JP2021011824A - Engine control - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress knocking in a high load operation region and improve thermal efficiency by injecting water into an intake air. An intake port 3 and an exhaust port 4 connected to a combustion chamber 2 of an engine 1, a fuel injection device 9 for injecting fuel into an intake air supplied into the combustion chamber 2, and ignition for burning the fuel. An ignition device 7 that generates a spark, water injection devices 11 and 12 that inject water into the intake air, a water injection amount determining means 21 that determines the amount of water injected by the water injection devices 11 and 12, and a water injection device 11. The water injection device 11 and 12 include a water injection control means 22 for controlling the injection of water by This is an engine control device in which one water injection A and a second water injection B that injects water during the expansion stroke are set. [Selection diagram] Fig. 1

Description

The present invention relates to an engine control device including a mechanism for injecting water into intake air.

Intake air is supplied to the combustion chamber of the engine through an intake passage (hereinafter, referred to as an intake port) provided in the cylinder head. In addition, a fuel injection device is provided in the intake port, and the fuel injected from the fuel injection device diffuses in the combustion chamber together with the sucked air, and the diffused fuel is compressed by the piston and then faces the combustion chamber. It is ignited and burned by a spark plug provided.

By the way, the mixture of fuel and air sent into the combustion chamber may cause abnormal combustion, so-called knocking, in which the mixture ignited by the spark plug and ignited before the flame generated is propagated. As means for suppressing knocking, various factors such as ignition timing, compression ratio, supercharging pressure when a supercharger is provided, air-fuel ratio of the air-fuel mixture, antiknock property of fuel, etc. are appropriately adjusted according to the operating condition. Setting to the state is mentioned.

For example, Patent Documents 1 and 2 disclose a technique for injecting an aqueous solution containing water or an antiknock agent into an intake port at low, medium speed and high load of an engine in order to suppress the occurrence of knocking. There is.

Further, as a technique for injecting water into the intake air, for example, in Patent Documents 3 and 4, supercritical water having a higher density than ordinary gaseous water is injected into a high-temperature and high-pressure combustion chamber to inject the wall surface of the combustion chamber. In addition to improving the heat insulation performance in the vicinity, cooling loss is suppressed to improve fuel efficiency. Further, for example, in Patent Document 5, in a diesel engine, water vapor is generated by injecting water into the combustion chamber, fuel consumption is reduced by the expansion force of the steam, and the heat of vaporization of water is used to enter the combustion chamber. It complements the decrease in inhalation efficiency of fresh air.

Jikkai Sho 56-50769 Japanese Unexamined Patent Publication No. 60-23554 Japanese Unexamined Patent Publication No. 2017-25774 Japanese Unexamined Patent Publication No. 2017-25775 Japanese Unexamined Patent Publication No. 60-184923

By the way, in recent years, in gasoline engines, knocking in a high load region is suppressed by injecting water into the intake air, and the ignition timing is advanced, the exhaust temperature is reduced, rich operation is avoided, and the stoichiometric operation area is expanded. Furthermore, a water injection system for the purpose of improving fuel efficiency is attracting attention.

However, in an engine that employs this type of water injection system, combustion tends to be delayed due to the injection of water into the intake air. Therefore, under the same ignition timing, the isochoricity may decrease, and as a result, the fuel consumption may deteriorate. Here, the isochoricity is the thermal efficiency that occurs as the combustion leaves the top dead center, assuming that the thermal efficiency of the ischoric combustion cycle, which is assumed to be performed at once without changing the volume at the top dead center, is 1. The degree of decrease is integrated with respect to the entire combustion stroke. That is, the larger the isochoricity is, the shorter the time the air-fuel mixture is burned in the combustion chamber, and the higher the thermal efficiency and the combustion speed are.

Here, the theoretical thermal efficiency η in the isochoric combustion cycle (Otto cycle) is calculated assuming that the compression ratio is ε and the specific heat ratio of the working fluid is κ.
η = ^1-1 / ε ^κ-1
It is expressed by the formula of. Therefore, even if the compression ratio ε is constant, improvement in thermal efficiency can be expected by increasing the specific heat ratio κ.

However, if water is injected into the intake air before the compression stroke, the specific heat ratio of the unburned mixed gas in the compression stroke (about 1.34) and the specific heat ratio of the combustion gas in the expansion stroke (about 1.37). relative), steam is 3 atom molecules (H 2 _O: adding a specific heat ratio 1.33), the specific heat ratio of the gas in the entire combustion chamber is greater is considered unchanged. Therefore, although the injection of water in the pre-stage of the compression stroke is effective in suppressing knocking, it cannot be expected to have a great effect in improving the thermal efficiency. Therefore, it is required to achieve both suppression of knocking in a high load operation region by injecting water into the intake air and improvement of thermal efficiency.

Therefore, an object of the present invention is to achieve both knocking suppression in a high load operation region and improvement of thermal efficiency by injecting water into the intake air.

In order to solve the above problems, the inventor of the present application has noticed that the specific heat ratio is a function of temperature, and that the specific heat ratio of gas increases as the temperature decreases. That is, while the decrease in the combustion gas temperature during the compression stroke due to the water injection to the intake air is about 20 k, the decrease in the combustion gas temperature during the expansion stroke due to the water injection to the intake air is as large as about 100 to 200 k. Regarding the injection of water, we focused on the high effect of increasing the specific heat ratio in the expansion stroke.

That is, the present invention provides an intake port and an exhaust port connected to the combustion chamber of an engine, a fuel injection device that injects fuel into the intake air supplied to the combustion chamber, and an ignition spark for burning the fuel. An ignition device to be generated, a water injection device for injecting water into the intake air, a water injection amount determining means for determining the injection amount of water by the water injection device, and a water injection for controlling water injection by the water injection device. The water injection device includes a control means, and the water injection device includes a first water injection that injects water during an intake stroke or an intake stroke and a compression stroke during one combustion cycle of the engine, and water during an expansion stroke. We adopted an engine control device in which a second water injection for injection is set.

Here, the first water injection can adopt a configuration in which the first water injection is performed only during the intake stroke.

Further, the water injection device includes a first water injection device that injects water into the intake port and a second water injection device that directly injects water into the combustion chamber, and the first water injection device is the same. It is possible to adopt a configuration in which the first water injection device is used and the second water injection is performed by the second water injection device.

The combustion gas temperature estimating means for estimating the temperature of the gas in the combustion chamber and the specific heat ratio estimating means for estimating the specific heat ratio of the gas in the combustion chamber are provided, and the water injection amount determining means is stoichiometric during rich operation. The water injection amount during the one combustion cycle for obtaining the ignition timing advance required for shifting to the operation is determined as the first water injection amount, which is the injection amount of water by the first water injection, and the combustion gas. The temperature estimating means estimates the temperature reduction amount of the combustion gas obtained by injecting water corresponding to the first water injection amount, and the specific heat ratio estimating means estimates the temperature change of the combustion gas corresponding to the temperature reduction amount. The water injection amount determining means is necessary for estimating the specific heat ratio increase amount of the obtained combustion gas and making the specific heat ratio increase amount equal to or more than the predetermined value when the specific heat ratio increase amount is less than a predetermined value. A configuration for determining the second water injection amount, which is the injection amount of water by the second water injection, can be adopted.

In addition, the water injection amount determining means injects water by the first water injection to obtain the ignition timing advance angle required for shifting to the stoichiometric operation during the rich operation. It is determined as the first water injection amount, which is the amount, the total amount of water injection that can be supplied to the maximum per one combustion cycle is calculated according to the operating conditions, and when the first water injection amount is smaller than the total water injection amount. As the amount of water injected by the second water injection, a configuration can be adopted in which the second water injection amount corresponding to the difference between the total amount of water injection and the first water injection amount is determined.

In the present invention, the first water injection is performed during the intake stroke, the intake stroke, and the compression stroke in one combustion cycle of the engine, and the second water injection is performed during the expansion stroke, so that the effect of increasing the specific heat ratio is obtained. Due to the effect of water injection in the high expansion stroke, knocking suppression in the high load operation region and improvement of thermal efficiency can be achieved at the same time.

It is an enlarged view of the main part of the engine which concerns on embodiment of this invention. It is a chart diagram of the control which concerns on embodiment of this invention. (A) is a required advance amount map, and (b) is a possible advance amount map. (A) to (e) are maps showing changes in the specific heat ratio of the burnt gas with respect to temperature.

Embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a vertical cross-sectional view showing the vicinity of the combustion chamber 2 and the cylinder head of the engine 1 of this embodiment.

A piston 8 is housed in the cylinder of the engine 1. The combustion chamber 2 is formed by the upper surface of the cylinder, the inner peripheral surface, the upper surface of the piston 8, and the like. The cylinder head above the combustion chamber 2 has an intake port 3 connected to the combustion chamber 2 of the engine 1 to send intake air into the combustion chamber 2, and an intake port 3 connected to the combustion chamber 2 to send out exhaust gas from the combustion chamber 2. It is provided with an exhaust port 4.

Further, the intake port 3 is provided with a fuel injection device (injector) 9 for injecting fuel into the intake air (intake) supplied into the combustion chamber 2. Further, the top of the combustion chamber 2 is provided with an ignition device 7 for generating an ignition spark for burning the fuel supplied into the combustion chamber 2.

The intake valve hole, which is an opening of the intake port 3 to the combustion chamber 2, is opened and closed by the intake valve 5. Similarly, the exhaust valve hole, which is an opening of the exhaust port 4 to the combustion chamber 2, is also opened and closed by the exhaust valve 6. Fuel is injected into the intake air in the intake port 3 by the fuel injection device 9, and an air-fuel mixture is formed. The formed air-fuel mixture moves to the combustion chamber 2, burns in the combustion chamber 2, and then the exhaust gas is discharged to the outside through the exhaust port 4.

In these drawings, the members and means on the intake side directly related to the present invention are mainly shown, and other members and the like are not shown. Further, although the drawing shows only one cylinder, the engine 1 may be a single cylinder or a multi-cylinder including a plurality of cylinders.

The cross-sectional shape of the intake port 3 is a so-called horizontally long oval shape in which the maximum diameter in the vertical direction connecting the upper surface 3a side and the lower surface 3b side of the passage is set smaller than the maximum diameter in the width direction orthogonal to the maximum diameter. It has become. Such an oval shape is a section from the intake passage in the intake manifold arranged upstream of the intake port 3 to the vicinity of the valve support portion where the valve stem 5b of the intake valve 5 is supported by the cylinder head 1. Continues at.

The fuel injection device 9 arranged in the intake port 3 is arranged so that the injection port 9a faces the space in the intake port 3 from the lower surface 3b side of the intake port 3. When the valve of the injection port 9a is opened, the fuel is injected toward the downstream side along the intake flow direction indicated by the arrow in the figure.

The engine 1 is provided with two water injection devices 10 that inject water with respect to intake air.

In the intake port 3, a water injection device 10 for injecting water into the intake air supplied to the combustion chamber 2 is arranged. The water injection device 10 in the intake port 3 is particularly referred to as a first water injection device 11. The first water injection device 11 is arranged so that the supply port 11a is directed from the upper surface 3a side of the intake port 3 toward the space side in the intake port 3. From the supply port 11a, water is ejected toward the downstream side along the intake flow direction.

Further, in the combustion chamber 2, a water injection device 10 for directly injecting water into the intake air in the combustion chamber 2 is arranged. The water injection device 10 in the combustion chamber 2 is particularly referred to as a second water injection device 12. The second water injection device 12 is arranged so that the supply port 12a is directed from the inner peripheral wall side of the combustion chamber 2 toward the cylinder axis of the combustion chamber 2. Water is injected from the supply port 12a toward the intake air in the combustion chamber 2.

In this embodiment, water is adopted as the fluid injected from the supply ports 11a and 12a of the first water injection device 11 and the second water injection device 12. As the fluid injected into the intake air, in addition to pure water, a mixture of water and other substances, for example, an aqueous solution containing an antiknock agent that suppresses the combustibility of fuel can be adopted. The fluid containing water injected from the first water injection device 11 and the second water injection device 12 is hereinafter simply referred to as water. Water is filled in a tank provided around the engine 1 or at any position of the vehicle on which the engine 1 is mounted, and is sent from the tank to the supply ports 11a and 12a by a pump or the like. When the valves of the supply ports 11a and 12a are opened, the water injected from the supply ports 11a and 12a merges with the intake air, and most of the water is sequentially vaporized (water vapor) in the combustion chamber 2. I will go.

The engine 1 is not limited to the one in which the fuel injection device 9 is provided in the intake port 3, but the fuel injection device 9 is provided so as to face the combustion chamber 2 and fuels the intake air in the combustion chamber 2. It may be an in-cylinder direct injection engine that directly injects fuel.

The vehicle equipped with the engine 1 includes an electronic control unit 20. The electronic control unit 20 controls the engine 1 and accessories in general, including opening / closing control of intake / exhaust valves 5 and 6, fuel injection control by the fuel injection device 9, ignition timing control, and the like. It also controls the installed equipment.

The electronic control unit 20 also controls water injection by the first water injection device 11 and the second water injection device 12 that constitute the water injection device 10. Here, the electronic control unit 20 includes a water injection amount determining means 21 for determining the water injection amount by the water injection device 10, and a water injection control means 22 for controlling the water injection by the water injection device 10. .. Further, the electronic control unit 20 includes a combustion gas temperature estimating means 23 for estimating the temperature of the gas in the combustion chamber 2 and a specific heat ratio estimating means 24 for estimating the specific heat ratio of the gas in the combustion chamber 2.

The water injection device 10 has, as a water injection form, a first water injection A that injects water during the intake stroke, or during the intake stroke and the compression stroke of the engine 1, and during the expansion stroke. A second water injection B for injecting water is set.

In this embodiment, as shown in FIG. 2, the first water injection A is performed only during the intake stroke in one combustion cycle including the exhaust stroke, the intake stroke, the compression stroke, and the expansion stroke. The period of the first water injection may be set to a period straddling the intake stroke and the compression stroke. Further, the end time of the first water injection A and the start time of the second water injection B are not simultaneous, and no overlapping period is set between the period of the first water injection A and the period of the second water injection B. That is, a water injection stop period in which water is not injected is set between the first water injection A and the second water injection B.

Further, in this embodiment, as shown in FIG. 2, the second water injection B starts water injection at a stage where a little time has passed from the compression top dead center, which is the boundary between the compression stroke and the expansion stroke. However, the start time of the second water injection B may be set to the compression top dead center. The end time of the first water injection A and the second water injection B is the time when the set amounts of water injection are completed.

Further, in this embodiment, the water injection device 10 includes two devices, a first water injection device 11 and a second water injection device 12, and the first water injection A is performed by the first water injection device 11. , The second water injection B is performed by the second water injection device 12. Further, the injection pressure of the second water injection device 12 is set to be higher than the injection pressure of the first water injection device 11.

Regarding the injection of fuel into the intake air, as shown in FIG. 2, the mode of the divided injection is such that the first fuel injection C performed during the intake stroke and the second fuel injection D performed during the compression stroke are performed. The injection form of the above is not limited to this divided injection. For example, a mode in which fuel injection is performed only during the intake stroke without performing split injection, a mode in which fuel injection is continuously performed from the intake stroke to the compression stroke, and the like can be considered.

The first control example of this invention will be described. Here, the operating region in which the air-fuel ratio, which is the mixing ratio of fuel and air, is the optimum value (1: 14.7) in which the fuel is theoretically completely combusted is referred to as the stoichiometric operating region based on the stoichiometric air-fuel ratio. Driving in the driving area is called stoichiometric driving.

In the first control example, the water injection amount determining means 21 is operating on the rich side of the stoichiometric operation region, that is, in the rich operation, the ignition timing advance angle required for shifting to the stoichiometric operation is determined. The injection amount of water for obtaining, that is, the first water injection amount is determined. The first water injection amount is calculated from the operating conditions at that time, for example, the engine speed and the load. The electronic control unit 20 holds information such as a map regarding the relationship between operating conditions such as engine speed and load, the amount of ignition timing advance required to shift to stoichiometric operation, and the required first water injection amount. doing. The determined first water injection amount is injected into the intake air by the first water injection A. When the first water injection A is performed, the occurrence of knocking is suppressed due to the decrease in the temperature in the combustion chamber 2, especially in the high load operation region, so that the ignition timing advance can be controlled.

When the air-fuel ratio that is the target of control is the stoichiometric air-fuel ratio (1: 14.7), the standardized air-fuel ratio λ (as an index showing how far the actual air-fuel ratio is from the stoichiometric air-fuel ratio). Lambda) is used. here,
The standardized air-fuel ratio λ = (actually supplied air-fuel ratio) / (theoretical required air-fuel ratio). Therefore, the air-fuel ratio actually supplied is the stoichiometric air-fuel ratio, and the standardized air-fuel ratio λ = 1. Further, regarding the control for shifting to the stoichiometric operation, the region of the standardized air-fuel ratio λ = 0.97 to 1.03 is called a lambda window, and the electronic control unit is set so that the standardized air-fuel ratio λ is within the range of this lambda window. Reference numeral 20 denotes a control thereof utilizing information from an O ₂ sensor (lambda sensor) provided in the exhaust passage.

Next, the combustion gas temperature estimating means 23 estimates the temperature reduction amount of the combustion gas obtained by injecting water corresponding to the first water injection amount. The amount of temperature reduction of the combustion gas can be theoretically calculated from variables such as the operating conditions at that time, for example, the engine speed, the intake air amount, and the intake air temperature. Alternatively, an empirical formula or the like may be created by an experiment using an engine of the same type as the type, and the calculation may be performed from the above variables based on the empirical formula. Then, the specific heat ratio estimating means 24 estimates the specific heat ratio increase amount of the combustion gas obtained by the temperature change of the combustion gas corresponding to the temperature reduction amount of the combustion gas. Similarly, the relationship between the temperature change of the combustion gas and the amount of increase in the specific heat ratio of the combustion gas may be calculated theoretically from the operating conditions at that time, or may be calculated based on an empirical formula or the like. The electronic control unit 20 maps the relationship between the first water injection amount and the temperature reduction amount of the combustion gas accompanying the water injection, and the relationship between the temperature change of the combustion gas and the specific heat ratio increase amount of the combustion gas. Etc. are held.

Here, the water injection amount determining means 21 is a second water injection required to increase the specific heat ratio increase amount to a predetermined value or more when the estimated specific heat ratio increase amount is less than a predetermined value. The amount of water injected by B, that is, the amount of second water injected is determined. The second water injection amount is calculated from the operating conditions at that time, for example, the engine speed and the load. The electronic control unit 20 holds information such as a map regarding the relationship between the operating conditions such as the engine speed and the load and the required second water injection amount. The determined second water injection amount is injected into the intake air by the second water injection B. If the second water injection B is performed, the thermal efficiency can be improved by increasing the specific heat ratio κ.

Here, as a predetermined value regarding the amount of increase in the specific heat ratio, for example, the amount of increase in the specific heat ratio κ caused by the injection of water Δκ = 0.1 can be adopted. When the amount of increase Δκ of the specific heat ratio κ by the first water injection A is less than 0.1, the second water injection B in the expansion stroke is performed to further increase the specific heat ratio. Since the second water injection B does not affect combustion, problems such as misfire due to water injection do not occur. Further, when the effect of increasing the specific heat ratio of the combustion gas can be sufficiently obtained only by the first water injection A (when it is equal to or more than a predetermined value), the second water injection B is not performed. As a result, it is possible to prevent an increase in water consumption and a shortage of water in the water tank due to spraying water more than necessary.

By the way, if too much water is injected in the first water injection A of the intake stroke or the compression stroke, misfire occurs due to deterioration of combustion, which leads to a decrease in torque and deterioration of drivability. Therefore, it is appropriate based on the amount set according to the operating condition. Control of the injection amount is required. On the other hand, in the second water injection B in the expansion stroke, the influence of the water injection on the combustion is small. Therefore, even if the first water injection A injects water to the combustion limit, the second water injection B can increase the water injection without causing deterioration of combustion. As a result, it is possible to promote an increase in the specific heat ratio and further improve fuel efficiency.

The second water injection amount injected by the second water injection B increases the specific heat ratio (combustion gas) by the additional injection when the increase in the specific heat ratio cannot be obtained by the first water injection A by a predetermined value or more. The lower limit is the amount that can be expected to be sufficiently reduced (temperature drop). Further, in order to suppress water consumption, the upper limit amount is determined from a map or the like based on operating conditions such as engine speed and load for the purpose of avoiding unnecessary water injection. Here, the higher the load and the higher the rotation speed, the larger the water injection amount.

FIGS. 3A and 3B are examples of a map (graph) for determining the first water injection amount corresponding to obtain the required ignition timing advance angle.

FIG. 3A is an ignition advance amount map required for so-called whole area stoichiometric operation (entire area λ = 1 operation). The points indicated by the arrows in the figure correspond to the engine speed (horizontal axis) and engine load (vertical axis) in the operating state at that time, and the points correspond to a large number of preset advance angles. The required advance amount can be read depending on which advance amount line is on the amount line. In the figure, one advance amount line corresponding to the indicated point is described. The ignition advance amount determined here is obtained by carrying out the first water injection A.

FIG. 3B is a map showing the relationship between the water injection rate (Mw / Mf) and the possible ignition advance amount. Here, Mw: water injection mass flow rate and Mf: fuel mass flow rate. Here, a one-dimensional map is adopted, but a two-dimensional map including a plurality of maps that differ depending on the engine speed can also be used. The water injection rate shown on the horizontal axis in the figure is determined based on the required ignition advance amount determined according to the operating state, that is, the advance angle amount shown on the vertical axis in the figure. Since the water injection rate determined here corresponds to the first water injection A, if this water injection rate (Mw / Mf) is multiplied by the fuel injection amount (Mf: fuel mass flow rate), the first water The injection amount can be determined.

Further, with reference to FIGS. 4 to 6, the amount of change in the specific heat ratio and the corresponding temperature reduction range are obtained for the amount of the first water injection amount of the first water injection A that is insufficient, and this temperature reduction range is obtained. The second water injection amount of the second water injection B required for the above may be determined.

The upper part of each of FIGS. 4A to 4E is a map (graph) with respect to the temperature of the specific heat ratio of various gas components contained in the burnt gas. The lower part of each of FIGS. 4A to 4E is a map (graph) of the relationship between the air-fuel ratio and the mole fraction of various components. FIG. 4 (a) shows carbon dioxide (CO ₂ ), FIG. 4 (b) shows water (H ₂ O), FIG. 4 (c) shows nitrogen (N ₂ ), and FIG. 4 (d) shows oxygen (O ₂ ). FIG. 4 (e) shows carbon monoxide (CO).

Here, using the lower maps of FIGS. 4A to 4E, the mole fractions of various gas components contained in the burned gas are read based on the air-fuel ratio at that time, and the various gas components are read. The average specific heat ratio of the burnt gas is calculated from the mole fraction of. The average specific heat ratio is determined by using the upper map of FIGS. 4A to 4E, the change characteristics of the specific heat ratio κ of the molecules constituting each gas component with respect to temperature, and the mole fraction of each gas component described above. Can be calculated based on.

Then, with respect to the predetermined value of the required specific heat ratio increase amount, the temperature corresponding to the specific heat ratio increase amount (necessary increase amount of the specific heat ratio in the second water injection B) that is insufficient in the first water injection A. The reduction width (required temperature reduction width in the second water injection B) is obtained, and the second water injection amount at which this temperature reduction width can be obtained is determined from the relationship between the water injection amount based on the average specific heat ratio and the heat of vaporization. Can be done. In order to reduce the number of maps, the specific heat ratio of air may be used instead of the average specific heat ratio.

Next, a second control example will be described.

In the second control example, the water injection amount determining means 21 first determines the water injection amount in one combustion cycle required to obtain the ignition timing advance required for shifting to the stoichiometric operation during the rich operation. It is determined as water injection A.

Then, in the first water injection A, the amount of water required for the stoichiometric operation is injected. Then, the total amount of water injection that can be supplied to the maximum per combustion cycle is calculated according to the operating conditions. That is, the maximum amount that can be injected due to the function of this injection device per combustion cycle is the total amount of water injection. Then, in the second water injection B in the expansion stroke, when the first water injection amount injected by the first water injection A is smaller than the total water injection amount, the difference between the total water injection amount and the first water injection amount A corresponding second water injection amount of water is injected. That is, the second water injection amount is determined by the difference between the total water injection amount and the first water injection amount (total water injection amount> first water injection amount).

That is, in the second control example, the total amount of water injection that can be supplied to the maximum per combustion cycle is calculated according to the operating conditions, and the first water injection for obtaining the ignition timing advance required for the stoichiometric operation is obtained. When the amount is calculated and the amount of the first water injection injected by the first water injection A is smaller than the total amount of water injection, the difference is used as the additional second water injection B for injection.

In the above embodiment, the engine 1 is provided with two water injection devices 10; 11 and 12 that inject water into the intake air supplied into the combustion chamber 2. Further, for the purpose of increasing the amount of water injected in the second water injection B in the expansion stroke, the second water injection B is based on a high-pressure in-cylinder injection valve (second water injection device 12). Further, the first water injection A in the intake stroke and the compression stroke is based on the low pressure port injection valve (first water injection device 11) arranged in the intake port 3. By making the second water injection B a higher pressure injection than the first water injection A, the specific heat ratio is instantly changed in the second water injection B in the expansion stroke, and the fuel efficiency improvement effect by reducing the heat loss is further improved. It gets higher. Further, by making the first water injection A in the intake stroke or the compression stroke a low pressure injection, it is possible to prevent water from adhering to the inner wall surface of the combustion chamber 2, and the intake temperature reduction effect by the water injection is more efficient. It becomes possible to obtain.

However, the effect of making the second water injection B a high pressure injection and the first water injection A a low pressure injection, or the second water injection B being injected by an in-cylinder injection valve and the first water injection A When the effect of the injection by the port injection valve is not desired, the first water injection A and the second water injection B may be performed by a single water injection device 10 without being limited to this embodiment. At this time, the first water injection A and the second water injection B may be low-pressure injections or high-pressure injections, respectively. Further, the first water injection A and the second water injection B may be injected by the in-cylinder injection valve, respectively, or may be injected by the port injection valve, respectively.

Although one embodiment of the present invention has been described above, the scope of the present invention is not limited to the above embodiment, and various modifications can be applied.

1 Engine 2 Combustion chamber 3 Intake port 4 Exhaust port 7 Ignition device 9 Fuel injection device 10 Water injection device 11 First water injection device 12 Second water injection device 20 Electronic control unit 21 Water injection amount determining means 22 Water injection control means 23 Combustion gas temperature estimation means 24 Specific heat ratio estimation means A First water injection B Second water injection

Claims (5)

Intake and exhaust ports connected to the combustion chamber of the engine,
A fuel injection device that injects fuel into the intake air supplied to the combustion chamber,
An ignition device that generates an ignition spark for burning the fuel,
A water injection device that injects water into the intake air,
A water injection amount determining means for determining the water injection amount by the water injection device,
A water injection control means for controlling the injection of water by the water injection device,
With
The water injection device has a first water injection that injects water during an intake stroke, an intake stroke, and a compression stroke in one combustion cycle of the engine, and a second water injection that injects water during an expansion stroke. The engine control device that is set. The engine control device according to claim 1, wherein the first water injection is performed only during the intake stroke. The water injection device includes a first water injection device that injects water into the intake port and a second water injection device that directly injects water into the combustion chamber.
The engine control device according to claim 1 or 2, wherein the first water injection is performed by the first water injection device, and the second water injection is performed by the second water injection device. A combustion gas temperature estimating means for estimating the temperature of the gas in the combustion chamber,
A specific heat ratio estimating means for estimating the specific heat ratio of the gas in the combustion chamber is provided.
The water injection amount determining means sets the water injection amount in the one combustion cycle for obtaining the ignition timing advance required for shifting to the stoichiometric operation in the rich operation by the water injection amount by the first water injection. Determined as a certain first water injection amount,
The combustion gas temperature estimating means estimates the temperature reduction amount of the combustion gas obtained by injecting water corresponding to the first water injection amount, and estimates the temperature reduction amount of the combustion gas.
The specific heat ratio estimating means estimates the specific heat ratio increase amount of the combustion gas obtained by the temperature change of the combustion gas corresponding to the temperature reduction amount.
The water injection amount determining means is the injection amount of water by the second water injection required to make the specific heat ratio increase amount equal to or more than the predetermined value when the specific heat ratio increase amount is less than a predetermined value. 2. The engine control device according to any one of claims 1 to 3 for determining a water injection amount. The water injection amount determining means sets the water injection amount in the one combustion cycle for obtaining the ignition timing advance required for shifting to the stoichiometric operation in the rich operation by the water injection amount by the first water injection. It is determined as a certain first water injection amount, the total amount of water injection that can be supplied to the maximum per one combustion cycle is calculated according to the operating conditions, and when the first water injection amount is smaller than the total water injection amount, the said The engine according to any one of claims 1 to 3, wherein the second water injection amount corresponding to the difference between the total water injection amount and the first water injection amount is determined as the water injection amount by the second water injection. Control device.

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