Abstract:
A power train for an amphibious vehicle includes an engine and transaxle arranged North-South, driving front, rear, or all four road wheels. A power take off with optional decoupler and constant velocity joint drives marine drive. The power take off may be taken from the input shaft of the transmission, and may use a synchronizer. The transaxle includes a differential. The rear wheels may be set back from the differential outputs, with intermediate drives by chains or belts. A sandwich type power take off may also be used. In the four wheel drive embodiment, a power take off is required from the rear differential. Decouplers may be provided in at least one wheel drive shaft on each driven axle.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a power train which is particularly suitable for use in an amphibious vehicle capable of travel on land and water, and more particularly to a means of adapting a conventional automotive transaxle drive arrangement to drive the wheels and the marine propulsion means of an amphibious vehicle. The invention also relates to an amphibious vehicle having such a power train. 
     In some automotive power train arrangements the engine has a crankshaft in line with the longitudinal axis of the vehicle, whereby the engine drives an in-line transmission with an integral differential which is typically located between the engine and the transmission, the differential being connected by drive shafts to the drive wheels of the vehicle. This arrangement is commonly known as a transaxle drive and has been employed in front engine, rear engine and mid engine power train layouts. 
     It is also known for transaxle power train arrangements to be adapted to provide four wheel drive. In such known four wheel drive arrangements, the transaxle will typically drive the front wheels of the vehicle, with a power take off from the transmission driving the rear wheels of the vehicle. 
     The transaxle drive arrangement is currently used by several large car manufacturers in the production of private passenger vehicles and is therefore produced in relatively high volumes, which makes the arrangement most procurable for use in an amphibious vehicle. In choosing a power train for a specialised low volume production vehicle, such as an amphibious vehicle, availability is an important factor. 
     EP 0 742 761 discloses a power train for an amphibious vehicle using a front wheel drive power train reversed, to mount the engine behind the rear axle. The marine power take off is by a gearbox taken from the timing end of the engine, opposite to the transmission mounting end. This power take off requires a number of custom designed parts to be designed, built, and assembled; and may require redesign and relocation of engine mounted accessories, such as the alternator drive belt. Also, the reversal of the power train may require additional gearing or other modifications to ensure that the road wheels rotate in the required and expected directions. The cost burdens and assembly requirements of such adaptations are particularly unwelcome to low volume vehicle manufacturers. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a power train for an amphibious vehicle in which a conventional transaxle drive is utilised and adapted to drive at least one pair of road wheels and a marine propulsion means. 
     According to a first aspect of the invention, there is provided power train for an amphibious vehicle comprising an engine and transaxle drive arranged in North-South alignment, that is with the front or timing end of the engine facing the front of the vehicle and with the engine in longitudinal alignment with the vehicle axis, the transaxle drive including a transmission and differential, the differential being adapted to provide drive to a pair of driven wheels of the vehicle, the power train further comprising a power take off adapted to provide drive to a marine propulsion means. 
     Preferably, the power take off is provided by means of a drive shaft connectable to an input shaft of the transmission. In a particularly preferred embodiment, the drive shaft is selectively connectable to the input shaft by means of a decoupler which may have means, such as a baulk ring, adapted to synchronize the speeds of the input shaft and the drive shaft as the shafts are coupled. Conveniently, the decoupler may comprise a gear wheel and synchro-mesh unit. 
     Alternatively, the power take off may comprise a sandwich power take off between the engine and the transaxle, which power take off provides drive to the marine propulsion means. Drive may be transmitted from the sandwich power take off to the marine propulsion unit by means of a prop shaft which may be connected to a drive shaft of the marine propulsion unit by a constant velocity joint. 
     In one embodiment, each wheel of the pair of the driven wheels is driven by an output shaft of the differential, the arrangement being such that the axis of rotation of the pair of driven wheels is offset along the length of the vehicle from the axis of rotation of the output shafts of the differential. In such an arrangement, drive may be transmitted between each said driven wheel and its respective differential output shaft via a chain or belt drive means. Preferably, the chain or belt drive means comprises a first sprocket mounted to the differential output shaft, a second sprocket mounted to a wheel drive shaft and a belt or chain interconnecting the two sprockets to transmit drive between the output shaft and the wheel drive shaft. 
     The power take off may provide drive only to the marine propulsion means or may provide drive to a second differential for diving a further pair of road wheels, with the drive to the marine propulsion unit being taken from the second differential. In an alternative arrangement for providing a four wheel drive facility, where the power take off is a sandwich power take off, a further power take off adapted to drive a further pair of wheels of the vehicle may also be provided. Preferably, the further power take off is provided by means of a shaft which is drivingly connectable to the transmission at a rearward end thereof, the shaft being adapted to drive a further differential for driving the further pair of wheels of the vehicle. 
     In all embodiments of the invention, the power train may be adapted such that the centre lines of the engine, transaxle, and marine propulsion unit are substantially aligned with each other and with the centre line or longitudinal axis of the vehicle. 
     Preferably, the or each power take off is arranged rearward of the engine. 
     According to a second aspect of the invention, there is provided an amphibious vehicle having a power train in accordance with the first aspect. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Several embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which: 
         FIG. 1  is a plan view of a conventional power train arrangement including a longitudinal engine, and a transmission and differential in a transaxle arrangement for driving the front wheels of a vehicle; 
         FIG. 2  is a plan view of a conventional power train arrangement including a longitudinal engine, and a transmission and differential in a transaxle arrangement adapted for driving all four wheels of a vehicle; 
         FIG. 3  is a plan view of a power train for an amphibious vehicle in accordance with the present invention, in which the power train is adapted to drive the rear wheels and the marine propulsion means of an amphibious vehicle; 
         FIG. 4  shows a schematic section through the transaxle arrangement for driving the rear wheels and marine propulsion means of the amphibious vehicle as shown in  FIG. 3 ; 
         FIG. 5  shows a schematic section through a prior art transaxle where the fifth gear is in a separate compartment to the other four gears; 
         FIG. 6  Shows a modification to the power train of  FIG. 3 , in which the transaxle of  FIG. 5  is adapted to provide an alternative power take off arrangement; 
         FIG. 7  is a plan view of a second embodiment of a power train for an amphibious vehicle in accordance with the invention, in which the power train is adapted to drive the rear wheels and the marine propulsion means of an amphibious vehicle; 
         FIG. 8  is a plan view of a third embodiment of a power train for an amphibious vehicle in accordance with the invention, in which the power train is adapted to drive the front wheels and the marine propulsion means of an amphibious vehicle; 
         FIG. 9  is a plan view of a fourth embodiment of a power train for an amphibious vehicle in accordance with the invention, in which the power train is adapted to drive all four wheels and the marine propulsion means of an amphibious vehicle; 
         FIG. 10  is a plan view of a fifth embodiment of a power train for an amphibious vehicle in accordance with the invention, in which the power train is adapted to drive the front wheels and the marine propulsion means of an amphibious vehicle; 
         FIG. 11  is a plan view of a sixth embodiment of a power train for an amphibious vehicle in accordance with the invention, in which the power train is adapted to drive the rear wheels and the marine propulsion means of an amphibious vehicle; 
         FIG. 12  is a plan view of an seventh embodiment of a power train for an amphibious vehicle in accordance with the invention, in which the power train is again adapted to drive the rear wheels and the marine propulsion means of an amphibious vehicle; and 
         FIG. 13  is a plan view of a eighth and final embodiment of a power train for an amphibious vehicle in accordance with the invention, in which the power train is adapted to drive all four wheels and the marine propulsion means of an amphibious vehicle. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The same reference numerals have been used throughout the drawings to denote common components. 
     Referring firstly to  FIG. 1 , a conventional transaxle drive arrangement, generally indicated at  10 , is shown driving the front wheels  14 , 16  of a vehicle  12 . An engine  18  is conventionally positioned forward of the front wheels  14 , 16  with the crankshaft of the engine  18  in axial alignment with the centre line, chain dotted at  20 , of the vehicle  12 . A transmission  22  is mounted in line with the engine  18  and drives a differential  24 . Drive shafts  26 , 28  drive the front wheels  14 , 16  of the vehicle from the differential  24 . The tear wheels  30 , 32  of the vehicle  12  are not driven. 
     A second conventional transaxle arrangement  11  for a vehicle  13  will now be described with reference to  FIG. 2 . Engine  18 , transmission  22 , and differential  24  are arranged to drive front wheels  14 ,  16  through drive shafts  26 , 28  as in the arrangement of  FIG. 1 . In this case, however, a power take off is located at the rear of transmission  22 , driving centre differential  31  and rear differential  33 . Drive shafts  27  and  29  drive rear wheels  30  and  32  respectively. This arrangement is a convenient way of offering a four wheel drive transmission in combination with a “North-South” mounted engine and transaxle as shown. 
     The term “North-South” will be understood by those skilled in the art to indicate a vehicle power train in which the engine is mounted so that the axis of the crankshaft is in alignment with or parallel to the axis of the vehicle and in which the front end of the engine, usually the timing end, faces towards the front of the vehicle. The term should be interpreted in this sense throughout the description and/or claims. 
     A first embodiment of the invention will now be described with reference to  FIGS. 3 and 4 . A North-South mounted engine  18  and in line transmission  22  are positioned at the rear of an amphibious vehicle  34 , with the crankshaft of the engine  18  in axial alignment with the axis  20  of the vehicle  34  and the front or timing end of the engine facing towards the front of the vehicle. The engine  18  is positioned forward of the centre line of the rear wheels  30 , 32 , and the transmission  22  drives a differential  24  in a transaxle arrangement, as described with reference to  FIG. 1 . Drive shafts  26 , 28  drive the rear-wheels  30 , 32  of the vehicle  34  from the differential  24 . 
     Decouplers  43 ,  45  are provided in the drive line between the differential  24  and the driven road wheels  14 ,  16 . The decouplers  43 ,  45  enable drive to the driven wheels to be decoupled when the vehicle is operated in marine mode. Alternatively, rather than providing a decoupler  43 ,  45  in the drive line between the differential and each driven wheel, a decoupler may be provided in the drive line between the transaxle and only one of the driven wheels  14 ,  16  or they may be omitted altogether. 
     As is best seen in  FIG. 4 , a power take off is provided on the transmission to drive a marine propulsion means in the form of a water jet  40 . An impeller shaft  36  drives an impeller  38  of the water jet  40  from the transmission  22 . The impeller shaft  36  can be selectively coupled to an extension of the input shaft  44  of the transmission by a decoupler  42 . Gears  46  mounted to the shaft  44  are engaged in known manner with corresponding gears  48  mounted on an output shaft  50 , which drives the differential  24 . The gears  46  and corresponding gears  48  provide the gear ratios of the transmission  22 . 
     In a preferred embodiment the decoupler  42  which selectively couples the input shaft  44  of the transmission to the impeller drive shaft  36  has means which are adapted to synchronise the speeds of the shafts as they are coupled. For example, the decoupler may be of the type disclosed in the applicants co-pending International patent application PCT/GB01/03493 which comprises a baulk ring for synchronizing the speeds of the shafts. 
     A modification to the first embodiment will now be described in relation to  FIGS. 5 and 6 . 
       FIG. 5  shows a conventional transaxle  22 ′ in which a fifth speed is provided by an ‘overhung’ pair of constant mesh gears  58 , 60  which are positioned in a separate compartment  61 , adjacent to the main compartment  63  of the transaxle  22 ′. A synchro-mesh unit  65  is employed to couple the drive gear  58  to the input shaft  44  whereby the drive gear  58  and the driven gear  60  may drive the output shaft  50  and thus the differential  24 . Similar synchro-mesh units (not shown) are conveniently employed to couple and decouple the gears  46  and  48  in the main compartment  63 . 
       FIG. 6  shows how the transaxle  22 ′ of  FIG. 5  can be modified to provide a power take off for use in the power train of  FIG. 3 . In the modified transaxle  22 ″ the driven gear  60  has been removed from the output shaft  50  whereby the fifth speed of the transaxle  22 ′ will no longer be available to drive the rear wheels  30 , 32  of the vehicle  34 . However, the drive gear  58  may still be coupled to the input shaft  44  by the synchro-mesh unit  65 , such that by coupling the fifth gear axially to the impeller shaft drive shaft  36 , as shown at  67 , drive to the water jet  40  may be provided in a manner similar to that described above in relation to  FIG. 4 , with the synchro-mesh unit  65  acting as a decoupler. 
     This modified arrangement provides an advantage over the arrangement of  FIG. 4 , in that the existing coupling system of synchro-mesh unit  65  may be employed as a decoupler in place of the additional decoupler  42  used in  FIG. 4 . 
     The modified power take off arrangement can of course be used with any transaxle in which a pair of overhung gears are located in a separate compartment of the transaxle. For example where the transaxle has a sixth speed gear in a separate compartment, the sixth speed gear can be used to provide the power take off as described above. 
     Whilst preferred forms of the power take off have been described, it will be understood by those skilled in the art that any suitable form of power take off can be used to drive the water jet  40  from the transmission. 
       FIG. 7  shows a second embodiment of the invention. The arrangement is similar to that of the first embodiment except that the engine  18  and transmission  22  have been moved forward in the vehicle to accommodate a longer jet drive  41 . The differential  24  has output drive shafts  26 ,  28  on which are mounted sprockets  21 ,  23 . The sprockets  21 ,  23  drive corresponding sprockets  21 ′,  23 ′ on offset wheel drive shafts  26 ′,  28 ′ by means of a belt or chain  47 ,  47 ′. This arrangement permits drive to be transmitted between the differential  24  and the driven wheels  30 ,  32  whose axis of rotation is offset along the length of the vehicle from the axis of rotation of the output shafts  26 ,  28  of the differential. 
     A decoupler  43 ,  45  is fitted in the drive line between the differential and each of the driven rear wheels  30 ,  32  in order that drive to the wheels can be disconnected when the vehicle is used in a marine mode. In the present embodiment a decoupler  43 ,  45  is fitted in each of the wheel drive shafts  26 ′,  28 ′ but it will be appreciated that the decouplers could be fitted in the differential output shafts  26 ,  28  instead. Alternatively only a single decoupler can be used in the drive path between the differential and one of the wheels. Where a single decoupler is used to disconnect drive between the differential and one of the driven wheels  30 ,  32 , the corresponding wheel pinion in differential  24  will spin without transmitting power, while the other pinion will not be driven. If it is found in practice that the other wheel drive shaft rotates, through transmission oil drag or whatever other reason, it may be locked by use of the vehicle handbrake. 
     In a third embodiment of the invention, shown in  FIG. 8 , the engine  18  of an amphibious vehicle  54  is mounted in the conventional position for a transaxle front wheel drive arrangement, that is forward of the centre line of the front wheels  14 , 16 . The front wheels  14 , 16  are driven by drive shafts  26 , 28  with at least one decoupler  43 ,  45  as described with reference to  FIG. 3 . A propeller shaft  52  is connected to a decoupler  42 , which is driven by the conventional input drive shaft  44  of the transmission  22 . The propeller shaft  52  is coupled to the input shaft by means of the decoupler  42  in a manner similar to way in which the impeller shaft  36  is connected to the input shaft in the  FIG. 4  embodiment. Alternatively, the propeller shaft  52  may connected to the input shaft by use of a fifth or sixth speed gear and synchro-mesh unit as described above in relation to  FIGS. 5 and 6 . The propeller shaft  52  runs axially of the vehicle  54  and is connected to the impeller shaft  36  by means of a constant velocity joint  56 . The impeller shaft  36  drives the impeller  38  of the water jet  40 , positioned at the rear of the vehicle  54 . 
       FIG. 9  shows a fourth embodiment of the invention, with all four road wheels of the vehicle  64  driven as well as a marine drive  40 . It should be noted that in this embodiment, the jet drive may be geared down or up according to the gear ratios of the transmission  22 ; whereas in the embodiments of  FIGS. 4 and 6 , the jet is driven at crankshaft speed. This embodiment generally follows the road car layout of  FIG. 2 , but incorporates at least one decoupler  43 ,  45  for the front wheel drive shafts  26 ,  28 , and at least one decoupler  43 ′,  45 ′, for rear wheel drive shafts  27 ,  29 . In this case, rear differential  33 ′ incorporates a power take off to take drive rearwards to decoupler  42  and marine drive  40 . It is not proposed to describe such a power take off in detail, because they are known in the power train art, for example for transmitting drive from the second to the third axle of a 6×6 truck. It is advantageous to use independent rear suspension with this layout, as this will allow differential  33 ′ to maintain a consistent position relative to water jet  40 . This in turn avoids any need for articulation of rearward drive shaft  25 ′, which would be difficult to arrange satisfactorily in the short shaft length available. 
       FIG. 10  shows a fifth embodiment of the invention, with front road wheels of the vehicle  74  driven as in the  FIG. 8  embodiment, but with an alternative power take off device. Engine  18  is offset forward compared to the  FIG. 8  embodiment, and a sandwich type power take off  53  is interposed between the engine and the transaxle. Sandwich power take off  53  will not be described in detail in the present application but may be constructed according to the applicant&#39;s co-pending British patent Application No. GB 0020884.3. The power take off  53  drives a propeller shaft  62 , which is necessarily installed at a lateral angle to the vehicle centre line  20 . A constant velocity joint  56  is fitted, to align the input drive of the water jet unit  40  with its output. Decoupler  42  may be fitted in the propeller shaft to enable the water jet drive to be disengaged during road driving. A further constant velocity joint (not shown) may be fitted at the front of the propeller shaft  62 , adjacent to power take off  53 . The further constant velocity joint may be combined with a decoupler, according to the applicant&#39;s co-pending International patent application No. PCT/GB01/03493, in which case the separate decoupler  42  can be omitted. 
       FIG. 11  shows a sixth embodiment of the invention. This embodiment is similar to the first embodiment shown in  FIG. 3 , except that drive to the marine propulsion unit  40  is provided from a sandwich power take off  53  between the engine  18  and the transaxle. The sandwich power take off unit  53  is the same as that described above in respect of the fifth embodiment as shown in  FIG. 10 . Use of a sandwich power take off has the advantage that decoupler(s) are not required in the wheel drive shafts  26 ,  28 , because the gearbox, whether manual or automatic, can be left in neutral gear when driving in marine mode. The sandwich power take off  53  drives the marine propulsion unit  40  by means of a prop shaft  62 ′ which is connected to a drive shaft  36  of the marine propulsion unit by a constant velocity (CV) joint  56  because of the angle of shaft  62 ′. A second CV joint will be required adjacent to the power take off. This may be combined with a decoupler  42  shown in  FIG. 11 . It will be noted here that drive shaft  36  is of vestigial length, for packaging reasons. 
       FIG. 12  shows a seventh embodiment of the invention, where the sandwich power take off arrangement described in relation to  FIGS. 10 and 11  is applied to the power train layout of the second embodiment of the invention, as shown in  FIG. 7 . 
       FIG. 13  shows an eighth and final embodiment of the invention, where the sandwich power take off arrangement as shown in  FIGS. 10 to 12  is applied to the power train layout of the fourth embodiment of the invention, as shown in  FIG. 9 . This layout is particularly advantageous in that it avoids the use of either two or four wheel drive shaft decouplers. 
     In each of the sandwich power take off embodiments described above in relation to  FIGS. 10 to 13 , a decoupler  42  is provided in the prop shaft adjacent to the power take off, and a CV joint  56  is incorporated in the marine propulsion unit. This is a preferred solution, because of control cable packaging; but it will be appreciated that the positions of CV joint and decoupler could be reversed if it is more convenient. 
     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, whilst it is preferred that the marine propulsion unit should be in the form of a water jet, any suitable marine propulsion means, such as a marine screw propeller, could be used.