Patent Publication Number: US-6334494-B1

Title: Control unit for hydraulic impact wrench

Description:
This application is a continuation of PCT/JP99/00858 filed Feb. 24, 1999. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to a control unit for a hydraulic impact wrench. More particularly, the present invention relates to a control unit for a hydraulic impact wench where a pulsed torque is controlled with high precision. Even more particularly, the present invention relates to a control unit that permits particularly simple construction. 
     Referring to FIG. 4, a conventional control unit for an impact wrench includes a cylinder casing  51  containing a main shaft  52 . Cylinder casing  51  is rotatively driven by an air motor (not shown). The distal end of main shaft  52  is adapted to be engage members to be torqued. An oil cylinder  53 , is formed inside cylinder casing  51 . The sectional contour of oil cylinder  53  consists of a pair of two circular arcs whose centers are displaced to slightly eccentric positions from the rotational center of main shaft  52 . The two circular arcs are aligned with each other to form a generally elliptical configuration. Sealed portions  53   a ,  53   b ,  53   c , and  53   d  are defined at substantially quadrisected positions on the inner circumferential surface of the oil cylinder  53 . Sealed portions  53   a ,  53   b ,  53   c , and  53   d  extend along the axial direction of the oil cylinder. Oil cylinder  53  is filled with hydraulic operating fluid (not shown). A proximal end portion of main shaft  52  is disposed in the oil cylinder  53  perpendicular to the plane of the drawing sheet of FIG.  4 . 
     A blade groove  54 , is defined by the site corresponding to the disposition of the proximal end portion of the main shaft  52  and the oil cylinder  53 . A pair of blades  55 ,  55  are placed slidably in the blade groove  54 . 
     Referring to FIG. 5, a spring  56  energizes blades  55 , 55  outwardly in the diametrical direction thereof to move the distal end portions of blades  55 , 55  into slidable contact with the inner circumferential wall of the oil cylinder  53 . Seal portions  52   a  and  52   b  in the main shaft  52  are formed at positions perpendicular to the respective blades  55 ,  55 . 
     Referring now also to FIG. 4, when cylinder casing  51  is rotatively driven by an air motor a relative rotating position, defined between the main shaft  52  and the oil cylinder  53 , changes. When respective seal portions  52   a ,  52   b  of the main shaft, and the distal ends of respective blades  55 , 55 , are in contact with the respective seal portions  53   a ,  53   b ,  53   c , and  53   d , a position shown in FIG. 5 is reached. When the position shown in FIG. 5 is reached, hydraulic operating fluid, contained on either side of the respective blades  55 ,  55 , defines a high pressure chamber H. Low pressure chamber L, not containing hydraulic operating fluid, is defined opposite the high pressure chamber H with respect to blades  55 ,  55 . The low pressure chamber L has a lower pressure than the high pressure chamber H. Containment of the hydraulic operating fluid produces a pulse of high pressure that rotatively acts upon a main shaft  52  to apply a pulsed torque condition to a member to be torqued. The same condition for the containment of hydraulic operating fluid, as described above, appears where the cylinder casing  51  rotates 180 degrees from the position shown in FIG.  5 . 
     A bypass mechanism is arranged so that one torque pulse is produced per rotation of the cylinder casing  51 . The communication path mechanism communicates pressure from high pressure chamber H to low pressure chamber L only under conditions where respective seal portions  53   b ,  53   d ,  52   a , and  52   b  are in contact with each other. 
     After the high pressure chamber H and the low pressure chamber L are defined in the oil cylinder  53 , a portion of the high pressure hydraulic operating fluid contained in the high pressure chamber H must be bypassed to the lower pressure chamber L to release cylinder casing  51  for further rotation. A bypass passage  57  is defined in the cylinder casing  51  for this purpose. A valve shaft insertion hole  58 , is bored on the cylinder casing  51  facing the bypass passage  57 . An adjustable valve shaft  59  is inserted into the insertion hole  58 . 
     A communication path  60  on the valve shaft  59  allows hydraulic operating fluid to penetrate the bypass passage  57 . The communication path  60  functions as a variable aperture where the flow passage area of communication path  60  changes through axial adjustment of valve shaft  59 . The peak pressure pulse in high pressure chamber H is controlled by the adjustment of the flow passage area. Thus the pulsed torque is controlled by varying the flow passage area of the communication path  60 . When the flow passage area is reduced, high peak pressure is produced and a high pulsed torque is obtained for the hydraulic pulse generation mechanism. 
     A mechanism for stopping automatically the operation of the hydraulic pulse generation mechanism when a predetermined pulsed torque is obtained includes a relief valve  61  mounted on a shaft end portion on the distal side of the valve shaft  59 . Relief valve  61  includes a ball  62  which is pressed by a spring  63  into contact with a shaft end surface of valve shaft  59 . Hydraulic operating fluid in communication path  60 , acts upon ball  62  through a pressure leading path  64 , defined in a shaft center portion of valve shaft  59 , so that pressure opposes the force of spring  63 . 
     A secondary side of relief valve  61  communicates with a cylinder chamber  65  on a top cover. A piston  66  is contained inside cylinder chamber  65 . An automatic shut off mechanism (not shown) is operated by a movement of a piston  66  upon a rod  67 . 
     As a result, during operation when a predetermined peak pressure is produced in the high pressure chamber H and hydraulic operating fluid in communication path  60  exceeds a predetermined pressure, relief valve  61  is opened against the force of spring  63 . Thus, the hydraulic operating fluid is released to flow into the cylinder chamber  65  to push a piston  66  and operate the automatic shut off mechanism through rod  67 . This ends the operation. 
     Pulsed torque in the hydraulic pulse mechanism is generated when valve shaft  59  is transferred axially to adjust the flow path area of communication passage  60 . At the same time valve shaft  59  adjusts the spring force of spring  63  in relief valve  61 . 
     When the pulsed torque is increased, valve shaft  59  is translated to the right side of FIG. 5 thus increasing the opening of the aperture in communication path  60 . This increases the peak pressure of hydraulic operating fluid produced in high pressure chamber H. Simultaneously, spring  63  of relief valve  61  is compressed to set the relief pressure to a high value. 
     The pulsed torque is influenced by two related values, the peak pressure of a hydraulic operating fluid in high pressure chamber H, and the spring force in relief valve  61 . When the peak pressure and the spring force repeat with the same characteristics as that of the original response to transfer of valve shaft  59  an operator achieves a similar torque. In a conventional hydraulic impact wrench, the peak pressure and the spring force are correlative but do not vary with quite the same characteristics. In hydraulic impact wrench operations where the spring force is more that the increase in peak pressure, relief valve  61  may not operate and thereby cause inconvenience to operators. In hydraulic impact wrench operations where a sufficient peak pressure is obtained, relief valve  61 , may open before a predetermined peak pressure is obtained if a sufficient spring force is not achieved. This results in less than the desired torque for the operator. 
     Conventional pulse generation mechanisms are particularly disadvantaged by very high dimensional accuracy requirements and close attention to manufacturing and assembly details to achieve the desired precision torque control and reduce persistent failures to operate. Manufacturing and assembly details, for conventional pulse general mechanisms, require close attention to the selection of force constant in spring  56 , the dimensional accuracy of valve shaft  59  and the assembly of respective members. 
     OBJECTS AND SUMMARY OF THE INVENTION 
     It is an object of the invention to provide a hydraulic impact wrench control unit structure that overcomes the foregoing problems. 
     It is a further object of the invention to provide a control unit where a fixed aperture is disposed at a position located nearer to a high pressure chamber than a branched section of a pressure leading path. 
     It is a further object of the invention to provide a control unit where a fixed aperture is disposed at a position located on a side nearer to a low pressure chamber than a branched section of a pressure leading path 
     According to an embodiment of the invention, there is provided a hydraulic impact wrench control unit comprising: a bypass passage, the bypass passage is defined between a high pressure chamber and a low pressure chamber, a pressure leading path is branched halfway through the bypass passage, a fixed aperture is disposed at a position located nearer to the high pressure chamber that a branched section of the pressure leading path, the pressure leading path is connected to a primary side of a relief valve, an automatic shut off mechanism is connectively linked by relieved hydraulic operating fluid that is disposed on a secondary side of the relief valve, the automatic shut off mechanism is constructed such that air supply to an air motor is stopped upon operation of the automatic shutoff mechanism, a relief pressure regulating means for regulating a relief pressure in the pressure relief valve is disposed between a primary side and a secondary side of the relief valve. 
     According to another embodiment of the invention, there is provided a a control unit further comprising: a fixed aperture , the fixed aperture being disposed at a position located on a side nearer to a low pressure chamber than a branched section of a pressure leading path is a bypass passage. 
     The above, and other objects, features and advantages of the present invention will become apparent from the following description read in conjunction with the accompanying drawings, in which like reference numerals designate the same elements. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic diagram showing a control unit for a hydraulic impact wrench according to an embodiment of the present invention. 
     FIG. 2 is a whole sectional view, in longitudinal sectional, showing an embodiment of the control unit for hydraulic impact wrench of FIG.  1 . 
     FIG. 3 is a partial sectional view, in the longitudinal section, showing an essential part of the control unit for hydraulic impact wrench of FIG.  2 . 
     FIG. 4 is a cross-sectional view showing a conventional control unit for hydraulic impact wrench. 
     FIG. 5 is a sectional view, in the longitudinal section, showing the conventional control unit for a hydraulic impact wrench. 
    
    
     DETAILED DESCRIPTION OF INVENTION 
     Referring to FIGS. 1 and 2, a hydraulic impact wrench, shown generally at  100 , includes a grip section  1  and a main body casing  10 , extending in a horizontal direction on the upper end of grip section  1 . Grip section  1 , contains an air intake port  2 , and operating lever  3 . The rear side portion of main body casing  10  contains a vane type air motor  11 . A front side portion of main body casing  10  contains a pulsed torque generating mechanism  20  driven by rotor  12  of air motor  11 . A main shaft  22  extends from the extreme end portion of main body casing  10  to an attachment section for an attachment (not shown) on the distal end. 
     Pulsed torque generating mechanism  20  may be similar to a conventional mechanism containing a cylinder casing  21  and main shaft  22 . Cylinder casing  21  is rotatively driven by rotor  12  of air motor  11 . Cylinder casing  21  forms hydraulic operating fluid cylinder  23 . A sectional contour of oil cylinder  23 , as shown in FIG. 1, describes a pair of circular arcs juxtaposed with centers displaced to slightly eccentric positions from the rotation center of main shaft  22  and smoothly aligned to each other forming an elliptical configuration. 
     Sealed portions  23   a ,  23   b ,  23   c , and  24   d , extending along the axial direction of oil cylinder  23 , are defined at substantially quadrisected positions on the inner circumferential surface of oil cylinder  23 . Oil cylinder  23  is filled with a hydraulic operating fluid. 
     Referring now also to FIG. 3, a proximal end portion of main shaft  22  is inserted in and disposed on oil cylinder  23 . A blade groove  24 , is defined by the site corresponding to the disposition of the proximal end portion of main shaft  22  and oil cylinder  23 . A pair of blades  25 ,  25  are placed slidably in blade groove  24 . Blades  25 ,  25  are energized by spring  26  to project outwardly in a diametrical directions. The extreme end portions of respective blades  25 ,  25  are in slidable contact with the inner circumferential wall of oil cylinder  23 . Seal portions  22   a  and  22   b  are disposed at right angles to blades  25 ,  25 . As seal portions  22   a  and  22   b  on main shaft  22  come into contact with seal portions  23   b  and  23   b , blades  25  and  25  are urged into contact seal portions  23   a  and  23   c  of oil cylinder  23 . 
     Referring specifically to FIG. 1, when cylinder casing  21  is rotated by air motor  11 , a relative rotating position, defined between main shaft  22  and oil cylinder  23  is reached. The respective seal portions  22   a ,  22   b  and distal portions of respective blades  25 , 25  reach a position where all portions are in contact with respective seal portions  23   a ,  23   b ,  23   c , and  23   d , of oil cylinder  23 . Hydraulic operating fluid is allowed to flow to both sides of respective blades  25 ,  25  to define a high pressure chamber H. Low pressure chamber L is defined opposite high pressure chamber H by respective to blades  25 ,  25 . Low pressure chamber L contains a lower pressure than the pressure in high pressure chamber H. Pulsed high pressure torque is produces by the periodic containment of the hydraulic operating fluid, as described above. The pulsed high pressure acts upon the main shaft  22  to apply pulsed torque to a member to be torqued. It is to be noted that the torque pulse is generated once per rotation of cylinder casing  21 , the same as in a conventional hydraulic impact wrench. 
     As shown in FIG. 3, bypass passage  27  communicates fluid between high pressure chamber H and low pressure chamber L. Bypass passage  27  is composed of a pair of fixed apertures  27   a ,  27   b  and part of pressure leading path  28 . Pressure leading path  28  extends along the axial direction of cylinder casing  21 . Fixed aperture  27   a , having a diameter small enough to restrict flow therethrough, communicates between pressure leading path and high pressure chamber H. Fixed aperture  27   b , also having a diameter small enough to restrict flow therethrough communicates pressure between leading path  28  and low pressure chamber L. Pressure leading path  28  leads to a top cover  29  of oil cylinder  23 . Pressure leading path  28  is connected to a primary side of a relief valve  31  inside top cover  29 . Relief valve  31  includes a ball  32  and a spring  33 . Ball  32  is resiliently urged into contact with an opening of pressure leading path  28  by the spring constant of spring  33 . 
     A cylinder chamber  35  is defined at the shaft center position of the top cover  29  of oil cylinder  23 . Cylinder chamber  35  is communicated with a secondary side of relief valve  31 . Cylinder chamber  35  communicates with a spring chamber  34  containing spring  33 . A piston  36  is slidably disposed in cylinder chamber  35 . A rod  37  is connected to piston  36 . Rod  37  passes through the shaft center portion of rotor  12  of air motor  11 . Rod  37  extends to the rear end portion of hydraulic impact wrench  100 . 
     As shown in FIG. 2, rear end portion of rod  37  abuts a ball valve  38 . Ball valve  38  urges a ball  40  and rod  37  toward the extreme end of hydraulic impact wrench  100 . Ball valve  38  is opened by forcible movement of ball  32  against the force of spring  39 , thereby supplying air to automatic shutoff mechanism  41 . This operates automatic shutoff mechanism  41 . 
     As shown in FIG. 3, relief valve  31  includes primary port  42 , ball  32 , and spring  33 , aligned with each other in the diametrical direction in top cover  29 . Spring  33  is pressed against primary port  42  by a relief pressure regulating means  43 . Relief pressure regulating means  43  regulates relief pressure. Relief pressure regulating means  43  is free to advance and retreat in the diametrical direction in top cover  29 . Relief pressure regulating means  43  is adjustable from outside top cover  29  by tightening to increase relief pressure or loosening it to reduce relief pressure, both by changing the force applied by spring  33 . Access for adjustment of regulating means is provided by removing removable stopper  45  from operating hole  44 . In this manner, torque is adjusted by adjusting the relief pressure controlled by relief valve  31 . 
     When air motor  11  is rotated by operating a control lever, cylinder casing  21  rotates. A pulse of torque is generated once per rotation of cylinder casing  21 , so that members to be torqued such as bolts, and nuts are torqued. During operation, the peak pressure produced in the high pressure chamber H, and the peak pressure in pressure leading path  28  both increase simultaneously. When peak pressure exceeds a predetermined value of pressure, relief valve  31  is opened against the force of spring  33 . Piston  36  in cylinder chamber  35  is forcibly moved by hydraulic operating fluid relieved into spring chamber  34 . Thus, transfer of rod  37 , opening of ball valve  38 , and operation of automatic shutoff mechanism  41  are carried out in order, and air supply to air motor  11  is stopped by operation of automatic shutoff mechanism  41 , so that torque generation is stopped automatically. As described, operation is automatically stopped, in the above described hydraulic impact wrench, when the peak pressure in high pressure chamber H exceeds a predetermined value of pressure. This effects the generation of a constant impact torque. 
     Referring to FIG. 3, in the hydraulic impact wrench, a spring force of spring  33  in relief valve  31  is adjusted for changing a setting the value of pulsed torque. More specifically, the position relief pressure regulating means  43  is screwed in or out to adjust the force on spring  33 . As a result, the pressure point at which relief valve  31  operates is adjusted. 
     In the prior art hydraulic impact wrench, two characteristic properties are adjusted. These properties are the peak pressure produced in high pressure chamber H and the relief pressure. In the present invention, only the relief pressure requires adjustment by adjusting the pressure setting of relief valve  31 . Accordingly, pulsed torque is controlled in the present invention with high precision and in a simple structure. 
     Having described preferred embodiments of the invention with reference to the accompanying drawings, it is to be understood that the invention is not limited to those precise embodiments, and that various changes and modifications may be affected therein by one skilled in the art without departing from the scope or spirit of the invention as defined in the appended claims. For example, although the above description, operates automatic shutoff mechanism  41  by operating piston  36 , rod  27  of relief valve  31 , any of other suitable technique may be substituted therefore without departing from the spirit and scope of the invention.