JP2022065713A - Engine control method and engine control device - Google Patents

Abstract

To stably execute knocking suppression control.SOLUTION: An engine controller 101: estimates imbalance in flame propagation inside a combustion chamber Ch of an engine 1; and executes knocking suppression control to suppress knocking when occurrence frequency (frequency C) of the estimated imbalance in the flame propagation is equal to or larger than a threshold C1 or the occurrence frequency (frequency C) of the estimated imbalance in the flame propagation is predicted to be equal to or larger than the threshold C1 from an increase rate of the occurrence frequency (frequency C) of the estimated imbalance in the flame propagation.SELECTED DRAWING: Figure 2

Description

The present invention relates to an engine control method and an engine control device for controlling a gasoline engine.

Patent Document 1 discloses an engine control method that retards the ignition timing in the next cycle in order to suppress the occurrence of knocking due to the carry-over of unburned fuel when the bias of flame propagation in the combustion chamber is detected. ing.

Japanese Unexamined Patent Publication No. 2019-167927

However, in the engine control method described in Patent Document 1, knocking suppression control is executed based on the determination result of one cycle. Therefore, in the case of an engine having a large cycle fluctuation, knocking suppression control is frequently executed, and the control may become unstable.

The present invention has been made in view of such technical problems, and an object of the present invention is to stably execute knocking suppression control.

According to an aspect of the present invention, the engine control method for controlling a gasoline engine estimates the bias of flame propagation in the combustion chamber of the gasoline engine, and the frequency of occurrence of the estimated bias of flame propagation is equal to or higher than the threshold value, or It is characterized in that knocking suppression control for suppressing knocking is executed when the frequency of occurrence of the bias of flame propagation is expected to be equal to or higher than the threshold value from the rate of increase in the frequency of occurrence of the bias of flame propagation estimated.

In this embodiment, even if the occurrence of the flame propagation bias is detected, the knocking suppression control is not immediately executed, and the occurrence frequency of the flame propagation bias exceeds the threshold value, or the estimated frequency of the flame propagation bias occurs. Knocking suppression control is executed when the frequency of occurrence of the bias of flame propagation is expected to exceed the threshold value from the increase rate of. As a result, it is possible to prevent the knocking suppression control from being frequently executed when the cycle fluctuation is large. Therefore, it is possible to prevent the control of the gasoline engine from becoming unstable and to stably execute the knocking suppression control.

FIG. 1 is a structural diagram showing a main part of an engine according to an embodiment of the present invention. FIG. 2 is a flowchart showing a control flow in the engine control method according to the embodiment of the present invention. FIG. 3 is a graph showing the relationship between the engine rotation speed and the tumble flow velocity. FIG. 4 is a diagram for explaining the flow of the air-fuel mixture in the vicinity of the spark plug. FIG. 5 is a graph showing changes in the voltage signal of the ignition voltage. FIG. 6 is a graph showing the relationship between the combustion period and the center of flame propagation.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a structural diagram showing a main part of the engine 1 according to the embodiment of the present invention. The engine 1 of the present embodiment is a spark-ignition type direct-injection gasoline engine.

The main body of the engine 1 is formed by the cylinder block 1A and the cylinder head 1B, and the cylinder S is formed as a space formed by the cylinder block 1A and the cylinder head 1B. The engine 1 has a plurality of cylinders S.

The piston 2 is inserted into the cylinder S (cylinder block 1A) so as to be reciprocally movable up and down along the central axis Ax of the cylinder S. The piston 2 is connected to a crankshaft (not shown) via a connecting rod 3. The linear reciprocating motion of the piston 2 is transmitted to the crankshaft through the connecting rod 3 and converted into the rotational motion of the crankshaft.

A cavity 21a is formed on the crown surface 21 of the piston 2. The cavity 21a is formed in a shape so that the air sucked into the cylinder S through the intake port 4a smoothly flows.

A pent-roof type combustion chamber Ch is formed on the upper part of the cylinder S. Specifically, the space formed between the lower surface of the cylinder head 1B and the crown surface 21 of the piston 2 forms the combustion chamber Ch.

The cylinder head 1B is formed so that a pair of intake passages 4 and a pair of exhaust passages 5 face each other with the central axis Ax as a passage for communicating the combustion chamber Ch and the outside of the engine 1. An intake valve 8 is installed in the port portion (intake port) 4a of the intake passage 4, and an exhaust valve 9 is installed in the port portion (exhaust port) 5a of the exhaust passage 5.

The air taken into the intake passage 4 from the outside of the engine 1 is sucked into the combustion chamber Ch during the opening period of the intake valve 8. The exhaust gas after burning in the combustion chamber Ch is discharged to the exhaust passage 5 during the opening period of the exhaust valve 9. A throttle valve (not shown) is installed in the intake passage 4, and the flow rate of air sucked into the combustion chamber Ch is controlled by the throttle valve.

Further, the cylinder head 1B is provided with a fuel injection valve 7 between the pair of intake ports 4a and 4a on the intake port 4a side of the central shaft Ax, and a pair of fuel injection valves 7 on the exhaust port 5a side of the central shaft Ax. A spark plug 6 is installed between the exhaust ports 5a. The fuel injection valve 7 is configured to receive fuel supplied from a high-pressure fuel pump (not shown) and to directly inject fuel into the cylinder. The fuel injection valve 7 is a multi-hole type fuel injection valve, and fuel is injected in a direction diagonally intersecting the central axis Ax. The positions of the spark plug 6 and the fuel injection valve 7 are not limited to the arrangement shown in FIG. 1, and can be appropriately arranged at appropriate positions.

A tumble control valve 10 is installed in the intake passage 4. The tumble control valve 10 substantially narrows the opening area of the intake passage 4, thereby enhancing the flow of air in the combustion chamber Ch. In the present embodiment, as the flow of air, the air sucked into the cylinder through the intake port 4a passes through the cylinder space on the side opposite to the intake port 4a with respect to the central axis Ax, in other words, on the exhaust port 5a side. A tumble flow is formed from the lower surface of the cylinder head 1B toward the crown surface 21 of the piston 2, and the tumble control valve 10 enhances the tumble flow. The enhancement of the in-cylinder flow can be achieved not only by installing the tumble control valve 10 but also by changing the shape of the intake passage 4. For example, the intake passage 4 may be in a state closer to upright so that air may flow into the cylinder at a gentler angle with respect to the central axis Ax, or the central axis of the intake passage 4 may be in a state closer to a straight line. Then, the shape may be such that air flows into the cylinder with a stronger force.

An exhaust purification device (not shown) is interposed in the exhaust passage 5. The exhaust gas after combustion discharged to the exhaust passage 5 is discharged into the atmosphere after the harmful components in the exhaust gas are purified by the exhaust gas purification device.

The operation of the engine 1 is controlled by the engine controller 101 as an engine control device.

In the present embodiment, the engine controller 101 is configured as an electronic control unit, and includes a central processing unit, various storage devices such as ROM and RAM, an input / output interface, and the like.

Detection signals from the accelerator sensor 201, crank angle sensor 202, cooling water temperature sensor 203, and in-cylinder pressure sensor 204 are input to the engine controller 101, as well as detection signals from an air flow meter, air-fuel ratio sensor, etc. (not shown). Will be done. In the present embodiment, a current sensor 205 and a voltage sensor 206 are further provided, and the detection signal thereof is also input to the engine controller 101.

The accelerator sensor 201 outputs a signal according to the amount of operation of the accelerator pedal by the driver. The operation amount of the accelerator pedal is an index of the load required for the engine 1.

The crank angle sensor 202 detects the crank angle (rotational position) of the crankshaft of the engine 1. By converting the unit crank angle signal or the reference crank angle signal detected by the crank angle sensor 202 into the rotation speed per unit time (engine rotation speed), the rotation speed of the engine 1 can be detected.

The cooling water temperature sensor 203 outputs a signal according to the temperature of the engine cooling water. Instead of the temperature of the engine cooling water, the temperature of the engine lubricating oil may be adopted.

The in-cylinder pressure sensor 204 detects the pressure in the combustion chamber Ch.

The current sensor 205 outputs a signal corresponding to the secondary current of the spark plug 6, specifically, the secondary current flowing between the electrodes when the spark plug 6 is discharged. The secondary current of the spark plug 6 can be detected, for example, by providing a resistance element for detecting the secondary current in series with the secondary coil of the drive circuit connected to the spark plug 6. be. In the present embodiment, the current sensor 205 includes this resistance element.

The voltage sensor 206 outputs a signal (voltage signal) corresponding to the secondary voltage of the spark plug 6, specifically, the voltage generated in the secondary coil of the drive circuit by the mutual induction action.

The engine controller 101 stores map data to which various operation control parameters of the engine 1 such as a fuel injection amount are assigned to an operating state such as a load, a rotation speed, and a cooling water temperature of the engine 1. The engine controller 101 detects the operating state of the engine 1, sets the fuel injection amount, the fuel injection timing, the ignition timing, etc. with reference to the map data based on the detection, and sets the spark plug 6, the fuel injection valve 7, and the like. A command signal is output to the drive circuit.

In the engine 1, combustion is started by discharging electric sparks by the spark plug 6 in the air-fuel mixture in which air and fuel are sufficiently mixed in the combustion chamber Ch. Then, the air-fuel mixture near the electrodes is activated to form a flame nucleus, and this flame nucleus further causes a combustion reaction in the surrounding air-fuel mixture, and by continuing this reaction, it propagates to the surroundings as a combustion wave. Flame propagation occurs. Due to such flame propagation, the air-fuel mixture in the combustion chamber Ch is burned.

However, when the engine 1 is driven at high rotation speed or high supercharging, the flow velocity based on the tumble flow increases, and the flame propagation tends to be biased in a specific direction (see FIG. 3). When the flame propagation is biased in this way, the progress of the flame surface to the intake side is delayed and the combustion period T becomes long. As a result, the piston 2 descends before the combustion of the air-fuel mixture in the combustion chamber Ch is completed. This produces unburned fuel, which may be carried over to the next cycle, resulting in knocking.

Therefore, when a bias in flame propagation is detected, it is conceivable to execute knocking suppression control for suppressing the occurrence of knocking. However, at the same time when the bias of flame propagation is detected, that is, when the knocking suppression control is executed based on the determination result of one cycle, the knocking suppression control is frequently executed and controlled in the case of an engine having a large cycle fluctuation. May become unstable.

Therefore, in the knocking suppression control of the present embodiment, the frequency of occurrence of the bias of flame propagation is calculated, and the knocking suppression control is executed based on the frequency of occurrence. Hereinafter, the knocking suppression control of the present embodiment will be specifically described with reference to the flowchart shown in FIG.

The knocking control of the present embodiment is executed based on a program stored in advance in the engine controller 101 when the engine 1 is operating at the stoichiometric air-fuel ratio.

In step S1, a cycle in which the flow velocity of the air-fuel mixture passing between the electrodes of the spark plug 6 (plug flow velocity U) is equal to or higher than the threshold value U1 is detected.

When the engine 1 is driven at high rotation speed and high supercharging, the flow velocity based on the tumble flow increases, and the plug flow velocity U also increases. Further, as described above, the flow velocity based on the tumble flow increases, and the flame propagation tends to be biased in a specific direction. From these facts, when the plug flow velocity U is equal to or higher than the threshold value U1, it can be inferred that the flame propagation is biased. The threshold value U1 is a value set according to the specifications of the engine 1.

Next, how to obtain the plug flow velocity U will be described. As shown in FIG. 4, as the plug flow velocity U increases, the discharge path between the electrodes of the spark plug 6 curves to the downstream side, and the discharge path length ΔX becomes longer.

As shown in FIG. 5, when the plug flow velocity U becomes faster, that is, when the discharge path length ΔX becomes longer, the voltage V1 at which the insulation between the electrodes is destroyed becomes larger and the ascending speed (slope θ) of the voltage V1 becomes larger. .. Therefore, in the present embodiment, the plug flow velocity U is estimated based on the rising speed (slope θ) of the voltage V1 detected by the voltage sensor 206. In step S1, the cycle in which the plug flow velocity U is estimated in this way and is equal to or higher than the threshold value U1 is detected.

In step S2, the frequency C of the cycle in which the plug flow velocity U is determined to be equal to or higher than the threshold value U1, that is, the frequency of occurrence of the flame propagation bias is calculated. Specifically, the engine controller 101 counts the number of cycles in which the plug flow velocity U is determined to be equal to or higher than the threshold value U1 among the preset number of cycles, and calculates the occurrence frequency (frequency C). The frequency C is calculated by dividing the number of cycles in which the plug flow velocity U is determined to be equal to or higher than the threshold value U1 by the preset number of cycles.

In step S3, it is determined whether or not the operating state of the engine 1 is the knocking occurrence region. Specifically, it is determined whether or not the frequency C calculated in step S2 is equal to or higher than the threshold value C1 (for example, 1/2). If the frequency C is equal to or higher than the threshold value C1, it is determined that the operating state of the engine 1 is in the knocking occurrence region, and the process proceeds to step S4. On the other hand, if the frequency C is less than the threshold value C1, it is determined that the operating state of the engine 1 is in the normal operating region, and the process proceeds to RETURN.

In step S4, knocking suppression control is executed. Specifically, the engine controller 101 retards the ignition timing of the spark plug 6. Alternatively, fuel injection is executed not only in the intake stroke but also in the compression stroke (hereinafter, such fuel injection is also referred to as "multi-stage injection"). When executing the multi-stage injection, the fuel injection amount in one cycle is made equal to the case where the injection is executed only in the intake stroke. Further, when the multi-stage injection is executed, the injection pressure is increased as compared with the case where the injection is executed only in the intake stroke. As a result, the operating state at the stoichiometric air-fuel ratio can be maintained even while the knocking suppression control is being executed, so that deterioration of fuel efficiency can be suppressed.

As described above, in the present embodiment, when the bias of the flame propagation is detected, the knocking suppression control is not immediately executed, but the knocking suppression control is executed based on the occurrence frequency (frequency C) of the bias of the flame propagation. Therefore, it is possible to prevent the knocking suppression control from being frequently executed when the cycle fluctuation is large. This can prevent the control from becoming unstable.

Further, in the knocking suppression control of the present embodiment, fuel injection is executed in the compression stroke in addition to the intake stroke. As a result, since the air-fuel mixture having a high concentration of fuel gas exists in the vicinity of the spark plug 6 at the time of ignition, the flame propagation can be made uniform. Therefore, knocking can be suppressed more reliably.

In the above embodiment, the larger the frequency of occurrence of the flame propagation bias (frequency C), the larger the fuel injection amount in the compression stroke may be. In this case, the fuel injection amount in the compression stroke may be increased within a range in which knocking can be suppressed and in a range in which knocking does not occur. This makes it possible to more reliably prevent the occurrence of knocking.

Further, in the above embodiment, the determination is made based only on the plug flow velocity U, but the determination is not limited to this, and the determination based on other operating conditions such as the engine rotation speed and the engine torque is added in addition to the plug flow velocity U. You may do so.

Further, in the above embodiment, the case where the bias of the flame propagation is estimated based on the plug flow velocity U has been described as an example, but the present invention is not limited to this, and the bias of the flame propagation is estimated based on the combustion period T of the engine 1. You may do so. It is known that there is a relationship between the combustion period T and the bias of flame propagation (the amount of deviation of the central axis of flame propagation from the central axis of the spark plug 6) as shown in FIG. As is clear from FIG. 6, the larger the deviation amount of the central axis of the flame propagation from the central axis of the spark plug 6, that is, the larger the bias of the flame propagation, the longer the combustion period T. Further, the combustion period T can be calculated based on the pressure in the combustion chamber Ch and the crank angle. Therefore, the combustion period T of the engine 1 is calculated based on the pressure in the combustion chamber Ch detected by the in-cylinder pressure sensor 204 and the crank angle detected by the crank angle sensor 202, and further, the calculated combustion period is calculated. The bias of flame propagation can be estimated based on T.

In the above embodiment, whether or not the engine is in the knocking occurrence region is determined based on whether or not the frequency C is equal to or higher than the threshold value C1, but the present invention is not limited to this, and for example, the rate of increase in frequency C over time. Therefore, when the frequency C is expected to be equal to or higher than the threshold value C1, the knocking suppression control may be executed. In this case, the knocking suppression control can be started before the frequency C becomes the threshold value C1 or more, so that it can be dealt with earlier.

The configuration, operation, and effect of the embodiment of the present invention configured as described above will be collectively described.

The engine controller 101 estimates the bias of flame propagation in the combustion chamber Ch of the engine 1, and when the estimated frequency of occurrence of the bias of flame propagation (frequency C) is equal to or higher than the threshold C1, or the estimated bias of flame propagation. When the occurrence frequency (frequency C) of the bias of flame propagation is expected to be equal to or higher than the threshold value C1 from the increase rate of the occurrence frequency (frequency C) of the above, knocking suppression control for suppressing knocking is executed.

In this configuration, knocking suppression control is not immediately executed when a bias in flame propagation occurs, and the frequency of occurrence of bias in flame propagation (frequency C) is equal to or higher than the threshold value C1, or the frequency of occurrence of bias in flame propagation (frequency C). ) Is expected to be equal to or higher than the threshold value C1, and knocking suppression control is executed. As a result, it is possible to prevent the knocking suppression control from being frequently executed when the cycle fluctuation is large. Therefore, it is possible to prevent the control of the engine 1 from becoming unstable and to stably execute the knocking control.

The engine controller 101 estimates the bias of flame propagation based on the voltage signal (voltage V1) of the spark plug 6.

In this configuration, the bias of flame propagation can be estimated by the existing device, so that the cost increase can be suppressed.

The engine 1 includes an in-cylinder pressure sensor 204 for detecting the pressure in the combustion chamber Ch and a crank angle sensor 202 for detecting the crank angle. The engine controller 101 calculates the combustion period T of the engine 1 based on the pressure in the combustion chamber Ch detected by the in-cylinder pressure sensor 204 and the crank angle detected by the crank angle sensor 202, and the calculated combustion. The bias of flame propagation is estimated based on the period T.

In this configuration, the bias of the flame propagation of the existing device can be estimated, so that the cost increase can be suppressed.

The engine controller 101 injects fuel only in the intake stroke during normal operation (when no bias in flame propagation occurs), and injects fuel in the intake stroke and compression stroke during knocking suppression control.

By executing fuel injection in the compression stroke in addition to the intake stroke during knocking suppression control, an air-fuel mixture having a high concentration of fuel gas exists in the vicinity of the spark plug 6 at the time of ignition. As a result, the flame propagation can be made uniform, so that knocking can be suppressed more reliably.

The engine controller 101 increases the fuel injection amount in the compression stroke during knocking control as the frequency of occurrence of bias (frequency C) increases.

With this configuration, knocking can be suppressed more reliably and a decrease in output can be prevented.

Although the embodiments of the present invention have been described above, the above-described embodiments show only a part of the application examples of the present invention, and the technical scope of the present invention is limited to the specific configuration of the above-described embodiments. not.

In the above embodiment, the direct injection engine has been described as an example, but a port injection type variable compression ratio engine may be used. In this case, knocking can be suppressed by lowering the compression ratio during knocking suppression control.

1 Engine 2 Piston 4 Intake passage 4a Intake port 5 Exhaust passage 5a Exhaust port 6 Spark plug 7 Fuel injection valve 8 Intake valve 9 Exhaust valve 101 Engine controller (engine control device)
201 Accelerator sensor 202 Crank angle sensor 203 Cooling water temperature sensor 204 In-cylinder pressure sensor 205 Current sensor 206 Voltage sensor

Claims (6)

It is an engine control method that controls a gasoline engine.
Estimating the bias of flame propagation in the combustion chamber of the gasoline engine,
When the estimated frequency of occurrence of the flame propagation bias is equal to or higher than the threshold value, or from the estimated rate of increase in the frequency of occurrence of the flame propagation bias, it is expected that the frequency of occurrence of the flame propagation bias will be equal to or higher than the threshold value. An engine control method characterized in that knocking suppression control for suppressing knocking is executed in some cases. The engine control method according to claim 1.
An engine control method comprising estimating the bias of flame propagation based on a voltage signal of a spark plug. The engine control method according to claim 1.
The gasoline engine
An in-cylinder pressure sensor that detects the pressure in the combustion chamber,
Equipped with a crank angle sensor that detects the crank angle,
The combustion period of the gasoline engine is calculated based on the pressure in the combustion chamber detected by the in-cylinder pressure sensor and the crank angle detected by the crank angle sensor.
An engine control method characterized in that the bias of the flame propagation is estimated based on the calculated combustion period. The engine control method according to any one of claims 1 to 3.
When the bias of flame propagation does not occur, fuel injection is performed only in the intake stroke.
An engine control method characterized in that fuel injection is performed in an intake stroke and a compression stroke during the knocking suppression control. The engine control method according to claim 4.
An engine control method characterized in that the fuel injection amount in the compression stroke at the time of knocking control is increased as the frequency of occurrence of the bias increases. An engine control device that controls a gasoline engine.
Estimating the bias of flame propagation in the combustion chamber of the gasoline engine,
When the estimated frequency of occurrence of the flame propagation bias is equal to or higher than the threshold value, or from the estimated rate of increase in the frequency of occurrence of the flame propagation bias, it is expected that the frequency of occurrence of the flame propagation bias will be equal to or higher than the threshold value. An engine control device, characterized in that it executes knocking suppression control that suppresses knocking in some cases.

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