JPH0712102A - Hydraulic circuit structure for working vehicle - Google Patents

Abstract

PURPOSE:To prevent occurrence of leakage of working fluid to a single acting hydraulic cylinder by a simple improvement of a structure. CONSTITUTION:In a hydraulic circuit structure for a working vehicle, a single acting hydraulic cylinder CY is provided for elevating a working device in respect to a running machine, and a three-position changeover valve V which can be switched to a descending position, a neutral stopping position, and an ascending position is arranged on the way of an operation oil supply/discharge passage in respect to the hydraulic cylinder CY. A pilot check valve 11 is arranged on the way of the operation oil supply/discharge passage for preventing discharge of oil from the side of the hydraulic cylinder CY. When the three position changeover valve V is switched to the descending position, pressure oil is supplied to a pilot oil passage 12 of the pilot check valve 11.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention comprises a single-acting hydraulic cylinder for driving and lifting a working device with respect to a traveling machine body, and a descending position, a neutral stopping position and an ascending position in a hydraulic oil discharge passage for the hydraulic cylinder. The present invention relates to a hydraulic circuit structure of a work vehicle in which a three-position switching valve that can be switched is interposed.

[0002]

2. Description of the Related Art Conventionally, in the hydraulic circuit structure of a work vehicle, in the conventional hydraulic oil supply passage for a single-acting hydraulic cylinder,
A check valve that is opened during pressure oil supply and closed during oil discharge is installed, and a variable throttle valve is connected in parallel with this check valve to adjust the oil discharge flow rate and work equipment. It was common to configure so as to suppress the high-speed descent due to its own weight.

[0003]

However, in the above-mentioned conventional structure, the edge of the valve spool in the three-position switching valve is worn due to fine dust or the like mixed in the hydraulic oil after long-term use. When the neutral position is operated while in the raised position, the pressure oil in the hydraulic cylinder leaks to the tank side through the variable throttle valve due to the weight of the working device, and the working device stops rising. There was a problem such as the position gradually dropping, and there was room for improvement. The present invention aims to eliminate the above-mentioned problems.

[0004]

In the hydraulic circuit structure for a working vehicle described at the beginning, a pilot structure for preventing drainage of oil from the hydraulic cylinder side is provided in the hydraulic oil supply / discharge passage. A hydraulic circuit is configured so that when a check valve is provided and the three-position switching valve is operated to the lowered position, pressure oil is supplied to the pilot oil passage of the pilot check valve.

[0005]

When the three-position switching valve is operated to the down position,
Pressure oil is supplied to the pilot oil passage of the pilot check valve, the pilot check valve is opened, and the hydraulic oil is discharged from the hydraulic cylinder side to the tank side through the hydraulic oil supply / discharge oil passage. When the 3-position switching valve is operated to the raised position, hydraulic oil is supplied to the hydraulic cylinder while forcibly opening the pilot check valve by the operating pressure of the hydraulic pump that is in communication with the hydraulic oil supply / discharge passage. Of.
When the 3-position switching valve is operated to the neutral stop position,
Since pressure oil is not supplied to either the pilot oil passage or the hydraulic oil supply / discharge oil passage for the hydraulic cylinder,
Even if the working oil in the hydraulic cylinder tries to be discharged through the hydraulic oil supply / discharge oil passage due to the weight of the work device, the pilot check valve reliably blocks the flow rate.

[0006]

Therefore, with the rational hydraulic circuit structure,
Since it is a single-acting hydraulic cylinder, it has a hydraulic piping structure that has only one hydraulic oil supply / exhaust passage, but even if the valve spool wears, it is possible to reliably prevent operational leaks. As a result, it is possible to prevent adverse effects such as the work device stopped in the ascending state gradually descending against the intention of the worker.

[0007]

Embodiments will be described below with reference to the drawings. Figure 2
Fig. 1 shows a passenger type rice transplanter which is an example of a work vehicle. In this rice transplanter, a seedling planting device 3 (an example of a working device) is connected to a rear portion of a riding type traveling body 1 via a link mechanism 2 so as to be driven up and down by a hydraulic cylinder CY.

As shown in FIG. 1, the hydraulic cylinder CY.
Is a single-acting type, and when the seedling planting device 3 is driven to rise, pressure oil is supplied from the hydraulic pump P driven by the engine 4 to extend and drive the seedling planting device 3. Is configured so that the weight of the seedling planting device 3 discharges the pressure oil in the hydraulic cylinder CY to the tank side and lowers it.
The operation of supplying / discharging the hydraulic oil to / from the hydraulic cylinder CY is interposed in the hydraulic oil discharge passage for the hydraulic cylinder CY, and is a three-position switching valve V that is switchable to each of the descending position D, the neutral stop position N and the ascending position U. It is configured to be performed by the switching operation of. The three-position switching valve V has a neutral stop position N.
In addition to being biased by a spring to the return position, switching to the lowered position D and the raised position U is an electromagnetic operation type in which the valve spool is directly operated by magnetically driving the electromagnetic solenoids SL, SL.

The switching operation of the three-position switching valve V can be performed based on the forward / backward swinging operation of the raising / lowering lever 5 provided in the body control section, and also by the operation of the swinging type raising / lowering operation switch SW1. Further, during the planting work, automatic switching can be performed so as to maintain the height of the seedling planting device 3 above the ground at a set value. That is, the electromagnetic solenoids SL, SL of the three-position switching valve V are configured to be driven and controlled by the control device 6 having a microcomputer, and the control device 6 has a potentiometer for detecting the swing operation amount of the elevating lever 5. Type lever sensor 7, potentiometer type float sensor 9 for detecting the amount of vertical swing based on the fluctuation of the ground pressure of the ground float 8 provided on the seedling planting device 3 so as to swing vertically around the rear fulcrum X, and a potentiometer-type sensitivity setter 10. The respective outputs of the lifting operation switch SW1 are given.

The control device 6 switches the switching valve V to the lifting position U when the elevating lever 5 is operated to the "up position", and switches the switching valve V to the neutral stop position N when operating to the "neutral position". When operated to the "down position" or the "planting position", the switching valve V is controlled to switch to the down position D. When the raising / lowering lever 5 is operated in the "automatic position", when the raising / lowering operation switch SW1 is operated, the seedling planting device 3 is alternately switched between the lowered state and the state in which it is raised to the maximum raised position for each operation. Control. or,
When the raising / lowering lever 5 is in the "automatic position" and the seedling planting device 3 is grounding and descending, the switching valve V is automatically switched so that the detection value of the float sensor 9 matches the setting value of the sensitivity setting device 10. Then, the automatic raising / lowering control is performed so that the planting depth of the seedlings is maintained substantially constant.

Incidentally, the detection of the rise to the maximum raised position is configured such that the link mechanism 2 acts on the limit switch SW2 attached to the rear portion of the machine body to detect it. Therefore, when the limit switch SW2 detects and operates during the ascending operation, the switching valve V is switched from the ascending position U to the neutral stop position N. In this way, when the seedling planting device 3 is set in the neutral stop state at the elevated position, if the hydraulic oil leaks due to wear of the valve spool, for example, the weight of the seedling planting device 3 causes the link mechanism 2 to move. It descends and moves away from the limit switch SW2 to become a non-detection state,
The switching valve V may be automatically controlled to switch to the raised position U again, and a leak may occur again, resulting in a problem that the seedling planting device 3 repeatedly vibrates up and down.

Therefore, in this rice transplanter, measures are taken to prevent the occurrence of the above-mentioned operational failure due to the leakage of hydraulic oil. That is, the pilot check valve 11 for preventing drainage of oil from the hydraulic cylinder CY side is provided in the hydraulic oil supply / discharge passage for the hydraulic cylinder CY for lifting / lowering drive, and the three-position switching valve V is operated to the lowered position D. Then, the hydraulic circuit is configured so that the pressure oil is supplied to the pilot oil passage 12 of the pilot check valve 11. Therefore, since the pressure oil is not supplied to the pilot oil passage 12 when the neutral stop position N is being operated, the check valve 11 reliably prevents the hydraulic oil from leaking from the hydraulic cylinder CY side to the tank. Become. During the ascending operation, the pump pressure can be used to push open the pilot check valve 11 to supply pressure oil, and during the descending operation, the pressure oil can be supplied to the pilot oil passage 12 of the pilot check valve 11 to push the check valve 11. Opened, hydraulic cylinder C
The oil from Y can be smoothly discharged. In the figure, 13 is a variable throttle valve that changes the descending speed of the seedling planting device.

It should be noted that reference numerals are added to the claims for facilitating the comparison with the drawings, but the present invention is not limited to the configurations of the accompanying drawings by the entry.

[Brief description of drawings]

FIG. 1 Control system diagram of 3-position switching valve

[Figure 2] Side view of rice transplanter

[Explanation of symbols]

 3 Working device 11 Pilot check valve 12 Pilot oil passage CY Hydraulic cylinder V 3 Position switching valve

Claims (1)

[Claims] 1. A single-acting hydraulic cylinder (CY) for driving and lifting a work device (3) with respect to a traveling machine body, and a lowered position in a hydraulic oil discharge passage for the hydraulic cylinder (CY).
A hydraulic circuit structure for a work vehicle, comprising a three-position switching valve (V) that can be switched between a neutral stop position and a raised position, wherein the hydraulic cylinder (C) is provided in the hydraulic oil supply / discharge passage.
Pilot check valve (1) to prevent oil discharge from Y side
1) is interposed and a hydraulic circuit is configured so that pressure oil is supplied to the pilot oil passage (12) of the pilot check valve (11) when the three-position switching valve (V) is operated to the lowered position. The hydraulic circuit structure of the working vehicle.