Abstract:
Amphibious vehicle power train  10  comprises a prime mover  12,  transfer drive  14,  transmission  16,  and differential  17.  A marine drive power take-off (PTO) comprises chain, belt, or gear drive, and optional decoupler  22.  Rotational axis  65  of marine drive shaft  64  and impeller shaft  66  of centrifugal pump  68  are substantially perpendicular to longitudinal vehicle axis  11.  The driven road wheels may be the rear wheels. Alternative embodiments comprise PTO drive from differential  17  (FIG.  3 ); from the crankshaft timing end ( 80,  FIG.  4 ); or by a sandwich PTO between engine and transmission ( 56,  FIG.  5 ). FIG.  6  shows PTO&#39;s from the gearbox of a motorcycle type power train, driving centrifugal pump  102  and differential  90.  At least one further decoupler may be provided in wheel driveshafts  23, 25,  to disconnect drive thereto while the amphibian is used in marine mode. The prime mover  12  may be an engine or may be an electric motor.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to a power train for an amphibious vehicle and in particular, though not exclusively, to a power train for driving the rear wheels and the marine propulsion means of an amphibious vehicle. The present invention also relates to an amphibious vehicle.  
         DESCRIPTION OF THE RELEVANT ART  
         [0002]    In an amphibious vehicle it is advantageous to use a power train in which the prime mover, which will typically be an engine, and transmission are positioned towards the rear of the vehicle for driving the rear wheels of the vehicle. The weight of the power train is therefore positioned towards the back of the vehicle, which is necessary for good vehicle performance when the vehicle is in marine mode and in particular when the vehicle is planing. Furthermore, the rearward position of the power train maximises the space available towards the front of the vehicle for the passenger compartment.  
           [0003]    It has been proposed in FIG. 3 of our co-pending European patent application No. EP 1 174 300 to provide a mid-engined vehicle having a transverse power train, with a power take-off for driving a water jet unit. However, as in other known amphibious vehicle arrangements, the drive shaft of the water jet unit is in line with the vehicle axis, and the axis of rotation of the power take-off is perpendicular to the vehicle axis. Consequently, it is necessary to turn the axis of drive from the power take-off through 90° by means of a pair of bevel gears.  
           [0004]    This arrangement has the disadvantages of reducing the power output of the power take-off to the water jet unit due to frictional losses in the bevel gears, and of being costly to produce. The bevel gears also occupy space in an area of the vehicle where space is at a premium, and require housing in a specially designed casing.  
         SUMMARY OF THE INVENTION  
         [0005]    It is an object of the invention to provide a power train for an amphibious vehicle in which the above mentioned disadvantages are reduced or substantially obviated. It is a further object of the invention to provide an amphibious vehicle having such a power train.  
           [0006]    According to a first aspect of the present invention, there is provided a power train for an amphibious vehicle, the power train comprising a prime mover, a transmission and a power take-off adapted to provide drive to an impeller of a marine propulsion means, in which a rotational axis of the power take-off and the rotational axis of the impeller are both substantially perpendicular to the longitudinal axis of the vehicle.  
           [0007]    Preferably, the power take-off comprises a driving sprocket which drives a driven sprocket by means of a belt or chain. Alternatively, the power take-off may comprise a series of two or more gears.  
           [0008]    Preferably, a decoupler is provided to selectively couple and decouple drive from the power take-off to the impeller of the marine propulsion means.  
           [0009]    Preferably, the marine propulsion means is a centrifugal pump.  
           [0010]    Advantageously, the prime mover and transmission are adapted to be mounted towards the rear of an amphibious vehicle so as to provide drive to a pair of rear wheels of the vehicle.  
           [0011]    Preferably, the prime mover is an engine. Alternatively, the prime mover may be an electric motor which may be powered by a fuel cell.  
           [0012]    In accordance with a second aspect of the invention, there is provided an amphibious vehicle comprising a power train in accordance with the first aspect of the invention. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]    The invention will now be described, by way of example only, with reference to the accompanying drawings in which:  
         [0014]    [0014]FIG. 1 shows a perspective view of a known arrangement of an engine and transmission in which a power take-off drives the drive shaft of a water jet unit through a pair of bevel gears;  
         [0015]    [0015]FIG. 2 shows a perspective view of a first embodiment of the invention including a transverse engine and transmission with a power take-off from the end of the transmission driving a centrifugal pump;  
         [0016]    [0016]FIG. 3 shows a perspective view of a second embodiment of the invention including a transverse engine, transmission, differential, and a power take-off from the differential driving a centrifugal pump;  
         [0017]    [0017]FIG. 4 shows a perspective view of a modification of the second embodiment, having an alternative form of power take off from the differential;  
         [0018]    [0018]FIG. 5 shows a perspective view of a third embodiment of the invention including a transverse engine, transmission, differential, and a power take-off from the crankshaft of the engine driving a centrifugal pump;  
         [0019]    [0019]FIG. 6 shows a perspective view of a fourth embodiment of the invention including a transverse engine and transmission, with a sandwich power take-off driving a centrifugal pump; and  
         [0020]    [0020]FIG. 7 shows a perspective of a fifth embodiment of the invention including a conventional motor cycle power train adapted to drive a centrifugal pump and a differential. 
     
    
     DETAILED DESCRIPTION  
       [0021]    Referring firstly to FIG. 1, a known power train arrangement as described in our copending European patent application No EP 1 174 300 is indicated generally at  10 . An engine  12  is mounted transversely in a vehicle (not shown), that is with the axis of the crankshaft of the engine positioned perpendicular to the longitudinal axis of the vehicle, which is indicated in chain dotted line at  1   1 . A transfer drive  14  transfers drive from the engine  12  to a transmission  16 , positioned parallel with, and behind the engine  12 . A differential  17  is driven from the right hand end (as viewed) of the transmission  16 , and drives a pair of drive shafts  23 ,  25 . The drive shafts  23 ,  25  provide drive to wheels (not shown) on either side of the vehicle. Decouplers may be fitted to one or both drive shafts  23 ,  25 , as is known in the art, to disconnect drive to the road wheels when the vehicle is in marine mode.  
         [0022]    A power take-off sprocket  18  extends from the left hand end (as viewed) of the transmission  16 , which drives a driven sprocket  20  by means of a belt or chain  21 . A decoupler  22  selectively couples and decouples drive from the driven sprocket  20  to a cardan shaft  24 . A first bevel gear  26  is mounted at the end of the cardan shaft  24 , which is in meshing engagement with a second bevel gear  28 . The bevel gears  26 ,  28  transfer drive through  90  degrees to a drive shaft  30  of an impeller  32  of a waterjet unit  34 . The drive shaft  30  is in axial alignment with the vehicle axis  11 .  
         [0023]    Referring to FIG. 2, a first embodiment of the invention will now be described. Common reference numerals will be used to designate parts in common with the parts in the known arrangement as shown in FIG. 1. A prime mover in the form of an engine  12  is arranged transversely to the longitudinal axis of the vehicle and drives a transmission  16 , positioned parallel with, and behind the engine  12 , by means of a transfer drive  14 . A differential  17  is driven from the right hand end (as viewed) of the transmission  16 , and drives a pair of drive shafts  23 ,  25 . The drive shafts  23 ,  25  provide drive to wheels (not shown) on either side of the vehicle in known manner. In a particularly preferred arrangement, the shafts  23 ,  25  are arranged so as to provide drive to a pair of rear wheels of the vehicle.  
         [0024]    A power take-off sprocket  18  extends from the left hand end (as viewed) of the transmission  16 , which drives a driven sprocket  20  by means of a belt or chain  21 . By the term “power take-off” is meant a means of enabling the engine power of the vehicle to be used to drive non-automotive apparatus, for example, a marine propulsion means. A decoupler  22  selectively couples and decouples drive between the drive sprocket  20  and a drive shaft  64 , which is coupled directly to an impeller shaft  66  of a centrifugal pump  68 . The axis of the drive shaft  64  and impeller shaft  66 , indicated at  65 , is perpendicular to the vehicle axis  11 . The centrifugal pump  68  provides propulsion of the amphibious vehicle when the vehicle is in marine mode.  
         [0025]    A second embodiment of the invention will now be described with reference to FIG. 3. Common reference numerals have been used to designate parts in common with the parts shown in FIGS. I and  2 . As in the previous embodiment, a transverse engine  12  drives a transmission  16 , positioned parallel with, and behind the engine  12 , by means of a transfer drive  14 . A differential  17  is driven from the right hand end (as viewed) of the transmission  16 , and drives a pair of drive shafts  23 ,  25 . The drive shafts  23 ,  25  provide drive to wheels (not shown) on either side of the vehicle in known manner.  
         [0026]    A carrier drive  70  of the differential  17  drives a power take-off sprocket  72 , which in turn drives a driven sprocket  74  through a belt or chain  76 . A decoupler  78  selectively couples and decouples drive from the driven sprocket  74  to an impeller shaft  66  of a centrifugal pump  68 . The axis of the impeller shaft  66 , indicated at  65 , is perpendicular to the vehicle axis  11 . The centrifugal pump  68  provides propulsion of the amphibious vehicle when the vehicle is in marine mode.  
         [0027]    [0027]FIG. 4 shows a modification to the second embodiment, in which the power take of from the differential is provided by means of a series of meshing gears  172 - 174  rather than by means of a drive belt or chain. In the arrangement shown, a first gear  172  mounted to a carrier drive of the differential engages with a second or idler gear  173  mounted to a counter shaft  175 . The second gear in turn meshes with a third gear  174  which is connected to the impeller shaft  66  by a decoupler. The arrangement transmits drive from the differential to the impeller and by use of an idle gear it can be arranged that the impeller rotates in the same direction as the differential output. In practice the gears would be contained within a casing or cover, which is not shown for clarity, and the counter shaft  175  would be supported by the casing or cover.  
         [0028]    A third embodiment of the invention will now be described with reference to FIG. 5, in which common reference numerals have been used to designate parts in common with the parts shown in FIG. 3. The third embodiment is similar to the second embodiment except that the drive for the marine propulsion means is taken from the timing end of the crankshaft of the engine rather than from the differential  17 . To this end, a power take-off sprocket  72  is mounted for rotation with the timing end of the crankshaft (indicated generally at  80 ) and drives a driven sprocket  74  through a belt or chain  76 . A decoupler  78  selectively couples and decouples drive from the driven sprocket  74  to an impeller shaft  66  of a centrifugal pump  68 . The axis of the impeller shaft  66 , indicated at  65 , is perpendicular to the vehicle axis  11 . The centrifugal pump  68  provides propulsion of the amphibious vehicle when the vehicle is in marine mode.  
         [0029]    A fourth embodiment of the invention will now be described with reference to FIG. 6. A prime mover in the form of an engine  40  and an in-line transmission  42  are mounted transversely in a vehicle (not shown). The longitudinal axis of the vehicle is indicated by the chain dotted line  11 . A transfer drive  44  from the drive output of the transmission  42  drives a differential  46  positioned with its centre line  47  offset to one side of, and parallel with the transmission  42 . A drive shaft  48  is driven from one side of the differential  46 , and a relay shaft  50 , which is parallel with the crankshaft of the engine  40 , is driven from the other side of the differential. The relay shaft  50  drives a further drive shaft  52 . The drive shafts  48 ,  52  drive wheels (not shown) on either side of the vehicle in known manner.  
         [0030]    A power take-off sprocket (not shown), which is mounted at the end of the crankshaft of the engine  40 , sandwiched between the engine and the transmission  42 , drives a driven sprocket  54  by means of a belt or chain  56 . The driven sprocket  54  drives a decoupler  58  which selectively couples and decouples drive to an impeller shaft  60  of a centrifugal pump  62 . The axis of the impeller shaft  60 , indicated at  63 , is perpendicular to the vehicle axis  11 . The centrifugal pump  62  provides propulsion of the amphibious vehicle when the vehicle is in marine mode.  
         [0031]    Finally, a fifth embodiment of the invention will now be described with reference to FIG. 7. A conventional motorcycle engine  80  and parallel transmission  82  are mounted transverse to the vehicle axis  11 , as in a motorcycle. An output shaft  84  of the transmission mounts a drive sprocket  86  and a power take-off sprocket  88 . The drive sprocket  86  drives a driven sprocket (not shown) mounted on the carrier of a differential  90 , by means of a belt or chain  92 . Drive shafts  94 ,  96 , on either side of the vehicle, are driven from the differential  90  and drive wheels (not shown) in known manner.  
         [0032]    The power take-off sprocket  88  drives a driven sprocket  98  by means of a belt or chain  100 . The driven sprocket  98  drives a decoupler  99  which selectively couples and decouples drive to an impeller shaft of a centrifugal pump  102 . As in the previous embodiments, the axis of the impeller shaft, indicated at  65 , is perpendicular to the vehicle axis  11 , and the centrifugal pump  102  provides propulsion of the amphibious vehicle when the vehicle is in marine mode.  
         [0033]    In all the embodiments of the invention described above, the prime mover is provided in the form of an engine. The engine can be of any suitable and type and may comprise a piston engine, a rotary engine or turbine and can be adapted to run on any suitable fuel such as petrol, diesel, gas, or liquid petroleum gas (LPG). However, it should be understood that the invention is not limited to power trains in which the prime mover is an engine but is intended to cover power trains having a prime mover of any suitable type. For example the prime mover could be an electric motor or it could be in the form of a hybrid combination of an engine with an electric motor. Where the prime mover comprises an electric motor, the electric motor could, for example, be powered by a fuel cell.  
         [0034]    A power train in accordance with the invention provides a compact and efficient means of driving both the road wheels and a marine propulsion unit of an amphibious vehicle. The arrangement is particularly suited for mounting towards the rear of an amphibious vehicle so as to drive the rear wheels of the vehicle.  
         [0035]    Whereas the invention has been described in relation to what is presently considered to be the most practical and preferred embodiments, it is to be understood that the invention is not limited to the disclosed arrangements but rather is intended to cover various modifications and equivalent constructions included within the spirit and scope of the invention. For example, the decoupler on the power take-off to the marine drive is not essential to the concept of the invention, and may therefore be omitted. Decouplers may also be fitted to one or both wheel drive shafts  23 ,  25 , to disconnect drive to the road wheels when the vehicle is in marine mode. Furthermore, whilst the preferred form of power take-off comprises a driving sprocket and a driven sprocket interconnected by means of a belt or chain, this need not be the case and any suitable form of power take-off can be used. For example, the power take-off could comprise driving and driven pulleys interconnected by means of a belt or the power take-off may be in the form of a series of two or more meshing gears as described with reference to FIG. 4.