Pneumopercussive soil penetrating machine

A self-propelled, pneumopercussive, cyclic action, ground penetrating machine (200) has decreased energy consumption and increased average working velocity compared to conventional machines. This is obtained in part by a valve-operated air-distribution mechanism (203) having separated forward and reverse compressed air supply lines (35, 37), which mechanism (203) does not limit the length of the forward and backward strokes of the striker (202). This mechanism allows the backward stroke chamber (75) to be connected with the atmosphere during the entire forward stroke of the striker (202). This eliminates generation of an air buffer in the backward stroke chamber (75) and, consequently, the striker (202) does not lose part of its kinetic energy before impact. The invention also provides a cyclic action braking mechanism (204), a forward/reverse mode control system (205) which can be pneumatically actuated, a movable chisel (207) which utilizes the energy of the striker more efficiently and has a gasket (72) to prevent jamming, and a sensor (208) for monitoring the impact frequency of the machine (200) so that it can be quickly switched to reverse mode upon encountering an obstacle.

FIELD OF THE INVENTION 
The present invention relates generally to pneumatic, self-propelled, 
percussive cyclic action underground penetrating machinery of the type 
used for making holes in the ground, driving pipes into the ground, or 
driving explosives into the ground for mining or military engineering. 
BACKGROUND OF THE INVENTION 
Air-operated self-propelled percussive cyclic action machines for making 
holes in the soil are known. These machines comprise a hollow cylindrical 
housing, having a pointed head section, a striker which reciprocates 
inside the housing, and an air-distributing mechanism. The principle of 
operation of these machines is as follows. During one cycle of machine 
operation the striker executes a forward and then a backward stroke. At 
the end of the forward stroke the striker, being accelerated by compressed 
air, imparts an impact to the front end of the housing. As a result, the 
machine penetrates the soil by a certain increment of displacement. During 
the backward stroke the striker is braked, e.g., by an air buffer which 
develops in the space between the rear end of the striker and the housing. 
The air buffer prevents a collision between the striker and the housing, 
so that the striker stops and a new cycle begins. Machines of this type 
are in Zinkiewicz, U.S. Pat. No. 3,137,483 and Zygmunt, U.S. Pat. No. 
3,407,884 
A number of inherent disadvantages have prevented the extensive utilization 
of these machines. One of the main shortcomings of these machines is the 
insufficient reliability of the air-distributing mechanism. Improved 
versions of these machines, based on a valveless air-distributing system, 
were later developed. The valveless air-distribution system described in 
U.K. Patent No. 800,725, published Sept. 3, 1958 was later used in a soil 
penetrating machine described in U.S. Pat. No. 3,410,354, issued to 
Sudnishnikov et al. in November, 1968. U.S. Pat. No. 3,651,874, issued to 
Sudnishnikov et al. in March, 1972, described a reversible valveless 
machine for making holes in the soil. This machine provided a threaded 
connection between the air supply sleeve and the machine body, allowing 
the stroke of the striker to be displaced rearwardly. 
Subsequent patents illustrate that the valveless machines of Sudnishnikov 
et al. suffered from various problems. U.S. Pat. No. 3,708,023 issued to 
Nazarov et al. in January, 1973, noted that prior selfpropelled machines 
did not possess sufficient impact power, and proposed to solve the problem 
by providing an auxiliary pressure chamber at the head of the machine. 
U.S. Pat. No. 3,727,701, issued to Sudnishnikov et al. in April, 1973, 
mentions that, in known reversible air-punching machines for making holes 
in the soil, pressure fluctuations may result in an uncontrollable 
shifting of the machine from the forward to reverse mode, and vise versa. 
In U.S. Pat. No. 3,744,576, issued to Sudnishnikov et al. in July, 1973, it 
is stated that the screw reversing mechanisms of known pneumopercussive 
machines, which require rotating the air supply hose to displace the 
stroke of the striker, are difficult and sometimes impossible to use. 
Nonetheless, Sudnishnikov et al., U.S. Pat. No. 3,756,328, issued 
September 1973, still shows a screw reversing mechanism which must be 
manually actuated by rotating the air hose. The '328 patent further 
describes a resilient shock-damping means having longitudinal air exhaust 
passages designed to prevent from early breakdown of the air-distributing 
mechanism. Machines based on U.S. Pat. No. 3,756,328 are still in use. 
Subsequent patents describe a variety of largely unsuccessful attempts to 
improve the reversing mechanism of valveless soil penetrating machines. 
Sudnishnikov et al., U.S. Pat. No. 4,078,619, issued in March, 1978, 
discloses an improvement to the reversing mechanism. According to this 
patent, the reversing mechanism is actuated by manually pulling on the air 
supply hose. Tkach et al., U.S. Pat. No. 4,121,672, issued in October, 
1978, offers an improvement to the means for rotating the air supply hose. 
U.S. Pat. No. 4,132,277, issued to Tupitsyn et al. in January, 1979, also 
describes a reversing mechanism which is activated by pulling the air 
supply hose. U.S. Pat. No. 4,214,638 issued July 1980 to Sudnishnikov et 
al., states that controlling the reverse mechanism by rotating or pulling 
the air supply hose is time consuming, difficult and, in certain cases, 
altogether impossible. This has proven true in practice particularly when 
it is necessary to reverse the machine when the machine is far 
underground. 
To address these problems, Schmidt, U.S. Pat. No. 4,295,533, issued 
October, 1981, suggests rotating a component in the reversing mechanism by 
a flexible shaft enclosed within the air supply hose. Bouplon, U.S. Pat. 
No. 4,662,457, issued May, 1987, offers an improved reversing mechanism 
which requires rotating the air-supplying hose approximately a quarter of 
a turn. U.S. Pat. No. 4,683,960, issued August, 1987, to Kostylev et al., 
describes a reversing mechanism based on pulling a separate cable instead 
of the airsupplying hose. None of these manually-operable reversing 
mechanisms have completely eliminated the problems with the screw reverse 
mechanism. 
A different approach to control the reversing mechanism is proposed in 
Schmidt, U.S. Pat. No. 4,250,972, issued February, 1981. According to this 
patent, the reversing mechanism is controlled by a secondary air supply 
line to the device, or electrically. However, this system has not found 
widespread use. 
This brief analysis of the valveless pneumo-percussive underground 
penetrating machines shows that, during the last two decades, many 
unsuccessful efforts were made to improve the control system of the 
reversing mechanism for underground penetrating machines. However, despite 
these efforts, the basic screw reverse operated by rotating the air supply 
hose a dozen times or more remains in widespread use. 
Other improvements to the valveless soil penetrating machine of U.S. Pat. 
No. 3,410,354 have also been proposed. Schmidt, U.S. Pat. No. 3,865,200, 
issued February, 1975, describes a movable chisel and an intermediate 
piston having interposed elastic members. This patent asserts that this 
reduces impact loading on the housing of the penetrating machine, and also 
reduces the required "percussion energy" in comparison with conventional 
driving machines. Although this design does reduce impact loading on the 
housing, there is an energy loss due to the intermediate piston. In 
addition, the movable chisel is ineffective because, after a number of 
working cycles, particles of soil penetrate fill the gap between the 
chisel and the housing, so that the chisel becomes jammed in the 
forwardmost position. The intermediate piston and movable chisel 
disappeared from the later machines by the same inventor (See Schmidt, 
U.S. Pat. Nos. 4,250,972 and 4,295,533). A movable chisel is also shown in 
the U.S. Pat. No. 4,100,980 issued to Jenne in July, 1978. This design is 
also unworkable for the same reasons as in the Schmidt device. 
Energy consumption and productivity are among the most important parameters 
of a working process of a machine. During the last decade several 
scientific papers, related to the energy consumption and productivity (or 
average velocity) of underground percussive penetrating machines have been 
published by the present inventor. See Minimization of Energy Consumption 
of Soil Deformation, Journal of Terramechanics, 1980, Volume 17, Number 2, 
pages 63 to 77; Principles of Soil-Tool Interaction, Journal of 
Terramechanics, 1981, Volume 18, Number 1, Pages 51 to 65; Motion of 
Soil-Working Tool Under Impact Loading, Journal of Terramechanics, 1981, 
Volume 18, Number 3, Pages 133 to 156; Working Process of Cyclic-Action 
Machinery for Soil Deformation-Part 1, Journal of Terramechanics, 1983, 
Volume 20, Number 1, Pages 13 to 41; Minimum Energy Consumption of Soil 
Working Cyclic Processes, Journal of Terramechanics, 1987, Volume 24, 
Number 1, Pages 95 to 107). According to the data presented in these 
papers, the process of vibratory soil penetration can be optimized to 
obtain minimum energy consumption. By comparing the performance of the 
conventional pneumopercussive hole making machines with the performance 
possible using minimum energy consumption, it becomes clear that 
conventional machines are characterized by relatively high energy 
consumption and relatively low productivity. Development of new machines 
based on optimization with respect to minimum energy consumption will 
decrease the flow rate of the compressed air and also simultaneously 
increase the average velocity of these machines. 
To optimize the boring process, it is essential to increase the kinetic 
energy that the housing obtains from an impact of the striker. One way to 
increase this kinetic energy consists of lengthening the forward stroke of 
the striker. However, the structure of the valveless air-distributing 
mechanism of known pneumopercussive underground penetrating machines makes 
it very difficult or almost impossible to increase the striker stroke 
length to a considerable extent. The reason is that the backward stroke of 
the striker occurs under the action of a portion of the compressed air 
which enters the rear stroke chamber through holes that remain open a 
short time. These holes are then closed by overlap of the striker during 
the beginning of its backward stroke. Pressure force of the expanding air 
moves the striker backward. In the forward stroke chamber there is 
constant air pressure. The striker moves backward because the active, 
cross-sectional area of the striker for the backward stroke exceeds the 
active cross-sectional area for the forward stroke. However, the backward 
stroke cannot be relatively long because the pressure of the expanding air 
in the backward stroke chamber air drops rapidly as the pressure in the 
forward stroke chamber brakes the striker. Thus, the valveless 
air-distributing mechanisms of the type discussed above inherently require 
relatively short striker stroke lengths. The valveless air-distributing 
mechanism of conventional machines is not appropriate for relatively long 
stroke machines, for example, 1.5 to 2 times. 
Another inherent disadvantage of conventional pneumopercussive underground 
boring machines is that the backward stroke chamber is connected with the 
atmosphere for just a brief period during the forward stroke of the 
striker. This creates an air buffer in the backward stroke chamber and 
brakes the striker before it imparts an impact, thereby decreasing the 
kinetic energy of the striker before impact. The auxiliary chamber 
proposed in the foregoing patent to Nazarov et al. has not proven an 
effective solution to this problem. 
A further disadvantage of known pneumo-percussive underground machines 
concerns the ratio between the external frictional force of the soil 
distributed over the surface of the housing and the rearward air pressure 
force applied to the inside rear end of the housing during the forward 
stroke of the striker, i.e., the recoil of the housing as the striker 
moves forward. Under working conditions this ratio is in the range from 
0.3 to 0.75, while the optimum value of this ratio, as taught in the 
literature, is 1.0. This means that, under actual working conditions, the 
housing moves backward during the forward stroke of the striker. Such 
movement negates a certain part of the stroke length, and the housing 
gains a negative velocity before the collision. The striker cannot 
actually utilize the entire stroke length and, consequently, has less 
kinetic energy before collision. The decreased kinetic energy of the 
striker and the backward velocity of the housing before collision in turn 
reduce the kinetic energy of the housing after the collision, reducing the 
overall efficiency of the machine. 
Still another inherent disadvantage of known pneumopercussive underground 
penetrating machines is associated with the transmission of kinetic energy 
from the striker to the housing. The best situation is when the rebound 
energy of the striker is equal to zero so that the housing gains the 
maximum possible energy from the striker. Collision theory dictates that, 
in order to obtain ideal transfer of energy from the colliding mass to a 
motionless collided mass, the ratio between the colliding mass and the 
collided mass must equal the value of the restitution coefficient of the 
two masses. However, in conventional pneumopercussive underground 
penetrating machines, the ratio of these masses is significantly less that 
the restitution coefficient. This causes the striker to rebound so that 
part of the kinetic energy of the striker is not transferred housing. 
Ideally, the striker should stop dead in the same way a billiard ball does 
when striking another ball. 
Still another inherent disadvantage of conventional pneumopercussive 
underground hole making machines is the lack of a means for independently 
controlling the compressed air in the forward and backward stroke 
chambers. Under some working conditions the striker can impart undesirable 
impacts to the rear end of the housing. These impacts can be avoided by 
controlling the air pressure in the backward stroke chamber. Similarly, 
when the machine is in reverse mode it may be necessary to control the 
pressure of the compressed air in the forward stroke chamber to prevent 
forward impacts. Independent control of the compressed air in the forward 
and backward stroke chambers can also improve the efficiency and 
restarting ability of the machine. 
One more inherent disadvantage of conventional pneumopercussive underground 
penetrating machines is the lack of a means for monitoring the working 
process of the machine. The striker frequency and pressure in the forward 
stroke chamber change depending on operating conditions. The impact 
frequency and air pressure for the forward penetrating mode and the 
reverse mode of the machine are different. The impact frequency also 
changes, e.g., when the machine meets an obstacle, or when the machine 
works in loosened soil. If the operator could be aware of these changes 
during operation, he or she could make appropriate decisions, for 
instance, when to reverse the machine when it meets an obstacle. In 
practice, these changes cannot be recognized by simply listening to the 
machine, and thus conventional boring machines lack any effective 
monitoring system. 
Still another disadvantage of conventional pneumopercussive boring machines 
is the high impact loading that the housing experiences during operation. 
Severe fatigue appears in the housing that considerably decreases its 
service life. 
The present invention addresses these disadvantages, making it possible to 
increase the efficiency of the machine to a considerable extent. 
SUMMARY OF THE INVENTION 
This invention provides a self-propelled, pneumopercussive, cyclic-action, 
ground penetrating machine having decreased energy consumption and 
increased average working velocity compared to conventional machines. This 
is obtained in part by a valve-operated air-distribution mechanism that 
does not limit the length of the forward and backward strokes of the 
striker. This mechanism allows the backward stroke chamber (the chamber in 
front of the striker) to be connected with the atmosphere during the 
entire forward stroke of the striker. This eliminates generation of an air 
buffer in the backward stroke chamber and, consequently, the striker does 
not lose part of its kinetic energy before impact. 
According to a further aspect of the invention, a valve-operated 
air-distributing mechanism also includes a cyclic-action braking mechanism 
which keeps the housing from moving backwards during the forward stroke of 
the striker. This permits the striker to utilize the entire length of the 
forward stroke and, consequently, to gain as much kinetic energy before 
impact as possible. This provides the machine housing with the highest 
possible kinetic energy after the collision. 
According to another aspect of the invention, improved transmission of 
energy from the striker to the housing during the collision and decreased 
periodic impact loading on the housing are attained by providing a movable 
chisel separate from the rest of the housing. An elastic seal is provided 
in the space between the chisel and the body of the housing to prevent 
soil from entering the space behind the chisel and jamming it. 
The chisel can have any desired mass. If the ratio between the mass of the 
striker and the motionless body it collides with (the chisel) equals the 
restitution coefficient for the collision, then the kinetic energy of the 
striker will be completely transmitted to the chisel. The resistance 
forces of motion of the chisel also include the inertia of the hollow part 
of the housing and associated parts secured thereto which are separate 
from the chisel. However, the gain in kinetic energy of the chisel 
resulting from the complete transmission of the kinetic energy from the 
striker to the chisel exceeds the loss due to inertia of the machine body, 
so that the machine is propelled forwardly. In a preferred embodiment, 
loading from the chisel to the hollow part of the housing is transmitted 
through an elastic element which transforms the instantaneous force 
applied to the chisel into a gradually changing force applied to the 
housing, protecting the housing from excessive impact loads. 
Another embodiment of the invention provides separate control of compressed 
air in the forward and backward stroke chambers. This is attained by 
providing the valve-operated air-distributing mechanism with two separate 
air supply lines connected by flexible hoses with the source of compressed 
air. Separate control of the compressed air in the forward and backward 
chambers improves the performance of the machine in the forward and 
reverse modes of operation. Control of compressed air in the backward 
stroke chamber can avoid undesirable impacts of the striker on the rear 
end of the housing during forward movement of the machine. Coordinated 
control of compressed air in the forward and backward chambers as 
described below can also improve the performance of the machine in the 
reverse mode of operation. In addition, compressed air flow in the forward 
and backward stroke chambers can be manipulated to allow starting or 
restarting of the machine in any striker position. 
A further embodiment of the invention provides the machine with a reliable 
reversible mechanism having a simple control system which avoids any need 
to rotate an air supply hose. This is achieved, for example, by providing 
the air-distributing mechanism with a mode control valve which is 
permanently connected by a small air hose to a valve mounted on the source 
of compressed air. The mode of the machine operation is changed by opening 
and closing the reversing valve. In the illustrated embodiment, when this 
valve is closed the machine works in the forward mode to penetrate the 
soil. When this valve is open the compressed air changes the position of 
the reversing valve, causing reverse operation of the machine. The mode 
control valve can also be electrically actuated. 
An additional feature of the invention is a sensor mounted on the machine 
which provides the machine operator with relevant current information 
about the working process of the machine. Such information facilitates 
decision-making, for instance, in determining when to switch to reverse 
mode. This can be achieved by providing a transducer connected to the 
forward stroke chamber. This transducer generates an electrical signal 
which reflects fluctuations of the compressed air in the forward stroke 
chamber, and can be electrically connected to a portable electronic device 
that analyzes the signal and provides a visible read-out on a screen or 
the like. Simulating different modes of the working process of the machine 
can be used to calibrate the transducer and aid in interpretation of the 
signals. These and other aspects of the invention will become apparent 
from the detailed description of the illustrated embodiments.

DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS 
A. General Description 
Referring to FIGS. 1a and 1b, a pneumo-percusive reversible soil 
penetrating machine 200 according to the invention includes, as major 
components, an elongated body 201 having an open rear end; a striker 202 
disposed for reciprocation within body 201; a valve-operated 
air-distributing mechanism 203 secured in body 201 rearwardly of striker 
202 for supplying compressed air to reciprocate striker 202; a cyclic 
action braking mechanism 204 actuated by air distributing mechanism 203 
and located towards the rear of body 201, which brakes machine 200 against 
recoil when a forward stroke chamber 20 is pressurized; a forward/reverse 
mode control system 205 which is connected to the air distributing 
mechanism 203 for altering the flow of compressed air therein to cause 
striker 202 to drive machine 200 rearwardly instead of forwardly, or the 
reverse; an air supply system 206 which supplies air to distributing 
mechanism 203, a movable chisel assembly 207 which receives forward 
impacts from striker 202. Each of these components will hereafter be 
described in detail. For purposes of brevity, details of the air flow 
passages formed in machine 200 as part of air distributing mechanism 203 
will be described only in the sections below on machine operation. 
As shown in FIGS. 1a, 1b, and 2-4, a generally torpedo-shaped body 201 
includes an elongated tubular housing 1 and a tubular tail nut 34 which is 
threadedly secured in the open rear end of housing 1 for retaining a stack 
of cylindrical, front middle and rear cylinders 10, 5, 2 which are rigidly 
secured together by a bolt (not shown) to form systems 203-205. Nut 34 
engages a rear flange 2A of rear cylinder 2 and holds it against the inner 
annular wall of a threaded, rearwardly opening counterbore 1B in housing 
1. Nut 34 may optionally include a dirt protector (not shown) for 
preventing soil and other foreign objects from penetrating into the 
central hole of nut 34, such as an elastomeric flapper valve and/or a 
rearwardly tapering frustoconical tailpiece similar to those used on 
conventional ground piercing machines. 
Referring to FIG. 3, housing 1 has lengthwise air flow passages 18, 49 and 
50 therein which are machined into the outer surface of housing 1 as 
grooves having inwardly tapering side walls which render the grooves 
trapezoidal in cross section. Trapezoidal, elongated inserts (covers) 19, 
48b, 48a are inserted into the associated grooves in housing 1 and secured 
by end clips 11 and lengthwise filling wedges 51. Grooves in the 
undersides of inserts 19, 48b, 48a define passages 18, 50, 49, 
respectively. FIGS. 15 and 16 illustrate an alternative housing 1a which 
lacks exterior grooves for forming the air flow passages. In lieu thereof, 
an inner sleeve 96 made of a low-friction material such as cast iron, 
bronze, or composite materials is disposed coaxially with housing 1a, and 
passages 18a, 49a, and 50a are machined into the outer surface of sleeve 
96. The low-friction material is important for decreasing frictional wear 
between the inner sleeve and the striker. 
Referring now to FIGS. 1b and 15, movable chisel assembly 207 is mounted in 
a threaded front counterbore 1c in housing 1 and makes up the frontwardly 
tapering nose of machine 200. Assembly 207 includes the chisel 74 having a 
frontwardly tapering head 74a (the nose of the machine), and an elongated, 
rearwardly extending shank 74b having a threaded rear end 74c. A nut 65 of 
greater diameter than shank 74b is threadedly secured to threaded end 74c. 
Nut 65 acts as the front anvil which receives forward impacts from striker 
202. 
To be effective for improving the efficiency of the energy transfer from 
striker 202, suitable means must be provided for supporting chisel 74 for 
sliding axial movement over a short distance. In the illustrated 
embodiment, a tubular adapter 70 having a front annular flange 70a of the 
same diameter as housing 1 is threadedly secured in threaded counterbore 
1c of housing 1. Adapter 70 has a bore 70b which includes a pair of 
enlarged diameter, frontwardly and rearwardly opening counterbores 70c, 
70d. Shank 74b is slidably disposed in a bushing 71 which is fitted into 
bore 70b between counterbores 70c,d. A pair of front and rear, elastic 
shock absorbers 73, 69, such as coil springs, Belleville springs, or 
elastomeric rings (shown), are mounted in counterbores 70c, 70d, 
respectively. Front shock absorber 73 is partly confined in a rearwardly 
opening recess 74d in head 74a of chisel 74. 
An annular elastic gasket (sealing ring) 72 is interposed between chisel 
head 74a and flange 70a of adapter 70. Gasket 72 is confined under a 
certain compression between the associated surfaces of head 74a and flange 
70a for filling the space therebetween during forward movement of chisel 
74. Rear shock absorber (spring) 69 biases chisel 74 towards the left, 
retracted shown in FIG. 1b and, in so doing, compresses gasket 72. Gasket 
72 thereby prevents particles of soil from entering behind head 74a which 
would jam chisel 74 in its forwardmost position, causing machine 200 to 
lose the benefit of efficient kinetic energy transfer between striker 202 
and chisel 74. 
A thrust journal 68 is coaxially secured to the outer periphery of shank 
74b rearwardly adjacent to shock absorber 69. Journal 68 has a stepped, 
rear annular flange 68a fitted with an external bushing 67 which is in 
sliding contact with the inner surface of housing 1. A spacer ring 66 is 
threadedly secured to threaded end 74c to retain journal 68 in a position 
which will suitably compress shock absorbers 69, 73 and gasket 72. Gap G, 
the clearance between journal 68 and adapter 70, exceeds the distance 
chisel 74 moves during a forward impact of striker 202. 
Referring again to FIG. 1b, striker 202 comprises a solid cylinder 63 
having a stepped front end 63a of reduced diameter for facilitating air 
flow about striker 202 and a rearwardly opening threaded recess 63b in 
which a shock-absorbing rear impact assembly is provided. The outer 
peripheral surface of cylinder 63 is in sealing, slidable contact with the 
interior of housing 1. Unlike prior machines which require the striker to 
be mounted on a stepped inner valve sleeve, the striker according to the 
present invention defines only a single sliding pair, thereby avoiding 
problems with air leakage around short bearing surfaces and jamming which 
occurs due to misalignment of the stepped sleeve and the striker. 
The rear impact assembly includes a shock absorbing ring 61 disposed in 
close conformity with the bottom of recess 63b. A flat thrust journal 76 
is disposed against the outer face of shock absorber 61, a rearwardly 
extending annular flange 76a thereof is in turn received in a central hole 
56a of a sleeve (rear impact hammer) 56. Sleeve 56 further has a rear 
radial flange 56b which functions as the rear impact surface of striker 
202 when the machine is in reverse mode, as described hereafter. A 
retaining ring 60 is mounted in an annular outer groove near the front end 
of sleeve 56 so that ring 60 projects radially therefrom. A nut 57 fitted 
with an inner bushing 59 is threadedly secured in recess 63b so that an 
outwardly directed annular flange of bushing 59 engages ring 60 and 
thereby secures sleeve 56, journal 76 and shock absorber 61 in a 
rearwardmost position in recess 63b. The cylindrical outer surface of 
sleeve 56 is slidably disposed in bushing 59 so that, when rear flange 56b 
engages a rear anvil 16, the resulting shock is dampened by compression of 
shock absorber 61. This results in less violent striker impacts when the 
machine is in reverse mode, lengthening machine life. 
A valve tappet 54 is centrally mounted in hole 56a for engaging a spring 
loaded stroke control valve 17 to initiate the forward stroke of striker 
202. Tappet 54 comprises a threaded rod received in a central threaded 
hole of a cylindrical holder 58 and clamped thereto by nut 55. A helical 
compression spring 62 confined between a front wall of holder 58 and the 
bottom of recess 63b inwardly of shock absorber 61 and thrust journal 76 
resiliently biases holder 58 against an inwardly directed retaining rim 
56c at the front end of hole 56a. By this means tappet 54, holder 58 and 
nut 55 can slide forwardly along hole 56a when tappet 54 engages valve 17, 
compressing spring 62. Tappet 54 extends rearwardly beyond flange 56b, so 
that PG,20 contact between tappet 54 and valve 17 occurs prior to contact 
between flange 56b and rear anvil 16. Spring 62 is designed so that tappet 
54 does not damage valve 17 during contact therewith, the main force of 
the rearward impact being exerted against anvil 16. When striker 202 moves 
away from rear anvil 16 during its forward stroke, spring 62 forces holder 
58 rearwardly back into contact with stop (rim) 56c. 
Referring now to FIGS. 1a and 3, the air distributing mechanism 203 
according to the invention includes a spring-loaded stroke control valve 
17 which is slidably disposed in a central bore 10a of front cylinder 10. 
Valve 17 has a rearwardly opening recess (blind hole) 26 therein which is 
in communication with a chamber 8 formed by a rear counterbore in cylinder 
10, i.e., an enlarged diameter rear portion of bore 10a. Cylinder 10 
further has an annular, frontwardly extending boss 10b on which the rear 
anvil 16 is secured by screws (not shown) to cylinder 10. Anvil 16 
resembles an annular cover and has a central hole 16a therein which 
permits tappet 54 to contact the front end wall of valve 17. A rear end 
portion of valve 17 extends into chamber 8 and ends in a rear, 
outwardly-directed annular flange 17a. A compression spring 9 is confined 
between flange 17a and an annular inner wall 8a of chamber 8 for biasing 
valve 17 to a left end position as shown in FIG. 9. Three parallel, 
spaced, annular grooves 24, 22 and 21 are formed in the outer periphery of 
valve 17. 
Groove 24 communicates with recess 26 through radial holes 25. Grooves 21, 
22 do not communicate with recess 26. Grooves 24, 22, 21 work in 
cooperation with passages 12, 15, 23 and 46 formed in cylinder 10 and 
associated passages in housing 1 for conducting compressed air to a 
forward stroke chamber 20 and a rearward stroke chamber 75. Forward stroke 
chamber 20 comprises the space within housing 1 forwardly of cylinder 10 
and rearwardly of striker 202, whereas rear stroke chamber 75 comprises 
the space within housing 1 forwardly of striker 202 and rearwardly of 
chisel 207. The volume of each of chambers 20, 75 varies depending on the 
position of striker 202. 
Referring to FIG. 1a, the compressed air supply system 206 according to the 
invention includes air supply pipes 37, 36 and 35 connected by respective 
flexible hoses to an air compressor provided with valves for separately 
controlling the air pressure in each of pipes 35-37. Pipe 37, which 
supplies compressed air for the forward stroke of the striker, is 
threadedly secured in a rearwardly opening passage 3 in rear cylinder 2. 
Passage 3 in turn communicates with passages 6, 7 in middle cylinder 5 
which leads to chamber 8. Compressed air from pipe 35 thus flows directly 
into chamber 8. 
Pipe 35 supplies compressed air for the rearward stroke of striker 202 
through a passage 28 in cylinders 2, 5, 10. During normal operation, 
compressed air or a similar pressure fluid is constantly supplied through 
both of pipes 35, 37. 
Referring to FIGS. 8 and 10, pipe 36 supplies compressed air into a chamber 
30 of the mode control system 205. Pipe 36 is constantly pressurized 
during reverse operation, and remains depressurized during forward 
operation. Chamber 30 in rear cylinder 2 communicates with passages 81, 
82, 86, 29 and 89 for changing the operation of distibuting mechanism 203 
and braking mechanism 204 as described hereafter. When no compressed air 
is supplied through pipe 36, a mode control valve 4 is biased to a left 
end position (FIG. 8) by a spring 31 confined between a rear wall of 
cylinder 5 and the bottom of a forwardly opening recess 4a. Valve 4 is 
biased to a right position when compressed air enters chamber 30 (FIG. 
10). In this position the front cylindrical end of valve 4 interrupts 
communication between passages 29 and 89, and an annular groove 32 in the 
outer periphery of valve 4 permits communication between passages 81, 82, 
and 86. 
Mode control system 205 further includes a cut-off valve 85 slidably 
secured in a rearwardly opening recess 2b in rear cylinder 2. A 
compression spring 84 confined between a vented plug 83 and a rearwardly 
opening recess in valve 85 resiliently biases valve 85 to a forward 
position as shown in FIGS. 8 and 10. A T-shaped passage 87, 88 in valve 85 
allows communication between passages 86 and 89 when valve 85 is in its 
forward (extended) position. 
Referring now to FIGS. 2, 8, 10 and 13, the cyclic action braking system 
204 cooperates with the air distributing mechanism 203 to cyclically 
extend and retract a plurality of pins 27. Pins 27 extend radially 
outwardly from housing 1 (FIG. 13) during the forward stroke of striker 
202 to engage the wall of the tunnel being formed in order to hold the 
machine body 201 against rearward movement (recoil) during forward 
movement of striker 202. For this purpose pins 27 are mounted in a 
cylindrical chamber 42 within cylinder 5, which chamber 42 is oriented 
transversely to the lengthwise direction of the machine. Cavity 42 
communicates directly with forward stroke chamber 20 through passages 43, 
89, 29 and chamber 30 when the machine is in forward mode. In reverse 
mode, valve 4 closes and isolates chamber 42 from chamber 20 (see FIG. 
10). 
Each pin 27 is slidably mounted in a bushing 38 which is screwed into a 
threaded opening 1d in housing 1. Each bushing 38 has an elastomeric (or 
plastic) front sealing ring 40 mounted in an internal annular groove 38a 
thereof which is in sealing contact with the exterior of pin 27 (see FIG. 
2). A pair of radial inner and outer flanges 27a, 27b disposed at the rear 
of each pin 27 retain a rear sealing ring 39 similar to front ring 40 for 
sliding, sealed engagement with the wall of chamber 42. A compression 
spring 41 confined between flange 27a and the inner surface of bushing 38 
biases each pin 27 towards the retracted position shown in FIG. 2. 
FIGS. 17-20 illustrate an alternative cyclical braking system 204A. In this 
embodiment pins 27 are replaced by blades 127. Cylinder 5 is replaced by a 
pair of front and rear end flanges 115b, 115a secured together by a 
turnbuckle 101 having internal passages 29a, 99 which communicate with 
chamber 30. A nut 105 disposed in a rearwardly opening recess 112 in rear 
flange 115a and threadedly coupled to a rear threaded end of turnbuckle 
101 secures flange 115a to a step in turnbuckle 101 (FIG. 17). The ends of 
a tubular flexible diaphragm 103 are secured to inwardly directed, 
opposing, undercut projections 128a, 128b of flanges 115a, 115b by a pair 
of clips 102. In this manner air fed into the internal space 100 of 
diaphragm 103 from front stroke chamber 20 inflates diaphragm 103. 
The front end of turnbuckle 105 and front flange 115b cooperate to define 
passages 6a, 7a (see FIG. 20) for feeding compressed air to chamber 8. 
Exterior space 98 (outside of diaphragm 103) cooperates with passages 44a, 
44b to perform the function of passage 44 in the embodiment illustrated in 
FIG. 7. The other air flow passages 3a, 43a, 28a, and 45a which pass 
through flanges 115a, 115b are isolated from space 98 by respective pipes 
113, 97, 116, and 104 spanning flanges 115a, 115b. 
Referring to FIGS. 18 and 19, each blade 127 includes a shank 128 slidably 
mounted on a guide plate 110 which is secured at its periphery (not shown) 
in an opening le in housing 1. Each plate 110 is secured by a cover 106 
lined with a sealing material 107 which prevents dirt penetration around 
the blade 127. Cover 106 is secured by any suitable means, such as screws 
(not shown), to housing 1. Shank 128 is secured by a pin 108 to a push 
button 109 having an inner concave head and an annular flange 129. A 
spring 130 confined between flange 129 and the inside of plate 10 biases 
each blade 127 to a retracted position. Upon pressurization of inner space 
100, diaphragm 103 engages each of buttons 109 and compresses springs 130 
to extend blades 127 to the position shown in FIGS. 18-20. 
Referring now to FIG. 14, a sensor 208 for monitoring the operation of 
machine 200 is, in the illustrated embodiment, a transducer comprising a 
magnetic core 93 coaxially disposed for axial movement inside a solenoid 
94 secured to a modified plug 84a. Core 93 is attached directly to the 
rear of a modified cutoff valve 85a and oscillates in unison therewith. A 
wire 95 conducts current induced in solenoid 94 by the movement of core 93 
to an external analyzer which provides the operator with a readout, e.g., 
a digital display that corresponds to the frequency of oscillation of 
valve 85. Valve 85 acts as an oscillator, i.e., it oscillates in tandem 
with striker 202, so that sensor 208 provides a continuous signal 
reflecting the state of operation of the machine. 
When machine 200 is operating normally in forward mode, the signal from 
sensor 208 will remain within a normal range that can be empirically 
determined. However, when machine 200 strikes a large rock or similar 
impassable obstacle, the impact frequency of the striker 202 will be 
altered because the machine body no longer moves forward with each stroke, 
changing the stroke length and hence its frequency. To prevent machine 200 
from deviating from its original course, the operator can then turn off 
the machine, or switch to reverse mode using mode control system 205. 
As shown in FIG. 21, according to a further alternative embodiment of the 
invention, an air compressor 230 which powers machine 200 may be provided 
with a control unit 231, such as a programmable logic controller, which 
receives the signal from wire 95. Controller 231 responds to an abnormal 
frequency signal by actuating a control valve 232 that switches the 
machine to reverse mode. Controller 231 could also be connected to 
suitable valves 233, 234 for depressurizing both of lines 37, 35 to stop 
machine 200. This type of automated control system eliminates the 
possibility that the machine will become lost due to operator error. A 
display device, such as an oscilloscope 236, may be connected to 
controller 231 to provide a continuous display of the working state of the 
machine. 
B. Assembly 
Machine 200 according to the invention is assembled as follows. Cylinders 
2, 5 and 10 containing most of the air distributing mechanism 203, 
cyclic-action braking mechanism 204, and mode control system 205 are 
rigidly connected to each other by fasteners (not shown) and inserted into 
the rear end of housing 1 or 1a. Then, braking pins 27 with sealing 
collars 39 and springs 41 are inserted through the corresponding openings 
1d, and screw bushings 38 with sealing rings 40 are secured thereover. To 
prevent jamming of pins 27, longitudinal adjustments of the inserted parts 
may be made by insertion of shims 33. The inserted parts are then secured 
by the tail nut 34. 
Striker 202 is then inserted into the housing or 1a through its front open 
end. Striker can also be inserted through the rear end of housing 1, if 
open, since housing 1 has the same inner diameter along substantially all 
its length. Chisel assembly 207 is then secured to the front end of the 
housing 1 or 1a. Elastic rings 69, 72, and 73 are preliminarily 
compressed, so that when the chisel 74 moves forward as a result of an 
impact, elastic link 72 expands and no longitudinal gap is created between 
components 70, 72, and 74. 
Forward Mode Operation 
In FIGS. 1a, 1b, machine 200 is shown at the beginning of the backward 
stroke of striker 202. Machine 200 will remain in this position so long as 
air supply line 37 of the forward stroke chamber 20 is pressurized, 
forcing valve 17 to its right end position, and supply line 35 is 
depressurized. Striker 202 can be brought to its front end position by 
pressurizing and depressurizing forward stroke air supply line 37 several 
times. To start machine 200 from this position, both of lines 35 and 37 
are depressurized. Stroke control valve 17, under the action of spring 9, 
then moves to its left end position, so that it presses against cylinder 5 
(see FIG. 9). 
Forward stroke chamber air supply line 37 is then pressurized so that 
compressed air flows through passages 3, 6, and 7 (FIGS. 1a and 2) and 
enters chamber 8 and recess 26 of stroke control valve 17 (FIGS. 1a and 
9). Such compressed air flows through holes 25, circular groove 24 and 
passages 90, 91 into forward stroke chamber 20, which is connected with 
the atmosphere through pasages 53, 49, 77, 78, and 44 (FIG. 7). The 
difference in pressure on opposite sides of control valve 17 then causes 
it to move to its right end position, at which it presses against rear 
anvil 16, compressing, spring 9. In this position, valve 17 overlaps holes 
90, and compressed air cannot enter chamber 20, which is still open to the 
atmosphere. 
Backward stroke air supply line 35 is then pressurized so that compressed 
air then flows through air passages 28, 23, circular groove 22, and 
passages 12, 13, 18, 64, and enters backward stroke chamber 75 (FIGS. 1a, 
1b). Under the action of the compressed air striker 202 moves rearwardly, 
overlaping hole 53 and starting to build up an air buffer in chamber 20. 
Continued movement of striker 202 opens hole 53 and connects chamber 75 
with the atmosphere. In chamber 20, the air pressure builds to a level at 
which the resulting force pushes valve 17 to its left end position. 
In this position, valve 17 overlaps holes 13 and 23, so that the compressed 
air can no longer enter chamber 75, wherein the pressure drops to 
atmospheric pressure. As shown in FIG. 9, at this position of valve 17, 
passage 90 is open and chamber 20 is now connected with air supply line 
37. Striker 202 is braked by the compressed air pressure in chamber 20 and 
stops before it reaches rear anvil 16. The forward stroke of striker 202 
then begins. 
Cyclic action braking mechanism 204 operates in tandem with striker 202. 
During the forward (penetrating) mode of operation, chamber 42 (FIG. 2) 
communicates by passages 43, 89, chamber 30, and passage 29 (FIGS. 2, 8, 
10) with chamber 20, so that the pressure in chambers 20 and 42 is always 
the same. When these chambers are pressurized, pins 27 (FIG. 13) move out, 
penetrating the soil and braking housing 1 against rearward movement. 
The second embodiment 204a of the cyclic action braking mechanism works 
similarly. As shown in FIG. 18, space 100 within diaphragm 103 is in 
constant communication with chamber 20. Blades 127 protract as chambers 
20, 100 are pressurized, then retract under the action of springs 130 when 
chambers 20, 100 are depressurized. 
During its forward stroke striker 202 overlaps hole 53. To avoid generating 
an air buffer in chamber 75 which would oppose forward movement of striker 
202 and reduce the efficiency of machine 200, an additional air bypass 
connecting chamber 75 with the atmosphere during the forward stroke of 
striker is provided. When hole 53 is overlapped as striker 202 moves 
forward, air from chamber 75 is expelled to the atmosphere through 
passages 64, 18, 14, 15, as shown in FIGS. 1a, 1b, and then through groove 
21 and passages 46, 47, 49, 78, 77, and 44 as shown in FIGS. 7, 12. 
Near the end of the forward stroke, striker 202 opens hole 53. Chamber 20 
is again open to the atmosphere, pins 27 are retracted by springs 41, and 
stroke control valve 17 moves to its right end (forward) position. At the 
end of the stroke, striker 202 imparts a blow to anvil 65. Chisel 74 
instantly obtains an initial velocity, while striker 202 becomes 
motionless. This type of collision results in maximum transfer of kinetic 
energy from striker 202 to chisel 74. 
Striker 202 becomes motionless after the collision only if the ratio of the 
mass of striker 202 to the mass of chisel 74 is equal to the magnitude of 
the restitution coefficient between these two masses. When the restitution 
coefficient is determined, then the mass of chisel 74 can be calculated by 
dividing the mass of striker 202 by the restitution coefficient. The mass 
of striker 202 is predetermined by energy aspects and design 
considerations. The optimium mass of chisel 74 can be obtained by changing 
the length of the cylindrical part of chisel 74. The striker/chisel weight 
ratio is typically from 0.65-0.7 for purposes of the present invention. 
Chisel 74 starts to penetrate into the soil ahead of machine 200 and, by 
means of elastic rings 69, 72, 73, pulls forward housing 1 and all of the 
other components of the machine. Elastic rings 69, 72, 73 act as shock 
absorbers and greatly reduce the peak impact loads acting on the machine 
components located rearwardly of chisel 74. As a result, threaded 
connections can be used to connect components to housing 1 (e.g., nut 34 
and adapter 70) without subjecting such connections to loads which might 
break the connections. This further allows housing 1 to be made from a 
drawn steel pipe rather than by machining a solid steel rod, resulting in 
a considerable cost reduction. Compressed air then begins to enter chamber 
75, and the backward stroke of striker 202 begins again. Forward movement 
of machine 200 during one cycle of operation occurs over a very short 
time, much shorter than the cycle frequency of striker 202. 
During forward operation, mode control valve 4 is held in its left end 
position by spring 31 (FIGS. 1a, 8, and 14). In this position, passage 89 
is open and passage 81 is overlapped. Cut-off valve 85 is always connected 
with the forward stroke chamber 20 through passages 43, 89, 88. When the 
pressure in chamber 20 increases, valve 85 moves to the left, and when the 
pressure in chamber 20 drops, valve 85 is returned to the right by spring 
84. Thus, valve 85 reciprocates during operation of machine 200. In the 
embodiment of FIG. 14, cut-off valve 85a reciprocates and an electrical 
current is induced in solenoid 94 and transmitted through wire 95 to the 
analyzer, e.g., controller 231 and display device 26 (FIG. 21). The 
operator thereby obtains current information about the performance of the 
machine. 
D. Reverse Mode Operation 
To change the mode of operation of machine 200, the operator opens a 
three-way valve to pressurize line 36. Control valve 4 moves to its right 
end position, overlapping passage 89 and connecting passages 81 and 82 by 
circular groove 32 (FIGS. 8, 10, and 14). Passage 86 also communicates 
with circular groove 32. 
With mode control valve 4 in this position, cyclic action braking mechanism 
204 is inoperative, since it is not needed for effective reverse machine 
movement. Forward stroke chamber 20 is now open to the atmosphere through 
hole 52, passages 50, 79, 80, 45, 81, circular groove 32, and passages 82, 
92 (FIG. 10). When forward stroke chamber 20 is opened to the atmosphere, 
stroke control valve 17 moves to its right end position, and compressed 
air enters into backward stroke chamber 75. 
Striker 202 then moves rearwardly, gaining kinetic energy. When hole 52 is 
overlapped by striker 202, chamber 20 is still connected with the 
atmosphere by passages 43, 89, calibrated hole 88, passages 87, 86, 
circular groove 32, and passages 82, 92. In this manner, valve 85 prevents 
an air buffer from being generated during the backward stroke of the 
striker 202, which imparts a blow at the end of its backward stroke to the 
rear anvil 16. Housing 1 thereby obtains a velocity in the retracting 
direction. Before sleeve 56 touches rear anvil 16, valve tappet 54 pushes 
the stroke control valve 17 to the left (FIG. 11). Valve tappet 54 and 
holder 58 are preloaded to the right by spring 62, protecting stroke 
control valve 17 from excessive impact loading. 
With stroke control valve 17 in its left end position, compressed air 
enters chamber 20 through holes 25, circular groove 24, and passages 90, 
91 (FIGS. 9, 11). From chamber 20 compressed air passes to cut-off valve 
85 through passages 43, 89 (FIG. 10). Passage 88 in valve 85 is a 
calibrated hole having a predetermined cross-sectional area such that 
passage 88 is not capable of relieving the high-pressure compressed air to 
the atmosphere, but is capable of relieving the lower air buffer pressure 
when striker 202 was moving rearwardly, as described above. By this means, 
cut-off valve 85 under pressure of the compressed air moves to its left 
end position and overlaps passage 86, which was previously open to the 
atmosphere with mode control valve 4 in the right end position. Chamber 20 
is thereby no longer open to the atmosphere. 
Stroke control valve 17 remains in its left end position because spring 9 
presses it to the left, the air pressure from both sides being equal. The 
forward stroke of striker 202 then begins. However, the stroke length of 
the striker is significantly shortened because hole 52 is open to the 
atmosphere. When striker 202 opens hole 52, the air pressure in chamber 20 
drops, stroke control valve 17 moves to the right, and compressed air 
begins to enter into backward stroke chamber 75. Hole 53 is then 
overlapped by striker 202, and the forward motion of striker 202 is braked 
by the compressed air in chamber 75. Striker 202 stops without reaching 
front anvil 65, and the backward stroke of striker 202 begins. Forward 
stroke chamber 20 is connected with the atmosphere, and cut-off valve 85, 
under the action of spring 84, moves to its right end position, opening 
chamber 20 to the atmosphere even after striker 202, moving to the left, 
overlaps hole 52. The cycle then repeats itself. 
E. Alternative Embodiments 
A variety of changes could be made in the described construction and 
different embodiments of the present invention can be made without 
departing from the scope of the invention as expressed in the claims. For 
example, the cyclic action braking mechanism may simply constitute an 
expandable rubber diaphragm which engages the tunnel wall instead of pins 
or blades. The cyclic action braking mechanism can also be conventiently 
repositioned so that it follows behind the body of the tool. Various 
aspects of the invention can be used in conjunction with other types of 
air distributing and reversing mechanisms. 
FIG. 22 illustrates a reversible machine 140 having a stepped bushing type 
of air distributing mechanism. The rear end of an air inlet pipe 141 is 
coupled to a compressed air supply hose 143. A tailpiece 144 is threadedly 
secured in the rear end of a tubular machine housing 146. A plurality of 
exhaust passages 147 extend lengthwise through tailpiece 144 for 
conducting spent compressed air to the atmosphere. A threaded outer 
surface along the midsection of pipe 141 is threadedly, coaxially secured 
in an associated threaded hole of tailpiece 144 to provide a screw reverse 
mechanism. Relative rotation of pipe 141 relative to tailpiece 144 is 
limited to a front end position by a radial flange 148 on pipe 141, and to 
a rear end position by a nut 142 threadly secured to pipe 141 at the rear 
of its threaded midsection. A flapper valve 145 mounted on tailpiece 144 
rearwardly of exhaust passages 147 prevents foreign matter from entering 
the machine through passages 147. 
The enlarged diameter front end of a stepped tubular bushing 149 slidingly 
engages a rearwardly opening cylindrical recess 152 in a striker 151 to 
provide a constant pressure chamber for propelling striker 151 forward. 
Step bushing 149 is coupled to pipe 141 by suitable means, such as an 
elastic pipe 163. In the alternative, stepped bushing 149 and pipe 141 can 
be formed as a single member. Radial ports 153 in the wall of the striker 
surrounding recess 152 provide for the rearward stroke of the striker in a 
manner well known in the art, i.e., compressed air passes into a front, 
variable volume chamber 150 to propel striker 151 rearwardly. Striker 151 
is slidably supported on the interior surface of housing 146 by front and 
rear bearing surfaces 151A, 151B. Rear bearing surface 151B is annular and 
sealingly engages the inner surface of housing 146, whereas front bearings 
151A include air passages for allowing compressed air to pass therethrough 
to force striker 151 rearwardly when front chamber 150 is pressurized. 
Striker 151 impacts against a ring-shaped rear anvil 158 which is seated on 
a cone-shaped rear end 169 of a movable chisel 156. Chisel 156 is movably 
secured in the open front end of tubular housing 146 by an adapter 157. 
The resulting shock is transmitted through a resilient spring 161 and 
resilient gasket 162 to the housing 146. Annular gasket 162 is loaded 
under compression between a tapered head 160 of chisel 156 and adapter 
157. Gasket 162 expands during forward movement of chisel 156 to prevent 
particles of soil from jamming chisel 156. 
Spring 161 is a coil spring in the illustrated embodiment, but other types 
of springs could be employed. Spring 161 is coaxially disposed around an 
elongated central shank 159 of chisel 156 and is confined for compression 
between adapter 157 and a ring 166. Ring 166 is slidably mounted on the 
inner surface of housing 146 and the outer surface of shank 159 near the 
rear end thereof. An adjustment nut 167 is threadedly secured behind ring 
166 to a rear, reduced diameter threaded portion 168 of shank 159. Spring 
161 urges ring 166 into abutment with nut 167. Nut 167 can be adjusted to 
vary the gap G, i.e., the maximum distance chisel 156 can move at each 
impact. 
The masses of striker 151 and chisel 156 are preferably selected to 
maximize the amount of kinetic energy transferred, as described above. The 
resulting machine 140 is of simple construction, improved efficiency, and 
eliminates the need to provide a shock absorber in the tail assembly of 
the machine for protecting the various threaded connections.