Draft control system with dual mode draft sensitivity

• US 5,143,159 A
• Filed: 06/03/1991
• Issued: 09/01/1992
• Est. Priority Date: 06/03/1991
• Status: Expired due to Term

• Current Assignee: Blue Leaf IP Incorporated (CNH Industrial N.V.)
• Original Assignee: Ford New Holland, Inc. (CNH Industrial N.V.)
• Inventors: Miller, Matthew T., Young, Steven C., Nielsen, Bradley A.
• Primary Examiner(s): Taylor, Dennis L.
• Assistant Examiner(s): WARNICK IV, SPENCER K
• Application Number:
  US07/709,185
• Time in Patent Office: 456 Days
• Field of Search: 172/7, 172/8, 172/1, 172/2, 364/424.07, 37/234, 37/DIG. 1, 37/DIG. 20
• US Class Current: 172/8
• CPC Class Codes: A01B 63/112 to control draught load, i.e. tractive force

Abstract

A tractor-mounted three-point hitch for pulling a tillage implement is controlled by a closed loop including draft sensors for sensing the draft on the hitch and providing a draft feedback signal. An operator-controlled quadrant lever provides command signals for commanding the positioning of the hitch relative to the ground. During rapid hitch movement commanded by movement of the quadrant lever while the implement is above the ground, the draft feedback signal, which is normally filtered to eliminate frequencies above about 3.2 Hz, is more heavily filtered to eliminate frequencies above 0.5 Hz. This makes the loop less sensitive to the draft feedback signal and reduces vibrations which would otherwise occur because of oscillations in the draft feedback signal. The oscillations are caused by interaction of the weight of the implement bouncing because of the pneumatic tires on the tractor, and movement of the hitch to correct for the apparent change in draft. As the hitch approaches the commanded position the system reverts to the normal filtering so that the system is more sensitive to the draft feedback signal.

Claims

1. In an automatic draft control system for controlling the movement of a vehicle-mounted hitch supporting a tillage implement to a position commanded by a draft command signal, said system including draft sensing means for producing a draft feedback signal representative of hitch draft, error determining means responsive to said draft command signal and said draft feedback signal for producing a position error signal, and means responsive to said position error signal for moving the hitch toward the position commanded, the improvement comprising:

draft sensitivity control means responsive to changes in said draft command signal for low pass filtering said draft feedback signal before it is applied to said error determining means; and

,

means for inhibiting said low pass filtering of said draft feedback signal when said implement is in contact with the ground.

2. The improvement as claimed in claim 1 wherein the draft sensitivity control means includes a first order low pass filter means with a cut-off frequency of 0.5 Hz and said filter means is responsive to said draft feedback signal for supplying to the error determining means a low pass filtered draft feedback signal.

3. In an automatic draft control system for controlling the movement of a vehicle-mounted hitch to a position commanded by a draft command signal, said system including draft sensing means for producing a draft feedback signal representative of hitch draft, error determining means responsive to said draft command signal and said draft feedback signal for producing a position error signal, and means responsive to said position error signal for moving the hitch toward the position commanded, the improvement comprising:

draft sensitivity control means responsive to changes in said draft command signal for low pass filtering said draft feedback signal before it is applied to said error determining means, said draft sensitivity control means including

first means responsive to said draft command signal for setting an indicator when said draft command signal changes; and

,

second means for supplying the low pass filtered draft feedback signal to the error determining means only while said indicator is set,

the second means supplying the draft feedback signal directly to said error determining means while said indicator is not set.

4. The improvement as claimed in claim 3 wherein said draft sensitivity control means includes means for resetting said indicator when said position error signal drops below a threshold value.

5. The improvement as claimed in claim 3 wherein said first means includes means for determining the rate of change of said draft command signal, and means for setting said indicator only if the rate of change of said draft command signal exceeds a threshold value.

6. The improvement as claimed in claim 3 wherein said second means includes a low pass filter with a cut-off frequency of about 0.5 Hz, said filter being responsive to said draft feedback signal for producing said low-pass filtered draft feedback signal, said second means further including means responsive to said indicator for selectively applying the low-pass filtered draft feedback signal from said low pass filter to the error determining means.

7. The improvement as claimed in claim 6 wherein said draft sensitivity control means includes means for resetting said indicator when said position error signal drops below a threshold value.

8. The improvement as claimed in claim 6 wherein said first means includes means for determining the rate of change of said draft command signal, and means for setting said indicator only if the rate of change of said draft command signal exceeds a threshold value.

9. The improvement as claimed in claim 8 wherein said hitch supports a tillage implement, and means for resetting said indicator when the implement is in contact with the ground.

10. In a system for controlling positioning of a hitch supporting an implement, said hitch being mounted on an vehicle having pneumatic tires whereby said vehicle bounces as said hitch is rapidly moved while the implement is above ground, said system including means for producing a command signal to represent a desired position of the hitch, and a feedback loop including draft sensing means for sensing the draft on the hitch and producing a draft signal and error determining means responsive to the draft signal and the command signal for producing an error signal for controlling movement of the hitch, a method of eliminating vehicle vibrations during movement of the hitch while the implement is above ground, said method comprising:

low pass filtering the draft signal before applying it to the error determining means to eliminate therefrom signal variations caused by the weight of the hitch and implement variably acting on the draft sensing means as the vehicle bounces said low pass filtering of the draft signal being initiated only when the rate of change of the command signal exceeds a threshold value.

11. The method as claimed in claim 10 wherein the filtering of the draft signal is terminated as the hitch position approaches the desired position.

12. The method as claimed in claim 10 wherein the draft signal is filtered only when there is no contact between the implement and the ground.

13. The method as claimed in claim 10 wherein the step of low pass filtering the draft signal comprises passing said draft signal through a first order low pass filter having a cut-off frequency of 0.5 hz.