Seal geometry for a machine component

Abstract

Seal profile geometry between two opposing components, the primary component 100 (e.g. motor rotor) has stepped outer profile 101 having a protrusion 108, secondary component 200 (e.g. motor stator) m

Description

The present disclosure relates to a seal geometry for a machine component, or for a device component. Particularly, the present disclosure relates to the shape of an outer, or external, surface of a machine or device component that will create a bleed fluid passage when the machine or device is assembled. BACKGROUND Leak reduction is a factor for the design and assembly of motor components, and particularly for relatively moving motor components requiring dynamic seals / dynamic sealing. SUMMARY OF THE INVENTION The present disclosure relates to reducing the amount of parasitic fluid flow, or leak fluid flow, or bleed fluid flow, since even a small amount of fluid lost from a motor (or a unit comprising the motor, e.g. a compressor unit in examples where the motor is to drive a compressor) is a loss and therefore a reduction in efficiency. In a motor comprising a rotor that rotates relative to a non-rotating stator, the rotor and stator may be separate, e.g. not in contact, since contact can lead to friction between the components leading to less efficient operation. Similarly, contact sealings (seals which are in contact with the rotor and / or the stator to fluidly seal the two components) may reduce but not eliminate friction. Additionally, the stator and rotor being in contact directly, or via a contact sealing, can also lead to small particles being produced (e.g. breaking off due to friction) which can become part of the fluid (e.g. refrigerant fluid in examples where the motor drives a compressor). If particles become part of the fluid then this can, in turn, lead to inefficiencies in any system reliant on the circulation and use of that fluid (e.g. this could affect the ability of a vapour-compression cycle using a refrigerant to exchange heat with its surroundings). Therefore, some sealings between a rotor and a stator are “contactless” and the present disclosure provides for such a contactless seal that reduces the amount of bleed fluid able to flow from outside of the motor, or from a unit that comprises the motor (e.g. a compressor unit) or from a device proximate the motor (e.g. a compressor), through the gap between. The present disclosure further provides for a such a contactless seal between relatively moving (e.g. rotating) components, and therefore provides for a dynamic seal. According to this disclosure there is provided a primary machine (e.g. a motor) component comprising an outer surface configured to be positioned proximate an outer surface of a secondary machine (e.g. a motor) component to create a bleed fluid passage between the outer surface of the primary motor component and the outer surface of the secondary motor component, the outer surface of the primary motor component comprising a stepped profile wherein the heights of each step, in the radial direction, decrease with successive steps in the axial direction of the primary motor component such that the radius of the primary motor component decreases in the axial direction, and wherein at least one step comprises a protrusion extending away from a portion of the surface of the step in the radial direction so as to increase the height of the at least one step in the radial direction at the portion of the surface of the at least one step to thereby affect the flow of fluid through the bleed fluid passage. In one example, each step comprises a respective protrusion extending away from a portion of the surface of the step in the radial direction so as to increase the height of each step in the radial direction at the portion of the surface of each step to thereby affect the flow of fluid through the bleed fluid passage. In another example, each alternate step comprises a respective protrusion extending away from a portion of the surface of the step in the radial direction so as to increase the height of that step in the radial direction at the portion of the surface of each step to thereby affect the flow of fluid through the bleed fluid passage. The primary motor component may have a proximal end and a distal end, and the heights of each step may decrease successively from the distal end to the proximal end such that the radius of the primary motor component decreases in the axial direction from the distal end to the proximal end, and wherein the portion of the surface of each step from which the protrusion extends is located at the proximal end of each step. A protrusion of at least one step may comprise a sloped surface or a stepped surface, having a height that increases in the radial direction from the distal end to the proximal end. The protrusion may have a sawtooth shape. At least one step may comprise a first portion having a constant height in the radial direction and a second portion, the second portion comprising the respective protrusion. At least one protrusion may comprise a sloped portion of its respective step and a third portion of the step, the third portion having a constant height in the radial direction that is greater than the height of the first portion, the sloped portion being between the first portion of the step and the third portion of the step. At least one protrusion may comprise a primary protruding element extending away from the surface of its respective step in the radial direction, and a secondary protruding element extending away from the primary protruding element in the axial direction to redirect bleed fluid advancing toward the protruding element in a reverse direction away from the protruding element. The height of at least one protrusion in the radial direction measured from the surface of each step may be approximately or substantially 0.1 mm. In one example, one of the rotor and stator comprises the primary motor component of any preceding claim, and the other one of the rotor and stator comprises the secondary motor component, wherein the radius of the secondary motor component increases in the axial direction such that the secondary motor component is configured to receive a portion of the primary motor component therein, the primary motor component being insertable into the secondary motor component in the axial direction to form the bleed fluid passage between the outer surfaces of the primary and secondary motor components, and wherein the outer surface of the secondary motor component comprises a toothed profile having a plurality of outwardly projecting teeth. The amount by which the teeth of the toothed outer profile of the secondary motor component project from the secondary motor component in the radial direction may be such that the stepped profile of the primary motor component can be fully inserted into the toothed profile of the secondary motor component in the axial direction. The primary and secondary motor components may be configured such that, when the stepped profile of the primary motor component is fully inserted into the toothed profile of the secondary motor component, the bleed fluid path is formed between the outer surfaces of the primary and secondary motor components, the projections of the primary motor component and the teeth of the secondary motor component protrude into the bleed fluid passage, the projections of the primary motor component oppose, and are offset in the axial direction from, the endpoints of the teeth of the secondary motor component, and the projections and teeth are located in pairs whose endpoints terminate at substantially the same position in the radial direction, wherein the height of each projection of each step of the primary motor component in the radial direction is configured such that the radial position of the endpoint of each projection is less than the radial position of the endpoint of the respective tooth in the pair so that there is a clearance in the radial direction between the projections and teeth in each pair, and such that the projections and teeth in each pair do not overlap in the radial direction. The teeth of the secondary motor component may comprise inclined teeth that project outwardly from the secondary motor component at an acute angle to the axial direction. In an example, the primary motor component is the rotor of the motor and the secondary motor component is the stator. According to an example of this disclosure there is provided a compressor unit comprising: a fluid compressor device; and a compressor motor, wherein the compressor motor comprises the motor as described above, and wherein a portion of the primary motor component is received within a portion of the secondary motor component so as to form the bleed fluid passage between the outer surface of the primary motor component and the secondary motor component. BRIEF DESCRIPTION OF THE DRAWINGS Examples of the present disclosure will be described in detail with reference to the accompanying drawings, which should not be considered limiting, in which: Figure 1 schematically shows primary and secondary motor components; Figures 2a-g schematically show cross-sections through a primary motor component, indicating example external geometries of the primary motor component; Figures 3a and 3b schematically show cross-sections through a motor, showing a primary motor component and a secondary motor component forming a bleed fluid passage therebetween, indicating example external geometries of the secondary motor component; Figure 4 schematically shows a cross-section through a motor, showing a primary motor component and a secondary motor component forming a bleed fluid passage therebetween, illustrating the relationship between certain dimensions of the primary and secondary motor components; and Figures 5a-c schematically show cross-sections through a motor, showing a primary motor component and a secondary motor component forming a bleed fluid passage therebetween, illustrating certain example dimensions of the primary and secondary motor components. DETAILED DESCRIPTION These drawings should not be considered limiting, rather they are used for explaining and understanding the present disclosure. Figure 1 schematically shows first and second motor components 1,2. The first component 1 may be a rotor and the second component 2 may be a stator. Alternatively, the first component 1 may be a stator and the second component 2 may be a rotor. In any case, in this example the first motor component 1 is axially receivable in the second motor component 2, as indicated by the arrow. More specifically, to assembly the motor the first motor component 1 may be inserted into the second motor component 2 in the axial direction z. The seal between the first and second motor components 1,2, is a contactless seal. The enlarged portion to the right of Figure 1 shows that between the first and second motor components there a bleed fluid passage 3 is formed, the bleed fluid passage 3 being the contactless seal. If not mitigated for, fluid may flow through this passage 3 (from right to left). Examples of this disclosure relate to the outer geometries of a motor component that mitigate instances of fluid to flow through the bleed fluid passage 3. Herein, various cross-sections are shown, these cross sections being equivalent to the portion of the motor of Figure 1 shown in the enlarged portion to the right of Figure 1. However, this is purely for ease of illustration. Figures 2a-g show example outer, or exterior, geometries of a primary motor component 100, only a portion of which are shown in these Figures. The primary motor component 100 may be any one of the first and second motor components 1, 2 as explained with reference to Figure 1. In other words, the primary motor component 100 may be a rotor of a motor, or may be a stator of the motor. The primary motor component 100 may be proximate a (not shown) secondary motor component which is the other one of the rotor or stator. Therefore, in examples where the primary motor component 100 is a motor rotor, the secondary motor component is a stator, and if the primary motor component 100 is a stator, the secondary motor component is a rotor. The secondary component is not shown in any of Figures 2a-g, the purpose of these figures being to show the external geometries of the primary motor component, but it will be appreciated that when a secondary motor component is positioned proximate the primary motor component 100, a bleed fluid passage as described above will be formed, one side of which will be defined by the upper surface of the portion of the primary motor component 100 that is shown in Figures 2a-g. The primary motor component 100 of each of the Figure 2a-g examples comprises an outer surface 101. As stated above, the outer surface will together with an outer surface of a secondary motor component create a bleed fluid passage therebetween, one of the first and second sides of the bleed fluid passage thereby being formed by the primary motor component and the other of the first and second sides of the bleed fluid passage being formed by the secondary motor component. One of the first and second sides of the bleed fluid passage is therefore formed by the outer surface 101 of the primary motor component 100. The outer surface 101 of the primary motor component 100 may also be referred to as an exterior surface. The outer surface 101 comprises a stepped profile. In other words, the outer surface 101 comprises a series, or a set, or a plurality, of steps 101a-101c (three being shown in Figures 2a-g by way of example only). As shown in each of Figures 2a-g the primary motor component defines an axial direction z and a radial direction r. Also shown in each of Figures 2a-g the height of each step in the radial direction r, as measured from the same point (e.g. from a centreline R), decreases with successive steps in the axial direction (from right to left relative to Figures 2a-g). Thus, the radius of the primary motor component 100 decreases in the axial direction (e.g. from right to left relative to Figures 2a-g). Each step 101 a-c comprises a protrusion 102 (the protrusion of a respective step 101a being labelled 102a etc.) which extends away from a portion of the surface 101 of the step in the radial direction. In this way, the height of each step 101 a-c in the radial direction r, at the portion of the surface 101 of the step, is increased to thereby affect the flow of fluid through the bleed fluid passage. It will be appreciated that the figures herein show each step comprising a protrusion of the same kind. This is purely for illustration. It should be appreciated that a given step may comprise a protrusion of a different type to any other step. Furthermore, each step may not comprise a protrusion. Examples of this disclosure include at least one step having a protrusion and at least one other step not having a protrusion. By way of one example, each alternate step may comprise a protrusion. The heights of the steps 101a-c are labelled in Figure 2a only but it will be appreciated how these dimensions will apply to other figures. The heights h1-h3 of the respective steps 101a-c decreases in the axial direction such that hi <h2 <h3 <... etc. In this example the heights of the steps h1-h3 are measured from a line R which denotes a centre line of the primary motor component. In this way, in these examples the heights h1-h3 of each step are equal to the radius r of the primary motor component 100 at those axial locations. In some examples, at any given axial location the height of each step may be equal to the radius of the primary motor component 100. However, the heights of each step (and the heights of the protrusion) may be measured from any point. The primary motor component 100 comprises a proximal end P and a distal end D, being defined along the axial direction z in these examples. In Figures 2a-g the heights of each step decrease successively along the axial direction from the distal end D to the proximal end P. The radius r of the primary motor component thereby decreases in the axial direction from the distal end D to the proximal end P. Each step therefore has a proximal end and a distal end (the proximal and distal ends of step 101a being 101a-P and 101a-D respectively). In the examples of Figures 2a-e the protrusions 102 are located at the proximal end 101-P of each step. In this way, the height of each step at the step’s distal end is a minimum and the height of each step at the step’s proximal end is a maximum (in the Figures 2a-e), the maximum height of each step being equal to the height of the protrusion. It will therefore be appreciated that the primary motor component 100 in these examples is insertable into the secondary motor component in the axial direction z in the proximal direction P. The (not shown) secondary motor component is therefore configured to receive the primary motor component 100 in the proximal direction P. In Figures 2a-c each protrusion 102 comprises a sloped surface. In these examples the height of each protrusion in the radial direction is nonconstant but increases in the axial direction from the distal end D to the proximal end P. The height of each protrusion may increase smoothly. The height of each protrusion may increase continuously. The height of each protrusion may increase at substantially a constant rate (as in Figure 2b and 2c) or may increase at a nonconstant rate (as in Figure 2a where the height of each protrusion increases at an increasing rate). As such, the height of each protrusion in these examples increases from a first, or minimal, height to a second, or maximal height. In these examples the first height is equal to the height of the step 101. The first heights of each protrusion may be equal and the second heights of each protrusion may be equal (by height of each protrusion it is meant the height as measured from the step, e.g. the outer surface of the step or the outer surface of the primary motor component at the step, as opposed to the height of the step itself which is measured from the centre axis R of the primary motor component 100). In Figures 2d-g each protrusion 102 comprises a stepped surface. In these examples the height of each protrusion 102 is constant. In Figures 2a and 2b the step therefore comprises a first portion 103 and a second portion 104. The first portion 103 has a constant height in the radial direction (being equal to the height of the step 101 in these examples). The second portion 104 comprises the protrusion. The protrusion 102 may comprise a sawtooth shape, as in Figure 2b. The protrusion 102 may comprise a curved shape, as in Figure 2a. Referring to Figure 2c, the protrusion 102 comprises a first portion 103 and a second portion 104 as described above, however the second portion 104 (e.g. the protrusion) comprises a sloped portion 105 and a third portion 106. The third portion 106 has a constant height in the radial direction, greater than the height of the first portion 103, and the sloped portion 105 is in between the first portion 103 and the third portion 106. The sloped portion 105 has a height that increases from a first, or minimal, height to a second, or maximal height, the first height in this example being equal to the height of the step 101 and the second height being equal to the height of the protrusion 102. In some examples the protrusion 102 comprises a hooked portion to redirect bleed air away from the protrusion 102. In the Figure 2a-g examples if bleed fluid were to flow through the bleed fluid passage it would flow from right to left, or from the distal end D to the proximal end P of the primary motor component. Figure 2d illustrates such a protrusion. Each protrusion 102 of the Figure 2d example comprises a primary protruding element 102-i and a secondary protruding element 102-ii. The primary protruding element 102-i extends away from the surface of the step 101 in the radial direction. The secondary protruding element 102-ii extends away from the primary protruding element 102-i in the axial direction. In this example the secondary protruding element 102-ii extends away from the primary protruding element 102-i in the axial direction from the proximal end P to the distal end D. In this way, the protrusion 102 is configured to redirect bleed fluid advancing toward the protruding element (e.g. from the distal end D to the proximal end P) in a reverse direction away from the protruding element (e.g. from the proximal end P to the distal end D). The protrusion 102 in this example may therefore be considered as a redirecting protrusion etc. as it is configured to direct bleed fluid advancing toward the protrusion, in a forward or first direction, away from the protrusion in a reverse or second direction (opposite to the forward or first direction). The forward direction in these examples is from the distal end D to the proximal end P and the reverse direction is from the proximal end P to the distal end D. Although depicted as having corners, in other examples the protrusion may comprise a curved profile, e.g. may be claw or talon shaped. Figure 2e, as for Figure 2b, shows a protrusion 102 having a first portion 103 and a second portion 104. Unlike Figure 2b where the second portion 104 is sloped (or curved, as in Figure 2a) the second portion 104 of the protrusion 102 in Figure 2e has a constant height in the radial direction. Figure 2f shows a protrusion 102 that is differently located on each step than the protrusions depicted in Figures 2a-e. As for Figure 2e the protrusion has a constant height in the radial direction, different to (and greater than) the height of the step (or the remainder of the height of the step). The purpose of Figure 2f is to indicate that the protrusion 102 may be positioned other than at the proximal end 101-P of each step. As indicated by Figure 2f, the protrusion is located at a position mid-way, or at a midpoint, or indeed at any point (not necessarily a midpoint) between the proximal end 101-P and the distal end 101-D of each step. For the avoidance of doubt the protrusion of Figure 2f may be any of the protrusions as shown in Figures 2a-e. In other words, any one of the protrusions as shown in Figures 2a-e may be located in a middle portion of the step, e.g. not at the proximal end of the step, as shown by the location of the protrusion in Figure 2f. Although each of Figures 2a-f show protrusions that are located at the same portion of their respective steps as the other protrusions (e.g. each protrusion in Figures 2a-e is located at the proximal end of a respective step) in some examples the protrusions may not be so evenly distributed on the primary motor component 100. For example, at least one protrusion may be located at the proximal end of a respective step, and at least one other protrusion may be differently relative to another step (e.g. at the midpoint as shown in Figure 2f). Figure 2g shows a perspective view of a “slice” of the primary motor component 100. Figure 2g shows that in some examples each step may comprise a plurality of protrusions 102. These may be evenly distributed or unevenly distributed. These may be spaced at regular intervals or irregular intervals. The distribution may be the same on each step or may be different between steps. Each step may comprise the same number of protrusions or a different number of protrusions. Each step may comprise the same type of protrusions or may comprise different types of protrusions (e.g. “mixed and matched”). For the avoidance of doubt, although Figure 2g depicts each step having a plurality of protrusions, six are depicted, that are of the Figure 2e / 2f form, these may be of any of the forms discussed above (e.g. 2a-d). Although each protrusion in Figure 2g is located at a midpoint of the step in some examples at least one protrusion on one or more steps may be located at the proximal end of that step. The motor and / or stator (one of which comprises the primary component may be an axial component or may be a radial component. In the latter examples, the primary motor component may comprise a circumferential direction. It should be appreciated that the crosssections depicted in Figure 2a-g may be identical along the circumference of the component. E.g. they may comprise circumferential cross sections. In this way the outer surface 101 may extend around a central axis R in a circumferential direction and each step may comprise a circumferential step, and each protrusion is therefore a circumferential protrusion etc. The bleed fluid passage may comprise an annular, or circumferential, bleed fluid passage. In this way the seal (which is the bleed fluid passage) between the primary and secondary motor components may be referred to as a radial seal extending circumferentially around the motor. In other examples however the principles of this disclosure extend to axial seals. In these examples, the cross sections of Figures 2a-f are constant radial (or width) cross sections along the length of the primary motor component. In these examples the axial direction may be referred to as the length direction and the radial direction may be referred to as the width or depth direction (depending on the orientation). Figures 3a and 3b show a cross-section through primary motor component 100 in combination with a secondary motor component 200. Either one of the primary or secondary motor components 100, 200 may be the rotor of a motor, the other one being the stator of the motor. The primary and secondary motor components 100, 200 are proximate one another so as to form a bleed fluid passage 3 therebetween. The secondary motor component 200 comprises an outer surface 201, and the bleed fluid passage 3 is formed between the outer surfaces 101, 201 of the primary and secondary motor components. The outer surfaces 101, 201 of the primary and secondary motor components therefore define the bleed fluid passage. Figures 3a and 3b are intended to show features of the exterior geometry of the secondary motor component 200. For purely illustrative purposes, the primary motor component 100 in Figure 3a is of the type shown in Figure 2b and the primary motor component 100 in Figure 3b is of the type shown in Figure 2c but it will be appreciated that the primary motor component 100 in Figures 3a or 3b may be of any type described above. As shown in Figures 3a and 3b, just as the radius of the primary motor component 100 decreases in the axial direction z (e.g. from the distal end D to the proximal end P), the radius of the secondary motor component 200 increases in the axial direction (from the distal end D to the proximal end P) so that the secondary motor component 200 (as shown) can receive the primary motor component 100 therein (e.g. the primary motor component 100 has been inserted into the secondary motor component in Figures 3a and 3b). The insertion of the primary motor component 100 into the secondary motor component 200 forms the bleed fluid passage 3 between the exterior surfaces 101, 201, the arrows indicating the potential flow of fluid through the bleed fluid passage 3. The outer, exterior, surface 201 of the secondary motor component 200 could also be referred to as an inner, or interior, surface 201 having regard to its orientation in the motor. The outer, or exterior, surface 201 of the secondary motor component 200 in the Figure 3a and 3b examples comprises a toothed profile (e.g. a toothed outer profile). Put another way, the secondary motor component 200 comprises a plurality of teeth 201. Three teeth are labelled in Figure 3a and 3b and it will be seen that each step 101a-c (and therefore each protrusion) of the primary motor component 100 has a corresponding, or respective, tooth 201a-c of the secondary motor component 200. Put another way, when the primary and secondary motor components 100, 200 are assembled as part of a motor, the steps (protrusions) and teeth are in pairs. In the Figures 3a and 3b examples, the motor comprises a first pair 101a, 201a, a second pair, 101b, 201b, and a third pair 101c, 201c. As stated above, the bleed fluid passage which constitutes a contactless seal between the primary and secondary motor components may be a radial seal or an axial seal. It will be understood that the geometry of the secondary motor component 200 will correspond to the primary motor component 100 in any example. Therefore, in examples where the cross sections of Figures 2a-f are constant radial (or width) cross sections along the length of the primary motor component, the cross sections of Figures 3a and 3b will be constant radial (or width) cross sections along the length of the secondary motor component. In these examples the axial direction may be referred to as the length direction and the radial direction may be referred to as the width or depth direction (depending on the orientation). When the primary and secondary motor components 100, 200 are assembled as part of a motor, each step 101 (and therefore each protrusion 102) and each tooth 201 project into the bleed fluid passage 3. To facilitate insertion of the primary motor component 100 into the secondary motor component 200, it will be seen that each one of the primary motor component 100 and the secondary motor component 200 (specifically the steps, protrusions, and teeth thereof) are configured such that the primary motor component 100 can be inserted (e.g. fully inserted) within the secondary motor component 200. More specifically, the amount by which the teeth 201 a-c of the toothed outer profile 201 of the secondary motor component 200 project from the secondary motor component 200 into the bleed fluid passage, and the amount by which the steps 101 a-c of the stepped outer profile 101 of the primary motor component 100 (e.g. the projections 102 thereof) project from the primary motor component 100 into the bleed fluid passage, is such that the stepped profile 101 of the primary motor component 100 can be fully inserted into the toothed profile 201 of the secondary motor component 200 in the axial direction, as shown in Figures 3a and 3b. Even more specifically, each projection 102 has an endpoint denoted by 108. Similarly, each tooth 201 as an endpoint denoted by 208. The end point 108 of each projection 102 is the terminal point of each projection in the radial direction, and the point farthest away from the step 101, the outer surface 101 and the body of the primary motor component 100. Similarly, the end point 208 of each tooth 202 is the terminal point of each tooth in the radial direction, and the point farthest away from the remainder of the tooth 202, the outer surface 201 and the body of the secondary motor component 200. As Figures 3a and 3b show, when the primary motor component 100 is inserted (e.g. fully inserted) into the secondary motor component 200 to form a motor, the bleed fluid path 3 is formed between the outer surfaces 101, 201 of the primary and secondary motor components 100, 200, the projections 102 of the primary motor component 100 and the teeth 201 of the secondary motor component 200 protrude into the bleed fluid passage 3, and the projections 102 of the primary motor component 100 (e.g. the endpoints 108 thereof) oppose, and are offset in the axial direction z from, the endpoints 208 of the teeth 201 of the secondary motor component 200. Furthermore, as stated above, the projections 102 and teeth 201 are located in pairs - (101a, 201a), (101b, 201b), and (101c, 201c). The endpoints 108, 208 of the projections and teeth in each pair terminate at substantially the same position in the radial direction. Figure 4 shows this in more detail. Figure 4 shows one pair of projections 102 and teeth 201, e.g. a projection 102 and its corresponding tooth 201. Note that although the secondary motor component 200 and teeth 201 are as shown in Figure 3b, Figure 4 and its description apply to any geometry of secondary motor component 200 (e.g. that depicted in Figure 3a). Similarly, the projection 102 of the step 101 may be of any type depicted above with reference to Figures 2a-g. The endpoint 108 of the projection 102 terminates at the position in the radial direction indicated by the dotted line to the left of the figure. Similarly, the endpoint 201 of the tooth 201 terminates at the position in the radial direction indicated by the dotted line to the right of the figure. These two lines are substantially equal, but not precisely equal, such that the endpoints 108, 208 terminate at substantially the same position in the radial direction, but not precisely the same position. Put another way, the height r1 of the projection 102 of each step 101 of the primary motor component 101 in the radial direction r is such that the radial position, r1, of the endpoint 108 of the projection 102 is less than the radial position r2 of the endpoint 208 of the respective tooth 201 in the pair (e.g. r1 <r2) so that there is a clearance C in the radial direction between the projections and teeth in each pair, the clearance C being defined as C = r2 - r1 in this example. The projection 102 and tooth 201 of the Figure 4 pair therefore do not overlap in the radial direction r. In this example the heights (or radiuses) r1, r2 of the protrusion 102 and tooth 201 are measured from the centre line R of the primary motor component 100 but will be appreciated that these heights may be measured from another line and the above relationship will hold provided that they are measured from the same line (e.g. both heights may be measured from the height of the step 101 in the pair and r1 <r2). It will be appreciated that this may be true for each pair (e.g. each projection and each tooth in each pair). It will furthermore be appreciated that this may facilitate ease of insertion of the primary motor component 100 into the secondary motor component 200 in the insertion direction I (equal to the axial direction from the distal end to the primary end in this example). In particular, the radial clearance C facilitates a smooth insertion because a consequence of the clearance is that the protrusion 102 can pass under its respective tooth 201. Indeed, the protrusion 102 may pass under the tooth 201 in its pair and all teeth before that tooth (before meaning prior to this tooth in the axial direction toward the distal end), since just as the heights of each step 102, in the radial direction, decrease with successive steps in the axial direction of the primary motor component (e.g. from the distal end to the proximal end) such that the radius of the primary motor component 100 decreases in the axial direction (e.g. from the distal end to the proximal end), the extent to which the teeth protrude, in the radial direction, increase with successive teeth in the axial direction of the primary motor component (e.g. from the distal end to the proximal end) such that the radius of the secondary motor component 200 increases in the axial direction (e.g. from the distal end to the proximal end). This is shown in Figures 3a and 3b. Referring back to Figure 3a, the Figure 3a teeth each comprise first and second tooth surfaces, one of which extends away from the body of the secondary motor component 200 at approximately 90-degrees, and the other of which extends at an inclined (e.g. acute) angle away from the body of the secondary motor component 200. Referring back to Figure 3b, the Figure 3b teeth each comprise first and second tooth surfaces, both of which extend away from the body of the secondary motor component 200 at inclined (e.g. acute) angles away from the body of the secondary motor component 200, the angle of one tooth surface being greater than the other. The teeth of the secondary motor component 200 may therefore be referred to as inclined teeth that project outwardly from the secondary motor component 200 at an acute angle to the axial direction. Figures 5a-c show examples of the steps of the primary motor component and of the teeth of the secondary motor component, and specifically show example dimensions of these components. All dimensions in Figures 5a-c are millimetres. Figure 5a shows that the length of the or each step may be 1mm. Figures 5a also shows that the height of each step may be 0.3mm. Put another way, the difference between the primary surfaces (e.g. the surface of the step not comprising the protrusion) of each step may be 0.3mm. The primary surface may be considered synonymous with the “first portion” of each step, as described above with reference to Figures 2a-g. Figure 5b shows that while the height (e.g. in the radial direction) of each step is 0.3mm as measured between the primary surfaces, or first portions, the height of each step may also be measured from the primary surface, or first portion, of one step to the protrusion (e.g. to the endpoint of the protrusion or to the maximum eight of the protrusion) of the other. As shown in Figure 5b, this height may be 0.4mm. In the Figure 5b example, the height (e.g. maximum height) of the or each protrusion (as measured from the primary surface or from the first portion of the step) may be 0.1mm. In the Figure 5b example, the length (e.g. in the axial direction) of the first portion is 0.65mm, and the length of the protrusion (or second portion) is 0.35mm, the protrusion comprising a sloped portion having a length of 0.25mm and a third portion having a length of 0.1mm. In some examples however the protrusion may have a length in the axial direction equal to its height in the radial direction (e.g. 1x1 mm), e.g. may be square. The protrusion may therefore have a height and a length both equal to 0.1mm. Figure 5c shows that the length (e.g. in the axial direction) of the endpoint of each tooth may be 0.15mm, and that the height of each tooth, e.g. as measured in radial direction from the body of the secondary motor component 200 may be 0.7mm. The length (e.g. in the axial direction) between teeth in this example is 0.5mm. This may be referred to as the axial offset between the teeth. The offset in the radial direction between the base of each tooth is 0.3mm in this example. Further, in this example (which illustrates teeth of the type shown in Figure 3b), the angle between first and second teeth surfaces is 25 degrees, and the angle that the first tooth surface makes with the secondary motor component 200 body is 50 degrees. These dimensions should be understood as exemplary only and indeed these components may have other dimensions, depending on the example. The difference between the end of the tooth in the distal direction and the end of the step of the preceding step (e.g. not the corresponding step in the pair) is 0.2mm in this example. These dimensions should be understood as exemplary only and indeed these components may have other dimensions, depending on the example. Furthermore, the primary and secondary motor components 100, 200 (e.g. the steps / protrusions and the teeth thereof) may be differently configured to what is shown in the Figure 5a-c examples and still have the dimensions shown in Figures 5a-c. E.g. the teeth may be of the Figure 3a geometry, and the steps / protrusions may be as shown in any of Figures 2a-g etc. As stated above, in one example the primary motor component 100 is the rotor of the motor and wherein the secondary motor component 200 is the stator of the motor, but in another example the primary motor component 100 may be the stator and the secondary motor component 200 may be the stator. Therefore, the rotor may be received within the stator and rotate therein, or the stator may be received within the rotor and the rotor is configured to rotate around the stator, depending on the example. In another example, the motor comprising the primary and secondary motor components 100, 200 described herein is part of a compressor motor to drive a compressor (e.g. a fluid compressor device, e.g. a compressor to compress refrigerant). It will be appreciated that the motor component outer geometry according to this disclosure provides for a contactless sealing that may substantially reduce, and may even eliminate, bleed fluid flow in between the motor components, while allowing ease of assembly and use. Indeed, the bleed fluid flow path formed by the motor components having one or more of the geometries described herein is labyrinthine so that any fluid passing through the bleed passage must take a labyrinthine, or tortuous, path which, in effect, may buffet and redirect the fluid such that a minimal amount ends up escaping via the passage. As used herein, the term “projection” should be considered synonymous with a “protrusion” or an “extension.” The person skilled in the art realizes that the present disclosure by no means is limited to what is explicitly described above. On the contrary, many modifications and variations are possible within the scope of the appended claims. Additionally, variations can be understood and effected by the skilled person in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims.

Claims

1. A motor comprising a rotor and a stator, wherein one of the rotor and stator5 comprises a primary motor component comprising:an outer surface configured to be positioned proximate an outer surface of a secondary motor component to create a bleed fluid passage between the outer surface of the primary motor component and the outer surface of the secondary motor component, the outer surface of the primary motor component comprising a10 stepped profile wherein the heights of each step, in the radial direction, decrease withsuccessive steps from a distal end of the primary motor component to a proximal end in the axial direction of the primary motor component such that the radius of the primary motor component decreases in the axial direction from the distal end to the proximal end, and15 wherein at least one step comprises a protrusion extending away from aportion of the surface of the step in the radial direction so as to increase the height of the at least one step in the radial direction at the portion of the surface of the at least one step to thereby affect the flow of fluid through the bleed fluid passage, the protrusion comprising a sloped surface or a stepped surface, having a height that20 increases in the radial direction from the distal end to the proximal end;and wherein the other one of the rotor and stator comprises the secondary motor component,wherein the radius of the secondary motor component increases in the axial direction such that the secondary motor component is configured to receive a portion of the primary25 motor component therein, the primary motor component being insertable into the secondary motor component in the axial direction to form the bleed fluid passage between the outer surfaces of the primary and secondary motor components, andwherein the outer surface of the secondary motor component comprises a toothed profile having a plurality of outwardly projecting teeth the teeth being inclined teeth that30 project outwardly from the secondary motor component at an acute angle to the axial direction.

2. The motor of claim 1, wherein each step comprises a respective protrusion extending away from a portion of the surface of the step in the radial direction so as to increase the35 height of each step in the radial direction at the portion of the surface of each step to thereby affect the flow of fluid through the bleed fluid passage.27 08 253. The motor of claim 1 or 2, wherein the portion of the surface of each step from which the protrusion extends is located at the proximal end of each step.

4. The motor of any preceding claim, the protrusion having a sawtooth shape.

55. The motor of any preceding claim, wherein at least one step comprises a first portion having a constant height in the radial direction and a second portion, the second portion comprising the protrusion.10 6. The motor of claim 5, wherein at least one protrusion comprises a sloped portion ofits respective step and a third portion of the step, the third portion having a constant height in the radial direction that is greater than the height of the first portion, the sloped portion being between the first portion of the step and the third portion of the step.15 7. The motor of any preceding claim, wherein at least one protrusion comprises aprimary protruding element extending away from the surface of its respective step in the radial direction, and a secondary protruding element extending away from the primary protruding element in the axial direction to redirect bleed fluid advancing toward the protruding element in a reverse direction away from the protruding element.

208. The motor of any preceding claim, wherein the height of at least one protrusion in the radial direction measured from the surface of each step is approximately 0.1 mm.

9. The motor of any preceding claim, wherein the amount by which the teeth of the25 toothed outer profile of the secondary motor component project from the secondary motor component in the radial direction is such that the stepped profile of the primary motor component can be fully inserted into the toothed profile of the secondary motor component in the axial direction.30 10. The motor of any preceding claim, wherein the primary and secondary motorcomponents are configured such that, when the stepped profile of the primary motor component is fully inserted into the toothed profile of the secondary motor component, the bleed fluid path is formed between the outer surfaces of the primary and secondary motor components, the protrusions of the primary motor component and the teeth of the secondary35 motor component protrude into the bleed fluid passage, the protrusions of the primary motor component oppose, and are offset in the axial direction from, the endpoints of the teeth of27 08 25the secondary motor component, and the protrusions and teeth are located in pairs whose endpoints terminate at substantially the same position in the radial direction, wherein the height of each protrusion of each step of the primary motor component in the radial direction is configured such that the radial position of the endpoint of each protrusion5 is less than the radial position of the endpoint of the respective tooth in the pair so that there is a clearance in the radial direction between the protrusions and teeth in each pair, and such that the protrusions and teeth in each pair do not overlap in the radial direction.

11. The motor of any preceding claim, wherein the teeth of the secondary motor10 component project outwardly from the secondary motor component in the distal direction, such that the surface of each tooth on the distal side of the tooth is at an acute angle to the axial direction.

12. The motor of any preceding claim wherein the primary motor component is the rotor 15 of the motor and wherein the secondary motor component is the stator.

13. A compressor unit comprising:a fluid compressor device; anda compressor motor, wherein the compressor motor comprises the motor of20 any preceding claim, and wherein a portion of the primary motor component isreceived within a portion of the secondary motor component so as to form the bleed fluid passage between the outer surface of the primary motor component and the secondary motor component.

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