Patent Application
20110180332
The present invention relates to steering systems. More specifically, the invention relates to a steering system for a vehicle having a pair of continuous tracks.
Tracked vehicles, that is vehicles whose motion over a surface is imparted by continuous belt-like “tracks” rather than a set of wheels, are known in the art. Vehicles such as earth-movers, tanks and various off-road vehicles can be provided with two or more continuous tracks, also called caterpillar tracks, which provide an increased area of contact between the vehicle and the ground. This increased contact area increases traction and is advantageous in many off-road situations, such as on snow, sand or soft earth. A track can be made of a continuous flexible belt or a plurality of rigid belt elements which are hingedly joined to one another.
It is known to provide tracked vehicles with four or more tracks which can be steered by directing the two front-most tracks, much as a conventional car is steered. It is more common however for tracked vehicles to comprise a single pair of tracks, one extending along either side of the vehicle. Such vehicles can be steered by varying the speed of one of the two tracks. To turn to the left, the right track is accelerated and/or the left track is decelerated. It is therefore known to provide the driver independent control of each track in order to enable turning. Typically, this independent control is enabled by having a motor drive a hydraulic pump, which in turn independently powers left and right side hydraulic motors.
However, because the market for such tracked vehicles is relatively small, it is also known to provide attachments or kits for adapting a conventional tractor to run on tracks. Such an attachment conveniently allows the use of a wheeled vehicle in the summer and a tracked vehicle in the winter.
However, conventional tractors typically comprise a pair of steered front wheels and a pair of driven rear wheels whose motive power comes from a motor through a transmission and a differential. When adapting such a tractor to run on tracks, the driven rear wheels are typically replaced with sprocket wheels which are used to drive the tracks. This arrangement is well suited for driving the tractor forwards or backwards, but conventional tractors do not typically provide independent control of the speed of the rear wheels. Various steering systems have been proposed to for conventional tractors adapted to run on tracks.
U.S. Pat. No. 5,343,960, issued Sep. 6, 1994 to Sylvain Gilbert, describes an attachment for converting a rear wheel drive tractor into a tracked snow grooming vehicle. A snow plow is mounted to the rear of the tractor and the converted tractor is steered by hydraulically actuating the coupling between the tractor and the trailing snow plow so as to control the orientation of the plow and thereby induce turning.
U.S. Pat. No. 3,710,886, issued Jan. 16, 1973 describes a mechanism for converting a wheeled vehicle into a tracked vehicle wherein the steering is accomplished by controlling the braking of the tracks in order to steer the vehicle.
Also known in the art are U.S. Pat. Nos. 1,665,470, 1,810,138, 2,356,931, 3,976,153, 4,448,273 4,821,824 and 4,865,141 which describe different continuous track devices for providing track propulsion for a vehicle.
However, it would be advantageous to provide an improved steering system for vehicles propelled by endless tracks which could operate in a more efficient manner than existing system. In particular, it would be advantageous to provide a steering system which varies the speed of the tracks in order to steer without employing the braking system, which represents an undesirable loss of motive power. It would also be advantageous to provide such a steering system which could be used to convert a rear wheel driven wheeled vehicle to a tracked vehicle.
In accordance with one aspect of the present invention, there is provided a steering system for a vehicle having left and right endless tracks for propelling the vehicle, left and right sprocket wheels for driving a respective one of the left and right endless tracks, a motor for providing primary motive power to the sprocket wheels and a hydraulic pump. The steering system includes left and right hydraulic motors each mounted to a respective one of the left and right sprocket wheels, a hydraulic circuit connecting the fluid outlet of the left hydraulic motor to the fluid inlet of the right hydraulic motor and the fluid outlet of the right hydraulic motor to the fluid inlet of the left hydraulic motor, thereby permitting the flow of hydraulic fluid between the left and right hydraulic motors, and a steering mechanism for receiving hydraulic pressure from the hydraulic pump and selectively distributing it to the first and second hydraulic motors. Each hydraulic motor includes a fluid inlet and a fluid outlet. Each hydraulic motor is able to provide additional motive power to the respective left and right sprocket wheel in response to the providing of a hydraulic pressure at its fluid inlet. The steering mechanism is in fluid communication with the fluid inlet of the left hydraulic motor to provide the hydraulic pressure in response to a first steering input from a user, and also in fluid communication with the fluid inlet of the right hydraulic motor to provide a hydraulic pressure in response to a second steering input from a user.
In accordance with another aspect of the present invention, there is provided an endless track attachment kit adaptable to a vehicle having a motor and a hydraulic pump. The kit includes left and right endless tracks for propelling the vehicle, left and right sprocket wheels for driving a respective one of the left and right endless tracks and which can be provided motive power by the motor, a frame for supporting the vehicle and about which the endless tracks are drivable, left and right hydraulic motors, a hydraulic circuit for connecting the fluid outlet of the left hydraulic motor to the fluid inlet of the right hydraulic motor and the fluid outlet of the right hydraulic motor to the fluid inlet of the left hydraulic motor, and a steering mechanism for receiving hydraulic pressure from the hydraulic pump and selectively distributing it to the first and second hydraulic motors. Each hydraulic motor is mountable to the frame and a respective one of the left and right sprocket wheels. Each hydraulic motor includes a fluid inlet and a fluid outlet. Each hydraulic motor is able to provide additional motive power to the respective left and right sprocket wheel in response to the providing of a hydraulic pressure at its fluid inlet. The hydraulic circuit permits the flow of hydraulic fluid between the left and right hydraulic motors. The steering mechanism includes a first connecting element for connecting to the fluid inlet of the left hydraulic motor to provide a hydraulic pressure in response to a first steering input from a user, and a second connecting element for connecting to the fluid inlet of the right hydraulic motor to provide a hydraulic pressure in response to a second steering input from a user.
Preferably, the steering mechanism includes a power steering unit. More preferably, the steering mechanism further includes a steering wheel coupled to the power steering unit which can provide a hydraulic pressure in response a rotation of the steering wheel by the user.
The objects, advantages and other features of the present invention will become more apparent and be better understood upon reading of the following non-restrictive description of the preferred embodiments of the invention, given with reference to the accompanying drawings. The accompanying drawings are given purely for illustrative purposes and should not in any way be interpreted as limiting the scope of the invention.
The present invention will be described more fully hereinafter with reference to the accompanying drawings in which like numerals refer to like elements throughout.
In the following description, the same numerical references refer to similar elements. The embodiments shown in the figures are preferred, for exemplification purposes only.
Although the preferred embodiments of the present invention as illustrated in the accompanying drawings comprise various components, etc., and consist of certain geometrical configurations as explained and illustrated herein, not all of these components and geometries are essential to the invention and thus should not be taken in their restrictive sense, i.e. should not be taken as to limit the scope of the present invention. It is to be understood, as also apparent to a person skilled in the art, that other suitable components and cooperations therebetween, as well as other suitable geometrical configurations may be used for the apparatus according to the present invention, as will be briefly explained herein and as can be easily inferred herefrom by a person skilled in the art, without departing from the scope of the invention.
With reference to
The tractor 10 comprises a motor for providing motive power and a transmission and differential for conveying that power to the propelling means. Prior to being adapted to run on tracks 12, a pair of conventional rear tractor wheels are used to propel the tractor 10. These rear wheels are then replaced by a pair of sprocket wheels 16, which engage and drive the tracks 12. The tractor 10 further comprises a hydraulic pump 84 (shown schematically in
The tracks 12 and sprocket wheels 16 can be provided as part of an attachment 18 for converting the tractor 10 to run on tracks. The attachment 18 also comprises a frame 20 for supporting the tractor 10, and a pair of track guides 22 about which tracks 12 are driven by the sprocket wheels 16. As is known in the art, the guides 22 can include a plurality of idler wheels 24 and/or sliders 26 to ensure a maximum contact between the tracks 12 and the ground and therefore maximum traction.
With additional reference to
The motor is therefore able to provide motive power to the sprocket wheels 16 in order to propel the tractor 10 forward or backward. A steering system 40 is further provided to enable the user to steer the tractor 10. The steering system 40 comprises, on each side of the attachment 18, a hydraulic motor 42 mounted to the respective torque arm 28. Each hydraulic 42 motor comprises a fluid inlet 46 and a fluid outlet 48. Supplying a pressurised hydraulic fluid at the fluid inlet 46 will result in the rotation of a power output 50. Having turned the power output 50, the fluid can then return via the fluid outlet 48. It will be appreciated that the rotation of the power output 50 can be reversed by pumping hydraulic fluid in the opposite direction.
While the hydraulic motors 24 are mounted to the torque arms 28, their power outputs 50 are each connected to their respective sprocket wheels 16 so as to enable the driver to provide of an additional motive power thereto and thereby steer the tractor 10. Preferably, the sprocket wheels 16 are not mounted directly to the power outputs 50, but rather via a bearing assembly 36 disposed between each torque arm 28 and its respective sprocket wheel 16 in order to allow the latter to rotate about the former. A gear assembly 52, such as a planetary gear box, can also be disposed between the power output 50 of the hydraulic motor 42 and the sprocket wheel 16. The planetary gear box 52 is preferably a gear down which reduces the speed of rotation but increases torque.
In the embodiment illustrated in
It will be appreciated that the bearing assembly 36, the hydraulic motor 42, the adapter 44, the planetary gear box 52 and the adapter ring 62 have been illustrated as a single cross-hatched unit in
With additional reference now to
Preferably however, the steering mechanism 70 is a power steering unit which is controlled by a steering wheel 82 (shown in
As used herein, the power steering unit 70 selectively directs hydraulic pressure from the tractor's hydraulic pump 84 to the fluid inlet of the right or left hydraulic motor 42 in response to a turning of the wheel. As long as the user continues to turn the steering wheel 82, the additional hydraulic pressure will continue to be provided to the associated hydraulic motor 42, thereby keeping that track 12 at a higher speed and continuing to turn the tractor 10. Advantageously, the use of a power steering unit 70 also provides a degree of feedback to the driver who will be able to sense when the tractor 10 is resisting the turning of the steering wheel 82.
With additional reference to
As described above, the tractor 10 may be steered to the left by turning the steering wheel 82 in counter-clockwise direction, which causes the power steering unit 70 to direct hydraulic pressure from the tractor's pump 84 through the hose 76 to the hydraulic circuit 80. The hydraulic circuit 80 comprises a control block 86 (also shown in
The hydraulic system illustrated in
The hydraulic pressure sent along hose 76 to the control block 86 will therefore pass through the first selection valve 94a and on to the first cross conduit 90a at junction 100a. Assuming the tractor 10 is travelling forward, a cross-flow in the hydraulic circuit 80 will have been induced and hydraulic fluid will be travelling from the outlet 48 of the left motor 42 to the inlet 46 of the right motor along the first cross-conduit 90a. The additional motive power provided by the hydraulic pressure at junction 100a will be fed to the inlet 46 of the right motor 42, thereby accelerating the right track 12 and turning the vehicle to the left.
Conversely, if the driver had turned the steering wheel 82 in the opposite direction and sent hydraulic pressure along the hose 74, this would have been fed to the second cross conduit 90b at junction 100b, which in turn would have provided hydraulic pressure to the inlet 46 of the left motor 42.
Preferably, the control block 86 further comprises a pair of bypass valves 102 for protecting the motors 42 and associated hoses from too high pressure. These bypass valves 102 open a conduit between the first and second cross conduits 90a, bypassing the motors 42, should the pressure in either conduit reach a certain predetermined threshold, such as 3500 psi.
A second pump 104 is preferably provided for ensuring a minimum operating pressure throughout the hydraulic system which, as will be appreciated by one of ordinary skill in the art, is generally required to assure the good functioning thereof. This second pump 104 can be the tractor's service gear pump and is connected to the first and second cross conduits 90a and 90b at junctions 106a and 106b via a charge valve 108 which keeps the supplied pressure from surpassing the minimum operating pressure, for example 400 psi.
In addition, the control block 86 preferably further comprises a drain conduit 116 which leads oil leaked from the hydraulic motors 42 back to the reservoir.
As discussed above, the tractor 10 may come equipped with various hydraulic features 110 which are powered by the pump 84. These features are normally connected directly to the pump 84 via a conduit 112, however given that the pump pressure is also used to steer the tractor 10, this conduit 112 is preferably disconnected and a priority valve assembly 114 is provided between the pump 84 and the hydraulically-actuated features 110. As such, it can be ensured that sufficient pressure is first and foremost distributed to the power steering unit 70 and that the activation of one of the features 110, accidental or otherwise, will not compromise the driver's ability to steer.
As being now better appreciated, the present invention is an improvement and presents several advantages over other related devices and/or methods known in the prior art. In particular, it will be appreciated that a steering system in accordance with the present invention, or indeed an attachment comprising such a steering system, advantageously enables the steering of a tracked vehicle by providing additional motive power to one or the other of the left and right tracks, rather than taking away motive power via braking or displacing a plow disposed therebehind.
In addition, for driving a tracked vehicle forwards or backwards it has been found that conveying motive power from a conventional motor, such as a diesel engine, to the tracks by hydraulic motors alone is not as efficient as conveying that power via a mechanical transmission. A steering system in accordance with the present invention can advantageously combine the more efficient forward/backward motive power of conventional tractor power train, while steering the left and right tracks by independent hydraulic control.
Of course, numerous modifications could be made to the above-described embodiments without departing from the scope of the invention, as apparent to a person skilled in the art.
