JP2885533B2 - Tractor work equipment control mechanism - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mechanism for switching between position control and draft control of a working machine mounted on a tractor.

[0002]

2. Description of the Related Art A conventional draft control device is disclosed in
This was configured as described in JP-A-20524. That is, the pressing force applied to the top link portion of the three-point link type working machine mounting device presses the draft sensor rod biased by spring, and the draft sensor rod mechanically moves the hydraulic valve for lifting and lowering the working machine. By switching, the work machine is raised when the traction force is large, and the work machine is lowered when the traction force is small, so that the draft force is controlled to be constant.

[0003]

According to the present invention, the draft force is not changed by switching the lift valve by moving the draft sensor rod by mechanically obtaining the pressing force applied to the top link as in the prior art. Is electronically detected by the electronic governor mechanism as a load factor of the engine, and the work implement elevating valve constituted by the electromagnetic switching valve is switched. This makes it possible to eliminate the mechanically configured draft sensor rod, and to connect the large biasing spring provided at the tractor side end of the top link and the switching valve to the draft sensor rod. The configuration is such that a complicated configuration can be deleted. Further, the switching and the interrelation between the draft control configured as an electronic control circuit and the position control for mechanically setting the position of the lift arm used when the tractor makes a headland turn are optimized. State.

[0004]

The problems to be solved by the present invention are as described above. Next, means for solving the problems will be described. In claim 1, it is attached to the side of the engine E.
The electronic governor mechanism A is connected to the rotation speed detection sensor 1 and the rack.
Position sensor 2, rack actuator 9, and electronic control unit G
Work machine lift to lift and lower the tractor work machine
The lowering mechanism B includes an ascending solenoid valve V1, a descending solenoid valve V2, and a lift
The electronic control unit C is composed of an electronic
A signal is exchanged between the control unit G and the lift electronic control unit C.
Between the lift electronic control unit C and the work implement lifting mechanism B
The electronic governor is communicated via the lift electronic control unit C.
-Mechanism A and work implement elevating mechanism B are connected as a control circuit,
A load factor setting device 6 for setting a load factor of the work implement;
A position setting device 7 for setting the vertical position of the industrial machine;
The detected load factor FS in the working state is determined by the electronic governor mechanism A.
Detected by the electronic control unit G of the
Indicates that the detected load factor FS detected by the electronic control unit G is negative.
Within the setting range of the set load factor F set by the load factor setting device 6
Draft control of the work machine to avoid
Position control converging to the set value of the position setting device 7
Is what you do . In claim 2, claim 1
In the tractor work machine control mechanism, the load factor setting device 6 in the draft control is also used by the position setting device 7 in the position control. Claim 3
, A work implement control mechanism for a tractor according to claim 1.
At the time of returning from the position control to the draft control, the position control is continued from the non-working state to the tillage depth set by the position setting device 7, and the detected load factor when shifting from the position control to the draft control. FS is detected, and draft control is performed using the detected load factor FS as a set load factor F in the subsequent draft control. According to claim 4, the truck according to claim 3 is provided.
If the detected load factor FS when shifting from the position control to the draft control is substantially equal to the maximum load factor of the engine, the position setting device 7
Is discarded, and draft control is performed to converge on the set load factor F set by the load factor setter 6. In claim 5, the tractor according to claim 1 is provided.
The work implement control mechanism lowers the work implement at a load rate smaller than the set load rate F when shifting from the position control to the draft control. In claim 6
Is a work implement control mechanism for a tractor according to claim 1.
Then , a one-touch lift switch 18 is provided on the operation panel, and the angle of the lift arm 13 at the position where the lift command of the one-touch lift switch 18 is received is stored. The lift arm 13 is lowered to the angle of the lift arm 13 and then returns to draft control.

[0005]

Next, the operation of the present invention will be described. In the conventional draft control mechanism, a mechanical sensor mechanism provided at the top link portion, a link and an arm, and the hydraulic switching valve is controlled by a feedback mechanism, but in the case of the present invention, The detection of the detected load factor FS is performed by the electronic governor mechanism A, the setting of the load factor is performed by the load factor setting device 6 or the position setting device 7, and all signals are obtained as electronic signals to enable the draft control. It is. However, a problem occurs when the tractor makes a headland turn or the like only by the draft control. Therefore, it is necessary to additionally provide a position control for setting the position of the lift arm 13 by the position lever 7a. The switching to the draft control is switched to the optimum state according to the situation. That is, by rotating the position lever 7a, the position set by the position setting device 7 is set as a switching position between the position control and the draft control, and the upper position is used as the position control, and the lower position is used as the draft control.

[0006]

Next, embodiments of the present invention will be described. 1 is a side view of a tractor equipped with a rotary tilling device as a working machine, FIG. 2 is a side cross-sectional view of an electronic governor mechanism A, FIG. 3 is a side view of the electronic governor mechanism A, and FIG. Drawing showing an example of the map, FIG. 5 is a hydraulic circuit diagram of a working machine lifting mechanism B having lift lifting / lowering solenoid valves V1 and V2. The configuration of the tractor will be described with reference to FIG. An engine E is disposed inside the hood of the tractor, and an electronic governor mechanism A is provided on a side of the engine E.
Is attached. An accelerator lever 14 for setting the number of revolutions of the engine E by an operator is rotatably supported by a dashboard portion of the hood, and an accelerator lever sensor 5 is disposed at a base of the accelerator lever 14. The accelerator lever sensor 5 indicates how much the operator has turned the accelerator lever 14,
Then, it detects how many revolutions are desired to be set.

A work machine control panel 15 is provided beside the seat of the tractor.
An automatic / manual changeover switch 8 for switching between automatic control and manual control of the working machine, a load factor setting device 6 for setting a load factor of the working machine, and a one-touch lifting / lowering switch 18 are arranged in the section. In addition, a position lever 7a is disposed at a portion operated by the operator with the right hand, and a position setting device 7 is disposed at a base of the position lever 7a. Further, the rotary tillage device R mounted on the rear of the tractor is provided with a tillage depth sensor 4 for detecting the tillage depth of the rotary tillage device R during the depth control of the working machine. Lift arm 13 for position control
The lift angle sensor 3 is arranged at the base of the.

The electronic governor mechanism A will be described with reference to FIGS. The electronic governor mechanism A is attached to a side surface of the engine E, and the magnetic rotating body 12 is fixed to a cam shaft 16 of the fuel pump. The rotation of the camshaft 16 is detected by the rotation speed detection sensor 1 of the magnetic rotator 12 to obtain the engine rotation speed. Further, the fuel supply amount of the electronic governor mechanism A is adjusted by moving the fuel rack 10 from side to side.
Is driven by the rack actuator 9. The fuel rack 10 moved by the rack actuator 9
The rack position sensor 2 detects the position of the vehicle and detects the fuel supply amount. A rack bar 11 connected to a fuel rack 10 is inserted through the rack position sensor 2 and the rack actuator 9.

Next, a control curve of the engine E by the electronic governor mechanism A will be described with reference to FIG. In the engine E, the engine output and the shaft torque are determined by the injection amount and the injection timing of the fuel injection pump and the engine speed. The fuel injection amount is adjusted by sliding the fuel rack 10 by the rack actuator 9. And it is obtained by measuring the injection amount based on the position of the fuel rack 10 and the engine speed. The injection timing is adjusted by a timing adjustment actuator (not shown). The engine speed is detected by a speed detection sensor 1. Accelerator lever 1 for operator in electronic control unit G
By rotating the rotation 4, the rotation speed is supported via the accelerator lever sensor 5. As the electronic control unit G, a microcomputer is used, and a program ROM storing a control program is arranged. In addition, a data ROM storing various data required for control calculation such as speed fluctuation rate characteristics is arranged.

In the data rom, what is the set value of the engine speed arbitrarily set according to the position of the accelerator lever 14 operated by the operator himself and the actual speed (actual value) according to the load. Such a speed variation characteristic is stored in the form of an arithmetic expression or a numerical table for each different work content. Regarding the speed fluctuation rate, the set value and the actual value of the period rotation speed are recognized, then the mode set by the operator is recognized, and the target rack position to be set is calculated by the droop rate map according to the mode. . A signal for changing the actual rack position to the corrected target rack position is output to the rack actuator 9, the fuel rack 10 is automatically adjusted, and the operation is performed within a predetermined speed fluctuation range. Normally, in order to recognize a predetermined speed fluctuation, control is performed according to the map d of the droop control in FIG. 4, the fuel rack 10 is changed, and the shaft torque is changed. The speed fluctuation characteristic is selected according to the mode of the work content. When constant rotation operation is required, the fuel consumption is increased or decreased and the rotation speed is made constant along the map i of the isochronous control in order to keep the rotation speed constant. , A constant rotation operation is performed. In addition, even in the case of isochronous control, especially in the case of special work, when the load increases and is close to the maximum shaft torque,
Conversely, it is also possible to increase the rotational speed, increase the shaft torque, and select a reverse droop control map r for preventing engine stall.

FIG. 5 shows a hydraulic circuit diagram of the working machine elevating mechanism B. The lift arm 13 is turned up and down by the expansion and contraction of the hydraulic cylinder 20,
Is provided with a lift angle sensor 3 for detecting the position. The lift hydraulic control valves V1 and V2 control the pressure oil to the hydraulic cylinder 20, and are constituted by a lift electromagnetic valve V1 and a downward magnetic valve V2. A signal for switching between the ascending solenoid valve V1 and the descending solenoid valve V2 is transmitted from the lift electronic control unit C.

FIG. 6 is a flow chart of the work implement control mechanism of the tractor according to the present invention. FIG. 7 is a detection signal between the electronic control section G of the electronic governor mechanism A, the lift electronic control section C, and the work implement elevating mechanism B. And FIG. 8 is a diagram for explaining the operation of the first embodiment.
6 and 7, the technology of claim 1 will be described. An electronic governor mechanism A constituted by a rotation speed detection sensor 1, a rack position sensor 2, a rack actuator 9, and an electronic control unit G; lift elevating solenoid valves V1 and V2; an accelerator lever sensor 5; , A position lever 7 a, a position setting device 7, and a lift angle sensor 3, and a detected load factor FS detected by the electronic control unit G in the working state is within a setting range of the set load factor F set by the load factor setting device 6. This is a technology for controlling the lifting and lowering of a working machine so that As shown in FIG. 7, signals are communicated between the electronic control unit G and the lift electronic control unit C of the electronic governor mechanism A, and the signals are also transmitted between the lift electronic control unit C and the work implement elevating mechanism B. Being communicated. The signal from the electronic governor mechanism A can be used as a control signal for the work implement elevating mechanism B. That is, the lift electronic control unit C
, The electronic governor mechanism A and the work implement elevating mechanism B are connected.

Next, FIG. 6 will be described along a flowchart. After the "start" of the control, "initial setting"
I do. Next, "The ascending solenoid valve V1 and the descending solenoid valve V2 are turned off.
Confirm "F". Next, "check of sensors" is performed.
Next, it is determined whether or not "check result is OK" by "NO".
If so, an alarm sounds. If "OK", automatic /
It is determined whether the manual changeover switch 8 is "automatic / manual". If "manual", position control is performed. If it is "automatic", "detection load factor FS" is read. Next, the set load factor F is read by the load factor setting device 6. The load factor setting device 6 is provided with a position lever 7a.
Is also used by the position setting device 7 provided at the base of the above. Next, it is determined based on the position of the position lever 7a whether or not the “working state” by the rotary tilling device R is present. If not in the working state, the operation shifts to position control. If it is in the working state, “read in dead zone width H” is performed next. Then, the detection load factor FS is increased or decreased by the dead zone width H.
S ”is calculated. Next, it is determined whether or not “F> HD”. If “F> HD”, “the ascending solenoid valve V1 is turned ON”. Unless "F>HD", the ascending solenoid valve V1
Is turned off. Next, “F <HS” is determined, and “F <H
If "S", the descending solenoid valve V2 is turned ON. "F <
If not "HS", the descending solenoid valve V2 is turned off. "HD
If <F <HS ”, the ascending solenoid valve V1 and the descending solenoid valve V
2 is also turned off. In claim 1, at the time of work,
Draft control is performed so that the detected load factor FS converges to the set load factor F, and position control is performed at a position set by the position lever 7a when not working. Even when the one-touch up / down switch 18 is operated, the process shifts to position control in the same manner as when the position lever 7a is operated.

Next, the drawing of FIG. 8 will be described. Whether the working machine is in the working state or the non-working state is determined based on the rotational position of the position lever 7a. When the position lever 7a is raised to the non-working position, position control is performed regardless of the position of the automatic / manual changeover switch 8. In addition, when the position lever 7a is in the working state, the draft control is performed if the automatic / manual changeover switch 8 is set to automatic.

Next, the technique of claim 2 will be described. In this technique, both of the load factor setting device 6 and the position setting device 7 which are separately arranged in the technology of claim 1 are shared by one. That is, in the case of the position control, it becomes the position setting device 7, and in the case of the draft control, it becomes the load factor setting device 6. Since both use electronic components such as a potentiometer, the signal of the set height of the lift arm 13 and the engine E
By setting the load factor as an electric signal such as voltage or current at the same level, the load factor setting device 6 and the position setting device 7 can be shared.

FIG. 9 is a flow chart for setting the deepest cultivation depth position by the rotation position of the position lever 7a. In this case, since the position lever 7a is turned to the deeper side of the working depth to set the position of the deepest working depth of the working machine, the value of the position setting device 7 is read as the deepest position. is there. The setting of this deepest position is
The rotation of the position lever 7a and the deepest position setting operation are separately stored in the memory. Thereafter, even if the position lever 7a is rotated to the normal set position, the deepest memory position does not disappear. Thus, the draft control is performed, and the deepest set position set by the position lever 7a is the deepest position of the working machine in the draft control.

Next, the technique of claim 3 will be described with reference to FIG. FIG. 10 is a flow chart in the case where the position control is performed up to the position set by the position lever 7a, the draft control is performed below the position control, and the load ratio when shifting from the position to the draft is controlled as the set load ratio F as it is. . That is, the position lever 7
It is determined whether or not the position set by a and the position of the work implement coincide with each other, and the detected load factor FS at the time of coincidence is read as the set load factor F and used as the set load factor F for the subsequent draft control. It is. FIG. 11 shows, in addition to the control of FIG.
10 is a flowchart to which the control of FIG. 9 is added to prevent the work implement from descending below the depth as the deepest tillage position.

FIG. 12 is a flowchart for controlling the engine speed by the electronic governor mechanism A prior to the control by raising and lowering the work implement when the engine E is in an overloaded state. That is, first, the magnitude of the detected load factor FS is compared with the set load factor F, and the detected load factor FS becomes equal to the set load factor F.
If it is larger, the control is returned to the original state and the electronic governor mechanism A performs the isochronous control.
Thus, the control is performed until the detected load factor FS becomes lower than the set load factor F, and thereafter, for the first time, the draft control for controlling the work implement elevating mechanism B is performed.

The technique according to claim 4 will be described with reference to FIG. FIG. 13 shows that the working machine reaches the position set by the position lever 7a, and in the draft control in which the load factor at that position is used as the set load factor F, the set load factor F matches the maximum load factor Fmax of the engine E. FIG. 9 is a flowchart in which, when the setting is performed, the set value set by the position lever 7a is discarded, and control is performed based on the set load factor F set by the load factor setting device 6. If the detected load factor FS is smaller than the maximum load factor Fmax, the detected load factor FS when shifting from the position control to the draft control is used as the set load factor F.

The technique according to claim 5 will be described with reference to FIG. FIG. 14 shows that in order to shift from the position control to the draft control, when lowering the work implement, the set load factor F is set to a small value, and when the work implement lands, it gradually descends without landing at once. It is a flowchart of the control comprised so. In this technique, the impact prevention load factor FX is calculated and obtained as a small fraction of the set load factor F, and draft control is performed based on the impact prevention load factor FX.

The technique of claim 6 will be described with reference to FIGS. FIG. 15 is a flowchart showing the control by operating the one-touch up / down switch 18, and FIG. When a lift instruction is given by the one-touch lift switch 18, the position L of the lift angle sensor 3 at that time is read, and
Next, the upper limit set value VU is read, and the solenoid valve V1 is raised until the upper limit set value VU and the position of the lift angle sensor 3 become equal.
Turn ON. When the one-touch lifting switch 18 is operated to the lower side, the lowering solenoid valve V2 is turned on so as to lower to the position L before the raising.

[0022]

The present invention is constructed as described above, and has the following remarkable effects. Electronic governor mechanism A attached to the side of engine E as claimed in claim 1.
Are replaced with a rotation speed detection sensor 1, a rack position sensor 2, and a rack.
An actuator 9 and an electronic control unit G
The work machine lifting mechanism B that lifts and lowers the work machine of the
The valve V1, the descending solenoid valve V2, and the lift electronic control unit C
The electronic control unit G of the electronic governor mechanism A and the lift electronic
Signals are exchanged between the control units C and the lift electronic control unit C
A signal is also exchanged between the
The electronic governor mechanism A and the work equipment are lifted and lowered via the child controller C.
The mechanism B is connected as a control circuit, and the load factor of the working machine is
Load factor setting device 6 for setting the working machine and setting the vertical position of the working machine
Provide a position setting device 7 that performs
The load factor FS is determined by the electronic control unit G of the electronic governor mechanism A.
In the working state by the work machine, the electronic control unit G
The detected load factor FS is set by the load factor setting device 6.
Drive the work equipment so that it falls within the set range of the set load
Shift control and the position setting device 7
Since the position control that converges to the set value is performed , the following effects are obtained. That is, the position setting device 7
Is used to set the convergence position of the position control.
Further, the position of the position setting device 7 can be a switching point between the working position and the non-working position. That is, position control is performed above the position set by the position setting device 7, and draft control is performed below the position. This configuration eliminates the need for the operator to switch between draft control during operation and position control during elevation.

Since the load factor setting device 6 is also used as the position setting device 7 in the position control, the components of the potentiometer can be omitted without providing the load factor setting device 6 separately. This leads to low cost.

Further, since the present invention is configured as in claim 3, the operator does not set the set load factor F specially by using the load factor setting device, and the boundary between the working position and the non-working position determined by the position of the position lever 7a. With the line, the detected load factor FS when changing from the position to the draft control is set as the set load factor F as it is, so that an operator who is not familiar with the technology can eliminate the hesitation as to what the set load factor F should be. .

[0025] Further, with the configuration as claimed in claim 4, the load factor when shifting from the position control to the draft control is as follows.
In the case where the load is to be read as the set load factor F, if the maximum load factor of the engine E matches before the shift from the position to the draft, the set load factor is discarded,
Draft control is performed based on the load factor set by the load factor setting device 6 separately. The set value set by the position lever 7a and the position setting device 7 is set to the deepest cultivation depth.

Also, when the tractor lowers the work machine at the end of the field end circuit, the load factor smaller than the set load factor F is set as the impact prevention load factor FX. By doing so, when the working machine bites into the ground, it gradually bites into the ground, so that impact can be prevented.

[0027] In addition, in the case of using the one-touch up / down switch 18, the present invention is configured as follows.
Since the position control is performed until the position set by the position lever 7a is reached and the draft control is performed thereafter, the tractor also starts to move when the work machine descends, so that the engine E is heavily loaded, and the load ratio is increased. Although accurate electronic control is not possible, as in the present invention, by reading the position before ascending, descending at the position to this position, and by drafting below that position,
It is possible to achieve accurate control.

[Brief description of the drawings]

FIG. 1 is a side view of a tractor equipped with a rotary tilling device as a working machine.

FIG. 2 is a side sectional view of the electronic governor mechanism A.

FIG. 3 is a side view of the electronic governor mechanism A.

FIG. 4 is a diagram showing an example of a control map by an electronic governor mechanism A.

FIG. 5 is a hydraulic circuit diagram of a working machine elevating mechanism B including lift elevating electromagnetic valves V1 and V2.

FIG. 6 is a flowchart of the work implement control mechanism of the tractor of the present invention.

FIG. 7 is a diagram illustrating movements of a detection signal and a command signal among an electronic control unit G, a lift electronic control unit C, and a work implement elevating mechanism B of the electronic governor mechanism A;

FIG. 8 is a diagram for explaining an operation state of the technique of claim 1;

FIG. 9 is a flowchart for setting a deepest plowing depth position by a rotation position of a position lever 7a.

FIG. 10 is a flowchart of a case in which position control is performed up to a position set by a position lever 7a, draft control is performed below the position, and control is performed as a set load ratio F without changing a load factor when shifting from position to draft. It is.

FIG. 11 In addition to the control shown in FIG.
10 is a flowchart to which the control shown in FIG. 9 is added, in which the turning position at the time of the operation a is set as the deepest plowing depth position, and the work implement is not lowered to a depth lower than that.

FIG. 12 is a flowchart for controlling the engine speed by the electronic governor mechanism A before the control by raising and lowering the work implement when the engine E is in an overloaded state.

FIG. 13 is a diagram illustrating a configuration in which the work implement reaches a position set by the position lever 7a and employs the load factor at the position as the set load factor F in the draft control, in which the set load factor F is set.
Is equal to the maximum load factor Fmax of the engine E,
6 is a flowchart illustrating a control in which a set value set by a position lever 7a is discarded and a control is performed based on a set load factor F set by a position setter 7;

FIG. 14 sets a small load factor F when lowering the work implement to shift from the position control to the draft control, and gradually lowers the work implement without landing at a stretch when the work implement lands. It is a flowchart drawing of the control comprised so that it may be.

FIG. 15 is a flowchart showing control by operating a one-touch lifting switch 18;

FIG. 16 is a drawing showing an arrangement of the one-touch lifting switch 18;

[Explanation of symbols]

 F Set load factor FS Detected load factor D Detected towing load DM Average calculated value A Electronic governor mechanism B Work implement elevating mechanism C Lift electronic control unit V1 Elevating solenoid valve V2 Descending solenoid valve 1 Rotation speed detection sensor 2 Rack position sensor 3 Lift angle Sensor 4 Tillage depth sensor 5 Accelerator lever sensor 6 Load factor setting device 7 Position setting device 7a Position lever 8 Automatic / manual changeover switch 9 Rack actuator 10 Fuel rack 11 Rack bar 12 Magnetic rotating body 18 One-touch lifting switch 20 Hydraulic cylinder

Claims (6)

(57) [Claims] 1. An electronic governor attached to a side surface of an engine E.
-The mechanism A is composed of a rotation speed detection sensor 1 and a rack position sensor 2
And a rack actuator 9 and an electronic control unit G
Work machine lifting mechanism B that lifts and lowers the work machine of the tractor
Is the lift solenoid valve V1, the fall solenoid valve V2, and the lift electronic control
And an electronic control unit G of the electronic governor mechanism A.
And signals between the lift electronic control unit C and the lift
Signal exchange between electronic control unit C and work implement lifting mechanism B
And an electronic governor mechanism A via the lift electronic control unit C.
And the work machine elevating mechanism B are connected in a control circuit.
A load factor setting device 6 for setting a load factor of an industrial machine;
Providing a position setting device 7 for setting the descending position,
The detection load factor FS is the electronic control of the electronic governor mechanism A.
Detected by the control unit G
The detected load factor FS detected by the control unit G is the load factor setting.
To be within the setting range of the set load factor F set by the heater 6
Draft control of work equipment, position when not working
A tractor working machine control mechanism for performing position control that converges to a set value of a vehicle setting device 7 . 2. A work machine control device for a tractor according to claim 1.
In the structure, the load factor setting device 6 in the draft control is
A work implement control mechanism for a tractor, which is also used by a position setting device 7 in position control. 3. A work machine control device for a tractor according to claim 1.
In the structure, when returning from the position control to the draft control, the position control is continued from the non-working state to the tillage depth set by the position setting device 7, and the detected load when shifting from the position control to the draft control is detected. A working machine control mechanism for a tractor, which detects a rate FS and performs draft control using the detected load rate FS as a set load rate F in subsequent draft control. 4. The tractor work implement control mechanism according to claim 3, wherein a position setting device is provided when the detected load factor FS when shifting from the position control to the draft control substantially coincides with the maximum load factor of the engine. 7. A working machine control mechanism for a tractor, wherein a set value set by the load factor setting unit 6 is discarded and draft control is performed so as to converge on the set load factor F set by the load factor setting unit 6. 5. A work machine control device for a tractor according to claim 1.
In structure, at the time of transition from the position control to the draft control, a small consisting load factor than the set load factor F, tractor work machine control mechanism, characterized in that lowering the work implement. 6. A work machine control device for a tractor according to claim 1.
In the structure, a one-touch lifting switch 18 is provided in the operation panel portion, the angle of the lift arm 13 at the position where the lifting command of the one-touch lifting switch 18 is received is stored, and when the lifting arm 13 is raised to the non-working position and receives the lowering command, A working machine control mechanism for a tractor, wherein the mechanism lowers the stored angle of the lift arm 13 and then returns to draft control.