JPH02215302A - Rise and fall structure of working device of working vehicle - Google Patents

Abstract

PURPOSE:To surely lower a working device even in light load by equipping an electromagnetic change valve which is opened to drain oil when drain oil pressure of hydraulic actuator becomes lower than a set value. CONSTITUTION:When a first on-off value 11 is opened by drain oil pressure from a hydraulic cylinder 5 (when detected value of a pressure sensor 22 is >=a set value), an electromagnetic change valve 20 remains closed. On the contrary, when drain oil pressure from the hydraulic cylinder 5 is extremely dropped and the first on-off valve 11 is not opened under the drain oil pressure (when the detected value of the pressure sensor 22 is <= the set value), the electromagnetic change valve 20 is operated to an open side by a control device 19. Consequently, an oil is surely drained from the hydraulic cylinder 5 and a lift arm 6 is operated downward.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a working vehicle such as an agricultural tractor, and more particularly to an elevating structure for a working device connected to a machine body.

[Conventional technology]

An example of an agricultural tractor, which is one type of work vehicle, is disclosed in Japanese Patent Application Laid-Open No. 61-293304. This is because when hydraulic oil is supplied to the hydraulic cylinder as a hydraulic actuator, the hydraulic cylinder expands and the rotary tilling device as a working device is lifted.The hydraulic oil is drained from the hydraulic cylinder and the hydraulic By contracting the cylinder, the rotary tiller is lowered.

[Problem to be solved by the invention]

In the disclosed structure, a pilot-operated on-off valve is provided in the oil drainage system of the hydraulic cylinder, and when lowering the work equipment, the on-off valve is operated to the open side by the drainage oil pressure from the hydraulic cylinder. Since the hydraulic cylinder is configured to drain oil, a small amount of pressure (enough pressure to open the on-off valve) is required to drain the oil from the hydraulic cylinder.

However, for example, when connecting a working device to the machine body (in the case of an agricultural tractor, the lift arm connected to the hydraulic cylinder is lowered and the working device placed on the ground is connected to the lift arm), etc. When retracting the hydraulic cylinder under a light load such as when nothing is connected to the aircraft, the hydraulic pressure discharged from the hydraulic cylinder is not sufficient, and the on-off valve does not open, making it difficult to retract the hydraulic cylinder properly. A situation arises where this is not possible.

The present invention has been made in view of the above-mentioned problems, and it is an object of the present invention to provide a structure that allows the lowering operation of the working device to be performed smoothly, especially under light load conditions.

[Means to solve the problem]

A feature of the present invention is that, in the above-mentioned working device elevating structure of a working vehicle, a pressure sensor is provided to detect the discharge oil pressure of the hydraulic actuator, and when the detected discharge oil pressure becomes less than a set value, the oil discharge system from the hydraulic actuator is The present invention is equipped with an electromagnetic switching valve that puts the motor in an unloaded state, and its functions and effects are as follows.

[For production]

With the configuration described above, even if the drain pressure from the hydraulic actuator is not sufficient to open the on-off valve of the oil drain system, the electromagnetic switching valve will force the oil drain system into the unloaded state. This ensures that oil is drained from the hydraulic actuator, and the working device descends.

〔Effect of the invention〕

As described above, it has become possible to reliably lower the working device even under a light load, and it has become possible to prevent problems such as the inability to lower the working device.

Further, since an electromagnetic switching valve is used for unloading operation, the operation is more reliable than that of a pilot-operated switching valve, and the structure of the operating system is not particularly complicated.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings, using an agricultural tractor as one of the working vehicles.

Figure 3 shows the rear of an agricultural tractor. A pair of left and right lower links (2) are provided at the bottom of the mission case (1), and a top link (3) is provided at the top, forming a three-point link mechanism. The working device (
A rotary tilling device as 4) is connected. A single-acting hydraulic cylinder as a hydraulic actuator (5) is provided in the upper part of the mission case (1), and a lift arm (6) and a lower link (2) are connected to this hydraulic cylinder (5). ), and a rod (7) is installed across it. As a result, by extending the hydraulic cylinder (5), the rotary tiller (4) is raised, and by contracting the hydraulic cylinder (5), the rotary tiller (4) is lowered. .

Next, to explain in detail the hydraulic circuit for the hydraulic cylinder (5), as shown in Fig. 1, one oil passage (9) from the pump (8) is connected to the hydraulic cylinder (5), and this oil passage (9) is provided with a check valve (14). and,
Check valve (14) on hydraulic cylinder (5) side and pump (8)
) side is connected with a first on-off valve (11) and a second on-off valve (13), and an eleventh and second electromagnetic on-off valve that adjusts the pilot pressure of each of the on-off valves (11) and (13). Valves (10) and (12) are provided.

With the above configuration, the second electromagnetic on-off valve (12) is opened and closed intermittently to lower the pressure on the pilot oil passage (15) side and narrow the opening degree of the second on-off valve (13). As a result, hydraulic oil from the pump (8) is supplied to the hydraulic cylinder (5), and the rotary tiller (4) is operated to rise.

Conversely, when the first electromagnetic on-off valve (10) is opened and closed intermittently to lower the pressure on the pilot oil passage (16) side, the pilot oil passage (23) is reduced by the discharged hydraulic pressure of the hydraulic cylinder (5).
Due to the pressure on the side, the first on-off valve (11) moves to the open side, and the hydraulic oil from the hydraulic cylinder (5) flows into the first on-off valve (11).
) through which the oil is drained. As a result, the rotary tiller (4) is operated downward.

As shown in FIG. 1, a potentiometer (17) for detecting the angle of the lift arm (6) is attached to the base of the lift arm (6), and a signal from the potentiometer (17) is transmitted to the control device (19). ) is entered. As a result, the control device (19) controls the first and second electromagnetic on-off valves (10) so that the angle of the lift arm (6) corresponds to the set value of the plowing depth setting device (18).
The operation signal is issued at (12).

In this case, the operation signal is intermittent as shown in Fig. 2, and the ratio (ti/T) of the start time (t, ) of the operation signal within one cycle (T) is changed to Adjust the pressure in the oil line (5) or (16). When starting the operation signal for the first time, it takes a slightly longer time (t2
) in order to increase the responsiveness of the pressure adjustment of the pilot oil passage (15) or (16).

As shown in Fig. 1, an electromagnetic switching valve (20) is connected in parallel to the first on-off valve (11), and a pressure sensor (22) is attached to this oil passage (21). There is. The first on-off valve (11) is connected to the hydraulic cylinder (
5), the electromagnetic switching valve (20) is closed when it is opened by the exhaust pressure from the valve (when the detected value of the pressure sensor (22) is greater than or equal to the set value).

Conversely, when the exhaust pressure from the hydraulic cylinder (5) becomes extremely low and the first on-off valve (11) does not open with this exhaust pressure (when the detected value of the pressure sensor (22) is below the set value) ), the solenoid switching valve (20) is controlled by the control device (19).
is operated to the open side. This allows the hydraulic cylinder (5)
After the oil is reliably drained, the lift arm (6) is lowered.

In the above-mentioned Figure 2, the operation signal is first transmitted for the time (t2), but instead of transmitting for the set time (t2), the lift arm (6) is activated by the potentiometer (17). The operation signal may be transmitted until the start of movement is detected, and thereafter the operation signal may be transmitted intermittently.

Incidentally, although reference numerals are written in the claims section for convenient comparison with the drawings, the present invention is not limited to the structure shown in the accompanying drawings.

[Brief explanation of the drawing]

The drawings show an embodiment of the working device elevating structure for a working vehicle according to the present invention, in which FIG. 1 is a hydraulic circuit diagram for a hydraulic cylinder, FIG. 2 is a time chart of operation signals for the first and second electromagnetic on-off valves, and FIG. Figure 3 is a side view of the rear half of the agricultural tractor. (4)...Working equipment, (5)...Hydraulic actuator, (11)...Opening/closing valve, (20
)...Solenoid switching valve, (22)...Pressure sensor Figure 3

Claims (1)

[Claims] The hydraulic actuator (
5), which is connected to the working device ( 5) is a working device elevating structure for a working vehicle configured to be lowered; the working device is provided with a pressure sensor (22) for detecting the discharge pressure of the hydraulic actuator (5); A working device elevating structure for a working vehicle, comprising an electromagnetic switching valve (20) that unloads the oil drain system from the hydraulic actuator (5) when the oil becomes below a set value.