Abstract:
An implement having a drive motor and a tool is provided. A drive shaft is mounted in a guide tube and interconnects the drive motor and tool for rotatingly driving the tool. The drive shaft includes a main member in the form of a hollow shaft having ends on which are disposed respective extensions that form a coupling connection for a positive engagement with coupling components of the drive motor and of the tool.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application is a continuation-in-part of application Ser. No. 09/549,767 filed Apr. 14, 2000, now abandoned. 

   BACKGROUND OF THE INVENTION 
   With implements such as brush cutters or the like, the tool is disposed at the end of a guide tube. The drive motor is customarily disposed at the rear end of the guide tube and drives the tool by means of a drive shaft mounted in the guide tube. In order to transfer torque, the drive shaft is coupled not only with a drive motor but also with the tool, with the free ends of the drive shaft having coupling connections that operate in a positively engaging manner. 
   It is an object of the present invention to improve an implement of the aforementioned general type in such a way that the weight of the implement is reduced. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     This object, and other objects and advantages of the present invention, will appear more clearly from the following specification in conjunction with the accompanying schematic drawings, in which: 
       FIG. 1  shows a brush cutter with a drive shaft mounted in the guide tube; 
       FIG. 2  is a partially cross-sectioned view of the drive shaft; 
       FIG. 3  is a plan view of an extension for the drive shaft; and 
       FIG. 4  is a cross-sectional view through a drive shaft in the region of the extension. 
   

   SUMMARY OF THE INVENTION 
   The implement of the present invention is characterized primarily in that the drive shaft includes a main member in the form of a hollow shaft, the ends of which carry extensions that form the coupling connection. 
   The hollow shaft, at a considerably lower weight, can transfer the same torque as can a comparable drive shaft having a solid cross-section. In particular for implements having long drive shafts, the use of a hollow shaft for driving a tool can reduce the weight of the implement. The inventive drive shaft includes a main member in the form of a hollow shaft, the ends of which carry extensions that form the coupling cross-section. The extensions, which during operation of the implement are exposed to high stresses as coupling pieces, are therefore made of wear-resistant material. 
   The hollow main member of the drive shaft is expediently made of a light material, especially or aluminum alloys. Fiber-reinforced polymeric materials, such as CFK, are also particularly suitable. The extensions have an extending axially coupling extension that in the installed state of the drive shaft are brought into operative engagement with corresponding cooperating coupling components of the motor and on the side of the tool. The coupling extensions have other than a circular cross-sectional configuration that is expediently symmetrical with respect to an angle of rotation and is therefore particularly easy during assembly of the drive shaft to bring into overlapping engagement with the cooperating coupling component. A polygonal, expediently square cross-sectional configuration is quite favorable with respect to torque transfer, resistence to wear, and for manufacture. The extensions on the light metal hollow shaft are advantageously made of steel, in which connection it is further proposed that the extensions be hardened, at least in the region of the coupling extensions. 
   On that side of the extensions disposed opposite from the coupling extensions is a shaft with which the extensions are secured in the interior of the hollow shaft. In this way, the extensions are easy to assemble thereby ensuring a reliable torque transfer between the hollow shaft and the extensions. The shaft of the extensions is expediently screwed or threaded into the end portion of the hollow shaft. However, it can also be advantageous to provide the shaft with a knurling or to press it into the hollow shaft or to provide a press connection via swaging. The connection between the extensions and the hollow shaft can be axially secured by gluing the shaft in. 
   Further specific features of the present invention will be described in detail subsequently. 
   DESCRIPTION OF PREFERRED EMBODIMENTS 
   Referring now to the drawings in detail,  FIG. 1  shows a manually guided brush cutter  1  for mowing grass, undergrowth or the like. The brush cutter  1  is provided with an internal combustion engine  2 , which is disposed at the back end  14  of a guide tube  3 . Mounted in the guide tube  3  is a drive shaft  4  by means of which the internal combustion engine  2  rotatingly drives the cutting tool  5  at the front end  13  of the guide tube  3 , in the present case a cutting blade or a cutting filament head. The brush cutter  1  is carried by an operator  15  by means of a belt or harness system  16 . Mounted on the guide tube  3  is a control handle  17 , the hand grips  18  disposed at the ends of which can be grasped by the operator in order to be able to move the cutting tool  5  back and forth over the area that is to be mowed in the direction of the arrow  19 . The control elements for the internal combustion engine  2 , such as a gas lever and the like, are also disposed in the hand grips  18  for guiding the brush cutter. 
     FIG. 2  shows the drive shaft  4  of the brush cutter; the free ends  21  of the drive shaft  4  are each provided with a coupling extension  8  that operates in a positively engaging manner. In the installed state of the drive shaft  4 , the coupling sections disposed at the ends thereof cooperate with correspondingly shaped coupling counter pieces on the driven end (the cutting tool) and on the drive end (the internal combustion engine). 
   The drive shaft  4  includes a hollow shaft  7  as a base member that with its ring-shaped cross-sectional configuration can, at comparatively less weight, transfer greater torque than can a drive shaft having a solid cross-sectional configuration. The hollow shaft  7  is made of aluminum or some other light metal material, as a consequence of which there results together with the feature of the hollow cross-sectional configuration a very low overall weight of the drive shaft accompanied by high strength. The ends  20  of the hollow shaft  7  carry extensions made of wear-resistant material, in the present case, steel. For a positive transfer of torque, the extensions  6  are provided with coupling extensions  8  having a square coupling cross-section. By means of a shaft  9  that is disposed on the side opposite from the coupling extensions  8 , the extensions  6  are guided into the interior of the hollow shaft, where they are secured. In the illustrated embodiment, the extensions  6  are threaded into the end sections of the hollow shaft  7 . As an alternative to being provided with a thread, the shaft  9  of the extensions  6  can also be provided with a knurling or the extension  6  can be pressed into the hollow shaft or can be inserted by swaging. The press connection between the extension  6  and hollow shaft  7  can be axially secured by adhesion. 
   The extensions are made of steel and are hardened, for example, via case hardening. This counteracts the occurrence of wear at the coupling extensions  8 . In addition to the low weight of the drive shafts, the inventive configuration with a hollow shaft main member of aluminum has a particularly advantageous elastic torsion spring effect. If during operation of the brush cutter the cutting tool strikes an obstacle, the thereby resulting sudden stress is further transferred to the internal combustion engine in a gently dampened manner. Furthermore, few vibrations are generated during operation of the brush cutter due to the low torsional rigidity of the aluminum shaft. 
   The length by which the shaft  9  of the extension  6  can be threaded in is delimited by a radial stop or abutment  10 . As the extensions  6  are threaded into the hollow shaft  7 , the stop  10  comes to an axial rest against an abutment of the shaft main member  7 . The extensions  6  are expediently mounted by means of a mounting sleeve  11 , each of which receives an end  20  of the hollow shaft  7 . By means of an inwardly extending collar, the mounting sleeves  11  are axially braced between the stop  10  of the extension  6  and the end faces of the ends  20  of the aluminum shaft. The sleeves  11  extend about the ends of the shaft and have a diameter that is greater than the diameter of the shaft. The stop  10  of the extensions  6  has a circular configuration and lines up approximately with the sleeve. The sleeves  11  secure the extensions  6  on the ends of the shaft, and preclude damage to the screw threads in the hollow shaft. 
     FIG. 3  shows an enlargement of an extension  6  as it has been illustrated in  FIG. 2  threaded into the end portion of the hollow aluminum shaft  7 . To facilitate illustration, the same reference numerals have been used in all of the drawing figures for the same features. The shaft  9  of the extension  6 , which is threaded into the hollow shaft, is provided in sections with a self-tapping or self-grooving thread  12 . The free end of the shaft  9 , which during assembly is initially introduced into the end of the hollow shaft, is not provided with a thread, although it can also be expedient to provide the thread over the entire length of the shaft  9 . Thread or screw connections are also conceivable where the end portions of the hollow shaft are provided with a thread, for example with a metric thread, before the correspondingly threaded extension  6  is screwed in. 
   The connection between the extension  6  and the hollow shaft  7  has a special configuration. 
   The extension  6  is divided into five sections, namely the coupling extension  8  that forms one end, the stop or abutment  10 , a non-threaded central section  22 , a threaded section  23  that is provided with the thread  12 , and the guide shaft  9 , which forms the other end of the extension  6 . 
   Placed onto the mounting end  20  of the hollow shaft  7  is the sleeve  11  which, via a radially inwardly extending collar  24 , is disposed between the end face of the mounting end  20  of the hollow shaft  7 , and the axial stop  10  of the extension  6 . 
   To mount the extension  6  in the end  20  of the hollow shaft  7 , the sleeve  11  is first placed onto the mounting end  20 . The sleeve  11  is intended to prevent an expansion of the end  20 . A critical feature is the radial collar  24  that is disposed between the axial stop  10  and the end face of the mounting end  20 . The guide shaft  9  is now inserted into the mounting end  20 , whereby the length of the guide shaft ensures a coaxial alignment of the extension  6  relative to the axis of the hollow shaft  7 . 
   After insertion of the guide shaft  9 , the thread  12  of the threaded section  23  comes into engagement with the end  20  of the hollow shaft  7 . This thread  12  is, as mentioned previously, a self-tapping or self-grooving, polygonal thread, which cuts into the inner wall of the hollow shaft  7 . 
   The axial stop  10  delimits the depth to which the thread  12  can be screwed into the hollow shaft  7 , whereby the non-threaded section  22  is disposed between the threaded section  23  and the stop  10 . The central section  22  extends into the mounting end  20  of the hollow shaft  7 , whereby after the thread  12 , and hence the threaded section  23 , have been threaded into the hollow shaft  7  as far as they can go (being delimited by the stop  10 ), the mounting end  20 , which has been slightly elastically expanded due to the thread  12 , carries out a return deformation and thus engages the thread  12  from behind in a positive manner. As a result, the extension  6  can be screwed out only with an appropriate application of force; this denotes a protection against the screwing-out of the thread  12  out of the hollow shaft  7 . 
   The thread  12  is screwed into the hollow shaft  7  to such an extent that the collar  24  of the sleeve  11  is securely clamped between the stop  10  and the end face of the mounting end  20 . During each rotation of the hollow shaft  7  via the extension  6 , the extension is moved in the sense of a tightening relative to the hollow shaft  7 . Since the sleeve  11 , and the collar  24 , protect the mounting end  20  of the hollow shaft  7 , a working of the stop  10  into the material of the hollow shaft  7  is reliably prevented. Even after a number of hours of operation, a fixed connection is ensured between the extension  6  and the hollow shaft  7 . 
   The specification incorporates by reference the disclosure of German priority document 199 17 238.2 of Apr. 16, 1999. 
   The present invention is, of course, in no way restricted to the specific disclosure of the specification and drawings, but also encompasses any modifications within the scope of the appended claims.