Abstract:
The power screwdriver comprises a functional part ( 11 ) with a housing ( 14 ) through which a shaft ( 17 ) passes. The shaft ( 17 ) is provided with a toothing ( 18 ), into which a ratchet lever of the functional part ( 11 ) engages. A splined shaft toothing ( 20 ) of the shaft ( 17 ) has an insertion recess ( 21 ) that changes into a cavity ( 22 ). The wall of the cavity ( 22 ) is provided with a torsion sensor ( 23 ) and forms a measuring section ( 25 ) that is located in the area of the shaft ( 17 ) covered by the housing ( 14 ). A torsion measurement is effected in the measuring section ( 25 ). Due to the measuring section ( 25 ) being located in the area of the shaft covered by the housing ( 14 ), the shaft ( 17 ) is relatively short whereby it may be used under tight spatial screwing conditions involving a low head height above the screw. The power wrench is additionally provided with an angle measuring device ( 33 ) whereby torque and angle of rotation can be simultaneously provided and can be used for controlling and recording.

Description:
BACKGROUND OF THE INVENTION 
   The invention relates to a pressure-operated hydraulic or pneumatic power wrench comprising a drive part and a functional part, said functional part having a shaft that is driven by a ratchet lever and includes a coupling device, and comprising a measuring section detecting the torsion element. 
   A hydraulic power wrench of this type is known from DE 296 07 207. In this power wrench, the shaft extends transversely through the housing of the functional part. Outside the housing, a measuring section adapted to be twisted is provided at the shaft. In this measuring section, a torsion sensor in the form of several extension measuring strips is mounted on the shaft. The torsion sensor forms an electric resistor arrangement the resistance of which depends on the torque. A coupling device adapted to be coupled with a tool or a screw head is located at the end of the shaft. 
   This power wrench with measuring cell permits to measure the torsional moment acting upon the screw whereby it is possible to detect the tightening torque directly at the screw connection. 
   It is the object of the invention to provide a pressure-operated power wrench with drive part, functional part and a measuring section, which has small dimensions in axial direction of the screw and thus can be used even if the headroom (above the screw) is small. 
   SUMMARY OF THE INVENTION 
   A first solution to this object is provided, according to the invention, by the features indicated in claim  1 . Accordingly, the measuring section is arranged at least partially in the region enclosed by the housing. This means that the measuring section is located in the region covered by the housing or at least projects into this region. This results in that the shaft or a part connected thereto has a slight axial projection beyond the housing and that the overall length of the shaft is very small so that the power wrench can also be used at narrow locations with very small headroom being available above the screw. 
   A second solution to the indicated object is defined by claim  2 . Accordingly, the measuring section is formed in a cavity of the shaft or a tubular portion connected thereto. Here, the torsion sensor of the measuring section is mounted to the inner wall of the cavity. At the outside of the shaft, no room is required for the torsion sensor. It can overlap with a toothing provided at the outside of the shaft and being engaged by the ratchet lever. Thus, the measuring section of the shaft does not require any additional length at all. Moreover, the torsion sensor is accommodated in the cavity so as to be protected against external influences and an additional encapsulation of the measuring section is not required. 
   A third solution to the object is defined by claim  3 . Accordingly, the coupling device is configured as a key socket being an integral part of the shaft. Here, the projection of the shaft beyond the housing is reduced to a minimum measure. The cavity of the key socket may extend as far as into the housing. Alternatively, it is also possible to configure the coupling device as a square, for example, onto which a key socket can be put. In this case, however, the length of the shaft including the key socket becomes greater. 
   A fourth solution to the object is indicated in claim  4 . Accordingly, the measuring section is arranged at or in a tubular portion of a key socket. The key socket may be an integral part of the shaft or may also be connected with the shaft. 
   At the housing, an angle sensor may be provided which detects the rotational angle of the shaft. Apart from the direct torque measurement in the interior of the apparatus, a direct rotational angle measurement is simultaneously effected. By integrating the angle sensor into the power wrench, the flat design is not substantially impaired so that the direct measurement can also be effected under extremely tight spatial conditions. It has been observed that the combined measurement of torque and rotational angle permits the most precise tightening method for highly sensitive screw connections. 
   Preferably, the angle sensor is arranged in a cap surrounding the one end of the shaft. Thus, the angle sensor is protected against mechanical damage and pollution. On the other hand, the lateral enlargement of the housing by the cap can be kept relatively small. Either by means of slip rings or by wireless transmission, data can be transferred through the cap. 
   Hereinafter, embodiments of the invention will be explained in detail with reference to the drawings. 
   In the Figures: 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  shows a schematic side view of a first embodiment of the power wrench, partially in section, 
       FIG. 2  shows a sectional view along the line II—II of  FIG. 1 , 
       FIG. 3  shows a sectional view of a second embodiment where the measuring section is arranged on the outside of the shaft, 
       FIG. 4  shows a sectional view of a third embodiment where the measuring section is arranged in the shaft interior, 
       FIG. 5  shows a sectional view of a fourth embodiment where the shaft is coupled with the key socket via an intermediate shaft, 
       FIG. 6  shows a fifth embodiment where the measuring section is arranged in a tubular portion of the key socket, 
       FIG. 7  shows a sixth embodiment where the measuring section is arranged on the outside of a tubular portion of the key socket, 
       FIG. 8  shows a seventh embodiment where the measuring section is arranged in a tubular portion of the key socket which, in turn, is connected with an intermediate shaft, and 
       FIG. 9  shows a version similar to that of  FIG. 8 , but with the measuring section being arranged outside. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   The power wrench according to  FIGS. 1 and 2  comprises a drive part  10  and a functional part  11 . The drive part  10  is exchangeably mounted to the functional part  11 . The drive part  10  includes a (non-illustrated) hydraulic cylinder in which a piston can be displaced. On the cylinder housing  12 , the drive part  10  comprises a pivotal connection device  13  for hydraulic hoses. 
   The functional part  11  comprises a housing  14  consisting of two assembled housing halves  14   a  and  14   b  here. In the housing  14 , there is a cavity  15  in which a (non-illustrated) ratchet lever can be pivoted to and fro by the drive part  10 . A shaft  17  is rotatably supported in a transverse bore  16  extending through the housing  14 . In the interior of the housing  14 , this shaft  17  comprises a circumferential toothing  18  into which a toothing of the ratchet lever engages. Thus, the shaft  17  is rotated about its axis by a specified angular amount with each stroke of the drive part  10 . Then, the return stroke of the ratchet lever is effected where the shaft  17  is not taken along. 
   At one end, the shaft  17  comprises a coupling device  20  configured as a key socket  40  and forming an insertion recess  21  of hexagonal cross section. The insertion recess  21  is located in the portion of the shaft  17  projecting from the housing  14  and extends as far as into the housing  14 . Thus, the portion of the shaft projecting from the housing can be kept relatively short. 
   The insertion recess  21  changes into a cavity  22  formed in the shaft  17 . The torsion sensor  23  in the form of extension measuring strips adhered to the circumferential wall is located at the circumferential wall of the cavity  22 . Between the insertion recess  21  and the cavity  22 , there is an annular flange  24  projecting inward and protecting the torsion sensor  23  against intrusions from outside. The portion of the shaft  17  carrying the torsion sensor  23  forms the measuring section  25 . The cavity  22  forms an axial extension of the insertion recess  21 . When the insertion recess  21  is put upon a screw nut to be turned, the cavity  22  is able to receive the screw shank projecting from the nut. Therefore, the insertion recess  21  may have a relatively small axial length. Alternatively, the insertion recess may also serve to receive the shank of a key socket or be configured as a square opening. 
   The cavity  22  is followed by a truncated transition  26  opening into a receiving room  27  in which a data transmission element  28  is included. From the torsion sensor  23 , a cable duct  29  extends to the data transmission element  28 . The data transmission element  28  is a slip ring arrangement, for example, which connects an external cable  30  with the torsion sensor  23  that is rotatable with the shaft  17 . Alternatively, the transmission may also be effected in a wireless manner. The cable  30  leads to a cable connection  31  ( FIG. 1 ) provided at a cantilever arm  32  of the housing  14 , to which a control or measuring apparatus can be connected. 
   Further, the hydraulic power wrench is equipped with a rotational angle measuring device  33 . The latter comprises a code disc  34  fastened on the end of the shaft  17  facing away from the insertion recess  21  and an angle sensor  35  reacting to the bars of the code disc  34  and detecting the rotational angle of the shaft thereby. The angle sensor  35  consists of a forkshaped light barrier into which the code disc  34  protruding radially from the shaft projects. 
   The angle sensor  35  is included in a cap  36  set upon a portion of the housing  14  and fastened by screws  37 . The cap  36  encloses the rear end of the shaft  17  facing away from the insertion recess  21  and simultaneously forms a protective housing for this shaft end and the angle measuring device  33 . From the angle sensor  35 , a cable  38  leads to the cable connection  31  so that both the torsion sensor  23  and the angle sensor  35  are electrically accessible at the cable connection  31 . 
   The operation of the power wrench can be exactly controlled and particularly, the desired screw tightening moment can be achieved purposefully with the torsion moment of the shaft  17  and the rotational angle of this shaft being continuously measured. It is also possible to store the data measured during a screw tightening process and deposit them in a memory to be able to document the screwing process later on. This is particularly important when screws relevant as to safety are tightened. 
   In the following embodiments, the drive part  10  and the functional part  11  each have the same construction as has been described with reference to  FIGS. 1 and 2 . What is different is the respective transmission of power from the shaft to the key socket, as will be explained hereinafter. 
   In the embodiment of  FIG. 3 , the shaft  17  is arranged in the housing over its entire length. On the one shaft half, it comprises a coupling device  20   a  in the form of a splined shaft toothing engaging with a corresponding outer toothing of a key socket  40 . The key socket  40  has a hexagonal insertion recess  21  in an enlarged head  41 . The head  41  partially extends as far as into the housing  14 . The head  41  is followed by a hollow shaft  42 . This hollow shaft comprises an outer wedge splining engaging with the coupling device  20   a  of the shaft  17 . Between this outer wedge splining and the head  41 , there is a measuring section  25  with a torsion sensor  23  arranged in the annular groove of the hollow shaft  42  so as to be countersunk. The torque is transferred to the hollow shaft  42  from the shaft  17 , and from there, it is transferred to the head  41  of the key socket  40  via the measuring section  25 . In this variant, even a part of the head  41  is arranged so as to be countersunk in the housing  14  so that the axial length of the power wrench can be kept extremely short. 
   The embodiment of  FIG. 4  corresponds to that of  FIG. 3 , but with the difference that the torsion sensor  23  is arranged at the inside of the hollow shaft  42 . Electric connection lines can be led through the hollow shaft to the torsion sensor very easily. 
   In the embodiment of  FIG. 5 , the shaft  17  projects from the housing  14  toward the rear end. At the projecting portion, it is provided with a splined shaft toothing  20   a  at the inside, which engages with a corresponding coupling device  20   a  at the outside of an intermediate shaft  44 . The intermediate shaft extends through the housing  14  as far as to the front and it comprises an inner splined shaft toothing  45  in its front portion and a bearing bore  46  in its rear portion. 
   The key socket  40  comprises a head  41  with an insertion recess  21 . This head is followed by a hollow shaft  42  on which a splined shaft section is provided which engages with the splined shaft toothing  45  of the intermediate shaft  44 . The hollow shaft  42  is followed by a hollow shaft section  47  supported in the bearing bore  46 . 
   In the region between the two splined shaft toothings  20   a  and  45 , there is the measuring section  25  with the torsion sensor  23  fastened in an outer groove of the intermediate shaft  44 . 
   In the embodiment according to  FIG. 5 , key socketes  40  of different wrench widths can be inserted into the intermediate shaft, even the largest wrench widths being possible. 
   The embodiment of  FIG. 5  may also be modified such that the torsion sensor  23  is included in a recess at the inner wall of the intermediate shaft  44 . 
     FIG. 6  shows an embodiment where the key socket  40  is connected with a hollow shaft  42  which engages into an inner coupling device  20   a  of the shaft  17 . The shaft  17  extends over the width of the housing  14 , but does not project substantially beyond it. With the hollow shaft  42 , the key socket  40  forms a structural unit which, as a whole, can be withdrawn from the shaft  17 . The measuring section  25  is located at the key socket  40 , namely in the region between the insertion recess  21  and the hollow shaft  42 . From the torsion sensor  23 , electric wires  48  extend through the hollow shaft to a data transmission element  28  arranged in the same manner as in  FIG. 2 , but being located in the interior of the hollow shaft  42  here. The power wrench is equipped with a rotational angle measuring device  33  comprising a code disc  34  seated on the hollow shaft  42  and an angle sensor  35  secured to the housing. 
   The embodiment of  FIG. 7  differs from that of  FIG. 6  only in that the torsion sensor  23  is arranged on the outside of the measuring section  25 . A bore  46  for the passage of the cables from the torsion sensor  23  leads through the hollow shaft  42  into the interior of the hollow shaft. 
     FIG. 8  shows an embodiment where the key socket  40  is extended by a hollow shaft  42  including a measuring section  25 , the torsion sensor  23  being arranged in the interior of the hollow shaft  42 . The hollow shaft  42  is connected with an intermediate shaft  49  engaging into an inner coupling device  20   a  of the shaft  17 . The cable from the torsion sensor  23  passes through the intermediate shaft  49  in order to emerge at the rear side. 
   The embodiment of  FIG. 9  differs from that of  FIG. 8  only in that the torsion sensor  23  is arranged on the outside of the measuring section  25 . From there, a bore  46  leads into the interior of the hollow shaft  42 . 
   Although a preferred embodiment of the invention has been specifically illustrated and described herein, it is to be understood that minor variations may be made in the apparatus without departing from the spirit and scope of the invention, as defined by the appended claims.