Sliding pressure control valve for pneumatic hammer drill

1. A pneumatic device control apparatus comprising:

a ported valve slidably fitted over a feed tube of a pneumatic device; and

a compliant biasing device operatively connected to and constraining motion of the ported valve and for providing asymmetric timing for extending pressurization of a power chamber of the pneumatic device and for reducing pressurization of a return chamber of the pneumatic device, the compliant biasing device is in a rest position when the ported valve is at a first point along the feed tube and the compliant biasing device is in a non-rest compressed position when the ported valve is at a second point along the feed tube, the second point along the feed tube is closer to a drill bit than the first point along the feed tube.

2. The apparatus of claim 1 wherein said ported valve comprises an open end, a rear face on the open end, a closed end, a front face on the closed end, and a sidewall comprising a plurality of openings.

3. The apparatus of claim 2 wherein said plurality of openings comprises at least one set of two openings spaced apart between said ends.

4. The apparatus of claim 2 wherein said plurality of openings comprises at least two openings on different circumferential portions of said sidewall.

5. The apparatus of claim 4 wherein said plurality of openings comprises at least four openings on different circumferential portions of said sidewall.

6. The apparatus of claim 5 wherein said plurality of openings comprises at least two sets of four openings, each set spaced apart between said ends.

7. The apparatus of claim 1 wherein said compliant biasing device comprises one or more devices selected from the group consisting of a spring, a Belleville washer, an elastomer, and an air cylinder.

8. The apparatus of claim 7 wherein said compliant biasing device comprises a die-spring.

9. The apparatus of claim 1 wherein the pneumatic device is a pneumatic hammer drill, comprising a reciprocating piston configured to cyclically impact the drill bit.

10. The apparatus of claim 9 , wherein the reciprocating piston comprises an inner shoulder that contacts a rear face of the ported valve, thereby limiting a rearward position of the ported valve.

11. A method of controlling a pneumatic device comprising the steps of:

slidably fitting a ported valve over a feed tube of the pneumatic device;

constraining motion of the ported valve via a compliant biasing device, and providing asymmetric timing for extending pressurization of a power chamber of the pneumatic device and for reducing pressurization of a return chamber of the pneumatic device; and

maintaining the ported valve between a first point along the feed tube and a second point along the feed tube, the compliant biasing device is in a rest position when the ported valve is at the first point and the compliant biasing device is in a non-rest compressed position when the ported valve is at the second point, the second point along the feed tube is closer to a drill bit than the first point along the feed tube.

12. The method of claim 11 wherein the ported valve comprises an open end, a rear face on the open end, a closed end, a front face on the closed end, and a sidewall comprising a plurality of openings.

13. The method of claim 12 wherein the plurality of openings comprises at least one set of two openings spaced apart between the ends.

14. The method of claim 12 wherein the plurality of openings comprises at least two openings on different circumferential portions of the sidewall.

15. The method of claim 14 wherein the plurality of openings comprises at least four openings on different circumferential portions of the sidewall.

16. The method of claim 15 wherein the plurality of openings comprises at least two sets of four openings, each set spaced apart between the ends.

17. The method of claim 11 wherein the compliant biasing device comprises one or more devices selected from the group consisting of a spring, a Belleville washer, an elastomer, and an air cylinder.

18. The method of claim 17 wherein the compliant biasing device comprises a die-spring.

19. The method of claim 11 wherein the pneumatic device is a pneumatic hammer drill with a front end and a back end, and further comprises a reciprocating piston configured to cyclically impact the drill bit located at the front end of the pneumatic device.

20. The method of claim 19 , wherein the reciprocating piston comprises an inner shoulder that contacts a rear face of the pneumatic valve, thereby limiting a rearward position of the pneumatic valve.

21. A method of controlling a pneumatic device comprising the steps of:

slidably fitting a ported valve over a feed tube of the pneumatic device; and

constraining motion of the ported valve via a compliant biasing device, and providing asymmetric timing for extending pressurization of a power chamber of the pneumatic device and reducing pressurization of a return chamber of the pneumatic device, wherein a reciprocating piston of the pneumatic device has an overall stroke length, and wherein the reciprocating piston cycles between a power stroke portion and a return stroke portion, and wherein the step of providing asymmetric timing comprises using the ported valve to:

a) control a point during the power stroke at which air flow from the feed tube to the power chamber is terminated during the power stroke, thereby permitting a termination point that is closer to the piston impact point, and also providing for the ability to pressurize the power chamber over a longer extent of the overall stroke, which improves overall efficiency;

b) control a point during the return stroke at which air flow from the feed tube to the power chamber is initiated during the return stroke, thereby permitting a power chamber pressurization point that is farther from the piston impact point than when air flow was terminated during the power stroke, and also providing for the ability to create a greater overall piston stroke length by delaying onset of pressure in the power chamber, during return motion of the reciprocating piston, which causes it to decelerate when it is moving away from a drill bit;

c) control a point during the power stroke at which air flow from the feed tube to the return chamber is initiated during the power stroke, thereby permitting an initiation point that is closer to the piston impact point, and also providing for the ability to delay pressurization of the return chamber prior to piston impact; and

d) control a point during the return stroke at which air flow from the feed tube to the return chamber is supplied during the return stroke, thereby permitting a pressure supply point that is farther from the piston impact point than a point at which pressurization was terminated during the power stroke, and also providing for the ability to start pressurizing the return chamber closer to the back end during the return stroke, as compared to the power stroke producing a longer overall piston stroke length.