JP2728309B2 - Multi-stage telescopic arm of hydraulic excavator - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a multistage telescopic arm of a hydraulic shovel.

(Prior Art) As a multistage telescopic arm of a hydraulic shovel, for example, Japanese Patent Publication No. Sho 62-27212 and Japanese Patent Publication No. Sho 62-27213 are known.
These use spring force as a protection device for the cylinder when the multistage telescopic arm is extended, but the spring force is also limited. For this reason, a more complete protection of the cylinder during elongation was desired.

(Problems to be Solved by the Invention) When the arm cylinder is operated with the telescopic arm extended, a large force acts on the telescopic arm cylinder and the cylinder may be bent. The aim of the present invention is to further improve the method of using the multi-stage telescopic arm so as to more completely prevent damage to the cylinder of the multistage telescopic arm.

(Means for Solving the Problems) An elevating cylinder for extending and retracting an extendable arm, a sheave holder attached to the lower end of the elevating cylinder, a guide attached to the sheave holder, and a limit switch provided on the outermost pipe of the extendable cylinder in contact with the guide And a limit switch provided below the limit switch that operates when the bucket is grounded. When the two limit switches operate, the relay operates to switch the switching valve, thereby operating the relief valve of the arm cylinder operation circuit. The holding pressure was temporarily reduced.

(Embodiment) FIG. 2 shows a state in which a three-stage telescopic arm 1 according to the present invention is mounted on the tip of a boom 2 of a hydraulic shovel. The outer pipe, 3b is the middle pipe, and 3c is the innermost pipe. The intermediate pipe 3b fits into the outermost pipe 3a, and the innermost pipe 3c fits into the intermediate pipe 3b in a telescopic manner. Reference numeral 5 denotes a clamshell bucket mounted on the lower end of the innermost pipe 3c.

Reference numeral 6 denotes a lifting cylinder of the three-stage telescopic arm 1, and a sheave holder 7 is attached to a lower end thereof. 8 is a guide for the sheave holder 7 (FIG. 4), 9 is a limit switch for detecting the intermediate extension position of the telescopic arm 1, and 10 is a limit switch for detecting the grounding of the clamshell bucket.

FIG. 1 is a control circuit diagram, 11 is a battery, 12, 13
Is a relay, 14 is a pilot lamp, and 15 is a buzzer.

When the clamshell bucket 5 attached to the lower end of the telescopic arm 1 is grounded, the limit switch 10 is actuated and the pilot lamp 14 and the buzzer 15 ground the relay 12, the limit switch 10, the pilot lamp 14 and the buzzer 15. Let the operator do what you do.

Branched from the piping of the arm cylinder 4 and the control valve 16, and an electromagnetic hydraulic switching valve via a check valve 17
The relay 13 is connected to 18. Further, the switching valve 18 is connected to a releap valve 19.

When the lifting cylinder 6 is contracted, the cylinder of the telescopic arm 1 extends,
When the guide 8 attached to the sheave holder 7 moves and the guide 8 moves to the limit switch 9, the limit switch 9 is operated. When the cylinder is extended and the clamshell bucket 5 is grounded, the limit switch 10 is operated, and the relay 12, 13 operates to switch the electromagnetic switching valve 18. When the arm cylinder 4 is operated in this state, the relief valve 19 operates to prevent a large force from being applied to the cylinder.

In FIG. 1, reference numerals 20 and 21 denote overload relief valves provided in the arm cylinder operation circuit. The force applied to the cylinder of the telescopic arm is reduced by reducing the set pressure, and the cylinder can be protected. However, when the telescopic arm 1 is contracted to the dump posture, a high pressure is required for the arm cylinder 4. If the set pressure of the overloader relief valves 20 and 21 is reduced, the telescopic arm 1 cannot be held, and the arm 1 may fall and be dangerous.

Therefore, in the present invention, the relief valve 19 is operated only when the telescopic arm 1 is extended and the bucket 5 is in contact with the ground, so that the cylinder constituting the telescopic arm can be protected.

(Effect) The extendable arm 1 is extended, the extension position in the middle is detected by a limit switch, and the fact that the bucket has touched the ground is detected by another limit switch. The provision of a device consisting of a switching valve for lowering and a relief valve provided more complete protection of the cylinder.

[Brief description of the drawings]

 FIG. 1 is a piping diagram of the present invention. FIG. 2 is a front view of a telescopic arm. FIG. 3 is a detailed view taken along the arrow III in FIG. FIG. 4 is a view on arrow IV in FIG. In the drawing: 1 ... Expansion arm, 2 ... Boom 3a ... Outermost pipe, 3b ... Intermediate pipe 3c ...... Innermost pipe, 4 ... Arm cylinder 5 ... Clamshell bucket 6 ... Elevating cylinder, 7 ... Sheave holder 8 ... Guide 9, 10 ... Limit switch 11 ... Battery, 12, 13 ... Relay 14 ... Pilot lamp, 15 ... Buzzer 16 ... Control valve 17 ... Check valve, 18 ... Switching Valve 19 …… Relief valve 20,21 …… Overload relief valve 22 …… Main relief valve

Claims (1)

(57) [Claims] 1. An elevating cylinder for extending and retracting a telescopic arm,
A sheave holder attached to the lower end of the lifting cylinder, a guide attached to the sheave holder (7), a limit switch provided on the outermost pipe of the telescopic cylinder in contact with the guide, and the limit switch (9) operated by grounding the bucket. Equipped with a limit switch provided below,
When the two limit switches are operated, the relay is operated to switch the switching valve, thereby operating the relief valve of the arm cylinder operation circuit to temporarily reduce the holding pressure thereof, and the multistage expansion and contraction of the hydraulic excavator. arm.