Engine control device

An engine control device includes a determination unit configured to determine whether or not an engine is in a complete explosion state, a calculation unit configured to calculate an integrated intake air amount that is an integrated value of an intake air amount of the engine after an affirmative determination is made by the determination unit, a setting unit configured to set a target equivalent ratio of the engine in accordance with the integrated intake air amount, and a control unit configured to control an intake air amount and a fuel injection amount of the engine such that an equivalent ratio of an air-fuel mixture becomes the target equivalent ratio.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority of the prior Japanese Patent Application No. 2022-175471, filed on Nov. 1, 2022, the entire contents of which are incorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates to an engine control device.

BACKGROUND

A target equivalent ratio of the engine is set in accordance with an integrated intake air amount which is an integrated value of the intake air amount of the engine. An operating state of the engine is controlled so that the actual equivalent ratio of the air-fuel mixture becomes the target equivalent ratio (see, for example, Japanese Unexamined Patent Application Publication No. 2022-084191).

The engine is started in the following manner. Fuel injection is performed while intake air is introduced into the engine by cranking. The air-fuel mixture is ignited and the engine is brought into a complete explosion state. Thus, the start of the engine is completed. Here, the time from the start of cranking to the complete combustion state might vary depending on factors such as the properties of the fuel used and the environmental temperature. Therefore, in the case where the integrated intake air amount is calculated from the start of cranking, there is a possibility that the integrated intake air amount at the time when the complete combustion state is reached varies. As a result, the target equivalent ratio set in accordance with the integrated intake air amount might vary. Therefore, the combustion state of the engine after the start might vary.

SUMMARY

It is therefore an object of the present disclosure to provide an engine control device in which variation in combustion state after starting is suppressed.

The above object is achieved by an engine control device including: a determination unit configured to determine whether or not an engine is in a complete explosion state; a calculation unit configured to calculate an integrated intake air amount that is an integrated value of an intake air amount of the engine after an affirmative determination is made by the determination unit; a setting unit configured to set a target equivalent ratio of the engine in accordance with the integrated intake air amount; and a control unit configured to control an intake air amount and a fuel injection amount of the engine such that an equivalent ratio of an air-fuel mixture becomes the target equivalent ratio.

The setting unit may be configured to set the target equivalent ratio from a value greater than one to a lower value as the integrated intake air amount increases.

The setting unit may be configured to set the target equivalent ratio to a value greater than one as a temperature of the engine is lower.

DETAILED DESCRIPTION

[Schematic Configuration of Engine]

FIG.1is a schematic configuration view of an engine10. The engine10is mounted on an engine vehicle, for example, but may be mounted on a hybrid vehicle. The engine10is a gasoline engine, but may be a diesel engine. A piston13is provided in each cylinder12of the engine10. The piston13is connected to a crankshaft15, which is an output shaft of the engine10, via a connecting rod14. The reciprocating motion of the piston13is converted into a rotational motion of the crankshaft15by the connecting rod14. The crankshaft15is connected to a starter motor25. The starter motor25is connected to the crankshaft15. The starter motor25cranks the engine10by rotating the crankshaft15when the engine10is started.

A combustion chamber16is formed in each cylinder12above the piston13. An ignition plug18for igniting an air-fuel mixture of fuel and air is attached to the combustion chamber16. The ignition timing of the air-fuel mixture by the ignition plug18is adjusted by an igniter19provided above the ignition plug18.

An intake passage20and an exhaust passage21communicate with the combustion chamber16. The intake passage20is provided with a throttle valve23for adjusting the amount of air introduced into the combustion chamber16. A catalyst50is provided in the exhaust passage21.

The engine10is provided with an in-cylinder injection valve17that injects fuel into each combustion chamber16. In addition to or instead of the in-cylinder injection valve17, a port injection valve that injects fuel into an intake port may be provided.

An ECU (Electronic Control Unit)30is an electronic control unit that performs control processing related to the engine10. The ECU30is mainly configured by a computer including a central processing unit (CPU) and a volatile or nonvolatile memory such as a random access memory (RAM) or a read only memory (ROM). Various sensors are connected to the ECU30, which will be described in detail later. The ECU30is an example of an engine control device, and functionally achieves a determination unit, a calculation unit, a setting unit, and a control unit, which will be described in detail later.

An accelerator opening degree sensor31, a coolant temperature sensor32, an air flow meter33, a crank angle sensor34, and an air-fuel ratio sensor35are connected to the ECU30. The accelerator opening degree sensor31detects an accelerator opening degree. The coolant temperature sensor32detects the temperature of the coolant that cools the engine10. The air flow meter33detects an intake air amount. The crank angle sensor34detects the rotational speed of the engine10. The air-fuel ratio sensor35is provided in the exhaust passage21upstream of the catalyst50. The air-fuel ratio sensor35detects the air-fuel ratio of the exhaust gas flowing into the catalyst50.

The ECU30sets the target equivalent ratio by a method described later. The ECU30controls the intake air amount and the fuel injection amount so that the equivalent ratio of the air-fuel mixture becomes the target equivalent ratio. The air fuel ratio of the air-fuel mixture is calculated by the ECU30based on the detection value of the air fuel ratio sensor35. Here, the equivalent ratio is an index value representing the fuel concentration in the air-fuel mixture, and is a value obtained by dividing the fuel amount corresponding to the stoichiometric air-fuel ratio by the actual fuel amount. When the air-fuel ratio of the air-fuel mixture is the stoichiometric air-fuel ratio, the equivalent ratio is “one”. When the air-fuel ratio of the air-fuel mixture is richer than the stoichiometric air-fuel ratio, the equivalent ratio is a value greater than “one”. When the air-fuel ratio of the air-fuel mixture is leaner than the stoichiometric air-fuel ratio, the equivalent ratio is a value smaller than “one”. The intake air amount is controlled according to the opening degree of the throttle valve23. The fuel injection amount is controlled according to the energization time of the in-cylinder injection valve17. The intake air amount and the fuel injection amount are adjusted based on a target torque that is set according to an accelerator opening degree, a vehicle speed, and the like.

FIG.2is a flowchart illustrating an example of equivalent ratio control executed by the ECU30. This control is repeatedly executed in the ignition-on state. The ECU30determines whether or not the engine10is in a complete explosion state (step S1). The complete explosion state means a state in which the start of the engine10is completed and the engine10can be autonomously operated. In other words, the complete combustion state means a state in which assistance by the starter motor25is not required during operation of the engine10. In the present embodiment, the ECU30uses the rotational speed of the engine10to determine whether or not the engine10is in a complete the engine10. More specifically, when the rotation speed of the engine10becomes equal to or higher than a predetermined rotation speed for a predetermined time or longer, it is determined that the engine10is in the complete explosion state. Step S1is an example of a process executed by a determination unit. When a negative determination is made in step S1, the present control ends.

When an affirmative determination is made in step S1, the ECU30calculates the integrated intake air amount based on the detection value of the air flow meter33(step S2). That is, the ECU30calculates the integrated intake air amount which is an integrated value of the intake air amount after the complete combustion state is determined in step S1. Step S2is an example of a process executed by a calculation unit.

Next, the ECU30sets a target equivalent ratio (step S3).FIG.3is an example of a map that defines the target equivalent ratio. This map is stored in the memory of the ECU30. The horizontal axis represents the integrated intake air amount, and the vertical axis represents the target equivalent ratio. In the map ofFIG.3, the target equivalent ratio corresponding to the temperature T1to T3of the coolant at the start of cranking of the engine10is defined. Among the temperatures T1to T3, the temperature T1is the lowest and the temperature T3is the highest. For example, the temperatures T1and T2are less than zero degree Celsius, and the temperature T3is equal to or higher than zero degree Celsius. The ECU30uses the coolant temperature as the temperature of the engine1. Therefore, the ECU30sets the target equivalent ratio by referring to the map illustrated inFIG.3based on the coolant temperature detected by the coolant temperature sensor32at the start of cranking and the integrated intake air amount. Step S3is an example of a process executed by a setting unit.

In a state in which the integrated intake air amount is small until reaching the predetermined value, the target equivalent ratio at the temperature T1is the largest and the target equivalent ratio at the temperature T3is the smallest among the temperatures T1to T3. That is, the target equivalent ratio is set to a greater value as the temperature of the engine10is lower. The lower the temperature of the engine10is lower, the wall surface temperature of the combustion chamber of the engine10is lower. As the wall surface temperature becomes lower, the amount of non-contributing fuel that adheres to the wall surface and does not contribute to combustion in the fuel injection amount increases. In order to compensate for this non-contributing fuel amount, the target equivalent ratio is set to a higher value as the temperature of the engine10is lower. Further, at the temperature T3, the target equivalent ratio is “one” regardless of the integrated intake air amount. This is because the amount of non-contributing fuel adhering to the wall surface of the combustion chamber is small at the temperature T3.

At the temperatures T1and T2, the target equivalent ratio decreases toward “one” as the integrated intake air amount increases until the integrated intake air amount reaches a predetermined value. As the integrated intake air amount after the complete combustion state increases, the wall surface temperature of the combustion chamber of the engine10increases. As a result, the amount of non-contributing fuel adhering to the wall surface in the fuel injection amount is reduced.

In a case of the temperatures T1and T2inFIG.3, the target equivalent ratio linearly decreases as the integrated intake air amount increases until the integrated intake air amount reaches a predetermined value. However, the target equivalent ratio may also decrease in a curved manner or stepwise. The target equivalent ratio may be calculated by an arithmetic expression using the integrated intake air amount and the temperature of the coolant as arguments.

Next, the ECU30controls the intake air amount and the fuel injection amount so that the actual equivalent ratio of the air-fuel mixture becomes the target equivalent ratio (step S4). Specifically, as described above, the ECU30controls the opening degree of the throttle valve23and the energization time of the in-cylinder injection valve17. Thus, the intake air amount and the fuel injection amount are controlled. Step S4is an example of a process executed by the control unit.

As described above, the target equivalent ratio is set based on the integrated intake air amount calculated after the complete combustion state is reached. For this reason, even if there is variation in the time from the start of cranking until the complete combustion state is reached, variation in the target equivalent ratio at the point in time when the complete combustion state is reached is suppressed. As a result, the variation in the combustion state after the start of the engine10is suppressed.

For the ECU30, the temperature of the lubricant oil that lubricates the engine10may be used as the temperature of the engine10. The contents of the above-described embodiment may be applied to, for example, a control device for an engine mounted on a motorcycle or the like, or a control device for an engine mounted on something other than a vehicle such as a ship or a construction machine.

Although some embodiments of the present disclosure have been described in detail, the present disclosure is not limited to the specific embodiments but may be varied or changed within the scope of the present disclosure as claimed.