JP6835003B2 - Engine control - Google Patents

Description

The present invention comprises a cylinder in which a combustion chamber is formed, and a control device for an engine in which compression self-ignition combustion in which a mixture of gasoline-containing fuel and air self-ignites in the combustion chamber is executed under predetermined conditions. Regarding.

Conventionally, in the field of engines, various measures have been taken to prevent knocking from occurring. Specifically, under the condition that the engine load is high and the temperature in the combustion chamber is high, the mixture of fuel and air self-ignites and burns in the outer periphery of the combustion chamber separately from the main combustion, and a high pressure wave is generated and knocking occurs. That is, the cylinder and piston vibrate. 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 injects water into a combustion chamber to lower the temperature in the combustion chamber before the air-fuel mixture starts an oxidation reaction in the combustion chamber, thereby preventing knocking. ..

JP-A-2016-065461

In the configuration of Patent Document 1, water is supplied to the combustion chamber at a relatively early timing, that is, before the oxidation reaction starts in the combustion chamber. Therefore, this water lowers the temperature of the entire gas in the combustion chamber, lowers the compression end temperature, and lowers the engine torque (fuel efficiency deteriorates).

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 the occurrence of knocking while improving fuel efficiency.

In order to solve the above problems, the present invention includes a cylinder in which a combustion chamber is formed, and compression self-ignition combustion in which a mixture of fuel containing gasoline and air self-ignites in the combustion chamber assists ignition. with and a control device for an engine that runs under predetermined conditions, the knock determination means for the occurrence of knocking in the combustion chamber, is predicted based on the degree of occurrence of low-temperature oxidation reaction of the mixture in the combustion chamber The combustion chamber is provided with a fluid injection means for injecting fluid at an injection pressure of 30 MPa or more, and the fluid injection means has an engine load equal to or higher than a preset reference load and an engine rotation speed is preset. When a low-temperature oxidation reaction in which knocking is predicted to occur is detected by the knock determination means in a high-load, low-speed operation region lower than the reference speed, during the period during which the low-temperature oxidation reaction of the air-fuel mixture is occurring in the combustion chamber. Alternatively, an engine control device is provided, characterized in that a fluid is injected into the combustion chamber during the first half of a period during which a high-temperature oxidation reaction of the air-fuel mixture occurs in the combustion chamber (claim 1).

Knocking occurs when the air-fuel mixture existing on the outer periphery of the combustion chamber becomes locally hot and self-ignites and burns.

On the other hand, in this configuration, when the occurrence of knocking is predicted or detected, it is during the period during which the low temperature oxidation reaction of the air-fuel mixture is occurring in the combustion chamber or during the first half of the period during which the high temperature oxidation reaction of the air-fuel mixture is occurring. The fluid is injected into the combustion chamber at a high pressure of 30 MPa or more. Therefore, when the temperature in the combustion chamber becomes high enough to cause a low-temperature oxidation reaction in the combustion chamber, and it is highly possible that the air-fuel mixture is locally raised to the extent that self-ignition is possible in the outer periphery of the combustion chamber. , This air-fuel mixture can be agitated by spraying a fluid jetted at high pressure to reduce local high temperature parts and excessively concentrated parts of the air-fuel mixture. Therefore, for example, the occurrence of knocking can be suppressed without lowering the temperature of the entire air-fuel mixture in the combustion chamber due to the latent heat of vaporization of water or the like. From this, according to this configuration, it is possible to suppress the occurrence of knocking while improving the fuel efficiency performance. In particular, in this configuration, the fluid is injected into the combustion chamber by the end of the first half of the period during which the high temperature oxidation reaction occurs. Therefore, it is possible to more reliably agitate the air-fuel mixture before the self-ignition of the air-fuel mixture starts locally and suppress the occurrence of knocking.

In the above configuration, the fluid injection means injects fuel into the combustion chamber, performs main injection for injecting fuel for generating engine torque, and after the end of the main injection, by the main injection. Fuel is injected into the combustion chamber during the period during which the low temperature oxidation reaction of the fuel and air injected into the combustion chamber occurs or during the first half of the period during which the high temperature oxidation reaction of the air-fuel mixture occurs. Is preferable (claim 2).

According to this configuration, a fluid for suppressing knocking can be injected into the combustion chamber by utilizing a fuel injection means for performing fuel injection for obtaining engine torque. Therefore, the structure of the engine can be simplified as compared with the case where a fluid other than fuel is injected into the combustion chamber.

Here, if a large amount of fuel is injected in a state where a high-temperature oxidation reaction of the air-fuel mixture, that is, combustion occurs, the injected fuel may burn in a state where it is not sufficiently mixed with air, and soot may increase.

Therefore, in the above configuration, the weight of the fuel injected from the fluid injection means into the combustion chamber during the period during which the low temperature oxidation reaction is occurring or during the first half of the period during which the high temperature oxidation reaction is occurring is one combustion cycle. It is preferably 10% or less of the total weight of the fuel supplied to the combustion chamber (claim 3).

According to this configuration, it is possible to suppress the occurrence of knocking while suppressing the increase of soot.

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. 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, the occurrence of knocking can be effectively suppressed (claim 4).

As described above, according to the engine control device of the present invention, it is possible to suppress the occurrence of knocking while improving the fuel efficiency performance.

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 figure which showed an example of the injection timing, the ignition timing, and the heat generation rate when knock avoidance control was not performed in a high load low speed region. It is a figure which showed an example of the injection timing, the ignition timing, and the heat generation rate when knock avoidance control was not performed in a high load high speed region. It is a flowchart which showed the flow of knock avoidance control. It is a figure for demonstrating the method of determining whether or not knocking occurs in a high load low speed region. It is a figure for demonstrating the occurrence process of knocking. It is a figure which showed an example of the injection timing, the ignition timing, and the heat generation rate when knock avoidance control was performed in a high load low speed region. It is a graph which showed the relationship between the in-cylinder pressure at the time of knock determination and knock strength. It is a graph which showed the change of the cylinder pressure near the compression top dead center in a high load high speed region. It is a figure which showed the relationship between the timing of additional injection, the engine torque, the combustion center of gravity timing, and the generated smoke in a high load low speed region. It is a figure which compared and showed the waveform of the heat generation rate when the additional injection was not performed and when it was performed in the high load low speed region.

(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 body 1, an intake passage 20 for introducing combustion air into the engine body 1, and an exhaust passage 30 for discharging the exhaust generated by the engine 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. A cavity 19 is formed on the crown surface of the piston 5 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 25 or less (for example, about 17).

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 cylinder head 4 is provided with an injector (fluid injection 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 (specifically, a hollow 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 toward the crown surface of the piston 5. It is configured to inject fuel. The taper angle (spray 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 increased to 30 MPa or more in the engine high load region where knocking is likely to occur, and fuel is injected from the injector 14 at a high pressure in the engine high load region. The injection pressure is preferably increased up to about 70 MPa. In this case, the fuel is injected at an injection pressure in the range of 50 MPa to 70 Ma in the high load region of the engine.

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 tip of the spark plug 13 is located near the center of the ceiling surface of the combustion chamber 6 and is arranged so as to face 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 engine speed. Further, an air flow sensor SN2 for detecting the amount of air sucked into each cylinder 2 through the intake passage 20 is provided. Further, the cylinder head 4 is provided with an in-cylinder pressure sensor SN3 that detects the pressure in the combustion chamber 6. One in-cylinder pressure sensor SN3 is provided for each cylinder 2. Further, the vehicle is provided with an accelerator opening sensor SN4 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 PCM 100 executes various calculations based on the input signals from the sensors SN1 to SN4 and controls each part of the engine such as the spark plug 13, the injector 14, the throttle valve 22, and the EGR valve 42.

(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. The operating area of the engine is divided into two areas according to the engine speed and the engine load. In the present embodiment, a low load region B in which the engine load is less than the preset reference load Tq1 and knocking is unlikely to occur, and a high load region A in which the engine load is equal to or more than the reference load Tq1 and knocking is likely to occur are set. There is. In the high load region A, knock avoidance control 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 present embodiment, 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 carried out. In this 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 and 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.

FIG. 4 is a diagram showing an example of fuel injection timing, ignition timing, and heat generation rate in the high load low speed region A1 when the basic control is executed (when the knock avoidance control is not executed). As shown in FIG. 4, for example, in the high load low speed region A1, fuel is injected from the injector 14 in two steps in the latter half of the intake stroke. That is, two fuel injections Q1_a and Q1_b are performed in the latter half of the intake stroke. Then, at the ignition timing CA2 set near the compression top dead center (at the compression top dead center in the example of FIG. 4), the spark plug 13 ignites the air-fuel mixture. The two fuel injections Q1_a and Q1_b are the main injections for achieving the required engine torque, that is, the main injections for injecting fuel for generating the engine torque, and the injection amounts Q1_a of the two fuel injections. , Q1_b is basically an amount corresponding to the required value of the engine torque. In the present specification, the above-mentioned latter half of the XX process refers to the first half and the second half when the implementation period (the period at the crank angle) of the XX process is evenly divided into two.

In the example of the heat generation rate shown in FIG. 4, the air-fuel mixture undergoes a low-temperature oxidation reaction and then a high-temperature oxidation reaction. The low-temperature oxidation reaction is a reaction that involves a slight amount of heat generation exceeding the cooling loss, and the high-temperature oxidation reaction is a reaction that emits high thermal energy while generating a flame.

Specifically, in the example shown in FIG. 4, the heat generation rate rises at the crank angle CA1. However, since it is still in the low temperature oxidation reaction stage, the heat generation rate hardly increases, and at the crank angle CA3 a while after the ignition energy is applied at the ignition timing CA2 (TDC: compression top dead center). As the high-temperature oxidation reaction of the air-fuel mixture starts, the heat generation rate increases toward a higher value after the crank angle CA3.

FIG. 5 is a diagram showing an example of fuel injection timing, ignition timing, and heat generation rate in the high load high speed region A2 when basic control is performed. For example, in the high load high speed region A2, the fuel injection Q1 is performed only once in the latter half of the intake stroke. Then, at the ignition timing CA12 set near the compression top dead center (at the compression top dead center in the example of FIG. 5), the air-fuel mixture is ignited by the spark plug 13. The fuel injection Q1 is the main injection for realizing the required engine torque, and the injection amount is basically an amount corresponding to the required value of the engine torque.

In FIG. 5, the heat generation rate dQ rises relatively rapidly from the ignition timing CA12 and rises as it is, and no clear low-temperature oxidation reaction is observed. As described above, in the high-load high-speed region A2, no low-temperature oxidation reaction occurs, or no clear low-temperature oxidation reaction is observed.

This is because when the engine speed is high, the rising speed of the piston 5 and the pressure rising speed in the combustion chamber 6 are high, so that the time during which the low temperature oxidation reaction of the main air-fuel mixture in the combustion chamber 6 occurs becomes very short, or It is considered that the main air-fuel mixture in the combustion chamber 6 is rapidly heated to start the high-temperature oxidation reaction with almost no low-temperature oxidation reaction.

(2-3) Knock avoidance control Next, the knock avoidance control performed in the high load region A will be described with reference to the flowchart of FIG. Each step of this flowchart is executed when the engine is running in the high load region A. 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 SN4.

In step S1, the PCM 100 first reads the value of the in-cylinder pressure sensor SN3. Next, in step S2, the PCM 100 calculates the heat generation rate dQ using the in-cylinder pressure detected by the in-cylinder pressure sensor SN3. As a method for calculating the heat generation rate dQ, a conventionally used method can be adopted, and the description thereof is omitted here.

Next, in step S3, the PCM 100 determines whether the engine is operating in the high load low speed region A1.

If the determination in step S3 is YES and the engine is operating in the high load low speed region A1, the process proceeds to step S4.

In step S4, the PCM 100 determines (predicts) whether or not knocking occurs.

The inventors of the present application have found that knocking is likely to occur when a low-temperature oxidation reaction occurs in the high-load low-speed region A1. Therefore, in step S4, it is determined whether or not knocking occurs depending on whether or not the low temperature oxidation reaction has occurred.

In the present embodiment, after the heat generation rate dQ exceeds 0, the time during which the value of the heat generation rate dQ becomes equal to or less than the preset low temperature oxidation determination heat generation rate dQ_j is equal to or longer than the preset low temperature oxidation determination time t_j. If it continues, it is determined that a low temperature oxidation reaction has occurred. For example, in the example shown in FIG. 7, after the heat generation rate dQ exceeds 0 at the crank angle CA21, the heat generation rate dQ is continuously determined to be low temperature oxidation until the crank angle CA23 is reached after the low temperature oxidation determination time t_j. The heat generation rate is dQ_j or less. From this, it is determined that the low temperature oxidation reaction has occurred at the determination time elapsed angle CAx after the low temperature oxidation determination time t_j from the crank angle CA21. The specific method for determining whether or not the low temperature oxidation reaction has occurred is not limited to this. For example, it may be determined that the low temperature oxidation reaction has occurred when the heat generation rate dQ is at least a predetermined value at a preset predetermined crank angle at which the low temperature oxidation reaction is likely to occur.

Here, it is considered that knocking is likely to occur when a low temperature oxidation reaction occurs in the high load low speed region A1 for the following reason.

FIG. 8 is a schematic cross-sectional view of the combustion chamber 6 schematically showing the inside of the combustion chamber 6 near the compression top dead center when knocking occurs. Each line in FIG. 8 is a line connecting points having the same temperature.

There is no escape place for the air-fuel mixture near the outer peripheral edge of the combustion chamber 6. Therefore, due to the compression action of the piston 5, the flame generated in the center of the combustion chamber 6 propagates toward the outer peripheral side as shown by the arrow in FIG. 8, so that in the vicinity of the outer peripheral edge of the combustion chamber 6, The air-fuel mixture is locally compressed. As a result, a high-temperature / high-pressure air-fuel mixture is locally formed at a plurality of locations P in the vicinity of the outer peripheral edge of the combustion chamber 6. Knocking occurs when each of these air-fuel mixture ignites individually.

Here, the time when the low temperature oxidation reaction occurs in the combustion chamber 6 is when at least one of the temperature and the pressure in the combustion chamber 6 is high. Therefore, when a low-temperature oxidation reaction occurs in the combustion chamber 6, the air-fuel mixture near the outer peripheral edge of the combustion chamber 6 is likely to self-ignite. Therefore, when a low-temperature oxidation reaction occurs in the high-load low-speed region A1, knocking is likely to occur. When a low-temperature oxidation reaction occurs, the temperature inside the combustion chamber 6 is further raised by the heat of reaction. Therefore, when a low-temperature oxidation reaction occurs, knocking is likely to occur.

Returning to the flowchart of FIG. 6, if the determination in step S4 is YES and knocking is predicted to occur in the high load low speed region A1, the process proceeds to step S5.

In step S5, the PCM 100 performs additional injection Q2 and injects fuel into the combustion chamber 6 by the injector 14. Step S5 is executed as soon as the determination in step S4 is YES. That is, the PCM 100 injects into the injector 14 immediately after the crank angle CAx (hereinafter, appropriately referred to as the determination time elapsed angle CAx) in which the low temperature oxidation determination time t_j elapses for the time when the heat generation rate dQ becomes the low temperature oxidation determination heat generation rate dQ_j or less. An start command is issued and additional injection Q2 is carried out. For example, additional injection Q2 is performed at about 10 ° CA after the compression top dead center.

Here, at the determination time elapsed angle CAx, the heat generation rate dQ is still equal to or less than the low temperature oxidation determination heat generation rate dQ_j, and the low temperature oxidation reaction is in progress. Therefore, the additional injection Q2 is carried out during the low temperature oxidation reaction. Alternatively, if the low temperature oxidation reaction ends immediately after the determination time elapsed angle CAx and there is a drive delay of the injector 14, the additional injection Q2 is performed immediately after the end of the low temperature oxidation reaction.

As described above, when it is determined (predicted) that knocking occurs in the high load low speed region A1, as shown in FIG. 9, the main injection Q1 consisting of two fuel injections Q1_a and Q1_b to be performed in the latter half of the intake stroke is performed. In addition, during the low temperature oxidation reaction or immediately after the end of the low temperature oxidation reaction, additional injection Q2 for further injecting fuel into the combustion chamber 6 is performed.

The amount of the additional injection Q2 is set sufficiently lower than that of the main injection Q1. In the present embodiment, the amount of the additional injection Q2 is 10% or less of the total amount of the fuel injected into the combustion chamber 6 in one combustion cycle, that is, the total amount of the injection amount of the main injection Q1 and the injection amount of the additional injection Q2. The amount is set. For example, the amount of additional injection Q2 is set to about 5% of the total amount of fuel.

Returning to FIG. 6, when the determination in step S4 is NO and knocking is not predicted to occur, step S20 is performed. In step S20, the PCM 100 does not carry out the additional injection Q2, but only the normal main injection Q1.

Returning to step S3, if the determination in step S3 is NO and the engine is operating in the high load high speed region A2, the process proceeds to step S10. Also in step S10, the PCM 100 determines (predicts) whether or not knocking occurs.

However, as described above, when the engine speed is increased, the low temperature oxidation reaction does not occur or a clear low temperature oxidation reaction cannot be observed. Therefore, in the high-load high-speed region A2, it is difficult to determine whether or not knocking occurs depending on whether or not the low-temperature oxidation reaction has occurred.

Therefore, in step S10, instead of the determination method of step S4, it is determined whether or not knocking occurs based on the in-cylinder pressure near the compression top dead center.

In step S10, the PCM 100 determines that knocking occurs when the in-cylinder pressure at the knock determination timing set near the compression top dead center is equal to or higher than the preset knock determination pressure. In the present embodiment, a plurality of periods near the compression top dead center are set as knock determination periods, and the in-cylinder pressures detected at these plurality of periods are averaged, and this average value and the knock determination pressure are compared. For example, the knock determination time is set to a period from the compression top dead center to 9 ° CA after the compression top dead center, and the average value of the in-cylinder pressure during this period is compared with the knock determination pressure.

FIG. 10 shows the relationship between the in-cylinder pressure at the knock determination time (specifically, the average value of the in-cylinder pressure from the compression top dead center to 9 ° CA after the compression top dead center) and the knock strength in a plurality of combustion cycles. It is a graph shown. The knock intensity shown in FIG. 10 is the maximum value of the amplitude of the waveform having a predetermined frequency or higher included in the in-cylinder pressure waveform.

As shown in this graph, when the in-cylinder pressure near the compression top dead center (knock determination timing) becomes high, the knock strength becomes larger than 0, the frequency of knocking increases, and the knock strength becomes high. From this, it is possible to appropriately determine whether or not knocking occurs by a determination method in which knocking occurs when the in-cylinder pressure near the compression top dead center (knock determination timing) is equal to or higher than a predetermined value.

As described above, in the present embodiment, the in-cylinder pressure sensor SN3 and the PCM100 function as knock determination means for predicting whether or not knocking occurs.

Returning to FIG. 6, when the determination in step S10 is NO and knocking is not predicted to occur, step S20 is performed. In step S20, the PCM 100 does not carry out the additional injection Q2, but only the normal main injection Q1.

On the other hand, if the determination in step S10 is YES, the process proceeds to step S11. In step S11, the PCM 100 determines whether or not knocking has occurred in the state where the additional injection Q2 is performed in the previous combustion cycle.

In the present embodiment, the PCM 100 determines whether or not knocking has occurred based on the in-cylinder pressure detected by the in-cylinder pressure sensor SN3. The method for determining whether or not knocking has occurred using the in-cylinder pressure sensor SN3 is not particularly limited, but is determined by, for example, the following method. The output value of the in-cylinder pressure sensor SN3 is applied to a high-pass filter. Then, the maximum value of the amplitude of the waveform output from the high-pass filter, that is, the waveform of the in-cylinder pressure having a predetermined frequency or higher is extracted. Then, if this maximum value is equal to or greater than a predetermined value, it is determined that knocking has occurred, and if this maximum value is less than a predetermined value, it is determined that knocking has not occurred. Instead of this determination, a knocking sensor may be attached to a cylinder block or the like to detect whether or not knocking has occurred by the knocking sensor.

When the determination in step S11 is NO and the additional injection Q2 is not performed in the previous combustion cycle, or when the additional injection Q2 is performed in the previous combustion cycle and knocking does not occur. , Step S12.

In step S12, the PCM 100 performs additional injection Q2. That is, after the main injection Q1, the fuel is further injected into the combustion chamber 6.

In step S12, after the oxidation reaction occurs in the combustion chamber 6, additional injection is performed after a preset standby angle. Specifically, the PCM 100 determines that the oxidation reaction has occurred when the calculated heat generation rate dQ exceeds 0, and the time after the standby angle from the time when the heat generation rate dQ exceeds 0 is the time when the additional injection Q2 is performed. Set as (injection timing). Then, the PCM 100 injects fuel from the injector 14 into the combustion chamber 6 at the set implementation time of the additional injection Q2.

The standby angle is an angle that is half of the combustion period and is set to the following value, which is an angle obtained in advance by an experiment or the like. Here, as described above, the low temperature oxidation reaction hardly occurs in the high load high speed region A2, and the combustion period is almost the same as the period in which the high temperature oxidation reaction occurs. From this, in the high-load high-speed region A2, as shown by the broken line in FIG. 5, the additional injection Q2 was evenly divided into two in the first half of the period in which the high-temperature oxidation reaction occurred (the period in which the high-temperature oxidation reaction occurred). It will be carried out during the first half of the time.

Specifically, the combustion period when the additional injection is not performed is detected by an experiment or the like, and half the period is obtained. Then, an angle of half or less of the obtained combustion period is set as a standby angle and stored in the PCM 100. Further, in the present embodiment, the standby angle is set to be equal to or less than the period from the start of combustion to the time of the center of gravity of combustion. The combustion center of gravity period is the period (angle) at which 50% of the total amount of heat generated during one combustion cycle is generated. For example, the standby angle is an angle from the start of heat generation to the time when heat generation of about 30% of the total amount of heat generation generated in one combustion cycle is generated, and is set to about 15 ° CA. There is.

The injection amount of the additional injection Q2 carried out in step S12 is 10% or less of the total amount of fuel injected into the combustion chamber 6 in one combustion cycle, similarly to the injection amount of the additional injection Q2 carried out in step S5. About 5%).

On the other hand, if the determination in step S11 is YES, that is, if knocking occurs even though the additional injection Q2 was performed in the previous combustion cycle, the process proceeds to step S13.

In step S13, the additional injection Q2 is stopped, and the air-fuel ratio in the combustion chamber 6 is made leaner than the theoretical air-fuel ratio (larger than the theoretical air-fuel ratio). That is, except when step S13 is performed, the air-fuel ratio in the combustion chamber 6 is richer than the theoretical air-fuel ratio or the theoretical air-fuel ratio (a value smaller than the theoretical air-fuel ratio). Specifically, except when step S13 is performed, the injection amount of the main injection Q1 is set to an amount such that the air-fuel ratio in the combustion chamber 6 becomes the stoichiometric air-fuel ratio, and the basic control is performed. During normal operation (when additional injection Q2 is not implemented), the air-fuel ratio in the combustion chamber 6 is the stoichiometric air-fuel ratio, and when additional injection Q2 is implemented, the air-fuel ratio in the combustion chamber 6 is the stoichiometric air-fuel ratio. Become richer than.

On the other hand, in step S13, the injection amount of the main injection Q1 is set so that the air-fuel ratio in the combustion chamber 6 is leaner than the stoichiometric air-fuel ratio. In the present embodiment, the amount of air corresponding to the required engine torque is calculated, and the amount of fuel whose air-fuel ratio is leaner than the stoichiometric air-fuel ratio with respect to this amount of air is set as the injection amount of the main injection Q1. Here, as described above, during normal operation, the injection amount of the main injection Q1 is set so that the air-fuel ratio becomes richer than the stoichiometric air-fuel ratio or the stoichiometric air-fuel ratio with respect to the air amount corresponding to the engine torque. There is. Therefore, in step S13, the injection amount of the main injection Q1 is reduced as compared with the normal operation.

As described above, in the high load high speed region A2, if the pressure near the compression top dead center (knock determination timing) is equal to or higher than the knock determination pressure, it is determined that knocking occurs. Then, when knocking is predicted to occur, the additional injection Q2 is first performed. At this time, in the high-load high-speed region A2, additional injection is performed after a preset standby time (after heat generation occurs) after combustion starts in the combustion chamber 6 and before the combustion center of gravity. Q2 will be implemented.

Further, in the high load high speed region A2, when knocking occurs even though the additional injection Q2 is performed, the additional injection Q2 is stopped and the air-fuel ratio in the combustion chamber 6 is made leaner than the stoichiometric air-fuel ratio.

(3) Action, etc. FIG. 11 is a graph showing the change in the in-cylinder pressure near the compression top dead center in the high load high speed region A2. The solid line in FIG. 11 is the change in the in-cylinder pressure when the additional injection Q2 is performed. The broken line in FIG. 11 is the change in the in-cylinder pressure when the additional injection Q2 is not performed. The operating conditions when the change in the in-cylinder pressure shown by the solid line occurs and the operating conditions when the change in the in-cylinder pressure shown by the broken line occurs are the same except whether or not the additional injection Q2 is performed.

As shown in FIG. 11, when the additional injection Q2 is performed, the amplitude of the high-frequency component of the in-cylinder pressure is smaller than that when the additional injection is not performed, and the knock strength is suppressed to be small. .. In this way, the knock strength can be reduced by carrying out the additional injection Q2.

FIG. 12 is a diagram showing the relationship between the execution timing of the additional injection Q2, the combustion center of gravity timing, the engine torque, and the generated smoke under the predetermined operating conditions of the high load low speed region A1. Each point in this figure shows the experimental results when the knock strengths are the same (the knock strengths are about 0 and knocking does not occur), and the knock strengths are the same. The ignition timing is adjusted so as to. The base values shown in the graphs of FIG. 12 are the combustion center of gravity timing and engine torque when the ignition timing is adjusted so that the knock strength is the same as that of each point in FIG. 12 without performing the additional injection Q2. The value of the smoke generated. The base value is the result of injecting the fuel in the sum of the injection amount of the main injection Q1 and the injection amount of the additional injection Q2 when the additional injection Q2 is performed by the main injection Q1.

13 shows the heat generation rate dQ (broken line) when the result of the base value shown in FIG. 12 is obtained, and the heat generation rate dQ (solid line) when the additional injection Q2 is performed at the crank angle CAb in FIG. It is a figure which compared and showed.

As shown in FIGS. 12 and 13, when the additional injection Q2 is performed, the combustion center of gravity timing is on the advance side and the engine torque is higher than when the additional injection Q2 is not performed. In this way, when the knock strength is set to the same level, when the additional injection Q2 is performed, it is possible to obtain a higher engine torque than when the additional injection Q2 is not performed. Specifically, when additional injection is performed, knocking is suppressed, so that the ignition timing can be advanced and a high engine torque can be obtained.

As described above, in the present embodiment, the additional injection Q2 that injects fuel at a high pressure of 30 Mpa or more when knocking is predicted to occur in the high load low speed region A1 and the high load high speed region A2 is carried out in these regions. In A1 and A2, the knock strength can be reduced, and the engine torque can be increased while preventing the occurrence of knocking, that is, the fuel efficiency can be improved.

The above effect is obtained because the high-temperature / high-pressure air-fuel mixture that causes knocking is agitated by a high-pressure, high-penetration spray that is a spray of additionally injected fuel.

That is, when fuel is injected at a high pressure of 30 MPa or more, a strong flow is generated in the combustion chamber 6 by this fuel spray. As shown in FIG. 8, the air-fuel mixture that is the core of knocking formed near the outer peripheral edge of the combustion chamber 6 is agitated by this flow, and the high-temperature / high-pressure air-fuel mixture that is the core of knocking is mixed with the surrounding air-fuel mixture. Mix and cool. Further, by stirring the air-fuel mixture, the portion having a high fuel concentration (excessive portion of the air-fuel mixture) can be extinguished locally. This prevents the high-temperature / high-pressure air-fuel mixture from self-igniting and causing knocking. That is, the knocking nucleus can be extinguished by the stirring, and the occurrence of knocking can be avoided.

Further, as described above, in the high load low speed region A1, a low temperature oxidation reaction occurs when the combustion chamber 6 is at high temperature and high pressure, and knocking is caused by the high temperature and high pressure of the combustion chamber 6 in this way. A high-temperature / high-pressure mixture, that is, a knocking core, is formed. In addition, the temperature of the air-fuel mixture is further increased by the heat of reaction of the low-temperature oxidation reaction. Therefore, knocking nuclei are likely to be formed during the low temperature oxidation reaction. On the other hand, in the high-load high-speed region A2 where the low-temperature oxidation reaction does not occur or the time of the low-temperature oxidation reaction is very short, the temperature inside the combustion chamber 6 rises with the start of the high-temperature oxidation reaction, causing knocking. Air-fuel mixture, that is, a knocking core is formed. On the other hand, in the present embodiment, the additional injection is carried out during the period during which the low temperature oxidation reaction is occurring or during the first half of the period during which the high temperature oxidation reaction is occurring. Therefore, the knocking nuclei can be agitated during or immediately after the formation of the knocking nuclei, and the knocking nuclei can be effectively extinguished.

Then, in the present embodiment, knocking is prevented by the action of stirring by the additional injection Q2 in this way. Therefore, the temperature drop of the entire combustion chamber 6 can be suppressed as compared with the case where water or excess fuel is supplied to the combustion chamber 6 in order to lower the temperature of the entire combustion chamber 6 in order to prevent knocking. That is, when the temperature of the entire combustion chamber 6 is lowered to prevent knocking, a large amount of water or fuel is required to realize this temperature drop. On the other hand, in the present embodiment, knocking is prevented by stirring the high-temperature / high-pressure mixture that is the core of knocking by high-pressure fuel spray as described above, so that the temperature of the entire combustion chamber 6 is increased. A large amount of fuel is not required, and the amount of additional fuel to be injected may be small. Therefore, according to the present embodiment, knocking can be prevented while suppressing a decrease in temperature of the entire combustion chamber 6 and a decrease in engine torque accompanying the decrease.

Here, the crank angle CA_0 in FIG. 12 is substantially the same as the time when the low temperature oxidation reaction starts. As shown in FIG. 12, when the execution time of the additional injection Q2 is retarded from the time CA_0 when the low temperature oxidation reaction starts, the engine torque increases accordingly. However, when the execution time of the additional injection Q2 exceeds the predetermined time, the engine torque decreases.

The engine torque increases as the timing of the additional injection Q2 is delayed from the time when the low temperature oxidation reaction starts, and the core of knocking is clear after a while after the low temperature oxidation reaction starts. This is because it is formed in and can be effectively extinguished. The reason why the engine torque decreases when the additional injection Q2 is executed after the predetermined time is that the fuel is injected in a state where the high temperature oxidation reaction occurs when the additional injection Q2 is executed later. This is because the injected fuel does not mix well with the air and the fuel does not burn properly. This can be seen from the fact that, as shown in FIG. 12, the generation of smoke increases as the execution time of the additional injection Q2 is delayed.

On the other hand, in the present embodiment, as described above, during the period during which the low temperature oxidation reaction is occurring, or the first half of the period during which the high temperature oxidation reaction is occurring, that is, the first half of the period during which the high temperature oxidation reaction is occurring. Since the additional injection is carried out at a relatively early stage until the end of the process, it is possible to secure a high engine torque and suppress knocking while suppressing an increase in smoke.

In particular, in the present embodiment, in the high load low speed region A1, additional injection is performed during the low temperature oxidation reaction or immediately after the low temperature oxidation reaction, so that the increase in smoke is more reliably suppressed and the engine torque is high. Knocking can be suppressed while ensuring.

Further, in the present embodiment, when knocking occurs even though the additional injection Q2 is performed in the high load high speed region A2, the additional injection Q2 is stopped and the air-fuel ratio of the air-fuel mixture is leaner than the stoichiometric air-fuel ratio. I have to. Therefore, it is possible to more reliably prevent knocking from occurring continuously, which adversely affects the piston and the like.

(4) Modification Example In the above embodiment, the case where the fluid injected into the combustion chamber 6 in the additional injection Q2 is used as fuel has been described, but this fluid does not have to be fuel. For example, it may be a part of water or exhaust gas. However, if fuel is used as the fluid, additional injection can be performed using the injector 14. Therefore, it is not necessary to separately provide a device for injecting the fluid, and the structure can be simplified.

In the above embodiment, a case where the injection amount of the additional injection Q2 (the amount of fuel supplied to the combustion chamber 6 by the additional injection) is 10% or less of the total amount of fuel supplied to the combustion chamber 6 in one cycle will be described. However, the injection amount of the additional injection may be larger than 10%.

However, as described above, if the amount of fuel additionally injected increases, the temperature inside the combustion chamber 6 may drop significantly as the fuel vaporizes. Further, as described above, when a large amount of fuel is added to the air-fuel mixture in which the oxidation reaction is occurring, the mixture of the fuel and air becomes insufficient and smoke is likely to occur. Therefore, the amount of fuel to be additionally injected is preferably set as described above.

Further, 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 this engine.

Further, in the above embodiment, the case where the additional injection is performed during the period in which the low temperature oxidation reaction is occurring or immediately after the low temperature oxidation reaction in the high load low speed region A1 has been described, but the additional injection causes the low temperature oxidation reaction. It may be carried out during the period or in the first half of the period during which the high temperature oxidation reaction is occurring. Therefore, even in the high-load low-speed region A1, even if the additional injection is performed at a time included in the first half of the period in which the high-temperature oxidation reaction occurs after a predetermined angle set in advance after the start of the high-temperature oxidation reaction. Good. However, as described above, since the amount of smoke generated increases when the timing of the additional injection is delayed, it is preferable that the additional injection is carried out at a relatively early time after the start of the low temperature oxidation reaction.

Further, in the above embodiment, the case where it is determined (predicted) that knocking occurs after the low temperature oxidation reaction occurs in the high load low speed region A1 has been described, but also in the high load low speed region A1, the high load high speed region A2 Similarly, it may be determined (predicted) whether or not knocking occurs based on the pressure near the compression top dead center.

Further, in the above-described embodiment, the case where knocking or not is predicted and the additional injection is performed when knocking is predicted to occur has been described, but instead of this, whether or not knocking actually occurs or not. This may be detected and additional injection may be performed 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.

1 Engine body 2 Cylinder 6 Combustion chamber 13 Spark plug 14 Injector (fluid injection means)
100 PCM

Claims (4)

In an engine having a cylinder in which a combustion chamber is formed, compression self-ignition combustion in which a mixture of fuel containing gasoline and air self-ignites in the combustion chamber is executed under predetermined conditions with ignition assist. It ’s a control device,
A knock determination means for predicting the occurrence of knocking in the combustion chamber based on the degree of occurrence of a low-temperature oxidation reaction of the air-fuel mixture in the combustion chamber.
A fluid injection means for injecting a fluid at an injection pressure of 30 MPa or more is provided in the combustion chamber.
In the fluid injection means, knocking is predicted by the knock determination means in a high load and low speed operating region where the engine load is equal to or higher than the preset reference load and the engine speed is lower than the preset reference speed. When the low temperature oxidation reaction is detected, the combustion chamber is in the period during which the low temperature oxidation reaction of the air-fuel mixture is occurring in the combustion chamber or in the first half of the period during which the high temperature oxidation reaction of the air-fuel mixture is occurring in the combustion chamber. An engine control device characterized by injecting fluid into an engine. In the engine control device according to claim 1,
The fluid injection means
Fuel is injected into the combustion chamber.
In addition to carrying out the main injection that injects fuel to generate engine torque
After the end of the main injection, during the period during which the low temperature oxidation reaction of the fuel and air injected into the combustion chamber by the main injection occurs or the first half of the period during which the high temperature oxidation reaction of the air-fuel mixture occurs. An engine control device for injecting fuel into the combustion chamber. In the engine control device according to claim 2.
The weight of the fuel injected from the fluid injection means into the combustion chamber during the period during which the low temperature oxidation reaction is occurring or the first half of the period during which the high temperature oxidation reaction is occurring is supplied to the combustion chamber in one combustion cycle. An engine control device characterized in that it is 10% or less of the total weight of the fuel. In the engine control device according to any one of claims 1 to 3.
An engine control device characterized in that the geometric compression ratio of the cylinder is set to 15 or more.