WO2015155137A1

WO2015155137A1 - Drive arrangement with integrated damper and clutch

Info

Publication number: WO2015155137A1
Application number: PCT/EP2015/057405
Authority: WO
Inventors: Naomi GOLD; David Wardle; Gary Jackson; Colin LEA
Original assignee: Jaguar Land Rover Ltd
Current assignee: Jaguar Land Rover Ltd
Priority date: 2014-04-11
Filing date: 2015-04-02
Publication date: 2015-10-15
Anticipated expiration: 2016-10-11
Also published as: GB2525037A; GB201406544D0

Abstract

A drive arrangement comprises an electric machine including a rotor, and a driveshaft, the driveshaft being arranged to receive torque from an internal combustion engine and apply torque to the rotor through a damping mechanism. The damping mechanism is arranged to damp transfer of torque between the driveshaft and the rotor so as to damp torque transferred from the rotor to a vehicle transmission. The damping mechanism is situated within an envelope defined by the electric machine and located radially inward of the rotor in a space between the rotor and the driveshaft. The damping mechanism is integrated with the rotor in a rotor assembly.

Description

DRIVE ARRANGEMENT WITH INTEGRATED DAMPER AND CLUTCH

FIELD OF THE INVENTION This invention relates to a drive arrangement for a vehicle. In particular, but not exclusively, this invention relates to a drive arrangement including means for damping transfer of torsional loading throughout the drive arrangement on engagement of a clutch assembly. Another aspect of the invention relates to a vehicle comprising such a drive arrangement. BACKGROUND

It is commonplace to implement damping into modern vehicle clutch arrangements. The damping serves to smooth torque peaks corresponding to individual engine cylinder combustion events, resulting in smooth power delivery. The damping also reduces stresses and vibrations induced in drivetrain components when torsional loading is applied as the clutch is engaged.

A clutch plate 10 belonging to a known damped clutch assembly is shown in Figures 1 and 2. The clutch plate 10 is arranged to be positioned between a flywheel and a clutch cover (not shown) in use, to damp transmission of torque from the flywheel to a driveshaft of the vehicle. Figure 1 provides a perspective view of the clutch plate 10, while Figure 2 illustrates a portion of the clutch plate 10 in cross-section.

The clutch plate 10 consists of a hub 12, a retaining plate 14 and a friction plate 16, all held in concentric relation. The hub 12 is coupled to the driveshaft, while the friction plate is arranged to engage the flywheel.

The retaining plate 14 is disposed annularly around the hub 12 in a manner that permits relative rotation between the parts. As best illustrated in Figure 2, the friction plate 16 is composed of an adapter plate 18 that carries a layer of friction material 20 on either side. The friction plate 16 is rigidly attached to the retaining plate 14, and is arranged to engage with the flywheel on one side and the clutch cover plate on the other.

When the clutch assembly is closed, torque from a vehicle engine is applied through the flywheel to the friction plate 16. Torque is then transferred by way of a set of springs 22 from the retaining plate 14 to the hub 12 and on to the rest of the drivetrain components. The springs 22 are received within respective cavities 24 defined by the retaining plate 14. The cavities 24 also accommodate spokes 26 which extend radially from the hub 12. Each spring 22 is arranged to abut an end wall 28 of its respective cavity 24 at one end, and a respective spoke 26 of the hub 12 at the other end.

As the friction plate 16 is rotated by the flywheel, the end walls 28 of the retaining plate 14 compress the springs 22 against the spokes 26 of the hub 12. This transfers torsional load from the friction plate 16 to the hub 12 and on to the drivetrain in a manner that dampens the peak torsional outputs from the vehicle engine, providing smoother power delivery compared with a rigid connection. Therefore, the maximum force exerted downstream of the hub 12, along with any associated components, is reduced. In this way, the clutch arrangement is damped.

In order to accommodate the springs 22, the clutch plate 10 is deeper than a non-damped clutch plate. In particular, the need to house the springs 22 entails axial enlargement of the overall clutch arrangement. This can be problematic in environments in which surrounding components constrain the overall depth of the clutch assembly.

At present, it is necessary to design drivetrains so as to accommodate clutch assemblies such as described above. However, as the size of surrounding components such as electric generators or motors increases, this becomes increasingly challenging. There is therefore a desire for a damped clutch arrangement that is suitable for vehicles in which axial space is tightly constrained. Against this background, it is one object of the present invention to provide an alternative drive arrangement which can be used in a vehicle having a radial flux motor and which still provides adequate damping through the drive train.

SUMMARY OF THE INVENTION

According to an aspect of the invention there is provided a drive arrangement comprising an electric machine including a rotor, and a driveshaft, the driveshaft being arranged to receive torque from an internal combustion engine and apply torque to the rotor through a damping mechanism; wherein the damping mechanism is arranged to damp transfer of torque between the driveshaft and the rotor so as to damp torque transferred from the rotor to a vehicle transmission; wherein the damping mechanism is situated within an envelope defined by the electric machine and located radially inward of the rotor in a space between the rotor and the driveshaft, and wherein the damping mechanism is integrated with the rotor in a rotor assembly.

An advantage of the above described arrangement is that it can be coupled to an internal combustion engine by means of an undamped clutch, which beneficially reduces the axial space required between the internal combustion engine and the transmission, whilst simultaneously allowing for decoupling of the electric machine from the internal combustion engine. The transmission may comprise, for example, a torque convenor coupled to an automatic transmission. Furthermore the above described arrangement provides downstream mechanical damping of the transmission and the electric machine in a compact and concentric package.

According to an aspect of the invention there is provided a drive arrangement comprising an electric machine including a rotor, and a driveshaft arranged to apply torque to the rotor through a damping mechanism. The damping mechanism is arranged to damp transfer of torque between the driveshaft and the rotor. The damping mechanism is situated within an envelope defined by the electric machine.

The damping mechanism is preferably implemented so as to provide a coupling between the rotor and the driveshaft. This means that the driveshaft applies torque to the rotor through the damping mechanism.

The drive arrangement of the invention is particularly suitable for use in vehicle applications, especially in arrangements in which axial space is constrained. However, the drive arrangement may also find application in other contexts, for example in power generation, in a train, or in a ship.

The damping mechanism is arranged to damp transfer of torque so as to provide a smoothing effect where a torque supply is not steady. For example, the torque output of an internal combustion engine is typically oscillatory, due to the discrete nature of combustion events in the engine cylinders; the damping mechanism acts to reduce the peaks and raise the troughs in such a supply, so as to provide a more consistent torque to the rotor.

The envelope defined by the electric machine is the total space occupied by the electric machine, with reference to its outer dimensions, and including the internal space between the radially outer components of the machine (e.g. the rotor and a stator) and the driveshaft. For example, the damping mechanism may be suitably located radially inward of the rotor in the space between the rotor and the driveshaft.

The damping mechanism may comprise at least one spring and may, for example, comprise a set of springs equi-spaced along a circular path orthogonal to and centred on the driveshaft. By way of example, the or each spring is arranged orthogonally with respect to central and radial axes of the rotor. In alternative embodiments, the damping mechanism may comprise hydraulic or pneumatic damping means. The drive arrangement may comprise a clutch assembly arranged to selectively couple the driveshaft to a source of torque such as an internal combustion engine, wherein the damping mechanism is arranged to damp transfer of torque between the driveshaft and the rotor when the clutch assembly is engaged. In this embodiment, the damping mechanism not only acts to the smooth steady state supply, but also reduces the magnitude of peak stresses arising as the clutch engages.

In this embodiment, a particular function of the damping mechanism is to damp high torsional inputs to downstream components or systems from the source of torque, which may be an internal combustion engine for example. In this application the damper springs protect the clutch and associated spline from high torsional loads.

In certain situations where the length of the axial package is constrained, there may be insufficient space to house the damping springs in the clutch assembly, as would be conventional. In this embodiment, the damping mechanism is beneficially disposed post clutch and integrated into an electric machine rotor assembly. This topology minimises the overall axial length.

Advantageously, the damping mechanism may be located radially inward of the rotor in a space between the rotor and the driveshaft. In this embodiment, the damping mechanism may be integrated with the rotor in a rotor assembly. To aid integration, the rotor assembly may further comprise a rotor support, in which case the rotor support may house at least a portion of the damping mechanism.

The rotor support may be rigidly coupled to the rotor, and the damping mechanism is arranged to damp transfer of torque between the rotor support and the driveshaft. In an alternative embodiment, the rotor support is rigidly coupled to the driveshaft, and the damping mechanism is arranged to damp transfer of torque between the rotor support and the rotor.

The driveshaft may comprise a radially enlarged portion having a set of axially extending fingers which are arranged to engage with the rotor assembly.

The damping mechanism may comprise at least one spring. The damping mechanism may comprise a set of springs equi-spaced along a circular path orthogonal to and centred on the driveshaft. In either arrangement, the or each spring may be housed in a respective cavity defined in the rotor support.

The electric machine may be a radial flux machine.

According to another aspect, there is provided a vehicle comprising the drive arrangement of the previous aspect of the invention.

The vehicle may comprise an internal combustion engine which is a source of torque for the drive arrangement. The electric machine may be operable as an electric motor, such that the electric machine is a secondary source of torque. In this embodiment, the electric machine may suitably be arranged to provide motive power when the clutch is disengaged, such that the vehicle operates as a hybrid vehicle.

Within the scope of this application it is expressly envisaged that the various aspects, embodiments, examples and alternatives set out in the preceding paragraphs, in the claims and/or in the following description and drawings, and in particular the individual features thereof, may be taken independently or in any combination. For example, features disclosed in connection with one embodiment are applicable to all embodiments, except where such features are incompatible.

BRIEF DESCRIPTION OF DRAWINGS Figures 1 and 2 illustrate a known damped clutch arrangement, and are described above. Embodiments of the present invention will now be described, by way of example only, with reference to the remaining accompanying drawings, in which like components are assigned like numerals, and in which:- Figure 3 is a schematic drawing showing in cross-section a portion of a drive arrangement according to an embodiment of the invention;

Figure 4 is a perspective view of a rotor hub of an electric machine forming part of the drive arrangement of Figure 3;

Figure 5 is a perspective view of the rotor hub of Figure 4 with damping springs installed;

Figure 6 is an exploded perspective view of the rotor hub of Figure 4 assembled with a driveshaft forming part of the drive arrangement of Figure 3, as viewed from behind;

Figure 7 is an exploded perspective view of the rotor hub of Figure 4 assembled with a driveshaft forming part of the drive arrangement of Figure 3, as viewed from in front; and

Figure 8 is an exploded perspective view of the rotor hub assembly in Figures 5 to 7 including a rear cover plate.

Throughout the description, directional terms such as 'left', 'right' and 'uppermost' are used with reference to the orientation of the components as illustrated, although it will be understood by the skilled person that in use the orientation and relative positions of the components could be different to that shown.

DETAILED DESCRIPTION

Figure 3 shows in schematic form a portion of a drive arrangement 30 according to an embodiment of the invention. It should be noted that only one half of the arrangement is illustrated; the remaining half is substantially a mirror image of the portion shown about central axis L, and many components of the arrangement have rotational symmetry about axis L. The drive arrangement 30 includes a driveshaft 32 that extends centrally through the drive arrangement 30 between a crank palm 34 of a crankshaft of a vehicle engine and a torque converter 36. At the crankshaft end, the driveshaft 32 is journalled on a bearing 37 within a cavity 38 defined in an end face of the crank palm 34. The other end of the driveshaft 32 includes an axial recess 40 arranged to engage with a central axially extending input shaft 42 of the torque converter 36. In this way, the driveshaft 32 is supported by the crank palm 34 and the torque converter 36.

The drive arrangement 30 of this embodiment is arranged for use in a hybrid vehicle, and further includes an electric machine 44 of the radial flux type which acts either as a generator or as a motor. In this arrangement, typically the electric machine 44 is driven by an internal combustion engine as a generator when a clutch is engaged, and is operable to act in reverse to supply torque to a torque converter 36 when the clutch is disengaged. The skilled reader will appreciate that such arrangements represent a portion of a powertrain of the vehicle, the powertrain being a combination of a drivetrain and a source of motive power.

The electric machine 44 is situated between the crank palm 34 and the torque converter 36, and comprises a generally tubular rotor 46 disposed within a stator 48 in a concentric arrangement, the stator 48 and rotor 46 having rotational symmetry around the central axis L of the driveshaft 32. The driveshaft 32 therefore extends through the rotor 46 and the stator 48 centrally. The rotor 46 and the stator 48 each carry a set of magnets (not shown), which interact to produce an electrical current when the rotor 46 rotates within the stator 48. The rotor 46 includes a rotor support in the form of a rotor hub 50 which is carried on a bearing 52 attached to a casing 54, the rotor 46 and rotor hub 50 being rigidly coupled to rotate together. The casing 54 also supports the stator 48, and substantially encases the electric machine. A radially enlarged portion 56 of the driveshaft 32 engages with the rotor hub 50, such that in operation the rotor hub 50 is driven by the driveshaft 32. The rotor hub 50 is described in more detail later with reference to Figures 4 to 8.

The driveshaft 32 is arranged to transfer torque from the crank palm 34 to the rotor hub 50 of the electric machine 44 upon engagement of a clutch assembly 58. The clutch assembly 58 comprises a flywheel 60 and a clutch plate 62, which are selectively engaged and disengaged under the control of a clutch slave cylinder 64 which is mounted to the casing 54. The flywheel 60 is attached to the crank palm 34, and the clutch plate 62 is attached to a spline 66 of the driveshaft 32 in a manner that permits axial sliding of the clutch plate 62 as the clutch opens and closes. Therefore, when the clutch assembly 58 is engaged, torque is transferred between the crank palm 34 and the driveshaft 32 through the flywheel 60 and the clutch plate 62. The clutch plate 62 includes a friction plate 78 situated at the radial position at which the flywheel 60 and the clutch plate 62 make contact.

As will be appreciated by the skilled reader, the torque output from a vehicle engine is cyclical, taking a generally sinusoidal form. This is due to the fact that the engine output is produced by regular, discrete combustion events in each engine cylinder, with these combustion events corresponding to the peaks in the torque output. It is desirable to smooth this torque output such that a more consistent torque is supplied to a transmission of the vehicle, in order to improve refinement and reduce wear and fatigue.

For this reason, a damping mechanism 68 in the form of a set of springs is provided between the driveshaft 32 and the rotor hub 50. The damping mechanism 68 is arranged to smooth the cyclical torque output from the engine. The damping mechanism 68 also acts to reduce the instantaneous loading that the driveshaft 32 and the clutch assembly 58 are subjected to when the clutch assembly 58 is engaged, as will be explained in more detail later with reference to Figures 4 to 8.

A clutch cover 71 is fixed to the flywheel 60, and the clutch plate 62 is housed between the clutch cover 71 and the flywheel 60. A diaphragm spring 72 extends radially into a space between the clutch plate 62 and the clutch cover 71 , making contact with the clutch cover 71 at pivot point 71 a. A pressure plate 74 is rotatably fixed to the diaphragm spring 72 by way of pivot points 76, the pivot points 76 being disposed around the diaphragm spring 72 in a circular pattern. It is noted that only one pivot point 76 is visible in the figure, since the assembly is depicted in cross section. The diaphragm spring 72 is pivotally attached to the clutch cover 71 of the flywheel 60 at the radially innermost point of the clutch cover 71 .

The primary function of the clutch assembly 58 is to engage the engine to provide torque to the transmission. Additionally, when the clutch assembly 58 is engaged, the rotor 46 is driven by the engine, and so electrical power is produced in the electric machine 44.

A second bearing 70 is provided to support the rotor hub 50 where it meets the driveshaft 32.

The clutch slave cylinder 64 is operable to switch between an extended state in which the cylinder extends towards the clutch plate 62, and a retracted state in which the cylinder is withdrawn relative to the clutch plate 62. The extended and retracted states of the clutch slave cylinder 64 correspond respectively to what may be referred to as "open" and "closed" states of the clutch. Figure 3 shows the clutch slave cylinder 64 in the retracted state.

If the clutch slave cylinder 64 moves to the extended state, pressure is applied to the diaphragm spring 72 in the vicinity of the driveshaft 32. The pressure causes pivotal movement of the radially inner section of the diaphragm spring 72 about the pivot point 71 a of the clutch cover 71 (from right to left as viewed in Figure 3). This causes a radially outer region of the diaphragm spring 72, which is the uppermost part of the diaphragm spring 72 in Figure 3 and which is above the pivot point 71 a at which the diaphragm spring 72 is attached to the clutch cover 71 , to pivot in the opposite direction, i.e. from left to right. The pressure plate 74 moves with the radially most outward section of the diaphragm spring 72 as pressure is applied by the clutch slave cylinder 64 and so moves away from the clutch plate 62. When the clutch slave cylinder 64 returns to the retracted state, pressure on the diaphragm spring 72 is relieved. The diaphragm spring 72 then relaxes and moves in the opposite sense to that described above, until the pressure plate 74 mates with the clutch plate 62. The pivot point 76 enables the pressure plate 74 to orient correctly for face-to-face mating with the clutch plate 62. Friction material may be provided to ensure a firm grip and controlled engagement between the pressure plate 74 and the clutch plate 62.

Therefore, as the clutch slave cylinder 64 changes state, the pressure plate 74 is urged either towards or away from the clutch plate 62. Movement of the pressure plate 74 towards the clutch plate 62 applies pressure to the clutch plate 62 which causes it to slide along the spline 66, until the clutch plate 62 presses against the flywheel 60, thereby engaging the clutch assembly 58. The friction plate 78 ensures firm engagement as the clutch plate 62 and the flywheel 60 make contact. When the pressure plate 74 moves away from the clutch plate 62 the clutch plate 62 is released from the flywheel 60, thus disengaging the clutch assembly 58. In this way, the clutch slave cylinder 64 is operable to selectively engage and disengage the clutch assembly 58.

On engagement of the clutch assembly 58, the inertia of the rotor 46, the torque converter 36 and other components downstream of the driveshaft 32 places a high load on the components of the drive arrangement 30. An impulse must be delivered to the downstream components in order to raise their momentum to provide the required rotational speed. Thereafter, the torque that is supplied to the flywheel is cyclical, corresponding to the cyclical nature of the output of the vehicle engine resulting from individual combustion events in the engine cylinders. As noted above it is desirable to smooth the cyclical torque so as to reduce the peaks and troughs, as this improves refinement and reduces wear and fatigue in drivetrain components. For these reasons, as discussed above, it is desirable to implement damping that both extends the time over which an impulse is delivered as the clutch engages, and to smooth the cyclical torque supply. This damping reduces the peak stresses that the components of the drive arrangement 30 are subjected to, reduces wear and fatigue, improves refinement, and also reduces vibration and slippage of the flywheel 60 and the clutch plate 62 as they engage.

A disc-like flex plate 80 is disposed between the electric machine 44 and the torque converter 36. As the skilled reader will appreciate, the torque converter 36 is subjected to a degree of expansion and contraction resulting from varying internal pressure in response to varying input speed. For this reason, in conventional manner the flex plate 80 is used to mount the torque converter 36 to the electric machine 44 in a way that accommodates the resulting axial movement of the torque converter 36 without applying pressure to the electric machine 44 or the driveshaft 32. When the clutch assembly 58 is engaged, the driveshaft 32 drives both the rotor 46 and the torque converter 36. The torque converter 36 then transmits torque onto a transmission system of the vehicle. The flex plate 80 and the torque converter 36 are housed within a transmission case 82. As shown in Figure 3, the electric machine is relatively wide, leaving little space for the clutch assembly 58. The result of this is that only a simple clutch assembly 58 can be used; there is not sufficient room available to accommodate a clutch assembly having integrated damping, such as that described above. The arrangement shown in Figure 3 is used for illustrative purposes only, to exemplify a system with severe axial space constraints. It should be appreciated, however, that the present invention is not limited to use in this specific context, and is applicable to a wide range of arrangements.

To address the space constraints, in the present invention, and as noted above, a damping mechanism 68 is integrated into the rotor hub 50 such that it is contained within an envelope defined by the electric machine, i.e. the total space occupied by the electric machine and including the volume of space radially inward of the tubular rotor 46 and stator 48. This provides a space efficient arrangement in which all components are amply accommodated. In this way, in this embodiment the present invention provides an electric machine with integrated damping, which removes the requirement to provide damping within the clutch arrangement. As will become clear in the description that follows, integration of the damping mechanism 68 into the rotor hub 50 is achieved with minimal space requirements as the damping mechanism 68 is located radially inward of the electric machine 44 such that it is contained within the space between the rotor 46 and the driveshaft 32. Therefore, this embodiment of the invention can be implemented into current arrangements having tight axial space constraints without the need for significant re-design.

By relocating the damping mechanism 68, a simpler form of clutch plate can be used which does not have cavities for accommodating damping springs. This means that the overall axial space occupied by the clutch arrangement can be significantly reduced compared with the known damped clutch arrangement described earlier.

A potential added benefit is that this allows for the mass of the flywheel 60 to be increased whilst still offering reduced outer dimensions relative to the known damped clutch arrangement. This is beneficial, since this enables the flywheel 60 to store a higher amount of energy, and so maximise the primary inertia upstream of the driveshaft 32. This helps to ensure smooth running of the drive arrangement 30 with minimal loss of momentum on engagement of the clutch.

The manner in which the damping mechanism 68 is integrated into the rotor hub 50 will now be described in further detail with reference to Figures 4 to 8.

In this embodiment, the rotor hub 50 is formed in two pieces: a main body 84 and an end cap (not shown in Figure 4, shown in Figure 8). Figure 4 shows in isolation the main body 84 of the rotor hub 50. The main body 84 is generally tubular, with a central aperture 86 defining a cylindrical inner wall 88 that encircles the driveshaft 32 when the drive arrangement 30 is assembled.

A planar end face of the main body 84 includes an annular recess 90 that extends axially into the body to a uniform depth. The recess 90 includes a series of equi-spaced, radially enlarged sections which divide the recess 90 into two alternating groups of slots: a set of relatively large slots 92 and a set of relatively small slots 94, the relatively large slots 92 being both radially wider and circumferentially longer than the relatively small slots 94. Due to the difference in width between the relatively large slots 92 and the relatively small slots 94, end walls 96 are defined at either end of each relatively large slot 92. In the embodiment illustrated in Figure 4 there are twelve slots in total, including six large slots 92 and six small slots 94. At the centre of each relatively large slot 92 a radially narrow portion defines a tab 98, the purpose of which is described below.

Turning now to Figure 5, as illustrated each relatively large slot 92 is configured to receive a spring assembly 100 comprising an inner spring 102 disposed within an outer spring 104 of equal length, held together by a pair of disc-like end stops 106. Each end stop 106 includes a central stud 108, and the inner spring 102 fits over the central studs 108 at each end, thereby locating the inner spring 102 and preventing it from moving out of alignment and interfering with the outer spring 104. A circular outer edge of each end stop 106 carries a lip 1 10 which fits closely over the outer spring 104 to lock it in place. To aid assembly, the ends of the outer spring 104 are machined to provide a flat surface 1 12 against which a respective end stop 106 is pressed.

This twin spring arrangement offers an increase in overall strength without increasing the space occupied by the spring assembly. It will be appreciated that many alternative spring arrangements to that exemplified here could be used.

Each spring assembly 100 is inserted into one of the relatively large slots 92 such that each end stop 106 abuts a respective end wall 96 of the slot. Since the large slots 92 are formed into the annular recess 90, the spring assemblies 100 are aligned along a circular path orthogonal to and centred on the driveshaft 32. The spring assemblies 100 are therefore oriented orthogonally with respect to both the central axis of the rotor 46, and a radial axis of the rotor which extends radially from the centre of the rotor 46 to meet the spring assembly 100. The springs 102, 104 may be selected such that a small amount of compression is required to install them, meaning that the spring assembly 100 is securely held in position by virtue of compression forces exerted on each end wall 96. The tab 98 of the slot performs the role of positioning the spring correctly, since the width of the spring is similar to the narrower portion of the large slot 92 defining the tab 98. The larger portions of the slot on either side of the tab 98 provide space around the spring assembly 100 which aids installation and maintenance. Figures 6 and 7 show the rotor hub 50 in combination with a portion of the driveshaft 32 in an exploded arrangement. As noted above the driveshaft 32 includes a radially enlarged portion 56. The radially enlarged portion 56 carries a series of fingers 1 14 extending in parallel with the shaft, the fingers 1 14 forming a castellated structure. The fingers 1 14 are sized for a close fit into the relatively small slots 94 of the rotor hub 50, with a respective finger 1 14 provided for each relatively small slot 94. Accordingly, in this embodiment the enlarged portion 56 of the driveshaft 32 carries six fingers 1 14. The driveshaft 32 is configured such that the fingers 1 14 can be aligned with the relatively small slots 94 when the driveshaft 32 is positioned coaxially with the rotor hub 50.

Moving on to Figure 8, the driveshaft 32 is shown as assembled with the rotor hub 50, such that the fingers 1 14 are located in the relatively small slots 94. The end cap 1 16 of the rotor hub 50 is then fitted over the driveshaft 32 and attached to the main body 84 of the rotor hub 50 using bolts (not shown) inserted through boltholes 1 18 which extend axially through both the main body 84 and the end cap 1 16. The end cap 1 16 and the main body 84 of the rotor hub 50 together encase the enlarged portion 56 of the driveshaft 32, along with the spring assemblies, therefore protecting them from damage and ingress of debris.

Since the spring assemblies are contained within the rotor hub 50, they are entirely radially inward of the rotor 46 and the rest of the electric machine 44.

As best illustrated in Figures 7 and 8, when the driveshaft 32 is assembled with the rotor hub 50, each finger 1 14 of the driveshaft 32 sits between a pair of spring assemblies. It is noted that the relatively large slots 92 of the rotor hub 50 are not closed off from the relatively small slots 94, and therefore there is nothing between the fingers 1 14 and the spring assemblies. Therefore, when assembled, rotation of the rotor 46 causes each finger 114 to apply pressure to an end stop of a neighbouring spring assembly 100. The finger 1 14 urges the end stop 106 away from its respective end wall 96, which compresses the springs. This in turn increases the force that is exerted on the end wall 96 remote from the finger 1 14 by the spring assembly 100. As the driveshaft 32 continues to rotate the springs are compressed further, increasing the force exerted by each spring assembly 100 on the respective end walls 96, and so gradually inducing rotation of the rotor hub 50. This continues until the forces reach equilibrium, which occurs when the rotor hub 50 rotates at the same speed as the driveshaft 32.

By transmitting force from the driveshaft 32 to the rotor hub 50 through the spring assemblies, the time period over which the impulse required to bring the rotor hub 50 up to speed is extended. This reduces the maximum force that is applied to the rotor hub 50 by the driveshaft 32, and therefore the maximum torsional loading in the driveshaft 32 and the clutch, compared with driving the rotor hub 50 directly. In this way the spring assemblies and the fingers 1 14 of the driveshaft 32 cooperate to act as a damping mechanism 68.

The skilled reader will appreciate that the damping mechanism 68 described above operates in a very similar manner to the known damped clutch arrangement described earlier; it is primarily the location at which damping occurs that has changed. Therefore, the damping mechanism 68 of this embodiment retains the advantages of the known arrangement by continuing to provide sufficient damping of the system, whilst enabling a space efficient arrangement which is compatible with the space constraints imposed by current designs for drive arrangements.

It will be appreciated by a person skilled in the art that the invention could be modified to take many alternative forms to that described herein, without departing from the scope of the appended claims.

For example, while the electric machine 44 described above is used in a hybrid arrangement in which the electric machine 44 acts as both a motor and as a generator, in an alternative embodiment the electric machine 44 operates as a simple generator. It is noted that in embodiments in which the electric machine 44 operates as a simple generator, the damping mechanism 68 still acts to damp transfer of torque between the rotor hub 50 and the driveshaft 32.

In another embodiment, the driveshaft 32 is rigidly coupled to the rotor hub 50, and a damping mechanism is implemented between the rotor hub 50 and the rotor 46, for example using a series of annular springs disposed between the rotor hub 50 and the rotor 46.

In other embodiments, the damping mechanism 68 may employ pneumatic or hydraulic damping in addition to or instead of spring damping.

In another embodiment in which the vehicle is an electric vehicle, the clutch arrangement is dispensed with altogether. The damping mechanism is still located inside the electric machine, and therefore continues to damp torque peaks through the drivetrain. In this embodiment, the torque peaks result from torque ripple in the output of the electric machine, as will be familiar to the skilled person. In such embodiments it may be preferable to couple the flex plate to the enlarged portion of the driveshaft rather than to the rotor hub. In another embodiment the damping mechanism is integrated into an electric machine of the axial flux type.

Further aspects of the present invention are set out in the following numbered Clauses:

1 . A drive arrangement comprising an electric machine including a rotor, and a driveshaft arranged to apply torque to the rotor through a damping mechanism; wherein the damping mechanism is arranged to damp transfer of torque between the driveshaft and the rotor, and wherein the damping mechanism is situated within an envelope defined by the electric machine.

2. A drive arrangement according to Clause 1 , comprising a clutch assembly arranged to selectively couple the driveshaft to a source of torque, wherein the damping mechanism is arranged to damp transfer of torque between the driveshaft and the rotor when the clutch assembly is engaged.

3. A drive arrangement according to Clause 1 , wherein the damping mechanism is located radially inward of the rotor in a space between the rotor and the driveshaft.

4. A drive arrangement according to Clause 3, wherein the damping mechanism is integrated with the rotor in a rotor assembly.

5. A drive arrangement according to Clause 4, wherein the rotor assembly comprises a rotor support.

6. A drive arrangement according to Clause 5, wherein the rotor support houses at least a portion of the damping mechanism.

7. A drive arrangement according to Clause 5, wherein the rotor support is rigidly coupled to the rotor, and the damping mechanism is arranged to damp transfer of torque between the rotor support and the driveshaft.

8. A drive arrangement according to Clause 5, wherein the rotor support is rigidly coupled to the driveshaft, and the damping mechanism is arranged to damp transfer of torque between the rotor support and the rotor. A drive arrangement according to Clause 3, wherein the driveshaft comprises a radially enlarged portion having a set of axially extending fingers which are arranged to engage with the rotor assembly.

A drive arrangement according to Clause 1 , wherein the damping mechanism comprises at least one spring.

A drive arrangement according to Clause 10, comprising a set of springs equi-spaced along a circular path orthogonal to and centred on the driveshaft.

A drive arrangement according to Clause 10 wherein the rotor assembly comprises a rotor support, and wherein the or each spring is housed in a respective cavity defined in the rotor support.

A drive arrangement according to Clause 1 , wherein the electric machine is a radial flux machine.

A vehicle including a drive arrangement, the drive arrangement comprising an electric machine including a rotor, and a driveshaft arranged to apply torque to the rotor through a damping mechanism; wherein the damping mechanism is arranged to damp transfer of torque between the driveshaft and the rotor, and wherein the damping mechanism is situated within an envelope defined by the electric machine.

A vehicle according to Clause 14, comprising an internal combustion engine which is a source of torque for the drive arrangement.

A vehicle according to Clause 15, wherein the electric machine is operable as an electric motor, such that the electric machine is a secondary source of torque.

A vehicle according to Clause 16 wherein the drive arrangement comprises a clutch assembly arranged to selectively couple the driveshaft to a source of torque; wherein the damping mechanism is arranged to damp transfer of torque between the driveshaft and the rotor when the clutch assembly is engaged; and wherein the electric machine is arranged to provide motive power when the clutch is disengaged, such that the vehicle operates as a hybrid vehicle. An electric machine for a vehicle comprising: an input shaft; a rotor arranged to rotate on application of torque to the input shaft; and an integrated damping mechanism arranged to damp transfer of torque between the input shaft and the rotor.

Claims

A drive arrangement comprising an electric machine including a rotor, and a driveshaft, the driveshaft being arranged to receive torque from an internal combustion engine and apply torque to the rotor through a damping mechanism; wherein the damping mechanism is arranged to damp transfer of torque between the driveshaft and the rotor so as to damp torque transferred from the rotor to a vehicle transmission; wherein the damping mechanism is situated within an envelope defined by the electric machine and located radially inward of the rotor in a space between the rotor and the driveshaft, and wherein the damping mechanism is integrated with the rotor in a rotor assembly.

A drive arrangement according to claim 1 , comprising a clutch assembly arranged to selectively couple the driveshaft to an internal combustion engine, wherein the damping mechanism is arranged to damp transfer of torque between the driveshaft and the rotor when the clutch assembly is engaged.

A drive arrangement according to claim 1 or claim 2, wherein the rotor assembly comprises a rotor support.

A drive arrangement according to claim 3, wherein the rotor support houses at least a portion of the damping mechanism.

A drive arrangement according to claim 3 or claim 4, wherein the rotor support is rigidly coupled to the rotor, and the damping mechanism is arranged to damp transfer of torque between the rotor support and the driveshaft.

A drive arrangement according to claim 3 or claim 4, wherein the rotor support is rigidly coupled to the driveshaft, and the damping mechanism is arranged to damp transfer of torque between the rotor support and the rotor.

A drive arrangement according to any one of the preceding claims, wherein the driveshaft comprises a radially enlarged portion having a set of axially extending fingers which are arranged to engage with the rotor assembly.

8. A drive arrangement according to any preceding claim, wherein the damping mechanism comprises at least one spring.

5 9. A drive arrangement according to claim 8, comprising a set of springs equi-spaced along a circular path orthogonal to and centred on the driveshaft.

10. A drive arrangement according to claim 8 or claim 9 when dependent on claim 3, wherein the or each spring is housed in a respective cavity defined in the rotor o support.

1 1 . A drive arrangement according to any preceding claim, wherein the electric machine is a radial flux machine. 5 12. A vehicle including a drive arrangement according to any preceding claim.

13. A vehicle according to claim 12, comprising an internal combustion engine which is a source of torque for the drive arrangement. 0 14. A vehicle according to claim 13, wherein the electric machine is operable as an electric motor, such that the electric machine is a secondary source of torque.

15. A vehicle according to claim 14 when dependent on claim 2, wherein the electric machine is arranged to provide motive power when the clutch is disengaged, such5 that the vehicle operates as a hybrid vehicle.

16. A drive arrangement substantially as herein described with reference to Figures 3 to 8.