Patent Application
20090032314
This disclosure relates generally to a drive system for a machine, and more particularly, to a drive system for a skid steer loader.
Skid steer loaders are highly maneuverable compact machines used in a variety of applications ranging from asphalt milling to earth moving, depending on the job and type of attachment being utilized. Skid steer loaders achieve this maneuverability through a differential transmission system, which allows an operator to separately control the speed of the wheels or track on each side of the machine. Typically, two drives are used to drive the skid steer loader—one drive for the left side and another for the right side. For wheeled machines, balancing the weight ratio between the front and rear axles during loaded and unloaded conditions enhances maneuverability. Balancing the weight ratio is accomplished, in part, by positioning the engine at the rear of the machine and the load or attachment being carried at the front.
When carrying a heavy load, a skid steer loader's combined center of gravity shifts to the front of the machine, resulting in an increased load and a higher normal force on the front axle. As a result, typical drive systems for skid steer loaders anticipate greater loads on the front axle than on the rear axle. An example of this can be seen in U.S. Pat. No. 4,131,225 to Bauer et al. and entitled “Method of Making a Vehicle Transmission Case” (“the '225 patent”). The '225 patent discloses a transmission having a pair of hydraulic motors that each have an output shaft having an inner and outer drive sprocket. A first endless chain connects the inner drive sprocket to the front wheel sprocket, while a second endless chain connects the outer drive sprocket to the rear wheel sprocket.
This configuration may work adequately for smaller machines. However, as a machine size increases, machines having drive systems as described in the '225 patent may be subjected to increased drive system failures. The present disclosure is directed to overcome one or more of the problems as set forth above.
In one aspect of the present disclosure, a machine is provided. The machine has a frame, an implement attached to a front end, a power source, a first and a second drive motor, a left front and rear axle, and a right front and rear axle. The first and second drive motors are powered by the power source, and each of the first and second drive motors has an inner and an outer sprocket. The left rear axle is coupled to the inner sprocket of the first drive motor and rotatably coupled to the frame. The left front axle is coupled to the outer sprocket of the first drive motor and rotatably coupled to the frame. The right rear axle is coupled to the inner sprocket of the second drive motor and rotatably coupled to the frame. The right front axle is coupled to the outer sprocket of the second drive motor and rotatably coupled to the frame.
In another aspect of the present disclosure, a drive system for a skid steer loader having a frame and a power source, is provided. The drive system has a first and a second drive motor powered by the power source, and each of the first and second drive motors has an inner and an outer sprocket. The left rear axle is coupled to the inner sprocket of the first drive motor and rotatably coupled to the frame. The left front axle is coupled to the outer sprocket of the first drive motor and rotatably coupled to the frame. The right rear axle is coupled to the inner sprocket of the second drive motor and rotatably coupled to the frame. The right front axle is coupled to the outer sprocket of the second drive motor and rotatably coupled to the frame.
In a third aspect of the present disclosure, a method of providing a drive system for a machine having a power source is provided. The method includes the step of powering a first and a second drive motor by the power source, wherein each of the first and second drive motors has an inner and an outer sprocket. The method also includes the step of operably coupling a left rear axle to the inner sprocket of the first drive motor. The method also includes the step of operably coupling a left front axle to the outer sprocket of the first drive motor. The method also includes the step of operably coupling a right rear axle to the inner sprocket of the second drive motor. The method also includes the step of operably coupling a right front axle to the outer sprocket of the second drive motor.
A machine 6 such as a skid steer loader 10 in accordance with the present disclosure is illustrated in
As seen in
The drive system 50 shown in
Referring back to
During operation of the machine 6, an operator (not shown) can independently control the speed and direction of the left and right wheels 30 to control the speed and direction of the machine 6. The engine 40 supplies power to the variable displacement pumps 52 of the drive system 50, which supply pressurized hydraulic fluid to the drive motors 60, 70 through supply lines 53. The drive motors 60,70 provide an output torque through output shafts 62, 72. The inner sprockets 64, 74 transmit the torque to rear wheel sprockets 38 through endless drive chains 54, while the outer sprockets 66, 76 transmit the torque to front wheel sprockets 36 through endless drive chains 56. This torque is transmitted from wheel sprockets 36, 38 to wheels 30, controlling the speed and direction of the machine 6.
This configuration of drive system 50 allows for the drive motors 60, 70 to be properly supported. The drive motors 60, 70 each have a bearing pack which must support the radial load generated by the chains that transfer the drive motor power to the axles 32, 34. The inner sprockets 64, 74, positioned closest to the bearing packs, are coupled to the rear wheel sprockets 38 because the rear wheels—not the front wheels, see the greatest loads.
The rear wheels and axles see greater loads than the front wheels and axles because as machine sizes increase, the combined center of gravity of the machine and load shifts backwards. As a result, a larger machine is less likely to have its rear wheels lifted off of the ground. Moreover, applications such as grading or back dragging, where the work tool is in contact with the ground and pressure is applied through the work tool, also raise the front of the machine and may lift the front tires off of the ground.
Further, when the machine is under certain load conditions, such as applications to pry, doze or lift material, the machine experiences high vertical loads at the work tool. These loads may compress the front tires of the machine so that the effective rolling radius of the front tires is smaller than the effective rolling radius of the rear tires. The tires having the largest effective rolling radius or the tires that remain in contact with the ground will drive the machine. Therefore, the components powering these tires experience the greatest loads. Because skid steer loaders are frequently equipped with solid or polyfill tires and are commonly used in rental applications involving relatively unskilled operators, relying on increased front tire pressures is not practical.
While the disclosure has been described with reference to details of the illustrated embodiments, these details are not intended to limit the scope of the disclosure as defined in the appended claims. For example, the drive motors have been described as hydraulic motors. However, it may be desired to substitute electric motors for the hydraulic motors described above. In such a case, the engine may be used to power a generator, which powers the motors. As described above, other power sources may be substituted for the engine, as well. Further, drive belts may be substituted for the endless chains. Other aspects, objects and advantages of this disclosure can be obtained from a study of the drawings, the disclosure, and the appended claims.
