Percussion tool

1. A percussion tool driven by pressurized air for demolition or breaking work, and connectable to an insert tool via a tool holder, said percussion tool comprising a percussion cylinder, a piston arranged to travel in the bore of the percussion cylinder, and a valve unit which alternatingly during operation connects the upper or lower end of the percussion cylinder to a source of pressurized air, which is connectable to the percussion tool, thereby enabling a repeated reciprocating motion of the piston, wherein the insert tool connected to the percussion tool performs repeated striking motions under the action of the piston, said percussion tool being further arranged so that the axial striking position of the piston in the bore of the cylinder, which corresponds to the position of the piston where the energy of the piston is transmitted to the connected insert tool, is dependent on a feeding force by which the percussion tool, via the connected insert tool, is pressed against an object being worked, the percussion tool further comprising an elastic buffer arranged to, during operation, absorb the impact energy not transmitted to the object when the striking position of the piston is furthest downward, which corresponds to the position of the piston when the feeding force is at or below a predetermined value, wherein the percussion tool comprises means for automatically preventing the reciprocating motion of the piston at a predetermined degree of wear on the buffer when the feeding force is at or below said predetermined value, said percussion tool including means for selectively overriding said means for automatically preventing said reciprocating motion only after said reciprocating motion has stopped.

2. The percussion tool according to claim 1 , wherein said means for automatically preventing the reciprocating motion comprises a channel which, when the buffer has reached a predetermined degree of wear, at least when the piston is in Its lower dead center, creates a connection between a first end of the cylinder bore and either the atmospheric pressure of the air surrounding the tool, or a second end of the cylinder bore, thereby preventing the alternating applying of pressure to the two ends of the piston.

3. The percussion tool according to claim 2 , wherein the first end of the cylinder bore is the lower end.

4. The percussion tool according to claim 2 , wherein the piston prevents the connection via the channel until the predetermined degree of wear on the buffer is reached and the piston is at its lower dead center and the feeding force is at or below said predetermined value.

5. The percussion tool according to claim 1 , wherein the means for automatically preventing the reciprocating motion further comprises an upper sleeve, movably arranged in the cylinder bore and arranged to allow or prevent the reciprocating motion of the piston depending on its axial position.

6. The percussion tool according to claim 5 , wherein the axial position of said upper sleeve during operation depends on the feeding force and, at or below said predetermined value, the degree of wear on the buffer.

7. The percussion tool according to claim 5 , wherein the upper sleeve has inner surfaces causing it to move upward in the percussion tool when the insert tool is pressed against the object being worked.

8. The percussion tool according to claim 1 , also comprising a lower sleeve lying against the buffer and responding to wear on the buffer with a displacement in the lengthways direction of the percussion tool, and an upper sleeve which lies against the lower sleeve and follows its displacement, wherein said means for automatically preventing the reciprocating motion comprises a channel, and the displacement of the upper sleeve is utilized for blocking or opening of the channel.

9. The percussion tool according to claim 1 , wherein the means for automatically preventing the reciprocating motion furthermore is arranged to apply pressure to the lower end of the cylinder during the alternating applying of pressure to the ends of the cylinder.

10. The percussion tool according to claim 8 , wherein the lower sleeve comprises a wear indicator, said wear indicator not visible to the operator as long as the buffer has not reached the predetermined degree of wear, and visible to the operator when the predetermined degree of wear of the buffer is reached.

11. The percussion tool according to claim 1 , wherein said percussion tool is a rivet buster.

12. The percussion tool according to claim 6 , wherein the upper sleeve has inner surfaces causing it to move upward in the percussion tool when the insert tool is pressed against the object being worked.

13. The percussion tool according to claim 9 , said percussion tool comprising a lower sleeve lying against the buffer and responding to wear on the buffer with a displacement in the lengthways direction of the percussion tool, and an upper sleeve which lies against the lower sleeve and follows its displacement, and the displacement of the upper sleeve is utilized for blocking or opening of the means for automatically preventing the reciprocating motion, wherein the lower sleeve comprises a wear indicator, said wear indicator not visible to the operator as long as the buffer has not reached the predetermined degree of wear, and visible to the operator when the predetermined degree of wear of the buffer is reached.

14. The percussion tool according to claim 2 , wherein the means for automatically preventing the reciprocating motion further comprises an upper sleeve, movably arranged in the cylinder bore and arranged to allow or prevent the reciprocating motion of the piston depending on its axial position.

15. The percussion tool according to claim 14 , wherein the axial position of said upper sleeve during operation depends on the feeding force and, at or below said predetermined value, the degree of wear on the buffer.

16. The percussion tool according to claim 14 , wherein the upper sleeve has inner surfaces causing it to move upward in the percussion tool when the insert tool is pressed against the object being worked.

17. The percussion tool according to claim 2 , also comprising a lower sleeve, lying against the buffer and responding to wear on the buffer with a displacement in the lengthways direction of the percussion tool, and an upper sleeve which lies against the lower sleeve and follows its displacement, and the displacement of the upper sleeve is utilized for blocking or opening of the means for automatically preventing the reciprocating motion.

18. The percussion tool according to claim 2 , wherein the means for automatically preventing the reciprocating motion furthermore is arranged to apply pressure to the lower end of the cylinder during the alternating applying of pressure to the ends of the cylinder.

19. The percussion tool according to claim 18 , wherein the lower sleeve comprises a wear indicator, said wear indicator not visible to the operator as long as the buffer has not readied the predetermined degree of wear, and visible to the operator when the predetermined degree of wear of the buffer, is reached.

20. The percussion tool as claimed in claim 1 , wherein said insert tool is a chisel.

21. The percussion tool according to claim 1 , wherein said means for selectively overriding said means for automatically preventing said reciprocating motion comprise a channel arranged to permit application of a feeding force greater than zero after said predetermined degree of wear on said buffer has occurred.

22. The percussion tool according to claim 1 , wherein said means for automatically preventing said reciprocating motion and said means for selectively overriding said means for automatically preventing said reciprocating motion comprises a single channel arranged to prevent reciprocating motion of said piston when said feeding force is at or below said predetermined value and said predetermined degree of wear on said buffer has occurred, and to permit movement of said piston after said predetermined degree of wear on said buffer has occurred by applying a feeding force that is greater than zero.