DE112011105943T5 - Engine and shutdown method for an engine - Google Patents

Abstract

The invention relates to a method for switching off a two-stroke engine with crankcase flushing, the engine operating speed ranging from idling to a maximum speed, the method comprising the following steps: a) actuating a stop switch (33) of the engine (1), b) detecting a stop event from the actuated stop switch (33), c) stopping the supply of fuel to the engine in response to the stop event, d) setting an ignition stop threshold value that is less than or equal to a delay time period (t2-t1), the delay time period at Idling is in the range of 100-1000 ms, and e) if the stop switch (33) is operated until the ignition stop threshold is reached after the detected stop event, 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 ignition pulse If the ppthreshold has been reached after the stop event is detected, resume fueling the engine. The invention also relates to a two-stroke engine with crankcase flushing for implementing the method.

Description

TECHNICAL AREA

The present invention relates to a method of shutting off a two-stroke crankcase scavenged engine wherein the engine operating speed ranges from idle to maximum engine speed. The invention also relates to a two-stroke engine with crankcase scavenging for implementing the method.

STATE OF THE ART

Crankcase scavenged two-stroke engines are commonly used in hand-held products, such as chainsaws and circular saws. To reduce weight and size, these machines typically have no batteries. Instead, they are powered by a flywheel type magnetoelectric generator and are started with a recoil starter.

Fuel may be delivered to the crankcase chamber through a carburetor which supplies an air-fuel mixture to the space. Alternatively, a low pressure injection system may be used which injects fuel directly into the crankcase space. From the crankcase, air and fuel are drawn to the combustion chamber of the engine via one or more purge passages connecting the crankcase chamber to the combustion chamber at certain piston positions. In certain engines, additional or purge air is used when the combustion gases are expelled to reduce emissions.

A flooded engine is an internal combustion engine that has been supplied with an excessively rich air-fuel mixture that can not be ignited. The dripping can occur when the engine is stopped after it has warmed up and a start attempt is made shortly thereafter. Therefore, to deflate the engine, the operator may need to pull on the cable several times to achieve an air-fuel ratio that allows the engine to start. This can be annoying for the operator, and he could even assume that the device is broken.

OBJECT OF THE INVENTION

It is an object of the invention to make it easy for an operator to restart a crankcase scavenged two-stroke engine after successful operation.

BRIEF SUMMARY OF THE INVENTION

• a) Aktivieren eines Stoppschalters der Maschine,
• b) Erfassen eines Stoppereignisses von dem betätigten Stoppschalter,
• c) Stoppen der Kraftstoffzufuhr zu der Kraftmaschine als Reaktion auf das Stoppereignis,
• d) Einstellen eines Zündungsstoppschwellenwerts, der kleiner oder gleich einer Verzögerungszeitspanne ist, wobei die Verzögerungszeitspanne bei Leerlauf in dem Bereich von 100–1000 ms liegt, und
• e) falls der Stoppschalter betätigt wird, bis der Zündungsstoppschwellenwert nach dem erfassten Stoppereignis erreicht ist, Stoppen der Zündungen nach dem Verstreichen der Verzögerungszeitspanne ab dem erfassten Stoppereignis, oder
• f) falls der Stoppschalter deaktiviert wird, bevor der Zündungsstoppschwellenwert erreicht ist, nachdem das Stoppereignis erfasst wurde, Wiederaufnahme der Kraftstoffzufuhr zu der Kraftmaschine.

This object is achieved by the method mentioned at the outset, which comprises the following steps:

• a) activating a stop switch of the machine,
• b) detecting a stop event from the operated stop switch,
• c) stopping the fuel supply to the engine in response to the stop event,
• d) setting an ignition stop threshold that is less than or equal to a delay period, wherein the idling delay period is in the range of 100-1000 ms, and
• e) if the stop switch is actuated until the ignition stop threshold is reached after the detected stop event, stopping the ignitions after the lapse of the delay period from the detected stop event, or
• f) if the stop switch is deactivated before the ignition stop threshold is reached after the stop event has been detected, resuming fueling to the engine.

By having a delay period from the time when the fuel supply is stopped and until the ignitions are stopped, the excessively rich air-fuel mixture from the crankcase can be eliminated. This reduces the risk of a drowned engine when restarting a warmed up engine. The prime mover can therefore probably be started with a single turn if restarted within a few minutes after a successful operation. This means that the pull rope does not have to be pulled several times to remove an excessively rich air-fuel mixture from the crankcase. If the engine is restarted after a slightly longer period of time, for example after 10 minutes or more, it is possible that the operator must start with choke. However, this is much more convenient than removing an excessively rich air-fuel mixture.

Preferably, the idling delay period is within the range of 100-600 ms, more preferably 200-400 ms. The range is sufficient to ensure that the engine does not have an excessively rich air-fuel mixture and that the air-fuel mixture is not so lean at the same time that the engine must be started with a choke when it does, within a few minutes after a successful operation is started.

Preferably, the maximum speed delay period is within the range of 0-240 ms, more preferably 20-150 ms.

Preferably, the ignition stop 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 ignition stop threshold is equal to the delay period.

Preferably, the ignition stop threshold is within the range of 50-500 ms, more preferably 100-300 ms, most preferably 100-200 ms.

In one embodiment, the ignition stop threshold is set to zero ms at all engine speeds such that step e) is always performed after a stop event has been detected.

• – ein Kraftstoffzuführsystem in der Form eines Vergasers oder eines Niederdruck-Einspritzsystems,
• – eine Zündkerze zum Zünden eines Luft-Kraftstoffgemischs in einer Brennkammer der Kraftmaschine,
• – Steuermittel zum Steuern der Kraftstoffzufuhr zu der Kraftmaschine und der Zündungen der Zündkerze,
• – einen Stoppschalter, der elektrisch mit dem Steuermittel verbunden ist, wobei das Steuermittel als Reaktion auf ein Betätigen des Stoppschalters eingerichtet ist, um die Maschine gemäß dem oben beschriebenen Verfahren abzuschalten.

The invention also relates to a crankcase scavenged two-stroke engine having:

• A fuel supply system in the form of a carburettor 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, the control means being arranged in response to an actuation of the stop switch to shut down the machine according to the method described above.

The invention also relates to a hand-held product incorporating the crankcase scavenged two-stroke engine. The engine may be of the type that uses additional air.

BRIEF DESCRIPTION OF THE DRAWINGS

1 FIG. 12 is a schematic drawing of a two-stroke engine with crankcase scavenging; FIG.

2 schematically shows a shutdown sequence of an engine.

3 schematically shows two scenarios for the development of the air-fuel ratio of an engine, which is switched off from its idle.

4 shows upper and lower limits of the delay period according to two embodiments.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

In the sketch of the 1 denotes the reference numeral 1 an internal combustion engine 1 of the two-stroke type. His crankcase has flushing, that is, a mixture 40 out of air 3 and fuel from a fuel delivery system 20 (For example, a carburetor or a low-pressure fuel injection system) is sucked into the crankcase of the engine. From this crankcase, the mixture is passed through one or more purge passages 14 to the combustion chamber 41 the engine high. The combustion chamber is with a spark plug 32 , which ignites the compressed air-fuel mixture provided. exhaust 42 pass through the exhaust port 43 and through a silencer 13 out. The engine 1 has a cylinder 5 with a piston 6 with alternating movement, by means of a connecting rod 11 on a crankshaft 12 , which is equipped with a counterweight attached. In this way, the crankshaft is rotated. In 1 takes the piston 6 an intermediate position, wherein flow through both an inlet opening 44 as well as through the flushing passage 14 and the exhaust port 43 is possible. The fuel delivery system 20 has an intake passage 21 for the air-fuel mixture. The mouth of the inlet passage 21 in the cylinder 5 becomes inlet opening 44 called. The intake passage 21 is therefore due to the piston 6 locked. By opening and closing the inlet opening 44 , different flow rates and pressures within the intake passage become 21 created. The fuel delivery system 20 sucks fuel from a fuel tank 26 and has an electronically controlled fuel valve 23 , which controls the flow of fuel through the fuel delivery system 20 through controls. Preferably, the fuel valve 23 an electronically controlled bistable valve operating between two stable states, namely open and closed. An example of such a valve is in WO 2009/116902 A1 shown. However, other types of electronically controlled valves may also be used. The pressure variations in the intake passage greatly affect the amount of fuel supplied when the fuel supply system 20 of the carburetor type. Therefore, since a carburetor has a non-significant fuel supply pressure, the amount of fuel supply thereof becomes complete from the pressure changes in the intake passage 21 influenced by the opening and closing of the latter and whether the fuel valve 23 closed or open, caused.

The idling of an engine of this type, for example, when used in a chain saw, is about 40-50 rpm, and the maximum speed is typically about 200-250 rpm. The maximum speed is the speed at which the engine is running at full throttle without any workload. The maximum speed of the engine may be limited by an engine control unit, for example, by stopping ignitions or changing the air-fuel 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 having. The spark plug 32 is in the cylinder opening of the cylinder 5 leading to the combustion chamber 41 extends, mounted. The spark plug 32 is also with the ignition control unit 31 connected, and igniting the spark plug 32 is from the ignition control unit 31 controlled. A fuel control unit 30 is with the fuel valve 23 connected and controls the opening and closing of the fuel valve 23 , A magneto-electric generator with flywheel (not shown) supplies 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 with power. A stop switch 33 is with the ignition control unit 31 connected, and the ignition control unit 31 is with the fuel control unit 30 connected.

In the example shown, the ignition control unit 31 and the fuel control unit 30 shown as two separate units. You could, however, two units 30 . 31 which are installed as a control unit, which both the ignition of the spark plug 32 as well as the position of the fuel valve 23 controls. In addition, the stop switch can 33 alternatively directly with the fuel control unit 30 or independently with both control units 30 . 31 be wired.

The invention will now be described according to a first and preferred embodiment for switching off the engine. In the first and preferred embodiment, when the stop switch is activated 33 for example, by pressing a stop button, a stop signal to the ignition control unit 31 Posted. A stop event is detected upon receiving the stop signal, and the ignition control unit 31 sends the stop signal again to the fuel control unit 30 , The fuel control unit 30 then turn the fuel valve 23 to the closed position, whereby the fuel supply to the engine is stopped.

Optionally, it may be necessary to operate the stop switch during an actuation period before a stop event is determined to be detected. The operation period is for avoiding unintentional stopping when branches, etc. touch the stop switch. The actuation period may be a period of engine revolutions or a period of time and may be up to 200 ms. The length of the actuation period may be configured to be dependent on engine speed. However, in the most preferred embodiment, there is no actuation period, and the stop event is therefore detected as soon as the stop switch is actuated.

In the preferred embodiment, the ignition controller monitors 31 Furthermore, whether the stop switch 33 continues to be actuated after the fuel control unit 30 was instructed the fuel valve 23 close. If the stop switch 33 is actuated until an ignition stop threshold is reached, the ignition control unit stops 31 ignitions of a spark plug 32 after a delay period has elapsed from the original detection of the stop event. If the stop switch 33 is deactivated before the ignition stop threshold is reached, sends the ignition controller 31 a signal to the fuel control unit 30 to resume the fuel supply to the engine and the fuel valve 23 in accordance with a normal operating mode, and maintains ignition of the ignition in the normal operating mode so that the engine continues to run.

The described stop procedure is active at idle, and preferably also over the full speed range, from idle to maximum engine speed. At idle, 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 drains the engine to avoid an excessively rich air-fuel mixture, and preferably allows the engine to be restarted by a single drag when restarted within a few minutes after the engine is stopped, for example, until to 5 minutes or up to 15 minutes after stopping the engine. When the engine is restarted after a long period of time, the operator may need to restart with choke, but that is not as impractical as a flooded engine. At maximum speed, the delay period is preferably within the range below 400 ms, more preferably within the range of 0-240 ms, most preferably 20-100 ms. Further, in order for the engine to achieve a desired air-fuel ratio, the delay period preferably becomes gradually or sequentially shorter as it moves from idle to maximum engine speed is moving, such as in 4 visible, noticeable. Here the upper continuous line corresponds 101 an upper limit of the delay time period from 600 ms at idle to 240 ms at maximum speed, while the lower continuous drawn lines 104a . 104b a lower limit of the delay time period starting at 100 ms at idle and reaching zero ms at engine speed between idle and maximum speed, for example 100-150 rpm. The upper dashed line 102 corresponds to an upper limit of the delay period, which starts at 400 ms at idle, to 100 ms at maximum speed, while the lower dashed line 103 corresponds to a lower limit starting at 100 ms at no-load, to 20 ms at maximum speed. One reason why one has the shorter delay period at maximum engine speed is that the engine makes more firings per second at higher rpm, that is, has a higher combustion rate. Another reason is that it requires more revolutions due to pure inertia for the engine to stop rotating from maximum engine speed than when starting from idle.

In one embodiment, the ignition stop threshold is equal to the delay period. However, in the preferred embodiment, the ignition stop threshold is shorter than the delay period.

Preferably at idle in the range of 50-500 ms, more preferably 100-300 ms, most preferably 100-200 ms. In addition, it is preferred that the ignition stop threshold be between 20-80% of the delay period, preferably 30-70% of the delay period, most preferably 40-60% of the delay period. If the ignition stop threshold is shorter than the delay period, the operator needs the stop switch 33 not to press during a time that is perceived as too long. At the same time, the risk of unintentional operation of the stop switch 33 reduced.

In another embodiment, the ignition stop threshold is less than 50 ms or even set to zero ms. If the ignition stop threshold is zero ms, the ignitions are stopped after the delay time period has elapsed, regardless of whether or not the stop switch has been operated. An advantage of this embodiment is that the operator releases the stop switch 33 only needs to be operated temporarily.

As mentioned above, the delay period is preferably continuous or becomes sequentially shorter from idle to maximum engine speed. According to another embodiment, therefore, the delay time period in the speed range from idle 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 U / s ( Revolutions per second). Preferably, the lower limit is at least (-1 * N + 150) ms for N up to 150 U / s and zero ms for N over 150 U / s. At higher engine speed, therefore, the ignitions and fuel delivery may be simultaneously stopped, that is, using larger amounts of engine revolutions that the engine requires to stop from a higher speed than, for example, idle. That is, it may not be necessary to combust fuel to deflate the crankcase and achieve the desired air-fuel ratio because the engine may be sufficiently vented by the coasting of the revolutions induced by rotational inertia. Preferably, however, the lower limit is at least (-1N + 250) ms.

In 2 the stop sequence of the engine is shown schematically. When a stop event is detected, fuel delivery is stopped first. The ignitions are maintained and consequently the air-fuel ratio increases. After the elapse of the delay period, the ignitions are stopped. When the ignitions are stopped, the engine speed drops until the engine finally comes to a standstill. During the time from stopping the ignitions and until the engine finally comes to a standstill, the air-fuel ratio continues to increase. In consideration of the effect of increasing the air-fuel ratio both during the delay period and during the time after stopping the ignitions until the rotation of the engine stops, an optimum air-fuel ratio for restarting the engine can be adjusted by controlling the duration of the delay time period ,

In 3 The development of air-fuel ratio is shown schematically for two scenarios of engine shutdown at idle. In the figure, the air-fuel ratios AF1 and AF2 represent an interval at which the engine can be started with a pull on the pull rope. For air-fuel ratios below AF1, the engine is too rich and the user has to pull more than once to remove an excessively rich air-fuel mixture from the engine before a successful start can be achieved, that is, the engine is drowned. For air-fuel ratios above AF2, the choke (or other enrichment) must be used when starting the engine.

The first line 201 schematically shows the air-fuel ratios of an engine in which the ignition and the fuel supply are stopped simultaneously at a first time t1. At a third time t3, turning of the engine stops, and at a sixth time t6, the air-fuel ratio has reached the air-fuel ratio AF1. A user who restarts the machine before time t6 will not be able to start the machine. Instead, multiple trains may be required to vent the engine and increase the air-fuel ratio.

The second line 202 schematically shows the development of the air-fuel ratio of an engine having the shutdown sequence of the invention, that is, in which the fuel supply at the first time t1 is stopped, and in which the ignitions are stopped at a second time t2 after a delay period means that t2 - t1 has elapsed from stopping the fuel supply. At a fourth time t4, shortly after the ignition stops, the engine's rotation stops. Here, the delay time period t2-t1 has been selected such that when the engine comes to a standstill, the air-fuel ratio is above AF1. Finally, the air-fuel ratio exceeds AF2 at a fifth time t5. Typically, the time is t5-t4 up to 5-15 minutes. Therefore, a user pulling the tow rope just after stopping the engine is in the desired range AF1-AF2. Further, if the engine does not start easily, the user knows that the engine is likely to have an air-fuel ratio above AF2 and therefore can activate the throttle when a previous launch attempt was unsuccessful. Alternatively, the fuel control unit 30 be implemented to the fuel valve 23 to control the air-fuel ratio (enrichment) in such a situation. It is emphasized that the positions of the lines 201 and 202 to each other in 3 are just an illustration of an example. In fact, they may occupy two different positions while still describing the present embodiment of the invention. For a two-stroke engine for a small chain saw, for example, a general slope of the second line 202 steeper than a general slope of the line 201 , Therefore, the time from simultaneous fuel cutoff and interruption of the ignition t1 until reaching t6, entering the range between AF1 and AF2, can follow the line 201 (without any delay period) about 2 minutes while a corresponding chain saw adopting one embodiment of the inventive idea is that of the line 202 follows, well up to 15 minutes (t5 - t4 = 15 minutes) can remain in the trainable area between AF1 and AF2. Furthermore, the lines 201 and 202 are also affected by environmental conditions, such as ambient temperature, as well as the size of the engine and configuration, and could also vary depending on the position in which the piston 6 comes to rest, vary.

While the invention has been shown and described in connection with the preferred embodiments thereof, it will be understood that many changes, substitutions, and additions may be made within the broad scope of the following claims. From the above it can be seen that the present invention fulfills at least one of the stated objects.

The ignition stop threshold may be set to the delay time period, for example.

The delay period and / or the ignition threshold may be measured, for example, in number of revolutions as well as time.

Claims (11)

Method for switching off a two-stroke engine with crankcase scavenging ( 1 ), wherein the engine operating speed ranges from an idle to a maximum speed, the method comprising the steps of: a) actuating a stop switch ( 33 ) of the engine ( 1 b) detecting a stop event from the operated stop switch (FIG. 33 c) stopping the fuel supply to the engine in response to the stop event, d) setting an ignition stop threshold that is less than or equal to a delay period (t2-t1), the idling delay period being in the range of 100-1000 ms, and e) if the stop switch ( 33 ) is activated until the ignition stop threshold is reached after the detected stop event, stopping the ignitions after the lapse of the delay period (t2 - t1) from the detected stop event, or f) if the stop switch ( 33 ) is deactivated before the ignition stop threshold is reached after the stop event has been detected, resumption of fuel supply to the engine. The method of claim 1, wherein the delay time period (t2-t1) at idle within the Range of 100-600 ms, preferably 150-500 ms, more preferably 200-400 ms. A method according to claim 1 or 2, wherein the delay time period (t2-t1) at maximum speed is within the range of 0-240 ms, preferably 20-150 ms. The method of claim 1, wherein the delay time period (t2-t1) in the speed range from idle 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 U / s is. A method according to claim 1 or 4, wherein the delay time period (t2-t1) in the speed range from idle to maximum speed is at least a maximum of (-1 x N + 150.0) ms, preferably at least (-1 x N + 250) ms. where N is the engine speed in U / s. Method according to one of claims 1 to 5, wherein the ignition stop threshold is between 20-80% of the delay period (t2-t1), preferably 30-70% of the delay period, most preferably 40-60% of the delay period. The method of any one of claims 1 to 5, wherein the ignition stop threshold is equal to the delay period. The method of claim 6 or 7, wherein the ignition stop threshold at idle is within the range of 50-500 ms, more preferably 100-300 ms, most preferably 100-200 ms. The method of any of claims 1 to 5, wherein the ignition stop threshold is set to zero ms at all engine speeds such that step e) is always performed after a stop event has been detected. Two-stroke engine with crankcase scavenging ( 1 ), comprising: - a fuel delivery system ( 20 ) in the form of a carburettor 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 . 31 ) 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, the control means being arranged in response to actuation of the stop switch to shut down the machine according to the method of any of claims 1-9. A handheld product comprising a crankcase scavenged two-stroke engine according to claim 10.

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