Vehicle with control system for raising and lowering implement

• US 4,518,044 A
• Filed: 03/22/1982
• Issued: 05/21/1985
• Est. Priority Date: 03/22/1982
• Status: Expired due to Term

• Current Assignee: Deere & Company
• Original Assignee: Deere & Company
• Inventors: Wiegardt, Gordon K., Kittle, Carl E., Hanks, Thomas W.
• Primary Examiner(s): Stouffer, Richard T.
• Application Number:
  US06/360,748
• Time in Patent Office: 1,156 Days
• Field of Search: 172/2, 172/3, 172/4, 172/4.5, 172/7, 172/8, 172/9, 172/10, 172/11, 172/12, 37/DIG. 1, 180/197, 340/517, 340/519, 340/521, 340/522, 340/527, 340/529, 340/530, 364/433, 364/424, 318/587, 318/590, 318/611, 318/632, 318/633, 318/636, 318/646
• US Class Current: 172/7
• CPC Class Codes: A01B 63/1117 using a hitch position sensor
• CPC Class Codes: A01B 67/00 Devices for controlling the tractor motor by resistance of tools preventing overstrain A01B61/00

Abstract

A tractor includes a hitch for pulling a ground-engaging implement. A hydraulic cylinder is extendable and retractable to lower and raise the implement. A control system senses operating parameters, including wheel slip, engine speed, draft force and implement or rackshaft position. Error signals derived from the sensed wheel slip, engine speed and draft force are combined into a composite or combined error signal. The larger of the combined error signal, or a separately determined position error signal, is selected and converted to a pulsewidth modulated valve control signal which is applied to a control valve which then actuates the cylinder to move the implement to reduce the magnitude of the selected error signal.

Claims

1. In a vehicle having connecting means for attaching a ground-penetrating implement thereto and actuating means for raising and lowering the implement to vary the ground penetration thereof in response to signals applied to an input thereof:

sensing means for sensing an operating parameter of a machine system comprising the vehicle, the connecting means and the implement, and for generating a parameter signal representative thereof;

set point means for deriving a parameter set point signal from the parameter signal;

difference means for generating a parameter error signal representing a difference between the parameter signal and the parameter set point signal; and

means for converting the parameter error signal to a control signal and for applying the control signal to the input of the actuating means, the actuating means being adapted to move the implement in response to the control signal.

2. The control system of claim 1, further comprising:

operator-adjustable command means for generating a command signal representing a desired magnitude of a further operating parameter of the machine system; and

means for momentarily modifying the parameter error signal in response to a predetermined operator-induced change in the command signal.

3. The control system of claim 1, further comprising:

operator-adjustable command means for generating a command signal representing a desired magnitude of a further operating parameter of the machine system; and

means for redetermining the parameter set point signal from a filtered signal generated a predetermined delay time period after occurance of said predetermined change in the command signal.

4. The control system of claim 3, wherein:

the duration of the delay time period is a function of the magnitude of the change in the command signal.

5. In a vehicle having connecting means for attaching a ground-penetrating implement thereto and actuating means for raising and lowering the implement to vary the ground penetration thereof in response to signals applied to an input thereof, a control system comprising

means for generating a parameter error signal representing a difference between a sensed value of an operating parameter of a machine system comprising the vehicle, the connecting means and the implement and a reference value of said parameter;

operator-adjustable command means for generating a command signal representing a desired magnitude of a further operating parameter of the machine system;

means for momentarily modifying the parameter error signal in response to a predetermined operator-induced change in the command signal;

means for redetermining the reference value a predetermined time period after occurance of said predetermined change in the command signal; and

means for converting at least the parameter error signal to a control signal and for applying the control signal to the input of the actuating means, the actuating means being adapted to move the implement in response to the control signal.

6. In a vehicle having a driven wheel, connecting means for attaching a ground-penetrating implement thereto and actuating means for raising and lowering the implement to vary the ground penetration thereof in response to signals applied to an input thereof, a control system comprising:

means for generating at least one parameter signal derived from at least one sensed operating parameter of a machine system comprising the vehicle, the connecting means and the implement;

operator-adjustable command means for generating a command signal representing a desired magnitude of a further operating parameter of the machine system;

means for generating a position feedback signal derived from a sensed position of the implement and from a reference position value;

means for redetermining the reference position value in response to changes in the command signal,

means for generating a combined signal derived by combining at least the parameter signal and the position signal; and

means for applying the combined signal to the input of the actuating means, the actuating means being adapted to move the implement in response to the combined signal.

7. In a vehicle having a driven wheel, connecting means for attaching a ground-penetrating implement thereto and actuating means for raising and lowering the implement to vary the ground penetration thereof in response to signals applied to an input thereof, a control system comprising:

means for generating a parameter signal derived from at least one sensed operating parameter of a machine system comprising the vehicle, the connecting means and the implement;

means for generating a position signal representing an actual position of the implement;

means for generating a filtered position signal derived by filtering the position signal;

means for storing a selected filtered position signal;

means for generating a normalized feedback value representing a difference between the position signal and the stored filtered position value;

means for generating a combined signal derived by combining at least the parameter signal and the normalized feedback values, and

means for applying the combined signal to the input of the actuating means, the actuating means being adapted to move the implement in response to the combined signal.

8. In a vehicle having connecting means for attaching a ground-penetrating implement thereto and actuating means for raising and lowering the implement to vary the ground penetration thereof in response to signals applied to an input thereof, a control system comprising:

a first parameter means for generating a first parameter error signal derived from at least one sensed operating parameter of a machine system comprising the vehicle, the connecting means and the implement;

a second parameter means for generating a second parameter error signal derived from at least another sensed operating parameter of the machine system;

selection means comaring the first and second parameter error signals with each other and for automatically selecting one of the first and second parameter error signals when a predetermined relationship therebetween occurs;

first and second operator-detectable indicators;

means for energizing the first indicator when the first parameter error signal is selected and for energizing the second indicator when the second parameter error signal is selected;

threshold means operable when the selected signal is changing from one to the other of the parameter error signals for preventing changes in energization of the indicator devices unless the magnitude of the other parameter error signal exceeds a predetermined threshold level; and

means for applying the selected signal to the input of the actuating means, the actuating means being adapted to move the implement in response to the selected signal.

9. In a vehicle having an engine, connecting means for attaching a ground-penetrating implement thereto and actuating means for raising and lowering the implement to vary the ground penetration thereof in response to signals applied to an input thereof, a control system comprising:

means for generating a first error signal derived from an engine speed error signal repesenting a difference between a sensed and a desired engine speed;

position means for generating a position error signal with a magnitude proportional to a difference between an actual and a desired position of the implement;

selecting means comparing the first error and the position error signals with each other and for automatically selecting one of the first error and position error signals when a predetermined relationship therebetween occurs; and

means for applying the selected error signal to the input of the actuating means, the actuating means being adapted to move the implement in response to the selected error signal.

10. In a vehicle having a driven wheel, connecting means for attaching a ground-penetrating implement thereto and actuating means for raising and lowering the implement to vary the ground penetration thereof in response to signals applied to an input thereof, a control system comprising:

wheel slip means for generating a slip error signal indicative of the amount of slippage of the driven wheel;

parameter means for generating a parameter signal derived from a sensed operating parameter other than wheel slippage in a machine system comprising the vehicle, the connecting means and the implement;

selection means for comparing the slip error and parameter signals with each other and for automatically selecting one of the slip error and parameter signals when a predetermined relationship therebetween occurs; and

means for applying the selected signal to the input of the actuating means, the actuating means being adapted to move the implement in response to the selected signal.

11. In a vehicle having a driven wheel, connecting means for attaching a ground-penetrating implement thereto and actuating means for raising and lowering the implement to vary the ground penetration thereof in response to signals applied to an input thereof, a control system comprising:

wheel slip means for generating a slip error signal indicative of the amount of slippage of the driven wheel;

position means for generating a position error signal with a magnitude proportional to a difference between an actual and a desired position of the implement;

selecting means for comparing the slip error and position error signals with each other and for selecting one of the slip error and position error signals when a predetermined relationship therebetween occurs; and

means for applying the selected error signal to the input of the actuating means, the actuating means being adapted to move the implement in response to the selected error signal.

12. In a vehicle having connecting means for attaching a ground-penetrating implement thereto and actuating means for raising and lowering the implement to vary the ground penetration thereof in response to signals applied to an input thereof, a control system comprising:

first, second and third parameter means for generating first, second and third parameter signals, each derived from a separate sensed operating parameter of a machine system comprising the vehicle, the connecting means and the implement;

means for generating a combined signal derived by combining the first and second parameter signals;

selection means for comparing the magnitude of the combined signal with the magnitude of the third signal and for automatically selecting one of the combined and third signals when a predetermined relationship between the magnitudes thereof occurs; and

means for applying the selected signal to the input of the actuating means, the actuating means being adapted to move the implement in response to the selected signal.

13. In a vehicle having an engine, a driven wheel, connecting means for attaching a ground-penetrating implement thereto, and actuating means for raising and lowering the implement to vary the ground penetration thereof in response to signals applied to an input thereof, a control system comprising:

draft means for generating a draft error signal derived from a sensed draft force produced by interaction between the implement and the ground and from a reference draft force;

engine speed means for generating an engine speed error signal indicative of a difference between a sensed and a desired engine speed;

position means for generating a position error signal with a magnitude proportional to a difference between an actual and a desired position of the implement;

signal combining means for generating a combined signal derived by combining the draft error and engine speed error signals;

selecting means for selecting one of the combined error and position error signals when a predetermined relationship therebetween occurs; and

means for applying the selected error signal to the input of the actuating means, the actuating means being adapted to move the implement in response to the selected error signal.

14. In a vehicle having a driven wheel, connecting means for attaching a ground-penetrating implement thereto and actuating means for raising and lowering the implement to vary the ground penetration thereof in response to signals applied to an input thereof, a control system comprising:

wheel slip means for generating a slip error signal indicative of the amount of slippage of the driven wheel;

draft means for generating a draft error signal derived from a sensed draft force produced by interaction between the implement and the ground and from a reference draft force;

position means for generating a position error signal with a magnitude proportional to a difference between an actual and a desired position of the implement;

signal combining means for generating a combined signal derived by combining the slip error and draft error signals;

selecting means for selecting one of the combined error and position error signals when a predetermined relationship therebetween occurs; and

means for applying the selected error signal to the input of the actuating means, the actuating means being adapted to move the implement in response to the selected error signal.

15. In a vehicle having an engine, a driven wheel, connecting means for attaching a ground-penetrating implement thereto, and actuating means for raising and lowering the implement to vary the ground penetration thereof in response to signals applied to an input thereof, a control system comprising:

wheel slip means for generating a slip error signal indicative of the amount of slippage of the driven wheel;

engine speed means for generating an engine speed error signal indicative of a difference between a sensed and a desired engine speed;

position means for generating a position error signal with a magnitude proportional to a difference between an actual and a desired position of the implement;

signal combining means for generating a combined signal derived by combining the slip error and engine speed error signals;

selecting means for selecting one of the combined error and position error signals when a predetermined relationship therebetween occurs; and

means for applying the selected error signal to the input of the actuating means, the actuating means being adapted to move the implement in response to the selected error signal.

16. In a vehicle having an engine, a driven wheel, connecting means for attaching a ground-penetrating implement thereto, and actuating means for raising and lowering the implement to vary the ground penetration thereof in response to signals applied to an input thereof, a control system comprising:

wheel slip means for generating a slip error signal indicative of the amount of slippage of the driven wheel;

draft means for generating a draft error signal derived from a sensed draft force produced by interaction between the implement and the ground and from a reference draft force;

engine speed means for generating an engine speed error signal indicative of a difference between a sensed and a desired engine speed;

position means for generating a position error signal with a magnitude proportional to a difference between an actual and a desired position of the implement;

signal combining means for generating a combined signal derived by combining the slip error, draft error and engine speed error signals;

selecting means for selecting one of the combined error and position error signals when a predetermined relationship therebetween occurs; and

means for applying the selected error signal to the input of the actuating means, the actuating means being adapted to move the implement in response to the selected error signal.

17. In a vehicle having an engine and connecting means for attaching a ground-penetrating implement thereto, a control system comprising:

implement draft force responsive means for increasing implement depth in response to decreases in sensed draft force due to decreased vehicle velocity;

means for counteracting the draft force responsive means in response to a reduced engine speed, and

means for limiting the effect of the counteracting means to an amount which is proportional to a desired amount of implement draft force.

18. In a vehicle having connecting means for attaching a ground-penetrating implement thereto and actuating means for raising and lowering the implement to vary the ground penetration thereof in response to signals applied to an input thereof, a control system comprising:

means for generating a filtered draft signal derived from periodically sampled unfiltered values of sensed draft force;

means for setting a variable gain factor to preselected values, depending upon the value of the filtered draft signal;

means for generating a control signal derived from at least the variable gain factor and the periodically sampled unfiltered draft force values; and

means for applying the control signal to the input of the actuating means, the actuating means being adapted to move the implement in response to the control signal.

19. In an engine-driven vehicle having connecting means for attaching a ground-penetrating implement thereto and actuating means for raising and lowering the implement to vary the ground penetration thereof in response to signals applied to an input thereof, a control system comprising:

engine speed means for periodically generating an engine speed error signal indicative of a difference between a sensed and a reference engine speed;

means for generating an increasing engine error signal which increases periodically and incrementally by a first increment in response to increasing engine speed error;

means for generating a decreasing engine error signal which decreases periodically and incrementally by a second increment smaller than the first increment in response to decreasing engine speed error; and

means for generating a control signal derived from at least one of the increasing and decreasing engine error signals and for applying the control signal to the input of the actuating means, the actuating means being adapted to move the implement in response thereto.

20. In a vehicle having a driven wheel, connecting means for attaching a ground-penetrating implement thereto and actuating means for raising and lowering the implement to vary the ground penetration thereof in response to signals applied to an input thereof, a control system comprising:

wheel slip means for generating a slip error signal indicative of the amount of slippage of the driven wheel;

at least one parameter means for generating at least one parameter signal derived from at least one sensed operating parameter, other than wheel slippage, of a machine system comprising the vehicle, the connecting means and the implement;

signal combining means for generating a combined signal derived by combining the slip error signal and the at least one parameter signal; and

means for applying the combined signal to the input of the actuating means, the actuating means being adapted to move the implement in response to the combined signal.

21. In a vehicle having an engine, a driven wheel, connecting means for attaching a ground-penetrating implement thereto, and actuating means for raising and lowering the implement to vary the ground penetration thereof in response to signals applied to an input thereof, a control system comprising;

first parameter means for generating a first parameter error signal having a magnitude representing a difference between sensed and desired magnitudes of a first operating parameter of a machine system comprising the vehicle, the connecting means and the implement;

second parameter means for generating a second parameter error signal having a magnitude representing a difference between sensed and desired magnitudes of a second operating parameter of the machine system;

at least a third parameter means for generating at least a third parameter error signal having a magnitude representing a difference between sensed and desired magnitudes of at least a third sensed operating parameter of the machine system;

signal combining means for generating a combined signal derived by combining at least the first, second and third parameter error signals; and

means for applying the combined signal to the input of the actuating means, the actuating means being adapted to move the implement in response to the combined signal.

22. In an engine-driven vehicle having connecting means for attaching a ground-penetrating implement thereto, and actuating means for raising and lowering the implement to vary the ground penetration thereof in response to signals applied to an input thereof, a control system comprising:

draft means for generating a draft error signal derived from a sensed draft force produced by interaction between the implement and the ground and from a reference draft force;

engine speed means for generating an engine speed error signal indicative of a difference between a sensed and a desired engine speed;

signal combining means for generating a combined signal derived by combining the draft error and engine speed error signals; and

means for applying the combined signal to the input of the actuating means, the actuating means being adapted to move the implement in response to the combined signal.

23. In a vehicle having a driven wheel, connecting means for attaching a ground-penetrating implement thereto and actuating means for raising and lowering the implement to vary the ground penetration thereof in response to signals applied to an input thereof, a control system comprising:

wheel slip means for generating a slip error signal indicative of the amount of slippage of the driven wheel;

draft means for generating a draft signal derived from at least a sensed draft force produced by interaction between the implement and the ground;

signal combining means for generating a combined signal derived by arithmetically combining the slip error signal with the draft signal; and

means for applying the combined signal to the input of the actuating means, the actuating means being adapted to move the implement in response to the combined signal.

24. The control system of claim 23, further comprising:

means for maintaining the slip error signal not less than a predetermined minimum value to prevent a reduction in the magnitude of the combined signal and a corresponding increase in implement depth when the slip error decreases below a minimum value.

25. The invention of claim 23, wherein:

the connecting means comprises a movable hitch coupled between the implement and the vehicle, the actuation means being coupled between the hitch and the vehicle and being capable of moving the hitch to thereby raise and lower the implement.

26. In a vehicle having a driven wheel, connecting means for attaching a ground-penetrating implement thereto and actuating means for raising a lowering the implement to vary the ground penetration thereof in response to signals applied to an input thereof, a control system comprising:

wheel slip means for generating a slip error signal indicative of the amount of wheel slippage of a driven wheel of the vehicle;

means for selecting a predetermined slip gain factor from a plurality of slip gain factors, depending upon the magnitude of the slip error signal;

means for generating modified slip error signals derived by multiplying the slip error signal by the selected slip gain factor; and

means for deriving a control signal from at least the modified slip error signal and for applying the control signal to the input of the actuating means, the actuating means being adapted to move the implement in response to the control signal.

27. In a vehicle having a driven wheel, connecting means for attaching a ground-penetrating implement thereto and actuating means for raising and lowering the implement to vary ground penetration thereof in response to signals applied to an input thereof, a control system comprising:

a draft sensor for generating a sensed draft signal derived from a sensed draft force produced by implement-ground interaction;

reference means for generating a reference draft signal representing a desired draft force level;

means for sensing slippage of the driven wheel and for generating a slip error signal representing a difference between a sensed wheel slippage and a reference amount of wheel slippage,

signal combining means for generating a combined signal derived by arithmetically combining the sensed draft signal, the reference draft signal and slip error signals; and

means for applying the combined signal to the input of the actuating means, the actuating means being adapted to move the implement in response to the combined signal.

28. The control system of claim 27, wherein the actuating means comprises:

a source of fluid pressure;

a hydraulic piston for raising the implement in response to fluid communicated thereto; and

electrohydraulic valve means with an input for receiving the combined signal and for controlling the rate of fluid flow between the fluid pressure source and the piston as a function of the magnitude of the combined signal.

29. In a vehicle having an engine, connecting means for attaching a ground-penetrating implement thereto and actuating means for raising and lowering the implement to vary the ground penetration thereof in response to control signals applied to an input thereof, a control system comprising;

a draft sensor for generating a draft signal representing a sensed draft force produced by implement-ground interaction;

operator-adjustable load command means for generating a load command signal representing a desired draft force;

an engine speed means for generating an engine speed error signal representing a difference between a sensed and desired engine speed;

signal combining means for generating a combined signal derived by arithmetically combining the draft signal, the load command signal and the engine speed error signal;

means for applying the combined signal to the input of the actuating means, the actuating means being adapted to move the implement in response to the combined signal; and

means for momentarily modifying the engine speed error signal in response to a predetermined operator-induced change in the load command signal.

30. In a vehicle having an engine, a driven wheel, connecting means for attaching a ground-penetrating implement thereto and actuating means for raising and lowering the implement to vary the ground penetration thereof in response to signals applied to an input thereof, a control system comprising:

a draft sensor for generating a draft signal indicative of a sensed draft force produced by interaction between the implement and the ground;

operator-adjustable load command means for generating a load command signal indicative of a desired amount of draft force;

engine speed sensing means for generating an engine speed signal representing the speed of the vehicle engine;

reference means for generating a reference engine speed signal;

threshold means for generating a threshold signal representing a predetermined change in vehicle engine speed;

arithmetic means for generating an engine speed error signal as a function of the engine speed, engine speed reference and threshold signals;

signal combining means for generating a combined signal derived by arithmetically combining the draft, load command and engine speed error signals; and

means for applying the combined signal to the input of the actuating means, the actuating means being adapted to move the implement in response to the combined signal.

31. The control system of claim 30, further comprising:

means for momentarily modifying the engine error signal in response to a predetermined change in the load command signal.

32. The control system of claim 30, further comprising:

means for redetermining the threshold signal based on engine speed and reference engine speed signals generated a predetermined time interval after adjustment of the load command means.

33. In a vehicle having an engine, a driven wheel, connecting means for attaching a ground-penetrating implement thereto, and actuating means for raising and lowering the implement to vary the ground penetration thereof in response to signals applied to an input thereof, a control system comprising:

wheel slip means for generating a slip error signal indicative of the amount of slippage of the driven wheel;

draft means for generating a draft error signal derived from a sensed draft force produced by interaction between the implement and the ground and from a reference draft force;

engine speed means for generating an engine speed error signal indicative of a difference between a sensed and a desired engine speed;

signal combining means for generating a combined signal derived by combining the slip error, the draft error and engine speed error signals; and

means for applying the combined signal to the input of the actuating means, the actuating means being adapted to move the implement in response to the combined signal.

34. In a vehicle having an engine, a driven wheel, connecting means for attaching a ground-penetrating implement thereto, and actuating means for raising and lowering the implement to vary the ground penetration thereof in response to signals applied to an input thereof, a control system comprising:

a draft sensor for generating a draft signal derived from a sensed draft force produced by interaction between the implement and the ground;

wheel slip means for generating a slip error signal representative of slippage of the driven wheel;

engine speed means for generating an engine speed error signal indicative of a difference between a sensed and a desired engine speed;

signal combining means for generating a combined signal derived by arithmetically combining the draft signal with the engine speed error and the slip error signals; and

means for applying the combined signal to the input of the actuating means, the actuating means being adapted to move the implement in response to the combined signal.

35. The control system of claim 34, wherein the engine speed means comprises:

an engine speed sensor coupled to the engine for generating a sensed engine speed signal indicative of an actual speed of the engine;

means for generating a reference engine speed signal representing a designated speed of the vehicle engine;

means for generating a threshold engine speed signal representing a predetermined difference between the sensed and reference engine speed signals; and

means for generating the engine speed error signal as an arithmetic function of the sensed engine speed signal, the reference engine speed signal and the threshold engine speed signal.

36. The control system of claim 35, wherein:

the reference engine speed generator means includes speed control means for controlling the vehicle engine and sensing means coupled to the speed control means for sensing the operational status of the speed control means and for converting the sensed status to the reference engine speed signal.

37. The control system of claim 34, wherein the actuating means comprises:

a source of fluid pressure;

a hydraulic piston for raising the implement in response to fluid communicated thereto; and

electrohydraulic valve means responsive to the combined signal for controlling the rate of fluid flow between the fluid pressure source and the piston as a function of the magnitude of the combined signal.

38. In a vehicle having an engine, a driven wheel, connecting means for attaching a ground-penetrating implement thereto, and actuating means for raising and lowering the implement to vary the ground penetration thereof in response to signals applied to an input thereof, a control system comprising:

wheel slip means for generating a slip error signal indicative of the amount of slippage of the driven wheel;

a draft sensor for generating a draft signal representing a draft force produced by interaction between the implement and the ground;

operator-adjustable load command means for generating a load command signal indicative of a desired amount of draft force;

means for generating a draft error signal representing a difference between the draft and load command signals;

engine speed means for generating an engine speed error signal indicative of a difference between a sensed and a desired engine speed;

position means for generating a position error signal with a magnitude proportional to a difference between an actual and a desired position of the implement;

signal combining means for generating a combined signal derived by combining the slip error, the draft, the load command and engine speed error signals;

selecting means for selecting one of the combined error and position error signals when a predetermined relationship therebetween occurs; and

means for applying the selected error signal to the input of the actuating means, the actuating means being adapted to move the implement in response to the selected error signal.

39. In a vehicle having an engine, a driven wheel, connecting means for attaching a ground penetrating implement thereto and actuating means for raising and lowering the implement to vary the ground penetration thereof in response to signals applied to an input thereof, a control system comprising:

a draft sensor for generating a draft signal derived from at least a sensed draft force produced by interaction between the implement and the ground;

a wheel slip means for generating a slip error signal indicative of the amount of slippage of the driven wheel;

engine speed means for generating an engine speed error signal indicative of a difference between a sensed and a desired engine speed;

signal combining means for generating a combined signal derived by arithmetically combining the draft signal with the engine speed error and the slip error signals;

a position means for generating a position error signal with a magnitude proportional to a difference between an actual and a desired position of the implement;

selecting means for selecting one of the combined error and position error signals when a predetermined relationship therebetween occurs;

means for applying the selected error signal to the input of the actuating means, the actuating means being adapted to move the implement in response to the selected error signal;

means for generating a draft limit signal proportional to a desired amount of draft force;

means for limiting the magnitude of the engine speed error signal to the magnitude of the draft limit signal; and

means for generating a downshift signal when the engine speed error signal is limited by the limiting means concurrently with the slip error signal having a lesser magnitude than that of the engine speed error signal.

40. In a vehicle having an engine, a driven wheel, connecting means for attaching a ground-penetrating implement thereto and actuating means for raising and lowering the implement in response to signals applied to an input thereof, a control system comprising:

draft force means for generating a draft signal derived from at least a sensed draft force produced by implement-ground interaction;

wheel slip means for generating a slip error signal indicative of the amount of slippage of the driven wheel;

engine speed means for generating an engine speed error signal indicative of a difference between sensed and a desired speed of the vehicle engine;

signal combining means for generating a combined signal derived by arithmetically combining the above signals;

a position monitor for generating a position error signal with a magnitude proportional to a difference between a sensed and a desired position of the implement;

selecting means for selecting one of the combined and position error signals according to a predetermined relationship therebetween; and

means for applying the selected signal to the input of the actuating means, the actuating means being adapted to move the implement as a function of the selected one signal.

41. The control system of claim 40, wherein the selecting means comprises means for selecting the most positive of the combined and position error signals.

42. The control system of claim 40, wherein the engine speed means comprises:

an engine speed sensor coupled to the engine for generating a sensed engine speed signal indicative of an actual speed of the engine;

means for generating a reference engine speed signal representing a designated speed of the vehicle engine;

means for generating a threshold engine speed signal representing a difference between the sensed and reference engine speed signals; and

means for generating the engine speed error signal as an arithmetic function of the sensed engine speed signals, the reference engine speed signal and the threshold engine speed signal.

43. The control system of claim 40, further comprising:

operator-controlled means for generating a load command signal representing a desired amount of draft force;

means for generating a draft limit signal proportional to the load command signal; and

means for limiting the magnitude of the engine speed error signal to the magnitude of the draft limit signal.

44. In a vehicle having connecting means for attaching a ground-penetrating implement thereto and actuating means for raising and lowering the implement to vary the ground penetration thereof in response to signals applied to an input thereof:

means for generating a parameter signal representing a sensed operating parameter of a machine system comprising the vehicle, the connecting means and the implement;

set point means for deriving a parameter set point signal from the parameter signal;

difference means for generating a parameter error signal representing a difference between the parameter signal and the parameter set point signal;

means for converting the parameter error signal to a control signal and for applying the control signal to the input of the actuating means, the actuating means being adapted to move the implement in response to the control signal;

operator-adjustable command means for generating a command signal representing a desired magnitude of a further operating parameter of the machine system; and

means for redetermining the parameter set point signal from a filtered signal generated a predetermined delay time period after occurrence of said predetermined change in the command signal, the duration of the delay time period being a function of the magnitude of the change in the command signal.

45. In a vehicle having connecting means for attaching a ground-penetrating implement thereto and actuating means for raising and lowering the implement to vary the ground penetration thereof in response to signals applied to an input thereof:

means for generating a parameter error signal representing a difference between a sensed value of an operating parameter of a machine system comprising the vehicle, the connecting means and the implement and a reference value of said parameter;

operator-adjustable command means for generating a command signal representing a desired magnitude of a further operating parameter of the machine system;

means for momentarily modifying the parameter error signal in response to a predetermined operator-induced change in the command signal;

means for redetermining the reference value a predetermined delay time period after occurrence of said predetermined change in the command signal; and

means for converting at least the parameter error signal to a control signal and for applying the control signal to the input of the actuating means, the actuating means being adapted to move the implement in response to the control signal, the duration of the delay time period being a function of the magnitude of the change in the command signal.

46. In a vehicle having a driven wheel, connecting means for attaching a ground-penetrating implement thereto and actuating means for raising and lowering the implement to vary the ground penetration thereof in response to signals applied to an input thereof, a control system comprising:

wheel slip means for generating a slip error signal indicative of the amount of slippage of the driven wheel;

draft means for generating a draft signal derived from at least a sensed draft force produced by interaction between the implement and the ground;

signal combining means for generating a combined signal derived by arithmetically combining the slip error signal with the draft signal;

operator-adjustable load command means for generating a load command signal indicative of a desired amount of draft force;

means for momentarily modifying the slip error signal in response to a predetermined operator-induced change in the load command signal; and

means for applying the combined signal to the input of the actuating means, the actuating means being adapted to move the implement in response to the combined signal.

48. The control system of claim 46, wherein:

the wheel slip means includes sensor means for generating a wheel slippage signal representing slippage of the driven wheels, means for generating a slip set signal representing a predetermined amount of wheel slippage and difference means for generating the slip error signal representing a difference between the wheel slippage and slip set signal.

49. The control system of claim 48, further comprising:

means for redetermining the slip set signal based on a wheel slippage signal generated a predetermined time interval after adjustment of the load command means.

47. The control system of claim 59, wherein:

the modifying means comprises means for incrementally and periodically decreasing the slip error signal in a non-linear manner.

50. In a vehicle having a driven wheel, connecting means for attaching a ground-penetrating implement thereto and actuating means for raising and lowering the implement to vary the ground penetration thereof in response to signals applied to an input thereof, a control system comprising:

wheel slip means for generating a slip error signal indicative of the amount of slippage of the driven wheel, the wheel slip monitor comprising a ground speed sensor for sensing vehicle ground speed, a wheel speed sensor for sensing the rotation speed of the driven wheel and for converting the rotation speed to a wheel travel velocity, divider means coupled to the ground and wheel speed sensors for generating a ratio signal corresponding to a quotient derived by dividing the ground speed by the travel velocity of the driven wheel, means for generating a slip set signal representing a reference value of wheel slippage, the slip set signal generating means comprising filter means for generating a filtered slip signal derived from periodically generated values of the ratio signal and means for adding a predetermined increment to the filtered slip signal, the resulting signal comprising the slip set signal, and comparator means for producing the slip error signal when the ratio signal exceeds the slip set signal, the magnitude of the slip error signal being proportional to a difference between the ratio and the slip set signals;

draft means for generating a draft signal derived from at least a sensed draft force produced by interaction between the implement and the ground;

signal combining means for generating a combined signal derived by arithmetically combining the slip error signal with the draft signal; and

means for applying the combined signal to the input of the actuating means, the actuating means being adapted to move the implement in response to the combined signal.

51. In a vehicle having an engine, a driven wheel, connecting means for attaching a ground-penetrating implement thereto, and actuating means for raising and lowering the implement to vary the ground penetration thereof in response to signals applied to an input thereof, a control system comprising:

a draft sensor for generating a draft signal derived from a sensed draft force produced by interaction between the implement and the ground;

wheel slip means for generating a slip error signal representative of slippage of the driven wheel;

engine speed means for generating an engine speed error signal indicative of a difference between a sensed and a desired engine speed, the engine means comprising an engine speed sensor coupled to the engine for generating a sensed engine speed signal indicative of an actual speed of the engine, means for generating a reference engine speed signal representing a designated speed of the vehicle engine, means for generating a threshold engine speed signal representing a predetermined difference between the sensed and reference engine speed signals, means for maintaining the engine speed error signal not less than a predetermined minimum value, and means for generating the engine speed error signal as an arithmetic function of the sensed engine speed signal, the reference engine speed signal and the threshold engine speed signal;

signal combining means for generating a combined signal derived by arithmetically combining the draft signal with the engine speed error and the slip error signals; and

means for applying the combined signal to the input of the actuating means, the actuating means being adapted to move the implement in response to the combined signal.

52. In a vehicle having an engine, a driven wheel, connecting means for attaching a ground-penetrating implement thereto and actuating means for raising and lowering the implement to vary the ground penetration thereof in response to signals applied to an input thereof, a control system comprising:

a draft sensor for generating a draft signal derived from a sensed draft force produced by interaction between the implement and the ground;

wheel slip means for generating a slip error signal representative of slippage of the driven wheel;

engine speed means for generating an engine speed error signal indicative of a difference between a sensed and a desired engine speed, the engine speed means comprising an engine speed sensor coupled to the engine for generating a sensed engine speed signal indicative of an actual speed of the engine, means for generating a reference engine speed signal representing a designated speed of the vehicle engine, means for generating a threshold engine speed signal representing a predetermined difference between the sensed and reference engine speed signals, means for maintaining the threshold engine speed signal not less than a predetermined minimum value, and means for generating the engine speed error signal as an arithmetic function of the sensed engine speed signal, the reference engine speed signal and the threshold engine speed signal;

signal combining means for generating a combined signal derived by arithmetically combining the draft signal with the engine speed error and the slip error signals; and

means for applying the combined signal to the input of the actuating means, the actuating means being adapted to move the implement in response to the combined signal.

53. In a vehicle having an engine, a driven wheel, connecting means for attaching a ground-penetrating implement thereto, and actuating means for raising and lowering the implement to vary the ground penetration thereof in response to signals applied to an input thereof, a control system comprising:

a draft sensor for generating a draft signal derived from a sensed draft force produced by interaction between the implement and the ground;

wheel slip means for generating a slip error signal representative of slippage of the driven wheel;

engine speed means for generating an engine speed error signal indicative of a difference between a sensed and a desired engine speed;

signal combining means for generating a combined signal derived by arithmetically combining the draft signal with the engine speed error and the slip error signals;

means for applying the combined signal to the input of the actuating means, the actuating means being adapted to move the implement in response to the combined signal;

operator-controlled means for generating a load command signal representing a desired amount of draft force;

means for generating a draft limit signal as a function of the load command signal; and

means for limiting the magnitude of the engine speed error signal to the magnitude of the draft limit signal.

54. In a vehicle having an engine, a driven wheel, connecting means for attaching a ground-penetrating implement thereto, and actuating means for raising and lowering the implement to vary the ground penetration thereof in response to signals applied to an input thereof, a control system comprising:

a draft sensor for generating a draft signal derived from a sensed draft force produced by interaction between the implement and the ground;

wheel slip means for generating a slip error signal representative of slippage of the driven wheel;

engine speed means for generating an engine speed error signal indicative of a difference between a sensed and a desired engine speed;

signal combining means for generating a combined signal derived by arithmetically combining the draft signal with the engine speed error and the slip error signals;

means for applying the combined signal to the input of the actuating means, the actuating means being adapted to move the implement in response to the combined signal;

operator-adjustable load command means for generating a load command signal representing a desired draft force; and

means for momentarily modifying the slip error and engine speed error signals in response to a predetermined operator-induced change in the load command signal, the signal combining means generating the combined signal as an arithmetic combination of the draft signal, the load command signal, the wheel slip error signal and the engine speed error signal.

55. In a vehicle having an engine, a driven wheel, connecting means for attaching a ground-penetrating implement thereto, and actuating means for raising and lowering the implement to vary the ground penetration thereof in response to signals applied to an input thereof, a control system comprising:

a draft sensor for generating a draft signal derived from a sensed draft force produced by interaction between the implement and the ground;

wheel slip means for generating a slip error signal representative of slippage of the driven wheel;

engine speed means for generating an engine speed error signal indicative of a difference between a sensed and a desired engine speed, the engine speed means comprising an engine speed sensor coupled to the engine for generating a sensed engine speed signal indicative of an actual speed of the engine and means for generating a reference engine speed signal representing a designated speed of the vehicle engine, the reference engine speed generator means including speed control means for controlling the vehicle engine and sensing means coupled to the speed control means for sensing the operational status of the speed control means and for converting the sensed status to the reference engine speed signal, the engine speed means also comprising means for generating a threshold engine speed signal representing a predetermined difference between the sensed and reference engine speed signals, and means for generating the engine speed error signal as an arithmetic function of the sensed engine speed signal, the reference engine speed signal and the threshold engine speed signal;

means for limiting raising of the implement in response to a predetermined change in the reference engine speed signal;

signal combining means for generating a combined signal derived by arithmetically combining the draft signal with the engine speed error and the slip error signals; and

means for applying the command signal to the input of the actuating means, the actuating means being adapted to move the implement in response to the combined signal.

56. In a vehicle having connecting means for attaching a ground-penetrating implement thereto and actuating means for raising and lowering the implement to vary the ground penetration thereof in response to signals applied to an input thereof;

means for generating a parameter signal representing a sensed first operating parameter of a machine system comprising the vehicle, the connecting means and the implement;

operator-adjustable command means for generating a command signal representing a desired magnitude of a further operating parameter of the machine system;

means for momentarily modifying the parameter signal in response to a predetermined operator-induced change in the command signal; and

means for converting the parameter signal to a control signal and for applying the control signal to the input of the actuating means, the actuating means being adapted to move the implement in response to the control signal.