JPS6215751B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for controlling the fuel-air mixture ratio or the exhaust gas feedback rate of an internal combustion engine, which varies depending on changes in the operating parameters of the internal combustion engine.

Due to stringent exhaust gas regulations and general fuel shortages, methods are being sought to operate an internal combustion engine in an operating range that minimizes harmful components of its exhaust gases and/or minimizes fuel consumption.

In order to meet this type of requirement, it has first been proposed to operate the internal combustion engine with a fuel-air mixture ratio as lean as possible, that is to say to operate the internal combustion engine at the so-called lean running limit. In this operating range, the harmful components of the exhaust gas are considerably reduced, and a reduction in fuel consumption can also be expected. In this case, first, the variation in pressure inside the cylinder of the internal combustion engine is used as the value for identifying the lean running limit.

However, if we consider the above issues in more detail,
It has become clear that the pressure characteristics are determined by changes in the uncontrollable operating parameters of the internal combustion engine, such as air excess, charge, turbulence, etc. When the pressure in the combustion chamber is measured via the instantaneous value of the angular velocity at the crankshaft, interference factors occur due to fluctuations other than those mentioned above, such as vibrating objects in the crank mechanism, irregularities in the road of the car, or some force applied to the internal combustion engine itself. are doing. The above-mentioned fluctuations, which are superimposed on the normal pressure characteristics in the cylinders of the internal combustion engine and manifest themselves as fluctuations in the angular velocity of the crankshaft, can be avoided by means of a low-pass filter. However, the use of this type of filter is highly problematic. This is because the internal combustion engine must be operated over a wide rotational speed range. Therefore, it is difficult to manufacture a filter suitable for both small and large rotational speeds (frequencies).

Starting from the above-mentioned problems, the object of the present invention is to propose a new control method of a different kind, which avoids the method of exploiting pressure fluctuations inside the cylinders of an internal combustion engine, which has the above-mentioned disadvantages.

In the present invention, for the control, a change in the travel time of the flame front determined from the ion current in the combustion chamber of the internal combustion engine, that is, a difference in travel time values is utilized. It is known that this variation depends on the fuel-air mixture ratio.

The object of the invention is to take advantage of the above-mentioned dependencies and to control the fuel-air mixture ratio of the internal combustion engine to the value of the lean running limit, i.e. in such a way that a lean but still ignitable mixture ratio is created. That's true. This avoids the drawbacks of the method using the combustion chamber pressure described above. This problem is solved according to the invention in the following way: the change between the travel time values of two successive flame fronts in the combustion chamber of the internal combustion engine is used as the actual value of the operation of the internal combustion engine. , this actual value is compared with a predetermined value to determine a deviation to be controlled, and depending on this control deviation, the fuel-air mixture ratio or the exhaust gas feedback ratio of the internal combustion engine is controlled in the desired manner.

In an embodiment of the invention, a device is shown for implementing the method described above, which allows the aforementioned control to be carried out simply and reliably. The first objective in this case is to ensure that this control device operates reliably even in the case of rough driving of the vehicle and, if necessary, to be able to cooperate with the measured value transmitter already installed in the vehicle. It is to compose. Furthermore, the device must be inexpensive to manufacture.

Next, the method according to the present invention will be explained in detail using the drawings. With this method, the internal combustion engine is to be operated at least partially in the operating range of the lean running limit. In this case, the so-called lean running limit is the operating range in which the combustion delay first appears.
The combustion delay is 5 to 10 times higher than when the excess air ratio is λ=1.
%, that is, when the mixture is clearly lean. In such a given driving limit range, the fuel consumption is generally equal to that in the operating range of the internal combustion engine supplied with a fuel-air mixture having a stoichiometric stoichiometric ratio (air excess ratio λ=1). It is clearly less than the fuel consumption.

When two electrodes are installed in the combustion chamber of an internal combustion engine, during the combustion process when the flame reaches both electrodes,
An ionic current flows between these two electrodes. This ion current is used to identify the operating region in which the internal combustion engine is operating. In this case, the ion current is dependent on the excess air ratio λ of the fuel-air mixture supplied to the internal combustion engine. The graph in Figure 1 shows the time t
The course of the ionic current for In this figure, the first curve belongs to the first cylinder, the second curve belongs to the second cylinder, the third curve belongs to the third cylinder, and the fourth curve belongs to the fourth cylinder. If these ionic currents are integrated in each case over a given time range, or, more suitable for the purpose, over one cycle of the piston of an internal combustion engine, an electrical signal is generated which varies with the excess air ratio λ. be able to.

The ion current can be detected by, for example, an ion current probe 10 shown in FIG. In this case, the ion current sensor is arranged inside the cylinder head 11 of the internal combustion engine. Here is spark plug 1
2 is also installed. In this case, the ion current probe 10 does not need to be a special component when detecting the ion current flowing between the two electrodes during the combustion process; for example, the spark plug 12 itself can also be used as an ion current probe.

The device shown in FIG. 2 with an ionic current probe 10 and a spark plug 12 in a cylinder head 11 of an internal combustion engine is characterized in that a flame front starts from the spark plug 12 and reaches the ionic current probe 10 after a predetermined time. Used to detect time. In FIG. 3, the frequency distribution of the ignition point in the spark plug 12 and the frequency distribution of the arrival time of the flame front in the ionic current sonde 10 are shown on the time axis t. In this case, the time between the center of the frequency distribution of the ignition trigger, denoted 13, and the center of the frequency distribution of the arrival time to the ion current sonde, denoted 14, is equal to the average transit time T _L of the flame front. The absolute value of the travel time T _L of the flame front also changes with the excess air ratio λ.

When the fuel-air mixture ratio is constant, that is, when the value of λ is constant, the respective travel time values of the flame front are distributed around a predetermined average value T _L , as shown in FIG. do.

From the deviation between this average value and the individual running time values,
An average value ΔT _L of the deviations is formed. The respective average values T _L and ΔT _L depend on the value of λ. ΔT _L /T _L
also depends on λ. That is, the rate of change of the running time value T _L also changes with the excess air ratio λ. This relationship is shown in FIG. In this figure, the vertical axis is the value obtained by dividing the average value of the change in travel time by the average value of the travel time, and the horizontal axis is the excess air ratio λ. From this figure, it can be seen that the rate of change of the traveling time value increases with the excess air ratio λ.

The device shown in FIG. 5 is particularly suitable for measuring the transit time of the flame front. This is because with this device it is not necessary to provide additional holes in the cylinder head of the internal combustion engine for mounting the ion current probe. Figure 5 shows two ignition source poles 1.
A spark plug socket 15 having 6,17 is shown. There are two more electrodes 1 in the socket 15.
8 and 19 are attached, and the ionic current flows between these two electrodes. Pairs 16, 17 and 1 between both electrodes
8 and 19 is only a few millimeters away. This distance is sufficient to measure travel time values.

FIG. 6 shows a block diagram of an embodiment of an apparatus for carrying out the method of the invention. In the figure, 1 designates a device for detecting the running time of an ionic current during successive working cycles of an internal combustion engine. This detection device 1
is the ionic current sonde 10 shown in FIG.
corresponds to Reference numeral 2 indicates a device for converting the transit time of the detected ion current into an electrical signal, for example a circuit stage configured as an amplifier. Reference numeral 3 denotes a sample and hold circuit, which is a circuit stage that forms a signal representing a change in the transit time value of the ion current. Reference numeral 4 indicates a memory formed by, for example, a capacitor, which holds this changing signal. 5 designates a comparator which compares the actual value signal representing the change in the transit time value of the ion current with a set value that depends on the operating parameters of the internal combustion engine, such as the rotational speed n and the intake manifold pressure Ps. This setpoint value is formed by a setpoint generator indicated at 8. 6 indicates an integrator that integrates the deviation between the set value and the actual value. Reference numeral 7 designates an adjustment operation member that changes the mixture ratio of the fuel-air mixture, such as a solenoid valve, or an adjustment operation member that controls the amount of exhaust gas returned. In this way, depending on the value of the detected deviation,
The mass ratio of the fuel-air mixture or the amount of exhaust gas recirculation is controlled.

In order to determine the change in the transit time value of the ion current as described above, a sample and hold circuit, which is known per se, is provided. This circuit makes it possible to store at least two measured values one after the other. The difference signal is obtained each time from both measured values, and the fifth
The method described in the figure forms a change that can be compared with the set value. In other words, a sample-and-hold circuit is used to form the difference between the transit time values of each two successive flame fronts as the actual value. This actual value difference is then compared with a predetermined value for the travel time difference, i.e. whether the actual value difference is within the range of values characterizing the given operating state of the internal combustion engine. Detect. A control signal is obtained from the comparison result, and depending on this value, the mass ratio of the fuel-air mixture or the amount of exhaust gas returned is controlled.

[Brief explanation of the drawing]

Fig. 1 is a waveform diagram showing the time change of the ionic current in various cylinders of an internal combustion engine, Fig. 2 is a combustion chamber of the internal combustion engine in which a spark plug and an ion current sonde are arranged, and Fig. 3 is a diagram showing the spark plug A diagram showing the frequency distribution of the ignition point (ignition angle) at , and the frequency distribution H of the arrival time (arrival angle) of the device in FIG. 2 to the ion current sonde on the _time axis. _L
FIG. 5 is a front view of a device in which a spark plug and an ion current sensor are integrated, and FIG. 6 is a block diagram of a circuit device for carrying out the method of the present invention. 1... Ion current sonde, 2... Circuit stage for converting the ion current into an electrical signal, 3... Sample hold circuit, 4... Memory device, 5... Comparison stage, 6...
Integrator, 7... Adjustment member, 8... Operating parameter transmitter, 10... Ion current probe, 11... Cylinder head, 12... Spark plug, 15... Socket, 16, 17... Ignition electrode, 18 ,19...
...Ion current detection electrode.

Claims (1)

[Claims] 1. A method for controlling the fuel-air-mixing ratio or the exhaust gas feedback rate of an internal combustion engine that changes depending on changes in operating parameters of the internal combustion engine, the method comprising: detecting an ion current in a combustion chamber of the internal combustion engine with an ion current probe; The travel time of the flame front in the combustion chamber of the internal combustion engine is determined from the ion current, and each successive 2
The change between two travel time values is compared as an actual value with a set value, and the fuel-air-mixture ratio or the exhaust gas feedback ratio of the internal combustion engine is varied via a regulating element as a function of the control deviation. A method for controlling the fuel-air-mixing ratio or exhaust gas return rate of an internal combustion engine.