Water injection engine

Abstract

To provide a water injection-type engine that can suppress knocking while suppressing dilution of oil.SOLUTION: A water injection valve 40 is provided for injecting water to a combustion chamber 10 or an intake port 6. When knocking is detected by a knock detection means SN2, knock measures control is performed where water injection with the water injection valve 40 is prohibited and an ignition timing at which an ignition plug 12 ignites is delayed if an engine torque is larger than a target torque, whereas water injection with the water injection valve 40 is performed and delay in the ignition timing is suppressed if the engine torque is equal to or smaller than the target torque.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a water injection engine provided with a water injection valve.

Background Art

[0002] Conventionally, in engines and the like mounted on vehicles, it has been considered to provide a water injection valve for injecting water in order to introduce water into the combustion chamber. For example, Patent Document 1 discloses an engine provided with a water injection valve, which is configured such that water is injected from the water injection valve into the intake port.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] If water is introduced into the combustion chamber, the temperature in the combustion chamber can be reduced by the latent heat of vaporization of water, and the occurrence of knocking can be suppressed. However, when water is introduced into the combustion chamber, water may adhere to the piston crown surface and the inner peripheral surface of the combustion chamber, and the oil dilution may occur when the water mixes into the oil that lubricates the piston.

[0005] The present invention has been made in view of the above circumstances, and an object thereof is to provide a water injection engine capable of suppressing knocking while suppressing oil dilution.

Means for Solving the Problems

[0006] To solve the aforementioned problems, the present invention provides a water injection engine comprising: an engine body including a combustion chamber and an intake port communicating with the combustion chamber; an intake valve for opening and closing the opening end of the intake port on the combustion chamber side; an air volume adjustment means for adjusting the amount of air supplied to the combustion chamber; an ignition plug for igniting the air-fuel mixture in the combustion chamber; a water injection valve for injecting water into the combustion chamber or the intake port; a knock detection means for detecting knocking of the engine body; and a control means for controlling the air volume adjustment means, the spark plug, and the water injection valve. The system is characterized by setting a target torque, which is a target value for the engine's torque, and controlling the air volume adjustment means and the spark plug so that the target torque is achieved. When knocking is detected by the knock detection means, if the engine torque is greater than the target torque, the system prohibits water injection by the water injection valve and retards the ignition timing, which is the time when the spark plug ignites. On the other hand, if the engine torque is less than or equal to the target torque, the system performs water injection by the water injection valve and suppresses retardation of the ignition timing, thereby implementing knock prevention control.

[0007] In this invention, a water injection valve is provided to inject water into the combustion chamber or intake port, thereby introducing water into the combustion chamber. As a result, the latent heat of vaporization of water reduces the temperature of the combustion chamber, thereby suppressing the occurrence of knocking.

[0008] Furthermore, in this invention, even if knocking is detected, if the engine torque is greater than the target torque, water injection by the water injection valve is prohibited and the ignition timing is retarded. Therefore, by retarding the ignition timing, the engine torque can be reduced to approach the target torque while suppressing the occurrence of knocking, and oil dilution can be suppressed by reducing the opportunities for water injection. Also, when knocking is detected and the engine torque is below the target torque, water injection is performed, while the retardation of the ignition timing is suppressed, that is, the retardation of the ignition timing is prohibited, or the amount of retardation of the ignition timing is reduced compared to when knocking is detected and the engine torque is greater than the target torque, so that the occurrence of knocking can be suppressed while avoiding a decrease in engine torque.

[0009] In the above configuration, preferably, the control means performs the knock prevention control only when the engine load is higher than a predetermined determination load (Claim 2).

[0010] With this configuration, water is injected into the combustion chamber when the engine load is high, which tends to raise the temperature of the combustion chamber and thus make knocking more likely, thus suppressing the occurrence of knocking. Also, when the engine load is low and knocking is less likely, water injection is stopped, so oil dilution can be reliably suppressed.

[0011] 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 less than a predetermined first rotational speed, the amount of water injected by the water injection valve is greater than when the engine is operating in a high-speed region where the engine speed is greater than the first rotational speed and above a second rotational speed, and when the engine is operating in a medium-speed region where the engine speed is greater than the first rotational speed and above but less than the second rotational speed, the amount of water injected is less than when the engine is operating in the high-speed region (Claim 3).

[0012] It is known that knocking is more likely to occur in the low-speed range, followed by the high-speed range and then the medium-speed range. Therefore, with the above configuration, the amount of water injected, and thus the amount of water introduced into the combustion chamber, is increased in the order of the speeds most likely to cause knocking. As a result, knocking can be suppressed while avoiding excessive water introduction into the combustion chamber, thereby suppressing oil dilution.

[0013] In the above configuration, if knocking is detected by the knock detection means after water injection by the water injection valve, and the engine torque is less than or equal to the target torque, the control means increases the amount of water injected by the water injection valve (Claim 4).

[0014] In this configuration, if the engine torque remains below the target torque and knocking persists even after water injection, the amount of water injected is increased to lower the combustion chamber temperature. This helps to suppress further knocking.

[0015] In the above configuration, preferably, the water injection valve injects water into the intake port, and when the water injection valve performs water injection, the control means causes the water injection valve to inject water when the intake valve starts to open (Claim 5).

[0016] With this configuration, water is injected into the intake port, which prevents water from being forcefully scattered within the combustion chamber compared to a configuration that injects water into the combustion chamber. This suppresses the adhesion of water to the piston crown and the inner surface of the combustion chamber. Consequently, oil dilution can be suppressed more reliably. [Effects of the Invention]

[0017] As described above, the water injection engine of the present invention can suppress knocking while suppressing oil dilution. [Brief explanation of the drawing]

[0018] [Figure 1] This is a schematic diagram of the area around the engine body included in a water-injection engine according to an embodiment of the present invention. [Figure 2] It is a schematic diagram showing a part of the engine. [Figure 3] It is a block diagram showing the control system of the engine. [Figure 4] It is a schematic diagram showing the state of the water spray ejected from the water injection valve. [Figure 5] It is a schematic diagram showing the state of the water spray ejected from the water injection valve. [Figure 6] It is a graph showing the relationship between the engine speed, the intake air flow rate, and the injection speed. [Figure 7] It is a flowchart showing a part of the engine control procedure. [Figure 8] It is a flowchart showing a part of the high-load control. [Figure 9] It is a diagram showing the operating region of the engine. [Figure 10] It is a graph showing the relationship between the engine speed and the water injection pressure. [Figure 11] It is a graph showing the relationship between the engine speed and the water injection amount.

Mode for Carrying Out the Invention

[0019] (1) Overall Configuration of the Engine Hereinafter, a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 is a schematic configuration diagram around an engine body 1 included in a water injection type engine E according to an embodiment of the present invention. FIG. 2 is a schematic diagram showing a part of the water injection type engine E. The water injection type engine E shown in FIGS. 1 and 2 is a four-cycle engine mounted on a vehicle as a power source for traveling, and includes an engine body 1, an intake passage 20 through which intake air introduced into the engine body 1 flows, and an exhaust passage 30 through which exhaust discharged from the engine body 1 flows. Hereinafter, the water injection type engine E will be simply referred to as the engine E as appropriate.

[0020] The engine body 1 comprises a cylinder block 3 with cylinders 2 formed inside, a cylinder head 4 mounted on the upper surface of the cylinder block 3 so as to block the cylinders 2 from above, and pistons 5 fitted into each cylinder 2 so as to be reciprocally slidable. The cylinders 2 are substantially cylindrical in shape. 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 direction in which the cylinders 2 are arranged will be referred to as the cylinder arrangement direction. The vertical direction, that is, the direction in which the cylinder block 3 and cylinder head 4 are arranged and the direction perpendicular to the cylinder arrangement direction will be referred to as the engine width direction.

[0021] Cylinder 2 is divided into a cylindrical combustion chamber 10 centered on the cylinder axis O1 which extends in the vertical direction. Specifically, the combustion chamber 10 is defined above the piston 5 by the inner circumferential surface of cylinder 2, the crown surface of the piston 5, and the bottom surface of the cylinder head 4. The ceiling surface 10A of the combustion chamber 10 is formed by a 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 and burns in the combustion chamber 10, and the piston 5, pushed down by the expansion force of this combustion, reciprocates in the vertical direction.

[0022] Below the piston 5 is a crankshaft 15, which is the output shaft of the engine body 1. The crankshaft 15 is connected to the piston 5 via a connecting rod (not shown) and rotates around its central axis in accordance with 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 only, or fuel containing by-components such as bioethanol in addition to gasoline. The cylinder block 3 is fitted with a crank angle sensor SN1 that detects the rotation angle of the crankshaft 15, i.e., the engine speed. The cylinder block 3 is also fitted with a knock sensor SN2 that detects knocking of the engine body 1. In this embodiment, the knock sensor SN2 detects vibrations of the engine body 1, and based on this detection result, it is determined whether or not knocking has occurred in the engine body 1. This knock sensor SN2 corresponds to the "knock detection means" of the present invention.

[0023] The cylinder head 4 has an intake port 6 that communicates with the combustion chamber 10 and supplies intake air to the combustion chamber 10. The intake port 6 opens into the ceiling surface 10A of the combustion chamber 10. In other words, the ceiling surface 10A of the combustion chamber 10 has a downstream opening end 61 which is the opening end of the intake port 6 on the combustion chamber 10 side and is on the downstream side of the intake, that is, the opening end on the downstream side in the direction of intake air flow. In this embodiment, each cylinder 2 has two intake ports 6 communicating with it, and each cylinder has two downstream opening ends 61 formed on the ceiling surface 10A of the combustion chamber 10.

[0024] The cylinder head 4 has an exhaust port 7 that communicates with the combustion chamber 10 and discharges the burnt gas (exhaust gas) from the combustion chamber 10. The exhaust port 7 opens into the ceiling surface 10A of the combustion chamber 10. In other words, an exhaust port opening end 71, which is the upstream opening end in the direction of exhaust flow of the exhaust port 7, is formed on the ceiling surface 10A of the combustion chamber 10. In this embodiment, each cylinder 2 has two exhaust ports 7 communicating with each other, and each combustion chamber 10 has two exhaust port opening ends 71 ​​formed on the ceiling surface 10A.

[0025] The intake port 6 and exhaust port 7 are located on opposite sides of the engine width direction, straddling the cylinder axis O1, which is the centerline of the combustion chamber 10. Here, the engine width direction is the direction perpendicular to the vertical direction, that is, the direction perpendicular to the cylinder axis O1. In this embodiment, the engine width direction is also perpendicular to the cylinder arrangement direction. As shown in Figure 2, when viewed from above, each intake port 6 and each exhaust port 7 are located on opposite sides of the engine width direction, straddling a virtual line X1 that passes through the cylinder axis O1 of each combustion chamber 10 and extends along the cylinder arrangement direction. Hereafter, with respect to the engine width direction, the side where the intake port 6 is formed will be referred to as the intake side, and the opposite side, that is, the side where the exhaust port 7 is formed, will be referred to as the exhaust side.

[0026] The cylinder head 4 is equipped with an intake valve 8 that opens and closes the intake port 6, and an exhaust valve 9 that opens and closes the exhaust port 7. The valve configuration of the engine in this embodiment is a 4-valve configuration with 2 intake valves and 2 exhaust valves, and there are two intake ports 6, two exhaust ports 7, two intake valves 8, and two exhaust valves 9 for each cylinder 2. The intake valves 8 and exhaust valves 9 are opened and closed in conjunction with the rotation of the crankshaft 15 by a valve drive device (not shown).

[0027] The cylinder head 4 is provided with one set of fuel injectors 11 for each cylinder 2 that inject fuel into the combustion chamber 10. Figure 1 shows a case where a side-injection type fuel injector 11 is used, which injects fuel into the combustion chamber 10 from the intake side, but the fuel injector 11 is not limited to the side-injection type.

[0028] The cylinder head 4 is equipped with one set 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 mounted on the cylinder head 4 so as to face the inside of the combustion chamber 10 from the ceiling surface 10A of the combustion chamber 10. The spark plugs 12 are located approximately in the center of the ceiling surface 10A of the combustion chamber 10.

[0029] The cylinder head 4 is fitted with a water injection valve 40 that injects water into the intake port 6. One water injection valve 40 is provided for each intake port 6, and water is individually injected into each intake port 6 from the water injection valve 40. This water injection valve 40 corresponds to the "water injection valve" of the present invention.

[0030] The vehicle is equipped with a water tank 51 that stores water internally. 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. The water tank 51 may be supplied with water from outside the vehicle or with water generated from exhaust gas.

[0031] Engine E is equipped with a water pump 53 and a water injection motor 55 that drives the water pump 53, in addition to the water injection valve 40. The water pump 53 is located 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 towards the water injection valve 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 to each water injection valve 40 from the same water pump 53. 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 valve 40, i.e., the injection pressure of the water injection valve 40. The driving force of the water pump 53 by the water injection motor 55 is changeable, and the discharge pressure of the water pump 53 and, consequently, the injection pressure of the water injection valve 40 are changed by the water injection motor 55. A water injection pressure sensor SN3 is installed in the portion of the water supply pipe 52 downstream of the water pump 53 to detect the water pressure in the water supply pipe 52, that is, the water injection pressure which is the injection pressure of the water injection valve 40. The water injection motor 55 described above corresponds to the "injection pressure changing means" of the present invention.

[0032] The intake passage 20 is connected to the intake side of the cylinder head 4 so as to communicate with the intake port 6. A surge tank 21 is provided in the middle of the intake passage 20. Downstream from the surge tank 21, the intake passage 20 branches into four passages, 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 through the intake passage 20 and the intake port 6.

[0033] A throttle valve 14 is provided in the intake passage 20 upstream of the surge tank 21 to adjust the flow rate of intake air, which is the air introduced into the combustion chamber 10 by opening and closing the intake passage 20. An airflow sensor SN4 for detecting the intake air volume, which is the flow rate of intake air, is also attached to the intake passage 20. For example, the airflow sensor SN4 is attached to the portion of the intake passage 20 upstream of the throttle valve 14. The throttle valve 14 described above corresponds to the "air volume adjustment means" of the present invention.

[0034] The exhaust passage 30 is connected to the exhaust side of the cylinder head 4 so as to communicate with the exhaust port 7. The burnt gas (exhaust gas) generated in the combustion chamber 10 is discharged to the outside through the exhaust port 7 and the exhaust passage 30.

[0035] (2) Detailed structure of the intake port This section describes the details of the intake port and its surrounding structure. In this description, the upstream and downstream sides of the intake, i.e., the upstream and downstream sides in the direction of intake air flow, will simply be referred to as the upstream and downstream sides.

[0036] The downstream opening end 61 is formed in the intake-side region of the ceiling surface 10A of the combustion chamber 10 with respect to the cylinder axis O1, which is the centerline of the combustion chamber 10, and the imaginary line X1. In other words, when viewed along the vertical direction, the downstream opening end 61 is formed at a position where its center O2 is shifted towards the intake side relative to the center of the combustion chamber 10.

[0037] The intake port 6 extends upward and in the engine width direction towards the intake from the downstream opening end 61.

[0038] Specifically, the intake port 6 has a first portion 62 extending upward from the downstream opening end 61, and a second portion 63 extending towards the intake side from the upper end, i.e., the upstream end, of the first portion 62. The first portion 62 is composed of a downstream portion 62A that extends almost straight upward from the downstream opening end 61 with a slight incline towards the intake side, and a curved portion 62B that curves towards the intake side from the upper end of the downstream portion 62A. In detail, the curved portion 62B is curved so that it is located towards the intake side as it moves away from the downstream portion 62A, and extends upward and towards the intake side from the upper end of the downstream portion 62A. The second portion 63 extends almost straight upward and towards the intake side from the upper end of the curved portion 62B with a greater incline towards the intake side than the downstream portion 62A.

[0039] The upper end of the second section 63, which is the end opposite to the downstream opening end 61 of the intake port 6, i.e., the upstream end, opens to the intake side of the cylinder head 4.

[0040] The water injection valve 40 has a tip from which nozzles 41 are formed, and it injects water from this tip. The number of nozzles 41 is not particularly limited, but the water injection valve 40 in this embodiment is a multi-nozzle type injection valve, and multiple nozzles 41 are formed at the tip. For example, the water injection valve 40 has 12 nozzles 41. The water injection valve 40 is mounted on the cylinder head 4 in a position where it is looking at the second part 63 from above and the nozzles 41A are facing downward. In other words, the water injection valve 40 is mounted on the cylinder head 4 such that its tip is looking at the inside of the second part 63 from the upper surface of the second part 63. The amount of the tip of the water injection valve 40 protruding from the upper surface of the second part 63 is smaller than the radius of the second part 63, and the tip of the water injection valve 40 is located near the upper surface of the second part 63.

[0041] The water injection valve 40 is mounted in a position where its nozzle 41 is directed downstream and toward the lower surface of the second portion 63. Specifically, the water injection valve 40 is mounted such that its injection shaft X10, that is, the central axis of the nozzle, extends downward from the tip toward the exhaust side. In this embodiment, the inclination of the injection shaft X10 of the water injection valve 40 toward the intake side with respect to the vertical direction is smaller than the inclination of the shaft X3 of the second portion 63 toward the intake side with respect to the vertical direction, and the injection shaft X10 of the water injection valve 40 and the shaft X3 of the second portion 63 intersect. Therefore, if water is injected from the water injection valve 40 when there is no intake airflow in the intake port 6, the water spray will move along the injection shaft X10 of the water injection valve 40 and collide with the lower surface of the second portion 63.

[0042] (3) Control system Figure 3 is a block diagram showing the control system of engine E. The PCM100 shown in this figure is a microprocessor for comprehensively controlling the engine and is composed of a well-known CPU, ROM, RAM, etc. This PCM100 corresponds to the "control means" of the present invention.

[0043] The PCM100 receives detection signals from various sensors. For example, the PCM100 is electrically connected to the crank angle sensor SN1, the knock sensor SN2, the water injection pressure sensor SN3, and the airflow sensor SN4. The vehicle is also equipped with an accelerator sensor SN5 that detects the accelerator opening, which is the degree to which the accelerator pedal (not shown) is opened by the driver operating the vehicle, and the PCM100 is electrically connected to the accelerator sensor SN5 as well. At least the information detected by these sensors SN1 to SN5, namely the engine speed, the vibration of the engine body 1, the water injection pressure, the intake air volume, and the accelerator opening, is sequentially input to the PCM100.

[0044] The PCM100 controls various parts of the engine E while performing various judgments and calculations based on input signals from each sensor. The PCM100 is electrically connected to the fuel injector 11, spark plug 12, throttle valve 14, water injector 40, water injection motor 55, etc., and outputs control signals to these devices based on the results of the above calculations.

[0045] The PCM100 switches the water injection valve 40 between open and closed to enable and stop water injection from the water injection valve 40 into the intake port 6. In other words, the water injection valve 40 is equipped with a device that opens and closes its nozzle, and this device opens and closes the nozzle of the water injection valve 40 in response to a signal from the PCM100. The PCM100 also changes the opening period of the water injection valve 40. When the water injection pressure is the same, the longer the opening period of the water injection valve 40, the greater the amount of water injected from the water injection valve 40. The PCM100 also changes the driving force of the water injection motor 55 to change the discharge pressure of the water pump 53 and, consequently, the water injection pressure of the water injection valve 40. The PCM100 also switches the fuel injection valve 11 between driven and stopped, and changes the opening period of the fuel injection valve 11, that is, the fuel injection period. Furthermore, the PCM100 drives the spark plug 12 to ignite the fuel-air mixture. The PCM100 also changes the opening degree of the throttle valve 14.

[0046] (Overview of water injection control) First, we will explain the overview of the control related to water injection using Figures 4 and 5. Figures 4 and 5 are schematic diagrams to explain the movement of water injected from the water injection valve 40.

[0047] The purpose of water injection in this embodiment is to suppress knocking by lowering the temperature inside the combustion chamber 10 through the heat of vaporization of water. Therefore, it is desirable to perform water injection at a timing when the water flows into the combustion chamber 10 at a lower temperature. If water is injected into the intake port 6 before the intake valve 8 opens, the water temperature will rise due to heat from the wall surface of the intake port 6 between the time the water is injected and 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 intake valve opening start time, which is when the intake valve 8 opens, the period of heat absorption from the wall surface of the intake port 6 is shortened, and water can be introduced into the combustion chamber 10 at a lower temperature. Therefore, in this embodiment, the PCM 100 drives the water injection valve 40 to inject water into the intake port 6 at the start of the intake valve 8 opening.

[0048] As described above, introducing water into the combustion chamber 10 can suppress knocking. On the other hand, introducing water into the combustion chamber 10 may cause oil dilution. Specifically, if the introduced water adheres to the inner surface of cylinder 2 or the crown surface of piston 5, the water may mix with the oil that lubricates these surfaces, potentially diluting the oil.

[0049] Here, as described above, when viewed along the vertical direction, the center O2 of the downstream opening end 61 is shifted toward the intake side relative to the center of the combustion chamber 10, i.e., the cylinder axis O1. Also, the intake port 6 extends upward and toward the intake side from the downstream opening end 61. Due to this configuration, the lower surface of the intake port 6 is connected to the inner surface of the cylinder 2. Therefore, as shown by arrow Y1 in Figure 4, if the water is injected so that most of it collides with the lower surface of the intake port 6, the water (W10) will flow down the lower surface of the intake port 6 into the combustion chamber 10 and easily adhere to the inner surface of the cylinder 2. On the other hand, as shown by arrow Y2 in Figure 4, if the water is injected so that it collides with the upper surface of the intake port 6, the water (W20) can be introduced near the center of the combustion chamber 10, and adhesion to the inner surface of the cylinder 2 can be suppressed. However, even on the upper surface of the intake port 6, the position close to the water injection valve 40 is far from the combustion chamber 10, and the temperature of the water rises due to heat absorption 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 make the water strike a position on the upper surface of the intake port 6 that is far from the water injection valve 40 (closer to the combustion chamber 10). Accordingly, in this embodiment, the water injection valve 40 is controlled so that the water strikes 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).

[0050] However, the inventors of this invention discovered that when water is injected from the water injection valve 40 at the start of opening of the intake valve 8, the intake airflow affects the water spray, and depending on the intake airflow velocity, the impact position of the water may shift from the exhaust side inner circumferential surface 65. Specifically, when the intake airflow velocity is high, the water spray tends to shift in the direction of the intake airflow relative to the direction of water injection. As a result of diligent research on this, the inventors of this invention discovered that if the ratio between the water spray velocity and the intake airflow velocity is kept constant, the impact position of the injected water can be kept constant regardless of the intake airflow velocity. Hereinafter, the water injected by the water injection valve 40 will be referred to as injected water.

[0051] Furthermore, as shown by the solid line in the upper graph of Figure 6, the intake airflow velocity increases with increasing engine speed. Therefore, as shown by the dashed line in the upper graph of Figure 6, we found that by increasing the water spray velocity as the engine speed increases, the ratio of intake airflow velocity to spray velocity can be kept constant, as shown in the lower graph of Figure 6. In addition, since the spray penetration increases and the spray velocity increases as the injection pressure increases, we found that by keeping the ratio of engine speed to water injection pressure constant, the impact position of the injected water can be kept constant regardless of the intake airflow velocity.

[0052] Based on the above findings, in this embodiment, the water injection pressure is controlled so that the value obtained by dividing the engine speed by the water injection pressure is maintained at a predetermined determination value obtained through experiments, etc., which is the value at which the injected 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 injected 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. That is, the water impact target position, which is the position where the water collides, 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 PCM100 controls the water injection pressure so that the injected water collides with the exhaust-side inner circumferential surface of the curved portion 62B.

[0053] (Control details) The control performed by the PCM100, including the control related to water injection described above, will be explained using the flowchart in Figure 7. Each step shown in Figure 7 is repeatedly performed in a predetermined calculation cycle while the engine E is running.

[0054] First, the PCM100 reads various pieces of information detected by the sensors (step S1).

[0055] Next, the PCM100 calculates the target torque, which is the target value of the engine torque (step S2). The PCM100 calculates the target torque from the accelerator opening and engine speed, etc.

[0056] Next, the PCM100 sets the target intake volume, target fuel volume, and ignition timing based on the target torque (step S3). The target intake volume is the target value of the intake volume. The target fuel volume is the target value of the amount of fuel injected from the fuel injector 11. The ignition timing is the timing at which the spark plug 12 ignites the air-fuel mixture. The PCM100 sets each of the above values ​​based on the target torque and engine speed, etc., so that the target torque is achieved.

[0057] Next, the PCM100 adjusts the opening of the throttle valve 14 so that the target intake volume is achieved (step S4).

[0058] Next, the PCM100 determines whether the condition that engine E is operating within the first region A1 is met (step S5). As shown in Figure 9, in this embodiment, the region within the operating range of engine E where the engine load is less than or equal to a preset determination load T1 is set as the first region A1, and the region where the engine load is higher than the determination load T1 is set as the second region A2. The PCM100 calculates the engine load from the engine speed and intake air volume, etc., and determines whether engine E is operating within the first region A1 based on the calculated engine load. The determination load T1 is preset and stored in the PCM100.

[0059] 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 the high-load control described later, but controls the fuel injector 11 so that the target fuel amount set in step S3 is achieved, and controls the spark plug 12 so that ignition occurs at the ignition timing set in step S3. After step S6, the PCM 100 returns to the processing of step S1. In this normal control, water injection is prohibited. Therefore, in step S6, the drive of the water injector 40 is stopped. Also, in step S6, the water injection execution flag described later is set to 0.

[0060] On the other hand, if the determination in step S5 is YES and engine E is operating in the second region A2, PCM100 performs high-load control (step S7). After step S7, that is, after the high-load control is performed, PCM100 returns to the process of step S1. The above high-load control corresponds to the "knock prevention control" of the present invention.

[0061] The details of high-load control will be explained using the flowchart in Figure 8.

[0062] When high-load control is performed, the PCM100 first determines whether or not knocking is occurring (step S11). The PCM100 makes this determination based on the signal from the knock sensor SN2.

[0063] If the determination in step S11 is YES and it is determined that knocking is occurring, the PCM100 determines whether the actual torque is less than or equal to the target torque set in step S3 (step S12). The actual torque is the current engine torque of engine E, and the PCM100 calculates the actual torque based on the intake volume, engine speed, etc.

[0064] If the determination in step S12 is YES and the actual torque is less than or equal to the target torque, the PCM100 sets the ignition correction amount to 0 (zero) (step S13). The ignition correction amount is the amount of correction for the ignition timing.

[0065] Following step S13, the PCM100 determines whether the value obtained by dividing the engine speed by the water injection pressure matches the determination value (step S14). The PCM100 performs this determination using the current engine speed detected by the crank angle sensor SN1 and the current water injection pressure detected by the 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 the curved section 62B, and is preset and stored in the PCM100. Hereafter, the value obtained by dividing the current engine speed by the current water injection pressure will be referred to as the injection pressure ratio.

[0066] If the determination in step S14 is YES and the injection pressure ratio matches the determination value, the PCM100 proceeds to step S18.

[0067] On the other hand, if the determination in step S14 is NO and the injection pressure ratio does not match the determination value, the PCM100 determines whether the injection pressure ratio is greater than the determination value (step S15).

[0068] 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 and the determination value match, the PCM 100 increases the water injection pressure (step S16). Specifically, the PCM 100 increases the driving force of the water injection motor 55 and raises the discharge pressure of the water pump 53 so that the water injection pressure increases to a pressure at which the injection pressure ratio and the determination value match. Conversely, 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 and the determination value match, the PCM 100 decreases the water injection pressure (step S17). Specifically, the PCM 100 decreases the driving force of the water injection motor 55 and reduces the discharge pressure of the water pump 53 so that the water injection pressure decreases to a pressure at which the injection pressure ratio and the determination value match. After steps S16 and S17, the PCM 100 proceeds to step S18.

[0069] As steps S14 to S17 are performed, the water injection pressure is controlled to a value where the injection pressure ratio is a predetermined value. In other words, the water injection pressure is controlled to a value obtained by dividing the current engine speed by the predetermined value. The predetermined value is a constant value. Thus, as shown in Figure 10, as steps S14 to S17 are performed, the water injection pressure is controlled to be higher as the engine speed increases, in proportion to the engine speed.

[0070] In step S18, the PCM 100 determines whether either the condition that the injection execution flag is 0 or the condition that the speed range has changed is met (step S19). The injection execution flag is a flag that is 1 if water injection was performed in the previous calculation cycle, that is, if water was injected into the intake port 6 by the water injection valve 40 in the previous calculation cycle, and 0 otherwise. Furthermore, a change in the speed range means that the engine's operating range has changed between the three regions A21 to A23 shown in Figure 11. Figure 11 is a graph showing the relationship between engine speed and water injection amount. As shown in Figure 11, in this embodiment, the second region A2 is further divided into three regions according to the water injection amount. Specifically, the second region A2 is divided into a low-speed region A21 where the engine speed is less than the first rotational speed N1, a medium-speed region A22 where the engine speed is N1 or greater and less than the second rotational speed N2, and a high-speed region A23 where the engine speed is N2 or greater. The condition that the speed range has changed is met when the region in which engine E is operating changes between the low-speed region A21, the medium-speed region A22, and the high-speed region A23. PCM100 makes this determination based on the current engine speed and the engine speed a predetermined time ago. For example, PCM100 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.

[0071] If the determination in step S18 is YES, the injection execution flag is 0, and the conditions that water injection was not performed in the previous calculation cycle, or that the velocity range has changed, are met, then proceed to step S19.

[0072] In step S19, the PCM100 sets the water injection amount. The water injection amount is the basic amount of water injected from the water injection valve 40.

[0073] The water injection amount is set for each of the three speed ranges A21 to A23 mentioned above. 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 engine E is operating in the low-speed range A21 is the first injection amount W1, then when engine E is operating in the medium-speed range A22, the water injection amount is set to the second injection amount W2, which is smaller than the first injection amount W1. Furthermore, when engine E is operating in the high-speed range A23, the water injection amount is set to the third injection amount W3, which is smaller than the first injection amount W1 and larger than the second injection amount W2. After step S19, PCM100 proceeds to step S20.

[0074] On the other hand, if the determination in step S18 is NO and the injection execution flag is 1, that is, if water injection was already performed one calculation cycle ago, and the condition that the speed range has changed is not met, that is, if the engine E continues to be operated in the same speed range A21 to A23, then the PCM100 increases the amount of water injected (step S20). Specifically, the PCM100 sets the amount of water injected to a greater amount than the amount of water injected one calculation cycle ago. After step S20, the PCM100 proceeds to step S21.

[0075] In step S21, the PCM 100 performs water injection at the same time as the intake valve 8 starts to open. That is, the PCM 100 drives the water injection valve 19 to inject water at the same time as the intake valve 8 starts to open (step S21). At this time, the PCM 100 opens the water injection valve 19 only for the period of time during which the amount of water injected set in step S19 or step S20 is achieved.

[0076] In step S22, which proceeds after step S21 has been performed and water injection has been carried out, the PCM100 sets the water injection flag to 1. If the water injection flag is already 1, it is maintained at that value.

[0077] Step S22 is followed by step S23. In step S23, the PCM100 determines the final ignition timing. In step S23, the PCM100 determines the final ignition timing by correcting the ignition timing from one calculation cycle prior by an ignition correction amount. Specifically, the final ignition timing (i) is calculated using the ignition timing (i-1) from one calculation cycle prior, as follows: ignition timing (i) = ignition timing (i-1) + ignition correction amount. In this embodiment, the ignition correction amount is set to a value greater than 0 when correcting the ignition timing toward the advance side, and to a value less than 0 when correcting the ignition timing toward the retard side. Furthermore, if the ignition timing set in step S3 changes by a predetermined value or more from the value from one calculation cycle prior 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) from one calculation cycle prior, and a correction is made to this basic ignition timing.

[0078] If knocking occurs during high-load control (judgment in step S11 is YES) and the actual torque is less than or equal to the target torque (judgment in step S12 is YES), the ignition correction amount is set to 0 (zero) in step S13. In this case, the final ignition timing is maintained at the ignition timing from one calculation cycle prior. As described above, if the ignition timing set in step S3 changes by a predetermined value or more from the value one calculation cycle prior, 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.

[0079] 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 fuel-air mixture in the combustion chamber 10 (step S24). At this time, the PCM 100 drives the spark plug 12 so that the ignition timing set in step S23 is achieved. The PCM 100 also drives the fuel injector 11 so that the target fuel amount set in step S3 is achieved.

[0080] After step S24, PCM100 returns to processing step S1.

[0081] Thus, when high-load control is being performed and knocking occurs (the judgment in step S11 is YES) and the actual torque is less than or equal to the target torque (the judgment in step S12 is YES), water is injected from the water injection valve 19 into the intake port 6. The water injection pressure at this time is set to a pressure that matches the judgment value obtained by dividing the engine speed by the water injection pressure. Here, as described above, the intake airflow 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 judgment value, the ratio of the intake airflow 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 judgment in step S11 is YES) and the actual torque is less than or equal to the target torque (the judgment in step S12 is YES), the PCM 100 controls the water injection pressure so that the ratio of the intake airflow velocity to the water spray velocity is maintained at a constant value regardless of the engine speed.

[0082] Furthermore, if knocking occurs during high-load control (the judgment in step S11 is YES) and the actual torque is less than or equal to the target torque (the judgment in step S12 is YES), the water injection amount is set according to the engine speed, and if water injection has already been performed in the previous calculation cycle, the water injection amount is increased. On the other hand, if knocking occurs during high-load control (step S11) and the actual torque is less than or equal to the target torque (step S12), no correction is made to the ignition timing, and the ignition timing is set to the ignition timing from the previous calculation cycle, or to the basic ignition timing set based on the target torque.

[0083] Returning to step S12, the process for when the determination in step S12 is NO will be explained next. If the determination in step S12 is NO, and high load control is being performed and knocking has occurred (the determination in step S11 is YES), and the actual torque is greater than the target torque, the PCM 100 will prohibit water injection (step S31). In other words, the PCM 100 will not drive the water injection valve 40 even when it is time for the intake valve 8 to start opening, and will maintain the stop. Also, in step S31, the PCM 100 will set the injection execution flag to 0. If the water injection execution flag is already 0, it will maintain this value.

[0084] Following step S31, the PCM100 sets the ignition correction amount (step S32). At this time, the PCM100 sets the amount of ignition timing retardation. In this embodiment, the amount of retardation is set to a constant value regardless of the operating state of the engine E. This amount of retardation is preset and stored in the PCM100.

[0085] After step S32, the process proceeds to step S23. In step S23, following step S31, the ignition timing is retarded by the amount of ignition correction set in step S32 relative to the ignition timing of the previous calculation cycle. If the ignition timing set in step S3 changes by a predetermined amount or more from the value of the previous calculation cycle, the ignition timing is retarded by the amount of ignition correction 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 so that the ignition timing set in step S22 is achieved, and drives the fuel injector 11 so that the target fuel amount set in step S3 is achieved. As described above, after step S24, the PCM 100 returns to the process of step S1.

[0086] Thus, if knocking occurs during high-load control (the judgment in step S11 is YES) and the actual torque is greater than the target torque (the judgment in step S12 is NO), water injection is stopped while the ignition timing is retarded.

[0087] Returning to step S11, the process for when the determination in step S11 is NO will be explained next. If the determination in step S11 is NO, and high-load control is being performed and knocking has not occurred, the PCM 100 prohibits water injection (step S41). In other words, the PCM 100 does not drive the water injection valve 40 even when it is time for the intake valve 8 to start opening, and maintains the stopped state. Also, in step S41, the PCM 100 sets the injection execution flag to 0. If the water injection execution flag is already 0, it is maintained at this value.

[0088] Following step S41, the PCM100 determines whether the actual torque is less than the target torque set in step S3 (step S42).

[0089] If the determination in step S42 is YES and the actual torque is less than the target torque, the PCM100 sets the ignition correction amount (step S43). At this time, the PCM100 sets the 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 PCM100.

[0090] After step S43, the process proceeds to step S23. In step S23, following step S43, the ignition timing is advanced by the amount of ignition correction set in step S43 relative to the ignition timing of the previous calculation cycle. If the ignition timing set in step S3 has changed by a predetermined amount or more from the value of the previous calculation cycle, the ignition timing is advanced by the amount of ignition correction set in step S32 relative to the ignition timing set in step S3. After step S23, the process proceeds to step S24.

[0091] Returning to step S42, if the result of step S42 is NO and the actual torque is greater than or equal to the target torque, the PCM100 sets the ignition correction amount to 0 (zero) (step S44).

[0092] After step S44, the process proceeds to step S23. In step S23, following step 44, the ignition correction amount is set to 0 (zero) in step S44, so the ignition timing is maintained at the ignition timing from one calculation cycle prior. If the ignition timing set in step S3 changes by a predetermined value or more from the value one calculation cycle prior, it is maintained at the ignition timing set in step S3. After step S23, the process proceeds to step S24.

[0093] 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 process of step S1.

[0094] Thus, if knocking does not occur during high-load control (the judgment in step S11 is NO), water injection is stopped. Furthermore, if knocking does not occur during high-load control (the judgment in step S11 is NO), and the actual torque is less than the target torque, the ignition timing is advanced.

[0095] (4) Effects, etc. As described above, in the engine of the above embodiment, water is injected into the intake port 6 from the water injection valve 40 and introduced into the combustion chamber 10. Therefore, the temperature of the combustion chamber can be reduced by the latent heat of vaporization of water, thereby suppressing the occurrence of knocking.

[0096] Furthermore, if knocking occurs during high-load control (the judgment in step S11 is YES) and the actual torque is greater than the target torque (the judgment in step S12 is NO), water injection is stopped while the ignition timing is retarded. Therefore, by retarding the ignition timing, the engine torque is reduced, bringing the actual torque closer to the target torque while suppressing the occurrence of knocking, and the opportunities for water injection are reduced, thereby suppressing oil dilution.

[0097] Furthermore, if knocking occurs during high-load control (the judgment in step S11 is YES) and the actual torque is below the target torque (the judgment in step S12 is YES), water injection is performed, but the ignition timing is not corrected, and retardation of the ignition timing is prohibited. Therefore, it is possible to suppress the occurrence of knocking while avoiding a decrease in engine torque.

[0098] Furthermore, if high-load control is being performed and knocking occurs (the judgment in step S11 is YES) and the actual torque is less than or equal to the target torque (the judgment in step S12 is YES), and water injection has already been performed one calculation cycle prior, that is, if knocking continues despite water injection being performed, the amount of water injected is increased. This further reduces the temperature of the combustion chamber 10 and prevents further knocking.

[0099] Furthermore, in the above embodiment, water is injected into the intake port 6. This suppresses the scattering speed of water within the combustion chamber 10, preventing water from adhering to the piston crown surface. Also, since water is injected when the intake valve 8 starts to open, the water can be introduced into the combustion chamber 10 at a relatively short time after injection. This significantly reduces the time the water receives heat from the wall surface of the intake port 6, allowing the water to be introduced into the combustion chamber 10 at a lower temperature, thereby enhancing the temperature-reducing effect of the water on the combustion chamber 10 and ultimately the knock suppression effect.

[0100] In particular, in the above embodiment, the water impact point is set to the exhaust-side inner circumferential surface 65, specifically 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, and more specifically, to the upper part of this exhaust-side inner circumferential surface 65 corresponding to the curved portion 62B (the exhaust-side inner circumferential surface of the curved portion 62B). When water injection is performed, 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 predetermined determination value obtained by experiments, etc., which is the value when the injected water impacts the exhaust-side inner circumferential surface 65. Therefore, the direction of the water spray can be maintained almost constant regardless of the engine speed, and water can be made to impact the exhaust-side inner circumferential surface 65 regardless of the engine operating state. Consequently, water can be more reliably prevented from running down the inner circumferential surface of the intake port 6 and adhering to the inner circumferential surface of the combustion chamber 10, and thus oil dilution can be more reliably suppressed.

[0101] Furthermore, in the above embodiment, water injection is stopped in the first region A1 where the engine load is less than or equal to the judgment load T1, and water is injected into the combustion chamber 10 only in the second region A2 where the engine load is higher than the judgment load T1 and knocking is likely to occur. Therefore, oil dilution can be suppressed by reducing the opportunities for water injection while suppressing knocking.

[0102] Furthermore, in the above embodiment, the amount of water injected in the low-speed region A21, where knocking is most likely to occur, is set to the first injection amount W1, which is the largest amount. Next, the amount of water injected in the high-speed region A23, where knocking is most likely to occur, is set to the third injection amount W3, which is smaller than the first injection amount W1. The amount of water injected in the medium-speed region A22, within the second region A2, where knocking is least likely to occur, is set to the second injection amount W2, which is smaller than the third injection amount W3. Therefore, while suppressing knocking, the amount of water introduced into the combustion chamber 10 can be suppressed, thereby suppressing oil dilution.

[0103] (5) Variant Furthermore, although the above embodiment described a case where the water impact position is set on the exhaust-side inner circumferential surface of the curved portion 62B, the water impact position is not limited to the above position and can be any position included in the exhaust-side inner circumferential surface 65 (the exhaust-side inner circumferential surface of the first portion 62). However, if the water impact position is set on the exhaust-side inner circumferential surface of the curved portion 62B, water can be introduced into the combustion chamber 10 via the curved portion 62B, allowing for smooth introduction of water into the combustion chamber 10.

[0104] Furthermore, although the above embodiment described a case where the water injection pressure is changed according to the engine speed, the water injection pressure may be changed according to the engine load regardless of the engine speed. Alternatively, the water injection pressure may be maintained at a constant pressure regardless of the engine speed or engine load.

[0105] Furthermore, although the above embodiment described a case where the amount of water injected is changed according to the engine speed, the amount of water injected may be changed based on other parameters regardless of the engine speed. Also, the amount of water injected may be maintained at a constant amount regardless of the operating state of the engine E. In addition, the control to increase the amount of water injected when knocking continues may be omitted.

[0106] Furthermore, the timing of water injection is not limited to when the intake valve 8 starts to open. Also, although the above embodiment describes a case where the water injection valve 40 is arranged to face the intake port 6, the water injection valve 40 may be mounted on the engine body 1 to face the combustion chamber 10, similar to the spark plug 12.

[0107] Furthermore, although the above embodiment described the case where engine E is an inline four-cylinder engine, the number of cylinders and the cylinder arrangement structure of engine E are not limited to this. [Explanation of Symbols]

[0108] 1. Engine body 2-cylinder 6 Intake Ports 8. Intake valve 10 Combustion chamber 12 Spark plugs 14. Throttle valve (means for adjusting air volume) 40 Water injection valve (water injection valve) 100 PCM (Control Means) E-engine SN2 Knock Sensor (Knock Detection Means)

Claims

1. A water-injection engine, An engine body including a combustion chamber and an intake port communicating with the combustion chamber, An intake valve that opens and closes the opening end of the intake port on the combustion chamber side, Air volume adjustment means for adjusting the amount of air supplied to the combustion chamber, A spark plug that ignites the mixture of air and fuel in the combustion chamber, A water injection valve for injecting water into the combustion chamber or the intake port, A knock detection means for detecting knocking in the engine body, The system comprises the aforementioned air volume adjustment means, the spark plug, and the water injection valve, The control means is The system sets a target torque, which is the target value of the engine's torque, and controls the air volume adjustment means and the spark plug so that the target torque is achieved. A water injection engine characterized by the implementation of knock prevention control, in which, when knocking is detected by the knock detection means, if the engine torque is greater than the target torque, water injection by the water injection valve is prohibited and the ignition timing, which is the time when the spark plug ignites, is retarded, while if the engine torque is less than or equal to the target torque, water injection by the water injection valve is performed and the retardation of the ignition timing is suppressed.

2. In the water injection engine according to claim 1, The control means is characterized in that it performs the knock prevention control only when the engine load is higher than a predetermined judgment load.

3. In the water injection engine according to claim 1, The control means, when water injection is performed by the water injection valve, When the engine is operating in a low-speed range where the engine speed is less than a predetermined first rotational speed, the water injection valve is controlled so that the amount of water injected by the water injection valve is greater than when the engine is operating in a high-speed range where the engine speed is greater than the first rotational speed (second rotational speed or higher), A water injection engine characterized in that, when the engine is operating in a medium-speed range where the engine speed is greater than or equal to the first rotational speed and less than the second rotational speed, the water injection valve is controlled so that the amount of water injected is less than when the engine is operating in the high-speed range.

4. In the water injection engine according to claim 1, The control means is characterized in that, after water injection by the water injection valve, knocking is detected by the knock detection means and the engine torque is less than or equal to the target torque, the amount of water injected by the water injection valve is increased.

5. In a water injection engine according to any one of claims 1 to 4, The water injection valve injects water into the intake port, A water injection engine characterized in that, when water injection is performed by the water injection valve, the control means causes water to be injected into the water injection valve when the intake valve starts to open.

Images