Hydraulically actuated breaker with lost-motion prevention devic

Motors: expansible chamber type – Cyclically operable – Working member controlled motive fluid for distributor motor

Patent

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Details

91281, 91321, F01L 2502, F01B 718

Patent

active

061520136

DESCRIPTION:

BRIEF SUMMARY
TECHNICAL FIELD

The present invention relates to a hydraulically actuated breaker with a lost-motion preventing device, which is mounted on an arm of a hydraulic shovel for the purpose of crushing concrete and so forth.


BACKGROUND ART

As shown in FIG. 1, for example, as a hydraulically actuated breaker, there has been known one, in which a cylinder portion 6 is constructed by inserting a piston 3 within a cylinder bore 2 of a breaker main body 1 and thus defining a first chamber 4 and a second chamber 5 at opposite sides, a chisel 8 is inserted into a chisel insertion hole 7 of the breaker main body 1, and a supply of a pressurized fluid to the first chamber 4 and the second chamber 5 is controlled to drive the piston 3 upwardly and downwardly to hammer the chisel 8.
For performing a crushing operation by mounting the above-mentioned hydraulically actuated breaker on a hydraulic shovel, as shown in FIG. 1, the breaker main body 1 is mounted on an arm 10 of the hydraulic shovel 9. A boom 13 and the arm 10 are pivoted downwardly to slightly lift a crawler 11 to apply a downward force to the breaker main body 1. In this condition, the piston 3 is driven reciprocally to hammer the chisel 8 to crush concrete 12. When the concrete 12 is crushed, the arm 10, the boom 13 and the crawler 11 are dropped together with the breaker. Then, the operator terminates the operation of the breaker, and shifts an objective position of impact by the chisel 8 by performing pivoting of the hydraulic shovel 9 or so forth in a condition where the boom 13 and the arm 10 are pivoted upwardly, to again actuate the breaker in this condition.
As set forth above, upon performing the crushing operation, if the operator cannot visually detect the fact that a crack is formed in the concrete 12 and thus it is crushed, and the operation of the breaker is continued, a penetration resistance to the chisel 8 becomes so significantly small that the chisel 8 is hammered into the crack to perform only hammering of the chisel 8 without acting the penetration resistance also acting on the chisel 8.
On the other hand, when the tip end of the chisel 8 continues to penetrate the concrete during the crushing thereof, the crawler which has been lifted, contacts with the ground surface. Subsequently, the penetration resistance does not act on the chisel 8 to perform only hammering of the chisel 8.
As set forth above, when only hammering of the chisel 8 is performed without the penetration resistance acting on the chisel, the piston 3 does not hammer the chisel 8 but hammers the breaker main body 1 (hereinafter referred to as "a lost motion"). Thus, the breaker main body 1 may be damaged. Also, the breaker is actuated wastefully to degrade an efficiency of the crushing operation.
The foregoing lost-motion will be discussed concretely. Normally, since the breaker main body 1 is pushed downwardly by a force in a direction shown by an arrow a, the chisel 8 is pushed onto the piston 3 by a penetration resistance in a direction shown by an arrow b to move a hammering position of the chisel by the piston 3 to a position c. Thus, the piston 3 hammers the chisel 8. However, when a crack is formed in the concrete 12 and thus the penetration resistance to the chisel 8 becomes significantly small, the piston 3 is lowered down to a stroke end d to hammer the breaker main body 1 without hammering the chisel 8.
As a structure for preventing the foregoing lost motion, there has been known a first construction, in which a pressurized fluid filled damping chamber for braking the piston when the piston is lowered beyond a predetermined stroke, is provided to stop the piston by the pressurized fluid filled damping chamber or to prevent a collision with the breaker main body.
On the other hand, as disclosed in Japanese Unexamined Utility Model Publication No. Showa 53-101001, there has been known a second structure, in which a hydraulically actuated switching valve actuated with a pressure of the cylinder applying a force to the breaker as a pilot pressure, is provided to

REFERENCES:
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