Patent Publication Number: US-7587964-B2

Title: Pneumatic power wrench with pre-set torque levels

Description:
This application is a U.S. National Phase Application under 35 USC 371 of International Application PCT/SE2005/001833 filed Dec. 5, 2005. 
   The invention relates to a pneumatic power wrench which includes a motor, and a pressure responsive shut-off valve located in the pressure air supply passage to the motor for limiting the output torque of the motor, wherein the pressure shut-off valve has a bias spring which is supported in one direction by a valve element and in the opposite direction by a movable spring support, and a manually operated torque setting mechanism which is arranged to set the position of the spring support in various positions to thereby vary the tension of the bias spring and, hence, the output torque from the motor. 
   In this type of power wrench a change in torque output is obtained by manual re-setting of the shut-off valve. When using a wrench of this type at a working site where a number of different types of screw joints are to be tightened to different torque levels the shut-off valve has to be re-set when moving the wrench from one type of screw joint to another. Such re-setting procedures are rather time consuming. An alternative way of action would be to use two or more wrenches all set at different torque output levels. 
   In order to simplify the work at a working site as described above avoiding repeated re-setting of one power wrench for the different types of screw joint or avoiding use of more than one wrench for the job the present invention provides a new type of pneumatic power wrench offering a quick and easy shifting between two or more pre-set torque levels. 

   
     A preferred embodiment of the invention is described below in detail with reference to the accompanying drawings. 
     In the drawings, 
       FIG. 1  shows a perspective view of a power wrench according to the invention. 
       FIG. 2  shows a longitudinal section through the torque setting mechanism of the power wrench in  FIG. 1 . 
       FIG. 3  shows a longitudinal section through the spring support and a stop element as indicated by line III-III in  FIG. 4 . 
       FIG. 4  shows a rear end view of a power wrench according to the invention. 
       FIG. 5  shows a longitudinal section through the shut-off valve and an adjustable stop element according to the invention. 
   

   The power wrench shown in the drawing figures comprises a housing  10  with a pistol type handle  11 , and a connection  12  for a pressure air conduit at the lower end of the handle  11 . The wrench comprises a pneumatic motor  13  which is coupled to an output shaft  14  via a non-disclosed reduction gearing. The motor  13  is supplied with pressure air via an inlet port  15  and an air supply passage  16  in the housing  10 , and a torque limiting pressure responsive shut-off valve  17  is located in the pressure air supply passage  16  and arranged to shut off the motor  13  at a desired predetermined torque level. A certain counter pressure level in the motor inlet port  15  corresponds to a certain motor torque level and, hence, a certain output torque level on the output shaft  14 . 
   The shut-off valve  17  comprises a tubular valve casing  20  mounted in the housing  10 , and an axially movable valve element  21 . The valve casing  20  is formed with a rear end surface  22  for sealing co-operation with the valve element  21  in a closed position of the valve  17 . In its open position the valve element  21  co-operates with an elastic seal ring  23  for sealing off a rear end surface  24  of the valve element  21 , thereby preventing the pressure air in the supply passage  16  from reaching and acting on the end surface  24 . The valve element  21  is biased against the seal ring  23  by a spring  25  which acts between an adjustable spring support  26  and cap member  27  supported at one end of a valve element push rod  28  and a screw  29  secured to the valve element  21 . The space inside the seal ring  23  communicates continuously with the inlet port  15  via a control passage  18  so as to balance the valve element  21  between the spring  25  and the counter pressure in the motor inlet port  15 . It is evident that the harder the spring  25  is pre-tensioned the higher pressure from the motor inlet port  15  and the higher output torque of the motor  13  is required to move the valve element  21  towards closed position. 
   The spring support  26  is provided with a roller  30  and is backed by either one of four identical adjustable stop elements  31  which are carried on an adjustment unit  32 . The latter forms a torque setting mechanism and is rotatively supported in the housing  10  about an axis A. Each stop element  31  comprises a contact block  33  having a central spindle  34  engaged by a set screw  35 . The contact block  33  is formed with a double cam profile  36  for co-operation with the roller  30  on the spring support  26 . See  FIG. 3 . The contact block  33  is formed with a central notch  38  to engage the spring support roller  30  to thereby arrest the adjustment unit  32  in a correct position relative to the spring support  26 . The adjustment unit  32  is manually rotated between four distinct angular positions, defined by the notch  38  on each contact block  33 , to put one at a time of the stop elements  31  into engagement with the spring support  26 . At its rear end surface the adjustment unit  32  has a maneuver knob  39  which is foldable not to cause any unintentional shifting of the adjustment unit  32 . The maneuver knob  39  has a position indicator in the form of an arrow  40 , and the housing  10  is provided with four marking surfaces  41   a - d  where the actual torque setting for each position of the adjustment unit  32  can be marked. 
   Each one of the stop elements  31  is individually set by the screw  35  to accomplish a certain pretension of the spring  25  and to, thereby make the shut-off valve element  21  shift to closed position at a certain air pressure in the motor inlet port  15 . In other words, the different stop elements  31  are set to make the wrench deliver four different torque levels. You just have to rotate the adjustment unit  32  to align the stop element  31  that has been set to a certain torque level with the spring support  26 . It is to be noted that each one of the stop elements  31  is adjustable between a maximum torque output position and a minimum torque output position, which means that any desired torque level within the entire torque range of the wrench is available to the operator in each position. 
   When preparing the wrench for operation, the different stop elements  31  of the adjustment unit  32  are individually set at four different positions meeting the torque level requirements of four different screw joints to be tightened. This is obtained by adjusting the set screws  35 . The set torque level for each stop element  31  is marked on the respective marking surface  41   a - d  on the housing  10  on which the arrow  40  points. Each setting of the set screw  35  makes the spring support  26  pretension the spring  25  to a certain extent to thereby exert a bias force on the cap  27 , the rod  28 , the screw  29  and the valve element  21 . The valve element  21  is urged against the seal ring  23  and leaves an annular air flow opening relative to the valve casing end surface  22 . The seal ring  23  prevents pressure air from the supply passage  16  from reaching the rear end surface  24  of the valve element  21 , and since at the start of a tightening cycle there is no pressure in the motor inlet port  15  and the control passage  18  the bias force of the spring  25  will be unchallenged and the valve element  21  will be kept in its open position. 
   It is to be observed that in  FIGS. 2 ,  3 , and  5  the set screws  35  are set to give a minimum torque output from the power wrench, i.e. the stop elements  31  occupy their most retracted positions. 
   At the start of a screw joint tightening cycle pressure air is fed through the supply passage  16  into the valve casing  20 , through the annular opening past the rear end surface  22  of the casing  20  and through the motor inlet port  15 . The motor starts operating to deliver an output torque to the output shaft  14  and to the screw joint to be tightened. As the torque resistance in the screw joint becomes higher the counter pressure in the motor inlet port  15  and the control passage  18  increases and, accordingly, the pressure acting on the rear end surface  24  of the valve element  21 . When the torque resistance in the screw joint has reached the intended final torque level the air pressure communicated to the rear end surface  24  of the valve element  21  via passage  18  will dominate the bias force of the spring  25  such that the valve element  21  will start moving towards closed position. As soon as the valve element  21  has separated from the seal ring  23  the even higher supply pressure in passage  16  will reach the rear end surface  24  of the valve element  21 . This results in an increased closing force on the valve element  21 , and the pressure air supply to the motor  13  is distinctly shut off, i.e. the valve element  21  is brought into sealing engagement with the end surface  22  of the valve casing  20 . 
   The above described operation order of the shut-off valve  17  is the same no matter the set torque level or which one of the stop elements  31  is actually brought into co-operation with the spring support  26 . Just by rotating the adjustment unit  32  into different positions four pre-set torque levels are readily available to the operator. This means a considerable time saving when working at a site where a number of screw joints of different sizes have to be tightened to different final torque levels.