Patent Publication Number: US-6905042-B2

Title: Tank for holding an operating medium

Description:
FIELD OF THE INVENTION 
   The invention relates to a tank for holding an operating medium for a drive unit, especially for an internal combustion engine of a portable handheld work apparatus. 
   BACKGROUND OF THE INVENTION 
   Tanks for holding an operating medium are known for holding operating substances such as oil or fuel which function to supply a work tool with oil or to supply fuel to an engine. A tank for an operating medium for an internal combustion engine of a portable handheld work apparatus is blown as one piece from plastic and has a fill opening and an output opening for the operating medium. The operating medium tank is provided with assembly openings for mounting on the drive unit. Attachment elements for connecting the tank to the drive unit are guided through the assembly openings. In an operating medium tank, the assembly on the drive unit is made difficult especially because of a lack of adjusting devices. In addition, the danger is present that the operating medium tank will develop a leak because of possible fractures of the assembly openings. 
   SUMMARY OF THE INVENTION 
   It is an object of the invention to provide a tank for an operating medium for a drive unit which is operationally safe while being simple to manufacture and which can be easily mounted. 
   The operating medium tank of the invention is for a drive unit including an internal combustion engine of a portable handheld work apparatus. The operating medium tank includes: a housing having a housing wall defining an interior for the operating medium; the housing wall having a fill opening and an output opening formed therein; a base on the housing wall and a lug extending from the base; the base and the lug formed as one piece from the housing wall; a receptacle on the drive unit; and, means for releasably fixing the tank with the lug to the receptacle so as to permit the tank to be mounted form-tight on the drive unit. 
   The operating medium tank is easily mounted because a preferably full wall base having a lug is formed as one piece therewith and, with the aid of the lug, the tank can be releasably fixed on a receptacle of the drive unit. 
   When a tear or fracture of the lug occurs during manipulation of the operating-medium tank, a blow causing a leak of the tank is virtually avoided because the base of the lug prevents the housing wall of the tank from breaking open. This is effected by an especially stiff and flat connection of the base to the tank or also via a configuration of the base in the form of a set break location between the lug and the housing wall. The operating medium tank can be fixed between two housing parts of the drive unit which enclose the operating medium tank. The lug functions for a preassembly of the operating medium tank to the drive unit; whereas, the housing parts of the drive unit hold the operating medium tank. 
   The operating medium tank is advantageously fixed between the housing parts of the drive unit. The housing parts partially or completely surround the operating medium tank. The housing parts are supported directly on the housing wall of the operating-medium tank. An outwardly projecting holding arm is formed on the housing wall of the operating medium tank in accordance with an advantageous embodiment thereof. It is advantageous to provide several holding arms (preferably two holding arms) which are so configured that they each extend as one piece from the housing wall in order to connect the operating medium tank at several defined locations with the drive unit. The holding arms are so arranged with respect to a longitudinal center axis of the operating medium tank that the holding arms lie approximately in planes which pass approximately perpendicularly through the longitudinal center axis of the operating medium tank. The holding arms, especially the ends of the holding arms, lie form-tight between the housing parts of the drive unit. The operating medium tank can, in this way, be preassembled in the receptacle of the drive unit with the aid of the lug. Thereafter, the operating medium tank is clamped or in another manner fixed with the holding arms between the housing parts of the drive unit. 
   Preferably, the housing parts are engine housing parts such as a crankcase made of light metal or plastic and a starter housing cover. It is advantageous to provide radial play between the lug and the receptacle in order to compensate for the play between the lug and the receptacle and for the clamp-free fixing of the operating medium tank to the drive unit. To compensate for the play, a damping element made of elastic material can be mounted radially between the lug and the receptacle. The damping element is provided as a sleeve-shaped component and is pushed over the lug and preferably has a thickening at the base end of the lug. The damping element can be produced by spraying on and securing an elastic mass on the lug. In this way, the lug is axially and radially damped with respect to the receptacle and is held in a clamp-free manner. 
   If the assembly direction of the operating medium tank is selected in approximately the direction of a longitudinal center axis of the tank, then it is practical to mount the lug at a spacing radially to the longitudinal center axis and preferably also the housing wall of the tank. For an improved form-tight preassembly of the operating medium tank, two or more lugs are formed from the housing wall with these lugs having longitudinal axes preferably approximately aligned parallel to each other. 
   The operating medium tank is made of thermoplastic synthetic material such as polyamide in order to make possible an adequate length of the lugs. Preferably, the operating medium tank is produced from a first half shell and a second half shell. The half shells are manufactured as injection molded parts or pressed parts and are connected to each other material-tight, force-tight or form-tight by gluing, frictional welding or in other suitable types of connection. When manufacturing the half shells in the injection molding or press process, it is possible to form sufficiently long lugs on a half shell as one piece therewith. 
   In a preferred embodiment of the operating medium tank, the holding arms are arranged on the first half shell and the lugs on the second half shell. In order to avoid a possible overstressing of the operating medium tank (the tank could tear and develop a leak at the lugs and holding arms), it is practical to configure the base, that is, the component between housing wall and lug, as a predetermined break location. 
   The operating medium tank is preferably utilized as a fuel tank for a drive unit of a portable handheld work apparatus such as a brushcutter, cutoff machine, motor-driven chain saw or the like. The drive unit is configured as a two-stroke or four-stroke internal combustion engine. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will now be described with reference to the drawings wherein: 
       FIG. 1  is a perspective view of an operating-medium tank according to the invention; 
       FIG. 2  is a perspective view of the tank of  FIG. 1  shown in the condition ready for assembly; 
       FIG. 3  is a perspective view of the operating medium tank which is fixed between two housing parts of a drive unit; 
       FIG. 4  is a perspective exploded view of the tank of  FIG. 3 ; 
       FIG. 5  is a perspective view of the tank in the direction of arrow V in  FIG. 3 ; 
       FIG. 6  is a perspective exploded view of the tank of  FIG. 5 ; and, 
       FIG. 7  is a perspective view of the tank on an internal combustion engine of a portable handheld work apparatus. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION 
     FIG. 1  shows a perspective view of an operating medium tank  1  for a drive unit  2  shown in FIG.  7 . The drive unit  2  is an internal combustion engine  3  for a portable handheld work apparatus. The operating medium tank  1  is suitable as a store for an operating medium such as oil, fuel or the like. 
   The operating medium tank  1  functions as a fuel tank  26  in the embodiment shown and is for a two-stroke internal combustion engine  3  of a brushcutter (see FIG.  7 ). The operating medium tank  1  is essentially manufactured as a two-part plastic component comprising a first half shell  22  and a second half shell  23  manufactured in accordance with an injection-molding process. The two half shells  22  and  23  are joined via friction welding, adhesive or fusion along an abutting interface  29 . The abutting interface  29  lies in a plane  30  running transversely to a longitudinal center axis  13 . The operating medium tank  1  is a hollow body having a tight housing wall made of thermoplastic synthetic material such as polyamide. The hollow body has a kidney-like shape when viewed in cross section and is approximately of a rectangular shape when viewed in plan. 
   Two circularly-shaped openings are provided at the upper end  31  of the tank  1 , namely, a fill opening  4  and an output opening  5 . The fill opening  4  has an inner diameter approximately twice as large as the inner diameter of the output opening  5 . Both openings are surrounded by collars ( 32 ,  32 ′) which each project from the upper end  31  of the tank  1 . The collar  32  of the fill opening  4  has a thread  34  on the inner side  33  thereof for fixing a tank cap  35  (see FIG.  7 ). 
   To provide for a simple preaseembly of the tank  1  on the drive unit, it is a feature of the invention to form from the housing wall  6  of the tank  1  a pedestal or base  7  having a lug  8  as one piece. The lug  8  projects out from the base  7 . In the embodiment shown in  FIG. 1 , two cylindrically-shaped lugs or studs ( 8 ,  8 ′) are mounted on the housing wall  6  of the tank  1 . The axial lengths of the lugs ( 8 ,  8 ′) are approximately twice as large as their diameters. The lug  8 , which is mounted in the region of the upper end  31  of the tank, and the lug  8 ′ project with their respective bases  7  into a plane  20  from the housing wall  6 . The lug  8 ′ is arranged in the region of the base  36  of the tank  1  and the plane  20  is disposed transversely to the longitudinal center axis  13 . The lugs ( 8 ,  8 ′) are arranged with a radial spacing ( 37 ,  37 ′) from the longitudinal center axis  13  and with a radial spacing ( 27 ,  27 ′) from the housing wall  6  so that they can be pushed into receptacles  9  of a housing part  10  of the drive unit  2  as shown in  FIGS. 3 ,  4  and  6 . In the embodiment shown, the receptacles  9  are cylindrically-shaped openings in an engine housing  16 , especially a crankcase  17 . 
   The housing part  11  is formed as a truncated conically-shaped thin walled starter housing cover  18  of the internal combustion engine  3 . The operating medium tank  1  can be clamped via direct contact of its housing wall  6  between the two housing parts  10  and  11  as well as being provided with one or more holding arms  12  (preferably two holding arms) as shown in  FIGS. 1  to  7 . The holding arms  12  function to form-tightly and force-tightly connect the tank  1  to the drive unit  2 . For this purpose, the holding arms  12  are formed in one piece on the housing wall  6  as flat lugs having feet  39  correspondingly reinforced by ribs  38 . As shown in  FIG. 4 , the holding arms  12  lie in respective planes  14  and  15 . The planes ( 14 ,  15 ) are aligned at a spacing to each other and are approximately perpendicular to the longitudinal center axis  13  of the tank  1 . The holding arms  12  have ends  40  which are thickened axially and lie at a distance from the housing wall  6 . Through bores  28  pass through the ends  40  transversely to the respective longitudinal axes of the holding arms. The through bores  28  or eyes function for receiving reinforcement sleeves  41  having a collar  42 . The reinforcement sleeves  41  are made especially of metal. As shown in  FIG. 2 , the reinforcement sleeves  41  extend axially through the through bores  28  in the assembled condition. As  FIGS. 4 and 6  show, the reinforcement sleeves  41  function to accommodate threaded bolts  43 . The threaded bolts  43  are guided through holes  44  on the starter housing cover  18  and through the reinforcement sleeves  41  and into threaded bores  45  in the crankcase  17 . In this way, the holding arms  12  are clamped and held between the starter housing cover and the crankcase (see FIGS.  3  and  5 ). 
   The tank  1  is formed of two half shells ( 22 ,  23 ) in an injection molding process and the lugs ( 8 ,  8 ′) are formed as one piece on the second half shell  23  and the holding arms  12  are formed as one piece on the first half shell  22 . For this reason, the lug and the holding arms can be configured to have almost any desired axial extent. To support the preassembly of the tank  1  to the crankcase  17  and for the elastic form-tight fixing of the lugs ( 8 ,  8 ′) of the tank  1  in the receptacles  9 , the diameter or the clear width of the receptacles  9  are selected greater than the lug diameters. In this way, elastic damping elements  19  can be mounted radially between the lugs ( 8 ,  8 ′) and the receptacles  9 . 
     FIGS. 1 and 2  show cylindrically-shaped sleeve-like damping elements  19  provided with a collar  45 . These damping elements are pushed onto the lugs ( 8 ,  8 ′) as shown in FIG.  2 . The collar  45  comes to rest against the particular base  7  of a lug ( 8 ,  8 ′) in the assembled condition. The outer diameter of the particular damping element  19  is so selected that the damping element  19  together with the particular lug ( 8 ,  8 ′) can be pushed into the receptacle  9  with slight radial jamming of the damping element. In the assembled condition of the operating medium tank  1 , the damping elements  19  prevent the tank from coming to rest between the housing parts ( 10 ,  11 ) of the drive unit  2  in a static unwanted manner or in an excessive axial and/or radial clamped state. It can be practical to configure the base  7  as a set break location to prevent leakage of the tank  1  when there is a possible tear of one or several lugs ( 8 ,  8 ′). 
   It is understood that the foregoing description is that of the preferred embodiments of the invention and that various changes and modifications may be made thereto without departing from the spirit and scope of the invention as defined in the appended claims.