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An apparatus is disclosed for controlling the propulsion and steering of a machine. The machine includes a hydrostatic system that drives a pair of ground engaging traction devices. An electronic controller receives operator signals indicative of a desired travel speed and direction, and determines

An apparatus is disclosed for controlling the propulsion and steering of a machine. The machine includes a hydrostatic system that drives a pair of ground engaging traction devices. An electronic controller receives operator signals indicative of a desired travel speed and direction, and determines a desired rotational speed of the ground engaging traction devices. The electronic controller produces command signals indicative of the determined speeds to regulate the speed of the ground engaging traction devices to the desired speed.

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1. An apparatus for controlling the propulsion of a machine having a hydrostatic system that drives a plurality of ground engaging traction devices, comprising:means for producing a desired travel speed signal indicative of a desired speed of machine travel;means for producing a steering angle signa

1. An apparatus for controlling the propulsion of a machine having a hydrostatic system that drives a plurality of ground engaging traction devices, comprising:means for producing a desired travel speed signal indicative of a desired speed of machine travel;means for producing a steering angle signal indicative of a desired steering angle of the machine travel;means for receiving the desired travel speed and steering angle signals, determining a desired rotational speed of the ground engaging traction devices to steer the machine at the desired steering angle, and producing command signals indicative of the desired rotational speeds; andmeans for receiving the command signals and responsively controlling the speed of the ground engaging traction devices to the desired speed to cause the machine to steer at a desired turning radius that is independent to the actual speed of travel. 2. An apparatus, as set forth in claim 1, including means for determining the desired turning radius of the machine, the means including a plurality of software maps, each map being comprised of several programmable curves corresponding to varying speed ranges, wherein each curve represents the desired turning radius as a function of the desired strength angle. 3. An apparatus, as set forth in claim 1, wherein the hydrostatic drive system includes:a plurality of hydraulic motors for driving a respective ground engaging traction device;a plurality of variable displacement pumps for delivering pressurized fluid to the hydraulic motors in response to receiving command signals; andan internal combustion engine for driving the variable displacement pumps. 4. An apparatus, as set forth in claim 3, including:a plurality of spring applied brakes to stop the ground engaging traction devices; anda brake pedal to conduit the travel speed of the machine, wherein the amount of depression of the brake pedal is proportional to the attenuation of the speed of travel. 5. An apparatus, as set forth in claim 4, including means for controlling the pump displacement to slow the machine in response to the depression of the brake pedal and controlling the application of brakes to hold the machine in place in response to the machine being stopped. 6. An apparatus, as set forth in claim 3, including means for controlling the displacement of each pump to limit the total horsepower drawn by the pumps to less than the available engine horsepower. 7. An apparatus, as set forth in claim 3, including means for automatically calibrating the magnitude of the command signals to correspond to a calibration track speed. 8. An apparatus, as set forth in claim 3, wherein the ground engaging traction devices include a pair of endless belts. 9. A method of controlling the propulsion of a machine having a plurality of ground engaging traction devices, comprising the steps of:producing a desired travel speed signal indicative of a desired speed of machine travel;producing a steering angle signal indicative of a desired steering angle of the machine travel;receiving the desired travel speed and steering angle signals, determining a desired rotational speed of the ground engaging traction devices to steer the machine at the desired steering angle, and producing command signals indicative of the rotation speeds; andreceiving the command signals and responsively controlling the speed of the ground engaging devices to the desired speed to cause the machine to steer at a desired turning radius that is independent to the actual speed of travel. 10. A method, as set forth in claim 9, including steps of:storing a plurality of software maps, each map being comprised of several programmable curves corresponding to varying speed ranges, wherein each curve represents the desired turning radius as a function of the desired steering angle; andselecting a curve and producing a desired turning radius signal in response to the desired steering angle. 11. A method, as set forth in claim 10, including the step s of:producing a maximum speed signal indicative of a maximum travel speed;producing a propel signal indicative of a desired percentage of maximum travel speed and direction of travel;producing a braking signal indicative of a desired attenuation of the machine travel speed; andreceiving the maximum, propel, braking and desired turning radius signals, and responsively producing the desired travel speed signal. 12. A method, as set forth in claim 11, wherein the desired rotational speed of the ground engaging traction devices are calculated as follows: outer =V desired (2−2R/G+2R) inner =V outer (R/R+G)where:V desired =the desired machine travel speed;R=the desired turning radius; andG=the gage of the machine. 13. A method, as set forth in claim 12, including the step of modifying the desired rotational speeds in response to the calculated inner rotational speed being less than a minimum limit. 14. A method, as set forth in claim 13, including the step of modifying the desired rotational speeds in response to the calculated outer rotational speed being greater than a maximum limit. 15. A method, as set forth in claim 14, including the step of monitoring the speed of the ground engaging traction devices and producing signals indicative of the actual speed of the ground engaging devices. 16. A method, as set forth in claim 15, including the step of modifying the maximum limit in response to the actual rotational speed being less than the desired rotational speed. 17. A method, as set forth in claim 16, including the steps of receiving the desired and actual speed signals, comparing the signals to each other, and adjusting the magnitude of the command signals in response to the comparison. 18. A method, as set forth in claim 17, including the step of adjusting the speed of the ground engaging traction devices to provide for the machine to track straight. 19. A method for controlling the propulsion of a machine having a plurality of ground engaging traction devices, comprising: determining a desired travel speed of the machine; determining a desired steering angle of the machine; determining a respective desired rotational speeds for the ground engaging traction devices to steer the machine at a predetermined turn radius, the predetermined turn radius being a function of the desired steering angle and independent to the actual travel speed of the machine, and the desired rotational speeds being a function of the desired travel speed and the desired steering angle; and controlling the rotational speeds of the ground engaging traction devices to the desired rotational speeds to cause the machine to steer at the predetermined radius. 20. The method of claim 19 wherein determining the rotational speeds for the ground engaging traction devices comprises determining the rotational speeds for the ground engaging traction devices to steer the machine at a predetermined turn radius over a predetermined range of travel speeds. 21. The method of claim 19, further comprising determining a speed range of the machine, the desired rotational speeds of the ground engaging traction devices further being a function of the speed range. 22. The method of claim 19 wherein the ground engaging traction devices comprise tracks. 23. The method of claim 19 wherein the ground engaging traction devices comprise belts. 24. A method for controlling the propulsion of a machine having a plurality of ground engaging traction devices, comprising: determining a desired travel speed of the machine; determining a desired steering angle of the machine; determining a difference in the respective desired rotational speeds for the ground engaging traction devices to steer the machine at a predetermined turn radius, the predetermined turn radius being a function of the desired steering angle and independent to the actual travel speed of the machine, and the difference in the desired rotational speeds being a function of the desired travel speed and the desired steering angle; and controlling the rotational speeds of the ground engaging traction devices to have the difference in the desired rotational speeds to cause the machine to steer at the predetermined radius. 25. The method of claim 24 wherein determining a difference in the rotational speeds for the ground engaging traction devices comprises determining a difference in the rotational speeds for the ground engaging traction devices to steer the machine at a predetermined turn radius over a predetermined range of travel speeds. 26. The method of claim 24, further comprising determining a speed range of the machine, the difference in the desired rotational speeds of the ground engaging traction devices further being a function of the speed range. 27. The method of claim 24 wherein the ground engaging traction devices comprise tracks. 28. The method of claim 24 wherein the ground engaging traction devices comprise belts. 29. A method for controlling the propulsion of a machine having a plurality of ground engaging traction devices, comprising: determining a desired travel speed of the machine; determining a desired steering angle of the machine; determining respective desired rotational speeds for the ground engaging traction devices to steer the machine at a predetermined turn radius, the predetermined turn radius being one of: a function of the desired steering angle and independent to the actual travel speed of the machine when the machine is traveling between a first and second predetermined travel speeds, and a function of the desired steering angle and the actual travel speed of the machine when the machine is traveling between a third and fourth predetermined travel speeds, and the desired rotational speeds being a function of the desired travel speed and the desired steering angle; and controlling the rotational speeds of the ground engaging traction devices to the desired rotational speeds to cause the machine to steer at the predetermined radius. 30. The method of claim 29 wherein the ground engaging traction devices comprise tracks. 31. The method of claim 29 wherein the ground engaging traction devices comprise belts. 32. A method for controlling the propulsion of a machine having an operating speed range and a plurality of ground engaging traction devices, comprising: determining a desired travel speed of the machine; determining a desired steering angle of the machine; determining respective desired rotational speeds for the ground engaging traction devices to steer the machine at a predetermined turn radius, the predetermined turn radius being a function of the desired steering angle and independent to the actual travel speed of the machine for at least a portion of the operating speed range of the machine, and the desired rotational speeds being a function of the desired travel speed and the desired steering angle; and controlling the rotational speeds of the ground engaging traction devices to the desired rotational speeds to cause the machine to steer at the predetermined radius.