Patent Publication Number: US-6988939-B2

Title: Hand-guided electric tool comprising a guard

Description:
BACKGROUND OF THE INVENTION 
   The invention is based on a hand-guided electrical tool with a housing and a guard hood. 
   Right angle grinders with a guard hood are known, whose clamping strap has a projection on the inside. The clamping strap of the guard hood can be attached to a receiving collar, which is disposed around a spindle axle for a rotating insert tool. The projection engages in a groove in the receiving collar of the machine. As a result, the projection assures that the guard hood does not detach from the receiving collar during operation. This is also the case even if the locking element, which presses the clamping strap against the receiving collar, opens. This increases the safety of the right angle grinder and reduces the risk of injury that it represents since the guard hood cannot fall off. For example, it is known to use screws, quick-action levers, or the like as locking elements. It is also known to bring projections of different widths on the clamping strap into engagement with correspondingly embodied grooves in the receiving collar of the machine. The combination of various projections produces a coding so that particular guard hoods only fit particular machines with a receiving collar adapted to them. As a result, a guard hood with a particular diameter can only be used in connection with a particular tool diameter. In addition, this permits a guard hood to be matched to a corresponding machine, which has a particular speed of the insert tool. Usually in small right angle grinders or single-handed right angle grinders, the receiving collar of the machine is only slightly bigger than a support flange, which supports the insert tool on its side oriented toward the machine. As a result, in order to mount the guard hood on the right angle grinder, it is first necessary to remove the support flange since the internal projections of the clamping strap do not fit over the support flange. After the guard hood has been mounted, the support flange must be reattached to the right angle grinder. This is a very time-consuming process. In right angle grinders that have a quick-action attachment in the support flange, it is impossible for the user to remove the support flange. Such devices cannot be equipped with guard hoods that have a projection oriented toward the machine. 
   SUMMARY OF THE INVENTION 
   An electrical tool according to the invention has the advantage over the prior art that the guard hood provided with the features according to the invention can also be mounted on an electrical tool, a particular a right angle grinder, whose support flange cannot be removed and in which the support flange diameter is only slightly smaller than the diameter of the machine&#39;s receiving collar for the guard hood. This is made possible by virtue of the fact that the clamping strap is slid with its recess over the protrusion of the receiving collar until it is situated entirely beneath the protrusion and is then rotated around the drive axis in relation to the receiving collar, and by virtue of the fact that the guard hood has no elements, which have a smaller diameter than that of the receiving collar. As a result, beneath the protrusion, there is a region of the clamping strap in which the clamping strap does not have any recess. Consequently, the guard hood is prevented from moving out of the way in the axial direction. The free rotation of the clamping strap in relation to the receiving collar is assured by virtue of the fact that the width of the clamping strap corresponds approximately to the distance between the protrusion and the housing. 
   It is advantageous if the protrusion and the recess are disposed so that the guard hood can be slid over the protrusion only in a position in which it does not make sense to operate the electrical tool. This prevents the guard hood from unintentionally coming off when it is in the working position, even when the clamping element is released. This increases user safety and reduces the risk of injury. 
   It is also advantageous if the protrusion and/or the recess are the shape of circular segments in the axial direction of the spindle axle. Such a design is particularly easy to produce and is also safe to use. 
   It is also advantageous if the clamping element forms recess. As a result, the clamping element can be used to slide over the protrusion on the receiving collar. Such an embodiment is particularly easy to produce since the clamping element is as a rule embodied as a moving part, which is particularly easy to provide with such a shape. 
   It is also advantageous if the electrical tool has a number of protrusions and recesses, which are disposed at reciprocally matched distances. In a particularly advantageous manner, this makes it possible for the guard hood to be coded for use with particular electrical tools. In principle, the same shape can be used here for all of the protrusions and recesses, but a large number of different codings is still possible. In contrast to the case in which there is only a single form for the protrusion and the recess, where very complex forms would be required. 
   It is also advantageous if the protrusions and recesses each have different, reciprocally matched sizes and/or distances from one another. This makes it possible to produce still more variations for the coding of the guard hood since both the sizes and the distances can be varied. 
   It is also advantageous if the electrical tool has a support flange, which is disposed concentrically around the spindle axle and whose diameter is only slightly smaller than that of the receiving collar. This assures a good support of the insert tool, wherein the contact surface on the support flange is enlarged in relation to the prior art. Previously, because of the projections pointing inward from the clamping strap, either the support flange had to be significantly smaller than the receiving collar or else the support flange had to be removed in order to install the guard hood. 
   The invention will be explained in detail in the description below in conjunction with an exemplary embodiment shown in the drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  shows a top view of a guard hood according to the invention, 
       FIG. 2  is a perspective view of the guard hood from  FIG. 1 , 
       FIG. 3  is a top view of a housing of a right angle grinder with a receiving collar according to the invention, 
       FIG. 4  is a perspective view of the housing of the right angle grinder from  FIG. 3 , 
       FIG. 5  is a top view of a right angle grinder with the housing of  FIGS. 3 and 4  and with the guard hood of  FIGS. 1 and 2  in its installed position, 
       FIG. 6  is a perspective view of the right angle grinder from  FIG. 5 , 
       FIG. 7  is a top view of the right angle grinder with the guard hood in a first working position, and 
       FIG. 8  is a top view of the right angle grinder from  FIG. 7 , whose guard hood is disposed in a second working position. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENT 
   In the following, identical parts are provided with the same reference numerals. 
     FIGS. 1 and 2  show two views of a guard hood  1  for a hand-guided electrical tool  3 , in the current instance a right angle grinder ( FIGS. 5  to  8 ). The guard hood  1  has a flat, semicircular hood part  18 , to which a clamping strap  16  is attached by means of a transition  15  so that between the clamping strap  16  and the hood part  18 , an opening  10  is formed. This opening  10  has a changeable area F. A clamping element  13 ,  14  is affixed to the clamping strap  16  in order to change the area F. The clamping strap  13 ,  14  here is comprised of a clamping lever  13 , which is rotatably supported on a first end  19  of the clamping strap  16 , and, by means of a spring  14  rotatably supported on the clamping lever  13 , cooperates with a second end  17  of the clamping strap  16 . The second end  17  is curved so that it forms a counterpart support for the spring  14 . When the clamping lever  13  is rotated, this changes the area F of the opening  10  by moving the two ends  19 ,  17  of the clamping strap  16  either closer together or further apart from each other. This principle is known and is therefore not discussed in detail here. 
   The clamping strap  16  is not embodied in the shape of the circumference surface of a cylinder, which would correspond to an unchanged second diameter d 2  of the opening  10 , but rather has several recesses  12 , in which a first diameter d 1  of the opening  10  is greater than the second diameter d 2 . In the exemplary embodiment depicted, three recesses  12  are embodied on the clamping strap  16 . These are the shape of circular segments when viewed from above. In addition, the region of the clamping element  13 ,  14  is likewise embodied as a recess  12 . This is achieved by virtue of the fact that the clamping strap  16 , in the vicinity of its second end  17 , is not formed along a circular arc of the opening  10 , but is bent outward away from the center of the opening  10 . 
   The clamping strap  16  has a width b and is fastened to the hood part  18  in the usual, known manner. In the vicinity of the hood part  18  that adjoins the cylindrical region in which the hood part  18  is attached to the clamping strap  16 , a transition region  15  is provided. In the current exemplary embodiment, this transition region  15  is embodied in the form of a radius r. The geometry of the transition region is significant for preventing detachment in the event of a released clamping element  13 ,  14 , which will be explained in more detail in the description relating to  FIGS. 5 and 6 . 
     FIGS. 3 and 4  show two views of a housing  2  for a right angle grinder  3  ( FIGS. 5  to  8 ). A receiving collar  20  is disposed concentrically around a spindle axle  5  and is used to fasten the guard hood  1  to the housing  2 . Over most of its area, the receiving collar  20  has a diameter that corresponds to the second diameter d 2  of the guard hood  1  when the clamping element  13 ,  14  is closed. A number of protrusions  21  protrude beyond this second diameter d 2 , outward in the radial direction from the spindle axle  5 . These protrusions have the shape of circular segments. A total of four protrusions  21  are provided, whose shape corresponds to that of the indentations  12  on the clamping strap  16 . At the same time, the number of protrusions  21  corresponds to the number of indentations  12 . In the axial direction, the receiving collar  20  has a height h, which essentially corresponds to the width b of the clamping strap  16 ; the height h can be slightly greater than the width b. The protrusions  21  are embodied in the axial direction on the housing  2  so that they constitute the negative form of the transition region  15  of the guard hood  1 . 
   A support flange  4  is also embodied concentric to the spindle axle  5  and serves to support an insert tool (not shown). This support flange  4  has a diameter that is only slightly smaller than the second diameter d 2  of the clamping strap  16  in its closed position. 
     FIGS. 5 and 6  show two views of a right angle grinder  3 ; the guard hood  1  is shown in a position in which it is mounted directly onto the housing  2 . The clamping strap  16  here is shown in its open position, i.e. the area F of the opening  10  is at its greatest in this position. The protrusions  21  of the receiving collar  20  and the recesses of the clamping strap  16  are respectively embodied as a positive and negative form. Both the recesses  12  and the protrusions  21  have an identical distance a between respective adjoining elements. It is therefore possible for the opening  10  of the clamping strap  16  to be slid over the receiving collar  20  until the entire width b of the clamping strap  16  lies beneath the protrusions  21  of the receiving collar  20 , i.e. within the height h of the receiving collar  20 . The position of the guard hood  1  in relation to the housing  2  of the right angle grinder  3  is selected so that the right angle grinder  3  cannot be logically used for either cutting or grinding. The reciprocally matched protrusions  21  and recesses  12  also permit the guard hood  1  to be mounted only in this one special position. In any other position of the guard hood  1  in relation to the housing  2 , it is not possible to slide the clamping strap  16  over the protrusions  21  of the receiving collar  20  since they do not coincide with the recesses  12  of the clamping strap  16 . Through the embodiment of the protrusions  21 , which point away from the spindle axle  5 , and the recesses  12 , which likewise point away from the spindle axle  5 , it is also possible to mount the guard hood  1  on a right angle grinder  3  that has a wide support flange  4 . Even with a support flange  4  that has a diameter, which is only slightly smaller than the second diameter d 2 , it is possible to mount the guard hood  1  without first having to remove the support flange  4 . From the mounting position shown in  FIGS. 5 and 6 , it is possible to switch over into one of the positions shown in  FIGS. 7 and 8  through a simple rotation of the guard hood  1 . The guard hood  1  is rotated within the area of the receiving collar  20 , which has the height h. The geometry of the protrusions  21  in the axial direction is embodied in a transition region  23  from the first diameter d 1  to the second diameter d 2 . This transition region  23  is embodied with a predetermined radius r, which corresponds to the radius r in the transition region  15  of the guard hood  1 . As a result, a positive and negative form with regard to the guard hood  1  and the receiving collar  20  are produced in the axial direction as well. As a result, the guard hood  1 , which is disposed in a working position, is secured against coming off, even when the clamping element  13 ,  14  is released. 
     FIGS. 7 and 8  show the right angle grinder  3  with the guard hood  1  in two working positions. As a rule, the right angle grinder  3  is used for grinding in the working position shown in FIG.  7  and is used for cutting in the working position shown in FIG.  8 . In the two positions of the guard hood  1  shown the recesses  12  of the clamping strap  16  are not congruent with the protrusions  21  on the receiving collar  20 . In addition, the clamping strap  16  is tightened by means of the clamping element  13 ,  14  until it rests snugly against the receiving collar  20 . The firm pressure of the clamping strap  16  against the receiving collar  20  prevents the guard hood  1  from rotating in relation to the housing  2  into the only possible mounting position depicted in  FIGS. 5 and 6 . Even if the clamping element  13 , 14  is released, the guard hood  1  cannot be detached from the receiving collar  20  since the protrusions  21  of the receiving dollar  20  and the recesses  12  of the clamping strap  16  do hot coincide with one another. In addition, the positive and negative form of the transition region  23  on the receiving collar  20  and of the transition region  15  on the guard hood  1  prevents the guard hood  1  from coming off.