JP2021102968A - Engine control device - Google Patents

Abstract

To provide an engine control device capable of restraining knocking while securing a high fuel consumption performance.SOLUTION: An engine comprises fuel supply means 14 for supplying fuel containing petrol into a combustion engine 6, and ignition means 13 for igniting air-fuel mixture. In a high load region A in which an engine load is higher than a predetermined load, when knocking occurs if ignition is performed at a reference ignition timing set nearer a retard angle side than MBT that is an ignition timing at which an engine torque becomes highest, an ignition advance angle side control for making the ignition means 13 ignite at a timing nearer an advance angle side than the reference ignition timing is performed.SELECTED DRAWING: Figure 6

Description

The present invention relates to an engine control device including a cylinder in which a combustion chamber is formed.

Conventionally, in the field of engines, various measures have been taken to prevent knocking from occurring. Specifically, under conditions where the engine load is high and the temperature in the combustion chamber is high, a mixture of fuel and air self-ignites and burns in the outer periphery of the combustion chamber separately from the main combustion, generating a high pressure wave and knocking. That is, vibration of the cylinder and the piston occurs. When knocking occurs, noise may increase and the piston or the like may be damaged, and it is required to prevent this.

For example, Patent Document 1 discloses an engine that delays the ignition timing when knocking occurs.

Japanese Unexamined Patent Publication No. 2008-291758

When the ignition timing is simply retarded to avoid knocking as in the engine of Patent Document 1, the basic ignition timing is set on the retard side of the MBT, which is the ignition timing at which the engine torque is highest. Under operating conditions, the engine torque decreases due to the retardation of the ignition timing. In particular, when the compression ratio is high, the engine torque may drop significantly. Specifically, when the compression ratio is high, knocking is likely to occur, combustion becomes steep, combustion noise increases, and the amount of NOx produced increases. Ignition timing (basic ignition timing according to the operating range of the engine and operating environment) is set, and there is a high tendency for combustion to start after compression top dead center. On the other hand, since the compression ratio is high, the amount of change in the piston position with respect to the change in the crank angle at the initial stage of the expansion stroke is larger than when the compression ratio is low. Therefore, when the compression ratio is high, the piston position during combustion is significantly lowered (at compression top dead center) even if the ignition timing is retarded by a small amount with respect to the basic ignition timing. The amount of separation from the position is significantly increased), and the engine torque and thus the fuel efficiency performance are significantly reduced.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an engine control device capable of suppressing knocking while ensuring high fuel efficiency.

As a result of diligent research on the above-mentioned problems, the present inventors have set the ignition timing from a predetermined ignition timing (ignition timing on the retard side of the basic ignition timing) at which knocking on the retard side of the MBT does not occur. As the angle is advanced, knocking occurs, and when the angle is advanced by a predetermined amount, knocking that exceeds the permissible knock strength that leads to a decrease in the reliability of the engine body occurs, but if the ignition timing is further advanced, knocking does not occur. Or, it was found that the knocking strength becomes weaker than the above-mentioned allowable knocking strength. Further, in order to avoid knocking, even if knocking does not occur in the same manner when the ignition timing is advanced from the reference ignition timing, which is the basic ignition timing, and when the ignition timing is retarded. It was found that the engine torque obtained when the ignition timing was advanced was higher than when the ignition timing was retarded. In particular, in an engine having a high expansion ratio with a high compression ratio, the engine torque is higher when the ignition timing is advanced than the reference ignition timing than when the ignition timing is retarded.

This is considered to be due to the following reasons.

If the ignition timing is set to the advance angle side sufficiently, a relatively large amount of fuel can be burned early, and then the amount of fuel that is locally overheated in the outer periphery of the combustion chamber and causes knocking is small. It can be suppressed and knocking can be suppressed.

If the ignition timing is set to the advance side, the fuel burns at a timing when the amount of change in the piston position with respect to the change in the crank angle is relatively small, so even if some reverse torque acts on the engine (reverse rotation direction on the piston). It is possible to obtain an engine torque that exceeds this (even if the torque of the above acts a little). Specifically, when the ignition timing is set to the retard side, the combustion center of gravity deviates greatly from the timing when the piston is effectively pushed down, and combustion proceeds when the expansion allowance of the combustion chamber becomes relatively large. The speed also slows down and the engine torque drops significantly. On the other hand, if the ignition timing is set sufficiently to the advance angle side (when the ignition timing is set to the advance angle side larger than the compression top dead center), the combustion center of gravity timing becomes close to the compression top dead center (near the compression top dead center). Since a fast combustion speed is ensured even after the combustion center of gravity has passed, even if a slight reverse torque acts on the engine, a higher engine torque can be obtained than when the ignition timing is on the retard side. .. The combustion center of gravity period is a period at which 50% of the total amount of heat generated during one combustion cycle is generated, and is a crank angle at the time when the in-cylinder pressure rise due to combustion reaches its peak.

From this, if the ignition timing is set to the advance angle side larger than the reference ignition timing set on the retard side of the MBT, knocking can be avoided or the knocking strength can be kept below the allowable knock strength even if knocking occurs. It can be weakened (less momentary increase in cylinder pressure during knocking). If knocking can be avoided or the knocking strength can be reduced to the allowable knocking strength, it is possible to suppress a decrease in reliability of the engine body.

The present invention has been made based on this finding, and is an engine control device including a cylinder in which a combustion chamber is formed, and is a fuel supply means for supplying fuel containing gasoline into the combustion chamber. An ignition means for igniting a mixture of fuel and air supplied into the combustion chamber by the fuel supply means and a control means for controlling the ignition means are provided, and the control means has an engine load higher than a predetermined load. If knocking occurs when the engine is ignited at the reference ignition timing set on the retard side of the MBT, which is the ignition timing at which the engine torque is highest in the high load region, the advance angle side is higher than the reference ignition timing. It is characterized in that the ignition advance control for causing the ignition means to ignite is performed at the time of.

The case where the knocking occurs refers to a knocking that leads to a decrease in the reliability of the engine body and a knocking strength exceeding the allowable knocking strength.

According to this configuration, in the high load region, the ignition means is ignited at a timing on the advance side of the reference ignition timing set on the retard side of the MBT, for the reason as described above. It is possible to obtain high engine torque while suppressing the occurrence of knocking, that is, high fuel efficiency.

In the above configuration, when the maximum value of the pressure in the combustion chamber is predicted to exceed a preset reference pressure when the ignition advance control is performed, the control means also performs the ignition advance control. It is preferable to control the fuel supply means so that the amount of fuel supplied to the combustion chamber is reduced.

According to this configuration, the maximum in-cylinder pressure, which is the maximum value of the pressure in the combustion chamber, can be suppressed to a low level by reducing the fuel, and the fuel efficiency performance is improved by implementing the ignition advance control while reducing the adverse effect on the piston and the like. While knocking can be suppressed.

In the above configuration, an effective compression ratio changing means capable of changing the effective compression ratio of the cylinder is provided.
When the control means predicts that the maximum value of the pressure in the combustion chamber exceeds a preset reference pressure when the ignition advance control is performed, the control means performs the ignition advance control and the high load. It is preferable to control the effective compression ratio changing means so that the effective compression ratio of the cylinder in the region is lower than when the ignition advance control is not performed.

According to this configuration, the maximum in-cylinder pressure can be suppressed low by reducing the effective compression ratio, and knocking can be suppressed while improving fuel efficiency by implementing ignition advance control while reducing adverse effects on the piston and the like. it can.

Further, as a configuration different from the above configuration, when the control means predicts that the maximum value of the pressure in the combustion chamber exceeds a preset reference pressure when the ignition advance control is performed, the ignition advance control means the ignition. The ignition means may be configured to ignite at a timing on the retard side of the reference ignition timing without performing advance angle control.

With this configuration as well, the maximum in-cylinder pressure can be suppressed to a low level, and it is possible to prevent adverse effects on the piston and the like.

In the above configuration, when knocking occurs after the ignition advance control is performed, or when knocking is predicted to occur due to the ignition advance control, the control means is more than the reference ignition timing. It is preferable that the ignition means is ignited at the retard side ignition timing on the retard side.

In this way, knocking can be more reliably prevented (knocking continues).

Here, if the geometric compression ratio of the cylinder is high, the temperature in the combustion chamber becomes high and knocking is likely to occur. Further, when the geometric compression ratio is high, the amount of decrease in engine torque with respect to the amount of retardation of the ignition timing when the ignition timing is retarded in the range on the retard side of the MBT becomes large. Therefore, if the present invention is applied to an engine in which the geometric compression ratio of the cylinder is set to 15 or more, knocking can be suppressed while effectively suppressing a decrease in engine torque.

As an engine to which the present invention is applied, in at least a part of the high load region, partial compression in which a part of the air-fuel mixture is burned by ignition by the ignition means and then the other air-fuel mixture is burned by self-ignition. Ignition combustion is carried out.

As described above, according to the engine control device of the present invention, knocking can be suppressed while ensuring high fuel efficiency.

It is a figure which showed the structure of the engine system which concerns on one Embodiment of this invention. It is a block diagram which shows the control system of an engine. It is a figure which showed the control map. It is a graph which showed the relationship between the ignition timing, knock strength and the maximum cylinder pressure. (A) It is a figure which showed the heat generation rate at a different ignition timing. (B) It is a figure which showed the cylinder pressure at a different ignition timing. It is a flowchart which showed the procedure of knock avoidance control. It is a flowchart which showed the procedure of knock avoidance control which concerns on 2nd Embodiment. It is a flowchart which showed the procedure of knock avoidance control which concerns on 3rd Embodiment.

(1) Overall Configuration of Engine FIG. 1 is a diagram showing a configuration of an engine system to which the control device of the engine of the present invention is applied. The engine system of the present embodiment includes a 4-stroke engine main body 1, an intake passage 20 for introducing combustion air into the engine main body 1, and an exhaust passage 30 for discharging the exhaust generated by the engine main body 1. And.

The engine body 1 is, for example, an in-line 4-cylinder engine in which four cylinders 2 are arranged in series in a direction orthogonal to the paper surface of FIG. This engine system is mounted on a vehicle, and the engine body 1 is used as a drive source for the vehicle. In the present embodiment, the engine body 1 is driven by being supplied with fuel including gasoline. The fuel may be gasoline containing bioethanol or the like.

The engine body 1 includes a cylinder block 3 in which a cylinder 2 is formed, a cylinder head 4 provided on the upper surface of the cylinder block 3, and a piston 5 fitted in the cylinder 2 so as to be reciprocating (up and down). Has.

A combustion chamber 6 is formed above the piston 5. The combustion chamber 6 is a so-called pent roof type, and the ceiling surface of the combustion chamber 6 formed by the lower surface of the cylinder head 4 has a triangular roof shape composed of two inclined surfaces, an intake side and an exhaust side. On the crown surface of the piston 5, a cavity is formed in which a region including the central portion thereof is recessed on the opposite side (lower side) of the cylinder head 4. Here, the space between the crown surface of the piston 5 and the ceiling surface of the combustion chamber 6 in the inner space of the cylinder 2 regardless of the position of the piston 5 and the combustion state of the air-fuel mixture is referred to as the combustion chamber 6.

The geometric compression ratio of the engine body 1, that is, the ratio of the volume of the combustion chamber 6 when the piston 5 is at the bottom dead center and the volume of the combustion chamber 6 when the piston 5 is at the top dead center is 15 or more. It is set to 30 or less (for example, about 20).

The cylinder head 4 has an intake port 9 for introducing the air supplied from the intake passage 20 into the cylinder 2 (combustion chamber 6) and an exhaust gas generated in the cylinder 2 to be led out to the exhaust passage 30. An exhaust port 10 is formed. Two intake ports 9 and two exhaust ports 10 are formed for each cylinder 2.

The cylinder head 4 is provided with an intake valve 11 that opens and closes an opening on the cylinder 2 side of each intake port 9, and an exhaust valve 12 that opens and closes an opening on the cylinder 2 side of each exhaust port 10.

The intake valve 11 and the exhaust valve 12 are opened and closed in conjunction with the rotation of the crankshaft 7 by a valve operating mechanism including a pair of camshafts and the like arranged on the cylinder head 4. The valve operating mechanism for the intake valve 11 has a built-in intake valve variable mechanism 11a (see FIG. 2) that can change the opening / closing timing of the intake valve 11, and the valve opening timing and valve closing timing of the intake valve 11 are set. It is changed according to the operating conditions. When the opening / closing timing of the intake valve 11 is changed, the effective compression ratio of the cylinder 2 changes. As described above, in the present embodiment, the intake valve variable mechanism 11a functions as an effective compression ratio changing means for changing the effective compression ratio of the cylinder 2.

The cylinder head 4 is provided with an injector (fuel supply means) 14 for injecting fuel. The injector 14 is attached so that the tip end portion on which the injection port is formed is located near the center of the ceiling surface of the combustion chamber 6 and faces the center of the combustion chamber 6. The injector 14 has a plurality of nozzles at its tip, and has a cone shape centered on the central axis of the cylinder 2 from the vicinity of the center of the ceiling surface of the combustion chamber 6 toward the crown surface of the piston 5 (specifically, a hollow cone shape). It is configured to inject fuel into the ceiling. The taper angle (spraying angle) of the cone is, for example, 90 ° to 100 °. The specific configuration of the injector 14 is not limited to this, and may be a single injector.

The injector 14 injects fuel pumped from a high-pressure pump (not shown) into the combustion chamber 6. The injection pressure of the injector 14 is set to 20 MPa or more, and fuel is injected from the injector 14 at a high pressure. For example, this injection pressure is set to about 25 MPa.

The cylinder head 4 is provided with a spark plug 13 for igniting the air-fuel mixture in the combustion chamber 6. At the tip of the spark plug 13, an electrode is formed that discharges sparks to ignite the air-fuel mixture and imparts ignition energy to the air-fuel mixture. The spark plug 13 is arranged so that its tip is located near the center of the ceiling surface of the combustion chamber 6 and faces the center of the combustion chamber 6.

The intake passage 20 is provided with an air cleaner 21 and a throttle valve 22 for opening and closing the intake passage 20 in this order from the upstream side. In the present embodiment, the throttle valve 22 is basically maintained at a fully open position or an opening close to this during engine operation, and is closed and intake air only under limited operating conditions such as when the engine is stopped. Block the passage 20.

The exhaust passage 30 is provided with a purification device 31 for purifying the exhaust gas. The purification device 31 has, for example, a built-in three-way catalyst.

The exhaust passage 30 is provided with an EGR device 40 for returning a part of the exhaust gas passing through the exhaust passage 30 to the intake passage 20 as EGR gas. The EGR device 40 opens and closes the EGR passage 41 and the EGR passage 41 that communicate the portion of the intake passage 20 downstream of the throttle valve 22 and the portion of the exhaust passage 30 upstream of the purification device 31. It has an EGR valve 42. Further, in the present embodiment, the EGR passage 41 is provided with an EGR cooler 43 for cooling the EGR gas passing through the EGR passage 41, and the EGR gas is cooled by the EGR cooler 43 and then returned to the intake passage 20. To.

(2) Control system (2-1) System configuration FIG. 2 is a block diagram showing an engine control system. The engine system of this embodiment is collectively controlled by a PCM (powertrain control module, control means) 100. As is well known, the PCM 100 is a microprocessor composed of a CPU, a ROM, a RAM, and the like.

Various sensors are provided in the vehicle, and the PCM 100 is electrically connected to these sensors. For example, the cylinder block 3 is provided with a crank angle sensor SN1 that detects the rotation angle of the crankshaft 7 and thus the engine rotation speed (engine rotation speed). Further, an air flow sensor SN2 and an intake air temperature sensor SN3 for detecting the amount and temperature of air sucked into each cylinder 2 through the intake passage 20 are provided. Further, the cylinder head 4 is provided with a cylinder pressure sensor SN4 that detects the cylinder pressure, which is the pressure inside the combustion chamber 6. One in-cylinder pressure sensor SN4 is provided for each cylinder 2. Further, the vehicle is provided with an accelerator opening sensor SN5 that detects an opening degree (accelerator opening degree) of an accelerator pedal (accelerator opening degree) which is not shown and is operated by the driver.

The PCM100 executes various calculations based on the input signals from the sensors SN1 to SN5 and the like to generate various parts of the engine such as the spark plug 13, the injector 14, the throttle valve 22, the EGR valve 42, and the intake valve variable mechanism 11a. Control.

(2-2) Basic Control FIG. 3 is a control map in which the horizontal axis is the engine speed and the vertical axis is the engine load, and the operating area of the engine is divided according to the control content. Specifically, a low load region B in which the engine load is equal to or less than a preset reference load (predetermined load) Tq1 and knocking is unlikely to occur, and a high load region A in which the engine load is higher than the reference load Tq1 and knocking is likely to occur. It is partitioned into. In the high load region A, knock avoidance control, which will be described later, is implemented in order to suppress the occurrence of knocking. In the present embodiment, as described above, the geometric compression ratio of the engine body 1 is set to 15 or more, and the temperature in the combustion chamber 6 is raised to a very high temperature. Therefore, knocking is particularly likely to occur. The high load region A is further divided into a high load low speed region A1 in which the engine speed is less than the preset reference speed N1 and a high load high speed region A2 in which the engine speed is equal to or higher than the reference speed N1. ..

In the low load region B and the high load low speed region A1, compression self-ignition combustion (SPCCI combustion, SPCCI: Spark Control Compression Ignition) by ignition assist is performed. In compression self-ignition combustion, first, fuel is injected from the injector 14 into the combustion chamber 6 before the compression top dead center (TDC). This fuel mixes with air by near compression top dead center. The air-fuel mixture formed in the combustion chamber 6 is discharged from the spark plug 13 near the compression top dead center. As a result, the air-fuel mixture around the spark plug 13 is forcibly ignited. Then, the flame propagates from around the spark plug 13 to the surroundings, the temperature of the surrounding air-fuel mixture is raised, and self-ignition occurs.

On the other hand, in the high load high speed region A2, it becomes difficult to self-ignite the air-fuel mixture at a desired time, so SI combustion (spark ignition combustion, SI: Spark Ignition) adopted in a normal gasoline engine is carried out. SI combustion is a combustion form in which almost the entire air-fuel mixture is burned by flame propagation. Discharge is performed from the spark plug 13 near the compression top dead center, and the air-fuel mixture around the spark plug 13 is forcibly ignited. .. Then, the flame propagates from around the spark plug 13 to the surroundings, and the remaining air-fuel mixture is forcibly burned by the flame propagation.

In the low load region B, the amount of fuel injected into the combustion chamber 6 by the injector 14 (hereinafter, appropriately referred to as the injection amount) is set so that the air-fuel ratio of the air-fuel mixture in the combustion chamber 6 becomes the stoichiometric air-fuel ratio. Specifically, the PCM 100 calculates the amount of air corresponding to the required engine torque, and changes the opening degrees of the throttle valve 22 and the EGR valve 42 so that this amount of air is realized. Next, the PCM 100 calculates the amount of air introduced into the combustion chamber 6, calculates the amount of fuel whose air-fuel ratio is the stoichiometric air-fuel ratio with respect to this amount of air, and sets it as the injection amount.

Even in the high load region A, the injection amount is basically set so that the air-fuel ratio of the air-fuel mixture in the combustion chamber 6 becomes the stoichiometric air-fuel ratio.

(2-3) Knock Avoidance Control The outline of the knock avoidance control implemented in the high load region A will be described with reference to FIGS. 4, 5 (a), and 5 (b). FIG. 4 is a graph showing the relationship between the ignition timing (crank angle) and the knocking strength (hereinafter referred to as knock strength), and the ignition timing and the maximum in-cylinder pressure which is the maximum value of the in-cylinder pressure. FIG. 5A is a diagram showing a change in the crank angle of the heat generation rate. Further, FIG. 5B is a diagram corresponding to FIG. 5A and showing a change in the crank angle of the in-cylinder pressure. The knock intensity shown in FIG. 4 is the maximum value of the amplitude of the waveform having a predetermined frequency or higher included in the waveform of the in-cylinder pressure. The lines of FIGS. 5 (a) and 5 (b) show the heat generation rate and the in-cylinder pressure under operating conditions in which the ignition timings are different from each other.

In order to improve fuel efficiency (to increase engine torque), it is preferable to set the ignition timing to MBT (Minimum spark advance for Best Torque), which is the timing when the engine torque is highest. However, in the high load region A, knocking is likely to occur when the ignition timing is set to MBT due to the high temperature and pressure in the combustion chamber 6. In particular, in a high compression ratio engine having a geometric compression ratio of 15 or more, knocking always occurs when the ignition timing is set to MBT due to the high temperature and pressure in the combustion chamber 6 in the high load region A. Furthermore, the combustion tends to be steep and the combustion noise and the amount of NOx generated tend to increase. On the other hand, if the ignition timing is set to the retard side (expansion stroke) that is considerably later than the MBT, combustion can be generated when the temperature and pressure in the combustion chamber 6 are kept low, and knocking is suppressed. It is possible to suppress combustion noise and NOx production amount.

Here, in the present specification and claims, knocking occurs (occurs) means that unacceptable knocking occurs, and knocking simply occurs (occurs) and unacceptable knocking occurs (occurs). ) Both cases and are included.

From the above, in the high load region A, as will be described later, the reference ignition timing, which is the basic ignition timing, is set to the timing on the retard side of the MBT.

However, when the air-fuel ratio of the air-fuel mixture in the combustion chamber 6 deviates from a desired value during acceleration or the like, knocking may occur even if the ignition timing is set as the reference ignition timing. Here, in such a case, knocking can be suppressed by further setting the ignition timing to the retard side. However, if the reference ignition timing is set to the retard side of the MBT, and if the ignition timing is further changed to the retard side, many air-fuel mixture will be at a time very retarded from the compression top dead center. (That is, the combustion center of gravity is on the very retarded side of the compression top dead center), so the engine torque drops significantly (fuel efficiency deteriorates significantly). The time of the center of gravity of combustion is the time (angle) at which 50% of the total amount of heat generated during one combustion cycle is generated.

On the other hand, as a result of diligent research, the inventors of the present application advance the ignition timing from a time when knocking on the retard side of the MBT does not occur, and knocking occurs when the ignition timing is advanced by a predetermined amount. However, it was found that knocking does not occur (knock intensity decreases) when the ignition timing is further advanced (although the knock intensity increases). That is, as shown in the upper graph of FIG. 4, the knock strength is high (the knock strength is higher than the predetermined allowable knock strength defined by the reliability of the engine, etc.) in the predetermined knock region. When the ignition timing is set in R2, and the ignition timing is set in the retard side region R3 on the retard side of the knock region R2 and the advance side region R1 on the advance side of the knock region R2. It was found that the knock strength can be reduced (the knock strength can be made smaller than the allowable knock strength). The allowable knock strength is the maximum value of the knock strength that can ensure the reliability of the engine, and is defined from the reliability of the engine and the like. Further, the allowable knock strength may be 0. Here, as shown in FIG. 4, the knock region R2 includes the compression top dead center. Further, in FIG. 4, the MBT exists in the knock region R2. For example, the MBT is approximately in the middle of the knock region R2.

It is considered that the knock strength can be reduced (knocking can be avoided) by advancing the ignition timing to the timing within the advance angle side region R1 in this way for the following reasons. That is, if the ignition timing is set to the advance side sufficiently, the ignition energy is applied in the state of higher temperature and higher pressure in the combustion chamber 6, and the result is that a certain amount of fuel can be burned earlier. It is considered that the amount of fuel that is locally overheated in the outer peripheral portion of the combustion chamber and causes knocking can be suppressed to a small amount, and the knocking strength is reduced.

Further, the inventors of the present application should set the ignition timing to a timing within the advance angle side region R1 even when knocking does not occur (when the knock strength becomes the same level) in the engine. It was found that even if a slight reverse torque acts, the engine torque becomes higher than when the ignition timing is set to the timing within the retard side region R3.

This is the time when most of the air-fuel mixture is closer to the compression top dead center when the ignition timing is set in the advance angle side region R1 than when the ignition timing is set in the retard angle side region R3. It is considered that the combustion temperature rises and the combustion speed becomes faster due to the combustion (when the combustion center of gravity is closer to the compression top dead center).

Specifically, the heat generation rate dQ1 in FIG. 5A is the heat generation rate when the ignition timing is set to the first period CA1, which is the most retarded period among the periods included in the first region R1. is there. The heat generation rate dQ0 in FIG. 5A is the heat generation rate when the ignition timing is set to the limit time CA0 on the advance angle side of the first time CA1. The heat generation rate dQ2 in FIG. 5A is the heat generation rate when the ignition timing is set to the second period CA2, which is the time on the retard side of the time included in the second region R2. The heat generation rate dQ3 in FIG. 5A is set to the third period CA3, which is the most advanced period among the periods included in the third region R3 on the retard side of the second period CA2. It is the heat generation rate at the time.

As is clear from the comparison of the heat generation rates in FIG. 5 (a), when the ignition timing is set to the third period CA3, which is the most advanced period of the retard side region R3, the heat generation rate. As shown by dQ3, the combustion period becomes very long. On the other hand, when the ignition timing is set in the first timing CA1 included in the advance angle side region R1, the combustion period is suppressed to be short as shown by the heat generation rate dQ1.

When the ignition timing is set on the retard side of the third time CA3 in the time within the retard side region R3 in order to avoid knocking, it is a time relatively far from the compression top dead center and the piston 5 Since most of the air-fuel mixture burns in a state where the amount of decrease from the compression top dead center is large, the combustion energy cannot be efficiently converted into a force for pushing down the piston 5. On the other hand, when the first period CA1 included in the advance angle side region R1 is set as the ignition timing, combustion occurs mainly near the compression top dead center, so that the combustion energy is efficiently pushed down by the piston 5. It can be converted and the engine torque can be increased.

Further, the volume change of the combustion chamber 6 with respect to the change of the crank angle becomes larger as the distance from the compression top dead center increases (in the latter half of the compression stroke and the first half of the expansion stroke). Therefore, when the ignition timing is set in the retard side region R3, the amount of change in the volume of the combustion chamber 6 at the time when most of the air-fuel mixture burns (combustion center of gravity time) with respect to the retard amount of the ignition timing. Becomes larger. Therefore, when the ignition timing is set within the retard angle side region R3, the amount of decrease in engine torque with respect to the retardation amount becomes large when the ignition timing is retarded.

On the other hand, as shown in FIGS. 4 and 5 (b), the maximum in-cylinder pressure increases as the ignition timing is advanced. It is known that if the maximum in-cylinder pressure exceeds a predetermined pressure, damage to the piston 5 and the like may occur. Therefore, the maximum in-cylinder pressure is required to be suppressed to this predetermined pressure or lower. Specifically, the in-cylinder pressures P0, P1, P2, and P3 in FIG. 5 (b) correspond to the heat generation rates dQ0, dQ1, dQ2, and dQ3 in FIG. 5 (a), respectively, and the ignition timing is limited. It is the in-cylinder pressure when the time CA0, the first time CA1, the second time CA2, and the third time CA3 are set, and the maximum in-cylinder pressure for advancing the ignition timing to the limit time CA0 rises to the above-mentioned predetermined pressure.

From this, the range in which the maximum in-cylinder pressure can be suppressed to a predetermined pressure or less and the knock strength can be kept below the allowable knock strength, that is, the range in which the ignition timing can be set is a part of the advance angle side region R1. Region R10. This region R10 is a very narrow range.

Based on the above findings, in the present embodiment, the ignition timing is basically set to the retard side of the MBT in the high load region A. Then, even if ignition is performed at the reference ignition timing, the knock strength exceeds the allowable knock strength, that is, when there is a possibility that unacceptable knocking may occur, or when knocking that is actually unacceptable occurs, the ignition timing is set as the reference ignition timing. Instead of retarding from, the ignition timing is advanced to the timing included in the advance side region R1 to maintain high engine torque (maintain high fuel efficiency).

The specific flow of knock avoidance control will be described with reference to the flowchart of FIG. Each step of this flowchart is executed when the engine is operating in the high load region A. That is, the PCM 100 determines in which operating region the engine is operating from the current engine speed and the engine load. Then, when it is determined that the engine is operating in the high load region A, step S1 is performed. In this determination step, the value detected by the crank angle sensor SN1 is used as the engine speed. The engine load is calculated based on the accelerator opening degree and the engine speed detected by the accelerator opening degree sensor SN5.

In step S1, the PCM 100 first sets the reference ignition timing. The reference ignition timing is preset and stored in the PCM 100.

In the present embodiment, the reference ignition timing for the engine speed and the engine load is obtained by an experiment or the like and stored in the PCM 100 as a map. In step S1, the reference ignition timing corresponding to the current engine speed and engine load is extracted from this map.

After step S1, the process proceeds to step S2. In step S2, the PCM 100 determines (predicts) whether or not knocking occurs.

In the present embodiment, whether or not knocking occurs is predicted based on the last calculated combustion center of gravity time (hereinafter referred to as the current combustion center of gravity time) and the state amount of the gas in the combustion chamber 6. The time of the center of gravity of combustion can be obtained by calculating the amount of heat generated using the in-cylinder pressure.

Specifically, the PCM 100 constantly calculates the combustion center of gravity timing using the in-cylinder pressure detected by the in-cylinder pressure sensor SN4. The combustion center of gravity time is calculated after the combustion is completed (for example, after the expansion stroke is completed). The PCM 100 calculates the difference between the calculated current combustion center of gravity time and the reference value stored in advance. As for this reference value, the wall surface temperature of the combustion chamber 6 is a predetermined value, the amount of EGR gas in the combustion chamber 6 and the amount of fuel supplied to the combustion chamber 6 are in accordance with the command values, and at the reference ignition timing. It is the combustion center of gravity time obtained when ignition is performed accurately. This reference value is obtained in advance by experiments or the like for the engine speed and the engine load, and is stored in the PCM 100.

Further, the PCM 100 estimates, as the state amount of gas in the combustion chamber 6, the amount of intake air in the combustion chamber 6 after the intake valve 11 is closed, the temperature of intake air, the amount of EGR gas, and the like. These are estimated based on the detection value of the air flow sensor SN1, the detection value of the crank angle sensor SN2, the detection value of the intake air temperature sensor SN4, the command value of the opening degree of the EGR valve 42, and the like.

The PCM 100 predicts whether or not knocking will occur from the difference between the calculated combustion center of gravity timing and the reference value and the estimated state amount of the gas in the combustion chamber 6. For example, when the detected combustion center of gravity is significantly ahead of the reference value or when the intake air temperature is high, the air-fuel mixture is more likely to burn than expected, and knocking occurs. is expected.

When the determination in step S2 is NO and it is predicted that knocking will not occur even if ignition is performed at the reference ignition timing, the process proceeds to step S11. In step S11, the PCM 100 determines the ignition timing as the reference ignition timing, and causes the spark plug 13 to ignite at the reference ignition timing.

If the determination in step S2 is YES and knocking is predicted to occur, the process proceeds to step S3.

In step S3, the PCM 100 sets a first ignition timing (advanced angle side ignition timing) and a third ignition timing (retarded angle side ignition timing) as ignition timing candidates.

The third ignition timing is set within the retard side region R3, on the retard side of the reference ignition timing, and on the retard side of the compression top dead center. The PCM100 sets the timing on the retard side by a preset first angle from the reference ignition timing set in step S1 as the third ignition timing. When the determination in step S2 is YES and knocking is predicted to occur, the reference ignition timing is in the second region R2 where knocking occurs (knock strength exceeds the allowable knock strength). Therefore, if ignition is performed at this timing with the ignition timing as the third ignition timing on the retard side of the reference ignition timing, the combustion center of gravity timing will be later than when the ignition timing is the reference ignition timing. , Knocking is less likely to occur.

The first ignition timing is a timing within the advance angle side region R1 and is set to a timing on the advance angle side with respect to the reference ignition timing. In the present embodiment, the first ignition timing is set to the most retarded ignition timing among the ignition timings included in the advance angle side region R1, that is, the first timing CA1 described above. As described above, the first period CA1 set at the first ignition timing is a period in which knocking does not occur and the fuel efficiency performance is relatively high (the obtained engine torque is relatively high) if ignition is performed at this period. is there.

After step S3, the process proceeds to step S4. In step S4, the PCM 100 predicts the maximum in-cylinder pressure Pmax when the ignition timing is the first ignition timing, and determines whether or not the predicted maximum in-cylinder pressure Pmax is equal to or less than the reference pressure. The reference pressure is a pressure that may lead to damage to the piston 5 and the like if the in-cylinder pressure exceeds this value, and is preset and stored in the PCM 100.

In the present embodiment, the maximum in-cylinder pressure Pmax when the ignition timing is set as the first ignition timing based on the current combustion center of gravity timing, the state amount of gas in the combustion chamber 6, and the first ignition timing set in step S3. Predict and compare this with the reference pressure.

If the determination in step S4 is YES, the process proceeds to step S5. In step S5, the PCM 100 predicts and predicts the maximum value of dP / dθ, which is the rate of increase in the in-cylinder pressure (the amount of increase in the in-cylinder pressure per unit crank angle) when the ignition timing is the first ignition timing. It is determined whether or not the maximum value of dP / dθ is equal to or less than the reference pressure increase rate. The reference pressure increase rate is a value at which the combustion noise exceeds a predetermined level when dP / dθ exceeds this value, and is set in advance and stored in the PCM 100.

In the present embodiment, dP / dθ when the ignition timing is the first ignition timing based on the current combustion center of gravity timing, the state amount of the gas in the combustion chamber 6, and the first ignition timing set in step S3. Predict the maximum value.

If the determination in step S5 is YES, the process proceeds to step S6. In step S6, the PCM 100 determines the ignition timing to the first ignition timing. Then, the PCM 100 performs ignition advance control for causing the spark plug 13 to ignite at the first ignition timing.

On the other hand, when the determination in step S4 is NO or the determination in step S5 is NO, the process proceeds to step S10.

In step S10, the PCM 100 determines the ignition timing at the third ignition timing, and causes the spark plug 13 to ignite at the third ignition timing.

As described above, in the present embodiment, when knocking is predicted to occur when ignition is performed at the reference ignition timing, the maximum in-cylinder pressure Pmax does not exceed the reference pressure and the maximum value of dP / dθ increases the reference pressure. As long as the rate is not exceeded, the ignition timing is set to the first ignition timing on the advance side of the reference ignition timing, and the air-fuel mixture is ignited at this first ignition timing. On the other hand, when it is predicted that knocking will occur if ignition is performed at the reference ignition timing, if the ignition timing is the first ignition timing, the maximum in-cylinder pressure Pmax exceeds the reference pressure, or the maximum value of dP / dθ is the reference. When the pressure increase rate is exceeded, the ignition timing is set to the third ignition timing on the retard side of the reference ignition timing, and the air-fuel mixture is ignited at this third ignition timing. Then, the air-fuel mixture is ignited at the reference ignition timing (second ignition timing) only when it is predicted that knocking will not occur if the ignition is performed at the reference ignition timing.

(3) Action, etc. As described above, in the present embodiment, when knocking occurs when ignition is performed at the reference ignition timing set on the retard side of the MBT in the high load region A, the ignition timing candidate. One of the above is to set the first ignition timing on the advance side of the reference ignition timing, which is included in the advance side region R1. Then, when ignited at this first ignition timing, if the maximum in-cylinder pressure does not exceed the reference pressure and the maximum value of dP / dθ does not exceed the reference pressure increase rate, the air-fuel mixture is ignited at this first ignition timing. I do.

Therefore, it is possible to prevent knocking while improving fuel efficiency as compared with the case where the ignition timing is set to the retard side of the reference ignition timing and the ignition is performed at the time further retarded from the reference ignition timing. it can.

Further, in the present embodiment, the ignition timing is set as the first ignition timing when it is predicted that the maximum in-cylinder pressure Pmax does not exceed the reference pressure. Therefore, when the ignition timing is set to the first ignition timing, the maximum in-cylinder pressure Pmax exceeds the reference pressure, which can prevent the piston and the like from being adversely affected.

Further, in the present embodiment, the ignition timing is set as the first ignition timing when it is predicted that the maximum value of dP / dθ does not exceed the reference pressure increase rate. Therefore, when the ignition timing is set to the first ignition timing, dP / dθ becomes equal to or higher than the reference pressure increase rate, and thereby it is possible to prevent the combustion noise from exceeding a desired level.

Further, when knocking occurs when ignition is performed at the reference ignition timing, and when ignition is performed at the first ignition timing, the maximum in-cylinder pressure Pmax exceeds the reference pressure, or the maximum value of dP / dθ exceeds the reference pressure increase rate. Is configured to ignite the air-fuel mixture at the third ignition timing on the retard side of the reference ignition timing. Therefore, although the fuel consumption performance is lower than that when ignited at the first ignition timing, knocking can be prevented more reliably.

(4) Second Embodiment FIG. 7 is a flowchart of knock avoidance control according to the second embodiment. The second embodiment is different from the first embodiment in the control contents of the steps (steps S21, S22, S23) that proceed when NO is determined in step S4 or step S5. The steps excluding these steps S21, S22, and S23 are the same in the first embodiment and the second embodiment, which are the embodiments described above. Here, the details of the steps excluding steps S21, S22, and S23. The explanation will be omitted.

In the second embodiment, if NO is determined in step S4 or step S5, the process proceeds to step S21.

In step S21, when the ignition timing is set to the first ignition timing and the injection amount of the injector 14 is reduced by a preset reference reduction amount from the basic injection amount (hereinafter, the injection amount is appropriately reduced). The maximum in-cylinder pressure Pmax is predicted, and it is determined whether or not the predicted maximum in-cylinder pressure Pmax is equal to or less than the reference pressure. The basic injection amount is the injection amount of the injector 14 during normal operation (during operation except when step S23 described later is performed), and is the amount of fuel corresponding to the required engine torque. The reference reduction amount is, for example, an amount of about 10% or less of the basic injection amount, which is preset and stored in the PCM 100.

If the determination in step S21 is YES and the predicted maximum in-cylinder pressure Pmax is equal to or less than the reference pressure, the process proceeds to step S22. In step S22, the ignition timing is set as the first ignition timing (ignition advance control is performed), and the maximum value of dP / dθ when the injection amount is reduced is predicted, and the predicted maximum of dP / dθ is predicted. Determine if the value is less than or equal to the reference pressure increase rate.

If the determination in step S22 is YES and the predicted maximum value of dP / dθ is equal to or less than the reference pressure increase rate, the process proceeds to step S23. In step S23, the PCM 100 determines the ignition timing to the first ignition timing. Further, in step S23, the injection amount of the injector 14 is set to an amount reduced by a reference reduction amount from the basic injection amount.

On the other hand, if the determination in step S21 is NO or the determination in step S22 is NO, the process proceeds to step S10 and the ignition timing is set to the third ignition timing. In the second embodiment, in step S10, the injection amount is the basic injection amount.

When the injection amount of the injector 14 is reduced, the combustion amount is reduced, so that the maximum in-cylinder pressure Pmax and dP / dθ are also reduced. On the other hand, in the second embodiment, as described above, knocking is predicted to occur when ignition is performed at the reference ignition timing in the high load region A, and the maximum in-cylinder pressure Pmax exceeds the reference pressure, or Even when the maximum value of dP / dθ is predicted to exceed the reference pressure increase rate, if the injection amount of the injector 14 is reduced by the reference reduction amount from the basic injection amount, the maximum in-cylinder pressure Pmax will be below the reference pressure. When the maximum value of dP / dθ is equal to or less than the reference pressure increase rate, the air-fuel mixture is ignited at the first ignition timing while reducing the injection amount of the injector 14 by the reference reduction amount from the basic injection amount. Even if the injection amount of the injector 14 is reduced by the reference reduction amount from the basic injection amount, the maximum in-cylinder pressure Pmax exceeds the reference pressure or the maximum value of dP / dθ becomes higher when the ignition timing is ignited at the first ignition timing. When the reference pressure increase rate is exceeded, the ignition timing is set as the third ignition timing.

Therefore, according to the second embodiment, it is possible to increase the chances of ignition at the first ignition timing while preventing adverse effects on the piston and the like and preventing combustion noise from exceeding a desired level, and knocking. It is possible to further improve the fuel efficiency performance while suppressing the noise.

(5) Third Embodiment Further, instead of the above-described embodiment, the knock avoidance control may be configured as shown in FIG. FIG. 8 is a flowchart of knock avoidance control according to the third embodiment. In the flowchart of FIG. 8, the steps excluding steps S31, S32, and S33 are the same as the steps having the same reference numerals in the first embodiment. Therefore, the description of the steps excluding steps S31, S32, and S33 will be omitted here.

In the second embodiment, if NO is determined in step S4 or step S5, the process proceeds to step S31.

In step S31, the PCM 100 predicts the maximum value of the in-cylinder pressure when the ignition timing is set to the first ignition timing and the effective compression ratio of the cylinder 2 is set to the compression ratio for ignition advance, and the predicted maximum in-cylinder pressure Pmax is obtained. Determine if the pressure is below the reference pressure. The compression ratio for ignition advance is set to a value smaller than the effective compression ratio (normal effective compression ratio) when step S33, which will be described later, is not performed. For example, when step S33 is not performed, the effective compression ratio is approximately a geometric compression ratio (15 in this embodiment). On the other hand, the compression ratio for ignition advance is set to a value of about 0.65 to 0.8 times the geometric compression ratio. In the present embodiment, the geometric compression ratio is 15, while the compression ratio for ignition advance is set to a value of 10 or more and 12 or less (for example, 11).

If the determination in step S31 is YES and the predicted maximum in-cylinder pressure Pmax is equal to or less than the reference pressure, the process proceeds to step S32. In step S32, the maximum value of dP / dθ is predicted when the ignition timing is set to the first ignition timing and the effective compression ratio of the cylinder is set to the compression ratio for ignition advance, and the predicted maximum value of dP / dθ is used as a reference. Determine if the pressure increase rate is less than or equal to.

When the determination in step S32 is YES and the predicted maximum value of dP / dθ is equal to or less than the reference pressure increase rate, the process proceeds to step S33. In step S33, the PCM 100 sets the ignition timing to the first ignition timing (ignition advance control is performed).

Further, in step S33, the effective compression ratio of the cylinder is changed to the compression ratio for ignition advance. Specifically, the PCM 100 changes the closing timing of the intake valve 11 by the intake valve variable mechanism 11a so that the effective compression ratio becomes the compression ratio for ignition advance. As described above, the effective compression ratio when Tep S33 is not carried out is larger than the compression ratio for ignition advance. Therefore, in step S33, the effective compression ratio is reduced as compared with the normal time. In the present embodiment, in the high load region A, the valve closing timing of the intake valve 11 is set to be on the retard side of the intake bottom dead center, and in step S33, the valve closing timing of the intake valve 11 is retarded. As a result, the effective compression ratio is reduced.

On the other hand, if the determination in step S31 is NO or the determination in step S32 is NO, the process proceeds to step S10 and the ignition timing is set to the third ignition timing. In the third embodiment, in step S10, the injection amount is the basic injection amount, and the effective compression ratio is the normal effective compression ratio.

When the effective compression ratio decreases, the in-cylinder pressure decreases, so that the maximum in-cylinder pressure Pmax and dP / dθ also decrease. On the other hand, as described above, in the third embodiment, knocking is predicted to occur when ignition is performed at the reference ignition timing in the high load region A, and the maximum in-cylinder pressure Pmax exceeds the reference pressure, or Even when the maximum value of dP / dθ is predicted to exceed the reference pressure increase rate, if the effective compression ratio is reduced to the compression ratio for ignition timing, the maximum in-cylinder pressure Pmax will be below the reference pressure and When the maximum value of dP / dθ is equal to or less than the reference pressure increase rate, the air-fuel mixture is ignited at the first ignition timing while reducing the effective compression ratio to the compression ratio for ignition advance. Even if the effective compression ratio is reduced to the compression ratio for ignition advance, the maximum in-cylinder pressure Pmax exceeds the reference pressure or the maximum value of dP / dθ increases the reference pressure when the ignition timing is ignited at the first ignition timing. When the rate is exceeded, the ignition timing is set as the third ignition timing.

Therefore, according to the third embodiment, it is possible to increase the chances of ignition at the first ignition timing while preventing adverse effects on the piston and the like and preventing combustion noise from exceeding a desired level. Therefore, the fuel efficiency can be further improved while suppressing knocking.

(6) Other modifications The geometric compression ratio of the cylinder is not limited to 15 or more. However, when the geometric compression ratio of the cylinder is 15 or more, knocking is likely to occur. Therefore, it is effective to apply the above embodiment to an engine having a cylinder geometric compression ratio of 15 or more.

Further, in the above-described embodiment, the case where knocking or not is predicted and the ignition timing is changed when knocking is predicted to occur has been described, but instead of this, whether or not knocking actually occurs or not. The ignition timing may be changed in the next combustion cycle when knocking occurs. Then, in this case, it may be configured to determine whether or not knocking has occurred based on the detected value of the knock sensor or the like.

Specifically, in the flowcharts of FIGS. 6 to 8, step S2 is omitted, and after step S3, a step of determining whether or not knocking has occurred is performed. Specifically, it is determined whether or not knocking has occurred in the combustion cycle one combustion cycle before. Then, when this determination is YES and knocking occurs, the process proceeds to step S4, and when this determination is NO and knocking does not occur, the process may proceed to step S11.

In this way, it is possible to reliably prevent knocking from occurring continuously.

Further, as described above, if the ignition advance control is performed, knocking can be basically avoided. However, when the combustion state of the air-fuel mixture deviates from the assumed state, knocking may occur even if the ignition advance control is performed. Therefore, if knocking occurs after the ignition advance control is performed, the ignition timing may be set to the third ignition timing in the next combustion cycle. Specifically, in the flowcharts of FIGS. 6 to 8, when it is determined that knocking has occurred after the ignition advance control is performed, the third ignition timing is set and then the process proceeds to step S10 to set the ignition timing to the third ignition. It may be set at the time.

In this way, it is possible to more reliably prevent knocking from occurring continuously.

Further, in the above embodiment, the case where the first ignition timing is set to the most retarded side of the advance angle side region R1 has been described, but the first ignition timing may be the time on the advance angle side of the MBT. , The specific timing is not limited to the above.

Further, in the flowcharts of FIGS. 6, 7, and 8, step S5 may be omitted.

Further, even if the injection amount of the injector 14 is reduced by the reference reduction amount from the basic injection amount by combining the second embodiment and the third embodiment, the maximum in-cylinder pressure Pmax is obtained when the ignition timing is ignited at the first ignition timing. Exceeds the reference pressure, or even when the maximum value of dP / dθ exceeds the reference pressure increase rate, if the effective compression ratio is reduced to the ignition advance compression ratio, the maximum in-cylinder pressure Pmax becomes less than or equal to the reference pressure. When the maximum value of dP / dθ is equal to or less than the reference pressure increase rate, the injection amount of the injector 14 is reduced from the basic injection amount by the reference reduction amount, and the effective compression ratio is reduced to the ignition advance compression ratio. The ignition timing may be set to the first ignition timing while reducing the ignition timing. Alternatively, even if the effective compression ratio is reduced to the compression ratio for ignition advance, the maximum in-cylinder pressure Pmax exceeds the reference pressure when the ignition timing is ignited at the first ignition timing, or the maximum value of dP / dθ increases the reference pressure. Even when the rate is exceeded, if the injection amount of the injector 14 is reduced by the reference reduction amount from the basic injection amount, the maximum in-cylinder pressure Pmax will be below the reference pressure, and the maximum value of dP / dθ will be below the reference pressure increase rate. In this case, the ignition timing should be set to the first ignition timing while reducing the injection amount of the injector 14 from the basic injection amount by the reference reduction amount and reducing the effective compression ratio to the compression ratio for ignition advance. It may be configured as.

Further, in the flowcharts of FIGS. 6 to 8, it is added a determination as to whether or not knocking occurs between steps S5 and S6, between steps S22 and S23, and between steps S32 and S33. May be good.

Specifically, in the flowcharts of FIGS. 6 to 8, when the determination in step S5 is YES, knocking occurs when the ignition timing is set to the first ignition timing before proceeding to step S6. May proceed to step S6 (the ignition timing is determined to be the first ignition timing) only when it is predicted that this determination is NO and knocking does not occur. Then, if the determination is YES and knocking is predicted to occur even if the ignition timing is set as the first ignition timing, the process may proceed to step S10 or steps S21 and S31.

Further, in the flowchart of FIG. 7, when the determination in step S22 is YES, the injection amount of the injector 14 is set to the amount reduced by the reference reduction amount from the basic injection amount before proceeding to step S23, and the ignition timing is set to the second ignition timing. It predicts whether knocking will occur when one ignition timing is set, and proceeds to step S23 only when this determination is NO and knocking does not occur (the ignition timing is determined to be the first ignition timing). Then, the injection amount of the injector 14 may be reduced by a reference reduction amount from the basic injection amount). Then, when the determination is YES and knocking is predicted to occur even if the injection amount of the injector 14 is reduced by the reference reduction amount from the basic injection amount and the ignition timing is set as the first ignition timing, the process is performed in step S10. It may be configured to be willing to determine the ignition timing at the third ignition timing.

Further, in the flowchart of FIG. 8, when the determination in step S32 is YES, the effective compression ratio is set to the ignition advance compression ratio and the ignition timing is set to the first ignition timing before proceeding to step S33. It predicts whether or not knocking will occur, and proceeds to step S23 only when this determination is NO and knocking does not occur (the ignition timing is determined as the first ignition timing, and the effective compression ratio is ignited. The compression ratio for advance angle may be used). If the determination is YES and knocking is predicted to occur even if the effective compression ratio is set to the ignition advance compression ratio and the ignition timing is set to the first ignition timing, the process proceeds to step S10 to set the ignition timing. It may be configured to be determined at the third ignition timing.

2 cylinders 6 combustion chamber 11a Intake valve variable mechanism (effective compression ratio changing means)
13 Spark plug (ignition means)
14 Injector (fuel supply means)
100 PCM (control means)

The present invention has been made based on this finding, and is an engine control device including a cylinder in which a combustion chamber is formed, and is a fuel supply means for supplying fuel containing gasoline into the combustion chamber. An ignition means for igniting a mixture of fuel and air supplied into the combustion chamber by the fuel supply means and a control means for controlling the ignition means are provided, and the control means has an engine load higher than a predetermined load. If knocking occurs when the engine is ignited at the reference ignition timing set on the retard side of the MBT, which is the ignition timing at which the engine torque is highest in the high load region, the advance angle side is higher than the reference ignition timing. In an engine control device that performs ignition advance control for causing the ignition means to ignite at the timing of the above , the control means maximizes the amount of increase in the in-cylinder pressure per unit crank angle when the ignition advance control is performed. When the value is predicted to exceed a preset reference pressure increase rate, the ignition means is ignited at a timing retarded from the reference ignition timing without performing the ignition advance control. It is characterized by that.

Further, when knocking occurs when ignition is performed at the reference ignition timing, when the ignition advance control is performed and the maximum value of the increase in the in-cylinder pressure per unit crank angle exceeds the reference pressure increase rate, the ignition advance is performed. It is configured to ignite the air-fuel mixture at the ignition timing on the retard side of the reference ignition timing without performing angle control. Therefore, although the fuel efficiency is lower than that when the ignition is performed at a timing on the advance side of the reference ignition timing, knocking can be prevented more reliably.

On the other hand, when it is predicted that the maximum value of the increase in the in-cylinder pressure per unit crank angle does not exceed the reference pressure increase rate, the ignition advance control is performed. As a result, it is possible to prevent the occurrence of a situation in which the amount of increase in the in-cylinder pressure per unit crank angle becomes equal to or greater than the reference pressure increase rate and the combustion noise exceeds a desired level.

Claims (7)

An engine control device equipped with a cylinder in which a combustion chamber is formed.
A fuel supply means for supplying fuel containing gasoline into the combustion chamber, and
An ignition means for igniting a mixture of fuel and air supplied into the combustion chamber by the fuel supply means, and an ignition means.
A control means for controlling the ignition means is provided.
Knocking occurs when the control means ignites at a reference ignition timing set on the retard side of the MBT, which is the ignition timing at which the engine torque is highest, in a high load region where the engine load is higher than a predetermined load. In the case of an engine, the engine control device comprises performing ignition advance control for causing the ignition means to ignite at a timing on the advance side of the reference ignition timing. In the engine control device according to claim 1,
When the control means predicts that the maximum value of the pressure in the combustion chamber exceeds a preset reference pressure when the ignition advance control is performed, the control means performs the ignition advance control and the combustion chamber. An engine control device, characterized in that the fuel supply means is controlled so that the amount of fuel supplied to the engine is reduced. In the engine control device according to claim 1 or 2.
Equipped with an effective compression ratio changing means that can change the effective compression ratio of the cylinder
When the control means predicts that the maximum value of the pressure in the combustion chamber exceeds a preset reference pressure when the ignition advance control is performed, the control means performs the ignition advance control and the high load. An engine control device for controlling the effective compression ratio changing means so that the effective compression ratio of the cylinder in the region is lower than when the ignition advance control is not performed. In the engine control device according to claim 1,
When the control means predicts that the maximum value of the pressure in the combustion chamber exceeds a preset reference pressure when the ignition advance control is performed, the control means does not perform the ignition advance control and the reference. An engine control device characterized in that the ignition means is ignited at a timing on the retard side of the ignition timing. In the engine control device according to any one of claims 1 to 4.
If knocking occurs after the ignition advance control is performed, or if knocking is predicted to occur even if the ignition advance control is performed, the control means is on the retard side of the reference ignition timing. An engine control device characterized in that the ignition means is ignited at a retard side ignition timing. In the engine control device according to any one of claims 1 to 5.
An engine control device characterized in that the geometric compression ratio of the cylinder is set to 15 or more. In the engine control device according to any one of claims 1 to 6.
In at least a part of the high load region, partial compression ignition combustion is performed in which a part of the air-fuel mixture is burned by ignition by the ignition means and then the other air-fuel mixture is burned by self-ignition. The engine control device.

Images