Patent Description:
<CIT> discloses an internal combustion engine and its controller. The internal combustion engine disclosed in this publication includes cylinders, an intake passage connected to the cylinders, and water injection valves located in the intake passage. The controller disclosed in this publication causes the water injection valves to inject water when the internal combustion engine is in a high-load running state. The water injected by the water injection valves flows into the corresponding cylinders through the intake passage and evaporates in the cylinders. When the water evaporates, the heat of vaporization lowers the temperatures in the cylinders.

When water is injected from the water injection valve in a period during which an intake valve that selectively opens and closes a connection port between the intake passage and corresponding one of the cylinders is open, the water is supplied to the cylinder through the intake passage. However, depending on the amount of water requested, the water injection valve may be unable to fully inject the requested amount of water during the period in which the intake valve is open. To solve this problem, water may be injected from the water injection valve not only in the open period of the intake valve but also in the closed period of the intake valve, which is before the open period.

The water injected by the water injection valve in the closed period of the intake valve accumulates in the intake passage until the intake valve opens. During the accumulation period, the water may collect on the wall surface of the intake passage in the form of a film. The larger the amount of water that collects on the wall surface, the thicker the liquid film and the less likely the water is to evaporate. If the water forming the liquid film remains in the intake passage, there is a possibility that the necessary amount of water cannot be supplied to the cylinders. <CIT> discusses a device for injection of water for an internal combustion engine, which comprises a water tank for storage of water, a conveying element for conveying the water, wherein the conveying element is connected to the water tank, a drive for driving the conveying element, at least one water injector for the injection of water, which water injector is connected to the conveying element, and a control unit which is arranged in order to open the water injector for the injection of water, wherein the water injector is arranged in order to inject water in the direction of a valve element of an inlet valve of the internal combustion engine. This document further relates to an internal combustion engine having a device according to the above and to a method for the injection of water. <CIT> discusses methods and systems for water injection into an engine and adjusting engine operation based on engine dilution demand and engine knock and includes injecting water into an intake manifold via a port water injector or a manifold water injector and adjusting engine operation and adjusting engine operation based on a change in engine dilution or knock. However, neither of these documents disclose at least the following features of appended claim <NUM>: control the pressure adjustment device such that the pressure of the water supplied to the water injection valve becomes higher in the second injection process than in the first injection process.

An aspect of the present disclosure provides a controller for an internal combustion engine. The internal combustion engine includes: a cylinder; an intake passage connected to the cylinder; a water injection valve configured to inject water into the intake passage; an intake valve configured to selectively open and close a connection port between the intake passage and the cylinder; and a pressure adjustment device configured to adjust pressure of water supplied to the water injection valve. The controller is configured to execute a first injection process that causes the water injection valve to inject water when the intake valve is open and a second injection process that causes the water injection valve to inject water when the intake valve is closed. The controller is further configured to control the pressure adjustment device such that the pressure of the water supplied to the water injection valve becomes higher in the second injection process than in the first injection process.

Another aspect of the present disclosure provides a control method for an internal combustion engine. The internal combustion engine includes: a cylinder; an intake passage connected to the cylinder; a water injection valve configured to inject water into the intake passage; and an intake valve configured to selectively open and close a connection port between the intake passage and the cylinder. The control method includes: executing a first injection process that causes the water injection valve to inject water when the intake valve is open; executing a second injection process that causes the water injection valve to inject water when the intake valve is closed; and setting pressure of the water supplied to the water injection valve to be higher in the second injection process than in the first injection process.

An embodiment of the present disclosure will now be described with reference to the drawings.

As shown in <FIG>, a vehicle <NUM> includes an internal combustion engine <NUM>. The internal combustion engine <NUM> is a driving force of the vehicle <NUM>.

The internal combustion engine <NUM> includes a cylinder block <NUM>, cylinders <NUM>, pistons <NUM>, connecting rods <NUM>, a crank chamber <NUM>, and a crankshaft <NUM>. <FIG> shows only one of the cylinders <NUM>. The same applies to the pistons <NUM> and the connecting rods <NUM>. The number of the cylinders <NUM> is four. Each cylinder <NUM> is a space defined in a cylinder block <NUM>. In the cylinder <NUM>, the air-fuel mixture of intake air and fuel burns. The crank chamber <NUM> is a space defined by the cylinder block <NUM> and an oil pan (not shown). The crank chamber <NUM> is located below the cylinders <NUM>. The crank chamber <NUM> connects to the cylinders <NUM>. The crank chamber <NUM> accommodates the crankshaft <NUM>. Each piston <NUM> is disposed in a corresponding cylinder <NUM>. The piston <NUM> is located in the cylinder <NUM>. The piston <NUM> reciprocates in the cylinder <NUM>. The piston <NUM> is coupled to the crankshaft <NUM> by the connecting rod <NUM>. As the piston <NUM> operates, the crankshaft <NUM> rotates.

The internal combustion engine <NUM> includes a cylinder head <NUM>, ignition plugs <NUM>, and fuel injection valves <NUM>. <FIG> shows only one of the ignition plugs <NUM>. The same applies to the fuel injection valves <NUM>. The ignition plugs <NUM> and the fuel injection valves <NUM> are attached to the cylinder head <NUM>. Each ignition plug <NUM> is disposed in a corresponding cylinder <NUM>. The ignition plug <NUM> ignites the air-fuel mixture in the cylinder <NUM>. Each fuel injection valve <NUM> is disposed in a corresponding cylinder <NUM>. The fuel injection valve <NUM> directly injects fuel into the cylinder <NUM> without using an intake passage <NUM>, which will be described below.

The internal combustion engine <NUM> includes the intake passage <NUM> and a throttle valve <NUM>. The intake passage <NUM> is a passage into which intake air is drawn into each cylinder <NUM>. The intake passage <NUM> is connected to the cylinders <NUM>. Specifically, the downstream portion of the intake passage <NUM> has intake ports 12A defined in the cylinder head <NUM>. The intake passage <NUM> branches into intake ports <NUM> at a certain position. <FIG> shows only one of the intake ports 12A. Each intake port 12A is disposed in a corresponding cylinder <NUM>. The intake port 12A is connected to the cylinder <NUM>. The throttle valve <NUM> is located upstream of the intake ports 12A in the intake passage <NUM>. The throttle valve <NUM> regulates an amount GA of the intake air flowing through the intake passage <NUM>.

The internal combustion engine <NUM> includes water injection valves <NUM>. Each water injection valve <NUM> is disposed in a corresponding cylinder <NUM>. The water injection valves <NUM> are attached to the cylinder head <NUM>. The tip of each water injection valve <NUM> is located in a corresponding intake port 12A. The water injection valve <NUM> injects water into the intake port 12A. The water injected by the water injection valve <NUM> flows through the intake port 12A into the cylinder <NUM>.

The internal combustion engine <NUM> includes an exhaust passage <NUM>. The exhaust passage <NUM> is a passage out of which exhaust gas is discharged from the cylinders <NUM>. The exhaust passage <NUM> is connected to the cylinders <NUM>. The upstream portion of the exhaust passage <NUM> has exhaust ports 13A defined in the cylinder head <NUM>. <FIG> shows only one of the exhaust ports 13A.

The internal combustion engine <NUM> includes a valvetrain for intake air. The valvetrain for intake air includes intake valves <NUM>, an intake rocker arm <NUM>, an intake camshaft <NUM>, and an intake valve timing varying device <NUM>. The valvetrain for intake air is attached to the cylinder head <NUM>. <FIG> shows only one of the intake valves <NUM>. The same applies to the intake rocker arms <NUM>. Each intake valve <NUM> is disposed in a corresponding intake port 12A. The intake valve <NUM> is located at a connection port between the intake port 12A and the cylinder <NUM>. The intake valve <NUM> is coupled to the intake camshaft <NUM> by the intake rocker arm <NUM>. As the intake camshaft <NUM> rotates, the intake valve <NUM> operates to selectively open and close the connection port between the intake port 12A and the cylinder <NUM>. Rotation of the crankshaft <NUM> is transmitted to the intake camshaft <NUM>. That is, the intake camshaft <NUM> rotates in conjunction with the crankshaft <NUM>. The intake valve timing varying device <NUM> changes the rotation position of the crankshaft <NUM> relative to the rotation position of the intake camshaft <NUM> (hereinafter referred to as the crank position Scr). This changes the timing of selectively opening and closing the intake valve <NUM> relative to the crank position Scr. The intake valve timing varying device <NUM> is, for example, an electric device that is driven by an electric motor.

The internal combustion engine <NUM> includes a valvetrain for exhaust gas. The valvetrain for exhaust gas includes exhaust valves <NUM>, an exhaust rocker arm <NUM>, an exhaust camshaft <NUM>, and an exhaust valve timing varying device <NUM>. The valvetrain for exhaust gas is attached to the cylinder head <NUM>. <FIG> shows only one of the exhaust valve <NUM>. The same applies to the exhaust rocker arms <NUM>. Each exhaust valve <NUM> is disposed in a corresponding exhaust port 13A. The exhaust valve <NUM> is located at a connection port between the exhaust port 13A and the cylinder <NUM>. The exhaust valve <NUM> is coupled to the exhaust camshaft <NUM> by the exhaust rocker arm <NUM>. As the exhaust camshaft <NUM> rotates, the exhaust valve <NUM> operates to selectively open and close the connection port between the exhaust port 13A and the cylinder <NUM>. Rotation of the crankshaft <NUM> is transmitted to the exhaust camshaft <NUM>. That is, the exhaust camshaft <NUM> rotates in conjunction with the crankshaft <NUM>. The exhaust valve timing varying device <NUM> changes the rotation position of the exhaust camshaft <NUM> relative to the crank position Scr. This changes the timing of selectively opening and closing the exhaust valve <NUM> relative to the crank position Scr. The exhaust valve timing varying device <NUM> is, for example, an electric device that is driven by an electric motor.

The internal combustion engine <NUM> includes a water supply mechanism <NUM>. The water supply mechanism <NUM> includes a tank <NUM>, a supply passage <NUM>, a pump <NUM>, branch passages <NUM>, return passages <NUM>, and adjustment valves <NUM>. The tank <NUM> stores water. The supply passage <NUM> extends from the tank <NUM>. Each branch passage <NUM> is disposed in a corresponding water injection valve <NUM>. The branch passages <NUM> branch from the supply passage <NUM>. Each branch passage <NUM> is connected to a corresponding water injection valve <NUM>. The pump <NUM> is located in the supply passage <NUM>. The pump <NUM> is an electric pump that is driven by an electric motor. The pump <NUM> forcibly delivers water from the tank <NUM> to the branch passages <NUM> through the supply passage <NUM>. Each return passage <NUM> is disposed in a corresponding branch passage <NUM>. The return passage <NUM> connects the branch passage <NUM> to the tank <NUM>. The return passage <NUM> is a passage through which water returns from the branch passage <NUM> into the tank <NUM>. In <FIG>, the return passages <NUM> are shown by the dotted lines. Each adjustment valve <NUM> is disposed in a corresponding return passage <NUM>. The adjustment valve <NUM> is located in the return passage <NUM>. The adjustment valve <NUM> is an electric valve that is driven by an electric motor. The adjustment valve <NUM> is of a butterfly type. That is, an open degree D of the adjustment valve <NUM> is adjustable. Depending on the open degree D of the adjustment valve <NUM>, the flow passage area of the return passage <NUM> changes. Further, a change occurs in the amount of water that returns to the tank <NUM> through the return passage <NUM>. Furthermore, a change occurs in the pressure in a portion of the branch passage <NUM> downstream of the part connected to the return passage <NUM> (i.e., the pressure of water supplied to the water injection valve <NUM>). That is, the adjustment valve <NUM> is a pressure adjustment device that adjusts the pressure of water supplied to the water injection valve <NUM>. Depending on the open degree D of each adjustment valve <NUM>, the pressure of the water supplied to a corresponding water injection valve <NUM> changes. The open degrees D of the adjustment valves <NUM> can be adjusted individually.

The internal combustion engine <NUM> includes a crank position sensor <NUM>, an intake cam position sensor <NUM>, an exhaust cam position sensor <NUM>, and an air flow meter <NUM>. The crank position sensor <NUM> detects the crank position Scr. The intake cam position sensor <NUM> detects a rotation position CG of the intake camshaft <NUM>. The exhaust cam position sensor <NUM> detects a rotation position CE of the exhaust camshaft <NUM>. The air flow meter <NUM> is located upstream of the throttle valve <NUM> in the intake passage <NUM>. The air flow meter <NUM> detects the amount GA of the intake air flowing through the portion of the intake passage <NUM> where the air flow meter <NUM> is disposed. These sensors each repeatedly send a signal corresponding to the detected information to a controller <NUM> (described later).

The internal combustion engine <NUM> includes water pressure sensors <NUM> and open degree sensors <NUM>. <FIG> shows only one of the water pressure sensors <NUM>. The same applies to the open degree sensors <NUM>. Each water pressure sensor <NUM> is disposed in a corresponding branch passage <NUM>. Each water pressure sensor <NUM> detects a pressure WP of the water supplied to a corresponding water injection valve <NUM> (hereinafter referred to as water pressure WP). Each open degree sensor <NUM> is disposed in a corresponding adjustment valve <NUM>. Each open degree sensor <NUM> detects the open degree D of a corresponding adjustment valve <NUM>. These sensors each repeatedly send a signal corresponding to the detected information to the controller <NUM> (described later).

The vehicle <NUM> includes an accelerator sensor <NUM> and a vehicle speed sensor <NUM>. The accelerator sensor <NUM> detects an accelerator operation amount ACC, which is the depression amount of the accelerator pedal of the vehicle <NUM>. The vehicle speed sensor <NUM> detects a vehicle speed SP, which is the travel speed of the vehicle <NUM>. These sensors each repeatedly send a signal corresponding to the detected information to the controller <NUM> (described later).

As shown in <FIG>, the vehicle <NUM> includes the controller <NUM>. The controller <NUM> may include processing circuitry including one or more processors that execute various processes in accordance with a computer program (software). The controller <NUM> may include processing circuitry that includes one or more dedicated hardware circuits such as application specific integrated circuits (ASICs) that execute at least part of various processes or may include processing circuitry that includes a combination of the processors and the dedicated hardware circuits. The processor includes a CPU <NUM> and a memory <NUM>, such as a RAM or a ROM. The memory <NUM> stores program codes or instructions configured to cause the CPU <NUM> to execute the processes. The memory <NUM>, or a computer-readable medium, includes any type of media that are accessible by general-purpose computers and dedicated computers. The memory <NUM> is, an electrically-rewriteable non-volatile memory.

The controller <NUM> repeatedly receives detection signals from the various sensors of the vehicle <NUM>. Based on the received detection signals, the controller <NUM> calculates the following parameters when necessary. Based on the crank position Scr detected by the crank position sensor <NUM>, the controller <NUM> calculates an engine rotation speed NE, which is the rotation speed of the crankshaft <NUM>. Based on the engine rotation speed NE and the amount GA of the intake air detected by the air flow meter <NUM>, the controller <NUM> calculates the engine load factor KL. The engine load factor KL is the ratio of the current cylinder inflow air amount to a cylinder inflow air amount obtained during steady operation of the internal combustion engine <NUM> with the throttle valve <NUM> fully open at the current engine rotation speed NE. The cylinder inflow air amount refers to the amount of the intake air flowing into one cylinder <NUM> in the intake stroke.

The controller <NUM> controls the internal combustion engine <NUM>. Based on the accelerator operation amount ACC, the vehicle speed SP, the engine rotation speed NE, the engine load factor KL, and the like, the controller <NUM> performs various types of control on the internal combustion engine <NUM> (e.g., fuel injection by the fuel injection valves <NUM>, the ignition timings of the ignition plugs <NUM>, the adjustment of the open degree of the throttle valve <NUM>). By performing such control, the controller <NUM> causes air-fuel mixture to sequentially burn in the cylinders <NUM>.

As part of the various control of the internal combustion engine <NUM>, the controller <NUM> controls the timing of the opening and closing of the intake valves <NUM> (hereinafter referred to as the intake valve timing) and the timing of the opening and closing of the exhaust valves <NUM>. For example, the controller <NUM> executes the following control related to the control of the intake valve timing. In the present embodiment, the controller <NUM> treats, as <NUM> (initial value), a state in which the intake valve timing is most retarded. By adjusting the advancement amount of the intake valve timing from the initial value, the controller <NUM> adjusts the intake valve timing. To adjust the intake valve timing, the controller <NUM> calculates a target advancement amount, which is a target value of the advancement amount of the intake valve timing, based on the engine rotation speed NE, the engine load factor KL, and the like. Then, the controller <NUM> controls the intake valve timing varying device <NUM> such that the advancement amount of an actual intake valve timing coincides with the target advancement amount. The controller <NUM> stores, in advance, the crank position Scr at which the intake valve <NUM> of each cylinder <NUM> reaches a valve-opening time TS when the intake valve timing has the initial value. Thus, by calculating a crank position Scr that is advanced from the valve-opening crank position Scr by the target advancement amount, the controller <NUM> obtains the current crank position Scr at which the intake valve <NUM> reaches the valve-opening time TS. Likewise, the controller <NUM> stores, in advance, the crank position Scr at which the intake valve <NUM> of each cylinder <NUM> reaches a valve-closing time TC when the intake valve timing has the initial value. This allows the controller <NUM> to obtain the current crank position Scr at which the intake valve <NUM> reaches the valve-closing time TC. In such a manner, the controller <NUM> uses the crank position Scr corresponding to the initial value and the target advancement amount to constantly obtain the crank position Scr at which the intake valve <NUM> of each cylinder <NUM> reaches the valve-closing time TS and the crank position Scr at which the intake valve <NUM> reaches the valve-closing time TC.

The controller <NUM> is capable of executing water injection control. The water injection control is executed to control the ignition timing, injection amount, and injection pressure of the water from each water injection valve <NUM>. In the present embodiment, a single combustion cycle is defined as a period from when the intake valve <NUM> of a specific cylinder <NUM> closes to when the intake valve <NUM> closes again after opening. That is, as shown in <FIG>, the single combustion cycle is a period from the valve-closing time TC, at which the intake valve <NUM> closes, to a valve-closing time TCA, at which the intake valve <NUM> closes again after the elapse of the valve-opening time TS, at which the intake valve <NUM> opens. In the single combustion cycle, the specific cylinder <NUM> enters each of the compression stroke, the expansion stroke, the exhaust stroke, and the intake stroke. The period during which the intake valve <NUM> is closed (i.e., the period from the valve-closing time TC to the valve-opening time TS of the intake valve <NUM>) is hereinafter referred to as a valve-closed period U1 of the intake valve <NUM>. The period during which the intake valve <NUM> is open (i.e., the period from the valve-opening time TS to the valve-closing time TCA of the intake valve <NUM>) is hereinafter referred to as a valve-open period U2 of the intake valve <NUM>.

As part of the water injection control, the controller <NUM> can execute a target calculation process. In the target calculation process, the running state of the internal combustion engine <NUM> is used to calculate a target injection amount Qs. The target injection amount Qs is a target value of the amount of water supplied to one cylinder <NUM> during the single combustion cycle. The controller <NUM> stores, in advance, a target water amount map M1 as the information used to calculate the target injection amount Qs. The target water amount map M1 represents the relationship between the engine rotation speed NE, the engine load factor KL, and a requested water amount. The requested water amount is the amount of water that needs to be supplied to one cylinder <NUM> in the single combustion cycle. In the target water amount map M1, the engine rotation speed NE, the engine load factor KL, and the requested water amount have the following relationship. When the engine load factor KL is less than a set load factor (described below), the requested water amount is <NUM> regardless of whether the engine rotation speed NE is relatively high or low. When the engine load factor KL is greater than or equal to the set load factor, the requested water amount is greater than <NUM> regardless of whether the engine rotation speed NE is relatively high or low. Specifically, when the engine load factor KL is greater than or equal to the set load factor, the requested water amount becomes larger as the engine load factor KL becomes higher at a certain engine rotation speed NE. The water injected by the water injection valve <NUM> evaporates in the cylinder <NUM>. When the water evaporates, the heat of vaporization lowers the temperature in the cylinder <NUM>. The requested water amount that is set for the target water amount map M1 has a value allowing for cooling in the cylinder <NUM> that is requested depending on each engine running state. Further, the set load factor is the lowest value of the engine load factor KL at which the temperature in the cylinder <NUM> needs to be lowered through the supply of water from the water injection valve <NUM>. The target water amount map M1 is created based on, for example, experiments or simulations.

As part of the water injection control, the controller <NUM> can execute a determination process. The determination process is a process that determines whether the target injection amount Qs of water can be supplied from the water injection valve <NUM> to the cylinder <NUM> during the valve-open period U2 of the intake valve <NUM> in the single combustion cycle. The maximum value of the amount that can be supplied to each cylinder <NUM> by injecting water from a corresponding water injection valve <NUM> during the valve-open period U2 of the intake valve <NUM> in the single combustion cycle is hereinafter referred to as an allowable injection amount Qv. The allowable injection amount Qv is determined based on a prior condition in which the water pressure WP has a value used for a first injection process (described later). In the determination process, the controller <NUM> determines whether the allowable injection amount Qv is greater than or equal to the target injection amount Qs. The controller <NUM> stores, in advance, a reach period L as the information needed to calculate the allowable injection amount Qv. The reach period L is the length of time from when the water injection valve <NUM> injects water to when the water reaches the inside of the cylinder <NUM>. The reach period L is defined based on, for example, experiments or simulations. In the present embodiment, the reach period L has a fixed value. The controller <NUM> further stores, in advance, an injection map M2 as the information needed to calculate the allowable injection amount Qv. The amount of water injected by one water injection valve <NUM> over a certain injection period under a certain water pressure WP is hereinafter referred to as a possible injection amount. The possible injection amount changes depending on the injection period. As described above, the injection period is a period during which the water injection valve <NUM> continues to inject water. The injection map M2 represents the relationship between the injection period, the water pressure WP, and the possible injection amount. In the injection map M2, the injection period, the water pressure WP, and the possible injection amount have the following relationship. At a certain water pressure WP, the possible injection amount becomes larger as the injection period becomes longer. In a certain injection period, the possible injection amount becomes larger as the water pressure WP becomes higher. The injection map M2 is created based on, for example, experiments or simulations.

As part of the water injection control, the controller <NUM> can execute the first injection process and a second injection process. The first injection process is a process that causes the water injection valve <NUM> to inject water during the valve-open period U2 of the intake valve <NUM> in the single combustion cycle. The second injection process is a process that causes the water injection valve <NUM> to inject water during the valve-closed period U1 of the intake valve <NUM> in the single combustion cycle. When the determination result of the determination process is affirmative, the controller <NUM> executes only the first injection process. In this case, the controller <NUM> causes the water injection valve <NUM> to inject the target injection amount Qs of water through the first injection process. When the determination result of the determination process is negative, the controller <NUM> executes the first and second injection processes as shown in <FIG>. In this case, the controller <NUM> causes the water injection valve <NUM> to inject the allowable injection amount Qv of water through the first injection process and causes the water injection valve <NUM> to inject the set injection amount Qr of water through the second injection process. The set injection amount Qr is the amount of the difference between the allowable injection amount Qv and the target injection amount Qs. In this manner, when the determination result of the determination process is negative, the controller <NUM> executes the two injection processes so that the water injection valve <NUM> injects the target injection amount Qs of water.

As shown in <FIG>, the controller <NUM> sets a different water pressure WP for each of the first and second injection processes. Specifically, the controller <NUM> controls the adjustment valve <NUM> such that the water pressure WP becomes a first value WP1 during the execution of the first injection process. The controller <NUM> controls the adjustment valve <NUM> such that the water pressure WP becomes a second value WP2 during the execution of the second injection process. The second value WP2 is higher than the first value WP1. That is, the controller <NUM> controls the adjustment valve <NUM> such that the water pressure WP becomes higher in the second injection process than in the first injection process. This means that the controller <NUM> sets the injection pressure of water from the water injection valve <NUM> to be higher in the second injection process than in the first injection process. The first value WP1 is predetermined through, for example, experiments or simulations. The second value WP2 is predetermined through, for example, experiments or simulations. The controller <NUM> stores the first value WP1 and the second value WP2 in advance. The reason for changing the water pressure WP between the first and second injection processes will be described in the Operation section. The details of the first value WP1 and the second value WP2 will also be described. In the present embodiment, the controller <NUM> sets the water pressure WP to the first value WP1 over the entire period during which the first injection process is executed. The controller <NUM> sets the water pressure WP to the second value WP2 over the entire period during which the second injection process is executed.

To control the water pressure WP depending on each injection process, the controller <NUM> substantially changes the open degree D of each adjustment valve <NUM>. The state in which the amount of water discharged by the pump <NUM> is a constant set discharge amount is referred to as a first state. The open degree D of the adjustment valve <NUM> needed to set the water pressure WP to the first value WP1 in the first state is referred to as a first open degree D1. The open degree D of the adjustment valve <NUM> needed to set the water pressure WP to the second value WP2 in the first state is referred to as a second open degree D2. The rotation speed of the pump <NUM> needed to set the discharge amount of the pump <NUM> to the set discharge amount is referred to as a set rotation speed. The controller <NUM> stores the first open degree D1, the second open degree D2, and the set rotation speed in advance. The first open degree D1, the second open degree D2, and the set rotation speed are defined based on, for example, experiments or simulations, with the flow passage area of the adjustment valve <NUM> corresponding to the adjustment valve <NUM> and the discharging performance of the pump <NUM> taken into account. To change the open degree D of the adjustment valve <NUM> to the first open degree D1 or the second open degree D2, the controller <NUM> refers to a detection value of the open degree sensor <NUM> as necessary and controls the electric motor of the adjustment valve <NUM> such that the requested open degree D is obtained.

As part of the water injection control, the controller <NUM> can execute a first injection time calculation process. The first injection time calculation process is a process that calculates a start time of the first injection process (hereinafter referred to as the first start time V1A) and an end time of the first injection process (hereinafter referred to as the first end time V1B). As shown in <FIG>, the controller <NUM> sets the valve-opening time TS of the intake valve <NUM> to the first start time V1A in the first injection time calculation process. Further, the controller <NUM> sets the first end time V1B to be before a limit time in the first injection time calculation process. The limit time is before the valve-closing time TCA of the intake valve <NUM> by the reach period L. The valve-closing time TCA of the intake valve <NUM> is the end time of the single combustion cycle.

As part of the water injection control, the controller <NUM> can execute a second injection time calculation process. The second injection time calculation process is a process that calculates a start time of the second injection process (hereinafter referred to as the second start time V2A) and an end time of the second injection process (hereinafter referred to as the second end time V2B). In the second injection time calculation process, the controller <NUM> determines the second start time V2A such that the second injection process ends before the first start time V1A by a specified period K. To make such a determination, the controller <NUM> sets the second start time V2A and the second end time V2B as follows. The controller <NUM> sets the second end time V2B to be before the first start time V1A by the specified period K. Further, the controller <NUM> sets the second start time V2A to be before the second end time V2B by a period needed for the injection of the set injection amount Qr of water from the water injection valve <NUM>. The minimum period for changing the water pressure WP from the second value WP2 to the first value WP1 is referred to as the necessary period. The necessary period is a period for changing the open degree D of the adjustment valve <NUM> from the second open degree D2 to the first open degree D1. In the present embodiment, the controller <NUM> sets the specified period K to the necessary period. The controller <NUM> stores the necessary period in advance. The necessary period is defined in advance through, for example, experiments or simulations. The changes in the water pressure WP shown in <FIG> and the flow of the injection processes will be described in detail below in the Operation section.

The series of processes related to the water injection control described below are executed for one cylinder <NUM>. That is, the controller <NUM> executes the following series of processes related to the water injection control for each cylinder <NUM> (i.e., each water injection valve <NUM>). When the internal combustion engine <NUM> is running (i.e., when the engine rotation speed NE is greater than <NUM>), the controller <NUM> repeatedly executes the water injection control. For each cylinder <NUM>, the controller <NUM> executes the series of processes related to the water injection control once in the single combustion cycle. In each combustion cycle, the controller <NUM> starts the water injection control at the start time of the single combustion cycle (i.e., the valve-closing time TC of the intake valve <NUM>). Based on the newest crank position Scr received from the crank position sensor <NUM>, the controller <NUM> determines the time of starting the water injection control. That is, when the newest crank position Scr coincides with the crank position Scr at which the intake valve <NUM> reaches the valve-closing time TC, the controller <NUM> determines that the intake valve <NUM> has reached the valve-closing time TC. Although the details will not be described, the valve-closing time TC and the valve-opening time TS of the intake valve <NUM> referred to and used by the controller <NUM> in the series of processes of the water injection control are related to the cylinder <NUM> for which the water injection control is executed. While the internal combustion engine <NUM> is running, the controller <NUM> controls the pump <NUM> such that the rotation speed of the pump <NUM> coincides with the set rotation speed. At the point in time when the internal combustion engine <NUM> is started, the controller <NUM> controls the adjustment valve <NUM> such that the open degree D of the adjustment valve <NUM> coincides with the first open degree D1. Thus, when the water injection control is executed for the first time after the internal combustion engine <NUM> is started, the open degree D of the adjustment valve <NUM> at the point in time when the water injection control is started is the first open degree D1.

As shown in <FIG>, when starting the water injection control, the controller <NUM> first executes the process of step S110. In step S110, the controller <NUM> calculates the target injection amount Qs. Specifically, the controller <NUM> refers to the newest engine rotation speed NE, the newest engine load factor KL, and the target water amount map M1. As described above, the target water amount map M1 represents the relationship between the engine rotation speed NE, the engine load factor KL, and the requested water amount, which is the amount of water that needs to be supplied to the cylinder <NUM>. Based on the target water amount map M1, the controller <NUM> calculates, as the target injection amount Qs, the requested water amount corresponding to the newest engine rotation speed NE and the newest engine load factor KL. Subsequently, the controller <NUM> advances the process to step S120. The process of step S110 is the target calculation process.

In step S120, the controller <NUM> calculates the allowable injection amount Qv. As described below, the allowable injection amount Qv is the amount of water that can be injected by the water injection valve <NUM> during a period in the valve-open period U2 of the intake valve <NUM> excluding the reach period L. As described above, the reach period L is the length of time to when the water injected by the water injection valve <NUM> reaches the inside of the cylinder <NUM>. To calculate the allowable injection amount Qv, the controller <NUM> first uses the newest engine rotation speed NE to convert the reach period L into a crank rotation amount corresponding to the newest engine rotation speed NE. Then, the controller <NUM> sets the obtained crank rotation amount as an offset value. The crank rotation amount represents the rotation angle of the crankshaft <NUM> obtained when the crankshaft <NUM> rotates from a rotation position to another rotation position. The higher the engine rotation speed NE, the larger the offset value. After calculating the offset value, the controller <NUM> calculates a limit crank position. Specifically, the controller <NUM> calculates the crank position Scr before, by the offset value, the crank position Scr at which the intake valve <NUM> reaches the valve-closing time TCA as the limit crank position. As shown in <FIG>, the valve-closing time TCA is the end time of the current combustion cycle. After calculating the limit crank position, the controller <NUM> calculates an allowable rotation amount. The allowable rotation amount is a crank rotation amount obtained from the crank position Scr at which the intake valve <NUM> reaches the valve-opening time TS to the limit crank position. After calculating the allowable rotation amount, the controller <NUM> uses the newest engine rotation speed NE to convert the allowable rotation amount into the length of a time that corresponds to the newest engine rotation speed NE. Then, the controller <NUM> sets the obtained value as an allowable period. At the same allowable rotation amount, the higher the engine rotation speed NE, the shorter the allowable period. Subsequently, the controller <NUM> refers to the injection map M2 and the first value WP1, which is the water pressure WP used for the first injection process. As described above, the injection map M2 represents the relationship between the injection period, the water pressure WP, and the possible injection amount. The controller <NUM> uses the injection map M2 to calculate, as the allowable injection amount Qv, the possible injection amount corresponding to the first value WP1 and the allowable period. In this case, the controller <NUM> only needs to apply the allowable period to the injection period in the injection map M2. As shown in <FIG>, after calculating the allowable injection amount Qv, the controller <NUM> advances the process to step S130.

In step S130, the controller <NUM> determines whether the allowable injection amount Qv calculated in step S120 is greater than or equal to the target injection amount Qs calculated in step S110. When this determination is affirmative, the target injection amount Qs of water can be supplied to the cylinder <NUM> from the water injection valve <NUM> during the valve-open period U2 of the intake valve <NUM> in the single combustion cycle. When the allowable injection amount Qv is greater than or equal to the target injection amount Qs (step S130: YES), the controller <NUM> advances the process to step S140. The process of step S130 is the determination process.

In step S140, the controller <NUM> calculates the first injection time. Specifically, the controller <NUM> calculates the first start time V1A, which is the start time of the first injection process, and the first end time V1B, which is the end time of the first injection process. First, the controller <NUM> calculates the first start time V1A. Specifically, the controller <NUM> sets the crank position Scr of the first start time V1A to the crank position Scr at which the intake valve <NUM> reaches the valve-opening time TS. Next, the controller <NUM> calculates the first end time V1B. Specifically, the controller <NUM> refers to the first value WP1, which is the water pressure WP for the first injection process, the target injection amount Qs calculated in step S110, and the injection map M2. The controller <NUM> uses the injection map M2 to calculate, as a normal injection period, the injection period corresponding to the first value WP1 and the target injection amount Qs. Subsequently, the controller <NUM> uses the newest engine rotation speed NE to convert the normal injection period into a crank rotation amount corresponding to the newest engine rotation speed NE. The controller <NUM> sets the obtained value as a normal rotation amount. Then, the controller <NUM> calculates, as the crank position Scr of the first end time V1B, the crank position Scr retarded from the crank position Scr of the first start time V1A by the normal rotation amount. After calculating the first end time V1B, the controller <NUM> advances the process to step S150. The process of step S140 is the first injection time calculation process. After starting the water injection control, the controller <NUM> immediately executes the processes of step S110 to S140. Thus, the time at which the process is advanced to the next step S150 is substantially equal to the time at which the single combustion cycle starts.

In step S150, the controller <NUM> executes the first injection process. Specifically, the controller <NUM> waits until the first start time V1A calculated in step S140. When the first start time V1A is reached, the controller <NUM> causes the water injection valve <NUM> to start injecting water. Then, the controller <NUM> continues the water injection until the first end time V1B calculated in step S140. When the first end time V1B is reached, the controller <NUM> causes the water injection valve <NUM> to stop injecting water. During the execution of the first injection process, the water pressure WP has the first value WP1 in relation to the process of step S260 in which the previous water injection control was executed. To start the first injection process in step S150, the controller <NUM> determines in the following manner that the first start time V1A is reached. The controller <NUM> repeatedly refers to the newest crank position Scr received from the crank position sensor <NUM>. Then, when determining that the newest crank position Scr coincides with the crank position Scr of the first start time V1A, the controller <NUM> determines that the first start time V1A is reached. In the same manner, when determining that the newest crank position Scr coincides with the crank position Scr of the first end time V1B, the controller <NUM> determines that the first end time V1B is reached. After executing the first injection process, the controller <NUM> temporarily ends the series of processes related to the water injection control. When the start time of the single combustion cycle is reached, the controller <NUM> executes the process of step S110 again.

When determining that the allowable injection amount Qv is less than the target injection amount Qs (step S130: NO), the controller <NUM> advances the process to step S210.

In step S210, the controller <NUM> calculates the first injection time. That is, the controller <NUM> calculates the first start time V1A and the first end time V1B in the same manner as step S140. In step S210, the controller <NUM> sets the crank position Scr of the first start time V1A to the crank position Scr at which the valve-opening time TS of the intake valve <NUM> is reached. The controller <NUM> sets the first end time V1B as follows. The controller <NUM> sets the crank position Scr of the first end time V1B to the limit crank position calculated in correspondence with the calculation of the allowable injection amount Qv in step S120. Subsequently, the controller <NUM> advances the process to step S220. The process of step S210 is the first injection time calculation process.

In step S220, the controller <NUM> calculates the set injection amount Qr, which is the difference between the target injection amount Qs and the allowable injection amount Qv. Specifically, the controller <NUM> sets the set injection amount Qr to a value obtained by subtracting the allowable injection amount Qv from the target injection amount Qs. Then, the controller <NUM> advances the process to step S230.

In step S230, the controller <NUM> calculates the second injection time. Specifically, the controller <NUM> calculates the second start time V2A, which is the start time of the second injection process, and the second end time V2B, which is the end time of the second injection process. The controller <NUM> first calculates the second end time V2B. Specifically, the controller <NUM> refers to the necessary period stored in advance and the newest engine rotation speed NE. Then, the controller <NUM> uses the newest engine rotation speed NE to convert the necessary period into a crank rotation amount corresponding to the newest engine rotation speed NE. The controller <NUM> sets the obtained crank rotation amount as a necessary rotation amount. The higher the engine rotation speed NE, the larger the necessary rotation amount. Subsequently, the controller <NUM> calculates the crank position Scr before, by the necessary rotation amount, the crank position Scr of the first start time V1A calculated in step S210 as the crank position Scr of the second end time V2B. Next, the controller <NUM> calculates the second start time V2A. Specifically, the controller <NUM> refers to the second value WP2, which is the water pressure WP for the second injection process, the set injection amount Qr calculated in step S220, and the injection map M2. The controller <NUM> uses the injection map M2 to calculate, as a set injection period, the injection period corresponding to the second value WP2 and the set injection amount Qr calculated in step S220. Subsequently, the controller <NUM> uses the newest engine rotation speed NE to convert the set injection period into a crank rotation amount corresponding to the newest engine rotation speed NE. Then, the controller <NUM> sets the obtained crank rotation amount as the set rotation amount. In the same manner as the necessary rotation amount, the higher the engine rotation speed NE, the larger the set rotation amount during the same set injection period. Then, the controller <NUM> calculates the crank position Scr before, by the set rotation amount, the crank position Scr of the calculated second end time V2B as the crank position Scr of the second start time V2A. After calculating the second start time V2A, the controller <NUM> advances the process to step S240. The process of step S230 is the second injection time calculation process. In the same manner as step S140, after starting the water injection control, the controller <NUM> immediately executes the processes of step S110 to S230. Thus, the time at which the process is advanced to the next step S240 is substantially equal to the time at which the single combustion cycle starts.

In step S240, the controller <NUM> changes the water pressure WP to the second value WP2. The water pressure WP at the point in time when the process is advanced to S240 has the first value WP1 in relation to the process of step S260 in which the previous water injection control was executed. The open degree D of the adjustment valve <NUM> is the first open degree D1. Specifically, in the process of step S240, the controller <NUM> controls the adjustment valve <NUM> such that the open degree D of the adjustment valve <NUM> coincides with the second open degree D2. The open degree D of the adjustment valve <NUM> is accordingly changed from the first open degree D1 to the second open degree D2. After executing the process of step S240, the controller <NUM> advances the process to step S250.

In step S250, the controller <NUM> executes the second injection process. Specifically, the controller <NUM> waits until the second start time V2A calculated in step S230. When the second start time V2A is reached, the controller <NUM> causes the water injection valve <NUM> to start injecting water. Then, the controller <NUM> continues the water injection until the second end time V2B calculated in step S230. When the second end time V2B is reached, the controller <NUM> causes the water injection valve <NUM> to stop injecting water. The determination of the second start time V2A and the second end time V2B is made in the same manner as step S150. After calculating the second injection process, the controller <NUM> advances the process to step S260.

In step S260, the controller <NUM> changes the water pressure WP from the second value WP2 to the first value WP1. Specifically, the controller <NUM> controls the adjustment valve <NUM> such that the open degree D of the adjustment valve <NUM> coincides with the first open degree D1. The open degree D of the adjustment valve <NUM> is accordingly changed from the second open degree D2 to the first open degree D1. The change in the open degree requires the necessary period (i.e., the specified period K of the present embodiment). After executing the process of step S260, the controller <NUM> advances the process to step S270. In the setting of the second end time V2B, the crank position Scr at the point in time when the process is advanced to the next step S270 is the crank position Scr of the first start time V1A.

In step S270, the controller <NUM> executes the first injection process. Specifically, when the process is advanced to step S270, the controller <NUM> immediately causes the water injection valve <NUM> to start injecting water. Then, the controller <NUM> continues the water injection until the first end time V1B calculated in step S210. When the first end time V1B is reached, the controller <NUM> causes the water injection valve <NUM> to stop injecting water. The determination of the first start time V1A and the first end time V1B is made in the same manner as step S150. After executing the first injection process, the controller <NUM> temporarily ends the series of processes related to the water injection control. When the start time of the single combustion cycle is reached, the controller <NUM> executes the process of step S110 again.

At the point in time when the single combustion cycle starts (i.e., at the valve-closing time TC of the intake valve <NUM>), the open degree D of the adjustment valve <NUM> is the first open degree D1. As shown in <FIG>, the water pressure WP thus has the first value WP1 at the valve-closing time TC of the intake valve <NUM>. If, for example, the target injection amount Qs is relatively large or the engine rotation speed NE is relatively high, the allowable injection amount Qv may be less than the target injection amount Qs (step S130: NO). In this case, as shown in <FIG>, at the valve-closing time TC of the intake valve <NUM>, the controller <NUM> quickly changes the open degree D of the adjustment valve <NUM> from the first open degree D1 to the second open degree D2 (step S240). This causes the water pressure WP to change from the first value WP1 to the second value WP2. Then, as shown in <FIG>, the controller <NUM> executes the second injection process in the valve-closed period U1 of the intake valve <NUM> with the water pressure WP kept at the second value WP2 (step S250). Then, the controller <NUM> causes the water injection valve <NUM> to inject the set injection amount Qr of water. The controller <NUM> ends the second injection process at the second end time V2B, which is before the valve-opening time TS of the intake valve <NUM> by the specified period K. Subsequently, the controller <NUM> changes the open degree D of the adjustment valve <NUM> from the second open degree D2 to the first open degree D1 (step S260). This causes the water pressure WP to change from the second value WP2 to the first value WP1 as shown in <FIG>. The change in the water pressure WP requires the necessary period, which is set as the specified period K. Accordingly, at the point in time when the water pressure WP has been changed, the valve-opening time TS of the intake valve <NUM> is reached. As shown in <FIG>, the controller <NUM> executes the first injection process (step S270). The controller <NUM> causes the water injection valve <NUM> to inject the allowable injection amount Qv of water during the valve-open period U2 of the intake valve <NUM>. By executing the first and second injection processes in this manner, the controller <NUM> causes the water injection valve <NUM> to inject the target injection amount Qs of water as a total amount in the single combustion cycle.

<FIG> shows the necessary period, which is needed to change the water pressure WP from the second value WP2 to the first value WP1, in an exaggerated manner to facilitate the understanding of the situation in which the water pressure WP is changed between the second injection process and the first injection process. The same applies to the period during which the water pressure WP is changed from the first value WP1 to the second value WP2. The injection period of the first injection process and the injection period of the second injection process are just exemplary and do not always coincide with actual injection periods.

When water is injected from the water injection valve <NUM>, the injected water may collect at one position on the wall surface of the intake port 12A in a concentrated manner. In this case, the collected water forms a relatively large water droplet at that position of the wall surface of the intake port 12A. Since the thickness of the liquid film formed by the water droplet is relatively large, it is difficult for the water droplet to evaporate. The water droplet remains on the wall surface of the intake port 12A or flows into the cylinder <NUM> together with intake air. If the water droplet flows into the cylinder <NUM>, the water droplet runs down the wall surface of the cylinder <NUM> and eventually flows into the crank chamber <NUM>. Thus, the water droplet does not cool the inside of the cylinder <NUM>. In addition to the situation in which a relatively large water droplet formed in the intake port 12A flows into the cylinder <NUM>, a relatively large water droplet may directly form on the wall surface of the cylinder <NUM>. For example, when water collects at one position on the wall surface of the cylinder <NUM>, the collected water forms a relatively large water droplet at that position on the wall surface of the cylinder <NUM>. Such a water droplet flows into the crank chamber <NUM> without evaporating in the cylinder <NUM>. Even if water evaporates, the heat of the vaporization cools the wall surface of the cylinder <NUM> but does not significantly cool the gas in the cylinder <NUM>. Thus, when a relatively large water droplet with a relatively large thickness liquid film is formed in the intake port 12A or the cylinder <NUM>, the water droplet does not achieve evaporative cooling of the gas in the cylinder <NUM>. Accordingly, even when the water injection valve <NUM> injects the target injection amount Qs of water, the formation of a relatively large water droplet as described above cannot cool the inside of the cylinder <NUM> as intended.

To solve this problem, the present embodiment improves the water injection control to prevent the formation of a relatively large water droplet as described above. Specifically, a different water pressure WP is used for each of the first and injection processes. More specifically, the water pressure WP of the second injection process is higher than the water pressure WP of the first injection process. This means that the injection pressure of the water injection valve <NUM> is higher in the second injection process than in the first injection process. Such a configuration is employed for the reason described below.

When the intake valve <NUM> is in the valve-closed period U1, the water injection valve <NUM> may inject water into the intake port 12A. If the injection pressure of the water injection valve <NUM> is relatively high, the water is dispersed in every direction with momentum from an injection hole of the water injection valve <NUM>. Thus, when the injection pressure of the water injection valve <NUM> is relatively high, the water injected from the water injection valve <NUM> is widely dispersed. That is, as illustrated in <FIG>, the injection range of water with a relatively high injection pressure shown by Y1 is broader than the injection range of water with a relatively low injection pressure shown by Y2. When the same amount of water is injected, the amount of water collecting at each position on the wall surface of the intake port 12A becomes smaller as the injection range of water becomes broader. Thus, the thickness of the liquid film formed by the collected water is relatively small at each position on the wall surface of the intake port 12A. The smaller the thickness of the liquid film, the more quickly the liquid film evaporates. Thus, increasing the injection pressure of the water injection valve <NUM> prevents the formation of a relatively water droplet on the wall surface of the intake port 12A. In this point of view, the controller <NUM> sets the water pressure WP to be higher and consequently sets the injection pressure of the water injection valve <NUM> to be higher in the second injection process. In a situation in which the intake valve <NUM> is in the valve-closed period U1, the injection pressure that allows water to be dispersed so widely as to prevent the formation of a relatively large water droplet is hereinafter referred to as a second injection pressure J2. The second value WP2, which is the water pressure WP for the second injection process, is the water pressure WP used when the injection pressure of the water injection valve <NUM> is the second injection pressure J2. The second value WP2 and the second injection pressure J2, on which the second value WP2 is based, are values that have been defined in advance through, for example, experiments or simulations. The defining of the second injection pressure J2 takes into account, for example, the pressure of intake air corresponding to the engine running state when the target injection amount Qs is greater than <NUM>. The difference between the pressure of the intake air and the pressure of the injection from the water injection valve <NUM> may affect the injection range.

As described above, increasing the injection pressure of the water injection valve <NUM> is effective for preventing the formation of a relatively water droplet on the wall surface of the intake port 12A, but is not effective for preventing the formation of a relatively large water droplet on the wall surface of the cylinder <NUM> for the following reason. When the intake valve <NUM> is in the valve-open period U2, the water injection valve <NUM> may inject water with a relatively high injection pressure. In this case, as the injection range of water becomes wider, the water may reach a farther position. Additionally, the flow of intake air toward the cylinder <NUM> occurs in the valve-open period U2 of the intake valve <NUM>. The flow of this intake air causes the water injected by the water injection valve <NUM> to flow toward the cylinder <NUM>. If the flow of intake air toward the cylinder <NUM> occurs and the water injection valve <NUM> injects water to a farther position, the water injected by the water injection valve <NUM> flows into the cylinder <NUM> with momentum. Further, as shown by Z1 in <FIG>, the water is moved a longer distance. The water may reach the wall surface of the cylinder <NUM>. If the water locally collects on the wall surface of the cylinder <NUM> in a concentrated manner, the collected water forms a relatively large water droplet. That is, increasing the injection pressure of the water injection valve <NUM> in the valve-open period U2 of the intake valve <NUM> may rather form a relatively large water droplet. In this regard, decreasing the injection pressure of the water from the water injection valve <NUM> shortens the movement distance of the water injected from the water injection valve <NUM>. This prevents situations in which the water reaches the wall surface of the cylinder <NUM>. In this point of view, the controller <NUM> sets the water pressure WP to be lower and consequently sets the injection pressure of the water injection valve <NUM> to be lower in the second injection process. In a situation in which the intake valve <NUM> is in the valve-open period U2, the injection pressure that prevents the water injected by the water injection valve <NUM> from reaching the wall surface of the cylinder <NUM> is hereinafter referred to as a first injection pressure J1. The first value WP1, which is the water pressure WP for the first injection process, is the water pressure WP used when the injection pressure of the water injection valve <NUM> is the first injection pressure J1. The first value WP1 and the first injection pressure J1, on which the first value WP1 is based, are values predetermined through, for example, experiments or simulations. The defining of the first injection pressure J1 takes into account, for example, the amount GA of intake air corresponding to the engine running state when the target injection amount Qs is greater than <NUM>. The amount GA of the intake air may affect the movement distance of the water injected from the water injection valve <NUM>.

In the present embodiment, the specified period K from the second end time V2B to the first start time V1A is set as the necessary period, which is a minimum period needed for changing the water pressure WP. Thus, when the water pressure WP is changed between the period from the second end time V2B to the first start time V1A, the period from the second end time V2B to the first start time V1A is minimized. Accordingly, in addition to the configuration of advantage (<NUM>), in which a different injection pressure is used for each of the entire period for executing the second injection process and the entire period for executing the first injection process, the second injection process can be executed at a time as close as possible to the valve-opening time TS of the intake valve <NUM>. This is effective in preventing a relatively large water droplet from being formed on the wall surface of the intake port 12A.

The above embodiment may be modified as follows. The above embodiment and the following modifications can be combined as long as the combined modifications remain technically consistent with each other.

The water pressure WP may be changed during the execution of the first and second injection processes. For example, when these injection processes are being executed, the running state of the internal combustion engine <NUM> may change. Further, during the execution periods of the injection processes, the injection pressure of the water injection valve <NUM> suitable for preventing the formation of a relatively large water droplet may change depending on the change in the running state. With these problems taken into account, the water pressure WP may be changed depending on the running state of the internal combustion engine <NUM>. For example, if a map representing the relationship between the running state of the internal combustion engine <NUM> and an optimal water pressure WP is created in advance, the water pressure WP can be changed during the execution of the injection processes.

The specified period K is not limited to the example in the above embodiment. Instead, the specified period K does not have to be the necessary period. For example, the specified period K may be longer than the necessary period. In this case, the water pressure WP can be changed from the second value WP2 to the first value WP1 before the first start time V1A. Thus, the second injection process allows the water pressure WP to be kept at the second value WP2 until the end time of the second injection process. Further, the first injection process allows the water pressure WP to be kept at the first value WP1 until the start time of the first injection process. When the specified period K is longer than the necessary period, the water pressure WP may be changed at any point in time of the specified period K. For example, the open degree D of the adjustment valve <NUM> may be changed subsequent to a predetermined period from the second end time V2B. Further, the timing of changing the open degree D of the adjustment valve <NUM> may be calculated based on the running state of the internal combustion engine <NUM>.

The specified period K does not have to be used. Further, the second injection process and the first injection process may be executed continuously. In this case, for example, the water pressure WP may start to be lowered during the second injection process so that the water pressure WP has a value suitable for the first injection process at the start time of the first injection process. The water pressure WP in at least part of the period during the execution of the second injection process only needs to be higher than the water pressure WP in at least part of the period during the execution of the first injection process. This configuration prevents the formation of a relatively large water droplet during part of at least the period.

The first start time V1A is not limited to the example in the above embodiment. Instead, the first start time V1A may be subsequent to the valve-opening time TS of the intake valve <NUM>. For example, when the target injection amount Qs is sufficiently smaller than the allowable injection amount Qv, the first start time V1A may be subsequent to the valve-opening time TS of the intake valve <NUM>. This allows the water injection valve <NUM> to fully supply the target injection amount Qs of water during the valve-open period U2 of the intake valve <NUM>.

The configuration of the water supply mechanism <NUM> is not limited to the example in the above embodiment. The water supply mechanism <NUM> only needs to be configured to correctly adjust the water pressure WP for the water injection valve <NUM>. For example, instead of arranging each return passage <NUM> on a corresponding branch passage <NUM> as in the above embodiment, the water supply mechanism <NUM> may include only one return passage. In addition, the water supply mechanism <NUM> may include only one adjustment valve <NUM>. In this case, in the same manner as the above embodiment, the pump <NUM> is located in the supply passage <NUM> that extends from the tank <NUM>, and each branch passage <NUM> branches from the supply passage <NUM>. Further, the return passage connects the tank <NUM> to the portion of the supply passage <NUM> downstream of the pump <NUM> and upstream of the portions branched into the branch passages <NUM>. Furthermore, the adjustment valve <NUM> is located in the return passage. In this case, the pressure of water flowing downstream of the pump <NUM> in the supply passage <NUM> changes depending on the open degree D of the adjustment valve <NUM>. This changes the water pressures WP for all the water injection valves <NUM>. In such a manner, a common adjustment valve may be disposed on all the water injection valves <NUM>, and this adjustment valve may be used to collectively change the water pressures WP for all the water injection valves <NUM>. This configuration may be employed if it is already clear that the period for executing the first injection process for a specific cylinder <NUM> does not overlap the period for executing the second injection process for another cylinder <NUM> because of, for example, the setting of the target injection amount Qs in the target water amount map M1.

The pump <NUM> does not have to be driven by an electric motor. The pump <NUM> may be driven by, for example, the crankshaft <NUM>. In this case, the open degree D of the adjustment valve <NUM> only needs to be adjusted in correspondence with a driven state of the pump <NUM> to obtain a correct water pressure WP.

Each adjustment valve <NUM> does not need to have the configuration of the above embodiment. The adjustment valve <NUM> only needs to change the water pressure WP. The adjustment valve <NUM> may be, for example, a ball valve.

The pressure adjustment device is not limited to the example in the above embodiment. For example, the pressure adjustment device may change the water pressure WP by changing the discharge amount of the pump <NUM> and the open degree D of each adjustment valve <NUM>. In this case, the pressure adjustment device includes the pump <NUM> and the adjustment valves <NUM>. Instead, the pressure adjustment device may change the water pressure WP by changing only the discharge amount of the pump <NUM>. In this case, the pressure adjustment device includes the pump <NUM>. The pressure adjustment device is not limited to a pump or a valve. The pressure adjustment device only needs to correctly change the water pressure WP. Based on the configuration of the pressure adjustment device that is to be controlled, the controller <NUM> needs to control the pressure adjustment device. Depending on the configuration of the pressure adjustment device, the controller <NUM> may refer to the detection value of the water pressure sensor <NUM> and perform feedback control on the pressure adjustment device such that a correct water pressure WP is obtained.

The reach period L is not limited to a fixed value and may be changed depending on, for example, the amount GA of intake air. The reach period L may be <NUM>. In this case, most of the target injection amount Qs of water reaches the inside of each cylinder <NUM>.

The content of the target water amount map M1 is not limited to the example in the above embodiment. The target water amount map M1 only needs to be set depending on the engine running state to inject water needed to cool the inside of the cylinder <NUM> by a necessary amount.

The method for obtaining the crank position Scr at which the intake valve <NUM> reaches the valve-opening time TS is not limited to the example in the above embodiment. For example, detection values of the crank position sensor <NUM> and the intake cam position sensor <NUM> may be used to obtain the crank position Scr at which the intake valve <NUM> reaches the valve-opening time TS. If the crank position Scr at which the intake valve <NUM> reaches the valve-opening time TS can be correctly obtained, any method may be employed. The same applies to the crank position Scr at which the intake valve <NUM> reaches the valve-closing time TC.

The overall configuration of the internal combustion engine <NUM> is not limited to the example of the above embodiment. For example, the number of the cylinders <NUM> may be changed. The internal combustion engine <NUM> only needs to include the water injection valves <NUM>, the intake valve <NUM>, and the pressure adjustment device.

The number of the water injection valves <NUM> in each cylinder <NUM> is not limited to the example of the above embodiment. For example, as shown in <FIG>, one cylinder <NUM> may include two water injection valves <NUM>. The two water injection valves <NUM> may inject water into the cylinder <NUM> through the intake port 12A. The two water injection valves <NUM> are hereinafter referred to as a first water injection valve 14A and a second water injection valve 14B. When one cylinder <NUM> includes the first water injection valve 14A and the second water injection valve 14B, the following configuration may be employed. A water supply mechanism 70A is used such that each of the first water injection valve 14A and the second water injection valve 14B is supplied with water with a different water pressure WP. Specifically, the first water injection valve 14A is connected to a first passage <NUM> that extends from the tank <NUM>, and the second water injection valve 14B is connected to a second passage <NUM> that extends from the tank <NUM>. For example, a first pump is disposed in the first passage <NUM> as a first pressure adjustment device <NUM>, and a second pump is disposed in the second passage <NUM> as a second pressure adjustment device <NUM>. The controller <NUM> controls driving of the first pump such that the water pressure WP of the water supplied to the first water injection valve 14A has the first value WP1. Further, the controller <NUM> controls driving of the second pump such that the water pressure WP of the water supplied to the second water injection valve 14B has the second value WP2, which is greater than the first value WP1. The controller <NUM> uses the first water injection valve 14A as a water injection valve <NUM> dedicated for the first injection process and uses the second water injection valve 14B as a water injection valve <NUM> dedicated for the second injection process. Unlike the configuration of the above embodiment, in which the first and second injection processes are executed using a common water injection valve <NUM>, the configuration of this modification eliminates the need for the pressure adjustment device to change the water pressure WP depending on the execution of each injection process. Thus, even if the specified period K for changing the water pressure WP is not provided, a different injection pressure can be used for each of the entire period during which the second injection process is executed and the entire period during which the first injection process is executed. That is, this configuration allows the second injection process and the first injection process to be executed continuously while also using a different injection pressure in the entire period of each of the two injection processes. While <FIG> shows only one of the cylinders <NUM>, the first water injection valve 14A and the second water injection valve 14B are disposed on another cylinder <NUM> in the same manner. The first water injection valve 14A corresponding to a further cylinder <NUM> is connected to a first branch passage <NUM> branched ing pefrom a portion of the first passage <NUM> downstream of the first pressure adjustment device <NUM>. The second water injection valve 14B corresponding to yet another cylinder <NUM> is connected to a second branch passage <NUM> branched from a portion of the second passage <NUM> downstream of the second pressure adjustment device <NUM>. In a case in which each cylinder <NUM> includes multiple water injection valves <NUM>, the configuration of the water supply mechanism is not limited to the example of <FIG>. The water supply mechanism only needs to supply each water injection valve <NUM> with the water having a correct water pressure WP.

The overall configuration of the vehicle <NUM> is not limited to the example of the above embodiment. For example, the vehicle <NUM> may include a motor generator as the driving source of the vehicle <NUM>, in addition to the internal combustion engine <NUM>.

The amount of water injected from the water injection valves <NUM> in the first injection process and the amount of water injected from the water injection valves <NUM> in the second injection process are not limited to the examples of the above embodiment. For example, when the allowable injection amount Qv is less than the target injection amount Qs, the amount of water injected from the water injection valves <NUM> in the first injection process may be less than the allowable injection amount Qv. In this case, the set injection amount Qr by which water is injected from the water injection valves <NUM> in the second injection process may be increased accordingly.

In the comparison between the second injection process in a specific combustion cycle and the first injection process in a different combustion cycle, the use of a different water pressure WP in each of the injection processes is effective for preventing the formation of a relatively large water droplet. In this regard, for example, the following configuration may be employed. In the specific combustion cycle, only the second one of the first and second injection processes is executed. Then, the water pressure WP in the second injection process is set to be higher than the water pressure WP in the first injection process of the different combustion cycle.

Claim 1:
A controller (<NUM>) for an internal combustion engine (<NUM>), the internal combustion engine (<NUM>) including:
a cylinder (<NUM>);
an intake passage (<NUM>) connected to the cylinder (<NUM>);
a water injection valve (<NUM>) configured to inject water into the intake passage (<NUM>);
an intake valve (<NUM>) configured to selectively open and close a connection port between the intake passage (<NUM>) and the cylinder (<NUM>); and
a pressure adjustment device (<NUM>; <NUM>; <NUM>, <NUM>) configured to adjust pressure of water supplied to the water injection valve (<NUM>),
wherein the controller (<NUM>) is configured to:
execute a first injection process that causes the water injection valve (<NUM>) to inject water when the intake valve (<NUM>) is open and a second injection process that causes the water injection valve (<NUM>) to inject water when the intake valve (<NUM>) is closed, characterised in being configured to
control the pressure adjustment device (<NUM>; <NUM>; <NUM>, <NUM>) such that the pressure of the water supplied to the water injection valve (<NUM>) becomes higher in the second injection process than in the first injection process.