CA1261944A - Control apparatus and proportional solenoid valve control circuit for boom-equipped working implement - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
A control apparatus having a boom control system for controlling the movement of a liftable boom supported by a vehicle body and a working device control system for controlling a working device pivoted to the boom. Each of the control system includes a proportional solenoid valve and comprises an instruction circuit for producing an insturction signal in accordance with the amount of manipulation of an operating lever, discrim-inating circuit for determining the direction of operation of the valve from the instruction signal, a reference signal generator, a comparison circuit for comparing the instruction signal with the reference signal from the generator to obtain a pulse signal of a width in proportion to the amount of manipulation, and drive circuit for converting the pulse signal into a current to drive the valve in the direction determined by the discriminating circuit. The boom, as well as the working device, is movable at a speed corresponding to the amount of manipulation of the operating lever.

Description

TII'LE OF THE INVEMTION
CONTROL APPARAl~S A~PROPORTIONAL SOLENOID VALVE CONTROL
CIRCUIT FOR BOOM-EQUIPPED WORKING IMPLEMENT

FIELD OF THE INVENTION AND RELATED ART STATEMENT
The present invention relates to a control apparatus and a proportional solenoid valve control circuit for boom-equipped working implements.
Working implements comprising a boom assembly liftably pivoted to a vehicle body and working means pivotably connected to the forward end of the boom assembly include a tractor-attached front loader and various other implements.
The tractor-attached front loader comprises a pair of opposite booms liftably pivoted to the body :~ 15 of the tractor, and a bucket pivotably connected to :~ the forward end of each boom. A hydraulic circuit for a boom cylinder and a bucket cylinder for operating " the boom and the bucket has solenoid valves in corresponding relation to these cylinders for controlling : 20 the upward or downward movement of the boom and the rotation of the bucket in a scooping or dumping : . direction The control system for such a working implement generally has an operating lever which ls moved forward ~:. .:: -. , . - ... . .: , - ~-9~
or rearward or sidewise to operate a switch, which in turn energizes or deenergizes the corresponding solenoid valve.
However, the conventional on-off drive type S control system, which merely opens or closes the solenoid valve, is not adapted to control the flow of the working fluid, so that the cylinder is operated at a constant speed at all times and is not operable at a very low speed. Accordingly, the system has the drawback of necessitating great skill for operating the working implement which requires a delicate movement.
For example, when earth or sand is to be transported by the front loader after scooping with the bucket and lifting the booms, the booms, if merely raised, incline the bucket with its front end raised, permitting ~ the contents of the bucket to spill rearward. To avoid ; this, the bucket is rotated very slowly toward the dumping direction with the rise of the booms to cause the bucket to assume a corrected posture with its opening positioned horizontally.
Further when earth or sand lS to be scooped up again after dumping~the contents of the bucket at its ralsed position and lowering the booms, the bottom of the bucket must be placed on the ground horizontally.
In this case also, therefore, the bottom is positioned

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horizontally correctly by rotating the bucket slowly when the booms are lowered.
Additionally, there arises a need to raise or lower the booms very slowly, for example, to diminish impact upon stopping.
Thus, the operation of the front loader requires low-speed movement of the booms and the bucket, whereas with the conventional control system of the on-off type incorporating switches, the solenoid valve is not adapted for flow control, consequently necessitating great skill for the operation of the loader.
Further conventionally, the solenoid valves are operated merely in operative relation with the manipulation of the operating lever, so that the control system is not adapted to preset the posture of the bucket and to bring the bucket into the preset posture when the booms are raised or lowered.
On the other hand, control circuits for propor-tional solenoid valves for use in such control systems include one which has a servo mechanism. The servo mechanism is SQ operated as to vary the resistance value of a variable resistor in accordance with the amount of ,. :
; manipulation of the operating lever, whereby an energizing current proportional to the movement of the manipulating ~ 25 lever is passed through the valve for controlling the :
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flow of working fluid.
Nevertheless, the control circuit, which necessitates the servo mechanism or the like, has the drawbacks of being very complex in construction, cumber-some to make and liable to malfunctions.
OBJECTS AND SUMM~RY OF THE INVENTION
The present invention has been accomplished in order to solve the foregoing problems heretofore encountered.
More specifically, a first object of the present invention is to provide a control apparatus comprising operating means, a control system for a boom and a control system for a working device, each of the systems having a proportional solenoid valve which is operable in a specified direction in proportion to the amount of manipulation of the operating means when the operating means is manipulated in the specified direction -to move the boom or the working device at a speed corresponding ;~ to the amount of manipulation.
;; 20 : A second object of the invention is to provide :~a control apparatus of the type stated wherein the proportional solenoid valve is operable in proportional relation with the manipulation of the operating means easily and reliably by processing electric signals ~` ~ 25 :instead of the servo mechanism or the like conventionally ; -4-used.
To fulfill these objects, the present invention provide a control apparatus comprising a boom control system and a working device control system each having a proportional solenoid valve, each of the systems comprising instruction means for producing an instruc-tion signal in accordance with the amount of manipula-tion of operating means, discriminating means for discriminating the direction of operation of the proportional solenoid valve from the instruction sisnal, ; means for gene~ating a specified reference signal, comparison means for comparing the instruction signal with the reference signal to obtain a pulse signal having ~ a pulse width in proportion to the amount of manipulation : 15 of the operating means, and drive means for converting the pulse signal from the comparison means into an electric current to drive the proportional solenoid valve in the direction discriminated by the discriminat~
ing means.
~ third object of the present invention is to provide a control apparatus of the type described wherein the boom control system is proportionally ~; controllable and the posture of the working devic:e is ~.
presettable by the working device control system to : 25 render the working device automatically controllable to ~ ~ .

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, -the contemplated posure smoothly when the boom ls raised or lowered.
To fulfill this object, the working device control system of the present invention comprises a sensor for detecting the rotated posture of the working device, means for setting the desired posture of the working device, deviation detecting means for determining the difference between a signal from the posture sensor and a signal from the setting means to produce a deviation signal, means for discriminating from the :
deviation signal the direction in which the working device is to be rotated, comparator means for comparing the deviation signal with the reference signal from the reference signal generating means to produce a pulse -15 signal of a pulse width in proportion to the devlation signal, and drive means for converting the pulse signal from the comparator means into an electric current to drive the proportional solenoid valve in the direction of rotation of the working device determined by l_he discriminating means.
~ fourth object of the present invention is to provide a control circuit which is most suitable for controlling the proportional solenoid valve included in the control apparatus for the working implement of the type described.

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-For this purpose, the invention provides a control circuit comprising instruc~ion means for producing an instruc-tion signal in accordance with the amount of manipula-tion of operating means, discriminating means for discriminating the direction of operation of the proportional solenoid valve from the instruction signal, means for generating a specified reference signal, comparison means for comparing the instruction signal with the reference signal to obtain a pulse signaL having a pulse width in proportion to the amount of manipulation of the operating means, and drive means for converting the pulse signal from the comparison means into an electric current to drive the proportional solenoid valve in the direc~ion discrimina.ed by the discriminat-ing means.
BRIEF DESCRIPTION OF THE DRAWINGS
Figs. 1 to 15 show a first embodiment of thepresent invention;
Fig. 1 is a side elevation showing a tractor and a front loader attached thereto;
Fig. 2 is a sectional view showing a sensor;
Fig. 3 is a rear view showing operating means;
Fig. 4 is a rear view in section showing the operating means;
Fig. 5 is a view in section taken alonq the ~; :

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Fig. 6 is a view in section taken along the line Y-Y in Fig. 4;
Fig. 7 is a diagram of a hydraulic circuit;
Flg. 8 is an electric circuit diagram of control systems;
Fig. 9 is a diagram showing the waveforms of signals, Fig. 10 is a diagram illustrating control positions;
Fig. 11 shows postures o~ a bucket as xelated to the sensor;
Fig~ 12 is a diagram illustrating voltage setting;
Figs. 13 and 14 are diagrams for illustrating operation;
Fig. 15 is a diagram showing the relation between the posture of the tractor and sensors;
Flgs. 16 to 22 show a second embodiment of the invention;
Fig. 16 is a hydraulic circuit diagram;
~ Flgs. 17 and l8 are electric circuit cliagrams ;~ ~ showing control systems;
Fig. 19 is a diagram showing signal waveforms;
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operating means;
Fig. 21 is a rear view in section showing the operating means;
Figs. 22 to 24 are electric circuit diagrams showing other embodiments of the invention; and Fig. 25 is a hydraulic circuit diagram showing another embodiment of the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention will be described below in detail with reference to the illustrated preferred embodiments.
Figs. l to 15 show a front loader embodying the invention and attached to a tractor.
With referenct Flg. l, indicated at l is the tractor body, at 2 front wheels, at 3 rear wheels, at

4 a rear wheel fender, and at 5 a driver's seat. The front loader, which is indicated at 6, comprises a pair ; of opposite masts 8 removabl~ attached in an upright position to opposite sides of the tractor body l by a pair of opposite mount frames 7, a pair of opposite booms 10 liftably mounted by pivots 9 on the upper ends of the masts 8, a pair o~ opposite boom cylinders 11 ~ for raising or lowering the booms 10, a bucket (working -~ device) 13 rotatably supported by a pivot 12 on the forward end of each boom 10, and a pair of opposite ~ _9_ : . ,, ' bucket cylinders 14 for pivotally moving (rotating) the bucket 13.
An inclination sensor 15 for detecting the inclination of the tractor body 1 is mounted on the front loader 6, for example, on one of the pair of masts 8. A posture sensor 16 for detecting the posture of the bucket 13 when it is rotated is attached to a bracket 17 on the rear side of the bucket 13. ~s seen in Fig. 2, these sensors 15, 16 comprise a weight plate 21 and a variable resistor 22 provided respectively in t~o separated chambers 19 and 20 within a box-shaped case 18. The weight plate 21 is mounted on a rotatable shaft ~ 23 supported by the case 18, while the variable resistor ; 22 is operatively connected by the shaft 23 to the weight plate 21. Accordingly, a change in the posture of the tractor body 1 or the bucket 13 moves the weight plate 21, causing the resistor 22 to produce a voltage signal in accordance with the posture. A damper oil 23a is contained in the chamber 19.
With reference to Figs. 3 to 6, operating means 24 comprises a case 25 mounted on the rear-wheel fender 4 at one side of the driver's seat 5, an operating lever : .:
` ~ 26 movable forward, rearward, leftward, rightward or in :: .
any one o~ different oblique directions and supported by the case 25, first and second variable resistors 27, j .

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28 accommodated in the case 25 and operatively connected to the operating lever 26, etc. More specifically, the operating lever 26 is supported by a transverse rod 30 on a movable frame 29 which is rectangular when seen from above and which is supported by longit~dinal rods 31 on the case 25. Accordingly, the operating lever 26 is movable in a desired direction as indicated by arrows in Fig. 6, about the two axes, intersecting each other at right angles, of the transverse rod 30 and the . 10 longitudinal rods 31. The lever 26 is resiliently held in a neutral position by unillustrated spring means.
The first variable resistor 27 constitutes raising-lowering : instruction means for instructing the booms to rise or lower, is operable by the forward or rearward movement of ~; 15 the operating lever 26 through the transverse rod 30 and produces a raising or lowering (up-down) instruction signal of a voltage which varies with the amount of movement or manipulation of the operating lever 26. The ; second variable resistor 28 constitutes rotation instruction means for instructing the bucket 13 to rotate, is operable by the leftward or rightward movement of the operating lever 26 through the longitudinal rod 31 and the movable frame 29 and produces an instruction signal of a voltage which varies with the amount of manipulation of the lever 26.

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The operating lever 26 has a posture holding switch 32 o~ the push button type at its upper end and a semispherical actuating portion 33 at its lower end.
Provided within the case 25 at its bottom are a raising switch 34, lowering switch 35, dumping switch 36 and a scooping switch 37 which are arranged around the actuating portion 33 in front and rear thereof and at - left and right sides thereof, respectively. These switches are actuated by the portion 33 when the operating lever 26 is manipulated to the greatest extent. Indicated at 38 is a flexible cover.
Fig. 7 shows a hydraulic circuit for the lift cylinder 11 and the bucket cylinder 14. A first propor-tional solenoid valve 39 of the flow proportional type for controlling the lift cylinder 11 has a raising solenoid 40 and a lowering solenoid 41. A seconcl ~; proportional solenoid valve 42 of the flow proportional t~pe for controlling the bucket cylinder 14 has a dumping solenoid 43 and a scooping solenoid 44.
The proportional solenoid valves 39 and 42 ; are driven under the control of a control circuit shown in Fig. a. With reference to Fig. 8, first discriminating means 45 for discriminating the direction of upward-downward movement comprises two comparators 46, 47, a variable resistor 43 provided therebetween for setting ~ .
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a dead zone + alpha, etc. When the instruction signal from the first variable resistor 27 is greater than an upper reference value, l/2V + alpha, the comparator 46 produces an up signal, while if the signal is smaller than a lower reference value, 1/2 V - alpha, -the compa-rator 47 produces a down signal. Second discriminating means 49 for discriminating the direction of movement for dumping or scooping comprises two comparators 50, 51, a variable resistor 52, etc. like the first means 45.
The comparator 50 produces a dumping signal, or the comparator 51 produces a scooping signal 51, in accord-ance with the instruction signal from the second variable resistor 28.
A triangular wave oscillation circuit 53 serving as a reference signal generating means generates a reference signal of predetermined frequency, i.e. a triangular wave signal a as seen in Fig. 9. First comparison means 54 comprises two comparators 55, 56 and compares the instruction signal b from the first variable resistor 27 with the triangular wave signal a from the oscillation circuit 53 to produce a pulse signal c of a width ln proportion to the variation of the instruction signal b, i.e. to the amount of manipulation of the operating lever 26, as seen in Fig. 9. The comparators 55 and 56 are in opposite relation to each ' ; ' ",,,, ~ :
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other with respect to the input of the instruction signal _ and the triangular wave signal a. The comparator 55 is on when the instruction signal b is greater than the triangular wave signal a and is off when the signal b is smaller than the signal a, producing the pulse signal c of Fig. 9. The comparator 56 is on when the signal b is smaller than the signal _ and is off when the signal b is greater, in reverse relation to the case shown in Fig. 9. Second comparison means 57 comprises two comparators 58, 59 and, like the first comparison means 54, produces a pulse signal of a width in proportion to the instruction signal from the second variable resistor 28, based on the instruction signal ~ and the triangular wave signal from the oscillation ; 15 circuit 53.
First drive means 60 converts the pulse signal from the first comparison means 54 into an electric current to drive the first proportlonal solenoid valve 39.
The drive means comprises switching elements 61, 62 connected to the solenoids 40, 41 and analog switches 63, ; ~ 64 for applying the pulse signal from the comparators 55, 56 to the elements 61, 62, respectively. When the signal from the comparators 55, 56 of the first discriminating means 5~ is fed to the analog switches 63, 25 ~ 64, the swi~ching elements 61, 62 are turned on and off ';
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in synchronism with the pulse signal. Like the first drive means 60, second drive means 65 for converting the pulse signal from the second comparison means 57 into an electric current to drive the second solenoid valve 42 comprises switching elements 66, 67 and analog switches 68, 69.
Sample holding means 70 is adapted to hold an input signal from the posture sensor 16 for a predetermined period of time when the holding switch 32 on the grip of the operating lever 26 is turned on. Means 71 for setting the desired position of the bucket 13 comprises a posture selection switch 72 for selecting and setting one of a bottom horizontal voltage Vrl required for making the bottom of the bucket 13 horizontal, an opening horizontal voltage Vr2 required for making the bucket opening horizontal and a voltage supplied from the inclination sensor 15 and indicating the inclination of the tractor body 1. The inclination sensor 15 is used for placing the bottom of the bucket 13 on the ground. A change-over switch 73 is provided for selecting the signal from the sample holding means 70 or the signal from the setting means 71.
Inversion means 74 is adapted to invert the signal from the change-over switch 73 with reference to a reference voltage 1/2 V at an N terminal. Deviation detection means 75 adds the signal from the inversion means 74 to the : ~ .
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signal from the posture sensor 15 to detec-t the differ2nce therebetween, which is then amplified by an invert~er 76. A
manual-automa-tic change switch 77 is closed at a contact 77a for manual control to transmit the instruction signal from the second variable resistor 28, or at a contact 77b for automatic control to transmit the signal from the deviation detection means 76. The signal is fed from the switch 77 to the second discrimating means 49 and to the second comparison means 57. As seen in Fig. 3, the switches 72, 73 and 77 are mounted on the rear side of the case 25 along with a power suppl~
switch 78.
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The first variable resistor 27, first discrimi-~` nating means 45, first comparison means 54, first drive means 60 and first proportional solenoid valve 39 constitute a boom control system. The second variable resistor 28, second discriminating means 49, second comparison means 57, second drive means 65 and second , proportional solenoid valve 42 constitute a working device control system. The triangular wave oscillation i:
circult 53 is provided singly for the two control systems in common.

When the inclination sensor 15 is mounted on ~ ~ the mast 8 oE the front loader 6 as seen in Fig. 1, this -~ 25 means that the front loader 6 is provided with both the :' ": :
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posture sensor 16 and -the inclination sensor 15, assuring the advantages that the sensors are adjustable at -the factory when the front loader is manufactured and that the loader is easy to attach to or remove from the tractor body 1. However, the inclination sensor lS may be attached to the tractor body 1.
Further if the signal from the inclination sensor 15 is shown on a display such as an array of diodes, the display is usable as an inclination indicator for the tractor. Further if the output of the posture sensor 16 is made visible on a display, the display ; serves as a posture indicator for the bucket 13.
Although the change-over switch 73 is provided in addition to the selection switch 72 as seen in Fig. 8, the change-over switch 73 can be dispensed with if the sample holding means 70 is incorporated into the settlng means 71.
The working device is not limited to the bucket 13 but may be a fork or some other attachement. In ~;~ 20 this case, the working devices can be made interchangeable as desired by pivoting a mount bracket to the forward ends of the booms and removably attaching the device t:o the bracket as by pins. The posture sensor 16 is then attached to the mount bracket. This assures great convenience, eliminating the need to attach the sensor 16 :: ~

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The control apparatus operates as follows for the operation of the front loader 6.
For manual control, the manual-automatic change switch 77 is closed at the contact 77a for manual control. Subsequen-tly, the operating lever 26 is manipulated. The operating lever 26 is movable in the directions of arrows shown in Fig. 6 for the upward and downward movements of the booms lO, dumping and scooping movements of the bucket 13 and combinations of such movements (see Fig. lO). When released from the ; hand, the lever 26 automatically returns to the neutral position in the center.
Now, when the lever 26 is turned rearward toward "UP"i the first variable resistor 27 is operated ` through the transverse rod 30, giving an altered resistance value in accordance with the amount of manipulation and producing an instruction signal of : .
- increased voltage. It is assumed that when the lever 26 is in its neutral position, the resistance value of the resistor 27 is l/2 of its maximum value and that the voltage then available is l/2 of the supply voltage V.
This will be referred to as a "neutral point." The ~ instruction signal from the first resistor 27 is fed to ; ~ 25 the comparators~46, 47 of the first discriminating means ~ ~ -18 ~, ....
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45. Since the signal is greater than the neutral point, the comparator 46 interpretsthis as indicating an upward movement to produce an up signal, which actuates the analog switch 63 of the first drive means 60. The instruction signal from the first resistor 27 is fed also to the comparators 55, 56 of the first comparison means 54. Since the instruction signal is greater than the neutral point, the comparator 55 compares the signal with a triangular wave signal from the oscillation circuit 53, producing a pulse signal which is on when the instruction signal is greater than the triangular wave signal as seen in Fig. 9. The greater the difference between the two signals, the greater is the pulse width of the pulse signal. The switching element 61 is repeatedly turned on and off by the pulse signal through the analog switch 63 of the first drive means 60, intermittently passing an energizing current of given value through the up solenoid 40 of the first solenoid - valve 39. The valve 39 is opened at the up side to a ;~ 20 degree in proportion to the amount of manipulation of the lever 26 by virtue of the dither effect involved, : : consequently extending the boom cylinder 11 at a :
: predetermined speed and raising the boom 10 abou~ the : pivot 9. A variation in the amount of manipulation of the operating lever 26 varies the opening degree of the .: :
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:. - `~: ". j ' first solenoid valve 39 to control the flow of pressure oil to be supplied to the boom cylinder ll. As a result, the boom lO is raised at a speed proportional to the amount of manipulation of the operating lever 26. The speed is controllable from very low to high as desired.
The lever 26, when returned to its neutral position, returns the valve 39 to its neutral position to stop the boom lO at the raised position. When the lever 26 is returned slowly at this time, the boom 10 is brought to a stop smoothly and slowly.
The control apparatus operates similarly when the lever 26 is moved forward to lower the boom 10 ; or when the lever is moved rightward or leftward to cause the bucket 13 to perform a scooping action or dumping ` 15 action.
~ When the lever 26 is moved forward or rearward 6 or sidewise through the greatest angle, the actuator 33 closes the corresponding one of the switches 34 to 37, .~
operating the valve 39 or 42 by energizing the correspond-20 ing one of the solenoids 40 to 44. Thus, the valve 39 ~ ~ ~ or 42 is operable without resorting to the operation P of the control system. In this case, however, propor-tional control is not available. This mode of control is therefore effected only in the event of a malfunction.
For automatic control, the manual-automatic , ~
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: .-change switch 77 is closed at the automatic contact 77b.
The automatic control is limited only to the posture control of the bucket 13. The boom 10 is controlled in the same manner as above for upward or downward movement by manipulating the lever 26 foward or rearward.
In this case, the posture sensor 16 for detecting the posture of the bucket 13 is used. Fig.
11, (I) to (IV) shows the relation between the posture sensor 16 and the posture of the bucket in scooping, up-down movement with the opening kept horizontal or with the bottom kept horizontal and dumping. Fig. 12 shows the relation be-tween the voltage and the posture sensor 16 for bottom horizontal up-down movement and opening horizontal up-down movement.
Posture control is effected in the following manner for bottom horizontal posture, opening horizontal posture, posture holding and bottom grounding.
Bottom horizontal posture control is resorted to when the boom 10 is lowered to bring the bottom of ~ 20 the bucket 13 into contact with the ground horizontally.
-~ In this case, the change-over switch 73 is closed for the setting means 71, and bottom horizontal voltage Vrl ;
~ is selected by the selection switch 72. When the bottom .~
of the bucket 13 is in parallel with the horizontal, 25; the voltage (resistance) of the posture sensor 16 is ::`: :
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constant at all times irrespective of the posture of the boom 11 or of that of the tractor body 1.
Accordingly, the voltage is set equal to the bottom horizontal voltage Vrl by the potentiometer within the setting means 71 as shown in Fig. 12.
When the selection switch 72 is closed for bottom horizontal, the voltage Vrl is inverted by the inversion means 74 to a voltage Vrl' about the 1/2 V
voltage at the N terminal. The voltage Vrl' is added to the voltage detected by the posture sensor 16 and indicating the current posture of the bucket 13 by the deviation detection means 75 to determine the difference between the two -voltages, and the resulting output is inverted and amplified by the inverter 76. Fig. 13, (I) to (III) shows these characteristics.
If the voltage from the posture sensor 16 is Vrl, the difference is zero, indicating that there is no need to correct the posture of the bucket 13. ~he subsequent portion of the system therefore does not function. When the bucket 13 is in a rotated position off a horizontal plane toward the dumping direction, the posture sensor 16 ~ives an increased voltage, with the result that the deviation detection means 75 pxoduces ~ ~ .
a deviation voltage (3) as shown in Fig. 13 (III) and lower than the neutral point voltage. From this `'~

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deviation voltage, the second discrimlnating means 49 detects the need for a correction toward the scooping direction. Further the second comparison means 57 compares the deviation voltage with the triangular signal, generating a pulse signal of a width in accordance with the deviation voltage. The signal energizes the scooping solenoid 44 of the second solenoid valve 42 via the analog switch 69 and the switching element 67 of the second drive means 65, whereby the bucket cylinder 14 is contracted to correct the posture of the bucket 13 toward the scooping direction. As the posture of the bucket 13 approaches the bottom-horizontal posture, the ` voltage fro~ the sensor 16 diminishes to diminish the deviation voltage and decrease the width of the pulse lS signal. The bucket cylinder 14 is slowed down and completes the correcting action at zero deviation. Thus, the bucket 13 is slowed down as it is brought closer to ` the bottom horizontal posture and eventually comes to a halt smoothly.
Conversely, if the bucket 13 is inclined toward :
the scooping direction, the deviation voltage is in the state (2) shown in Fig. 13 (III), the bucket 13 is " ~
moved toward the dumping direction and corrected to the ~ bottom horizontal posture.

-~ 25 Opening horizontal posture control is effected ~ 23-,~ .. , :: , :: :

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when the boom 10 is raised while holding the opening of the bucket 13 horizontal after scooping up earth or sand with the bucke-t. For this mode of control, opening horlzontal posture is selected by the selection switch 72. In this case, opening horizontal voltage Vr2 is set on the potentiometer of the setting means 71 so that the voltage from the posture sensor 16 becomes e~ual to this voltage when the opening is brought to the horizon-tal position as seen in Fig. 12.
The control system operates in the same manner as for bottom horizontal posture control, and the operation characteristics are shown in Fig. 14, (I) to ~III).
; For posture holding control, the change-over switch 73 is closed for posture holding, and the holding switch 32 is turned on.
When the boom 10 is raised after a compost heap ;
of the like is scooped up with the bucket 13, the bucket 13 must be maintained in the scooping state. Otherwise, the upward movement would cause the heap to spill from the bucket 13 toward the operator. In such a case, therefore, there arises a need to raise the bucket 13 as held in the scooping posture.
Thus, the holding switch 32 is turned on, with the change-over switch 73 set to posture holding, whereupon ~ ~ 25 a voltage indlcating the current posture of the bucket 13 :

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is fed to the sample holding means 70 and is held for a predetermined period of time. The held voltase is inverted by the inversion means 74, whereupon the dif-ference between the voltage and the voltage from the S posture sensor 16 is determined by the deviation detection means 75, which produces an inverted voltage. The posture of the bucket 13 is controlled by this deviation voltage in the same manner as in the foregoing bottom or opening horizontal posture control. Consequently, the boom 10 is raised with the bucket 13 retained in the original posture.
"Bottom grounding posture" refers to the state :: .
; in which the bottom of the bucket 13 is on the ground at the same plane as the ground on which the front and rear wheels 2, 3 of the tractor body 1 areplaced or the bottom is on a plane in para~llel with the plane as seen in Fig.
15, (I). Bottom groundlng control is resorted to when the bucket 13 is lowered onto the ground or is used for ": ~
scooping along the ground surface. This mode of control is very convenient when the bucket 13 is to be placed on the ground since the bonnet then blocks the sight of the operator in the seat 5.
The~bottom grounding control differs sre~tly ;from the bottom horizontai control, etc. in that in the latter case, control l;s effectsd with reference to the ~" ~

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angular deviation of the buc]cet 13 from the direction of gravity, whereas the bottom grounding control involves another factor, i.e. the inclinatlon of the tractor body 1, besides the posture of the bucket 13.
Accordingly, the inclination sensor 15 is used for control. As seen in Fig. 15, (II), the setting is so made that the inclination sensor 15 and the posture sensor 16 deliver the same signal voltage (resistance) when the bottom of the bucket 13 is grounded.
The selection switch 72 and the change-over switch 73 are set to the inclination sensor side for ~; bottom grounding. When the tractor body 1 is inclined, the inclination sensor 15 produces an altered voltage detecting the incllnation. If the bucket 13 is on the same ground surface as the tractor body at this time, the posture sensor 16 delivers the same signal voltage as the inclination sensor 15. However, when the voltage from the posture sensor 16 is different, the bucket cylinder 14 functions through the same operation as in .
the foregoing bottom horizontal posture control to bring the bucket to a corrected posture in which the bottom is on the ground.
Figs. 16 to 22 show a second embodiment of the present invention.~ A first proportional solenoid valve 39 for the boom control ~system and a seconcl ~,, :~ :

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proportional solenoid valve 42 for the working device control system are connected in series with each other as seen in Fig. 16. When these valves 39, 42 are operated at the same time, a hydraulic pump 78 feeds pressure oil to a boom cylinder 11, and the return oil from the cylinder 11 is fed to a bucket cylinder 14.
Incidentally in this case, the boom cylinder 11 and the bucket cylinder 14 are mounted in a reverse direction to the case shown in Fig. 1. Whlle the cylinders 11, 14 used are approximately identical in capacity and stroke, the cylinders 11, 14 may be different from each other in accordance with the length of the boom 10 or the size of the bucket 13. Further although the proportional solenoid valves 39, 42 are approximately identical in size and configuration, these valves 39, 42 may also be different from each other depending on the size of the cylinders 11, 14, the boom 10 and the bucket 13.
Indicated at 79 is a relief valve, and at 80 a hydraulic unit on the tractor body for lifting a working implement.
The proportional solenoid valves 39, 42 are controlled approximately in the same manner, and the boom control system and the working device control system are predominantly in corresponding relation to each other in respect of the constituent circuits and other components, ~; 25 so that like corresponding parts are designated by like :`:~: ~
: ~ -27-:.;

: . ,.
:: : . , -. ' ''' ; '; '' :

reference numerals, with an adscript "a" attached to the numeral for the boom control system or with an adscript "b" attached for the working device control system.
Figs. ]7 and 18 show a main switch 81, a NOT
circuit 82, NAND circuits 83, 84, a prepositioned pulse generating circuit 85, instruction pulse generating circuits 86a, 86b and reference pulse generating circuits 87a, 87b.
By the action of a monostable multivibrator, each of these pulse generating circuits 85, 86a, 86b, 87a, 87b delivers from an output terminal Q a pulse signal whichrises with the rise of an input signal to an input terminal A and which falls with a time constant dependent on a time-constant circuit of capacitor and resistor connected to the circuit. While the NOT circuit 82 is producing a high-voltage output, the prepositioned pulse generating circuit 85 produces a pulse signal El ; of given frequenc~ from an output terminal Q and a pulse signal E2 from an output terminal Q. As seen in Fig. 19, (I), the pulse signal El has a pulse width Tl which is ;~ 20 determined by the time constant of the circuit of capacitor Cl and resistor R2. The signal E2 is signal El as inverted as shown in Fig. 19, (II). The instruc-tion pulse generatlng circuit 86a (86b), which constitutes instruction means along with a variable resistor 88a ~. ~
(~8b), receives at an input terminal A the pulse signal :;
: ` :
.~.

- . :
: ~ - , , ~'' ~. . ' ' ' .
: :~ ' ' ~

El from the circuit 85 and delivers from an ou-tput terminal Q a pulse signal Fl which, as seen in Fig. 19, (III), rises with the rise of the signal El and has a pulse width T2 dependent on the time constant circuit of capacitor C2 and resistor R2 and the variable resistor 88a (88b). The circuit 86a (86b) further delivers from an output terminal Q a pulse signal F2, which is pulse signal Fl as inverted, as shown in Fig. 19, (IV). The resistance of the variable resistor 88a (88b) is variable by a slider 89a (89b). The reference pulse generating circuit 87a (87b), which serves as reference signal generating means, receives at an input terminal A
the pulse signal El from the prepositioned pulse generat-ing circuit 85, delivers from an output terminal ~ a pulse signal Gl which, as shown in Fig. 11, (V), rises :~:
with the rise of the pulse signal El and has a pluse width T3 determined by the time constant circuit of capacitor C3 and resistor R3, and further delivers from :
; an output terminal Q a pulse signal G2 which is obtained by inverting the pulse signal Gl as seen in Fig. 19, (VI).

Comparators 90a, 91a (9Ob, 91b) constitute ~ discriminating means and compair an instruction signal : ~ from the slider 89a (89b) on the variable resistor 88a ~88b) with a ~oltage 1/2 VDD. When the slider 88a (88b) is moved toward the direction of arrow d (f) beyond a 29- `
.
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neutral position n which is the midpoint of the resistor 89a (89b), the comparator 90a (90b) produces a high-voltage output. When the slider is moved toward the direction of arrow e (g) beyond the neutral position, the comparator 91a (9lb) produces a high-voltage output.
An exclusive OR circuit 92a (92b, 93a, 93b) serving as comparison means compares the pulse signal from the instruction pulse generating cicuit 86a (86b) with the reference pulse signal from the reference pulse generating circuit 87a t87b).
Indicated at 94a (94b, 95a, 95b) is an AND
circuit, and at 96a (96b, 97a, 97b) a field-e~fect transistor, which is connected in series with the solenoid 40 (43, 41, 44). A comparator 98a (98b, 99a, 99b) is connected between the AND circuit 94a (94b, 95a, 95b) and the gate of the field-effect transistor 96a (96b, 97a, 97~) for intermittently driving the transistor with the pulse signal from the AND circuit. One terminal of the comparator 98a (98b, 99a, 99b) is connected~between the field-effect~transistor 96a (96b,~97a, 97b) and a resistor~lOOa (lOOb, 101a, 101b)~connected in series with the transistor to receive a voltage signal from this : :
resistor. The comparator detects the variation in the energizing current through the solenoid 40 (43, 41, 44) 25~ and controls the current ampli~fication by the field-, ~, ~ 30-~ ~ , : : :

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:

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effect transistor 96a, (96b, 97a, 97b) so as to renaer the current constant. A circuit 102a (102b, 103a, 103b) for protecting the solenoid 40 t43, 41, 44) comprises a diode, capacitor and resistor.
A pressure switch 104 is included in the hydraulic circuit of Fig. 16 at the scooping side of the bucket cylinder 14 and is turned on when the internal pressure of the bucket cylinder 14 exceeds a predetermined level (overload). Figs. 17 and 18 further show a mode change switch 105, NOT circuits 106, 107r NAND circuits 108 to 116 and an AND circuit 117.
Figs. 20 and 21 show operating means for the variable resistors 88a and 88b. An operating lever 118 is supported by a spherical bearing member 120 on the top plate of a control box 119. The lever 118 has a grip 121 at its upper end and an actuating plate 122 at its lower end. Variable resistors 123a, 124a of the slider type ~- are provided upright within the control box 119 as opposed to each other longitudinally of the box. Variable resistors L23b, 124b of the slider type are provided upright within the box 119 as opposed to each other transversely of the box. The resistors of each pair are arrangedsymmetrically of the operating lever 118.
The resist~or 123a (123b, 124a, 124b) has a vertically movable slider 125a (125b, 126a, 126b), which is biased ::
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:

;. `' : ~ , ': : : ' vertically by a coiled sprlng 127a (127bl 128a, 128b) in pressing contact with the lower side of the actuating plate 122. The resistor 123a (123b, 124a, 124b) has its resistance value varied by the movement of the slider 125a (125b, 126a, 126b) and is connected to lead wires on a circuit base plate 129. The resistors 123a, 124a constitute the variable resistor 88a, and the resistors 123b, 124b constitute the variable resistor 88b.
When the operating lever 118 is in a vertical neutral position N, the sliders 89a, 89b in Fig. 17 are in a neutral position n. When the operating lever 118 is moved rearward as indicated by an arrow D from this position, the slider 89a moves in the direction of arrow d. The lever, when moved in the direction of arrow E, moves the slider 89a in the direction of arrow e. When the lever 118 is moved leftward as indicated by an arrow F, the slider 89b moves in the direction of arrow f.
When the lever is moved rightward as indicated by an arrow G, the slider 89b moves in the direction of arrow g. Further if the lever 118 is moved leftwardly rearward, the sliders 89a, 89b are moved in the directions of arrows d, f, respectively. When the lever 118 is moved rlghtwardly rearward, the sllders are moved in the direction of arrows d, g, respectively. When moved leftwardly forward, the lever 118 moves the sllders 89a, ~: ~

~: ' ' '` ~;: ' :
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9~L~

89b in the directions of arrow e, f, while when mc,ved rightwardly forward, the lever moves these sliders in the directions of arrows e, g~ The mode change switch 105 is provided at the top end of the grip 126 of the operating lever 118. When depressed, the switch is turned on.
With the present embodiment, the capacitors Cl, C2, C3 connected to the pulse generating circuits 85, 86a, 86b, 87a, 87b are identical in capacity, while the resistor R3 is one-half of the resistor Rl in resistance value. The resistance of the resistor R2 and the maximum resistance of the variable resistors 88a, 88b are one-third the resistance of the resistor Rl. Accordingly, the pulse width T3 of the pulse signal Gl from the ~;~ 15 reference pulse generating circuits 87a, 87b is 1/2 of the pulse width T1 of the pulse signal El from the prepositioned pulse generating circuit 85o When the sliders 89a, 89b are in the neutral position n, the pulse width T2 of the pulse signal Fl from the instruction ~` 20 pulse generating circuits 86a, 86b is 1/2 of the pulse width Tl of the pulse signal El. As the sliders 89a, 89b move from the neutral position toward the direction of arrow d or f, the fall of the pulse signal Fl is delayed, gradually increasing the pulse width T2. When the sliders 89a, 89b are moved in the direction of arrow e or g, : , , . : : ~. , .

. . .
:
. : , :
' ' :' :, ' ' :
, ' ' ~''''" ''''~ :, the pulse signal E`l falls earlier, progressively decreasing : the pulse width T2.
The operation of the present embodiment will be described with reference to the voltage waveform diagram of Fig. 19. When the main switch 81 is turned on, the NAND circuit 8~ applies a high voltage to the prepositioned pulse generating circuit 85, which i.n turn ; delivers a pulse signal El from the output terminal Q
and a pulse signal E2 from the output terminal Q. The instruction pulse generating circuits 86a, 86b and the reference pulse generating cicuits 83a, 83b receive the pulse signal El from the circuit 85. The instruct:ion pulse generating circuits 86a, 86b deliver a pulse signal Fl from the output terminal Q and a pulse signal F2 from the output terminal Q. The reference pulse generating circuits 87a, 87b produce a pulse signal Gl from the output terminal Q and a pulse signal G2 from the output terminal Q.
When the operatiny lever 118 is in the neutral position N at this time, the sliders 89a, 89b are in the neutral positlon n. The pulses Fl, F2 of the instruction pulse generating circuits 86a, 86b then have the same ;~ ~ pulse width as the pulse signals Gl, G2 of the reference pulse generatlng circuits 87a, 87b, with the result that the exclusive OR circuits 92a, 92b, 93a, 93b produce no ~ .

' :'' i~ . '', .-- . :
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: ' : ;, , :,~ ~

pulse signal. Further since the slidexs 89a, 89b are in the neutral position n, no signal is delivered from the comparators 90a, 90b, 91a, 91b. Consequently, no signal is produced from the AND circuits 94a, 94b, 95a, 95b or S from the comparators 96a, 96b, 97a, 97b, and the solenoids 40, 41, 43, 44 remain unenergized.
When the boom 10 is to be lowered by operating the first proportional solenoid valve 39 of the boom control system, the operating lever 118 is moved rearward from the neutral position N. The rearward movement (in the direction of arrow D) of the lever 118 from the neutral position N moves the slider 89a in the direction of arrow d, consequently increasing the pulse widlh T2 of the pulse signal Fl of the instruction pulse generating circuit 86a in proportion to the amount of movement or ~ manipulation of the operating lever 118. The width T2 ;; of the pulse signal Fl therefore becomes larger than the ~-~ width T3 of~the pulse signal G1 of the reference pulse generating circuit 87a, causing the exclusive OR circuit 20 ~ 92a to produce a pulse signal Hl as seen in Fig. 19, tVII).
On the other hand, the voltage signal of the slider 89a ~;; which is moved in the direction of arrow d is lowered, permitting the comparator 90a to pro~uce an up signal of high voltage, which opens the gate of the AND circuit 94a. As a result, the circuit 94a transmits the pulse 35- ~
, : .

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~ ~ :, .

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signal Hl, which is delivered to the field-effect transistor 96a via the comparator 98a. The transistor 96a repeats an on-off action in timed relation with the pulse signal Hl. An energizing current of given value S therefore in~ermittently flows through the up solenoid 40. By virtue of the dither effect involved, the first proportion solenoid valve 39 operates with a degree of opening in accordance with the amount of manipulation of the lever ; 118 to control the flow of oil through the boom cylinder, consequently raising the ~oom 10 at a speed in proportion to the amount of forward manipulation of the operating lever 118.
When the operating lever 118 is moved forward (toward the direction of arrow E) from the neutral ~: 15 position N, the slider 89a moves in the direction of arrow e, consequently increasing the pulse width of the pulse signal F2 of the instruction pulse generating ~` circuit 86a and causing the exclusive OR circuit 93a to produce a pulse signal H2 as seen in Fig. 19, (VIII).
Further the movement of the slider 89a toward the direc-tion of arrow e causes the comparator 91a to produce a :~ signal, which opens the gate of the AND circuit 95a.
Consequently, the transistor 97a repeats an on-off action as in the foregoing case, permitting an energi~ing current o given ~alue to flow through the down solenoid 41 :`

~ -36-~ : :

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. .
-': ' ' : . , , '`
:, ,:
: : :
~ :' ; `' :

intermittently. By virtue of the dither effect involved, the first proportional solenoid valve 39 effects -low control in accordance with the amount of rearward movement of the lever 118 to lower the boom 10 at a speed in proportion to the amount of rearward movement of the lever 118.
Next, when the bucket 13 is to be used for scooping by operating the second proportional solenoid valve 42 of the working device control system, the operating lever 118 is moved leftward (in the direction of arrow F) from the neutral position N, whereby the slider ~; 89b is moved in the direction of arrow f. Consequently, in the same manner as already described, the e~c~usive OR circuit 92b produces a pulse signal Hl as shown in Fig. 19, (VII), and the gate of the AND circuit 94b is opened to pass the pulse signal Hl therethrough. Further if the operating lever 118 is moved rlghtward (in the direction of arrow G) from the neutral position N, the slider 89b moves in the direction of arrow g, consequently causing the exclusive OR circuit 93b to produce a pulse signal H2 as seen in Flg. 19, (VIII) and opening the gate `~ ~of the AND circuit 95b, which in turn passes the pulse ~ signal H2 therethrough.
`~ ~ When the mode change switch 105 is offl the NOT circuit 107 applies a low voltage to the NAND circuits 37- ~

:: :
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.; ~

: .

: ~ ,, , :

: , :
. -: :
- -.
:

109, 110 and to the NAND circuits 113, 114, and the NAND
circuit 111 produces the output signal of the AND circuit 94a as inverted. The pulse signal H2 of the AND circuit 95a is delivered as inverted from the NAND circuit 110.
Further via the NAND circuit 115, the pulse signal Hl from the AND circuit 94b is delivered as it is from the NAND circuit 116.
When the mode change switch 105 is on, the NOT
circuit 107 applies a high voltage to the NAND circuits 109, 110 and to the NAND circuits 113, 114, the NAND
circuit 109 delivers an output of low voltage, and the NAND circuit 111 delivers an output of high voltage.
Via the NAND circuit 110, the pulse signal H2 from the AND circuit 95a is delivered as it is from the NAND
circuit 11~. Similarly, via the NAND circuit 114, the pulse signal Hl from the AND circuit 94a is delivered as it ls from the NAND circuit 116.
~;~ When the pressure switch 104 is off, the NOT
clrcuit delivers an output of low voltage, permitting the NAND circult 108 to produce an output of high voltage and opening the gate of the AND circuit 117. The pulse signal H2 from the AND cixcuit 95b is fed out as it is rom the AND circuit 117.
When the pressure switch 104 is on, the output of the NOT circuit 106 is of high voltage, so that if ' ~

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:~ . . . ~ : .

:': ; ~ . :: :

the output of the comparator 9Oa is a high voltage, that is, if the operating lever 118 is in a rearwardly turned position, the NAND circuit 108 produces a :Low voltage and the NAND circuit 111 produces a high voltage.
In this case, the output of the output..of the comparator : 31a is a low voltage, so that the output of the NAND
circuit 110 is a high voltage, permitting the NAND circuit -112 to produce a low voltage. On the other hand, if the output of the comparator 90a is low, that is,unless the ~ 10 lever 118 is in a rearwardly moved position, the pulse ; signal H2 of the ~ND circuit 95b is delivered at it is : from the AND circuit 117.
Accordingly, when the mode change switch 105 is off, the pulse signal H2 from the AND circuit 94b is produced from the NAND circuit 116, and the pulse signal H2 from the AND circuit 95b is delivered from the NAND
:~ circuit 112. Alternatively, if the mode change switch 105 is on, the pulse signal Hl of the AND circuit 94a is ; produced from the NAND circuit 116, and the pulse signal H2 of the AND circuit 95a is fed out from the NAND
~: ~ circuit 112. However, when the pressure switch 104 is on with the operating lever 118 in a rearwardly turned :
: position, the NAND circuit 112 delivers a low voltage irrespective of whether the mode change switch 105 is on :or off.

., ~ , ~ 39--: :

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: : ,, : :-, ~
:. - , - ~ .: , - .
, .

When the operating lever 118 is moved leftward with the mode change switch 105 in its off state, the ; pulse signal Hl from the AND circuit 94b is fed to the field-effect transistor 96b via the NAND circuits 115, 116 and the comparator 98b, causing the transistor 96b to repeat an on-off action in synchronism with the pulse signal Hl. Consequently, an energizing current of given value intermittently flows through the dumping solenoid 43 and, owing to the dither effect involved, the second proportional solenoid valve 42 effectsflow control in accordance with the amount of leftward movement of the ~ operating lever 118, thereby causing the bucket 13 to ; perform a dumping motion at a speed in proportion to the amount of leftward manipulation of the lever 118.
Further when the operating lever 118 is moved rightward, ; the pulse signal H2 from the AND clrcuit 95b is fed to the field-effect transistor 97b via the AND circuit 117, NAND circuits 111, 112 and comparator 99b, causing the translstor 97b to repeat an on-off action and allowing an energizing current of given value to intermittently flow through the scooping solenoid 44. By virtue of the dither effect involved, the second proportioral ~`~ solenoid valve 42 operates for flow control in accordance with the amount of rightward manipulation of the lever 118, permitting the bucket 13 to perform a scooping motion ::

,`' - .
'' ~ :

'. ' , ' ~ :

at a speed in proportion to the amount of rightward manipulation of the lever 118. When the operating lever 118 is moved rightwardly rearward to raise the boom 10 with the scooping motion of the bucket 13, the forward , 5 end of the bucket 13 is likely to bite into hard earth or to become engaged by a rock or the like. If the internal pressure of the bucket cylinder 14 exceeds a specified level in such an event, the pressure switch 104 is turned on, whereupon the NAND circuit 112 produces a low voltage to discontinue the scooping action of the bucket 13, thereafter allowing only the rise of the boom 10 with the bucket 14 held at rest. This obviates the damage due to overloading and eliminates the need to discontinue the operation.
On the other hand, when the operating lever 118 ~ is rearwardly moved with the mode change switch 105 held : in on state by depression, the pulse signal Hl from the AND circuit 94a is fed to the field-effect transistor 96b via the NAND circuits 114, 116 and the comparator 98b, ~ 20 causing the transistor 96b to repeat an on-off action - in synchronism with the pulse signal Hl. Consequently, ; ~ the boom 10 rises at a speed in proportion to the amount ~ of rearward manipulation of the operating lever 118, and :~, ~ at the same time, the bucket 13 performs a dumping ; 25 motion at a corresponding speed. Thus, the boom 10 rises . , ~

:, ~
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.
' : ' `'' ',', ' , "' ~ ` ` `', ~, ', ' .

with the bucket 13 held substantially at a definite angle of inclination with respect to a horizontal plane.
Further if the lever 118 is similaxly moved forward, the pulse signal H2 from the AND circuit 95a is fed to the field-effect transistor 97b by way of the NAND circuits 110, 112 and -the comparator 99b, causing the transistor 97b to repeat an on-off action. As a result, the boom 10 lowers at a speed in proportion to the amount of Eorward movement of the operating lever 118 and, at the same time, the bucket 13 performs a scooping motion at a corresponding speed. Thus, the boom 10 lowers with the bucket 13 held at a given angle of inclination with respect to a horizontal pLane.
The mode change means comprises the mode change 15 switch 105, NAND circuits 109 to 112, NAND circuits 113 ~ to 116, etc. The means for discontinuing the scooping ;~ ~ motion of the bucket 13 comprises the NOT circuit 106, NAND circuit 108, AND circuit 117, etc.
Figsr 22 and 23 show other embodiments. Fig.
` 22 shows Darlington pairs of transistors 130a, 130b, 131a, 131b, 132a, 132b, 133a, 133b substituting for the fore-going switching circuits of field-effect transistors 96a, 96b, 97a, 97b. Flg. 23 shows solenoid protecting ~;~ c~ircults 102a, 102b, 103a, 103b each comprising a Zener diode.

~: ` .

: ~

, . " : .
;: . ':, , ~. : . .` , Fig. 24 shows another embodiment which is obtained by omitting from the foregoing embodiment the mode change switch 105, NOT circuit 107, NAND circuits 109 to 112 and NAND circuits 113 to 116.
S The pulse width and the frequency of the pulse signals to be generated by the circuits 85, 86a, 86b, 87a, 87b are adjustable by variably setting the values of the resistors RL, R2,R3, 35a, 35b so as to be most suited to the performance or characteristics of the proportional solenoid valves 39, 42.
Although the operating lever 118 is used as operating means for raising or lowering the boom 1 and for movlng the bucket 13 for scooping or dumping, the ; operating means is not limited to the lever 118 but can lS be of the dial type. Further separate operating means are usable; one for moving the boom 10 and the other for moving the bucket 13.
Fig. 25 shows another embodiment of hydraulic circuit. Channels 134, 135 for connecting the boom cylinder 11 to the proportional solenoid valve 39 are provide~d with a floatLng solenold valve 136 for bringing the channels 134, 135 into or out of communication with each other. When the valve 136 is energlzed, the two cylinder chambers of the boom cylinder 11 communciate 25 with each other via the channels 134, 135 to render the boom 10 movabl~e upward~or downward in a floating state.

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Claims (18)

What is claimed is:

1. A control apparatus for a boom-equipped working implement having a boom control system for controlling the upward-downward movement of a boom liftably supported by a vehicle body and a working device control system for controlling a working device pivotally movably mounted on the boom, each of the control systems including a proportional solenoid valve, the control apparatus being characterized in that each of the control systems comprises instruction means for producing an instruction signal in accordance with the amount of manipulation of operating means, discriminating means for discriminating the direction of operation of the propor-tional selenoid valve from the instruction signal, means for generating a specified reference signal, comparison means for comparing the instruction signal with the reference signal to obtain a pulse signal having a pulse width in proportion to the amount of manipulation of the operating means, and drive means for converting the pulse signal from the comparison means into an electric current to drive the proportional solenoid valve in the direction discriminated by the discriminating means.

2. A control apparatus as defined in claim 1 wherein the instruction means comprises a variable resistor for producing a voltage signal, and the reference signal generating means comprises a triangular wave oscillation circuit for producing a triangular wave signal to obtain the pulse signal by comparing the voltage signal with the triangular wave signal by the comparison means.

3. A control apparatus as defined in claim 1 wherein the instruction signal has a variable resistor operatively connected to the operating means and a pulse generating circuit for producing pulse signals of opposite phases, and the variable resistor is connected to a time-constant circuit for adjusting the pulse width of the pulse generating circuit.

4. A control apparatus as defined in claim 1 wherein each of the instruction means and the reference signal generating means has a pulse generating circuit for producing pulse signals of opposite phases, and the comparison means compares pulse signals from the two pulse generating circuits of these means.

5. A control apparatus as defined in claim 1 wherein the boom control system and the working device control system have the operating means in common with each other, and the instruction means of the boom control system is operatively associated with the forward-rearward manipulation of the operating means, the instruction means of the working device control system being operatively associated with the rightward-leftward manipulation of the operating means.

6. A control apparatus as defined in claim 1 wherein the boom control system and the working device control system have the reference signal generating means in common with each other.

7. A control apparatus as defined in claim 1 which further comprises a sensor for detecting an excessive load acting on the working device so that when the boom and the working device are in movement at the same time, the working device is stopped from pivotal movement upon functioning of the sensor.

8. A control apparatus as defined in claim 1 wherein the proportional solenoid valve of the working device control system is operable by the pulse signal from the boom control system so that when the boom is in upward-downward movement, the working device is moved in a direction opposite to the direction of the movement of the boom.

9. A control apparatus for a boom-equipped working implement having a boom control system for controlling the upward-downward movement of a boom liftably supported by a vehicle body and a working device control system for controlling a working device pivotally movably mounted on the boom, each of the control systems including a proportional solenoid valve, the control apparatus being characterized in that the boom control system comprises instruction means for producing an instruction signal in accordance with the amount of manipulation of operating means, discriminating means for discriminating the direction of upward-downward movement of the boom from the instruction signal, means for generating a specified reference signal, comparison means for comparing the instruction signal with the reference signal to produce a pulse signal having a pulse width in proportion to the amount of manipulation of the operating means, and drive means for converting the pulse signal from the comparison means into an electric current to drive the solenoid valve of the boom control system in the direction of movement of the boom discriminated by the discriminating means, the working device control system comprising a posture sensor for detecting the pivotally moved posture of the working device, means for setting the desired posture of the working device, deviation detecting means for determining the difference between a signal from the posture sensor and a signal from the setting means to produce a deviation signal, discrimination means for discriminating from the devia-tion signal the direction in which the working device is to be pivotally moved, comparator means for comparing the deviation signal with the reference signal from the reference signal generating means to produce a pulse signal of a pulse width in proportion to the deviation signal, and drive means for converting the pulse signal from the comparator means into an electric current to drive the solenoid valve of the working device control system in the direction of movement of the working device determined by the discrimination means.

10. A control apparatus as defined in claim 9 wherein the reference signal generating means comprises a triangular wave oscillation circuit.

11. A control apparatus as defined in claim 9 wherein the working device is a bucket, and the bottom horizontal, opening horizontal or bottom grounding posture of the bucket is selectively settable by the setting means.

12. A control apparatus as defined in claim 9 which further comprises sample holding means for storing a signal from the posture sensor upon actuation of a posture holding switch on the operating means and in which the deviation detecting means determines the difference between a signal from the posture sensor and a signal from the sample holding means.

13. A control apparatus as defined in claim 12 which further comprises a switch for selectively connecting the sample holding means or the setting means to the input side of the deviation detecting means.

14. A proportional solenoid valve control circuit comprising instruction means for producing an instruction signal in accordance with the amount of manipulation of operating means, discriminating means for discriminating the direction of operation of the propor-tional selenoid valve from the instruction signal, means for generating a specified reference signal, comparison means for comparing the instruction signal with the reference signal to obtain a pulse signal having a pulse width in proportion to the amount of manipulation of the operating means, and drive means for converting the pulse signal from the comparison means into an electric current to drive the proportional solenoid valve in the direction discriminated by the discriminating means.

15. A control circuit as defined in claim 14 wherein the instruction means comprises a variable resistor for producing a voltage signal, and the reference signal generating means comprises a triangular wave oscillation circuit for producing a triangular wave signal to obtain the pulse signal by comparing the voltage signal with the triangular wave signal by the comparison means.

16. A control circuit as defined in claim 14 wherein the instruction signal has a variable resistor operatively connected to the operating means and a pulse generating circuit for producing pulse signals of opposite phases, and the variable resistor is connected to a time-constant circuit for adjusting the pulse width of the pulse generating circuit.

17. A control circuit as defined in claim 14 wherein each of the instruction means and the reference signal generating means has a pulse generating circuit for producing pulse signals of opposite phases, and the comparison means compares pulse signals from the two pulse generating circuits of these means.

18. A control circuit as defined in claim 17 wherein the comparison means is an exclusive OR circuit.