Abstract:
The apparatus includes a watertight elongated housing extending along a longitudinal axis and defining an inner chamber, a track disposed around the housing on its longitudinal axis and enabling the apparatus to move when the track is rotatably driven around the housing, and a track-driving motor. The motor is located within the inner chamber of the housing and includes an output shaft mechanically connected to the track. The apparatus can also include a ventilation circuit for ventilating the inner chamber of the housing and a generator for producing electricity. A method of operating a motorized pulling apparatus is also disclosed.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation-in-part of U.S. patent application Ser. No. 13/650,965 filed on 12 Oct. 2012, which is a continuation of PCT Patent Application No. PCT/CA2011/050202 filed on 15 Apr. 2011, which PCT Patent Application claims priority to U.S. Provisional Patent Application Ser. No. 61/342,538 filed on 15 Apr. 2010, the entire contents of which applications are hereby incorporated by reference in their entirety. 
     
    
     TECHNICAL FIELD 
       [0002]    The technical field relates to compact pulling apparatuses capable of travelling over difficult terrains, such as terrains covered with snow, sand, mud, etc. 
       TECHNICAL BACKGROUND 
       [0003]    Various apparatuses have been suggested over the years for travelling on difficult terrains. Of these, several are compact apparatuses allowing one person, in particular a person on skis, to be pushed or pulled using a track rotatably driven by a motor. Examples can be found in documents FR-2,431,304 (Jaulmes) published on 15 Feb. 1980 and in U.S. Pat. No. 4,519,470 (Allisio) published on 28 May 1985. Numerous other examples exist. Most of these apparatuses use a gasoline engine to rotatably drive the track. Some use an electric motor. Apparatuses of this sort can be useful as light means of transportation, particularly where it is difficult or even forbidden to travel using a larger vehicle. For example, in terrains with a snow-covered surface, the snow could be too powdery or too deep to use a snowmobile. Another advantage of such apparatuses is that it is much more simple and easy to transport them in another vehicle than is the case with a larger and heavier vehicle, for instance a snowmobile. 
         [0004]    Unfortunately, none of the previously-suggested apparatuses has proven fully adapted to the very rigorous winter conditions encountered during parts of the year in places where such apparatuses are likely to be useful. For instance, a very cold temperature can significantly hinder the reliability and the autonomy of an apparatus using an electric motor powered using batteries. In the case of a gasoline engine, the combination of cold weather and heat released from the engine can cause ice and compacted snow to build up at sensitive points of the apparatus. Moreover, milder temperatures are more likely to cause water infiltrations into the apparatus, which can then result in failures difficult to repair, especially if they occur deep into the forest or in other places that are difficult to access. 
         [0005]    Also, the previously-suggested apparatuses do not allow an electric generator to be easily transported to places that are difficult to access. 
         [0006]    It is therefore clear that improvements in the related technical field are still needed. 
       SUMMARY 
       [0007]    According to one aspect, there is provided a method of operating a compact pulling apparatus of the type including a watertight elongated housing extending along a longitudinal axis and defining an inner chamber inside which a motor is located, and also including a track disposed around the housing along its longitudinal axis and enabling the apparatus to move when the track is rotatably driven around the housing by the motor, the method including the following simultaneous steps: maintaining a minimum temperature in the inner chamber using heat released by the motor; evacuating heat from within the inner chamber if the temperature exceeds a given threshold; and maintaining a positive pressure within the inner chamber. 
         [0008]    More details on this aspect, as well as on other aspects of the proposed concept, will become apparent in light of the detailed description which follows and the appended figures. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0009]      FIG. 1  is an isometric view of an example of an apparatus designed using the proposed concept; 
           [0010]      FIG. 2  is a side view of the apparatus shown in  FIG. 1 ; 
           [0011]      FIG. 3  is a view similar to  FIG. 1  but shows the apparatus without its track and without the lateral walls on the sides of its housing; 
           [0012]      FIG. 4  is a view similar to  FIG. 3  but shows the left side of the apparatus, as seen from the rear; 
           [0013]      FIG. 5  is a right side view of the apparatus shown in  FIG. 3 ; 
           [0014]      FIG. 6  is a top view of the apparatus shown in  FIG. 3 ; 
           [0015]      FIG. 7  is a view similar to  FIG. 1  but where the operator is standing on a sled hitched to the apparatus; and 
           [0016]      FIGS. 8 to 13  are views similar to  FIGS. 1 to 6  but show a second example of the apparatus in which an electric motor is used. 
       
    
    
     DETAILED DESCRIPTION 
       [0017]      FIG. 1  is an isometric view of an example of an apparatus  10  including the proposed concept. In this example, the apparatus  10  uses a gasoline engine to rotate a track  12  disposed around a watertight housing  14  having an elongate form. It should be noted that in the present context, the word “gasoline” must be understood as a liquid fuel and is not meant to exclude liquid fuels such as diesel or any other suitable kinds and/or mixtures of liquid fuels. It should also be noted at this point that the reference to a “watertight” housing means that its construction is watertight but this does not exclude the presence of a ventilation circuit for the interior of the housing  14 . This ventilation circuit includes at least one air inlet and one air outlet. The ventilation circuit makes it possible, among other things, to cool the interior of the housing  14  when its temperature exceeds an upper threshold, for example above 25° C. Other values are also possible. 
         [0018]    The rotation of the track  12  around the housing  14  enables the apparatus  10  to move. The housing  14  is low-slung in order to keep its center of gravity as low as possible. The housing  14  includes a lateral wall  16  on each side. The housing  14  can, for example, be made of a metallic material, a plastic material, or both. Aluminum is an example of one possible material for the housing  14  since this material is light and strong. The track  12  can be made of rubber or some other polymer. Other materials are possible. 
         [0019]    The illustrated apparatus  10  includes a handlebar  20  which is connected to the housing  14 . The handlebar  20  extends substantially rearward of the apparatus  10 . The handlebar  20  is intended to be held and manipulated by an operator  22  who is at the rear of the apparatus  10 , as shown in a semi-schematic manner in  FIG. 1 . The handlebar  20  can be pivotal or fixed, depending on the needs. When pivotal, it is possible to limit the pivoting of the handlebar  20  between a minimum angle and a maximum angle with respect to the horizontal. 
         [0020]    It should be noted that the handlebars  20  may be omitted in some implementations. 
         [0021]    In the illustrated implementation, the operator  22  can be provided with skis  24  (or the equivalent) or be on board a sled hitched to the apparatus  10 . As can be seen in  FIG. 1 , the center of gravity of the apparatus  10  is at a height that is below the knees of the operator  22 . 
         [0022]    The operator  22  has controls available on the handrests of the handlebar  20  which allow, among other things, controlling the travelling speed of the apparatus  10  and other functions. The controls (not shown) can be connected to the housing  14  using wires and/or by wireless communication means, for instance. Depending on the model, it is also possible to provide a device which enables the apparatus  10  to back up by its own motor power which can be very useful in certain circumstances. Levers for operating a brake can also be provided (see  FIG. 13 ). These levers can be placed similarly to those of the brakes on a bicycle or a motorcycle, for instance. Other elements can be provided on the handlebar  20  according to requirements, such as a lamp, indicator dials, etc. Other configurations and arrangements are possible as well. 
         [0023]    When travelling forward, the apparatus  10  pulls the operator  22  along and, if required, transports a payload such as a payload placed on board a sled hitched to the apparatus  10  or on a rack over the apparatus  10 . Such apparatus  10  can easily pull a load equivalent to at least twice its own weight in powder snow. For example, tests carried out using an apparatus weighing 125 kg (275 lbs) have shown that such an apparatus was able to pull a load of more than 225 kg (550 lbs) over a distance of 150 km on a single fuel tank. 
         [0024]    The operator  22  can change the direction of the apparatus  10  by moving the handlebar  20  sideways in the direction opposite the turn to be made. This maneuver is similar to the one made by the operator of a small conventional lawn mower. 
         [0025]      FIG. 2  is a side view of the apparatus  10  shown in  FIG. 1 .  FIGS. 1 and 2  illustrate the assembled apparatus  10 .  FIG. 3  is a view similar to  FIG. 1  but shows the apparatus without its track  12  and without the lateral walls  16  on the sides of its housing  14 .  FIG. 4  is a view similar to  FIG. 3  but shows the left side of the apparatus  10  as seen from the rear.  FIG. 5  is a right side view of the apparatus  10  shown in  FIG. 3 . 
         [0026]    As can be seen particularly in  FIGS. 3 and 4 , the housing  14  defines an inner chamber  30  in which different parts of the apparatus  10  are located, in particular the engine  32 . The housing  14  also includes a top wall  14   a,  a bottom wall  14   b,  a front wall  14   c  and a rear wall. The housing  14  has a reinforced structure which can include one or several internal walls to divide the inner chamber  30 . The compartments communicate with each other. 
         [0027]    A pair of top skids  34  is disposed longitudinally on the top wall  14   a  of the housing  14 . A pair of bottom skids, similar to those on the top wall  14   a,  is disposed longitudinally on the bottom wall  14   b  of the housing  14 . The skids are made of a material having a very low friction coefficient. They allow, among other things, the track  12  to rotate around the housing  14  and to reduce friction between the inner face of the track  12  and the outside of the housing  14 . They also serve as guides to keep the track  12  in registry with the axis of the apparatus  10 . The skids extend for several centimeters beyond the front and rear ends of the top wall  14   a  and the bottom wall  14   b  so as to support the track  12  along almost the entire length of the apparatus  10 . 
         [0028]    If desired, the skids can be used together with one or more pairs of rollers or small wheels that are operatively connected to the housing  14  and that are engaging the inner face of the track  12 . They will further reduce the friction between the inner face of the track  12  and the outside of the housing  14 . 
         [0029]    At least one front roller is rotatably connected on the front of the housing  14 . In the illustrated example, two front rollers  40  are provided. The front rollers  40  are coaxially mounted around a front transversal axle  42  which is supported by an internally-greased axle connected at its ends to two opposite plates  44  which are disposed parallel to the longitudinal axis of the apparatus  10 . The plates  44  are rigidly connected to the front of the housing  14 . Also in the illustrated example, a bumper  46  is provided at the front of the apparatus  10 . The ends of the bumper  46  are connected to the two plates  44 , as shown particularly in  FIGS. 3 and 4 . Sufficient clearance is provided between the interior of the bumper  46  and the front rollers  40  to allow the track to rotate around the housing  14  without interfering with the interior of the bumper  46 . 
         [0030]    At least one rear roller is rotatably connected at the rear of the housing  14 . In the illustrated example, two rear rollers  50  are provided. The rear rollers  50  are coaxially mounted around a rear transversal axle  52  which is supported at its ends by bearings located in two opposite plates  54  disposed parallel to the longitudinal axis of the apparatus  10 . The plates  54  are rigidly connected to the rear of the housing  14 . Also in the illustrated example, a mechanical connection is provided between the output shaft of a transmission  60  located within the housing  14  and the rear transversal axle  52 . The rear rollers  50  are thus used to drive the track  12  in rotation so as to move the apparatus  10 . 
         [0031]    Different types of mechanical connections can be used between the transmission  60  and the rear transversal axle  52 . The illustrated one includes a chain  62  or drivebelt and provides a reduction of the rotation speed between the output shaft of the transmission  60  and the rear transversal axle  52 . Other types of connections and configurations are also possible. The mechanical connection between the motor  32  and the transmission  60  is provided by a chain  64  or drivebelt. The transmission  60  can enable either a forward or reverse motion of the apparatus  10 , for instance. It can have one or more speeds or be a variable speed transmission. The transmission  60  can include and/or be used together with a clutch, such as a centrifugal clutch, to initiate the motion of the apparatus  10 . 
         [0032]    In the illustrated example, and as best shown in  FIG. 4 , the chain  62  goes inside the housing  14  through ports made in the rear wall thereof. It engages a corresponding sprocket that is mechanically connected to the output shaft of the transmission  60 . The area around this sprocket is sealed from the rest of the housing  14 . 
         [0033]    In the illustrated example, the rear transversal axle  52  also carries a brake disk  66 , as shown in  FIG. 4 . This brake disk  66  is disposed near the left end of the rear transversal axle  52 . The brake pads are attached to the housing  14  and can be operated by the operator  22 , for instance from the handlebar  20  (see  FIG. 13 ). Other configurations and arrangements are also possible. 
         [0034]    As aforesaid, the drive motor for the track  12  of the example illustrated in  FIGS. 1 to 6  is a gasoline engine  32 . It is located immediately in front of the transmission  60 . An intermediary transversal wall  14   d  is present in the illustrated example so as to reinforce the area between the engine  32  and the transmission  60 . The engine  32  is supplied with fuel from a fuel tank  70  located at the front of the inner chamber  30  of the apparatus  10 . A battery or battery unit  72  is disposed beside the fuel tank  70 . This battery or battery unit  72  is, among other things, provided to power the electric starter of the engine  32 . The operator  22  is thus able to start or to stop the engine  32  without having to access it directly. 
         [0035]    The apparatus  10  shown in  FIGS. 1 to 6  also includes a generator  80  provided in the inner chamber  30  and can produce electricity intended to power one or more external equipment at a voltage, corresponding in particular to that of a domestic electrical outlet, for example 110V or 220V/240V at 60 Hz or also at 50 Hz. One or more electrical sockets are available on the apparatus  10  and/or on the generator  80  itself. The generator  80  includes an internal rotor which can be rotatably driven by the engine  32 . The possibility of generating electricity within the apparatus  10  can be very advantageous to users such as workers operating power tools at remote sites, or to owners of cottages located far from inhabited areas. Many other uses can be devised. A generator with a power rating of 4000 to 6000 W can be provided in an apparatus  10  of the size shown. A smaller or even a larger generator is also possible. 
         [0036]    The axis of the generator  80  is disposed transversely with reference to the longitudinal axis of the apparatus  10 . The generator  80  could also be disposed in some other way in certain models. It is mechanically connected to the output shaft of the engine  32 , for instance by a chain  82  or drivebelt. An electric clutch  84  can be provided on the output shaft of the generator  80 . This activates the mechanical connection between the generator  80  and the engine  32  to be engaged or disengaged remotely. Thus, when there is no need for the generator  80  to be used, for instance when the apparatus  10  is in motion, unnecessary rotation of the rotor of the generator  80  can be avoided. When the generator  80  is in operation, the transmission  60  of the apparatus  10  is set to neutral. Other configurations and arrangements are also possible. 
         [0037]    The admission of fresh air into the interior of the inner chamber  30  of the housing  14  is effected through a series of apertures  90  provided on at least one side of the housing  14 , immediately beneath the top wall  14   a,  in the illustrated example. These apertures  90  have a relatively small diameter so as to minimize snow and debris ingestion, such as twigs or others. Air passing through the apertures  90  goes into an inlet box  92  which collects the air coming from all the apertures  90  on each side of the housing  14 . When the apparatus  10  is in operation, the inlet box  92  is heated from below by the heat released from the engine  32  and which circulates in the inner chamber  30 . This heat allows the inner chamber  30  to be kept well above freezing point (0° C.) even if the outside temperature is very cold, for example below −20° C. With this heat, any snow particle entering the inlet box  92  can melt and drip out toward the exterior, even during cold weather. The air exits the inlet box  92  through an exit pipe  94  which is circular in the illustrated example. The top of the exit pipe  94  can be raised several millimeters above the bottom of the inlet box  92  so as to prevent the flow of water directly toward the inner chamber  30 . Variants are possible as well. 
         [0038]      FIG. 6  is a top view of the apparatus  10  shown in  FIG. 3 . The air inlet box  92  is seen in this figure. Air leaving the inlet box  92  is then channeled into a flexible duct  95  (schematically illustrated in  FIG. 4 ) leading to the inlet  33  of the cooling fan shroud located on the engine  32 . The fan in the engine  32  thus generates the necessary suction force to draw air through the apertures  90 . The cooling air passes around the cylinder or cylinders of the engine  32  and ends up in the interior of the inner chamber  30 . 
         [0039]    The evacuation of air from the interior of the illustrated apparatus  10  can be effected in two ways. On the one hand, the fuel combustion in the engine  32  generates exhaust gases. The air used in this combustion process is admitted into the interior of the engine  32  from the interior of the inner chamber  30  or it can also come directly from the inlet box  92  for some engines. The exhaust gases coming out of the cylinder or cylinders are then directed toward the rear of the apparatus  10  using an exhaust pipe  96  which is shown in  FIG. 6 . In the illustrated example, the exit of the exhaust pipe  96  is located in the space  98  where the rear transversal axle  52  and the two rear rollers  50  are located. This space  98  is partially blocked by the presence of the track  12  when the apparatus  10  is assembled. This configuration, among other things, reduces noise as well as preventing any possible contact between the skin or cloths of the operator  22  and the hot exit of the exhaust pipe  96 . Other configurations and arrangements are also possible. 
         [0040]    Some air is also evacuated from the interior of the inner chamber  30  through an air outlet which forms part of the ventilation circuit. Air passing through the outlet goes first into the cooling circuit of the generator  80  and then flows through a flexible duct  104  (shown schematically in  FIG. 4 ) up to the entrance of the air outlet box  100 . The outlet box  100  has a similar structure to that of the inlet box  92 . The air is then evacuated through the apertures  102  located on at least one side of the housing  14 . Other configurations and arrangements are also possible. 
         [0041]    When the generator  80  is in operation, the fan, which is integrated into the generator  80 , contributes to the displacement of air so as to increase the air flow that cools it. Additional fans disposed in series on the flexible ducts connected to the air inlet and air outlet can further increase the air flow if the temperature inside the inner chamber  30  becomes too high. These fans can be automatically switched on and off using a thermostat provided with a temperature sensor or another mechanism. Again, other configurations and arrangements are also possible. 
         [0042]    The apparatus  10  is configured in such a way that a positive pressure is created in the inner chamber  30 . This can be achieved by providing an overall air inlet area greater than the overall air outlet area. In the example, the number of apertures  90  is greater than the number of apertures  102 . The positive pressure, among other things, improves the watertightness of the housing  14 . 
         [0043]    When the apparatus  10  is in motion, the sides of the housing  14  are made watertight using lateral walls  16  shown in  FIGS. 1 and 2 . These lateral walls  16  are bolted or otherwise attached to the rest of the housing  14 . The interior of the housing  14  thus remains watertight and dry while the apparatus  10  is in operation. 
         [0044]    As is shown in  FIG. 5 , the underside of the housing  14  is convex at its center. This heightening is about  3  cm at the front and at the rear of the track  12  in the apparatus  10  of the illustrated example. This central part corresponds to about one third of the length of the apparatus  10 . The heightening, in particular, facilitates a yawing motion when making a turn as well as the manual pivoting of the apparatus  10  on hard and rough surfaces, for example on asphalt or concrete. 
         [0045]    Moreover, the front of the bottom wall  14   b  defines an angle with reference to the horizontal. The front transversal axle  42  is thus higher than the rear transversal axle  52 . This also facilitates passage over obstacles. Variants are possible as well. 
         [0046]      FIG. 7  is a view similar to  FIG. 1  but where the operator is standing on a sled  200  hitched to the apparatus  10 . The hitch  202  of the sled  200  is connected to a support  210  which, in the illustrated example, is in the form of a transversal strut that is straight or slightly curved towards the rear at its center. The transversal strut  210  is supported using two corresponding plates  212  projecting towards the top of the housing  14 . The hitch  202  includes two retainer arms of the sled  200 , which arms are attached to a plate  204  and can pivot around a vertical axis where it joins a fastening element  206 . The fastening element  206  can slide from left to right along the transversal strut  210  using two pulleys provided on either side of the fastening element  206 . In a turn, the fastening member  206  can thus move toward one of the ends of the transversal strut  210 , this facilitating handling of the apparatus  10  and reducing the effort required from the operator  22 . 
         [0047]    Another possible implementation is to provide the apparatus  10  with a generator  80  that can also be used as a motor, thus as a generator/motor, in an electrical power mode. The electrical power to operate the generator/motor  80  in the electrical power mode can be provided for instance by the battery unit  72  and/or from additional batteries. The operator could choose between a fuel power mode and the electrical power mode, depending on the needs. For instance, when minimizing the noise is required, turning off the engine  32  and using the electrical power mode will be very useful. Both modes can even be selected automatically and/or be possibly used as the same time to create a “hybrid” mode. 
         [0048]    Still, if desired, the transmission  60  can be simplified by omitting the gears allowing the apparatus  10  to back up. Instead, one can use the generator/motor  80  to rotate the track  12  in the opposite direction, thereby moving the apparatus  10  in the reverse direction. Another possible implementation is to provide the engine  32  with an electronic engine reversing system that can make the engine  32  rotate in the opposite direction to back up. This way, the transmission  60  can be made smaller and lighter. Some implementations may even omit the transmission  60  entirely. 
         [0049]      FIGS. 8 to 13  are views similar to  FIGS. 1 to 6  but show a second model of apparatus  300  in which only an electric motor is used. This apparatus  300  is otherwise similar to the apparatus  10  shown in the previous example. The apparatus  300  includes, among other things, a track  302 , a watertight housing  304  and a handlebar  306 , which handlebar  306  is held by an operator  308 . The apparatus  300  can also be used with the sled  200  shown in  FIG. 7 . 
         [0050]    The track  302  of the apparatus  300  is rotatably driven by an electric motor  310  ( FIG. 10 ). This motor  310  is powered using electricity from one or several batteries  312  are also located within the inner chamber  314  of the housing  304 . The electric motor  310  can either be of type AC or DC, with or without permanent magnets. A group of four deep cycle lead batteries  312  is shown in the illustrated example. The number and type of batteries  312  can differ according to requirements. The batteries  312  are connected to an electric controller which the operator  308  can control from the handlebar  306 . The various electrical connections are not shown in the figures so as to simplify the illustrations. 
         [0051]    Other configurations and arrangements are possible. For instance, the handlebar  306  can be omitted in some implementations. 
         [0052]    In operation, the electric motor  310  releases heat. This heat can account for about 10% of the electrical energy drawn from the batteries  312 , depending on the kinds of batteries being used. The heat thus dissipated is used within an inner chamber  314  of the apparatus  300  to keep the batteries  312  warm when the outside temperature is very cold. This heat thus makes it possible to keep the batteries at an optimal temperature despite very cold weather. The optimal temperature can be for instance in the range of 20 to 25° C. Other temperatures are also possible. This heat recovery is beneficial because most batteries lose their efficiency in cold weather. This is particularly the case of lead batteries. Although other batteries with better performance exist, lead batteries remain an attractive choice because they are easily available and relatively inexpensive. They withstand cold weather better than nickel or lithium batteries for instance. However, the efficiency of lead batteries diminishes almost linearly with reference to temperature, going for example from 100% at 25° C. down to 30% at −40° C., depending on the exact type of battery. The decrease in efficiency thus has a direct impact on the autonomy of the apparatus  300 . By keeping the heat inside the housing  304  during cold weather, the batteries  312  can then maintain a much higher efficiency than that at low temperatures. The interior of the housing  304  can also be insulated to help conserve heat. 
         [0053]    An internal ventilation circuit is provided in case of overheating, for example when the apparatus  300  is operating in relatively mild weather and the electric motor  310  is intensively solicited. This internal ventilation circuit is part of the ventilation circuit. It can include a thermostat which can activate at least one fan providing a supply of air from the outside to dissipate interior heat. The air inlet and air outlet can be located in the top part of the handlebar  306  at a certain distance from one another. The air then circulates in the tubes forming the sides of the handlebar  306 . The fan or fans can be provided in the housing  304  or alternatively in the handlebar  306 . 
         [0054]    The junction between the handlebar  306  and the housing  304  is configured so as to provide an air passage between them. This way, the housing  304  can have a very watertight structure up to the height of the air inlet and the air outlet on the handlebar  306 . A positive pressure is maintained within the interior of the inner chamber  314  to mitigate the risks of having water infiltration at locations which may not be completely watertight. The apparatus  300  can then even be immersed in water from time or time, as might be required for instance when the apparatus  300  must cross an unfrozen stream or similar body of water. 
         [0055]      FIG. 13  is a top plan view of the apparatus  300 . Air can circulate in an air path circuit going around the batteries  312 , for instance going forward in a space along the left side thereof, then from left to right in a space at the front of the inner chamber  314 , and going backward in a space along the right side of the batteries  312  before exiting the housing  304 . The spaces at the left and the right side of the batteries  312  can be separated from one another using a longitudinally-disposed foam element or the like provided along the top side of the batteries  312  and, if necessary, along the bottom side thereof. Other configurations and arrangements are also possible. 
         [0056]    If desired, it is possible to provide a heating element, for instance a heating cable, inside the housing  304  to keep the batteries  312  warm when they are being charged outdoors during cold weather and also when they are being stored outdoors. 
         [0057]    It is also possible to provide a fixed support located above the track  12 ,  302  and connected to the housing  14 . This support can be provided on either of the examples of apparatus  10 ,  300  shown herein. The support can be useful for carrying equipment, for example as a tool box and/or a cargo box and/or a fuel tank and/or batteries. 
         [0058]    The present detailed description and appended figures are only examples. A person working in this field will be able to see that variations can be made while still staying within the framework of the proposed concept.