Differential lock control in articulated work machine

• US 20070250236A1
• Filed: 04/20/2006
• Published: 10/25/2007
• Est. Priority Date: 04/20/2006
• Status: Active Grant

• Current Assignee: Caterpillar Incorporated
• Original Assignee: Caterpillar Incorporated
• Inventors: Gharsalli, Imed, Newberry, Phillip
• Granted Patent: US 7,766,104 B2
• Time in Patent Office: Days
• US Class Current: 701/51
• CPC Class Codes: B60K 23/04 for differential gearing
• CPC Class Codes: B60K 28/16 responsive to, or preventing, skidding of wheels brake control systems for vehicle drive stability B60T8/1755; arrangements responsive to a speed condition for adjusting wheel braking force B60T8/32; control of vehicle driving stability otherwise than by controlling the propulsion unit only B60W30/02; preventing wheel slippage by reducing power in rail vehicles B61C15/00
• CPC Class Codes: B60K 28/165 acting on elements of the vehicle drive train other than the propulsion unit and brakes, e.g. transmission, clutch, differential acting on brakes B60T8/17
• CPC Class Codes: B60W 2520/26 Wheel slip
• CPC Class Codes: B60W 2540/18 Steering angle
• CPC Class Codes: B60Y 2200/411 Bulldozers, Graders
• CPC Class Codes: E02F 3/841 Devices for controlling and guiding the whole machine, e.g. by feeler elements and reference lines placed exteriorly of the machine construction of roads E01C19/008
• CPC Class Codes: E02F 9/2045 Guiding machines along a predetermined path for graders E02F3/841; machines for construction of roads E01C19/004

Abstract

A method of operating an articulated work machine includes sensing an articulation angle in a wheel steering angle of the work machine, and controlling a locking state of a differential responsive to a steering radius of the work machine. An articulated frame wheeled work machine is further provided, and includes a front frame unit with a wheel steering apparatus, a back frame unit and an articulation apparatus coupled between the front and back frame units. First and second sensors are operable to sense a wheel steering angle and an articulation angle of the work machine, and an electronic control is provided which is configured to selectively lock or unlock a differential of the back frame unit responsive to a steering radius of the work machine.

Claims

1. A method of operating an articulated work machine comprising the steps of:

determining a value indicative of an articulation angle of the work machine;

determining another value indicative of a wheel steering angle of the work machine that is separate from the articulation angle; and

controlling a locking state of a differential of the work machine responsive to a steering radius thereof.

2. The method of claim 1 further comprising the step of determining a minimum steering radius for a locked differential state, wherein the step of controlling a locking state of the differential comprises commanding unlocking of the differential responsive to the steering radius being less than or equal to the minimum steering radius.

3. The method of claim 2 comprising the step of operating the work machine with the differential in a default locked state.

4. The method of claim 2 further comprising the step of sensing a ground speed of the work machine, wherein:

the step of determining a value indicative of an articulation angle includes sensing an articulation angle between front and back frame units of the work machine;

the step of determining a value indicative of a wheel steering angle includes sensing a wheel steering angle between front wheels of the work machine and a portion of the front frame unit; and

controlling a locking state of the differential includes controlling the locking state responsive to the sensed ground speed.

5. The method of claim 4 further comprising the step of determining a rollover stability condition of the work machine based at least in part on sensed ground speed and sensed articulation and wheel steering angles, wherein the step of determining a minimum steering radius for a locked differential state includes determining a minimum steering radius that is based at least in part on the determined rollover stability condition.

6. The method of claim 4 further comprising the step of determining indicia of stress on the work machine, wherein the step of determining a minimum steering radius for a locked differential state includes determining a minimum steering radius that is based at least in part on the determined indicia of stress.

7. The method of claim 6 wherein the step of determining indicia of stress on the work machine comprises a step of sensing at least one operating parameter indicative of a stress condition of the work machine.

8. The method of claim 7 wherein the step of sensing at least one operating parameter indicative of a stress condition of the work machine includes sensing an operating parameter indicative of powertrain stress of the work machine.

9. The method of claim 6 wherein sensing at least one operating parameter indicative of powertrain stress includes sensing at least one operating parameter indicative of torque through at least a portion of the powertrain of the work machine.

10. The method of claim 7 wherein the step of sensing at least one operating parameter indicative of a stress condition of the work machine includes sensing at least one operating parameter indicative of frame stress on the work machine.

11. The method of claim 6 wherein determining indicia of stress on the work machine includes mapping at least one set of operating parameter values associated with a stress condition of the work machine to minimum steering radii.

12. The method of claim 11 further comprising the step of determining a wheel slip condition of the work machine, wherein the step of controlling a locking state of the differential comprises commanding locking of the differential responsive to the determined wheel slip condition, unless a locking unsuitability condition exists.

13. The method of claim 12 further comprising the step of receiving an operator requested differential locking control signal, wherein the step of controlling a locking state of the differential comprises overriding the control signal, if a locking unsuitability condition is present, including at least one of a frame stress condition, a powertrain stress condition, a steering radius condition and a rollover stability condition.

14. An articulated work machine comprising:

a front frame unit including a wheel steering apparatus operable to steer the work machine;

a back frame unit coupled with the front frame unit and including a lockable differential;

an articulation apparatus coupled between the front and back frame units and also operable to steer the work machine; and

an electronic controller configured to control at least one of locking and unlocking of the differential responsive to a steering radius of the work machine.

15. The work machine of claim 14 wherein said electronic controller is configured to determine indicia of stress on said work machine, and to determine a minimum steering radius based at least in part thereon, said electronic controller further being configured to generate a differential unlocking control signal to said differential where the determined steering radius is less than or equal to the minimum steering radius.

16. The work machine of claim 15 wherein said electronic controller is further configured to determine the minimum steering radius at least in part via a map having a first coordinate associated with an operating parameter of said work machine, a second coordinate associated with at least one stress condition of said work machine and a third coordinate associated with minimum steering radii for said work machine.

17. The work machine of claim 15 further comprising:

a wheel steering sensor and an articulation sensor coupled with said electronic controller and configured to sense a wheel steering angle and an articulation angle, respectively, of said work machine; and

a ground speed sensor and a transmission gear sensor, each coupled with said electronic controller;

wherein said electronic controller is configured to determine a steering radius of said work machine via inputs from said wheel steering and articulation sensors, and configured to determine said indicia of stress on said work machine at least in part via inputs from said wheel steering sensor, said articulation sensor, said ground speed sensor and said transmission gear sensor.

18. The work machine of claim 17 further comprising a wheel slip sensor coupled with said electronic controller, wherein said electronic controller is configured to generate a differential locking command to said differential unless a locking unsuitability condition corresponding with said indicia of stress is satisfied.

19. An electronic controller configured to control a locking state of a differential in an articulated work machine responsively to a comparison of a steering radius of the work machine with a minimum steering radius that is based at least in part on stress indicia associated with at least one work machine operating parameter.

20. The electronic controller of claim 19 wherein the at least one work machine operating parameter includes a range of possible parameter values, said electronic controller further being configured to vary the minimum steering radius responsive to a value of said work machine operating parameter.