JPH045579Y2 - - Google Patents

Description

[Detailed Description of the Invention] <Technical Field> The present invention relates to a boom shock absorber for a construction vehicle such as a tractor shovel.

<Prior Art> In order to raise a boom arm (hereinafter referred to as a boom) in a cargo handling mechanism of a tractor shovel, oil discharged by a hydraulic pump is controlled by a switching valve to operate a boom cylinder and raise the boom. There are various types of switching valves such as mechanical type and hydraulic pilot type, but in particular, when controlling a boom cylinder using a hydraulic pilot type (pressure control type) switching valve, conventionally, when the switching valve is activated to raise the boom, Since the boom rises to the end of the boom cylinder and rises at a constant speed (without slowing down), a large shock is applied to the vehicle body at the end of the boom cylinder.

Conventionally, boom shock absorbers for construction vehicles have included a cushion mechanism installed in the rod direction of the boom cylinder body, but this type of boom cylinder has two left and right, and the manufacturing Because of the variation in dimensions, the left and right boom cylinders could not enter the cushioning process at the same time, and the left and right boom cylinders entered the cushioning process at different times, which adversely affected the strength of the boom, frame, etc.

<Purpose> Therefore, the purpose of the present invention is to provide a boom shock absorber for a construction vehicle that automatically controls the amount of oil sent to the left and right boom cylinders slightly before the end of the boom cylinder, thereby softening the shock at the end of the stroke.

<Embodiment> Hereinafter, an embodiment of the present invention will be explained based on FIGS. 1 and 2. In this, a pilot-operated switching valve whose spool moves in proportion to pilot pressure is a switching valve for boom cylinder 1. 2, an electric signal actuated cushion valve 3 (electromagnetic valve) is provided to control the pilot pressure of the switching valve 2, and the cushion valve 3 connects the pilot chamber 2a of the switching valve 2 to the first relief valve 4. The normal position 3a connected to the pilot circuit 5 has a normal pressure Po, which is the relief pressure of circuit 7
An electric switch (limit switch) 9 is provided at a position where the boom 8 abuts, and which operates before the top dead center of the boom 8 and switches the cushion valve 3 to the cushion position 3b by an electric signal. ing.

Note that 10 is a pilot hydraulic pump, 11 is a pilot valve, and 12 is a cargo handling hydraulic pump.

The pilot pressure for operating the switching valve 2 is a relief valve 4, which is kept at a certain pressure (PoKg/
^cm2 ). The pilot pressure controlled by the relief valve 4 passes through the pilot valve 11 for switching the pilot pressure, passes through the valve 3, and operates the switching valve 2, so that the pressure oil sent from the hydraulic pump 12 for the boom cylinder 1 is transferred to the boom cylinder. 1 and raise the boom 8. When the boom 8 comes to the position where the electric switch 9 is set, a current is sent to move the cushion valve 3 in the direction A. At that time pump 1
The pressure oil sent from 2 is blocked by the cushion valve 3 and drained by the relief valve 4, and the normal pressure Po that had already been generated between the cushion valve 3 and the switching valve 2 is reduced by the movement of the cushion valve 3 in the direction A. , through the relief valve 6 and drained by the already set cushion pressure P1. However, Po>P1.

The switching valve 2, which was pressed by Po pressure, moves the spool to P.
1 pressure, the flow rate to the boom cylinder 1 decreases, the rising speed of the boom 8 decreases (decelerates), and the shock at the end of the stroke decreases.

However, the pilot pressure and the amount of movement of the spool of the switching valve 2 are as shown in FIG.

<Effects> As is clear from the above explanation, in the present invention, a pilot-operated switching valve whose spool moves in proportion to the pilot pressure is used as a switching valve for a boom cylinder, and the pilot pressure of the switching valve is controlled. An electrically signal actuated cushion valve is provided which has a normal position connecting the pilot chamber of the switching valve to a pilot circuit at normal pressure and a switching valve connecting the pilot chamber of the switching valve to a cushion circuit at a cushion pressure slightly below said normal pressure. A boom for a construction vehicle, characterized in that an electric switch is provided at a boom abutting position, and an electric switch is provided at a boom abutting position, which operates before top dead center of the boom and switches the cushion valve to the cushion position based on an electric signal. This relates to a shock absorber.

Therefore, according to the present invention, even if the boom cylinder is raised at full speed, the rising speed is automatically reduced at a certain arbitrary set position, thereby reducing the shock at the end of the stroke of the boom cylinder and improving the load handling mechanism. It has an excellent effect in that it can be operated quickly without any problems in terms of strength.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an embodiment of the present invention, and FIG. 2 is a diagram showing the relationship between the pilot pressure of the switching valve and the amount of spool movement. 1...Boom cylinder, 2...Switching valve, 2a...
...Pilot chamber, 3...Electric signal actuated cushion valve, 3a...Normal position, 3b...Cushion position, 4...First relief valve, 5...Pilot circuit, 6...Second relief valve, 7... ...Cushion circuit, 8...Boom, 9...Electric switch (limit switch).

Claims (1)

[Scope of utility model registration request] A pilot-operated switching valve whose spool moves in proportion to the pilot pressure is used as a switching valve for the boom cylinder, and an electric signal-operated cushion valve is provided to control the pilot pressure of the switching valve, and the cushion valve: It has a normal position where the pilot chamber of the switching valve is connected to a pilot circuit with normal pressure, and a cushion position where the pilot chamber of the switching valve is connected with a cushion circuit with a cushion pressure slightly lower than the normal pressure, and the boom is located at the top dead center of the boom. 1. A boom shock absorber for a construction vehicle, characterized in that an electric switch is provided at a boom abutting position and operates in front to switch a cushion valve to a cushion position by an electric signal.