Patent Publication Number: US-10774803-B2

Title: Control device for internal combustion engine

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority based on Japanese Patent Application No. 2018-44668 filed with the Japan Patent Office on Mar. 12, 2018, the entire contents of which are incorporated into the present specification by reference. 
     FIELD 
     The present disclosure relates to a control device for an internal combustion engine. 
     BACKGROUND 
     Japanese Unexamined Patent Publication No. 2017-089587 discloses to inject water into an intake passage of an internal combustion engine and use the latent heat of vaporization of the water to cool the air before flowing into a combustion chamber. Further, it discloses to keep the unevaporated water from ending up flowing into a combustion chamber together with the air by controlling the amount of water injected into the intake passage so that the amount of moisture in the air before flowing into the combustion chamber becomes the saturated steam amount or less. 
     SUMMARY 
     However, in the above-mentioned Japanese Unexamined Patent Publication No. 2017-089587, the amount of water vaporizing inside a combustion chamber was not considered at all, so the cooling effect on the air-fuel mixture due to the latent heat of vaporization of water is liable to be unable to be sufficiently obtained. 
     The present disclosure was made focusing on such a viewpoint and has as its object to improve the cooling effect on an air-fuel mixture due to the latent heat of vaporization of water. 
     To solve this problem, according to one aspect of the present disclosure, there is provided a control device for an internal combustion engine equipped with an engine body, a water injector for injecting water to the inside of an intake passage of the engine body, and a fuel injector for injecting fuel to be burned in a combustion chamber of the engine body, wherein the control device comprises a water injection control part configured to control the amount of injection of water from the water injector so that in a combustion cycle in which fuel is injected from the fuel injector, water vaporizing in the intake passage during an intake stroke and water vaporizing in a combustion chamber during a compression stroke are generated. 
     According to this aspect of the present disclosure, it is possible to make water vaporize not only inside an intake passage, but also inside a combustion chamber, so it is possible to improve the cooling effect on an air-fuel mixture due to the latent heat of vaporization of water. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a schematic view of the configuration of an internal combustion engine and an electronic control unit for controlling the internal combustion engine according to one embodiment of the present disclosure. 
         FIG. 2  is a flow chart explaining water injection control and ignition timing control according to one embodiment of the present disclosure. 
         FIG. 3  is a flow chart explaining processing for calculation of a maximum vaporization amount. 
         FIG. 4  is a flow chart explaining processing for calculation of a maximum intake passage vaporization amount. 
         FIG. 5  is a table for calculating a first ignition timing correction amount based on a combustion chamber vaporization amount. 
         FIG. 6  is a table for calculation of a second ignition timing correction amount based on an intake passage vaporization amount. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Below, referring to the drawings, an embodiment of the present disclosure will be explained in detail. Note that in the following explanation, similar component elements are assigned the same reference signs. 
       FIG. 1  is a schematic view of the configuration of an internal combustion engine  100  and an electronic control unit  200  controlling the internal combustion engine  100  according to one embodiment of the present disclosure. 
     As shown in  FIG. 1 , the internal combustion engine  100  comprises an engine body  1 , an intake system  20 , an exhaust system  30 , fuel injectors  41 , spark plugs  51 , and a water injector  61 . 
     The engine body  1  comprises a cylinder block  2 , a cylinder head  3  attached to a top part of the cylinder block  2 , a crankcase  4  attached to a bottom part of the cylinder block  2 , and an oil pan  5  attached to a bottom part of the crankcase  4 . 
     The cylinder block  2  is formed with a plurality of cylinders  6 . Inside of the cylinders  6 , pistons  7  receiving combustion pressure and reciprocating inside the cylinders  6  are held. The pistons  7  are connected through connecting rods  8  to a crankshaft  9  supported rotatably inside the crankcase  4 . Due to the crankshaft  9 , the reciprocating motions of the pistons  7  are converted to rotary motion. The spaces defined by the inside wall surface of the cylinder head  3 , the inside walls surfaces of the cylinders  6 , and the piston crown surfaces form combustion chambers  10 . 
     The cylinder head  3  is formed with intake ports  11  opening at one side surface of the cylinder head  3  and opening into the combustion chambers  10  and exhaust ports  12  opening at the other side surface of the cylinder head  3  and opening into the combustion chambers  10 . 
     Further, at the cylinder head  3 , intake valves  13  for opening and closing openings between the combustion chambers  10  and intake ports  11 , exhaust valves  14  for opening and closing openings between the combustion chambers  10  and exhaust ports  12 , an intake camshaft  15  driving operation of the intake valves  13 , and an exhaust camshaft  16  driving operation of the exhaust valves  14  are attached. 
     The intake system  20  is a system for guiding air through the intake ports  11  to the insides of the individual combustion chambers  10  and comprises an air cleaner  21 , intake pipe  22 , compressor  23   a  of a turbocharger  23 , intercooler  24 , intake manifold  25 , electronic control type throttle valve  26 , air flow meter  211 , outside air temperature sensor  212 , outside air pressure sensor  213 , outside air humidity sensor  214 , surge tank temperature sensor  215 , and surge tank pressure sensor  216 . 
     The air cleaner  21  removes sand and other foreign matter contained in the air. 
     The intake pipe  22  is connected at one end to the air cleaner  21  and is connected at the other end to a surge tank  25   a  of the intake manifold  25 . 
     The turbocharger  23  is one type of supercharger. It utilizes the energy of the exhaust to forcibly compress air and send the compressed air to the individual combustion chambers  10 . Due to this, the charging efficiency is raised, so the engine output increases. The compressor  23   a  is a part forming a portion of the turbocharger  23  and is provided at the intake pipe  22 . The compressor  23   a  is turned by a turbine  23   b  of the turbocharger  23  explained later provided coaxially and forcibly compresses the air. Note that instead of the turbocharger  23 , it is also possible to use a supercharger which is mechanically driven utilizing the rotational force of the crankshaft  9 . 
     The intercooler  24  is provided at the intake pipe  22  downstream from the compressor  23   a  and cools the air which was compressed by the compressor  23   a  and became high in temperature. Due to this, it is possible to keep down the drop in volume density and further raise the charging efficiency and to keep down the rise in temperature of the air-fuel mixture due to high temperature air being sucked into the individual combustion chambers  10  so as to keep knocking etc. from occurring. 
     The intake manifold  25  is provided with the surge tank  25   a  and a plurality of intake runners  25   b  branched from the surge tank  25   a  and connected to openings of individual intake ports  11  formed at the side surface of the cylinder head. The air guided into the surge tank  25   a  is evenly distributed through the intake runners  25   b  to the insides of the individual combustion chambers  10 . In this way, the intake pipe  22 , intake manifold  25 , and intake ports  11  form the intake passage for guiding air to the insides of the individual combustion chambers  10 . 
     The throttle valve  26  is provided at the inside of the intake pipe  22  between the intercooler  24  and the surge tank  25   a . The throttle valve  26  is driven by a throttle actuator (not shown) and changes the passage cross-sectional area of the intake pipe  22  continuously or in stages. By using the throttle actuator to adjust the opening degree of the throttle valve  26 , it is possible to adjust the flow rate of air sucked into the individual combustion chambers  10 . 
     The air flow meter  211  is provided inside the intake pipe  22  at the upstream side from the compressor  23   a . The air flow meter  211  detects the flow rate of air flowing through the inside of the intake passage and finally sucked into the individual combustion chambers  10 . 
     The outside air temperature sensor  212  is provided inside the intake pipe  22  at the upstream side from the compressor  23   a . The outside air temperature sensor  212  detects the temperature of the air sucked into the intake pipe  22  at the upstream side from the compressor  23   a  through the air cleaner  23   a , that is, the outside air temperature. 
     The outside air pressure sensor  213  is provided inside the intake pipe  22  at the upstream side from the compressor  23   a . The outside air pressure sensor  213  detects the pressure of the air sucked into the intake pipe  22  at the upstream side from the compressor  23   a  through the air cleaner  23   a , that is, the outside air pressure (atmospheric pressure). 
     The outside air humidity sensor  214  is provided inside the intake pipe  22  at the upstream side from the compressor  23   a . The outside air humidity sensor  214  detects the humidity of the air sucked into the intake pipe  22  at the upstream side from the compressor  23   a  through the air cleaner  21 , that is, the outside air humidity. 
     The surge tank temperature sensor  215  is provided inside the surge tank  25   a . The surge tank temperature sensor  215  detects the temperature of the air inside the surge tank (below, referred to as the “surge tank temperature”). The surge tank temperature corresponds to the temperature of the air finally sucked into the combustion chambers. 
     The surge tank pressure sensor  216  is provided inside the surge tank  25   a . The surge tank pressure sensor  216  detects the pressure of the air inside the surge tank (below, referred to as the “surge tank pressure”). The surge tank pressure corresponds to the pressure of the air finally sucked into the combustion chambers. 
     The exhaust system  30  is a system for purifying combustion gas (exhaust) generated inside the combustion chambers  10  and discharging it into the outside air and is provided with an exhaust manifold  31 , exhaust pipe  32 , turbine  23   b  of a turbocharger  23 , exhaust bypass passage  33 , and exhaust post-treatment device  34 . 
     The exhaust manifold  31  is provided with a plurality of exhaust runners connected to openings of individual exhaust ports  12  formed at a side surface of the cylinder head and a header bundling the exhaust runners into one. 
     The exhaust pipe  32  is connected at one end to a header of the exhaust manifold  31  and is open at the other end. Exhaust discharged from the individual cylinders  6  through the exhaust ports  12  to the exhaust manifold  31  flows through the exhaust pipe  32  and is discharged to the outside air. 
     The turbine  23   b  is a part forming a portion of the turbocharger  23  and is provided at the exhaust pipe  32 . The turbine  23   b  is turned by the energy of the exhaust and drives a compressor  23   a  provided coaxially. 
     The exhaust bypass passage  33  is a passage connected to the exhaust pipe  32  at the upstream side of the turbine  23   b  and the exhaust pipe  32  at the downstream side so as to bypass the turbine  23   b.    
     The exhaust bypass passage  33  is provided with a wastegate valve  36  driven by a wastegate actuator  35  and is able to adjust the passage cross-sectional area of the exhaust bypass passage  33  continuously or in stages. If the wastegate valve  36  is opened, part or all of the exhaust flowing through the exhaust pipe  32  flows into the exhaust bypass passage  33 , bypasses the turbine  23   b , and is discharged to the outside air. For this reason, by adjusting the opening degree of the wastegate valve  36 , it is possible to adjust the flow rate of the exhaust flowing into the turbine  23   b  and control the rotational speed of the turbine  23   b . That is, by adjusting the opening degree of the wastegate valve  36 , it is possible to control the pressure of the air compressed by the compressor  23   a.    
     The exhaust post-treatment device  34  is provided in the exhaust pipe  32  at the downstream side from the turbine  23   b . The exhaust post-treatment device  34  is a device for purifying exhaust, then discharging it to the outside air and comprises various catalysts for removing harmful substances (for example, three-way catalysts) supported on a support. 
     The fuel injectors  41  inject fuel for being burned inside the individual combustion chambers  10 . In the present embodiment, the fuel injectors  41  are attached to the individual intake runners  25   b  of the intake manifold  25  so as to enable fuel to be injected into the intake ports  11 . The opening times (amounts of injection) and opening timings (timings of injection) of the fuel injectors  41  are changed by control signals from the electronic control unit  200 . If the fuel injectors  41  open, fuel is injected from the fuel injectors  41  to the insides of the intake ports  11  and fuel is supplied to the combustion chambers  10 . Note that the fuel injectors  4  may also be attached to the cylinder head  3  so as to enable fuel to be directly injected to the insides of the combustion chambers  10 . 
     The spark plugs  51  are attached to the cylinder head  3  so as to face the combustion chambers  10 . The spark plugs  51  generate sparks inside the combustion chambers  10  to ignite the air-fuel mixture of the fuel injected from the fuel injectors  41  and the air. The ignition timings of the spark plugs  51  are controlled to any timings by control signals from the electronic control unit  200 . 
     The water injector  61  injects water for vaporization inside the intake passage and inside the combustion chambers  10  into the intake passage. In the present embodiment, the water injector  61  is attached to the surge tank  25   a  and injects water inside the surge tank  25   a . The opening time (amount of injection) and opening timing (timing of injection) of the water injector  61  are changed by control signals from the electronic control unit  200 . If the water injector  61  is opened, water is injected from the water injector  61  to the inside of the surge tank  25   a . The water injected to the inside of the surge tank  25   a  is vaporized in the process of flowing through the intake passage while being supplied to the insides of the individual combustion chambers  10  and is vaporized inside the individual combustion chambers  10  during the compression stroke. 
     The electronic control unit  200  is comprised of a digital computer provided with components connected with each other by a bidirectional bus  201  such as a ROM (read only memory)  202 , RAM (random access memory)  203 , CPU (microprocessor)  204 , input port  205 , and output port  206 . 
     The input port  205  receives as input the output signals of various sensors such as the above-mentioned air flow meter  211  through corresponding AD converters  207 . Further, the input port  205  receives as input the output voltage of a load sensor  221  generating an output voltage proportional to the amount of depression of the accelerator pedal  220  corresponding to the engine load through a corresponding AD converter  207 . Further, the input port  205  receives as input an output signal of a crank angle sensor  222  generating an output pulse every time the crankshaft  9  of the engine body  1  rotates by for example 15° as a signal for calculating the engine rotational speed etc. In this way, the input port  205  receives as input output signals of various sensors required for control of the internal combustion engine  100 . 
     The output port  206  is electrically connected to the fuel injectors  41  and other various control parts through corresponding drive circuits  208 . 
     The electronic control unit  200  outputs control signals for controlling the different control parts from the output port  206  based on the output signals of the various sensors input to the input port  205  to control the internal combustion engine  100 . Below, the control of the internal combustion engine  100  according to the present embodiment which the electronic control unit  200  performs will be explained. 
     The electronic control unit  200  controls the ignition timings of the spark plugs  51  to the optimum ignition timing (MBT; Minimum advance for the Best Torque) or the knock limit ignition timing based on the engine operating state (engine rotational speed and engine load). Specifically, the electronic control unit  200  controls the ignition timings to the optimum ignition timing if there is an engine operating point determined by the engine rotational speed and the engine load inside the operating region where the optimum ignition timing becomes the retarded side from the knock limit ignition timing. On the other hand, the electronic control unit  200  controls the ignition timings to the knock limit ignition timing if there is an engine operating point inside the operating region where the optimum ignition timing becomes the advanced side from the knock limit ignition timing. This is because if making the ignition timings advance from the knock limit ignition timing, over the allowable range of knocking will occur and the engine output and engine durability are liable to fall. 
     Here, if, in the operating region where the optimum ignition timing becomes the advanced side from the knock limit ignition timing, the ignition timings can be made to approach the optimum ignition timing, the engine output and fuel efficiency can be improved. 
     Therefore, in the present embodiment, in an operating region where the optimum ignition timing becomes the advanced side from the knock limit ignition timing, water is injected from the water injector  61  and the temperature of the air-fuel mixture finally ignited in the combustion chambers  10  is lowered by the latent heat of vaporization of water. By doing this, knocking can be kept from occurring, so it is possible to make the ignition timings advance from the knock limit ignition timings more than when not injecting water and the ignition timings can be made to approach the optimum ignition timing. 
     At this time, the cooling effect of the air-fuel mixture due to the latent heat of vaporization of water (temperature lowering effect) differs between the case when making water vaporize inside the intake passage and the case when making water vaporize inside the combustion chambers  10 . The cooling effect of the air-fuel mixture becomes larger in the case when making water vaporize inside the combustion chambers  10 . 
     This is because the air or the air-fuel mixture cooled by the latent heat of vaporization of water inside the intake passage ends up rising in temperature due to the heat received from the inside wall surface of the intake passage in the process of flowing through the inside of the intake passage and being sucked into the combustion chambers  10 . On the other hand, the time period during which the air-fuel mixture cooled by the latent heat of vaporization of water inside the combustion chambers  10  receives heat from the inside wall surfaces of the combustion chambers  10  is shorter than the time period during which it receives heat from the inside wall surface of the intake passage. Further, the surface areas inside of the combustion chambers  10  are also smaller than the surface area inside the intake passage. 
     For this reason, the air-fuel mixture cooled by the latent heat of vaporization of water inside the combustion chambers  10  is kept down in rise in temperature more than the air or the air-fuel mixture cooled by the latent heat of vaporization of water inside the intake passage. As a result, the cooling effect of the air-fuel mixture becomes greater when making water vaporize inside the combustion chambers  10 . 
     Therefore, if, like in the above-mentioned patent literature, ending up controlling the amount of water injected from the water injector  61  so that the amount of moisture in the air before flowing into the combustion chambers  10  becomes the saturated steam amount or less, water will not vaporize inside the combustion chambers  10 , so sometimes the cooling effect of the air-fuel mixture due to the latent heat of vaporization of water cannot be sufficiently obtained. 
     Therefore, in the present embodiment, in the combustion cycle where fuel is injected from the fuel injectors  41 , the amount of water injected from the water injector  61  is controlled so that water which vaporizes inside the intake passage during the suction stroke and water which vaporizes inside the combustion chambers  10  during the compression stroke are generated. Due to this, it is possible to make water vaporize not only inside the intake passage but also inside the combustion chambers  10 , so the cooling effect of the air-fuel mixture due to the latent heat of vaporization of water can be improved and in turn knocking can be kept from occurring. 
     Further, if in this way enabling the cooling effect of the air-fuel mixture due to the latent heat of vaporization of water to be enhanced and occurrence of knocking to be suppressed, the ignition timing can be made to advance by the amount of improvement of the cooling effect. Therefore, in the present embodiment, it was decided to correct the ignition timings to the advanced side corresponding to the amount of water injected from the water injector  61 . Due to this, the engine output and fuel efficiency can be improved. 
     Below, referring to  FIG. 2  to  FIG. 6 , water injection control and ignition timing control according to the present embodiment will be explained. 
       FIG. 2  is a flow chart explaining the water injection control and ignition timing control according to the present embodiment. The electronic control unit  200  repeatedly executes the present routine by a predetermined processing period during engine operation. 
     At step S 1 , the electronic control unit  200  reads in an engine rotational speed calculated by an output signal of the crank angle sensor  222  and an engine load detected by the load sensor  221  and detects the engine operating state (engine operating points). 
     At step S 2 , the electronic control unit  200  refers to a map prepared in advance by experiments etc. and calculates a basic ignition timing based on the engine operating state. The “basic ignition timing” is the target ignition timing in the case of not injecting water. Therefore, if not injecting water, when there is an engine operating point inside the operating region where the optimum ignition timing becomes the retarded side from the knock limit ignition timing, the basic ignition timing is set for the optimum ignition timing corresponding to the engine operating state. On the other hand, if not injecting water, when there is an engine operating point inside the operating region where the optimum ignition timing becomes the advanced side from the knock limit ignition timing, the basic ignition timing is set for the knock limit ignition timing corresponding to the engine operating state. 
     At step S 3 , the electronic control unit  200  refers to a map prepared in advance by experiments etc. and judges if an engine operating point is within the water injection region. In the present embodiment, if not injecting water, an operating region where the optimum ignition timing ends up becoming the advanced side from the knock limit ignition timing is set for the water injection region. The electronic control unit  200  proceeds to the processing of step S 5  if an engine operating point is within the water injection region. On the other hand, the electronic control unit  200  proceeds to the processing of step S 4  if an engine operating point is not within the water injection region. 
     At step S 4 , the electronic control unit  200  does not inject water and controls the ignition timings to the basic ignition timing, that is, the optimum ignition timing. 
     At step S 5 , the electronic control unit  200  judges if the engine temperature is less than a predetermined temperature. The electronic control unit  200  proceeds to the processing of step S 6  if the engine temperature is less than a predetermined temperature since water injected from the water injector  61  is liable to be unable to be sufficiently vaporized. On the other hand, the electronic control unit  200  proceeds to the processing of step S 7  if the engine temperature is a predetermined temperature or more. 
     At step S 6 , the electronic control unit  200  does not inject water, but controls the ignition timings to the basic ignition timing, that is, the knock limit ignition timing. 
     At step S 7 , the electronic control unit  200  performs processing for calculating the maximum amount of water WTm which can theoretically be made to vaporize inside the combustion chambers  10  during the compression stroke (below, referred to as the “maximum vaporization amount”). The maximum vaporization amount WTm is a value unambiguously determined by the temperature and pressure inside the combustion chambers  10  during the compression stroke. Below, details on the processing for calculation of the maximum vaporization amount WTm will be explained with reference to  FIG. 3 . 
       FIG. 3  is a flow chart explaining the content of processing for calculation of the maximum vaporization amount WTm. 
     At step S 71 , the electronic control unit  200  calculates the temperature TC 1  inside the combustion chambers  10  before compression (below, referred to as the “pre-compression combustion chamber temperature”) and the pressure PC 0  inside the combustion chambers  10  before compression (below, referred to as the “pre-compression combustion chamber pressure”). In the present embodiment, the electronic control unit  200  makes the surge tank temperature the pre-compression combustion chamber temperature TC 0  and makes the surge tank pressure the pre-compression combustion chamber pressure PC 0 . 
     At step S 72 , the electronic control unit  200  calculates the temperature TC 1  inside of the combustion chambers  10  after compression (below, referred to as the “post-compression combustion chamber temperature”) based on the pre-compression combustion chamber temperature TC 0  from a formula for estimation of the combustion chamber temperature TC in the case assuming the air-fuel mixture is adiabatically compressed inside the combustion chambers  10 , that is, the following formula (1):
 
 TC   1   =TC   0 ×( V   0   /V   1 ) k−1   (1)
 
     In formula (1), V 0  is the pre-compression combustion chamber volume, V 1  is the post-compression combustion chamber volume, and “k” is the specific heat ratio (polytrope indicator). In the present embodiment, the pre-compression combustion chamber volume V 0  is made the cylinder volume at the intake valve closing timing, but for simplicity, it may also be made the cylinder volume when the piston  7  is positioned at bottom dead center. Further, in the present embodiment, the post-compression combustion chamber volume V 1  is made the cylinder volume at the basic ignition timing, that is, the cylinder volume at the time of start of combustion, but for simplicity, the cylinder volume at any timing during the compression stroke (for example, cylinder volume when the piston  7  is positioned at top dead center) may also be made the post-compression combustion chamber volume V 1 . 
     Note that the cylinder volumes at the intake valve closing timing and basic ignition timing are values which are mechanically determined if the intake valve closing timing and basic ignition timing are determined. Therefore, in the present embodiment, a table linking the intake valve closing timing and the pre-compression combustion chamber volume V 0  and a table linking the basic ignition timing and the post-compression combustion chamber volume V 1  are respectively prepared in advance by experiments etc. and these tables are referred to so as to calculate the pre-compression combustion chamber volume V 0  and post-compression combustion chamber volume V 1 . 
     At step S 73 , the electronic control unit  200  calculates the pressure PC 1  inside the combustion chambers  10  after compression (below, referred to as the “post-compression combustion chamber pressure”) based on the pre-compression combustion chamber pressure PC 0  from a formula for estimation of the combustion chamber pressure PC in the case of assuming the air-fuel mixture is adiabatically compressed in the combustion chambers  10 , that is, the following formula (2):
 
 PC   1   =PC   0 ×( V   0   /V   1 ) k   (2)
 
     At step S 74 , the electronic control unit  200  refers to a map linking the pressure and temperature with the saturated steam amount and calculates the saturated steam amount MC [g/m 3 ] inside the combustion chambers  10  after compression, that is, inside the combustion chambers  10  at the basic ignition timing, based on the post-compression combustion chamber temperature TC 1  and post-compression combustion chamber pressure PC 1 . 
     At step S 75 , the electronic control unit  200  subtracts from the saturated steam amount MC inside the combustion chambers  10  at the basic ignition timing the amount of moisture per unit volume contained in the outside air calculated based on the outside air humidity and multiplies the result with the post-compression combustion chamber volume V 1  to calculate the maximum vaporization amount WTm. 
     Returning to  FIG. 2 , at step S 8 , the electronic control unit  200  corrects the maximum vaporization amount WTm while considering the time from the timing of closing of the intake valve to the basic ignition timing (below, “first vaporization time”) etc., makes it actually vaporize inside the combustion chambers  10  within the first vaporization time, and, further, calculates the estimated amount of water WT enabling the vaporized water (steam) to fully diffuse inside the combustion chambers  10  (below, referred to as the “vaporizable amount”). This vaporizable amount WT becomes the target injection amount of water injected from the water injector  61 . In the present embodiment, the electronic control unit  200  calculates the vaporizable amount WT based on the following formula (3). Note that the first vaporization time for simplicity sake may also be made the time from when a piston  7  moves from bottom dead center to top dead center.
 
 WT=WTm×c 1× c 2  (3)
 
     In formula (3), the first correction coefficient c1 is a coefficient considering the error in calculation of the maximum vaporization amount WTm and is a positive value of less than 1 (for example, 0.8). The second correction coefficient c2 is a coefficient considering the first vaporization time and is set to a positive value of less than 1 corresponding to the engine rotational speed. Specifically, the first vaporization time becomes shorter the higher the engine rotational speed, so the second correction coefficient c2 is basically set to a smaller value when the engine rotational speed is high compared to when it is low. 
     At step S 9 , the electronic control unit  200  performs processing for calculation of the maximum amount of water WSm theoretically able to be made to vaporize inside the intake passage (below, referred to as the “maximum intake passage vaporization amount”). The maximum intake passage vaporization amount WSm is a value unambiguously determined by the temperature and pressure of the air inside of the intake passage, but the temperature and pressure of the air inside the intake passage change in the process of the air flowing through the inside of the intake passage. 
     Therefore, the maximum intake passage vaporization amount WSm is preferably calculated based on the temperature and pressure inside the intake passage after the temperature and pressure inside of the intake passage finish fluctuating. In the present embodiment, the temperature and pressure of the air inside the intake passage fluctuate due to air being compressed by the compressor  23   a , fluctuate due to air being cooled by the intercooler  24 , and further fluctuate due to air being reduced in pressure corresponding to the opening degree of the throttle valve  26 . Therefore, in the present embodiment, the maximum intake passage vaporization amount WSm is calculated based on the temperature and pressure in the intake passage at the downstream side from the throttle valve  26  in the direction of flow of intake (in the present embodiment, the surge tank temperature and surge tank pressure). Below, details of the processing for calculation of the maximum intake passage vaporization amount WSm will be explained while referring to  FIG. 4 . 
       FIG. 4  is a flow chart explaining the content of the processing for calculation of the maximum intake passage vaporization amount WSm. 
     At step S 91 , the electronic control unit  200  calculates the temperature TI inside the intake passage at the downstream side from the throttle valve  26  in the direction of flow of intake (below, referred to as the “intake passage temperature”) and the pressure PI inside the intake passage at the downstream side from the throttle valve  26  in the direction of flow of intake (below, referred to as the “intake passage pressure”). In the present embodiment, the electronic control unit  200  makes the surge tank temperature the intake passage temperature TI and makes the surge tank pressure the intake passage pressure PI. 
     At step S 92 , the electronic control unit  200  refers to a map linking the pressure and temperature with the saturated steam amount and calculates the saturated steam amount MS [g/m 3 ] inside the intake passage at the downstream side from the throttle valve  26  in the direction of flow of intake based on the intake passage temperature TI and the intake passage pressure PI. 
     At step S 93 , the electronic control unit  200  multiplies the saturated steam amount MS inside the intake passage at the downstream side of the throttle valve  26  in the direction of flow of intake with the volume inside of the intake passage at the downstream side of the throttle valve  26  in the direction of flow of intake to calculate the maximum intake passage vaporization amount WSm. 
     Returning to  FIG. 2 , at step S 10 , the electronic control unit  200  corrects the maximum intake passage vaporization amount WSm while considering the time until the water injected from the water injector  61  flows inside of the combustion chambers  10  (below, referred to as the “second vaporization time”) and calculates the estimated amount of the water actually able to be made to vaporize inside the intake passage in a second vaporization time (below, referred to as the “intake passage vaporization amount”) WS. In the present embodiment, the electronic control unit  200  calculates the intake passage vaporization amount WS based on the following formula (4):
 
 WS=WSm×c 3  (4)
 
     In formula (4), the third correction coefficient c3 is a coefficient considering the second vaporization time and is set to a positive number of less than 1 corresponding to the engine rotational speed. Specifically, the second vaporization time becomes shorter the higher the engine rotational speed, so the third correction coefficient c3 is basically set to a small value when the engine rotational speed is high compared to when it is low. 
     At step S 11 , the electronic control unit  200  subtracts the intake passage vaporization amount WS from the vaporizable amount WT and calculates the estimated amount of water WC vaporizing after flowing into the combustion chamber  10  in the water injected from the water injector  61  (below, referred to as the “combustion chamber vaporization amount”). 
     At step S 12 , the electronic control unit  200  calculates the ignition timing correction amount dsa. In the present embodiment, the electronic control unit  200  refers to the table of  FIG. 5  prepared in advance by experiments etc. and calculates the first ignition timing correction amount gc based on the combustion chamber vaporization amount WC. Further, the electronic control unit  200  refers to the table of  FIG. 6  prepared in advance by experiments etc. and calculates the second ignition timing correction amount gs based on the intake passage vaporization amount WS. Further, the electronic control unit  200  calculates the sum of the first ignition timing correction amount gc and the second ignition timing correction amount gs as the ignition timing correction amount dsa. 
     As shown in  FIG. 5  and  FIG. 6 , if comparing the first ignition timing correction amount gc and the second ignition timing correction amount gs in the case where the combustion chamber vaporization amount WC and the intake passage vaporization amount WS are the same, the first ignition timing correction amount gc becomes larger than the second ignition timing correction amount gs. This is because, as explained above, the cooling effect of the air-fuel mixture due to the latent heat of vaporization of water becomes larger in the case of making water vaporize inside the combustion chambers  10  compared with the case of making water vaporize inside the intake passage. 
     At step S 13 , the electronic control unit  200  judges if the corrected ignition timing obtained by subtracting the ignition timing correction amount dsa from the basic ignition timing (knock limit ignition timing) becomes the advanced side from the optimum ignition timing. The electronic control unit  200  proceeds to the processing of step S 14  if the corrected ignition timing is at the advanced side from the optimum ignition timing. On the other hand, the electronic control unit  200  proceeds to the processing of step S 15  if the corrected ignition timing is at the retarded side from the optimum ignition timing. 
     At step S 14 , the electronic control unit  200  injects the vaporizable amount WT of water at any timing during the suction stroke from the water injector  61  and controls the ignition timing to the optimum ignition timing. 
     At step S 15 , the electronic control unit  200  injects the vaporizable amount WT of water from the water injector  61  at any timing during the suction stroke and controls the ignition timing to the corrected ignition timing. 
     According to the present embodiment explained above, there is provided an electronic control unit  200  (control device) of an internal combustion engine  100  which is provided with an engine body  1 , a water injector  61  for injecting water inside of an intake passage of the engine body  1 , and a fuel injector  41  for injecting fuel for burning in a combustion chamber  10  of the engine body  1 . The electronic control unit  200  is provided with a water injection control part controlling the amount of injection of water from the water injector  61  in the combustion cycle in which fuel is injected from the fuel injector  41  so that water which vaporizes inside the intake passage during the suction stroke and water which vaporizes inside the combustion chambers  10  during the compression stroke are generated. 
     Specifically, the water injection control part is configured so as to control the amount of injection of water from the water injector  61  so that the amount of injection of water from the water injector  61  becomes the total of the amount of water which vaporizes inside the intake passage, defined as the intake passage vaporization amount WS, and the amount of water which vaporizes inside the combustion chambers  10  in the compression stroke after flowing into the combustion chambers  10 , defined as the combustion chamber vaporization amount WC. 
     As explained above, the cooling effect of the air-fuel mixture due to the latent heat of vaporization of water (temperature lowering effect) differs between the case of making water vaporize inside the intake passage and the case of making water vaporize inside the combustion chambers  10 . The cooling effect of the air-fuel mixture becomes larger in the case of making the water vaporize in the combustion chambers  10 . For this reason, by controlling the amount of injection of water so that water which vaporizes not only inside the intake passage, but also inside the combustion chambers  10  is formed like in the present embodiment, it is possible to raise the cooling effect of the air-fuel mixture. 
     Further, by enhancing the cooling effect of the air-fuel mixture, it is possible to reduce the temperature of the exhaust. For this reason, if the electronic control unit  200  is configured to perform control for correcting the fuel injection amount to increase it when the catalyst temperature becomes a predetermined value or more so as to for example prevent overheating of the catalyst of the exhaust post-treatment device  34  (so-called OT increasing correction), it is possible to reduce the frequency of correcting the fuel injection amount to increase it. For this reason, it is possible to keep the fuel efficiency from deteriorating. 
     Further, the electronic control unit  200  according to the present embodiment is further comprised of an ignition timing control part controlling the ignition timing of the spark plugs  51  for igniting the air-fuel mixture inside the combustion chambers  10  based on the engine operating state and an ignition timing correction part correcting the ignition timings to the advanced side based on the amount of injection of water from the water injector  61 . Further, the ignition timing correction part is configured to calculate the first ignition timing correction amount gc based on the combustion chamber vaporization amount WC, calculate the second ignition timing correction amount gs based on the intake passage vaporization amount WS, and correct the ignition timings to the advanced side based on the total amount of the first ignition timing correction amount gc and the second ignition timing correction amount gs, defined as the “ignition timing correction amount dsa”. 
     In this way, if using spark plugs  51  to ignite the air-fuel mixture, by controlling the water injection amount so that water vaporizing not only inside the intake passage but also inside the combustion chambers  10  is formed and enhancing the cooling effect of the air-fuel mixture, it is possible to keep knocking from occurring. For that reason, it is possible to correct the ignition timing to the advanced side according to the water injection amount and possible to improve the engine output and fuel efficiency. 
     Further, as explained above, the cooling effect of the air-fuel mixture due to the latent heat of vaporization of water differs between the case of making water vaporize inside the intake passage and the case of making water vaporize inside the combustion chambers  10 . If correcting the ignition timings to the advanced side according to the water injection amount, the ignition timing amount able to be advanced based on the combustion chamber vaporization amount WC and the ignition timing amount able to be advanced based on the intake passage vaporization amount WS also differ. 
     Therefore, like in the present embodiment, by calculating the first ignition timing correction amount gc based on the combustion chamber vaporization amount WC and calculating the second ignition timing correction amount gs based on the intake passage vaporization amount WS, it is possible to respectively calculate suitable ignition timing correction amounts corresponding to the cooling effect of the air-fuel mixture in the case of making water vaporize inside the intake passage and the cooling effect of the air-fuel mixture in the case of making water vaporize inside the combustion chambers  10 . 
     Further, the water injection control part according to the present embodiment is configured to calculate the maximum amount of water which can be made to vaporize inside the combustion chambers  10  during the compression stroke, that is, the maximum vaporization amount WTm, based on the saturated steam amount MC inside the combustion chambers  10  as determined according to the state inside the combustion chambers  10  during the compression stroke, calculate the estimated amount of water which can actually be made to vaporize inside the combustion chambers  10  during the compression stroke, that is, the vaporizable amount WT, based on the maximum vaporization amount WTm and the first vaporization time of water inside the combustion chambers  10  as it changes according to the engine rotational speed, and control the amount of injection of water from the water injector  61  while deeming the vaporizable amount WT as the total amount of the intake passage vaporization amount WS and the combustion chamber vaporization amount WC. 
     Furthermore, the water injection control part is configured to calculate the maximum amount of water which can be made to vaporize inside the intake passage, that is, the maximum intake passage vaporization amount WSm, based on the saturated steam amount MS inside the intake passage determined according to the state inside the intake passage, calculate the intake passage vaporization amount WS based on the maximum intake passage vaporization amount WSm and the second vaporization time of water inside the intake passage as it changes according to the engine rotational speed, and calculate the combustion chamber vaporization amount WC based on the vaporizable amount WT and intake passage vaporization amount WS. 
     Due to this, the intake passage vaporization amount WS and the combustion chamber vaporization amount WC can be calculated precisely. In controlling the amount of injection of water from the water injector  61  so that water vaporizing inside the intake passage during the suction stroke and water vaporizing inside the combustion chambers  10  during the compression stroke are generated, it is possible to control the water injection amount to a suitable amount. That is, it is possible to keep water from being excessively injected and to conversely keep water from becoming insufficient and a sufficient cooling effect from no longer being able to be obtained. 
     Above, an embodiment of the present disclosure was explained, but the embodiment only shows part of the examples of application of the present disclosure. It is not meant to limit the technical scope of the present disclosure to the specific constitution of the above embodiment. 
     For example, if the internal combustion engine  100  is provided with an exhaust gas recirculation system for making part of the exhaust gas discharged from the combustion chambers  10  be recirculated to the intake passage, it is also possible to consider the exhaust gas recirculation rate (EGR rate) in calculating the intake passage vaporization amount WS. 
     Further, in the above embodiment, a spark ignition type internal combustion engine  100  was explained as an example, but in a premix compression ignition type internal combustion engine or an internal combustion engine making fuel burn by diffusion, it is also possible to perform the water injection control explained in the above embodiment if there is a demand for reducing the temperature of the intake air or air-fuel mixture inside the combustion chambers.