Patent Publication Number: US-10330038-B2

Title: Method for adapting the composition of a mixture of fuel and combustion air

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims priority of European patent application no. 17 400 006.7, filed Feb. 1, 2017, the entire content of which is incorporated herein by reference. 
     FIELD OF THE INVENTION 
     The invention relates to a method for initiating adaptation of the composition of a mixture of fuel and combustion air, wherein the mixture is supplied to a combustion chamber of a mixture-lubricated combustion engine in a work apparatus. At least a partial quantity of the fuel which is supplied to the combustion engine is supplied via an electromagnetically controlled fuel valve, wherein, in an operating state of the combustion engine, the supplied partial quantity of fuel is added in a metered manner by opening and closing the electromagnetic fuel valve depending on operating parameters of the combustion engine. 
     BACKGROUND OF THE INVENTION 
     Adapting the mixture comprising fuel and combustion air is dependent to a particular extent on the atmospheric pressure and, more specifically, on the altitude of the site of use of the work apparatus. It is known that the user can use a corresponding work tool to make adjustments to the mixture formation unit of the combustion engine for the purpose of adapting the elevation of the site of work, for example by manually turning the carburetor screw using a work tool such as a screwdriver or the like. This is complicated and requires a work tool to be carried. The mixture comprising fuel and combustion air is expediently also adapted when components of the work apparatus have been cleaned or replaced, such as an air filter which purifies the combustion air for example. 
     SUMMARY OF THE INVENTION 
     It is an object of the invention to provide a method for adapting the composition of a mixture comprising fuel and combustion air, which method can be initiated by the user in a simple manner without a special work tool. 
     According to the invention, the object is achieved in that, in a method for adapting the composition of a mixture comprising fuel and combustion air, which mixture is supplied to the combustion chamber of a mixture-lubricated combustion engine, at least a partial quantity of the fuel is supplied to the combustion engine via an electromagnetically controlled fuel valve and, in an operating state of the combustion engine, the supplied partial quantity of fuel is added in a metered manner by the electromagnetic fuel valve depending on operating parameters by way of the composition of the mixture being adapted in a special operating state which differs from the operating state of the combustion engine and, for the purpose of initiating the special operating state, the combustion engine being initially started by the user and, after starting, being operated in a first rotational speed range for a prespecified operating time and, after the prespecified operating time has elapsed, the special operating state for adapting the composition of the mixture being initiated by a user action. 
     First of all, it is provided that the adaptation of the composition of the mixture is executed in a special operating state which differs from the operating state of the combustion engine. In order to initiate this special operating state of the combustion engine, the user initially has to start the combustion engine and, after starting, operate the combustion engine in a first rotational speed range for a prespecified operating time. Once the prespecified operating time has elapsed and the first rotational speed range is maintained during the first operating time, the user can initiate the special operating state by a simple user action for the purpose of adapting the composition of the mixture. An expedient user action may comprise pressing the throttle lever and/or the locking lever once or several times. 
     The user advantageously does not perform any further actions during the first operating time of the combustion engine and leaves the combustion engine in its operating state. 
     A user action for initiating the special operating state expediently involves the rotational speed of the combustion engine being increased to a second rotational speed range by the user action. The second rotational speed range advantageously lies above the first rotational speed range and is achieved in a simple manner by the user operating the combustion engine in the second rotational speed range under full throttle. The user can therefore initiate the special operating state after the prespecified operating time has elapsed by pressing down the throttle lever of the work apparatus, in particular pressing down the throttle lever completely, that is, applying full throttle. In the process, the internal combustion engine is operated in the first and/or second rotational speed range, in particular in a load-free manner. 
     Starting of the combustion engine is, in particular, cold starting, so that the combustion engine is operated in the first rotational speed range after cold starting with starting gas during the prespecified operating time. The machine runs warm and in a conditioned manner in this first rotational speed range. 
     In order to initiate the user action, a time window expediently opens after the prespecified operating time has elapsed. After the prespecified operating time has elapsed, the time window extends over a time period advantageously of from 15 seconds to 360 seconds, in particular over a time period of from 30 seconds to 90 seconds, particularly advantageously of from 30 seconds to 60 seconds. If no prespecified user action is performed within the time window, the combustion engine is operated in the normal operating state. 
     The calibration or adaptation of the composition of the mixture is performed, in particular, in a plurality of successive calibration steps. In this case, the mixture can be adapted at nominal rotational speed of the combustion engine in a first calibration step. The first calibration step advantageously serves to adjust the maximum power of the work apparatus. 
     In an advantageously following second calibration step, the mixture is adapted at the maximum rotational speed of the combustion engine. 
     In an embodiment of the invention, provision is made to enable a third calibration step if the first and the second calibration step have been successfully completed. In a third calibration step of this kind, the mixture can be adapted for idling. The third calibration step can advantageously be carried out only under prespecified further boundary conditions, for example only with connection of a diagnosis apparatus. 
     During the adaptation of the mixture in the different calibration steps, provision is made to terminate the special operating state and switch off the combustion engine if one calibration step is not successfully completed. This serves, for example, as feedback to the user that the calibration of the machine was not successful. 
     If the calibration step is successfully completed, the user receives corresponding feedback, for example a reduction in the rotational speed n of the combustion engine to a rotational speed which advantageously lies below the second rotational speed range. The rotational speed n feedback  advantageously lies above the first rotational speed range and below the second rotational speed range. It may be expedient in the case of successful completion of, for example, the third calibration step to switch off the combustion engine by means of the control unit. 
     The supplied partial quantity of fuel is added in a metered manner, in particular by clocked opening of the electromagnetic fuel valve by a control unit. The total quantity of fuel which is supplied to the combustion air is advantageously added in a metered manner via the electromagnetic fuel valve. 
     The mixture in the combustion chamber is ignited by the ignition sparks of a spark plug which is actuated by a control unit. In order to adjust the nominal rotational speed of the combustion engine, it is advantageously provided to adjust the rotational speed by suppressing the ignition spark. This is also called “desynchronization”. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will now be described with reference to the drawings wherein: 
         FIG. 1  is a schematic sectional view through a first work apparatus comprising a combustion engine; 
         FIG. 2  shows a side view of a further work apparatus comprising a combustion engine; 
         FIG. 3  shows a flowchart for adapting the composition of a mixture comprising fuel and combustion air for a combustion engine; 
         FIG. 4  shows a schematic representation of a method sequence of a plurality of successive calibration steps; and, 
         FIG. 5  is a schematic of a method sequence of successive calibration steps with a calibration step for adapting the mixture at idle rotational speed. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION 
     The work apparatus  1  shown in  FIG. 1  is a chain saw  2  including a combustion engine  3  which drives, as work tool  5 , a saw chain which revolves on a guide bar  4 . The rotational speed of the combustion engine  3  is controlled by a user by way of a throttle lever  6  which has an associated throttle lever lock  7 . For the purpose of increasing the rotational speed of the combustion engine  3 , the throttle lever  6  can advantageously then first be pressed down in arrow direction  8  towards full throttle when the throttle lever lock  7  is actuated. The throttle lever  6  and the throttle lever lock  7  are provided in a rear handle  19  of the work apparatus  1 . 
     In the embodiment shown, the combustion engine  3  is a preferably mixture-lubricated combustion engine, in particular a two-stroke engine, a mixture-lubricated four-stroke engine or the like. The combustion engine  3  is, in particular, a single-cylinder combustion engine. 
     For the purpose of operating the combustion engine  3 , a mixture  10  comprising fuel and combustion air is supplied by a mixture formation unit  9 . The mixture  10  fills a combustion chamber  11  of the combustion engine  3  and is ignited by a spark plug  12  by way of an ignition spark being outputted. 
     At least a partial quantity of the fuel, which is supplied to the inflowing combustion air by means of the mixture formation unit  9 , is added in a metered manner via an electromagnetic fuel valve  13 . In an operating state I of the combustion engine  3 , which can also be called the normal operating state, the composition of the mixture  10  is changed by controlling the electromagnetic fuel valve  13  in dependence upon operating parameters. To this end, a control unit  15 , which is supplied with the rotational speed of the combustion engine  3  as a first operating parameter by a rotational speed sensor  16  for example, can be provided. The pressure in the crankcase  18  and/or the temperature in the crankcase  18  can be reported to the control unit  15  as further operating parameters by a further sensor  17 . The list of operating parameters is exemplary; it is possible for more or fewer operating parameters to be processed in the control unit  15 . 
     The control unit  15  is connected to the fuel valve  13  via a control line  14 . The control unit  15  controls the opening time of the fuel valve  13 . The opening time of the fuel valve  13  determines the supplied partial quantity of fuel which is supplied to the combustion engine. 
     The fuel valve  13  is expediently a clocked fuel valve, that is, the fuel valve  13  is opened and closed by applying a clock frequency; by virtue of changing the clock frequency, the total opening duration of the fuel valve  13  can be adjusted and therefore the quantity of fuel flowing to the mixture formation unit, in particular a partial quantity of fuel, can be added in a metered manner. 
     The fuel valve  13  is advantageously an electromagnetic fuel valve which is open when no current is applied. An electromagnetic fuel valve which is closed when no current is applied can also be advantageous. 
     The delivery of the fuel to the mixture formation unit  9  is performed, in particular, above the negative pressure which is present in the intake channel of the mixture formation unit  9 ; if the fuel valve  13  is open, fuel is drawn in. 
     The embodiment of a work apparatus shown in  FIG. 2  is a cut-off machine  20 , a combustion engine corresponding to  FIG. 1  being arranged in the housing of the cut-off machine. The rotational speed of this combustion engine can also be controlled by the throttle lever  6 , wherein the throttle lever  6  can advantageously be pivoted in arrow direction  8  toward full throttle only after actuation of the throttle lever lock  7 . The throttle lever  6  and the throttle lever lock  7  are provided in a rear handle  19  of the work apparatus  1 . 
     In combustion engines  3  of this kind, the mixture  10  comprising fuel and combustion air changes depending on the atmospheric pressure and/or depending on the altitude of the site of use of the work apparatus  1 . If the density of the combustion air changes, the mixture  10  would become too rich with the same quantity of fuel added in a metered manner; therefore, before commissioning the work apparatus  1 , it is practical to calibrate the mixture formation unit  9  in such a way that the composition of the mixture  10  comprising fuel and combustion air is matched to the atmospheric pressure and/or to the altitude of the site of use of the work apparatus  1 . 
     In line with the method according to the invention as per the flowchart in  FIG. 3 , the combustion engine  3  is moved from a first operating state I to a second operating state, which corresponds to a special operating state II, for the purpose of initiating the process of adapting the composition of the mixture  10  comprising fuel and combustion air. In the special operating state II, the mixture formation unit  9  is calibrated and the composition of the mixture  10  comprising fuel and combustion air is adapted. The first operating state I can also be called the normal operating state of the combustion engine, in which normal operating state the work apparatus is used as intended. 
     The process of adapting the composition of the mixture  10  comprising fuel and combustion air is initiated depending on at least one prespecified user action, in particular by means of the operator control elements which are provided for operating the work apparatus  1 , such as the throttle lever  6  and/or the throttle lever lock  7  for example. In order to arrive at a special operating state II, which is necessary for adapting the composition of the mixture  10 , from the first operating state I of the combustion engine  3 , the combustion engine  3  first has to be started by the user. In this case, starting of the combustion engine  3  is expediently cold starting. A corresponding cold starting flap or the like can be operated on the mixture formation unit  9  for the purpose of cold starting. Cold starting is understood to mean first starting of the combustion engine, in which starting operation the combustion engine  3  is at most at ambient temperature during starting. If the combustion engine  3  is at ambient temperature, it can be assumed that the combustion engine  3  is being commissioned for the first time. This corresponds to cold starting. 
     After starting of the combustion engine  3  shown in field  36  in  FIG. 3 , the combustion engine has to be operated for a prespecified operating time BZ of the duration T min  in a first rotational speed range. This first rotational speed range can be determined by a prespecified rotational speed band and/or by a limit rotational speed n limit , as shown in the left-hand column of  FIG. 3 . During this operating time BZ, for example with starting gas, a check is made to determine whether the actual rotational speed n act  is lower than a prespecified limit rotational speed n limit . When a rotational speed band is prespecified, the lower limit of the rotational speed band, for example a minimum rotational speed, can also be checked. If the prespecified condition is met, operation is performed in the first rotational speed range B, as shown in  FIGS. 4 and 5 . The maximum limit rotational speed n limit  can correspond to a starting rotational speed n STR . 
     In accordance with the flowchart in  FIG. 3 , operation with starting gas is initially established in field  37 . The actual rotational speed n act  is, as shown in a first decision rhombus  30 , monitored at least to check that a prespecified limit rotational speed n limit  is not exceeded. Thereafter, a check is made, as shown by decision rhombus  31 , to determine whether the actual rotational speed n act  is lower than the limit rotational speed n limit  over a prespecified minimum operating time T min . If this condition is met, a time window ZF is opened according to field  32 . The time window ZF according to field  32  has an upper time limit T max  which, as shown in the decision rhombus  33 , is monitored. If the time limit T max  is reached without a prespecified user action being executed, the combustion engine  3  continues to run in a normal operating state, the first operating state I. This first operating state I is indicated in field  35 . The combustion engine  3  is always operated in the first operating state I when the result of the checks according to the decisions in the decision rhombuses  30 ,  31  and  33  is answered with “No”. 
     If the time window ZF according to decision rhombus  33  is open and the user executes a prespecified user action, this is checked in the process sequence, as shown in the decision rhombus  34 . If a prespecified user action is established, a changeover is made from the operating state I to the special operating state II. 
     The established user action, see rhombus  34  in  FIG. 3 , expediently leads to an increase in the rotational speed n act  of the combustion engine  3  into a second rotational speed range C and/or D ( FIGS. 4, 5 ). As shown in  FIGS. 4 and 5 , the second rotational speed range C and/or D lies above the first rotational speed range B. In particular, the user action is given by the user completely pressing down the throttle lever  6  in arrow direction  8 ; the combustion engine is therefore operated by the user under full throttle in the second rotational speed range C and/or D. At the position “full throttle” of the throttle lever  6 , the special operating state II is initiated and the full throttle position is maintained—preferably by the user—until the combustion engine  3  provides the user with feedback that the calibration was successful. 
     With the initiation of the special operating state II, the user keeps the throttle lever  6  permanently operated, advantageously pushed up to an end stop, this corresponding to a full throttle position. It may be advantageous for the control unit  15  to take over control of the combustion engine  3  with the initiation of the special operating state II by a prespecified user action and for the method for adapting the composition of the mixture  10  comprising fuel and combustion air to be automatically carried out until an end of the method. 
     Provision can also be made for the user to have to carry out the prespecified user action permanently over a prespecified time period in order to initiate the special operating state II. Following this, the combustion engine  3  in conjunction with the control unit  15  can automatically carry out the method for adapting the composition of the mixture  10  comprising fuel and combustion air until an end of the method. 
     Within the scope of the invention, starting of the combustion engine  3  can also be warm starting. Starting after previous running of the combustion engine  3  is called warm starting. The combustion engine  3  can be at a temperature which is higher than the ambient temperature. If a user wishes to adapt the composition of a mixture  10  comprising fuel and combustion air after warm starting, he can carry out the warm starting in a starting position of the mixture formation device  9  for the purpose of initiating the special operating state. The warm starting is identified by the control unit  15  and then detected as first starting of the combustion engine  3 . If the user does not perform any further user actions during the first operating time, the combustion engine  3  is operated for a prespecified operating time T min  in a first rotational speed range B in a first operating state. After the operating time T min  has elapsed, the time window ZF for jumping to a special operating state II is opened after execution of a prespecified user action, for example full throttle being applied. 
     The composition of the mixture  10  comprising fuel and combustion air is adapted, in particular, in a load-free manner, that is, without loading on the work tool  5 . For example, in the embodiment according to  FIG. 1 , a saw chain is fitted on the guide rail as work tool  5 , but the method for adapting the mixture is carried out only when the saw chain is not being used for cutting wood. The saw chain can run concomitantly in a load-free manner. The same applies, for example, for a work apparatus according to  FIG. 2 . 
     The method for adapting the composition of a mixture  10  comprising fuel and combustion air is advantageously performed in a plurality of calibration steps  40 ,  50 ,  60 . According to the embodiment, the composition of the mixture  10  comprising fuel and combustion air is adapted in three calibration steps  40 ,  50 ,  60 , in particular in an automated manner without further mandatory user actions, after the special operating state II ( FIG. 3 ) is initiated. 
     On account of the user action “full throttle” prespecified in the embodiment, the combustion engine  3  initially runs at a nominal rotational speed n nom . This operation at nominal rotational speed n nom  has to be performed for a minimum time T N . During this minimum time T N , calibration is performed in the first calibration step  40  at nominal rotational speed n nom . This nominal rotational speed n nom  is—even under full throttle—achieved by desynchronization of the ignition. The mixture  10  in the combustion chamber  11  is ignited by ignition sparks of the spark plug  12  which is actuated by an ignition device, in the embodiment the control unit  15 . The nominal rotational speed n nom  is regulated by suppression of the ignition spark by the control unit  15 . The combustion engine  3  is adjusted down to the nominal rotational speed n nom . 
     After the first calibration step  40  is concluded, a check is made according to the decision rhombus  41  to determine whether the calibration was successful. If no fault is established, the method branches in the manner shown in the decision rhombus  41 . The method branches to the second calibration step  50  in branch “Yes”. If the calibration was not successful, the method branches to field  19  via the “No” branch according to the decision rhombus  41  and the combustion engine  3  is switched off. 
     If the first calibration step  40  was completed successfully, the rotational speed n act  of the combustion engine  3  increases to a maximum rotational speed n max . This rotational speed range of the maximum rotational speed n max  advantageously lasts for a minimum time T H . During this minimum time T H , calibration is performed in the second calibration step  50  for the purpose of further adapting the mixture  10  comprising fuel and combustion air. As shown in the decision rhombus  51 , a check is then made in the method to determine whether the calibration in the second calibration step  50  was successful. In the event of a fault in the second calibration step  50 , the decision rhombus  51  branches to the “No” branch which leads to field  19  and to the combustion engine  3  being switched off. 
     As an alternative, the calibration can be completed after successful completion of the second calibration step  50 . The successful calibration is reported to the user by feedback. As feedback to successful calibration, the rotational speed of the combustion engine  3  can be lowered to a feedback rotational speed n feedback  as shown in field  52 . It can also be expedient to switch off the combustion engine as feedback to the user. 
     If the calibration was also successful in the second calibration step  50 , the third calibration step  60  can advantageously be enabled only under prespecified further boundary conditions. For example, it may be necessary to permit the third calibration step  60  to be carried out only when a diagnosis apparatus is connected. The third calibration step  60  can expediently be started up only during servicing at a workshop. The mixture is calibrated at idling rotational speed n LL  in the third calibration step  60 . If the third calibration step  60  was successfully completed, the combustion engine  3  is preferably switched off, as shown in field  62 . 
     In order to report back to the user about the successful calibration of the combustion engine  3  after successful completion of the calibration steps  40  and  50  on-site, the rotational speed n of the combustion engine  3  is advantageously lowered to a feedback rotational speed n feedback  after completion of the second calibration step  50 . The feedback rotational speed n feedback  is advantageously lower than n max , in particular lower than n nom . The feedback rotational speed n feedback  is preferably greater than n STR  and, respectively, n LL , but, in particular, can be zero and can be achieved by switching off the combustion engine  3 . 
     After the feedback, the user—if he is still keeping the throttle lever  6  pressed—can release the throttle and move the throttle lever  6  to the idling position against arrow direction  8 . As an alternative, the composition of a mixture  10  comprising fuel and combustion air can then be adapted in the idle state in the calibration step  60 . As shown in the decision rhombus  61 , a check is then made to determine whether the calibration of the third calibration step  60  was successful. If a fault occurred, the method branches to field  19  via the “No” branch and the combustion engine  3  is switched off. If the calibration of the third calibration step  60  was successful, the combustion engine  3  is advantageously switched off. Switching off the combustion engine serves as feedback to the user, wherein it is possible to read out, in particular via a connected diagnosis apparatus, whether the calibration was successful. 
     One example of the method sequence for adapting the composition of a mixture  10  comprising fuel and combustion air is shown in a first advantageous embodiment in  FIG. 4 . In section A, the combustion engine  3  is started using starting gas, as a result of which the combustion engine  3  runs at a starting rotational speed n STR . The starting rotational speed n STR  corresponds to a limit rotational speed n limit . This starting run has to last for a fixed operating time BZ of the duration T min  of, in the embodiment, 30 seconds, so that the time window ZF for the purpose of initiating the special operating mode II is opened. 
     If the user operates the throttle lever  6 , in particular applies full throttle, within this time window ZF indicated in  FIG. 3 , the rotational speed n increases to the rotational speed n nom . In a first calibration step  40 , so-called full-load calibration takes place in this second rotational speed range C at increased rotational speed n. The combustion engine is advantageously adjusted down at a defined rotational speed during the full-load calibration. During the adjustment down, the ignition is advantageously desynchronized and the mixture adapted. If the adjustment criterion, for example a prespecified rotational speed, cannot be achieved in the second rotational speed range C of the calibration step  40 , the calibration is aborted due to lowering of the rotational speed in accordance with falling flank H. In particular, the rotational speed n falls to ‘zero’. The combustion engine  3  is switched off. 
     If the calibration in the second rotational speed range C was successful, the desynchronization of the ignition is suppressed, so that—since the user is advantageously applying full throttle in an unchanged manner—the combustion engine  3  runs up to a maximum rotational speed n max . During this further second rotational speed range D at increased rotational speed, the mixture is calibrated in the high rotational speed range in the second calibration step  50 . 
     If the second calibration step  50  is successfully completed in the further, second rotational speed range D, the rotational speed n of the combustion engine  3  is advantageously lowered to a feedback rotational speed n feedback  in a method section E by means of the control unit  15 . This significant reduction in the rotational speed is advantageously performed by the control unit  15  even though full throttle continues to be applied by the user, as shown in the profile of the throttle lever position over time. According to the switching indicator in  FIG. 4 , the throttle lever is in position “1”, that is, in the “full throttle” position, in method step E too. 
     When the feedback rotational speed n feedback  is identified, the user releases the throttle in section F; the throttle lever  6  moves to the idling position and the combustion engine  3  runs at the idling rotational speed n LL . The combustion engine  3  is matched to changed boundary conditions, for example matched to the altitude of the site of use or the prevailing atmospheric pressure or to newly installed replacement parts or to a cleaned air filter, by the calibration. 
     It is left to the user to keep the rotational speed at a maximum rotational speed n max  in section G by continuing to apply full throttle. 
       FIG. 5  shows an alternative method sequence for initiating a method for adjusting the composition of a mixture  10  comprising fuel and combustion air. According to  FIG. 5 —the combustion engine  3  is started under starting gas in section A; the combustion engine  3  is run up to starting rotational speed n STR  The rotational speed range B is maintained for an operating time BZ with a duration T min  of 30 seconds as indicated in the embodiment; after the minimum operating time BZ has elapsed, the time window ZF is open according to field  32  in  FIG. 3 . The user moves the throttle lever from the position “0” (idling) to the position “1” (full throttle), as shown in the view of the throttle lever position over time beneath the rotational speed profile. The rotational speed n of the combustion engine  3  is run up to a nominal rotational speed n nom  and calibration is carried out over a time period T N  of advantageously 30 seconds. If the calibration in the second rotational speed range C over the minimum time T N  is faulty, the rotational speed according to the falling flank H drops to 0. The combustion engine  3  turns off. If the calibration is successful, the rotational speed drops to a feedback rotational speed n feedback  in section E under the action of the control unit  15 —in spite of the position of the throttle lever at “1” (full throttle). The user identifies completed calibration and releases the throttle; the throttle lever assumes the position “0” (idling). The combustion engine  3  falls to the idling rotational speed n LL . In the rotational speed range F, idling calibration according to calibration step  60  in  FIG. 3  can now take place, the combustion engine  3  being switched off after the idling calibration is successfully completed. The mixture  10  which is supplied to the combustion engine  3  is matched to the density of the combustion air. 
     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.