Water injection type engine

Abstract

To provide a water injection type engine capable of enhancing a temperature drop effect of a combustion chamber due to water while suppressing oil dilution.SOLUTION: A water injection type engine has a water injection valve 40 that injects water into an intake port 6, and injection pressure change means 55 that changes a water injection pressure from the water injection valve 40. The water injection type engine causes the water injection valve 40 to inject water when an intake valve 8 starts to open, and causes the injection pressure change means 55 to adjust the injection pressure according to at least one of an engine speed and an engine load so that the water injected from the water injection valve 40 collides with an exhaust-side inner peripheral surface 65 of a first portion 62 of an intake port 6 that extends upward from an opening end on a combustion chamber 10 side.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a water-injected engine equipped with a water injection valve. [Background technology]

[0002] In the past, in engines mounted on vehicles, etc., supplying water into the combustion chamber has been considered to prevent the temperature inside the combustion chamber from becoming excessively high. For example, Patent Document 1 discloses an engine equipped with a water injection valve, in which the injection port of the water injection valve is disposed so as to face the intake port, and water is injected from the water injection valve into the intake port. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2019-78248 Summary of the Invention [Problem to be solved by the invention]

[0004] A configuration in which water is injected into the intake port, as in Patent Document 1, is more likely to suppress oil dilution than a configuration in which water is injected directly into the combustion chamber. Specifically, when water is injected directly into the combustion chamber, the water spreads rapidly in the combustion chamber, causing the water to adhere to the piston crown surface and easily mix with the oil that lubricates the piston. In contrast, injecting water into the intake port suppresses water adhesion to the piston crown surface.

[0005] However, even with a configuration in which water is injected into the intake port, there is a problem in that water may adhere to the inner surface of the cylinder along the wall of the intake port. Furthermore, simply injecting water into the intake port can result in the injected water being heated by the wall of the intake port, causing it to heat up. If the temperature of the water rises before it is introduced into the combustion chamber, the effect of the water in lowering the temperature of the combustion chamber is reduced. Thus, the configuration of Patent Document 1 leaves room for improvement in terms of oil dilution and achieving a temperature-lowering effect in the combustion chamber.

[0006] The present invention has been made in consideration of the above circumstances, and aims to provide a water-injected engine that can suppress oil dilution while increasing the effect of water on lowering the temperature of the combustion chamber. [Means for solving the problem]

[0007] In order to solve the above problems, the present invention provides an engine body including a cylindrical combustion chamber centered on a cylinder axis and an intake port opening to a ceiling surface of the combustion chamber, an intake valve that opens and closes a downstream opening end of the intake port that is an opening end on the combustion chamber side, a water injection valve that injects water into the intake port, an injection pressure changing means that changes the injection pressure of water by the water injection valve, and a control means that controls the water injection valve and the injection pressure changing means, and in the engine width direction perpendicular to the cylinder axis, the side on which the intake port is formed is an intake valve. When the intake side is defined as the intake side and the opposite side as the exhaust side, the intake port includes a first portion extending upward from the downstream opening end and a second portion extending from an upper end of the first portion toward the intake side, the water injection valve is disposed in the second portion, and the control means causes the water injection valve to inject water when the intake valve starts to open, and causes the injection pressure change means to adjust the injection pressure in accordance with at least one of the engine speed and the engine load so that the water injected from the water injection valve collides with the inner surface of the exhaust side of the first portion.

[0008] In the present invention, water is injected into the intake port. This reduces adhesion of water to the piston crown surface compared to a configuration in which water is injected directly into the combustion chamber. Also, in the present invention, water is injected when the intake valve opens. This reduces the time that water remains in the intake port and the time that water receives heat from the wall of the intake port.

[0009] Furthermore, in this invention, the injection pressure is changed in response to at least one of the engine speed and the engine load, and the water injection pressure changing means is controlled so that water impinges on the exhaust-side inner circumferential surface of the first section. Therefore, even if the intake air flow velocity changes with changes in engine speed or engine load, changing the influence of the intake air on the direction of the water spray, water can be impinged on the exhaust-side inner circumferential surface of the first section regardless of this change. The target water impingement position, where the water impinges, is set on the exhaust-side inner circumferential surface of the first section, which is closer to the combustion chamber than the second section, and on a surface of the first section's inner circumferential surface that is close to the cylinder axis and extends upward from near the center of the combustion chamber. This reliably shortens the time it takes for water to reach the combustion chamber, allowing water to be introduced into the combustion chamber at a lower temperature. Furthermore, by flowing water into the combustion chamber via this surface, water adhesion to the cylinder inner circumferential surface is suppressed. Therefore, this invention can suppress oil dilution caused by water adhesion to the piston crown and the cylinder inner circumferential surface, and can enhance the combustion chamber temperature reduction effect of water.

[0010] Preferably, the first portion has a downstream portion located downstream of the intake air and a curved portion that curves from the upper end of the downstream portion toward the upstream side of the intake air, and the control means controls the injection pressure changing means to adjust the injection pressure so that water injected from the water injection valve collides with the inner surface of the curved portion on the exhaust side (Claim 2).

[0011] With this configuration, water can be smoothly introduced into the combustion chamber along the curved portion.

[0012] In the above configuration, preferably, the water injection valve has a nozzle hole at its tip, which is an outlet for water, and is attached in a position where the nozzle hole points toward the lower surface of the second portion (claim 3).

[0013] According to this configuration, the direction of the water spray injected toward the underside of the second portion changes under the influence of the intake air, making it easier to make the water spray impinge on the water impingement target position.

[0014] In the above-mentioned configuration, preferably, the control means controls the injection pressure changing means so that the injection pressure is higher when the engine speed is high than when the engine speed is low (claim 4).

[0015] As the engine speed increases, the intake air flow velocity increases, making it easier for the water spray to deviate in the intake air flow direction. In contrast, with this configuration, as the engine speed increases, the injection pressure increases and the penetration of the water spray increases, making it possible to suppress deviation of the water spray in the intake air flow direction and to make the water impinge on the above-mentioned water impingement target position regardless of the engine speed.

[0016] In the above configuration, preferably, the control means controls the injection pressure changing means to change the injection pressure so that the ratio between the flow velocity of the intake air flowing through the intake port and the spray velocity of the water injected by the water injection valve remains constant regardless of the operating state of the engine (claim 5).

[0017] With this configuration, the direction of the water spray can be maintained substantially constant regardless of the operating state of the engine, and the water can be caused to impinge on the water impingement target position regardless of the operating state of the engine.

[0018] In the above configuration, preferably, the control means causes the water injection valve to inject water only when the engine load is higher than a predetermined judged load (claim 6).

[0019] With this configuration, water is injected into the combustion chamber when the engine load is high and the temperature in the combustion chamber is likely to rise, thereby preventing the temperature in the combustion chamber from becoming excessively high. Also, when the engine load is low and there is little need to lower the temperature in the combustion chamber, water injection is stopped, thereby suppressing oil dilution by the injected water.

[0020] In the above-mentioned configuration, preferably, the control means controls the injection pressure changing means so that the injection pressure is higher when the engine load is high than when the engine load is low (claim 7).

[0021] When the engine load increases, the amount of intake air introduced into the combustion chamber increases, which increases the flow velocity of the intake air, making it easier for the water spray to deviate in the direction of the intake air flow.In contrast, with this configuration, the injection pressure is increased when the engine load increases, so it is possible to suppress the water spray from deviating in the direction of the intake air flow, and the water can be made to impinge on the above-mentioned water impingement target position regardless of the engine load.

[0022] In the above configuration, preferably, the control means controls the water injection valve so that a water injection amount, which is the amount of water injected from the water injection valve, is changed in accordance with the engine speed (claim 8).

[0023] When the water injection amount changes, the amount of water introduced into the combustion chamber changes, and the amount of temperature drop in the combustion chamber also changes. Therefore, with this configuration, the amount of water introduced into the combustion chamber is changed according to the engine speed, so the temperature of the combustion chamber can be lowered more appropriately according to the engine speed.

[0024] In the above configuration, preferably, the control means controls the water injection valve so that, when the engine is operating in a low-speed region where the engine speed is below a predetermined first speed, the water injection amount is greater than when the engine is operating in a high-speed region where the engine speed is equal to or greater than a second speed that is greater than the first speed, and controls the water injection valve so that, when the engine is operating in a medium-speed region where the engine speed is equal to or greater than the first speed but less than the second speed, the water injection amount is less than when the engine is operating in the high-speed region (Claim 9).

[0025] It is known that knocking is most likely to occur in the low speed range, followed by the high speed range and the medium speed range. Therefore, with the above configuration, the water injection amount, and therefore the amount of water introduced into the combustion chamber, is increased in the order of the ranges in which knocking is most likely to occur. Therefore, knocking can be suppressed while suppressing oil dilution due to excessive water injection. [Effects of the Invention]

[0026] As described above, the water injection engine of the present invention can suppress oil dilution while enhancing the effect of water on lowering the temperature of the combustion chamber. [Brief explanation of the drawings]

[0027] [Figure 1] 1 is a schematic configuration diagram of the periphery of an engine body included in a water injection engine according to an embodiment of the present invention. [Figure 2] FIG. 1 is a schematic diagram showing a portion of an engine. [Figure 3] FIG. 2 is a block diagram showing a control system of the engine. [Figure 4] 3 is a schematic diagram showing the state of water spray injected from a water injection valve. FIG. [Figure 5] 3 is a schematic diagram showing the state of water spray injected from a water injection valve. FIG. [Figure 6] 10 is a graph showing the relationship between engine speed, intake flow velocity, and injection velocity. [Figure 7] 3 is a flowchart showing a part of a control procedure of the engine. [Figure 8] 10 is a flowchart showing a part of high load control. [Figure 9] FIG. 2 is a diagram showing an operating range of the engine. [Figure 10] 1 is a graph showing the relationship between engine speed and water injection pressure. [Figure 11] 1 is a graph showing the relationship between engine speed and water injection amount. [Figure 12] 1 is a graph showing the relationship between engine load and water injection pressure. DETAILED DESCRIPTION OF THE INVENTION

[0028] (1) Overall engine configuration A preferred embodiment of the present invention will be described in detail below with reference to the accompanying drawings. Fig. 1 is a schematic diagram of the periphery of an engine main body 1 included in a water-injected engine E according to an embodiment of the present invention. Fig. 2 is a schematic diagram showing a portion of the water-injected engine E. The water-injected engine E shown in Figs. 1 and 2 is a four-stroke engine mounted on a vehicle as a power source for traveling, and comprises the engine main body 1, an intake passage 20 through which intake air introduced into the engine main body 1 flows, and an exhaust passage 30 through which exhaust gas discharged from the engine main body 1 flows. Hereinafter, the water-injected engine E will be referred to simply as engine E where appropriate.

[0029] The engine body 1 has a cylinder block 3 in which cylinders 2 are formed, a cylinder head 4 attached to the upper surface of the cylinder block 3 so as to close the cylinders 2 from above, and pistons 5 fitted into each cylinder 2 so as to be able to slide back and forth. The cylinders 2 are approximately cylindrical. In this embodiment, the engine body 1 is an in-line four-cylinder engine, and the cylinder block 3 has four cylinders 2 arranged in a row. Hereinafter, the arrangement direction of the cylinders 2 will be referred to as the cylinder arrangement direction.

[0030] Each cylinder 2 defines a cylindrical combustion chamber 10 centered on a cylinder axis O1 extending in the vertical direction. Specifically, the combustion chamber 10 is defined above the piston 5 by the inner circumferential surface of the cylinder 2, the crown surface of the piston 5, and the bottom surface of the cylinder head 4. A ceiling surface 10A of the combustion chamber 10 is formed by part of the bottom surface of the cylinder head 4. Fuel is supplied to the combustion chamber 10 by injection from a fuel injection valve 11, which will be described later. The supplied fuel mixes with air in the combustion chamber 10 and burns, and the piston 5 is pushed down by the expansion force caused by this combustion, causing it to reciprocate in the vertical direction.

[0031] A crankshaft 15, which is the output shaft of the engine body 1, is provided below the piston 5. The crankshaft 15 is connected to the piston 5 via a connecting rod (not shown) and rotates around its central axis in response to the reciprocating motion of the piston 5. In this embodiment, the engine is a gasoline engine that uses gasoline as its main fuel, and the engine body 1 is supplied with gasoline alone or a fuel that includes gasoline and a secondary component such as bioethanol. A crank angle sensor SN1 is attached to the cylinder block 3 to detect the rotation angle of the crankshaft 15, i.e., the engine speed. A knock sensor SN2 is also attached to the cylinder block 3 to detect vibrations of the engine body 1.

[0032] The cylinder head 4 is formed with intake ports 6 that communicate with the combustion chambers 10 and supply intake air to the combustion chambers 10. The intake ports 6 open to a ceiling surface 10A of the combustion chambers 10. That is, a downstream opening end 61 is formed in the ceiling surface 10A of the combustion chambers 10, at the opening end of the intake port 6 facing the combustion chamber 10 and located downstream of the intake air, i.e., downstream in the flow direction of the intake air. In this embodiment, two intake ports 6 communicate with each cylinder 2, and two downstream opening ends 61 are formed in the ceiling surface 10A of each combustion chamber 10.

[0033] Exhaust ports 7 are formed in the cylinder head 4, which communicate with the combustion chambers 10 and discharge burned gas (exhaust gas) within the combustion chambers 10. The exhaust ports 7 open to a ceiling surface 10A of the combustion chambers 10. That is, an exhaust port opening end 71, which is an opening end on the upstream side in the exhaust flow direction of the exhaust port 7, is formed in the ceiling surface 10A of the combustion chambers 10. In this embodiment, two exhaust ports 7 communicate with each cylinder 2, and two exhaust port opening ends 71 are formed in the ceiling surface 10A of each combustion chamber 10.

[0034] The intake port 6 and the exhaust port 7 are provided on opposite sides in the engine width direction across the cylinder axis O1, which is the center line of the combustion chamber 10. Here, the engine width direction is a direction perpendicular to the up-down direction, i.e., a direction perpendicular to the cylinder axis O1. In this embodiment, the engine width direction is also a direction perpendicular to the cylinder arrangement direction. As shown in FIG. 2 , when viewed from above, the intake ports 6 and the exhaust ports 7 are provided on opposite sides in the engine width direction across an imaginary line X1 that passes through the cylinder axis O1 of each combustion chamber 10 and extends along the cylinder arrangement direction. Hereinafter, in the engine width direction, the side on which the intake port 6 is formed is referred to as the intake side, and the opposite side, i.e., the side on which the exhaust port 7 is formed, is referred to as the exhaust side.

[0035] The cylinder head 4 is provided with intake valves 8 that open and close the intake ports 6, and exhaust valves 9 that open and close the exhaust ports 7. The engine of this embodiment is a four-valve type with two intake valves and two exhaust valves, and each cylinder 2 is provided with two intake ports 6, two exhaust ports 7, two intake valves 8, and two exhaust valves 9. The intake valves 8 and exhaust valves 9 are opened and closed by a valve drive device (not shown) in conjunction with the rotation of the crankshaft 15.

[0036] The cylinder head 4 is provided with a set of fuel injection valves 11 for each cylinder 2, which inject fuel into the combustion chamber 10. Note that while Fig. 1 shows a case where the fuel injection valves 11 are side injection type fuel injection valves 11 that inject fuel into the combustion chamber 10 from the side of the intake side, the fuel injection valves 11 are not limited to the side injection type.

[0037] The cylinder head 4 is provided with a pair of spark plugs 12 for each cylinder 2, which ignite the fuel-air mixture formed in the combustion chamber 10. The spark plugs 12 are attached to the cylinder head 4 so as to face the inside of the combustion chamber 10 from a ceiling surface 10A of the combustion chamber 10. The spark plugs 12 are provided approximately in the center of the ceiling surface 10A of the combustion chamber 10.

[0038] Water injectors 40 that inject water into the intake ports 6 are attached to the cylinder head 4. One water injector 40 is provided for each intake port 6, and water is injected individually from each water injector 40 into each intake port 6. This water injector 40 corresponds to the "water injector" of the present invention.

[0039] The vehicle is equipped with a water tank 51 that stores water inside. The water injection valve 40 is connected to the water tank 51 via a water supply pipe 52, and injects water introduced from the water tank 51 through the water supply pipe 52 into the intake port 6. Note that water may be supplied to the water tank 51 from outside the vehicle, or water generated from exhaust gas may be supplied to the water tank 51.

[0040] In addition to the water injection valves 40, the engine E is equipped with a water pump 53 and a water injection motor 55 that drives the water pump 53. The water pump 53 is provided in the water supply pipe 52. The water pump 53 is driven by the water injection motor 55 to pump water from the water tank 51 toward the water injection valves 40. The water supply pipe 52 branches downstream of the water pump 53, and each branch pipe is connected to each water injection valve 40. Water is pumped from the same water pump 53 to each water injection valve 40. The water pressure in the portion of the water supply pipe 52 downstream of the water pump 53 is approximately the same as the pressure inside the water injection valves 40, i.e., the injection pressure of the water injection valves 40. The driving force of the water pump 53 by the water injection motor 55 is variable, and the discharge pressure of the water pump 53, and therefore the injection pressure of the water injection valves 40, is changed by the water injection motor 55. A water injection pressure sensor SN3 is attached to the water supply pipe 52 downstream of the water pump 53. The water injection pressure sensor SN3 detects the water pressure in the water supply pipe 52, i.e., the water injection pressure of the water injection valve 40. The water injection motor 55 corresponds to the "injection pressure changing means" of the present invention.

[0041] The intake passage 20 is connected to the intake side of the cylinder head 4 so as to communicate with the intake ports 6. A surge tank 21 is provided midway along the intake passage 20. The intake passage 20 branches into four passages downstream from the surge tank 21, and each branch passage 22 communicates with the two intake ports 6 of each cylinder 2. The air (fresh air) that has passed through the intake passage 20 is introduced into the combustion chamber 10 via the intake passage 20 and the intake ports 6.

[0042] A throttle valve 14 is provided in the intake passage 20 at a portion upstream of the surge tank 21 to open and close the intake passage 20 to adjust the flow rate of intake air, which is air introduced into the combustion chamber 10. An air flow sensor SN4 is also attached to the intake passage 20 to detect the intake air amount, which is the flow rate of intake air. For example, the air flow sensor SN4 is attached to a portion of the intake passage 20 upstream of the throttle valve 14.

[0043] The exhaust passage 30 is connected to the exhaust side surface of the cylinder head 4 so as to communicate with the exhaust port 7. Burned gas (exhaust gas) generated in the combustion chamber 10 is discharged to the outside through the exhaust port 7 and the exhaust passage 30.

[0044] (2) Detailed structure of intake port The intake port and its surrounding structure will now be described in detail. In this description, the upstream and downstream sides of the intake air, i.e., the upstream and downstream sides in the flow direction of the intake air, will simply be referred to as the upstream and downstream sides.

[0045] The downstream opening end 61 is formed in an area of the ceiling surface 10A of the combustion chamber 10 on the intake side with respect to the cylinder axis O1 and imaginary line X1, which are the center lines of the combustion chamber 10. In other words, when viewed in the vertical direction, the downstream opening end 61 is formed at a position where its center O2 is shifted toward the intake side with respect to the center of the combustion chamber 10.

[0046] The intake port 6 as a whole extends upward from a downstream opening end 61 toward the intake side in the engine width direction.

[0047] Specifically, the intake port 6 has a first portion 62 extending upward from a downstream opening end 61 and a second portion 63 extending from the upper end, i.e., the upstream end, of the first portion 62 toward the intake side. The first portion 62 is composed of a downstream portion 62A extending upward in a substantially straight line from the downstream opening end 61 while being slightly inclined toward the intake side, and a curved portion 62B curving from the upper end of the downstream portion 62A toward the intake side. More specifically, the curved portion 62B is curved so that the further away it is from the downstream portion 62A, the closer it is to the intake side, and extends upward from the upper end of the downstream portion 62A toward the intake side. The second portion 63 extends upward in a substantially straight line toward the intake side from the upper end of the curved portion 62B while being inclined more toward the intake side than the downstream portion 62A.

[0048] The upper end of the second portion 63, which is the end opposite to the downstream opening end 61 of the intake port 6, that is, the upstream end, opens to the side surface of the cylinder head 4 on the intake side.

[0049] The water injector 40 has a tip end with a nozzle hole 41 formed therein, and injects water from the tip end. While the number of nozzle holes 41 is not particularly limited, the water injector 40 of this embodiment is a multi-hole type injector with multiple nozzle holes 41 formed at the tip end. For example, the water injector 40 has 12 nozzle holes 41. The water injector 40 faces the second portion 63 from above, and is attached to the cylinder head 4 with the nozzle hole 41A facing downward. In other words, the water injector 40 is attached to the cylinder head 4 so that its tip end faces the inside of the second portion 63 from the upper surface of the second portion 63. The amount by which the tip end of the water injector 40 protrudes from the upper surface of the second portion 63 is smaller than the radius of the second portion 63, and the tip end of the water injector 40 is located near the upper surface of the second portion 63.

[0050] The water injector 40 is mounted with its nozzle hole 41 facing downstream and toward the underside of the second section 63. Specifically, the water injector 40 is mounted so that its injection axis X10, i.e., the central axis of the nozzle hole, extends downward from the tip toward the exhaust side. In this embodiment, the inclination of the injection axis X10 of the water injector 40 toward the intake side relative to the vertical direction is smaller than the inclination of the axis X3 of the second section 63 toward the intake side relative to the vertical direction, and the injection axis X10 of the water injector 40 and the axis X3 of the second section 63 intersect. Therefore, if water is injected from the water injector 40 when there is no intake air flow in the intake port 6, the water spray travels along the injection axis X10 of the water injector 40 and collides with the underside of the second section 63.

[0051] (3) Control system Fig. 3 is a block diagram showing the control system of engine E. The PCM 100 shown in this diagram is a microprocessor for overall control of the engine, and is composed of a well-known CPU, ROM, RAM, etc. This PCM 100 corresponds to the "control means" of the present invention.

[0052] Detection signals from various sensors are input to the PCM 100. For example, the PCM 100 is electrically connected to a crank angle sensor SN1, a knock sensor SN2, a water injection pressure sensor SN3, and an air flow sensor SN4. The vehicle is also provided with an accelerator sensor SN5 that detects the degree of accelerator operation, which is the degree of opening of an accelerator pedal (not shown) operated by the driver of the vehicle, and the PCM 100 is also electrically connected to the accelerator sensor SN5. At least the information detected by each of these sensors SN1 to SN5, namely, the engine speed, vibration of the engine body 1, water injection pressure, intake air volume, and accelerator operation, is sequentially input to the PCM 100.

[0053] The PCM 100 performs various determinations and calculations based on input signals from each sensor, while controlling each part of the engine E. The PCM 100 is electrically connected to the fuel injector 11, the spark plug 12, the throttle valve 14, the water injector 40, the water injection motor 55, etc., and outputs control signals to each of these devices based on the results of the above calculations, etc.

[0054] The PCM 100 switches the water injector 40 between open and closed states, thereby switching between on and off the injection of water from the water injector 40 into the intake port 6. That is, the water injector 40 is provided with a device that opens and closes its nozzle hole, and this device opens and closes the nozzle hole of the water injector 40 in response to a signal from the PCM 100. The PCM 100 also changes the open period of the water injector 40. Under the same water injection pressure, the longer the open period of the water injector 40, the greater the water injection amount (the amount of water injected from the water injector 40). The PCM 100 also changes the driving force of the water injection motor 55 to change the discharge pressure of the water pump 53 and, ultimately, the water injection pressure (the injection pressure of the water injector 40). The PCM 100 also switches between on and off the fuel injector 11 and changes the open period of the fuel injector 11, i.e., the fuel injection period. The PCM 100 also drives the spark plug 12 to ignite the air-fuel mixture, and changes the opening of the throttle valve 14.

[0055] (Outline of water injection control) First, an overview of the control related to water injection will be explained using Figures 4 and 5. Figures 4 and 5 are schematic diagrams for explaining the movement of water injected from the water injection valve 40.

[0056] The purpose of water injection in this embodiment is to reduce the temperature in the combustion chamber 10 by using the heat of vaporization of water to suppress the occurrence of knocking. Therefore, it is desirable to perform water injection at a timing when water flows into the combustion chamber 10 at a lower temperature. If water were injected into the intake port 6 before the intake valve 8 opens, the temperature of the water would rise due to heat from the wall surface of the intake port 6 between the time the water is injected and the time the intake valve 8 opens and the water flows into the combustion chamber 10. In contrast, if water is injected into the intake port 6 at the time the intake valve 8 starts to open, the period during which heat is absorbed from the wall surface of the intake port 6 and the like is shortened, allowing water to be introduced into the combustion chamber 10 at a lower temperature. Therefore, in this embodiment, the PCM 100 drives the water injector 40 to inject water into the intake port 6 when the intake valve 8 starts to open.

[0057] As described above, knocking can be suppressed by introducing water into the combustion chamber 10. However, introducing water into the combustion chamber 10 may cause oil dilution. Specifically, if the introduced water adheres to the inner circumferential surface of the cylinder 2 or the crown surface of the piston 5, the water may mix with the oil that lubricates these surfaces, diluting the oil.

[0058] As described above, when viewed in the vertical direction, the center O2 of the downstream opening end 61 is offset toward the intake side relative to the center of the combustion chamber 10, i.e., the cylinder axis O1. The intake port 6 extends upward and toward the intake side from the downstream opening end 61. With this configuration, the lower surface of the intake port 6 is connected to the inner circumferential surface of the cylinder 2. Therefore, if water is injected so that most of it collides with the lower surface of the intake port 6, as indicated by arrow Y1 in FIG. 4, the water (W10) will flow along the lower surface of the intake port 6 into the combustion chamber 10 and easily adhere to the inner circumferential surface of the cylinder 2. In contrast, if water is injected so that it collides with the upper surface of the intake port 6, as indicated by arrow Y2 in FIG. 4, the water (W20) can be introduced near the center of the combustion chamber 10, thereby preventing it from adhering to the inner circumferential surface of the cylinder 2. However, even on the top surface of the intake port 6, a position close to the water injector 40 is far from the combustion chamber 10, and the temperature of the water rises due to heat received from the intake port 6 before it reaches the combustion chamber 10. For this reason, as shown by arrow Y3 in Figure 5, it is desirable to have the water impinge on a position on the top surface of the intake port 6 that is far from the water injector 40 (closer to the combustion chamber 10). Therefore, in this embodiment, the water injector 40 is controlled so that the water impinges on the exhaust-side portion of the inner circumferential surface of the first portion 62 of the intake port 6 that is close to the cylinder axis O1, that is, the exhaust-side inner circumferential surface 65 of the first portion 62 (hereinafter referred to as the exhaust-side inner circumferential surface 65).

[0059] However, the inventors have discovered that if water is injected from the water injector 40 when the intake valve 8 begins to open, the flow of intake air affects the water spray, and depending on the flow velocity of the intake air, the impact position of the water may deviate from the exhaust-side inner circumferential surface 65. Specifically, as the flow velocity of the intake air increases, the water spray is more likely to deviate in the direction of the intake air flow relative to the water injection direction. After extensive research into this issue, the inventors have discovered that if the ratio of the water spray velocity to the intake air flow velocity is kept constant, the impact position of the injected water can be kept constant regardless of the intake air flow velocity. Hereinafter, the water injected by the water injector 40 will be referred to as injected water, where appropriate.

[0060] Furthermore, since the intake air flow velocity increases as the engine speed increases, as shown by the solid line in the upper graph of Fig. 6, we found that if the water spray velocity increases as the engine speed increases, as shown by the dashed line in the upper graph of Fig. 6, the ratio of intake air flow velocity to spray velocity can be kept constant, as shown in the lower graph of Fig. 6. Furthermore, since the spray penetration increases and the spray velocity increases as the injection pressure increases, we discovered that if the ratio between engine speed and water injection pressure is kept constant, the impingement position of the injected water can be kept constant regardless of the intake air flow velocity. Note that the graph of engine speed and intake air flow velocity in Fig. 6 shows these relationships when the engine load is kept approximately constant.

[0061] Based on the above findings, in this embodiment, the water injection pressure is controlled so that the value obtained by dividing the engine rotation speed by the water injection pressure is a judgment value determined in advance by experiments or the like, and is maintained at the value at which the jetted water collides with the exhaust-side inner circumferential surface 65. In particular, in this embodiment, the above value is set to the value at which the jetted water collides with the upper part of the exhaust-side inner circumferential surface 65 corresponding to the curved portion 62B, in other words, the exhaust-side inner circumferential surface of the curved portion 62B. In other words, the water collision target position, which is the position at which the water is to be collided, is set to the exhaust-side inner circumferential surface of the curved portion 62B (the upper part of the exhaust-side inner circumferential surface 65), and the PCM 100 controls the water injection pressure so that the jetted water collides with the exhaust-side inner circumferential surface of the curved portion 62B.

[0062] (Control details) The control performed by the PCM 100, including the control related to the water injection described above, will be described using the flowchart of Fig. 7. Each step shown in Fig. 7 is repeatedly performed at a predetermined calculation cycle while the engine E is running.

[0063] First, the PCM 100 reads various pieces of information detected by the sensors (step S1).

[0064] Next, the PCM 100 calculates a target torque, which is a target value of the engine torque (step S2). The PCM 100 calculates the target torque from the accelerator opening, the engine speed, and the like.

[0065] Next, the PCM 100 sets a target intake air amount, a target fuel amount, and ignition timing based on the target torque (step S3). The target intake air amount is a target value for the intake air amount. The target fuel amount is a target value for the amount of fuel injected from the fuel injection valve 11. The ignition timing is the timing at which the spark plug 12 ignites the air-fuel mixture. The PCM 100 sets each of the above values based on the target torque and engine speed, etc., so that the target torque is achieved.

[0066] Next, the PCM 100 adjusts the opening of the throttle valve 14 so as to achieve the target intake amount (step S4).

[0067] Next, the PCM 100 determines whether or not the condition that the engine E is operating within the first region A1 is satisfied (step S5). As shown in Fig. 9, in this embodiment, the region of the operating region of the engine E where the engine load is equal to or less than a predetermined judgment load T1 is set as the first region A1, and the region where the engine load is higher than the judgment load T1 is set as the second region A2. The PCM 100 calculates the engine load from the engine speed, intake amount, etc., and determines whether or not the engine E is operating within the first region A1 based on the calculated engine load. The judgment load T1 is set in advance and stored in the PCM 100.

[0068] If the determination in step S5 is YES and the engine E is operating within the first region A1, the PCM 100 performs normal control (step S6). Specifically, the PCM 100 does not perform high load control, which will be described later, but controls the fuel injector 11 so as to achieve the target fuel amount set in step S3, and controls the spark plug 12 so as to perform ignition at the ignition timing set in step S3. After step S6, the PCM 100 returns to the processing of step S1. Here, water injection is prohibited in normal control. As a result, in step S6, the operation of the water injector 40 is stopped. Also in step S6, a water injection execution flag, which will be described later, is set to 0.

[0069] On the other hand, if the determination in step S5 is YES and the engine E is operating in the second range A2, the PCM 100 performs high load control (step S7). After step S7, that is, after the high load control is performed, the PCM 100 returns to the processing of step S1.

[0070] The high load control will be described in detail with reference to the flowchart of FIG.

[0071] When the high load control is performed, the PCM 100 first determines whether knocking is occurring (step S11). The PCM 100 makes this determination based on a signal from the knock sensor SN2.

[0072] If the determination in step S11 is YES and it is determined that knocking is occurring, the PCM 100 determines whether the actual torque is equal to or less than the target torque set in step S3 (step S12). The actual torque is the current engine torque of the engine E, and the PCM 100 calculates the actual torque based on the intake air amount, engine speed, etc.

[0073] If the determination in step S12 is YES, that is, the actual torque is equal to or less than the target torque, the PCM 100 sets the ignition correction amount to 0 (zero) (step S13). The ignition correction amount is a correction amount for the ignition timing.

[0074] After step S13, PCM 100 determines whether the value obtained by dividing the engine speed by the water injection pressure matches a determination value (step S14). PCM 100 makes this determination using the current engine speed detected by crank angle sensor SN1 and the current water injection pressure detected by water injection pressure sensor SN3. As described above, the determination value is the ratio of the engine speed to the water injection pressure when the injected water collides with the inner circumferential surface on the exhaust side of curved portion 62B, and is set in advance and stored in PCM 100. Hereinafter, the value obtained by dividing the current engine speed by the current water injection pressure will be referred to as the injection pressure ratio, where appropriate.

[0075] If the determination in step S14 is YES, that is, the injection pressure ratio matches the determination value, the PCM 100 proceeds to step S18.

[0076] On the other hand, if the determination in step S14 is NO, meaning that the injection pressure ratio does not match the determination value, the PCM 100 determines whether or not the injection pressure ratio is greater than the determination value (step S15).

[0077] If the determination in step S15 is YES and the injection pressure ratio is greater than the determination value, that is, if the current water injection pressure is less than the water injection pressure at which the injection pressure ratio matches the determination value, the PCM 100 increases the water injection pressure (step S16). Specifically, the PCM 100 increases the driving force of the water injection motor 55 to increase the discharge pressure of the water pump 53 so that the water injection pressure increases to a pressure at which the injection pressure ratio matches the determination value. On the other hand, if the determination in step S15 is NO and the injection pressure ratio is less than the determination value, that is, if the current water injection pressure is greater than the water injection pressure at which the injection pressure ratio matches the determination value, the PCM 100 reduces the water injection pressure (step S17). Specifically, the PCM 100 reduces the driving force of the water injection motor 55 to reduce the discharge pressure of the water pump 53 so that the water injection pressure decreases to a pressure at which the injection pressure ratio matches the determination value. After steps S16 and S17, the PCM 100 proceeds to step S18.

[0078] By performing steps S14 to S17, the water injection pressure is controlled to a value at which the injection pressure ratio becomes the judgment value. In other words, the water injection pressure is controlled to a value obtained by dividing the current engine speed by the judgment value. The judgment value is a constant value. Thus, by performing steps S14 to S17, the water injection pressure is controlled to a pressure that is proportional to the engine speed, and increases as the engine speed increases, as shown in FIG. 10.

[0079] In step S18, the PCM 100 determines whether either the injection execution flag is set to 0 or the speed range has just changed is satisfied. The injection execution flag is set to 1 if water injection was performed one calculation cycle ago, i.e., if water was injected into the intake port 6 by the water injector 40 one calculation cycle ago, and is set to 0 otherwise. A change in the speed range means that the engine operating range has changed between three ranges A21 to A23 shown in FIG. 11. FIG. 11 is a graph showing the relationship between engine speed and water injection amount. As shown in FIG. 11, in this embodiment, the second range A2 is further divided into three ranges depending on the water injection amount. Specifically, the second range A2 is divided into a low-speed range A21 where the engine speed is less than the first rotation speed N1, a medium-speed range A22 where the engine speed is equal to or greater than the first rotation speed N1 but less than the second rotation speed N2, and a high-speed range A23 where the engine speed is equal to or greater than the second rotation speed N2. The condition that the speed range has just changed is met when the region in which engine E is operating has changed between the low-speed region A21, the medium-speed region A22, and the high-speed region A23. PCM 100 makes this determination based on the current engine speed and the engine speed a predetermined time ago. For example, PCM 100 determines that the condition that the speed range has changed is met when the current operating region of engine E is one of the low-speed region A21, the medium-speed region A22, and the high-speed region A23, and the operating region one calculation cycle ago was one of the other two regions.

[0080] If the determination in step S18 is YES, the injection execution flag is 0, and water injection was not performed in the previous calculation cycle, or the condition that the speed range has just changed is met, the process proceeds to step S19.

[0081] In step S19, the PCM 100 sets the water injection amount. The water injection amount set in step S19 is the basic amount of water injection, which is the amount of water injected from the water injector 40.

[0082] The water injection amount is set for each of the three speed ranges A21 to A23. When the engine is operating in the same range, in step S19, the water injection amount is set to the same value regardless of the engine speed. If the water injection amount set when the engine E is operating in the low speed range A21 is a first injection amount W1, when the engine E is operating in the medium speed range A22, the water injection amount is set to a second injection amount W2 that is smaller than the first injection amount W1. When the engine E is operating in the high speed range A23, the water injection amount is set to a third injection amount W3 that is smaller than the first injection amount W1 and larger than the second injection amount W2. After step S19, the PCM 100 proceeds to step S20.

[0083] On the other hand, if the determination in step S18 is NO and the injection execution flag is 1, that is, water injection was already performed one calculation cycle ago, and the condition that the speed range has changed is not established, that is, if the engine E continues to operate in the same speed range A21 to A23, the PCM 100 corrects the water injection amount to increase it (step S20). Specifically, the PCM 100 sets the water injection amount to an amount greater than the water injection amount one calculation cycle ago. After step S20, the PCM 100 proceeds to step S21.

[0084] In step S21, the PCM 100 performs water injection simultaneously with the start of opening of the intake valve 8. That is, the PCM 100 drives the water injector 19 to inject water simultaneously with the start of opening of the intake valve 8 (step S21). At this time, the PCM 100 opens the water injector 19 for only the period during which the water injection amount set in step S19 or step S20 is achieved.

[0085] In step S22, which is reached after step S21 has been performed and water injection has been performed, the PCM 100 sets the water injection execution flag to 1. If the water injection execution flag is already 1, it maintains this value.

[0086] After step S22, the process proceeds to step S23. In step S23, the PCM 100 determines the final ignition timing. In step S23, the PCM 100 determines the final ignition timing by correcting the ignition timing of one calculation cycle before with the ignition correction amount. Specifically, the final ignition timing (i) is calculated using the ignition timing (i-1) of one calculation cycle before as ignition timing (i) = ignition timing (i-1) + ignition correction amount. Note that in this embodiment, the ignition correction amount is set to a value greater than 0 when correcting the ignition timing to the advance side, and a value less than 0 when correcting the ignition timing to the retard side. Furthermore, if the ignition timing set in step S3 has changed by more than a predetermined value from the value of one calculation cycle before due to a significant change in the target torque, the basic ignition timing set in step S3 is used instead of the ignition timing (i-1) of one calculation cycle before, and this basic ignition timing is corrected.

[0087] If knocking occurs during high load control (the determination in step S11 is YES) and the actual torque is equal to or less than the target torque (the determination in step S12 is YES), the ignition correction amount is set to 0 (zero) in step S13. As a result, in this case, the final ignition timing is maintained at the ignition timing one calculation cycle before. As described above, if the ignition timing set in step S3 has changed by more than a predetermined value from the value one calculation cycle before, the basic ignition timing set in step S3 is used as the ignition timing to be corrected, and therefore the final ignition timing is determined to be the ignition timing set in step S3.

[0088] After step S23, the PCM 100 drives the fuel injector 11 to inject fuel into the combustion chamber 10, and drives the spark plug 12 to ignite the air-fuel mixture in the combustion chamber 10 (step S24). At this time, the PCM 100 drives the spark plug 12 so as to achieve the ignition timing set in step S23. The PCM 100 also drives the fuel injector 11 so as to achieve the target fuel amount set in step S3.

[0089] After step S24, the PCM 100 returns to the processing of step S1.

[0090] Thus, when high load control is being performed and knocking occurs (the determination in step S11 is YES) and the actual torque is equal to or lower than the target torque (the determination in step S12 is YES), water is injected from the water injector 19 into the intake port 6. The water injection pressure at this time is set to a pressure at which the value obtained by dividing the engine speed by the water injection pressure matches the determination value. As described above, the intake air flow velocity increases as the engine speed increases, and the water spray velocity increases as the injection pressure increases. Therefore, by controlling the water injection pressure so that the value obtained by dividing the engine speed by the water injection pressure matches the determination value, the ratio of the intake air flow velocity to the water spray velocity is maintained at a constant value. In other words, when high load control is being performed and knocking occurs (the determination in step S11 is YES) and the actual torque is equal to or lower than the target torque (the determination in step S12 is YES), the PCM 100 controls the water injection pressure so that the ratio of the intake air flow velocity to the water spray velocity is maintained at a constant value regardless of the engine speed.

[0091] Furthermore, if knocking occurs during high load control (the determination in step S11 is YES) and the actual torque is equal to or less than the target torque (the determination in step S12 is YES), the water injection amount is set according to the engine speed, and if water injection has already been performed one calculation cycle prior, the water injection amount is increased. On the other hand, if knocking occurs during high load control (step S11) and the actual torque is equal to or less than the target torque (step S12), the ignition timing is not corrected, and the ignition timing is set to the ignition timing one calculation cycle prior or the basic ignition timing set based on the target torque.

[0092] Returning to step S12, the process when the determination in step S12 is NO will now be described. If the determination in step S12 is NO and the actual torque is greater than the target torque while high load control is being performed and knocking has occurred (the determination in step S11 is YES), the PCM 100 prohibits water injection (step S31). That is, the PCM 100 does not drive the water injector 40 even when the intake valve 8 begins to open, and keeps it stopped. Also, in step S31, the PCM 100 sets the injection execution flag to 0. Note that if the water injection execution flag is already 0, it is maintained as 0.

[0093] After step S31, the PCM 100 sets an ignition correction amount (step S32). At this time, the PCM 100 sets an ignition timing retard amount. In this embodiment, the retard amount is set to a constant value regardless of the operating state of the engine E. This retard amount is set in advance and stored in the PCM 100.

[0094] After step S32, the process proceeds to step S23. In step S23 after proceeding to step S31, the ignition timing is retarded by the ignition correction amount set in step S32 relative to the ignition timing of the previous calculation cycle. If the ignition timing set in step S3 has changed by a predetermined value or more from the value of the previous calculation cycle, the ignition timing is retarded by the ignition correction amount set in step S32 relative to the ignition timing set in step S3. After step S23, the process proceeds to step S24. In step S24, the PCM 100 drives the spark plug 12 to achieve the ignition timing set in step S22, and drives the fuel injector 11 to achieve the target fuel amount set in step S3. As described above, after step S24, the PCM 100 returns to the processing of step S1.

[0095] In this way, when high load control is being performed and knocking occurs (the determination in step S11 is YES) and the actual torque is greater than the target torque (the determination in step S12 is NO), water injection is stopped while the ignition timing is retarded.

[0096] Returning to step S11, the process when the determination in step S11 is NO will now be described. If the determination in step S11 is NO, high load control is being performed, and knocking is not occurring, the PCM 100 prohibits water injection (step S41). That is, the PCM 100 does not drive the water injector 40 even when the intake valve 8 begins to open, and keeps it stopped. Also, in step S41, the PCM 100 sets the injection execution flag to 0. Note that if the water injection execution flag is already 0, it is maintained at this value.

[0097] After step S41, the PCM 100 determines whether the actual torque is less than the target torque set in step S3 (step S42).

[0098] If the determination in step S42 is YES, that is, the actual torque is less than the target torque, the PCM 100 sets an ignition correction amount (step S43). At this time, the PCM 100 sets an advance amount of the ignition timing. In this embodiment, the advance amount is set to a constant value regardless of the operating state of the engine E. This advance amount is set in advance and stored in the PCM 100.

[0099] After step S43, the process proceeds to step S23. In step S23 after proceeding to step S43, the ignition timing is advanced by the ignition correction amount set in step S43 relative to the ignition timing of one calculation cycle before. Note that if the ignition timing set in step S3 has changed by more than a predetermined value from the value of one calculation cycle before, the ignition timing is advanced by the ignition correction amount set in step S32 relative to the ignition timing set in step S3. After step S23, the process proceeds to step S24.

[0100] Returning to step S42, if the determination in step S42 is NO and the actual torque is equal to or greater than the target torque, the PCM 100 sets the ignition correction amount to 0 (zero) (step S44).

[0101] After step S44, the process proceeds to step S23. In step S23 after proceeding to step S44, the ignition timing is maintained at the ignition timing of one calculation cycle before, because the ignition correction amount was set to 0 (zero) in step S44. Note that if the ignition timing set in step S3 has changed by more than a predetermined value from the value of one calculation cycle before, the ignition timing set in step S3 is maintained. After step S23, the process proceeds to step S24.

[0102] In step S24, as described above, the PCM 100 drives the spark plug 12 to achieve the ignition timing set in step S22, and drives the fuel injector 11 to achieve the target fuel amount set in step S3. As described above, after step S24, the PCM 100 returns to the processing of step S1.

[0103] In this way, if knocking does not occur during execution of the high load control (determination in step S11 is NO), water injection is stopped. If knocking does not occur during execution of the high load control (determination in step S11 is NO), and the actual torque is less than the target torque, the ignition timing is advanced.

[0104] (4) Effects, etc. As described above, in the engine of this embodiment, water is injected into the intake port 6. This reduces the speed at which water splashes within the combustion chamber 10, thereby preventing the water from adhering to the piston crown surface. The impact position of the water is set on the exhaust-side inner circumferential surface 65 of the first portion 62 of the intake port 6 that is closer to the combustion chamber 10, more specifically, on the upper portion of the exhaust-side inner circumferential surface 65 corresponding to the curved portion 62B (the exhaust-side inner circumferential surface of the curved portion 62B). This shortens the time it takes for the water to heat up within the intake port 6, allowing water to be introduced into the combustion chamber 10 at a lower temperature, and preventing the water from adhering to the inner circumferential surface of the combustion chamber 10 along the inner circumferential surface of the intake port 6. This enhances the temperature-lowering effect of the water on the combustion chamber 10, while also preventing oil dilution.

[0105] Furthermore, since the water is injected when the intake valve 8 starts to open, it can be introduced into the combustion chamber 10 at an early timing after being injected. Therefore, the time during which the water receives heat from the wall surface of the intake port 6 can be reliably shortened.

[0106] However, as described above, if water is injected when the intake valve 8 starts to open, the collision position of the water changes depending on the flow velocity of the intake air, and the collision position may deviate from the exhaust-side inner circumferential surface 65. In contrast, in this embodiment, the injection pressure is changed depending on the engine speed. Therefore, even if the flow velocity of the intake air changes with changes in engine speed, the water can be made to collide with the exhaust-side inner circumferential surface 65. Therefore, the above-mentioned effect can be obtained regardless of the engine speed.

[0107] In particular, in this embodiment, the water injection pressure and therefore penetration are higher when the engine speed is high and the intake air flow rate is high than when the engine speed is low and the intake air flow rate is low, so that deviation of the water spray in the direction of the intake air flow that occurs due to high intake air flow rate can be suppressed, and water can be reliably collided with the exhaust side inner surface 65.

[0108] Furthermore, in this embodiment, the water injection pressure is adjusted so that the value obtained by dividing the engine speed by the water injection pressure is maintained at a judgment value determined in advance by experiment or the like, which is the value at which the injected water collides with the exhaust-side inner circumferential surface 65. Therefore, the direction of the water spray can be maintained approximately constant regardless of the engine speed, and the water can be made to collide with the exhaust-side inner circumferential surface 65 regardless of the operating state of the engine.

[0109] In this embodiment, water injection is stopped in a first region A1 where the engine load is equal to or less than the reference load T1, and water is injected into the combustion chamber 10 only when the engine load is in a second region A2 where the engine load is higher than the reference load T1 and knocking is likely to occur. Therefore, knocking can be suppressed while reducing the number of opportunities for water injection and suppressing oil dilution.

[0110] In addition, in this embodiment, the amount of water injection is changed according to the engine speed, and the amount of water introduced into the combustion chamber 10 is changed. Therefore, the temperature of the combustion chamber can be lowered more appropriately according to the engine speed.

[0111] In particular, in this embodiment, the water injection amount in the low speed region A21 where knocking is most likely to occur is set to the largest first injection amount W1, the water injection amount in the high speed region A23 where knocking is next most likely to occur is set to the third injection amount W3 which is smaller than the first injection amount W1, and the water injection amount in the medium speed region A22 where knocking is least likely to occur in the second region A2 is set to the second injection amount W2 which is smaller than the third injection amount W3. Therefore, it is possible to suppress oil dilution by suppressing the amount of water introduced into the combustion chamber 10 while suppressing knocking.

[0112] (5) Variations In the above embodiment, the water injection pressure is changed in accordance with the engine speed based on the fact that the intake air flow rate increases as the engine speed increases. However, as the engine load increases, the amount of intake air increases, which increases the intake air flow rate. Therefore, the water injection pressure may be changed in accordance with the engine load. Specifically, as shown in FIG. 12, the water injection motor 55 may be controlled so that the water injection pressure increases as the engine load increases.

[0113] With this configuration, the intake air flow velocity increases as the engine load increases, which prevents the water spray from being easily deviated in the intake air flow direction, and allows water to impinge on the exhaust-side inner circumferential surface 65 regardless of the engine load. In particular, if the water injection pressure is changed in accordance with the engine load so that the ratio between the water spray velocity and the intake air flow velocity is constant, water can be more reliably impinged on the exhaust-side inner circumferential surface 65, as described above. The water injection pressure may also be changed based on both the engine speed and the engine load. For example, the water injection pressure may be set based on the engine speed, and this set pressure may be corrected in accordance with the engine load.

[0114] Furthermore, in the above embodiment, the case where the collision position of water is set on the exhaust-side inner circumferential surface of curved portion 62B has been described, but the collision position of water is not limited to the above position as long as it is a position included in exhaust-side inner circumferential surface 65 (the exhaust-side inner circumferential surface of first portion 62). However, if the collision position of water is set on the exhaust-side inner circumferential surface of curved portion 62B, water can be introduced into combustion chamber 10 along curved portion 62B, and water can be introduced into combustion chamber 10 smoothly.

[0115] In the above embodiment, the water injector 40 is mounted in a position where the nozzle hole 41 at the tip thereof is directed toward the underside of the second portion 63, but the mounting position of the water injector 40 is not limited to this. However, if the water injector 40 is mounted in the above position, the direction of the water spray injected toward the underside of the second portion will change due to the influence of the intake air, making it easier for the water spray to collide with the exhaust-side inner circumferential surface 65.

[0116] Furthermore, in the above embodiment, the engine E is an in-line four-cylinder engine, but the number of cylinders and the arrangement of the cylinders of the engine E are not limited to this. [Explanation of symbols]

[0117] 1 Engine body 2-cylinder 6 intake port 8 intake valve 10 Combustion chamber 40 Water injection valve (water injection valve) 53 Water Pump 55 Water injection motor (injection pressure changing means) 61 Downstream open end 62 Part 1 62B curved section 63 Part 2 65 Exhaust side inner circumferential surface (exhaust side inner circumferential surface of the first portion) 100 PCM (control means) E-Engine

Claims

1. an engine body including a cylindrical combustion chamber centered on a cylinder axis and an intake port opening to a ceiling surface of the combustion chamber; an intake valve that opens and closes a downstream opening end of the intake port that is an opening end on the combustion chamber side; a water injection valve that injects water into the intake port; an injection pressure changing means for changing the injection pressure of the water injection valve; a control means for controlling the water injection valve and the injection pressure changing means, When the side on which the intake port is formed in the engine width direction perpendicular to the cylinder axis is defined as the intake side and the opposite side is defined as the exhaust side, the intake port includes a first portion extending upward from the downstream side opening end and a second portion extending from an upper end of the first portion toward the intake side, the water injection valve is disposed in the second portion; The control means Injecting water from the water injection valve when the intake valve starts to open, a water injection valve for adjusting the injection pressure in accordance with at least one of an engine speed and an engine load so that water injected from the water injection valve collides with the inner peripheral surface of the exhaust side of the first portion.

2. 2. The water injection engine according to claim 1, the first portion has a downstream portion located on the intake downstream side and a curved portion curved from an upper end of the downstream portion toward the intake side, a control means for controlling the injection pressure change means to adjust the injection pressure so that the water injected from the water injection valve collides with the inner circumferential surface of the exhaust side of the curved portion;

3. 2. The water injection engine according to claim 1, The water injection valve has a nozzle hole at its tip, which is an outlet for water, and is attached in a position where the nozzle hole is directed toward the underside of the second portion.

4. 2. The water injection engine according to claim 1, 10. A water injection engine, wherein the control means controls the injection pressure changing means so that the injection pressure is higher when the engine speed is high than when the engine speed is low.

5. 2. The water injection engine according to claim 1, a control means for controlling the injection pressure changing means to change the injection pressure so that a ratio between a flow velocity of intake air flowing through the intake port and a spray velocity of water injected by the water injection valve is constant regardless of an operating state of the engine.

6. 2. The water injection engine according to claim 1, The water injection engine is characterized in that the control means causes the water injection valve to inject water only when the engine load is higher than a predetermined judgment load.

7. 2. The water injection engine according to claim 1, 10. A water injection engine, wherein the control means controls the injection pressure changing means so that the injection pressure is higher when the engine load is high than when the engine load is low.

8. The water injection engine according to any one of claims 1 to 7, A water injection engine characterized in that the control means controls the water injection valve so that a water injection amount, which is the amount of water injected from the water injection valve, is changed according to engine speed.

9. 9. The water injection engine according to claim 8, The control means When the engine is operated in a low speed range where the engine speed is less than a predetermined first speed, the water injection valve is controlled so that the water injection amount is greater than when the engine is operated in a high speed range where the engine speed is equal to or greater than a second speed that is greater than the first speed; a water injection valve that controls the water injection amount when the engine is operated in a medium speed range where the engine speed is equal to or higher than the first speed and lower than the second speed, so that the water injection amount is smaller than when the engine is operated in the high speed range.

Images