Abstract:
A pneumatically reversible ram boring device includes a percussion piston ( 8 ) that is situated in a casing ( 1 ) and is movable back and forth by operation air supplied via an operational-air supply via an operational-air line ( 5 ), a control pipe ( 4, 36, 54 ) having at least one control opening ( 13 ), an outer pipe ( 15, 65 ), and a control sleeve ( 10, 60 ) that can be displaced by compressed air from a control chamber ( 16, 66 ). An essentially torsion-resistant operational-air line ( 5 ) can be rotatably connected to a rotary valve ( 4, 40, 70 ) that supplies the control chamber with operational air or vents air from the chamber.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to a pneumatically reversible ram boring device, in particular for trenchless preparation of ground bores and for trenchless installation of lines into the earth. 
     Ram boring devices of this type are also used for upsizing ground bores and for destructive replacement of underground pipes; they include a self-controlling percussion piston which automatically moves back and forth in a casing by means of compressed air and which transfers its kinetic energy to the casing in forward travel at a front dead center and in backward travel at a rear dead center. 
     Switchover from forward travel to backward travel is accomplished with the assistance of a reversing system which with the aid of operational air decelerates the percussion piston at its forward dead center essentially without transferring kinetic energy to the casing, and also moves the rear dead center backwards, thereby ensuring that the percussion piston transfers its kinetic energy at that point to the casing. 
     Several versions of such reversing systems are known. They employ for adjusting the two dead center positions a control sleeve which is disposed on a control pipe for axial movement by means of compressed air, on one hand, and oftentimes by means of a pre-tensioned compression spring, on the other hand, whereby the control pipe is arranged immobile in the device casing. The reversal is implemented essentially by way of two lines of development which differ in principle from one another by using different sources for the compressed air applied to the control sleeve during switchover. 
     For example, British Patent 1 540 344, which corresponds to U.S. Pat. No. 4,708,211, discloses a reversal in which the operational air (compressed air) is supplied via a compressed-air hose and a non-rotatable and immovable control pipe to the percussion piston for longitudinal movement of a control sleeve, when switching from forward travel to backward travel. Switchover from backward travel to forward travel is accomplished by interrupting the supply of operational air to the device, allowing the spring-biased control sleeve to move from its rear position to the forward position. 
     German Patent DE 39 09 567 C2, and the corresponding U.S. Pat. No. 5,148,878 discloses a spring-pneumatic reversal for reversing from forward travel to backward travel, using a spring-biased control sleeve, which is arranged in a guide sleeve for limited rotation by means of the compressed-air hose, for releasing a control sleeve under spring tension. This spring tension is dimensioned such that the control sleeve overcomes the spring bias when the operational air is fully applied, thereby moving the control sleeve from its forward position for the forward travel to its reverse position for the backward travel. To switch from backward travel to forward travel, the pressure of the operational air opposing the compression spring needs to be reduced to allow the compression spring to move the control sleeve to its forward position. In both positions, the control sleeve is rotated about its longitudinal axis by elastic means and thereby locked in place in the axial direction. 
     A drawback of these spring-pneumatic reversing systems is the particularly complex and expensive construction and the use of operational air from a single source for both the operation of the percussion piston and also for reversing the direction so that the operational air has to be switched off, causing an interruption of the operation of the device; or only a reduced device power is available in the event the pressure is reduced during reversing operation. 
     To enable reversal of the control sleeve independent of the operational air, ram boring devices are also known which use air from a separate compressed-air source to control the axial movement of a spring-biased control sleeve. Such a device is described in the German Patent DE 198 58 519 C2, which corresponds to U.S. Pat. No. 6,371,220. 
     SUMMARY OF THE INVENTION 
     The invention is therefore directed to a ram boring device with a reversing system which is relatively simple in structure and in particular eliminates the need for an additional control-air source. 
     The invention is based on the concept to reverse direction with the operational air itself instead of with an additional air source, regardless as to how the actual technical implementation is realized. To this end, a pneumatic reversing system is proposed by which the control sleeve is moved by the operational air with the assistance of a valve. 
     The invention is based on the concept to reverse direction with the operational air itself instead of with an additional air source, regardless as to how the actual technical implementation is realized. To this end, the invention proposes in claim  1  a pneumatic reversing system by which the control sleeve is moved by the operational air with the assistance of a valve. 
     The valve can be constructed in many ways and is in its simplest form implemented as a closable opening in the control pipe. The valve (hereinafter also referred to as rotary valve) is connected according to the invention with a torsion-resistant hose for operational air; preferably, the valve can in its end position for the backward travel supply the control chamber of the control sleeve with operational air, and can vent the control chamber after a rotation of for example 90° into the end position for the forward travel. The rotary valve thereby enables axial displacement of the control sleeve through application of operational air. A pre-tensioned spring can also be used for returning the control sleeve. 
     The rotary valve can be constructed of a rotatably supported control pipe or portion of the control pipe with a radial branch bore and a longitudinal channel. The radial branch bore can be operatively connected with a operational-air opening of the control chamber in one end position of the control pipe or control pipe section, when the longitudinal channel is closed, whereas after the control pipe has been turned back into the other end position the radial bore is closed and the control chamber can be connected with the longitudinal channel for venting. As an alternative, venting may also occur, for example, via the pressure-relieve space of the percussion piston. 
     The control pipe can be locked in either of the two end positions by providing between the rear end of the control pipe and a connection sleeve for the operational-air hose a pressure chamber which is made, for example, of several portions and subjected to the pressure of the operational air and in which a compression spring is preferably arranged to replace the operational air in the event of a breakdown in operation or a loss of pressure so as to maintain the locked position. To provide a permanent rotational connection between the control pipe and the connection sleeve, the connection sleeve of the pressure chamber can engage an end face of the control pipe in a claw-like fashion. 
     For locking the control pipe in either of the two end positions, a counter sleeve which is fixed to the casing and has saddle-shaped depressions and elevations in its end face, can cooperate with a pin which is connected to the control pipe when subjected to pressure from the operational air in the compression chamber and/or from the compression spring arranged therein. The pin may, however, be arranged on the casing side and the depressions on the control pipe side. 
     In the rotary valve control according to the invention, the control pipe can also be arranged non-rotatably and immovably in the device casing. In one case, operational air is supplied to the control chamber of the spring-biased control sleeve via a radial branch bore for operational air and a radial channel in a control disk by way of a tubular rotary valve arranged on the control pipe in the rear section of the casing, whereas the control chamber is vented in its other end position through an axis-parallel bore, when the radial channel is closed. 
     The rotary valve can be constructed of a metallic disk and a coating of a permanently elastic material which includes the two aforementioned channels. 
     With this control technique, the spring-biased control sleeve is advantageously moved from its position for forward travel to its position for backward travel merely by a rotation—in the simplest embodiment of the control pipe—with a partial flow of the operational air branched off inside the device. 
     According to another preferred embodiment, the control sleeve can be displaced axially by operational air without using a spring, i.e. in both directions. The control sleeve can be constructed such that the control sleeve is moved into a functional position by pressure from the operational air (for example, into position for return travel by the driving air operating on the end face of the control sleeve), while the control sleeve returns again to the other functional position when operational air is admitted through an additional channel. This can be attained in that the operational air being admitted acts upon a comparatively larger effective area of the control sleeve. As a consequence of the supplied operational air, the control sleeve overcomes the smaller force operating in the opposite direction and resulting from the operational-air pressure supplied on the other side. In this embodiment, the rotary valve can be implemented as an independent unit or as a component of the control pipe for allowing operational air to be admitted via a randomly configured closable opening, so that this operational-air supply opposes the action of the air supply on the side of the percussion piston. As a result, operational air acting upon the end face of the control sleeve can cause a backward movement of the control sleeve, whereas the control sleeve returns again to the forward position as operational air is admitted via the closable opening. 
     According to the invention, axial displacement of the hose during reversal can be essentially prevented. The reversing system according to the invention is thus applicable also for great hose diameters or long hoses, i.e., for heavy hoses, without interfering in the reversing operation. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
       Exemplary embodiments of the invention will now be described in greater detail with reference to the drawings. The drawings show in: 
         FIG. 1   a  complete illustration of a ram boring device by way of an axial longitudinal section, wherein the control pipe operates as rotary valve, 
         FIGS. 2   a / 2   b  a view, on an enlarged scale, of the device ( 2   a  control sleeve side; rear end  2   b ) with the spring-biased control sleeve and a rear lock in forward-travel position, 
         FIG. 3  a vertical section, taken along the line III-III in  FIG. 2 , 
         FIGS. 4   a / 4   b  an illustration corresponding to  FIG. 2 , however with the control pipe and control sleeve in backward-travel position, 
         FIG. 5  an illustration corresponding to  FIG. 3 , however taken along the line V-V in  FIG. 4  with the control pipe and control sleeve in backward-travel position, 
         FIG. 6  a view, on an enlarged scale, of the rear end of the ram boring device according to the  FIGS. 2 to 5 , 
         FIG. 7  a longitudinal section, taken along the line VII-VII in  FIG. 6 , 
         FIG. 8  a cross section, taken along the line VIII-VIII in  FIG. 6 , 
         FIGS. 9   a / 9   b  a different rotary valve control ( 9   a  control sleeve side; rear end  9   b ) with a rotary valve arranged in the rear section of the device casing in forward-travel position, 
         FIG. 10  a top view on a control disk of the rotary control of  FIG. 12 , 
         FIG. 11  the rotary valve control of  FIG. 9  in backward-travel position, 
         FIG. 12  another rotary valve control with a rotary valve arranged in the rear section of the device casing in backward-travel position, 
         FIG. 13  a further rotary valve control with a rotary valve arranged in the rear section of the device casing in backward-travel position, and with the control sleeve without being acted upon by a spring, 
         FIG. 14  the rotary valve control of  FIG. 13  in forward-travel position, 
         FIG. 15  a view, on an enlarged scale, of the front end of the rotary valve control of  FIG. 13 , 
         FIG. 16  a view, on an enlarged scale, of the rear end of the rotary valve control of  FIG. 13 , 
         FIG. 16   a  a section of the rear end of the rotary valve control, taken along the line N-N in  FIG. 16 , and 
         FIG. 17  the rotary valve control of  FIG. 13  in forward-travel position and illustration of the vent passageways. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     The ram boring device shown in to  FIG. 1  includes a casing  1  having an interior for accommodation of a stop ring  2  with axis-parallel vent channels  3 . A control pipe  4  immovably supported in the casing  1  and supplied with operational air via a torsion-resistant hose. The front end of the control pipe  4  projects into a chamber  7  which is part of a percussion piston  8  and provided with control openings  6 . 
     An axially movable control sleeve  10 , which is movably supported on the control pipe portion  11  of greater diameter, is disposed between the control pipe  4  and the outer jacket  9  of the percussion piston chamber  7 . An outer collar  12  is located at the front end surface of the control pipe  4  or control pipe portion  11  of greater diameter and covers the front face of the control sleeve  10  and is flush with the control sleeve  10  ( FIG. 2   a ). Furthermore, control openings  13  are arranged in the front section  11  of the control pipe  4  of greater diameter and are covered by the control sleeve  10  during forward operation of the ram boring device, as illustrated in  FIGS. 2 ,  3 . An inner collar  14  used to guide the control sleeve  10  on the outer pipe  15  surrounding the control pipe  4  is disposed in the rear section of the control sleeve  10 . A control chamber  16  in which a connecting channel  17  feeds into is located between the inner collar  14  and the rear side of the control pipe portion  11  of greater diameter. Following the connecting channel  17  is a longitudinal channel  18  which is offset radially inwards. The channel  18  includes a longitudinal groove  19  disposed in the wall of the control pipe  4  and covered to the outside by the outer pipe  15 . 
     The control sleeve  10  is supported in the area of the rear end of the outer pipe by a return spring  20  under tension and bears in its forward position ( FIGS. 2 ,  3 ) with its inner collar  14  upon the rear side  16  of the control pipe section  11  of greater diameter and is positioned in its backward position ( FIGS. 4 ,  5 ) with its rear end  21  anteriorly of a stop shoulder  22  of the outer pipe  15 . 
     The control pipe  4  has a branch opening  23  which is closed during forward travel ( FIGS. 2 ,  3 ) by the wall of the outer pipe  15  ( FIG. 3 ), while the control chamber  16  is connected to atmosphere, i.e., vented, through the longitudinal channel  18  ( FIG. 2 ). 
     In the operating position for backward travel ( FIGS. 4 ,  5 ), the branch opening  23  of the control pipe  4  is connected, after a 90° rotation, with the control chamber  16  via the radially outwardly offset front section of the connecting channel  17  ( FIGS. 4   a    4   b ), whereas the longitudinal channel  18  is closed by a shoulder  24  of the control pipe in conjunction with the outer pipe  15  ( FIG. 5 ). As a result, the control sleeve  10  moves from its forward position ( FIGS. 2 ,  3 ) against the force of the pre-tensioned spring  20  backwards into its position for the backward travel ( FIGS. 4 ,  5 ). 
     The operating direction of the ram boring device can hence be changed in one or the other direction by a simple quarter turn of the control pipe which assumes the function of a rotary valve. 
     For locking the control pipe  4  in either of the two operating positions, a pressure chamber  26  made of two parts and accommodating a compression spring  27  is located between the rear end of the control pipe  4  and a connection sleeve  25  for the operational-air hose  5 . Both the rear end of the control pipe  4  and the front end of the connection sleeve  25  are arranged in a tubular extension  28  of the outer pipe  15 . The end surface of this extension is provided with saddle-shaped indentations  29   a ,  29   b  which cooperate with complementary elevations  30  of a counter sleeve  32  secured with a union nut  31 . The union nut is screwed together with the free end of the casing extension such that it can move the connection sleeve  25  slightly out of the device casing in the axial direction either with the help of the operational air in the pressure chamber  26  and the compression spring  27  or, if no pressure is applied to the device, with the compression spring  27  alone. 
     When the operational air hose  5  with a connection sleeve  25  is turned by 90°, the control pipe is locked in place by moving a pin  33  out of an indentation  29   a  on the counter sleeve  32 , until the pin  33  encounters, starting from its position illustrated in  FIG. 8 , an exposed stop surface  34  and—by moving across the elevations  30  located between the indentations—latches in another indentation  29   b  which is not visible in the illustration of  FIG. 7  and associated with the stop surface  34  or the other operating position. 
     In the exemplary embodiment illustrated in  FIGS. 9 to 11 , a typical control pipe  36  is non-rotatably and immovably arranged in the device casing  1 . The control pipe  36  includes a longitudinal channel  37  which feeds at  38  directly into the control chamber  16 . A rotary valve  40  with a branch bore  39  is provided in the region of the rear end of the control pipe  36 . The rotary valve  40  includes a connection sleeve  41  for the operational-air hose  5  and a control disk  42  with a permanently elastic coating  43 . The control disk  42  is connected with the connection sleeve  41  to form a single part, and sealingly presses the coating  43  against the rear casing wall of the protective casing  1  with the assistance of the operational air in the pressure chamber  44 . 
     The longitudinal channel  37  continues with different cross section and different path via the device interior to a two-part vent channel. This vent channel has an L-shaped opening  45  in the elastic coating  43  and a vent bore  46  which is located in the rear casing wall and aligned in a valve position for forward travel ( FIG. 9   b ). 
     The vent bore  46  illustrated in  FIG. 9   b  is actuality arranged in front of the rear casing wall at an angular offset of 90° relative to the mouth of the longitudinal channel  37  and is connected in the operating position for forward travel with the longitudinal channel through a kidney-shaped groove  48  in the coating  43  ( FIG. 10 ). 
     In addition, an operational-air channel  50  extends through the coating  43  of the control disk  42  and connects the branch bore  39  with the rear, approximately U-shaped end of the longitudinal channel  37  in the operating position for backward travel ( FIG. 11 ). As a result, the control pipe  36  supplies operational air to the control chamber  16  which moves the control sleeve  10  from the operating position illustrated in  FIG. 9  to the rear operating position according to  FIG. 11 . 
     The exemplary embodiment of  FIG. 12  differs from the exemplary embodiment of  FIGS. 9 and 11  only in that the branch bore  39  is eliminated and operational air is supplied to the control chamber  16  from the pressure chamber  35 . This is accomplished through an axis-parallel bore  51  extending through the control disk  42  and the coating  43 , with the bore  51  being aligned in the rotary valve position for the backward travel with the open end of the longitudinal channel ( FIG. 12 ). 
     In the exemplary embodiments of  FIGS. 9 and 12 , the pressure secured the control disk in its respective position by friction. In the operating position for forward travel, the control chamber  16  is vented in the same manner as illustrated for the other rotary valve variant in  FIG. 9 . 
       FIGS. 13 to 17  illustrate an exemplary embodiment of a rotary valve control in which the control pipe  54  is arranged immovably in the device casing and non-rotatably by way of an L-shaped bolt  74 , whereas the rear section of the control pipe has a rotary valve  70 . The inner collar  60   a  of a control sleeve  60  is guided on a slide ring  61  on the front section of the control pipe and on an outer collar  65   a  of an outer pipe  65  surrounding the control pipe  54 . The control sleeve  60  can be moved with operational air in both directions. A control chamber  66 , in which a longitudinal channel  68  feeds into, is located between the inner collar  60   a  and an outer collar  65   a . The channel  68  includes a longitudinal groove  69  in the wall of the control pipe  54  which is covered to the outside by the outer pipe  65 . 
     The rotary valve  70  has a branch bore  79  in the region of the rear end of the control pipe  54 . The branch bore  79  is closed during the backward travel ( FIG. 13 ) by the wall of the control pipe  541  whereas the control chamber  66  is connected to atmosphere, i.e. vented, through the longitudinal channel  68  and a vent channel  69   a  having vent bores  69   b ,  69   c.    
     For the operating position for forward travel ( FIGS. 14 ,  15 ), the branch opening  79  of the rotary valve  70  is connected with the control chamber  66  through the longitudinal channel  68  by a 90° rotation ( FIG. 14 ). 
     The effective areas inside the control chamber  66  are acted upon by the operational air supplied through the longitudinal channel  68  and dimensioned relative to the effective areas located at the end face  62  of the control sleeve  60  such that the same operational-air pressure in the control chamber  66  and in the area of the end face  62  causes displacement of the control sleeve  60  toward the slide ring  61  and hence into the operating position for forward travel. The inner collar  60   a  ( FIGS. 14 ,  15 ,  17 ) of the control sleeve  60  bears hereby upon the backside  61   a  of the slide ring  61 , and migrates to the outer collar  65   a  of the outer pipe  65 , when switching to the return-travel position ( FIG. 13 ). 
     A simple turning of the operational-air hose by 90° therefore causes the control sleeve  60  to move from its return-travel position ( FIG. 13 ) in opposition to the operational air acting on the end face  62  of the control sleeve  60  forwards to its position for forward travel ( FIGS. 14 ,  15 ,  17 ), whereas a turning of the operational-air hose back by 90° causes the control sleeve to return to the operating position for the backward travel due to the operational-air pressure acting on the end face  62  of the control sleeve  60 , i.e. when the control chamber  66  is vented. 
     Thus, a simple quarter turn of the rotary valve in either direction enables a reversal of the device solely by means of operational air pressure.