Patent Description:
Gear assemblies are known from documents: <CIT>, <CIT> or <CIT>.

In some applications, the dimensions of a single plate clutch are too great and there is a need for a more compact clutch for transferring the required torque. This can be obtained by multiple-plate clutches, which allows for smaller diameters with a maintained total friction force. Multiple-plate clutches is a well-established technology. In road vehicles, they are typically found in motorcycles and high-performance cars. Multiple-plate clutches have several driving members interleaved with several driven members, typically collected in a clutch pack. There is a need to further reduce the dimensions of clutches, or at least to maintain current dimensions, with improved efficiency.

The friction elements, or driving and driven members, of a dry clutch are not subjected to a cooling lubricating liquid and rely on mechanical friction to engage. In a wet clutch, the friction elements are typically immersed in a cooling and lubricating liquid allowing for a smoother performance and longer life.

In some applications, the viscous drag in the clutch pack of a wet clutch that is unengaged for a prolonged period may result in efficiency losses. Such wet clutches are typically designed such that they are disengaged when not activated and engaged when actively activated. Thus, there is a need for a multiple-plate wet clutch that reduces the viscous drag when the clutch is disengaged.

The clutch basket of a multi-plate wet clutch can be attached to a gear wheel centered on the same shaft. The gear wheel, and in extension the clutch basket, are rotationally supported relative to the shaft, for example by rolling-element bearings. When the wet clutch is engaged and torque is transferred to the gear wheel, the gear wheel may be subjected to, or generate, an axial load in the direction of the wet clutch, which can put a strain on the bearings and cause an axial shift of the gear wheel.

It is an object of the present invention to improve the efficiency and reduce the overall dimensions of multiple-plate wet clutches. It is a further object to improve the axial stability of gear assembly that includes a wet clutch and a gear wheel.

In a first aspect of the present invention, a gear assembly for mounting on a shaft is provided. The gear assembly comprises: a gear wheel, or cog wheel, configured to be rotationally supported with respect to the shaft and a multiple-plate wet clutch. The wet clutch comprises: a clutch hub configured to be mounted on the shaft, a front part, or collar, configured to be fixed relative to, or mounted on, the shaft, a back part, or radially extending flange, configured to be fixed relative to, or mounted on, the shaft, a clutch basket attached to, or mounted on, the gear wheel and a clutch pack operationally connecting the clutch hub and the clutch basket, wherein the clutch pack is positioned between the front part and the back part. The wet clutch further comprises: an actuator supported by the front part and configured to engage the clutch pack and press the clutch pack against the back part. The clutch pack has: an unengaged state in which the clutch hub and the clutch basket are unlocked, and an engaged state in which the clutch hub and the clutch basket are locked together. Additionally, the back part is spaced apart from the gear wheel in the unengaged state, and the back part engages, or contacts, the gear wheel in the engaged state, or the gear assembly is configured such that the back part engages, or contacts, the gear wheel in the engaged state.

In a second aspect of the present invention, a shaft assembly is provided that comprises: a shaft, and a gear assembly according to the first aspect of the proposed technology that is mounted on the shaft.

The gear assembly and the shaft assembly may be for used in a gearbox of a road vehicle. In a third aspect of the proposed technology, a gearbox is provided that comprises the shaft assembly according to the second aspect of the invention.

It is understood that the wet clutch is configured to be mounted on the shaft. The clutch basket being attached to the gear wheel and the gear wheel being rotationally supported with respect to the shaft means that the clutch basket is also rotationally supported with respect to the shaft. It is understood that the clutch basket is rotationally fixed relative to the gear wheel. It is further understood that the clutch hub and the clutch basket can spin at different speeds when they are unlocked in the unengaged state, and that they spin at the same speed when they are locked together in the engaged state. It is understood that the gear wheel and the back part extend radially relative to the shaft, and that the shaft may define a rotational axis.

The back part may be positioned, or at least partly positioned, between the clutch pack and the gear wheel. The back part being spaced apart from the gear wheel in the unengaged state is understood to encompass the back part and the gear wheel being separated and forming a gap between them. The gap may be less than <NUM>, less than <NUM>, or less than <NUM>. The back part engaging the gear wheel in the engaged state is understood to encompass the back part and the gear wheel contacting, or pressing against, one another.

The gear assembly, and in extension the gear wheel and the wet clutch, may form a through-going hole for receiving the shaft. In the shaft assembly, the shaft may pass through the complete gear assembly. This means that the shaft passes through the wet clutch and the gear wheel, and in extension through the clutch hub, the front part, the back part, the clutch basket, and the clutch pack. The front part may be juxtaposed, or attached, to the clutch hub. Similarly, the back part may be juxtaposed, or attached, to the clutch hub. The clutch hub and the clutch basket may be concentric relative to the shaft. Similarly, the front part, the rear part, the actuator, and the gear wheel may be concentric relative to the shaft.

The back part and the gear wheel engaging one another has the effect that the gear wheel is prevented from shifting axially along the shaft towards the front part. The clutch basket will be stabilized and supported in one direction along the shaft in the engaged state. This will relieve any bearing that supports the clutch basket from axial loads along the shaft, which is particularly important at high axial loads and high rotational velocities.

The gear wheel may be a monolithic structure. Alternatively, it may be a composite structure composed of a plurality of parts. The back part may be a monolithic structure. The monolithic gear wheel and the monolithic back part may be of steel.

When going from the unengaged state to the engaged state, the back part and gear wheel may engage one another after reaching the engaged state. When going from the unengaged state, the clutch basket may reach the engaged state at a first force generated by the actuator, and the back part and the gear wheel may engage one another at a second force generated by the actuator that is greater than the first force. Here, it is understood that the state of the clutch pack transitions from unengaged to engaged at an increase in the force supplied by the actuator.

When going from the engaged state to the unengaged state, the back part and gear wheel may disengage from one another before reaching the unengaged state. When going from the engaged state, the clutch basket may reach the unengaged state at a third force generated by the actuator, and the back part and the gear wheel may disengage from one another at a fourth force generated by the actuator that is greater than the third force. Here, it is understood that the state of the clutch pack transitions from engaged to unengaged at a decrease in the force supplied by the actuator.

The back part may be configured to elastically deform and engage the gear wheel when the clutch pack is in the engaged state. Here, it is understood that the deformation is caused by the clutch pack being pressed against the back part by actuator. The deforming of the back part may encompass the back part bending, or a portion of the back part shifting towards the gear wheel. For example, it may be a radially outer portion of the back part that shifts towards the gear wheel.

In the engaged state, the gear wheel may generate, or be subjected to, an axial load, or axial thrust, along the shaft, at a meshing with a cooperating gear wheel. For example, this may be at a transfer of torque to the cooperating gear wheel. The gear wheel may be a helical gear wheel, which can give a corresponding axial load. The direction of the axial load typically depends on the rotational direction of a helical gear wheel.

The axial load may push the gear wheel in the direction of, or towards, the back part, whereby the back part engages (or contacts) the gear wheel, or the load pushes the gear wheel and the back part into contact, or engagement. It is understood that the torque transferred to the cooperating wheel is in a direction resulting in the axial load being towards the back part. The back part is fixed relative to the shaft, which prevents any further axial shifts and reduces axial loads on any bearings supporting the gear wheel.

The back part may have, or form, a first contact area, or first contact surface, facing the gear wheel, and the gear wheel may have, or form, a second contact area, or second contact surface, facing the first contact area, wherein the first contact area engages the second contact area in the engaged state.

The first contact area and the second contact area may be separated in the unengaged state. They may also form, or define, the gap between the back part and the gear wheel in the unengaged state. The first contact area may be flush, or mate, or cooperate, with the second contact area in the engaged state. The first contact area may also conform to the second contact area in the unengaged state with a gap between the two areas. It is understood that the contact areas can have a high aspect ratio. For example, each of the first contact area and the second contact may be an annular disc with a narrow width, that is with inner and outer edges that are circular, concentric, and separated by a width that is less than <NUM> % of the radius of the inner edge, such as less than <NUM> % or less than <NUM>%.

The first contact area and the second contact area may have a planar geometry at a right angle to the shaft, or to the axis of rotation. They may be concentric relative to the shaft.

Additionally, or alternatively, the first contact area may define a male contact and the second contact area may define a cooperating female contact. The first contact area and the second contact area may have a frustoconical geometry concentric with, or rotationally symmetric relative to, the shaft, or to the axis of rotation. This may be in addition to the above-mentioned planar geometry. The wide end of the frustoconical geometry may be in the direction of, or face, the front part, and the narrow end of the frustoconical geometry may be in the direction away from, or face away from the front part. Additionally, or alternatively, the first contact area and the second contact area may have a curved, or smoothly curved, geometry concentric. The geometry may be rotationally symmetric with respect to, the shaft, or to the axis of rotation.

The first contact area and the second contact area may have a first and a second contact surface, respectively, that are smooth. This reduces friction between the back part and the gearwheel.

The back part may comprise a plate-like portion, or structure, extending radially with respect to the clutch hub, or the shaft. The plate-like portion may be a flange or disc-like. It may be concentric relative to the shaft. The actuator may press the clutch pack against the plate-like portion in the engaged state, and the plate-like portions of the back part may engage the gear wheel in the engaged state. The first contact area may be located on the plate-like portion. The plate-like portion, or the complete pressure plate, may have planar geometry.

The back part may have one or more axially through-going holes or openings. Additionally, or alternatively, it may have one or more cutouts. The cutouts may be at the radially outer edge of the back part. The holes or cutouts may be located on the plate-like portion of the back part This allows for a greater flexibility of the back part in a direction along the shaft and a greater deformation for a given force generated by the actuator.

The clutch basket may comprise, or be composed of, a cylindrical portion that is attached to the gear wheel. Alternatively, the clutch basket may comprise, or be composed of, a radial portion and a cylindric portion, wherein the radial portion is located at, or attached to, the gear wheel. The back part and the cylindrical portion may be separated in the engaged state. This means that there will be no wear on the clutch basket during operation. It is understood that the radial portion extends radially relative to the shaft. The cylindrical portion may connect to and extend from the radial portion in the direction of the front part. It is understood that the radial portion and the cylindrical portion are concentric relative to the shaft.

The clutch pack may comprise a plurality of inner plates attached, or connected, to the clutch hub and a plurality of outer plates attached to, or connected to, the clutch basket. It is understood that the clutch pack is a multiple-plate clutch pack with the inner and outer plates stacked to form the clutch pack. For example, the inner plates may be driving plates and the outer plats may be driven plates.

The outer plates may be attached, or connected, to the cylindrical portion of the clutch basket. It is understood that the plates are slidably attached allowing for an axial shift in position. This way, the inner plates and the outer plates can be separated in the unengaged state and pressed together in the engaged state.

The back part may have an outer edge. The first contact area of the back part may be radially separated from the outer edge. The radial portion of the clutch basket may have an inner edge that is closer to the shaft than the outer edge of the back part. This means that the outer edge of the back part may be at a first radius relative to the shaft, and the inner edge of the radial portion may be at a second radius relative to the shaft that is smaller than the first radius.

The back part may comprise, or be composed of, an inner portion and an outer portion. The inner portion may be rotationally symmetric relative to the shaft. Similarly, the outer portion may be rotationally symmetric relative to the shaft. It is understood that the inner portion is located closer to the shaft than the outer portion. It is further understood that the inner portion and the outer portion are connected or juxtaposed.

The back part may further have, or form, a support area facing the clutch pack, wherein the clutch pack is pressed against, or engages, the support area, in the engaged state. It is understood that the support area extends radially relative to the shaft. The complete support area may be positioned on the outer portion of the back part. Alternatively, the support area may in part be positioned on the outer portion of the back part and in part positioned on the inner portion of the back part.

In one alternative, the outer portion may engage the gear wheel in the engaged state. The first contact area may be positioned on, or formed by, the outer portion. Here, it is understood that the inner portion is separated from the gear wheel, or the radial portion of the clutch basket, in the engaged state, which means that it does not engage the gear wheel.

In another alternative, the inner portion may engage the gear wheel in the engaged state. The first contact area may be positioned on, or formed by, the inner portion. It is understood that the outer portion is separated from the gear wheel, or the radial portion of the clutch basket, in the engaged state. Thus, it does not engage the gear wheel.

The clutch pack may further have: a slipping state in which the clutch hub and the clutch basket are partly locked together and can spin at different speeds, wherein the clutch pack changes from the unengaged state to the engaged state via the slipping state at an axial compression, or compression along the shaft, of the clutch pack. In the slipping state, torque may be transferred between the inner plates and the outer plates by kinetic friction between the two types of plates. This means that there is a slipping mechanical coupling between the clutch hub and the clutch basket. In the engaged state, the torque may instead be transferred by static friction. This means that there is a non-slipping mechanical coupling between the clutch hub and the clutch basket. In the unengaged state, no torque is mechanically transferred there between. A torque transfer caused only by a fluid coupling of the coolant is not considered a mechanical torque transfer in this context.

The gear assembly may further comprise: a first rolling bearing, or first rolling-element bearing, rotationally supporting the gear wheel relative to the shaft. Additionally, the gear assembly may further comprise: a second rolling bearing, or second rolling-element bearing, rotationally supporting the gear wheel relative to the shaft. The first rolling bearing and the second rolling bearing may be juxtaposed.

The shaft may comprise an internal shaft conduit for a lubricant. It is understood that the lubricant also can have the function of a coolant. The gear assembly may further comprise: a bearing conduit configured to operationally connect to the internal shaft conduit and to release the lubricant at the first rolling bearing and/or at the second rolling bearing. It may be configured to release the lubricant between the first rolling bearing and the second rolling bearing. In the shaft assembly, the bearing conduit is instead operationally connected to the internal shaft conduit.

For example, the shaft may be hollow and form a cylindrical tube with an inside constituting the internal shaft conduit. The tube may further have an aperture, or form a hole, through which the lubricant can pass. The bearing conduit may have an inlet connected to the aperture and an outlet from which the lubricant is released. The outlet may be positioned between the first rolling bearing and the second rolling bearing.

It is understood that the rolling bearings are concentric relative to the shaft. The rolling bearings may be radial rolling bearings. More specifically, the rolling bearings may be angular contact ball bearings. They may be positioned in a back-to-back configuration. The radial rolling bearings may define an axial rest position along the shaft for the gear wheel. It is understood that the rest position is the position without any axial load on the gear wheel. The rolling bearings may allow for an axial shift, or a shift along the shaft, of the gear wheel, for example in the direction of, or towards, the back part. The axial shift may be in the engaged state. Additionally, or alternatively, the axial shift may be greater than the gap between the back part and the gear wheel in the unengaged state.

Each of the first rolling bearing and the second rolling bearing may comprise an inner race, an outer race, and a plurality of rolling-elements, such as balls. It is understood that the rolling elements are positioned between the inner race and the outer race. The outer race may be attached, or fixed, to the gear wheel. It may form part of the gear wheel.

The inner race may be attached, or fixed, to the shaft. Alternatively, the gear assembly may further comprise: a radial spacer configured to be fixed to, or mounted on, the shaft. In this alternative, the inner race is attached, or fixed, to the radial spacer. The abovementioned axial rest position may be defined by the relative rest positions of the inner race and outer race, at no, or small axial loads. The radial spacer has the effect of a greater radius of the rolling bearing, which allows for greater radial loads on the gear assembly. Additionally, it reduces the mass that rotates relative to the shaft, which allows for a faster response when engaging the wet clutch.

The inner race of the first rolling bearing may contact, be fixed relative to, or be preloaded by the wet clutch, or by the back part of the wet clutch. Here, it is understood that the inner race of the first rolling bearing and the wet clutch are juxtaposed. The inner races of the first rolling bearing and the second rolling bearing may be separated by an axial spacer. The axial spacer may fix, or preload, the inner race of the second rolling bearing relative to the inner race of the first rolling bearing.

The bearing conduit may, at least in part, be formed by the inner races of the first rolling bearing and the second rolling bearing. For example, the inner races may be separated to allow the lubricant to pass between them. Additionally, the bearing conduit may, at least in part, be formed by the radial spacer.

The gear wheel may have a central through bore, or hole, with a rotationally symmetric inner wall through which the shaft can pass, or passes, in the case of the shaft assembly. The outer race may conform to, or be attached to, the inner wall of the through bore. The radial spacer may have a ring-shaped body. The body may be hollow or partly hollowed. The radial spacer may be attached to, or mounted on, the clutch hub. The clutch hub in turn may be configured to be mounted on and rigidly attached directly to the shaft. This way, the radial spacer is configured to be rotationally fixed relative to the shaft.

The wet clutch may further comprise: a plurality of individual clutch conduits, wherein each clutch conduit has a collar portion formed by the collar and a hub portion formed by the clutch hub. The collar portion has an inlet for receiving the coolant, and the hub portion is coupled to the collar portion and has one or more outlets at the clutch pack for releasing the coolant. The wet clutch may further comprise: a plurality of valves, wherein each valve is operationally connected to a single clutch conduit configured to control the flow of coolant through the clutch conduit. Additionally, the actuator may be configured to simultaneously engage the clutch pack and operate the plurality of valves.

The plurality of clutch conduits allows for a compact construction of the wet clutch. Additionally, the fact that the actuator engages the clutch pack and operates the plurality of valves means that it controls both the operation, or engagement and disengagement, and the cooling of the clutch pack. This joint function also allows for a more compact construction.

The front part may be ring-shaped, and the front part being fixed relative to the shaft and the actuator being supported by the front part allows for a more compact construction, for example in comparison with a wet clutch having the actuator supported by an enclosing housing or casing. The proposed technology also allows for a supply of coolant where it has the greatest effect, which is at the inside of the clutch packs.

The actuator may be a single actuator. This means that there is only one actuator operating the clutch pack and the plurality of valves. The fact that a single actuator can provide this function further contributes to a more compact construction.

The clutch hub may be configured to be rigidly attached directly to the shaft, for example by way of splines. The front part may be rigidly attached to the clutch hub, for example by way of bolts. Alternatively, it may be rigidly attached directly to the shaft. This way, the clutch hub and the front part may be rotationally and axially, or lengthwise, fixed relative to the shaft. When the wet clutch is installed, the fact that the clutch hub and the front part are rotationally and axially fixed relative to the shaft means that they cannot rotate relative to the shaft and cannot shift lengthwise relative to the shaft.

That the gear wheel and in extension the clutch basket are rotationally supported with respect to the shaft, means that they can rotate relative to the shaft, provided that they is not prevented from rotating by the clutch pack.

The clutch hub may constitute a unitary body manufactured from a single piece of material. Similarly, the front part may constitute a unitary body manufactured from a single piece of material. The clutch hub may form a through hole for receiving the shaft. Similarly, the front part, rear part, and gear wheel may form a through hole for receiving the shaft.

The lubricant, or coolant, may be a liquid. The lubricant may be oil-based.

The actuator may be configured to engage the clutch pack when activated. This means that the wet clutch must be actively engaged or locked. When the actuator is deactivated, the clutch pack, and in extension the wet clutch, is disengaged or open.

The plurality of individual clutch conduits may comprise ten or more clutch conduits. The hub portion of each clutch conduit may be elongated and aligned with the shaft or extend in parallel with the shaft. Each hub portion may have a cylindrical portion, which means that the portion is shaped like a cylinder. It may have a circular cross-section. The cylindrical portion may have an axis that is parallel to the shaft, or to the axis of the shaft. The cylindrical portions of all hub portions may have parallel cylinder axes. The features specified here enable a compact conduit arrangement, which in turn allows for a more compact wet clutch.

The through hole of the front part may have has a circumferential inner wall portion facing the shaft, and the front part forms a circumferential groove, or channel, in the inner wall portion for receiving the coolant from the internal shaft conduit, wherein the inlet of the front part portion of each clutch conduit connects to the groove. For example, the internal shaft conduit may have an outlet and when the wet clutch is installed, the circumferential groove may be located at and in fluid communication with the outlet. For example, if the shaft is a cylindrical tube with an inside constituting the internal shaft conduit, the single outlet may be an aperture, or hole, in the tube. The inner wall portion facing the shaft may be configured to be flush with the shaft and prevent coolant from leaking between the front part and the shaft.

The front part portions of the clutch conduits may be evenly distributed around the shaft. Similarly, the hub portions of the clutch conduits may be evenly distributed around the shaft. The distribution around the shaft is understood to be an angular distribution with respect to the rotational axis of the shaft. For example, if there are <NUM> front part portions, there is a <NUM>-degree separation with respect to the rotational axis of the shaft between the centers of neighboring front part portions.

The plurality of clutch conduits and the groove may form part of, or constitute, a conduit arrangement configured to operationally connect the shaft conduit to the outlets and to allow a flow of coolant there between. The conduit arrangement then constitutes a manifold distributing the coolant. Each clutch conduit may be configured to operationally connect to the internal shaft conduit for receiving a lubricant, or coolant, therefrom. In the shaft assembly, each clutch conduit is instead operationally connected to the internal shaft conduit.

Each clutch conduit, or hub portion, may have a plurality of outlets that are distributed axially with respect to the clutch hub. In extension, this means that outlets are distributed axially with respect to the shaft. Alternatively, each clutch conduit, or hub portion, may have a single outlet that is elongated and extends axially with respect to the clutch hub. This allows for an axial distribution of the coolant, which in turn allows for clutch packs with a greater number of plates and a reduced diameter, thus contributing to a more efficient and compact wet clutch.

The clutch hub and the clutch pack may form, or be connected by, a spline joint, wherein the spline joint comprises a plurality of axially extending ridges and grooves in the clutch hub. The one or more outlets of each clutch conduit may then be located at the bottom of a single groove. In an alternative wording, the spline joint may comprise a plurality of male splines in the clutch hub, and the one or more outlets of each clutch conduit may be located between two neighboring male splines. The number of ridges or male splines may be an integer multiple of the number of clutch conduits. For example, the number of clutch conduits may be fifteen and the number of male splines may be forty-five, corresponding to an integer multiple of three. The plurality of axially extending ridges and grooves may form a male spline cooperating with a female spline formed by the clutch pack.

The clutch pack may be concentric with respect to the clutch hub, and in extension with respect to the shaft. The clutch basket may be concentric with respect to the clutch pack, and in extension with respect to the clutch hub. The clutch pack may have an annular shape and extend both radially and axially with respect to the clutch hub, and in extension with respect to the shaft.

The inner plates can move axially relative to the clutch hub and are rotationally, or angularly, fixed relative to the clutch hub, and the outer plates can move axially relative to the clutch basket and are rotationally, or angularly, fixed relative to the clutch basket. This means that the clutch hub constitutes an inner plate carrier, and the clutch basket constitutes an outer plate carrier.

The inner and outer plates may be positioned alternately in the clutch pack. In the unengaged state there is no mechanical friction between the inner plates and the outer plates, in the slipping state there is a kinetic friction between the inner plates and the outer plates, and in the engaged state there is a static friction between the inner plates and the outer plates.

The actuator may be configured to compress the clutch pack axially. The clutch pack may change from the unengaged state (a) to the engaged state (c), via the slipping state (b), when it is compressed axially.

The clutch pack may form a plurality radially extending channels for the coolant between the inner and outer plates, or through the clutch pack, when the clutch pack is in its engaged state. The channels may be formed in the inner plates and define a square or rectangular grid pattern. The radially extending channels contribute to an efficient cooling of the clutch pack.

The clutch hub may have a plurality of male splines and each of the plurality of inner plates may have a plurality of female splines cooperating with the plurality of male splines of the clutch hub. The clutch basket may have a plurality of female splines and each of the plurality of outer plates may have a plurality of male splines cooperating with the plurality of female splines of the clutch basket.

The valve may: (i) prevent, or limit, the flow of coolant when the clutch pack is in its unengaged state, (ii) allow the flow of coolant when the clutch pack is in its slipping state, and (iii) allow the flow of coolant when the clutch pack is in its engaged state. The flow of coolant may be greater when the clutch pack is in its engaged state than when it is in its slipping state. For example, the flow in the slipping state may be in the range <NUM>% to <NUM>%, or <NUM>% to <NUM>% of the flow in the engaged state.

The wet clutch may further comprise an annular pressure plate concentric relative to the shaft and positioned between the actuator and the clutch pack, and the pressure plate may be configured to engage the clutch pack. The pressure plate may form part of each valve. It is understood that the position of the pressure plate can shift axially, or along the shaft. The pressure plate may be planar or have planar geometry. For each valve, the front part may form a valve seat at the coupling, or connection, between the hub portion and the front part portion of the clutch conduit to which the valve is connected. The seat may be a hard seat that is integral with the front part. This means that there is no elastomer gasket providing the sealing. The pressure plate may be disk-shaped and/or have rotational symmetry with respect to the shaft. It may have a central hole and the pressure plate may have, or form, a plurality of protrusions, or lugs, each extending radially inwards in the central hole, or with respect to the central hole. Each protrusion of the pressure plate may constitute a valve member, or valve disc, of a single valve of the plurality of valves. The protrusion may contact, or seal against, the valve seat of the valve when the wet clutch is in its unengaged state. In its engaged state, the wet clutch may present a gap between the protrusion and the valve seat, thus allowing a flow of the lubricant past the protrusions and into the hub portions.

The pressure plate may form part of or be integral with the actuator. In the slipping state and in the engaged state, the clutch pack may be axially loaded by the pressure plate.

The wet clutch may further comprise a plurality of springs individually positioned in the hub portions of the plurality clutch conduit, wherein each spring engages, or biases, the pressure plate. This means that there is a spring in the hub portion of each clutch conduit. It is understood that the spring biases, or pushes, the pressure plate towards the actuator, or front part.

If the hub portions have cylindrical portions, the springs may be positioned in the cylindrical portions of the hub portions. Each spring may engage the protrusion of the pressure plate. Provided that the protrusions form parts of the valves, this means that the springs jointly act to close the valves. Each spring may be a compression coil spring and oriented to compress and extend parallel to the shaft.

The pressure plate, or the protrusion, may block the front part portions of the clutch conduits, when the clutch pack, or wet clutch, is in its unengaged state. This way, the coolant is prevented from flowing through the clutch conduits and reaching the clutch pack.

The actuator may comprise: an annular recess formed by the front part and concentric with the shaft, and a ring-shaped piston positioned in the recess and configured to move axially relative to the shaft.

The annular recess may face, or be open in the direction of, the clutch pack or the pressure plate. The ring-shaped piston may engage or contact the annular pressure plate. In the slipping state and in the engaged state, the ring-shaped piston axially loads, or presses against, the pressure plate. The plurality of springs may bias, or push, the pressure plate towards, or against, the ring-shaped piston.

The shaft may have an additional internal shaft conduit for a hydraulic fluid and the actuator may be configured to operationally connect to the additional internal shaft conduit. More precisely, the annular recess may be configured to connect to, or for a fluid communication with, the additional internal shaft, for example by way of a connecting conduit. When installed, this means that the actuator is activated by increasing the pressure of the hydraulic fluid, which causes the ring-shaped piston to move towards the clutch pack, or the pressure plate, and engage the wet clutch. In the shaft assembly, it is understood that the actuator instead is operationally connected to the additional internal shaft conduit.

The back part has the function of an abutment, or end plate, against which the clutch pack is pressed by the actuator. In the slipping state and in the engaged state, the clutch pack is then axially loaded by the pressure plate and the back part. The back part may be concentric with respect to the shaft. It may have an annular shape. The back part allows for a compact construction of the wet clutch.

The clutch basket may have a cylindrical shape or may be ring-shaped. This means that the clutch basket has a limited radial extent and that it does not form an end plate extending in the radial direction. The clutch basket comprises, or forms, a plurality of apertures for allowing the coolant to escape the wet clutch in the radial direction. This means that the wet clutch is not sealed, and that the coolant is not contained in the wet clutch. Thus, no circulation system for the coolant is required within the wet clutch as such, which allows for a more compact construction. Instead, the coolant may be circulated by an external system. Additionally, this allows for the wet clutch to be free from coolant when the wet clutch, or clutch pack, is not engaged. Additionally, or alternatively, there may be a gap between the clutch basket and the front part through which the coolant can escape the wet clutch.

The shaft may have an additional internal shaft conduit for a hydraulic fluid and the actuator may be configured to operationally connect to the additional internal shaft conduit. In the shaft assembly, the actuator is instead operationally connected to the additional internal shaft conduit.

The gear wheel may have, or form, an axially extending flange concentric with the shaft, wherein the clutch basket and the flange overlap. The clutch basket may be attached to the flange. The clutch basket and the flange may have conforming shapes at the overlap. The outer side of the flange may conform to the inner side of the clutch basket at the overlap.

It is understood that the term "gear wheel" does not encompass sprockets, or sprocketwheels, commonly used for meshing with chains, belts, or the like.

A more complete understanding of the abovementioned and other features and advantages of the proposed technology will be apparent from the following detailed description of preferred embodiments of the proposed technology in conjunction with the appended drawings, wherein:.

<FIG> schematically illustrates a shaft assembly <NUM> for a gearbox of road vehicle. The shaft assembly <NUM> has a shaft <NUM> with an internal shaft conduit <NUM> intended for carrying a combined coolant and lubricant that is oil based. It also has a gear assembly <NUM> that is mounted on the shaft <NUM> and connected to the internal shaft conduit <NUM>. The gear assembly <NUM> forms a through hole <NUM> receiving the shaft <NUM>, whereby the shaft <NUM> passes through the complete gear assembly <NUM>.

The gear assembly <NUM> has a gear wheel <NUM> that is rotationally supported with respect to shaft <NUM>. It also has a wet clutch <NUM> that is mounted on the shaft <NUM> and operationally connected to the internal shaft conduit <NUM>.

The gear wheel <NUM> and the wet clutch <NUM> are concentric with respect to the shaft <NUM>. The gear wheel <NUM> has an axially extending flange <NUM> that is also concentric with the shaft <NUM>. The clutch basket <NUM> and the flange <NUM> overlap at the flange <NUM>. The outer side of the flange <NUM> conforms to the inner side of the clutch basket <NUM> at the overlap, whereby the clutch basket <NUM> is attached to the flange <NUM>, and in extension to the gear wheel <NUM>, which can be seen in <FIG> and <FIG>.

The wet clutch <NUM> is a multi-plate clutch and the shaft <NUM> passes through the complete wet clutch <NUM>. The wet clutch <NUM> has a clutch hub <NUM> that is mounted on the shaft <NUM> and radially fixed relative to the shaft <NUM> by way of splines <NUM>. It further has a clutch basket <NUM> that is rotationally supported relative to shaft <NUM> and a clutch pack <NUM> that connects the clutch hub <NUM> and the clutch basket <NUM>. The wet clutch <NUM> also has a front part <NUM> that is juxtaposed and attached to the clutch hub <NUM> by way of bolts. This way, the front part <NUM> is mounted on and rotationally fixed relative to the shaft <NUM>.

The clutch hub <NUM> and the clutch basket <NUM> are concentric with respect to the shaft <NUM>. The clutch hub <NUM> forms a through hole <NUM> and the front part <NUM> forms another through hole <NUM>, see <FIG>. This means that the clutch hub <NUM> forms a through hole <NUM> that receives the shaft <NUM>.

The gear assembly <NUM> has a radial spacer <NUM> that is rotationally fixed relative to the clutch hub <NUM> by way of bolts. Thus, it is also rotationally fixed relative to the shaft <NUM>. The gear assembly <NUM> further has a first rolling bearing <NUM> and a second rolling bearing <NUM> rotationally supporting the gear wheel <NUM> relative to the shaft <NUM>. The rolling bearings <NUM> and <NUM> are radial rolling bearings, more precisely angular contact ball bearings, positioned in a back-to-back configuration, for example as shown in <FIG> and <FIG>. Each of the first rolling bearing <NUM> and the second rolling bearing <NUM> has an inner race <NUM>, an outer race <NUM>, and a plurality of rolling-elements <NUM> in the form of spherical balls position between the inner race <NUM> and the outer race <NUM>. The inner race <NUM> is attached to the radial spacer <NUM> and the outer race <NUM> is attached to the gear wheel <NUM>.

The gear wheel <NUM> has a central through bore <NUM> with a rotationally symmetric inner wall <NUM>, see for example <FIG> and <FIG>. The outer race <NUM> conforms to and is attached to the inner wall <NUM>. The radial spacer <NUM> has a ring-shaped partly hollow body.

The rolling bearings <NUM> and <NUM> define an axial rest position for the gear wheel <NUM> with respect to the shaft <NUM>. The rest position is the position of the gear wheel <NUM> in the absence of loads or torque transfer. The rolling bearings <NUM> and <NUM> can allow for a small axial shift, which becomes greater when they have been subjected to wear.

The inner race <NUM> of each rolling bearing <NUM> and <NUM> is attached to the radial spacer <NUM>, while the outer race <NUM> is attached to the gear wheel <NUM>. The gear wheel <NUM> has a central through bore <NUM> with a cylindrical inner wall, and the outer race <NUM> conforms to and engages the inner wall of the through bore <NUM>.

Clamps (not shown) are positioned on the shaft <NUM> on either side of the gear assembly <NUM> that axially fix the wet clutch <NUM> and the radial spacer <NUM>, and in extension the clutch hub <NUM>, the clutch basket <NUM>, and the front part <NUM> relative to the shaft <NUM>.

The clutch hub <NUM> has been manufactured from a single piece of steel. Similarly, the front part <NUM> has been manufactured from a single piece of steel. This means that both components individually constitute a unitary body.

The wet clutch <NUM> has <NUM> individual clutch conduits <NUM>. Each has a front part portion <NUM> formed by the front part <NUM> and a hub portion <NUM> formed by the clutch hub <NUM>. The front part portion <NUM> has an inlet <NUM> that can receive the combined coolant and lubricant. The hub portion <NUM> is coupled to the front part portion <NUM> and has three outlets at the clutch pack <NUM> through which the combined coolant and lubricant can be released. The outlets <NUM> are distributed axially with respect to the clutch hub <NUM>, which means that they are distributed lengthwise with respect to the shaft <NUM>.

The hub portion <NUM> of each clutch conduit <NUM> is elongated and aligned with the shaft <NUM>. Each hub portion <NUM> has a cylindrical portion <NUM> with a circular cross-section and an axis that is parallel to the axis <NUM> of the shaft <NUM>, as can be seen in <FIG> and <FIG>. This means that all cylindrical portions <NUM> have parallel cylinder axes.

The through hole <NUM> of the front part <NUM> that receives the shaft <NUM> has a circumferential inner wall portion <NUM> facing the shaft <NUM>. The front part <NUM> forms a circumferential groove <NUM> in the inner wall portion <NUM> that can receive the combined coolant and lubricant from the shaft conduit <NUM>, and the inlet <NUM> of the front part portion <NUM> of each clutch conduit <NUM> connects to the groove <NUM>. The inner wall portion <NUM> facing the shaft <NUM> is flush with the outer surface of the shaft <NUM>. This way, the individual clutch conduits <NUM> form part of a conduit arrangement <NUM> that connects the shaft conduit <NUM> to the outlets <NUM>. The conduit arrangement <NUM> allows a flow of combined coolant and lubricant from the shaft conduit <NUM> to be distributed at the clutch pack <NUM>, thus having the function of a manifold.

The front part portions <NUM> and the hub portions <NUM> of the clutch conduits <NUM> are evenly distributed around the shaft <NUM>. They have a <NUM>-degree separation with respect to the rotational axis <NUM> of the shaft <NUM> between neighboring clutch conduits <NUM>.

The clutch hub <NUM> has a number of axially extending ridges <NUM> that form part of a spline joint with the clutch pack <NUM>. The outlets <NUM> of each clutch conduit <NUM> are located between a pair of neighboring ridges <NUM>, or more precisely at the bottom of the single groove between neighboring ridges <NUM>. There are forty-five ridges <NUM> and fifteen clutch conduits <NUM>, which means that there are three times more of the former than the latter. The axially extending ridges <NUM> form male splines <NUM> cooperating with female splines <NUM> formed by the clutch pack <NUM>.

The clutch pack <NUM> has three states. In the first state, or the unengaged state, the clutch hub <NUM> and the clutch basket <NUM> are unlocked and can spin at different speeds. In extension, this means that the gear wheel <NUM> can spin freely relative to the shaft <NUM>. In the second state, or the slipping state, the clutch hub <NUM> and the clutch basket <NUM> are partly locked together but can spin at different speeds. This means that some torque is transferred from the shaft <NUM> to the gearwheel <NUM>. In the third state, or the engaged state, the clutch hub <NUM> and the clutch basket <NUM> are locked together and spin at the same speed. This means that all torque supplied to the shaft <NUM> is transferred to the gear wheel <NUM>.

The wet clutch <NUM> has <NUM> valves <NUM>. Each valve <NUM> controls the flow of combined coolant and lubricant through a single clutch conduit <NUM>. The wet clutch <NUM> further has a single actuator <NUM> supported by the front part <NUM> and an annular pressure plate <NUM> that is concentric with respect to the shaft <NUM>. The pressure plate <NUM> is positioned between the actuator <NUM> and the clutch pack <NUM> such that it can engage the clutch pack <NUM> when the actuator <NUM> is activated. Additionally, the pressure plate <NUM> forms part of each valve <NUM>, which means that it simultaneously engages the clutch pack <NUM> and operates the valves <NUM>.

When activated, the actuator compresses the clutch pack <NUM> axially and the clutch pack <NUM> changes from the unengaged state to the engaged state, via the slipping state, when it is compressed axially.

The clutch pack <NUM> is concentric with respect to the clutch hub <NUM> and the shaft <NUM>. The clutch basket <NUM> is concentric with respect to the clutch pack <NUM>, and in extension with respect to the clutch hub <NUM>. The clutch pack <NUM> has an annular shape and extends both radially and axially with respect to the axis of the shaft <NUM>.

The clutch pack <NUM> has eight inner plates <NUM> attached to the clutch hub <NUM>, which constitutes an inner plate carrier, and seven interleaved outer plates <NUM> attached to the clutch basket <NUM>, which constitutes an outer plate carrier. The inner plates <NUM> can move axially relative to the clutch hub <NUM> and are rotationally fixed relative to the clutch hub <NUM>. Similarly, the outer plates <NUM> can move axially relative to the clutch basket <NUM> and are rotationally fixed relative to the clutch basket <NUM>.

The inner and outer plates <NUM> and <NUM> are positioned alternately in the clutch pack <NUM>. In the unengaged state there is no mechanical friction between the inner plates and the outer plates, in the slipping state there is a kinetic friction between the inner plates <NUM> and the outer plates <NUM>, and in the engaged state there is a static friction between the inner plates <NUM> and the outer plates <NUM>.

The clutch pack <NUM> forms channels <NUM> in a square grid pattern on both sides of each inner plate <NUM>. Even though not radially oriented, the square grid on the circular plate <NUM> mean that all the channels <NUM> to some extent extend radially with respect to the shaft <NUM>, which enables the combined coolant and lubricant to flow radially outwards through the clutch pack <NUM>.

As mentioned above, the clutch hub <NUM> has a number of outer male splines <NUM> and each inner plate <NUM> has the same number female splines <NUM> that cooperated with the male splines <NUM>. Similarly, the clutch basket <NUM> has female splines <NUM> and each of the outer plates <NUM> has male splines <NUM> cooperating with the female splines <NUM>.

The valves <NUM> have been constructed to prevent the flow of combined coolant and lubricant through the clutch conduits <NUM> when the clutch pack <NUM> is in its unengaged state. It further allows the flow of the combined coolant and lubricant when the clutch pack <NUM> is in its slipping state and its engaged state. In some embodiments, the flow of the combined coolant and lubricant is up to ten times greater when the clutch pack <NUM> is in its engaged state than in its unengaged state, this means that there is a flow even if the valves <NUM> are in the closed state.

The front part <NUM> forms a valve seat <NUM> at each coupling between the hub portions <NUM> and the front part portions <NUM> of the clutch conduits <NUM>. The valve seat <NUM> is a hard seat integral to the front part <NUM>.

The pressure plate <NUM> is disc-shaped, planar, and has a rotational symmetry with respect to the axis <NUM> of the shaft <NUM>. It has a central through hole <NUM> and forms a number of protrusions <NUM>, more precisely <NUM> protrusions <NUM>, each extending radially inwards in the central hole <NUM> as illustrated in <FIG>. Each protrusion <NUM> constitutes a valve member, or valve disc, of a single valve <NUM> and seals against one of the valve seats <NUM> when the wet clutch <NUM> is in its unengaged state. In its engaged state, the pressure plate <NUM> is pushed by the actuator <NUM> such that a gap is formed between the protrusion <NUM> and the valve seats <NUM>, thus allowing a flow of the combined coolant and lubricant past the protrusions <NUM> and into the hub portions <NUM>, from where it is expelled via the outlets <NUM>.

A compression coil spring <NUM> is positioned in the cylindrical portion <NUM> of each hub portion <NUM>. Each spring <NUM> engages a single protrusion <NUM> of the pressure plate <NUM>, and the springs <NUM> jointly bias the pressure plate <NUM> with respect to the clutch hub <NUM> and pushes the pressure plate towards the actuator <NUM>, thus acting to close the valves <NUM>.

A valve is closed when the clutch pack <NUM>, or wet clutch <NUM>, is in its unengaged state, at which the protrusions <NUM> block the front part portions <NUM> of the clutch conduits <NUM>. This way, the combined coolant and lubricant is prevented from flowing through the clutch conduits <NUM> and reaching the clutch pack <NUM>.

The actuator <NUM> has an annular recess <NUM> formed by the front part <NUM> and concentric with the axis <NUM> of the shaft <NUM>, which can be seen in Figs. P and <NUM>. It further has a ring-shaped piston <NUM> positioned in the recess <NUM> and configured to move axially relative to the shaft <NUM>. The piston <NUM> is sealed by gaskets <NUM> preventing leakage of a hydraulic fluid past the piston <NUM>.

The ring-shaped piston <NUM> engages the annular pressure plate <NUM>. In the slipping state and in the engaged state, the piston <NUM> presses against and axially loads the pressure plate <NUM>. The plurality of springs <NUM> provides a counter force pushing the pressure plate <NUM> against the ring-shaped piston <NUM>. By way of the pressure plate <NUM>, the actuator <NUM> is configured to simultaneously engage the clutch pack <NUM> and operate the plurality of valves <NUM>.

The shaft <NUM> has an additional internal shaft conduit <NUM> for a hydraulic fluid, and the annular recess <NUM> is connected to the additional internal shaft conduit <NUM>. The actuator <NUM> is activated by increasing the pressure of the hydraulic fluid, which causes the ring-shaped piston <NUM> to move towards the clutch pack <NUM> and engage the wet clutch <NUM>.

The wet clutch <NUM> further has a radially and outwardly extending back part <NUM> mounted on and concentric with the shaft <NUM>. The back part <NUM> is juxtaposed to the clutch hub <NUM> and the clutch pack <NUM> is positioned between the back part <NUM> and the front part <NUM>. The back part <NUM> is attached to the clutch hub <NUM> by way of bolts. The clutch pack <NUM> is pressed against the back part <NUM> when the clutch pack <NUM> is engaged by the actuator <NUM> in the slipping state and in the engaged state of the wet clutch <NUM>.

The back part <NUM> is partly positioned between the clutch pack <NUM> and the gear wheel <NUM> The back part <NUM> and the gear wheel <NUM> are spaced apart and forms a gap <NUM> between them in the unengaged state, as can be seen in <FIG>. The size of the gap <NUM> is exaggerated to illustrate the function of the back part <NUM> and gear wheel <NUM>. A gap <NUM> of about <NUM> is shown in the perspective cross-section of <FIG>. The back part <NUM> engages the gear wheel <NUM> in the engaged state, as can be seen in <FIG>. The contacting between the back part <NUM> and the gear wheel <NUM> is a combination of an elastic deformation of the back part <NUM>, as depicted in <FIG>, and an axial shifting of the gear wheel <NUM> towards the back part <NUM>, as depicted in <FIG>. In alternative embodiments, the contacting may be cause by either an elastic deformation or a shifting.

The back part <NUM> and the gear wheel <NUM> engaging one another has the effect that the gear wheel <NUM>, and in extension the clutch basket <NUM>, are prevented from shifting further towards the front part <NUM>. This way the gear wheel <NUM> and the clutch basket <NUM> are stabilized and axially supported in the direction towards the front part <NUM>. This relieves the first rolling bearing <NUM> and the second rolling bearing <NUM> from axial loads in the direction of the back part <NUM>.

The gear wheel <NUM> is a monolithic structure formed from a single piece of steel. Similarly, the back part <NUM> is a monolithic structure made of a steel that can elastically deform under the load of the actuator <NUM>.

When going from the unengaged state to the engaged state, the back part <NUM> and the gear wheel <NUM> engage one another, as is shown in <FIG>. The clutch basket <NUM> reaches the engaged state before the back part <NUM> contacts the gear wheel <NUM>. The engaged state is reached at a first force generated by the actuator <NUM>, and the contacting is achieved at a greater second force generated by the actuator. Conversely, with the cutch basket <NUM> in the engaged state, the back part <NUM> and the gear wheel <NUM> disengage before the clutch basket <NUM> reaches the disengaged state.

The back part <NUM> deforms and engages the gear wheel <NUM> when the clutch pack <NUM> is in the engaged state, as is shown in <FIG>. The clutch pack <NUM> is pressed against the back part <NUM>, which causes the radially outer part of the back part <NUM> to bend and contact the gear wheel <NUM>.

The gear wheel <NUM> is a helical gear that generates an axial load along the shaft <NUM> when it meshes with a cooperating gear wheel (not shown). The teeth of the gear wheel <NUM> are oriented such that the gear wheel <NUM> is pushed towards the back part <NUM> by the direction of the intended maximum torque. This way, the gear assembly <NUM> is configured such that the gear wheel <NUM> engages the back part <NUM>, as is schematically illustrated in <FIG>. The back part <NUM> is fixed relative to the shaft <NUM> by way of the clutch hub <NUM>, which prevents any further axial shifts of the gear wheel <NUM>.

The back part <NUM> forms a first contact area <NUM> facing the gear wheel <NUM>, and the gear wheel <NUM> forms a second contact area <NUM> facing the first contact area <NUM>. In the engaged state, the first contact area <NUM> engages the second contact area <NUM>, as is shown in <FIG>. In the unengaged state, the first contact area <NUM> and the second contact area <NUM> are separated from one another by the gap <NUM> between the back part <NUM> and the gear wheel <NUM>. The first contact area <NUM> and the second contact area <NUM> are both planar and at a right angle to the shaft <NUM>, thus conforming to one another in both the unengaged and engaged state.

The planar geometry of the first contact area <NUM> and the second contact area is shown in <FIG>. In an alternative embodiment, the first contact area <NUM> and the second contact area <NUM> have a frustoconical geometry that is concentric with the shaft <NUM>, as is shown in <FIG>. The wide end of the frustoconical geometry is in the direction of the front part <NUM>, and the narrow end of the frustoconical geometry is in the opposite direction. In another alternative embodiment, the first contact area <NUM> and the second contact area <NUM> have a curved geometry that is concentric with the shaft <NUM>, as is shown in <FIG>. In the two alternative embodiments, the first contact area <NUM> defines a male contact and the second contact area <NUM> defines a cooperating female contact.

The first contact area <NUM> has a smooth first contact surface <NUM>, and the second contact area <NUM> has a smooth second contact surface <NUM>.

The back part <NUM> has a plate-like portion <NUM> that extends radially relative to the shaft <NUM> to form a flange with planar geometry with respect to the clutch hub <NUM>. The actuator <NUM> presses the clutch pack <NUM> against the plate-like portion <NUM> in the engaged state, and the plate-like portion <NUM> in turn engages the gear wheel <NUM>. The first contact area <NUM> is located on the plate-like portion <NUM>.

A front view of the back part <NUM> is shown in <FIG>. In an alternative embodiment, the back part <NUM> has a plurality of cutouts <NUM> in the radially outer edge of the back part <NUM>, as is shown in <FIG>. In another alternative embodiment, the back part <NUM> has a plurality of axially through-going holes <NUM>. The cutouts <NUM> and the holes <NUM> gives a greater flexibility for a given thickness of the plate like portion <NUM>.

The clutch basket <NUM> is cylindrical and attached to the gear wheel <NUM> by way of the flange <NUM>, see for example <FIG> and <FIG>. This means that the clutch basket <NUM> is composed of a cylindrical portion <NUM>. In an alternative embodiment shown in <FIG>, the clutch basket <NUM> is composed of a radial portion <NUM> and a cylindric portion <NUM>. The radial portion <NUM> is attached to the gear wheel <NUM>. The back part <NUM> and the cylindrical portion <NUM> are separated in the engaged state, as can be seen in <FIG>. The cylindrical portion <NUM> is connected to and extends from the radial portion <NUM> in the direction of the front part <NUM>. The outer plates <NUM> of the clutch pack <NUM> are slidably attached to the cylindrical portion <NUM> of the clutch basket <NUM> allowing for an axial shift in position.

The back part <NUM> has an outer edge <NUM>. In the alternative embodiments of <FIG>, the first contact area <NUM> of the back part <NUM> is radially separated from the outer edge <NUM>. The radial portion <NUM> of the clutch basket <NUM> has an inner edge <NUM> that is closer to the shaft <NUM> than the outer edge <NUM> of the back part <NUM>. The outer edge <NUM> is then at a first radius relative to the shaft, and the inner edge <NUM> is at a smaller second radius.

Apart from the clutch basket <NUM> and the back part <NUM>, the alternative embodiment of <FIG> has the same features as the embodiment of the main embodiment, for example described in relation to <FIG>.

The back part <NUM> is composed of an inner portion <NUM> and an outer portion <NUM> that are rotationally symmetric relative to the shaft <NUM>. The back part <NUM> has a radially extending support area <NUM> that faces the clutch pack <NUM>, and the clutch pack <NUM> is pressed against the support area <NUM> in the engaged state. The support area <NUM> is in part positioned on the outer portion <NUM> and in part positioned on the inner portion <NUM>.

In the embodiment of <FIG>, the first contact area <NUM> is formed by the outer portion <NUM>, and the outer portion <NUM> engage the gear wheel <NUM> in the engaged state. The inner portion <NUM> is separated from the gear wheel <NUM> in the engaged state.

In the alternative embodiment of <FIG>, the inner portion <NUM> engages the gear wheel <NUM> instead of the outer portion <NUM> in the engaged state. The first contact area <NUM> is or formed by the inner portion <NUM>. The outer portion <NUM> does not engage the gear wheel <NUM> in the engaged state.

Claim 1:
A gear assembly (<NUM>) for mounting on a shaft (<NUM>), wherein the gear assembly (<NUM>) comprises:
- a gear wheel (<NUM>) configured to be rotationally supported with respect to the shaft (<NUM>),
- a multiple-plate wet clutch (<NUM>) comprising:
- a clutch hub (<NUM>) configured to be mounted on the shaft (<NUM>),
- a front part (<NUM>), or collar (<NUM>), configured to be fixed relative to the shaft (<NUM>),
- a back part (<NUM>), or radially extending flange (<NUM>), configured to be fixed relative to the shaft (<NUM>),
- a clutch basket attached to the gear wheel (<NUM>),
- a clutch pack (<NUM>) operationally connecting the clutch hub (<NUM>) and the clutch basket (<NUM>), wherein the clutch pack (<NUM>) is positioned between the front part (<NUM>) and the back part (<NUM>), and
- an actuator (<NUM>) supported by the front part (<NUM>) and configured to engage the clutch pack (<NUM>) and press the clutch pack (<NUM>) against the back part (<NUM>),
wherein the clutch pack (<NUM>) has:
- an unengaged state in which the clutch hub (<NUM>) and the clutch basket (<NUM>) are unlocked, and
- an engaged state in which the clutch hub (<NUM>) and the clutch basket (<NUM>) are locked together, characterized in that, the back part (<NUM>) is spaced apart from the gear wheel (<NUM>) in the unengaged state, and the back part (<NUM>) engages (or contacts) the gear wheel (<NUM>) in the engaged state.