Abstract:
This invention relates to a flexible intake system for a crankcase scavenged two-stroke internal combustion engine ( 10 ) having an additional air supply to its transfer ducts. The intake system comprises a flexible intake duct ( 22 ) connecting a fuel supply unit ( 21 ) e.g. a carburetor with an engine cylinder ( 11 ) and at least one flexible air duct ( 40 ) connecting a valve housing ( 42 ) for additional air with the engine cylinder. The end portion of the flexible intake duct ( 22 ) and at least one air duct ( 40 ) is secured to the cylinder by means of a baffle ( 23 ) made of a stiffer material than the ducts ( 22, 40 ) themselves.

Description:
TECHNICAL FIELD 
     This invention relates to a flexible intake system for a crankcase scavenged two-stroke internal combustion engine having an additional air supply to its transfer ducts, the intake system comprising a flexible intake duct connecting a fuel supply unit e.g. a carburettor with an engine cylinder and further comprising at least one flexible air duct connecting a valve housing for additional air with the engine cylinder. 
     BACKGROUND OF THE INVENTION 
     Internal combustion engines of the type mentioned above are intended to be used for driving different kind of hand held tools such as chain saws and power cutters. In order to decrease the vibrations transferred from the engine to the handle portion the engine is usually separated from the handle portion by means of a flexible damping arrangement and to further decrease the vibrations usually certain details of the mass system, such as the carburettor, the air filter system and the fuel tank are usually secured to the handle portion. This also decreases vibrations for the carburettor thereby increasing carburettor reliability. Consequently there is a demand for flexible connections between the different details on the handle portion and the engine but since these connections have to be secured to the engine at a rather concentrated area the assembling procedure becomes complicated. In particular the assembling procedure for securing the different intake ducts for mixture and air to the cylinder of the engine is time consuming and it is also difficult to dismount the arrangement when making maintenance and repairing the hand held tool. Further there is a need for a more stable and reliable fastening arrangement for the different ducts. 
     SUMMARY OF THE INVENTION 
     The purpose of this invention is to eliminate or at least reduce the drawbacks mentioned above in order to get a simple arrangement connecting the cylinder of the engine with the different ducts thereby facilitating assembly and dismounting. This is achieved by means of a device having the characteristics mentioned in the claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
       The invention will be described in the following with reference to the accompanying drawing figures, which show two preferred embodiments of the invention. 
         FIG. 1  is a vertical section of a first embodiment of a hand held tool provided with the invention. 
         FIG. 2  is an enlarged view of a part of  FIG. 1 . 
         FIG. 3  is a perspective view of a detail of the embodiment in  FIG. 1 . 
         FIG. 4  is an exploded view of some details according to the arrangement in  FIG. 1-3 . 
         FIG. 5   a  is a front perspective view of a second embodiment of the invention whereas  FIG. 5   b  is a rear perspective view of said second embodiment. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     The arrangement shown in  FIG. 1-3  comprises a two-stroke internal combustion engine  10  having a cylinder  11  with a cylinder bore  12  in which a piston  13  is movable. The piston  13  is via a piston rod  14  connected to a crankshaft  15  rotating in a crankcase  16 . The cylinder is in a conventional way provided with an exhaust outlet  17 , connected to a muffler  18 , and with a spark plug  19 . Further there is a fuel tank  20  to which a carburettor  21  is connected. 
     The carburettor  21  is via an air/fuel duct  22  connected to a baffle  23  that is secured to the cylinder  11 . The air/fuel duct  22  is made of a flexible material such as rubber or plastic whereas the baffle is manufactured of a stiffer material such metal or a heat resisting plastic. The baffle  23  comprises a plate shaped lower part  24  provided with one opening  25  in which one end of the air/fuel duct  22 , that is provided with an end flange  26 , is inserted. The end flange  26  rests in a recess  27  arranged around the edge of the opening  25  at the side of the baffle  23  that faces the cylinder  11  and serves as a sealing against a flat seat portion  28  arranged at the cylinder  11  around an inlet opening  29  for the air/fuel supply. Preferably the shape of the recess  27  is such that it is more narrow close to the edge of the opening than it is at a distance from the opening thereby safeguarding that the end flange  26  does not fall out of the recess  27 . There also is an additional flange  26   a  arranged at a distance from the end flange  26  and safeguarding that the baffle  23  is clamped at the outer end of the air/fuel duct  22  between the flanges. 
     The upper portion of the baffle  23  is provided with an L-shaped part  30  (as seen in a vertical section) having a first leg  31  (see  FIG. 2-3 ) that is mainly parallel to an outer surface  32  of the cylinder  11 , said surface being inclined about 45° with respect to the flat seat portion  28 , and a second leg  33  that is provided with an opening  34  through which a screw  35  is inserted and fixed to the cylinder. The lower portion of the baffle  23  is provided with an end portion  36  that is clamped between a yoke member  37  (see  FIG. 4 ) fixed to the cylinder by means of screws inserted through openings  38  arranged in the yoke member and secured to the outside of the cylinder wall. 
     The plate shaped lower part  24  of the baffle  23  is provided with two additional openings  39  that in the similar way as the lower opening  25  each are connected to an air duct  40  of flexible material. The openings  39  are aligned with air transfer ducts inlets (not shown in  FIG. 1-4 ) arranged at the flat seat portion  28  close to the inlet  29  for the air/fuel supply. One end of each air duct  40  is connected to an air inlet  41  via a valve arrangement  42  in order to supply additional air to the transfer ducts whereas the other end of the air duct  40  is provided with an end flange  40   a  inserted in a corresponding recess  39   a  arranged around the openings  39  of the baffle  23 . Each air duct is also provided with an additional flange  40   b  operating in the similar way as the additional flange  26   a  described above. Also the air inlet side of the carburettor  21  is connected to said air inlet  41 . There is an impulse nozzle  62  pressed into the baffle. An impulse hose  61  is attached to it. 
     The air inlet  41  constitutes an internal channel within a bracket  43  that is secured to handle part  44  of the hand held tool together with the fuel tank  20 . The handle part  44  is separated from the engine  10  and the tool driven by the engine by means of a flexible support arrangement (not shown) that dampens the vibrations from the engine to the handle. 
     The upper part of the bracket  43  constitutes a main filter bottom  45  supporting a sealing  46  on which a main filter  47  is placed. The main filter  47  is clamped between the sealing  46  and a filter cover  48  comprising a lower and an upper cover part  49 ,  50  enclosing a prefilter  51  for the flow of air from the atmosphere to the air inlet  41 . The filter cover  48  is secured to the handle part  44  by means of one or several screws  52 . The main filter bottom  45  is also provided with an opening  53  placed in line with the axial direction of the screw  35  such that the screw can be removed in order to remove the baffle  23 . This opening is normally covered by the sealing  46 . The screw  35  is inclined downwards, i.e. its lower end is pointing somewhat towards the crankcase  16 , and preferably more than 20° and less than 40°. 
     The arrangement mentioned above is assembled in the following manner. In a pre-mounting stage the air/fuel duct  22  as well as the air ducts  40  are inserted into the openings  25  and  39  of the baffle  23  such that the end flanges  26 ,  40   a  are taken up by the recesses  27 ,  39   a , whereas the flanges  26   a  serve as clamping means for the baffle  23 . Then the carburettor  21 , the valve arrangement  42  and the bracket  43  with the main filter bottom  45  are secured to the different ducts such that the complete arrangement can be treated as one unit. This unit is then fastened to the cylinder by pushing the end portion  36  of the baffle  23  in between the yoke member  37  and the cylinder wall such that the end flanges  26 ,  40   a  create a sealing between the baffle  23  and the seat portion  28 . Simultaneously the second leg  33  of the L-shaped part  30  will come into engagement with the corresponding surface of the cylinder such that the screw  35  can be inserted through the opening  53  of the main filter bottom  45  and be fixed to the cylinder  11 . Then the sealing  46  and the main filter  47  is placed on the main filter bottom  45  and finally the filter cover  48  with the pre-filter  51  is placed on top of the main filter and is secured to the handle portion by means of the screw  52  and additional screws if necessary. 
     The second embodiment of the invention according to  FIGS. 5   a  and  5   b  differs from the first embodiment in that the air/fuel duct  22 ′ as well as the air ducts  40 ′ are secured to the baffle  23 ′ by means of molding or vulcanizing methods or by means of chemical bindings. Also in this embodiment the ducts are arranged through the openings in the baffle  23 ′ such that the ends create a sealing at the side facing the seat  28 ′ of the cylinder of the engine  10 ′.  FIG. 5   a  also shows the inlet ports  54 ′ of the air ducts  40 ′. A number of sealing ridges  55 ′,  56 ′,  57 ′ are formed in the flexible material facing the seat  28  of the cylinder  11 ′. Each ridge encloses an inlet port  54 ′,  61 ′ provided in the seat  28 ′. Each ridge is surrounded by a ditch  58 ′,  59 ′,  60 ′. For this embodiment there is a ditch on both sides of each ridge. This is useful when the ridge is pressed against seat  28 ′. 
     For the other embodiment as seen in  FIG. 2  sealing ridge  56  is enclosed by an outer ditch  59 . This figure is schematic as ridge  56  will be compressed and not seat  28 .