Power takeoff for tracked vehicle

A tracked vehicle such as a snowmobile is provided with a power takeoff by substitution of a gear wheel for an existing idle wheel around which the track of the vehicle is wound. The gear wheel has a circumference which is equal to the distance between two preselected drive lugs on the track.

FIELD OF THE INVENTION

This invention relates to power takeoffs and more particularly to modifications to existing vehicles propelled by continuous tracks, sometimes referred to as caterpillar tracks, to equip them with power takeoffs.

CROSS-REFERENCE TO RELATED PRIOR APPLICATION

This application claims priority pursuant to 35 USC 119 of Canadian application no. 2,869,030 filed in the Canadian Intellectual Property Office on Oct. 28, 2014 which application is herein incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

Vehicles propelled by tracks or so-called “tracked vehicles” are useful in travelling over terrain which is inaccessible to vehicles driven by wheels. For example, tracked vehicles such as All Terrain Vehicles (ATV's) are capable of travelling over steep rolling terrain or terrain littered with rocks and other debris. Such vehicles are particularly useful in mineral exploration and in search and rescue work. Other tracked vehicles such as snowmobiles are capable of travelling over snow and ice and are useful for carrying out work in the arctic and also in search and rescue work.

Existing tracked vehicles are usually restricted in the type of terrain over which they are capable of travelling. For example, existing snowmobiles are usually constructed to travel on ice or snow but not on pavement. Existing ATV's are usually restricted to travel on hard ground but not on ice and snow. As well such vehicles are usually not capable of carrying out tasks that are frequently required by persons who travel on snowmobiles or ATV's. For example hunters commonly use tracked vehicles to reach game in dense bush. If heavy game such as moose or deer is bagged, a hoist may be required to remove the game from the bush. Most tracked vehicles lack a hoist. A hoist may also be needed by persons involved in search and rescue work in situations where a persons must be pulled from water or from crevasses.

A power takeoff (“PTO”) is a useful addition to an existing tracked vehicle in the above situations. A PTO can be used to activate a hoist, a generator and it can also be used to drive wheels on a snowmobile. In the case of a snowmobile, it is most commonly used for recreational purposes involving travel over snow-covered trails. Such trails are frequently crossed by roads which may be paved or covered by gravel. Pavement and gravel are very damaging to the runners and tracks of snowmobiles. If a snowmobile is equipped with wheels which may be lowered for use and raised when not in use, the wheels can be lowered to lift their runners and track off the ground when the vehicle is travelling over pavement or gravel and can be raised when the vehicle is travelling over snow. A PTO on a snowmobile can be used to activate the wheels.

SUMMARY OF THE INVENTION

I have invented a way in which an existing tracked vehicle can be equipped with a PTO. Briefly my invention involves the substitution of a gear wheel for one of the idle wheels around which the caterpillar track of the existing vehicle is wound. The teeth of the gear wheel are arranged and constructed to mesh with and to be rotated by the drive lugs of the track. The gear wheel has a circumference which is equal to a first distance which is measured parallel to the direction of travel of the track when lying substantially flat and which extends between points at which the leading faces of two selected drive lugs meet the inner wall. The circumference of the gear wheel is closer to the circumference of the idle wheel which it replaces than the distance between any other pair of the drive lugs in the same row of lugs

In the detailed description of my invention which follows, the vehicle which is modified by the addition of a PTO is snowmobile but it is to be emphasized that my invention is not limited to the modification of a snowmobile in this manner. Any tracked vehicle may be modified by the addition of a power takeoff according to my invention including large tracked vehicle used by the military such as tanks, and tracked vehicles used in heavy industry such as cranes, power shovels and the like.

Like reference characters refer to like parts throughout the following description.

DESCRIPTION OF PREFERRED EMBODIMENTS

With reference toFIGS. 1 and 2, a conventional snowmobile, generally10, is illustrated. The snowmobile is equipped with a track12, sometimes referred to as a caterpillar track, near the rear end of the vehicle for propelling the vehicle forward and runners14at the front end of the vehicle on which the vehicle slides on snow or ice. The tracks are wound around front and rear idle wheels16,18and around a drive wheel20. The drive wheel is driven by a prime mover usually a gasoline powered engine (not illustrated) which is mounted within a cowl22. A handle bar24is provided for steering the vehicle and a bench26is provided for the driver of the vehicle.

The oppositely facing circular walls20a,bof the drive wheel are provided with studs28which mate with drive lugs30on the inner wall12aof the track. The drive lugs are arranged in longitudinally extending rows32which extend along the entire inner wall of the track.

With reference toFIG. 3, usually four rear idle wheels18a,b,canddare provided around which the track winds as it changes direction from movement toward the rear of the vehicle in its lower stretch of travel indicated by arrow34ato movement in the opposite direction as indicated by arrow34b.

Each of the idle wheels is mounted in bearings and revolves around a rear axle36which is oriented normal to the direction of travel of the track. The axle is fixed to a pair of parallel longitudinally extending skids or stringers. Attachment is made at points midway between the ends of the axle so that the ends are free and unattached to any part of the snowmobile. The axle being attached to the skids or stringers of a snowmobile remains stationary relative to the frame of the vehicle.

The foregoing description is of a conventional snowmobile. The following description is a preferred embodiment of the applicant's invention which adds a power takeoff to the conventional snowmobile. With reference first toFIG. 4, a snowmobile, generally40, is equipped with a forward roller or wheels42which pivot from a position above the runners44of the vehicle (not illustrated) to a position below the runners and directly beneath stem46of the vehicle. The roller and wheels are conventional and are provided to allow a snowmobile to travel over a pavement or other abrasive surface without damage to the runners. However what is not conventional is a pair of rear wheels50which is mounted for rotation at the rear of the vehicle.

With reference toFIG. 5, the outer idle wheels18a, dofFIG. 3have been replaced by gear wheels52a, b. The two idle wheels54a, band the two gear wheels52a, bofFIG. 5are all mounted in bearings for rotation about a rear axle56. The axle is fixed to skids or stringers of the vehicle the frame while the idlers and gears are mounted in bearings and revolve freely about the axle. At least one half of the teeth of the gear wheels make contact with drive lugs, referred to below, as the track travels around the gear wheel.

On the outer wall57of the track laterally extending ribs58are formed. Studs59are spaced along the length of each rib. On the lower stretch of the track the studs extend downwardly and function to grip whatever is beneath the snowmobile as it travels forward. The studs accordingly function to improve the traction of the snowmobile on slippery surfaces such as ice or hard packed snow.

InFIG. 6, a collar or coupling60is attached to gear wheel52aby welding or otherwise and the cylindrical opening of the collar receives a spindle62connected to wheel50. The collar is attached to the spindle by a cotter pin (not illustrated) which passes through apertures60a,62ain the collar and spindle respectively. The wheel accordingly revolves with gear wheel52a.

InFIG. 7a hoist, generally66is substituted for the wheel ofFIG. 6. The hoist consist of a pulley68around which a rope70is wound. A hook72is attached to the free end of the rope. The pulley revolves with a spindle74which is attached to collar60by a cotter pin so that the pulley is caused to rotate by gear wheel52a.

As illustrated inFIG. 4, track79is generally flat when it is travelling from the array of forward idle wheels80to the array82of gear wheels at the rear of the snowmobile. The flat segment of the track is shown in larger scale inFIGS. 8 and 9. With reference first toFIG. 8, on the inner wall79aof the track which faces upward when flat, drive lugs86are arranged in parallel rows88and each lug is spaced apart from adjacent lugs in the same row an equal distance. When the snowmobile is moving forward and the flat segment of the track is moving in the opposite direction indicated by arrow89, each lug has a so-called leading face86band an oppositely facing trailing face86a.

With reference toFIG. 5, as the flat segment of the track reaches the array of gear wheels52and idle wheels54the idle wheels enter the space between the rows88of drive logs while the gear wheels enter and into engagement with the rows of drive lugs.

The gear wheels which are to be substituted for the idle wheels on an existing snowmobile such as the rear idle wheels18on the snowmobile illustrated inFIGS. 1-3will not necessarily have the same diameter. That is because the profile of the gear wheels must take into account the dimensions of the drive lugs and the distance between adjacent lugs in the same row. The profile of the gear wheels can be determined by reference toFIG. 9and by carrying out the following steps:

(1) while the track lies flat, two drive lugs86-1,86-2are selected which lie approximately as far apart as the circumference of the existing idle wheels18(FIG. 3) to be replaced. The circumference of the idle wheels will of course be calculated using the formula:
πD
and such circumference is referred to as an “idle wheel circumference”.
(2) the distance, measured parallel to the direction of travel of the track between where the leading faces86bof the selected lugs meet the inner wall79aof the track is measured (marked “x”).
(3) if the distance is larger than the circumference of the idle wheel, two lugs which are closer together are selected and the distance apart of them is measured. Alternatively, if the distance is significantly less than the idle wheel circumference, the distance between two other drive lugs which are farther apart is measured.
(4) once two lugs are selected which are close to and separated from one another by a distance that is less than idle wheel circumference, then that distance becomes a so-called “first distance” and is the required circumference of the gear wheel which is to replace the existing idle wheel.

The number of teeth in the gear wheel is then determined by counting the number of drive lugs between the leading faces of the selected pair of lugs i.e. 4

With reference toFIG. 10, there should be a gap90between a drive lug86and adjacent wall of a tooth92, measured at the circumference of the gear wheel, to allow the lugs to enter and exit the space between the teeth of gear wheel52smoothly and without binding as the gear wheel revolves. The shape of the gap of course reflects the shape of the teeth and the drive lugs and is designed so that the gear wheels turns smoothly as the drive lugs mesh with their teeth. Whatever the shape of the teeth and drive lugs, the diameter of the gear wheel remains the same.

With reference toFIG. 11the gear wheel generally98has a periphery defined in part by teeth100and in part by a smooth circular surface102similar to that of an idle wheel. Portion102is disposed at the outside end of the rear axle while the toothed portion100is inside the portion102and faces the idle wheels on the axle. Gear wheel98has an advantage of providing better support to the outer edge of the track than a gear wheel simply having teeth at its periphery.

It should be noted that the circumference of the idle wheels which revolve around the same axle as the gear wheels should be the same as the circumference of the gear wheels. Thus for example, the idle wheels54illustrated inFIG. 5must have the same circumference as the gear wheels to function in concert with them.

As will be evident from the preceding description, gear wheels substituted for the idle wheels of a conventional snowmobile function as a power takeoff for a hoist, for wheels, for a generator, a pump and for many other purposes.

It will be understood, of course, that modifications can be made in the structure of the power takeoff described above without departing from the scope and purview of the invention as defined in the following claims.