illustrated inFIG.3, there are provided a first portion114aconfigured to be connected to the differential unit10, a second portion114bconfigured to be connected to a wheel8, and two intermediate portions114c,114d, which are movable the one into the other along axis12to form a telescopic intermediate piece, in order to adjust the drive shaft length to the suspension stroke. The first portion114ahas an axis115.

As can be seen inFIGS.1to3, the longitudinal direction X is defined as a direction parallel to the axis12of a driven wheel system6, which joins the wheels8when the drive shaft11is in a straight configuration as illustrated inFIG.3. In the operating position, i.e. when the differential unit is mounted under the vehicle1, as shown inFIG.1, the longitudinal direction X corresponds the transverse direction Y′ of the vehicle1. Direction X is substantially horizontal when the vehicle1is on a horizontal surface.

Besides, the transverse direction Y is defined as the direction which is orthogonal to the longitudinal direction X and substantially horizontal when the vehicle1is on a horizontal surface. Direction Y corresponds the longitudinal direction X′ of the vehicle1. The axis13of the input shaft3is roughly parallel to the transverse direction Y, i.e the longitudinal direction X′ of the vehicle1, or inclined relative to the transverse direction Y, horizontally and/or vertically, by preferably less than 5°.

Moreover, direction Z is defined as the vertical direction—when the vehicle1is on a horizontal surface.

The invention will be described when the vehicle1is on a horizontal surface.

Portion114aand portion114d, on the one hand, and portion114band portion114c, on the other hand, are connected by a joint110. In the embodiment illustrated in the figures, each 35 joint110is a universal joint. However, this should not be considered as limitative; any other type of joint which is configured for transmitting rotary motion between said adjacent portions114could be implemented.

The joint110has a radial dimension D, which is defined as the largest dimension of the joint110in a plane (Y,Z). In other word, the radial dimension is the diameter of the smallest cylinder C (called “enveloping cylinder”) which has its centre on the axis12, and which fully contains the joint110, when the drive shaft has a straight configuration.

For example, with a universal joint as illustrated inFIG.3, the joint110comprises two U-shaped pieces116,117each having a median plane, the median planes being orthogonal the one relative to the other. One U-shaped piece116has a radial length D1, i.e. the radial length between the ends of the U; the other U-shaped piece117has a radial length D2which is larger than D1. In this embodiment, the radial dimension D of the joint110is defined along a direction which is inclined relative to the directions along which D1and D2are defined; D is a bit higher than D2.

Reference is now made toFIGS.4ato9which show a first embodiment of the invention.FIG.4amore specifically illustrates an axle system150including a differential unit10and one drive shaft11on both sides of the differential unit10.

One variant of this first embodiment is illustrated inFIGS.4ato8e.

The differential unit10comprises a differential carrier housing20, which can made of a first housing portion20aand a second housing portion20b(also shown inFIG.8d) secured to one another by means of appropriate fasteners (not shown). In another implementation, the differential carrier housing20can made of a single piece.

The differential unit can comprise a differential15—i.e. a mechanical differential.

30 Inside the differential carrier housing20can be located a crown wheel22having a longitudinal axis23. The crown wheel22is driven in rotation around said longitudinal axis23by the input shaft3, by engagement of teeth arranged on a pinion21mounted on said input shaft3and teeth arranged on the crown wheel22.

Inside the crown wheel22is arranged the differential15which comprises differential side pinions16, for example four differential side pinions, which are fitted on a joint cross17attached to the crown wheel22, and two differential side gears18. Each differential side gear18meshes with at least one differential side pinion16and is fastened to the first end111of one of the drive shafts11, i.e. to the first end111of the portion114aof the drive shaft111. In the mounted position, the axis115of said portion114aand the axis23of the crown wheel22are coincident.

The differential unit10further comprises, inside the differential carrier housing20, a differential housing arrangement24which contains the differential15and part of the drive shafts11, more specifically part of the portion114aof each drive shaft11. The differential housing arrangement24is secured to the crown wheel22. It may be made of two parts, namely two differential housings24a,24beach forming a sleeve around the corresponding differential side gears18and partly around the drive shaft11. Said differential housings24a,24bmay be fastened on both sides of the joint cross17; other implementations may however be envisaged.

Thus, on each side of the joint cross17, the differential side gear18is mounted at the first end111of the drive shaft11in a rotationally fixed manner, for example by means of the splines113. Furthermore, both the differential side gear18and the drive shaft11are rotatably mounted relative to the differential housing24a,24baround the longitudinal axis23. The crown wheel22, differential15, and differential housing24are rotating parts inside and with respect to the differential carrier housing20.

In this application, the differential housing24is also referred to as “first housing24”, while the differential carrier housing20is also referred to as “second housing20”.

The differential unit10may further comprise a blocking system25for blocking the differential unit operation, when required.

It has to be noted that, according to an alternative implementation ofFIG.4a, not show, the first housing24and joint cross17could be made to rotate not by a crown wheel driven by the engine2, but by an motor (electric motor, hydraulic motor, etc.). In such a configuration of the vehicle1, the motor output shaft may be mechanically connected to the first housing24and joint cross17by means of a transmission system preferably including a gear system.

The way one drive shaft11, more precisely the portion114aof the drive shaft11, is arranged in the differential unit10will now be described, bearing in mind that the left and right arrangements are structurally identical, while their respective dimensions may be different.

The axle system150comprises a first bearing30which is secured around the drive shaft11, and placed between the drive shaft11and the first housing24. The drive shaft11is thus rotationally received in the first housing24. The first bearing30includes an inner ring31and an outer ring32, as well as rolling elements33which may be balls.

The first bearing inner ring31is rotationally fastened to the drive shaft11and further axially fastened to the drive shaft11. To that end, the first bearing inner ring31may be pushed against a shoulder19of the drive shaft11—forming a radial abutment—by means of an appropriate element such as nut29. The first bearing inner ring31may be in contact with the shoulder19(see for exampleFIG.12d), or an intermediate piece may be provided between the inner ring31and the shoulder19(see for exampleFIG.4b).

The axle system150also comprises a second bearing40which is placed between the first housing24and the second housing20. The second bearing40includes an inner ring41and an outer ring42, as well as rolling elements43which may be tapered rollers.

In a particularly compact non limitative embodiment, the outer diameter D30of the first bearing30is smaller than the inner diameter D41of the second bearing40. Furthermore, the first bearing30and the second bearing40may have median planes P30, P40, respectively, which are orthogonal to the axis23and which are substantially coincident. Thus, the first bearing30and the second bearing40can be arranged coaxially the one inside the other. This significantly improves compactness, specifically in the longitudinal direction X (i.e. the transverse direction Y′ of the vehicle1).

According to the invention, the outer diameter D30of the first bearing30is smaller than the radial dimension D of the joint110. Having a small bearing is advantageous, especially in terms of compactness, but the consequence is that access to the first bearing30is complicated, or even impossible, when the drive shaft11is mounted in the first housing24. As the first bearing30is generally secured around the drive shaft11before the drive shaft11is inserted inside the first housing24, then the first bearing30is necessarily hidden, or hard to access, when it is located in the first housing24. However, the first bearing30has to be maintained axially, without mechanical play, for an efficient and robust implementation of the axle system150.

To solve this problem, there axle system150comprises at least one tightening member50configured to axially lock the first bearing outer ring32relative to the first housing24. Furthermore, said tightening member50comprises at least one manoeuvring portion51which is arranged in an offset relation relative to the joint110, when looking axially towards the differential unit10. As a consequence, the tightening member manoeuvring portion51is visible and accessible despite the joint110, at least during a tightening phase of the mounting process of the axle system150.

For example, the tightening member50can be configured to axially tighten the first bearing outer ring32against a radial wall26of the first housing24. In practice, the first housing24can form substantially a sleeve around axis23, provided with an inwardly projecting rib forming said radial wall26.

In the embodiment shown inFIG.4a, the tightening member50comprises a nut. As best seen inFIG.5, the tightening member50has an axis53. It comprises a tightening portion52, which may be formed as a sleeve coaxial with the drive shaft11in use and which is configured for abutting against the outer ring32of the first bearing30. The tightening portion52may have an outer thread (not shown) for cooperating with an inner thread of the first housing24. The tightening member50also comprises an outer annular flange54. The flange54comprises at least one notch51which opens outwardly and which forms one manoeuvring portion. Preferably, the flange54comprises several notches51regularly circumferentially spaced, forming a crenulated peripheral area A. Alternatively, the notch or notches51could open axially.

As shown inFIG.4b, the peripheral area A including the notches51has at least an outer diameter D51that is larger than the radial dimension D of the joint110, and preferably also an inner diameter that is larger than the radial dimension D of the joint110.

Thus, the notches51—i.e. the manoeuvring portions of the tightening member50—are located in an area A of the tightening member50which is radially outwardly offset from the joint110, when looking axially towards the differential unit10, or at least partially radially outwardly offset. The notches51can therefore receive a tool capable of moving the tightening member50axially relative to the first housing24.

The axle system may comprise a contact piece60secured around the drive shaft11. Said contact piece60forms an intermediate piece between the inner ring31and the shoulder19as previously described.

The contact piece60has a blocking portion61which may be formed as a sleeve coaxial with the drive shaft11, and which is configured for abutting against the inner ring31of the first bearing30. The first bearing inner ring31is therefore tightened between the contact piece blocking portion61and the nut29.

The contact piece60also has a contact portion62such as a cylindrical contact portion coaxial with the drive shaft11. The contact portion62is arranged not to hide, or not to fully hide, the manoeuvring portion(s)51, when looking axially towards the differential unit10, in order to allow access to said manoeuvring portion(s)51, for tightening the first bearing outer ring32against the first housing24. For that purpose, the contact portion62preferably has an outer diameter D62that is less than the outer diameter D51of the tightening member peripheral area A. The contact portion62can be fully radially inwardly offset relative to the tightening member manoeuvring portion51, or only partially offset, i.e. partly facing the peripheral area A along the longitudinal direction X, as shown inFIG.4b.

In the mounted position, the axle system150also comprises an annular cover70having a central opening71for receiving the drive shaft11. The annular cover70is removably fastened to the second housing20by means of appropriate fasteners73(seeFIGS.4aand8e).

An annular seal72is mounted in the central opening71of the annular cover70and is in contact with the contact portion62of the contact piece60. In other words, the annular seal72is arranged between the contact piece60—secured to the drive shaft11—and the annular cover70—secured to the second housing20. In this embodiment, the annular seal72can have an inner diameter (i.e. where the contact with the opposite piece occurs) that is larger than the radial dimension D of the joint110(in other words, D62>D). This makes it possible to change the annular seal72when needed, for maintenance operations during the service life of the axle system150, without requiring the drive shaft11to be removed from the differential unit10. This also avoids damaging the annular seal72when the drive shaft11is mounted.

A mounting process of the axle system will now be described, with reference toFIGS.8ato8e.

As shown inFIG.8a, the differential unit10is prepared, with the differential15, the first housing24, the second bearings40(on either side of the joint cross17), and possibly the blocking system25. Then, as shown inFIG.8b, the assembly ofFIG.8ais inserted in the second housing20. Differential nuts44are tightened to set the bevel set backlash and the preload of the second bearings40.

Two drive shaft sub-assemblies160are also prepared.

A shown inFIG.8c, one drive shaft sub-assembly160comprises a drive shaft11including at least one joint110between the first portion114aconfigured to be connected to the differential unit10and an intermediate portion114d. The drive shaft sub-assembly160also includes:the contact piece60secured around the drive shaft11, more specifically around the drive shaft first portion114a;the first bearing30, with its inner ring31secured around the drive shaft11and axially tightened by the nut29against the contact piece blocking portion61which itself is abutting against the shoulder19of the drive shaft11;the tightening member50, mounted on the drive shaft11and axially located between the first bearing outer ring32and the contact piece60. Advantageously, there may be provided a member for preventing a radial movement of the tightening member50as long as the assembling process has not been completed. This member can be a centring collar (not shown) protruding from the contact piece60towards the first bearing30and configured to be in contact with the inner face of the tightening portion52of the tightening member50.

Then the annular seal72is mounted in the central opening71of the annular cover70, for both covers70. This step is not illustrated.

The drive shaft sub-assembly160is then engaged in the assembly illustrated inFIG.8b, in the first housing24, in order to connect the drive shaft11to the differential unit10, i.e. to insert the end of the drive shaft first portion114ainto the corresponding differential side gear18and to rotationally link the first portion114aand the differential side gear18. The first bearing30is thus placed between the drive shaft11and the first housing24, as illustrated inFIG.4a.

At this stage of the mounting process, the axle system150is as illustrated inFIGS.6and8d. It can be seen that the first bearing30is not visible, because of its small diameter D30. On the contrary, the tightening member50is not fully hidden, as its manoeuvring portion(s)51are radially located outward from the contact piece60and the joint110, and inward from the differential nut44. The manoeuvring portion(s)51being visible and accessible by an operator, the tightening member50can thus be operated, during a tightening phase of the axle system mounting process. In practice, a tool can be introduced in the notches51in order to rigidly secure (i.e. without play) the first bearing outer ring32relative to the first housing24.

The tightening member50is thus a partly external piece—at least during the tightening phase—which makes it possible to ensure tightening while the drive shaft11has already been mounted.

Once the first bearing30has been properly axially locked, the annular cover70equipped with the annular seal72can be mounted, by being engaged around the drive shaft11(on both sides of the second housing20). In the mounted position, illustrated inFIGS.8e,74aand4b, the annular seal72is in contact with the outer face of the contact piece contact portion62, and the annular cover70is fastened to the second housing20by the fasteners73.

InFIG.7, the annular cover70is represented as a transparent piece, only its edge being illustrated with a dotted line. It can thus be seen that the tightening member manoeuvring portions51are not visible any more, as they are hidden by the annular seal72, when looking axially towards the differential unit10.

The annular cover70may comprise at least one pin (not shown) protruding axially towards the differential15and configured to engage the differential nut44, preferably the inner part thereof, to prevent rotation i.e. untightening of said differential nut44.

A variant of the first embodiment is illustrated inFIG.9.

In this variant, there is not provided a mechanical differential. Rather, the differential effect is achieved by the fact that the wheels are driven independently by a dedicated motor and corresponding transmission system, in a so-called torque vectoring technology. InFIG.9, the motor is electric, however, other kinds of motors could be envisaged, such as a hydraulic motor.

The driven wheel system6comprises one powertrain module170for rotating one drive shaft11and another powertrain module170for rotating the other drive shaft11. One powertrain module170comprises a casing171and a powertrain system which is configured to drive the drive shaft11, and which comprises:at least one motor175having an output shaft176;a transmission system between the motor175and the drive shaft11, which is housed in the casing171.

In an embodiment, the transmission system may comprise a first epicyclic gear train100having a first axis A100, and a second epicyclic gear train200having a second axis A200which is parallel to the first axis A100. In the operating position, i.e. when the powertrain module170is mounted on the vehicle1, the axes A100and A200are parallel to direction Y′. In a variant, the first epicyclic gear train100may be omitted and replaced by a more conventional parallel gear train reduction arrangement.

The first epicyclic gear train100can comprise:a sun101connected to the motor output shaft176and arranged as an inner component of the first epicyclic gear train100;a ring102arranged as an outer component of the first epicyclic gear train100;a planet carrier103fixedly secured to the casing171, or made as a single piece with the casing171;

planet gears104(for example four planet gears) arranged between the sun101and the ring102. The planet gears104are rotationally mounted on the planet carrier103.

The second epicyclic gear train200can comprise:a sun201fixedly secured to a hub205that meshes with the ring102of first epicyclic gear train100. The sun201is arranged as an inner component of the second epicyclic gear train200;a ring202arranged as an outer component of the second epicyclic gear train200;a planet carrier203which rotates the drive shaft11;planet gears204(for example four planet gears) arranged between the sun201and the ring202. The planet gears204are rotationally mounted on the planet carrier203.

A first bearing30is mounted between the drive shaft11and the casing171, while a second bearing40is mounted between the casing171and the hub205. A tightening member50having an accessible manoeuvring portion51, at least during a tightening phase of the mounting process, is provided to axially lock the first bearing outer ring32relative to the casing171.

Reference is now made toFIGS.10to12dwhich show a second embodiment of the invention.

The axle system150may be devoid of a contact piece60as previously described. Rather, the drive shaft11—more specifically the first portion114a—may comprise a stepped portion including a transverse face or shoulder19which forms an axial abutment for the first bearing30and a cylindrical face which forms a contact portion63with which the annular seal72is in contact in use.

The diameter of the cylindrical face63can be less than the radial dimension D of the joint110, which means that the annular seal72has an inner diameter that is smaller than the radial dimension D of the joint110. Besides, the diameter of the cylindrical face63is preferably larger than the first bearing inner diameter.

The mounting process of the axle system will now be described.

35 Two drive shaft sub-assemblies160are prepared as shown inFIG.10.

One drive shaft sub-assembly160comprises a drive shaft11including at least one joint110between the first portion114aconfigured to be connected to the differential unit10and an intermediate portion114d. The drive shaft sub-assembly160also includes:the first bearing30, with its inner ring31secured around the drive shaft11and axially tightened by the nut29against the shoulder19of the stepped portion of the drive shaft11;the annular cover70, the drive shaft11being received in the central opening71, and the annular seal72being mounted between the drive shaft11and said central opening71. The annular cover70is thus mounted around the drive shaft11, and is located between the first bearing30and the joint110.

A bearing rotation lock35can further be provided on the side of the first bearing30that is opposite the annular cover70, i.e. towards the inside of the differential unit10.

The annular cover70comprises at least one aperture74(seeFIG.11), preferably several apertures74arranged substantially on one and the same circle around axis115. When looking axially towards the differential unit10, the apertures74are located in an area A74which is at least partially included in the joint enveloping cylinder C. However, the annular cover70is placed or can be placed around the drive shaft11so that the apertures74are in a circumferentially offset position from the joint110, i.e. in a circumferentially offset position from both U-shaped pieces116,117.

The differential unit10is also prepared, with the differential15, the first housing24, the second bearings40(on either side of the joint cross17), and possibly the blocking system25.

Then, as shown inFIG.12a, the drive shaft sub-assembly160ofFIG.11is inserted in the differential unit10,

The drive shaft sub-assembly160is then engaged in the assembly illustrated inFIG.8b, in the first housing24, in order to connect the drive shaft11to the differential unit10, i.e. to insert the end of the drive shaft first portion114ainto the corresponding differential side gear18and to rotationally link the first portion114aand the differential side gear18. The first bearing30is thus placed between the drive shaft11and the first housing24.

The engagement of the drive shaft11can continue until the first bearing30abuts against the first housing24, as illustrated inFIG.12b.

Then, the tightening phase of the first bearing outer ring32can be carried out, in order to axially lock the first bearing outer ring32relative to the first housing24. To that end, in this embodiment, there are provided at least one tightening member50as a separate piece.

One tightening member50may comprise a plate configured for abutting against the outer ring32of the first bearing30. The plate can be substantially flat. It is designed to be inserted through one aperture74of the annular cover70, and therefore is dimensioned appropriately. Each plate50comprises at least one hole, and preferably at least two holes, which form a manoeuvring portion51of the tightening member50, as a tool can be engaged in the hole51to move the plate50axially relative to the first housing24.

There are preferably provided several tightening members50, preferably one for each aperture74.

In other words, in this embodiment, the tightening members50are arranged substantially on one and the same circle. Moreover, when looking axially towards the differential unit10, the manoeuvring portions51are located in an area A74at least partially included in the joint enveloping cylinder C but are circumferentially offset from the U-shaped pieces116,117of the joint110.

Then one tightening member, i.e. one plate50, is inserted through several or each aperture74, until it abuts against the outer ring32of the first bearing30, as shown inFIG.12b. The aperture74axially facing the tightening member50, it allows access to the holes51, i.e. the manoeuvring portions. The bearing30can thus be properly axially locked.

30 The annular cover70can then be removably plugged or fastened to the second housing20, by means of the fasteners73. The annular seal72is thus arranged between the drive shaft11and the annular cover70secured to the second housing20.

Although this second embodiment has been described with a mechanical differential, it35could be implemented with a torque vectoring solution.

The invention applies to vehicles having an independent wheel suspension arrangement in which, for mechanical strength reasons, for providing enough space to allow operational movements of the components, and for improving fuel efficiency, the drive shafts must have a minimum length that may not be easily compatible with the legal constraints, namely the regulatory maximum transverse length of the vehicle.

In this context, the invention gives a solution for providing an axle system which offers both stronger support for the drive shafts, because of the first and second bearings, and robustness, as axial blocking is achieved without play which avoid relative movements and resulting components wear.

Moreover, the mutual arrangement of the bearings offers the required compactness, especially in the transverse direction of the vehicle.

Besides, the invention allows easing maintenance on the drive shafts, which can be disassembled without disassembling the differential (as disassembling the drive shafts occurs at an early stage of the disassembling process), and also easing maintenance on the seal, as it can be quickly changed, at least in the first embodiment.

The invention advantages are all the more significant as independent wheel suspension configuration is a key solution to develop an optimized electrified driveline, which is a promising development in transportation industry.