GB2157769A - A supercharger for heat engines of vehicles - Google Patents

Abstract

This supercharger comprises a main body 2 having a working chamber 3 in which rotate at least two bodies 4 continuously sealed along at least one generatrix parallel to the axis of this main body 2, and this working chamber 3 is in communication with inlet ducts 14 and outlet ducts 15 which are formed in this main body 2 along directions parallel to its axis. The two rotating bodies 4 and end caps 5, 6 of the main body may each comprise a rigid support structure, e.g. of metal, having an external form obtained by injection moulding plastics material onto the structure (Figs. 14-16). Surfaces on the rotating bodies and the internal surface of the working chamber may be ribbed to enhance sealing (Figs. 3, 10, 12). End faces of plastics plugs inserted into cavities in the rotating bodies may initially be inclined to the facing surfaces of the end caps but become parallel thereto in use due to relative thermal expansion (Fig. 11). <IMAGE>

Description

SPECIFICATION A supercharger for heat engines of vehicles The present invention relates to a supercharger for supplying heat engines of vehicles, in particular for supplying the cylinders of sparkignition internal combustion engines or diesel engines of motor vehicles.

Known superchargers for the said application comprise a main body having a working chamber in which rotate two lobed bodies which always form a seal against one another along a generatrix parallel to the axis of the main body; moreover, this working chamber is in communication with intake and outlet ducts which are disposed radially in this main body. This known configuration involves, however, various disadvantages such as a relatively high transverse size of this main body, the necessity of having to perform various working stages on the body, and a relatively high weight of the supercharger.

The object of the present invention is to provide a supercharger for supplying heat engines of motor vehicles which overcomes the above indicated disadvantages, which is very much more economic to produce and has a much reduced weight, combined with simplified working stages for its production and a simple adaptability to different technical performances.

Other objects and advantages obtained with the supercharger of the present invention will become apparent from the following description.

According to the present invention there is provided a supercharger for supplying motor vehicle heat engines, comprising a main body having a working chamber in which rotate at least two bodies continuously sealed along at least one generatrix parallel to the axis of the said main body, and in which the said chamber is in communication with intake and outlet ducts, characterised by the fact that the said ducts are formed in the said main body and extend in directions parallel to its axis.

For a better understanding of the present invention there will now be described, purely by way of non limitative example, various particular embodiments with reference to the attached drawings, in which: Figure 1 is a sectioned side view of a first embodiment of a supercharger according to the present invention; Figure 2 is a sectioned view taken on the line ll-ll of the supercharger of Fig. 1; Figure 3 is a sectioned view taken on the line Ill-Ill of the supercharger of Fig. 2; Figures 4 and 4' are side views at the left and right hand ends respectively of the supercharger of Fig. 1; Figures 5 and 6 are partially sectioned side views taken on the lines V-V and VI-VI respectively in Fig. 8, of a compressor unit utilising a pair of superchargers according to the present invention;; Figure 7 is a side view of the right hand part of the supercharger unit of Figs. 5 and 6; Figure 8 and 9 are sectional views taken on the lines VIII-VIII and IX-IX of the supercharger unit of Fig. 5; Figure 10 is a partial end view of an inner rotating body of the supercharger of Fig. 1; Figures 11 and 12 are respectively side and upper partial sectioned views of the rotating body of Fig. 10, with a broken line indication of a different configuration assumed during operation; Figure 13 is a transverse sectioned view of a different embodiment of rotating body in the working chamber of the supercharger of Fig.

1; Figure 14 is a sectioned side view of a different embodiment of the supercharger of the present invention; Figure 15 is a sectioned side view of a rotating body of the supercharger of Fig. 14; Figure 16 is a partial front view of an end cap of the supercharger of Fig. 14; and Figures 17, 18 and 19 are sectional views taken on the lines XVII-XVII, XVIII-XVIII and XIV-XIV respectively of the end cap of Fig. 1 6 shown in complete representation.

With reference to Figs. 1 to 5, the reference numeral 1 generally indicates a supercharger or compressor according to the present invention, which comprises a main body 2 defining within it a working chamber 3 in which rotate two bodies 4 and 4' which are continuously sealed at least along a generatrix parallel to the longitudinal axis of the main body 2. This working chamber 3 is closed at the ends by two end caps 5 and 6 which are sealingly connected onto the main body 2 by means of six rods 7 which pass through the main body 2 parallel to its axis and have threaded ends, one of which is screwed into respective threaded blind holes 8 formed in the end cap 6, whilst the other projects externally of the opposite end cap 5 and onto which is screwed a corresponding locking nut 9 with an interposed washer.The precise positioning between the main body 2 and the end plates 5 and 6 is moreover determined by centring pins 12 (Fig. 2).

The main body 2 therefore has a longitudinal development along the axis of the working chamber 3, and conveniently is made by extrusion in aluminium alloy with lightening cavities 1 3. In communication with the working chamber 3 there are formed in the main body 2, in opposite positions, an intake duct 14 and an outlet duct 1 5 which lie generally parallel to the axis of the main body 2 and extend for the whole of its length. These ducts 14, 1 5 are in communication in the end cap 6 with respective passages 1 6 and 1 7 formed in the end cap 6, which also extend in a direction parallel to the longitudinal axis of the supercharger 1.

The two rotating bodies 4 and 4', as can be seen better in Fig. 3, have a substantially lobed shape with a conjugate perimetral profile having mutual sealing contact along a substantially continuous line during the rotation of the bodies themselves; these have a length substantially equal to that of the work ing chamber 3 and can conveniently be made by extrusion in aluminium alloy; they also have through cavities 1 9 extending along their whole length in their parts of greater section.These rotating bodies 4 and 4' are fixed, for example by adhesive, onto respective spindles 21 and 22, conveniently made from steel, disposed parallel to the axis of the main body and supported at the ends by ball bearings 23 housed in the end caps 5 and 6 respectively, which completely close the ends of the working chamber 3 with the exception of the ducts 16 and 1 7 for the end cap 6, and have only passages for the ends of these spindles 21 and 22 with housings for circular sealing rings 25, whilst lip-type seals 26 are disposed in contact with the ends of the spindles 21 and 22 between the sealing rings 25 and the ball bearings 23.The two ball bearings 23 housed in the end cap 5 are axially positioned by an outer metal plate 28 fixed with screws 29 onto the outer surface of the end cap 5 whilst the two ball bearings 23 lodged in the end cap 6 are positioned in a manner which permits automatic adjustment of axial play by means of bushes 31 acting on the outer front surfaces of the bearings 23, which can slide axially in the seat formed in the end cap 6. These bushes 31 have an outer perimetral edge on which rests one end of a respective spring 32 on the other end of which acts a cup 33 which is fixed with screws 34 onto the outer surface of the end cap 6.

The spindle 21 at the left hand end projects from the plate 28 through a hole in which is interposed an annular seal 35, and on its end a driving pulley 37 is secured for rotation, by means of a key 36, the pulley 37 being fixed in an axial sense by means of a nut 38 screwed on the threaded end of the spindle 21. At the other end, the spindle 21 and the contiguous end of the spindle 22 pass through the respective bushes 31 with the interposition of an annular lip-type seal 39, and have a frusto-conical end section on which are fixed respective gear wheels 41 and 41', meshing together externally of the cup 33. These gear wheels 41 and 41' are axially fixed by means of nuts 42 locked on the threaded ends of these spindles 21 and 22.

The space containing the gear wheels 41 and 41' is closed by a casing 43 which is fixed on the end cap 6 by means of screws 44 (Fig.

4). The space enclosed by the casing 43 is suitably filled with lubricating material for the gear wheels 41 and 41!, conveniently lubricating grease. Above the casing 43 a further casing is connected by screws 45, the casing 46 having inlet and outlet ducts 47 and 48 respectively for a cooling fluid.

For the purpose of improving the fluid seal in the working chamber 3 for the fluid which is transferred between the intake duct 14 and the outlet duct 15, there is provided a seal of labyrinth type both between the facing surfaces of the two rotating bodies 4 and 4' and between the surfaces of these rotating bodies 4 and 4' and the inner surfaces of the working chamber 3, and also between the end surfaces of these rotating bodies 4 and 4' and the end caps 5 and 6.Such sealing means are particularly formed with a plurality of superficial facing ribs 50, formed on the surfaces of the rotating bodies 4 and 4' along generatrices parallel to the axis as is visible in Fig. 10; by means of a plurality of facing superficial ribs 51 formed on the inner surface of the working chamber 3 of the main body 2, in directions parallel to its longitudinal axis, as is visible in the detail A of Fig. 3; and by means of plugs 53 inserted into the cavities 1 9 of the rotating bodies 4 and 4', such plugs 53 being provided with parallel superficial ribs 54 (Fig. 10). As is visible in Figs. 11 and 12, these rotating bodies 4 and 4' have an end surface 55 inclined such as to be spaced progressively from the facing surfaces of the end caps 5 and 6 with an increase in the distance from the spindles 21 and 22 respectively.In this way, during operation of the compressor 1, since there is a thermal expansion of the rotating bodies 4 and 4' which is greater than that of the spindles 21 and 22, the expansion of these bodies 4 and 4' is very reduced in the portions near to the spindles 21 and 22 on which they are fixed, whilst it increases progressively with an increase in the distance from these spindles, such that a final configuration of the form which is represented in broken outline in Figs.

11 and 1 2 is achieved, thus coming to be substantially parallel and facing the front surface of the heads 5 and 6 respectively.

Conveniently the plugs 53 can be made of abrasive material such as to be self adapting dimensionally by abrasion on the facing surfaces of the heads 5 and 6. Such plugs 53 can conveniently be made in a material resistant to petrol and to high temperatures, for example a plastics material such as teflon (Registered trade-mark). The rotating bodies 4 and 4' can have a skin coating of several tenths of a millimetre, for example by means of teflon, and the peaks of the ribs 50, 51 and 54 can be of the order of 0.1 5 mm.

As is visible in Fig. 1 3 the rotating bodies 4 and 4', generally indicated 4"' can have a conjugate perimetral profile with mutual sealing contact along a discontinuous rather than a continuous line, being formed by spaces 56 having a smaller height and without the ne cessity of high precision of surface working, such that there is no mutual contact between the two rotating bodies in that the contact takes place directly between generatrices 57 and 58 at the two sides of each space 56 concerned.

With reference to Figs. 5 and 6 there is shown a compressor unit 61 which comprises two supercharger compressors of the type described with reference to Fig. 1, mounted coaxially. In particular, this unit 61 has two main bodies 2' and 2" which are separated by an intermediate plate 62 and are delimited by two end caps 5' and 6' similar to the end caps 5 and 6 of Fig. 2. On the outer faces of the end cap 6' there is fixed, by means of screws 1 30 screwed into respective holes 1 31 of the cap 6', a casing 143 which defines an internal space 144 closed against the face of the cap 6', in which are contained gearwheels similar to the meshing gear wheels 41 and 41', and carried by respective spindles 21 and 22 on which are secured for rotation two pairs of rotating bodies 4 and 4' within the main bodies 2' and 2".In the end caps 5' and 6', in a similar manner to the end caps 5 and 6 there are formed housings for ball bearings 23 for supporting the two spindles 21 and 22, and for sealing rings 25, the liptype seal 26 and the bushes 31. A pulley 37' outside the end cap 5' (and, with the other component elements at the two ends of the spindles 21 and 22 similar to those of Fig. 2 indicated with the same reference numeral with a prime) controls the rotation of the first spindle 21, which carries the two first coaxial rotating bodies 4' and to this spindle 21 there is angularly fixed the gear-wheel 41 which meshes with the second gear-wheel 41' carried by the second spindle 22 controlling the rotation of the two second coaxial rotating bodies 4.The assembly comprising the main bodies 2' and 2" with the end caps 5' and 6' and the intermediate plate 62 is secured axially as a pack by means of a plurality of rods 7' a first threaded end of which is screwed into threaded holes 1 34 in the end cap 6', whilst the other threaded end projects out from the end cap 5' and is locked by nuts 9'.

In the passage between the different bodies, centring bushes 1 36 are disposed around these rods 7'. Individual centring pins 12' similar to the pins 1 2 of Fig. 3 are also provided. As can be seen in Fig. 5, the main body 2' has a working chamber 3' in which the rotating bodies 4 and 4' are rotatable, and this chamber is in communication with diagonally disposed axial ducts 14' and 15' for inlet and outlet of fluid respectively. In this main body 2' there are further provided two other ducts 69 and 70 (Fig. 6) which lie parallel to the axis of the body 2' for inlet and outlet of fluid, these being disposed in a position diagonally opposite the ducts 14' and 15'.These two ducts 69 and 70 traverse the intermediate plate 62 and extend into the main body 2" in which they are in communication with the respective working chamber 3' in which is contained the other pair of rotating bodies coaxial with the rotating bodies 4 and 4' present in the body 2', and mounted on the same spindles 21 and 22. Therefore, as well as the passages defined by the ducts 69 and 70, this intermediate plate 62 also has sealed apertures for the passage of the spindles 21 and 22. The end cap 5' on the other hand has only sealed apertures for the passage of the spindles 21 and 22, whilst the end cap 68, visible in Fig. 9, as well as the apertures 71 and 72 for the fluid tight passage of the spindles 21 and 22, has passages 69', 14", 70' and 15" for communication with the respective ducts 69, 14', 70 and 15' of the body 2'.In the casing 143 (Figs. 5 and 6) there are therefore provided passages 69", 14"', 70" and 1 5"', in communication with the apertures 69', 14", 70' and 15" of the end cap 6': the passages 69" and 15"' are therefore in communication with external bushes 76 and 77 for the intake and outlet respectively, whilst a passage 78 puts the ducts 40"' and 70" in communication.

The embodiment illustrated in Fig. 14 differs from that of Fig. 2 mainly by the different formation of the rotating bodies 4 and 4' and the end caps 5 and 6. These component parts are in fact made with a relatively rigid supporting structure, conveniently metal, and have and external form produced by moulding, conveniently injection moulding, of plastics material onto the support structure.In particular the two rotating bodies indicated 4", and illustrated in greater detail in Fig. 15, have a support structure 80 which is made of sheet metal the length of which is almost equal to the length of the body 4" and shaped with a form similar to that of the outer form of the body 4"; in particular this support structure 80 is made from two sheets 81 and 82 the ends 83 of which are fixed, conveniently, for example, welded, onto respective spindles 21 or 22 thus having diametrically oppositely facing sections 84 which then diverge outwardly and are again fixed to the spindles 21 and 22 with intermediate portions 85.These sheets 81 and 82 have a plurality of holes 87 which, as well as allowing passage of the welding electrodes for fixing the ends 83 and the portions 85 onto the spindles 21 and 22, allow the passage of the material 88 which is moulded onto the support structure 80 into the desired external form for the rotating body 4" which, as illustrated in Fig. 15, has a conjugate perimetral shape with mutual sealing contact along a substantially continuous line with the cooperating rotating body, as shown in the illustrated configuration of the rotating bodies 4 and 4' for example in Fig. 3, or else can have a conjugate perimetral shape with mutual sealing contact along a discontinuous line, for example as shown in the configuration illustrated in Fig. 1 3 for the rotating body 4"'.

The end caps 5" and 6" as illustrated in Fig. 1 6 have a support structure 90 conveniently made of sheet metal suitably shaped and pierced so as to form the various holes for receiving and connecting together the various component parts. On the support structure 90 there is therefore moulded, conveniently by injection moulding of plastics material 91, a body of external form similar to the external form of the end caps 5 and 6 of the supercharger of Fig. 1. In particular, in the support structure 90 there are formed two holes 92 in which are housed ball bearings 23 for support of the two spindles 21 and 22, and in the material 21 there are formed, coaxially with these holes 92, housings 93 (Figs. 17, 1 8 and 19) for the sealing rings 25, the lip seals 26 and the bushes 31.In this support structure 90 there are also formed two pairs of holes 95 in which are inserted the threaded ends of the respective rods 7 for axial assembly of the supercharger 1, and on these threaded ends, in a space 96 formed in the material 91, are screwed nuts 97 (Fig. 18); the other threaded ends of the rods 7 project from the end cap 5" and onto these are locked the nuts 9. Towards the central region of this support structure 90 there are formed, in diagonally opposite positions, two holes 98 into which extend the threaded ends of another two rods 7 on which are locked nuts 99 housed in associated cavities 100 of corrsponding section formed in the material 91 of the end cap 6"; the terminal end of these rods 7 then project from the end cap 6" and onto it are screwed nuts 101 which lock the casing 43 onto the end cap 6" itself.This casing 43 is further locked at the other two corners by means of two screws 103 which pass through holes 104 formed in the structure 90 (Figs. 16 and 17). In this support structure 90 there are therefore formed four holes 106 in which the screws 34 which lock the cup against the end cap 6" are screwed.

This support structure 90 also has four holes 109 at the four corners in which can be disposed elements (not illustrated) for fixing it to a convenient support; there are also provided other holes 11 0 which facilitate the diffusion of the material 91.

The supercharger 1 formed according to the present invention therefore has various advantages such as a great simplicity of working and therefore economy of manufacture, together with a relatively low weight and ease in providing different performances simply by varying the length of the main body 2. These various advantages are mainly obtainable with the production of the main body 2 by extrusion, with the characteristic that the inlet duct 14 and outlet duct 1 5 are disposed in a direction parallel to the longitudinal axis of the main body 2.This main body 2 can therefore be made in aluminium or in other light alloy, has a relatively low transverse size in that the inlet and outlet openings for fluid can be made on the end face of one of the end caps 5 or 6; this main body 2 does not necesitate expensive working stages in that it is necessary to work with precision only the inner surface of the working chamber 3 and the end surfaces which are contacted by the end caps 5 and 6 and moreover it is extremely simple and easy to form superchargers disposed coaxially to obtain the composite unit 61 illustrated in Fig. 6.

In the composite unit 61 the fluid enters through the mouth 76 (Fig. 6), through the ducts 69", 69' and passes through the duct 69 formed in the main body 2' of the first supercharger to arrive in the working chamber 3" of the left hand supercharger and is then sent to the duct 70 which passes into the main body 2" of the right hand supercharger, and from there, through the duct 70' and 70" it enters the duct 78 which carries it to the duct 14"', (Fig. 5), and then to the inlet ducts 14" and 14' leading to the working chamber 3' of the main body 2' of the right hand supercharger, from where it flows out through the outlet ducts 15', and subsequently 15" and 15"' to leave through the outlet opening 77.With the supercharger formed according to the present invention there is therefore the advantage of being able to arrange two compressors coaxially, which therefore function with the rotating bodies 4 and 4' carried by the same spindles 21 and 22 without increasing the external transverse size of a single compressor in that the section of the main body relating to one of the two compressors contains both the inlet and outlet ducts (14' and 15') for a first compressor and both the inlet and outlet ducts (69 and 70) which belong to the second coaxial compressor all of which lie in directions parallel to the axis of the compressor itself. In this way, by utilising two compressors the work required, for the same final performance, from a single supercharger, is reduced; moreover the specific technical characteristics can be varied in dependence on the length of the two main bodies 2' and 2". A reduction of the required compression work can moreover be obtained by making the liquid or air coolant circulate around the duct 78 which carries the fluid leaving the first compressor to the intake of the second compressor.

The fluid seal in the working chamber 3 is moreover guaranteed in an extremely satisfactory manner by means of the ribs 50 formed on the surfaces of the rotating bodies 4 and 4', by means of the ribs 51 formed on the inner surfaces of the working chamber 3, and by the ribs 54 formed on the outer surfaces of the plugs 53; such ribs can moreover be formed only partially on some component parts according to the required characteristics of the supercharger. With these ribs, as well as providing the above described seal, there is obtained the benefit of being able to adopt the widest play between the rotating bodies 4 and 4' and between the rotating bodies 4 and 4' and the fixed bodies 2, 5, 6; with much higher working tolerances, then, a greater manufacturing economy results.Also advantageous for the formation of the fluid seal in the working chamber 3 is the formation of the axial play compensation of the ball-bearings 23 by means of the bushes 31 on which act the springs 32 resting on the cup 33.

Also, the composition of the rotating bodies 4"', with the shape illustrated in Fig. 13, that is to say, with mutual sealing contact along a discontinuous line, allows an economy of fabrication in that the working precision required for the spaces 56 is reduced.

The provision of rotating bodies 4 and 4' either by extrusion processes, provided with through cavities 19, or by means of a supporting structure 80 covered with moulded material 88 of the desired form, allows these rotating bodies to be made relatively light, with low moment of inertia, thus permitting higher speeds of rotation with superior performance. It is also advantageous to form the end caps 5" and 6" with a supporting structure 90 which guarantees the required rigidity, and onto which is moulded the material 91 in the external form of the desired internal spaces, thus obtaining characteristics of economy of manufacture and lightness, together with sufficient robustness.Moreover, this production technique makes it possible for the thermal expansion to be made principally dependent on that of the supporting structure 80 and 90 which is made of the same material, conveniently steel, permits the thermal expansions to be similar and contained.

The circulation of a cooling fluid, for example the cooling fluid of the engine from the inlet duct 47 to the outlet duct 48, of the casing 46 which is disposed in thermal contact with but sealed from the casing 43, allows the heat generates between the gear wheels 40 and 41' to be dissipated.

Finally it is clear that the described embodiments of the supercharger of the present invention can be modified or varied without departing from the scope of the invention itself. Among other things the described characteristics for the various details, such as those of the rotating bodies 4 and 4', 4" and 4"', for the end caps 5 and 6, 5" and 6" for the various ribs 50, 51 and 54 and for the casing 46 for the passage of coolant fluid, which can also be omitted, can be combined differently from the manner described. Moreover, the supporting structure 90 for the end caps 5 and 6 can have a different configuration from that described and, among other things, in place of or together with the securing holes 109, can have tabs at the four corners, folded for example at 90', with convenient holes for fixing to a support.

Claims (23)

1. A supercharger for a heat engine of a motor vehicle, comprising a main body having a working chamber in which rotate at least two bodies continuously sealed along at least a generatrix parallel to the axis of the said main body and in which the said chamber is in communication with intake ducts and outlet ducts characterised by the fact that the said ducts are formed in the said main body in directions parallel to its axis.

2. A supercharger according to Claim 1, characterised by the fact that the said main body is made by extrusion.

3. A supercharger according to Claim 1 or Claim 2, characterised by the fact that the said body is enclosed between two end caps axially delimiting the said working chamber in one of the said two end caps there being formed substantially axial communication apertures for communication with the said intake ducts and outlet ducts.

4. A supercharger according to Claim 3, characterised by the fact that it includes a plurality of connection elements disposed parallel to the axis of the said main body and sealingly securing the said end caps onto the said main body.

5. A supercharger according to any preceding Claim, characterised by the fact that it includes fluid tight sealing means, for sealing between the said two rotating bodies and/or between the said rotating bodies and the said main body and/or between the end portions of the said two rotating bodies and the said end caps.

6. A supercharger according to Claim 5, characterised by the fact that the said sealing means include a plurality of ribs formed on at least one of the facing surfaces of the pair, to form a labyrinth type seal.

7. A supercharger according to Claim 6, characterised by the fact that the said ribs are formed of a material which adapts itself by abrasion.

8. A supercharger according to any preceding Claim, characterised by the fact that the said two rotating bodies have a conjugate perimetral shape with sealed mutual contact along a substantially continuous line.

9. A supercharger according to any of Claims 1 to 7, characterised by the fact that the said two rotating bodies have a conjugate perimetral shape with sealed mutual contact along a discontinuous line.

10. A supercharger according to any preceding Claim, characterised by the fact that the said two rotating bodies are made by extrusion.

11. A supercharger according to any preceding Claim, characterised by the fact that the said two rotating bodies are carried by a respective axial shaft and have longitudinal hollow portions in which are disposed respective end plugs and in which the said plugs and the said bodies have an inclined end shape such as to be spaced progressively from the facing surface of the said end cap with an increase in distance from the said axial shaft.

1 2. A supercharger according to any preceding Claim, characterised by the fact that the said main body and/or the said two rotating bodies are made of aluminium.

1 3. A supercharger according to any of Claims from 1 to 9, characterised by the fact that the said two rotating bodies have a relatively rigid support structure fixed to an associated axial shaft and have an external form obtained by moulding onto the said support structure.

14. A supercharger according to Claim 3 or any of Claims 4 to 1 3 when dependent on Claim 3, characterised by the fact that each end cap has a relatively rigid supporting structure and an external form obtained by injection moulding onto the said supporting structure.

1 5. A supercharger according to Claim 14, characterised by the fact that the said supporting structure has apertures and seats for housing and/or fixing component elements of the said supercharger.

1 6. A supercharger according to any of Claims from 1 3 to 15, characterised by the fact that the said rotating bodies and/or the said end caps are made by injection moulding plastics material onto the said metal supporting structure.

1 7. A supercharger according to any preceding Claim, in which rotary movement is imparted from outside to one of the said two rotating bodies which carries the other of the said two rotating bodies into rotation by means of a meshing coupling, characterised by the fact that the said meshing coupling is disposed externally of the said main body within a space filled with lubricating grease, and that there is provided a second space in thermal contact with the said space but hermetically separated therefrom, in which a cooling gluid is made to pass.

18. A supercharger according to Claim 17, characterised by the fact that the said second space is formed by a casing having intake ducts and outlet ducts, and through which is made to pass the liquid from the coolant circuit of the said engine.

19. A supercharger unit, characterised by the fact that it comprises two superchargers according to any preceding Claim disposed coaxially.

20. A supercharger unit according to Claim 19, characterised by the fact that the said inlet ducts and outlet ducts are formed in the said main body of a first of the said two superchargers together with parallel ducts for communication with the said inlet and outlet ducts for the second of the said two superchargers, an end cap being located at one end of the said first supercharger and having pairs of apertures for inlet and outlet of the said two superchargers; respective intake and outlet apertures of the said supercharger unit being in communication with the said apertures, and an outer duct for communication between the outlet apertures of one of the superchargers and the inlet aperture of the other.

21. A supercharger unit according to Claim 20, characterised by the fact that the cooling fluid is made to pass in thermal contact with the said outer duct but hermetically sealed therefrom.

22. A supercharger unit according to any of Claims from 1 9 to 21, characterised by the fact that it includes a single pair of spindles carrying coaxial pairs of said rotating bodies of the said two superchargers.

23. A supercharger substantially as described with reference to the accompanying drawings