Note: Descriptions are shown in the official language in which they were submitted.
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AUTOMATIC POS~TION CONTROL APPARATUS
FOR GROUND WORKING VEHICLE
BACKGROUND O~ THE INVENTION
The present invention relates to an automatic
position control apparatus for a ground working vehicle equipped
with a liftable working implement, and more par-ticularly to such
a control apparatus by which lifting and lowering of the working
implement can be automatically controlled so that the devia-tion
of the drag produced by the working implement and detected by a
drag detector from a drag value preset by a drag setting unit
is maintained within a permissible range preset by a sensitivity
setting unit.
Automatic position control apparatus of this type are
provided for maintaining the ground working implement at a
!, constant level above the ground with a position control system
while, and at the same time, preventing stalling of the engine
of the working vehicle br damage to the implement with a drag
control system responsive to the drag produced by the implement.
Such autornatic position control apparatus heretofore
known are adapted to automatically control the lift of the
, working implement during the entire period of time when the above-
mentioned deviation is above the maximum permissible value of a
preset permissible range. In this case, the automatic lift
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i~ control is discontinued when the deviation has decreased so as
,~ to lie within the permissible range, entailing electrical,
mechanic~l or hydraulic hysteresis and a delay in operation.
This leads to excessive lift control of the implement and
excessive deviation of the im~lement from the specified level
relative to the ground. Further when the permissible drag
; 30 deviation range is narrow for high-sensitivity control, the
excessive lift control causes hunting which leads to instability
of the system.
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! These problems are attributable to the fact that atten-
tion has been directed solely to the protection of the working
vehicle and implement from excessive drag loads. In other words,
the above-mentioned hystereses has not been taken into account in
designing automatic high sensitivity lift or lowering control
systems.
In view o~ the foregoing problems, an object of the in-
: vention is to prevent the hunting due to the excessive lift con-
trol stated above and to thereby assure stable automatic lift and
lowering control with high overall sensitivity.
Accordingly, the present invention provides an automa-
tic position control apparatus for a ground working vehicle equip-
` ped with a liftable working implement, which apparatus is adapted
to automatically control liftin~ and lowering of the working
implement so that the deviation of the drag produced by the work-
ing implement and detected by a drag detector from the drag value
~ preset by a drag setting unit is maintained within a permissible
'~ range preset by a sensitivity setting unit, the improvement com-
; prising means for detecting the condition that the drag deviation
','!1, 20 is not decreasing, said condition detecting means being arranged
to allow raising of the working implement when the drag deviation
is above said maximum value and said condition is fulfilled.
Thus the lift of the working implement is controlled
only when the deviation is not decreasing and outside the permis-
sible range above the maximum permissible value thereof, so that
when the deviation is above the maximum permissible value of the
: permissible ranqe and is decreasing, the lift control of the work-
ing implement has already been discontinued.
~ This prevents the resulting time lag of operation and
-~ 30 excessive lift control which would otherwise occur. Even if the
preset permissible deviation range is narrow to ensure high-
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sensitivity control, stable drag con-trol can be effected free
of hunting.
The invention will now be described in more detail,
b~7 way of example only, with reference to the accompanying
drawings, in which:--
Fig. 1 is a side elevation of a farm tractor in itsentirety;
Fig. 2 is a block diagrarn showing one embodiment of a
position control system in accordance with the invention;
Fig. 3 is a graph showing the rela-tion of position
control relative to varying deviations; and
Fig. 4 is a graph showing ranges of control operations.
Fig. 1 shows a tractor 1 serving as a ground working
vehicle and equipped with a plow 2 as a ground working implement.
The plow 2 is liftably connected to the rear portion of the tractor
1 by a top link 3 and a pair of lower links 4, 4. In response
, to an electric signal, one of the hydraulic control valves to
be described later is selectively operated to expand or contract
a hydraulic cylinder 5 housed in a transmission case lA on the
~20 tractor 1 and pivotally raise or lower a pair of lift arms 6, 6
' operatively connected to the hydraulic cylinder 5. By way of
;~ lift rods 7, 7 and the lower links 4, 4, this movement of the
lift arms 6, 6 raises or lowers the plow 2.
Fig. 2 shows an automatic position control apparatus
`~ for the plow 2. The control apparatus comprises a drag control
, system for automatically controlling the position of the plow 2
so that the deviation of the actually detected drag value of
the plow from the preset drag value is maintained within a
permissible range, and a position control system for automatically
controlling the position of the plow 2 to bring the plow in-to
proximity of the target level which is intentionally variable
in accordance with the level of the plow 2 detected relative to
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the tractor 1. The drag control system has -the following
construction.
The system includes a drag detector 9 which detects
the deflection of -the connecting rod 8 of the lower links 4, 4
due to the pulling force acting on the rod 8 through the links
4, 4 and which is the actual drag produced by the plow 2, and
a drag setting unit 10 for varying and presetting the proper
drag value in accordance with the working depth for the plow 2
and the hardness of the ground. The drag value Vfx actually
detected by the drag detector 9 and the drag value Vfo preset
by the drag setting unit 10 are fed to first and second
subt~acting units llA, llB respectively to calculate the drag
deviation IVfx - VfoI (hereinafter represented by "a'');
Lifting and lowering comparators 13A, 13B receive the deviation
a from the subtracting units llA, llB and a permissible set
deviation Vd from a drag sensitivity setting unit 12 which is
capable of varying the permissible range A of deviations a.
The lifting and lowering comparators 13A, 13B
determine whether or not the deviation a from the first or
second subtracting unit llA or llB is in the range A from a
maximum permissible value _ to a minimum permissible value b'
set by the drag sensitivity setting unit 12. The comparators
apply a lift or lowering control signal to a drive circuit 16A
for a lifting valve 16 or to a drive circuit 17A for a lowering
valve 17 via an OR circuit 14 or AND circuit 15 to automatically -
control the lift or lowering of the plow 2 so -that the deviation
a is maintained within the permissible range A. In other words,
the plough is not raised or lowered when the drag lies within :
the permissible range A. ~;
The position control system has the following .
construction.
The system includes a level detector 18 for detecting
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the actual level of the plow 2 relative to the -t~ac-tor 1 f~om the
angle o~ turn of the lift arms 4, 4, and a level setting unit 19
for lntentionally varying the target level of -the plow 2 relative
; to the tractor 1. The value Vpx detected by the level detector
1~ and the value Vpo set by the level setting unit 19 are fed to
third and fourth subtracting units 20A, 20B respectively to
calculate the level deviation. LiEting and lowering comparators
22A, 22B receive the deviation from the subtracting units 20A,
':'
20B and a permissible set deviation Vp from a position
1~ sensitivity set-ting unit 21 for setting the permissible range of
level deviations.
The lifting and lowering comparators 22A, 22B judge
whether or not the deviation from the third or fourth subtracting
unit 20A or 20B is in the range of from a maximum permissible
value to a minimum permissible value set by the position
sensitivity setting unit 21. The comparators apply a lift or
lowering control signal to the drive circuit 16A of the lifting
valve 16 or to the drive circuit 17A of the lowering valve 17
via the O~ circuit 14 or AND circuit 15 to automatically control
the lift or lowering of the plow so that the level deviation
is maintained within the set permissible range.
,
The position of the plow 2 is automatically controlled
so that the drag deviation a is in proper balance with the level
deviation. When the drag deviation a exceeds the maximum
permissible value _ or decreases below the minimum permissible
value b' with a variation in the actually detected drag Vfx,
the lift or lowering oE the plow will be controlled to stabilize
the drag, while the rise or fall of the plow will produce a
variation in the level deviation. Accordingly, the drag
variation a is adapted to be maintained within the permissible
range A while permitting the plow to rise or fall an amount which
is smaller b~ the amount corresponding to the variation in the
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level deviation. Briefly the automatic position control is
effected in accordance with the variation of the actually
detected drag value Vfx while allowing the plow 2 to be positi.oned
as close as possible to the target level.
` The present control apparatus further includes a
detector 23 for detecting that the drag deviation a is not
decreasing toward the maximum permissible setting h, based on
the variatio~ per unit time of the drag deviation a given by the
first subtracting unit llA of the drag control system. In other
words, the detector 23 detects that the deviation a is increasing
or is constant. The apparatus further includes a lift inhibiting
,~ circuit 2~ which is adapted to operate only when the detector 23
does not detect that the drag is decreasing to stop application
of the control signal from the lifting comparator 13A to the drive
circuit 16A of the lifting valve 16. Therefore, while the
detector 13A detects that the drag deviation a is not decreasing
toward the maximum permissible setting b, the lifting comparator
13A feeds a lifting control signal c to the drive circuit 16A '
of the lifting valve 16 through the OR circuit 14 as shown in
Fig. 3 so as to automatically con-trol the lift of the plow 2.
A substantially equivalent effect can be achieved even if the
detector 23 is adapted to detect only that the deviation a is
increasing or is constant. The ob]ect of the invention can be
fulfilled also when the apparatus is adapted to intermittently
interrupt automatic lift of the plow when the detector 23 detects
; a decreasing drag. Although the drag deviation a from the first
subtracting unit llA is fed to the detector 23 according to the ~:
present embodiment, the actually detected drag value Vfx from the
drag detector 9 can be applied directly to the detector 23.
To automatically control the lowering of the plow by
the drag control system, a lowering control signal c' is fed
from the lowering comparator 13B to the drive circuit 17A of the
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lowering valve 17 through the AND circuit 15 while the drag
!' deviation a from the second subtacting unit llB .is below the
minimum permissible setting b'.
.~ Furthermore there is provided a determination unit
. 28 for receiving the drag deviation a from the second subtracting
. unit llB of the drag control system, the permissible deviation
. setting from the drag sensitivity setting unit 12, and a
. reference draft~value ~, set by a second draft setting unit 27,
for determining whether or not the drag deviation a has increased
by more than a definite value based on the minimum permissible
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setting b'. The determination unit 28 determines the drag
deviation a from the second subtracting unit llB to be small when
it is in the range of from the minimum permissible setting b'
to the reference drag value V~,, or to be large when it is above
the value V~. When the unit 28 determines the drag deviation a
to be small, an oscillator circuit 26 functions in response
to the determination and emits a pulse signal of high frequency
(e.g. 60 Hz) to energize a lowering preventing circuit 25, which
in turn intermittently stops the lowering signal from the lowering
comparator circuit 13B. Conversely if the dra~ deviation a has
been determined to be large by the unit 28, the oscillator circuit
26 does not function and keeps the lowering preventing circuit
25 out of operation and permits the lowering signal from the
comparator 13B to drive the valve 17 continuously.
Thus when the absolute value of the deviation a is
large, the valve 17 is operated in response to the variation of
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~, the deviation a to efficiently control the position of the plow
2, whereas if the absolute value of the deviation a is small,
the valve 17 is operated for relatively short periods of time
with a pulse signal of high frequency, based on the variation
of the deviation a. This serves to inhibit the jerky movement
of the tires and abrupt reduction in the propelling force that
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would result from an abrupt drop of the pressure of the
cylinder especially when con-trolling the lowering of the plow
2. The position of the plow 2 is therefore controllable without
giving a severe shock to the operator.
; With reference to Fig. 4 showing the position control
operation ranges by draft control, indicated at QO is a drag
setting line, at b a line Ofmaximum permissible values, and at
b' is a line indicating minimum permissible values. The region
between the lines _ and b', namely, the permissible sensitivity
range A is the range in which raising and lowering the plow is
; prevented. The region above the line _ is a lifting range U,
and the region below the line b' is a lowering range D.
Indicated at Q2 is a reference drag line obtained by adding
a definite value (set by the second drag setting unit 27) to the
line b' for determining intermittent lowering. The region
between the line Q2 and the range A is an intermittent lowering
.
range Dl, and the region below the line Q2 is a continuous lowering
, range D2.
The range of drag devia-tions may be divided into three
stages for controlling the lowering of the plow 2 by comparative
judgment, such that the lowering valve 17 is operated with a
continuous lowering signal when the drag deviation a is judged
to be large, or with a pulse signal of 30 Hz when the deviation
a is judged to be medium, or with a pulse signal of 60 ~Iz when
the deviation a is judged to be small.
The control means for operating the valve with such
pulse signals of different frequencies can be incorporated into
the draft control system for automatically controlling the lift
of the plow.
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