WO2013089599A1 - Engine and a shut down method for an engine - Google Patents
Engine and a shut down method for an engine Download PDFInfo
- Publication number
- WO2013089599A1 WO2013089599A1 PCT/SE2011/051505 SE2011051505W WO2013089599A1 WO 2013089599 A1 WO2013089599 A1 WO 2013089599A1 SE 2011051505 W SE2011051505 W SE 2011051505W WO 2013089599 A1 WO2013089599 A1 WO 2013089599A1
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- Prior art keywords
- engine
- stop
- delay period
- speed
- ignition threshold
- Prior art date
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Classifications
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
- F02D—CONTROLLING COMBUSTION ENGINES
- F02D37/00—Non-electrical conjoint control of two or more functions of engines, not otherwise provided for
- F02D37/02—Non-electrical conjoint control of two or more functions of engines, not otherwise provided for one of the functions being ignition
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
- F02B—INTERNAL-COMBUSTION PISTON ENGINES; COMBUSTION ENGINES IN GENERAL
- F02B33/00—Engines characterised by provision of pumps for charging or scavenging
- F02B33/02—Engines with reciprocating-piston pumps; Engines with crankcase pumps
- F02B33/04—Engines with reciprocating-piston pumps; Engines with crankcase pumps with simple crankcase pumps, i.e. with the rear face of a non-stepped working piston acting as sole pumping member in co-operation with the crankcase
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
- F02D—CONTROLLING COMBUSTION ENGINES
- F02D41/00—Electrical control of supply of combustible mixture or its constituents
- F02D41/02—Circuit arrangements for generating control signals
- F02D41/04—Introducing corrections for particular operating conditions
- F02D41/042—Introducing corrections for particular operating conditions for stopping the engine
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
- F02P—IGNITION, OTHER THAN COMPRESSION IGNITION, FOR INTERNAL-COMBUSTION ENGINES; TESTING OF IGNITION TIMING IN COMPRESSION-IGNITION ENGINES
- F02P5/00—Advancing or retarding ignition; Control therefor
- F02P5/04—Advancing or retarding ignition; Control therefor automatically, as a function of the working conditions of the engine or vehicle or of the atmospheric conditions
- F02P5/045—Advancing or retarding ignition; Control therefor automatically, as a function of the working conditions of the engine or vehicle or of the atmospheric conditions combined with electronic control of other engine functions, e.g. fuel injection
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
- F02B—INTERNAL-COMBUSTION PISTON ENGINES; COMBUSTION ENGINES IN GENERAL
- F02B63/00—Adaptations of engines for driving pumps, hand-held tools or electric generators; Portable combinations of engines with engine-driven devices
- F02B63/02—Adaptations of engines for driving pumps, hand-held tools or electric generators; Portable combinations of engines with engine-driven devices for hand-held tools
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
- F02D—CONTROLLING COMBUSTION ENGINES
- F02D17/00—Controlling engines by cutting out individual cylinders; Rendering engines inoperative or idling
- F02D17/04—Controlling engines by cutting out individual cylinders; Rendering engines inoperative or idling rendering engines inoperative or idling, e.g. caused by abnormal conditions
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
- F02D—CONTROLLING COMBUSTION ENGINES
- F02D2400/00—Control systems adapted for specific engine types; Special features of engine control systems not otherwise provided for; Power supply, connectors or cabling for engine control systems
- F02D2400/04—Two-stroke combustion engines with electronic control
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
- F02D—CONTROLLING COMBUSTION ENGINES
- F02D2400/00—Control systems adapted for specific engine types; Special features of engine control systems not otherwise provided for; Power supply, connectors or cabling for engine control systems
- F02D2400/06—Small engines with electronic control, e.g. for hand held tools
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
- F02D—CONTROLLING COMBUSTION ENGINES
- F02D41/00—Electrical control of supply of combustible mixture or its constituents
- F02D41/02—Circuit arrangements for generating control signals
- F02D41/04—Introducing corrections for particular operating conditions
- F02D41/06—Introducing corrections for particular operating conditions for engine starting or warming up
- F02D41/062—Introducing corrections for particular operating conditions for engine starting or warming up for starting
- F02D41/065—Introducing corrections for particular operating conditions for engine starting or warming up for starting at hot start or restart
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
- F02D—CONTROLLING COMBUSTION ENGINES
- F02D41/00—Electrical control of supply of combustible mixture or its constituents
- F02D41/02—Circuit arrangements for generating control signals
- F02D41/14—Introducing closed-loop corrections
- F02D41/1438—Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor
- F02D41/1477—Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor characterised by the regulation circuit or part of it,(e.g. comparator, PI regulator, output)
- F02D41/1481—Using a delaying circuit
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
- F02N—STARTING OF COMBUSTION ENGINES; STARTING AIDS FOR SUCH ENGINES, NOT OTHERWISE PROVIDED FOR
- F02N2300/00—Control related aspects of engine starting
- F02N2300/20—Control related aspects of engine starting characterised by the control method
- F02N2300/2011—Control involving a delay; Control involving a waiting period before engine stop or engine start
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
- F02P—IGNITION, OTHER THAN COMPRESSION IGNITION, FOR INTERNAL-COMBUSTION ENGINES; TESTING OF IGNITION TIMING IN COMPRESSION-IGNITION ENGINES
- F02P11/00—Safety means for electric spark ignition, not otherwise provided for
Definitions
- the present invention relates to a method for shutting down a two stroke crank case scavenged engine, the engine operating speed ranging form idle speed to a maximum engine speed.
- the invention also relates to a two stroke crank case scavenged engine for implementing the method.
- Crank case scavenged two stroke engines are commonly used in hand held products such as chainsaws saws and power cutters. To minimize weight and size these machines are typically without batteries. Instead they are powered by a flywheel magneto generator and a started by a recoil starter mechanism.
- Fuel can be delivered to the crank case volume by a carburetor supplying an air/fuel mixture to the volume.
- a low pressure injection system can be used, injecting fuel directly into the crank case volume.
- From the crank case air and fuel is drawn to the combustion chamber of the engine via one or more scavenging passages that connects the crank case volume to the combustion chamber at certain piston positions.
- additional or scavenging air is used when evacuating combustion gases in order to reduce emissions.
- a flooded engine is an internal combustion that has been fed an excessively rich air-fuel mixture that cannot be ignited. Flooding can occur when the engine is stopped after having run warm and an attempt to restart is performed shortly after. To clear the engine the operator may therefore be required to pull the cord several times to reach an air/fuel ratio that enables the engine to start. This can be frustrating for the operator and he might even think that the machine is broken.
- a stop ignition threshold being less or equal to a delay period, said delay period at idle speed being within the range of 100-1000 ms, and e) if the stop switch is activated until the stop ignition threshold is reached after the detected stop event, then stopping the ignitions after the delay period has elapsed from the detected stop event; or f) if the stop switch is deactivated before the stop ignition threshold has been reached after the detected stop event, then resuming fuel supply to the engine.
- the crank case can be cleared from an excessively rich air-fuel mixture. This decreases the risk of a flooded engine when restarting a warm engine. Therefore the engine is likely to be started by a single pull when restarted within few minutes from a successful run. I.e. there is no need to pull the starting cord several times to clear the crank case from an excessively rich air-fuel mixture. If the engine is restarted after a slightly longer time period, e.g. 10 minutes or more, the operator may be required to start on choke. This is however, much more convenient than clearing an excessively rich air-fuel mixture.
- the delay period at idle speed is within the range of 100-600 ms, more preferably 200-400 ms. This range is sufficient to ensure that the engine does not have an excessively rich air-fuel mixture and at the same time the air-fuel mixture is not too lean so that the engine is required to be started with a choke when started within a few minutes from a successful run.
- the delay period at maximum speed is within the range of 0-240 ms, preferably 20-150 ms.
- the stop ignition threshold is between 20- 80 % of the delay period, preferably 30-70 % of the delay period, most preferably 40-60 % of the delay period.
- the stop ignition threshold is equal to the delay period.
- the stop ignition threshold is within the range of 50-500 ms, more preferably 100-300 ms, most preferably 100-200 ms.
- the stop ignition threshold at all engine speeds being set to zero ms, such that step e) is always executed after a stop event is detected.
- the invention also relates to a two stroke crank case scavenged engine including: a fuel delivery system in the form of carburetor or a low pressure injection system,;
- a spark plug for igniting an air/fuel mixture in a combustion chamber of the engine
- control means for controlling the fuel supply to the engine and the ignitions of the spark plug; - a stop switch electrically connected to the control means; wherein the control means in
- the invention also relates to a hand held product including the two stroke crank case scavenged engine.
- the engine may be of a kind using additional air.
- FIG. 1 is a schematic drawing of a two stroke crank case scavenged engine
- Fig. 2 is schematically shows a shut down sequence of an engine.
- Fig. 3 schematically shows two scenarios over the development of the A/F ratio of an engine shut down from idle speed.
- Fig. 4 shows upper limits and lower limits of the delay period according to two embodiments.
- reference numeral 1 designates an internal combustion engine 1 of a two- stroke type. It is crankcase scavenged, i.e. a mixture 40 of air 3 and fuel from a fuel delivery system 20 (e.g. a carburetor or a low pressure fuel injection system) is drawn into the engine crankcase. From the crankcase, the mixture is carried through one or several scavenging passages 14 up to the engine combustion chamber 41. The chamber is provided with a spark plug 32 igniting the compressed air- fuel mixture. Exhausts 42 exit through the exhaust port 43 and through a silencer 13.
- a fuel delivery system 20 e.g. a carburetor or a low pressure fuel injection system
- the engine 1 has a cylinder 5 with a reciprocating piston 6, which by means of a connecting rod 11 is attached to a crankshaft 12 equipped with a counterweight. In this manner the crankshaft is rotated.
- the piston 6 assumes an intermediate position, wherein flow is possible both through an intake port 44, through the scavenging passage 14, and the exhaust port 43.
- the fuel delivery system 20 has an intake passage 21 for the mixture of air and fuel.
- the mouth of the intake passage 21 into the cylinder 5 is called intake port 44.
- the intake passage 21 is closed by the piston 6.
- the fuel delivery system 20 draws fuel from a fuel tank 26 and has electronically controlled fuel valve 23 controlling the fuel flow through the fuel delivery system 20.
- the fuel valve 23 is an electronically controlled bistable valve, operating between two stable states, open and closed.
- An example of such valve is shown in WO 2009/116902 Al.
- other types of electronically controlled valves may also be used.
- the pressure variations in the intake passage largely affect the amount of fuel supplied when the fuel delivery system 20 is of carburetor type. Therefore since a carburetor has an insignificant fuel feed pressure, the amount of its fuel feed is entirely affected by pressure changes in the intake passage 21 that are caused by the opening and the closing of the latter and whether the fuel valve 23 is closed or open.
- a chainsaw is typically around 40-50 RPS and the maximum speed is typically around 200-250 RPS.
- the maximum speed is the speed when the engine is run at full throttle without any working load.
- the maximum engine speed may be limited by an engine control unit, e.g. cutting ignitions or changing the A/F ratio to keep the engine speed below a maximum speed limit.
- the engine further includes an ignition system including an ignition control unit 31 and a spark plug 32.
- the spark plug 32 is mounted in cylinder bore of the cylinder 5 that extends to the combustion chamber 41.
- the spark plug 32 is further connected to the ignition control unit 31 and the firing of the spark plug 32 is controlled by the ignition control unit 31.
- a fuel control unit 30 is connected to the fuel valve 23 and controls the opening and closing of the fuel valve 23.
- a fly wheel magneto generator (not shown) powers the ignition control unit 31, the ignitions of the spark plug 32, the fuel control unit 30 and the opening and closing of the fuel valve 23.
- a stop switch 33 is connected to the ignition control unit 31, and the ignition control unit 31 is connected to the fuel control unit 30.
- the ignition control unit 31 and the fuel control unit 30 are shown as two separate units. It would however be possible to have the two units 30, 31 integrated as one control unit, controlling both the firing of the spark plug 32 and the position of the fuel valve 23. Furthermore the stop switch 33 may alternatively be directly wired to the fuel control unit 30 or to both of the control units 30, 31 independently.
- a stop signal is sent to the ignition control unit 31.
- a stop event is detected upon receiving of the stop signal, and the ignition control unit 31 resends the stop signal to the fuel control unit 30.
- the fuel control unit 30 then sets the fuel valve 23 in closed position, thereby stopping the fuel supply to the engine.
- the stop switch may be required to be activated for an activation period before a stop event is determined to be detected.
- the activation period is for avoiding unintended stops by twigs etc touching the stop switch.
- the activation period may be a period of engine revolutions or a time period, and may be up to 200 ms.
- the length of the activation period may be arranged to depend on the engine speed. However, in the most preferred embodiment there is no activation period, and hence the stop event is detected as soon as the stop switch is activated.
- the ignition control unit 31 further monitors whether the stop switch 33 is continued to be activated after having instructed the fuel control unit 30 to close the fuel valve 23. If the stop switch 33 is activated until a stop ignition threshold has been reached the ignition control unit 31 stops the ignitions of the spark plug 32 after a delay period has elapsed from initially detecting the stop event. If the stop switch 33 is deactivated before the stop ignition threshold is reached, the ignition control unit 31 sends a signal to the fuel control unit 30 to resume the fuel supply to the engine and operate the fuel valve 23 according to a normal running mode and keeps ignition firing according to normal running mode so that the engine continues to run.
- the described stop procedure is active at idle speed and preferably also at the entire speed range from idle speed up to maximum engine speed.
- the delay period is preferably within the range of 100-1000 ms, more preferably 100-600 ms, and most preferably 200-400 ms. This delay clears the engine so as to avoid an excessively rich air-fuel mixture and preferably enables the engine to be restarted by a single pull when restarted within a few minutes from the engine stop, e.g. up to 5 minutes or up to 15 minutes after the engine stop. If the engine is restarted after a longer period of time the operator may be required to start with choke, but this is much less inconvenient than having a flooded engine.
- the delay period is preferably below 400 ms, more preferably within the range of 0-240 ms, most preferably 20-100 ms. Further, for the engine to reach a desired A/F ratio, the delay period is preferably continuously or sequentially getting shorter when moving from idle to maximum engine speed, as can e.g. be seen in Fig. 4.
- the upper full drawn line 101 corresponds to an upper limit of the delay period starting from 600 ms at idle speed to 240 ms at maximum speed
- the lower full drawn lines 104a, 104b corresponds to a lower limit of the delay period starting from 100 ms at idle speed and reaching zero ms at an engine speed between idle speed and maximum speed, e.g. around 100-150 RPS.
- the upper dashed line 102 corresponds to an upper limit of the delay period starting from 400 ms at idle speed to 100 ms at maximum speed
- the lower dashed line 103 corresponds to a lower limit starting from 100 ms at idle speed to 20 ms at maximum speed.
- One reason for having the shorter delay period at maximum engine speed is that engine will make more firings per second at higher RPS, i.e. having a higher burn rate. Another reason is that it will take more revolutions due to sheer inertia for the engine to stop revolving from maximum engine speed in comparison to a stop from idle speed.
- the stop ignition threshold is the same as the delay period. However, in the preferred embodiment the stop ignition threshold is shorter than the delay period.
- the stop ignition threshold is within 20- 80 % of the delay period, preferably 30-70 % of the delay period, and most preferably 40-60 % of the delay period.
- the stop ignition threshold is lower than 50 ms or even set to zero ms. When the stop ignition threshold is zero ms the ignitions are stopped after the delay period elapsed regardless if the stop switch was continued to be activated or not.
- the delay period is preferably continuously or sequentially getting shorter when moving from idle to maximum engine speed. Therefore according another embodiment the delay period in the speed range from idle speed to maximum speed is at most (-2*N+700) ms, preferably at most (-1.5*N+475) ms, where N is the engine speed in RPS (Revolutions Per Second).
- the lower limit is at least (-1 *N+150) ms for N up to 150 RPS and zero ms for N above 150 RPS.
- the ignitions and the fuel supply may be stopped at the same time, i.e. relying on the larger amounts of engine revolutions it takes for the engine to stop from a higher speed than from e.g. idle speed. I.e.
- the engine may be sufficiently vented by the coast down revolutions induced by the rotational inertia.
- the lower limit is at least (-1N+250) ms.
- Fig. 2 the stop sequence of the engine is schematically shown.
- the fuel supply is first stopped.
- the ignitions are still maintained and as a consequence the A/F ratio is increasing.
- the ignitions are stopped.
- the engine speed drops until the engine finally comes to a standstill.
- the A/F ratio will continue to increase.
- FIG. 3 the development of A/F ratio is schematically shown for two scenarios of an engine shut down at idle speed.
- the A/F ratios AFl and AF2 represents an interval where the engine can be started with one pull of the starting cord.
- the engine choke or other enrichment is required to be used when starting the engine.
- the first line 201 schematically shows the A/F ratios of an engine where the ignition and the fuel supply are simultaneously stopped at a first time tl .
- the engine stops revolving and at sixth time t6 the A/F ratio has reached the A/F ratio AFl .
- a user that restarts the engine before time t6 will not succeed in starting the engine. Instead, several pulls might be needed to vent the engine to increase the A/F ratio.
- the second line 202 schematically shows the development of the A/F ratio of an engine having the shut down sequence of the invention, i.e. where the fuel supply is stopped at the first time tl and where the ignitions are stopped at a second time t2 after a delay period, i.e. t2-tl, has elapsed from the fuel supply stop.
- a delay period i.e. t2-tl
- the delay period t2-tl has been chosen so that the when the engine comes to standstill, the A/F ratio is above AF1.
- the A/F ratio will exceed AF2.
- the time t5- t4 is up to 5-15 minutes.
- the fuel control unit 30 can be implemented to control the fuel valve 23 to reduce the A/F (enrichment) in such a situation.
- the positions of lines 201 and 202 relative to each other in Fig 3 is just a way of illustrating an example. In reality they can take many different positions while still describing the present embodiment of the invention. E.g.
- a general slope of second line 202 may be steeper than a general slope of the line 201.
- lines 201 and 202 may also be affected by environmental conditions such as ambient temperature and also by engine size and configuration and might also vary depending on which position the piston 6 comes to rest in.
- the ignition stop threshold may be set equal to the delay period.
- the delay period and/or the ignition threshold can be measured in number of revolutions as well as in time.
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- Chemical & Material Sciences (AREA)
- Combustion & Propulsion (AREA)
- Mechanical Engineering (AREA)
- General Engineering & Computer Science (AREA)
- Electrical Control Of Air Or Fuel Supplied To Internal-Combustion Engine (AREA)
- Combined Controls Of Internal Combustion Engines (AREA)
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Abstract
The invention relates to a method for shutting down a two stroke crank case scavenged engine, the engine operating speed ranging form an idle speed to a maximum speed, said method comprising the steps of: a) activating a stop switch (33) of the engine (1); b) detecting a stop event from the activated stop switch (33); c) stopping the fuel supply to the engine in response to said stop event; d) adopting a stop ignition threshold being less or equal to a delay period (t2-t1), said delay period at idle speed being within the range of 100-1000 ms, and e) if the stop switch (33) is activated until the stop ignition threshold is reached after the detected stop event, then stopping the ignitions after the delay period (t2-t1) has elapsed from the detected stop event; or f) if the stop switch is deactivated before the stop ignition threshold has been reached after the detected stop event, then resuming fuel supply to the engine. The invention also relates to a two stroke crank case scavenged engine for implementing the method.
Description
ENGINE AND A SHUT DOWN METHOD FOR AN ENGINE TECHNICAL FIELD
The present invention relates to a method for shutting down a two stroke crank case scavenged engine, the engine operating speed ranging form idle speed to a maximum engine speed. The invention also relates to a two stroke crank case scavenged engine for implementing the method.
BACKGROUND
Crank case scavenged two stroke engines are commonly used in hand held products such as chainsaws saws and power cutters. To minimize weight and size these machines are typically without batteries. Instead they are powered by a flywheel magneto generator and a started by a recoil starter mechanism.
Fuel can be delivered to the crank case volume by a carburetor supplying an air/fuel mixture to the volume. Alternatively a low pressure injection system can be used, injecting fuel directly into the crank case volume. From the crank case air and fuel is drawn to the combustion chamber of the engine via one or more scavenging passages that connects the crank case volume to the combustion chamber at certain piston positions. In some engines additional or scavenging air is used when evacuating combustion gases in order to reduce emissions.
A flooded engine is an internal combustion that has been fed an excessively rich air-fuel mixture that cannot be ignited. Flooding can occur when the engine is stopped after having run warm and an attempt to restart is performed shortly after. To clear the engine the operator may therefore be required to pull the cord several times to reach an air/fuel ratio that enables the engine to start. This can be frustrating for the operator and he might even think that the machine is broken.
OBJECT OF THE INVENTION
It is an object of the invention to make it easy for an operator to restart a two stroke crank case scavenged engine after a successful run. SUMMARY OF THE INVENTION
This object is met by the method mentioned initially which comprises the steps of:
a) activating a stop switch of the engine;
b) detecting a stop event from the activated stop switch;
c) stopping the fuel supply to the engine in response to said stop event;
d) adopting a stop ignition threshold being less or equal to a delay period, said delay period at idle speed being within the range of 100-1000 ms, and
e) if the stop switch is activated until the stop ignition threshold is reached after the detected stop event, then stopping the ignitions after the delay period has elapsed from the detected stop event; or f) if the stop switch is deactivated before the stop ignition threshold has been reached after the detected stop event, then resuming fuel supply to the engine.
By having a delay period from the time that the fuel supply is stopped till the ignitions are stopped, the crank case can be cleared from an excessively rich air-fuel mixture. This decreases the risk of a flooded engine when restarting a warm engine. Therefore the engine is likely to be started by a single pull when restarted within few minutes from a successful run. I.e. there is no need to pull the starting cord several times to clear the crank case from an excessively rich air-fuel mixture. If the engine is restarted after a slightly longer time period, e.g. 10 minutes or more, the operator may be required to start on choke. This is however, much more convenient than clearing an excessively rich air-fuel mixture.
Preferably, the delay period at idle speed is within the range of 100-600 ms, more preferably 200-400 ms. This range is sufficient to ensure that the engine does not have an excessively rich air-fuel mixture and at the same time the air-fuel mixture is not too lean so that the engine is required to be started with a choke when started within a few minutes from a successful run.
Preferably the delay period at maximum speed is within the range of 0-240 ms, preferably 20-150 ms.
Preferably the stop ignition threshold is between 20- 80 % of the delay period, preferably 30-70 % of the delay period, most preferably 40-60 % of the delay period. Alternatively the stop ignition threshold is equal to the delay period.
Preferably the stop ignition threshold is within the range of 50-500 ms, more preferably 100-300 ms, most preferably 100-200 ms.
According to one embodiment the stop ignition threshold at all engine speeds being set to zero ms, such that step e) is always executed after a stop event is detected.
The invention also relates to a two stroke crank case scavenged engine including: a fuel delivery system in the form of carburetor or a low pressure injection system,;
a spark plug for igniting an air/fuel mixture in a combustion chamber of the engine;
control means for controlling the fuel supply to the engine and the ignitions of the spark plug; - a stop switch electrically connected to the control means; wherein the control means in
response to an activation of the stop switch is arranged to shut down the engine according to the method described above.
The invention also relates to a hand held product including the two stroke crank case scavenged engine. The engine may be of a kind using additional air.
BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a schematic drawing of a two stroke crank case scavenged engine, Fig. 2 is schematically shows a shut down sequence of an engine.
Fig. 3 schematically shows two scenarios over the development of the A/F ratio of an engine shut down from idle speed.
Fig. 4 shows upper limits and lower limits of the delay period according to two embodiments. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
In the schematic Fig. 1, reference numeral 1 designates an internal combustion engine 1 of a two- stroke type. It is crankcase scavenged, i.e. a mixture 40 of air 3 and fuel from a fuel delivery system 20 (e.g. a carburetor or a low pressure fuel injection system) is drawn into the engine crankcase. From the crankcase, the mixture is carried through one or several scavenging passages 14 up to the engine combustion chamber 41. The chamber is provided with a spark plug 32 igniting the compressed air- fuel mixture. Exhausts 42 exit through the exhaust port 43 and through a silencer 13. The engine 1 has a cylinder 5 with a reciprocating piston 6, which by means of a connecting rod 11 is attached to a crankshaft 12 equipped with a counterweight. In this manner the crankshaft is rotated. In Fig. 1, the piston 6 assumes an intermediate position, wherein flow is possible both through an intake port 44, through the scavenging passage 14, and the exhaust port 43. The fuel delivery system 20 has an intake passage 21 for the mixture of air and fuel. The mouth of the intake passage 21 into the cylinder 5 is called intake port 44. Thus, the intake passage 21 is closed by the piston 6. By opening and closing the intake port 44, varying flow speeds and pressures are created inside the intake passage 21. The fuel delivery system 20 draws fuel from a fuel tank 26 and has electronically controlled fuel valve 23 controlling the fuel flow through the fuel delivery system 20. Preferably the fuel valve 23 is an electronically controlled bistable valve, operating between two stable states, open and closed. An example of such valve is shown in WO 2009/116902 Al. However, other types of electronically controlled valves may also be used. The pressure variations in the intake passage largely affect the amount of fuel supplied when the fuel delivery system 20 is of carburetor type. Therefore since a carburetor has an insignificant fuel feed pressure, the amount of its fuel feed is entirely affected by pressure changes in the intake passage 21 that are caused by the opening and the closing of the latter and whether the fuel valve 23 is closed or open.
The idle speed of an engine of this kind when used in e.g. a chainsaw is typically around 40-50 RPS and the maximum speed is typically around 200-250 RPS. The maximum speed is the speed when the engine is run at full throttle without any working load. The maximum engine speed may be limited by an engine control unit, e.g. cutting ignitions or changing the A/F ratio to keep the engine speed below a maximum speed limit.
The engine further includes an ignition system including an ignition control unit 31 and a spark plug 32. The spark plug 32 is mounted in cylinder bore of the cylinder 5 that extends to the combustion chamber 41. The spark plug 32 is further connected to the ignition control unit 31 and the firing of the spark plug 32 is controlled by the ignition control unit 31. A fuel control unit 30 is connected to the fuel valve 23 and controls the opening and closing of the fuel valve 23. A fly wheel magneto generator (not shown) powers the ignition control unit 31, the ignitions of the spark plug 32, the fuel control unit 30 and the opening and closing of the fuel valve 23. A stop switch 33 is connected to the ignition control unit 31, and the ignition control unit 31 is connected to the fuel control unit 30.
In the shown example the ignition control unit 31 and the fuel control unit 30 are shown as two separate units. It would however be possible to have the two units 30, 31 integrated as one control unit, controlling both the firing of the spark plug 32 and the position of the fuel valve 23. Furthermore the stop switch 33 may alternatively be directly wired to the fuel control unit 30 or to both of the control units 30, 31 independently.
The invention will now be described according to a first and preferred embodiment for shutting down the engine. In the first and preferred embodiment, when activating the stop switch 33, e.g. by pressing a stop button, a stop signal is sent to the ignition control unit 31. A stop event is detected upon receiving of the stop signal, and the ignition control unit 31 resends the stop signal to the fuel control unit 30. The fuel control unit 30 then sets the fuel valve 23 in closed position, thereby stopping the fuel supply to the engine.
Optionally the stop switch may be required to be activated for an activation period before a stop event is determined to be detected. The activation period is for avoiding unintended stops by twigs etc touching the stop switch. The activation period may be a period of engine revolutions or a time period, and may be up to 200 ms. The length of the activation period may be arranged to depend on the engine speed. However, in the most preferred embodiment there is no activation period, and hence the stop event is detected as soon as the stop switch is activated.
In the preferred embodiment, the ignition control unit 31 further monitors whether the stop switch 33 is continued to be activated after having instructed the fuel control unit 30 to close the fuel valve 23. If
the stop switch 33 is activated until a stop ignition threshold has been reached the ignition control unit 31 stops the ignitions of the spark plug 32 after a delay period has elapsed from initially detecting the stop event. If the stop switch 33 is deactivated before the stop ignition threshold is reached, the ignition control unit 31 sends a signal to the fuel control unit 30 to resume the fuel supply to the engine and operate the fuel valve 23 according to a normal running mode and keeps ignition firing according to normal running mode so that the engine continues to run.
The described stop procedure is active at idle speed and preferably also at the entire speed range from idle speed up to maximum engine speed. At idle speed the delay period is preferably within the range of 100-1000 ms, more preferably 100-600 ms, and most preferably 200-400 ms. This delay clears the engine so as to avoid an excessively rich air-fuel mixture and preferably enables the engine to be restarted by a single pull when restarted within a few minutes from the engine stop, e.g. up to 5 minutes or up to 15 minutes after the engine stop. If the engine is restarted after a longer period of time the operator may be required to start with choke, but this is much less inconvenient than having a flooded engine. At maximum speed the delay period is preferably below 400 ms, more preferably within the range of 0-240 ms, most preferably 20-100 ms. Further, for the engine to reach a desired A/F ratio, the delay period is preferably continuously or sequentially getting shorter when moving from idle to maximum engine speed, as can e.g. be seen in Fig. 4. Here the upper full drawn line 101 corresponds to an upper limit of the delay period starting from 600 ms at idle speed to 240 ms at maximum speed, whereas the lower full drawn lines 104a, 104b corresponds to a lower limit of the delay period starting from 100 ms at idle speed and reaching zero ms at an engine speed between idle speed and maximum speed, e.g. around 100-150 RPS. The upper dashed line 102 corresponds to an upper limit of the delay period starting from 400 ms at idle speed to 100 ms at maximum speed, whereas the lower dashed line 103 corresponds to a lower limit starting from 100 ms at idle speed to 20 ms at maximum speed. One reason for having the shorter delay period at maximum engine speed is that engine will make more firings per second at higher RPS, i.e. having a higher burn rate. Another reason is that it will take more revolutions due to sheer inertia for the engine to stop revolving from maximum engine speed in comparison to a stop from idle speed. According to one embodiment the stop ignition threshold is the same as the delay period. However, in the preferred embodiment the stop ignition threshold is shorter than the delay period. At idle speed preferably within the range of 50-500 ms, more preferably 100-300 ms, most preferably 100-200 ms. Furthermore, it is preferred that the stop ignition threshold is within 20- 80 % of the delay period, preferably 30-70 % of the delay period, and most preferably 40-60 % of the delay period. By having a shorter stop ignition threshold than the delay period, the operator is not required to activate the stop switch 33 for a time which is conceived as too long. At the same time the risk of accidental activating the stop switch 33 is reduced.
In another embodiment the stop ignition threshold is lower than 50 ms or even set to zero ms. When the stop ignition threshold is zero ms the ignitions are stopped after the delay period elapsed regardless if the stop switch was continued to be activated or not. An advantage of this embodiment is that the operator only need to momentarily activate the stop switch 33.
As mentioned above the delay period is preferably continuously or sequentially getting shorter when moving from idle to maximum engine speed. Therefore according another embodiment the delay period in the speed range from idle speed to maximum speed is at most (-2*N+700) ms, preferably at most (-1.5*N+475) ms, where N is the engine speed in RPS (Revolutions Per Second). Preferably the lower limit is at least (-1 *N+150) ms for N up to 150 RPS and zero ms for N above 150 RPS. Thus at higher engine speed the ignitions and the fuel supply may be stopped at the same time, i.e. relying on the larger amounts of engine revolutions it takes for the engine to stop from a higher speed than from e.g. idle speed. I.e. it may not be necessary to burn off fuel to clear the crank case and reach the desired A/F ratio, the engine may be sufficiently vented by the coast down revolutions induced by the rotational inertia. Preferably though, the lower limit is at least (-1N+250) ms.
In Fig. 2 the stop sequence of the engine is schematically shown. When a stop event is detected the fuel supply is first stopped. The ignitions are still maintained and as a consequence the A/F ratio is increasing. After the delay period has elapsed the ignitions are stopped. When the ignitions are stopped the engine speed drops until the engine finally comes to a standstill. During the period from the stop of the ignitions until the engine finally comes to the standstill the A/F ratio will continue to increase. Taken into consideration the effect of increasing A/F ratio both during the delay period and the period after the ignitions are stopped until the engine stops revolving, an optimum A/F ratio for restarting the engine can be set by controlling the duration of the delay period.
In Fig. 3 the development of A/F ratio is schematically shown for two scenarios of an engine shut down at idle speed. In the figure the A/F ratios AFl and AF2 represents an interval where the engine can be started with one pull of the starting cord. For A/F ratios below AFl the engine is too rich and the user needs more than one pull to clear the engine from an excessively rich A/F mixture before a successful start can be achieved, i.e. the engine is flooded. For A/F ratios above AF2 the engine choke (or other enrichment) is required to be used when starting the engine.
The first line 201 schematically shows the A/F ratios of an engine where the ignition and the fuel supply are simultaneously stopped at a first time tl . At a third time t3 the engine stops revolving and at sixth time t6 the A/F ratio has reached the A/F ratio AFl . A user that restarts the engine before time
t6 will not succeed in starting the engine. Instead, several pulls might be needed to vent the engine to increase the A/F ratio.
The second line 202 schematically shows the development of the A/F ratio of an engine having the shut down sequence of the invention, i.e. where the fuel supply is stopped at the first time tl and where the ignitions are stopped at a second time t2 after a delay period, i.e. t2-tl, has elapsed from the fuel supply stop. At a forth time t4 shortly after the ignitions are stopped the engine stops revolving. Here the delay period t2-tl has been chosen so that the when the engine comes to standstill, the A/F ratio is above AF1. Eventually at a fifth time t5 the A/F ratio will exceed AF2. Typically the time t5- t4 is up to 5-15 minutes. Thereby a user who pulls the starting cord recently after the engine has stopped will be in the desired range AF1-AF2. Furthermore if the engine doesn't start easily, the user knows that the engine most likely has an A/F ratio above AF2 and he can therefore enable choke if a previous start attempt was unsuccessful. Alternatively, the fuel control unit 30 can be implemented to control the fuel valve 23 to reduce the A/F (enrichment) in such a situation. It should be noted that the positions of lines 201 and 202 relative to each other in Fig 3 is just a way of illustrating an example. In reality they can take many different positions while still describing the present embodiment of the invention. E.g. for a two stroke engine for a small chainsaw a general slope of second line 202 may be steeper than a general slope of the line 201. Thereby the time from a simultaneous fuel shut off and ignition cut-out tl to the reach of t6, entering the area between AF 1 and AF2, following line 201 (without any delay period) may be about 2 minutes, while for a corresponding chainsaw adopting an embodiment of the inventive idea following line 202 may well stay in the one pull startable area between AF1 and AF2 for up to 15 minutes (t5-t4 = 15 minutes). Further, lines 201 and 202 may also be affected by environmental conditions such as ambient temperature and also by engine size and configuration and might also vary depending on which position the piston 6 comes to rest in.
Whereas the invention has been shown and described in connection with the preferred embodiments thereof, it will be understood that many modifications, substitutions, and additions may be made, which are within the intended broad scope of the following claims. From the foregoing, it can be seen that the present invention accomplishes at least one of the stated objectives.
For instance, the ignition stop threshold may be set equal to the delay period. For instance, the delay period and/or the ignition threshold can be measured in number of revolutions as well as in time.
Claims
1. A method for shutting down a two stroke crank case scavenged engine (1), the engine
operating speed ranging form an idle speed to a maximum speed, said method comprising the steps of:
a) activating a stop switch (33) of the engine (1);
b) detecting a stop event from the activated stop switch (33);
c) stopping the fuel supply to the engine in response to said stop event;
d) adopting a stop ignition threshold being less or equal to a delay period (t2-tl), said delay period at idle speed being within the range of 100-1000 ms, and
e) if the stop switch (33) is activated until the stop ignition threshold is reached after the detected stop event, then stopping the ignitions after the delay period (t2-tl) has elapsed from the detected stop event; or
f) if the stop switch (33) is deactivated before the stop ignition threshold has been reached after the detected stop event, then resuming fuel supply to the engine.
2. A method according to claim 1 wherein the delay period (t2-tl) at idle speed is within the range of 100-600 ms, preferably 150-500 ms, more preferably 200-400 ms.
3. A method according to claim 1 or 2 wherein the delay period (t2-tl) at maximum speed is within the range of 0-240 ms, preferably 20-150 ms.
4. A method according to claim 1 wherein the delay period (t2-tl) in the speed range from idle speed to maximum is at most (-2*N+700) ms, preferably less than (-1.5*N+475) ms, where N is the engine speed in RPS.
5. A method according to claim 1 or 4 wherein the delay period (t2-tl) in the speed range from idle speed to maximum speed is at least max(-l*N+150, 0), preferably at least (-l*N+250) ms, where N is the engine speed in RPS.
6. A method according to any one of claim 1-5 wherein the stop ignition threshold is between 20- 80 % of the delay period (t2-tl), preferably 30-70 % of the delay period, most preferably 40-60 % of the delay period.
7. A method according to any one of claims 1-5 wherein the stop ignition threshold is equal to the delay period.
8. A method according to claim 6 or 7 wherein the stop ignition threshold at idle speed is within the range of 50-500 ms, more preferably 100-300 ms, most preferably 100-200 ms.
9. A method according to any one of claims 1-5 wherein the stop ignition threshold at all engine speeds being set to zero ms, such that step e) is always executed after a stop event is detected.
10. A two stroke crank case scavenged engine (1) including:
a fuel delivery system (20) in the form of carburetor or a low pressure injection system;
a spark plug (32) for igniting an air/fuel mixture in a combustion chamber (41)of the engine; control means (30, 3 l)for controlling the fuel supply to the engine and the ignitions of the spark plug;
a stop switch (33) electrically connected to the control means; wherein the control means in response to an activation of the stop switch is arranged to shut down the engine according to the method of any one of claims 1-9.
11 A hand held product including a two stroke crank case scavenged engine according to claim 10.
Priority Applications (2)
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PCT/SE2011/051505 WO2013089599A1 (en) | 2011-12-13 | 2011-12-13 | Engine and a shut down method for an engine |
DE112011105943.4T DE112011105943B4 (en) | 2011-12-13 | 2011-12-13 | Engine and shutdown method for an engine |
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PCT/SE2011/051505 WO2013089599A1 (en) | 2011-12-13 | 2011-12-13 | Engine and a shut down method for an engine |
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Cited By (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
FR3080890A1 (en) * | 2018-05-07 | 2019-11-08 | Continental Automotive France | METHOD FOR MANAGING THE INJECTION AND IGNITION OF AN INTERNAL COMBUSTION ENGINE |
Citations (2)
Publication number | Priority date | Publication date | Assignee | Title |
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JPS58140474A (en) * | 1982-02-16 | 1983-08-20 | Nissan Motor Co Ltd | Control device for engine |
US6318334B1 (en) * | 2000-03-01 | 2001-11-20 | Daimlerchrysler Corporation | Method for sparking engine cylinders after fuel shutdown for reduced emissions |
Family Cites Families (4)
Publication number | Priority date | Publication date | Assignee | Title |
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DE10332242A1 (en) | 2003-07-16 | 2005-02-03 | Andreas Stihl Ag & Co. Kg | Hand-held implement |
US8950381B2 (en) | 2008-03-17 | 2015-02-10 | Husqvarna Ab | Fuel supply unit |
DE102009053047A1 (en) | 2009-11-16 | 2011-05-19 | Andreas Stihl Ag & Co. Kg | Method for operating an internal combustion engine |
DE102010005597A1 (en) | 2010-01-25 | 2011-07-28 | BOMAG GmbH, 56154 | Soil compacting device with removable fuel line |
-
2011
- 2011-12-13 WO PCT/SE2011/051505 patent/WO2013089599A1/en active Application Filing
- 2011-12-13 DE DE112011105943.4T patent/DE112011105943B4/en active Active
Patent Citations (2)
Publication number | Priority date | Publication date | Assignee | Title |
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JPS58140474A (en) * | 1982-02-16 | 1983-08-20 | Nissan Motor Co Ltd | Control device for engine |
US6318334B1 (en) * | 2000-03-01 | 2001-11-20 | Daimlerchrysler Corporation | Method for sparking engine cylinders after fuel shutdown for reduced emissions |
Cited By (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
FR3080890A1 (en) * | 2018-05-07 | 2019-11-08 | Continental Automotive France | METHOD FOR MANAGING THE INJECTION AND IGNITION OF AN INTERNAL COMBUSTION ENGINE |
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