FR2739142A1 - Control of richness of air=fuel mixture fed to internal combustion engine used in e.g. garden tool - Google Patents

Abstract

The mixture richness control operates by varying the richness of the mixture and measuring resulting variations in the operation of the engine. The quantity of air (Qa) delivered to the engine is varied using a calibrated compressed air injector (20), inducing a number of steps in the richness of the mixture. The speed of the engine is monitored and if a corresponding variation in speed occurs its sign is determined and recorded. A variation in speed implies that the engine is not operating at its maximum torque, and the sign of the speed variation is used to alter the air/fuel ratio to reduce the level of incomplete combustion. The magnitude of the measured speed variation is used to indicate the required air adjustment.

Description

 The present invention relates to a method for controlling the richness of an air I fuel mixture supplying an internal combustion engine and a corresponding device. More particularly, these internal combustion engines are called upon to equip, for example, gardening tools (chainsaws, brushcutters, etc.), generators, etc.

 To date there are standards limiting the emission of pollutants, applicable to the engines of motor vehicles. In the coming years these standards will be imposed on the above-mentioned engines and the manufacturers of small engines will have to equip them with electronic systems for controlling the richness of combustion or even injection.

 Indeed, the control of the richness of the fuel supplying an engine makes it possible to optimize the combustion of this fuel and therefore reduce the emission of pollutants. Thus maintaining the richness of the autow mixture of a set value, ensures a correct level of engine pollutant emissions. These pollutants are essentially constituted by HC hydrocarbons, carbon oxides CO, and nitrogen oxides NOx.

In addition, the control of the richness of the mixture makes it possible to decrease the operating temperature of the engine, which makes it possible to remain below the critical temperature of the components of the engine.

 The object of the present invention is therefore to create a method and a device for controlling the richness of the mixture supplying an internal combustion motew, inexpensive (the cost of tools using these small engines is low) and not requiring specific sensors. .

To this end, the present invention relates to a method for controlling the richness of an air / fuel mixture supplying an internal combustion engine, said method being of the type consisting in varying the richness of the mixture and in measuring variations in engine speed. corresponding, said process being characterized in that it consists in:
- vary the amount of air supplied to the engine at speed
permanent by means of a compressed air injector calibrated to
create a plurality of wealth jumps in the mix,
- detect if a concomitant variation in speed appears, and in
this case determine its sign,
- deduce that the engine does not run at richness
corresponding to the optimal torque and determine the amount of air to
inject in steady state to minimize the pollution created by
engine.

 Thus the method according to the invention uses an additional air generator to create richness jumps in the mixture supplying the engine. When these richness jumps cause a variation of the engine rotation speed, we deduce that it is not at its optimal speed, and we determine the amount of air to be injected in steady state for the engine to operate. be optimal.

 According to the invention, the carburetor originally associated with the small engine is kept, in order to obtain a fuel flow proportional to the air flow, for proper engine operation in stabilized mode and in transient mode.

However according to the invention in order to refine the adjustment of the richness of the mixture in steady state, a short air circuit is established which bypasses the throttle intake valve, and opens directly into the engine intake manifold. This additional air circuit allows surplus air to be injected into the mixture supplying the engine (that is, to make richness jumps).

 Advantageously, these surplus air are produced by compressed air delivered by a solenoid valve. This solenoid valve is controlled by an electronic computer conventionally associated with the small engine.

 According to the invention the solenoid valve is a three-way valve. A first channel receives air at atmospheric pressure and is used to adjust the amount of air supplying the engine in steady state, a second channel receives compressed air and is used to create the wealth jumps. The third way delivers air at atmospheric pressure, or compressed air, to the engine's intake manifold.

 Advantageously, all of these functions are carried out by means of a valve. In addition, the use of compressed air for making the richness jumps makes it possible to create substantially instantaneous variations in the richness, which improves the sensitivity of the curve linking the torque as a function of the richness.

Other objects, characteristics and advantages of the present invention will emerge from the description which follows, by way of nonlimiting example, and with reference to the appended drawings in which:
- Figure I is a schematic view showing a small motor equipped
of a device according to the invention,
- Figure 2 is a schematic view illustrating the variations of
torque depending on the richness of the mixture,
- Figures 3a and 3b are schematic views, illustrating the implementation
implementation of the process according to the invention respectively, when the
initial mixture in steady state is poor and when it is rich,
- Figures 4a and 4b are schematic views showing a
solenoid valve according to the invention, respectively, in the supply phase
in air at atmospheric pressure and in the air supply phase
tablet, according to a first embodiment of this solenoid valve,
and
- Figures 5a to 6b are views similar to Figures 4a and 4b
showing respectively a second and a third variant of
realization of the solenoid valve according to the invention.

 According to the embodiment shown in FIG. 1, a small engine 10 is conventionally associated with a carburetor 11. This carburetor is supplied on the one hand, with air at atmospheric pressure via a filter 12 , and secondly in fuel via a carburetor tank 13.

 Conventionally, the carburetor It operates the mixing, in predetermined proportions, of air and fuel by regulating the proportion of each of these elements according to the position of a throttle valve 14. The mixture thus produced is then brought to the intake manifold 15 of the small engine 10. This small engine is also provided, in known manner, with an electronic computer 16 adapted to receive and manage a plurality of engine operating parameters.

 According to the invention an additional air circuit 17 is arranged between the air filter 12 and the intake manifold 15. This additional circuit comprises a pump 18, driven by variations in the vacuum prevailing in the casing, a reservoir d compressed air 19, and a three-way solenoid valve 20. This solenoid valve is controlled via a conventional coil 21, by the computer 16.

 The additional circuit also includes a line 22 for supplying the solenoid valve 20 with air at atmospheric pressure and a line 24 connecting the solenoid valve and the intake manifold 15 of the small engine.

 As is clearly visible in FIG. 1, the additional air circuit 17 short-circuits the carburetor 11 and brings air either compressed or at atmospheric pressure directly to the intake manifold 15.

 It will be noted that the pump 18 makes it possible to compress the air coming from the filter 12 and to store it in a compressed air tank 19. When this is necessary this compressed air is sent to the solenoid valve 20.

 The solenoid valve 20 is a three-way valve. A first channel receives air at atmospheric pressure through line 22 and is used to adjust the amount of air supplying the engine in steady state, a second channel 23 receives compressed air and is used to create the jumps of wealth. The third channel 24 delivers air at atmospheric pressure, or compressed air, to the intake manifold 15 of the engine.

 According to the invention, variations in the richness r are caused to determine the maximum torque of the engine. As can be seen in FIG. 2, around the maximum torque value, the variations in richness only slightly modify the value of the torque. According to the invention, variations in the richness are therefore caused and the corresponding variations in torque are observed.

If these variations in richness cause little or no variation in torque, it can be deduced therefrom that the engine operating point is located at maximum torque.

 In FIG. 2, the curve in solid lines represents the variations of the torque as a function of the richness for an engine powered by a conventional carburetor. The dashed curve represents the variations in torque as a function of the richness of the mixture in the case where an additional air flow is used.

 Note that if the mixture is rich, for example, if the engine operating point is at A, if a reduction in b richness of the mixture is caused by an additional air flow (we follow the dotted curve ) we arrive at operating point B. If this same richness had been reached only using a conventional carburetor (curve in solid line), operating point C would have been reached. However, the variation in torque ACAg between the operating points A and B is much greater than the variation in torque between the points A and C.

 It follows from this observation that when one causes variations in richness in a rich mixture by sending compressed air, one causes clear and easily detectable torque variations.

 On the other hand, when variations in richness by additional air supply take place in a lean mixture, variations in torques are produced that are much less significant than those obtained with a conventional carburetor. For this purpose it suffices to note that the variation of ACAge between point A 'and point B' is much less significant than that appearing between points A 'and C.

 It is concluded that when a device according to the invention is used, that is to say an additional compressed air supply, it is preferable to always work with a rich initial mixture.

 Therefore, in the case where it is detected that an initial mixture is poor it will be advantageous to significantly reduce the amount of additional air supplied in steady state, in order to end up with a rich mixture. By working with a rich mixture and with variations in richness caused by compressed air, the sensitivity of the torque response is increased.

 The operation of the device consisting of the additional air circuit will be detailed at the same time as the method for controlling the richness of the mixture.

 This process is carried out as described below.

 First of all the small motor 10 is started. Conventionally, the carburetor operates the mixture of air and fuel depending on the position of the throttle valve. The additional air circuit supplies the engine with a low additional air flow rate, via the line 22 and the solenoid valve 20. This establishes a minimum air flow by default.

 A permanent regime is established.

 To check whether the engine is running well at its optimum speed, that is to say at its point of minimum pollution, the computer 16 causes a plurality of richness jumps SI (FIG. 3a) in the mixture supplying the engine. To do this, the solenoid valve 19 sends in the pipe 24 surplus compressed air taken from the tank 19. The mixture present in the intake manifold 15 therefore receives a plurality of additional puffs of air. These leaps in wealth momentarily and substantially instantly deplete the mixture feeding the small engine. If the engine does not operate at its optimum speed, this depletion causes variations in the engine speed N.

 Referring to FIG. 3a, it can be seen that the additional amounts of air Oa supplied to the engine concomitantly cause variations V1 of the engine speed. We even notice that these variations are negative and correspond to decreases in engine speed. We therefore conclude that by temporarily depleting the mixture, the engine speed was reduced, so the initial mixture was already poor. We also conclude that the initial mixture was not optimal, since it made it possible to create detectable regime variations. Consequently, a reduction D of the air supply is imposed in steady state, so as to end up in steady state in the case of a rich mixture (as has been explained above). wealth jumps S2 by providing, as previously described, additional breaths of air to the engine.

 It is noted that these jumps in wealth now cause variations V2 of the engine rotation speed corresponding to increases in this speed.

 Since these variations are detected and are positive, the method according to the invention is continued to be applied by slightly increasing, in a predetermined manner, b quantity of air A supplied to the engine in steady state. Wealth jumps are carried out again until the concomitant variations in the rotation speed N of the engine are undetectable. We then conclude that the quantity of air supplied in steady state is optimal and that the engine is at its minimum point of pollutant emission. The engine is then fed in steady state with a mixture respecting the air / fuel proportions thus determined.

As shown in Figure 3b, the initial steady state of the motew, may well be too rich. This is easily detected because the first plurality S'1 of wealth jumps, imposed on the mixture, then cause variations V1 ′ of positive engine speed. In this case it is not necessary to cause a decrease D of the air supply in steady state (since one is already in a rich mixture), on the contrary one imposes a predetermined increase
Has this mixture in steady state. The rest of the process for determining the optimum richness is carried out in the same manner as in FIG. 3a.

The method according to the invention therefore consists in:
- vary the amount of air Qa supplied to the engine 10 at speed
permanent by means of a compressed air injector 20, calibrated to
create a plurality of wealth jumps S in the mixture,
- detect if a variation V, of concomitant regime appears, and
in this case determine its sign,
- deduce that the engine does not run at richness
corresponding to the maximum torque and determine the amount of air
A, to be injected under steady conditions, in order to minimize pollution
created by the engine.

 Note that one can take into account not only the sign of the variation in speed, but also its amplitude. In this case, the calculator makes it possible to determine, at a single time, that it is the ideal quantity of air to supply to the engine in steady state, so that it operates at its optimal speed. This avoids having to increase, little by little, the amount of air supplied in steady state, to obtain the ideal rotation regime and therefore the minimum point of pollution.

 The invention also relates to the solenoid valve 20. As shown in Figures 4a to 6b, three variants are envisaged. For all of these variants, the references of the elements having similar functions are the same.

 Figure 4a shows a solenoid valve 20, in the supply phase of the manifold 15 with air at atmospheric pressure. In this figure we note that a piston rod 30 on which are mounted two valves respectively, upper 31a and lower 31b, is held in the low position (pulled down in the drawing), by the coil 21. This coil is controlled by the computer 16 in a manner known per se, not detailed in the drawing. In this phase of supplying air at atmospheric pressure, there is direct communication between the pipe 22 and the pipe 24. The size of the section of the air passage (at the valve 31a) is controlled by the coil .

The supply of compressed air is made impossible by closing the lower valve 31b.

 In the following operating phase, the coil 21 exerts no force on the piston rod (FIG. 4b) which returns to the neutral position, under the action of the springs associated with each valve 3ira, 3nib. The compressed air line 23 is then in communication with the discharge line 24 to the manifold. Thereby the intake manifold 15 receives puffs of compressed air. Air supply at atmospheric pressure is then impossible since the upper valve 31a is closed.

 In this embodiment, the valve 20 is therefore controlled by the computer, via the coil 21, and the piston rod is movable between a high position and a neutral position. It is noted that in the context of this embodiment the valve 31b is either completely open or completely closed, while the dimension of the opening of the valve 31a is controlled by the coil.

 According to the second embodiment of the valve 20 (FIGS. 5a and 5b), the coil 21 actuates the piston rod between two modular positions which makes it possible to open more or less each of the valves 31a, 31b. This proportional opening of each of the valves makes it possible to modulate the amount of air injected during the wealth jumps. However this implies that the piston rod can be ac ': orée dars' es de = x ser, s. The springs associated with hiding apices must in this case be placed in the manner shown. Note that in this embodiment, the valve actually has two coils acting in opposite directions.

 According to the third embodiment of the invention shown in FIGS. 6a and 6b, the opening of the upper and lower valves is also modular, while the piston rod is only actuated in one direction (pulled down by the coil). Indeed the coil 21 allows by pulling more or less on the piston rod 30 to open the upper valve in a modulated manner, at the same time, a connecting mechanism of the valve 31b on the rod 30 is positioned in the disengaged position. There is therefore no connection between the rod 30 and the lower valve 31b. Therefore the movement of the rod 30 is not reflected in the valve 31a which remains closed. This allows the closure of the valve 31b and the free movement of the valve 31a.

 When the coil 21 (FIG. 6b) is no longer controlled, in fact, the rod 30 and the valve 31b are brought together by bracing of a connecting piece 32 on the rod. The action of the various springs then allows the opening of the valve 31b with a stroke corresponding to that of the valve 31a (in fact the movement of the valve 31a before the stop of the reel control is reflected in the valve 31b as soon as the reel is no longer ordered).

 The section of the passage discovered by the valve 31b is thus proportional to that discovered by the valve 31a. It is thus possible to control the amplitude of the variations in richness imposed on the engine.

 It will be noted that in this embodiment the upper and lower valves can be integral with the piston rod. In all the other embodiments, the two valves were slidably mounted on the piston rod.

It will be noted that, in the context of this third embodiment,
The opening of the compressed air valve 31b is proportional to the opening of the air inlet valve at atmospheric pressure 31a.

 In all the embodiments of the valve according to the invention, the piston rod 30 is adapted to selectively cause the closure of one or the other of the valves 3ira, 31b.

 Of course, the present invention is not limited to the embodiments described above. Thus, the additional air circuit may very well not include a compressed air tank. In this case, the compressed air is produced at the request of the computer 16, by the pump 18, when the computer wishes to make wealth jumps. Similarly, if the additional air circuit is not used when the engine is started, a "choke" effect is created due to the engine's fuel supercharging, during a cold start.

Claims (7)

CLAIMS the engine. inject in steady state to minimize the pollution created by corresponding to the maximum torque and determine the amount of air to - deduce that the engine is not running at richness in this case, determine its sign and, - detect if a variation in concomitant regime (V) appears, and create a plurality of wealth jumps (S) in the mixture, permanent by means of a calibrated compressed air injector (20), in order - to vary the quantity of air (Qa ) brought to the engine at speed 1] Method for controlling the richness of an air / fuel mixture supplying an internal combustion engine (10), said method being of the type consisting in varying the richness of the mixture and in measuring variations (V) in engine speed corresponding, said process being characterized in that it consists in: 2] A method according to claim 1, characterized in that it further consists in taking into account the amplitude of the speed variation (V) detected to determine the amount of air to be injected in steady state. 3] Method according to claim 1 or 2, characterized in that the variations (S) of the amount of air are substantially instantaneous. 4] Method according to any one of the preceding claims, characterized in that a minimum supply of air is carried out in steady state by means of an additional air circuit (17) short-circuiting the butterfly valve (14) d gas intake, in order to establish a minimum default air flow. 5] Method according to claim 4, characterized in that the additional circuit (17) of air, also generates the richness jumps (S). 6] Method according to any one of the preceding claims, characterized in that the determination of the maximum torque is carried out by depletion of an air mixture I rich fuel.  - a solenoid valve (20) controlled by a computer (16) receiving from the engine a plurality of operating parameters and being adapted to deliver on command into an intake manifold (15) of the engine a predetermined quantity of air on the one hand , at atmospheric pressure and on the other hand, in a compressed manner.  - air compression means (18), and 7] Device for controlling the richness of an air I fuel mixture, supplying an internal combustion engine (10), of the type implementing the method according to any one of claims 1 to 6, characterized in that it includes:  81 Device according to claim 7 characterized in that said solenoid valve (19) comprises an air inlet at atmospheric pressure (22), a compressed air inlet (23), a piston rod (30) associated with a pair of intake valves (31a, 3nib) each associated with one of the arrivals, the said rod being adapted to selectively cause the closure of one of the said arrivals (21, 23).  9l Device according to claim 7 or 8, characterized in that each of the two intake valves (3ira, 31b) is in the position either fully open, or completely closed.  10l Device according to claim 7 or 8, characterized in that the opening of the compressed air intake valve (31 b) is proportional to the opening of the air intake valve at atmospheric pressure (31a) .