Method for switching off a rotational speed limit in an internal combustion engine

Patent metadata

Field	Value
Publication number	US-9322329-B2
Application number	US-201313956088-A
Country	US
Kind code	B2
Filing date	Jul 31, 2013
Priority date	Jul 31, 2012
Publication date	Apr 26, 2016
Grant date	Apr 26, 2016

Abstract

A method controls the rpm of a combustion engine in a hand-held work apparatus such as a brushcutter. The engine drives a work tool via a clutch which engages as a function of the engine rpm (n). A spark plug is arranged in the combustion chamber and is driven by an ignition unit. During start of the engine, an rpm lock circuit is active and defines a control variable as a function of the instantaneous rpm (n act ) of the engine. According to the magnitude of this control variable, operating parameters of the engine are adapted to change the instantaneous rpm (n act ). A control variable is determined for the adaptation of the operating parameters by the rpm lock circuit. The switch-off of the rpm lock circuit is provided when the control variable of the control lies outside a predetermined bandwidth of the absolute magnitude of the control variables.

First claim

What is claimed is:

1. A method of controlling the rotational speed of a combustion engine in a handheld work apparatus, wherein the combustion engine is supplied with a fuel/air mixture; the combustion engine has a crankshaft configured to drive a work tool via a clutch configured to engage in dependence upon the rotational speed of the combustion engine; the clutch being configured to generate a drive connection with the crankshaft when above an engaging rotational speed (n K ) and to interrupt the drive connection when below the engaging rotational speed (n K ); the combustion engine further having a combustion chamber and a spark plug arranged in the combustion chamber; the combustion engine further having an ignition unit for driving the spark plug and an rpm lock circuit configured as a closed-loop control circuit; the rpm lock circuit being further configured to switch on when the combustion engine is started and to set the instantaneous rotational speed (n act ) of the combustion engine below the engaging rotational speed (n K ) of the clutch and, for this purpose, the rpm lock circuit further being configured to change a control variable and adapt operating parameters of the combustion engine in accordance with the value of the control variable to change the instantaneous rotational speed (n act ); the control variable being a control quantity or a manipulated variable, the method comprising the step of:
switching off the rpm lock circuit when the absolute value of the control variable for adapting the operating parameters drops below a lower limit value (G min ) or exceeds an upper limit value (G max ).

2. The method of claim 1 , wherein the rpm lock circuit is switched off when the manipulated variable or control quantity of the control loop lies outside a predetermined bandwidth; and, the bandwidth is defined by at least one of an absolute lower limit value (G min ) and an absolute upper limit value (G max ).

3. The method of claim 1 , wherein the control quantity is the amount of air supplied to the combustion engine.

4. The method of claim 1 , wherein the control quantity is the amount of fuel supplied to the combustion engine.

5. The method of claim 1 , wherein the control quantity is the ignition time point (ZZP).

6. The method of claim 1 , wherein the control quantity is the off-cycle ratio (ASR) of the ignition.

7. The method of claim 1 , wherein the fuel metering is controlled by a fuel valve and the actuating variable is the open time of the fuel valve.

8. The method of claim 1 , wherein the actuating variable is the number of sequential crankshaft revolutions with an ignition.

9. The method of claim 1 , wherein the actuating variable is the absolute ignition time point (ZZP).

10. The method of claim 1 , wherein the actuating variable is the magnitude of the ignition time point shift.

11. The method of claim 1 , wherein the work apparatus is one of a chain saw, a cutoff machine, a hedge trimmer and a blower.

12. A method for controlling the rotational speed of a combustion engine in a handheld work apparatus, wherein the combustion engine has a combustion chamber delimited by a piston with a fuel/air mixture being metered to the combustion chamber, the combustion engine has a crankshaft configured to drive a work tool via a clutch configured to engage in dependence upon the rotational speed (n) of the combustion engine; the clutch being configured to generate a drive connection with the crankshaft when above an engaging rotational speed (n K ) and to interrupt the drive connection when below the engaging rotational speed (n K ); the combustion engine further having a spark plug arranged in the combustion chamber; an ignition unit for driving the spark plug so as to cause an ignition spark to be triggered relative to the angular position of the crankshaft; an rpm lock circuit configured as a closed-loop control circuit; the rpm lock circuit being further configured to switch on when the combustion engine is started and to set the instantaneous rotational speed (n act ) of the combustion engine below the engaging rotational speed (n K ) of the clutch; the rpm lock circuit is configured to change the ignition time point (ZZP) of the spark plug to change the instantaneous rotational speed (n act ) of the combustion engine as a manipulated variable; the method comprising the steps of:
providing a pregiven ignition time point (ZZP deactive );
with each rotation of the crankshaft, comparing the ignition time point (ZZP) set by the rpm lock circuit to the pregiven ignition time point (ZZP deactive ); and,
switching off the rpm lock circuit when the set ignition time point (ZZP) exceeds the pregiven ignition time point (ZZP deactive ) over several sequential revolutions of the crankshaft.

13. The method of claim 12 , wherein a counter is increased by one increment when the pregiven ignition time point (ZZP deactive ) is exceeded and the rpm lock circuit is switched off when a counter limit value (z G ) is reached.

14. The method of claim 12 , wherein the pregiven ignition time point (ZZP deactive ) lies ahead of top dead center of the piston.

15. The method of claim 12 , wherein the ignition time point (ZZP i ) determined by the rpm lock circuit per crankshaft revolution is averaged over several sequential crankshaft revolutions.

16. The method of claim 12 , wherein said rpm lock circuit determines a control variable in dependence upon the instantaneous rotational speed (n act ) of the combustion engine.

17. The method of claim 12 , wherein the rpm lock circuit determines a control variable in dependence upon the difference of the instantaneous rotational speed (n act ) of the combustion engine and a pregiven limit rotational speed (n G ).

18. The method of claim 12 , wherein the work apparatus is one of a chain saw, a cutoff machine, a hedge trimmer and a blower.

Assignees

• Stihl Ag & Co Kg Andreas

Inventors

• Gegg Tim
• Koelmel Armin
• Dangelmaier Manuel

Classifications

• F02B63/02 Primary

  for hand-held tools · CPC title

• F02D31/009

  for maximum speed control · CPC title

• F02D45/00

  Electrical control not provided for in groups F02D41/00 - F02D43/00 · CPC title