1. Field of the Invention
The present invention relates in general to an all terrain vehicle having track assemblies driven by the wheels on the vehicle and more specifically to a vehicle that utilizes only certain of its wheels for driving the track assemblies.
2. Description of the Prior Art
Most modern skid steer type amphibious all terrain vehicles (AATV) use a single transmission to independently drive a set of axles and wheels on each side of the vehicle that are connected together and kept in time with one another through a series of chains and sprockets. Such machines require the use of soft, low pressure tires (which often vary slightly in total outside circumference) and it is known in the art to convert these vehicles to improve their traction by installing track assemblies on either side of the vehicle that surround the wheels and are driven thereby. There are several different track options to create a continuous band of tread that wraps around the tires such as rubber, plastic, metal and/or a combination of two or more materials. By the use of tracks, the vehicle is provided a larger footprint, while not giving up the added floatation provided by the rims and tires thereof.
When using tracks on any skid steer AATV, a slight variance in the outside circumference of the tires running inside of each track assembly creates problems in the form of a constant “scrubbing” affect that the tires have to make in order to continue to turn and cover unequal distances on the inside surface of the track assembly. Consequently, operational problems result such as:
1. Loss of power and performance due to excessive rolling resistance (rubbing) of the drive tires with the inside of track assembly, often resulting in excessive chain windup and severe chain binding or broken chains and chain tensioners, excessive and premature wear on outer axle bearings, seals and tires, broken axle assemblies, etc.
2. Difficulty in turning due to the larger flat contact area of the track assembly that must skid in order to pivot or rotate the vehicle to a new angle of direction.
3. Difficulty in climbing up severe approach angles or keeping forward momentum on soft surfaces that require greater floatation.
4. A difficult and time consuming task of modifying and reducing the final drive gearing of the vehicle for maximum low speed and high torque applications necessary with track assemblies, and then to return it to the higher gear setting desired for standard operation with out tracks using the wheels only.
Major AATV manufacturers have realized the above problems and are now instructing dealers or vehicle owners to first measure the outside circumference of each tire and then stagger each of the tires in a certain pattern with the smallest in the front, the largest next, then the next largest and lastly the next smallest. Such strategy does not eliminate the stress created, but helps spread it out over the entire drive chain and reduces the damage that is incurred due to the stress.
Manufacturers often make note in their assembly instructions that there is a range of about 3 inches of outside circumference tire variance, but in the inventor's experience it is not uncommon to see up to about 5 inches of difference. This means that even if a staggering of tires is performed, such difference in circumference will cause the second tire back to have to scrub as much as 5 inches on the inside of the track surface during a single rotation with similar affects on all other tires running inside of the track.
Another alternative for reducing the scrubbing action of the tires on the track assemblies is to remove certain chain loops on the rear axles and thereby allow them to turn freely. This eliminates the transfer of drive power to some of the axle and wheel assemblies of the vehicle, for example, to have only the front most axle and wheel assembly in driving engagement. However, this alternative is a difficult and messy solution to the problem and often will cause the tires of the powered wheels axle assemblies to slip and free spin inside of the tracks.
The present invention is adapted to provide a means for relatively quickly, easily and inexpensively adapting the driving action of the axle and wheel assemblies on AATV's in a manner so as to reduce or essentially entirely eliminate the deficiencies inherent in utilizing track assemblies on an AATV while maintaining drive power to both the front and rear tires of the vehicle.