Seal assembly

Abstract

A dynamic seal assembly 300 for a shaft of a drive unit comprises a housing 302 defining a passage 304 for receiving the shaft, and an annular seal 310 secured inside the passage. The seal defines an

Description

TECHNICAL FIELD The present disclosure relates to a dynamic seal assembly for a shaft of a drive unit. Aspects of the invention relate to a dynamic seal assembly, a drive unit, a vehicle, a shield for a seal assembly, and a method of installing a shaft in a drive unit housing. BACKGROUND It is known to provide a housing which defines a passage for receiving a shaft. For example, a housing of a drive unit for a vehicle (e.g., an electric drive unit (EDU)) may have a passage for receiving a shaft which connects to one or more drive components inside the housing. In this way, rotation of the drive components can be transferred to the shaft and any other components of the vehicle which are connected to the shaft, or vice versa. It is also known to provide a dynamic seal assembly for such a shaft, which provides a sealed system inside the housing and thereby inhibits ingress of contaminants (e.g., dirt,, debris, water, etc.) whilst still permitting rotation of the shaft within the passage. An example dynamic seal assembly includes an annular seal component which is secured inside the passage and which defines a seal aperture for forming a seal against the shaft when the shaft is received in the seal aperture. However, to provide an effective seal, the seal aperture must fit closely against the shaft. In some instances, the seal aperture can become damaged during insertion and / or removal of the shaft through the seal aperture (e.g., due to sharp features on an end of the shaft, such as splines). This may result in compromised seal performance. It is an aim of the present invention to address one or more of the disadvantages associated with the prior art. SUMMARY OF THE INVENTION Aspects and embodiments of the invention provide a dynamic seal assembly, a drive unit, a vehicle, a shield for a seal assembly, and a method of installing a shaft in a drive unit housing as claimed in the appended claims. According to an aspect of the present invention there is provided a dynamic seal assembly for a shaft, e.g. of a drive unit. The seal assembly comprises a housing which defines a passage for receiving a shaft, e.g. of a drive unit. The seal assembly also comprises an annular seal component which is secured inside the passage and defines a seal aperture for forming a seal against the shaft when the shaft is received in the seal aperture. The seal assembly also comprises a shield for the seal component which is secured inside the passage outboard of the seal component. The shield is separate to and spaced apart from the annular seal component. The shield defines a shield opening configured to guide a shaft into the passage during assembly. It will be understood that, because the shield is outboard of the seal component, the shield forms a protective barrier for the seal component (i.e., at least partially encloses the seal component within the passage). In this way, the shield may protect the seal component from physical damage (e.g., due to impact with a shaft or assembly tools) prior to or during insertion of the shaft into the passage and / or in use. Further, such an arrangement where the annular seal component and shield are separate components which are both secured inside the passage spaced apart from each other may be particularly beneficial because direct interaction between the two components can be avoided. This means that the annular seal component can be designed without having to consider requirements of the shield and vice versa. For example, the shield can be made from a material which is corrosion-resistant but not suitable for over-moulding of seal material. On the contrary, the annular seal component may have a support covered by a seal and the support may be made from a material which is suitable for over-moulding of the seal, but which does not have to be corrosionresistant (due to being covered by the seal material). Further, by securing the annular seal component and the shield in a spaced apart arrangement inside the passage, the shield can act to protect the seal component without impinging on the movement of the sealing portions of the seal component or requiring a redesign of the seal component in order to avoid such an impingement. This arrangement may also simplify assembly and commonality between different applications because a standard annular seal component (e.g., from an application which does not require shielding) may be secured inside the passage, and then the separate shield may be secured inside the passage. Optionally, the shield opening is configured to guide said shaft into the seal aperture as said shaft is inserted into the passage during assembly. The shield opening being configured to guide said shaft into the seal aperture as said shaft is inserted into the passage may reduce the likelihood of damage to the annular seal component due to any sharp features (e.g., splines) on the shaft. Optionally, the seal aperture and the shield opening are co-axial such that the shield opening aligns the shaft with the seal aperture during insertion of the shaft into the passage. This may further reduce the likelihood of damage to the annular seal component due to any sharp features (e.g., splines) on the shaft. Optionally, the shield comprises a peripheral surface which defines a radially outermost surface of the shield and which engages an inner wall of the passage to secure the shield inside the passage. This may simplify assembly (e.g., in comparison to arrangements where the shield is fastened inside the passage). Optionally, the peripheral surface is substantially flat and extends in an axial direction of the seal assembly. This may simplify assembly and / or provide a more secure fixation of the shield within the passage. Optionally, the peripheral surface of the shield is press-fitted into the passage to secure the shield within the passage. The peripheral surface being press-fitted may simplify securing of the shield inside the passage in comparison to other methods (e.g., snap-fitting, clips, fasteners, etc.). In addition, being press-fitted may provide a more robust means of securing the shield inside the passage in comparison to other methods (e.g., snap-fitting, clips, fasteners, etc.). The shield may be secured by other means, such as a friction or spring fit. In some embodiments, the peripheral surface of the shield may be resiliently deflected in a radially inward direction to secure the shield inside the passage. In some embodiments, the peripheral surface of the shield may be fastened or bonded to the inside of the passage. These provide alternative or additional means of securing the shield inside the passage. Optionally, the shield comprises a corrosion-resistant material. Being corrosion resistant may increase the longevity of the shield. In addition, because the shield is separate to the seal component, the shield can be formed of corrosion-resistant material without having to consider any requirements of the seal component (e.g., being suitable for overmoulding of seal material). Optionally, the shield comprises a base material coated with a corrosion-resistant coating. Having a base material coated with a corrosion-resistant coating may provide flexibility in choice of base material (e.g. for cost efficiency, ease of manufacturing, assembly etc.) whilst still providing good corrosion resistance. Optionally, the base material comprises high-strength low-alloy (HSLA) steel or mild steel and the corrosionresistant coating comprises a zinc-based coating. HSLA steel or mild steel with a zinc-based coating may be more cost effective and easier to manufacture than alternatives (e.g., stainless steel). These materials may also be suitable for press-fitting into the housing to secure the shield inside the passage. Optionally, the shield comprises metallic material, optionally steel material; Such materials may provide numerous benefits, such as rigidity for aligning the shaft with the seal aperture during assembly, ease of manufacture (e.g., by stamping / bending sheet metal), and ease of installation (e.g., by press-fitting into the passage). Optionally, the shield comprises high-strength low-alloy (HSLA) steel material or mild steel material. HSLA steel or mild steel (e.g., steel with less than 0.25% carbon by weight) may be more cost effective than alternatives such as stainless steel. In addition, HSLA steel or mild steel may be easier to form into shape (e.g., by bending, stamping, etc.) than alternatives such as stainless steel. Optionally, the shield is made from sheet metal material, wherein the shield comprises a main surface arranged transverse to an axial direction of the passage. Optionally, the shield comprises a peripheral rim (or “outer rim”). The peripheral rim may be bent from an outer edge of the main surface. Optionally, the peripheral rim extends from the main surface in an inboard direction of the passage. Such a peripheral rim provides a larger peripheral surface which increases contact area of the shield with an inside of the passage. This may provide a more robust securing (e.g., press-fit) of the shield inside the passage. Optionally, the shield comprises an interior rim (or “inner rim”) which defines the shield opening. The inner rim may be bent from an inner edge of the main surface and which defines the shield opening. Optionally, the interior rim extends from the main surface in an inboard direction of the passage. Such an interior rim provides a larger interior surface which increases contact area with a shaft as it is inserted through the shield opening. This may facilitate better guiding (e.g., axial alignment) of the shaft with the seal aperture. Optionally, the shield comprises an annular body. The shield comprising an annular body (and thus comprising an annular shield opening) may provide increased rigidity in comparison to alternatives (e.g., semi-annular bodies, or a plurality of circumferentially distributed bodies). This may facilitate better guiding (e.g., axial alignment) of the shaft as it is inserted through the annular shield opening. In other examples, the shield may comprise a part-annular body, for example having an incomplete ring shape such as a C-shaped shield body. The annular body may comprise a disc extending transversely to the passage. The disc may define the main surface of the shield. The annular body may comprise a peripheral (e.g., outer) rim at an outer periphery of the disc. The annular body may comprise an interior (e.g., inner) rim at an inner periphery of the disc. The inner rim may extend from the inner periphery in an axial direction of the seal assembly towards the seal component. Optionally, the annular body comprises one or more drain holes which each define a path between inboard and outboard sides of the annular body. Such one or more drain holes may facilitate draining of contaminants captured in the annular space defined between the seal component and the shield. In other words, such drain holes may inhibit captive contamination. Optionally, each drain hole comprises a width of at least 1.5mm, optionally at least 2mm, optionally at least 2.5mm, optionally at least 3mm, optionally at least 3.5mm. It will be understood that larger drain holes may permit more contaminants to pass into the annular space between the seal component and the shield, but will also allow better draining of contaminants from the annular space than smaller drain holes. Drain holes with a width (e.g., diameter) of at least 1.5mm have been found to provide better overall reduction of captive contamination than smaller drain holes (e.g., with a width of 1 mm), due to the improved drainage. Optionally, the seal assembly comprises a plurality of drain holes circumferentially distributed about the annular body. It will be understood that, although during normal use the majority of contaminants will drain through the lower drain hole(s), having a plurality of circumferentially-distributed drain holes facilitates draining of contaminants over a wider area (e.g., when on uneven ground). In addition, this may simplify assembly because the shield may be inserted into passage in any angular orientation whilst ensuring a drain hole will be positioned proximal to the lower end of the shield. According to a further aspect of the present invention there is provided a drive unit comprising a seal assembly as disclosed herein. Such a drive unit benefits from the advantages of the seal assembly outlined above. Optionally, the drive unit is an electric drive unit. Optionally, the housing of the seal assembly is defined by a housing of the drive unit. Optionally, the passage of the seal assembly is defined by the housing of the drive unit. In other examples, the housing of the seal assembly and / or the passage may be defined by an additional component which is affixed to the drive unit. According to a further aspect of the present invention there is provided a vehicle comprising a drive unit as disclosed herein. Such a drive unit benefits from the advantages of the seal assembly outlined above. According to a further aspect of the present invention there is provided a shield for a seal assembly as disclosed herein. The shield comprises an annular body which defines a shield opening for receiving a shaft in an axial direction. Optionally, the annular body comprises a peripheral rim which extends in the axial direction. Optionally, the peripheral rim defines a radially outermost surface of the shield. Optionally, the annular body is made of a corrosion-resistant material. Optionally, the annular body comprises a base material coated with a corrosion-resistant coating. Optionally, the base material comprises high-strength low-alloy (HSLA) steel or a mild steel and the corrosionresistant coating comprises a zinc-based coating. Optionally, the annular body comprises one or more drain holes which each define a path between first and second sides of the annular body. Optionally, each drain hole comprises a diameter of at least 1.5mm, optionally at least 2mm, optionally at least 2.5mm, optionally at least 3mm, optionally at least 3.5mm. Optionally, the annular body comprises a plurality of drain holes circumferentially distributed about the annular body. Optionally, the annular body is formed from sheet metal material, wherein the annular body defines a main surface and the peripheral rim is bent from an outer edge of the main surface. Optionally, the annular body comprises an interior rim which is bent from an inner edge of the main surface. According to a further aspect of the present invention there is provided a method of installing a shaft in a drive unit housing, the method comprising: a) providing a drive unit having a drive unit housing defining a passage for a shaft; b) securing an annular seal component of a dynamic seal assembly inside the passage, the annular seal component defining a seal aperture; c) subsequently securing a shield for the annular seal component inside the passage at a position outboard of and spaced apart from the annular seal component, the shield being separate to the annular seal component and defining a shield opening; d) inserting a shaft through the shield opening; e) guiding the shaft through the seal aperture using the shield opening to form a dynamic seal between the seal component and the shaft; and f) coupling the shaft with a drive output of the drive unit. It will be understood that, by guiding the shaft through the seal aperture using the shield opening the likelihood of damage to the annular seal component due to any sharp features (e.g., splines) on the shaft may be reduced. Further, such a method which involves securing the annular seal component and shield inside the housing in separate steps (i.e, separately) and spaced apart from each other, may be beneficial because direct interaction between the two components can be avoided. This means that the annular seal component can be designed without having to consider requirements of the shield and vice versa. For example, the shield can be made from a material which is corrosion-resistant but not suitable for over-moulding of seal material. On the contrary, the annular seal component may have a support covered by a seal and the support may be made from a material which is suitable for over-moulding of the seal, but which does not have to be corrosion-resistant (due to being covered by the seal material). This method may also simplify assembly and commonality between different applications because a standard annular seal component (e.g., from an application which does not require shielding) may be used in step b). Within the scope of this application, it is expressly intended 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. That is, all embodiments and / or features of any embodiment can be combined in any way and / or combination, unless such features are incompatible. The applicant reserves the right to change any originally filed claim or file any new claim accordingly, including the right to amend any originally filed claim to depend from and / or incorporate any feature of any other claim although not originally claimed in that manner. BRIEF DESCRIPTION OF THE DRAWINGS One or more embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 shows a vehicle in accordance with an embodiment of the invention; Figure 2 schematically shows functional units and a control system of the vehicle; Figure 3 shows a controller for use in the vehicle of Figure 2; Figure 4 shows a schematic cross-sectional view of an Electric Drive Unit (EDU) assembly of the vehicle of Figures 1 and 2; Figure 5 shows an underside view of the EDU assembly of Figure 4; Figure 6 shows an exploded perspective view of a seal assembly in accordance with an embodiment of the invention; Figure 7 shows a schematic cross-sectional view of the seal assembly of Figure 6 with a shaft inserted therethrough; Figure 8 shows a front view of a shield of the seal assembly of Figures 6 and 7; Figure 9 shows a side cross-sectional view of the shield of Figure 8; Figure 10 shows an enlarged side cross-sectional view of part of the shield of Figures 8 and 9; Figure 11 shows a schematic side cross-sectional view of part of the shield of Figures 8 to 10; and Figure 12 shows a flow chart of a method of installing a shaft in a drive unit housing, in accordance with an embodiment of the invention. DETAILED DESCRIPTION Figures 1 and 2 show an example of an electric vehicle (EV) 10. The electric vehicle 10 comprises a battery or battery pack 40. The battery 40 may be recharged from an external electrical source. The electric vehicle 10 comprises a pair of front wheels 12 at a front axle 28 and a pair of rear wheels 14 at a rear axle 38. The vehicle has at least one electric drive unit (EDU) by which one or more of the wheels are driven. In the illustrated embodiment, the vehicle comprises two electric drive units, each associated with one of the pairs of wheels. In other embodiments, the vehicle may have a dedicated EDU for each of the front wheels 12 and / or a dedicated EDU for each of the rear wheels 14. In the illustrated embodiment, the front wheels 12 are driven by a first electric drive unit (EDU) 20. The first EDU 20 comprises a first motor 22, a front transmission 24 and power electronics 26. The rear wheels 14 are driven by a second electrical drive unit (EDU) 30. The second EDU 30 comprises a second motor 32, a rear transmission 34 and power electronics 36. The first EDU 20 and the second EDU 30 each receive a DC supply from battery 40. The first EDU 20 can be called a first propulsion unit and the second EDU 30 can be called a second propulsion unit. As used herein, the term “transmission” may refer to a device with a plurality of gears through which torque can be transmitted from the drive unit to one or more of the wheels. For example, this may refer to a differential, transaxle, and / or a gearbox. The electric vehicle 10 has a control system with a controller 50 which controls operation of the first EDU 20 and the second EDU 30. In operation, the controller 50 controls the power output of each of the EDUs 20, 30 to supply torque to the wheels 12,14. Power electronics 26 comprise an inverter which converts the DC supply from battery 40 to an AC supply to drive the first motor 22. The first motor 22 drives the front transmission 24 which, in turn, drives the front axle 28 to apply torque to the front wheels 12. Power electronics 36 comprise an inverter which converts the DC supply from battery 40 to an AC supply to drive the second motor 32. The second motor 32 drives the rear transmission 34 which, in turn, drives the rear axle 38 to apply torque to the rear wheels 14. One or both of the front and rear axles 28, 38 may be a continuous shaft extending through their respective EDU, or a pair of half shafts which extend from their respective EDU. Figure 3 schematically shows the control system. The control system comprises one controller 50, although it will be appreciated that this is merely illustrative. The controller 50 comprises at least one processor 56 which may be any type of processor for executing instructions to control the operation of the system. The processor 56 is electrically connected to other components of the controller via one or more buses 57. Processorexecutable instructions 48 may be provided using any data storage device or computer-readable media, such as memory 58. The processor-executable instructions 48 comprise instructions for implementing the functionality of the described methods. The storage / memory 58 is of any suitable type such as non-volatile memory, a magnetic or optical storage device. The processor 56 is configured to access the memory 58 and 7 execute the stored instructions 48. Memory 58, or a separate memory / storage stores data 60 used by the processor 56. Data 60 may comprise data which defines a plurality of operating points of the first motor 22. Instructions 48 may comprise rules for selecting between plurality of operating points of the first motor 22. The controller 50 comprises an input interface 54. The input interface 54 is configured to receive one or more input signals 53 (e.g., a demand for acceleration or a demand for speed). The controller 50 comprises an output interface 55. The output interface 55 is configured to output outputs, such as the control signal 51 to control the first motor 22 (sent to power electronics 26) and the control signal 52 to control the second motor 32 (sent to power electronics 36). The controller 50 is configured to use one or more of the input signals 53 and stored data 60, to generate output signals 51,52. Optionally, the controller 50 may operate the vehicle in the following ways: (i) Rear-wheel drive (RWD). Torque is only supplied to the rear wheels 14 by operating the second motor 32 to drive the rear wheels 14. The front wheels 12 are not driven by the first motor 22; (ii) All-wheel drive (AWD). Torque is supplied to the rear wheels 14 and to the front wheels 12 by operating the second motor 32 to drive the rear wheels 14 and operating the first motor 22 to drive the front wheels 12; (iii) Front-wheel drive (FWD). Torque is only supplied to the front wheels 12 by operating the first motor 22 to drive the front wheels 12. The rear wheels 14 are not driven by the second motor 32. In some vehicles, the controller 50 may only operate according to options (i) and (ii), and may not operate according to option (iii). In other embodiments, the electric vehicle may include only one EDU 20, 30. For example, the second EDU 30 may be omitted in embodiments where the electric vehicle is a “front-wheel drive” vehicle, or the first EDU 20 may be omitted in embodiments where the electric vehicle is a “rear-wheel drive” vehicle. In further embodiments, one or more of the wheels may be driven individually by a dedicated EDU. For example, the front wheels 12 may each be connected to one of a pair of front EDUs. In a further example, the rear wheels 14 may be connected to a plurality of rear EDUs, and / or the front wheels 12 may be connected to a plurality of front EDUs. Referring now to Figures 4 and 5, an EDU assembly is indicated at 100. The EDU assembly 100 includes a motor 102 (shown schematically in Figure 4), a transmission 112 (shown schematically in Figure 4), and a housing 150 for the motor 102 and the transmission 112. It will be understood that the EDU assembly 100 illustrated in Figures 4 and 5 could be, or form part of, the first EDU 20 and / or the second EDU 30 illustrated schematically in Figure 2, along with the additional power electronics 26, 36 described above (not illustrated in the EDU assembly 100 of Figures 4 and 5). The motor 102 may be an induction motor (IM). An induction motor can also be called an induction machine, as it is capable of operating as a motor and as a generator. Alternatively, the motor 102 may be a permanent magnet (PM) synchronous motor. In either case, the motor 102 includes a rotor 104 and a stator 106 with electrical windings 108. The motor 102 is operated by suppling an AC supply to the stator windings 108 which causes movement of the rotor 104 about a rotational axis R. IM and PM motors are known and will therefore not be described in more detail. In some embodiments, the motor 102 is of a different kind, such as a DC motor, a universal motor, or a non-electrical motor such as a hydraulic motor. The rotor 104 is coupled to a motor output shaft 110. In other words, the rotor 104 and output shaft 110 are configured for co-rotation about the rotational axis R. In this way, as the rotor 104 is rotated by the AC supply to the stator windings 108, the output shaft 110 is also rotated. The output shaft 110 is supported for rotation relative to the housing 150 by an output shaft bearing arrangement 116 which, in this embodiment, includes a first bearing 116A (shown schematically in Figure 4) on a first side of the output shaft 110 and a second bearing 116B (shown schematically in Figure 4) on a second side of the output shaft 110. The firstand second bearings 116A, 116B may be ball bearings, roller bearings or any other suitable bearing. The transmission 112 is responsible for transmitting power from the output shaft 110 of the motor 102 to the front or rear wheels 12, 14 of the electric vehicle 10. Optionally, the transmission 112 includes a differential 118 (shown schematically in Figure 4) which allows half shafts (not shown in Figure 4 or 5) of the respective axle 28, 38 to be rotated at different speeds while receiving power from the motor 102. In some embodiments, the transmission 112 may comprise a gearbox between the output shaft 110 of the motor 102 and the differential 118. The differential 118 may be of any suitable configuration. The differential 118 may include one or more components which are supported for rotation relative to the housing 150 by a differential bearing arrangement (not shown) including one or more bearings. Although not illustrated in Figures 4 and 5, the half shafts of the respective axle 28, 38 may be coupled to the differential 118 via any suitable means (e.g., by engaging external splines on the half shafts with internal splines on a component of the differential 118). The half shafts may be supported for rotation relative to the housing by one or more half shaft bearings 130, which may be ball bearings, roller bearings or any other suitable bearing. The illustrated EDU assembly 100 includes a lubricant recirculation system 200, which supplies lubricant to one or more rotating components of the EDU (e.g., motor 110, bearings 116A, 116B, 130, and / or the differential 118 outlined above). The lubricant, such as oil, may both lubricate and cool those rotating components. The lubricant recirculation system 200 includes a sump 152 and a lubricant pump 202 which supplies lubricant along a flow path between the sump 152 and the interior of the housing 150. The flow path is at least in part defined by one or more conduits. The lubricant which is supplied into the housing 150 is then drained into the sump 152 at a lower end of the housing 150. A lubricant pick-up pipe 154 is provided adjacent to or in the sump 152. The lubricant pick-up pipe 154 has a lubricant inlet aperture 156 through which lubricant may be drawn into the pick-up pipe 154 by means of the lubricant pump 202. In this way, lubricant is recirculated by the lubricant pump 202 through the housing 150. The lubricant recirculation system 200 may also include a lubricant filter 204. In the illustrated embodiment, the lubricant filter 204 is located along the flow path downstream of the lubricant pump 202. In the illustrated embodiment, the housing 150 has a first portion 150A which houses the motor 102, and a second portion 150B which houses the transmission 112. In the illustrated embodiment, the first and second housing portions 150A, 150B are discrete components which are coupled together (e.g., via a bolting arrangement). The housing 150 may also include a cover 150C (shown schematically in Figure 4) which closes an end of the first housing portion 150A opposite to the second housing portion 150B. The cover 150C may be a discrete component which is coupled to the first housing portion 150A (e.g. via a bolting arrangement), or may instead be integrally formed with the first housing portion 150A. In alternative embodiments, any other suitable housing configuration may be used. The housing 150 may have one or more mounting features 132 for mounting the EDU assembly 100 to a subframe of the electric vehicle 10 and / or for reacting torsional forces generated by the EDU assembly. As will be described in more detail below, the illustrated EDU assembly 100 also includes seal assemblies 300 at opposite ends of the housing 150, for sealing against the half shafts of the respective axle 28, 38. Such seal assemblies 300 provide a sealed system inside the housing 150 and thereby inhibit ingress of contaminants (e.g., dirt,, debris, water, etc.) inside the housing 150. Referring now to Figures 6 and 7, one of the seal assemblies 300 is illustrated in more detail. It will be understood that the other seal assembly 300 may have a similar construction. The seal assembly 300 is a dynamic seal assembly. In other words, the seal assembly 300 is configured to seal against a rotating component which, in this embodiment, is a shaft 44. The shaft 44 may be a half shaft of the front or rear axle 28, 38. The seal assembly 300 has a housing 302 which defines a passage 304 for receiving the shaft 44 (as illustrated in Figure 7). In the illustrated embodiment, the housing 302 of the seal assembly is defined by the housing 150 of the EDU assembly 100. Similarly, the passage 304 of the seal assembly 300 is defined by the housing 150 of the EDU assembly 100. The seal assembly 300 has an annular seal component 310 which is secured inside the passage 304 and which defines a seal aperture 312 for forming a seal against the shaft 44 when the shaft 44 is received in the seal aperture 312 (as illustrated in Figure 7). The seal assembly 300 also has a shield 328 for the seal component 310 which is secured inside the passage 304 outboard of the seal component 310. The shield 328 is separate to and spaced apart from the annular seal component 310. It will be understood that, because the shield 328 is outboard of the seal component 310, the shield 328 forms a protective barrier for the seal component 310 (i.e., the shield 328 at least partially encloses the seal component 310 within the passage 304). In this way, the shield 328 may protect the seal component 310 from physical damage (e.g., due to impact with the shaft 44 or assembly tools) prior to or during insertion of the shaft 44 into the passage 304 during assembly or maintenance and / or in use. The shield 328 defines a shield opening 330 which is configured to guide the shaft 44 into the passage 304 during installation. In particular, the shield opening 330 is configured to guide the shaft 44 into the seal aperture 312 during assembly. This may reduce the likelihood of damage to the seal component 310 due to any sharp or edge features (e.g., splines) on the shaft 44. In the illustrated embodiment, the seal aperture 312 and the shield opening 330 are co-axial such that the shield opening 330 aligns the shaft 44 with the seal aperture 312 during insertion of the shaft 44 into the passage 304. This may further reduce the likelihood of damage to the seal component 310 due to any sharp features (e.g., splines) on the shaft. In the illustrated embodiment, the seal aperture 312 and shield opening 330 are co-axial with the rotation axis R of the EDU 100 described above. In the illustrated embodiment, the seal component 310 has a support or “can” 314 and seal material 316 which is over-moulded onto the support 314. The seal material 316 may be made of a polymer material, or any other suitable material. The seal material 316 is shaped to define a first lip 318, a second lip 320, and a third lip 322. The first, second and third lips 318, 320, 322 are separate and each engage the shaft 44 when it is received in the seal aperture 312. Therefore, there are three separate seals against the shaft 44. This increases robustness of the seal. However, in alternative embodiments, the seal material 316 may be shaped to define one, two, or more than three separate lips. In the illustrated embodiment, a supporting ring 324 is coupled to the seal material 316 proximal to the third lip 322. This limits radially outward deflection / stretching of the third lip 322 which may improve contact of the third lip 322 with the outer surface of the shaft 44. In the illustrated embodiment, the seal material 316 is also shaped to define an axial lip 326 which extends in an outboard axial direction (i.e. towards the shield 328). The axial lip 326 may act as a gutter which inhibits contaminants passing under gravity from an upper end of the seal component 310 towards the shaft 44 and / or first lip 318. In the illustrated embodiment, the support 314 of the seal component 310 is positioned fully inboard of the seal material 316. In other words, the seal material 316 covers the support 314 so that the support is isolated from the portion of the passage 304 outboard of the seal component 310. In this way, contact with the support 314 by outside contaminants can be minimised or prevented. This allows the support 314 to be made from a material which does not have to be corrosion-resistant. In some embodiments, the support 314 is made from high-strength low-alloy (HSLA) steel or mild steel. In some embodiments, the support 314 is coated with a phosphate coating, which may improve overmoulding of the seal material 316. In other embodiments, any other suitable material and / or coating may be used for the support 314. In the illustrated embodiment, the seal component 310 is press-fitted into the passage 304. In particular, the support 314 is designed to have an external diameter which is slightly larger than an internal diameter of the passage 304 so that the support 314 is deformed or compressed as the seal component 310 is inserted into the passage 304. In this way, a radially outermost surface of the support 314 engages an inner wall 306 of the passage 304 to secure the seal component 310 in place. In the illustrated embodiment, a shoulder 308 is provided in the inner wall 306. The shoulder 308 may facilitate axial positioning of the seal component 310 within the passage 304 and / or limit over-insertion of the seal component 310 into the passage. In alternative embodiments, any other suitable seal component 310 and any other suitable means of securing the seal component 310 within the passage 304 may be used. In the illustrated embodiment, the shield 328 has a peripheral surface 340 (described in more detail below with reference to Figures 8 to 10). The peripheral surface 340 defines a radially outermost surface of the shield 328 and engages the inner wall 306 of the passage 304 to secure the shield 328 inside the passage 304. In the illustrated embodiment, the peripheral surface 340 is substantially flat and extends in an axial direction of the seal assembly 300 (e.g., in an axially inboard direction parallel to the rotation axis R). In the illustrated embodiment, the peripheral surface 340 of the shield 328 is press-fitted into the passage 304 to secure the shield 328 within the passage 304 outboard of and separated from the seal component 310. In particular, the shield 328 is designed to have an external diameter defined by the peripheral surface 340 which is slightly larger than the internal diameter of the passage 304, so that the peripheral surface 340 is deformed or compressed as the shield 328 is inserted into the passage 304. In this way, the peripheral surface 340 engages the inner wall 306 of the passage 304 to secure the shield 328 in place. In some embodiments, the peripheral surface 340 of the shield 328 may be resiliently deflected in a radially inward direction to secure the shield 328 inside the passage 304. For example, the shield 328 may have a part-annular or “C-shaped” shape, which allows inward radial deflection to fit inside the passage 304. In some embodiments, the peripheral surface 340 of the shield may be fastened or bonded to the inside of the passage 304. In other embodiments, the shield 328 is secured in the passage 304 by any other suitable means (e.g., using a friction fit, a spring fit, a snap-fitting arrangement, and / or one or more clips, etc.). It will be understood that the lips 318, 320, 322 of the seal material 316 will inhibit contaminants from passing inboard of the seal component 310, and the shield 328 may inhibit contaminants from passing through the passage to the seal component 310. However, in the illustrated embodiment a flinger 46 is mounted to the shaft 44 as an additional barrier to inhibit contaminants passing along the shaft 44 to the seal assembly 300. This uses centrifugal force to eject contaminants and hinder their ingress into the passage 304. Referring now to Figures 8 to 11, the shield 328 will be described in more detail. In the illustrated embodiment, the shield 328 is an annular body 332. In particular, the annular body 332 has a disc or main surface 334 which extends transversely to the passage 304 when the shield 328 is secured in the passage 304. The annular body 332 also has a peripheral (e.g., outer) nm 342 at an outer periphery of the disc 334. The peripheral rim 342 defines the peripheral surface 340 described above. In the illustrated embodiment, the peripheral rim 342 extends from an outer edge 344 (e.g., an outer periphery) of the disc 334 in an inboard direction of the passage 304 when the shield 328 is secured in the passage 304. In other words, the peripheral rim 348 extends in an axial direction of the seal assembly 300 towards the seal component 310. As best illustrated in Figure 10, the peripheral rim 342 has an outer transition surface 346 at a free end 347 of the peripheral rim 342 distal the disc 334. The outer transition surface 346 tapers radially inwards towards the free end 347 of the peripheral rim 342. In other words, the peripheral surface 340 tapers radially inwards towards the free end 347 of the peripheral rim 342. In this embodiment, the outer transition surface 346 is chamfered (e.g., defining a linear taper). In other embodiments the outer transition surface 346 may be filleted (e.g., defining a curved taper) or have some irregular tapering shape. It will be understood that such an outer transition surface 346 may facilitate insertion of the shield 328 into the passage 304. This may be particularly useful in embodiments where the shield 328 is press-fitted into the passage 304. For example, away from the outer transition surface 346, the peripheral surface 340 may be wider than the diameter of the passage 304. In this way, the outer transition surface 346 acts as a guide surface to partially insert the peripheral rim 342 into the passage 304 before being deformed or compressed by the press-fit. The annular body 332 also has an inner (e.g., interior) rim 348 at an inner periphery of the disc 334. The inner rim 348 defines the shield opening 330. In the illustrated embodiment, the inner rim 348 extends from an inner edge 350 (e.g., an inner periphery) of the disc 334 in an inboard direction of the passage 304 when the shield 328 is secured in the passage 304. In other words, the inner rim 348 extends in an axial direction of the seal assembly 300 towards the seal component 310. As best illustrated in Figure 10, the annular body 332 has an inner transition surface 352 between the disc 334 and the inner rim 348. The inner transition surface 352 tapers radially inwards from the disc 334 to the inner rim 348. In this embodiment, the inner transition surface 352 is curved. It will be understood that such an inner transition surface 352 may facilitate insertion of the shaft 44 through the shield opening 330 during assembly. As such, the inner transition surface 352 can be considered as a guide surface for the shaft 44. In the illustrated embodiment, the annular body 332 has one or more drain holes 354 which each define a path between first and second sides 336, 338 (e.g., inboard and outboard sides) of the annular body 332. In particular, the annular body 332 has a plurality of drain holes 354 which are circumferentially distributed about the annular body 332. The drain holes 354 facilitate draining of contaminants captured in the annular space defined between the seal component 310 and the shield 328. In other words, the drain holes 354 inhibit captive contamination in this annular space. In the illustrated embodiment, each drain hole 354 has a width 356 of at least 1,5mm, optionally at least 2mm, optionally at least 2.5mm, optionally at least 3mm, optionally at least 3.5mm. For example, in some embodiments, the drain holes 354 each have a width 356 of around 3.5mm. Such drain holes 354 have been found to provide better overall reduction of captive contamination than smaller dram holes (e.g., with a width of 1 mm), due to the improved drainage. The shield 328 may be made from a corrosion-resistant material. For example, as illustrated in Figure 11, the shield 328 may have a base material 358 coated with a corrosion-resistant coating 360. In some embodiments, the base material 358 is a high-strength low-alloy (HSLA) steel or mild steel (e.g., steel with less than 0.25% carbon by weight). This may be more cost-effective than alternative materials. In some embodiments, the corrosion-resistant coating is a zinc-based coating. In other embodiments, the base material itself 358 may be corrosion-resistant (e.g., stainless steel). In such embodiments, the coating 360 may be omitted. In some embodiments, the shield 328 is made from sheet metal material. In such embodiments, the sheet metal material may be stamped and bent to form the annular body 332. For example, the disc 334 may be stamped from the sheet metal material, and the peripheral rim 342 and inner rim 348 may be bent from the inner and outer edges 344, 350 of the disc 334. Referring now to Figure 12, a method of installing the shaft 44 in the housing 150 of the EDU 100 is illustrated as a flow chart. The method comprises the following steps: a) providing a drive unit 100 having a drive unit housing 150 defining a passage 304 for a shaft 44; b) securing an annular seal component 310 of a dynamic seal assembly 300 inside the passage 304, the annular seal component 310 defining a seal aperture 312; c) subsequently securing a shield 328 for the annular seal component 310 inside the passage 304 ata position outboard of and spaced apart from the annular seal component 310, the shield 328 being separate to the annular seal component 310 and defining a shield opening 330; d) inserting a shaft 44 through the shield opening 330; e) guiding the shaft 44 through the seal aperture 312 using the shield opening 330 to form a dynamic seal between the seal component 310 and the shaft 44; and f) coupling the shaft 44 with a drive output of the drive unit 100 (e.g., by engaging splines on the shaft 44 with splines 126 on a side gear 124 of the differential 118 described above). It will be appreciated that various changes and modifications can be made to the present invention without departing from the scope of the present application. It should also be noted that whilst the appended claims set out particular combinations of features described above, the scope of the present disclosure is not limited to the particular combinations hereafter claimed, but instead extends to encompass any combination of features herein disclosed.

Claims

1. A dynamic seal assembly for a shaft of a drive unit, the seal assembly comprising:a housing which defines a passage for receiving a shaft of said drive unit;an annular seal component which is secured inside the passage and defines a seal aperture for forming a seal against the shaft when the shaft is received in the seal aperture; anda shield fortheseal component which is secured inside the passage outboard of the seal component, wherein the shield is separate to and spaced apart from the seal component, and wherein the shield defines a shield opening configured to guide said shaft into the seal aperture as said shaft is inserted into the passage during assembly.

2. The seal assembly of claim 1, wherein the seal aperture and the shield opening are co-axial such that the shield opening aligns the shaft with the seal aperture during insertion of the shaft into the passage.

3. The seal assembly of claim 1 or claim 2, wherein the shield comprises a peripheral surface which defines a radially outermost surface of the shield and which engages an inner wall of the passage to secure the shield inside the passage.

4. The seal assembly of claim 3, wherein the peripheral surface is substantially flat and extends in an axial direction of the seal assembly.

5. The seal assembly of claim 3 or claim 4, wherein the peripheral surface of the shield is press-fitted into the passage to secure the shield within the passage.

6. The seal assembly of any preceding claim, wherein the shield comprises a corrosion-resistant material.

7. The seal assembly of claim 6, wherein the shield comprises a base material coated with a corrosionresistant coating; optionally, wherein the base material comprises high-strength low-alloy steel or mild steel and the corrosion-resistant coating comprises a zinc-based coating.

8. The seal assembly of any preceding claim, wherein the shield comprises an annular body.

9. The seal assembly of claim 8, wherein the annular body comprises one or more drain holes whicheach define a path between inboard and outboard sides of the annular body.

10. The seal assembly of claim 9, wherein each drain hole comprises a width of at least 1,5mm, optionallyat least 2mm, optionally at least 2.5mm, optionally at least 3mm, optionally at least 3.5mm.11, The seal assembly of claim 9 or 10, comprising a plurality of dram holes circumferentially distributed about the annular body.

12. A drive unit comprising the seal assembly of any preceding claim; optionally, wherein the drive unit is an electric drive unit.

13. A vehicle comprising the drive unit of claim 12.

14. A shield for the seal assembly of any of claims 1 to 11, the shield comprising an annular body which defines a shield opening for receiving a shaft in an axial direction, wherein the annular body comprises a peripheral rim which extends in the axial direction and which defines a radially outermost surface of the shield, wherein the annular body is made of a corrosion-resistant material.

15. A method of installing a shaft in a drive unit housing, the method comprising:providing a drive unit having a drive unit housing defining a passage for a shaft;securing an annular seal component of a dynamic seal assembly inside the passage, the annular seal component defining a seal aperture;subsequently securing a shield for the annular seal component inside the passage at a position outboard of and spaced apart from the annular seal component, the shield being separate to the annular seal component and defining a shield opening;inserting a shaft through the shield opening;guiding the shaft through the seal aperture using the shield opening to form a dynamic seal between the seal component and the shaft; andcoupling the shaft with a drive output of the drive unit.17

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