JPS5842617Y2 - Ignition timing control device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an ignition timing control device for an engine, and more particularly to an ignition timing control device for an engine employing an exhaust gas recirculation method.

A part of the exhaust gas is fed to the intake system as a means of purifying nitrogen oxides, which are harmful to the human body through photochemical reactions among the harmful components in the gases emitted from automobiles, and dilutes the air-fuel mixture, thereby lowering the combustion temperature. The so-called exhaust gas recirculation method (E
It is well known that GR) is used.

In the exhaust gas recirculation system, there is a nearly proportional relationship between the recirculation rate of exhaust gas and the reduction rate of nitrogen oxides (NOx), and from the viewpoint of reducing NOx, a larger recirculation rate is preferable, but on the other hand, the average effective efficiency of the engine The rate of pressure decrease also increases in proportion to the amount of recirculation, which impedes driveability in a high output range.

The idea that ignition timing must be advanced when performing EGR is based on ``internal combustion engine, vot9, A23.
Some information is disclosed in ``Toyota Technology, Vol. 21, No. 3, pp. 20-24.''

However, although it was recognized that it was necessary to advance the ignition timing when simply performing EGR, how would the amount of EGR be detected and what kind of amount of EGR should be determined at a single point when it was actually put into practical use? There was no consideration as to whether the fire timing should be a characteristic.

The purpose of this invention is to provide a specific ignition timing control device for actual practical use.The feature is that the actual amount of exhaust gas recirculation is detected by a detector installed in the exhaust gas recirculation passage, and the exhaust gas The advance angle of the advance angle device is gradually increased in accordance with the increase in the recirculation amount.

The embodiments shown in the drawings will be described below.

FIG. 1 shows an intake and exhaust system of an engine embodying the present invention. Reference numeral 1 denotes a well-known carburetor, which includes a float chamber 2, a main nozzle 3, and a throttle valve 4.

5 is an intake pipe, which communicates the carburetor 1 with the combustion chamber 6 of the engine.

7 is an exhaust pipe, and 8 is an exhaust gas recirculation passage that communicates the exhaust pipe 7 and the intake pipe 5. A recirculation gas control valve 8a and a recirculation gas amount detection device 9 are provided in this passage.

10 is a power distributor directly connected to the engine shaft.

FIG. 2 shows an embodiment of the recirculation gas amount detection device 9 and the advance angle mechanism.

The reflux gas detection device includes a heater 11 installed in the reflux passage 8, upstream resistance temperature detectors 12 and 13, downstream resistance temperature detector 14, bridge circuit 15, amplification circuit 16, and bridge circuit 15. Constant voltage circuit 1 that supplies voltage
It is composed of 7.

The upstream temperature measuring element 12 is a resistor for gas density correction.

18 is a DC power source such as a battery, 19 is a vacuum advance mechanism connected to the power distributor 10 by a lever 20, and a part of the lever 30 is attracted by a coil 21 energized by the output of the reflux gas amount detection device 9. A plunger 22 is installed.

23 is connected to one end of the lever 22 by a diaphragm, and two chambers 24 are separated by the diaphragm 23.
．． 25 is formed, and intake pipe negative pressure is introduced into the chamber 24.

Atmospheric air is introduced into room 25.

FIG. 3 shows a specific example of the reflux gas amount detecting device 9, and the bridge circuit 15 is composed of resistance values of temperature measuring resistance elements 12, 13, and 14 and external variable resistors 26 and 27 for balance adjustment.

The constant voltage circuit 17 also has a constant current function, and is mainly composed of a plurality of transistors, resistors, capacitors, diodes, etc., and supplies a constant voltage (12 V) and a constant current (3.5 A) to the bridge circuit 15. do.

FIG. 4 shows the output characteristic of the reflux gas amount detection device 9, which is the output voltage with respect to the reflux gas amount, and has a substantially linear characteristic except for the minute flow rate portion.

In other words, there is a difference in the temperature of the exhaust gas upstream and downstream of the heater, and this difference is proportional to the gas flow rate, so the gas flow rate is measured by absorbing the temperature difference into a resistance change and extracting this as an output voltage. be able to.

When performing EGR, when the amount of recirculated gas is controlled by adjusting the recirculated gas control valve 8a according to the operating conditions, the ratio of the amount of air to the amount of fuel supplied to the engine 6, so-called air-fuel ratio A/F, changes accordingly. do.

As a result, combustion-related values such as the combustion speed and pressure rise within the engine cylinder change, which changes the engine output and changes the harmful components in the exhaust gas.

If the amount of recirculated gas increases due to certain operating conditions, the air-fuel mixture supplied to the engine 6 changes, and the concentrations of carbon monoxide (CO) and hydrocarbons (HC) in the exhaust gas increase.

On the other hand, intake of exhaust gas lowers the combustion temperature and reduces the NOx concentration, but the effective average pressure inside the cylinder also decreases, resulting in a decrease in output and temporary drivability problems, such as breathing during acceleration. .

Figure 5 shows the relationship between the EGR reflux rate, the NOx reduction rate, and the average effective pressure reduction rate, and shows that as the EGR reflux rate increases, the NOx reduction rate and the average effective pressure reduction rate both increase. As the reflux rate exceeds 15%, the average effective pressure decreases by about 20%, indicating that increasing the reflux rate any further impedes the operability.

Figure 6 shows the relationship between the NOx concentration in the exhaust gas divided by the output torque (NOx/T) and the ignition timing when the engine is operated at a constant speed and the ignition timing is changed.
The figure shows measurements taken at four speeds: low speed, medium speed, high speed, and maximum speed.

According to this figure, the characteristic A during low speed operation is a relatively gentle curve, and as it moves to medium speed B1 high speed C1 maximum speed, the range of the minimum value of NOx/T, that is, the optimum advance angle 4
The degree ranges a, b, c and d are gradually decreasing to 1.

During low-speed operation, the optimal advance angle range a is wide, and even if the ignition timing is slightly shifted during low-speed operation, the NOx concentration in the exhaust gas does not increase that much. The range of 4 degrees d is extremely small, and a slight deviation from this range indicates that the NOx concentration increases rapidly.

The data in Figure 6 shows the characteristics of an engine that does not perform EGR, but even when FGR is performed, the absolute value of the optimal ignition timing deviates overall, but as the optimal range widens from low speeds to high speeds, it becomes smaller. There is no change in this tendency.

Therefore, unlike the conventional technology, the ignition timing of the engine is
If R is not performed, set the vacuum advance mechanism so that the ignition timing is optimal according to the engine rotation speed, and use EGR.
Even if the engine does not change the ignition timing, if EGR is performed during high-speed operation, the air-fuel mixture supplied to the engine will naturally fluctuate, so EGR will not be performed at the optimum ignition timing required by the engine. Since the ignition timing deviates from the optimum ignition timing, the NOx concentration increases as a result.

In order to compensate for this drawback, it has been proposed to adjust the constant angle ignition timing when performing EGR, but this method has the following drawbacks.

Figure 7 shows the optimum ignition timing when the engine is operated at a constant speed and the EGR recirculation rate is 0 (L characteristic), 10% (M characteristic), and 15% (N characteristic). For example, when EGR is not performed, the optimum ignition timing t is
This indicates that as the R-reflux rate increases, further advancing the ignition timing is necessary to reduce the NOx concentration in the engine exhaust gas.

Therefore, when performing EGR, the method of increasing the ignition timing by a certain angle is to increase the reflux rate by 10 when the advance angle is set to θ1.
When the number is 15, the ignition timing becomes the optimum ignition timing, but when the number increases to 15, the ignition timing deviates from the optimum ignition timing.

Since the EGR recirculation rate changes depending on the engine speed and load, the characteristics shown in Figure 7, L and N, change depending on the engine condition at that time, and are uniquely constant during EGR. If the angle is advanced, a sufficient effect cannot be expected.

In particular, the operating range in which EGR is frequently performed is from medium speed to high speed, and in this range, a slight deviation in ignition timing results in a large drop in output or an increase in NOx concentration.

On the other hand, in the present invention, the detection signal of the reflux gas detection device 9 has a voltage approximately proportional to the reflux flow rate as shown in FIG. Due to the electromagnetic attraction force acting on the jar 22, the rod 20 displaces the ignition timing of the power distributor 10 in a direction that advances it in accordance with the amount of reflux.

A diaphragm 23 connected to the lower end of the rod 20 is displaced in accordance with the intake negative pressure of the engine, and a negative pressure advance mechanism provides the optimum ignition timing when EGR is not performed.

In FIG. 2, as the amount of exhaust gas flowing through the recirculation passage 8 increases, the difference in resistance value between the temperature measuring resistance elements 12 and 13 increases,
As the output voltage of the bridge circuit 15 increases and the attraction force of the coil 21 increases, the power distributor 10 adjusts the angle by adding the advance angle defined by the negative pressure advance mechanism and the advance angle due to the electromagnetic force acting on the plunger 22. I will proceed with 1.

Therefore, the ignition timing of the engine advances by an increasing amount in accordance with the EGR recirculation rate, and the engine requirements can be substantially satisfied.

It is difficult to uniformly regulate the amount of advance when performing EGR due to the capacity characteristics of the engine, but once the specifications of the engine are determined, the amount of advance can be determined experimentally.

Figures 8 and 9 show that the engine speed is kept constant;
The relationship between the EGR reflux rate and the advance ratio is shown using the suction negative pressure as a parameter.

As is clear from these figures, the advance ratio changes depending on the suction negative pressure, but the general tendency is that the advance ratio increases as the reflux rate increases.

The increase in the advance ratio with respect to the increase in the reflux rate increases as the suction negative pressure increases (lower the absolute pressure).
p, m) are larger.

The reason for this is that the engine is set so that the air-fuel mixture in the carburetor becomes rich when the engine is under high load and high speed, so when the intake negative pressure is low, that is, when the engine is under high load and high speed operation, the EGR recirculation amount is not the same. This is thought to be because even if there is, the decrease in output is small, so there is no need to increase the advance angle ratio so much.

Figure 10 shows the relationship between engine speed and optimum advance angle ratio.
This figure shows the GR reflux rate and suction negative pressure as parameters.

As is clear from this figure, the advance ratio tends to decrease as the engine speed increases, but the rate of change is relatively small and is thought to be approximately determined by the recirculation rate.

Therefore, according to the present invention, by changing the ignition timing of the engine depending on the EGR recirculation rate, the decrease in engine output can be reduced and the effect of reducing NOx due to EGR can be obtained.

As explained above, the present invention is also applicable to an exhaust gas purification system using the EGR method, in which the amount of recirculated gas is accurately measured using, for example, the principle of hot wire flow rate measurement, and the output is used to determine the vacuum advance angle. A new machine other than the one that operates with intake pipe negative pressure is added to the mechanism, and the ignition timing is controlled in order to improve drivability and other problems caused by EGR.

In other words, unlike conventional ignition timing control, this is a so-called feedback type closed-loop control that catches exhaust system signals and controls ignition timing, so the control accuracy is much higher than conventional ones, and the NOx obtained by EGR is There is no effect on the reduction effect of H
Great effects such as reduction of ClC0, improvement of drivability, and improvement of fuel efficiency can be expected.

Furthermore, exhaust gas contains a large amount of soot and moisture, and the exhaust gas temperature also increases to approximately 300°C between low and high loads.
It has been said that it is difficult to accurately measure this flow rate due to the difference in temperature, but in the experiments conducted in this invention, the effect of soot and moisture is small, and the output voltage fluctuation due to slight temperature can be suppressed by using a bridge circuit. It is so small that it can be ignored in practice.What is particularly remarkable is that a temperature measuring resistor 12 for gas density correction is used on one side of the bridge circuit, making it possible to accurately measure other gas flows regardless of exhaust gas. This is possible, and the implementation of the present invention has the effect of establishing highly accurate exhaust purification technology using an accurate EGR system.

In carrying out this study, in addition to electrical distributors with mechanical contacts, electronic ignition devices, which are currently in practical use as non-contact ignition devices, were used to control ignition timing. It is also possible to apply it to

In this case, the signal from the reflux gas amount detection device may be used as a signal for advancing the ignition timing.

[Brief explanation of drawings]

Fig. 1 is a system diagram of an engine incorporating the ignition timing control device implementing the present invention, Fig. 2 is a detailed view of its main parts, Fig. 3 is a circuit diagram of the detection device, and Fig. 4 is a characteristic diagram of the detection device. , 5th
The figure is a characteristic diagram of EGR recirculation rate, Figures 6 and 7 are ignition timing characteristic diagrams, Figures 8 and 9 are characteristic diagrams showing the relationship between recirculation rate and advance ratio, and Figure 10 is a characteristic diagram of engine rotation speed. and is a characteristic diagram of advance angle ratio. 1... Carburetor, 2... Float chamber, 3... Main nozzle, 4... Throttle valve, 5... Intake pipe,
6... Engine, 7... Exhaust pipe, 8... Exhaust gas recirculation passage, 8a... Reflux gas control valve, 9... Reflux gas amount detection device, 10... Power distributor, 11. ...Heating heater, 12, 13...Upstream side temperature sensing resistance element, 14...
・Downstream side temperature measuring resistance element, 15...Bridge circuit, 16
... Width increasing circuit, 17... Constant voltage circuit, 18... Battery, 19... Vacuum advance angle mechanism, 20... Lever,
21... Coil, 22... Plunger, 23...
Diaphragm, 24... Intake pipe negative pressure introduction chamber, 25...
・Air introduction chamber, 26, 27... Variable resistance for balance adjustment.

Claims (1)

[Scope of Claim for Utility Model Registration] A recirculation gas detection device that is provided in the middle of an exhaust gas recirculation passage that communicates an exhaust pipe and an intake pipe and directly detects the amount of recirculated exhaust gas flowing through the exhaust gas recirculation passage; a correction output signal generation means for outputting a correction output signal based on the detection signal of the detection device; and an ignition advance means for advancing the ignition timing depending on the rotational speed of the engine or the pressure generated in the intake system of the engine. : As the amount of recirculated exhaust gas flowing through the exhaust gas recirculation passage increases based on the correction output signal from the correction output signal generating means, in addition to advancing the ignition timing by the ignition advance means, the ignition timing is continuously adjusted. An ignition timing control device comprising ignition advance correction means for increasing the advance angle.