Force control system including bypass flow path for implement with relatively movable frame parts

A weight-balancing system for a farm implement, such as a disk harrow with foldable wings operated by wingfold cylinders, includes a selective control valve for controlling fluid communication to the head and rod ends of the wingfold cylinders. A pair of pressure-reducing/relieving valves permit individual adjustment of the pressures in both the head and rod ends to achieve the desired balance. In a preferred embodiment, a pilot-operated, two-position valve is connected between the rod ends and one of the pressure-responsive valves. The two-position valve is operated by pressure signals generated by a flow-responsive switching valve connected between the two-position valve and the selective control valve. The switching valve and the two-position valve cooperate to block the pressure-controlled outlet of the one pressure-responsive valve and the rod ends and to bypass return fluid flow from the rod ends to sump when the cylinders are being extended. Then, when cylinder motion stops and this return flow ends, the switching valve and the two-position valve are connected to the control pressure outlet of the one pressure-responsive valve to the rod ends to achieve the desired balance.

BACKGROUND OF THE INVENTION 
This invention relates to a hydraulic system for controlling the weight 
transfer between the main frame and wing sections of an agricultural 
implement, such as a disk harrow. 
One type of current disk harrow has a main frame and one or two wings which 
are attached pivotally (or hinged) with respect to the main frame. The 
main frame and the wings support gangs of disks which are drawn through 
the soil. In such disk harrows, the characteristic working or thrust 
force, due to implement-ground interaction, can create functional problems 
as soil conditions vary. These thrust forces act along the gang to create 
a moment about the hinge centerline of the wing which tends to pull the 
wing into the soil. Firm soils generate high thrust forces while loose 
soils generate relatively low forces. As a result, in firm soils, the 
wings may tend to penetrate deeper than the main frame while in loose 
soils, the wings tend to ride out. The result is unsatisfactory 
performance, i.e., ridging, incomplete cutout due to lack of penetration, 
etc. The weight balance between the wings and main frame is a delicate 
design parameter and is difficult to optimize for different wing sizes and 
soil conditions. Oftentimes, narrow wings tend to ride out and wide wings 
tend to penetrate too deeply, or vice versa. Currently, these problems are 
addressed by adding ballast to wing frames, by using compression springs 
in wingfold cylinders, and by using additional gang wheels on large wings. 
However, adjustment of ballast or of gauge wheels is inconvenient so that 
it is difficult to quickly adjust to changing soil conditions. Compression 
springs have a disadvantage in that the force they provide varies, 
depending upon the relative position between the main frame and the wing. 
Accordingly, some other more convenient system for adjusting disk harrow 
weight balance is desired. 
SUMMARY OF THE INVENTION 
An object of the present invention is to provide a disk harrow, weight 
transfer or ground-engaging force control system which is simple to 
adjust. 
Another object of the present invention is to provide disk harrow main 
frame to wing weight transfer by controlling fluid pressure in the 
wingfold cylinders. 
A further object is to provide such a weight transfer system wherein the 
weight transfer forces are independent of wing position. 
Another object is to provide a weight-balancing system in which wing 
folding and unfolding can be controlled via a single lever and with which 
the wingfold cylinders can be locked or floated. 
Another object is to maintain constant weight transfer independent of 
relative position of wing frame to main frame. 
A further object of this invention is to provide such a system using only a 
remote control valve such as a four-position, four-way valve with float, 
such as typically used on agricultural tractors. 
These and other advantages are achieved by the present invention wherein a 
pair of adjustable pressure-reducing/relieving valves are included in the 
hydraulic circuit which controls the unfolding and folding of the wings by 
extending and retracting hydraulic cylinders. The hydraulic circuit 
includes a 4-position, 4-way selective control valve connected to a pump 
and a reservoir. One pressure-reducing/relieving valve is coupled between 
one outlet of the control valve and the head ends of the wingfold 
cylinders. A second pressure-reducing/relieving valve is connected between 
another outlet of the control valve and the rod ends of the cylinders. 
Thus, weight transfer can be achieved by individual adjustment of the 
fluid pressures in the head and rod ends of the wingfold cylinders. 
A preferred embodiment also includes a pair of hydraulic wingfold 
cylinders, a pump, a reservoir and a selective control valve for 
controlling communication therebetween. A pair of 
pressure-reducing/relieving valves separately control the pressures in the 
head and rod ends of the cylinders. Both pressure-reducing/relieving 
valves have high pressure inlets connected to the same outlet port of the 
selective control valve. The controlled pressure outlet of one 
pressure-reducing/relieving valve is coupled directly to the head ends. 
The controlled pressure outlet of the other pressure-reducing/relieving 
valve is coupled to the rod ends via a two-position valve. A 
flow-responsive switching valve generates pressure signals which operate 
the two-position valve. During wing folding, (cylinder retraction), these 
valves operate to pressurize the cylinder rod ends while connecting the 
head ends to reservoir. The valves automatically shift from a wing folding 
mode to an unfolding mode in response to shifting of the selective control 
valve. During wing unfolding (cylinder extension), the switching valve and 
the two-position valve operate to bypass return fluid from the rod ends to 
sump without passing through the other pressure-reducing/relieving valve 
and to block communication between the rod ends and the controlled 
pressure outlet of the other pressure-reducing/relieving valve. Then, when 
the wings are unfolded and cylinder motion stops, the switching valve and 
the two-position valve operate to automatically connect the controlled 
pressure outlet of the other pressure-reducing/relieving valve to the rod 
ends to achieve the desired weight balancing.

DETAILED DESCRIPTION 
Referring to FIG. 1, a conventional disk harrow 10 includes a flexible 
3-part frame 12 with a main section 14, and right and left wing sections 
16 and 18, respectively. A wing-folding function is provided by wingfold 
hydraulic cylinders 20 and 22. 
Referring now to FIG. 2, a hydraulic circuit 30 controls fluid flow to and 
from the cylinders 20 and 22. Circuit 30 includes a pump 32, a reservoir 
34 and a 4-way, 4-position detent-held selective control valve 36 which 
may be mechanically connected to a manually operated control lever 38. 
Circuit 30 also includes pressure-reducing/relieving valves 40 and 42 
which may be reducing/relieving valve model PPDB made by Sun Hydraulics. 
Lines 41 and 43 connect valve 36 to valves 40 and 42. Valve 40 controls 
communication of lines 41 and 43 with the head end of cylinders 20 and 22 
via line 44. Valve 42 controls communication of lines 41 and 43 with the 
rod ends of cylinders 20 and 22 via line 46. 
Valve 36 includes an extend or unfold position 50, a shut-off position 52, 
a retract or fold position 54 and a float position 55. Valve 40 has 
opposed pressure-operated pilots 56 and 58 and is spring-biased towards 
its illustrated position by manually adjustable spring 60. Pilots 56 and 
58 are connected to lines 43 and 44, respectively. 
Valve 42 has opposed pressure-operated pilots 62 and 64 which are connected 
to lines 41 and 46, respectively. Valve 42 is spring-biased to its 
illustrated position by manually adjustable spring 66. 
When valve 36 is moved to the extend position 50, then line 41 is connected 
to pump 32 and line 43 is connected to sump 34. Valve 40 communicates a 
reduced pressure (0-700 psi, determined by the adjustment of manually 
adjustable spring 60) via line 44 to the head ends of cylinders 20 and 22. 
At the same time, pump pressure is communicated to pilot 62 of valve 42 
while sump pressure is communicated to pilot 64. Thus, valve 42 will 
connect the rod ends of cylinders 20 and 22 to sump 36 and the cylinders 
will extend. When the wings are unfolded and cylinder motion stops, then 
the amount of downward wing force can be controlled by adjusting spring 60 
of valve 40, which permits a pressure variation of 0 to 700 psi for the 
pressure in the head ends of cylinders 20 and 22. 
If, after the wings are unfolded, it is desired to reduce the downward wing 
force by pressurizing the rod ends of cylinders 20 and 22, then control 
valve 36 should be shifted to and held in its retract position 54. This 
pressurizes line 43 and connects sump 34 to line 41. With line 43 
pressurized, valve 40 is held in the position shown so that the head ends 
of cylinders 20 and 22 are connected to sump. At the same time, 
pressure-reducing/relieving valve 42 will pressurize line 46 and the rod 
ends of cylinders 20 and 22 to the pressure determined by pressure-adjust 
spring 66 (0-2500 psi). 
To fold the wings or retract the cylinders, the pressure-adjusting spring 
66 on valve 42 must be adjusted to maximize the pressure in line 46. Then, 
the control valve 36 is moved to position 54, whereupon valve 42 connects 
pump 32 to the rod ends of the cylinders 20 and 22 while valve 40 connects 
the head ends to sump 34. Thus, with hydraulic circuit 30, the wings 16 
and 18 may be folded or unfolded and the pressure in both the head and rod 
ends of cylinders 20 and 22 may be adjusted. 
Referring now to FIG. 3, the hydraulic circuit 170 controls the cylinders 
120 and 122. Circuit 170 includes a pump 132, a reservoir 134 and a 4-way, 
4-position, detent held selective control valve 136 which may be 
mechanically connected to a manually-operated control lever 138. Control 
valve 136 has a stop position 152, an extend position 150, a retract 
position 154 and a float position 156. The hydraulic circuit 170 includes 
a pair of pressure-reducing/relieving valves 172 and 174, such as 
reducing/relieving valve model PPDB, made by Sun Hydraulics. Valves 172 
and 174 are connected to one port of control valve 136 via line 141. Valve 
172 is preferably factory adjusted so that the maximum pressure in line 
144 and in the head end of cylinders 120 and 122 is 750 psi, whereas valve 
174 may be operator-adjusted to achieve a desired rod end pressure. Both 
valves 172 and 174 are connected to another port of control valve 136 via 
line 143. 
Line 143 is also connected to port 175 of 3-position switching valve 176. 
Valve 176 is spring-loaded to an intermediate position 178 by springs 180 
and 182, and is urged to positions 184 and 186 by pressure-operated pilots 
188 and 190, respectively. Valve 176 also has ports 192 and 194. Port 192 
is connected to pilot 188 via a restriction 189 and is connected to line 
196. Pilot 190 is connected to line 143 via a restriction 191. Port 194 is 
coupled to line 195. 
The circuit 170 also includes a two-position valve 200 with a port 202 
connected to line 196, a port 204 connected to valve 174 via line 206, and 
a port 208 which is coupled to the rod ends of cylinders 120 and 122 via 
line 209. Valve 200 is urged towards a position 210 by pilot 212 and 
towards position 214 by pilot 216 and spring 218. Pilot 212 is connected 
to port 194 of switching valve 176 and to line 144 via restriction 220 and 
check valve 222. Pilot 216 is connected to line 196 via restriction 224. 
Mode of Operation 
Assuming that the cylinders 120 and 122 are retracted, (and the wings 
folded), they may be extended by shifting valve 136 to position 150, 
whereupon fluid flows from pump 132 to the head ends of cylinders 120 and 
122 via line 141, valve 172 and line 144. The cylinders 120 and 122 extend 
and fluid flows out of the rod ends to the reservoir 134 via line 209, 
valve 200 (position 214), valve 176 (position 178), line 143 and control 
valve 136. This creates a pressure differential between ports 192 and 175 
of valve 176 which shifts valve 176 to position 184 wherein passage 185 
vents line 195 to sump. This maintains low pressure at pilot 212 and keeps 
valve 200 in position 214, as illustrated. Restriction 220 is made small 
enough to prevent pressurized fluid from bypassing the cylinders 120 and 
122. Thus, the return fluid flow from the rod ends to sump bypasses the 
pressure-reducing/relieving valve 174. Because of this, 
pressure-reducing/relieving valve 174 can be set to any desired setting 
and the resulting pressure in line 206 is blocked by valve 200 so that 
this pressure does not reduce the force which extends the cylinders when 
control valve 136 is initially in position 150 and oil is flowing. The 
check valve 222 prevents fluid flow from the rod ends back to the head 
ends if the control valve 136 is moved to position 152 before complete 
cylinder extension is achieved so that the wings can be stopped in a 
partly unfolded position. 
When the wings are unfolded and the motion of cylinders 120 and 122 stops, 
the flow across valve 176 ends, thus removing the differential pressure 
between ports 192 and 175, and valve 176 shifts back to its center 
position 178 wherein line 195 is blocked. Then, the full 750 psi pressure 
from line 144 is applied to pilot 212 to shift valve 200 to position 210 
wherein the rod ends of cylinders 120 and 122 are connected to valve 174 
via port 208, port 204 and line 206. At this point, the downward or upward 
force on wings 16 and 18 is automatically adjusted according to the 
setting of adjusting valve 174. 
To retract cylinders 120 and 122 and fold the wings, valve 136 is shifted 
to position 154 to pressurize line 143 and pilot 190. This shifts valves 
172 and 174 to the positions shown. It also shifts valve 176 to position 
186 and valve 200 to position 214, whereupon fluid flows from pump 132 to 
the rod ends of cylinders 120 and 122 via valve 136, line 143, valve 176, 
line 196, valve 200 and line 209, thereby bypassing valve 174 so that full 
pump pressure is available for wing folding. At the same time, fluid from 
the head ends of cylinders 120 and 122 flows to sump via line 144, valve 
172, line 141 and valve 136. 
Thus, the pressure-reducing/relieving valve 174 (which controls 
pressurization of the rod ends) can be preset to any desired pressure. 
Then, during wing fold or unfold, this preset pressure does not reduce the 
force tending to extend or retract the cylinders, but when the wings are 
unfolded and cylinder motion stops, this preset pressure is automatically 
applied to the rod ends to oppose the head end pressure from 
pressure-reducing/relieving valve 172, thus automatically achieving the 
desired wing force or weight balance. 
In the stop position 152 of valve 136, both lines 141 and 143 are blocked. 
Valve 200 assumes position 214 communicating line 209 with blocked line 
143. Valve 172 assumes the position shown and communicates line 144 with 
blocked line 141. As a result, flow is blocked in lines 144 and 209 and 
the cylinders 120 and 122 are immobilized. This stop mode is needed to 
halt motion during a folding or unfolding cycle, such as to prevent a wing 
from striking an obstruction. 
In the float position 156 of valve 136, lines 141 and 143 are both 
connected to reservoir 134. Valves 172, 176 and 200 assume the same 
positions which they assume in the stop mode so that lines 144 and 209 are 
both communicated with each other and with the reservoir. This allows free 
motion of the cylinders 120 and 122. This float mode is useful in the case 
of a system malfunction or in the case where the disk is operated in soil 
where no weight transfer is needed. 
In addition to weight balancing, this invention has other applications in 
the agricultural implement area. One such application would be disk harrow 
front-to-rear leveling. Front-to-rear leveling is used to control the 
relative disking depth of the front and rear gangs. Disk leveling is 
important to ensure uniform soil cutout and to maintain a level soil 
surface across the width of the machine. Some current level action disks 
use a mechanical linkage to control front-to-rear leveling. The linkage 
utilizes the relative position of the hitch to the main frame to control 
the compression of the leveling spring which, when relaxed, lets the front 
gangs penetrate deeper and, when compressed, pulls the front gangs out of 
the soil. The same effect could be realized if the leveling linkage were 
removed, a hydraulic cylinder installed between the hitch and main frame 
and the present balancing system installed to control the position of the 
cylinder. The system could be set to obtain a level disking job and the 
same front-to-rear disking depth would be maintained, regardless of the 
relative position of the hitch to the main frame (disking over small 
knolls or through low spots.) 
Another application would be for planting unit down force control. Current 
planting units utilize two extension springs to create a down force to 
help keep the unit in the soil. This force is not constant and decreases 
as the planting unit flexes down. The present balancing system would be 
connected to a hydraulic cylinder which would replace the springs to 
provide a constant force on the unit. Such a system would also be 
adjustable to compensate for varying soil conditions. 
While the invention has been described in conjuction with a specific 
embodiment, it is to be understood that many alternatives, modifications 
and variations will be apparent to those skilled in the art in light of 
the aforegoing description. Accordingly, this invention is intended to 
embrace all such alternatives, modifications and variations which fall 
within the spirit and scope of the appended claims.