Jack head apparatus

Abstract

A jack head 1 of a lifting jack for interfacing with a liftable part 2 comprises a main body 10 comprising a first end 11 and a second end 12 positioned along a longitudinal axis 13 and a surface of r

Description

TECHNICAL FIELD The present disclosure relates to a jack head apparatus and a corresponding interacting part thereof. More particularly, but not exclusively, the present disclosure relates to a jack head and to a corresponding liftable part or body to form a jacking interface for the lifting of a vehicle. Aspects of the invention relate to a jack head, to a liftable part and to a vehicle. BACKGROUND It is known to provide a variety of different customer jacking interfaces in the automotive industry for the lifting of a vehicle to, for example, change tires or perform repairs on the vehicle. Modern battery electric passenger vehicles are often significantly heavier than their internal combustion engine powered predecessors and often have a very large traction battery under the vehicle floor mounted between the structural sill sections. This traction battery is often nearly as wide as the rest of the vehicle in this area which takes some of the previously available space for a discreet jacking interface. A suitable interface is required on the vehicle body that allows the customer to lift any corner of the vehicle in order to change a wheel, despite the large battery. The jack in this case would typically be a scissor jack, supplied with the vehicle to enable the customer to conduct this procedure. There is also a service requirement to lift the car to enable the traction battery to be removed. It is important that the interaction between jack head of the lifting jack and the vehicle is intuitive for all users, is capable of taking the vertical loads during lifting, offers adequate security in horizontal directions and can accommodate real world ground conditions where a flat horizontal surface might not be available. Ideally, the same area of vehicle could also accommodate any size of trolley jack or air jack for recovery operators or garages to lift one or more corners of the vehicle without causing damage to the painted body or the frame of the traction battery. Ideally, these areas would also be suitable for the pads on a 2-post garage lift to lift the entire vehicle, again without causing any damage to the painted body or traction battery frame / enclosure. Current jacking interfaces in use may allow some angular mismatch between the ground beneath the jack and the interface on vehicle, but not to a satisfactory level for all ground surfaces. 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 jack head and a liftable part as claimed in the appended claims. According to an aspect of the present invention there is provided a jack head of a lifting jack for interfacing with a liftable part, the jack head comprising a main body comprising a first end and a second end positioned along a longitudinal axis passing through the first and second ends, and a surface of revolution about the longitudinal axis which separates the first and second ends. The surface of revolution comprises a contact portion for the liftable part which is symmetrical about a first plane of symmetry and symmetrical about a second plane perpendicular to the first plane of symmetry. A first distance between the contact portion and the longitudinal axis reduces towards the first and second ends, and a second distance between the first and second ends along the longitudinal axis is greater than a maximum length of the first distance. According to another aspect of the present invention there is provided a jack, head of a lifting jack for interfacing with a liftable part, the jack head comprising a main body comprising a first end and a second end positioned along a longitudinal axis passing through the first and second ends, and a surface of revolution about the longitudinal axis which separates the first and second ends. The surface of revolution comprises a contact portion for the liftable part which is symmetrical about a first plane of symmetry and symmetrical about a second plane aligned with the longitudinal axis. A first distance between the contact portion and the longitudinal axis reduces towards the first and second ends, and a second distance between the first and second ends along the longitudinal axis is greater than a maximum length of the first distance. According to another aspect of the present invention there is provided a jack head of a lifting jack for interfacing with a liftable part, the jack head comprising a main body comprising a first end and a second end positioned along a longitudinal axis passing through the first and second ends, and a surface of revolution about the longitudinal axis which separates the first and second ends. The surface of revolution comprises a contact portion for the liftable part which is symmetrical about a first plane of symmetry perpendicular to the longitudinal axis and symmetrical about a second plane aligned with the longitudinal axis and perpendicular to the first plane of symmetry. A first distance between the contact portion and the longitudinal axis reduces towards the first and second ends, and a second distance between the first and second ends along the longitudinal axis is greater than a maximum length of the first distance. According to another aspect of the invention, there is provided a liftable part for interfacing with a jack head of a lifting jack, the liftable part comprising a main body with a recessed portion comprising a first end and a second end separated by a surface of revolution about a longitudinal axis. The surface of revolution comprises a recessed contact portion for the jack head which is symmetrical in a first plane of symmetry perpendicular to the longitudinal axis and symmetrical about a second plane aligned with the longitudinal axis and perpendicular to the first plane of symmetry. A first distance between the recessed contact portion and the longitudinal axis perpendicular to the longitudinal axis is variable along the longitudinal axis between the first and second ends, and a second distance between the first and second ends along the longitudinal axis is greaterthan a maximum length of the first distance. The defining features of the jack head and the liftable part enable the accommodation of angular mismatches and offsets in different directions between the ground and the vehicle when lifting a vehicle, reducing the risk of slipping or mechanical failure due to the angular offset. This advantageously results in improved stability and safety when the vehicle is being lifted. The force supplied from the jack head to the liftable part is advantageously centred at the maximum length of the first distance where the jack head is strongest due to the corresponding maximum cross-section at the maximum length of the first distance. Optionally, a minimum distance between the contact portion and the longitudinal axis is at the first and second ends. This advantageously creates a gradient over the profile of the surface of revolution of the jack head and of the liftable part, allowing the jack head and liftable part to accommodate different angular offsets when in use. Optionally, a curve defined by an intersection of the surface of revolution and a second plane has a first radius of curvature that is greater than the maximum length of the first distance. This advantageously gives the profile of the surface of revolution a gradual curve, meaning force is distributed evenly over the surface while also maintaining stability over the contact portion of the jack head. Byway of example, the apparatus may comprise a protrusion or recess on the surface of revolution of the jack head and a corresponding recess or protrusion on the surface of revolution of the liftable part. The protrusion or recess of the jack head allows the jack head to be easily and quickly positioned in the recessed contact portion of the liftable part by locating the corresponding recess or protrusion of the liftable part, thereby providing a mechanism by which the angle between the jack head and liftable part can be limited. The protrusion or recess of the jack head and the corresponding recess, or the protrusion of the liftable part, may be positioned at the mid-point between the first and second ends of the jack head or the liftable part, respectively. When in use, force is advantageously transferred in a substantially equal manner over the contact portion of the jack head and the recessed contact portion of the liftable part. The surface of revolution may be symmetrical in the first plane of symmetry and has 360 degree rotational symmetry about the longitudinal axis. Optionally, the main body of the jack head has substantially the shape of a section of an outer surface of a truncated prolate spheroid (e.g. barrel-shaped). Optionally, the recessed portion of the liftable part has substantially the shape of a section of an internal surface of a truncated prolate spheroid. These features advantageously allow force to be distributed evenly over the surface of revolution, as well as improving machinability and ease of manufacture. In embodiments, the liftable part has a trapezoid-like shape in order to allow unimpeded removal and reinstallation of electric batteries on electrical vehicles. The batteries of electric vehicles typically have a very large surface area and are heavy, being typically placed under the vehicle floor and mounted between the structural sill sections. Advantageously, this shape allows the battery of an electric vehicle to be removed and reinstalled unimpededly. Optionally, the surface of revolution is an outer surface of the main body of both the jack head and the liftable part, respectively. Optionally, the recessed contact portion of the liftable part is configured to cooperate with the contact portion of the jack head, thus improving usability. The liftable part may comprise a first plurality of holes or channels to provide a drainage means for the liftable part. Optionally, the liftable part may comprise a second plurality of holes to provide an attachment means for attachment to a vehicle’s chassis or the like. By way of example, the linable part may comprise at least one recessed groove on the same surface as the recessed contact portion. This provides an additional contact surface of the liftable part is configured to cooperate with the contact surface of lifting equipment used in, for example, garages, factory lines, and the like. Optionally, the liftable part may comprise one or more side step brackets to extend the main part of the liftable part to advantageously increase the contact area for applicable lifting apparatuses other than lifting jacks. According to another aspect of the invention, there is provided a kit of parts comprising the jack head and the liftable part, wherein the contact portion of the jack head and the recessed contact portion of the liftable part are complementary features which cooperate for the lifting of the liftable part. According to another aspect of the invention, there is provided a lifting jack comprising the jack head. According to another aspect of the invention, there is provided a vehicle comprising the liftable part. 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 anyway 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 is a diagram of a known lifting jack; Figure 2 shows a vehicle with an example angular offset with respect to the ground in accordance with an embodiment of the invention; Figures 3a shows a perspective view of a jack head in accordance with an embodiment of the invention and Figure 3b shows the same view as Figure 3a, but with orthogonal planes of the jack head body illustrated; Figures 4a and 4b show schematic drawings of the jack head in a side view and in a front / rear view, respectively; Figure 5 shows a perspective view of a liftable part in accordance with an embodiment of the invention with orthogonal planes of the liftable part illustrated; Figures 6a and 6b show schematic drawings of the liftable part in a side view and in a front / rear view, respectively; Figure 7 shows the jack head placed in the recessed portion of the liftable part, from a perspective view; Figure 8 shows a cut-away view of the jack head and the hftable part in cooperation, from a perspective view; Figure 9 shows a cross section of the jack head and the liftable part in cooperation, from a side view; and Figure 10 shows the liftable part in an alternative embodiment. DETAILED DESCRIPTION With reference to Figures 1 and 2, a typical lifting jack 100 apparatus for the lifting of a vehicle 400 is shown, the lifting jack 100 comprising a jack head 200 which is cooperable with a lifting surface 300 defined by the underside of the vehicle 400. To operate the lifting jack 100, the lifting jack 100 is placed underneath the vehicle 400 at an initial height that is below the height of the underside of the vehicle 400 to the ground. The lifting jack 100 is activated such that the relative vertical height of the lifting jack with respect to the ground increases and the jack head 200 approaches the lifting surface 300. Once the lifting jack 100 moves through a height to reach the underside of the vehicle 400, the lifting jack 100 contacts the lifting surface 300 via the jack head 200. Any further increase in the height of the lifting hack will apply a force to the vehicle 400, through the jack head 200, that is opposed by the weight of the vehicle 400. The higher the applied force, the higher the vehicle 400 will be lifted off the ground, to the limit of extension of the lifting jack. The force required to lift a vehicle 400 may be substantial, therefore requiring the jack head 200 as the contact surface to withstand the high forces involved and to be able to remain stable to prevent the vehicle 400 slipping off the jack 100. The contact point on the vehicle 400 should also be similarly stable to prevent these failures. Angular mismatches, displacements, or offsets between the ground, and therefore the jack head 200, and the vehicle 400 can alter the contact surface and angle at which the force of the weight of the vehicle 400 is applied. In order to maintain an effective and stable contact surface between the lifting jack 100 and the vehicle 400, in embodiments the jack head 200 and the corresponding contact surface on the vehicle 400 are modified as explained in detail below. A jack head in accordance with an embodiment of the present invention is described herein with reference to the accompanying Figures 3-10. The jack head is used in conjunction with a cooperating liftable part or body on (but not limited to) a vehicle. With reference initially to Figures 3a, 3b, 4a, and 4b, the jack head 1 has a main body 10 comprises a first end 11 and a second end 12 positioned along a longitudinal axis 13 of the main body 10. The longitudinal axis 13 passes through the first and second ends 11,12 of the main body 10. For example, the first and second ends 11,12 may be parallel to one another. The first and second ends 11,12 are separated by a surface of revolution about the longitudinal axis 13. A through bore 17 extends along the longitudinal axis 13. The main body 10 is fixedly supported to first and second base supports 18, spaced axially along the longitudinal axis 13, which form a part of a lifting jack stem. At their uppermost ends, the base supports 18 connect with or are integral with a central support rod 19 which extends along the through bore 17 of the main body 10. At their lower ends, the base supports 18 extend from the underside of the main body 10. In other embodiments, the jack head 1 may be appropriately supported to form a part of the lifting jack stem and need not be fixedly supported. The surface of revolution comprises a contact portion 14 which cooperates with a corresponding recessed contact portion 24 of a liftable part 2 during a lifting process (the liftable part 2 will be described in detail below). The contact portion 14 is that portion of the main body 10 of the jack head 1 which may make contact with the liftable part 2 during a lifting and manoeuvring operation in which the jack head 1 is brought into engagement with the liftable part 2 and a force is applied to the liftable part 2, acting against its weight. It will be appreciated that the contact portion 14 extends only over a part of the full surface of revolution. The contact portion 14 of the surface of revolution is symmetrical about a first plane of symmetry X perpendicular to the longitudinal axis 13 and is symmetrical about a second plane Y aligned with the longitudinal axis 13 and perpendicular to the first plane of symmetry X, as shown in Figure 3b. As shown in Figure 4a, the distance D11 between the contact portion 14 and the longitudinal axis 13 in the first plane of symmetry X (i.e. perpendicular to the longitudinal axis 13) is variable along the longitudinal axis 13 between the first and second ends 11, 12. In the example shown, the distance D11 between the contact portion 14 and the longitudinal axis 13 in the first plane of symmetry X is smaller at the first and seconds ends 11,12 than at any point along the longitudinal axis 13 between the first and second ends 11, 12. This results in the distance D11 between the contact portion 14 and the longitudinal axis 13 perpendicularto the longitudinal axis 13 reducing towards the first and second ends 11,12. The distance D12 between the first and second ends 11,12 along the longitudinal axis 13 is greater than the distance D11 between the contact portion 14 and the longitudinal axis 13 in the first plane of symmetry X. In the example shown, the distance D12 between the first and second ends 11,12 along the longitudinal axis 13 is greater than the maximum distance D13 between the contact portion 14 and the longitudinal axis 13 in the first plane of symmetry X. The shape of the jack head 1 is therefore longer along the longitudinal axis 13 than it is wide in the first plane of symmetry X. In the example shown, the minimum distance between the contact portion 14 and the longitudinal axis 13 is at the first and second ends 11, 12. The maximum distance between the contact portion 14 and the longitudinal axis 13 is at the midpoint between the first and second ends 11,12 along the longitudinal axis 13. Therefore, the two-dimensional profile of the surface of revolution in a second plane of symmetry Y, which is aligned with the longitudinal axis 13 and perpendicularto the first plane of symmetry X, may be considered to be a curve defined by an intersection of surface of revolution and the second plane of symmetry Y. This curve may “peak” at the midpoint between the first and second ends 11, 12 and reduces in magnitude towards the first and second ends 11, 12. The curve may be considered to be mirrored about the first plane of symmetry X at the midpoint between the first and second ends 11,12 along the longitudinal axis 13, for example as can be seen in Figure 4a. The radius of curvature of the curve may be greater than the distance between the contact portion 14 and the longitudinal axis 13 in the first plane of symmetry X. This results in the change of gradient of the curve, and therefore the change of gradient of the contact portion 14, being gradual along the longitudinal axis 13. The corresponding hftable part 2 which cooperates with the lifting jack, in use, has a similar geometry to the outer surface of the jack head 1 but implemented as a recess (as will be described in further detail later). Advantageously, angular offsets caused by the misalignment of the ground and vehicle can be accommodated smoothly and evenly across the contact portion 14 when it engages with the corresponding surface of the liftable part 2. Having a steep change in the gradient of the contact portion 14 results in forces occurring over only a small portion of the available contact area and thus would reduce stability and increase the risk of mechanical failure of the jack head 1 and the lifting jack. These features combat these problems in a simple and effective manner, thereby improving stability whilst reducing the risk of mechanical failures in the system. In the example shown, the jack head 1 further comprises a location feature comprising a circumferential protrusion 15 on the surface of revolution which extends over the full contact portion 14. The protrusion 15 serves to aid the user in aligning the jack head 1 with the liftable part 2 when the two parts are brought together to cooperate. The protrusion 15 is positioned at the midpoint between the first and second ends 11,12 along the longitudinal axis 13 and acts as a locating feature for the jack head 1 when the main body 10 is received into a corresponding surface of the liftable part 2, as described further below. In other examples, the protrusion 15 may be positioned at any suitable position along the longitudinal axis 13. The jack head 1 may also comprise one or more cavities 16, as can be seen in Figure 3a. Only two of the cavities 16 are labelled. A central through bore 17 extends axially through the main body 10. The cavities 16 and the bore 17 reduce the amount of material needed to manufacture the jack head 1 whilst having a minimal impact on the surface area of the contact portion 14, thus reducing the cost for manufacture. In the example shown, the surface of revolution is symmetrical in the first plane of symmetry X and about a second plane Y aligned with the longitudinal axis 13 and perpendicular to the first plane of symmetry X. In addition, the contact portion 14 is symmetrical in the first plane of symmetry X and about a second plane Y aligned with the longitudinal axis 13 and perpendicular to the first plane of symmetry X. The surface of revolution and / or the contact portion 14 may also have rotational symmetry over their surfaces, relative to the longitudinal axis 13. This advantageously allows for the jack head 1 to be used in any suitable orientation when lifting a vehicle. The forces transferred through the contact portion 14 of the jack head 1 are also therefore uniform, improving the mechanical performance of the jack head 1 when under force. Because of the symmetrical properties of the jack head 1, the operator does not have change the orientation of the jack head 1 for use, improving usability. As will be appreciated from the foregoing description, the jack head 1 has a main body 10 which is substantially the shape of a truncated prolate spheroid (i.e. has a barrel-like shape). It will be appreciated that the main body 10 may be truncated in the first plane X such that the surface of revolution of the jack head 1 does not necessarily extend 360 degrees around the main body 10 (i.e. the barrel shape of the main body 10 may have a flat surface on its underside). Referring also to Figures 5, 6a and 6b, the liftable part for interfacing with the jack head 1 of the lifting jack is a liftable part 2 of the vehicle. The liftable part 2 may be implemented in a number of ways and, for example, may take the form of a jack pad attached to a vehicle chassis, or as an integrated part of a vehicle chassis or the like. The liftable part 2 has a mam body 20 defining a recessed contact portion 24 comprising a first end 21 and a second end 22 separated by a surface of revolution of the main body 20 about a longitudinal axis 23. The first and second ends 21, 22 may be parallel to one another. The recessed contact portion 24 is symmetrical in a first plane of symmetry X perpendicular to the longitudinal axis 23 and is symmetrical about a second plane Y aligned with the longitudinal axis 23 and perpendicular to the first plane of symmetry X. The main body 20 may be trapezoidal-like in shape. Advantageously, this shape allows the battery of an electric vehicle to be removed and reinstalled unimpededly. Other applicable shapes that accommodate the form and shape of the battery, such as cylindrical or cuboidal, may also be appropriate. The distance D21 between the recessed contact portion 24 and the longitudinal axis 23 perpendicular to the longitudinal axis 23 is variable along the longitudinal axis 23 between the first and second ends 21,22. In the example shown, the distance D21 between the recessed contact portion 24 and the longitudinal axis 23 perpendicular to the longitudinal axis 23 is smaller at the first and seconds ends 21,22 than at any point along the longitudinal axis 23 between the first and second ends 21,22. This results in the distance D21 between the recessed contact portion 24 and the longitudinal axis 23, perpendicularto the longitudinal axis 23, reducing towards the first and second ends 21,22. The distance D22 between the first and second ends 21,22 along the longitudinal axis 23 is greater than the distance D21 between the recessed contact portion 24 and the longitudinal axis 23 in the first plane of symmetry X. In an example, the distance D22 between the first and second ends 21,22 along the longitudinal axis 23 may be greater than the maximum distance D23 between the recessed contact portion 24 and the longitudinal axis 23 in the first plane of symmetry X. The shape of the recessed contact portion 24 of the liftable part 2 may therefore be longer along the longitudinal axis 23 than it is wide in the first plane of symmetry X. In the example shown, the minimum distance between the recessed contact portion 24 and the longitudinal axis 23 may be at the first and second ends 21,22. In addition, the maximum distance between the recessed contact portion 24 and the longitudinal axis 23 may be at the midpoint between the first and second ends 21, 22 along the longitudinal axis 23. The two-dimensional profile of the surface of revolution in a second plane of symmetry Y, which is aligned with the longitudinal axis 23 and perpendicularto the first plane of symmetry X, may therefore be considered to be a curve defined by an intersection of surface of revolution and the second plane of symmetry Y. This curve may “peak” at the midpoint between the first and second ends 21, 22 and reduces in magnitude towards the first and second ends 21, 22. The curve may also be considered to be substantially mirrored about the first plane of symmetry X at the midpoint between the first and second ends 21,22 along the longitudinal axis 23, for example as can be seen in Figure 6a. The radius of curvature of the curve may be greater than the distance between the recessed contact portion 24 and the longitudinal axis 23 in the first plane of symmetry X. This results in the change in gradient of the curve, and therefore the change in gradient of the recessed contact portion 24, being gradual along the longitudinal axis 23. From the foregoing description it will be appreciated that the recessed contact portion 24 of the main body 20 of the liftable part 2 defines a surface which is substantially a section of a truncated prolate spheroid (i.e. has a barrel-like shape). In use, the main body 10 of the jack head 1 is receivable within the recessed portion 24 of the liftable part 2 as the lifting jack is raised towards the vehicle. Figures 7 to 9 best show the cooperation of the jack head 1 with the liftable part 2 in use, when the main body 10 of the jack head 1 is received within the recessed contact portion 24 of the liftable part 2. As can be seen, the outer surface profiles of the jack head 1 and liftable part 2 in both the first plane of symmetry X and the second plane of symmetry Y correspond with and complement each other. The corresponding shaping of the contact portion 14 of the jack head 1 and the recessed contact portion 24 of the liftable part 2 advantageously allows for the liftable part 2 to interface with the jack head 1 in any suitable orientation when a vehicle is being lifted. The forces transferred through the jack head 1 onto the liftable part 2 are therefore also uniform, improving performance. Because of the symmetrical properties of the recessed contact portion 24 of the liftable part 2, the operator does not have to adjust the liftable part 2 at all when trying to correctly position the jack head 1, improving usability. The complementary shape and symmetry of the interfacing surfaces allows for any off-axis tilt of the liftable part 2 relative to the jack head 1, in any direction, without compromising the engagement of the surfaces, which allows for effective and secure lifting even on ground surfaces which are not aligned with the longitudinal axis 13 of the jack head 1. When the longitudinal axis 13 of the jack head 1 is aligned with the ground, the jack head 1 may be received centrally within the recessed contact portion 24 of the liftable part 2, with the protrusion 15 located centrally in the corresponding recess 25. In an alternative scenario, Figures 8 and 9 shows cross-sectional views of the jack head 1 and the liftable part 2 when the jack head 1 is received within the recessed contact portion 24, but with the jack head 1 tilted relative to the ground similar to the angular offset shown in Figure 2. Because of the complementary and symmetrical nature of the surfaces, the surfaces remain engaged in a stable manner, despite the misalignment, so that the force transmission from the jack head 1 to the vehicle is not compromised. The jack head 1 advantageously remains within the recessed contact portion 24 of the liftable part 2, thereby ensuring force is transferred correctly. Likewise, if the jack head 1 tilts in an orthogonal direction, perpendicular to the longitudinal axis 13 and to the plane of the ground, or in any plane misaligned with the ground, the symmetry of the cooperating surfaces ensures good contact remains between the parts and force transmission from the jack head 1 is not compromised. The provision of the protrusion 15 and the cooperation with the recess 25 provides a means to limit the extent of tilt of the jack head 1 within the recessed contact portion 24, further improving performance. It will be appreciated that if the jack head 1 tilts relative to the ground, in any direction, the jack head 1 does not maintain complete contact with the surface of the recessed contact portion 24 over the entire area and a small gap may open between the two parts depending on the extent of the tilt. However, the extent of contact between the surfaces remains sufficient to ensure adequate and stable force transmission to the liftable part 2. It will be appreciated that the contact portion 14 of the jack head 1 does not necessarily extend around the full surface of revolution of the barrel-shaped jack head 1 because only the upper portion of the main body 10 (which defines the contact portion 14) needs to be contactable with the recessed contact portion 24 of the liftable part 2. In the embodiment shown, the contact portion 14 is defined over a relatively upper portion of the outer surface of the main body 10 of the jack head 1. The dimensions of the recessed contact portion 24 of the liftable part 2 may be greater than corresponding dimensions of the main body 10 of the jack head 1. For example, the length of the recessed contact portion 24 of the liftable part 2 may be slightly greater than the length of the main body 10 of the jack head 1 when it is received into the recess during lifting. Advantageously, when the jack head 1 is mated with the corresponding recessed contact portion 24 of the liftable part 2, angular offsets caused by the misalignment of the ground and vehicle can be accommodated smoothly and evenly across the corresponding surfaces of the jack head 1 and the liftable part 2. As best seen in Figure 2, an angular offset occurs when, for example, one or more wheels of the vehicle 400 are misaligned or have different heights from the ground compared to the other wheels of the vehicle 400. Figure 2 shows a situation in which the front left wheel is at height H1 above the ground, the front right wheel is at height H2 above the ground, and the back right wheel is at height H3 above the ground (the back left wheel is not shown in this example). H3 is larger than H2 and H1, and H2 is largerthan H1, causing a misalignment. The invention is also equally applicable to other misalignments between the vehicle and the ground, in any direction. The misalignments are accommodated by the curved nature of the contact portion 14 and its symmetry about the first plane of symmetry X and rotationally about the longitudinal axis 13. Advantageously, the jack head 1 can be used to lift a vehicle 400 with angular offsets in any direction, vastly improving usability in different situations. As mentioned previously, and referring to Figures 8 and 9 in particular, the protrusion 15 on the main body 10 of the jack head 1 is cooperable with a corresponding recess 25 in the recessed contact portion 24 of the liftable part 2. Advantageously, cooperation between the protrusion 15 and the corresponding recess 25 provides a means of locating the jack head 1 within the recessed contact portion 24 as the parts 1, 24 are brought together during the lifting process. The protrusion 15 also serves as a stopping mechanism to prevent the jack head 1 from tilting too far longitudinally within the recessed contact portion 24 through engagement of the protrusion 15 with the ends 21,22, as best seen in Figures 8 and 9. The maximum angular offset which can be accommodated is determined by how far the jack head 1 can move longitudinally within the recessed contact portion 24. This may be limited by the relative sizes of the recess 25 and the protrusion 15. For example, if the recess 25 is much larger than the protrusion 15, the jack head 1 will be able to move over a wide range of angles before coming into contact with the ends 21,22 of the recess 25 and thus stopping. If the recess 25 and protrusion 15 are similarly sized, the jack head 1 will only be able to move over a limited range. The maximum angular offset may also be limited by the relative sizes of the distance between the first and second ends 11,12 of the longitudinal axes of the jack head 1 and the distance between the first and second ends 21,22 of the recessed contact portion 24. Although not shown, in an alternative embodiment the locations for the protrusion 15 and the corresponding recess 25 may be reversed so that the liftable part 2 comprises a protrusion 25 and a corresponding recess 25 is provided on body 10 of the jack head 1. The protrusion 15, 25 may be positioned at any suitable position along the longitudinal axis 23, for example at the midpoint between the first and second ends 21,22 of the recessed contact portion 24. It will be appreciated that the schematic views of Figures 4a, 4b and 6a, 6b do not illustrate the protrusion 15, nor the corresponding recess 25, for simplicity. A further feature of the liftable part 2 is that the main body 20 comprises a first plurality of holes or channels 26, only three of which are identified in Figure 5. The holes 26 extend fully through the main body 20, perpendicular to the longitudinal axis 23 and parallel to the first plane of symmetry X, from one side of the main body 20 to the other. The holes 26 provide a means for draining any incident water on the main body 20 that may otherwise, for example, become trapped by the liftable part 2. The liftable part 2 may further comprise a second plurality of holes 27 that are positioned in a similar manner on the main body 20 to the first plurality of holes 26. The second plurality of holes 27 may provide a part of an attachment means such that the liftable part 2 can be attached to, for example, the chassis of a vehicle. A vehicle may be lifted using different equipment in different situations, and so the invention extends to other lifting means as well as portable lifting jacks. For example, a vehicle being repaired in a garage may be lifted by a permanent lifting apparatus in order to give access to the parts and components that require attention. A vehicle being assembled on a factory line may also need to be lifted so that parts and components can be mounted efficiently and safely. For example, an electric vehicle may need to be lifted so that its battery can be removed and replaced. In these, and other appropriately similar situations, additional features may be provided on the main body 20 of the liftable part 2 of the vehicle to ensure that a vehicle with mounted liftable bodies is held securely and safely, in addition to those claimed as essential in accordance with the invention. For example, the protrusion 15 of the jack head 1 and recess 25 of the liftable part 2 may be used as fore-aft locating features during the assembly process. The liftable part 2 may be incorporated directly into the vehicle during assembly, for example in a body casing, body structure, or sill of the vehicle. While the shape of the liftable part 2 may vary, the liftable part 2 will retain the recessed contact portion 24 such that it can always cooperate with a corresponding jack head 1. For example, as can be seen in Figures 5, 8 and 9, the liftable part 2 may further comprise at least one recessed groove 28 on the same surface as the recessed contact portion 24 is provided. The recessed grooves 28 may be part-circular, may be centred on the longitudinal axis 23 at the midpoint between the first and second ends 21, 22, and may have increasing radii moving radially outwards from the recessed portion 24. The recessed grooves 28 advantageously provide an additional contact portion on the liftable part 2 for an interface with corresponding contacting pads (not shown) on the lifting apparatus. The liftable part 2 may additionally comprise one or more side step brackets 29 which extends the main body 20 of the liftable part 2 as shown in Figure 10. This advantageously increases the area on the liftable part 2 for interfacing with corresponding contacting pads on the lifting apparatus. 5 The jack head 1 and liftable part 2 as described may be comprised in a kit of parts. The contact portion 14 of the jack head 1 and the recessed contact portion 24 of the liftable part 2 are complementary features which cooperate for the lifting of the liftable part 2 and hence the object the liftable part 2 is cooperable with, such as a vehicle. 10 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.

Claims

1. A jack, head of a lifting jack for interfacing with a liftable part, the jack head comprising: a main body comprising a first end and a second end positioned along a longitudinal axis passing through the first and second ends, the main body further comprising a surface of revolution about the longitudinal axis which separates the first and second ends, wherein the surface of revolution comprises:a contact portion for the liftable part which is symmetrical about a first plane of symmetry perpendicular to the longitudinal axis and symmetrical about a second plane aligned with the longitudinal axis and perpendicular to the first plane of symmetry;wherein a first distance between the contact portion and the longitudinal axis reduces towards the first and second ends; andwherein a second distance between the first and second ends along the longitudinal axis is greater than a maximum length of the first distance.

2. The jack head of claim 1, wherein the maximum length of the first distance is in the first plane of symmetry.

3. The jack head of claim 1 or 2, wherein a minimum length of the first distance is at the first and second ends.

4. The jack head of any preceding claim, wherein a curve defined by an intersection of the surface of revolution and the second plane of symmetry, has a first radius of curvature that is greater than the maximum length of the first distance.

5. The jack head of any preceding claim, wherein the surface of revolution is an outer surface of the main body.

6. The jack head of any preceding claim, further comprising a protrusion or recess on the surface of revolution.

7. The jack head of claim 6, wherein the extrusion or recess is positioned at the mid-pointbetween the first and second ends.

8. The jack head of any preceding claim, wherein the surface of revolution is symmetrical in the first plane of symmetry and has 360 degree rotational symmetry about the longitudinal axis.

9. The jack head of any preceding claim, wherein the main body has substantially the shape of a truncated prolate spheroid and / or the contact portion has substantially the shape of a section of an outer surface of a truncated prolate spheroid.

10. A hftable part for interfacing with a jack head of a lifting jack, the liftable part comprising: a main body with a recessed portion comprising a first end and a second end separated by a surface of revolution about a longitudinal axis, wherein the surface of revolution comprises:a recessed contact portion for the jack head which is symmetrical about a first plane of symmetry perpendicular to the longitudinal axis and symmetrical about a second plane aligned with the longitudinal axis and perpendicular to the first plane of symmetry;wherein a first distance between the recessed contact portion and the longitudinal axis perpendicular to the longitudinal axis is variable along the longitudinal axis between the first and second ends; andwherein a second distance between the first and second ends along the longitudinal axis is greater than a maximum length of the first distance.

11. The liftable part of claim 10, wherein the recessed contact portion of the liftable part is configured to cooperate with the contact portion of the jack head according to any of claims 1-10.

12. The liftable part of claims 10 or 11, wherein the recessed contact portion has substantially the shape of a section of an internal surface of a truncated prolate spheroid.

13. A kit of parts of any preceding claim, comprising the jack head according to any of claims 1 -10 and the liftable part according to any of claims 10-12, wherein the contact portion of the jack head and the recessed contact portion of the liftable part are complementary features which cooperate for the lifting of the liftable part.

14. A lifting jack comprising the jack head according to any of claims 1 to 9.

15. A vehicle comprising the liftable part according to any of claims 10 to 12.15

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