fig1 of the drawings represents diagrammatically the relationship of a tractor draft load monitoring system , generally designated 10 , to a tractor power unit 11 . as exemplified , the tractor power unit 11 is constructed with the engine , transmission and transfer case or drop box as a single unit . the power unit 11 is coupled in a conventional manner to a tractor drive shaft 12 . the power unit 11 is mounted to a tractor frame 13 by resilient mounts 14 which permit the power unit to rotate slightly , but measurably , about the longitudinal axis of the drive shaft in reaction to the drive shaft torque . the resilient mounts 14 are located relatively high on the power unit 11 which causes the bottom 15 of the power unit 11 to move sideways or laterally relative to the drive shaft axis when the power unit rotates in reaction to the drive shaft torque . because this sideways movement is approximately proportional to drive shaft torque , this movement can be used as a measure of implement draft or drawbar pull plus rolling resistance of a tractor when the tractor is coupled to an implement ( not shown ) in which the implement draft is controlled by a single remote hydraulic lift means for raising and lowering the implement . the hydraulic lift means comprises a remote hydraulic circuit generally designated 16 ( see fig2 a ) that includes a double acting hydraulic lift cylinder 17 , a source of fluid under pressure indicated by an inlet pipe 18 and a supply valve 19 interposed between the source of fluid and the lift cylinder . the supply valve 19 is coupled to the lift cylinder 17 by a first conduit 21 communicating with the head end 22 of the lift cylinder and a second conduit 23 communicating with the rod end 24 of the lift cylinder . the supply valve contains a spool valve 25 which is maintained in a neutral position by a centering spring ( not shown ) in a conventional manner and when in this position no fluid will flow to the hydraulic lift cylinder 17 . movement of the spool valve 25 of the supply valve 19 is controlled by a control valve assembly , generally designated 26 , that is also connected to a source of fluid under pressure as indicated by an inlet pipe 27 at the top of the control valve assembly , see fig2 b . the control valve assembly 26 has several functions , the most important being to sense the sideways movement of the power unit 11 and to transmit that movement to the supply valve 19 to cause the latter to supply fluid to either the head end 22 or the rod end 24 of the lift cylinder 17 to raise or lower the implement as may be required to adjust the draft load on the tractor . the sideways movement of the power unit 11 is sensed by a flexible transmission cable 28 ( of the bowden cable type ) that has its transmission wire or control core 30 coupled at one end 29 ( see fig2 a ) to a retainer 31 secured to the bottom of the power unit 11 . the other end 32 of the transmission wire 28 has a spring - loaded connection through spring 33 to a clevis 34 having a pin 35 and slot 36 connection to a summing bar 37 pivoted at its upper end 38 to a link 39 pivotally secured at one end 41 to an arm 42 . the arm 42 is pivotally mounted intermediate its ends on a bracket 43 attached to a tractor frame portion 44 . at its lower end 45 of the summing bar 37 is pivotally connected to a clevis 46 coupled to one end of a spool 47 of an input valve 48 . the input valve 48 is shown as an integrated part of the control valve assembly 26 and its spool 47 may be considered as the actuator member of the control valve assembly . to summarize to this point : the power unit 11 is connected through a connecting means , cable 28 , to the actuator member or spool 47 of the input valve 48 of the control valve assembly 26 . the operation is as follows . first , it is assumed that the tractor is pulling an implement at a steady drawbar pull and that the remote or hydraulic lift cylinder 17 controlling the working depth of the implement is only partially extended from a fully retracted position so that it can move in either direction . under steady conditions , the input valve spool 47 will be centered as shown in fig2 b and no fluid will be flowing into the control valve assembly 26 . if the draft of the implement now increases due to a change in soil conditions , the drive shaft torque will increase and cause the power unit 11 to move about the axis of the drive shaft 12 . for purposes of discussion , it will be assumed the motion is clockwise as viewed in fig2 a . when this occurs , the bottom of the power unit 11 moves to the left and pulls on the transmission wire 30 . the other end 32 of the wire pulls on the summing bar 37 causing it to pivot in a counter - clockwise direction about the link 39 , as viewed in fig2 b . the movement of the summing bar 37 pushes the input valve spool 47 to the right so that fluid flows from the input conduit 27 to a passage 49a into a bore 51 in the control valve assembly 26 . the bore 51 contains a flow control spool 52 that normally is centered , as seen in fig2 a . the fluid flows past the centered spool 52 into passage 53a into a bore 54 containing an end of stroke spool 55a which is at its outermost position . the fluid continues to passage 56a into a servovalve cylinder 57 containing a double acting piston 58 . the fluid pressure causes the piston 58 to move to the left . the piston 58 is mounted on a piston rod 59 that extends outwardly of the control valve assembly casing 61 . the piston rod 59 and the spool valve 25 are coupled to each other by a coupling 62 . thus , movement of the piston 58 to the left causes corresponding movement of spool valve 25 directing fluid to port 63 of the supply valve 19 . fluid from port 19 flows through conduit 21 to the head end 22 of the lift cylinder 17 causing the latter to extend . the extension of the lift cylinder causes ( a ) the implement to raise thereby reducing the draft load , and ( b ) fluid to flow out of the rod end 24 of the lift cylinder through the conduit 23 toward the supply valve outlet port 65 . the conduit 23 contains a check valve 64 having a poppet 66 with an orifice hole 67 in it . at low fluid flow , the oil flows through the orifice 67 causing a pressure drop across the check valve 64 . as the flow increases , the pressure drop or pressure differential increases until the pressure entering the check valve 64 is greater than the pressure leaving the check valve plus the force of a check valve spring 68 causing the poppet to open and thereby permitting fluid flow around the latter . the conduit 23 is tapped above and below the check valve 64 by conduits 69 and 71 . whenever there is fluid flow through the check valve 64 , the pressure in conduit 69 is higher than that in conduit 71 . this pressure differential acts on the flow control spool 52 causing the latter to move to the left , shutting passage 49a and permitting fluid to flow from passage 53a through passage 72a to a sump 73 . thus , pressure is removed from the servovalve piston 28 permitting the supply valve centering spring to return the supply valve spool 25 to neutral . this cuts off fluid to conduit 21 stopping the operation of the remote cylinder 17 . if the position of the flexible cable wire 30 remains displaced from the original steady state position , the input valve spool 47 will remain displaced to the right , directing fluid into passage 49a . since the supply valve spool 25 has returned to neutral , pressures in passages 69 and 71 will be equal , allowing the flow control spool 52a to return to center . this permits fluid to flow from passage 49a to passage 53a and to the servovalve piston 51 , thereby initiating another implement raise cycle . the load monitor will continue raising the implement in small increments until the position of the flexible cable wire 30 indicates that the desired drawbar pull has been attained . now , if soil condition , etc . change to reduce drawbar pull , the load monitor will function in a similar manner but in opposite direction . when the draft is reduced , the power unit 11 rotates counter - clockwise allowing the attached cable 28 to move to the right . when this occurs , the summing bar 37 pivots left about its pivotal connection with upper link 39 pushed by the summing bar preload spring 74 . this pulls the input valve spool 47 left , directing fluid from the input conduit 27 to passage 49b , then to 53b and 56b to the servo cylinder 57 moving the servo piston 58 and remote valve spool 25 to the right . this directs fluid from the remote supply to port 65 through the orifice 67 in the check valve poppet 66 and to the head end 24 of the remote cylinder 17 . retracting the piston 75 of remote cylinder 17 will increase the draft of the implement . as the fluid goes through the orifice 66 in the check valve 64 , there will be a pressure drop and the pressure in passage 71 will be higher than in passage 69 . this causes the flow control valve spool 52 to move to the right closing off passage 49b and allowing the remote valve spool centering spring to center the spool 25 and shut , thus to stop the motion of the remote cylinder . this cycle will repeat until the position of the flexible cable 28 indicates that the desired drawbar pull has been reached . when the operator desires to operate at a different value of drawbar pull , he has to change the position of a control lever 76 . assume that a reduction in drawbar pull is desired . moving the upper end of the control lever 76 ( shown in fig2 b ) to the left will , through an adjustable link 77 , move the upper end 38 of the summing bar 37 to the left . as the upper end 38 moves left , the bar 37 pivots about the cable clevis 34 and its lower end 45 moves to the right pushing the input valve spool 47 to the right . this directs fluid to passage 49a then to 53a and 56a moving the servo piston 58 and remote valve spool 25 to the left . thus , fluid from the remote supply is directed to port 63 which extends the remote cylinder and raises the implement reducing drawbar pull . fluid passing through the check valve 64 orifice 67 causes the pressure in passage 69 to be higher than in passage 71 moving the flow control spool 52 to the left stopping the motion of the remote cylinder . as a result of the reduction in drawbar pull , the cable clevis 34 moves to the left moving the input valve spool 47 to the left towards the center position . if the drawbar pull reduction is sufficient , the input valve spool will be centered and no further load monitor action will occur . if the drawbar pull is still too high , the cycle will repeat until the desired drawbar pull level is reached . when an increase in drawbar pull is desired , the operator moves the control lever to the right . the load monitor system responds as above except in the opposite direction . a fast raise / fast lower mode is provided when the remote cylinder 17 is to be moved to fully extended or fully retracted position unhampered by the flow control cycling . for fast raise ( lift cylinder extend ) mode , the operator moves the control lever 76 to the left extreme of its travel . this moves the top of the summing bar 37 to the left first pivoting the summing bar about the pin 78 of the clevis 34 . when a pin 78 through the summing bar 37 and through a slotted hole 79 in link 81 reaches the left end of its travel , the summing bar 37 then pivots about this pin 78 . this compresses the preload spring 74 , releases the load on clevis 34 , and pushes the input valve spool 47 to its extreme right position . then the input fluid flows through the center axial hole 82 in the input spool 47 and to passage 83a . passage 83a bypasses the flow control spool 52 and the fluid flows directly to passage 53a . thus , in fast raise / fast lower mode , movement of the flow control spool 52 will not affect the fluid flow within the servovalve 51 . the fluid from 53a flows through the end of stroke bore 54 and through passage 56a causing fluid to be directed to the servovalve piston 58 . remote supply valve 19 fluid is then directed to port 63 and the remote cylinder extends . when the cylinder 17 reaches the end of its travel , the pressure rises in the line 21 between port 63 and the remote cylinder 17 and this pressure is transmitted by line 84 to the servovalve 51 . when the pressure ( limited by a supply valve pressure relief valve 85 ) acts on a pin 86a , the pin 86a pushes the right hand spool 55a to the left . this shuts off passage 53a , shuts off the left end of passage 87a , and opens passage 56a to sump 88a . the centering spring in the supply valve returns the supply valve spool 25 to neutral position and the remote cylinder 17 is held in its extended position . the pressure from passage 53a acts on the right end of the right hand spool 55a and keeps it in its extreme left position until the input valve spool 47 is centered again . for fast lower mode , the control lever is moved to the extreme right position . the system then functions similar to the fast raise mode except in the opposite direction with the control valve assembly components marked with the postscript &# 34 ; b &# 34 ; being involved . similarly , when the cylinder 17 reaches the end of its travel , the pressure build up in line 69 and its branch 69a causes the pin 86b to push the left hand spool 55b to the left . this shuts off passage 53b , shuts off the left end of passage 87b , and opens passage 56b to sump 88b . the supply valve centering spring returns the supply valve spool 25 to a neutral position and the remote cylinder is held in its retracted position . the pressure from passage or conduit 53b acts on the left end of the left end spool 55b and keeps it in its extreme right position until the input valve spool 47 is centered again . it is to be understood this invention is not limited to the exact construction illustrated and described above , but that various changes and modifications may be made without departing from the spirit and scope of the invention as defined by the following claims .
a tractor draft load monitoring system responsive to tractor and associated implement load changes . the system is particularly adapted for a tractor having an engine / transmission power unit coupled to its drive shaft . the power unit is mounted on the frame by resilient mounts that permit measurable angular displacement of the power unit relative to the frame about the drive shaft axis in reaction to changes in the drive shaft torque . the working depth of the implement , which may be tractor mounted , semi - mounted or a pull type implement , is raised or lowered by a hydraulic lift system that is controlled by a control valve assembly connected to a source of fluid under pressure . interposed between the power unit and the control valve assembly is a transmission cable and lever system that is operative to transmit angular displacement of the power unit to an actuating member of the control valve assembly to cause hydraulic actuation of the hydraulic lift device to change the working depth of the implement to compensate for changes in its draft load .