Patent Publication Number: US-7581582-B2

Title: Exhaust cooling system of an amphibious vehicle

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
   This application claims priority from Great Britain Application Serial No. 0426178.0, filed Nov. 29, 2004. 
   BACKGROUND OF THE INVENTION 
   The present invention relates to an exhaust cooling system of an amphibious vehicle. 
   In the case of dedicated land vehicles and marine vessels known in the art, the apparatus and methods employed for cooling exhaust systems are well established. In the case of a land vehicle, the exhaust system is typically slung below the floor panel of the vehicle such that it is exposed to ambient atmospheric air which passes over and cools external surfaces of the exhaust system. The cooling effect achieved is of course variable but satisfactory, being largely dependent upon factors such as vehicle speed and atmospheric conditions. In the case of marine vessels, it is usual to cool exhaust systems with water. This is normally achieved using the abundant resource of raw water outside the vessel which is drawn in and circulated around a water jacket enclosing the exhaust system and then exhausted back to the raw water source. Such exhaust cooling systems are highly efficient when the marine vessel is on water, but do not function when on land where the raw water source is no longer available. However, this is not particularly important for a marine vessel whose engine will only rarely be run on land, if at all (typically only for maintenance reasons where an artificial raw water source may be provided, e.g. via a hosepipe). 
   It is also known from U.S. Pat. No. 3,884,194 of Citroen to provide a water jacket for an exhaust manifold of an air cooled engine used in a land vehicle in order to recover heat energy. In particular, U.S. Pat. No. 3,884,194 discloses a steam generator used for heating the passenger compartment of vehicles equipped with air cooled engines. 
   In U.S. Pat. No. 4,991,546 of Sanshin Kogyo Kabushiki Kaisha, there is disclosed a water jacket based cooling system for marine watercraft used to cool both the internal combustion engine and exhaust manifold. The invention is concerned with preventing condensation forming in the exhaust manifold as a result of the cooling process. Raw water is used, this being sourced from outside the watercraft and is returned after circulation around the various water jackets of the system. In one embodiment, a supplementary radiator is used, but only for the purpose of providing a sealed cooling jacket for the engine, exhaust manifold and a portion of an exhaust elbow so that a coolant other than pure water may be employed in a closed system and kept separate from the raw water. Raw water is still required to be sourced, circulated and returned to the body of water outside of the watercraft. As such, this system cannot be employed in a land vehicle. 
   In the case of an amphibious vehicle, however, the problems of cooling of an exhaust system present quite unique problems and considerations. An amphibious vehicle is used extensively on land and on water and its exhaust system is liable to run at least as hot as that of any other road vehicle. Whereas land vehicles rely on the surrounding air to keep their exhaust systems cool, especially catalytic converters which have been known to run so hot (˜900° C.) as to ignite grass underneath parked vehicles, the underside of an amphibious vehicle is sealed to ensure buoyancy and hydrodynamic performance on water. This compounds the problem of providing adequate cooling since sealing the exhaust system inside the hull actually serves to insulate it from external cooling influences. Furthermore, it is desirable to seal in the exhaust system of an amphibious vehicle since there exists the potential for damaging thermal shock effects of quenching when a fully heated exhaust system which has been operating in land mode enters the water for the vehicle to operate in marine mode. Also, the catalytic converter is a very sensitive item which must be maintained at its optimum operating temperature to prevent damage to the catalyst. It is clear therefore that an amphibious vehicle presents conflicting requirements and dedicated prior art systems are poorly suited to the requirements of an amphibious vehicle. 
   SUMMARY OF THE INVENTION 
   The present invention provides, in a first aspect, an exhaust cooling system of an amphibious vehicle operable in land and marine modes, the exhaust cooling system comprising: 
   an exhaust system to be cooled; 
   at least one air-liquid heat exchanger; 
   at least one liquid-liquid heat exchanger; and 
   coolant liquid in thermal communication with the exhaust system and the at least one air-liquid heat exchanger and/or the at least one liquid-liquid heat exchanger, wherein: 
   when the amphibious vehicle is operated in land mode the coolant liquid is heated by the exhaust system and cooled by the at least one air-liquid heat exchanger; and 
   when the amphibious vehicle is operated in marine mode the coolant liquid is heated by the exhaust system and cooled by the at least one liquid-liquid heat exchanger. 
   These and other features and advantages of the present invention will become apparent from the following detailed description of the preferred embodiments which, taken in conjunction with the accompanying drawings, illustrate by way of example the principles of the invention. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic plan view illustrating a cooling system according to a first embodiment of the present invention installed in a sports car variant of amphibious vehicle; 
       FIG. 2  is a schematic side elevation view of the amphibious vehicle of  FIG. 1 ; 
       FIG. 3  is a schematic plan view illustrating a cooling system according to a second embodiment of the present invention installed in a quad bike variant of amphibious vehicle; and 
       FIG. 4  is a schematic side elevation view of the amphibious vehicle of  FIG. 3 . 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Referring first to  FIGS. 1 and 2 , there is illustrated a schematic view of a cooling system according to a first embodiment of the present invention installed in an amphibious vehicle  10 . A prime mover  40  provides power for propelling the amphibious vehicle  10  when operating in land and marine modes. In land mode, power is delivered to a land propulsion means such as, for example, road wheels  20 . In marine mode, power is delivered to a marine propulsion means such as, for example, a jet drive  30 . In this preferred embodiment, the prime mover  40  is an internal combustion engine from which the products of combustion leave via an exhaust system  50 . 
   The exhaust system  50  comprises a catalytic converter  51  and a silencer  52 , each enclosed within a water jacket  53 . The water jacket  53  has a liquid inlet  54  at a first distal end of the exhaust system  50  and a liquid outlet  55  at a second proximal end. 
   An air-water heat exchanger  60  in the form of a conventional radiator is provided and has a liquid inlet  61  and a liquid outlet  62 . An elongate conduit for coolant fluid connects liquid inlet  61  with liquid outlet  62  and is packaged in a serpentine, labyrinthine or other such tortuous form so as to maximise the length of flow path between liquid inlet  61  and liquid outlet  62 . This conduit is provided with a matrix of fins arranged in thermal contact on its outer surface such that a large surface area is presented to passing air to maximise the thermal pathway available and heat transfer possible between the cooling air passing through the matrix and the coolant liquid passing through the conduit. 
   A water-water heat exchanger  70  is also provided and has two liquid inlets  71 ,  73  and two liquid outlets  72 ,  74 . A first conduit for coolant liquid connects liquid inlet  71  with liquid outlet  72  and is packaged in a serpentine, labyrinthine or other such tortuous form, again so as to maximise the length of flow path between liquid inlet  71  and liquid outlet  72 . A second conduit for raw water connects liquid inlet  73  with liquid outlet  74  and is likewise packaged in a serpentine, labyrinthine or other such tortuous form so as to maximise the length of flow path between liquid inlet  73  and liquid outlet  74 . These conduits are arranged relative to one another so as to maximise the thermal pathway available between the two conduits and heat transfer possible between the cooling raw water passing through the second conduit and the coolant liquid passing through the first conduit. 
   A closed coolant liquid circuit  80  is formed by the series connection of the water jacket  53  of the exhaust system  50 , the air-water heat exchanger  60  and the first conduit of the water-water heat exchanger  70  using appropriate liquid conduits. An open raw water circuit  90  is formed using appropriate liquid conduits and in marine mode raw water enters or is pumped from outside the amphibious vehicle  10 , via a screen or filter (not shown), through the second conduit of the water-water heat exchanger  70 , and back out into the external water source. The raw water may be sourced, for example, from the pressurised side of the jet drive  30  to avoid the need for a separate pump. 
   In operation, coolant liquid may be simply pumped around the closed coolant liquid circuit  80  or pumped under thermostatic and/or other control regimes as is well known in the art (e.g. under the control of an electronic control unit (ECU) dependent upon vehicle operating parameters). When the amphibious vehicle is operated in land mode, coolant liquid at a first cooled temperature enters the exhaust system  50  via liquid inlet  54  and passes along the water jacket  53  containing the exhaust system  50 , passing from the cooler end of the exhaust system  50  at the rear of the vehicle  10  to the hotter end near the exhaust manifold(s) (so as to avoid quenching of the exhaust system and to prevent the formation of condensation in the exhaust manifold following a cold start). The heat present in the exhaust system  50  is transferred to the coolant liquid via the established heat transfer pathway, heating the coolant liquid and cooling the exhaust system  50 . Coolant liquid at a second elevated temperature leaves the water jacket  53  via liquid exit  55 . The coolant liquid next passes through a connecting conduit to the air-water heat exchanger  60 , entering via liquid inlet  61 . As the coolant passes along the conduit within the heat exchanger  60 , air passing over the matrix of fins arranged in thermal contact with the conduit draws heat from the coolant liquid at the second elevated temperature, thereby cooling the coolant liquid to a temperature below the second elevated temperature. The passing of air over the matrix of fins may be free-flow (ram effect), via ducted means (to increase the ram effect) and/or may be forced or supplemented by way of means such as an auxiliary fan (not shown). The coolant then leaves the heat exchanger  60  via liquid exit  62  and next passes to the water-water heat exchanger  70 , flowing via a connecting conduit and entering via liquid inlet  71 . In this land mode, the water-water heat exchanger  70  provides little or no effect since there is no raw water supply available via the open raw water circuit  90 . Accordingly, the coolant fluid leaves via liquid exit  72  at substantially the same temperature as it entered. Finally, a conduit conveys the coolant liquid from the liquid outlet  72  to the liquid inlet  54  of the exhaust system and the above process is repeated, with the coolant liquid being re-circulated. 
   When the amphibious vehicle  10  is operated in marine mode, the process as described above is identical but the cooling step provided by the air-water heat exchanger  60  is either supplemented or replaced with a cooling step effected as the coolant liquid passes through the water-water heat exchanger  70 . In this marine mode, the coolant liquid enters the water-water heat exchanger  70  either at an elevated temperature as compared to the first cooled temperature (in the case that the air-water heat exchanger  60  is effective to one degree or other) or at the second elevated temperature (in the case that the air-water heat exchanger  60  is not effective) and passes along the first conduit within the heat exchanger  70 . At the same time, raw water at external ambient water temperature is pumped in from outside the amphibious vehicle  10  via raw water liquid inlet  73 . This raw water passes through the second conduit within the water-water heat exchanger  70  and leaves via raw water liquid exit  74  and is discharged back into the outside body of water. The arrangement of the first and second conduits (reverse flow with respect to one another) maximises the thermal pathway available between the two conduits and the resultant heat transfer possible, such that the coolant liquid is cooled as the raw water is heated to an extent where the coolant liquid leaves via liquid exit  72  at a temperature below the second elevated temperature. The coolant liquid is then re-circulated. 
   It will be appreciated that the preferred embodiment of the present invention described above is just one example of many different layouts possible in accordance with the present invention. In particular, the preferred embodiment described adopts a layout suitable for a mid-engined sports car version of amphibious vehicle  10 . In this version of amphibious vehicle  10 , it is preferable to have the exhaust cooling system according to the present invention packaged as illustrated. However, the exhaust cooling system according to the present invention is very flexible and adaptable for packaging in very different types of amphibious vehicle such as, for example, a trike, a quad-bike, or an off-road utility vehicle. 
   To exemplify this,  FIGS. 3 and 4  illustrate a schematic view of a cooling system according to a second embodiment of the present invention installed in an amphibious vehicle  110  of quad-bike form. This is a ‘sit astride’ vehicle with a front seat  113  and a rear seat  116  arranged in tandem. As in the first embodiment described above, a prime mover  140  provides power for propelling the amphibious vehicle  110  when operating in land and marine modes. In land mode, power is delivered to a land propulsion means such as, for example, road wheels  120 . In marine mode, power is delivered to a marine propulsion means such as, for example, a jet drive  130 . In this preferred embodiment, the prime mover  140  is an internal combustion engine from which the products of combustion leave via an exhaust system  150 . The exhaust system  150  comprises a catalytic converter  151  and a silencer  152 , each enclosed within a water jacket  153 . The water jacket  153  has a liquid inlet  154  at a first distal end of the exhaust system  150  and a liquid outlet  155  at a second proximal end. 
   Two air-water heat exchangers  160 ,  165  in the form of conventional radiators (different sizes for packaging reasons) are provided and have respective liquid inlets  161 ,  166  and liquid outlets  162 ,  167 . Elongate conduits for coolant liquid connect respective liquid inlets  161 ,  166  with respective liquid outlets  162 ,  167  and are each packaged in a serpentine, labyrinthine or other such tortuous form so as to maximise the length of flow path between liquid inlets  161 ,  166  and liquid outlets  162 ,  167 . These conduits are provided with a matrix of fins arranged in thermal contact on their outer surfaces such that a large surface area is presented to passing air to maximise the thermal pathway available and heat transfer possible between the cooling air passing through the matrices and the coolant liquid passing through the conduits. These two air-water heat exchangers  160 ,  165  are connected in parallel in the Figures, but it will be appreciated that alternatively they may be connected in series. 
   A water-water heat exchanger  170  is also provided and has two liquid inlets  171 ,  173  and two liquid outlets  172 ,  174 . A first conduit for coolant liquid connects liquid inlet  171  with liquid outlet  172  and is packaged in a serpentine, labyrinthine or other such tortuous form again so as to maximise the length of flow path between liquid inlet  171  and liquid outlet  172 . A second conduit for raw water connects liquid inlet  172  with liquid outlet  174  and is likewise packaged in a serpentine, labyrinthine or other such tortuous form so as to maximise the length of flow path between liquid inlet  172  and liquid outlet  174 . These conduits are arranged relative to one another so as to maximise the thermal pathway available between the two conduits and heat transfer possible between the cooling raw water passing through the second conduit and the coolant liquid passing through the first conduit. 
   A closed coolant liquid circuit  180  is formed by the series connection of the water jacket  153  of the exhaust system  150 , the air-water heat exchangers  160 ,  165  and the first conduit of the water-water heat exchanger  70  using appropriate liquid conduits. In the embodiment illustrated, the air-water heat exchangers  160 ,  165  are themselves connected in parallel to one another, but alternatively could be connected in series. An open raw water circuit  190  is formed using appropriate liquid conduits and in marine mode raw water is pumped from outside the amphibious vehicle  110 , via a screen or filter (not shown), through the second conduit of the water-water heat exchanger  170 , and back out into the external water source. 
   Operation of the exhaust cooling system is as described above for the first embodiment, save for the coolant liquid passing through the two air-water heat exchangers  160 ,  165  in parallel. 
   In both embodiments described above, a closure means, e.g. hinged or sliding flaps, may be provided to protect the air-liquid heat exchanger(s) from water, wave strikes, and flotsam and jetsam encountered when operating the amphibious vehicle. The closure means can provide selective or total shielding of the air-liquid heat exchanger(s), and this may be controlled automatically (e.g. by ECU) or manually as operating conditions necessitate. The closure means may be used to protect the heat exchanger(s) from damage and/or to control or optimise the cooling regime. 
   It will be appreciated that whilst in the preferred embodiment described, the component parts and coolant flow paths are arranged in particular layouts, many different layouts are possible. For example, in an alternative embodiment, the present invention may make use of an air-water heat exchanger already present for cooling of an engine. Alternatively, the air-water heat exchanger as described in the preferred embodiment may be provided in addition to the air-water heat exchanger provided for an engine. Indeed, a plurality of air-water heat exchangers (e.g. smaller units) may be provided for packaging or other reasons and distributed around the vehicle. Likewise, a plurality of water-water heat exchangers may be provided and distributed accordingly. Whilst the component parts of the circuit shown in the preferred embodiment are arranged in series with the coolant liquid being pumped around the circuit in series, it will be appreciated that component parts may be arranged in parallel in addition to or in place of the existing arrangement. Furthermore, each heat exchanger (whether of the air-water or water-water type) may be provided in a separate circuit having its own or shared coolant liquid. In such a case, each circuit may be provided with its own separate water jacket, have access to a portion or sub-circuit within a common water jacket, or have access to a single common water jacket under the control of a flow control system. Also, it is of course possible to introduce control valves for controlling the flow of coolant liquid and this may be managed by electrically operated or thermostatically controlled flow valves and associated electronic processing/control means, such as, for example an electronic control unit (ECU) provided as part of or in addition to an already existing ECU of the amphibious vehicle  10 . This provides the facility to switch individual components in and out of the or each circuit as necessary to optimise performance of the system. Optionally, by-pass conduits may be provided for each component. 
   Whilst the air-water and water-water heat exchangers  60 ,  160 ,  165  and  70 ,  170  described above are of conventional design, it will be appreciated that alternative or bespoke designs may be beneficially employed. For example, the applicant has designed a bespoke water-water heat exchanger which is incorporated in the hull of one of its amphibious vehicle designs. The amphibious vehicle in question comprises a hull formed from aluminum, a good thermal conductor. A longitudinal section of the hull is closed off to form a closed volume, the hull forming one side of this closed volume. Coolant liquid may be pumped through the closed volume and when the amphibious vehicle is operating in the marine mode the coolant liquid is cooled by external raw water which is in direct contact with the hull surface. This design does away with the need to source raw water from outside of the vehicle, and thus there is no need for the raw water circuit  90  in the preferred embodiment described above. This design of water-water heat exchanger has proved so effective that the rate of flow of coolant liquid through the closed volume has had to be metered to keep the engine at an efficient working temperature. It may therefore be preferred to fit a bypass circuit to the water-water heat exchanger to allow it to be switched out, for example while the engine is warming up. Such a bypass could be controlled manually, thermostatically, by a timer switch, or by any other suitable control means (e.g. an ECU). Alternatively or additionally to the above, a water-water heat exchanger may be embodied in an existing apparatus of the vehicle, such as the jet drive  30 , for example. Cooling liquid may be circulated within or around components of the jet drive  30  and/or tines within a stone guard for the jet drive  30 . Large volumes of raw water at ambient temperature pass these components which are manufactured from metals which are good thermal conductors. Furthermore, additional cooling may be provided by injecting raw water directly into the exhaust stream of exhaust gas passing through and Out of the exhaust system. 
   It will be appreciated that the prime mover  40 ,  140  can take the form of any of a number of internal combustion engines, such as a piston engine, turbine or rotary. Furthermore, whilst the cooling system is presented as one for cooling an exhaust system, it could additionally be employed to cool other heat generating sources such as, for example, the marine propulsion means  30 ,  130 , the prime mover  40 ,  140  and/or braking components. 
   Furthermore, the prime mover  40 ,  140  may be mounted transversely as shown in  FIGS. 1 and 2  and as described in the applicant&#39;s co-pending application published as WO 02/07999; or longitudinally, as is found convenient. An example of a power train comprising a longitudinally mounted prime mover may be found in the applicant&#39;s co-pending application published as WO 02/12005. 
   As described above, the coolant liquid circulates around the closed circuit  80 ,  180  whilst the raw water is pumped in and out of the open circuit  90 ,  190  when available (i.e. in the marine mode). Because the coolant liquid is separated from the raw water and retained always in the closed circuit  80 ,  180 , antifreeze and its associated corrosion inhibitors may be used in the coolant liquid to protect the system components against low temperature and corrosive effects. For environmental reasons, this would not be possible in the case of known marine vessel exhaust cooling systems which pump all of the coolant liquid back into the raw water source. However, if it is desired to provide additional cooling when operating the vehicle  10 ,  110  in land mode, the system may be arranged to retain raw water in the open circuit  90 ,  190  and/or closed circuit  80 ,  180  when the vehicle is driven on land. Such a system may have added benefits in terms of providing ballast which can be controllably distributed around the vehicle to further optimise performance, for example. In this case, safety devices could be provided to protect the system against frost damage in case raw water is accidentally retained during cold atmospheric conditions. For example, bursting discs could be provided to relieve excess pressure as is known in the design and operation of chemical process plants. 
   It will be appreciated that the closed circuit  80 ,  180  need not necessarily be a closed circuit in the case where antifreeze and its associated corrosion inhibitors are not required to be present in the coolant liquid. In such a case raw water may instead be drawn in, circulated around the so-called closed circuit  80 ,  180  and either retained for further circulation or dispensed back into the raw water source. In the case where raw water is retained for further circulation (for land mode operation of the vehicle, for example) bursting discs or other sacrificial elements may be employed in the closed circuit for safety reasons as described above. In a yet further embodiment, preferably when the vehicle is operating in the marine mode, raw water may be drawn in and passed directly through the water jacket  53 ,  153  of the exhaust system  50 ,  150  only before being dispensed back into the raw water source. This provides cooling of the exhaust system  50 ,  150  without the need for circulation of coolant liquid around the remainder of the closed circuit  80 ,  180 . Such an arrangement may be achieved using flow control valves, for example. 
   Whilst in the preferred embodiments described above cooling of the exhaust system  50 ,  150  is achieved using a coolant liquid which is passed through a water jacket  53 ,  153  directly enclosing components of the exhaust system  50 ,  150 , it will be appreciated that the apparatus employed to effect this heat transfer and control thereof may take any suitable form. For example, the water jacket  53 ,  153  need not enclose all components of the exhaust system. Instead, only a selected component or selection of components may be enclosed. Indeed, a plurality of separate water jackets may be beneficially employed, each separately enclosing one or more components. Each water jacket may be selectively ‘plumbed’ in and out of a circuit using control valves or other flow control means. Furthermore, the or each water jacket may be thermally insulated to one degree or other from components of the exhaust system and/or designed so as to prevent coolant liquid coming into direct contact with them. This may be achieved, for example, by providing an air, gas or liquid filled gap directly between the water jacket and an exhaust component (e.g. using ribs, fins or other structural members to achieve a fixed (linear or graduated) spatial relationship therebetween). Such an air, gas or liquid filled gap may additionally or alternatively be partially or completely filled or lagged with an insulating material. Each of these alternatives may be employed separately or in combination to optimise the exhaust cooling regime of the vehicle. It will be appreciated also that control of the flow of coolant liquid is imperative in optimising the cooling regime and in particular for optimal cooling of each separate component in the exhaust system during different modes such as land mode, marine mode, vehicle start up, normal running and vehicle shut down. The catalytic converter is one such component for which optimal operating parameters are critical. It is also important to control cooling of exhaust manifolds to prevent condensation and sediment build up. Furthermore, thermal shock effects on exhaust components must be taken into consideration. 
   The exhaust cooling system according to the present invention may be particularly advantageously applied to a planing amphibious vehicle; and further to such a vehicle having wheels which are retractable when the vehicle is driven over water in a marine mode. Control aspects of the exhaust cooling system may be linked into a vehicle control system which offers a land mode and a distinct marine mode. It may also be particularly advantageous for the exhaust cooling system according to the present invention to cool the engine exhaust manifolds in a controlled manner to prevent the formation of condensation in the exhaust manifold following a cold start. 
   Whilst the heat exchangers described herein have been referred to as ‘air-water’ and ‘water-water’ heat exchangers, it will be appreciated that the term ‘water’ infers the use of any suitable liquid, e.g. water provided with antifreeze and associated corrosion inhibitors. 
   While a particular form of the present invention has been illustrated and described, it will also be apparent to those skilled in the art that various modifications can be made without departing from the spirit and the scope of the present invention. Accordingly, it is not intended that the invention be limited except by the appended claims.