Abstract:
A planing amphibious vehicle has at least one trim tab at its stern. A vehicle control system includes a mode change controller and a trim tab controller. The mode change controller informs the trim tab controller when a mode change event is taking place. The trim tab controller retracts the trim tabs if the mode change is from marine to land mode; and deploys the tabs if the change is from land mode to marine mode, to assist the vehicle in rising on to the plane. The controller may also retract the tabs if the vehicle reverses; and deploy the tabs if a change is made from reverse to forward motion. The vehicle control system may connect to actuators and sensors for retractable road wheels, which may use hydropneumatic struts. Safeguards against system faults and/or erroneous switch operation are included. Road wheel drive decouples are used; a marine drive decoupler may also be fitted.

Description:
BACKGROUND OF THE INVENTION 
   The present invention relates to an amphibious vehicle. 
   Amphibious vehicles are inherently required to carry both road vehicle and marine vessel dedicated equipment. Hence, amphibious vehicles are generally heavier than boats of a similar size and power. This is particularly true in the case of planing amphibians, which require a relatively heavy wheel streamlining mechanism, such as retractable suspension or the like. In the case of an amphibious vehicle with open wheel arches, the drag exerted by the arches can be considerable and hence the overall hull drag is greater than for a conventional boat. This additional weight and drag make it difficult for the vehicle to rise onto the plane without initial deployment of trim tabs. 
   Trim tabs are well known for marine vessels, and in particular planing boats, as means for controlling the trim and attitude of the vessel to compensate for changes in load, speed or sea conditions. Commonly these devices are in the form of flat tabs or planes, which are pivotably connected along a generally horizontal axis to the hull of the vessel below the waterline near the stem. The angle of orientation of the trim tabs is adjustable and hence determines the fore and aft attitude of the vessel, when it is being propelled through the water. For example, if the rear of the vessel is heavily loaded the bow will typically rise out of the water and lead to inefficient forward motion. In these circumstances the angle of the trim tabs relative to the hull can be increased to lower the bow, lift the stem, and hence get the boat back onto a plane. 
   The position of the trim tabs on a conventional boat, when docked, is not of great importance since it is unlikely that the tabs will come into contact with, and be damaged by a submerged obstacle. Nevertheless, since trim tabs are typically extended by means of hydraulic actuators it is generally desirable for trim tabs to be retracted, when the boat is not in use, to avoid unnecessary marine growth on the actuators. Retraction also minimises the risk of damage when a boat is lifted from the water, for example, to go into dry storage. In accordance with this U.S. Pat. No. 5,113,780 discloses a trim tab control system, which includes a facility for automatically retracting the trim tabs when the engine ignition is switched off. 
   The system described in U.S. Pat. No. 5,113,780 is designed specifically for marine only vessels and is of limited benefit in the case of amphibious vehicles fitted with trim tabs. The greatest risk of damage, in the case of amphibious vehicles, occurs during and after the transition from marine to terrestrial mode, whilst the engine is still switched on. If the tabs remain in an operational position when the vehicle leaves the water, there is a significant risk that they may strike the ground at speed. Similarly, reversing into an obstacle with the trim tabs deployed could damage the tabs, the actuators and the body of the vehicle. The risk of inadvertently leaving the trim tabs deployed is enhanced because during the marine to terrestrial transition period the operator has several other important control tasks to consider. 
   Furthermore, the requirement in U.S. Pat. No. 5,113,780 that the tabs be retracted after the ignition is switched off necessitates an ignition independent power supply for powering the retraction system. Such a supply, however, is undesirable because the power source remains permanently connected to the circuit that it powers. Hence, even a relatively small current drain from the retraction circuit could lead to a significant reduction in the life of the source. Whilst a permanent current drain may be unlikely to arise as a result of poor design there is a significant probability that it could occur as a result of malfunction. The risk of this is particularly high in marine vessels where the presence of water makes short circuits more likely. It will also be appreciated that short circuits of this type also constitute a safety hazard. 
   This latter problem has been tackled in U.S. Pat. No. 5,474,013, which describes a system for automatically retracting trim tabs on a boat independently of the operation of the ignition switch. In the system described, a capacitor is charged from the vessels battery and the charge stored can be discharged to fully retract the trim tabs. However, this system is also designed specifically for marine only vessels and again is of limited benefit in the case of amphibious vehicles, for the reasons discussed above in relation to U.S. Pat. No. 5,113,780. 
   There is, therefore, a need for an amphibious vehicle, which includes a trim tab deployment system to allow it to rise onto the plane. There is also a need for the trim tab system for the amphibious vehicle to overcome or at least to mitigate the problems referred to above. 
   SUMMARY OF THE INVENTION 
   According to one aspect of the present invention there is provided an amphibious vehicle adapted for use on land and on water including a vehicle body, and at least one trim tab, for adjusting the trim of the amphibious vehicle when it is in a marine mode, connected to the vehicle body and movable relative to the vehicle body between a retracted position and any one of a range of operational positions, and a control system for controlling the position of the or each trim tab including detecting means for detecting at least one mode change event and tab actuation means for moving the or each trim tab relative to the vehicle body, the control system being adapted to automatically move the or each trim tab either into the retracted position or into any one of a range of operational positions according to the mode change event detected. 
   Preferably, the mode change event, detectable by the detecting means, is a first mode change event indicative of an onset of transition into a marine mode from a terrestrial mode and the control system is adapted to automatically move the or each trim tab into one of a: range of operational positions on detection of said first mode change event. 
   Preferably the or a further mode change event, detectable by the detecting means, is a second mode change event indicative of an onset of a transition into the terrestrial mode from a marine mode and the control system is adapted to automatically move the or each trim tab into the retracted position on detection of said second mode change event. 
   Preferably the detecting means are also capable of detecting selection of reverse propulsion in a marine mode, and the control system is adapted to automatically move the or each trim tab into the retracted position on detection of the selection of reverse propulsion. 
   Preferably the detecting means are also capable of detecting a selection of forward propulsion when the vehicle is moving in the reverse direction in a marine mode and the control system is adapted to automatically move the or each trim tab into any one of a range of operational positions on the selection of forward propulsion. 
   Preferably the control system includes means for signalling an operator on detection of at least one event. 
   Preferably the vehicle has a set of wheels for supporting the vehicle when it is in terrestrial mode, and the control system further includes means for retracting the set of wheels on detection of a transition into marine mode and means for deploying the set of wheels on detection of a transition into terrestrial mode. 
   Preferably the vehicle has a jet drive for propelling the vehicle when it is in marine mode and a reversing bucket, and the control system includes means for deploying the reversing bucket on detection of selection of reverse propulsion. Alternatively, where a reversing bucket is not fitted, the jet drive may be driven in reverse through the vehicle transmission. 
   According to another aspect of the present invention there is provided a method for controlling a trim tab system for an amphibious vehicle including the steps of automatically detecting a mode change event, and on detection of the mode change event automatically moving the or each trim tab either into the retracted position or into any one of a range of operational positions according to the event detected. 
   Preferably the mode change event detected is an onset of transition into a terrestrial mode. 
   Preferably the mode change event detected is an onset of transition into a marine mode. 

   
     BRIEF DESCRIPTION OF THE DRAWING 
     An embodiment of the invention will now be described, by way of example only, with reference to the following drawings in which: 
       FIG. 1  shows diagrammatically a simplified side view, partially cut away, of an amphibious vehicle according to the invention; 
       FIG. 2  shows diagrammatically a simplified plan view, from beneath, of the amphibious vehicle of  FIG. 1 ; 
       FIG. 3  is a functional block diagram of part of an integrated control network for the amphibious vehicle of  FIG. 1 ; 
       FIG. 4  shows a control system logic sequence to initiate a mode change; 
       FIG. 5  shows a control system logic sequence for a mode change from terrestrial to marine mode, as initiated by the sequence shown in  FIG. 4 ; and 
       FIG. 6  shows a control system logic sequence for a mode change from marine to terrestrial mode, as initiated by the sequence shown in  FIG. 4 . 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   In  FIGS. 1 and 2  an amphibious vehicle is designated generally  10  and a trim tab system is designated generally  12 . The amphibious vehicle  10  is capable of operation in both a terrestrial mode, for travel on land, and a marine mode, for travel on water, The vehicle  10  includes a vehicle body  14  having a hull section  16  and an outer body section  18 . The hull section  16  is equivalent to the hull of a conventional boat and includes a transom  20  at the stern. 
   The trim tab system  12  includes two tabs  22  and two hydraulic actuators  26 , provided one on either side of a central longitudinal axis AA′ of the vehicle  10  as seen in  FIG. 2 . Whilst the figures show hydraulic actuators, any suitable actuation means may be used, for example electrically powered actuators. Each of the tabs  22  is connected to the base of the transom  20  by a corresponding hinge  24  along a generally horizontal axis to allow independent rotational movement of each tab relative to the transom  20 , as seen on  FIG. 1 . 
   The hydraulic actuators  26  are of conventional construction, each actuator  26  having a cylinder  28  into which one end of an actuator rod  30  is slidably received. The cylinder  28 , of each hydraulic actuator  26 , is mounted pivotally on the transom  20  above a corresponding tab  22  to which the protruding end of the actuator rod  30  is pivotally connected. Hence, in operation, extension and retraction of the actuator rod  30  lowers and raises the corresponding tab  22  respectively. 
   The amphibious vehicle  10  has the standard features associated with a road vehicle including transmission, suspension and a set of wheels  32 . The wheels  32  are provided with a retraction mechanism, which can be used to retract the wheels  32  from a protracted position  31  during a transition into marine mode. Similarly, the retraction mechanism can be used to protract the wheels  32  from a retracted position  33  during a transition into terrestrial mode. As shown in  FIG. 3 , the retraction mechanism makes up part of a mode change system  54  for converting the amphibious vehicle  10  from marine mode to terrestrial mode and vice versa. 
   The retraction mechanism may comprise any suitable means for retracting and protracting the wheels  32 . Preferably, however, the retraction mechanism is of the form described in European Patent No. 0742761. The retraction mechanism, as such, does not form part of the present invention and so will not be described here in detail. However, if the reader requires details of the operation and construction of a suitable retraction system then they should refer to EP 0742761, the contents of which are hereby incorporated by reference. 
   The suspension may be a conventional hydro-pneumatic system with suspension cylinders part filled with hydraulic fluid and part filled with pneumatic gas. Prior to road use, the suspension cylinders of the amphibious vehicle require charging to bring the vehicle to the correct road height. Typically, the charging will occur either when the vehicle engine is switched on in terrestrial mode or when the vehicle makes a transition from marine into terrestrial mode. It should be understood, however, that the vehicle may have any suitable suspension system. 
   Additionally, the amphibious vehicle  10  includes a marine drive  34  for providing propulsion when the vehicle  10  is in the marine mode. The marine drive  34  is a conventional jet drive, which in operation issues a jet of high pressure water to propel the vehicle  10  forward. The jet drive may be fitted with a reversing bucket  36 , which in use, may be deployed to divert the direction of the water jet to propel the vehicle  10  in reverse. Alternatively, where a reversing bucket is not fitted, the direction of rotation of the jet drive may be reversed through the vehicle transmission. It will be appreciated that other forms of marine drive could be employed, with corresponding reversing mechanisms, such as a marine propeller for example. 
   The mode change system  54  also includes means for decoupling the road wheel transmission and optionally engaging the marine drive  34  during transition into marine mode and means for charging the suspension, coupling the road wheel transmission and optionally disengaging the marine drive  34  during transition into terrestrial mode. 
   Referring now to  FIG. 3 , the trim tab system  12  also includes an electro-hydraulic system  40  for independently extending and retracting the rods  30  and hence operating the tabs  22 . The electro-hydraulic system  40  includes an electric motor  42 , which in operation, drives a fluid pump  44  to move fluid under pressure, via flow control valves  46 , either to or from the actuators  26 , to extend or retract the actuator rods  30  respectively. The flow control valves  46  allow independent selection and control of the actuators  26 . Alternatively, the system for independently extending and retracting the rods  30  could be purely electromechanical employing electric motors to operate mechanical actuators with no hydraulic parts. 
   In order to control the electro-hydraulic and electromechanical systems an integrated control network  50  is provided. The control network  50  has a main controller  52 , a set of input subsystems  56 , and a set of output subsystems  58 . The main controller  52  comprises a set of control subsystems  60 ,  62 ,  64 , which include a propulsion controller  60 , a mode change controller  62  and a trim tab controller  64 . The main controller  52  can be implemented using any suitable means such as a dedicated logic circuit or a pre-programmed micro-controller. 
   The input subsystems  56  include manually operated switches such as a reverse selector  66 , a mode change switch  68  and manual trim tab control switches  70 . The input subsystems  56  also include sensor means comprising suspension droop sensor apparatus  74 , for determining if the water buoyantly supports the vehicle  10 . The sensor system may comprise any suitable means for detecting when the vehicle  10  is in water and buoyantly supported by it. An amphibious vehicle incorporating suitable sensor means is described in the applicant&#39;s International patent application number PCT/GB2002/005359 that claims the benefit of priority from British application No. 0128338.1, the contents of which are hereby incorporated by reference. A water presence sensor  72  may also be provided, as a secondary sensor. 
   The output subsystems  58  include the mode change system  54 , the trim tab system  12 , a reversal system  76  and warning systems  48 ,  78 . 
   In operation, the main controller  52  accepts external inputs from the input subsystems  56  and directs them to at least one of the control subsystems  60 ,  62 ,  64  for processing. The control subsystems  60 ,  62 ,  64 , process the inputs and produce a corresponding set of outputs, which determine, and hence control, the behaviour of the output subsystems  58 . The outputs from any control subsystem  60 ,  62 ,  64 , can also form internal inputs to any other control subsystem  60 ,  62 ,  64 . 
   As seen in  FIG. 3  the trim tab controller  64  receives external inputs from the trim tab control switches  70  and the reverse selector  66 , and an internal input from the mode change controller  62 . The trim tab controller  64  produces a corresponding set of outputs for controlling the trim tab system. More specifically the trim tab controller  64  controls the motor  42 , the pump  44 , the flow control valves  46  and hence the relative positioning of the tabs  22 . The trim tab controller  64  also controls a trim tab warning system  48  for alerting the vehicle operator, when appropriate, to the position of the trim tabs  22 . 
   The reverse selector  66  also provides an external input to the propulsion controller  60 , which in turn produces an output to the reversal system  76  for either deploying or retracting the reversing bucket  36 ; or alternatively to reverse the rotation direction of the vehicle transmission. 
   The mode change controller  62  receives external inputs from the mode change switch  68 , the suspension droop sensor  74  and the water presence sensor  72 . The mode change controller  62  processes these external inputs and produces outputs to the mode change system  54 , a mode change warning system  78 , the propulsion controller  60  and trim tab controller  64 . 
   The mode change warning system  78  includes a visual warning device in the form of a warning light to alert the operator when the vehicle is undergoing a mode change and to inform the operator when the transition is complete. The mode change warning system  78  also includes an audible warning device in the form of a buzzer for warning people in the vicinity of the vehicle  10  when a mode change is imminent. 
   It will be appreciated that the some or all of the systems and subsystems making up the control network  50  maybe equipped with reset functions (not shown) for resetting the whole system or individual systems if required, for example, in the event of problems during mode changes. 
   In operation, the control system  50  follows the logic sequences shown in  FIGS. 4 and 5  to affect a transition from terrestrial into marine mode and the logic sequences shown in  FIGS. 4 and 6  to affect a transition from marine into terrestrial mode. The logic sequences include several mode change events interspersed with decision points. Mode change events are events that are associated with transition either to terrestrial mode or to marine mode. 
   In  FIG. 4  a control system logic sequence to initiate a mode change is designated generally  90 . While the vehicle  10  is operational, the mode change controller  62  monitors the status of the mode change switch  68  to determine if it has been activated. On activation of the mode change switch  68 , the logic sequence  90  initially establishes whether the switch has been activated in error. If the switch  68  is activated for less than three seconds then this is deemed to be indicative of accidental operation, for example by an operator pressing the wrong switch. Hence, no further action is taken and the mode change controller  62  reverts to its monitoring activity. 
   If the switch  68  is activated for more than three seconds then the mode change controller goes on to establish if the switch  68  is released within ten seconds. If the switch  68  remains activated after ten seconds then this is deemed to be indicative of malfunction or an enduring accidental operation, for example by an object being placed on or against the switch  68 . Hence, no further action is taken and the mode change controller  62  reverts to its monitoring activity. An alert system could also be included which warns the operator that the switch  68  has either been erroneously operated or is malfunctioning. 
   Thus, if the duration of the switch activation is between three and ten seconds the mode change controller  62  signals the mode change warning system  78  to flash the visual warning device and sound the audible warning device, prior to determining the current status of the vehicle and initiating an appropriate mode change logic sequence. 
   In  FIG. 5  a control system logic sequence for a mode change from terrestrial to marine mode is designated generally  100 . On initiation, the mode change controller  62  monitors the external inputs from the sensor subsystem to determine if conditions are suitable for transition to occur. If the external input to the controller  62 , from the suspension droop sensor apparatus  74  indicates that the vehicle  10  is not buoyantly supported, sufficient to allow safe retraction of the wheels  32 , no action is taken and monitoring continues. However, if the suspension droop sensor apparatus  74  indicates that safe retraction of the wheels  32  is possible, the mode change controller  62  goes on to test for external water presence by monitoring the external input received from the water presence sensor  72 . When external water presence is confirmed the vehicle  10  is deemed to be in water. If full droop and/or water presence are not detected within thirty seconds then conversion is stopped and the control system reverts to its general monitoring mode. 
   At this stage a system check is carried out and any faults detected result in termination of the process. If no faults are detected then the transition to marine mode can begin. 
   Transition to marine mode involves the mode change controller  62  initiating a number of mode change events  108 ,  110 ,  112 ,  114 . In accordance with this, outputs are produced for controlling the mode change system  54 , the mode change warning system  78 , and for further processing by the trim tab controller  64  and the propulsion controller  60 . 
   The mode change controller  62  signals the mode change system  54  to retract the wheels  32  and to decouple the road wheel transmission of the vehicle  10 . Similarly, where a marine drive decoupler is fitted, the propulsion controller  60  receives an internal input from the mode change controller  62  and makes a subsequent output to the mode change system  54  to engage the marine drive  34 . After this has occurred the mode change controller  62  signals the mode change warning system  78  to switch the visual warning device from flashing to continuous and the audible warning device to silent. 
   Additionally, on receipt of the internal input from the mode change controller  62  the trim tab controller  64  signals the trim tab system to automatically deploy the trim tabs from a retracted position  80  into a marine ready position  82 . As seen on  FIG. 1  the retracted position  80  lies at an angle substantially 13° above the horizontal and the marine ready position  82  lies substantially at an angle between 9° and 12° below the horizontal. 
   At this stage the mode change controller  62  interacts with the mode change system to establish when the wheels  32  are retracted. Once the wheels  32  are retracted the vehicle is ready for planing. However, fill engine power can be applied as soon as the road wheel drive is disengaged. 
   Whilst  FIG. 5  shows the mode change events  108 ,  110 ,  112 ,  114  occurring sequentially it will be appreciated that there are other sequences that maybe followed and some or all of the events  108 ,  110 ,  112 ,  114  may run concurrently to speed up the transition. 
   In  FIG. 6  a control system logic sequence for a mode change from marine to terrestrial mode is designated generally  120 . Initially a system check is carried out and any faults detected result in termination of the process. If no faults are detected then the transition to terrestrial mode can begin. 
   As with the transition to marine mode, the transition to terrestrial mode involves the mode change controller  62  initiating a number of mode change events  124 ,  128 ,  130 ,  132 ,  134 . In accordance with this, outputs are produced for controlling the mode change system  54 , the mode change warning system  78 , and for further processing by the trim tab controller  64  and the propulsion controller  60 . 
   The mode change controller  62  signals the mode change system  54  to protract the wheels  32  and then suspends further commands until the suspension droop sensor  74  indicates that the suspension has reached full travel. The mode change controller  62  then signals the mode change system  54  to charge the suspension and couple the transmission ready for road use. Similarly, where a marine drive decoupler is fitted, the propulsion controller  60  receives an internal input from the mode change controller  62  and makes a subsequent output to the mode change system  54  to disengage the marine drive  34 . 
   Additionally, on receipt of an internal input from the mode change controller  62  the trim tab controller  64  signals the trim tab system to automatically move the trim tabs to the retracted position  80  from any one of a range of operational positions. After retraction has occurred the mode change controller  62  signals the mode change warning system  78  to switch the visual warning device from flashing to off and the audible warning device to silent. 
   Whilst  FIG. 6  shows the mode change events  124 ,  128 ,  130 ,  132 ,  134  occurring sequentially it will be appreciated that there are other sequences that may be followed and some or all of the events  124 ,  128 ,  130 ,  132 ,  134  may run concurrently to speed up the transition. 
   When the vehicle  10  is operating in the marine mode the operator can use the trim tab control switches  70  to manually adjust the position of the trim tabs  22  depending on external conditions, the forward speed of the vehicle  10 , vehicle loading and any other requirements. In use, the trim tab control switches  70  provide an external input to the trim tab controller  64 . The trim tab controller  64  processes this external input and makes a resulting output to the trim tab system  12  to either increase or decrease the angle of the tabs  22 . For example, when the vehicle begins motion under forward propulsion the operator will typically increase the angle of the tabs from the marine ready position to an operational position. As the vehicle  10  accelerates and the bow begins to rise, the operator can further increase the angle of the tabs to correct fore and aft attitude. Similarly, if the vehicle  10  is unevenly loaded, such that it lists to one side, the tabs  22  maybe operated independently to correct the port/ starboard attitude of the vehicle  10  when it is in motion. 
   It will be appreciated that much of the manual tab control can be further automated to take account of standard conditions and loading. For example, the trim tab controller  64  could be provided with internal inputs from the propulsion controller  60  to automatically adjust the tabs depending on speed. Alternatively, a separate speed sensor could be used. A feedback mechanism involving a gyroscope, yaw rate sensor, or other attitude detector could also be included, which would allow automatic adjustment of the tabs depending on the attitude of the vehicle. Tab position feedback, to controller  64 , would be required for fully automatic trim tab control. 
   When the vehicle  10  is operating in the marine mode, under forward propulsion, and reverse propulsion is then selected, the reverse selector  66  provides external inputs, corresponding to reverse selection, to the trim tab and propulsion controllers  64 ,  60 . Consequently, the external inputs are processed by the appropriate control subsystem  60 ,  64  and appropriate outputs made to the related output subsystems  12 ,  76 . Specifically, the trim tab controller  64  makes outputs to the trim tab system  12  to move the tabs  22  to the retracted position  80 , and the propulsion controller  60  makes an output to the reversal system  76  to initiate the deployment of the reversing bucket  36 . 
   Conversely, when the vehicle  10  is operating in the marine mode, under reverse propulsion, and forward propulsion is then selected, the reverse selector  66  provides external inputs, corresponding to forward selection, to the trim tab and propulsion controllers  64 ,  60 . In this case, after processing the external input, the propulsion controller  60  initiates the retraction of the reversing bucket  36 , where fitted, by the reversal system  76 . Correspondingly, the trim tab controller  64  initiates the deployment of the tabs  22 , to the marine ready position  82 , by the trim tab system  12 . 
   It will be appreciated that the control system  50  may also be configured to respond to other events, such as engine ignition being switched on or off. For example, when the vehicle  10  is in the marine mode with the engine off, and the ignition is then switched on, external inputs maybe provided to the trim tab controller  64  to move the tabs  22  to the marine ready position  82 . Similarly, when the engine is switched off external inputs may be provided to the trim tab controller  64  to fully retract the tabs  22  or to move them to any other suitable default position. 
   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.