JPH0548410B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention is a combustion condition checking means for setting the ignition timing of an internal combustion engine to the point at which maximum rotational output is obtained. This invention relates to a flame front sensor for detecting when a flame reaches a specific position within a flame.

[Prior Art] In order to maximize the combustion efficiency of an internal combustion engine, that is, the rotational torque generated per unit of fuel consumed,
It is necessary to ignite when the piston occupies a specific position during its compression stroke, or in other words, when the crank angle reaches a specific angle. As a means of controlling the ignition timing, a method has already been developed in which a pressure sensor is installed inside the cylinder, and an electronic circuit is used to control the crank angle so that it matches a specific angle when the detected pressure reaches a peak value. has been done. Another method is as disclosed in Japanese Patent Application Laid-Open No. 57-99271,
An ion lobe is installed in the cylinder at a distance from the spark plug to measure the time it takes for the flame generated by ignition to reach the cylinder. A method of controlling the combustion device by means of a circuit has also been considered.

[Problems to be solved by the invention] Among the conventional techniques described in the previous section, the method using a pressure sensor maintains the required detection accuracy and can be installed in a cylinder without causing any problems. It has been difficult to fabricate a pressure pickup small enough for this purpose. In addition, in the latter method using an ion probe, if the insulation properties of the ion probe deteriorate due to carbon adhesion, etc.
There was a problem that the accuracy of combustion control deteriorated or it became uncontrollable.

The present invention solves the problem of the lack of operational reliability of conventional ion probes as a means of detecting combustion conditions in cylinders for determining the optimal ignition timing of internal combustion engines, and also provides higher accuracy. An object of the present invention is to provide a flame surface sensor that can detect the arrival of flame.

[Means for Solving the Problems] In order to achieve the above object, this invention is provided in the combustion chamber of an internal combustion engine, and detects the arrival of flame by capturing ions in the ignition flame by a spark plug. An ion probe for detecting a sensor, which is composed of a rod-shaped center electrode covered with an insulator except for the tip, and an outer electrode that is fitted around the insulator and functions as a mounting bracket for the sensor, A configuration was adopted in which a heating heater was embedded in the insulator to heat the rod-shaped center electrode and burn off carbon attached to the surface of the insulator.

[Operations and Effects of the Invention] When a high pulse voltage of 3 to 8 KV is applied to the ion probe of the flame surface sensor configured as described above, the combustion flame of the air-fuel mixture is ignited by the spark plug. If the ion probe reaches the ion probe, the ions of the charged particles generated within the flame will
It penetrates into the gap between the electrodes at the tip of the ion probe, and a discharge occurs between the electrodes. By detecting the presence or absence of this discharge, it is possible to detect that the flame surface has reached the ion probe. Therefore, since conventional ion probes rely on a method of detecting the amount of low-energy ions generated within the flame, if the ion probe becomes dirty and its insulation deteriorates, In contrast, the flame front sensor of the present invention applies a high pulse voltage to the ion probe, and generates a discharge current with a high electrical energy level when ions are present between the electrodes. The presence of ions, and therefore the arrival of the flame surface, is indirectly detected by capturing the ions, so the sensitivity of the ion probe is extremely high. Even if the insulation property deteriorates, the function will not be impaired. In addition, since the flame surface sensor of the present invention has a built-in heater for heating the insulator, it is possible to prevent the carbon from burning under adverse conditions such as low outside temperature, engine startup or low speed driving, and high air-fuel ratio. It is possible to avoid the serious inconvenience of causing a significant decline or loss of functionality due to contamination at the time when unburned components such as particles are most likely to be discharged in the highest concentration and when the movement of the flame surface sensor is most expected. can. This heater has the effect of burning out the adhering carbon and also preventing the flame that should be used to detect the presence of ions from being extinguished by heating the cold center electrode with the heater at low temperatures. .

[Example] The flame front sensor of the present invention will be described below based on an example shown in the accompanying drawings.

FIG. 1 is a cross-sectional side view of the upper half of the flame front sensor of the present invention along the center line, in which 1 is a rod-shaped center electrode made of a nickel-based alloy mixed with a small amount of chromium, manganese, silicon, etc.; 3 is a cylindrical insulator made of a ceramic material such as high-purity alumina or silicon nitride that covers the center electrode 1, and 3 is a nut-shaped main body made of iron-based metal, and is used for mounting a sensor that also serves as an outer electrode. metal fittings; 3a is a threaded part for mounting the sensor; 4 is a cylindrical fitting for fixing the mounting fitting 3 in a state where it is fitted onto the cylindrical insulator 2;
5 is a sealing material filled between the mounting bracket 3 and the fitting 4; 6 is a metal protective outer cylinder; 7 and 8 are power supply wiring for the insulator heating heater attached to the insulator 2; 9 is a grommet that seals the open end of the protective outer cylinder 6.

FIG. 2 is an enlarged side sectional view of the left end side portion of FIG. 1, and 10 is a heater for heating the insulator 2;
11 is an electrical insulating material layer covering the heater 10,
It is formed using a ceramic powder deposition sintering method, a sheet-shaped insulating material wrapping method, or other known techniques. The heater 10 is constructed by directly transferring a conductive composition containing powder of a metal such as tungsten or molybdenum, which has low electrical conductivity, onto the outer peripheral surface of the cylindrical insulator 2 onto a heater pattern, or by printing a pattern on an insulating film material. It is formed by winding a filament made of the same type of metal, or by winding a filament made of the same type of metal twice. Alternatively, when forming the electrical insulating material layer 11, a method may be used in which wires of high melting point metal such as W, Mo, or Pt are simultaneously buried.

FIG. 3 is a side view showing a cross section of the upper half of the flame surface sensor according to the second embodiment of the present invention along the center line.
This is common to the embodiment. The difference is that the outer electrode 3, which also serves as the sensor mounting bracket, has a cylindrical shape with a narrow gap between the left end and the cylindrical insulator 2 in this figure. The distal end surface thereof slightly protrudes from the distal end surface of the rod-shaped central electrode 1, and an ion gap a is formed between the distal ends of both electrodes.

FIG. 4 is an engine combustion control circuit diagram including a cylinder side sectional view of an automobile engine incorporating the flame surface sensor and crank angle sensor of the present invention, in which A is the cylinder head of the engine, B is a spark plug, 20 is an ion probe as a flame surface sensor of the present invention, C is a piston rod, D is a crankshaft, E is a rotary disk for crank angle detection attached to crankshaft D, and 25 is a crank angle sensor. 21 is an oscillation circuit for applying a pulse voltage to the ion probe 20, and 22 is a drive circuit thereof. 23 is a detection circuit for the discharge current generated between both electrodes of the flame surface sensor, and includes a circuit for counting the number of times discharge occurs.

24 is an analysis circuit, which includes a crank angle sensor 2.
Inputs from the control circuit 26 and detection circuit 23 of No. 5 are accepted. 27 is an ignition signal processing circuit, and 28 is a distributor to spark plug B. 2
9 is a signal comparison circuit for the engine exhaust recirculation system, 30 is a fuel injector, 31 is a valve for adjusting the amount of exhaust gas circulation, F is an inlet pipe, G
is the exhaust pipe.

Next, the operation of the flame surface sensor of the present invention will be explained. The ion probe 20 having the structure shown in FIG. The power supply wirings 7 and 8 are connected to an on-vehicle battery power supply via an energization control device, and the vicinity of the tip of the center electrode 1 is heated to about 600° C., which is the temperature at which the deposited carbon can be incinerated. The power supply to the heater 10 is as follows.
This is done only under operating conditions where carbon particles are particularly likely to form, such as when the outside air temperature is below the set temperature, when driving at low speeds, when the air-fuel ratio is high, or when the smoke detection level of the smoke sensor in the exhaust is high. The above control device can be set to Also, the center electrode 1
The terminal has a pulse width of 1 to 1 from the oscillation circuit 21.
Apply a pulse voltage of 3 to 8 KV for 5 μsec.
The discharge starting voltage between both electrodes of the ion probe 20 is
It is preset to be 8KV or higher. Therefore, even if a pulse voltage is applied to the ion probe 20, no discharge will occur between the electrodes unless there is an electric charge in the cylinder that helps the discharge.
Now, when the spark plug B is energized and a flame is generated by igniting the air-fuel mixture, charged particles (hereinafter referred to as ions) are generated within the flame. The flame generated at the position of the spark plug B gradually propagates into the surrounding air-fuel mixture and grows, and ions also enter between the two electrodes of the ion probe 20 located at the opposing position. When the ion concentration increases to a certain extent, in the case of ion probes with an interelectrode gap of around 0.7 mm,
The discharge that did not occur even when a voltage of 8KV was applied,
Due to the mediation of ions, it is possible to start even at a relatively low voltage of around 3KV. Therefore, if a discharge occurs by applying a voltage lower than the discharge starting voltage to the ion probe 20 in the absence of ions, this also means that the mixture generated at the position of the spark plug B It can be determined that the flame has reached the ion probe 20. However, in order to determine when the flame front reaches the ion probe 20 as an indicator of combustion control to maintain the combustion efficiency of the air-fuel mixture in the cylinder at the highest level, even if the operating conditions are constant, it is necessary to Since the values vary, it is necessary to find the average. Therefore, the pulse width of 1 to 1 is applied to the sensor electrode.
By applying a very short single pulse voltage of 5 μsec at a specific time, if the probability of a discharge occurring when the pulse voltage is generated is 1/2,
The specific time can be clearly understood as the time when the flame surface is reached.

As for the characteristics of the pulse voltage, if the output impedance is set to about 0.05MΩ, even if the insulation resistance of the ion probe 20 deteriorates to about 0.1MΩ over time due to carbon deposition, etc., it will be sufficient to cause a discharge. It will not cause any trouble. on the other hand,
With conventional ion probes that capture the ion current flowing between electrodes, vehicle speeds are limited to 40km/h.
Assuming a relatively slow speed, the ionic resistance inside the flame is measured at 300V and is 100MΩ.
In order to detect this degree of resistance change, the insulation resistance of the ion probe must be several hundred MΩ or more. It is extremely difficult to satisfy this requirement under all operating conditions from low speeds to high speeds only by devising the shape and structure of the ion probe.

Furthermore, if the pulse width is set to 1 to 5 μsec, even if the rotation speed of crankshaft D is 600 rpm, the crank rotation angle for each pulse generation period will be (5 × 10 ^-6 /10 × 10 ^-3 ) × 360=0.18°, and sufficient accuracy in detecting crank angle displacement can be maintained. Even if the operating conditions are kept constant, the timing of reaching the flame front will vary to some extent, but the distribution can be regarded as normal distribution, and σ
is around 5 degrees in terms of crank angle. After reaching the flame, the flame continues and ions are present until the crank rotates at least 10 degrees, so by applying a pulse voltage to the ion probe as described above, the pulse voltage By finding the time when the probability of a discharge corresponding to 1 reaches 1/2, it is possible to find the average value of the flame arrival time under the operating conditions at that time.

Next, a method for controlling engine combustion using the flame front sensor of the present invention will be explained with reference to FIG. When the voltage is applied to the center electrode 1 of the ion probe 20 via the drive circuit 22, the front side of the flame generated at the spark plug B position reaches the ion gap a portion between the electrodes 1 and 3b, as described above, and reaches the ion probe 20. Since the discharge starts at , this discharge current is input to the detection circuit 23 together with the pulse signal generated by the oscillation circuit 21 . Then, the time when the probability reaches 1/2 is taken as the time when the flame surface reaches the ion probe 20, and this is notified to the analysis circuit 24. Since the crank position information detected by the crank angle sensor 25 is sent to the analysis circuit 24 via the crank angle sensor control circuit 26, the crank position, or in other words, the crank angle, is determined when the flame reaches the flame surface. Then, it is checked whether the piston position in the cylinder defined by this crank angle is at the optimum position to maintain the maximum combustion efficiency of the engine, and if it deviates from the optimum position, this deviation is Information is transmitted to the ignition signal processing circuit 27 to correct the ignition timing, and the distributor 28 distributes the discharge current to the ignition plug B based on the ignition timing determined by this circuit. On the other hand, the input to the analysis circuit 24 is also delivered to the signal comparison circuit 29, where a control command for the fuel injector 30 is issued, and if an exhaust gas recirculation system is installed, the exhaust gas recirculation amount adjustment valve 31 is Opening control is also performed.

In the case of an ion probe having the electrode configuration of the embodiment shown in FIG. 1, the electrode shown in FIG. The mounting location is set so that an ion gap corresponding to ion gap a is formed. In this case, the outer electrode 3 is in electrical continuity with the wall surface constituting the cylinder head A.

FIG. 5 shows the relationship between the temperature of the center electrode 1 and the ion current detection sensitivity. It can be seen that when the heater 10 is energized at a voltage of about 10 volts, the detected ion current peak value increases by about 2 to 3 times, and the ion current detection accuracy can be improved. This results in
Ion probe 20 for cold engine starts, etc.
When the temperature of the center electrode 1 is low, the heater 10
By applying current to the ion current, the ionic current can be detected accurately.

[Brief explanation of the drawing]

FIG. 1 is a side view showing the center upper half of the flame surface sensor of the present invention in cross section, FIG. 2 is an enlarged side sectional view of the left end portion of FIG. 1, and FIG. 3 is a second embodiment of the present invention. A side view drawn in the same way as Figure 1, and Figure 4.
The figure is a combustion control circuit diagram of an automobile engine incorporating the flame front sensor and crank angle sensor according to the present invention, and FIG. 5 is a graph showing the relationship between the temperature of the center electrode and the ion current detection sensitivity. In the figure, 1...rod-shaped center electrode, 2...cylindrical insulator, 3...outer electrode/sensor mounting bracket, 7,
8... Heater, 10... Heater for heating.

Claims (1)

[Scope of Claims] 1. An ion probe installed in the combustion chamber of an internal combustion engine for detecting the arrival of flame by capturing ions in the flame ignited by a spark plug, which is insulated except for the tip. A rod-shaped center electrode covered by a body and an outer electrode fitted onto the insulator and functioning as a mounting bracket for the sensor are combined, and the rod-shaped center electrode is heated to the insulator and the A flame surface sensor characterized by having a heater embedded therein to burn out carbon attached to the surface of an insulator.