Patent Grant
9765730
The invention concerns a method of controlling the fuel supply to an internal combustion engine at start-up, the engine having a fuel supply system.
The invention also concerns a carburetor having an intake channel with a venturi section, a throttle valve mounted in the intake channel downstream of the venturi section, a choke valve mounted in the intake channel upstream of the venturi section, and a fuel supply system including a main fuel path connecting a diaphragm controlled regulating chamber to a main outlet in the region of the venturi section, the main fuel path including an actively controlled fuel valve, and an idling fuel path branching off from the main fuel path downstream of the valve and ending in at least one idling outlet in the region of the throttle valve.
Internal combustion engines of two-stroke or four-stroke type usually are equipped with a fuel supply system of carburetor type or injection type. In a carburetor, the throttle of the carburetor is affected by the operator's demand, so that a wide open throttle produces a minimum throttling in the carburetor barrel. The depression created by the passing air in the carburetor venturi draws fuel into the engine.
Diaphragm-type carburetors are particularly useful for hand held engine applications wherein the engine may be operated in substantially any orientation, including upside down. Such carburetors typically include a fuel pump that draws fuel from a fuel tank and feeds the fuel to a fuel pressure regulator via a needle valve. The fuel pressure regulator usually includes a fuel metering chamber that stores fuel fed from the fuel pump and the fuel metering chamber is generally separated from atmosphere by a diaphragm that adjusts the fuel pressure to a constant pressure. The needle valve opens and closes the fuel passage from the fuel pump to the fuel metering chamber as the diaphragm moves. From the fuel metering chamber fuel is delivered to the main air passage via a main channel and an idle channel. The main channel leads to a main nozzle in the main air passage fluidly prior to the throttle valve, whereas the idle channel leads to an idle nozzle fluidly shortly after the throttle valve.
When starting a crankcase-scavenged engine having a conventional carburetor, the choke valve is closed by the operator using a choke button and the throttle valve is set in a start gas position. When pulling the pulling cord to start the engine, an air and fuel mixture is delivered to the crankcase of the engine. When a first ignition is heard by the operator, the choke valve is opened so not to flood the engine with too much fuel. However, sometimes the operator misses the first ignition and the engine is flooded and the product cannot be started as desired.
U.S. Pat. No. 6,932,058 discloses a carburetor including a fuel supply system for supplying fuel from a diaphragm controlled regulating chamber to the intake channel of the carburetor. The fuel supply system includes a main fuel path having a control valve and an idling fuel path that branches off from the main fuel path downstream of the control valve. The control valve thereby controls all fuel supplied to the intake channel. It has however been found out that this solution provides an inadequate fuel supply in certain situations. In particular it is difficult to control the fuel supply at start up.
U.S. Pat. No. 7,603,983 shows a carburetor including a fuel supply system having two independent fuel paths for supplying fuel from a diaphragm controlled regulating chamber to the intake channel of the carburetor. The first fuel path includes a main fuel path having a control valve and an idling fuel path that branches off from the main fuel path downstream of the control valve. A first bypass line bypasses the control valve. The second fuel path connects the regulating chamber to an outlet in the region of the throttle valve and provides a second bypass line. A second valve is mounted in the second bypass line or alternatively in the first start fuel line. The opening and closing of the second valve is controlled by the position of the choke valve. The carburetor further includes an accelerator pump for supplying additional fuel to the main fuel path downstream of the control valve during acceleration. This solution improves the operational range of the fuel supply. It is however costly and includes several additional components compared to e.g. U.S. Pat. No. 6,932,058.
U.S. Pat. No. 6,880,812 discloses a carburetor having two independent fuel supply systems, each including an electromagnetically driven control valve. A control system controls the opening and closing of the valves by using input from an engine speed sensor and a temperature sensor. Also this solution is costly and complex.
US 2009/0013951 shows a carburetor including a fuel supply system having two fuel paths for supplying fuel from a diaphragm controlled regulating to the intake channel of the carburetor. A main path supplies fuel to the intake channel during normal operations. A startup fuel supply passage has a solenoid valve to control the timing of startup fuel delivery. In this carburetor the fuel supply cannot be electronically controlled during normal operations since the solenoid valve only operates on the startup fuel supply passage. This is inadequate.
One object of the invention is to provide a method of controlling the fuel supply when attempting to start a crankcase-scavenged engine.
Another object is to provide a carburetor for controlling the fuel supply when attempting to start a crankcase-scavenged engine so as to reduce the risk of flooding the engine at start up while being capable of delivering extra fuel during a start attempt.
At least one of these objects or problems mentioned above is addressed by a method of controlling the fuel supply to an internal combustion engine at start-up, the engine having a fuel supply system which can be set in at least two start modes, a lean mode, and a rich mode, the rich mode providing extra fuel during start-up of the engine, the method including:
Preferably, the fuel supply system is set in lean mode when the engine is stopped after a successful run so that a first start attempt is always executed in lean mode. Thereby the risk of flooding then engine at start up is reduced.
Preferably, a start attempt is determined in that the engine is started when set in a start position, and that the method includes the step of detecting that the engine is started in the start position, and where preferably the start position is having a throttle valve in a start gas position, e.g. having a throttle ratio in the interval 5-20, 20-40, 40-60, or 60-90%, for example, and a choke valve in closed position.
Preferably, in step a) the evaluation includes determining an ignition indication has occurred in the present start attempt based on at least one monitored engine parameter/s of the present start attempt, and wherein if an ignition indication is determined to have occurred, in step b) the fuel supply system is set or maintained in lean mode.
Preferably, the ignition indication is determined by monitoring the engine speed and evaluating the engine speed behavior during said start attempt, for instance a sudden increase in engine speed could indicate an ignition.
Preferably, the ignition indication is determined if an ignition quotient is larger than a predetermined ignition threshold value, the ignition quotient based on the quotient between the time from the lower dead point to upper dead point and the time from the upper dead point to the lower dead point.
Preferably, the engine parameter/s includes at least one of:
Preferably, the fuel supply system includes a main fuel path connecting a diaphragm controlled regulating chamber to a main outlet in the region of the venturi section, the main fuel path including an electronically controlled valve, and an idling fuel path branching off from the main fuel path downstream of the valve and ending in at least one idling outlet in the region of the throttle valve, the fuel supply system further including a start fuel line starting upstream or downstream of the valve and ending in at least one start fuel outlet to the intake channel.
In this context, the term “start fuel line” is used to designate a fuel line for supplying the additional amount of fuel that usually is required for starting a cold engine.
Preferably, the fuel valve is a bistable two position valve, having an open, first position and a closed, second position and being closed in lean mode and open in rich mode.
Suitably, at least said one start fuel outlet is located upstream of the venturi section, preferably in the region of the choke valve and downstream of it, for supplying fuel to the intake channel.
Preferably, the engine is a crankcase-scavenged engine.
Preferably, the engine is a two-stroke engine. However the engine may also be a four-stroke engine.
The invention also concerns the carburetor mentioned initially, wherein the fuel supply system has only one actively controlled valve, which is located between the regulating chamber and the intake channel and is actively controlled during operation of the engine, and in that the fuel supply system further includes a start fuel line starting upstream or downstream of the valve and ending in at least one start fuel outlet to the intake channel. Thereby a simple and robust fuel supply system can be achieved, still being able to have an adaptive fuel supply at start up.
In one preferred embodiment, the start fuel line starts upstream of the valve and the carburetor includes an air channel that connects ambient air to the start fuel line so that it can draw fuel from the regulating chamber and air from the air channel, thereby diluting the fuel concentration supplied from the start fuel outlet to the intake channel during operation of the engine.
In another preferred embodiment, the start fuel line starts downstream of the valve and the carburetor includes an air conduit that permits a leakage of air past the choke valve, so that it can draw fuel from the main fuel path and air through the conduit past the choke valve, thereby diluting the fuel concentration supplied from the start fuel outlet to the intake channel during operation of the engine.
Preferably, the choke valve is a butterfly valve having a closing mechanism in form of a disk, and wherein the air conduit, which permits a leakage of air past the choke valve, is either an enlarged bore through the disk or an additional bore through the disk to increase the air flow through the choke valve when the valve is closed.
Preferably, the actively controlled valve is a bistable two position valve, having an open, first position and a closed, second position.
Preferably, the actively controlled valve is electronically controlled.
Preferably, said at least one start fuel outlet is located upstream of the venturi section, preferably in the region of the choke valve and downstream of it, for supplying fuel to the intake channel.
The present invention primarily concerns crankcase scavenged, spark ignited, two- or four-stroke engines and any general reference to engines in the following description concerns these type of engines, although also non-crankcase-scavenged engines are possible.
A fuel pump 8 draws fuel from a fuel tank 9. The fuel pump 8 may be a known pulsation controlled diaphragm pump, driven by the pressure pulse generated by a crankcase of the engine that the carburetor is supplying air and fuel mixture to. The fuel pump 8 delivers fuel, via a needle valve (not shown), to a fuel metering chamber 12 of a fuel regulator 11. The fuel metering chamber 12 is separated from atmospheric pressure by a diaphragm 15 and can hold a predetermined amount of fuel.
A main fuel path 13 connects the fuel metering chamber 12 to a main outlet 22 in the intake channel 30, located in the region of the venturi 31. An actively controlled fuel valve 26 is mounted in the main fuel path 13. The actively controlled fuel valve 26 is preferably a bistable valve that can switch between an open and closed position.
Downstream of the electronically controlled fuel valve 26, an idling fuel path 14 branches off from the main fuel path 13. The idling fuel path 14 itself branches off into three idling outlets 19, 20, 21 to the intake channel 30, which are successively disposed in the region of the throttle valve 33. More precisely, the first idling outlet 19 is disposed upstream of the throttle valve 33 when the latter is closed, the second idling outlet 20 is disposed approximately in the region of a closed throttle valve 33, and the third idling outlet 21 is disposed downstream of the throttle valve 33.
The fuel valve 26 is controlled by an electronic control unit (ECU) 50 that receives sensor inputs, such as throttle position, from at least one throttle position sensor, engine speed from at least one engine speed sensor, and temperature from at least one temperature sensor. The electronic control unit 50 can e.g. use these sensor inputs to decide when to open or close the fuel valve 26.
A start fuel line 23 emanates from the fuel metering chamber 12 and has a start fuel outlet 25 in the region of the choke valve 32, downstream of it. An optional air channel 24, which is shown in
The main fuel path 13, the idling fuel path 14, and the start fuel line 23 each have a check valve 16-18 for preventing fuel flowing back to the fuel metering chamber 12.
The carburetor 10 can be set in a start position, as e.g. described in U.S. Pat. No. 7,611,131. In the start position, the choke valve 32 is closed, and the throttle valve 33 is slightly open (around 5-20, 20-40, 40-60, or 60-90%, of a fully opened position). When pulling a pull cord to start the engine while the carburetor 10 is in the start position, pressure variations in the intake channel 30 will draw fuel from the start fuel outlet 25. For those revolutions, the electronically controlled valve 26 is open, consequently fuel will be drawn from the main fuel outlet 22 as well as from the idling fuel outlets 19, 20, 21, thereby delivering an additional amount of fuel. However, for those revolutions the fuel valve 26 is closed, fuel will be drawn only from the start fuel outlet 25.
In one preferred embodiment of the invention, the fuel valve 26 is either closed or open for all revolutions during a start attempt (for other operating conditions the fuel valve 26 will open and close frequently to adjust the fuel ratio). In the mode when the fuel valve 26 is closed at the start attempt, the fuel supply system is referred to as being in lean mode, and when the fuel valve is open the fuel supply system is referred to as being in rich mode.
Moving from the start position, the choke valve 32 is released to a fully opened while the throttle valve 33 can take any position between closed (idle throttle) and fully open (maximum throttle). When the throttle valve 33 is closed, fuel will mainly be taken from the first idling outlet 19, and the electronically controlled valve 26 can control the fuel supply during idling by closing and opening the valve 26 according to an idling control scheme as e.g. described in WO 2009/038503, herewith incorporated by reference. In the same manner the fuel supply can be controlled by closing and opening the valve 26 to adjust the air fuel ratio of the as described in e.g. WO 2007/133125 and WO 2007/133148, herewith incorporated by reference.
Controlling the Fuel Supply to an Internal Combustion Engine at Start-Up
A method for controlling the fuel supply to an internal combustion engine at start-up will now be described in more detailed with reference to
The phantom lined box “Set carburetor in start position” 100 indicates that the operator sets the carburetor in a start position, e.g. closed choke valve 32 and slightly opened throttle valve 33. Thereafter the operator actuates the start mechanism at box 101, e.g. pulls the pulling cord, which box 101 is also drawn with phantom lines indicating that these steps do not form part of the method of the invention.
After actuating the start mechanism, the engine control unit is energized and determines in box “Start position?” 103 whether the carburetor is set in its start position, here, by using a throttle position from a throttle position sensor 113. If the carburetor is not in its start position, the fuel supply system is controlled by other controls methods as indicated by the box “Run mode” 104.
On the other hand, if the start position is detected, the next box “Idetect=True?” 107 checks whether a first ignition was detected in a previous start attempt, by receiving input from box “idetect” 114, i.e. a value symbolizing “True” or “False”. If the value is “True” the fuel supply system will be set or maintained in lean mode in box “set/maintain lean mode” 109. On the other hand, if it is “False”, the box “Cold or warm?” 108 follows, where it is determined whether the engine is considered to be started warm or cold.
In box 108, the decision of warm or cold is determined by using the engine parameters from box 115, which here represents parameters from the present start attempt and/or from the previous start attempt and/or last successful run. For instance, engine parameters such as a stop temperature T1 stored when the engine was stopped at the last successful run, a start temperature T2 of the present start attempt, and a duration t1 of the last successful run, and a time t2 since the last successful run. As an example, the conditions in box 108 could be:
The first example being the simplest one; if the engine hasn't been running recently, the engine is considered to be cold or else warm. In the second example, the engine is considered to be cold if the last engines run was short and if the temperature sensor indicates that it is very cold, e.g. when the engine is cooled during a cold winter day. In the third example, the time t2 since the last successful run is compared to a value that is dependent of the engine temperature T1 when the engine was stopped, i.e. if the engine is very hot when stopped it will take longer timer for it to cool. The specific conditions are shown as examples, of course more complex conditions could be used, for instance by combining one or more of the examples.
If the engine during the start attempt is determined to have been started warm, the fuel supply system is set or maintained in lean mode in box “Set/maintain lean mode” 109. If the engine is determined to have been started cold, the box “First ignition?” 110 follows.
At the box “First ignition?” 110, a function evaluates engine speed data 116 to detect whether any ignition has occurred during the start attempt. If an ignition is determined to have occurred, the variable “idetect” is set to be “True” in box “Idetect=True” 111. Thereafter, the fuel supply system is set in lean mode at box “Set/maintain lean mode” 109, so that the next start attempt will be performed in lean mode. This is done, since if a first ignition has been determined to have occurred, the engine should be close to starting and having a fuel ratio in the crankcase close to the optimal. Therefore, by setting the fuel supply system in lean mode, the risk of flooding the engine during the next start attempt is minimized.
On the other hand, if no ignition was detected in box 110, the fuel supply system is set or maintained in rich mode at box “Set/maintain rich mode” 112. Thereby, the next start attempt is performed with the fuel supply system in rich mode.
Of course, when the engine starts to run as indicated by the phantom lined box “Engine starts to run” 117, there will be no next start attempt, and other control schemes are activated to govern the fuel supply to the engine.
After a successful run of the engine and the engine is stopped as indicated by the phantom lined box 118, the fuel supply system is set in lean mode at box 119. Furthermore, during shut down, as indicated by box 120, engine parameters such as engine stop temperature T1 and the duration t1 of the successful run are stored, and a timer t2 is started. Also the variable “idetect” is set to “False” during shut down, as indicated by box 121. Thus, after a successful run, the engine will be started with a fuel supply system in lean mode and with the ignition detection set to “False”.
The fuel supply unit shown in
In
Further, an air conduit 424, which permits a leakage of air past the choke valve 32, is substituted for the air channel 24, which in
On pulling the start cord to start the engine, the fuel supply system of
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.
Alternatively, when shutting down the engine, the engine is set in lean or rich mode depending on one or more engine parameters. One example of conditions could be that if T1 is less than −5° C., then the engine at the first start attempt is started in rich mode and else in lean mode, i.e. expecting that the next start will be a cold start if T1 gives a low reading. Alternatively, even though it is not preferred, the engine could always be started in rich mode at the first start attempt.
The temperatures T1 and T2 can e.g. be measured by a temperature sensor mounted on a circuit board attached to the carburetor.
| Number | Date | Country | Kind |
|---|---|---|---|
| PCT/SE2010/050758 | Jul 2010 | WO | international |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/SE2011/050851 | 6/28/2011 | WO | 00 | 12/21/2012 |
| Publishing Document | Publishing Date | Country | Kind |
|---|---|---|---|
| WO2012/002888 | 1/5/2012 | WO | A |
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| Number | Date | Country | |
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| 20130133618 A1 | May 2013 | US |
