Patent Publication Number: US-6666283-B2

Title: Hand held power tool

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates generally to hand held power tools. 
     Hand power tools are known and widely utilized. In order to avoid uncontrollable rotation of a hammer drill which is held by a user during blocking a drill or a drill crown in a masonry, it is known to connect the drill or the drilling crown with a drive of the hammer drill through a safety coupling. The safety coupling opens when the drill is blocked. 
     German patent document DE 38 32 202 C1 discloses a hand power tool with such a safety coupling. The safety coupling for transmission of torque has a first radially inner coupling part and a second coupling part which surrounds the first coupling part. The coupling parts are connected with one another through arresting elements which are formed as rollers. The rollers are guided in a first coupling part in guiding passages. Springs are arranged in the guiding passages and are supported at their first ends against a passage bottom. With their second ends, they act radially outwardly on the rollers in direction to the second coupling part and press the rollers into the recesses of the second coupling part. When a predetermined torque is exceeded, the rollers are pressed radially inwardly from the recesses against the springs and open the safety coupling. The rollers slide subsequently over the recesses. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is an object of present invention to provide a hand power tool which is a further improvement of the existing hand power tools. 
     More particularly, it is an object of the present invention to provide a hand power tool with at least one safety coupling in a drive train which for transmission a torque around a rotary axis has at least two coupling elements connected with one another through an arresting element loaded by a spring and held in a guiding passage, which interrupts arresting in response to exceeding of a predetermined torque. 
     In keeping with these objects and with others which will become apparent hereinafter, one feature of present invention resides, briefly stated, in a hand power tool of the above mentioned type, in which the spring is supported in direction of the arresting element through a guiding element, which is non rotatably guided through guiding surfaces in the guiding passage at least around an axis extending parallel to the rotary axis. 
     A bending moment transmitted from the arresting element to the spring, a buckling of the spring, a contact of the spring with a passage wall and thereby loading and a spring breakage can be avoided, and a long service life can be obtained, in particular for fast rotating hand power tools. 
     The guiding passages can be produced by various methods and can have various cross-sections, for example round, ellipsoidal or conical cross-sections. The guiding passages can be for example drilled or sintered, and the guiding passages which are sintered can be formed for example with corners. 
     The spring can be supported in direction of the arresting element through various supporting surfaces which are shaped in a known manner, for example through a curved, concave and/or convex supporting surfaces. A tilting moment caused by the supporting surface can be avoided in a structurally simple and cost favorable manner by a flat supporting surface, whose normal line extends parallel to an actuating direction of the guiding element in the guiding passage. 
     In accordance with a further embodiment of the present invention, the spring at its end which faces the guiding element and/or at its end which faces away from the guiding element, is guided through a short recess and/or a short projection. The spring can be exactly positioned during mounting, and then during operation held in its position. The spring over its whole length can operate free without guidance. The guiding passage can be formed with a sufficient distance from the spring with its side walls, in the case of open safety coupling, or in other words with compressed spring. A contact between the side walls of the guiding passage and the spring, as well as friction and wear can be avoided, and a long service life can be provided. 
     In accordance with a further embodiment of the present invention, it is further proposed that the spring is oriented parallel to the side walls of the guiding passage. An equal distance between the spring and the side walls can be provided over the length of the spring, and in space economical manner, a contact between the spring and the side walls can be avoided. 
     When the elastic element is formed as a component which is rotatable around an axis extending parallel to the rotary axis, the friction and wear between the arresting element and the corresponding coupling element is reduced by a rolling movement. For saving additional components, mounting expenses and costs, the arresting element or the guiding element can be formed of one piece with one another. Furthermore, when the guiding element and the arresting element are formed of one piece, a gap-free connection between the arresting element and the guiding element can be provided. 
     The spring can act on the guiding element through one or several components or preferably directly. Additional components, structural space and costs can be therefore saved. 
     In accordance with another embodiment of the present invention, the arresting element can be pressed by the spring against an operational curve, on which the arresting element is always guided with a simple linear contact, and preferably through a linear contact which extends perpendicular to a movement direction of the arresting element. 
     The arresting element, in the case of the open safety coupling, can be guided along the operational curve in a strike-free manner. Sudden movements of the arresting element, the guiding element and the spring and thereby resulting spring breakage can be avoided, and in particular the settling phenomena of the spring can be reduced. 
     A hydrodynamic sliding film of lubricant can be provided between the arresting element and the operational curve. For this purpose the arresting element is supported on the operational curve, so that between the curve and the arresting element a diverging gap is formed in a movement direction of the arresting element. 
     The novel features which are considered as characteristic for the present invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a view showing a section of a safety coupling of an inventive hand power tool, in a closed condition; 
     FIG. 2 is a view showing the safety coupling of FIG. 1, in an open condition; 
     FIG. 3 is a view showing a section taken along the line III—III in FIG. 1; 
     FIG. 4 is a view showing a portion identified with reference IV in FIG. 1 on an enlarged scale; 
     FIG. 5 is a view showing a portion of a view as seen in direction  5  in FIG. 4; and 
     FIG. 6 is a view showing another variant of the embodiment of FIG. 4 for the inventive hand power tool. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 is a view showing a safety coupling  10  of a hammer drill, which has two coupling elements  14 ,  16  for transmission of a torque around a rotary axis  12 . The coupling elements include a coupling disk  16  which is connected to the shaft  46  through a press fit, and a spur tooth gear  14  which surrounds the coupling disk and is rotatably supported on the shaft  46 . The coupling disk  16  and the spur tooth gear  14  are connected with one another through seven arresting elements  22 . The arresting elements  22  are symmetrically distributed from the periphery. They are loaded with a spring  18  and held each in a guiding passage  20 . The guiding passages  20  are formed in the coupling disk  16  during sintering and have a rectangular cross-sectional surface. 
     In accordance with the present invention, the spring  18  are each supported in direction of the arresting element  22  on guiding pistons  26  which are formed of one piece with the arresting element  22 . The guiding pistons  26  are non rotatably guided via guiding surfaces  30  in the guiding passage, in particular around an axis extending parallel to the rotary axis  12 . The guiding pistons  26  have a rectangular cross-sectional surfaces which corresponds to that of the guiding passages  20 . 
     The spring  18  is supported in direction of the arresting element  22  on a flat supporting surface  32 , and is supported in direction facing away from the arresting element  22  on a flat supporting surface  48 , whose normals extend parallel to a movement direction  34  of the guiding piston  26  in the guiding passage  20 , as shown in FIGS. 1,  3 ,  4 . Furthermore, the spring  18  is oriented parallel to the side walls  40  of the guiding passages  20 . Inclines  50 ,  52 , for removing of the extruding coupling disk  16  and the spur tooth gear  14  from the mold, are shown in FIG.  3 . With the orientation of the supporting surfaces  32 ,  48  and the side walls  40  over the spring  18  taken into consideration, they are formed so that the movement direction  34  of the guiding piston  26  in the guided passage  20  encloses an angle  54  less than 90° to the rotary axis  12 . 
     The spring  18  is guided with a first end in a short, cylindrical recess  36  in the guiding piston  26 , and with a second, opposite end is guided in a short, cylindrical recess  38 . A guiding passage  20  extends conically toward the recess  38 , which is produced by drilling. 
     The arresting elements  22  can be pressed by the springs  18  radially outwardly against an operational curve  42  which is formed at the radially inwardly facing side of the spur tooth gear  14 . During a conventional operation, the arresting elements  22  are held on cams  56  of the operational curve  42 . When a predetermined torque is exceeded, for example when a drill of the hammer drill is blocked in a masonry, the arresting elements  22  are displaced with the guiding piston  26  in the guiding passages  22  against the springs  18  radially inwardly in the movement direction  34  as shown in FIG.  2 . The guiding passages  20  with their side walls have a sufficient distance from the springs  18  in the case of open safety coupling  10 , or in other words with the springs  18  are compressed. This reliably prevents contact of the springs  18  with the side walls  40  of the guiding passages  20 . 
     The arresting elements  22  are supported on the operational curve  42  always through a simple linear contact which extends perpendicular to a movement direction  60  of the arresting elements  22 . Thereby a jumpy movement of the arresting elements  20 , the guiding pistons  26  and the springs  18  during running over the cams  56  is avoided, as can be seen from FIG.  5 . Between the arresting element  22  and the operational curve  42  a gap  44  which diverges in the movement direction  60  of the arresting element  22  is provided. Therefore, a hydrodynamic sliding film can be formed between the arresting elements  32  and the operational curve  42  by a lubricant in the open condition of the safety coupling, as can be seen from FIG.  4 . 
     FIG. 6 shows an arresting element  24  which is formed as a roller. It is supported in a calotte of a guiding piston  28 . Substantially similar components are identified basically with the same reference numerals. Furthermore, similar features and operations corresponding to the embodiment of FIGS. 1-5 are not repeated. 
     In this embodiment the arresting element  24  which is formed as a roller can rotate around an axis extending parallel to the rotary axis  12 . Thereby the friction between the operational curve  42  and the arresting element  24  can be reduced. The guiding piston  28  is provided up to the arresting element  24 , in correspondence with the guiding piston  26 . It is non rotatably guided through the guiding surface  30  in the guiding passage  20 , in particular around the axis extending parallel to the rotary axis  12 . 
     It will be understood that each of the elements described above, or two or more together, may also find a useful application in other types of constructions differing from the types described above. 
     While the invention has been illustrated and described as embodied in hand held power tool, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirit of the present invention. 
     Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can, by applying current knowledge, readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention.