Patent Grant
8333174
The present disclosure relates to an idling speed control method for an engine in which the fuel metering during idling is adjusted so as to find an A/F ratio close to an optimal A/F ratio.
In most engines for a power saw, a power cutter, a lawn mover and similar consumer products, the A/F ratio is manually controllable when the engine is idling, e.g. the electronic control system is only active when the engine is at working speed or above. It would therefore be desirable to have a simple, non-expensive but efficient electronic control method, without the need of adjusting the fuel or air supply manually, when the engine is idling.
EP 0 715 686 B1 describes a method of controlling the engine A/F-ratio. Initially, the A/F-ratio is changed briefly. This could be effected for instance by briefly throttling or stopping the fuel metering. In connection with the change, a number of engine revolution times are measured. The revolution times relate to engine rotational speeds chosen in such a manner that at least one revolution of the engine is unaffected by the change, preferably an engine rotational speed that is sufficiently early for the A/F-ratio change not having had time to affect the engine rotational speed. Further at least one forthcoming revolution of the engine is chosen in such a manner that it is affected by the brief A/F-ratio change. In this manner it becomes possible to compute a revolution-time difference caused by an A/F-ratio change. On the basis of this revolution-time difference a change, if needed, of the mixture ratio in the desired direction towards a leaner or richer mixture is made. Thus using this method an optimal mixture can be achieved by testing how the engine reacts to a leaner or richer mixture. However this control is somewhat slow and mainly suitable for controlling the engine at working speeds.
PCT/SE06/000561 describes an idle speed control where the engine is started with a rich fuel setting and where the fuel setting is gradually moved towards a leaner setting until an engine speed interval is reached and if the engine speed comes above the engine speed interval the fuel setting is gradually moved towards a richer setting. It also describes a method for idle speed control using a single engine speed value where the fuel metering is decreased when the engine speed is below the engine speed value and increased when the engine speed is larger than the engine speed value. This method will find a desired engine speed; however the A/F ratio may come far from an optimal A/F ratio.
U.S. Pat. No. 6,769,394 describes a method for controlling the fuel supply to an internal combustion engine. An interval is allocated around a desired parameter value, e.g. the engine speed. When the measured parameter crosses the lower and/or upper threshold from below to above the fuel supply is cut off. And when the measured parameter crosses the upper and/or lower threshold from above to below fuel supply is switched on. The method can be used at idle. This method will fluctuate around a desired engine speed; however the A/F ratio may come far from the optimal A/F ratio.
EP 0 799 377 describes a method characterized primarily in that in the fuel supply system a fuel shut-off is effected during a part of the operating cycle by means of an on/off valve shutting off the entire fuel flow or a part flow, and in that the shut-off is arranged to take place to an essential extent during a part of the operating cycle when the intake passage is closed and consequently the feed of fuel is reduced or has ceased. This means that the amount of fuel supplied can be precision-adjusted by a slight displacement of one or both of the flanks of the on/off valve shut-off curve; this method will be referred to as Pulse Width Modulation (PWM) of the fuel supply. However, EP 0 799 377 also suggest that in particular for crank case scavenged two/four-stroke engines, the shut-offs can be performed every other, every third or possibly every forth engine revolution instead upon each engine revolution, in the case of a four-stroke engine, half as often. Of course the on/off valve could also be set to be open every revolution. In that case a major fuel amount adjustment is made instead, for instance by completely shutting off the fuel supply for a revolution. This can be done since the crank case in crank case scavenged two-stroke engines or crank case scavenged four-stroke engines can hold a considerable amount of fuel and consequently serve as a levelling reservoir, it is therefore not necessary to adjust the fuel supply for each revolution when controlling the fuel supply to the engine, i.e. adjusting the fuel supply in one revolution will affect the subsequent revolutions.
It is an object of the invention to provide a method for adjusting the fuel metering when the engine is operating at idle speed.
Another object of the invention is to provide a fuel metering during idling which tunes towards an A/F ratio that is close to an optimal A/F ratio and preferably an A/F ratio that is slightly biased towards a rich A/F ratio.
At least one of the above mentioned objects and/or problems are met by providing a method for controlling the fuel metering in a carburetor or a low pressure injection system of an internal combustion engine when the engine is operating at idle speed. The method comprising the steps of:
Preferably the first moving average algorithm addresses more weight to a lower number of monitored engine speeds when determining the first moving average while when determining the second moving average more weight is given to a higher number of monitored engine speeds, so that the first moving average algorithm is thereby arranged to react faster to an engine speed change than the second moving average algorithm.
It is also preferred that when determining the second variable the outcome from the second moving average algorithm is biased to correspond to a lower averaged engine speed for instance by subtracting the outcome with a positive constant or multiplying with a factor smaller than 1.
According to another example when determining the first variable the outcome from the first moving average algorithm is biased to correspond to an higher averaged engine speed for instance by adding the outcome with a positive constant or multiplying with factor larger than 1.
Further according to an embodiment the first moving average algorithm is based on a first plurality of samples of the monitored engine speed and the second moving average algorithm is based on a second plurality of samples of the monitored engine speed, where the first plurality includes fewer samples than the second plurality. And where preferably the first plurality of samples as well as the second plurality of samples are taken from the latest engine speed data of the monitored engine speed.
In a further example the comparison of step d) is performed when the second variable is within an engine speed interval which is provided by a first engine speed threshold and a second engine speed threshold, where the second engine speed threshold is larger than the first engine speed threshold. And where preferably if the second variable is higher than the second engine speed threshold: the fuel metering is set in the second richer setting, and where if the second variable is lower than the first engine speed threshold: the fuel metering is set in the first leaner setting.
According to one aspect of the invention the fuel metering is adjusted by means of a fuel valve, which fuel valve may e.g. be an on/off valve or a proportional valve. The fuel metering may also be adjusted by means of an air bleed valve.
If the fuel valve is an on/off valve the richer setting and the leaner setting can be effectuated by means of corresponding fuel valve control sequences determining which of the forthcoming engine revolutions the on/off valve is to be closed, during at least a portion of their corresponding intake periods, respectively open, where the leaner setting includes more closings than the richer setting. For instance the rich setting may corresponds to having the on/off valve fully opened and the leaner setting to having the on/off valve closed during the intake period of every second revolution.
Embodiments of the invention will be described in the following in closer details by means of various embodiments thereof with reference to the accompanying drawings, where
The invention is particularly suitable for controlling a two stroke or a four stroke crank case scavenged internal combustion engine at idle speed. The engine of
In
The fuel valve 24 may be any kind of on/off valves, i.e. a valve having two positions opened and closed. However, the fuel valve 24 may also be a proportional valve. The fuel supply could also be controlled through an air bleed valve controlling an amount of air bleed into a fuel supply line to thereby adjust the amount of fuel delivered through the fuel supply line.
The fuel valve 24 is preferably controlled by a control unit 9 which receives inputs from at least one sensor. An engine speed sensor(s) ESS provides engine speed data to the engine, for instance the engine speed could be measured as the time between two following ignition sparks. Further, the control unit 9 preferably receives inputs about the position of the throttle valve from a throttle position sensor(s) TPS. The throttle position sensor(s) could for instance be a sensor that detects if a throttle trigger of a device comprising the en engine is actuated, i.e. the throttle position is not zero, or it could be a sensor that detects if the engine is fully actuated, i.e. the throttle position is full, or it could be a sensor(s) detecting both zero throttle and full throttle or a more advanced sensor(s) detecting how much the throttle trigger is actuated. Needless to say other kinds of throttle position sensor(s) may also be used. Further, the control unit 9 may of course receive inputs from other kinds of sensors than those mentioned above.
The idle speed control method described below can be implemented means of a computer program in the control unit 9. For the control unit 9 to determine if the engine is operating at idle speed, the control unit 9 may use a wide variety of criterions. Such an idle criterion may be different depending on the kind of sensor inputs available to the control unit 9. For instance having a throttle position sensor only detecting full throttle, an idle criterion could be that full throttle is not detected and that the engine speed N is below a predetermined engine speed (e.g. that an averaged engine speed is below a threshold longer than a predetermined time period). However, also other considerations besides throttle position inputs and monitored engine speed may be taken into account, for instance during a period after start of the engine, the fuel valve may be controlled according to a different method even though full throttle is not detected and the engine speed is below a threshold. Further, if the throttle position sensor is able to detect zero throttle; an idle criterion could simply be that the throttle position is zero. It should be realized that the idle speed control method described below can be used regardless of the method on how to detect that the engine is operating at idle speed, i.e. the above mentioned examples of idle criterions is not intended to limit the scope of the claims but should rather be seen as examples on how to determine if the engine is operating at idle speed.
The idle control method which will be described below with reference to
The method comprises the steps of a) monitoring the engine speed regularly providing new engine speed data as the engine runs, b) determining a first variable A based on a first moving average algorithm using the monitored engine speed as input data; c) determining a second variable B based on a second moving average algorithm using the monitored engine speed as input data, where the first moving average algorithm is arranged to react faster to an engine speed change than the second moving average algorithm; and c) comparing the second variable B to the first variable A, where if 1) the second variable B is higher than the first variable A: the fuel metering is set in a first leaner setting, and where if 2) the second variable B is lower than the first variable A: the fuel metering is set in a second richer setting—thus the fuel metering will toggle between the second richer setting and the first leaner setting as long as the regulation is active as is indicated by the pulse shaped wave in
In step b) and c) it is preferred that the first moving average algorithm addresses more weight to a lower number of monitored engine speeds when determining the first moving average while when determining the second moving average more weight is given to a higher number of monitored engine speeds. For instance the first variable A could be calculated through a first moving average over a first plurality of samples ×1 of the latest received engine speed data and the second variable B could be calculated through a second moving average over a second plurality of samples ×2 of the latest received engine speed data, where the second plurality of samples ×2 are more than the first plurality of samples ×1. For instance the first variable A could then be calculated as a moving average over the three last measured engine speeds and the second variable B could e.g. be a moving average over the eight last measured engine speeds, i.e. A=(n1+n2+n3)/3 and B=(n1+n2+ . . . +n8)/8, where n1 is the last measured engine speed and n2 the second last and son on.
Preferably one or both of the variables A and B are biased so that the idle speed control is active at the rich side of the diagram in
The moving average algorithms for calculating the variables A and B could also be implemented by means of weighted moving averages, e.g. more weight could be addressed to the latest engine speed data. For instance A=(7*n1+5*n2+3*n3+n4)/16 and B=(n1+n2+n3+n4)/4−0.5, i.e. the first moving average algorithm addresses more weight to a lower number of monitored engine speeds when determining the first moving average while when determining the second moving average more weight is given to a higher number of monitored engine speeds, so that the first moving average algorithm is thereby arranged to react faster to an engine speed change than the second moving average algorithm.
Through the comparison between these two moving averages A and B the A/F ratio will tune in to an A/F ratio slightly on the rich side of the optimal A/F ratio, i.e. A/FIDLE
In a further embodiment the regulation using the comparison between the moving averages A and B is active when the second variable B is within an engine speed interval [y1, y2] which is provided by a first engine speed threshold y1 and a second engine speed threshold y2, where y1<y2. Whereas if the second variable B is higher than the second engine speed threshold y2: the fuel metering is set in the second richer setting to lower the engine speed, and where if the second variable B is lower than the first engine speed threshold y1: the fuel metering is set in a first leaner setting to increase the engine speed. The first threshold mainly serves to quickly adjust the fuel metering to an A/F ratio closer to the desired whereas the second threshold y2 mainly serves as an upper limit for the engine speed. Usually the upper threshold is above NIDLE
The engine idle speed control method described above requires that the fuel metering can be set in at least two distinct states, a second richer setting and a first leaner setting. Below a number of examples on how to adjust the fuel metering will be described as well as how to set in a rich or a lean setting.
Using a proportional fuel valve 24 the richer setting could e.g. be fully (100%) opened while having the fuel valve partly open e.g. 30% open in the leaner setting. Of course, any other combination where the richer setting is a more open valve than the leaner setting is possible.
Using an on/off valve 24 the two states can be enabled by using Pulse Width Modulation as described above in relation to EP 0 799 377. E.g. one state could be enabled by having the fuel valve 24 fully opened during the entire intake period while the other state could be enabled by having the fuel valve 24 closed during a portion of the intake period or during the entire intake period.
Another way of providing different levels of the fuel metering when using an on/off valve 24 is by executing shut-offs every second, every third, or every forth engine revolution, etc., and of course having no shut-offs. E.g. a richer setting could be implemented by having the on/off valve 24 open as long as the richer setting is active, i.e. no shut-offs, and the leaner setting by closing the on/off valve 24 every second revolution as long as the leaner setting is active, in this example the fuel metering would be toggling between 0% fuel reduction and 50% fuel reduction (as compared to the maximum fuel metering).
It is also possible to use a method where a shut-off schedule, as shown in
An easy way to achieve evenly distributed shut-offs during a period of revolutions can be done by calculating the fuel shut-off positions as; FCn=(n−1)*(PL−NS)/NS+n, for n=1 . . . NS, and rounding off the result to nearest integer. And where PL is the period length and NS is the number of shut-offs during the period. I.e. the fuel valve control sequence Ns/PL provides corresponding fuel shut-off positions [FC1, FC2, . . . , FCNS]. E.g. if the period length PL for example is 64 and the fuel valve control sequence is 6/64, i.e. a 9% decrease of fuel in relation to the maximum available fuel metering, the first fuel shut-off is done at the first revolution in the period, since FC1=(1−1)*(64−6)+1=1, the second fuel shut-off is done at the period position FC2=(2−1)*(64−6)/6+2=12, the third fuel shut-off is done at period position FC3=(3−1)*(64−6)/6+3=22, the forth fuel shut-off is done at the period position FC4=(4−1)*(64−6)/6+4=33, the fifth fuel shut-off is done at the period position FC5=(5−1)*(64−6)/6+5=44 and the sixth fuel shut-off is done at the period position FC6=(6−1)*(64−6)/6+6=54. The table of
Using a shut-off schedule with the period length PL of 32 revolutions, a rich setting could be e.g. the fuel valve control sequence 5/32, i.e. 16% fuel reduction, and lean setting could e.g. be the fuel valve control sequence 15/32, i.e. 47% fuel reduction. Of course, any other pair of fuel valve control sequences where the richer setting provides for a lesser fuel reduction than the leaner setting is possible. Further if the idle speed control method determines that it is suitable to shift from the leaner setting to the richer setting or vice versa in the middle of a period of revolutions, the current period can be stopped and a new period using a new scheme can be started.
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.
Even though the fuel supply system 8 has being described as being of carburetor type; the claimed method for controlling a fuel valve can also be suitable in a low pressure fuel injection system.
The on/off valve 24 can for instance be a solenoid valve, an electromagnetic valve, or a piezo valve.
Even though the engine have been shown with a crank case as a levelling reservoir, it would of course be possible to have other kinds of levelling reservoirs for the fuel supply. For instance in a four stroke engine, instead of using a crank case a buffer volume anywhere downstream the fuel supply system 8 and upstream the intake valve(s) of the engine could be used.
Further if n1, n2, n3, n4, n5, n6, n7, . . . are the latest measured engine speeds it would be possible to base the moving averages on a subset that to not include the absolute last measured engine speeds, e.g. the subset n3, n4, n5 could be used to calculate the first variable A.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/SE2007/000825 | 9/21/2007 | WO | 00 | 5/19/2010 |
| Publishing Document | Publishing Date | Country | Kind |
|---|---|---|---|
| WO2009/038503 | 3/26/2009 | WO | A |
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|---|---|---|---|
| 4785780 | Kawai | Nov 1988 | A |
| 5269271 | Kawai et al. | Dec 1993 | A |
| 5313395 | Kawai et al. | May 1994 | A |
| 5936152 | Nishioka et al. | Aug 1999 | A |
| 7792623 | Kuwahara et al. | Sep 2010 | B2 |
| Number | Date | Country | |
|---|---|---|---|
| 20100252011 A1 | Oct 2010 | US |
