Draw shear

A tree harvesting machine is disclosed in which a grappling arm functions to reach behind a tree and draw the machine forwardly to force a shearing blade through the tree close to the ground. The harvester frame holds the severed tree and includes spring-loaded holders which allow the tree to enter the collecting space but prevent its escape once severed. The grappling or draw arm is operated by two piston/cylinder devices connected mechanically in parallel but which are hydraulically actuated in a particular sequence and fashion which assures quick closing of the draw arm upon a tree, slow but powerful shearing action, and quick opening of the draw arm.

BACKGROUND OF THE INVENTION 
This invention relates to tree harvesting devices of the type in which a 
support assembly is provided with a shearing blade and carries means for 
reaching behind a tree to grapple it and draw the shearing blade into the 
tree. This general arrangement is disclosed in U.S. Pat. No. 3,785,415. 
BRIEF SUMMARY OF THE INVENTION 
A primary concern of this invention is to provide a tree cutting attachment 
carried by and operated from a conventional vehicle in which the 
attachment is of simple, rugged and economic construction. To this end, 
the attachment features a single draw arm or grapple to draw the shearing 
blade against the tree. The draw arm is of massive, rugged construction 
and is driven by a pair of hydraulic piston/cylinder devices mechanically 
connected in parallel to the draw arm and operative to swing the draw arm 
between an inoperative position in which it is swung aside to accept a 
tree and a fully swung position in which it has scissored with respect to 
the shearing blade. 
Another feature of the invention resides in the fact that the two 
piston/cylinder devices have dissimilar displacements over their working 
strokes and that control valve means operate to pressurize these devices 
in a particular sequence. The device which is of smaller displacement 
operates alone to swing the draw arm initially and this motion is 
characterized by rapid but low force-exerting capability. Subsequent to 
this initial movement the two devices are pressure operated in parallel so 
that the shearing force created by the two cylinder devices is 
characterized by slow but high force-exerting capability. Lastly, when the 
tree has been sheared the low displacement device remains in pressurized 
condition to grapple the draw arm while the pressure connection to the 
larger displacement device is reversed, with the net result that the draw 
arm is very rapidly returned to its inoperative position. 
Another feature of the invention is that the stored kinetic energy of the 
propelling vehicle in conjunction with a non-movable blade is used to 
partially sever larger trees or to completely sever small trees. 
Subsequent to this shear the draw arm will be operating at rapid speed low 
force to catch the severed tree and inject it into the spring loaded 
holder means. 
The piston/cylinder devices are actuated by the hydraulic pump means 
provided on the associated vehicle and a series of pressure-responsive 
devices are employed to sequence the pressure connections to the two 
devices. When the tree cutting attachment is actuated, the hydraulic 
system of the vehicle and in particular the normally provided pressure 
relief or overload valve device thereof is isolated from the hydraulic 
pump, thereby allowing the hydraulic system of the tree cutting attachment 
to operate at pressures higher than that allowed by such overload relief 
device. The control system embodies an electrohydraulic control 
arrangement and may include means for automatically declutching the 
powered vehicle or otherwise disabling its movement-transmitting 
capability during the shearing cycle. 
Another principal feature of this invention involves an arrangement whereby 
a number of trees may be accumulated but wherein the draw arm is free to 
move from closed to open position without losing control of a sheared tree 
or of others already accumulated. For this purpose, the attachment 
features spring loaded holder means which swing aside to accept a tree but 
which automatically kick in behind a sheared tree to retain it in the 
accumulator section, leaving the draw arm free to swing open ready to 
accomodate another tree. The draw arm includes a spring-loaded kicker 
member which assures that a sheared tree is kicked beyond the holding 
means so that the latter may kick back to its holding position. The 
holding means also include hydraulic mechanism for swinging the holding 
means aside from blocking position whereby to allow accumulated trees to 
be discharged. 
The harvesting device includes a frame of vertical channel or cradle-like 
form, preferably of open construction whereby the operator may observe 
operation, featuring a lower yoke or bifurcated frame portion which 
carries the shearing blade and draw arm, the blade being disposed to lie 
close to the ground surface. The frame also includes an upper yoke or 
bifurcated frame portion which mounts holder means, and additional holder 
means are also associated with the lower or shear frame portion. The shear 
frame portion presents a supporting floor formed at least partially by the 
shear blade itself so that the trees may be accumulated. The frame is 
attached to the hydraulic lift arm assembly of a conventional powered 
vehicle so that the cradle-like frame may be tipped back to transport 
accumulated tree and tipped forward to discharge them.

DETAILED DESCRIPTION OF THE INVENTION 
In FIG. 1, a tree harvesting attachment embodying certain principles of 
this invention is indicated generally by the reference character 10 and 
will be seen to consist essentially of a generally open framework 
including the two uprights 11 and 12 joining the lower frame portion 
indicated generally by the reference character 13 and an upper frame 
portion indicated generally by the reference character 14. Each of these 
portions 13 and 14 is bifurcated as will be described more particularly 
hereinafter and the forward ends of the arms or bifurcations are joined by 
the frame posts 15 and 16 so that the frame 10 defines a vertically 
extending channel or generally cradle-like device which can accommodate 
trees therewithin, all as more particularly described hereinafter. 
The rear sides of the uprights 11 and 12 are provided with upper bracket 
ears 17 and 18 and similar upwardly facing lower ears (FIGS. 4 and 5) are 
disposed therebelow to receive a conventional attaching frame assembly 
which includes an upper bar 21 received in the members 17 and 18 and 
connected to the lower frame piece through the upright portion 22. Each 
side of this attaching frame is defined by a vertical frame plate 23 one 
of which is shown in FIG. 1 and this frame plate carries the pivot pins 24 
and 25 which attach to the lifting/tilting arm mechanism 26 associated 
with the dirigible powered vehicle to which the tree harvesting attachment 
is attached. One such mechanism 26 is provided for each side frame plate 
23 and will be seen to include a forwardly projecting arm 27 carrying the 
upstanding pivoted crank mechanism 28 which is linked as at 29 to the 
upper pin 24, the arm 27 being linked to the lower pin 25 directly. A 
further link 30 connects to the lever or crank 28 and extends to the upper 
end of a further crank (not shown) pivoted centrally to the arm 27 and 
having a connection at its lower end pivotally to a piston/cylinder device 
hydraulically operated from the hydraulic system of the associated powered 
vehicle, all as is conventional in the art. In this fashion, the 
attachment 10 can both be lifted vertically and can be tilted backwardly 
and forwardly from the position shown in FIG. 1 for purposes which will be 
apparent hereinafter. 
The lower frame portion 13 is shown more particularly in FIG. 4 and will be 
seen to be of generally hollow configuration including a lower plate 
member 31 and an upper plate member 32, see particularly FIGS. 4 and 5 
having vertically registered cut outs to define the arm portions or 
bifurcations 33 and 34 on either side of the throat defined by such cut 
outs. The remainder of this lower frame or shear blade frame 13 is formed 
by vertical plate members interconnecting and rigidifying the structure 
between the two main plate portions 31 and 32. The bifurcations 33 and 34 
define a channel or throat indicated generally by the reference character 
35 which at its inner end is provided with a floor plate portion 36 which 
is adapted to support the severed or sheared trees by their butt ends as 
described more particularly hereinafter and immediately ahead of this 
floor plate portion 36 there is provided a shear blade 37. The inner side 
of the throat 35 is largely blocked off by the vertical plate member which 
includes the strip 38 projecting along the left-hand side of the throat 35 
to adjacent the tip of the bifurcations 33, the base of the throat being 
covered by the bight portion 39 and there lastly being another straight 
plate portion 40 extending partially along the right-hand side of the 
throat 35 as is shown most clearly in FIG. 4. The plate portion 38 has a 
suitable opening to receive one end of the shear blade 37 and likewise the 
portion 40 has an opening receiving same also, as will be evident from 
FIG. 4. The inner end of the shear blade 37 is pinned at 41 solidly to the 
frame structure and the outer end of the shear blade 37 is provided with a 
pin 42 which attaches a clevice 43 thereto, the threaded spindle 44 of the 
clevice projecting through swivel trunnion bracket 45 fixed to the 
framework and receiving, outboard thereof, an adjusting nut 46 by means of 
which the shear blade 37 may be placed under suitable tension. The outer 
plate member 47 is provided with an opening 48 allowing access to this 
adjusting nut 46, as will be clearly evident from FIG. 4. 
The lower frame 13 also pivotally mounts the draw arm generally indicated 
by the reference character 50 which is pivoted at one end through the post 
member 51 between the upper and lower plates 32 and 31. The draw arm 50 is 
provided on its inner side, radially displaced from the post 51, with a 
series of ear means 52 which receive a pin 53 pivotally linking the draw 
arm to the free ends of the upper and lower piston rods 54 and 55, see 
FIG. 2. The respective cylinders associated with these pistons 54 and 55 
are indicated by reference characters 56 and 57 and each of these 
cylinders is pinned as at 58 to the frame structure as is clearly shown in 
FIG. 4. Thus, the two piston/cylinder devices are mechanically linked in 
parallelism between the frame section 13 and the draw arm 15, the purpose 
of which will be presently apparent. 
The lower frame section 13 also pivotally carries, about the pivot pin 60, 
the holder indicated generally by the reference character 61, see 
particularly FIGS. 4 and 5. The holder 61 is of L-shaped configuration in 
vertical section including the depending plate portion 62 and the top 
plate portion 63 which is adapted to be moved between the full and dashed 
line positions shown in FIG. 4, again the purpose of which will be 
presently apparent. For this purpose, the holder 61 is provided with a 
bracket ear portion 64 which is pinned at 65 to the forward end of a 
spring loaded link 66. The link 66 slidably projects through the bearing 
block 67 and carries a cross head member 68 at its inner end, see FIG. 5 
in particular, between which cross head 68 and the inner end of the guide 
block 67 there is provided a compression spring 69. The guide block 67 if 
fixed to the forward ends of a pair of straps 70 and 71 which are pinned 
as at 72 to the lever member 73 fixed to a vertically extending shaft 74. 
As will be seen, rotation of the shaft 74 to dispose the lever 73 in the 
dashed line position shown in FIG. 4 will corresponding shift the holder 
61 to the dashed line position also shown in FIG. 4. However, the holder 
61 can be thrown aside back from the dashed line position to the full line 
position in opposition to the compression spring 69, as will be evident. 
The purpose of this construction will be present hereinafter. 
With reference to FIG. 3, the construction of the upper frame section 14 
will be seen therefrom. As is the case with the lower frame or shear frame 
section 13, the upper frame section 14 is built up of hollow configuration 
from suitable plate stock to define the bifurcations 80 and 81 and the 
closing plate 82 which closes the inner end or throat portion of the 
channel 35' defined between the bifurcations 80 and 81 terminates short of 
the forward ends of the bifurcations 80 and 81 to accommodate the two 
holder arms 83 and 84. These holder arms 83 and 84 normally are disposed 
in the full line position shown in FIG. 3 so as not to intrude in the 
channel or throat area 35' but are adapted to be disposed in the dashed 
line positions illustrated in FIG. 3 substantially completely blocking 
across the throat. Each arm 83 and 84 is provided with a lever ear 85 
pivotally supported as by pin 86 and pinned as at 87 to the rod 88 and 
this rod 88 slidably projects through the guide block 89 in each case and 
is provided at its inner end with the cross head member 90 which captures 
the compression spring 91 between the cross head 90 and the guide block 
89, similarly to the construction noted in conjunction with the holding 
means 61. The guide blocks 89 are connected by straps 92 to the link or 
lever 93 fixed to the previously mentioned vertical shaft 74 and a 
piston/cylinder device 94 is pivotally connected at its opposite ends at 
95 and 96 to the two levers 93. It will be noted that the second shaft 74' 
does not extend vertically between the upper and lower frame portions 
14,13. It will be appreciated that operation of the piston/cylinder device 
94 may be used either to position the arms 83 and 84 and also the arm 61 
either in the dashed or full line positions as previously described. 
The operation of the device will be clear from a study of FIGS. 6 and 7. As 
noted, the normal disposition of the holding means 61, 83 and 84 is in the 
inwardly swung, throat-closing position and as the attachment is advanced 
partially to accept a standing tree T, the lower holding arm 61 is first 
engaged and will be bunted or swung aside until the tree T is disposed 
within the channel 35 sufficiently to allow the draw arm 50 to swing 
around behind and grapple the tree. This is illustrated in FIG. 7 and FIG. 
7 also illustrates the operation of the kicker bar 100 pivotally attached 
as at 101 to the tip of the draw arm 50. The opposite end of the kicker 
bar 100 bears against a compression spring 102 housed within the housing 
103, see particularly FIGS. 1 and 2 and as the draw arm 50 engages against 
the tree and draws the attachment forward to force the shear blade 37 
against and then subsequently through the tree, the kicker bar is 
displaced against the compression spring 102 as is clearly evident in FIG. 
7. The draw arm 50 scissors with respect to the shear blade 37 ultimately 
to reach a position in which the shear blade 37 has been forced all the 
way through the tree, at which point the compression spring 102 will kick 
the bar 100 and force the tree backwardly into the accumulation space 104 
in the innermost portion of the throat 35 so that the tree trunk will be 
assured of being kicked past the inner ends of the holding arm 61, 83 and 
84 so that they can then kick in or snap in behind the tree trunk and 
block the throat as is shown in FIG. 6 thereby to retain the severed tree 
within the accumulation space. In this way, a number of trees can be 
accommodated in the accumulation space 104 as is shown in FIGS. 6 and 7 by 
dashed lines and when the accumulation space is full, the vehicle can be 
operated to transport the trees to a discharge point where they are 
discharged or piled. In the transporting position of the cradle-like 
frame, the frame is preferably tilted backwardly through operation of the 
hydraulic system of the associated vehicle and then when discharged, the 
cradle will be tipped either vertically or slightly forwardly and then the 
piston/cylinder assembly 94 is operated to open the holder means and allow 
the trees to fall by gravity out of the cradle-like frame. 
FIG. 8 shows a modified form of the invention wherein the throat 35" is 
much enlarged in its accumulation area 104' to allow a larger accumulation 
of severed trees, the floor plate 36' being thereby of appreciably greater 
area. Otherwise, the construction is described hereinbefore. 
It should be noted that the construction of the draw arm 50 is such that it 
is bifurcated at its free end to present the upper and lower draw arm tips 
110 and 111 to provide good stabilizing effect against the tree and also 
to assure that the tree is drawn in behind the holders in the top frame 
assembly portion 14. 
FIGS. 9 and 10 illustrate further important features of the present 
invention. FIG. 9 illustrates the hydraulic circuitry of the associated 
powered vehicle and of that of the tree harvesting attachment. The vehicle 
carries a hydraulic pump P having a predetermined maximum flow capacity 
which, for example, may be 35 gallons per minute. The discharge side line 
120 of this pump leads through a valve mechanism 121 to the main line 122 
which distributes hydraulic fluid to the hydraulic mechanism and valve 
control system indicated generally by reference character 123 which is 
normally associated with the vehicle as, for example, the raising and 
lowering mechanism for the lift arms and the like. Normally, this system 
123 will include a pressure relief valve which is set at some maximum 
pressure beyond which the vehicle or hydraulic mechanism should not be 
operated, typically such maximum pressure being in the order of 2500 psi. 
The valve 121 is solenoid operated as will be described more particularly 
hereinafter but normally is in the position shown in FIG. 9, thereby 
allowing the pump P to feed the hydraulic system 123 of the vehicle. The 
main discharge line is also connected through the line 124 to the three 
valves 125, 126 and 127 which form part of the attachment control valve 
system. These three valves 125, 126 and 127 are also solenoid actuated as 
will be described hereinafter. The valve 127 includes the pressure inlet 
port 128 and the fluid discharge port 129 and this valve is normally 
spring urged to the closed position as is illustrated in FIG. 9 and is 
provided with a solenoid winding which effects movement of the valve spool 
to cause the line 130 to be connected to the pressure port 128 while the 
line 131 is connected to the return portion 129. These two lines 130 and 
131 are connected at opposite ends to the piston/cylinder device 57 and 
when the pressure is connected to the line 130, the piston/cylinder device 
57 will be pressurized to cause the draw arm 50 to move from its 
inoperative position toward the shear blade 37. Connected to the line 130 
is a pressure switch PS1 which is set to close at some predetermined low 
pressure, for example 2500 psi to sense when the draw arm has pulled the 
attachment forward such that the shear blade 37 engages a tree trunk. As 
soon as the pressure switch PS1 is actuated, a solenoid associated with 
the valve 126 is energized to connected the line 132 to the pressure port 
133 and the line 134 to the return portion 135 so that now the two 
piston/cylinder devices 56 and 57 are pressurized to operate mechanically 
in parallel. It is a feature of the invention that the piston/cylinder 
device 56 has a larger displacement volume over its stroke than does the 
piston/cylinder device 57. For example, the piston 56 may displace 28.28 
cubic inches over its working stroke whereas the piston/cylinder device 57 
displaces 19.78 cubic inches over its working stroke. Thus, when the 
piston/cylinder device 57 alone is connected to the pump P, the time 
required per inch of movement of piston stroke will be approximately 0.147 
seconds and the draw arm will therefore quite rapidly grapple behind the 
tree and move the attachment forwardly until the shear blade 37 engages 
the tree trunk at which time the pressure will rise to 2500 psi and 
actuate the pressure switch PS1 to pressurize the piston/cylinder device 
56 in parallel therewith whereby now reducing the rate of travel of the 
piston (it will now require approximately 0.358 second per inch of piston 
travel) to impart a low speed but high force drawing action to the draw 
arm. The operation with the piston/cylinder device 57 alone, of course, 
operates as a high speed, low force transmitting device. 
The pressure switch PS2 is connected to the line 132 and is set to higher 
pressure than is the switch PS1, for example 3000 psi. The pressure in any 
event will not exceed that which is required to shear the tree but when 
the pistons reach the ends of their stroke, pressure will build up rapidly 
to exceed or reach 3000 psi and the switch PS2 will therefore operate and 
its function is to deenergize one solenoid coil associated with the valve 
126 and energize the other solenoid coil associated with the valve 126, 
the latter effecting connection of the line 132 to the return port 135 and 
line 135 to the pressure point 133. Thus, the piston/cylinder device 56 
will now be operated in a direction to open the draw arm. However, the 
piston/cylinder device 57 remains pressure connected to continue force and 
direction to close the blade. Thus, due to the greater displacement of 
piston/cylinder device 56 vs. piston/cylinder device 57 the return or 
opening movement of the draw arm 50 will take place, and is characterized 
by very low force but very high speed movement. 
The valve 125 has two solenoid coils associated with it either to expand or 
retract the piston/cylinder device 94 independently of the operation of 
the devices 56 and 57 as will now be described in conjunction with FIG. 
10. 
FIG. 10 represents the electrical diagram associated with the hydraulic 
system of FIG. 9. The electrical system includes the main control switch 
136 which may be moved either to the "on" or the "off" position. When this 
switch is on, a single cycle sequence of operations as described above in 
connection with the hydraulic circuit will be effected provided the two 
switches 137 and 138 also are manually closed. The two switches 137 and 
138 are the type which remain normally in open position but can be 
manually closed and, when closed each switch has a holding coil 139 or 140 
associated therewith which will maintain the switch in closed position. 
These holding coils 139 and 140, however, are not effective to pull the 
switches to closed position, but simply to maintain them in a closed 
position once attained until the holding coils are deenergized. The 
holding actions of the coils 139 and 140 can of course be manually 
overridden if desired. 
When the switch 136 is closed, line 141 is powered and consequently the 
four contacts 142, 143, 144 and 145 of switch 137 are powered as are the 
contacts 146, 147 and 148 of switch 138. However contact 149 of switch 138 
is powered only when switch 137 is returned to open position as shown in 
FIG. 10 and of course with the switch 136 in the "on" position. With the 
switch 136 "on" and the switch 137 manually moved to "closed" position 
four circuits controlled by contacts 142, 143, 144 and 145 are made. One 
circuit is made through a holding coil 139 through the contact 145 and 
pressure switch PS2 through the fixed contact 150 and movable contact 151 
thereof, through the line 152 to ground. A second circuit is made to the 
open contact 161 of the relay switch 160 through line 156 and contact 144, 
and to the open movable open contact 158 of pressure switch PS1. A third 
circuit is made through the solenoid or winding 153 to ground through line 
167 and contact 143. The solenoid coil or winding 153 is connected to or 
associated with the valve 127 so as to pressurize the piston cylinder 
device 57. At the same time, the movable contact 142 of the switch 137 
provides a fourth circuit through line 154 to the solenoid coil or winding 
155 which is associated with the valve 121 to move it to a position in 
which the pump P is isolated from the vehicle hydraulic system. 
Thus, the cycle of operation is initiated and the draw arm begins to close 
at its high rate of speed. As the cycle continues the pressure builds up 
due to increased resistance to movement of the draw arm 50 as the 
attachment is pulled forward to engage its shear blade with the tree, the 
pressure switch PS1 is actuated to move its movable contact 158 into 
contact with its fixed contact 159, thus completing the circuit through 
the pull-in winding coil 164 of relay switch 160 to ground through line 
156 and movable contact 144. When pull-in winding coil is energized, 
movable contact 162 engages the fixed contact 161 to complete a circuit 
from contact 144 through line 156, thence through line 170 to the solenoid 
coil or winding 166 to ground. While this same current will continue to 
pass through the pull-in winding coil 164 to ground to retain the movable 
contact 162 engaged to the fixed contact 161 even though the pressure into 
PS1 may disipate allowing movable contact 158 to open from fixed contact 
159. The solenoid coil or winding 166 which is associated with the valve 
126 to pressurize the hydraulic line 132 while connecting the hydraulic 
return line 134 to return so that, at this time, the two devices 56 and 57 
will be operating in parallel as described hereinbefore. 
A further feature of the invention incorporates the manually actuated 
switch 172 which, is in the "on" position to complete a circuit from 
movable contact 162 through line 173 to movable contact 169 to fixed 
contact 171 and the line 174 to the solenoid winding or coil 168 which is 
adapted to actuate mechanism which declutches the powered vehicle and 
assures that during the time when the relay switch 160 is energized the 
vehicle cannot be driven. This will be during the time of the cycle 
wherein the actual shearing is taking place as will be evident 
hereinafter. 
When the draw arm has reached the end of its stroke and the tree has been 
severed, the pressure will rapidly build up and the pressure switch PS2 
will be operated thereby breaking the circuit through the holding coil 139 
and allowing the switch 137 to return to its normal open position. At this 
time contacts 142, 143, 144 and 145 will open halting draw arm in closed 
position and reengaging declutched vehicle. 
If however, it is desired to have the cycle continue on to the draw arm 
open position, the switch 138 could have been "closed" at the same time as 
switch 137 was closed without altering the aforesaid sequence when both 
switches 137 and 138 are "closed" line 141 powered contacts 148, 147 and 
146 of the switch 138 make three circuits. One circuit is made through a 
holding coil 140 through the contact 148 line 175 and pressure switch PS3 
through fixed contact 165 and movable contact 177 through the line 178 to 
ground. This circuit through coil 140 is associated with holding switch 
138 in "closed" position. While a second and third circuit is made through 
contacts 147 and 146 through lines 179 and 180 to solenoid windings or 
coils 155 and 153 respectively, which are also respectively connected to 
switch 137 through contacts 143 and 142 and lines 167 and 154. 
When the switch 137 is returned to opened position due to actuation of the 
pressure switch PS2 contact 149 is connected to power through movable 
contact 145 of the switch 137 and line 157. The circuit made by contact 
149 through line 181 energizes the solenoid winding or coil 176 which is 
associated with valve 126 in FIG. 9 and connects the line 134 of the 
device 56 to pressure and line 132 of the device 56 to return. At the same 
time contacts 147 and 146 retain circuits through lines 179 and 180 
through solenoid windings or coils 155 and 153 to ground respectively, 
thus maintaining the pressure connection to the line 130 of the device 57 
in FIG. 9, the line 131 being connected of course simultaneously to 
return. While the circuit through solenoid winding 155 maintains the valve 
121 in the isolating position. 
When the draw arm has reached its open position, at the extension of its 
stroke, pressure will rapidly build up in pressure line 134 and the 
pressure switch PS3 will be operated thereby breaking the circuit through 
the holding coil 140 allowing the switch 138 to return to its normal open 
position halting the draw arm in the open position ready for reenergizing 
when the next tree is encountered. 
The control valve 125 which controls the device 94 for opening and closing 
the holder means is controlled by the manually actuated switch 182. In the 
open position, the movable contact 185 engages the fixed contact 183 and 
energizes the winding 184 to open the holder arms whereas in the closed 
position the movable contact 185 engages the fixed contact 187 to energize 
the winding 186 to close the holders to block the throat of the channel 
35. The movable contact 188 of the switch 182 serves the function in 
either of the open or closed position of engaging one of the contacts 191 
or 189 or maintain the winding 155 energized, which controls the valve 121 
of FIG. 9, it being noted that when the switch 137 or 138 is returned to 
open position by actuation of the pressure switch PS2 or PS3, the circuit 
to the winding 155 otherwise would have been broken. 
The control system can of course be overridden at any time by manual 
actuation of the switches 137 and 138. For example, if closing of the draw 
arm should be required to be interrupted, the switches 137 and 138 are 
simply opened manually and the cycle will terminate. If the cycle has 
reached the stage in which the draw arm is opening, termination will 
require only that the switch 138 be opened since the switch 137 will 
already be opened. On the other hand, only part of the cycle may be 
initiated by closing only the switch 137 in which case the draw arm 50 
will cycle to the point at which the draw arm is completely closed as 
aforesaid noted (unless the switch 137 is manually opened before that 
time). The cycle can then be completed manually by closing the switch 138. 
In the interest of rapid harvesting, however, one would normally allow the 
device automatically to execute a full cycle. 
Since the harvesting and vehicle hydraulic systems are isolated during the 
shearing cycle, the overload relief valve 190 is provided in the hydraulic 
circuit of FIG. 9 which would be set to some maximum valve, say 3150 psi, 
to avoid damage to the harvesting attachment.