Pneumatic hammer mechanism and control method

Patent metadata

Field	Value
Publication number	US-9132541-B2
Application number	US-69706610-A
Country	US
Kind code	B2
Filing date	Jan 29, 2010
Priority date	Jan 30, 2009
Publication date	Sep 15, 2015
Grant date	Sep 15, 2015

Abstract

A pneumatic hammer mechanism is disclosed. The hammer mechanism features: a flying mass, which is movable along an impact axis; an impact surface, which limits a movement of the flying mass along the impact axis in the impact direction; an exciting piston, which limits a movement of the flying mass along the impact axis opposite from the impact direction; a pneumatic chamber between the flying mass and exciting piston; a drive for periodically moving the exciting piston with a stroke along the impact axis, wherein the flying mass is excited to a periodic movement between the impact surface and exciting piston. The stroke is selected as a function of a maximum length of the pneumatic chamber such that the periodic movement of the flying mass on the path between an impact on the impact surface and a minimum approach of the exciting piston intermittently has a velocity of zero.

First claim

What is claimed is:

1. A pneumatic hammer mechanism, comprising:
a flying mass which is movable along an impact axis;
an impact surface which limits a movement of the flying mass along the impact axis in an impact direction;
an exciting piston which limits the movement of the flying mass along the impact axis opposite from the impact direction;
a pneumatic chamber disposed between the flying mass and the exciting piston; and
a drive for periodically moving the exciting piston with a stroke along the impact axis, wherein the flying mass is excited to a periodic movement between the impact surface and a minimum approach of the exciting piston in a cycle with a first phase and a second phase, wherein the first phase is a movement from the minimum approach of the exciting piston to the impact surface and the second phase is a movement from the impact surface to the minimum approach of the exciting piston, and wherein a graph of the movement of the first phase differs from a graph of the movement of the second phase;
wherein the stroke is a function of a maximum length of the pneumatic chamber such that the flying mass decelerates, accelerates, and then decelerates again during the second phase, wherein due to the deceleration, acceleration, and then deceleration again of the flying mass a duration of a period of time for the second phase is greater than a duration of a period of time for the first phase and the flying mass has a greater velocity during the first phase than during the second phase.

2. The pneumatic hammer mechanism according to claim 1 , wherein the stroke is a function of the maximum length of the pneumatic chamber such that the flying mass changes a direction of movement at least once during a movement between the impact surface and a following minimum approach of the exciting piston.

3. The pneumatic hammer mechanism according to claim 1 , wherein the stroke is a function of the maximum length of the pneumatic chamber such that the flying mass touches the impact surface at least twice between two successive minimum approaches of the exciting piston.

4. The pneumatic hammer mechanism according to claim 1 , wherein a mass (m 2 ) of the flying mass, a cross-sectional area (A) of the pneumatic chamber, a maximum length (L) of the pneumatic chamber, the stroke (H) of the exciting piston and an impact coefficient (q) fulfill the following inequality, if the hammer mechanism has an impact frequency (f) during percussive operation:

L
k

2
⁢

(

L
-
H

)

k

·

k

L
-
H

+

(

L
k

2
⁢

(

L
-
H

)

k

-
1

)

·

1
-
q

q

⁢

N

2
⁢
π
⁢

⁢
H

⁢

≥
!

⁢

m
2

A
·

p
0

·

N
2

⁢

f
2

wherein N is at least 4, p o designates an ambient pressure and K an isentropic coefficient of gas in the pneumatic chamber.

5. The pneumatic hammer mechanism according to claim 4 , wherein the impact coefficient (q) is 0.22 if a ratio m 1 /m 2 of a mass (m 1 ) of a snap die to the mass (m 2 ) of the flying mass is greater than 1.2 and otherwise the impact coefficient (q) is 0.12.

6. The pneumatic hammer mechanism according to claim 4 , wherein N is greater than 5.

7. The pneumatic hammer mechanism according to claim 4 , wherein N is greater than 7.

8. The pneumatic hammer mechanism according to claim 1 , wherein the flying mass decelerates to a velocity of zero.

9. A method of operating a pneumatic hammer mechanism, wherein the pneumatic hammer mechanism comprises:
a flying mass which is movable along an impact axis;
an impact surface which limits a movement of the flying mass along the impact axis in an impact direction;
an exciting piston which limits the movement of the flying mass along the impact axis opposite from the impact direction;
a pneumatic chamber disposed between the flying mass and the exciting piston; and
a drive for periodically moving the exciting piston with a stroke along the impact axis, wherein the flying mass is excited to a periodic movement between the impact surface and a minimum approach of the exciting piston in a cycle with a first phase and a second phase, wherein the first phase is a movement from the minimum approach of the exciting piston to the impact surface and the second phase is a movement from the impact surface to the minimum approach of the exciting piston and wherein a graph of the movement of the first phase differs from a graph of the movement of the second phase;
and comprising the step of:
decelerating, accelerating, and then decelerating the flying mass again during the second phase, wherein due to the deceleration, acceleration, and then deceleration again of the flying mass a duration of a period of time for the second phase is greater than a duration of a period of

Assignees

• John Alexander
• Schulz Reinhard
• Pfeiffer Eduard
• Hilti Ag

Inventors

• John Alexander
• Schulz Reinhard
• Pfeiffer Eduard

Classifications

• B25D11/005

  Arrangements for adjusting the stroke of the impulse member or for stopping the impact action when the tool is lifted from the working surface · CPC title

• B25D11/125 Primary

  with a fluid cushion between the crank drive and the striking body · CPC title

• B25D2250/245

  Spatial arrangement of components of the tool relative to each other · CPC title