JPH0510564Y2 - - Google Patents

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to a draft control device for a tractor.

(Prior Art) A tractor is equipped with a draft control device in order to control the traction load when a working machine such as a plow is attached to the tractor and performs work.

This type of draft control device is known, for example, as described in Japanese Utility Model Application Publication No. 59-196006. In this conventional type, the spool drive lever for loading and unloading the spool of the draft control is pivoted on the draft control lever side, and the spool drive lever is brought into contact with the wall of the case above the pivot point so that it can move toward and away from the wall of the case. and is in contact with the spool in a freely movable manner, below the pivot point and on the same side as the side that contacts the wall of the case, and below the point of contact with the spool, and on the same side as the contact side of the spool. The opposite side was in contact with the feedback pin so that it could move toward and away from the feedback pin.

(Problems to be Solved by the Invention) In the conventional device, the wall of the case, the spool, and the feedback pin can freely approach and separate from the spool drive lever, which is pivotally supported on the draft control lever side. Since they were in contact with each other, it was extremely difficult to adjust their positional relationship.

Therefore, it is possible to fix the positional relationship by pivoting the spool drive lever to the draft control lever, spool, and feedback pin, respectively, but if these are fixedly pivoted, the slight There was a problem in that the spool responded to movement, resulting in a so-called hunting phenomenon.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a draft control device for a tractor that makes assembly and adjustment of a draft control valve extremely easy and does not cause hunting.

(Means for Solving the Problems) A feature of the present invention for achieving the above object is that a working machine such as a plow is towed at the rear of a tractor via a three-point link mechanism, and the three-point link In the draft control device for a tractor, the mechanism is movable up and down by a hydraulic device provided on the tractor side, and detects the traction load of the working machine and operates the hydraulic system to raise and lower the working machine. The draft control device includes a draft control valve that controls hydraulic fluid to the hydraulic device;
It has a feedback link that detects the traction load of the work equipment, and a draft control lever that adjusts the vertical position of the work equipment, and the draft control valve is slidably provided with a spool that controls hydraulic oil. The spool is biased in the ascending direction of the working machine by an elastic member, and a spool drive lever is pivotally supported at the tip of the spool in a substantially T-shape orthogonal manner, and both ends of the spool drive lever A two-pronged engagement groove is provided in one of the engagement grooves, and a pivot pin that swings when the draft control lever is operated is rotatably and tightly fitted into one of the engagement grooves. To,
The feedback pin, which is oscillated by the feedback link, is loosely fitted.

(Function) According to the present invention, the position of the draft control lever is adjusted so that the working machine maintains a predetermined vertical position under a predetermined traction load. That is, the position of the pivot pin is fixed at a predetermined position, and the engagement groove at one end of the spool drive lever is tightly fitted to the pivot pin.

On the other hand, the engagement groove at the other end of the spool drive lever is loosely fitted to the feedback pin, and the spool is biased in the upward direction of the work machine by an elastic member, so the feedback pin There is play in the lifting direction of the work equipment.

If an abnormal load is applied to the work machine in this state, the feedback link moves and the feedback pin moves in the upward direction of the work machine. Then, when the load decreases, the feedback link and pin move in the opposite direction.

When the load is high, and the pin movement speed is fast and the amount of movement is greater than the play, the pin abuts the side wall of the engagement groove on the play side, causing the spool drive lever to swing around the pivot pin. to move the spool in the upward direction of the work equipment. This movement of the spool activates the hydraulic system and raises the work machine.

Further, when the moving speed of the pin is slow, the pin and the engagement groove maintain a state of contact due to the biasing force of the elastic member, and the spool moves in the upward direction of the working machine due to the biasing force of the elastic member.

Further, when the pin movement speed is high and the movement amount is less than the play, the spool is moved slowly by the elastic member behind the movement of the pin. At this time, if the load is immediately reduced, the pin will move in the opposite direction, but since the spool moves slowly, the pin will only wobble within the range of play and will not cause the spool to follow suit.

From the above phenomenon, when the load fluctuation is fast and small, the feedback pin only rattles in the engagement groove, and the spool does not follow it and does not move rapidly, so hunting does not occur.

On the other hand, if the spool biasing elastic member is biased in the downward direction of the working machine, which is opposite to the present invention,
When a high load is applied, the work equipment must be raised immediately, making it impossible to prevent hunting.

(Example) Hereinafter, an example of the present invention will be described in detail based on the drawings.

In FIG. 4, reference numeral 1 denotes a tractor, which has rear wheels 2, etc., and a working machine, for example, a plow 4, is attached to the rear of the tractor 1 via a three-point link mechanism 3. The three-point linkage mechanism 3 consists of a top link 5 and a pair of left and right lower links 6, and the top link 5 is connected to a swing bracket 8 of a load sensing device consisting of a torsion bar 7 and the like at the lower end. 9
is a hydraulic device for lifting and lowering work, and the plow 4 can be raised and lowered via a three-point linkage mechanism 3 by vertical movement of a pair of lift arms 10. Reference numeral 11 denotes a position valve of the hydraulic device 9, which can be operated by a position control lever 12. Reference numeral 13 denotes a draft control valve, which is attached to one side wall of the hydraulic device 9 with bolts or the like, and is operable by a draft control lever 14 and a feedback lever 15 interlocked with the swing bracket 8.

That is, as shown in FIGS. 1 to 3, the draft control valve 13 includes a valve body 18 having a pump port 16 and a drain port 17, a spool 19 inserted into the valve body 18 so as to be able to connect and disconnect between both ports 16 and 17, The hydraulic system is equipped with a spring 20 that biases the spool 19 in the closing direction (increasing direction). 9 operates in the upward direction, and the spool 19 slides in the downward direction (arrow b) against the spring 20 to open the space between the ports 16 and 17, the hydraulic device 9 operates in the downward direction. ing.
A case body 21 is integrally formed with the valve body 18, and a spool drive lever 23 for operating the spool 19 is operated by the case body 21 and a cover 22 detachably fastened to the case body 21 with bolts.
A case 24 is configured to house the following.

The spool drive lever 23 is pivoted to the tip of the spool 19 via a pivot pin 19a so as to be perpendicular to the tip of the spool 19 in a substantially T-shape. Two forked engagement grooves 23a and 23b are provided at the upper and lower ends of the spool drive lever 23.

A control lever shaft 25 and a feedback lever shaft 26 are vertically parallel and rotatably inserted and supported on the same side of the case 24, that is, the cover 22. A lever 27 is fixed to the inner end of the control lever shaft 25 in a downward direction, and a pivot pin 28 is provided at the lower end of the lever 27 to swingably support the spool drive lever 23 above the spool 19. There is.

That is, this pivot pin 28 and the engagement groove 23a at the upper end of the spool control lever 23 are tightly and rotatably fitted.

A disc spring 31 is fitted between flat washers 29 and 30 on the protrusion of the control lever shaft 25, and the flat washers 29 and 30 and the disc spring 31 are fastened with nuts 32 and 33. A draft control lever 14 is attached to the outer end of. Therefore, the spool drive lever 23 can be oscillated by the draft control lever 14, and the draft control lever 14 can be positioned at any desired operating position by the disc spring 31.

A lever 34 is fixedly attached downward to the inner end of the feedback lever shaft 26, and a feedback pin 35 is provided at the lower end of the lever 34. The feedback pin 35 is loosely fitted into the engagement groove 23b at the lower end of the spool drive lever 23 on the opposite side of the spool 19 from the pivot pin 28, that is, below the spool 19. A downwardly hanging feedback lever 15 is attached to the outer end of the feedback lever shaft 26, and the feedback lever 15 is operatively connected to the swing bracket 8 via a feedback link 36.

Note that the close fit between the pivot pin 28 and the engagement groove 23a at the upper end means that the pivot pin 28 has a diameter of 6.0 mm.
The groove width of the engagement groove 23a is approximately 6.2 mm, and the loose fit between the feedback pin 35 and the engagement groove 23b at the lower end means that the diameter of the feedback pin 35 is 6.0 mm.
The groove width of the engagement groove 23b is approximately 7.0 mm.

Figure 5 shows the hydraulic circuit, position valve 1
1 consists of a control valve 39, an unload valve 40, a check valve 41, etc. Draft valve 1
3 is branched and connected to an oil path 43 that connects the pump 42 and the hydraulic device 9. Note that 44 is a falling speed adjustment valve, and 45 is a relief valve.

Next, the operation of the above configuration will be explained. FIG. 3 shows the draft control lever 14 set at a predetermined position, and the draft control lever 14 is positioned by a disc spring 31.

When the tractive load of the plow 4 increases in the above state, a force in the direction of arrow c acts on the top link 5 as shown in FIG.
moves in the direction of arrow d, which causes the feedback pin 35 to move in the direction of arrow e as shown in FIG. At this time, since the pivot pin 28 remains unchanged, the spool 19 moves in the direction of arrow a, the pump port 16 and the drain port 17 are closed, and the oil passage 4
3 is supplied to the hydraulic system 9, which causes the plow 4 to rise.

When the load decreases, the draft control valve 13 operates in the opposite manner to the above, and the plow 4 descends.

In this way, the feedback pin 35 responds sensitively to changes in the load of the plow 4, so the hatching phenomenon is prevented since the feedback pin 35 and the engagement groove 23b are tightly fitted. It occurs, but
In the present invention, since there is play, the hatching phenomenon is prevented.

As a structure for giving the feedback mechanism some play, it is possible to make the pivot hole 60 of the feedback link 36 into a long hole as shown in FIG. If the spool drive lever 23 located at the closest position has play, the inertial force will be smaller and the hunting prevention effect will be greater.

Note that the present invention is not limited to the above embodiments.

(Effects of the invention) According to the invention, since play is provided at the engagement portion between the spool drive lever and the feedback pin, hunting of the hydraulic system can be effectively prevented.

[Brief explanation of the drawing]

Fig. 1 is a sectional view showing an embodiment of the present invention, Fig. 2 is a sectional view taken along the - line in Fig. 1, Fig. 3 is a perspective view, Fig. 4 is a side view, Fig. 5 is a hydraulic circuit diagram, and Fig. 5 is a hydraulic circuit diagram. FIG. 6 is a front view showing a comparative example. 8... Swing bracket, 13... Draft control valve, 14... Draft control lever, 19... Spool, 23... Spool drive lever, 23a, 23b... Engagement groove, 28
... Pivot pin, 35 ... Feedback pin, 3
6...Feedback link.

Claims (1)

[Claims for Utility Model Registration] A working machine such as a plow is towed at the rear of a tractor via a three-point link mechanism, and the three-point link mechanism is movable up and down by a hydraulic device provided on the tractor side, In a draft control device for a tractor that detects a traction load on the working machine and operates the hydraulic system to raise and lower the working machine, the draft control system includes a draft control valve that controls hydraulic fluid to the hydraulic system. and,
It has a feedback link that detects the traction load of the work equipment, and a draft control lever that adjusts the vertical position of the work equipment, and the draft control valve is slidably provided with a spool that controls hydraulic oil. The spool is biased in the ascending direction of the working machine by an elastic member, and a spool drive lever is pivotally supported at the tip of the spool in a substantially T-shape orthogonal manner, and both ends of the spool drive lever A two-pronged engagement groove is provided in one of the engagement grooves, and a pivot pin that swings when the draft control lever is operated is rotatably and tightly fitted into one of the engagement grooves. To,
A draft control device for a tractor, characterized in that a feedback pin that is oscillated by the feedback link is loosely fitted into the feedback pin.