JP2008190511A - Exhaust gas reduction device for direct injection gasoline engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a direct injection engine system capable of reducing the discharge of HC at the starting of an engine and an accelerating rise of an exhaust gas temperature. <P>SOLUTION: A time change of an engine rotational frequency is detected, the combustion stability of each cylinder is calculated and recorded by statistical processing, and based on the above, fuel injection timing, an injection amount, and ignition timing are controlled for each cylinder. Even if a variation occurs in spraying an injector initially or by aging, this can be corrected, and a sufficient ignition retard amount can be secured while maintaining combustion stability. Further, the exhaust gas temperature is raised, the early activation of a catalyst becomes possible, and HC and soot can be reduced while preventing a misfire. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an internal combustion engine in which fuel is directly injected into a cylinder and burned mainly by ignition.

  Conventionally, a spark ignition type gasoline engine in which fuel is directly injected into a cylinder is widely known. As a technology characteristic of this type of engine, it is effective by injecting fuel during the compression stroke at the time of starting, allowing the air-fuel mixture to be biased in the vicinity of the spark plug, and simultaneously retarding the ignition timing (retard). A method for increasing the exhaust temperature by increasing the proportion of so-called after-burning that does not result in excessive torque, increasing the exhaust temperature, and reducing unburned hydrocarbons (hereinafter referred to as HC) in the exhaust is widely known.

  As a technique corresponding to this, there is one as shown in Patent Document 1.

JP-A-8-291729

  In general, the larger the retard amount at the ignition timing, the higher the exhaust temperature can be, which is advantageous for the early activation of the catalyst, but the combustion stability tends to deteriorate with retard, so the engine vibration increases and the occupant There is a problem in that the amount of HC emission increases.

  In addition, the retard amount is determined by referring to a control computer map, but the allowable amount of ignition retard as an engine is, for example, initial manufacturing variations such as the spray direction of the injector, It has been found that it varies considerably depending on variations in direction, deposit on the combustion chamber and piston, and changes over time. Therefore, the target ignition timing map must be set to a considerably advanced angle in consideration of safety so as not to cause misfire, and there is a problem that sufficient exhaust temperature and exhaust purification performance cannot be obtained.

  In addition, since the ignition timing is set to the advance side, the time from fuel injection to ignition, that is, the vaporization time cannot be made sufficiently long, and soot (soot, particulate matter) generated by diffusion combustion of unvaporized fuel There is a problem that it is not possible to sufficiently reduce the substance (hereinafter referred to as soot).

  An object of the present invention is to ensure a sufficient amount of ignition retard immediately after starting with a simple configuration.

  An injector for injecting fuel into a combustion chamber formed by a cylinder and a piston, an ignition plug for igniting the fuel injected into the combustion chamber, an intake valve provided on the intake side of the cylinder, and an exhaust side of the cylinder In the control device for controlling an internal combustion engine having an exhaust valve provided in the engine, the internal combustion engine includes a combustion stability detection mechanism for detecting the combustion stability of the engine, and the control device drives the injector. An injector drive circuit and an ignition output circuit for outputting an ignition signal to the spark plug, and by controlling the injector drive circuit and the ignition output circuit based on the combustion stability, the ignition timing and the injection timing are A control device characterized by controlling.

  According to the present invention, a sufficient ignition retard amount can be ensured immediately after startup with a simple configuration.

  First, a mechanism for detecting the combustion stability of each cylinder of the engine, for example, detecting a time change of the engine speed, detecting a combustion pressure for each cylinder cycle, recording this, and performing statistical processing, A mechanism is provided for detecting the combustion stability of the cylinder and calculating and recording a combustion stability index.

  Furthermore, a mechanism is provided that can adjust parameters relating to combustion parameters such as fuel injection timing, fuel injection amount, and ignition timing for each cylinder when the engine is started.

  Then, combining these, the combustion parameters such as the fuel injection timing, the injection amount, and the ignition timing are adjusted for each cylinder based on the combustion stability index, and the ignition timing and fuel injection timing suitable for achieving retarded combustion are established. , A mechanism for setting the injection amount is provided.

  According to the present embodiment, the ignition timing retard amount can be increased as much as possible to increase the exhaust gas temperature, which is advantageous for early activation of the catalyst, maintains combustion stability, prevents misfire, and immediately after start-up. It is possible to reduce exhaust gas, especially HC and soot.

  Further, even when there is a variation in the spray or injection amount of the injector due to the initial or change over time, it is possible to correct this, maintain combustion stability, and reduce HC and soot while preventing misfire.

  Examples according to the present invention will be described more specifically below.

  FIG. 1 and FIG. 2 are block diagrams of the system in the first embodiment of the present invention. FIG. 1 shows the intake system and exhaust system from the side, and FIG. 2 shows the engine from above. In this embodiment, a multi-cylinder engine is mainly assumed. However, in the following drawings, one cylinder will be described for the sake of simplicity.

1 and 2, the intake pipe 101 is vertically divided by a partition plate 102 between an end surface on the cylinder head 118 side and the intake control valve 103. An intake control valve 103 provided upstream of the air flow is attached so as to close the lower passage of the intake pipe 101.

  The injector 122 is attached so as to inject fuel directly into the cylinder 123.

Air is drawn from the lower right side of FIGS. 1 and 2, passes through an air cleaner 106, measures the flow rate with an air flow meter 105, adjusts the flow rate with an electronic control throttle chamber 104, and then distributes it to each cylinder with a collector 116. . Thereafter, the air passes through the intake pipe 101 and flows into the cylinder 123 when the intake valve 111 is opened. The gas burned in the cylinder 123 passes through the exhaust valve 112, the exhaust pipe 110, and the catalyst 115, and is exhausted to the atmosphere through the silencer 117.

  The crank angle sensor 301 counts the number of teeth of the ring gear 302 attached to the crankshaft and measures it as a crank angle, and measures the time interval between the teeth to determine the engine speed and its change over time. it can. The greater the number of teeth of the ring gear, the higher the accuracy of measuring the crank angle. However, if the number is too large, the accuracy of the parts becomes necessary and expensive, so it is necessary to select an appropriate number of teeth. In this embodiment, the tooth position accuracy is ± 1 °, the number of teeth is 36 teeth or more, that is, the tooth width is 5 ° or less and the valley width is about 5 ° or less.

  The fuel injection timing of the injector 122, the ignition timing of the spark plug 113, and the opening degrees of the intake control valve 103 and the electronic control throttle 104 are the intake air amount measured by the air flow meter 105 and the fuel gallery measured by the fuel pressure sensor 133. Based on information such as the fuel pressure in the engine 132, the engine speed obtained by the crank angle sensor 301, the opening of the accelerator pedal, the engine water temperature, and the vehicle speed (none of which shows the input side sensor). In addition, the computer 201 sets and controls the value and timing appropriately.

  As for ignition, when an ignition pulse signal is given from the computer 201 to the ignition coil 114, a high voltage is generated, and an ignition spark is blown to the ignition plug 113.

As for fuel injection, when an injection pulse signal is given from the computer 201 to the injector 122, the injector 122 is operated at a valve opening time corresponding thereto. Note that since the actual fuel injection amount varies depending on the valve opening time and the pressure in the fuel gallery 132 measured by the fuel pressure sensor 133, the computer 201 determines the pulse width in consideration of this fuel pressure.

  Furthermore, in the computer 201, learning values are set for each cylinder so that the fuel injection timing and ignition timing can be retarded as much as possible within a range where the combustion of the engine can be kept stable, and stored even when the engine is stopped. To do. In particular, the range in which combustion can be maintained when the engine is started is set.

  When it is determined that the air flow is necessary for the engine, such as when the engine is under a low load, the computer 201 controls the intake control valve 103 in the closing direction so as to obtain a more optimal tumble strength.

  3 to 5 show flowcharts at the time of starting in the first embodiment.

  FIG. 3 shows a general flowchart at the time of starting. When the ignition key is turned on, the computer 201 is energized. Thereafter, when the starter switch is turned on, the starter motor is energized, and cylinder discrimination is performed as the engine rotates.

  Next, the starter is turned and the engine is started. Thereafter, when it is determined that the fast idle state after the start-up, the control proceeds to the right side of the flowchart in FIG.

  In the control on the right side of the flowchart of FIG. 3, the table for each cylinder of the ignition timing ADV and the injection timings IT1 and IT2 stored at the time of the previous cold engine start is read, and the computer 201 reads the injector 122 and the ignition coil. Fuel injection and ignition are performed by applying a pulse to 114, respectively. Thereafter, the routine proceeds to a combustion stability determination routine. Details of this routine are described in FIG. Here, the combustion stability means.

  Next, the ignition timing and fuel injection timing are retarded for each cylinder. This control is specific to the present embodiment, and is corrected and set to the fuel injection timing and ignition timing that lower the exhaust temperature, the soot amount, and the HC concentration as much as possible without impairing the combustion stability. Details of this routine will be described with reference to FIGS. After this control is performed for all cylinders, the temperature of the catalyst temperature sensor 303 or the exhaust temperature sensor 304 is referred to, and the ignition timing retard control of this embodiment is completed if the temperature condition for activating the catalyst is satisfied. Then, shift to normal control. If the temperature of the catalyst temperature sensor 303 has not yet increased, the combustion stability is determined again from the first cylinder, and an appropriate retard amount for the fuel injection timing or ignition timing is set.

  4 to 5 show sub-flowcharts of ignition and injection timing correction learning control. FIG. 4 shows the control when there is a margin in the combustion stability at the initial fuel injection timing and ignition timing. FIG. 5 shows the control when the combustion stability is insufficient at the initial fuel injection timing and ignition timing.

  In FIG. 4, when it is determined that the combustion stability at the ignition and injection timings in FIG. 3 is lower than the reference value, that is, on the stable side, the next control in FIG. Then, the process proceeds to the subroutine of FIG.

  When the combustion is stable, in the flow A of FIG. 4, first, only the first fuel injection timing IT1 is retarded by a predetermined Δt1, and injection and ignition are performed in the next cycle. Determine. Δt1 is a gain for control, and if it is too large, the change in combustion becomes large, but if it is too small, it takes time to search for an optimum value. In general, Δt1 is suitably about 2 ° to 5 ° in crank angle.

  At this time, if the stability is NG, the first fuel injection timing IT1 is returned to the original value, the fuel injection timing and the ignition timing are stored as data, and the subroutine is terminated. If the combustion stability is OK, in the flow B, the second fuel injection timing IT2 and the ignition timing ADV are retarded by Δt2 while the fuel injection timing IT1 is retarded. It is considered that Δt2 is appropriately the same value as Δt1, that is, a crank angle of about 2 ° to 5 ° is appropriate. In general, the combustion stable range is often distributed around a state in which the time from ignition to injection is substantially equal. Therefore, it is desirable that Δt1 and Δt2 have the same value from this point. That is, for example, if IT1 = 40 ° BTDC, IT2 = 14 ° ATDC, ADV = 16 ° ATDC, Δt1 = Δt2 = 4 °, then IT1 = 36 ° BTDC, IT2 = 18 ° ATDC, ADV = It looks like 20 ° ATDC.

Then, fuel injection and ignition are performed again to determine the combustion stability. At this time, if the stability is OK, the flow returns to the flow A with the aim of further retarding the fuel injection timing and ignition timing.
If it is NG, the first fuel injection timing IT2, ADV is returned to the original value, the fuel injection timing and the ignition timing are stored as data, and the subroutine is terminated.

  In FIG. 5, in flow C, the first fuel injection timing is advanced by Δt1, injection and ignition are performed, and combustion stability is determined. If combustion stability is OK, the fuel injection timing and ignition timing are stored as data, and the subroutine is terminated. If the combustion stability is NG, in the next flow D, the fuel injection timing IT2 and the ignition timing ADV are advanced by Δt2, injection and ignition are performed, and the combustion stability is determined again. If combustion stability is OK, data is stored and the subroutine is terminated. In the case of NG, since combustion stability is still insufficient, the flow C is returned to again. In this way, the fuel injection timing and the ignition timing are controlled as much as possible within the range where the combustion stability is OK.

6 and 7 show examples of determining the combustion stability from the detection waveform of the crank sensor. In FIGS. 6 and 7, since the work by compression is required near the top dead center of each cylinder, that is, near TDC, the rotational speed of the crankshaft 300 shown in FIG. The frequency of detection is also reduced, and waveforms such as b and d in FIG. 6 and b ′ and d ′ in FIG. 7 are obtained. In contrast, in the expansion stroke after compression top dead center, the speed of the crankshaft 300 increases due to explosion, and waveforms such as a and c in FIG. 6 and a ′ and c ′ in FIG. 7 are observed. Here, comparing c ′ in FIG. 6 and c ′ in FIG. 7, it can be seen that c has more peaks per unit time, and c has a higher speed of the crankshaft 300. That is, the higher the combustion pressure, the higher the speed of the crankshaft 300. Therefore, if the speed of the crankshaft 300 is detected with high time resolution and the difference in the rotational speed in the expansion stroke is quantified, Can be detected.

  Further, the standard deviation, that is, the combustion stability, can be obtained by acquiring data in a time series for each cylinder with respect to the rotation speed obtained here, that is, the combustion pressure.

  FIG. 8 shows a flowchart for determining the combustion stability. First, the tooth of the ring gear 302 detected by the crank angle sensor 301 is taken in as an engine rotation pulse, the rotational angular velocity is calculated every moment from the time interval between the teeth, and the driving torque is calculated therefrom. Then, referring to the crank angle, it is determined which cylinder is currently accelerating the crankshaft 300, that is, whether an explosion has occurred. These are repeated for one cycle, that is, for all the cylinders, and the fluctuation of the rotational speed is calculated as a function of the generated torque or the combustion pressure, and at the same time, the standard deviation of the rotational fluctuation in the previous cycles is obtained. Then, it is checked whether or not a predetermined number of cycles, for example, 10 cycles have been measured, and if the specified number of cycles has not been measured, the flow returns to the top of the flow. Store as an index of combustion stability and end the subroutine.

  Although not shown, in FIG. 3, FIG. 4, FIG. 5 and FIG. 8, when a high load operation request is made due to the driver's accelerator operation, etc., two injections at the time of fast idling are performed as interrupt processing. It is assumed that the control is terminated and the routine proceeds to normal injection control and ignition timing control.

  FIG. 9 and FIG. 10 show how the injection and ignition timing are changed according to the flow of FIG. 4 or FIG. FIG. 9 shows a case where the combustion stability has a margin and the injection and ignition timing are retarded. FIG. 10 shows a case where the combustion stability is NG and the injection and ignition timing are advanced to the point of stability OK. The numbers written at the grid points in the figure are representative values of the stability of combustion, and the smaller the number, the less the combustion fluctuation and the more stable. In this example, the stability limit is “20”.

  When the fuel injection timing is changed rather than the ignition timing, the change in the relative afterburning amount is small, the change in the exhaust temperature is small, and the change in the air amount and the fuel injection amount is also small. First, change the fuel injection timing, then change the ignition timing, then change the air amount and fuel injection amount so that the rotation speed of fast idle can be maintained or the torque required for fast idle can be maintained Let me respond.

  FIG. 11 shows the difference between the conventional example and the present example at the ignition timing during the retard control. In this example, for a four-cylinder engine, a graph when the ignition timing is changed and other parameters are made constant is shown. Due to differences in spraying and air flow, there is a difference in combustion stability between cylinders even with the same specifications. In the conventional example, the stability limit value of the second cylinder with the lowest retard limit is used to ensure sufficient stability. It must be ignited at 18 ° ATDC, more advanced than some 20 ° ATDC. On the other hand, in the control of this embodiment, the ignition timing can be retarded to the limit for each cylinder. Therefore, the first cylinder having a high stability with respect to the ignition timing retard is about 12 °, and the average retard performance is the third. The fourth cylinder can be further retarded by about 7 °, and the second cylinder with the lowest retard limit can be further retarded by 2 °.

  12 and 13 show a comparison of the HC emission amount, the exhaust temperature, and the soot amount between the present embodiment and the conventional example. FIG. 12 is a plot of how the HC emission amount, the exhaust temperature, and the soot amount change when the ignition timing is variable, as in FIG. According to the results of experiments by the inventors, even if there is a difference in combustion stability among the cylinders, if there is no misfire, the exhaust amount of HC and soot, the exhaust temperature, etc. can be regarded as almost the same, so conceptually Can be represented on one graph as shown in FIG. The first cylinder with a large retard amount also has a large exhaust temperature and a small soot amount and HC exhaust amount. Since the exhaust amount of HC and soot can be reduced and the exhaust temperature can be increased in each cylinder, as a result, the exhaust amount of HC and soot can be reduced and the exhaust temperature can be increased even in the total of four cylinders.

  FIG. 14 shows a second embodiment of the present invention. This figure corresponds to FIG. 2 of the first embodiment, and since the basic configuration as an engine is the same, the description thereof is omitted. Unlike the first embodiment, the torque sensor 305 is attached to the crankshaft 300, and the combustion stability is calculated from the time change of the torque, not the rotational fluctuation. The ignition timing and injection timing can be set near the retard limit. As a result, as in the first embodiment, the HC emission amount and the soot amount can be reduced, and the exhaust temperature can be raised to activate the catalyst 115 at an early stage.

  Although the present embodiment has been described with a configuration using a so-called side-injection type injector, the scope of the present invention is not necessarily limited to this, and even a so-called direct-injection type injector has combustion stability. Is clearly included in the scope of the present invention if the ignition retard amount is changed based on this.

  Further, the fuel injection mode during the retarded combustion is the compression-expansion two-time injection, but the scope of the present invention is not limited to this, and the combustion stability is detected, and the ignition retard is based on this. If the amount is variable, the present invention can be applied even when the number of injections is increased or decreased once, three times, four times, etc., or even at the injection timing such as intake stroke-compression stroke injection. It is included in the range.

  According to the above-described embodiment, an in-cylinder injection type gasoline engine that raises the exhaust gas temperature for early activation of the catalyst, reduces HC, secures a long fuel vaporization time, and reduces soot is provided. it can.

  Further, it is possible to provide an in-cylinder injection type gasoline engine that can achieve a prescribed combustion stability while preventing misfire even if the spray and the injection amount of the injector vary.

  The present invention is considered to be applicable as a power source not only for automobiles but also for a wide range of equipment, as long as it is an engine that directly injects fuel into a cylinder and has an ignition plug.

The block diagram which looked at the 1st example of the present invention from the cylinder substantial side. The figure which looked at the composition of the 1st example of the present invention from the engine upper side. The flowchart at the time of starting in 1st Example of this invention. The sub-flowchart of ignition in the retard direction and injection timing correction in the first embodiment. The sub-flowchart of ignition in the advance direction and injection timing correction in the first embodiment. Example 1 in which the combustion stability is determined from the detection waveform of the crank sensor in the first embodiment. Example 2 in which the combustion stability is determined from the detection waveform of the crank sensor in the first embodiment. The sub-flowchart which determines the combustion stability in 1st Example. The transition diagram which retards ignition and injection timing according to a flow in 1st Example. FIG. 6 is a transition diagram for advancing ignition and injection timing according to a flow in the first embodiment. The figure which showed the difference in the preset ignition timing of a prior art example and this invention in 1st Example. The figure which showed the change of ignition timing, exhaust temperature, HC discharge | emission amount, and soot in 1st Example. The figure which showed the difference in HC, soot, and exhaust gas temperature of a prior art example and this invention in 1st Example. The block diagram in 2nd Example of this invention.

Explanation of symbols

101 Intake pipe 102 Partition plate 103 Intake control valve 104 Electronic control throttle chamber 105 Air flow meter 106 Air cleaner 107 Piston 107a Projection 110 on piston Exhaust pipe 111 Intake valve 112 Exhaust valve 113 Spark plug 114 Ignition coil 115 Catalyst 116 Collector 117 Silencer 118 Cylinder head 120 Tumble 121 Mixture 122 Injector 123 Cylinder 125 Spray 132 Fuel gallery 133 Fuel pressure sensor 201 Computer 300 Crankshaft 301 Crank angle sensor 302 Ring gear 303 Catalyst temperature sensor 304 Exhaust temperature sensor 305 Torque sensor

Claims (5)

An injector for injecting fuel into a combustion chamber formed by a cylinder and a piston;
A spark plug for igniting the fuel injected into the combustion chamber;
An intake valve provided on the intake side of the cylinder; an exhaust valve provided on the exhaust side of the cylinder;
In a control device for controlling an internal combustion engine having
The internal combustion engine includes a combustion stability detection mechanism for detecting the combustion stability of the engine,
The control device controls ignition timing and injection timing based on the combustion stability. The combustion stability detection mechanism is a mechanism for measuring the rotational speed of the internal combustion engine,
The control device according to claim 1, wherein the control device calculates the combustion stability from a variation in the rotation speed.   2. The control device according to claim 1, wherein the control is performed to an unstable side within a range where the combustion is stable based on the combustion stability. Based on the combustion stability,
2. The control apparatus according to claim 1, wherein the air-fuel ratio, the fuel injection timing, and the ignition timing are changed for each cylinder.   5. The control apparatus according to claim 4, wherein the fuel injection timing is changed and then the ignition timing is changed.

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