Abstract:
An articulated shaft for an amphibian driveline includes at least two shaft portions and at least three points of articulation, wherein the articulated shaft is movable between a protracted position for use of the amphibian on land and a retracted position for use of the amphibian on water. An amphibian comprising the articulated shaft, and a powertrain comprising the articulated shaft is also provided.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The present invention relates to an articulated halfshaft particularly suitable for use in an amphibian capable of travel on land and water. More particularly, the articulated halfshaft is suitable for use with at least one retractable wheel or track drive in a high speed amphibian capable of planing on water. The present invention also relates to an amphibian incorporating such an articulated halfshaft. 
         [0002]    It is known, for example from U.S. Pat. No. 5,531,179 of the present applicant, for amphibians to have wheel and suspension assemblies which are retractable, so that the wheels are raised above the water line when the amphibian is operated on water. This reduces hydrodynamic resistance (drag), and allows for increased speed. The amphibian can then operate in a planing mode on water, and not just in a displacement mode only. However, known halfshafts, and in particular those used in automotive applications, have limited ability in terms of the angles of articulation possible. Furthermore, there are servicing and reliability issues when transmitting power and/or rotation at speed at increased angles of articulation. 
         [0003]    Prior art automotive halfshafts generally comprises two constant velocity (hereinafter “CV”) joints arranged in a spaced apart manner, joined by stub and/or intermediate shafts. The resulting driveshaft is commonly known as a halfshaft, axleshaft, CV shaft or CV axle. Whilst the halfshaft may transmit power and provide drive to a supported wheel in the manner of a driveshaft, it may also be used simply to support a wheel and not provide any power transmission or drive. 
         [0004]    The use of CV joints permits limited articulation at two points in the halfshaft such that vertical movement of a wheel is possible, usually supported via a suspension assembly. Splined connection of the stub and/or intermediate shafts or plunging CV joints may be used to accommodate geometry changes on movement of the wheel. Such an arrangement provides for bump and rebound, so as to improve the ride and handling characteristics of a vehicle. It also provides for a substantially constant rotating speed of a shaft over a range of angles between input and output. 
         [0005]    However, the degree of articulation achievable is limited due to the geometrical constraints of known articulating joints (CV joints, Rzeppa joints, tripod joints, Hooke&#39;s joints, Thompson CV joints and universal joints) since mechanical resistance to rotation and even geometric lock can occur beyond operational angles. Ultimately, this gives rise to servicing issues and failure of the articulating joint when it is operated at the larger angles of the limited articulation available. Such limitations do not present a problem in automotive applications where the amount of vertical travel of a wheel to be accommodated is limited. Furthermore, in amphibians where the dead rise angle of the hull is low (e.g. 0 to 5 degrees), it is still possible to retract the wheels sufficiently (wheel axle angles generally of between 15 and 45 degrees above the horizontal) to enable planing when the amphibian is operated on the water. 
         [0006]    However, there remains a need to retract wheel and track drives yet further, to achieve wheel or track axle angles of 90 degrees or more above the horizontal. This is of particular benefit in amphibians where the dead rise angle of the hull is more severe (e.g. 10 degrees or more), and/or where there is a need for improved ground clearance which in turn requires a greater height of upright in the suspension assembly. 
         [0007]    This presents significant problems in terms of the degree of articulation required (not to mention also the additional articulation about a vertical axis required for steering), packaging, weight distribution and also in terms of how the resulting power transmission pathways can be realised. 
         [0008]    The present invention seeks to address the aforementioned problems. 
       SUMMARY OF THE INVENTION 
       [0009]    Accordingly, the present invention provides, in a first aspect an articulated shaft for an amphibian driveline, the articulated shaft comprising: 
         [0010]    at least two shaft portions; and 
         [0011]    at least three points of articulation, wherein: 
         [0012]    the articulated shaft is movable between a protracted position for use of the amphibian on land and a retracted position for use of the amphibian on water. 
         [0013]    In a second aspect, the present invention provides an amphibian comprising the articulated shaft. 
         [0014]    In a third aspect, the present invention provides a powertrain comprising the articulated shaft. 
         [0015]    These and other features, advantages, and objects of the present invention will be further understood and appreciated by those skilled in the art by reference to the following specification, claims, and appended drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]    Preferred embodiments of the present invention will now be described by way of example only with reference to the accompanying drawings, in which: 
           [0017]      FIG. 1  is a schematic rear elevation view of a conventional road car transmission to a driven wheel, with the wheel shown at a normal ride height; 
           [0018]      FIG. 2  is a schematic rear elevation view of the conventional road car transmission of  FIG. 1  with the wheel shown at a full bump position; 
           [0019]      FIG. 3  is a schematic plan view from above of the conventional road car transmission of  FIGS. 1 and 2  with the wheel shown in two extremes of steering position; 
           [0020]      FIG. 4  is a schematic sectional view of a conventional plunging type CV joint; 
           [0021]      FIG. 5  is a schematic elevation view of a first preferred embodiment of halfshaft according to the present invention; 
           [0022]      FIG. 6  is a schematic elevation view of a further preferred embodiment of halfshaft according to the present invention; 
           [0023]      FIG. 7  is a schematic rear elevation view of amphibian transmission to a front steered wheel (optionally driven) incorporating the first preferred embodiment of halfshaft of  FIG. 5  according to the present invention, with the wheel shown at a normal ride height; 
           [0024]      FIG. 8  is a schematic rear elevation view of the amphibian transmission of 
           [0025]      FIG. 7 , with the wheel shown semi-retracted; 
           [0026]      FIG. 9  is a schematic rear elevation view of the amphibian transmission of 
           [0027]      FIG. 7 , with the wheel shown fully retracted; 
           [0028]      FIG. 10  is a schematic rear elevation view of amphibian transmission to a rear non-steered wheel (optionally driven) incorporating the further preferred embodiment of halfshaft of  FIG. 6  according to the present invention, with the wheel at shown at a normal ride height; 
           [0029]      FIG. 11  is a schematic front elevation view of the amphibian transmission of  FIG. 10 , with the wheel shown semi-retracted; 
           [0030]      FIG. 12  is a schematic front elevation view of the amphibian transmission of 
           [0031]      FIG. 11 , with the wheel shown fully retracted; and 
           [0032]      FIG. 13  is a detail schematic view in section of a centering mechanism for use in a halfshaft according to the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0033]      FIG. 1  shows a simplified schematic view of a known road car transmission to one driven left wheel, in a view taken along the car, looking forwardly from the rear. The transmission can be seen to comprise a differential  1 , a halfshaft generally indicated  5 , and a wheel  9 . An inner joint  3  is provided in the halfshaft  5 , commonly a CV joint. An outer CV joint  7  is also provided. As can be seen from  FIG. 1 , the total horizontal articulation angle αR for bump and rebound through which inner CV joint  3  must articulate is about 50 degrees for a typical road suspension (25 degrees above, and 25 degrees below horizontal). As the wheel  9  must remain substantially perpendicular to the road surface, outer CV joint  7  must also articulate through the same angle, but out of phase with the inner joint  3 , as shown in  FIG. 2 , where the wheel  9  is at full bump travel. 
         [0034]    Where the wheel  9  is also a steered wheel, the outer CV joint  7  has an additional function, as illustrated in  FIG. 3 .  FIG. 3  is a simplified plan view from above of the transmission of  FIGS. 1 and 2 . As shown, the steered wheel  9  rotates through an angle from position  9 R at full right steering lock to position  9 L (shown in dotted line) at full left lock. Hence, the range of vertical rotation β may be up to 90 degrees. The horizontal angle of rotation αR and the vertical angle of rotation β account for the full range of movement of the outer CV joint  7  (from full bump and right hand steerlog lock, to full rebound and left hand steering lock). 
         [0035]    To maintain a consistent track dimension between the left and right wheels on a given axle, the effective length of the wheel driveshaft must be able to alter as the wheel travels up and down in bump and rebound. This is achieved on a typical road car (e.g. with front wheels which provide drive and steering) by using a plunge type joint as the inner CV joint  3 , and a fixed joint as the outer CV joint  7 . Whilst a plunge joint can provide for changes in the effective length of the driveshaft, a plunge joint can only operate within a more limited range of driveshaft angles, because the driveshaft will contact the outer sleeve when these angles are exceeded, as can be seen from the indicated angle αC in  FIG. 4 . A fixed joint can operate through a larger range of angles, and is therefore used as the outer joint  7  to accommodate steering as well as suspension travel. A further reason why the plunge joint is used as an inner joint  3  rather than as an outer joint  7  is because it is bulkier than a fixed joint, so it is more easily packaged adjacent to the differential rather than at the wheel hub, where it would otherwise compete for space with many other components. Furthermore, if fitted to the wheel hub, the heavier plunge joint would add unwanted unsprung weight. 
         [0036]    In view of the foregoing, it will be appreciated that the need to retract wheel and track drives yet further, to wheel or track axle angles of 90 degrees or more above the horizontal, presents significant problems, not least in terms of the angle of articulation desired, packaging and weight. 
         [0037]    Referring next to  FIGS. 5 and 7  to  9 , there is shown a first preferred embodiment of halfshaft  10  according to the present invention.  FIG. 5  is a schematic elevation view of the halfshaft  10 . In the arrangement shown, the halfshaft  10  is for a front left hand steered wheel  400 , and optionally driven. The front left hand suspension upright  90  (omitted in  FIG. 5  for clarity) is mounted on a suspension upright stub shaft  20  of the halfshaft  10  at its left hand end. Drive is transferred from the halfshaft  10  (when driven) to the suspension upright  90  (which includes drop down drive to the wheel  400  by belt drive, gearing, etc.) via a key and keyway  22 . At its right hand end, suspension upright stub shaft  20  is mechanically connected via a shaft pin  23  to a housing plate  24 . In turn, the housing plate  24  is mechanically coupled, for example by way of a bolt or other mechanical fastening (omitted for clarity) to the outer raceway  32  of a first fixed CV joint  30 . The first fixed CV joint  30  forms a first articulated connection with a mid shaft  50 , the connection being formed by way of a ball spline connection formed between the CV outer raceway  32 , CV ball bearings (omitted for clarity), CV cage  34  and CV core  36 , and by way of the splined connection between the CV core  36  and the left hand end of the mid shaft  50 . The mid shaft  50  in fact comprises two parts  52 ,  54  each provided with respective male and female splines  56 ,  58  for splined connection so as to accommodate changes in the length of the halfshaft  10  during use. The right hand end of the midshaft  50  is connected via splined connection to the CV core  66  of a second fixed CV joint  60 . The second fixed CV joint  60  forms a second articulated connection with the midshaft  50 , the connection being formed by way of a ball spline connection formed between the CV outer raceway  62 , CV ball bearings (omitted for clarity), CV cage  64  and CV core  66 , and by way of the splined connection between the CV core  66  and the midshaft  50 . A third fixed CV joint  70  forms a third articulated connection with a differential stub shaft  80 , the connection being formed by way of a ball spline connection formed between the CV outer raceway  72 , CV ball bearings (omitted for clarity), CV cage  74  and CV core  76 , and by way of a splined connection between the CV core  76  and the differential stub shaft  80 . The respective CV outer raceways  62 ,  72  of the second and third fixed CV joints are mechanically coupled, for example by way of a bolt or other mechanical or other fastening method (omitted for clarity) so as to transmit torque. A centering mechanism (omitted from  FIG. 5  for clarity, but shown in detail in section in  FIG. 13  and described below) is preferably provided between the mid shaft  50  and stub shaft  80  to aid in controlling movement of the shafts in use. The right hand end of the differential stub shaft  80  is received in the differential  95  (omitted from  FIG. 5  for clarity), from which drive is received (when driven) via splines  82 . Each fixed CV joint  30 ,  60 ,  70 , in use, is packed with grease and protected by way of a cover (“boot”) and suitable retaining clips (omitted for clarity). 
         [0038]    The halfshaft  10  is illustrated schematically in protracted, semi-retracted and fully retracted positions in  FIGS. 7 ,  8  and  9  respectively. First, in  FIG. 7 , with front left steered (optionally driven) wheel  400  fully protracted, the first, second and third fixed CV joints  30 ,  60 ,  70  can be seen to have very shallow angles of articulation between each respective CV core  36 ,  66 ,  76  and CV outer raceway  32 ,  62 ,  72 . Next, in  FIG. 8 , with the front left steered wheel  400  semi-retracted, the first and second fixed CV joints  30 ,  60  can be seen to have very shallow angles of articulation between each respective CV core  36 ,  66  and CV outer raceway  32 ,  62 , whereas the third fixed CV joint  70  can be seen to have a more developed angle of articulation between its respective CV core  76  and CV outer raceway  72 . Finally, in  FIG. 9 , with the front left steered wheel  400  fully retracted, the first CV joint  30  can be seen to have a more developed angle αF 1  (˜20 degrees) of articulation between its respective CV core  36  and CV outer raceway  32 , and the second and third fixed CV joints  60 ,  70  can be seen to have very significant angles of articulation αF 2 , αF 3  between each respective CV core  66 ,  76  and CV outer raceway  62 ,  72  (˜73 degrees collectively). 
         [0039]    Referring next to  FIGS. 6 and 10  to  12 , there is shown a further preferred embodiment of halfshaft  100  according to the present invention.  FIG. 6  is a schematic elevation view of the halfshaft  100 . In the arrangement shown, the halfshaft  100  is for a rear left hand wheel  600 , and optionally driven. The rear left hand suspension upright  190  (omitted in  FIG. 6  for clarity) is mounted on a suspension upright stub shaft  120  at its left hand end. Drive is transferred from the halfshaft  100  (when driven) to the suspension upright  190  (which includes drop down drive to the wheel  600  by belt drive, gearing, etc.) via a key and keyway  122 . At its right hand end, suspension upright stub shaft  120  is mechanically connected via a shaft pin  123  to a stub shaft extension  121 . A first fixed CV joint  130  forms a first articulated connection with the stub shaft extension  121 , the connection being formed by way of a ball spline connection formed between the CV outer raceway  132 , CV ball bearings (omitted for clarity), CV cage  134  and CV core  136 , and by way of a splined connection between the CV core  136  and the right hand end of the stub shaft extension  121 . A second fixed CV joint  160  forms a second articulated connection with a midshaft  150 , the connection being formed by way of a ball spline connection formed between the CV outer raceway  162 , CV ball bearings (omitted for clarity), CV cage  164  and CV core  166 , and by way of a splined connection between the CV core  166  and the midshaft  150 . The respective CV outer raceways  132 ,  162  of the first and second fixed CV joints  130 ,  160  are mechanically coupled, for example by way of a bolt or other mechanical or other fastening method (omitted for clarity) so as to transmit torque. A centering mechanism (omitted from  FIG. 6  for clarity, but shown in detail in section in  FIG. 13  and described below) is preferably provided between the mid shaft  150  and stub shaft extension  121  to aid in controlling movement of the shafts in use. The mid shaft  150  in fact comprises two parts  152 ,  154  each provided with respective male and female splines  156 ,  158  for splined connection so as to accommodate changes in the length of the halfshaft  100  during use. The right hand end of the midshaft  150  is connected via splined connection to the CV core  176  of a third fixed CV joint  170 . The third fixed CV joint  170  forms a third articulated connection with the midshaft  150 , the connection being formed by way of a ball spline connection formed between the CV outer raceway  172 , CV ball bearings (omitted for clarity), CV cage  174  and CV core  176 , and by way of the splined connection between the CV core  176  and the midshaft  150 . In turn, a housing plate  124  is mechanically coupled, for example by way of a bolt or other mechanical fastening (omitted for clarity) to the outer raceway  172  of the third fixed CV joint  170 . The housing plate  124  further comprises a differential stub shaft  180 . The right hand end of the differential stub shaft  180  is received in the differential  195  (omitted from  FIG. 6  for clarity), from which drive is received (when driven) via splines  182 . Each fixed CV joint  130 ,  160 ,  170 , in use, is packed with grease and protected by way of a cover  188  (“boot”) and suitable retaining clips (omitted in  FIGS. 6 ,  10  and  11  for clarity). 
         [0040]    The halfshaft  100  is illustrated schematically in protracted, semi-retracted and fully retracted positions in  FIGS. 10 ,  11  and  12  respectively. First, in  FIG. 10 , with rear left (optionally driven) wheel  600  fully protracted, the first, second and third fixed CV joints  130 ,  160 ,  170  can be seen to have very shallow angles of articulation between each respective CV core  136 ,  166 ,  176  and CV outer raceway  132 ,  162 ,  172 . Next, in  FIG. 11 , with the rear left wheel  600  semi-retracted, the first and second fixed CV joints  130 ,  160  can be seen to have very shallow angles of articulation between each respective CV core  136 ,  166  and CV outer raceway  132 ,  162 , whereas the third fixed CV joint  170  can be seen to have a more developed angle of articulation between its respective CV core  176  and CV outer raceway  172 . Finally, in  FIG. 12 , with the rear left wheel fully retracted, the first and second fixed CV joints  130 ,  160  can be seen to have very significant angles of articulation αR 1 , αR 2  between each respective CV core  136 ,  166  and CV outer raceway  132 ,  162  (˜73 degrees collectively), and the third CV joint  170  can be seen to have a developed angle αR 3  (˜12 degrees) of articulation between its respective CV core  176  and CV outer raceway  172 . 
         [0041]      FIG. 13  illustrates, schematically in cross-section, a centering mechanism  800  suitable for use between two adjacently arranged CV joints  910 ,  920  and respective shafts  915 ,  925 . The CV joints  910 ,  920  can be the CV joints  60 ,  70  of  FIG. 5 , and the shafts  915 ,  925  can be the mid shaft  50  and stub shaft  80  of  FIG. 5 . Similarly, the CV joints  910 ,  920  can be the CV joints  130 ,  160  of  FIG. 6 , and the shafts  915 ,  925  can be the mid shaft  150  and stub shaft extension  121  of  FIG. 6 . The centering mechanism  800  can be seen to comprise an integral ball  850  and ball stub shaft  852 , an integral socket  810  and socket stub shaft  812 , and springs  820 ,  860 . The spring  820  and socket stub shaft  812  are slidingly received in an aperture  912  provided in shaft  915 , with the spring  820  acting to bias the socket stub shaft  812  against axial movement further into the aperture  912 . Similarly, the spring  860  and ball stub shaft  852  are slidingly received in an aperture  922  provided in shaft  925 , with the spring  860  acting to bias the ball stub shaft  852  against axial movement further into the aperture  922 . The ball  850  and socket  810  are arranged in close proximity, with the ball  850  being received in the socket  810  and free to rotate therein. The respective dimensions of the integral ball  850  and ball stub shaft  852 , integral socket  810  and socket stub shaft  812 , and springs  820 ,  860  are such that the ball  850  is urged into contact with the socket  810  under the biasing action of the springs  820 ,  860  in all articulations of the CV joints  910 ,  920  and shafts  915 ,  925 . In use, shaft  915  (acting as an input shaft) can transmit torque to shaft  925  (acting as an output shaft) via the respective external housings  914 ,  924  of the CV joints  910 ,  920  which are coupled together (e.g. via bolts (not shown) and/or a coupling/cover  980 ). The shaft  915  can pivot relative to the shaft  920  as provided for by the ball  850  and socket  810 . Both the ball  850  and the socket  810  are connected to their respective (input/output) shafts  925 ,  915  by their sliding stub shafts  852 ,  812  which can slide axially (into and out of) as well as rotate relative to the (input/output) shafts  915 ,  925 . The (input/output) shafts  915 ,  925  can move relative to the respective external housings  914 ,  924  by pivoting around the fixed pivot points P 1 , P 2 . When articulated about the fixed pivot points P 1 , P 2 , the adjacent ends of the (input/output) shafts  915 ,  925  must necessarily move away from each other. However, the ball  850  remains in contact with the socket  810  under the biasing action of the springs  860 ,  820 , with the stub shafts  852 ,  812  sliding axially ‘out’ of the apertures  922 ,  912  of shafts  925 ,  915  in order to provide for the increased distance. The springs  860 ,  820  are preload springs and help overcome friction and permit the ball  850  to remain in the socket  810 . Lubrication (and, optionally, packing with grease around the ball  850  and socket  810 ) may be provided as necessary. The centering mechanism  800  thus aids in controlling movement of the shafts  915 ,  925  in use. While a ball and socket arrangement has been described above, this is just one example. A universal joint with adequate angular capability could be beneficially employed in place of the ball and socket, as could any other mechanism which serves the same function. 
         [0042]    It will thus be appreciated that the articulated halfshaft  10 ,  100  according to the present invention can provide for significant angles of articulation between input and output. Furthermore, it is also capable of providing steering, drive (transmitting power) and/or a constant speed of rotation between input and output at these significant angles of articulation, yet does so without suffering from the known geometrical problems (mechanical resistance and lockup) of prior art halfshafts. 
         [0043]    Retractable wheel and suspension assemblies (selected parts are omitted from the attached Figures for clarity) as described in the applicant&#39;s patents and patent applications are particularly suitable for use with the articulated halfshaft  10 ,  100  of the present invention. 
         [0044]    Whilst not shown, it is possible also to provide decouplers separately or integrated in the transmission illustrated. The provision of decouplers allows drive to the wheels or track drives to be disengaged when the amphibian is operated on water. As decouplers should be mounted rigidly to encourage smoothness of operation, it is preferred that decouplers be used on the inner CV joints. The CV joints may also include a synchromesh unit for smooth engagement and disengagement of said decouplers. 
         [0045]    Whilst wheels  400 ,  600  have predominantly been referred to throughout for use as the land engaging and/or land propulsion means of the amphibian when operated on land, track drives or individual track drives (i.e. to replace a single wheel) may be used as an alternative or in combination with wheels. 
         [0046]    Furthermore, it will be appreciated that drive (power) may be provided by internal combustion engines, electric motors, hydraulic motors, or hybrid engines in any suitable location (e.g. hydraulic wheel hub motors). 
         [0047]    Although different embodiments of articulated halfshaft  10 ,  100  according to the present invention have been described above, any one or more or all of the features described (and/or claimed in the appended claims) may be provided in isolation or in various combinations in any of the embodiments. As such, any one or more these features may be removed, substituted and/or added to any of the feature combinations described and/or claimed. For the avoidance of doubt, any of the features of any embodiment may be combined with any other feature from any of the embodiments. 
         [0048]    Accordingly, whilst preferred embodiments of the present invention have been described above and illustrated in the drawings, these are by way of example only and non-limiting. It will be appreciated by those skilled in the art that many alternatives are possible within the ambit, spirit and scope of the invention, as set out in the appended claims.