Patent Description:
<CIT> discloses an engine that includes a water injection valve for injecting water into intake air.

In such an engine, some of the water injected into the intake air collects on the wall surface of the intake port. The amount of water collected on the wall surface of the intake port may increase as the water injection is repeatedly executed. In such a case, water droplets grow in the intake port. The grown large water droplets may flow into the cylinder.

Even if water droplets flow into the cylinder from the intake port, the water droplets evaporate in the cylinder if the water droplets are small. However, when large water droplets flow into the cylinder, the water droplets do not completely evaporate in the cylinder, but flow into the crankcase. The water droplets flowing into the crankcase may be mixed with the engine oil to emulsify the engine oil, or may evaporate to increase the internal pressure of the crankcase.

<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.

In one general aspect, a controller for an engine is provided, according to claim <NUM>. The engine includes a cylinder, intake ports connected to the cylinder, intake valves, and water injection valves. The intake valves respectively correspond to the intake ports. Each of the intake valves is configured to selectively allow for and block connection between the corresponding one of the intake ports and the cylinder. The water injection valves are installed in the respective intake ports. Each of the water injection valves is configured to inject water to the corresponding one of the intake ports. The controller is configured to selectively execute, for each of the intake ports, a synchronous injection that causes the corresponding one of the water injection valves to inject water only during a valve opening period of the corresponding one of the intake valves or an asynchronous injection that causes the corresponding one of the water injection valves to inject water during a valve closing period of the corresponding one of the intake valves. The controller is configured to perform, when executing a synchronous/asynchronous concurrent injection in which the intake ports includes an intake port in which the synchronous injection is executed and an intake port in which the asynchronous injection is executed, a switching process of switching the intake port in which the asynchronous injection is executed.

In another general aspect, a method for controlling an engine is provided, according to claim <NUM>. The engine includes a cylinder, intake ports connected to the cylinder, intake valves, and water injection valves. The intake valves respectively correspond to the intake ports. Each of the intake valves is configured to selectively allow for and block connection between the corresponding one of the intake ports and the cylinder. The water injection valves are installed in the respective intake ports. Each of the water injection valves is configured to inject water to the corresponding one of the intake ports. The method includes: selectively executing, for each of the intake ports, a synchronous injection that causes the corresponding one of the water injection valves to inject water only during a valve opening period of the corresponding one of the intake valves or an asynchronous injection that causes the corresponding one of the water injection valves to inject water during a valve closing period of the corresponding one of the intake valves; executing a synchronous/asynchronous concurrent injection in which the intake ports includes an intake port in which the synchronous injection is executed and an intake port in which the asynchronous injection is executed; and when executing the synchronous/asynchronous concurrent injection, executing a switching process of switching the intake port in which the asynchronous injection is executed.

Sequences of operations are exemplary, and may be changed as apparent to one of ordinary skill in the art, except for operations necessarily occurring in a certain order.

A first embodiment of the present disclosure will now be described with reference to <FIG>.

First, the configuration of the intake system of the engine <NUM> will be described with reference to <FIG>. The engine <NUM> is a hydrogen fuel engine that uses hydrogen gas as fuel. The engine <NUM> includes multiple (four in the present embodiment) cylinders <NUM>. Each cylinder <NUM> is provided with a hydrogen gas injection valve <NUM> and an ignition device <NUM>. The hydrogen gas injection valve <NUM> injects hydrogen gas into the corresponding cylinder <NUM>. The ignition device <NUM> causes a spark discharge to ignite hydrogen gas injected into the cylinder <NUM> by the hydrogen gas injection valve <NUM>.

An intake passage <NUM> of the engine <NUM> incorporates a throttle valve 14A. Each cylinder <NUM> is connected to the intake passage <NUM> via two intake ports: a first intake port <NUM> and a second intake port <NUM>. Intake valves <NUM> are respectively provided at a joint portion between each first intake port <NUM> and the corresponding cylinder <NUM> and a joint portion between each second intake port <NUM> and the corresponding cylinder <NUM>. The intake valves <NUM> each operate in conjunction with rotation of the crankshaft of the engine <NUM> to open and close the corresponding one of intake ports <NUM>, <NUM>. That is, the intake valves <NUM> each selectively allows for and blocks connection between the corresponding one of the intake ports <NUM>, <NUM> and the cylinder <NUM>. Each cylinder <NUM> is provided with two water injection valves: a first water injection valve <NUM> and a second water injection valve <NUM>. The first water injection valve <NUM> injects water into the first intake port <NUM>. The second water injection valve <NUM> injects water into the second intake port <NUM>.

Next, the configuration of a controller for the engine <NUM> will be described with reference to <FIG>. The controller includes an engine control module (ECM) <NUM>. The ECM <NUM> is an electronic control unit or processing circuitry that includes a processor <NUM> and a memory device <NUM>. The memory device <NUM> stores programs and data used to control the engine <NUM>. The processor <NUM> executes various processes related to control of the engine <NUM> by reading and executing programs stored in the memory device <NUM>.

The ECM <NUM> is connected to various types of sensor that acquire the operating state of the engine <NUM>. The sensors connected to the ECM <NUM> include an air flow meter <NUM>, a coolant temperature sensor <NUM>, an intake air temperature sensor <NUM>, and a crank angle sensor <NUM>. The air flow meter <NUM> detects the flow rate of intake air flow rate in the intake passage <NUM>. The coolant temperature sensor <NUM> detects the temperature of coolant of the engine <NUM>. The intake air temperature sensor <NUM> detects the temperature of intake air in the intake passage <NUM>. The crank angle sensor <NUM> detects the rotational phase of the crankshaft, which is an output shaft of the engine <NUM>. The ECM <NUM> obtains an engine rotation speed, which is a rotation speed of the engine <NUM>, based on a detection result of the crank angle sensor <NUM>. Further, the ECM <NUM> obtains an engine load factor, which is a filling factor of intake air of each of the cylinders <NUM>, based on the intake air flow rate, the engine rotation speed, and the like.

Based on the detection results of these sensors, the ECM <NUM> performs an engine control that includes a hydrogen gas injection control for the hydrogen gas injection valves <NUM>, an ignition timing control for the ignition devices <NUM>, and an opening degree control for the throttle valve 14A. As part of the engine control, the ECM <NUM> performs a water injection control for each first water injection valve <NUM> and each second water injection valve <NUM>.

Next, the water injection control, which is performed by the ECM <NUM>, will be described. In the case of an engine using liquid fuel such as gasoline, the inside of the cylinder is cooled by latent heat of vaporization of fuel. In contrast, in the case of the engine <NUM>, in which hydrogen gas is injected, cooling by latent heat of vaporization of fuel is not performed. Thus, the temperature inside the cylinders <NUM> is higher than that in the case of an engine using liquid fuel. Accordingly, abnormal combustion such as pre-ignition is likely to occur. Therefore, the engine <NUM> cools the inside of the cylinders <NUM> by using latent heat of vaporization of the water injected by the first water injection valves <NUM> and the second water injection valves <NUM>.

<FIG> is a flowchart of a water injection control routine executed by the ECM <NUM>. The ECM <NUM> repeatedly executes the routine at each specified control cycle during the operation of the engine <NUM>. The water injection control routine is executed, for example, for each cylinder <NUM> in every combustion cycle of the engine <NUM>.

When this routine is started, the ECM <NUM> first calculates a requested water injection amount QS based on the operating state of the engine <NUM> in step S100. In the present embodiment, the ECM <NUM> calculates the requested water injection amount QS based on the engine rotation speed and the engine load factor. The ECM <NUM> calculates, as a value of the requested water injection amount QS, an amount of water injection required to cool the inside of each cylinder <NUM> to a temperature at which abnormal combustion is avoided. In a high rotation speed and high load operation, a relatively large amount of heat is generated per unit time by combustion in each cylinder <NUM>. The ECM <NUM> calculates a greater value of the requested water injection amount QS during a high rotation speed and high load operation than during a low rotation speed and low load operation. The requested water injection amount QS represents a requested value of a total water injection amount, which is the sum of the water injection amounts for the first intake port <NUM> and the second intake port <NUM>. The requested water injection amount QS is a total water injection amount required during one combustion cycle of the engine <NUM>.

Subsequently, in step S110, the ECM <NUM> calculates the value of a maximum synchronous injection amount QDL based on the engine rotation speed. The maximum synchronous injection amount QDL represents the maximum value of the amount of water that can be injected during the valve opening period of the intake valves <NUM> in each cylinder <NUM>. Each cylinder <NUM> is provided with two water injection valves: the first water injection valve <NUM> and the second water injection valve <NUM>. Therefore, the maximum synchronous injection amount QDL is a value obtained by adding the maximum value of the amount of water that can be injected by the first water injection valve <NUM> during the valve opening period of the intake valves <NUM> and the maximum value of the amount of water that can be injected by the second water injection valve <NUM> during the valve opening period of the intake valves <NUM>. The valve opening period of the intake valves <NUM> is shortened as the engine rotation speed increases. Therefore, the ECM <NUM> calculates a smaller amount as the value of the maximum synchronous injection amount QDL as the engine rotation speed increases. The maximum synchronous injection amount QDL thus calculated represents the maximum value of the total water injection amount obtained when the synchronous injection is executed in both the first intake port <NUM> and the second intake port <NUM> during one combustion cycle of the engine <NUM>. The synchronous injection is water injection executed only during the valve opening period of the intake valves <NUM>. More strictly, the synchronous injection is water injection that is started end ended within the valve opening period of the intake valves <NUM>.

Next, in step S120, the ECM <NUM> determines whether the requested water injection amount QS exceeds the maximum synchronous injection amount QDL. When the requested water injection amount QS is less than or equal to the maximum synchronous injection amount QDL (S120: NO), the ECM <NUM> advances the process to step S130. In step S130, the ECM <NUM> calculates one half of the requested water injection amount QS as a synchronous injection amount command value QD. Subsequently, in step S140, the ECM <NUM> commands the first and second water injection valves <NUM> and <NUM> to execute synchronous injection with an amount equal to the synchronous injection amount command value QD. After the process of step S140, the ECM <NUM> ends the current process of this routine.

When the requested water injection amount QS exceeds the maximum synchronous injection amount QDL (S120: YES), the ECM <NUM> advances the process to step S150. In step S150, the ECM <NUM> calculates one half of the maximum synchronous injection amount QDL as the synchronous injection amount command value QD. The synchronous injection amount command value QD at this time is set to the maximum value of the amount of water that can be injected to a single intake port by the synchronous injection. That is, the synchronous injection amount command value QD at this time is calculated as the maximum value of the amount of water that can be injected by each of the first water injection valve <NUM> and the second water injection valve <NUM> alone within the valve opening period of the intake valves <NUM>. In step S150, the ECM <NUM> calculates a value obtained by subtracting the synchronous injection amount command value QD from the requested water injection amount QS as an asynchronous injection amount command value QH. In the subsequent step S160, the ECM <NUM> commands a water injection valve that executed the asynchronous injection as the latest injection to execute the synchronous injection with an amount equal to the synchronous injection amount command value QD. Further, in step S170, the ECM <NUM> commands a water injection valve that executed synchronous injection as the latest injection to execute the asynchronous injection with an amount equal to the asynchronous injection amount command value QH. The asynchronous injection is water injection executed during the valve closing period of the intake valves <NUM>. In the present embodiment, water injection by the asynchronous injection is executed during the exhaust stroke, which is before the intake valves <NUM> are opened.

In the processes of steps S160 and S170, both the first and second water injection valves <NUM> and <NUM> may have executed the synchronous injection as the latest injection. In such a case, in step S160, the ECM <NUM> commands a predetermined one of the first and second water injection valves <NUM> and <NUM> to execute the synchronous injection with an amount equal to the synchronous injection amount command value QD. Then, in step S170, the ECM <NUM> commands the other water injection valve to execute the asynchronous injection with an amount equal to the asynchronous injection amount command value QH.

In the present embodiment, the processes of steps S160 and S170 correspond to a switching process. Further, the process of step S100 corresponds to a first calculation process, and the process of step S110 corresponds to a second calculation process.

Operation and advantages of the present embodiment will now be described.

The ECM <NUM> performs the water injection control such that the first water injection valve <NUM> and the second water injection valve <NUM> inject an amount of water equal to the requested water injection amount QS, which is calculated based on the operating state of the engine <NUM>. At this time, if the requested water injection amount QS is less than or equal to the maximum synchronous injection amount QDL, an amount of equal to the requested water injection amount QS can be injected by the synchronous injection alone, in which water is injected during the valve opening period of the intake valves <NUM>. If the requested water injection amount QS exceeds the maximum synchronous injection amount QDL, an amount of water equal to the requested water injection amount QS cannot be injected by the synchronous injection alone. In this case, it is necessary to execute the asynchronous injection, in which water is injected while the intake valves <NUM> are closed.

In the synchronous injection, water injection is executed in a state in which the intake ports are open to the cylinder <NUM>. In this case, some of the injected water directly flows into the cylinder <NUM>. In addition, water is injected into the flow of intake air from the intake ports toward the cylinder <NUM>. Therefore, the synchronous injection restricts water from collecting on the wall surfaces of the intake ports. In the asynchronous injection, the water injection is executed in a state in which the intake ports are disconnected from the cylinder <NUM>. Therefore, by the asynchronous injection, water is more likely to collect on the wall surfaces of the intake ports than by the synchronous injection. If the asynchronous injection is continued in the same intake port, the amount of water collecting on the wall surface of that intake port gradually increases. As the amount of collected water increases, the water droplets collecting on the wall surface grow. If such grown and large water droplets flow into the cylinder, the water droplets may be mixed with the engine oil to cause clouding of the engine oil or an increase in the internal pressure of the crankcase due to the vapor pressure.

However, when the requested water injection amount QS is less than or equal to the maximum synchronous injection amount QDL, the ECM <NUM> commands both the first water injection valve <NUM> and the second water injection valve <NUM> to execute synchronous injection with half of the requested water injection amount QS. That is, when the requested water injection amount QS can be injected by the synchronous injection, the ECM <NUM> executes the water injection by the synchronous injection alone.

When the requested water injection amount QS exceeds the maximum synchronous injection amount QDL, the ECM <NUM> commands one of the first water injection valve <NUM> and the second water injection valve <NUM> to execute the synchronous injection with an amount equal to one half of the maximum synchronous injection amount QDL. The ECM <NUM> commands the other water injection valve to execute the asynchronous injection with the remaining amount. In the following description, a mode of water injection in a manner in which one of the first water injection valve <NUM> and the second water injection valve <NUM> executes the synchronous injection and the other executes the asynchronous injection in each cylinder <NUM> during one combustion cycle of the engine <NUM> will be referred to as a synchronous/asynchronous concurrent injection. In the synchronous/asynchronous concurrent injection, the intake ports corresponding to each cylinder <NUM> include, during one combustion cycle of the engine <NUM>, at least one intake port in which the synchronous injection is executed and at least one intake port in which the asynchronous injection is executed.

In the synchronous/asynchronous concurrent injection, the ECM <NUM> commands the water injection valve that executed the asynchronous injection as the latest injection to execute the synchronous injection, and commands the water injection valve that executed the synchronous injection as the latest injection to execute the asynchronous injection. That is, when executing the synchronous/asynchronous concurrent injection, the ECM <NUM> alternately switches between the water injection valve that executes the asynchronous injection between the first water injection valve <NUM> and the second water injection valve <NUM> for each injection. For example, a water injection valve that executed the asynchronous injection in the previous combustion cycle executes the synchronous injection in the current combustion cycle, and a water injection valve that executed the synchronous injection in the previous combustion cycle executes the asynchronous injection in the current combustion cycle. As a result, the asynchronous injection, with which the amount of water collecting on the wall surfaces of the intake ports is more likely to increase than with the synchronous injection, is not continued in the same intake port.

The engine controller of the present embodiment has the following advantages.

A second embodiment of the present disclosure will now be described with reference to <FIG>. Like or the same reference numerals are given to those components that are like or the same as the corresponding components of the first embodiment, and the detailed description will be omitted. The controller according to the present embodiment has the same configuration as the controller according to the first embodiment except that a part of the process of the water injection control routine is different.

<FIG> shows a flowchart of a water injection control routine executed by the controller of the present embodiment instead of the control routine of <FIG> in the first embodiment. The processes of steps S100 to S150 in the flowchart of <FIG> are common to the those in <FIG>. That is, in the present embodiment, when the requested water injection amount QS is less than or equal to the maximum synchronous injection amount QDL (S120: NO), the ECM <NUM> calculates one half of the requested water injection amount QS as the synchronous injection amount command value QD in step S130. Subsequently, in step S140, the ECM <NUM> commands the first and second water injection valves <NUM> and <NUM> to execute synchronous injection with an amount equal to the synchronous injection amount command value QD. In the present embodiment, the ECM <NUM> further resets the value of an asynchronous injection count C to <NUM> in step S200, and then ends the current processing of this routine. The asynchronous injection count C indicates the number of times of consecutive times the asynchronous injections has been executed in the same intake port.

Also, in the present embodiment, if the requested water injection amount QS exceeds the maximum synchronous injection amount QDL (S120: YES), the ECM <NUM> calculates one half of the maximum synchronous injection amount QDL as the synchronous injection amount command value QD in step S150. In step S150, the ECM <NUM> calculates a value obtained by subtracting the synchronous injection amount command value QD from the requested water injection amount QS as an asynchronous injection amount command value QH. In the present embodiment, the ECM <NUM> determines, in the subsequent step S210, whether the value of the asynchronous injection count C is greater than or equal to a specified threshold CMAX. The threshold CMAX is set to an integer greater than <NUM> in advance.

When the value of the asynchronous injection count C is less than the threshold CMAX (S210: NO), the ECM <NUM> commands, in step S220, the water injection valve that executed the synchronous injection as the latest injection to execute the synchronous injection with an amount equal to the synchronous injection amount command value QD. Further, in step S230, the ECM <NUM> commands the water injection valve that executed the asynchronous injection as the latest injection to execute asynchronous injection with an amount equal to the asynchronous injection amount command value QH. That is, the ECM <NUM> continuously executes the synchronous injection to the intake port in which the synchronous injection was executed as the latest injection. Also, the ECM <NUM> continuously executes the asynchronous injection to the intake port in which the asynchronous injection was executed as the latest injection. The ECM <NUM> increments the value of the asynchronous injection count C in step S240, and then ends the current processing of this routine.

When the value of the asynchronous injection count C is greater than or equal to the threshold CMAX (S210: YES), the ECM <NUM>, in step S250, commands the water injection valve that executed the asynchronous injection as the latest injection to execute the synchronous injection with an amount equal to the synchronous injection amount command value QD. Further, in step S260, the ECM <NUM> commands a water injection valve that executed synchronous injection as the latest injection to execute the asynchronous injection with an amount equal to the asynchronous injection amount command value QH. That is, the ECM <NUM> switches between the intake port in which the synchronous injection is executed and the intake port in which the asynchronous injection is executed. The ECM <NUM> then resets the value of an asynchronous injection count C to <NUM> in step S200, and then ends the current processing of this routine. In the present embodiment, the processes of steps S200 to S260 in the water injection control routine in <FIG> correspond to the switching process.

The controller of the present embodiment switches the intake port in which the asynchronous injection is executed each time the number of times of consecutive executions of the asynchronous injection in the same intake port reaches the threshold value CMAX, that is, each time the number of times of consecutive executions reaches a specified number of times. This configuration prevents the asynchronous injection from being continued in the same intake port. The present embodiment thus achieves the same advantages as the first embodiment.

A third embodiment of the present disclosure will now be described with reference to <FIG>. Like or the same reference numerals are given to those components that are like or the same as the corresponding components of the first embodiment, and the detailed description will be omitted. The controller according to the present embodiment has the same configuration as the controller according to the first embodiment except that a part of the process of the water injection control routine is different.

<FIG> shows a part of the water injection control routine according to the present embodiment that is different from the first embodiment. In the water injection control routine of the present embodiment, the processes after step S150 in <FIG> are replaced. The series of processes shown in <FIG> is executed subsequently to the process of step S150 in <FIG>. When the requested water injection amount QS exceeds the maximum synchronous injection amount QDL (S120: YES), the ECM <NUM> of the present embodiment calculates the synchronous injection amount command value QD and the asynchronous injection amount command value QH in step S150, and then proceeds to the process of <FIG>.

First, in step S300 of <FIG>, the ECM <NUM> reads a value of an estimated wet amount W1 of the first intake port <NUM> and a value of an estimated wet amount W2 of the second intake port <NUM> recorded in the memory device <NUM>. The estimated wet amounts W1, W2 are estimated values of water collected on the wall surfaces of the intake ports. The values of the estimated wet amounts W1, W2 are calculated in step S360, which will be discussed below. In step S310, the ECM <NUM> determines whether an estimated wet amount WH of the intake port in which the asynchronous injection was executed as the latest injection is greater than or equal to a specified threshold WMAX.

When the estimated wet amount WH is less than the threshold WMAX (S310: NO), the ECM <NUM> commands, in step S320, the water injection valve that executed the synchronous injection as the latest injection to execute the synchronous injection with an amount equal to the synchronous injection amount command value QD. In the following step S330, the ECM <NUM> commands the water injection valve that executed the asynchronous injection as the latest injection to execute the asynchronous injection with an amount equal to the asynchronous injection amount command value QH. That is, the ECM <NUM> commands each of the water injection valves to execute the same one of the synchronous injection or the asynchronous injection that that water injection valve executed as the latest injection. Thereafter, the ECM <NUM> advances the process to step S360.

When the estimated wet amount WH is greater than or equal to the threshold WMAX (S310: YES), the ECM <NUM> commands, in step S340, the water injection valve that executed the asynchronous injection as the latest injection to execute the synchronous injection with an amount equal to the synchronous injection amount command value QD. In the following step S350, the ECM <NUM> commands the water injection valve that executed the synchronous injection as the latest injection to execute the asynchronous injection with an amount equal to the asynchronous injection amount command value QH. That is, the ECM <NUM> switches between the water-injection valve that executes the synchronous injection and the water-injection valve that execute asynchronous injection. Thereafter, the ECM <NUM> advances the process to step S360.

When advancing the process to step S360, ECM <NUM> updates the values of the estimated wet amounts W1, W2. After the process of step S360, the ECM <NUM> ends the process of the water injection control routine in the current control cycle. In the present embodiment, the processes of steps S310 to S350 in the water injection control routine in <FIG> correspond to the switching process, and the process of step S360 correspond to an estimation process.

In the present embodiment, the amount of water collecting on the wall surface of each of the first intake port <NUM> and the second intake port <NUM> is estimated by updating the values of the estimated wet amounts W1, W2 in step S360 of <FIG>. Next, such estimation of the collected water amount will be described.

When updating the values of the estimated wet amounts W1, W2, the ECM <NUM> calculates a newly collected amount A1 at the first intake port <NUM> and a newly collected amount A2 at the second intake port <NUM>. The newly collected amounts A1, A2 represent the amount of water newly collected on the wall surfaces of the intake ports during the period from the current control cycle to the next control cycle. The newly collected amounts A1, A2 increase as the amount of water injected into the corresponding intake port increases. In addition, the newly collected amounts A1, A2 are larger in the case of the asynchronous injection than in the case of the synchronous injection even if the water injection amount is the same. On the other hand, when the intake air flow rate is relatively high, the air flow promotes atomization of injected water. Therefore, the newly collected amounts A1, A2 are smaller when the intake air flow rate is relatively high than when the intake air flow rate is relatively low. Further, the newly collected amounts A1, A2 are larger when the temperature of the wall surfaces of the intake ports and/or the temperature of the intake air is relatively low than when the temperature is relatively high. Taking these factors into consideration, a physical model of water collected on the wall surfaces of the intake ports is created, and the ECM <NUM> calculates the newly collected amounts A1, A2 based on the water injection amount, the water injection timing, the intake air flow rate, the coolant temperature, the intake air temperature, and the like in accordance with the created physical model. The timing of water injection indicates whether the water injection is the synchronous injection or the asynchronous injection.

When updating the values of the estimated wet amounts W1, W2, the ECM <NUM> calculates an evaporation amount B1 at the first intake port <NUM> and an evaporation amount B2 at the second intake port <NUM>. The evaporation amounts B1, B2 represent the amount of water evaporating from the wall surfaces of the intake ports during the period from the current control cycle to the next control cycle. The evaporation amounts B1, B2 increase as the amount of water collected on the wall surface increases. When the intake air flow rate is relatively high, the air flow in the intake ports becomes strong. Therefore, the evaporation amounts B1, B2 are larger when the intake air flow rate is relatively high than when the intake air flow rate is relatively low. The evaporation amounts B1, B2 are larger when the temperature of the wall surfaces of the intake ports and/or the temperature of intake air is relatively high than when the temperature is relatively low. Further, the period from the current control cycle to the next control cycle is shorter when the engine rotation speed is relatively high than when the engine rotation speed is relatively low. Accordingly, the evaporation amounts B1, B2 during the same period decrease when the engine rotation speed is relatively high. Taking these factors into consideration, a physical model of the evaporation of water from the wall surfaces of the intake ports is created, and the ECM <NUM> calculates the evaporation amounts B1, B2 based on the estimated wet amounts W1, W2, the intake air flow rate, the coolant temperature, the intake air temperature, the engine rotation speed, and the like in accordance with the created physical model.

The ECM <NUM> obtains an updated value of the estimated wet amount W1 by adding the newly collected amount A1 to the pre-update value of the estimated wet amount A1 and subtracting the evaporation amount B1 from the resultant (W1 [updated] ← W1 [pre-update] + A1 - B1). Also, the ECM <NUM> obtains an updated value of the estimated wet amount W2 by adding the newly collected amount A2 to the pre-update value of the estimated wet amount W2 and subtracting the evaporation amount B2 from the resultant (W2 [updated] ← W2 [pre-update] + A2 - B2).

The controller of the present embodiment switches the intake port in which the asynchronous injection is executed when the estimated wet amounts W1, W2 at the intake ports in which the asynchronous injection is executed exceed the threshold WMAX. This configuration prevents the asynchronous injection from being continued in the same intake port. The present embodiment thus achieves the same advantages as the first embodiment.

Depending on the operating state of the engine <NUM>, both the estimated wet amount W1 of the first intake port <NUM> and the estimated wet amount W2 of the second intake port <NUM> may exceed the threshold WMAX. In such a case, the intake port in which the synchronous injection is executed and the intake port in which the asynchronous injection is executed are alternately switched for each injection.

The above-described embodiments may be modified as follows. The above-described embodiments and the following modifications can be combined if the combined modifications remain technically consistent with each other.

In the above-described embodiments, the asynchronous injection is executed by executing water injection during the exhaust stroke before the intake valves <NUM> are opened. However, the asynchronous injection may be executed after the intake valves <NUM> are closed, for example, during the compression stroke or the combustion stroke.

In the above-described embodiments, when the requested water injection amount QS exceeds the maximum synchronous injection amount QDL, the synchronous/asynchronous concurrent injection is executed. However, the synchronous/asynchronous concurrent injection may be executed under a condition different from this. Whether to execute the synchronous/asynchronous concurrent injection may be determined based on the engine rotation speed, the engine load, the intake air temperature, and/or the coolant temperature.

In the above-described embodiments, the intake port in which the asynchronous injection is executed is switched based on the number of times of executions of the asynchronous injection in the same intake port or the estimated wet amounts W1, W2. The intake port in which the asynchronous injection is executed may be switched based on a parameter other than the above, such as the injection amount of water by the asynchronous injection.

The water injection control of the above-described embodiments can be similarly employed in an engine in which three intake ports are connected to each cylinder <NUM>. In this case, during the execution of the synchronous/asynchronous concurrent injection, the intake port in which the asynchronous injection is executed is sequentially switched among the three intake ports.

The controller is not limited to one including the ECM <NUM>, which includes the processor <NUM> and the memory device <NUM>. That is, the controller may be processing circuitry that has any one of the following configurations (a) to (c).

Claim 1:
A controller (<NUM>) for an engine (<NUM>), wherein
the engine (<NUM>) includes:
a cylinder (<NUM>);
intake ports (<NUM>, <NUM>) connected to the cylinder (<NUM>);
intake valves (<NUM>) that respectively correspond to the intake ports (<NUM>, <NUM>), each of the intake valves (<NUM>) being configured to selectively allow for and block connection between the corresponding one of the intake ports (<NUM>, <NUM>) and the cylinder (<NUM>); and
water injection valves (<NUM>, <NUM>) installed in the respective intake ports (<NUM>, <NUM>), each of the water injection valves (<NUM>, <NUM>) being configured to inject water to the corresponding one of the intake ports (<NUM>, <NUM>),
the controller (<NUM>) is configured to selectively execute, for each of the intake ports (<NUM>, <NUM>), a synchronous injection that causes the corresponding one of the water injection valves (<NUM>, <NUM>) to inject water only during a valve opening period of the corresponding one of the intake valves (<NUM>)or an asynchronous injection that causes the corresponding one of the water injection valves (<NUM>, <NUM>) to inject water during a valve closing period of the corresponding one of the intake valves (<NUM>), characterised in that
the controller (<NUM>) is configured to perform, when executing a synchronous and asynchronous concurrent injection in which the intake ports (<NUM>, <NUM>) include a first intake port (<NUM>) in which the synchronous injection is executed and a second intake port (<NUM>) in which the asynchronous injection is executed in a first period of time, a switching process of switching the intake port (<NUM>, <NUM>) in which the asynchronous injection is executed in a second period of time.