Patent Publication Number: US-10329994-B2

Title: Power tool

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to a power tool comprising an internal combustion engine to which fuel is supplied through an injection valve, wherein the internal combustion engine has a crankcase in which a crankshaft is rotatably supported so as to rotate about an axis of rotation. The power tool has a fan wheel for conveying cooling air to the internal combustion engine. The fan wheel is disposed in a fan wheel housing. 
     U.S. 2011/0140707 discloses a hand-held power tool, namely a cut-off machine, having an internal combustion engine in the form of a two-stroke engine that is supplied with fuel through a transfer passage by means of an injection valve. The crankshaft of the internal combustion engine drives a fan wheel arranged in a fan wheel housing. The back wall of the fan wheel housing delimits the crankcase of the internal combustion engine. 
     When the fuel in the fuel system, in particular in the injection valve, is heated too much, vapor bubbles can form that impair the supply of fuel to the internal combustion engine. In particular in case of fuel systems with low fuel pressure vapor bubble formation is observed already at comparatively low temperatures. 
     U.S. Pat. No. 6,196,170 discloses a lawn trimmer in which the injection valve is arranged at the output side above the fan wheel. The fuel valve as well as the engine block are therefore cooled by the sucked-in air. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a power tool of the aforementioned kind in which in a simple way an excellent cooling of the injection valve is achieved. 
     In accordance with the present invention, this is achieved in that in the fan wheel housing a connecting opening is formed and in that the injection valve is arranged in a cooling area into which cooling air that is conveyed by the fan wheel flows through the connecting opening. 
     In order to obtain an excellent cooling action of the injection valve and to prevent the formation of vapor bubbles in the injection valve, it is provided to cool the cooling area in which the injection valve is arranged in a targeted fashion. For this purpose, a connecting opening is provided in the fan wheel housing by means of which cooling air that is conveyed by the fan wheel flows into the cooling area. In this way, a targeted and excellent cooling action of the injection valve can be achieved. Accordingly, the connecting opening can be arranged on the suction side or the pressure side of the fan wheel, i.e., the cooling air can thus be sucked through the cooling area into the fan wheel or can be conveyed by the fan wheel into the cooling area. By means of the connecting opening, a targeted cooling action of the injection valve can be achieved that is separate from the cooling action of the cylinder. Through the connecting opening cool air that has not been heated by the internal combustion engine is transported into the cooling area. The cooling area in which the injection valve is arranged has advantageously a comparatively small volume so that an excellent and targeted cooling action is achieved. It is not necessary that the cooling area is a completely closed chamber. It is also not necessary that the injection valve is exposed directly to the cooling air that is coming into the cooling area but it can be indirectly cooled, for example, when the injection valve is arranged in a housing or holder that is arranged in the cooling area. In the cooling area, advantageously further components such as components of the fuel system, sensors or the like can be arranged also. 
     In particular in case of hand-guided portable power tools such as motor chainsaws, cut-off machines, trimmers or the like and in hand-guided drivable power tools such as lawnmowers or the like, small internal combustion engines, in particular, two-stroke engines are used. These engines, in particular two-stroke engines that run at high speeds heat up greatly in operation. At the same time, there is only little space available because such power tools are to be designed to be as compact as possible in order to ensure simple handling. These internal combustion engines have usually fuel pumps that are mechanically driven by the internal combustion engine and operate usually with comparatively low fuel pressure, for example, less than three bar overpressure, in particular, less than 1 bar overpressure relative to ambient pressure. 
     As a result of the high temperatures in operation of the internal combustion engine and the minimal pressure in the fuel system, vapor bubble formation is promoted. Vapor bubbles in the fuel system can prevent supply of fuel to the internal combustion engine because the pump output of the pump may be compensated partially or completely by the gas volume that has been formed. Vapor bubbles in the fuel system can therefore prevent operation of the internal combustion engine. In particular in two-stroke engines of hand-guided power tools that are operated at minimal fuel pressure and that produce a lot of heat in a small space, the vapor bubble formation is therefore a problem. 
     Advantageously, the connecting opening is arranged in an overpressure area of the fan wheel housing so that cooling air is conveyed by the fan wheel into the cooling area in which the injection valve is arranged. However, it can also be advantageous that the connecting opening is arranged in an underpressure area of the fan wheel housing and the cooling air is sucked into the fan wheel housing through the cooling area. In the arrangement of the connecting opening in the overpressure area a greater cooling air flow is provided in comparison to an arrangement in an underpressure area. Therefore, the arrangement in an overpressure area is particularly advantageous with regard to an effective cooling action. The connecting opening is advantageously connected by an air guiding passage with the cooling area so that a targeted guiding of the cooling air in the cooling area is possible. A simple configuration results when the cooling area is delimited by an air guiding component. Advantageously, the air guiding passage is also delimited by the air guiding component. In this way, a simple configuration is provided. The air guiding component is comprised advantageously at least partially of plastic material. The air guiding component acts then in a thermally insulating way. When the internal combustion engine is turned off, an excessive heating of the air guiding component by heat transfer from the still hot internal combustion engine is thus avoided in particular. In this way, excessive heat transmission onto the injection valve and thus vapor bubble formation in the injection valve can be prevented when the internal combustion engine is shut off and still hot. The air guiding component is advantageously arranged on the outer circumference of the crankcase. The cooling area in which the injection valve is arranged is advantageously delimited by the crankcase and the air guiding component. 
     The internal combustion engine is advantageously a mixture-lubricated internal combustion engine (fuel/oil mixture lubrication). The internal combustion engine can be a two-stroke engine or a four-stroke engine that is mixture-lubricated. The injection valve feeds the fuel advantageously directly into the crankcase interior. The fuel/air mixture formation is realized advantageously in the crankcase interior. The supply of fuel directly into the crankcase interior ensures excellent lubrication of the parts in the crankcase. Moreover, the injection valve can be arranged on the crankcase that in operation is significantly cooler than the cylinder of the internal combustion engine. The injection valve can be positioned on the crankcase comparatively far removed from the hot cylinder in order to keep the heat transmission onto the injection valve as minimal as possible. The injection valve is in particular arranged in a holder of plastic material which is attached to the crankcase and is arranged at least partially in the cooling area. The injection valve is therefore not directly exposed to the flow of the cooling air that is conveyed by the fan wheel but can be cooled indirectly by the holder. The surface of the holder is actively cooled. The reduced temperature of the holder leads to a reduced temperature of the injection valve or to a reduced heating of the injection valve. The holder of plastic material reduces also the heat transmission from the crankcase to the injection valve. In particular when the internal combustion engine is turned off, when cooling air is no longer conveyed, an excessive heating of the injection valve can therefore be avoided. The fuel is advantageously supplied to the injection valve by means of a fuel pressure damper. A simple configuration is provided when the fuel pressure damper is integrated into the holder of the injection valve. In this way, the cooling air flow that is conveyed through the connecting opening not only cools the injection valve but also the fuel pressure damper. The fuel pressure damper is advantageously also arranged in the cooling area. 
     The crankcase has advantageously a first and a second housing part between which a joint surface is formed. At the joint surface the two housing parts are advantageously connected to each other, in particular by interposition of a gasket. The joint surface is advantageously at least partially positioned in an imaginary parting plane. The joint surface may completely extend within the parting plane or can have, for example, at least one step so that only a section of the joint surface is located within the imaginary parting plane. The parting plane is oriented such that an imaginary extension of the joint surface is positioned perpendicular to the axis of rotation of the crankshaft, in this context, the arrangement of the joint surface relative to the axis of rotation of the crankshaft should be substantially perpendicular. Deviations of a few angle degrees relative to the exact perpendicular orientation are of no consequence. The parting plane is positioned parallel to the longitudinal cylinder axis. On the first housing part the fan wheel housing is arranged. The first housing part and the second housing part are in particular die cast parts on which further components are integrally formed. The two housing parts are advantageously made of die cast magnesium. The fan wheel housing is advantageously integrally formed on the first housing part, i.e., is monolithically formed together with it. The injection valve is advantageously also secured on the first housing part. 
     An independent aspect of the present invention concerns the separation of the crankcase. Advantageously, the crankcase is not divided centrally. The parting plane is advantageously positioned at a spacing relative to an imaginary center plane. The center plane is the plane that contains the longitudinal cylinder axis and that extends perpendicularly to the axis of rotation of the crankshaft. The parting plane and the center plane are two planes that extend parallel to each other. The axis of rotation of the crankshaft forms a straight line that intercepts the center plane and the parting plane at two points spaced apart from each other. The joint plane is extending in particular at the injection valve at the side of the imaginary plane that is remote from the fan wheel housing. At the level of the injection valve the joint surface is therefore displaced to the side of the imaginary plane that is remote from the fan wheel housing. Advantageously, the joint surface extends completely at the side of the imaginary plane that is remote from the fan wheel housing. The spacing is advantageously approximately 10% up to approximately 50% of the width of the crankcase interior measured parallel to the axis of rotation of the crankcase. It is particularly advantageous when the spacing is 30% to 40% of the width of the crankcase interior. 
     It has been found that the first housing part in operation as a result of cooling of the fan wheel housing by the fan wheel is significantly cooler than the second housing part. At the same time, the first housing part, as a result of the asymmetric arrangement of the joint surface relative to the center plane has a greater mass than the second housing part as well as a larger surface area. As a result of the greater mass the second housing part is heated slower than the first housing part. The greater surface area effects a faster heat transfer to the environment. By arranging the injection valve on the first housing part that is cooled a reduced heating of the injection valve is achieved. The joint surface is advantageously displaced toward the second housing part, at least in the area in which the receiving opening for the injection valve, respectively, the holder supporting the injection valve is arranged. The spacing between parting plane and center plane is advantageously provided at least in the area in which the receiving opening is arranged in a projection in the direction of the axis of rotation of the crankshaft onto the parting plane. The parting plane advantageously does not intercept a receiving opening for the injection valve that is formed on the crankcase. Since the parting plane adjacent to the injection valve is displaced toward the second housing part; sufficient space is available at the first housing part for the arrangement of the receiving opening, respectively, the injection valve. 
     The described arrangement of the joint surface and the arrangement of the injection valve on the housing part where the fan wheel is arranged represent an independent aspect of the invention that can be advantageous also independent of the arrangement of the connecting opening at the back wall of the fan wheel housing. The temperature difference between the first and the second housing part can be within a magnitude of approximately 10 K. This temperature difference between first and second housing parts, depending on the operational state of internal combustion engine and the pressure in the fuel system, can be decisive for a reliable fuel supply by means of the injection valve. 
     The components of the power tool that must be cooled are advantageously arranged on the first housing part. In this connection, in particular the injection valve is secured on the first housing part. In this connection, it is advantageously provided that the holder in which the injection valve is arranged is arranged on the first housing part, namely at a receiving opening formed on the first housing part at the outer circumference of the crankcase. The holder for the injection valve is advantageously sealed in the receiving opening by means of a radial seal. In order to enable an excellent radial sealing action of the holder, the receiving opening is advantageously completely formed in the first housing part. Since the holder is radially sealed, additional fastening means such as fastening screws are provided only for securing the holder on the crankcase. Therefore, by means of the securing means such as screws no sealing forces must be applied. The sealing forces are defined by the dimensions of the seal and of the receiving opening and are independent of the tightening force of the fastening screws. With this configuration, a reliable and simple sealing action can be achieved. Advantageously, the internal combust combustion engine has at least one sensor which is arranged on the outer circumference of the crankcase on the first housing part. The sensor is advantageously arranged at the exterior side of the crankcase. An arrangement in the interior of the crankcase on the crankcase wall forming the outer circumference of the crankcase may be advantageous also. Minimal temperatures are achieved also for the sensor as a result of the arrangement on the first housing part. The sensor can be, for example, a pressure sensor, a temperature sensor or a combined pressure temperature sensor. Also, the arrangement of several sensors on the first housing part can be advantageous. 
     The internal combustion engine has advantageously a cylinder which is attached to a cylinder connecting flange on the crankcase. The cylinder connecting flange extends advantageously perpendicular to the longitudinal cylinder axis and in particular perpendicular to the joint surface between the two housing parts of the crankcase. A first section of the cylinder connecting flange is advantageously formed by the first housing part and a second section of the cylinder connecting flange by the second housing part. By configuring the cylinder connecting flange at both housing parts, demoulding of the housing parts when producing them by die casting is enabled in the direction of the axis of rotation of the crankshaft. In this way manufacture is simplified. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         FIG. 1  is a side view of a cut-off machine. 
         FIG. 2  is a section view, partially schematic; of an internal combustion engine of the cut-off machine of  FIG. 1 . 
         FIG. 3  is a side view of the crankcase of the internal combustion engine in the direction of arrow III in  FIG. 2 . 
         FIG. 4  is a section view along the line IV-IV of  FIG. 2  wherein the holder of the injection valve is not shown in section. 
         FIG. 5  is a section view of the first housing part of the crankcase along the section line V-V in  FIG. 2  wherein the holder of the injection valve is not shown in section. 
         FIG. 6  is a section view of the first housing part and of the holder of the injection valve along the line VI-VI in  FIG. 3 . 
         FIG. 7  is a perspective illustration of the first housing part of the crankcase. 
         FIG. 8  is a side view of the internal combustion engine in the direction of arrow III in  FIG. 2 . 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  shows as an embodiment of a power tool a hand-guided cut-off machine  1 . The present invention is also advantageous for other power tools, in particular for hand-guided power tools such as motor chainsaws, trimmers, blowers or the like. The power tools can be hand-carried or can be carried as a backpack or can be pushed across the ground, for example, in the case of lawnmowers or cut-off machines with carriage. 
     The cut-off machine  1  has a housing  2  on which a cantilever arm  3  is secured. At the free end of the cantilever arm  3  a cutter wheel  4  is rotatably supported which is partially covered by a protective cover  5  about its circumference. For guiding the cut-off machine  1  a top handle  6  is provided that is monolithically formed with a hood  8  of the housing  2  and a grip pipe or handlebar  7  that spans the housing  2  at the front side of the housing  2  facing the cutter wheel  4  are provided. At the top handle  6  a throttle trigger  10  as well as a throttle lock  11  are pivotably supported. Instead of the top handle  6  also a rear handle can be provided. At the side of the housing  2  that is facing away from the cutter wheel  4 , an air filter cover  9  is secured on the housing  2 . In the housing  2  an internal combustion engine  12  is arranged that is to be started by a starter device. The starter device can be actuated by means of a starter grip  15 . However, also an electric starter device can be provided. In the housing  2  there is also a fuel pump  14  is arranged also, schematically shown in  FIG. 1 , that serves for conveying fuel to the internal combustion engine  12 . The cut-off machine  1  has support legs  13  with which it can be placed onto the ground or any other support surface. 
       FIG. 2  shows the internal combustion engine  12  in detail. The internal combustion engine  12  has a cylinder  19  that is placed at the parting plane  41  onto the crankcase  16 . In the crankcase  16  a crankshaft  26  is supported so as to the rotatable about axis of rotation  17  by bearings  51  that may be embodied as ball bearings. The crankshaft  26  is supported on both sides of a connecting rod (not shown in the Figures) that provides a connection to the piston. A first bearing  51  is arranged in the first housing part  36  and a second bearing  51  in the second housing part  37 . The crankshaft  26  is rotatingly driven by piston  25  that is reciprocatingly supported in the cylinder  19  in the direction of the longitudinal cylinder axis  29 . The piston  25  delimits a combustion chamber  24  formed in the cylinder  19 . The cylinder  19  has an inner diameter b. The inner diameter b is the diameter of the bore that is formed in the cylinder  19  and in which the piston  25  is arranged. An inlet  22  opens at the cylinder  19  and is controlled by the piston  25 . The inlet  22 , when the piston  25  is positioned at top dead center, is connected with the crankcase interior  18  and supplies combustion air into the crankcase interior  18 . The combustion air is supplied through intake passage  30  that extends with a portion thereof in a throttle housing  27 . In the throttle housing  27  a throttle element is pivotably supported, in the illustrated embodiment in the form of a throttle flap  28 , and the throttle trigger  10  is acting on this throttle element. An outlet  23  extends away from the combustion chamber  24  and is also controlled by the piston  25 . 
     On the outer circumference of the crankcase  16  a holder  33  is arranged that is sealed by means of radial seal  42  relative to the crankcase  16 . In the holder  33  a receptacle  34  for an injection valve  43  ( FIG. 6 ) is formed. The injection valve  43  supplies the fuel directly into the crankcase interior  18  by means of an outlet passage  35  formed in the holder  33 . The crankcase  16  has also a mounting opening  31  for a sensor that is also not shown in  FIG. 2 . The holder  33  is arranged immediately below the inlet  22  of the throttle housing  27  and the mounting opening  31  is arranged on the side of the holder  33  that is facing away from the throttle housing  27 . The crankcase interior is connected by one or several transfer passages  22  to the combustion chamber  24 . In the illustrated embodiment a transfer passage  20  is provided that branches into several branch passages and opens with several transfer ports  21  into the combustion chamber  24 . The transfer ports  21  are also controlled by the piston  25  and, when the piston  25  is at bottom dead center, the ports  21  open into the combustion chamber  24 . 
     When the piston  25  is at top dead center, combustion air is sucked in from the intake passage  30  through inlet  22  into the crankcase interior  18  in operation of the internal combustion engine. The combustion air is compressed upon downward stroke of the piston  25  in the crankcase interior  18 . Through the injection valve  43  ( FIG. 6 ) fuel is supplied also into the crankcase interior  18 . The fuel/air mixture flows through the transfer passage  20  and transfer ports  21  into the combustion chamber  24  when the piston  25  is at bottom dead center. Upon upward stroke of the piston  25  the fuel/air mixture in the combustion chamber  24  is compressed and is ignited by a spark plug (not shown) when the piston  25  is at top dead center. The piston  25  is accelerated by the combustion in the combustion chamber  24  in the direction of bottom dead center. As soon as the outlet  23  has been opened by piston  25 , the exhaust gases flow out of the cylinder  19  into the exhaust gas muffler (not shown in the drawing) that is connected to the outlet  23 . 
     As shown in  FIG. 2 , the holder  33  is arranged in a cooling area  64  which is covered by an air guiding component  44  and which is separated to a large extent from the environment.  FIG. 3  shows the air guiding component  44  in detail. On the air guiding component  44  an air guiding passage  45  is formed that extends to a connecting socket  46 . The connecting socket  46  is secured in a back wall  47  of a fan wheel housing  32  in the fan wheel housing  32  a fan wheel  35  is arranged that is rotatingly driven by the crankshaft  26 . The fan wheel  39  is advantageously connected fixedly with the crankshaft  26 . 
     The crankcase  16  comprises a first housing part  36  and a second housing part  37  between which a joint surface  40  is formed. The two housing parts  36  and  37  are advantageously resting on each other at the joint surface  40  with interposition of a gasket, in particular a paper gasket. The joint surface  40  can be, for example, approximately part-circular. The joint surface  40  extends in the illustrated embodiment parallel to an imaginary center plane  56  illustrated in  FIG. 3 . The center plane  56  contains the longitudinal cylinder axis  29  and extends perpendicular to the axis of rotation  17  of the crankshaft  26 . The joint surface  40  may have one or several steps. The joint surface  40  is positioned at least partially in an imaginary parting plane  68 . In the illustrated embodiment, the joint surface  40  has no steps and is positioned completely within the parting plane  68 . The angle α between the imaginary parting plane  68  and the axis of rotation  17  of the crankshaft  26 , schematically indicated in  FIG. 3 , is 90°. The center plane  56  corresponds to the section plane of  FIG. 2 . As is shown in  FIG. 3 , the joint surface  40  and thus also the parting plane  68  have relative to the center plane  56  a spacing a. The joint surface  40  and thus also the parting plane  68  have a greater spacing to a back wall  47  of the fan wheel housing  32  that is facing the crankcase  16  than the center plane  56 . The spacing α is advantageously at least approximately 10%, in particular at least approximately 15%, of the inner diameter b of the cylinder  19 . The spacing a is advantageously approximately 10% to approximately 50% in particular 20% to 40%, of the width c (see  FIG. 4 ) of the crankcase interior  18  that is measured parallel to the axis of rotation  17  of the crankshaft  26 . In the illustrated embodiment, the spacing a is approximately 30% of the width c of the crankcase interior  18 . The joint surface  40  is displaced relative to the center plane  56  in the direction toward a mounting flange  38  that is formed on the second housing part  37 . On the mounting flange  38 , a centrifugal clutch of the cut-off machine  1 , a pulley for driving the drive belt for the cutter wheel  4 , as well as a starter device for the internal combustion engine  12  can be arranged. Advantageously, the cantilever arm  3  is secured on the mounting flange  38 . 
     The spacing a is advantageously provided adjacent to the injection valve  43 , i.e., in the projection of the receiving opening  52  ( FIG. 7 ) for the holder  33  onto the center plane  56  in the direction of the axis of rotation  17  of the crankshaft  26 . The parting plane  68  extends advantageously outside of the receiving opening  52  on the side of the receiving opening  52  that is remote from the fan wheel housing  32 . 
     As shown in  FIGS. 3 and 4 , the holder  33  is completely arranged on the first housing part  36  so that also the injection valve  43  is secured only on the first housing part  36  and has no direct contact with the second housing part  37 . As shown in  FIG. 3 , the mounting opening  31  is also formed completely on the first housing part  36 . 
     As shown in  FIGS. 3 and 4 , the back wall  47  of the fan wheel housing  32  that is facing the crankcase  16  has a connecting opening  48  in which the connecting socket  46  is secured (see also  FIG. 5 ). The air guiding passage  45  adjoins the connecting opening  48 . In the air guiding passage  45  a flow guiding rib  45  is formed that divides the supplied air into several partial streams. The air guiding component  44  is comprised of plastic material. The holder  33  penetrates the cooling area  64  that is delimited by the air guiding component  44 . The fan wheel  39  is covered by the fan wheel cover  66  relative to the environment (the cover is schematically shown in  FIG. 4 ). The fan wheel cover  66  is secured on the fan wheel housing  32 . 
       FIG. 4  shows also the gasket  50  arranged between the housing parts  36  and  37 . The gasket  50  seals the transfer passage  20  relative to the crankcase interior  18 . In addition, on the joint surface  40  a paper gasket for sealing relative to the environment is provided advantageously. 
       FIG. 5  shows that the fan wheel  39  has at the side that is facing away from the crankcase  16  a front vane arrangement  60  and on its side that is facing the back wall  47  of the fan wheel housing  32  a rear vane arrangement  61 . The fan wheel housing  32  delimits a cooling air spiral, in an overpressure area of the cooling air spiral the connecting opening  48  is arranged. In this way, the cooling air that is conveyed by the fan wheel  39  is forced through the connecting opening  48  and the air guiding passage  45  into the cooling area  64 . On the holder  33  a fuel pressure damper  65  is integrated that is arranged immediately upstream of the injection valve in the flow path of the fuel. The fuel pressure damper  65  is also cooled by the cooling air conveyed through the connecting opening  48 . The cooling air flows in the direction of arrow  57  past the fuel pressure damper  65  through a gap  59  that is formed between the air guiding component  44  and the wall of the crankcase  16 . The cooling air flows also across the opposite side of the flow guiding rib  49  in the direction of arrow  58 . The cooling air that flows in the direction of arrow  58  flows about the holder  33  and exits at the side of the holder  33  that is facing away from the fan wheel housing  32  between crankcase  16  and air guiding component  44 . Advantageously, the gap  59  is designed to be circumferentially extending so that cooling air can exit across the entire rim of the air guiding component  44 . 
       FIG. 5  shows also that the receptacle  34  that is formed in the holder  33  for the injection valve  43  is open relative to the environment but not relative to the cooling area  44 . The cooling air that is conveyed underneath the air guiding component  44  does not cool the injection valve directly but flows about and cools the holder  33  so that an excessive heating of the injection valve  43  is prevented. 
     As also shown in  FIG. 5 , the holder  33  is arranged in a receiving opening  52  of the crankcase  16  and is sealed relative thereto by a radial seal  42 . As shown also in  FIG. 5 , the receiving opening  52  is formed completely within the first housing part  36  so that the radial seal  42  must not extend across the joint surface  40  between the two housing parts  36  and  37 . 
       FIG. 6  shows schematically the injection valve  43  that is arranged in the holder  33 . The fuel that is metered in through the injection valve  43  passes through the outlet passage  35  into the crankcase interior  18 . 
       FIG. 7  shows the arrangement of the connecting opening  48  in the back wall  47  of the fan wheel housing  32 . The air guiding component  44  is not shown and the holder  33  is also not shown.  FIG. 7  shows two fastening openings  62  on the first housing part  36  by means of which the holder  33  can be screw-connected to the crankcase  16 . As shown in  FIG. 6 , fastening screws  67  are screwed into the fastening openings  62  and secure also the air guiding component  44 . No additional fastening openings or fastening means are therefore required for fixation of the air guiding component  44 . 
     As shown in  FIG. 7 , adjacent to the mounting opening  31  two fastening openings  63  for attachment of a sensor in the mounting opening  31  are provided. The sensor  53  is shown in  FIG. 8 . The sensor  53  is a combined pressure and temperature sensor. As also shown in  FIG. 7 , the section of the transfer passage  20  which is formed in the crankcase  16  is also divided by the joint surface  40 . This is also shown in  FIG. 4 . On the side that is facing the cylinder  19  a first section  54  of a cylinder connecting flange is formed on the first housing part  36 . The cylinder  19  is secured on the cylinder connecting flange advantageously with interposition of a gasket. The gasket is in particular a paper gasket. This gasket between crankcase  16  and cylinder  19  effects an additional thermal insulation of cylinder  19  and crankcase  16  that reduces the heat transmission from the cylinder  19  into the crankcase  16 . As shown in  FIG. 8 , a second section  55  of the cylinder connecting flange is formed on the second housing part  37 . The first housing part  36  as well as the second housing part  37  delimit the cylinder connecting flange. In this way, both housing parts  36  and  37  can be demoulded in the direction of the axis of rotation  17  of the crankshaft  26  when produced by die casting. Only for forming the openings for the injection valve  43  and the sensor  53  additional slides are required, or these openings must be separately produced. 
     As shown in  FIG. 8 , the holder  33  and the fuel pressure damper  65  are arranged immediately adjacent to the connecting opening  48 . In this way, the cooling air conveyed by the fan wheel  39  flows immediately about the holder  33  with injection valve  43  and the fuel pressure damper  65 . 
     As an alternative, it may be provided to arrange the connecting opening  48  in the underpressure area of the fan wheel. The injection valve  43  is then cooled by the cooling air that is sucked in by the fan wheel. 
     The holder  33  as well as the air guiding component  44  are comprised of plastic material. The components thus act as insulators so that the heat transfer from the crankcase to the injection valve is bad. In this way, even when the machine is shut down, it can be ensured that the injection valve is not heated too much even when the fan wheel is no longer driven but the crankcase and the cylinder are still hot. By arranging the injection valve on the crankcase, heating of the injection valve is reduced significantly in comparison to the arrangement on the cylinder. Alternatively, the holder  33  could be completely or partially made of metal. A configuration is particularly advantageous in which areas of the holder  33  that are in contact with the crankcase  16  are made of plastic material and effect an insulation relative to the crankcase  16 . The area of the holder  33  that is not directly in contact with the crankcase  16  but is exposed to the flow of cooling air can advantageous be made of metal so that the heat in the holder  33  can be dissipated by means of the metallic section into the environment, in particular transferred to the cooling air. Alternatively or additionally, it can be provided that the holder  33  is provided in the area that is exposed to the cooling air has at least one cooling rib for improving the heat transfer to the cooling air. Advantageously, the injection valve  43  itself can also be contact with the cooling air and/or have at least one cooling surface that is formed advantageously on a cooling rib. 
     The fan wheel housing  32  in the illustrated embodiment is formed integrally on the first housing part  36  of the crankcase  16 . However, it can also be advantageous to embody the air filter housing  32  as a separate component. The air filter housing  32  can be of a single-part or a multi-part configuration and can be comprised at least partially of plastic material. The air filter housing  32  can also be formed or delimited partially or completely, by neighboring components. 
     The specification incorporates by reference the entire disclosure of German priority document 10 2011 120 464.8 having a filing date of Dec. 7, 2011. 
     While specific embodiments of the invention have been shown and described in detail to illustrate the inventive principles, it will be understood that the invention may be embodied otherwise without departing from such principles.