Patent Publication Number: US-2019178210-A1

Title: Work apparatus with a gas-operated combustion engine

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims priority of German patent application no. 10 2017 011 345.9, filed Dec. 8, 2017, the entire content of which is incorporated herein by reference. 
     FIELD OF THE INVENTION 
     The invention relates to a work apparatus with a gas-operated combustion engine which has a cylinder with a combustion chamber which is delimited by a piston. The combustion engine has an intake channel for feeding in combustion air and an exhaust gas outlet for discharging combustion gases. A flammable gas is fed to a mixture formation unit via a supply line. The gas enters into an opening of the supply line within a gas tank of the work apparatus, it being possible for the position of the opening of the supply line in the gas tank to be adjusted. 
     BACKGROUND OF THE INVENTION 
     A handheld work apparatus of this type is known from U.S. Pat. No. 8,807,240 B2. The gas tank is an exchangeable gas cartridge which is inserted upside down into a receptacle on the housing of the work apparatus. In a manner which is dependent on the operating position of the work apparatus which is configured as a brushcutter, the user has to adjust an extraction stub which lies in the liquid gas and adapt it to the operating position of the work apparatus, in such a way that an undisruptive extraction of liquid gas is ensured. If the user changes the operating position of the work apparatus without adjusting the extraction stub in the gas cartridge, the extraction stub can protrude out of the liquid gas, with the result that only gaseous gas is extracted, which can lead to operating disruptions of the combustion engine. 
     SUMMARY OF THE INVENTION 
     It is an object of the invention to configure a handheld work apparatus with a gas-operated combustion engine and a gas tank in such a way that the feed of liquid gas is ensured in every operating position of the work apparatus without an intervention of the user. 
     The object can, for example, be achieved via a handheld work apparatus including: a gas-operated combustion engine having a cylinder with a combustion chamber; the combustion engine including a piston and an intake channel for feeding in combustion air; a supply line for a flammable gas; the combustion chamber being delimited by the piston; the combustion engine including a mixture formation unit; a gas tank; the supply line having an opening defining a position in the gas tank; the supply line being configured to feed liquid gas to the mixture formation unit, the liquid gas entering into the opening of the supply line within the gas tank, wherein the position of the opening in the gas tank is adjustable; the supply line including a longitudinal section disposed within the gas tank; and, the longitudinal section including a flexible hose and a weight arranged in a region of the opening in such a manner that the liquid gas is fed via the opening to the supply line. 
     In order to ensure that liquid gas is extracted from the gas tank in every operating position of the work apparatus, a longitudinal section of the supply line, which longitudinal section lies within the gas tank, is configured as a flexible hose. A weight is arranged, in particular a weight body is attached, in the region of the opening of the flexible hose, as a result of which a weight force always acts on the free end of the flexible hose independently of the operating position of the work apparatus. This ensures that the opening of the hose of the supply line lies in each case in the liquid gas independently of the operating position of the work apparatus, with the result that liquid gas is fed to the mixture formation unit in every operating position of the work apparatus. Disruption-free operation of the handheld work apparatus is ensured independently of its operating position. 
     The opening of the supply line is advantageously configured as a suction housing, the weight being arranged in the suction housing. 
     In order to ensure a high movability of that longitudinal section of the supply line which lies within the gas tank, it is provided that the elastic hose is provided from the opening of the supply line as far as a pass through of the supply line through the tank wall. 
     The gas tank is configured, in particular, as a refillable gas tank which is attached fixedly on the combustion engine or the work apparatus as an operating medium tank which is fixed on the apparatus. The gas tank can thus be connected to the crank case of the combustion engine in a mechanically fixed manner, expediently via holding elements which are configured on the crank case. 
     The gas tank has a fill valve for liquid gas, a pressure relief valve for gaseous gas and an extraction valve for liquid gas. In one particular development, a level gage which indicates a predefined filling level of the gas tank is arranged in the gas tank. The level gage is expediently configured as a float which closes at least the fill valve when a predefined filling level is reached. It can also be expedient to close the pressure relief valve via the float. In one particular development, both the fill valve and the pressure relief valve can be controlled by a common float. 
     In an embodiment, the level gage lies within a protective cage which is provided within the gas tank. The flexible hose of the supply line, which flexible hose is arranged in the gas tank, lies outside the protective cage, with the result that a mechanical impediment of the level gage by way of the hose which moves in the gas tank in a manner which is dependent on changing operating positions is prevented. 
     The liquid gas which is extracted from the gas tank is fed to an evaporator which is heated, in particular, by the waste heat of the combustion engine. The thermal energy which is necessary for evaporating can thus be provided in a simple way. 
     The evaporator advantageously lies in the spatial region of the cylinder of the combustion engine and/or in a spatial region of the exhaust muffler of the combustion engine. Sufficient waste heat which can be sufficient for heating the evaporator arises in the spatial regions. 
     A pressure reliever is connected downstream of the evaporator, the outlet of which pressure reliever opens into the control chamber of a membrane carburetor. It can be expedient that the gaseous gas which is to be fed to the membrane carburetor is raised toward the temperature of the combustion air which is fed in, before the introduction into the mixture formation unit. This is achieved simply by virtue of the fact that the gaseous gas is guided through a heat exchanger, around which the inflowing combustion air flows. 
     Further advantageous embodiments result from any desired combination of the features of the mentioned and described embodiments. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will now be described with reference to the drawings wherein: 
         FIG. 1  shows a diagrammatic side view of a handheld work apparatus using the example of a motorized chainsaw; 
         FIG. 2  shows a diagrammatic side view of a handheld work apparatus using the example of a blower; 
         FIG. 3  shows a diagrammatic illustration of a combustion engine with a flange-connected gas tank as an operating medium tank; 
         FIG. 4  shows a diagrammatic partially sectioned view of the gas tank as an operating medium tank on a combustion engine in accordance with  FIG. 3 ; 
         FIG. 5  shows a schematic illustration for feeding liquid gas to a mixture formation unit of a combustion engine; and, 
         FIG. 6  shows a schematic illustration in accordance with  FIG. 5  with a heat exchanger which is provided in the air inflow of the combustion engine. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION 
       FIG. 1  shows a handheld work apparatus  1  using the example of a motorized chainsaw. The work apparatus  1  has a housing  2  which has a rear handle  3  and an upper bale handle  4 . The handle  3  extends in the longitudinal direction of the work apparatus  1 ; a guide bar  5  which is provided at the front end of the housing  2  also extends in the longitudinal direction. A saw chain  6  circulates on the guide bar  5 , which saw chain  6  is driven via a chain sprocket (not shown) by a combustion engine  10  which is provided in the housing  2 . The combustion engine  10  which is shown physically in  FIGS. 3 and 4  is operated using liquid gas from a gas tank  11  which is provided as an operating medium tank  50 . In the embodiment in accordance with  FIG. 1 , the gas tank  11 , as operating medium tank  50 , lies in the housing  2  of the work apparatus  1  below an air filter  7  in the region of the rear handle  3 . 
     The operation of the saw chain is monitored by way of a safety brake device; a hand protective bracket  8  as an actuating element of the safety brake device in front of the front, upper bale handle  4 . 
     In the embodiment which is shown, the combustion engine  10  is started by way of a pull-rope starter  9 . A spring starter, an electric starter or a starting device of this type can also be provided as starting device. 
       FIG. 2  shows a work apparatus  1  in the form of a blower, in the housing  2  of which a combustion engine  10  is arranged. The combustion engine  10  drives a fan impeller which is arranged in a blower housing  12 . The blower housing  12  opens into a blower tube  13  which can be operated via a handle  14 . 
     A spray fluid which is stored in a spray fluid tank  16  is fed to the blown air flow via a line  15 . 
     A gas tank  11  as operating medium tank  50  lies below the combustion engine  10  between the carrier frame  17  of the back-pack blower and the housing  2  of the drive. Liquid gas is fed as operating medium from the gas tank  11  to the combustion engine  10 . 
       FIGS. 3 and 4  show in detail how the gas tank  11  is connected to the combustion engine  10  and in what way gas is fed in a liquid phase from the gas tank  11  to a mixture formation unit  30  of the combustion engine  10 . 
     The gas-operated combustion engine  10  has a cylinder  18  with a combustion chamber  19  which is delimited by a piston  20 . An intake channel  31  is configured, expediently on the mixture formation unit  30 , for feeding in combustion air  21 . Gas  23  is fed to the mixture formation unit  30  via a supply line  22 . The gas  23  is advantageously fed in a liquid phase, to which end the supply line  22  ends within the gas tank  11  of the work apparatus  1  by way of an opening  24 , into which liquid gas enters. The opening  24  is expediently configured as a suction housing  25 . A weight  26 , in particular a weight body, is preferably arranged on the opening. The weight  26  is advantageously provided in the suction housing  25 . A longitudinal section  27  of the supply line  22 , which longitudinal section  27  is provided within the gas tank  11 , is configured as a flexible hose  28 . As a result of the flexible hose  28 , the opening  24  of the hose  28  which is weighed down with a weight  26  is dipped under the action of the weight force into the liquid phase of the stored gas  29  in the gas tank  11 . This ensures that exclusively liquid gas of the stored gas  29  which is provided in the gas tank  11  enters into the opening  24  of the hose  28 . The flexibility of the hose  28  ensures that the position of the opening  24  of the supply line  22  in the gas tank  11  changes under the action of the weight force and the operational position of the work apparatus  1 . 
     The elastic longitudinal section  27  of the supply line  22  extends as a hose  28  from the opening  24  in the liquid gas phase as far as a pass through  32  in the tank wall  33 . An extraction valve  34  is preferably provided in the pass through  32 , which extraction valve  34  makes the extraction of the stored, liquid gas  29  from the gas tank  11  possible. 
     As  FIG. 3  shows, the gas tank  11  is fixed on the crank case  40  of the combustion engine  10  in the embodiment which is shown. To this end, the crank case has at least one, preferably two carrying clamps  41 ,  42  which can be configured, in particular, in one piece with the crank case  40 . The cylinder  18  is fixed on the crank case  40 , a crank shaft  43  being mounted in the crank case, which crank shaft  43  is connected to the piston  20  via a connecting rod  44 . 
     The combustion engine  10  is a reed valve-controlled combustion engine  10 , in particular a two stroke engine. That inlet  45  of the combustion engine  10  which is connected to the mixture formation unit  30  opens into the crank case  40 . The mixture which enters into the crank case  40  via the inlet  45  is compressed in the case of a downwardly moving piston  20  and is pushed out into the combustion chamber  19  of the cylinder  18  via transfer channels  46 ,  47 . In the case of an upwardly moving piston  20 , the mixture is compressed and, in the region of the top dead center of the reciprocating movement, is ignited by way of an ignition apparatus (not shown in greater detail), as a result of which the piston  20  is driven downward again. The combustion gases are discharged via an exhaust gas outlet  48 . The inlet  45 , the transfer channels  46  and  47  and the exhaust gas outlet  48  are controlled by way of the piston  20  which moves up and down. 
     In addition to the extraction valve  34 , the gas tank  11  has a fill valve  35  and expediently a pressure relief valve  36  for gaseous gas. As  FIGS. 3 and 4  show, furthermore, a protective cage  38  is provided within the gas tank  11 , in which protective cage  38  a level gage  49  is arranged. The level gage  49  is expediently configured as a float  39  which includes a hollow body  51  which floats on the liquid surface of the filling level  37 . A predefined filling level  37  of the gas tank  11  can be indicated via the level gage  49 . It is provided in one advantageous embodiment of the construction that the float  39  controls at least the fill valve  35  via a control lever  52 . If the filling level  37  in the gas tank  11  reaches a predefined height, at least the fill valve  35  is closed via the control lever  52 . It can be expedient, as an alternative to the fill valve  35 , to control the pressure relief valve  36  via the float  39 . 
     The fill valve  35  and the pressure relief valve  36  open into the gas tank within the protective cage  38 . The movable float  39  and the control lever  52  are likewise provided in the protective cage  38 . This ensures that the hose  28 , the position of which in the gas tank  11  can move, does not impair the mechanism of the level gauge  49  and/or its float  39 . The elastic, flexible hose  28  lies permanently outside the protective cage  38 . 
     In the following text, the feeding of gas to the mixture formation unit  30  of the combustion engine  10  will be described using the diagrammatic illustrations of  FIGS. 5 and 6 . 
     The liquid gas  23  flows in the arrow direction  60  to an evaporator  53 . For temperature equalization, the evaporator  53  expediently lies in the spatial region of a heat source, in particular in the spatial region  63  of the discharged exhaust gases  61 . The evaporator  53  is heated by the waste heat of the combustion engine  10 . In a simple way, the evaporator  53  is arranged in the spatial region  62  of the cylinder and/or in a spatial region  63  of an exhaust muffler  64  of the combustion engine  10 . It can also be provided that the exhaust gases  61  are routed in such a way that they flow around the evaporator  53 . 
     The evaporator  53  ensures the transition of the liquid gas  23  which is fed in a liquid phase in the arrow direction  60 . A pressure reliever  54  is connected downstream of the evaporator  53 . The outlet  55  of the pressure reliever  54  opens via a pressure-controlled control valve  56  into the control chamber  57  of a carburetor, in particular a membrane carburetor. The control chamber  57  is delimited by way of a flexible membrane  58 . If gas flows from the control chamber  57  into the mixture formation device  30 , the pressure in the control chamber  57  will decrease and the membrane  58  will dip into the control chamber  57 . The membrane  58  opens the control valve  56  via a lever assembly  59 , with the result that gas in a gaseous phase can flow out of the pressure reliever  54  into the mixture formation unit  30 . 
     The illustration in  FIG. 6  corresponds substantially to that in accordance with  FIG. 5 . In addition, a heat exchanger  66  is provided between the outlet  55  of the pressure reliever  54  and the line connection to the control valve  56 , around which heat exchanger  66  the combustion air  21  which is fed in flows. As a result, the gaseous gas  65  is raised in the direction of the temperature of the combustion air  21  which is fed in, before the introduction into the mixture formation unit  30 . As  FIG. 6  shows, the combustion air  21  which flows in is cleaned by way of an air filter  7  before it flows through the heat exchanger. 
     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.