JP7124516B2 - Combustion control device for internal combustion engine - Google Patents

Description

The present invention relates to a combustion control device for an internal combustion engine.

In Patent Document 1, the ideal amount of heat release is calculated based on the fuel injection amount, and the actual amount of heat release in the cylinder is calculated based on the actual measurement value of an in-cylinder pressure sensor installed in the engine cylinder. It is described that ignition retardation control is performed when the heat release amount is lower than a predetermined ratio of the ideal heat release amount, and ignition is stopped when the heat release amount is higher.

JP 2011-208540 A

However, in Patent Document 1, since the ideal amount of heat release is calculated based on the fuel injection amount, when there is a large amount of residual fuel (unburned gas), etc., Even if a margin is given to the comparison threshold, an erroneous determination is made and combustion is stopped.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a combustion control apparatus for an internal combustion engine that can determine abnormal combustion and stabilize combustion.

In order to solve the above-mentioned problems, the present invention provides a cylinder pressure sensor for detecting the pressure in a cylinder of an internal combustion engine, a heat release rate is calculated from the cylinder pressure detected by the cylinder pressure sensor, and based on the change in the heat release rate. and a control unit for determining abnormal combustion of the internal combustion engine, wherein CI combustion occurs after SI combustion due to a spark plug occurs, wherein the control unit determines the rate of heat release. The start point of the CI region where the heat release rate due to the CI combustion becomes zero is calculated from the maximum slope value, the time when the slope reaches the maximum value, and the value of the heat release rate at that time, and the CI Abnormal combustion in the internal combustion engine is determined based on the time between the starting point of the region and the ignition timing of the SI combustion .

Thus, according to the present invention, abnormal combustion can be determined and combustion can be stabilized.

FIG. 1 is a schematic configuration diagram of a combustion control system for an internal combustion engine according to one embodiment of the present invention. FIG. 2 is a diagram showing an example of starting points of the CI region of the combustion control system for an internal combustion engine according to one embodiment of the present invention. FIG. 3 is a diagram showing changes in the heat release rate when pre-ignition occurs in the combustion control system for an internal combustion engine according to one embodiment of the present invention. FIG. 4 is a flow chart showing the procedure of combustion stabilization processing of the combustion control system for an internal combustion engine according to one embodiment of the present invention.

A combustion control apparatus for an internal combustion engine according to an embodiment of the present invention calculates a heat release rate from a cylinder pressure sensor that detects the pressure in a cylinder of an internal combustion engine, and the cylinder pressure detected by the cylinder pressure sensor, and calculates the heat release rate. and a control unit that determines abnormal combustion of the internal combustion engine based on the change in the rate.

As a result, the combustion control apparatus for an internal combustion engine according to the embodiment of the present invention can determine abnormal combustion and stabilize combustion.

A combustion control device for an internal combustion engine according to an embodiment of the present invention will now be described in detail with reference to the drawings.

In FIG. 1, a vehicle 1 equipped with a combustion control system for an internal combustion engine according to an embodiment of the present invention includes an internal combustion engine type engine 2 and an ECU (Electronic Control Unit) 3 as a control section. be.

A cylinder 5 is formed in the engine 2 as a cylinder. A cylinder 5 accommodates a piston 6 capable of reciprocating vertically within the cylinder 5 . A combustion chamber 7 is provided above the cylinder 5 .

The engine 2 is a so-called four-stroke gasoline engine in which a series of four strokes consisting of an intake stroke, a compression stroke, an expansion stroke and an exhaust stroke are performed as one cycle while the piston 6 makes two reciprocations within the cylinder 5 .

Also, the piston 6 is connected to the crankshaft via a connecting rod (not shown). The connecting rod converts the reciprocating motion of the piston 6 into rotational motion of the crankshaft.

A spark plug 8 and an in-cylinder pressure sensor 31 are provided in the combustion chamber 7 . The ignition plug 8 is disposed in the combustion chamber 7 with an electrode projecting therefrom, and the ignition timing thereof is controlled by the ECU 3 . The in-cylinder pressure sensor 31 detects the in-cylinder pressure, which is the pressure inside the cylinder 5 .

The engine 2 is provided with an intake port 11 and an exhaust port 21 . The intake port 11 communicates the combustion chamber 7 with an intake passage 14a, which will be described later. An intake valve 12 is provided in the intake port 11 .

The intake valve 12 is opened and closed so as to establish or block communication between the intake passage 14 a and the combustion chamber 7 . Opening and closing of the intake valve 12 is performed by an intake side variable valve mechanism 13 .

As the intake side variable valve mechanism 13, for example, an electromagnetic variable valve mechanism that opens and closes the intake valve 12 by means of an electromagnetic actuator composed of an electromagnet, a spring, and the like can be used. Specifically, the intake-side variable valve mechanism 13 attracts the movable portion fixed to the intake valve 12 by the excitation of an electromagnet, so that the intake valve 12, which is always biased in the valve-closing direction by a spring, It is designed to move in the valve opening direction.

As the intake side variable valve mechanism 13, a hydraulic variable valve mechanism using a hydraulic actuator may be used instead of the electromagnetic actuator. Further, as the intake side variable valve mechanism 13, a mechanical variable valve mechanism that can change the opening/closing timing of the intake valve 12 using cam members such as a main cam and a sub cam may be used.

Further, the intake side variable valve actuation mechanism 13 is configured such that the excitation current for the electromagnet is adjusted by the ECU 3, for example, so that the lift amount of the intake valve 12 can be varied continuously along with the opening/closing timing of the intake valve 12. may be

An intake pipe 14 is connected to the intake port 11 . An intake passage 14 a communicating with the intake port 11 is formed inside the intake pipe 14 .

The intake port 11 is partitioned into a pair of passages consisting of a first passage 11a on the outside of the combustion chamber and a second passage 11b on the center side of the combustion chamber by a partition wall 15 provided so as to extend in the flow direction of intake air flowing therein. It has a part that has been

A tumble control valve 16 is arranged at the end of the partition wall 15 on the upstream side of the flow of intake air, and opens and closes the first passage 11a.

The flow velocity of the tumble flow in the combustion chamber 7 changes depending on the degree of opening of the tumble control valve 16 . The degree of opening of the tumble control valve 16 is controlled by the ECU 3 . The ECU 3 can control the flow velocity of the tumble flow by controlling the opening of the tumble control valve 16 .

An injector 9 is provided in the second passage 11 b of the intake port 11 . The injector 9 injects fuel supplied by a fuel pump from a fuel tank (not shown) into the intake port 11 .

On the other hand, the exhaust port 21 is provided with an exhaust valve 22 . The exhaust valve 22 is opened and closed so as to connect or block communication between an exhaust passage 24a and the combustion chamber 7, which will be described later. Opening and closing of the exhaust valve 22 is performed by an exhaust side variable valve mechanism 23 .

Since the exhaust side variable valve mechanism 23 has the same configuration as the intake side variable valve mechanism 13 described above, a detailed description thereof will be omitted. The opening/closing timing of the valve 22 is arbitrarily changed. As the exhaust side variable valve mechanism 23, a hydraulic variable valve mechanism using a hydraulic actuator may be used instead of the electromagnetic actuator. Further, as the exhaust side variable valve mechanism 23, a mechanical variable valve mechanism that can change the opening/closing timing of the exhaust valve 22 using cam members such as a main cam and a sub cam may be used. Therefore, the ECU 3 can easily adjust the valve opening period of the exhaust valve 22 .

An exhaust pipe 24 is connected to the exhaust port 21 . An exhaust passage 24 a communicating with the exhaust port 21 is formed inside the exhaust pipe 24 .

The ECU 3 is configured by a computer unit having a CPU (Central Processing Unit), a RAM (Random Access Memory), a ROM (Read Only Memory), a flash memory, an input port, and an output port.

The ROM of the computer unit stores various control constants, various maps, and the like, as well as a program for causing the computer unit to function as the ECU 3 . That is, the computer unit functions as the ECU 3 by the CPU executing the program stored in the ROM.

An input port of the ECU 3 is connected to various sensors such as the in-cylinder pressure sensor 31 described above.

On the other hand, the output port of the ECU 3 is connected to various control objects such as the spark plug 8, the injector 9, the intake side variable valve mechanism 13, the exhaust side variable valve mechanism 23, and the like.

As shown in FIG. 2, the engine 2 is configured such that compression ignition combustion (CI (Compression Ignition) combustion) occurs after spark ignition combustion (also called SI (Speak Ignition) combustion) by the spark plug 8 occurs. It has become. When CI combustion becomes abnormal combustion, knocking occurs.

In normal CI combustion, the heat release rate changes more rapidly than in SI combustion, so the slope (variation) of the heat release rate reaches its maximum in the first half of the change in the heat release rate due to CI combustion. .

The ECU 3 calculates the heat release rate from the in-cylinder pressure detected by the in-cylinder pressure sensor 31, and determines abnormal combustion of the engine 2 based on the change in the heat release rate.

The ECU 3 calculates the heat generation rate dQ at predetermined time intervals according to the formula shown in Formula 2, which is derived from the relational expression between the first law of thermodynamics shown in Formula 1 and the ratio of specific heat.

where Q is the heat quantity, U is the internal energy, p is the pressure, V is the cylinder volume, T is the temperature, C _p is the constant pressure specific heat, C _v is the constant volume specific heat, R is the gas constant, and m is the air-fuel mixture in the cylinder. is the mass of

The ECU 3 calculates the slope of the calculated heat release rate dQ (difference from the previous value), and, for example, calculates the maximum slope of the heat release rate dQ from the compression stroke to the expansion stroke.

For example, in the graph of the heat release rate for each crank angle as shown in FIG. , and the crank angle axis (the crank angle at which the heat release rate is zero) is the starting point of the CI region.

The starting point of the CI region can be obtained, for example, from the maximum value of the slope of the heat release rate, the crank angle at which the slope reaches its maximum value, and the value of the heat release rate at which the slope reaches its maximum value. can.

The ECU 3 determines that the CI combustion is stable if the time from the ignition timing to the start point of the CI region is equal to or greater than a predetermined threshold value.

If the time from the ignition timing to the start point of the CI region is less than a predetermined threshold value, the ECU 3 determines that knocking occurs, and performs ignition retardation control to stabilize combustion. The predetermined threshold value is calculated from experimental values obtained by changing the engine speed and load.

As shown in FIG. 3, the ECU 3 determines that pre-ignition is occurring when the slope of the heat release rate exceeds a specified value before the ignition timing, controls the valve timing, and controls the engine combustion. Implement control to lower the room temperature. The prescribed value for judging this pre-ignition is calculated from measured experimental values.

Combustion stabilizing processing by the combustion control apparatus for an internal combustion engine according to the present embodiment configured as described above will be described with reference to FIG. Note that the combustion stabilization process described below is executed for each combustion cycle of each cylinder, for example, after an expansion stroke.

In step S<b>1 , the ECU 3 uses the in-cylinder pressure sensor 31 to measure the in-cylinder combustion pressure.

In step S2, the ECU 3 calculates the heat release rate from the in-cylinder combustion pressure using the above equation (2).

In step S3, the ECU 3 calculates the maximum slope of the heat release rate from the calculated heat release rate.

In step S4, the ECU 3 determines whether or not the slope of the heat release rate is equal to or less than a specified value before the ignition timing.

If it is determined that the slope of the heat release rate is equal to or less than the specified value at a stage before the ignition timing, in step S5, the ECU 3 calculates the starting point of the CI region from the maximum slope of the heat release rate, and calculates the start point of the CI region from the ignition timing. The time to the start point of the CI region is calculated as the time to the CI region.

In step S6, the ECU 3 determines whether or not the calculated time to the CI region is equal to or greater than a predetermined threshold.

When it is determined that the time to reach the CI region is equal to or longer than the predetermined threshold value, in step S7, the ECU 3 determines that the CI combustion is stable, and terminates the process.

When it is determined in step S6 that the time to the CI region is not equal to or greater than the predetermined threshold value, in step S8, the ECU 3 determines knocking, retards the ignition, and terminates the process.

If it is determined in step S4 that the slope of the heat release rate is not equal to or less than the specified value at a stage before the ignition timing, in step S9, the ECU 3 determines that preignition has occurred, and controls the valve timing to lower the engine combustion chamber temperature. and terminate the process.

As described above, in the above-described embodiment, the combustion pressure in the cylinder is measured by the cylinder pressure sensor 31, the heat release rate in the cylinder is calculated from the measured value, and abnormal combustion in the engine 2 is detected based on the change in the heat release rate. judge.

Thereby, abnormal combustion of the engine 2 can be determined, and combustion can be stabilized.

Also, the starting point of the CI region is calculated from the maximum value of the slope of the heat release rate, the crank angle at which the slope reaches its maximum value, and the value of the heat release rate at which the slope reaches its maximum value. Abnormal combustion in the engine 2 is determined based on the time between the starting point of the region and the ignition timing.

As a result, abnormal combustion can be determined accurately from the maximum value of the slope of the heat release rate, the crank angle when the slope reaches its maximum value, and the value of the heat release rate when the slope reaches its maximum value. Abnormal combustion can be determined.

Moreover, when the time between the start point of the CI region and the ignition timing is less than a predetermined threshold value, it is determined that abnormal combustion has occurred. Therefore, abnormal combustion can be accurately determined in real time by calculation.

In addition, when the slope of the heat release rate exceeds a specified value before the ignition timing, it is determined that preignition has occurred, so preignition can be accurately determined and combustion can be stabilized. can.

Further, when it is determined that abnormal combustion has occurred in the engine 2, the control for retarding the ignition timing is performed, so that the abnormal combustion can be normalized by retarding the ignition timing.

Further, since the pressure in the cylinder is always detected, appropriate CI combustion control can be performed, and knocking can be suppressed before knock vibration occurs.

In addition, even if minute vibrations occur in the cylinder, if it is determined that CI combustion is stable, it is possible to continue operation as it is, so it is possible to perform CI combustion over a wider area. As a result, fuel efficiency can be improved and exhaust gas can be suppressed.

In this embodiment, an example in which the ECU 3 makes various determinations and calculations based on various sensor information has been described. Various judgments and calculations are performed by the external device based on the detection information of various sensors transmitted from the unit, the judgment results and calculation results are received by the communication unit, and the received judgment results and calculation results are used to perform various may be controlled.

Although embodiments of the present invention have been disclosed, it will be apparent that modifications may be made by those skilled in the art without departing from the scope of the invention. All such modifications and equivalents are intended to be included in the following claims.

1 vehicle 2 engine (internal combustion engine)
3 ECU (control unit)
8 spark plug 31 in-cylinder pressure sensor

Claims (4)

a cylinder pressure sensor that detects the pressure in the cylinder of the internal combustion engine;
a control unit that calculates a heat release rate from the in-cylinder pressure detected by the in-cylinder pressure sensor and determines abnormal combustion of the internal combustion engine based on a change in the heat release rate, wherein SI combustion due to a spark plug occurs. A control device for an internal combustion engine in which CI combustion occurs later,
The control unit controls the CI at which the heat release rate due to the CI combustion is zero, based on the maximum value of the slope of the heat release rate, the time when the slope reaches the maximum value, and the value of the heat release rate at that time. A combustion control device for an internal combustion engine that calculates a start point of a region and determines abnormal combustion of the internal combustion engine based on the time between the start point of the CI region and the ignition timing of the SI combustion . 2. The combustion control device for an internal combustion engine according to claim 1 , wherein said control unit determines that abnormal combustion is occurring when the time between the start point of said CI region and ignition timing is less than a predetermined threshold value. 3. The combustion control for an internal combustion engine according to claim 1 , wherein the control unit determines that pre-ignition is occurring when the slope of the heat release rate exceeds a specified value before ignition timing. Device. 3. A combustion control apparatus for an internal combustion engine according to claim 1 , wherein said control section performs control to retard ignition timing when determining that abnormal combustion is occurring in said internal combustion engine.

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