Threshold current control system for hydraulic valves

• US 6,058,343 A
• Filed: 05/06/1998
• Issued: 05/02/2000
• Est. Priority Date: 07/25/1996
• Status: Expired due to Term

• Current Assignee: Blue Leaf IP Incorporated (CNH Industrial N.V.), CNH America Llc (CNH Industrial N.V.)
• Original Assignee: Case Corporation (CNH Industrial N.V.)
• Inventors: Schubert, William L., Carr, Donald D., Seymour, Steven W., Orbach, Abraham
• Primary Examiner(s): LOUIS JACQUES, JACQUES H
• Application Number:
  US09/073,590
• Time in Patent Office: 727 Days
• Field of Search: 701/50, 172/2, 172/3, 172/4, 172/4.5, 172/7, 172/8, 172/9
• US Class Current: 701/50
• CPC Class Codes: A01B 63/1006 the hydraulic or pneumatic means structurally belonging to the tractor
• CPC Class Codes: E02F 9/2029 Controlling the position of implements in function of its load, e.g. modifying the attitude of implements in accordance to vehicle speed control for hydraulic or pneumatic drives E02F9/2203, E02F9/2221 and E02F9/2253 take precedence
• CPC Class Codes: E02F 9/2203 Arrangements for controlling the attitude of actuators, e.g. speed, floating function
• CPC Class Codes: E02F 9/2207 for reducing or compensating oscillations

Abstract

A system or method for controlling the position of an implement coupled to a work vehicle. The implement is moveable by a hydraulic positioning assembly including an actuator and a valve assembly which control the flow of fluid to the actuator in response to control signals. The valve assembly includes raise and lower valves, each valve requiring a control signal equal to a threshold value before the valve opens and fluid begins to flow. The system includes a sensor to detect the position of the implement and a control circuit. In response to a change in a position command, the control circuit applies a control signal to the appropriate raise or lower valve based upon the respective threshold value. The control signal may include a component for moving the implement at a desired rate of movement. After undesirable implement movement is detected, the control circuit modifies the threshold value. The modification may occur when the control circuit detects that the implement is moving at an excessive rate due to the effects of valve hysteresis and implement weight. The control circuit may detect the undesirable movement by determining that the position error value is more negative than a predetermined value. The modified threshold value then replaces the threshold value for subsequent implement movement. The new threshold value prevents the undesirable movement in subsequent implement movement.

Claims

1. A system for controlling the position of an implement coupled to a work vehicle, the implement being moveable by a hydraulic positioning assembly comprising an actuator and a valve assembly configured to control the flow of fluid to and from the actuator in response to control signals, the valve assembly requiring control signals substantially equal to a first threshold value before fluid begins to flow, the system comprising:

a sensor configured to detect the position of the implement and to generate a signal representative thereof;

a control circuit coupled to the sensor and the valve assembly, the control circuit configured to generate the control signals applied to the valve assembly based upon the first threshold value in response to a change in a position command signal and, after detecting undesirable implement movement based at least upon the sensed position signal, to generate the control signals based upon a modified threshold value; and

a memory circuit coupled to the control circuit, the memory storing the modified threshold value and wherein the control circuit uses the modified threshold value as the first threshold value for subsequent valve actuation.

2. The system of claim 1 wherein the valve assembly comprises a lower valve, and the control signals include a lower control signal applied to the lower valve.

3. The system of claim 1 wherein the valve assembly comprises a raise valve and the control signals include a raise control signal applied to the raise valve.

4. The system of claim 1 wherein the control signals are pulse-width-modulated signals and the rate of movement of the actuator is proportional to the duty cycle of the control signals.

5. The system of claim 1 wherein, when the control signals are based upon the first threshold value, the control circuit is configured to generate the control signals to include a component representing a desired rate of movement of the actuator.

6. The system of claim 5 further comprising an operator-adjustable rate of movement device configured to generate signals representing the desired rate of movement.

7. The system of claim 1 wherein the control circuit is configured to modify the threshold value upon detecting an excessive rate of implement movement.

8. The system of claim 1 wherein the control circuit is configured to determine an error value based upon the difference between the sensed position signal and the position command signal, and to detect undesirable implement movement when the error value becomes more negative than a predetermined value.

9. The system of claim 8 wherein the control circuit decreases the modified threshold value until the magnitude of the error value is no longer increasing.

10. The system of claim 9 wherein the control circuit decreases the modified threshold value until the error value becomes less than a predetermined value.

11. The system of claim 10, wherein the predetermined value is twice the deadband value of the actuator.

12. The system of claim 1 wherein the control circuit, after detecting undesirable implement movement, decreases the threshold value until a change in the derivative of the sensed position signal is detected.

13. The system of claim 1 wherein the control circuit is configured to determine the position of the implement based on the sensed position signal and to detect undesirable implement movement when the position of the implement is greater than an upper limit.

14. The system of claim 13 wherein the control circuit is configured to decrease the threshold value by a predetermined value.

15. The system of claim 1 wherein, when the control signals are based upon the modified threshold value, the control circuit is configured to generate the control signals to substantially equal the modified threshold value.

16. The system of claim 1 wherein the memory stores the first threshold value.

17. The system of claim 1 wherein the first threshold value is modified by a first variable to compensate for temperature error.

18. The system of claim 17 wherein the control circuit determines a modified variable to compensate for temperature error for the modified threshold, and wherein the modified threshold value is modified by the modified variable to compensate for temperature error.

19. The system of claim 16 wherein a different implement is coupled to the hydraulic positioning assembly and the control circuit reads the stored first threshold value from memory for generating control signals for actuating the different implement.

20. A method for controlling the position of an implement coupled to a work vehicle, the implement being moveable by a hydraulic positioning assembly comprising an actuator and a valve assembly configured to control the flow of fluid to and from the actuator in response to control signals, the valve assembly requiring control signals substantially equal to a first threshold value before fluid begins to flow, the method comprising the steps of:

(a) generating the control signals applied to the valve assembly based upon the first threshold value in response to a change in a commanded position;

(b) detecting undesirable implement movement;

(c) upon detecting undesirable implement movement, modifying the threshold value used to generate the control signal until control is achieved; and

(d) replacing the first threshold value with the modified threshold value for generating subsequent control signals.

21. The method of claim 20 wherein the valve assembly comprises a lower valve, and the control signals include a lower control signal applied to the lower valve.

22. The method of claim 20 wherein the valve assembly comprises a raise valve and the control signals include a raise control signal applied to the raise valve.

23. The method of claim 20 wherein, in step (a), the control signal includes a component representing a desired rate of movement of the actuator.

24. The method of claim 20 wherein, in step (b), undesirable implement movement is detected when an error value determined based upon the difference between a sensed position signal and the commanded position becomes more negative than a predetermined value.

25. The method of claim 20 wherein step (b) further comprises the steps of determining a rate of implement movement based upon changes in a sensed position signal and comparing the rate of implement movement to a predicted rate, wherein undesirable implement movement is detected based upon a predetermined relationship therebetween.

26. The method of claim 25 further comprising the step of modifying the threshold value until the sensed position signal and the commanded position becomes less negative than a predetermined value.

27. The method of claim 20 wherein step (b) further comprises the steps of determining the position of the implement based on a sensed position signal and detecting undesirable implement movement when the position of the implement is greater than an upper limit.

28. The method of claim 27 further comprising the step of modifying the threshold value by subtracting a preselected value when an undesirable implement movement is detected.

29. The method of claim 20 wherein, in step (c), the control signal substantially equals the modified threshold value.

30. The method of claim 20 further comprising the step of storing the first threshold value.