Control device for the forward movement and rearward movement of pneumatic ram boring devices

Control device for the forward movement and rearward movement of self-driven pneumatic ram boring devices with an impact piston which is axially displaceable between two abutments in a tubular housing, with the axial forward movement and rearward movement of the ram boring device being controllable by rigid control edges of an adjustable control sleeve, the latter being supported on a bearing ring arranged in the rear part of the housing. Through the bearing ring there is led a part of the control sleeve forming a feed tube for the compressed air for connection to a compressed air hose, the sleeve having a piston-like control head containing the control edges; the control head engaging in a cylindrical recess at the rear end of the impact piston cooperates with radial control bores which are formed in the area of the recess in the impact piston. The control sleeve is mounted non-displaceably in the axial direction however rotatably in the bearing ring and is provided with at least four control edges. The control edges respectively are each arranged in pairs with axial spacing corresponding to the control stroke of the impact piston and are offset in the peripheral direction as well as in the longitudinal direction, such that respectively only one pair of the control edges cooperates with the control bores. The bores are arranged only on a part of the periphery of the impact piston and the impact piston is non-rotatably guided in the housing.

The invention relates to a control device for the forward movement and 
rearward movement of self-propelled pneumatic ram boring devices with an 
impact piston which is axially displaceable between two abutments in an 
altogether tubular-shaped housing, whereby the axial forward movement and 
rearward movement of the ram boring device is controllable by rigid 
control edges of an adjustable control sleeve, the latter being supported 
on a bearing ring arranged in the rear part of the tubular-shaped housing, 
through which bearing ring a part of the control sleeve (which part is 
formed as a feed tube for the compressed air) is guided-through for the 
connection to a compressed air hose, and which sleeve has a piston-shaped 
control head containing the control edges, the control head engaging in a 
cylindrical recess at the rear end of the impact piston cooperates with 
radial control bores, which are formed in the area of the recess in the 
impact piston. 
A control device of the previously described type is known for example from 
the German Auslegeschrift AS No. 2 537 176. The reversing of the ram bore 
device between forward movement and rearward movement takes place by an 
axial displacement of the control sleeve with respect to the housing. For 
this purpose a part of the control sleeve is formed as a polyhedron 
section, the length of which corresponds to the axial displacement 
movement of the control sleeve between its end positions. In the bearing 
ring of the housing, which bearing ring supports the control sleeve, there 
is formed an axial opening which corresponds to the polyhedron section of 
the control sleeve. At both sides of the polyhedron section there join 
cylindrical sections of the control sleeve, the front section of which has 
a diameter including the polyhedron cross-section and its rear section has 
a circular cross-section, the diameter of the latter being included by the 
polyhedron diameter. 
In order to achieve the forward movement of the ram bore device, the 
control sleeve is brought into a forward end position; in this forward end 
position the corners of the polyhedron section of the control sleeve 
engage on the front face surface of the bearing ring (the corners 
projecting or rising over the diameter of the smaller rear cylindrical 
section), for which a rotation of the control sleeve disposed in the 
forward end position with respect to the bearing ring and to the housing, 
respectively, is required, and indeed by half the amount of the angle 
which is formed by the corners of the polyhedron section. The control 
sleeve must be turned by this angle if the ram bore device is to be 
reversed from the forward movement to the rearward movement. After such a 
rotation which brings about a coincidence between the polyhedron section 
of the control sleeve and the corresponding axial opening of the bearing 
ring, the control sleeve can be shifted in the axial direction toward the 
rear until the forward cylindrical section with its parts (which project 
or rise over the polygonal section) in the shape of circular sections 
engages on the forward face surface of the bearing ring. The axial 
displacement of the control sleeve corresponds in this case to the 
displacement stroke for the rigid control edges which are formed on the 
piston-like control head of the control sleeve by the front face surface 
of the control sleeve and a circular-shaped control edge, respectively, 
which results in an axial spacing relative to the front face surface by a 
reducing of the diameter of the control sleeve. 
With the known control device in addition to a rotation of the control 
sleeve with respect to the housing and to the bearing ring, respectively, 
by a certain angle each time an axial displacement is necessary, if the 
bore device is to be reversed between forward movement and rearward 
movement. This reversing which even then must be able to be carried out if 
the ram bore device is located in the ground, takes place by a rotation 
and displacement of the compressed air hose which is fastened with its 
front end on the rear end of the control sleeve. Particularly the axial 
displacing of the control sleeve with respect to the housing in this case 
gives difficulties. As a further disadvantage of the known control device 
it is to be considered that the engagement of the control sleeve on the 
bearing ring (which supports it) in the housing only takes place over 
comparatively small surfaces which consequently are subjected to a very 
high loading and frequently cause disturbances of function or damage. 
Starting from a reversing of the introductory-described type, the invention 
is based on the task of creating the control device for the forward 
movement and rearward movement of self-propelled pneumatic ram bore 
devices, which on the one hand can be operated simply and on the other 
hand functions without problems, whereby particularly high local loadings 
of the control sleeve should be avoided and the reversing operation should 
be possible even during the working of the ram bore device, i.e. under 
compressed air. 
The solution of this task, by the invention is characterized in the manner 
that the control sleeve is mounted non-displaceably in the axial direction 
however rotatably in the bearing ring and is provided with at least four 
control edges which control edges respectively each are arranged in pairs 
with identical axial spacing, the latter corresponding to the control 
stroke of the impact piston, and are offset in the peripheral direction as 
well as in the longitudinal direction such that only respectively from 
time to time each one pair of the control edges cooperate with the control 
bores, the latter being arranged only on a part of the periphery of the 
impact piston, which impact piston is guided non-rotatable in the housing. 
As a result of the formation of the control sleeve in accordance with the 
invention with control edges which are arranged in pairs, the control 
edges cooperating as well exclusively alternately with the control bores, 
which control bores are arranged in the non-rotatably guided impact 
piston, with the control device in accordance with the invention a 
rotation of the control sleeve with respect to the housing suffices in 
order to provide a reversing of the ram bore device between forward 
movement and rearward movement. The control sleeve can consequently be 
reliably supported on the bearing ring of the housing by means of 
sufficiently sized or dimensioned engagement surfaces, so that local peak 
loadings and consequently the danger of damage and functional disturbances 
are prevented. Simultaneously the operation of the ram bore device is 
quite considerably simplified with the reversing, since the axial 
displacement of the control sleeve with respect to the housing of the ram 
bore device is eliminated. With the known control device this axial 
displacement leads to considerable difficulties since the flexible 
compressed air hose is barely suited to transmit the necessary pressure 
forces for the axial displacement of the control sleeve with respect to 
the housing of the ram bore device. 
With the formation in accordance with the invention with at least four 
pair-wise arranged control edges, respectively from time to time only half 
of the control edges cooperate with the radial control bores of the impact 
piston, since these control bores only are arranged on one part of the 
periphery of the impact piston, the latter being guided non-rotatably in 
the housing, so that only the control edges which are determined for the 
respective movement direction from time to time are overlapped or run over 
by the control bores of the impact piston; the respective other half of 
the control edges which are formed rigidly on the control sleeve remain 
inoperative since they then lie respectively outside of the range of the 
control bores. The selection of the control edges which are operative with 
the control bores from time to time is brought about in a simple manner by 
rotation of the control sleeve with respect to the housing and 
consequently with respect to the impact piston, the latter which is guided 
non-rotatably in the housing. 
With the simplest form of the formation in accordance with the invention 
the four control edges each respectively are formed extending over 
180.degree. of the periphery of the control sleeve. With a preferred 
additional development of the invention eight control edges each extend 
over 90.degree. of the periphery of the control sleeve, whereby identical 
control edges are formed diametrically oppositely on the control sleeve. 
In this manner a symmetrical flow takes place inside of the ram bore 
device. Of course it is possible to form another multiple, namely 12 or 16 
control edges on the control sleeve. This is particularly possible with 
ram bore devices with large diameter. 
According to a further feature of the invention the front pair of control 
edges can be formed on the one hand by the front face edge of the control 
sleeve by the front face edge of the control sleeve, and on the other hand 
by an edge of a recess, the latter starting from the rear end of the 
piston-like control head, and the rear pair of control edges can be formed 
by the arc or curve (which extends in the peripheral direction) of a 
recess (which recess starts from the front face edge) and by the rear face 
edge of the control head, respectively. Of course even other specialized 
formations of the control edge pairs are possible. 
In an additional development of the main concept of the invention the 
impact piston can be secured against rotation by means of a longitudinal 
groove and a ridge which is formed on the cylindrical inner wall of the 
housing. Alternatively to this it is possible to provide the impact piston 
with a longitudinal groove in which there engage at least two projections 
which are disposed spaced apart from one another, which projections are 
arranged on the inner wall of the housing. A particularly simple formation 
for the non-rotatable guiding of the impact piston in the housing takes 
place in accordance with a further feature of the invention when the 
projections are formed by screws which are screwed into the housing. 
With the invention finally it is proposed to secure the control sleeve 
which is rotatable between two end positions in the bearing ring in each 
end position by a non-positive--and/or positive--rotational-securing 
against unintentional rotation.

The ram boring device illustrated as the embodiment example has a 
tubular-shaped housing 1, on the front end of which there is fastened a 
guide ring 2. In a central bore of the guide ring 2, as impact tip or 
point 3 is displaceable in the axial direction about a path which 
corresponds approximately to the bore advance of the ram boring device 
each impact impulse. An impact piston 4 cooperates with this impact point 
3, the piston being axially moveable in the housing 1, however 
non-rotatably guided. For this purpose with the illustrated embodiment the 
impact piston 4 is provided with a longitudinal groove 4a, which groove is 
guided on a ridge 1a, the latter being formed on the cylindrical inner 
wall of the housing 1. 
Instead of this ridge 1a, at least two projections which lie spaced from 
one another can be formed on the cylindrical inner wall of the housing 1, 
which projections engage in the longitudinal groove 4a of the impact 
piston 4 as a rotation-preventive. As such type of projections screws 1a' 
(FIG. 5a) can be used which are preferably screwed in the housing 1, the 
screws engaging with their front end in the longitudinal groove 4a. Of 
course the heads of these screws 1a' can be arranged sunk into the housing 
1. 
The non-rotatably guided impact piston 4 is moved back and forth in the 
housing 1 by means of compressed air, whereby it exerts its impact action 
selectively on the impact tip 3 or on a bearing ring 5 which is secured on 
the rear end of the tubular-shaped housing 1. If the impact piston 4 
exerts its impact action on the impact tip 3, the ram boring device moves 
in the advance or positive drive direction. If to the contrary the impact 
direction of the impact piston 4 is reversed, so that the force which is 
produced by the impact piston 4 is exerted on the bearing ring 5, the ram 
boring device runs back. 
The feed of the compressed air and the reversing between forward and 
rearward movement takes place by a control sleeve 6 as the embodiment 
example which is illustrated in enlarged scale in FIG. 6. The altogether 
tubularly-shaped control sleeve 6 which has a piston-like thickened 
control head 6a projects with a cylindrical part 6b through a centering 
bore in the bearing ring 5. On the end of the cylindrical part 6b, which 
end projects from the bearing ring 5 toward the rear, there is fastened a 
compressed air hose 7, through which there is fed the compressed air which 
is needed for driving the impact piston. The air which is depressurized by 
driving the impact piston 4 escapes from the housing 1 through bores 5a 
which are provided in the bearing ring 5. 
In the area of the control head 6a on the control sleeve 6 there are formed 
at least four fixed or rigid control edges 8a, 8b and 9a, 9b, which form 
two different types of pairs, namely one type of pairs being 8a, 8b and 
the other type being 9a, 9b. Each of these pairs is arranged with axial 
spacing 10 and 11, respectively, from one another corresponding to the 
control stroke of the impact piston 4. These spacings 10 and 11 are drawn 
in FIG. 6. To the contrary of the known formations, in this manner the 
possibility is provided to form the distance 10 and 11, respectively, 
between the control edges 8a, 8b for the forward movement of the entire 
ram boring device and the control edges 9a, 9b for the rearward movement 
of the entire ram boring device, differently, whereby the run-on 
characteristic and the bounce or striking speed may be optimized much more 
favorably. Moreover a shorter total length of the ram bore device is 
possible, since for the rearward movement only a shorter distance 11 of 
the control edges 9a, 9b is necessary. 
The control edge pair which is formed by the control edges 8a and 8b is 
offset in the peripheral direction with respect to the control edge pair 
made of the control edges 9a and 9b. With the illustrated embodiment 
example the axis of the control edges 8a, 8b, 9a, 9b respectively each are 
circumferentially offset by 90.degree. so that all together there result 
eight control edges, whereby the same control edges each respectively lie 
diametrically oppositely on the control sleeve 6. Of course also a 
formation is possible with only four control edges each extending over 
180.degree. of the periphery (FIG. 6a). Particularly with ram bore devices 
with a larger diameter, moreover it is possible to provide a larger number 
of control edges, whereby the number however respectively is a multiple of 
four. 
The embodiment of the control sleeve 6 which is illustrated in the drawing 
with altogether eight control edges 8a, 8b, 9a, 9b provides a flow course 
of the compressed air which is symmetrical to the prevailing longitudinal 
center plane at the time; consequently the use of only four control edges 
is preferred. 
The front control edge 8a of the first pair of control edges is formed by 
the front edge of the control head 6a. The rear control edge 8b of this 
pair is formed by an edge, which edge is made by a recess 12, the latter 
starting from the rear end of the piston-like control head 6a. By means of 
the control edges 8a and 8b, the inpact piston 4 obtains its drive in the 
advance direction. 
For creating the forward control edge 9a of the second pair of control 
edges, respectively one recess 13 is provided, which recess originates 
from the front face edge of the control sleeve 6. The curve of this recess 
13, which curve runs in the peripheral direction, which runs spaced, 
however parallel to the front edge of the control head 6a over an arc of 
less than 90.degree., forms the control edge 9a of the second pair of 
control edges. The corresponding rear control edge 9b is formed by the 
rear rim of the control head 6a, which control head transfers or passes at 
this end by a hollowing rounding out or filleting into a middle section 6c 
of the control sleeve 6. The middle section with respect to the control 
head 6a has an altogether smaller diameter. The outer diameter of the 
middle section 6c is however considerably larger than the outer diameter 
of the rear cylindrical part 6b, so that the annular surface which is 
formed at the transfer transition between the middle section 6c and the 
cylindrical part 6b serves as a support surface for the control sleeve 6 
on the bearing ring 5. 
The rigid control edges 8a, 8b, 9a, 9b which are formed on the control 
sleeve 6 cooperate with the control bores 4b, the latter being formed as 
radial bores in the rear part of the impact piston 4. In this rear part 
this impact piston 4 has a cylindrical recess 4c. The control sleeve 6 
with the control head 6a projects in the cylindrical recess 4c. These 
control bores 4b are disposed only on a part of the periphery of the 
impact piston 4 which is non-rotatably guided in the housing 1, so that 
they cooperate either with the pair of control edges 8a and 8b or with the 
pair of control edges 9a and 9b, and indeed depending upon the position of 
the control sleeve 6, the latter being rotatable in the bearing ring 5 
between two positions. The annular area about the impact piston 4 is 
sealed off from communication with the bores 5a in the bearing ring 5 by 
means of an annular sealing member 4d, except from time to time via the 
control edges 8b, 9b. 
For driving the ram boring device in the advance direction, the control 
sleeve 6 is turned in that position (not shown) in which the control edges 
8a and 8b cooperate with the control bores 4b. In this case the compressed 
air which is supplied through the compressed air hose 7 as well as the 
control sleeve 6 drives the impact piston 4 with high energy against the 
impact point 3, so that the ram boring device moves in the advance 
direction. In order to reverse the direction of movement of the ram bore 
device, the control sleeve 6 is turned by 90.degree. in the bearing ring 5 
(by means of the compressed air hose 7) into the position illustrated in 
FIG. 1 of the embodiment example. As a result of the non-rotatable 
arrangement of the impact piston 4 in the housing 1, by this rotation of 
the control sleeve 6 relative to the housing 1, now the control edges 9a 
and 9b can cooperate with the control bores 4b in the impact piston 4. 
Since relative to the control edges 8a, 8b, the control edges 9a, 9b are 
formed rearwardly offset on the control head 6a in the longitudinal 
direction of the ram bore device, these control edges 9a and 9b cause the 
compressed air to be applied on the front face surface of the impact 
piston 4, such that the impact piston 4 is moved rearwardly and the impact 
energy of the impact piston 4 is exerted on the bearing ring 5. The entire 
ram bore device consequently moves rearwardly in the previously bored 
hole. 
The flow paths during the back and forth movement of the impact piston 4 
are basically the same for both of the two working cycles of forward 
(advancement) and rearward (retraction) movement of the overall ram boring 
device discussed above. However in the rearward working cycle the control 
edges 9a, 9b are aligned to cooperate with the control bores 4b, whereas 
in the forward working cycle the control edges 8a, 8b are operatively 
aligned with the control bores 4b, the relatively offset rearward 
displacement of the control edges 9a, 9b, bringing about with the latter a 
displacement toward the rear of the range of the control stroke, namely 
the range of the back and forth reciprocation of the impact piston 4 in 
the housing 1 causing the piston 4 to impact the rear bearing ring 5 
instead of the front impact tip 3. Impact at the front tip 3 occurs only 
in the forward working cycle since the control edges 8a, 8b are relatively 
forwardly shifted. This shift of the range of the control stroke of the 
impact piston 4 is a result of earlier or later communication of the 
respective control edges with the control bores 4b also causing the 
build-up of air cushions to be stronger or weaker at the front of the 
piston 4 and at the rear in chamber 4c. The flow paths are as follows, 
starting for example at the beginning of the rearward position of the 
impact piston 4, where the compressed air flows through the center of the 
controlled sleeve 6 into the then sealed chamber 4c in the impact piston, 
thereby driving the impact piston forward. Simultaneously the annular 
space around the impact piston 4 communicates via the overlapping control 
bores 4b and the control edges 8b (or 9b depending on the working cycle) 
and the recesses 12 (or the middle section 6c) with the bores 5a of the 
bearing ring for the exhaust. During the next portion of the advance 
stroke of the piston 4, when the control bores 4b move forwardly beyond 
the control edges 8b (or 9b), this last-mentioned communication is 
blocked. Thereafter near the end of the advance stroke of the impact 
piston, the control bores 4b overlap the control edges 8a (or 9a) of the 
control sleeve, whereupon the compressed air flow starts entering into the 
outer annular space around the impact piston 4. 
After impact at the front tip 3 and/or after the compressed air build-up 
develops at the area at the front of the impact piston 4 the compressed 
air drives the impact piston 4 in the rearward direction. In the course of 
the rearward motion of the impact piston 4, its control bores 4b are again 
closed, as they move past the edge 8a (or 8b) of the control sleeve 6. 
Exiting of the compressed air from the chamber 4c of the control sleeve 6 
is blocked, while the impact piston 4 continues to move rearwardly 
building-up a dampening air cushion (which has a smaller dampening effect 
in the retraction working cycle as a result of the rearwardly displaced 
control edges 9a, 9b). Before the impact piston 4 reaches the rearward 
reversal point, its control bores 4b are again exposed as they move 
rearwardly over the edge 8b (or 9b) of the control recess, thus allowing 
the residual air pressure in the annular space between the piston 4 and 
the housing 1 to be discharged from the device through the bores 5a of the 
bearing ring 5. After the rearwardmost position the piston 4 again begins 
to move forward and the control edges 8a, 8b (or 9a, 9b) again 
sequentially cooperate with the control bores 4a as described above and 
the operation is repeated. 
In order to define the respective end position of the control sleeve 6 
which is rotatable in the bearing ring 5, and to prevent an unintentioned 
rotation of the control sleeve 6 relative to the bearing ring 5, the 
control sleeve 6 is secured in every end position by a forced, 
non-positive, spring-actuated or -biased and/or positive or frictional fit 
(without rubbing or slipping) securing against rotation. This rotational 
prevention or securing for example can be formed by correspondingly formed 
inclined surfaces and/or spring-biased abutment bodies.