Hammer drill device

Hammer device comprising a machine housing (1) with a hammer piston (2) movable to-and-fro. The movement to-and-fro of the hammer piston is controlled by a valve body (6) movable to-and-fro in the machine housing. In order to speed up the turning of the hammer piston at its rear end position the machine housing is provided with a room (10) which by the hammer piston is separated from connection with the valve body (6) at the same time as the rear end surface (5) is supplied with pressure fluid via a connection (11) opened by the hammer piston to the pressure source (8) when the hammer piston approaches its rear end position.

BACKGROUND OF THE INVENTION 
The present invention relates to a hammer device of the type incorporated 
in rock drilling machines. 
In prior art hammer devices of the above mentioned kind a valve controlled 
by the hammer piston is used to alternatingly connect a drive surface of 
the hammer piston either to a pressure supply conduit or to a return 
conduit in order to drive the hammer piston in a movement to-and-fro in 
order to exert a drill tool to impacts. With these known designs it has 
turned out to be difficult to achieve impact frequencies exceeding 80-100 
Hz. 
SUMMARY OF THE INVENTION 
It has long been a desire to increase the impact frequency substantially in 
order to make the drilling work more efficient. 
The present invention, which is defined in the subsequent claims, aims at 
achieving a hammer device which can be driven with substantially higher 
impact frequencies, e.g. of the order of 150 Hz.

DESCRIPTION OF THE PREFERRED EMBODIMENT OF THE INVENTION 
The hammer device shown in the drawings comprises a machine housing 1 in 
which a hammer piston 2 is movable to-and-fro in order to exert a tool 3 
to impacts. The tool is provided with a drill bit (not illustrated) in the 
usual way. The hammer piston is provided with a first drive surface 4 
which in the shown example is continuously pressurized by a pressure 
source 8 via a channel 15. The hammer piston is furthermore provided with 
a second drive surface 5 which in the shown example is the rear end 
surface of the hammer piston. Drive surface 5 is alternatingly connected 
to pressure source 8 and to the low pressure of tank 9 via a channel 7 and 
a valve body 6 movable to-and-fro in the machine housing. One can as an 
alternative connect both drive surfaces alternatingly to the pressure 
source or the low pressure. In the shown example pressurization of the 
first drive surface 4 strives at moving the hammer piston to the right in 
the figure. Since the area of the second drive surface 5 is substantially 
larger than the area of the first drive surface 4, pressurization of drive 
surface 5 gives as a result that the hammer piston is driven to the left 
in the figure against the action of the pressure on drive surface 4. Valve 
body 6 is made as a tubular slide provided with a first end surface 12 
which is exerted to the pressure in first chamber 16. Chamber 16 is via 
channel 17 connected to pressure source 8. Valve body 6 is furthermore 
provided with a second end surface 13 which is exerted to the pressure in 
a second chamber 18. Chamber 18 is via channel 19 connected with the 
cylinder bore of hammer piston 2. Since the first end surface 12 is 
continuously pressurized and the second end surface 13 is larger than the 
first, the movement to-and-fro of the valve body 6 is controlled by the 
pressure changes, in channel 19. In order to achieve these pressure 
changes hammer piston 2 is provided with a section 14 with reduced 
diameter. Through this, channel 19 is connected either to pressure source 
8 via channels 20 and 15 as shown in FIG. 1, or via channel 21 to tank 9 
as shown in FIGS. 2 and 3. Valve body 6 is provided with two flanges 22 
and 23 which cooperate with annular sections 24 and 25 respectively in the 
machine housing. The inner space of valve body 6 is connected to low 
pressure, not shown. Machine housing 1 comprises a room 10 into which 
hammer piston 2 can enter so that it separates room 10 from channel 7. At 
about the same time as hammer piston 2 enters into room 10, hammer piston 
2 opens a connection 11 between channel 15 and room 10. Through this 
arrangement the backwards movement of the hammer piston is braked by the 
pressure in room 10 before valve body 6 has changed position so that 
pressure fluid is supplied via channel 7 for driving hammer piston 2 to 
the left in the figure. 
The hammer device shown in the drawings works in the following way. In the 
position shown in FIG. 1, hammer piston 2 has just impacted tool 3. 
Shortly before valve body 6 has been moved to the position shown in FIG. 1 
through pressure fluid supply from pressure source 8 via channels 15 and 
20, the space about section 14 with reduced diameter on the hammer piston, 
and channel 19 to chamber 18. In this position room 10 is drained via 
channel 7 and passed the valve body 6 to tank 9. This means that hammer 
piston 2 is driven to the right in the figure by the pressure on first 
drive surface 4. When the hammer piston has come to the position shown in 
FIG. 2, the hammer piston has closed the connection between channel 20 and 
the space about section 14 with reduced diameter on the hammer piston. 
Furthermore the hammer piston has opened a connection between channel 19 
and channel 21 through which chamber 18 is connected with tank 9. Valve 
body 6 then starts moving to the right in the figure. When hammer piston 2 
has come to the position shown in FIG. 3, the hammer piston has separated 
room 10 from channel 7 and opened connection 11 between channel 15 and 
room 10. Through this, pressure fluid is supplied to room 10 via 
connection 11 in order to brake the backwards movement of hammer piston 2. 
In the position shown in FIG. 3, valve body 6 has closed the connection 
between channel 7 and tank 9. Furthermore a connection has been opened 
between pressure source 8 and channel 7. The hammer device is designed 
such that connection 11 for supply of pressure fluid to room 10 is opened 
earlier than the connection between the pressure source and channel 7. 
Through this, it is achieved that the change of direction of the movement 
of the hammer piston is initiated substantially earlier than what is 
possible through change of position of valve body 6. The result is that 
the hammer device can be driven with substantially higher impact frequency 
than what is possible if the movement to-and-fro is controlled by valve 
body 6 alone. From the position shown in FIG. 3, hammer piston 2 is driven 
to the left in the figure towards the position shown in FIG. 1. On the way 
there, the connection between channels 15 and 19 is opened so that the 
above described process is repeated.