JPH0474964B2 - - Google Patents

Description

[Detailed description of the invention] (a) Industrial application field The present invention relates to a three-point linkage device for a tractor,
Specifically, the present invention relates to a hydraulic system for controlling a three-point linkage device in which one of the top link and the lift rod is made into a hydraulic cylinder to perform horizontal control and top link control.

(b) Conventional technology Conventionally, in a three-point linkage device, one side of the lift rod is configured to be extendable and retractable as a hydraulic cylinder.
Horizontal control is possible to keep rotary and other working equipment horizontal regardless of the machine's inclination, and the top link is configured as a hydraulic cylinder so that it can expand and contract, allowing the top link to be moved when turning the tractor or plowing during plowing. There are some that can be shortened to perform top link control that increases the lifting height of the work implement or shortens the plowing time. However, the conventional three-point link device simply controls expansion and contraction of the hydraulic cylinder using an ordinary switching valve, and its accuracy is not high.

In addition, in the horizontal control of extending and retracting the lift rod, a solenoid valve for pulse width modulation (hereinafter referred to as PWM) control is used, and the valve is inching controlled at the end of the control to slow down the expansion and contraction speed and control the position with high precision. There are things you can do.

Therefore, when trying to use a 3-position solenoid valve for PWM control that can be controlled with high precision for horizontal control and top link control, as shown in FIG. , and further communicated via a flow priority valve 5 to an ordinary 2-position switching valve 6, and at the switching valve 6, each PWM
It is configured to communicate with a hydraulic cylinder 10 forming a lift rod and a hydraulic cylinder 11 forming a top link via control three-position switching valves 7 and 9. That is, when performing horizontal control, the switching valve 6 is switched to the lift rod side,
The lift rod cylinder 10 is extended and retracted with high precision by operating the PWM control switching valve 7, and when performing top link control, the switching valve 6 is switched to the top link side, and the other PWM control switching valve 9 is operated. The top link cylinder 11 is expanded and contracted with high precision.

(c) Problems to be solved by the invention For this reason, the hydraulic system that is an extension of the prior art needs to use two 3-position solenoid valves for PWM control, but the valves for PWM control are The shape is larger than that of the switching valve, and
They are extremely expensive, and using two such PWM control valves in a tractor makes space design complicated and increases costs. Furthermore,
The hydraulic circuit is also complicated, and there is a risk that leaks from the 3-position solenoid valve for PWM control will be large, leading to increased pressure loss.

(d) Means for solving the problem The present invention aims to solve the above-mentioned problems, and as shown in FIG.
First, a normally open type 2-position switching valve (solenoid valve) 12 for PWM control is arranged in a branched manner, and then two ordinary 3-position switching valves 13 and 15 are arranged in parallel in the oil path R. The valve is characterized in that a lift rod cylinder 10 and a top link cylinder 11 are connected to these ordinary switching valves, respectively.

(e) Effect When performing horizontal control based on the above configuration, the switching valve 13 for lift rod control is switched with the switching valve 15 for top link control in the neutral closed position and the valve 12 for PWM control in the closed position. Then, oil is forced into or discharged from the hydraulic cylinder 10 to control expansion and contraction of the lift rod. Then, when the work equipment approaches the horizontal position, the solenoid valve 12 for PWM control is inching controlled by pulse width modulation that intermittently repeats the closing position and the drain position, thereby press-fitting into the hydraulic cylinder 10. The amount of oil is gradually restricted, the amount of expansion and contraction of the cylinder 10 is gradually reduced, and the cylinder 10 is stopped at a set position. Similarly, when performing top link control, the switching valve 15 for top link control is operated with the switching valve 13 for lift rod control and the valve for PWM control in the closed position to control expansion and contraction of the top link, and then Inching control is performed by a solenoid valve 12 for PWM control at the extension/retraction end of the top link.

(f) Examples Examples of the present invention will be described below with reference to FIGS. 2 to 4.

The tractor 20 has wheels 2 as shown in FIG.
It has a fuselage 22 supported by 1,
The fuselage 22 has an engine 23 mounted at its front, a transmission case 24 which also serves as an oil tank 1 at its rear, and various hydraulic equipment. That is, hydraulic filter 2,
Gear pump 3, flow divider 4, flow priority valve 5 and control valve 2
5, and an electromagnetic switching valve 13 for the lift rod cylinder, an electromagnetic switching valve 15 for the top link cylinder, and a solenoid valve 12 for PWM control. Furthermore, the left and right lift arms 2 are installed at the rear of the fuselage 22 by hydraulic cylinders 27 (Fig. 3).
9 is rotatably disposed, and left and right lower links 30 are pivotally supported. Further, the lift arm 29 and the lower link 30 are connected to the lift rod 3.
1 and 31, and furthermore, a top link 32 is pivotally supported at the rear center portion, and these lower link 30 and top link 32 constitute a three-point link device 33. One of the lift rods 31, 31 is made up of a hydraulic cylinder 10 and is extendable and retractable, and the top link 32 is also made of a hydraulic cylinder 11 and is extendable and retractable.

As shown in FIG. 3, the position sensor 35 and the depth sensor 36 are connected to a master controller 37a in a control box 37, and the control valve 2 of the hydraulic cylinder 27 for the lift arm 29 is connected from the controller 37a.
It is output to 5. Further, the right lift rod length sensor 39 or the left lift rod length sensor 40 and the tilt angle sensor 41 are connected to the level controller 37b in the box 37, and the controller 37b
3 position solenoid switching valve 13 for lift rod and
It outputs to a normally open type 2-position solenoid valve 12 for PWM control. Further, the top link length sensor 42 is connected to the top link controller 37c in the box 37, and further connected to the top link 3-position electromagnetic switching valve 15 and the PWM control solenoid valve 12 from the controller 37c.
It is output to.

Since this embodiment has the above-described configuration, the master controller 37a of the control box 37 performs processing such as calculation based on the signal from the position sensor 35 or the depth sensor 36, and the rising or falling signal from the controller is processed. The control valve 25 is controlled by the control valve 25, the hydraulic cylinder 27 is controlled to expand and contract, the lift arm 29 is rotated, and the position of the working machine is controlled to rise and fall by position control or depth control. In addition, the signal from the top link length sensor 42 is processed by the top link controller 37c, which is switched by the contraction signal or extension signal of the controller 37c to control the expansion and contraction of the hydraulic cylinder 11 provided on the top link 32, and at the same time. Changes in the length of the top link 32 due to expansion and contraction of the cylinder 11 are sent by the sensor 42 to the controller 37b. At this time, the lift rod switching valve 13 is in the neutral closed position,
In addition, the PWM control solenoid valve 12 is in the closed position, so that the PWM control solenoid valve 12 is in the closed position.
As shown in b, from time 0 to y when the top link 32 extends to positions a to c based on the extension signal,
controlled to be the shortest possible time. When the top link 32 reaches a position c slightly short of the preset extended position b, the controller 37
An inching signal is emitted from c, and the solenoid valve 12 for PWM control repeats opening and closing so that the pulse width gradually becomes shorter.
The pressure oil from is not drained into the tank 1 and sent to the switching valve 15 and hence to the hydraulic cylinder 11, but is sent to the cylinder 11 only in the closed position of the valve 12,
The top link 32 slowly extends while gradually decreasing its extension speed (y to x). When the top link 32 reaches the predetermined extension position b, the extension signal and inching signal from the controller 37c are cut off, the switching valve 15 becomes the neutral closed position, and the PWM control valve 12 is returned to the open position. The top link 32 is accurately positioned and stopped. In addition, the left and right lift rod length sensors 39,
40 and the tilt angle sensor 41 are processed by the level controller 37c, and the signals from the controller 3
The switching valve 13 is operated by a rising signal or a falling signal from 7b, and one of the lift rods 31
At the same time, the change in the length of the lift rod 31 due to the expansion and contraction of the hydraulic cylinder 10 is sent to the controller 37b by the sensors 39 and 40, and in the same way as the top link control described above, the change in the length of the lift rod 31 is sent to the controller 37b. An inching signal is issued from the controller 37b at the end of expansion and contraction, and the PWM control solenoid valve 12 repeats opening and closing with pulse width modulation, and the hydraulic cylinder 1
The working machine is controlled to be accurately horizontal by gradually decreasing the amount of expansion/contraction at 0.

(g) Effects of the Invention As explained above, according to the present invention, the switching valve 13 for operating the hydraulic cylinder 10 of the lift rod 31 and the switching valve 15 for operating the hydraulic cylinder 11 of the top link 32 are replaced with ordinary ones not for PWM control. Using the 3-position switching valve, only one normally open 2-position switching valve 12 is sufficient for PWM control, so the storage space can be reduced and it can be easily installed in a crowded place at the rear of the tractor 1. In addition to being easy to install, it is greatly advantageous in terms of cost, and the hydraulic circuit is simplified.Furthermore, since the PWM control switching valve 12, which has a lot of leakage, is normally drained, leakage from the valve is greatly reduced. pressure loss can be significantly reduced.

[Brief explanation of the drawing]

FIG. 1 is a hydraulic circuit diagram showing a hydraulic system for controlling a three-point linkage device according to the present invention, FIG. 2 is an overall side view showing a tractor to which the present invention can be applied, and FIG. 3 is a diagram showing an embodiment of the present invention. The control block diagram shown in FIG. 4a,
b is a diagram showing its operation, and FIG. 5 is a hydraulic circuit diagram that is an extension of the conventional device. 1... Tank, 3... Pump, 10, 11...
Hydraulic cylinder, 12...Pulse width modulation (PWM)
Control switching valve (solenoid valve), 13,1
5... Ordinary 3-position switching valve, 20... Tractor, 29... Lift arm, 30... Lower link, 31... Lift rod, 32... Top link, 33... Three-point link device, R... Oil Road.

Claims (1)

[Claims] 1 At least one of the left and right lift rods 31 is composed of a hydraulic cylinder 10, and the top link 32
is a three-point linkage device 33 consisting of a hydraulic cylinder 11.
, the normally open type two-position switching valve 12 for pulse width modulation control is connected to the oil path R from the pump 3.
Furthermore, two ordinary three-position switching valves 13 and 15 are arranged in parallel in the oil path from the pump, and these ordinary switching valves are connected to the hydraulic cylinder 10 of the lift rod and the top link, respectively. A hydraulic system for controlling a three-point linkage device configured by connecting hydraulic cylinders 11.