Method for operating a work apparatus having a combustion engine

Abstract

The invention relates to a method for operating a work apparatus having a combustion engine. An ignition device is provided for triggering an ignition spark at a spark plug for igniting a fuel/air mixture in a combustion chamber of the combustion engine. The combustion chamber is bounded by a piston which drives a crankshaft in a rotating manner. In order to avoid the combustion engine stopping in rich mode, the speed (n) of the combustion engine is monitored over the period of time (t, ΔT) and the ignition point (ZZP) of the ignition device is advanced if the speed (n) of the combustion engine lies within a predefined speed range (n.sub.min; n.sub.max) within a predefined period of time (t, ΔT) and then the speed n drops below a speed limit value (n.sub.G).

Claims

1. A method for operating a work apparatus having a combustion engine including a combustion chamber, a piston delimiting the combustion chamber, a spark plug, an ignition device configured to trigger an ignition spark at the spark plug so as to ignite a fuel/air mixture in the combustion chamber, the ignition device being configured to trigger an ignition spark at the spark plug at an ignition time point (ZZP) in dependence upon the rotational position of the piston, a work tool, a crankshaft configured to drive the work tool, a centrifugal clutch arranged between the crankshaft and the work tool, the method comprising the steps of: monitoring the rotational speed (n) of the combustion engine; advancing the ignition time point (ZZP) when the following sequentially occurring conditions are satisfied: i. a rich fuel/air mixture is supplied to the combustion chamber, ii. the rotational speed (n) lies in a predetermined rotational speed range (n.sub.min; n.sub.max) within a predetermined time period (ΔT), wherein the predetermined rotational speed range (n.sub.min; n.sub.max) is between 3,000 revolutions per minute and 5,000 revolutions per minute, and, iii. the rotational speed (n) of the combustion engine drops off to below a rotational speed limit value (n.sub.G) after the conditions (i) and (ii) are satisfied, so that, after the conditions (i), (ii) and (iii) are fulfilled, a stopping of the combustion engine is prevented as a result of the advancing of the ignition time point (ZZP).

2. The method of claim 1 further comprising the steps of: setting a status indicator (I) when said first condition (i) is satisfied; and, advancing the ignition time point (ZZP) when there is a drop of the rotational speed to below a rotational speed limit value (n.sub.G) with said status indicator being set.

3. A method for operating a work apparatus having a combustion engine including a combustion chamber, a piston delimiting the combustion chamber, a spark plug, an ignition device configured to trigger an ignition spark at the spark plug so as to ignite a fuel/air mixture in the combustion chamber, the ignition device being configured to trigger an ignition spark at the spark plug at an ignition time point (ZZP) in dependence upon the rotational position of the piston, a work tool, a crankshaft configured to drive the work tool, a centrifugal clutch arranged between the crankshaft and the work tool, the method comprising the steps of: monitoring the rotational speed (n) of the combustion engine; advancing the ignition time point (ZZP) when the following sequentially occurring conditions are satisfied: i. the rotational speed (n) lies in a predetermined rotational speed range (n.sub.min; n.sub.max) within a predetermined time period (ΔT), and, ii. the rotational speed (n) of the combustion engine drops off to below a rotational speed limit value (n.sub.G) after the condition (i) is satisfied, so that, after the conditions (i) and (ii) are fulfilled, a stopping of the combustion engine is prevented as a result of the advancing of the ignition time point (ZZP); setting a status indicator (I) when said first condition (i) is satisfied; advancing the ignition time point (ZZP) when there is a drop of the rotational speed to below the rotational speed limit value (n.sub.G) with said status indicator being set; and, maintaining the set status indicator (I) until the rotational speed (n) drop below the rotational speed limit value (n.sub.G).

4. The method of claim 3 further comprising holding the set status indicator (I) for a predetermined amount of time (t).

5. The method of claim 3, wherein the time period (ΔT) is determined by a predetermined number of sequential crankshaft rotations.

6. The method of claim 5, wherein the time period (ΔT) is determined by five to fifty sequential crankshaft rotations.

7. The method of claim 5, wherein the crankshaft rotations directly follow one another.

8. The method of claim 3, wherein the rotational speed limit value (n.sub.G) lies below the predetermined rotational speed range (n.sub.min; n.sub.max).

9. The method of claim 3, wherein the centrifugal clutch has an engagement speed lying within the predetermined rotational speed range (n.sub.min; n.sub.max).

10. The method of claim 3, wherein the predetermined rotational speed range (n.sub.min; n.sub.max) is between 3,000 revolutions per minute and 5,000 revolutions per minute.

11. The method of claim 3 further comprising the step of supplying a rich fuel/air mixture to the combustion chamber of the combustion engine.

12. A method for operating a work apparatus having a combustion engine including a combustion chamber, a piston delimiting the combustion chamber, a spark plug, an ignition device configured to trigger an ignition spark at the spark plug so as to ignite a fuel/air mixture in the combustion chamber, the ignition device being configured to trigger an ignition spark at the spark plug at an ignition time point (ZZP) in dependence upon the rotational position of the piston, a work tool, a crankshaft configured to drive the work tool, a centrifugal clutch arranged between the crankshaft and the work tool, the method comprising the steps of: monitoring the rotational speed (n) of the combustion engine; advancing the ignition time point (ZZP) when the following sequentially occurring conditions are satisfied: i. the rotational speed (n) lies in a predetermined rotational speed range (n.sub.min; n.sub.max) within a predetermined time period (ΔT), and, ii. the rotational speed (n) of the combustion engine drops off to below a rotational speed limit value (n.sub.G) after the condition (i) is satisfied, so that, after the conditions (i) and (ii) are fulfilled, a stopping of the combustion engine is prevented as a result of the advancing of the ignition time point (ZZP); setting a status indicator (I) when said first condition (i) is satisfied; advancing the ignition time point (ZZP) when there is a drop of the rotational speed to below the rotational speed limit value (n.sub.G) with said status indicator being set; and, removing the set status indicator (I) when the rotational speed (n) increases above the predetermined rotational speed range (n.sub.min; n.sub.max).

13. The method of claim 12 further comprising holding the set status indicator for a predetermined amount of time (t).

14. The method of claim 12, wherein the time period (ΔT) is determined by a predetermined number of sequential crankshaft rotations.

15. The method of claim 14, wherein the time period (ΔT) is determined by five to fifty sequential crankshaft rotations.

16. The method of claim 14, wherein the crankshaft rotations directly follow one another.

17. The method of claim 12, wherein the rotational speed limit value (n.sub.G) lies below the predetermined rotational speed range (n.sub.min; n.sub.max).

18. The method of claim 12, wherein the centrifugal clutch has an engagement speed lying within the predetermined rotational speed range (n.sub.min; n.sub.max).

19. The method of claim 12, wherein the predetermined rotational speed range (n.sub.min; n.sub.max) is between 3,000 l/min and 5,000 l/min.

20. The method of claim 12 further comprising the step of supplying a rich fuel/air mixture to the combustion chamber of the combustion engine.

21. A method for operating a work apparatus having a combustion engine including a combustion chamber, a piston delimiting the combustion chamber, a spark plug, an ignition device configured to trigger an ignition spark at the spark plug so as to ignite a fuel/air mixture in the combustion chamber, the ignition device being configured to trigger an ignition spark at the spark plug at an ignition time point (ZZP) in dependence upon the rotational position of the piston, a work tool, a crankshaft configured to drive the work tool, a centrifugal clutch arranged between the crankshaft and the work tool, the method comprising the steps of: —monitoring the rotational speed (n) of the combustion engine; advancing the ignition time point (ZZP) when the following sequentially occurring conditions are satisfied: i. a rich fuel/air mixture is supplied to the combustion chamber, ii. the rotational speed (n) lies in a predetermined rotational speed range (n.sub.min; n.sub.max) within a predetermined time period (ΔT), wherein the predetermined rotational speed range (n.sub.min; n.sub.max) is between 3,000 revolutions per minute and 5,000 revolutions per minute, iii. the rotational speed (n) of the combustion engine drops off to below a rotational speed limit value (n.sub.G) after the conditions (i) and (ii) are satisfied, wherein the rotational speed limit value (n.sub.G) lies below the predetermined rotational speed range (n.sub.min; n.sub.max), so that, after the conditions (i) to (iii) are fulfilled, a stopping of the combustion engine is prevented as a result of the advancing of the ignition time point (ZZP).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention will now be described with reference to the drawings wherein:

(2) FIG. 1 is a perspective view of a work apparatus having a combustion engine, using the example of a chainsaw;

(3) FIG. 2 is a perspective view of a work apparatus having a combustion engine, using the example of a cut-off grinder;

(4) FIG. 3 is a schematic of a device for controlling the ignition point for ignition of the combustion engine;

(5) FIG. 4 is a sequence diagram for the operation of the work apparatus; and,

(6) FIG. 5 is an ignition point curve in the form of a bifurcated curve.

DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

(7) FIG. 1 shows a chainsaw as an example of a work apparatus 1 having a combustion engine, the saw chain 3 of which chainsaw, the saw chain revolving on a guide rail 2, being driven by the combustion engine 5. The work apparatus has a rear handle 11 which substantially extends in the longitudinal direction of the work apparatus 1. A throttle lever 28 for controlling the combustion engine 5 is provided in the rear handle 11. A front handle 12 is configured as a bale handle and engages over the housing 13 of the work apparatus 1 from the one longitudinal side to the other longitudinal side thereof. A hand guard 14 is provided in front of the front handle 12, the hand guard being provided as a trigger for a safety brake 16 located under a sprocket cover 15.

(8) FIG. 2 shows a cut-off grinder as a further example of a work apparatus 1 having a combustion engine, the cutting disk 3a of which cut-off grinder is driven by the combustion engine 5. The cutting disk 3a is assigned a hood 2a which engages over the cutting disk 3a to provide protection and extends over a circumferential angle of 180°. The work apparatus 1 configured as a cut-off grinder has a rear handle 11 which substantially extends in the longitudinal direction of the work apparatus 1. A throttle lever 28 for controlling the combustion engine 5 is provided in the rear handle 11. A front handle 12 is configured as a bale handle and engages over the housing 13 of the work apparatus 1 from the one longitudinal side to the other longitudinal side thereof.

(9) The combustion engine 5 arranged in the housing of the work apparatus 1 is reproduced in a schematic illustration in FIG. 3 and includes a cylinder 4 with a combustion chamber 6 which is bounded by a piston 7. The piston 7 drives a crankshaft 9, which is mounted in a crankcase 10, via a connecting rod 8.

(10) The combustion engine 5 draws in ignitable fuel/air mixture into the crankcase 10 via an air filter 17 and a mixture-forming device, which is illustrated by way of example and is a carburetor 18 in the embodiment. The mixture-forming device may also be an electronically controlled carburetor, or may include a fuel injection pump. During a downward movement of the piston 7, the ignitable fuel/air mixture formed in the mixture-forming device is conveyed from the crankcase 10 via at least one transfer channel 19 into the combustion chamber 6. During a following upward movement of the piston 7, the mixture in the combustion chamber 6 is compressed and is ignited by a spark plug 20. The combustion pressure building up during the combustion drives the piston 7 downward again, with the combustion gases being discharged via an outlet 21.

(11) The mixture-forming device, the carburetor 18 in the embodiment, has a throttle valve 22, the rotational position of which can be controlled via the throttle lever 28 (FIGS. 1, 2) in the rear handle 11 of the work apparatus 1.

(12) The spark plug 20 is activated by an ignition device 30 which triggers an ignition spark 27 at the spark plug 20 depending on the rotational position of the crankshaft 9 at an ignition point ZZP.

(13) The rotating crankshaft 9 drives the tool, in the embodiment the saw chain 3 of the chainsaw according to FIG. 1, via a clutch 23. To this end, the clutch 23 drives a sprocket 24 via which the saw chain 3 is driven.

(14) If the combustion engine runs under full load, for which purpose the throttle valve 22 is completely open (dashed line), a rich fuel/air mixture is supplied to the combustion chamber 6. If, for example, the hand guard 14, which acts as a trigger, of the safety brake 16 is then triggered, the output side of the clutch 23, which is configured as a centrifugal clutch, is braked. The rotational speed of the combustion engine drops; the combustion engine operates contrary to the applied safety brake 16.

(15) A comparable situation arises if the tool which is driven by the combustion engine via the centrifugal clutch blocks. For example, the saw chain 3 or the cutting disk 3a may become wedged in the cut.

(16) According to the invention, it is provided that the rotational speed (n) of the combustion engine 5 is monitored, in particular is permanently monitored. For this purpose, a rotational speed sensor 25 is arranged on the crankshaft, the output signal of which rotational speed sensor is supplied to a rotational speed monitoring circuit 26. The rotational speed monitoring circuit 26 is preferably integrated into the ignition device 30 in order to set the ignition point ZZP; the rotational speed monitoring circuit 26 is electrically connected to the ignition device 30.

(17) During the operation of the combustion engine 5, the rotational speed sensor 25 indicates the current rotational speed (n) of the rotational speed monitoring circuit 26. The latter processes the signal in accordance with the sequence diagram in FIG. 4. First of all, it is monitored in a first element 50 whether the rotational speed (n) is within a rotational speed range which is determined by the minimum rotational speed n.sub.min and the maximum rotational speed n.sub.max. The engagement rotational speed n.sub.engage of the clutch 23 configured as a centrifugal clutch lies outside this rotational speed range n.sub.min<n<n.sub.max. The engagement rotational speed n.sub.engage can be, for example, around approximately 3500 revolutions per minute. The minimum rotational speed n.sub.min can advantageously be around approximately 3700 revolutions and the maximum rotational speed n.sub.max around approximately 5000 revolutions. The rotational speed range determined by the minimum rotational speed n.sub.min and the maximum rotational speed n.sub.max can also be referred to as a rotational speed window.

(18) If the rotational speed monitoring circuit 26 determines that the current rotational speed (n) for a period of time Δt lies within the rotational speed range n.sub.min<n<n.sub.max, a first condition is fulfilled. When the first condition is fulfilled, a status indicator I is advantageously set in the rotational speed monitoring circuit 26. A status indicator of this type is also referred to as a “flag” in information technology.

(19) It is expediently monitored via a time element 51 whether the first condition is applied over a time frame ΔT. If this is the case and then the rotational speed drops under a rotational speed limit value n.sub.G, the rotational speed monitoring circuit 26 acts on the ignition device 30 in such a manner that the current ignition time ZZP is adjusted toward “early”. The effect achieved by this is that the combustion engine 5 does not stop in rich mode even when the throttle lever 28 is let go of. The rotational speed limit value n.sub.G lies below the minimum rotational speed n.sub.min of the predefined rotational speed range (n.sub.min; n.sub.max).

(20) If, despite the current rotational speed (n) being within the rotational speed range n.sub.min<n<n.sub.max, the rotational speed does not drop below the rotational speed limit value n.sub.G even after expiry of the time ΔT in the time element 51, a branch is made back via the branch 54 to the junction point 53 and the rotational speed (n) is continued to be monitored. An adjustment of the ignition point ZZP to early does not take place.

(21) If, once the first condition is present, the rotational speed drops below the rotational speed limit value n.sub.G in accordance with the interrogation 55, the ignition point ZZP is adjusted toward early.

(22) For the storage of the state that the first condition has been satisfied, a status indicator I can be set, as reproduced by the field 60. If the status indicator I is set, and the rotational speed n drops below the rotational speed limit value n.sub.G, the ignition point ZZP is adjusted toward early.

(23) If a status indicator I is set, the latter is deleted whenever the rotational speed (n) lies above the predefined rotational speed range. The deletion takes place if the rotational speed (n) rises above the maximum rotational speed n.sub.max of the rotational speed range. This is interrogated in the field 61, wherein the status indicator I is deleted at the onset of the event.

(24) The status indicator can also be deleted if—as interrogated in the field 55—the current rotational speed (n) drops below the rotational speed limit value n.sub.G. This takes place via the branch 62.

(25) It can be provided that the status indicator I which is set is kept for a predefined period of time t. The period of time t and the period of time ΔT in the field 51 may be a predefined time span of, for example, 2 to 3 seconds. The period of time t and/or the period of time ΔT is advantageously determined by a predetermined number of consecutive crankshaft revolutions, wherein expediently five to fifty crankshaft revolutions are provided. In particular, ten successive crankshaft revolutions are established in order to determine the period of time, wherein the crankshaft revolutions expediently directly follow one another.

(26) FIG. 5 reproduces an ignition point curve 70 over the rotational speed (n), which may also be referred to as a bifurcated curve. The one curve branch 71 in the form of a solid line reproduces the adjustment curve, which is effective for the normal operation of the combustion engine 5, of the ignition point ZZP which is indicated on the Y axis of the diagram. The curve branch 72, shown by dashed lines, reproduces the course of the adjustment curve of the ignition point ZZP when the conditions for switching over the ignition point ZZP toward “early” are satisfied. For this purpose, the rotational speed (n) has to lie within the rotational speed range (n.sub.min; n.sub.max) for a predetermined time frame ΔT, that is, has to be greater than the minimum rotational speed n.sub.min and lower than the maximum rotational speed n.sub.max. After this first condition is met, the rotational speed has to drop below a rotational speed limit value n.sub.G that lies below the predefined rotational speed range n.sub.min<n<n.sub.max. If this condition is also satisfied, the rotational speed monitoring circuit 26 acts on the ignition device 30 in such a manner that, instead of the curve branch 71, the curve branch 72 is passed through, that is, the ignition point is adjusted toward “early”. The early ignition point ZZP lies within a range of between 20° CA and 27° CA and ensures that the combustion engine 5 does not stop in rich mode. As FIG. 5 also shows, the ZZP of the early adjustment within the rotational speed range of below 3000 r/min is earlier than the ZZP at rotational speeds above 5000 r/min. Whereas an adjustment of the ZZP to up to 25° before the upper dead center takes place on the curve branch 71 during normal operation within a speed range of above 5000 revolutions, the ZZP is set to up to 27° CA before the upper dead center at rotational speeds below 3000 revolutions according to the adjustment toward early according to the invention.

(27) If the combustion engine 5 is switched off, the rotational speed monitoring circuit 26 and the ignition device 30 also become permanently deenergized. The interrogation states according to FIG. 4 are lost. When the combustion engine 5 is started up again, the system is reset, that is, the system adopts a predefined starting state. The system and the interrogations according to FIG. 4 are restarted from the starting state.

(28) 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.