Abstract:
A supercharger arrangement for an engine assembly  10  is disclosed, the arrangement including first and second superchargers  22 A,  22 B that are mounted on the engine assembly by means of separate first and second mounting members  46, 48  respectively. Each mounting member defines an integrated supercharger lubrication conduit  62 A,  62 B,  64 A,  64 B and the present invention is characterized in that the superchargers  22 A,  22 B are of substantially identical construction and are separable from the first and second mounting members  46, 48.  The integrated lubrication conduits  62 A,  62 B,  64 A,  64 B are routed through their respective said mounting members in such a manner as to enable the first and second superchargers to be mounted on the engine assembly  10  in substantially mirror image orientations thereabout

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to supercharger arrangements for engine assemblies and in particular to a supercharger arrangement for an engine equipped with a plurality of superchargers.  
         BACKGROUND TO THE INVENTION  
         [0002]    It is known to provide an engine with one or more superchargers, which may be embodied in the form of exhaust driven turbochargers. Superchargers usually require a lubrication system and many such lubrication systems are closed circuits often using engine oil as a lubricant. The lubrication system usually includes an oil feed conduit and an oil return conduit. The oil feed supplies oil under pressure from an oil pump of the engine to the or each supercharger concerned and the oil return comprises a conduit adapted to drain the oil away towards a collection area such as an oil sump of the engine. Life expectancy of a turbocharger relies considerably on a steady flow of clean oil supplied to its bearings under pressure from the engine&#39;s lubrication system and on the free exit of that oil for its return back to the engine sump.  
           [0003]    In U.S. Pat. No. 4,716,735, an exhaust gas driven turbocharger arrangement is proposed in which an engine mounting is integrated with a bearing housing of the turbocharger. Oil supply and return passages are defined through the mounting for use in lubrication of the turbocharger bearings. Such an arrangement requires a custom-made turbocharger in order to integrate its bearing housing with the engine mounting of a particular installation. Custom-made turbochargers may prove more expensive than using mass-produced items.  
           [0004]    The arrangement proposed in U.S. Pat. No. 4,716,735 is best suited to use in engine assemblies having only one turbocharger and may not prove suitable for use in an arrangement calling for a plurality of turbochargers. For example, in a multi-cylinder engine having its cylinders arranged in banks in a ‘V’ or ‘W’ configuration, it may be desirable to provide a plurality of turbochargers.  
           [0005]    Taking the example of a ‘V’ configured engine and attempting to fit a plurality of turbochargers according to U.S. Pat. No. 4,716,735 dedicated one to each bank, it will be found that a symmetrical set-up is not possible. In order to bolt a second example of the same component to the opposite side of the engine block, the whole turbocharger and integrated mounting assembly of that second example must be rotated 180°. One problem with such an arrangement is that the compressor and exhaust turbines of the opposing turbochargers will point towards opposite ends of the engine. This may lead to complex and less than ideal inlet and exhaust ducting. To reverse the orientation of the turbocharger would require an inverted casting for the bearing housing, resulting in a customized turbocharger on each side of the engine. Rather than reducing piece cost by doubling volume, such an arrangement might prove cost prohibitive as it would significantly increase the investment necessary in producing both right- and left-handed parts. In addition, it would necessitate precautions in parts delivery to the side of the production line, e.g. to ensure smooth delivery of the right parts to the assembly stations affected in equal volumes of each and to their appropriate sides of the line.  
           [0006]    In U.S. Pat. No. 4,583,367 an arrangement is proposed for integration of a turbocharger arrangement with an engine mounting. This proposal deals with a single turbocharger and is concerned with defoaming and degassification of the oil being returned to the engine sump. Neither reversibility of the turbo installation between sides of the engine nor twin-turbochargers are considered. Reversing between sides or doubling up on turbochargers would suffer similar problems to those discussed in that respect for U.S. Pat. No. 4,716,735.  
           [0007]    EP-1176301 proposes an engine crankcase that includes an integral turbocharger mounting. In similar fashion to U.S. Pat. No. 4,583,367, this document deals only with a single turbocharger and reversibility of the turbocharger installation between sides of the engine or twin-turbochargers are not considered. Reversing between sides or doubling up on turbochargers would suffer similar problems to those discussed in that respect for U.S. Pat. No. 4,716,735  
           [0008]    EP-0952329 proposes a single and very complicated casting that acts as a one-piece integrated front-end for a large industrial engine. The use of such a one piece front end is expensive and is cost prohibitive for mass production. Such an arrangement also lacks flexibility in moving the position of the turbochargers around between variations in an engine range. The turbochargers can only be mounted high up on the engine and this makes the arrangement unsuitable for adaptation for use in a passenger vehicle due to the height restrictions inherent in under-hood installations.  
           [0009]    DE-10122406 proposes a single carrier casing having two turbocharger mountings integrated into it and adapted to carry a pair of turbochargers. The casting is reversible in its mounting position in co-operation with a manifold arrangement. In similar fashion to EP-0952329, integration of both turbocharger mountings into the same casting largely limits use of this arrangement to mounting the turbochargers on top of the engine. That limits design flexibility and may impose height problems in some under-hood installations, notable for passenger vehicles.  
           [0010]    There is therefore a continuing need to seek improved arrangements for mounting multiple superchargers to engines, in particular for use in installations for passenger vehicles.  
         SUMMARY OF THE INVENTION  
         [0011]    It is an object of the present invention to provide improved supercharger arrangements for engine assemblies and in particular to provide an improved arrangement for an engine equipped with a plurality of superchargers.  
           [0012]    Accordingly, the present invention provides a supercharger arrangement for an engine assembly, the arrangement including first and second superchargers that are mounted on said engine assembly by means of individual first and second mounting members respectively, each said mounting member defining therethrough a supercharger lubrication conduit, wherein said superchargers are of substantially identical construction and are separable from said first and second mounting members and said lubrication conduits are routed through their respective said mounting members in such a manner that said first and second superchargers are mounted on said engine assembly in substantially mirror image orientations thereabout.  
           [0013]    Among the advantages of the present invention is the provision of a low cost arrangement for using a plurality of substantially identical superchargers on the same engine while achieving substantially mirror image orientations of those units around the engine. This saves costs by raising the volumes of an expensive part of a supercharging arrangement, the supercharger itself, rather than necessitating several different and possibly custom units. Using individual mountings increases flexibility in under-hood installations and the arrangement is not limited to mounting the superchargers on top of the engine.  
           [0014]    Said mounting members may be disposed on opposite sides of a crankcase of said engine assembly and said lubrication conduits may connect said superchargers to an engine lubrication circuit through the sides of said crankcase.  
           [0015]    Said lubrication conduits may each comprise a lubricant feed passage and a lubricant return passage and the routing of at least part of said feed and return passages may be inverted between said mounting members.  
           [0016]    Inversion of said feed and return passages may take operative effect at respective supercharger mounting faces of said first and second supercharger mounting members.  
           [0017]    When said superchargers are mounted on said engine assembly, at least one of corresponding pairs of charge air entries, charge air exits, exhaust gas entries or exhaust gas exits of said superchargers may be disposed at substantially the same orientation as each other with respect to said engine assembly.  
           [0018]    At least one said mounting member may comprise a casting or a molding and is a component that is separable from both its associated said supercharger and from the rest of said engine assembly.  
           [0019]    The present invention also provides an engine assembly including first and second superchargers mounted thereto on individual first and second supercharger mounting members respectively, each said mounting member having integrated therewith a lubrication feed passage and a lubrication return passage, wherein said superchargers are separable from their associated said mounting members and the routing of said feed and return passages is substantially inverted between said mounting members in the region of respective supercharger mounting faces thereof in such a manner that said superchargers are mountable interchangeably between said first and second mounting members with substantially mirror image orientations and regardless of which said supercharger is mounted to which said mounting member.  
           [0020]    Said engine assembly may comprise a multi-bank engine having a crankcase and defining a plurality of cylinders that are disposed in banks at an angle with respect to each other, said first and second mounting members being disposed on opposite sides of said crankcase and said first and second superchargers being associated with different said banks of said engine assembly.  
           [0021]    The present invention also provides a set of supercharger mounting members for use in a supercharger arrangement of an engine assembly, said mounting members comprising individual components and each individual said supercharger mounting member defining therethrough a supercharger lubrication feed passage and a supercharger lubrication return passage and end portions of said feed and return passages being substantially inverted between a pair of mounting members in the region of supercharger mounting faces thereof, whereby said mounting members are mountable to substantially opposing sides of a said engine assembly so that substantially identical superchargers are mountable one each to said mounting faces and are thereby disposed in substantially mirror image orientations about said engine assembly.  
           [0022]    The present invention also provides a method of mounting a plurality of superchargers on an engine assembly, the method including;  
           [0023]    a) providing on substantially opposing sides of said engine assembly individual first and second supercharger mountings, each of which mountings has defined therethrough a lubrication feed passage and a lubrication return passage whose routing is substantially inverted between said mounting members in the region of respective supercharger mounting faces thereof; and  
           [0024]    b) connecting first and second substantially identical superchargers to said first and second mountings respectively in substantially mirror image orientations about said engine assembly. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0025]    The present invention will now be described by way of example only and with reference to the accompanying drawings, in which:  
         [0026]    [0026]FIG. 1 is a schematic diagram of an engine assembly incorporating an arrangement according to the present invention:  
         [0027]    [0027]FIG. 2 is a schematic representation of a section through an engine assembly incorporating an embodiment of the arrangement of FIG. 1;  
         [0028]    [0028]FIG. 3 is a close-up view of a first portion of FIG. 2;  
         [0029]    [0029]FIG. 4 is a close-up view of a second portion of FIG. 2;  
         [0030]    [0030]FIG. 5 is a perspective front view of a component of a practical embodiment of the arrangement of FIGS.  1  to  4 ;  
         [0031]    [0031]FIG. 6 is a perspective rear view of the component of FIG. 5;  
         [0032]    [0032]FIG. 7 is a perspective front view of a further component of a practical embodiment of the arrangement of FIGS.  1  to  4 ;  
         [0033]    [0033]FIG. 8 is a perspective rear view of the component of FIG. 7;  
         [0034]    [0034]FIG. 9 is a plan view of the disposition of the components of FIGS.  5  to  8  in an installed position, shown with respect to a possible but non-limiting installation in which the front of the engine assembly is marked “F”;  
         [0035]    [0035]FIG. 10 is an end view of the arrangement of FIG. 9, viewed from one end (e.g. a front end “F”) of the engine assembly;  
         [0036]    [0036]FIG. 11 is the plan view of FIG. 9 having a supercharger mounted onto each of the components of FIGS.  5  to  8 ;  
         [0037]    [0037]FIG. 12 is the view of FIG. 10 having a supercharger mounted onto each of the components of FIGS.  5  to  8 ,  
         [0038]    [0038]FIG. 13 is the view of FIG. 12 seen from the opposite end (e.g. a rear end “R”) of the engine assembly; and  
         [0039]    [0039]FIG. 14 is a bottom view of the arrangement of FIGS.  11  to  13 . 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0040]    Referring to the drawings, a preferred embodiment of a supercharger arrangement is disclosed for an engine assembly  10 . The engine  10  includes a cylinder crankcase  12 , preferably in the form of a multi-bank engine block in which a plurality of cylinders (e.g. four, six, eight, ten or twelve) are connected to the crankcase  12  and are disposed in banks at an angle with respect to each other (e.g. a “V”). For the sake of example, the engine  10  of this embodiment may be considered as a V-6 engine fitted in use into an engine bay defined in a front portion of a vehicle and the engine  10  being disposed transverse to a centerline of the vehicle.  
         [0041]    For convenience and in keeping with an exemplary but non-limiting transverse installation of a V-engine, the opposing banks of the engine  10  will be referred to as its front bank  14  and its rear bank  16 . The banks of cylinders  14 ,  16  of the engine  10  are associated with respective front and rear cylinder heads  18 ,  20 . It will be appreciated, however, that the present invention is not limited to only transverse installations and may be suitable for embodiment in the form of longitudinal, middle or rear mounted installations or in installations other than vehicles (e.g. generators or marine use).  
         [0042]    The engine  10  is provided with a plurality of superchargers in the form of exhaust-gas driven variable geometry turbochargers  22 A,  22 B, each of which is assembled in association with an actuator  24  and are associated one each with the front bank  14  and the rear bank  16 . In a variable geometry turbocharger, a valve is provided in the turbocharger casing. The valve is controlled by the actuator  24  and is used to vary the attack angle of exhaust gases driving the exhaust turbine so as to control its speed. For example, at low engine speeds the exhaust gas can provide only a low driving force to the exhaust turbine. The valve is then moved towards a closed position so as to increase the gas speed and thereby keep exhaust turbine speed up, even for low gas flows. On the other hand, at high engine speeds the valve is moved towards an open position so as to keep down the driving force. Such turbochargers may, therefore, be controlled to operate within a tight speed range. The present invention is not limited to only variable geometry turbochargers  22 A,  22 B and these may be replaceable by other types or equivalents such as waste-gate actuated turbochargers.  
         [0043]    The turbochargers  22 A,  22 B are of substantially identical construction and each comprises an exhaust turbine portion  26  and a compressor turbine portion  28 . The exhaust turbine portion  26  includes an exhaust gas entry  30 , an exhaust gas turbine and an exhaust gas exit  32  and the compressor portion  28  includes a charge air entry  34 , a charge air compressor and a charge air exit  36 . The exhaust turbine and compressor turbine are drivingly joined by means of a turbine shaft  38  that is supported on a turbine bearing arrangement  40 . The turbine bearing arrangement  40  is lubricated by a lubricant, e.g. in the form of engine oil that is supplied under pressure by an engine oil pump and then drained back to a lubricant reservoir such as an engine sump.  
         [0044]    The turbochargers  22 A,  22 B are mounted to the engine  10  one on each side of the crankcase  12  by means of a pair of individual mounting members protruding outwardly from substantially opposing sides of the crankcase  12 , referred to for convenience as the turbocharger front mounting  46  and rear mounting  48 . One or more of the individual front and rear turbocharger mountings  46 ,  48  may be integrated with the crankcase  12 , whilst still being separate from each other and from the turbochargers. For ease of manufacture of the mountings  46 ,  48 , however, it may be found preferable to produce them as separate components, separated from the crankcase  12  as well as from the turbochargers  22 A,  22 B and mountable to the crankcase  12 . Such an individual and separate construction is the form illustrated by way of example in the present embodiment.  
         [0045]    Each turbocharger  22 A,  22 B communicates with exhaust ports of at least its directly associated cylinder head  18 ,  20  via a connection  42  between its exhaust gas entry  30  and an exhaust arrangement  44  that includes one or more of header pipes and an exhaust manifold.  
         [0046]    In the present embodiment, the individual turbocharger mountings  46 ,  48  each comprise a separate one-piece casting or molding having a back plate  50 A,  50 B and a support arm  52 A,  52 B extending away from the back plate. As illustrated with particular reference for the moment to FIGS.  5  to  10 , one or both of the back plates  50 A,  50 B may be essentially triangular and planar in form and may be canted to one side, i.e. towards one end of the crankcase  12 . In the arrangement of the present embodiment, the back plates  50 A,  50 B each have a base portion  54  with a mounting hole  56  defined therethrough at each end and a raised peak  58  defining an upper mounting hole  56 . For substantial symmetry or mirror image, in use the raised peaks  58  are canted towards the same end of the engine assembly  10  while the support arms  52 A,  52 B each extend outwardly from a position substantially centralized with respect to the base mounting holes  56 .  
         [0047]    The mountings  46 ,  48  each have an integral lubrication conduit in the form of a lubricant feed passage  62 A,  62 B and a lubricant return passage  64 A,  64 B. The lubricant feed  62 A,  62 B and return  64 A,  64 B passages may be in the form of ducting defined through the support arms  52 A,  52 B and the back plates  50 A,  50 B, e.g. formed in the casting/molding process. These lubricant passages  62 A,  62 B,  64 A,  64 B are adapted to connect respective front and rear lubricant supply  68 A,  68 B and return  70 A,  70 B ports of the crankcase  12  to turbochargers  22 A,  22 B mounted in use on turbocharger mounting faces  72 A,  72 B, e.g. via mechanical fixings such as bolts screwed through a turbocharger-mounting flange and into mounting holes  60  defined in predetermined positions on the mounting faces. The positioning of the mounting holes  60  positions the turbochargers  22 A,  22 B in a predetermined orientation about the engine  10 , e.g. along, towards or away from the cylinder crankcase  12 .  
         [0048]    It will be noted that the lubricant return passages  64 A,  64 B and crankcase return ports  70 A,  70 B are of a larger cross-sectional area that the lubricant feed ports  68 A,  68 B and lubricant feed passages  62 A,  62 B. This is because in the present embodiment the lubricant is supplied in the form of engine oil under pressure from an engine oil pump and under such circumstances the lubricant return passages  64 A,  64 B and crankcase return ports  70 A,  70 B are preferably be wider to accommodate gas bubbles in the spent oil returning to the engine sump.  
         [0049]    In use, the lubricant feed and return passages  62 A,  62 B,  64 A,  64 B interface with lubricant inlets  74  and lubricant outlets  76  of the turbochargers  22 A,  22 B at the mounting faces  72 A,  72 B of the support arms  52 A,  52 B. The lubricant feed and return passages  62 A,  62 B,  64 A,  64 B are routed through their respective turbocharger mountings  46 ,  48  in such a manner as to enable the turbochargers  22 A,  22 B to be mounted on the engine  10  via the super-charger mounting holes  60  in substantially mirror image orientations thereabout.  
         [0050]    In such a mirror image disposition, the turbochargers  22 A,  22 B can be mounted with at least one of their corresponding pairs of charge air entries  34 , charge air exits  36 , exhaust gas entries  30  or exhaust gas exits  32  being disposed at substantially the same orientation with respect to the engine  10 . For example, the charge air entries  34  and exhaust gas exits  32  of the turbochargers  22 A,  22 B of each cylinder bank  14 ,  16  may be aligned substantially parallel with a centerline C/L running longitudinally through the cylinder crankcase  12 . Such a situation is illustrated in the present embodiment and may be found useful in design of an associated air intake system or exhaust piping. Similar considerations may be applied to the charge-air exits  36  and/or the exhaust gas entries  30 .  
         [0051]    The lubricant supply ports  68 A,  68 B and return ports  70 A,  70 B may be positioned symmetrically on opposing sides of the cylinder crankcase  12 . This means that if identical supercharger mountings were to be used on either side of the cylinder crankcase  12 , the turbochargers  22 A,  22 B would point in opposite directions between opposing side of the engine  10 . In order to compensate for this and to allow the use of substantially identical turbochargers  22 A,  22 B oriented in mirror image, e.g. pointing in substantially the same direction, the lubricant feed passages  62 A,  62 B and lubricant return passages  64 A,  64 B are operatively inverted between the mountings  46 ,  48 .  
         [0052]    The inversion preferably takes place in a cross-over region  66  of one mounting, shown by way of example as inside the rear bank mounting  48  and visible schematically with particular reference to FIGS.  1  to  4 . Crankcase symmetry may be maintained between its lubricant supply and return ports  68 A,  68 B,  70 A,  70 B as illustrated schematically in FIG. 2, but this may not prove practical for mass production. What is necessary, however, is for substantial inversion of the lubricant feed and return passages  62 A,  62 B,  64 A,  64 B to take operative effect at the turbocharger mounting faces  72 A,  72 B. For example, in the embodiment illustrated the lubricant return passage  64 A of the front mounting  46  is inboard of its associated lubricant feed passage  62 A. The lubricant return passage  64 B of the rear mounting  48  is therefore outboard of its associated lubricant feed passage  62 B such that inversion has taken place.  
         [0053]    While the inversion has be described in relation to implementation inside the rear mounting  48 , the invention is not limited to this embodiment. The disposition of the lubricant feed and return passages  62 A,  62 B,  64 A,  64 B will usually depend on the disposition of the lubricant inlets  74  and outlets  76  of the turbochargers  22 A,  22 B, whose disposition on the mountings  46 ,  48  will depend in turn on which direction about the engine  10  the turbochargers  22 A,  22 B need to face and the positioning of their mounting holes  60 .  
         [0054]    To achieve the inversion through practical mountings  46 ,  48 , it may be found easier to implement an off-set relationship between the lubricant feed and return passages  62 B,  64 B at their interface with the cylinder crankcase  12 . An example may be seen with particular reference to the views of FIGS. 6 and 8. In the rear face  80  (i.e. crankcase interface side) of the front mounting  46 , the lubricant feed and return passages  62 A,  64 A are side-by-side with the mounting  46  in its in-use position. In the rear face  82  of the rear mounting  46 , the lubricant feed passage  62 B is offset upwards from the lubricant return passage  64 B. This arrangement may ease manufacture of the mounting  48  that includes the internal crossover between the lubricant feed and return passages  62 B,  64 B, e.g. by keeping down the number of drilling operations used. For either mounting  46 ,  48 , so as to reach its destination on the turbocharger mounting face  72 A,  72 B, the lubricant feed passage  62 A,  62 B may pass through one or more portions of their associated mounting  46 ,  48  that also acts as a fillet  78 .  
         [0055]    The inversion will now be considered for the moment with particular reference to the schematic diagram of FIG. 1. Symmetry across opposing sides of the cylinder crankcase  12  is preferably maintained for the lubricant supply passages  68 A,  68   b  and return passages  70 A,  70 B, inversion  66  being effected through one of the mountings  48  so that feed and return passages  62 A,  62 B,  64 A,  64 B at the interface  72 A,  72 B,  60  between the mountings  46 ,  48  and the turbochargers  22 A,  22 B are functionally swapped over between sides of the engine  10  in accordance with the inversion arrows  66 A. The arrangement therefore facilitates a method of mounting a pair of substantially identical turbochargers  22 A,  22 B to opposite sides of an engine  10  in mirror orientation, e.g. so that an axis through equal parts of each of those turbochargers  22 A,  22 B is disposed at substantially the same orientation as each other about the rest of the engine  10 .  
         [0056]    Referring for the moment in particular to FIGS.  2  to  4 , it can be seen that use of identical turbochargers  22 A,  22 B in substantially mirror image orientations about the engine  10  may offset certain parts of the turbochargers  22 A,  22 B towards or away from the engine. For example, in FIGS.  2  to  4  it can be seen that the exhaust gas entry  30  of the front bank turbocharger  22 A is offset away from the engine  10 , whereas the exhaust gas entry  30  of the rear bank turbocharger  22 B is offset towards the engine  10 . This situation may effect the design of the exhaust arrangement  44  supplying the turbochargers  22 A,  22 B, e.g. with respect to primary tract length or routing.  
         [0057]    In addition, packaging concerns may make it necessary to position one of the turbochargers  22 A at a different spacing from the cylinder crankcase  12  than the other  22 B. Such a situation is illustrated by way of example and the front bank turbocharger  22 A is spaced away from the cylinder crankcase  12  by more than the rear bank turbocharger  22 B. Although the spacing away from the cylinder crankcase  12  is different, the turbochargers  22 A,  22 B are still orientated in substantially mirror fashion about the engine  10 , with both their charge air entries  34  and exhaust gas exits  32  oriented in substantially the same way, e.g. with respect to a centerline C/L running through the cylinder crankcase  12  the turbine shaft  38  of each turbocharger  22 A,  22 B runs substantially parallel to that centerline C/L with corresponding parts  32 ,  34  pointing in the same direction front F or rear R of the engine  10 .  
         [0058]    The spacing, alignment and inclination of the turbochargers  22 A,  22 B with respect to the cylinder crankcase  12  is defined by the dimensions, angles and turbocharger fixing points  60  of the arms  52 A,  52 B. By way of example, the arm  52 A of the front mounting  46  extends further out from its back plate  50 A than does the arm  52 B of the rear mounting  48  from its back plate  50 B. This positions the front bank turbocharger  22 A further away from the cylinder crankcase  12  than is positioned the rear bank turbocharger  22 B by its mounting  48 . The dimensions of fillets  78  and/or other strengthening features may vary between mountings  46 ,  48 , e.g. in dependence on their individual packaging or load requirements.  
         [0059]    Referring for the moment in particular to FIGS. 12 and 13, it can be seen that in the illustrated embodiment the corresponding charge air exits  36  and exhaust gas entries  30  do not necessarily line up with each other. This may be the case even though their corresponding charge air entries  34  and exhaust gas exits  32  are in substantially even orientation with respect to the cylinder crankcase  12 . Whether or not more than one pair or set of corresponding orifices  30 ,  32 ,  34 ,  36  between the turbochargers  22 A,  22 B will be aligned once they are in a practical installation, may depend on the particular model of turbocharger used.  
         [0060]    Among the advantages of the invention is the provision of a low cost arrangement for using a plurality of substantially identical turbo chargers on the same engine while achieving substantially mirror image orientations of those units around the engine. This saves costs by raising the volumes of the expensive part of a turbo-charging arrangement, the turbocharger itself, rather than necessitating several different and possibly custom units. The piece price of individual custom mountings being, of course, much lower than that of custom turbochargers. Furthermore, the arrangement may provide greater supplier choice as standard or off-the-shelf units may be employed. The arrangement also helps achieve optimum packaging and design for inlet and exhaust systems by aligning two or more entries or exits of the turbochargers in substantially the same direction. Changes in design between variants of an engine family or installation may also be accommodated by design changes to only the separate mountings, whose tooling and development costs are not high.  
         [0061]    The mounting being separate can be mounted with greater flexibility than in installations that propose a one-piece mounting for twin superchargers, e.g. lower down which save height in under-hood. This is particularly advantageous where the engine assembly concerned is to be used in a passenger vehicle or light truck where hood height is an important design constraint.  
         [0062]    While the present invention has been particularly shown and described with respect to a preferred embodiment, it will be understood by those skilled in the art that changes in form and detail may be made without departing from the scope and spirit of the invention.