JP2021076052A - Internal combustion engine control device - Google Patents

Abstract

To prevent knocking when a methane concentration of fuel is reduced.SOLUTION: A control device to control an internal combustion engine 1 using natural gas as fuel comprises: a density sensor 25 which detects density of fuel in a liquid state; and a control unit 100 which is configured to correct ignition time on the basis of the fuel density detected by the density sensor. The control unit stores a map or a function defining a relation between a correction value to correct the ignition time and the fuel density and corrects the same on the basis of the correction value obtained from the map or the function.SELECTED DRAWING: Figure 1

Description

The present disclosure relates to a control device for an internal combustion engine, and more particularly to a control device for controlling an internal combustion engine whose fuel is natural gas.

In an internal combustion engine that uses natural gas as fuel, the fuel may be stored in a fuel tank in a liquefied state, that is, as liquefied natural gas (LNG (Liquefied Natural Gas)).

Japanese Unexamined Patent Publication No. 9-257195

In such an internal combustion engine, the methane concentration of the fuel in the fuel tank decreases due to a long period of time or the like, the composition of the fuel changes, and a weathering phenomenon occurs in which the fuel becomes heavy. As the fuel becomes heavier, the methane value decreases, so knocking may occur if ignition is performed at the usual timing.

Therefore, the present disclosure was conceived in view of such circumstances, and an object of the present disclosure is to provide a control device for an internal combustion engine capable of suppressing knocking when the methane concentration of a fuel decreases.

According to one aspect of the present disclosure
A control device for controlling an internal combustion engine whose fuel is natural gas.
A density sensor that detects the density of liquefied fuel,
A control unit configured to correct the ignition timing based on the fuel density detected by the density sensor.
A control device for an internal combustion engine is provided.

Preferably, the control unit stores a map or function that defines the relationship between the correction value for correcting the ignition timing and the fuel density, and corrects the ignition timing based on the correction value obtained from the map or function. To do.

Preferably, the control unit corrects the ignition timing to the retard side as the detected fuel density increases.

Preferably, the density sensor is composed of a Coriolis flow meter.

Preferably, the internal combustion engine is mounted on the vehicle.

According to the present disclosure, knocking can be suppressed when the methane concentration of the fuel is reduced.

It is the schematic which shows the internal combustion engine and its control device which concerns on this Embodiment. It is a flowchart of a fuel injection amount control routine. It is a graph which shows the map and the relationship used in control. It is a flowchart of the ignition timing control routine. A map for calculating the ignition timing correction coefficient is shown.

Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings. It should be noted that the present disclosure is not limited to the following embodiments.

FIG. 1 is a schematic view showing an internal combustion engine and a control device thereof according to the present embodiment. The internal combustion engine (also referred to as an engine) 1 uses natural gas as fuel and is mounted on a vehicle, particularly a large vehicle such as a truck, as a power source. However, the use of the engine is arbitrary, and it may be applied to a moving body other than a vehicle, for example, a ship, a construction machine, or an industrial machine. Further, the engine does not have to be mounted on a moving body, and may be a stationary engine. The fuel is stored in the fuel tank 9 in a liquefied state, that is, as LNG.

A catalyst 3 for purifying exhaust gas is provided in the exhaust passage 2 of the engine 1. The catalyst 3 is formed by, for example, a three-way catalyst. An air cleaner 5 and an intake throttle valve 6 are provided in the intake passage 4 of the engine 1 in this order from the upstream side. The engine 1 is a multi-cylinder engine, and includes a fuel injection injector 7 and a spark plug 8 for each cylinder. The engine 1 may be provided with a turbocharger.

The injector 7 may inject fuel into the intake port or may inject fuel directly into the cylinder. Fuel is sent from the fuel tank 9 to the injector 7 through the fuel passage 10. A regulator (pressure reducing valve) 11 is provided in the fuel passage 10. The regulator 11 decompresses and vaporizes the liquefied fuel sent from the fuel tank 9, adjusts the vaporized fuel to a predetermined pressure, and then sends the liquefied fuel to the injector 7. Therefore, the vaporized fuel is injected from the injector 7.

The control device for controlling the engine 1 includes an electronic control unit (called an ECU (Electronic Control Unit)) 100 as a control unit. The control device includes a rotation sensor 21, an accelerator opening sensor 22, a lambda sensor 23, a flow rate sensor 24, and a density sensor 25. These sensors are electrically connected to the ECU 100. The ECU 100 is configured and programmed to control the injector 7, the spark plug 8 and the intake throttle valve 6 based on the detected values of these sensors.

The rotation sensor 21 is a sensor for detecting the rotation speed of the engine, specifically, the rotation speed (rpm) per minute. The accelerator opening sensor 22 is a sensor for detecting the accelerator opening that is increased or decreased by the driver. The ECU 100 controls the opening degree of the intake throttle valve 6 based on the detected accelerator opening degree, and specifically, the opening degree of the intake throttle valve 6 increases as the accelerator opening degree increases.

The lambda sensor 23 is provided in the exhaust passage 2 on the upstream side of the catalyst 3 and detects the excess air ratio of the exhaust. Here, the control is performed based on the excess air ratio, but the control may be performed based on the air-fuel ratio. Since both the excess air ratio and the air-fuel ratio are index values indicating the mixing ratio of fuel and air, the air-fuel ratio is conceptually included in the case of the excess air ratio.

The flow rate sensor 24 is provided in the intake passage 4 on the downstream side of the air cleaner 5 and on the upstream side of the intake throttle valve 6, and detects the flow rate of intake air, that is, the amount of intake air per unit time.

The density sensor 25 is provided in the fuel passage 10 on the upstream side of the regulator 11 and detects the density of the liquefied fuel before it is vaporized by the regulator 11. In the case of this embodiment, the density sensor 25 is composed of a Coriolis flow meter. As is well known, the Coriolis type flow meter is originally for measuring the mass flow rate of a liquid which is an object to be measured. However, the Coriolis flowmeter can also measure the density of liquids at the same time. Therefore, in the present embodiment, this density measurement function is used to detect the fuel density in the liquefied state with a Coriolis flow meter.

The density sensor 25 may be composed of other types of sensors or measuring instruments, and may be composed of, for example, a vibration type density meter, a float type density meter, or a radiation type density meter.

Next, the control of the present embodiment executed by the ECU 100 will be described.

First, control of the fuel injection amount will be described. The ECU 100 controls the fuel injection amount injected from the injector 7 according to the routine shown in FIG. At this time, the ECU 100 feedback-controls the fuel injection amount based on the actual excess air ratio detected by the lambda sensor 23. This is called lambda feedback control. The routine of FIG. 2 is repeatedly executed every one engine cycle (= 720 ° CA).

Here, the fuel injection amount means the amount of fuel injected per cylinder in one engine cycle. In practice, the fuel injection amount can be rephrased as the injection time or the injection width because the control is performed by the time when the injector 7 is turned on and the fuel injection is executed, that is, the injection time or the injection width.

First, in step S101, the ECU 100 acquires the engine speed Ne and the intake flow rate Ga detected by the rotation sensor 21 and the flow rate sensor 24, respectively.

Next, in step S102, the ECU 100 injects fuel based on the acquired engine speed Ne and intake flow rate Ga (that is, engine operating state) according to a map (may be a function; the same applies hereinafter) as shown in FIG. 3 (A). The basic injection amount Qb, which is the basic value of the amount, is calculated. The map is created in advance through a test or the like and stored in the ECU 100.

Next, in step S103, the ECU 100 acquires the excess air ratio λ detected by the lambda sensor 23.

Then, in step S104, the ECU 100 calculates the excess rate difference Δλ, which is the difference between the detected actual excess air rate λ and the predetermined target air excess rate λt. The excess rate difference Δλ is calculated from the equation: Δλ = λt−λ. The target excess air ratio λt is, for example, 1.

In step S105, the ECU 100 calculates a correction coefficient α, which is a correction value for correcting the fuel injection amount, based on the excess rate difference Δλ. Then, in step S106, the ECU 100 calculates the final injection amount Qf by multiplying the basic injection amount Qb by the correction coefficient α (Qf = α × Qb). Finally, in step S107, the ECU 100 injects an amount of fuel equal to the final injection amount Qf from the injector 7. Specifically, the injector 7 is turned on for the injection time or the injection width corresponding to the final injection amount Qf.

FIG. 3B shows the relationship between the excess rate difference Δλ and the correction coefficient α. When the excess rate difference Δλ is zero, the correction coefficient α is 1, and no correction is substantially made. When the excess ratio difference Δλ is larger than zero, the actual excess air ratio λ is smaller than the target excess air ratio λt, and the exhaust air-fuel ratio is richer than the air-fuel ratio (for example, the theoretical air-fuel ratio) corresponding to the target air excess ratio λt. Therefore, a correction coefficient α smaller than 1 is calculated in order to correct the basic injection amount Qb to the weight loss side. However, α> 0. The larger the value of the excess rate difference Δλ, the smaller the value of the correction coefficient α.

On the contrary, when the excess ratio difference Δλ is smaller than zero, the actual excess air ratio λ is larger than the target excess air ratio λt, and the exhaust air-fuel ratio is leaner than the air-fuel ratio corresponding to the target excess air ratio λt. Therefore, a correction coefficient α larger than 1 is calculated in order to correct the basic injection amount Qb to the increase side. The smaller the value of the excess rate difference Δλ, the larger the value of the correction coefficient α.

Such calculation of the correction coefficient α can be performed according to, for example, a known PID control method. Alternatively, the relationship between the excess rate difference Δλ and the correction coefficient α shown in FIG. 3B is stored in advance in the ECU 100 in the form of a map, and the correction coefficient α corresponding to the excess rate difference Δλ is calculated from this relationship. You may try to do so.

In this way, the basic injection amount Qb is corrected based on the excess rate difference Δλ, and the actual excess air rate λ is brought close to the target excess air rate λt. Then, the fuel injection amount is controlled so that the catalyst 3 operates with as high efficiency as possible.

By the way, in the fuel tank 9 in which the fuel is stored in a liquefied state, that is, as LNG, the methane concentration of the fuel decreases due to a long period of time or the like, the composition of the fuel changes, and a weathering phenomenon occurs in which the fuel becomes heavy. As the fuel becomes heavier, the methane value decreases, so knocking may occur if ignition is executed by the spark plug 8 at the usual timing.

This will be explained in more detail. LNG in the fuel tank 9 is a mixture of methane, which is the main component, and a relatively small amount of ethane, propane, and the like. When the fuel in the fuel tank 9 receives heat from the surroundings, methane having the lowest boiling point evaporates and boil-off gas is generated. Since the boil-off gas is discharged from the tank in order to prevent the pressure in the tank from rising, the methane concentration of LNG in the fuel tank 9 decreases. When the methane concentration of LNG decreases in this way, the methane value decreases, the antiknock property of the fuel decreases, and knocking easily occurs. Therefore, when the fuel becomes heavy, knocking is likely to occur.

Therefore, in the present embodiment, the ignition timing is corrected according to such a change in fuel properties. Specifically, the density sensor 25 detects the fuel density that correlates with the methane value of the fuel, and corrects the ignition timing based on the detected fuel density.

The lower the methane value of the fuel, the higher the fuel density. Therefore, in the present embodiment, the ignition timing is corrected to the retard side as the detected fuel density increases. As a result, even if the methane concentration and methane value of the fuel in the fuel tank 9 decrease due to a long period of time or the like, the ignition timing can be appropriately corrected for retardation and knocking can be suppressed. is there.

The ignition timing control will be described below. The ECU 100 controls the timing of ignition executed by the spark plug 8 according to the routine shown in FIG. The routine of FIG. 4 is also repeatedly executed every one engine cycle (= 720 ° CA).

First, in step S201, the ECU 100 acquires the engine rotation rate Ne, the intake flow rate Ga, and the fuel density ρ detected by the rotation sensor 21, the flow rate sensor 24, and the density sensor 25, respectively.

Next, in step S202, the ECU 100 calculates the basic ignition timing θb, which is the basic value of the ignition timing, based on the acquired engine speed Ne and the intake flow rate Ga according to the map as shown in FIG. 3C. The map is created in advance through a test or the like and stored in the ECU 100. The basic ignition timing θb is set to an ignition timing that does not cause knocking and is advanced as much as possible when the engine is in steady operation and the fuel is the reference fuel described later.

Next, in step S203, the ECU 100 calculates a correction coefficient β, which is a correction value for correcting the ignition timing, based on the acquired fuel density ρ, according to a map as shown in FIG. Then, in step S204, the ECU 100 calculates the final ignition timing θf by multiplying the basic ignition timing θb by the correction coefficient β (θf = β × θb). Finally, in step S205, the ECU 100 turns on the spark plug 8 and executes ignition at the same time when the final ignition timing θf actually arrives. The ignition timing is on the retard side as the value increases.

In the map shown in FIG. 5, the relationship between the fuel density ρ and the correction coefficient β is defined. This map is stored in the ECU 100 in advance. When the fuel is a reference fuel having a reference methane value that has not yet become heavy, the fuel density ρ is the reference density ρb, and the corresponding correction coefficient β is 1. Therefore, at this time, the ignition timing is not substantially corrected. For example, the reference fuel is 13A, which is a general type of city gas, and the reference methane value is 64. For convenience, in the map, the correction coefficient β is set to 1 even when the fuel density ρ is smaller than the reference density ρb.

As the methane value of the fuel decreases from the standard methane value and the fuel becomes heavier (the severity increases), the fuel density ρ increases. As the fuel density ρ increases, the value of the correction coefficient β increases from 1. When β> 1, the ignition timing is corrected to the retard side of the basic ignition timing θb. The ignition timing is corrected to the retard side as the fuel density ρ becomes larger than the reference density ρb.

As described above, according to the present embodiment, since the ignition timing is corrected based on the detected fuel density, it is possible to suppress knocking when the methane concentration of the fuel decreases.

Although the embodiments of the present disclosure have been described in detail above, various other embodiments and modifications of the present disclosure can be considered.

(1) For example, the correction value for correcting the ignition timing may be an additional correction amount β'added to the basic ignition timing θb instead of the correction coefficient β. In this case, β = 1 corresponds to β'= 0, and β> 1 corresponds to β'> 0.

(2) In addition to the ignition timing correction according to the fuel density ρ, another ignition timing correction may be performed, for example, the ignition timing correction may be performed according to the output of the knock sensor.

(3) The installation position of the density sensor 25 can be changed, and may be installed in, for example, the fuel tank 9.

The embodiments of the present disclosure are not limited to the above-described embodiments, and all modifications, applications, and equivalents included in the ideas of the present disclosure defined by the scope of claims are included in the present disclosure. Therefore, the present disclosure should not be construed in a limited manner and may be applied to any other technique belonging within the scope of the ideas of the present disclosure.

1 Internal combustion engine 25 Density sensor 100 Electronic control unit (ECU)

Claims (5)

A control device for controlling an internal combustion engine whose fuel is natural gas.
A density sensor that detects the density of liquefied fuel,
A control unit configured to correct the ignition timing based on the fuel density detected by the density sensor.
A control device for an internal combustion engine, which is characterized by being equipped with. The control unit stores a map or a function that defines the relationship between a correction value for correcting the ignition timing and the fuel density, and corrects the ignition timing based on the correction value obtained from the map or the function. The control device for an internal combustion engine according to 1. The control device for an internal combustion engine according to claim 1 or 2, wherein the control unit corrects the ignition timing to the retard side as the detected fuel density increases. The control device for an internal combustion engine according to any one of claims 1 to 3, wherein the density sensor is composed of a Coriolis flow meter. The control device for an internal combustion engine according to any one of claims 1 to 4, wherein the internal combustion engine is mounted on a vehicle.

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