Impact tool

An impact tool is described which is capable of developing percussive forces for rock drilling, pile driving, seismic exploration and other repetitive high force applications. The tool contains a hammer and a valve which may be hydraulically actuated so as to oscillate; repetitively executing forward and return strokes during each cycle of oscillation. The valve is actuated in the forward stroke direction by being engaged by the hammer, and in the return stroke direction by fluid pressure means so as to switch the pressure in a cavity in which both the valve and the hammer are disposed for developing forces on the hammer so as to sustain its oscillation. A fluid filled pocket is provided into which the valve enters as it moves in the forward stroke direction, after having switched the pressure in the cavity. A passage is provided on the hammer which is dimensioned so that fluid in the cavity is either connected to a channel, the cavity, or entrapped in the pocket, depending on the position of the hammer. A control valve in the channel determines the flow through the channel, and thus the displacement of the valve into the pocket. The displacement is maintained until communication between the pocket and the cavity is provided via the passage. Control is thereby provided over the stroke of the valve and the period between switching of the pressure in the cavity. The hammer stroke length and the frequency and energy of the impacts delivered by the hammer are dependent upon the switching period, and may be varied by the use of the control valve.

The present invention relates to pressurized fluid oscillators and 
particularly to impact tools having an oscillatory hammer and a valve 
which controls the application of pressurized fluid forces to the hammer 
to maintain the oscillation thereof for the purpose of delivering 
repetitive impacts to a load. 
The invention is especially suitable for use in rock drills, pile drivers, 
and demolition tools as well as a seismic sound source in geophysical 
exploration. The invention is also applicable for use in hydroacoustic 
apparatus of the type disclosed in U.S. Pat. Nos. 3,896,899; 3,903,972 and 
3,911,789, and in U.S. Patent application, Ser. No. 522,977, filed Nov. 
11, 1974, in the name of John V. Bouyoucos, et al, now U.S. Pat. No. 
4,005,637, and in U.S. Patent Application, Ser. No. 666,733, filed Mar. 
15, 1976 in the name of John V. Bouyoucos now U.S. Pat. No. 4,077,304. 
More particularly, the invention is an improvement upon the apparatus 
described in application Ser. No. 666,733. 
It is particularly desirable to control the impact or blow frequency as 
well as the impact or blow energy which is generated by an impact tool so 
as to generate percussive energy in a manner which may be most effectively 
utilized, as in penetrating a rock formation. In order to make most 
efficient use of the available input power, the control of blow frequency 
and the energy delivered by each blow should be obtained without wasting 
the input power or otherwise derogating the performance of the impact 
tool. It is also desirable that the mechanism for varying the blow 
frequency and energy be implemented without complicating the design of the 
impact tool and significantly increasing its cost. 
It is the aim of this invention to provide an improved impact tool capable 
of delivering repetitive percussive energy or impacts at frequencies and 
energy per impact which may be varied. 
It is another aim of this invention to provide an improved impact tool with 
blow energy and frequency control which also has high operating 
efficiency. 
It is a still further aim of the present invention to provide an improved 
impact tool wherein blow frequency and energy control may be economically 
implemented. 
Briefly described, a pressurized fluid oscillator embodying the invention, 
which may be used in an impact tool so as to provide blow frequency and 
energy control, includes a hammer and a valve wherein the valve is 
actuated by hammer engagement when the hammer travels in the forward 
direction to an impact position. The valve may be fluid pressure actuated 
in the return stroke direction so as to have a hybrid-mechanical/fluid 
pressure actuation cycle. Both the valve and the hammer are movably 
disposed in a cavity in which pressurized fluid is switched between supply 
and return, alternately, by the valve as it travels in the forward and 
return stroke direction so as to develop forces which effect oscillation 
of the hammer in the forward and return stroke directions. A pocket 
extends into this cavity and is entered by the valve upon its movement in 
the forward stroke direction, after it has been engaged by the hammer and 
has switched the pressure in the cavity. This occurs, preferably, when the 
hammer has reached the impact position such that it is arrested and the 
valve travels under its own momentum into the pocket. The hammer is 
provided with a passage such as a porting groove which provides 
communication of the fluid trapped in the pocket through a channel which 
may be connected to a fluid pressure outlet to supply. In this channel 
there may be disposed a control valve which controls the flow of the fluid 
from the pocket during a first interval of time. By closing the control 
valve the displacement of the valve into the pocket, and thus the stroke 
of the valve and the time interval between the switching of the pressure 
in the cavity can be controlled. Accordingly, the control valve serves to 
control both the frequency and the length of the hammer stroke, thereby 
effectively controlling the blow frequency and blow energy. 
As the hammer travels away from the impact position in the return stroke 
direction, the porting groove in the hammer first closes the pocket to 
trap the fluid and the valve therein for a second interval of time. Then 
the porting groove connects the pocket with the cavity, thus releasing the 
valve from the pocket and enabling the development of pressurized fluid 
forces on the valve so as to drive it rapidly in the return stroke 
direction after the first and second time intervals during which the fluid 
flows out of the pocket and is trapped in the pocket. The fluid pressure 
in the cavity is thus switched rapidly due to the rapid movement of the 
valve both upon engagement by the hammer and by the pressurized fluid 
forces, alternately between return and supply pressure so as to maintain 
the efficiency of operation of the oscillator and the impact tool in which 
it is used.

Referring to FIGS. 1 and 2, there is shown a hydraulic fluid operated 
impact tool 10. Such tools are also known as percussive tools or 
percussive drills. The tool 10 contains a pressurized hydraulic fluid 
operated, hydroacoustic oscillator which includes a hammer 12, a valve 
element 14, and supply and return accumulators 16 and 18, in a housing 20 
to which the accumulators 16 and 18 are attached. The hammer 12, acting 
like a piston, oscillates reciprocally in a central opening or cavity 22. 
The opening 22 extends axially of the housing 20 and is in the form of a 
bore in a cylindrical sleeve or liner 24. The opposite ends of the hammer 
12 are slidably disposed in bearing members 26 and 28 which are located at 
opposite ends of the liner 24. An end cap 30, the upper end of which 
contains wrenching flats 32, is threadedly engaged at the upper end of the 
housing 20 and retains the liner 24 and the bearing members 26 and 28 
within the housing 20. 
The hammer 12 impacts upon a shank 34. A chuck assembly 36 holds the shank 
for rotation by means of a hydraulic motor 38. The other end of the shank 
34 extends beyond the chuck assembly for connection to a drill steel. The 
shank is part of an anvil system which transmits the percussive forces or 
blows created by the impact of the lower end of the hammer 12 upon the 
shank 34 to a load which may be the drill steel with a rock bit at the end 
thereof engaged with a rock formation. Reference may be had to U.S. Pat. 
No. 3,640,351, issued Feb. 8, 1972 for further information respecting the 
design of the shank 34 and chuck assembly 36. The above referenced patent 
also discusses the use of passages such as a bore 42 in the hammer 12 and 
in the shank in which a tube 44 is located for the passage of cleansing 
fluid, suitably air or water, for flushing and cleaning the holes drilled 
by the tool. A coupling 46 in the end cap 30 provides for connection of a 
hose which carries the cleansing fluid to the tube 44. 
The hammer 12 oscillates in opposite directions along the axis of the 
opening 22. One of these directions is the forward stroke direction of the 
hammer towards an impact position where the lower end of the hammer 
impacts the shank 34. The hammer is shown in FIG. 1 travelling in the 
forward stroke direction just before it reaches this impact position. The 
hammer travels in the reverse stroke direction away from the impact 
position. 
The hammer has a central section 48 of diameter slightly less than the 
diameter of the liner bore. The central section 48 divides the cavity 22 
into a lower cavity 50 and an upper cavity 52. The opposite sides of the 
section 48 present areas on which forces are developed in planes normal to 
the direction of hammer motion for driving the hammer. The drive area 
presented to the lower cavity 50 is larger than the drive area presented 
to the upper cavity 52; the drive area presented to the lower cavity being 
suitably twice as large as that presented to the upper cavity. 
The upper cavity 52 receives supply pressure from a cylindrical gallery 54. 
This gallery 54 is connected by way of a lateral passage 56 to the supply 
accumulator 16. A lower cylindrical gallery 58 is connected to the return 
accumulator 18 by way of a lateral passage 60. Channels 62 and 64 (see 
FIG. 2) through which hydraulic fluid at supply and return pressures are 
supplied to the upper and lower galleries 58 and 60 are located in the 
housing. The channel 64 is connected to the lower gallery 60 by way of a 
lateral passage 66. The supply pressure channel 62 is connected to the 
upper gallery 54 by way of a passage 68. A coupling 70 in the housing 
connects the return channel 64 to the return side of a hydraulic pump or 
to a reservoir connected to the return side of the pump. A coupling 72 in 
the housing 20 connects the supply channel 62 to the supply or high 
pressure side of the pump. The upper cavity 52 is in continuous 
communication with the supply gallery 54 through lateral passages 74, 
several of which are radially disposed circumferentially around the liner 
24. Supply pressure in the upper cavity thus continuously urges the hammer 
in the forward stroke direction. 
A supply port 76 and a return port 78 are provided by several holes which 
extend radially through the liner 24. These holes are spaced from each 
other circumferentially around the liner 24 and provide a large porting 
area around the periphery of the liner 24. The supply port 76 communicates 
supply pressure from the supply gallery 54, and the return port 78 
communicates return pressure from the return gallery 58. 
The valve element 14 is a cylindrical sleeve in sliding contact with the 
peripheral surface of the liner 24 and is in porting relationship with the 
supply and return ports 76 and 78. The valve element 14 is movable in the 
directions of the forward and return stroke of the hammer to switch fluid 
pressure in the lower cavity 50 alternately from supply to return pressure 
in order to maintain the oscillation of the hammer. The length of the 
valve element 14 is nearly equal to the distance between the upper and 
lower edges of the supply and return ports 76 and 78 such that the ports 
will be alternately opened and closed as the hammer slides within the 
bore. Suitable seals and "O" rings are used to keep the pressurized fluid 
confined in the cavities 50 and 52 within the housing. 
The valve element 14 is provided with a step 80 which faces in the return 
stroke direction and forms, with a step 82 in the liner 24, a valve cavity 
84. This valve cavity is in continuous communication with the return 
gallery 58 by way of lateral passages 86. The upper end 88 of the valve 
element 14 is in interfering relationship with the side 90 of the hammer 
section 48 which faces the lower cavity 50. 
The hammer 12 has a portion 92 which tapers inwardly towards the axis of 
the hammer and away from the side 90. The upper end 88 of the valve 
element 14 and the surface of the tapered portion 92 form a tapered pocket 
out of which fluid can flow through a variable area orifice between the 
tapered surface of the portion 92 and the inner edge 94 of the upper end 
88 of the valve element 14. Thus the hammer step 90 may be in engagement 
with the valve element 88 through the hydraulic fluid in the partially 
confined volume therebetween. This arrangement for controlling the motion 
of the valve element 14 and gradually accelerating it upon engagement with 
the hammer is also described in the above-referred to U.S. Patent 
Application, Serial No. 522,977. 
The lower bearing member 28 has an upper portion 96 which is in sliding 
contact with the peripheral surface of the hammer 12. The upper end of 
this portion 96 is formed with a lip 98 having an outer diameter slightly 
smaller than the inner diameter of the lower end 100 of the valve element 
14. The portion 96 forms a pocket 102 at the lower end of the cavity 50 
which is defined between the wall of the liner 24 and the portion 96. In 
other words, the portion 96 is between the surface of the hammer 12 and 
the surface of the liner 24. The lower end of the valve element is 
received in the pocket 102 when the valve element 14 travels to the lower 
end of its forward stroke. The extent of the displacement of the valve 
element in the forward stroke direction into the pocket 102 is 
controllable by the position of the valve 106. 
Channels 104 and 105 which extend laterally from the surface of the lower 
bearing member 28 to the supply gallery 54 are provided with a flow 
control valve mechanism 106. This valve mechanism 106 includes a plunger 
or stem 108 which is adjustably positioned with respect to a seat 110 in 
the housing 20 so as to provide a variable area orifice in the channel 104 
to supply via the supply gallery 54. The valve mechanism 106 may be set by 
the set screw arrangement 112 which is accessible from the outside of the 
housing 20. By virtue of such control and also of the trapping of the 
valve in the pocket 102, the stroke of the hammer and the frequency and 
energy of the blows delivered by the hammer upon impact with the shank 34 
is made controllable as will be described more fully hereinafter. 
A port 114 is provided by a plurality of holes which are circumferentially 
spaced around the portion 96 just below the lip 98. A passage in the form 
of a peripheral groove 116 in the hammer 12 first connects the port 114 
with the channel 104 for a first interval of time as the hammer 12 reaches 
the impact position. As the hammer moves upwardly in the return stroke 
direction, the peripheral groove 116, acting as a porting groove, closes 
the connection to the channel 104 to trap the fluid and the valve 14 in 
the pocket 102 for a second interval of time. Then the groove 116 connects 
the ports 114 to the lower cavity 50. The valve 106 controls the 
displacement of the valve element 14 into the pocket during the first 
interval. The valve 106 controls the flow of fluid from the pocket under 
the pressure created by the lower end 100 of the valve 14. The distance 
which the valve element 14 will travel in the forward stroke direction is 
a function of the setting of the valve 106. The flow out of the pocket is 
to supply. This reduces hydraulic losses as would be the case if the flow 
from the pocket went to return. The only loss due to the frequency and 
blow control feature is the dissipation of the kinetic energy of the valve 
element 14 in the passage of fluid through the hydraulic resistor in the 
channels 104 and 105. The saving in hydraulic losses, in terms of the 
power requirements of the pump and its drive motor, can be from 10% to 
20%. 
Prior to the entry of the valve 14 into the pocket 102, the supply ports 76 
are opened and the lower cavity 50 is switched to supply. The hydraulic 
forces on the hammer 12 drive it upwardly in the return stroke direction. 
The groove then for an interval of time (referred to above as the second 
interval of time) closes off the pocket 102 (see FIG. 4) by cutting off 
communication with the channel 104. Supply pressure can not build up in 
the pocket since the channel 104 is closed off from the pocket. Flow with 
respect to the pocket is cut off and the valve is locked in the position 
it reached during the forward stroke for this second interval of time. The 
distance which the valve travels into the pocket (viz, the displacement of 
the valve into the pocket) determines the frequency and blow energy 
parameters of the tool. By virtue of the trapping of the valve, variations 
in this distance are prevented and the frequency and blow energy selected 
by the valve 106 are exactly obtained during operation. 
Another feature obtained by trapping the valve 14 is that the step 80 in 
the valve 14 may be made larger than would be the case in the absence of 
trapping. The larger the area of the step 80 the greater the hydraulic 
forces on the valve 14. These larger forces could start to drive the valve 
out of the pocket prematurely if the valve 14 were not trapped. Large 
forces are desirable during the return stroke, however, since they produce 
rapid switching of the pressure in the lower cavity from supply to return 
at the end of the return stroke to initiate the next forward stroke. These 
larger hydraulic forces are tolerated and obtained due to the trapping 
action of the system. Further the need for a smaller step 80 which would 
be difficult, and in small tools impractical, to machine is obviated. 
The valve 14 is pressure actuated in the return stroke direction by virtue 
of the force due to the pressure across the differential area of the valve 
(viz, the area of the step 80) in plane normal to the direction of valve 
element motion. After the valve element leaves the pocket 102, this force 
is essentially constant and thus the time required for the valve to switch 
the pressure in the lower cavity 50 is a function of the displacement of 
the valve into the pocket 102 which is in turn controlled by the setting 
of the valve 106. The length of the return stroke of the hammer and the 
following forward stroke is thus variable in accordance with the position 
of the valve 106. The impact or blow energy is directly related to the 
hammer stroke and the frequency of the impact is inversely related to the 
length of the hammer stroke. Accordingly, the valve 106 provides both blow 
frequency and blow energy control. The operation of the tool and its 
variable blow energy and blow frequency characteristics will be more 
apparent from FIGS. 3 through 6 which illustrate the impact tool 10 with 
its hammer 12 and valve 14 in different positions during a cycle of 
oscillation. 
Consider the hammer to be at impact position as shown in FIG. 3. The hammer 
has a high downward velocity because the lower cavity 50 has been opened 
to return through the return port 78 (see FIG. 1 for the position of the 
hammer 12 and valve 14 just prior to impact). The hammer 12 is driving the 
valve 14 in the forward stroke direction at substantially the same 
velocity as that of the hammer. At impact, the velocity of the hammer is 
suddenly arrested. The valve element 14 is free to coast in the forward 
direction at or near the velocity of the hammer. Just as the hammer 
reaches the impact position the valve element 14 opens the supply port 76 
and closes the return port 78. The opening of the supply port relieves any 
fluid in the partially confined volume between the side 90 of the hammer 
and the upper end 88 of the valve element 14. There is then no fluid 
retained in this partially confined volume to retard the valve element 14 
or to cause cavitation therein. 
The peripheral groove 116 is disposed in position to connect the port 114 
(to the pocket 102) to the channel 104. The valve element 14 coasts into 
the pocket as shown in FIG. 4. The opening between the seat 110 and the 
upper end of the stem 108 of the valve 106 determines how far the valve's 
momentum will carry it in the forward stroke direction into the pocket 
102. By opening the valve 106 and increasing the gap between the stem 
surface 108 and the seat 110 the displacement of the valve element into 
the pocket may be increased. Conversely by closing the gap between the 
stem 108 and the seat 110 the displacement of the valve element into the 
pocket will be reduced. 
Once the valve 14 velocity is arrested and the hammer has retracted to 
close the channel 104, the pressure in Pocket 102 is reduced below supply 
pressure. Accordingly, since the upper end 88 of the valve element 14 
presents an area in a plane normal to the valve motion to supply pressure, 
there exists a differential pressure across the ends of the valve which 
tends to hold the valve element 14 in the pocket until the peripheral 
groove 116 has moved to a position for connecting the pocket 102 to the 
lower cavity 50. 
Immediately after the supply port 76 is opened, the pressure in the lower 
cavity 50 is switched to supply. There is then a net force across the 
hammer, due to a larger area being presented to supply pressure in the 
lower cavity than to supply pressure in the upper cavity 52. This net 
force drives the hammer in the return stroke direction away from the 
impact position. As the hammer 12 leaves the impact position, the 
connection to the channel 104 is closed. Inasmuch as there is no flow from 
the pocket 102 (the pocket still being at reduced pressure in FIG. 4) the 
valve element is trapped in the pocket until the hammer 12 moves upwardly 
a sufficient distance to connect the pocket to the lower cavity 52 by way 
of the port 114 and groove 116. The valve element 14 is then pressure 
actuated in the return stroke direction due to the difference in the 
pressures in the lower cavity 52, which is at supply, and the valve cavity 
84, which is at return. 
The valve element 14 continues to move upwardly in the return stroke 
direction until it reaches the switching position shown in FIG. 5. The 
valve then closes the supply port 76 while opening the return port 78. 
Supply pressure in the upper cavity 52 exerts a force on the hammer 12 in 
the forward stroke direction and causes the hammer to be decelerated to 
zero velocity at the top of its travel in the return stroke direction 
which position is shown in FIG. 6. The valve element 14 continues to move 
upwardly to the position shown in FIG. 6 since the pressures are balanced 
on the valve element after it switches the pressure in the lower cavity 50 
while travelling in the return stroke direction. After reaching the top of 
its stroke, the hammer is accelerated downwardly in the forward stroke 
direction. The hammer side 90 then again engages the valve element 14, and 
the cycle repeats with another impact occurring at the shank. 
The energy delivered to the hammer on each return stroke is equal to the 
differential pressure (P.sub.S - P.sub.R) across the hammer central 
section 48 multiplied by the area of the hammer (A.sub.H) exposed to the 
lower cavity (viz, the area of the side 90 and so much of the area of the 
tapered portions 92 which are in a plane perpendicular to the direction of 
motion of the hammer) multiplied by displacement of the hammer (X.sub.H). 
Accordingly, the blow energy delivered to the shank is equal to (P.sub.S - 
P.sub.R)A.sub.H X.sub.H. The hammer stroke X.sub.H is, in accordance with 
the equation of motion of the hammer, equal to 
EQU 1/2 P.sub.S (A.sub.H - A.sub.C) (1/M.sub.H)t.sub.1.sup.2, 
where (A.sub.C) is the area of the hammer exposed to the upper cavity, 
(M.sub.H) is the mass of the hammer, and t.sub.1 is the period of time 
during which the supply port 76 is open. In this illustrative embodiment 
the area A.sub.C is approximately equal to one-half the area A.sub.H. By 
closing the control valve 106 the valve element 114 will stop quickly and 
have only a small displacement into the pocket. Thus the valve element 14 
will have a short distance to travel in the return stroke direction to the 
switching position after the groove 116 connects the pocket 102 to the 
lower cavity 50 and releases the valve element 14. Thus by closing the 
control valve 106 and reducing the orifice between the stem 108 and seat 
110, t.sub.1 and therefore X.sub.H are reduced; thus reducing the blow 
energy and increasing the blow frequency. Conversely, by opening the valve 
106 the displacement of the valve element 14 into the pocket 102 is 
increased and the hammer stroke is correspondingly increased. The blow 
energy is then increased while the blow frequency is reduced. 
From the foregoing description it will be apparent that there has been 
provided an improved hydraulic oscillator and impact tool utilizing the 
same. Variations and modifications in the illustrated impact tool will 
undoubtedly become apparent to those skilled in the art. Accordingly, the 
foregoing description should be taken as illustrative and not in any 
limiting sense.