JP2014227981A - Control device for spark ignition type engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To secure the ignitability and/or combustion stability of air-fuel mixture, independently of the property of fuel, in an engine into which the fuel is to be supplied including alcohol having a lower evaporation rate than gasoline under the conditions of a specified temperature or lower, when the temperature state of the engine is a predetermined temperature or lower and the operating condition of the engine is in a predetermined high-load and high-rotation region.SOLUTION: When the temperature state of an engine body (an engine 1) is a predetermined temperature or lower and the operating condition of the engine body is in a predetermined high-load and high-rotation region, a controller (an engine controller 100) carries out fuel injection so that the fuel injection started in an intake stroke is finished during a compression stroke. The controller also shortens a fuel injection period so that a fuel injection finishing timing is faster as the concentration of alcohol in fuel is higher.

Description

  The technology disclosed herein relates to a control device for a spark ignition engine, and more particularly to control of a spark ignition engine configured to be supplied with a fuel containing alcohol having a lower vaporization rate than gasoline under a specific temperature or lower. Relates to the device.

  In recent years, biofuels have attracted attention from the viewpoint of environmental problems such as global warming, and FFVs (Flexible Fuel Vehicles) that can run with a fuel in which gasoline and bioethanol, for example, are mixed at an arbitrary mixing ratio have been put into practical use. Yes. The range of the ethanol concentration of the fuel in FFV differs depending on the mixing ratio of gasoline and ethanol as fuels distributed in the market. For example, when changing from E25 (gasoline 75%, ethanol 25) to E100 (ethanol 100%), Or it may change from E0 (gasoline 100%) to E85 (gasoline 15%, ethanol 85%). In addition, E100 here includes E100 (ethanol 95%, water 5%) which contains about 5% of water, in which water is not sufficiently removed during the ethanol purification process.

  In such FFV, the properties of the fuel differ depending on the concentration of ethanol in the fuel. In other words, since gasoline, which is a multi-component fuel, has a boiling point in the range of 27 to 225 ° C., for example, as shown in FIG. But the vaporization rate is relatively high. On the other hand, since ethanol is a single component fuel and its standard boiling point is 78 ° C., when the temperature is relatively low, the vaporization rate becomes 0, which is lower than the gasoline vaporization rate. When the temperature is relatively high, the vaporization rate is 100%, which is higher than the vaporization rate of gasoline. Therefore, in the FFV, when the engine temperature state is a low temperature below a predetermined temperature, the higher the ethanol concentration in the fuel and the lower the engine temperature state, the worse the fuel vaporization performance in the cylinder. That is, if the weight ratio of the amount of fuel that contributes to combustion to the amount of fuel supplied into the cylinder is defined as the vaporization rate, the vaporization rate decreases as the ethanol concentration increases and the engine temperature state decreases. . For example, during the cold operation of the engine when using E100, there arises a problem that the ignitability and / or combustion stability of the air-fuel mixture deteriorates due to the low vaporization rate. In particular, E100 containing water has a large problem.

  For example, in Patent Document 1, in the engine system for FFV, when performing the catalyst warm-up promotion process in which fuel is injected in each of the intake stroke and the compression stroke during the first idle after the cold start, the alcohol concentration in the fuel The higher the is, the more the amount of fuel injected during the compression stroke is relatively increased, thereby preventing misfire and promoting warm-up of the catalyst device. It is described that the fuel injection amount to be injected is limited to a predetermined value, thereby preventing an increase in the amount of fuel that is not vaporized and preventing a warm-up delay of the catalyst device due to an ignition failure or the like. .

  Further, in Patent Document 2, in the engine system for FFV, the difference between the theoretical air-fuel ratio of gasoline and the theoretical air-fuel ratio of alcohol causes a necessary fuel injection amount to increase when the alcohol concentration is high. Since the maximum discharge capacity of the fuel pump is exceeded in the high rotation / high load range where the fuel consumption per hour increases, the charging efficiency is limited on the assumption that the fuel injection amount is set to the maximum discharge capacity. Thus, it is described that the actual air-fuel ratio is prevented from deviating from the stoichiometric air-fuel ratio to the lean side.

JP 2008-274789 A JP 2009-191650 A

  By the way, in an engine operating region where the engine is running at a high speed and a high load, the air-fuel ratio of the air-fuel mixture is made richer than the stoichiometric air-fuel ratio from the viewpoint of engine reliability and prevention of overheating of the catalyst device. The combustion temperature and the exhaust gas temperature are lowered using the latent heat of vaporization (hereinafter, such control may be referred to as overrich control for convenience of explanation).

  In FFV, as described above, the higher the alcohol concentration in the fuel, the higher the alcohol concentration in the fuel due to the difference between the theoretical air-fuel ratio of gasoline and the theoretical air-fuel ratio of alcohol. When the fuel vaporization rate is low, such as when the fuel concentration is low and the fuel ethanol concentration is high, the amount of fuel supplied into the cylinder is increased in advance so as to compensate for the low vaporization rate and obtain the desired vaporized fuel amount. Control is performed.

  Therefore, in the FFV, if the above-described overrich control is performed, particularly when the engine temperature is relatively low, the fuel injection amount increases greatly as the ethanol concentration increases. Even if the injection is started, the fuel injection will continue until the latter half of the compression stroke.

  On the other hand, the higher the alcohol concentration in the fuel, the more difficult it is to vaporize at low temperatures. Therefore, there is a demand for ensuring a longer vaporization time, but as described above, the higher the alcohol concentration, the later the fuel injection end time is delayed. Moreover, since the time per cycle is shortened in the high rotation range, a sufficiently long vaporization time cannot be secured before ignition, resulting in a decrease in the ignitability and / or combustion stability of the mixture. There is a risk of causing it. In addition, although the fuel injected into the cylinder does not vaporize, the amount of fuel remaining as droplets increases, and the droplet fuel remaining in the cylinder further worsens the vaporization of the fuel. Furthermore, as a result of the unburned fuel being supplied to the catalytic device, it may occur that the catalyst burns after. As described above, overrich control that lowers the combustion temperature using the latent heat of vaporization of the fuel reduces the ignitability and / or combustion stability of the air-fuel mixture when the fuel vaporization deteriorates in FFV. In addition, the reliability of the engine may be reduced and the catalyst device may be overheated.

  The technology disclosed herein is a technology that takes the above-mentioned circumstances into consideration, and the purpose of the technology is that in an engine that is supplied with a fuel containing an alcohol having a lower vaporization rate than gasoline under a condition below a specific temperature. To ensure the ignitability and / or combustion stability of the air-fuel mixture regardless of the fuel properties when the temperature is below the specified temperature and the engine is operating in the specified high load / high rotation range It is in.

  Specifically, the technology disclosed herein relates to a control device for a spark ignition engine. The control device for the spark ignition engine has an engine main body configured to be supplied with fuel containing alcohol having a lower vaporization rate than gasoline under conditions of a specific temperature or lower, and a fuel injection valve for injecting the fuel. And a fuel supply mechanism configured to supply the fuel injected by the fuel injection valve into a cylinder of the engine body, and configured to operate the engine body through at least control of the fuel supply mechanism. A controller.

  When the temperature of the engine main body is equal to or lower than a predetermined temperature and the operating state of the engine main body is in a predetermined high load / high rotation range, the controller performs fuel injection started during the intake stroke. The fuel is injected such that the fuel injection ends during the compression stroke, and the controller also increases the fuel injection end timing as the concentration of the alcohol in the fuel increases. Shorten the injection period.

  Here, the “alcohol having a lower vaporization rate than gasoline under a condition below a specific temperature” specifically refers to ethanol or methanol, etc., and is a single component fuel, which is a condition below the boiling point of the alcohol. Below, the vaporization rate can be lower than gasoline. The alcohol here includes biological alcohol such as bioethanol made from sugarcane or corn.

  The “fuel containing alcohol” includes both a fuel obtained by mixing alcohol and gasoline, and a fuel containing only alcohol. There is no restriction | limiting in particular in the mixing ratio of gasoline and alcohol, Arbitrary mixing ratios can be employ | adopted. The fuel supplied to the engine body may have a constant mixing ratio between gasoline and alcohol, or may change as needed. When the alcohol is ethanol, the “fuel containing alcohol” specifically includes fuels having an arbitrary ethanol concentration in a range from E25 in which 25% ethanol is mixed with gasoline to E100 in which ethanol is 100%. included. Further, the above-described configuration does not exclude that fuel containing no alcohol is supplied to the engine body. For example, when alcohol is ethanol, the fuel to be supplied to the engine body is a fuel having an arbitrary ethanol concentration in a range from gasoline (that is, E0 not containing ethanol) to E85 in which gasoline is mixed with 85% ethanol. Is included. Further, the “fuel containing alcohol” may contain water. Therefore, E100 containing about 5% of water is also included in the “fuel containing alcohol”. The alcohol concentration in the fuel can be detected or estimated by various methods.

“Vaporization rate” can be defined as the weight ratio of the amount of fuel contributed to combustion to the amount of fuel supplied into the cylinder. Such a vaporization rate can be calculated based on a detection value of an O ₂ sensor attached to the exhaust passage of the engine. Under conditions where the temperature of the engine body is equal to or lower than a predetermined temperature, the higher the alcohol concentration in the fuel and the lower the temperature state of the engine body, the lower the vaporization rate.

  The “fuel injection valve” may be a fuel injection valve that directly injects fuel into the cylinder. By doing so, it is possible to supply fuel into the cylinder when the cylinder is in the intake stroke and when it is in the compression stroke. In addition to such a direct injection fuel injection valve, a fuel injection valve for injecting fuel into the intake port may be provided separately.

  “When the temperature of the engine body is below a predetermined temperature” means a semi-warm-up state where the engine body has not reached the warm-up state, and the vaporization rate of the alcohol-containing fuel is relatively low. Is the time.

  “The operating state of the engine body is in a predetermined high load / high rotation area” means that the engine operating state is in a high load area including a fully open load and the engine speed range is temporarily It may be defined as being in a high rotation area when divided into a low rotation area and a high rotation area. More specifically, by setting the air-fuel ratio of the air-fuel mixture to be richer than the stoichiometric air-fuel ratio, the combustion temperature is lowered using the latent heat of vaporization of the fuel, thereby ensuring the reliability of the engine body. This is an operation region in which overheating of the catalyst device provided on the exhaust side of the engine body is prevented. This air-fuel ratio may be an air-fuel ratio richer than the so-called power air-fuel ratio (also referred to as output air-fuel ratio) that gives the highest engine torque, and in this way, combustion using the vaporization latent heat of the fuel A decrease in temperature is realized. Specifically, over-rich is equivalent to an equivalent ratio φ = 1.4 (1.2 <φ ≦ 1...) When the equivalent ratio of the power air-fuel ratio is about φ = 1.2, for example. 4).

  According to the above configuration, when the temperature state of the engine body is equal to or lower than the predetermined temperature and the fuel vaporization rate is relatively lowered, and the operating state of the engine body is a predetermined high load / high rotation region In this case, the fuel injection period becomes longer as the fuel injection amount increases. As a result, the fuel injection started from the intake stroke continues to the compression stroke. In addition, since the theoretical air-fuel ratio of alcohol is different from the stoichiometric air-fuel ratio of gasoline, the higher the alcohol concentration in the fuel, the higher the fuel injection amount. At low temperatures, the alcohol concentration in the fuel increases. In order to compensate for the lowering vaporization rate, the fuel injection amount increases. As a result, the higher the alcohol concentration in the fuel, the longer the fuel injection period and the later the injection end timing (that is, the closer to the ignition timing).

  As described above, when the fuel injection period is long, in the above configuration, the fuel injection period is shortened so that the higher the alcohol concentration in the fuel is, the more the fuel injection end timing is advanced. To shorten the fuel injection period, for example, even if the fuel pressure is increased to achieve the same injection amount, the injection period may be shortened, or the fuel pressure cannot be increased further. Alternatively, the injection period may be shortened by reducing the injection amount. As described above, when the operating state of the engine body is in a predetermined high load / high rotation range, the air-fuel ratio of the air-fuel mixture is set to be richer than the stoichiometric air-fuel ratio. However, the air-fuel ratio of the air-fuel mixture only approaches the stoichiometric air-fuel ratio. That is, when reducing the injection amount, it is preferable to reduce the injection amount in a range where the air-fuel ratio of the air-fuel mixture does not become leaner than the stoichiometric air-fuel ratio. By doing so, a reduction in exhaust emission performance is avoided.

  Then, by shortening the fuel injection period and advancing the fuel injection end timing, it becomes possible to lengthen the period from the end of injection to ignition. In the above configuration, as the alcohol concentration in the fuel increases, the injection end timing is advanced. As a result, as the fuel vaporization rate becomes relatively low, the period from the end of fuel injection to ignition becomes longer. It becomes advantageous for vaporization. As a result, the ignitability and / or combustion stability of the air-fuel mixture is improved regardless of the properties of the fuel.

  In particular, when the injection period is shortened by reducing the fuel injection amount, the amount of fuel that is not vaporized in the cylinder is reduced, so that the droplet fuel is prevented from remaining in the cylinder and the fuel vaporization is deteriorated. Can be avoided. Further, the reduction of the fuel injection amount is effective in preventing overheating of the catalyst device by suppressing unburned fuel from being supplied to the catalyst device connected to the exhaust side of the engine body.

  The control device for the spark ignition engine further includes a catalyst device connected to an exhaust side of the engine body and configured to purify exhaust gas discharged from the engine body, and the controller includes the catalyst When the temperature of the apparatus is equal to or higher than a predetermined temperature, the fuel injection amount is decreased so that the higher the alcohol concentration in the fuel is, the more the fuel injection end timing is advanced. The filling efficiency of the engine body may be lowered so as to correspond to the decrease.

  Here, it is assumed that “filling efficiency” follows the following definition. That is, the ratio of the weight of air sucked into one cylinder when the air weight of one cylinder of the total displacement is 1 in the standard atmosphere (25 ° C., 1 atm).

  As described above, when the fuel injection amount is decreased to advance the fuel injection end timing when the engine body is in the high load / high rotation region, the air-fuel ratio of the mixture is overrich. Approaches the power air-fuel ratio. As a result, the combustion temperature and the exhaust gas temperature rise. The increase in the fuel temperature and the exhaust gas temperature is not a big problem when the temperature of the catalyst device is relatively low, but when the temperature of the catalyst device is higher than a relatively high predetermined temperature, the increase in the combustion temperature or the like Can cause overheating. Therefore, when the temperature of the catalyst device is equal to or higher than the predetermined temperature and it is desired to avoid the temperature of the catalyst device from rising further, the charging efficiency of the engine body is reduced so as to correspond to the decrease in the fuel injection amount. In other words, by reducing both the fuel injection amount and the air amount, the air-fuel ratio of the air-fuel mixture can be kept richer than the power air-fuel ratio, and the rise in combustion temperature and exhaust gas temperature is suppressed. Is done. As a result, overheating of the catalyst device is suppressed or avoided.

  The control device for the spark ignition engine further includes a variable valve mechanism that is provided in the engine body and is configured to be able to change the opening and closing timing of the intake valve, and the controller passes through the variable valve mechanism. The charging efficiency may be lowered by setting the closing timing of the intake valve to a predetermined timing after intake bottom dead center.

  That is, by setting the closing timing of the intake valve to a so-called delayed closing by the variable valve mechanism, the charging efficiency can be reduced without increasing the pump loss. Note that the charging efficiency of the engine body may be lowered, for example, by reducing the opening of the throttle valve.

  The fuel supply mechanism further includes a fuel pump that boosts the pressure of the fuel injected by the fuel injection valve, and the controller is configured to control the fuel based on at least an operating state of the engine body and a fuel vaporization rate. An injection amount of the fuel injected by the injection valve is set, and the controller controls the alcohol in the fuel even when the set injection amount is smaller than a maximum injection amount determined by a performance limit of the fuel pump. The injection amount may be decreased according to the concentration of the fuel.

  Here, the fuel pump may be configured to be driven by the engine main body or may be configured to be driven by a drive source different from the engine main body (for example, an electric pump). For example, in a plunger-type configuration in which the fuel pump is driven by the engine body, the plunger pressure is increased by a predetermined number of times each time the crankshaft of the engine body rotates once, while the fuel pressure increases. Specifically, the fuel injection is performed as many times as the plunger is pushed. Here, when the amount of fuel injection per one time is so large that it exceeds the capacity of the fuel pump, the fuel pressure gradually decreases without the pump boosting in time. “Maximum injection amount determined by the performance limit of the fuel pump” can be defined as the maximum fuel injection amount in such a range that the pressure of the pump cannot be increased in time and the fuel pressure does not gradually decrease. It is.

  As described above, when the temperature state of the engine body is equal to or lower than the predetermined temperature and the operation state of the engine body is in a predetermined high load / high rotation region, the fuel injection amount relatively increases. Further, when the concentration of alcohol in the fuel is high, the fuel injection amount increases as compared with gasoline, and the fuel injection amount further increases in order to compensate for a low vaporization rate at low temperatures. As a result, the fuel injection amount set based on the engine operating state and the fuel vaporization rate may be longer than the maximum injection amount determined by the performance limit of the fuel pump. In this case, since it is impossible to operate beyond the performance limit of the pump, the fuel injection amount is limited to the maximum injection amount.

  On the other hand, in the above configuration, even when the fuel injection amount set based on the operating state of the engine body and the fuel vaporization rate is smaller than the maximum injection amount determined by the performance limit of the fuel pump, For the purpose of ensuring a long period from the end timing of injection to ignition, when the alcohol concentration in the fuel is high, the injection amount is reduced. As a result, in the above-described configuration, the engine body is in a predetermined high load and high state when the temperature of the engine body is a low temperature that is equal to or lower than a predetermined temperature and the operating state of the engine body sets the air-fuel ratio of the air-fuel mixture to overrich. In the region of rotation, the ignitability and / or combustion stability of the air-fuel mixture can be ensured regardless of the nature of the fuel.

  As described above, according to the spark ignition type engine control apparatus, the engine body is in a predetermined high load / high rotation range when the temperature of the engine body is equal to or lower than a predetermined temperature. Sometimes, the higher the alcohol concentration in the fuel, the shorter the fuel injection period that starts during the intake stroke and ends during the compression stroke, and advances the fuel injection end timing, thereby reducing the vaporization time before ignition. The higher the alcohol concentration, the longer it becomes, and the ignitability and / or combustion stability of the air-fuel mixture is improved regardless of the properties of the fuel.

It is the schematic which shows the structure of a spark ignition type engine and its control apparatus. It is a figure which compares the change of the distillation amount of gasoline with respect to temperature, and the change of the distillation amount of ethanol. It is a conceptual diagram which shows the driving | operation area | region of an engine. It is a figure which illustrates the relationship between ethanol concentration and injection period at the time of low temperature and in a high load and high rotation region. It is an example of the flowchart regarding the setting of the fuel injection amount and the charging efficiency at a low temperature and in a high load / high rotation range.

  Hereinafter, an embodiment of a spark ignition engine will be described with reference to the drawings. In addition, the following description of preferable embodiment is an illustration. As shown in FIG. 1, the engine system includes an engine (engine body) 1, various actuators associated with the engine 1, various sensors, and an engine controller 100 that controls the actuators based on signals from the sensors. The engine system includes a high compression ratio engine 1 having a geometric compression ratio of 12 or more and 20 or less (for example, 12).

  The engine 1 is a spark ignition type four-stroke internal combustion engine. Although only one is shown in FIG. 1, the engine 1 has first to fourth four cylinders 11 arranged in series. However, an engine to which the technology disclosed herein is applicable is not limited to an in-line four-cylinder engine. The engine 1 is mounted on a vehicle such as an automobile, and its output shaft is connected to drive wheels via a transmission, although not shown. The vehicle is propelled by the output of the engine 1 being transmitted to the drive wheels.

  The engine 1 is supplied with fuel containing ethanol (including bioethanol). In particular, this vehicle is an FFV that can use fuel of any concentration from 25% ethanol (that is, E25 having a gasoline concentration of 75%) to 100% (that is, E100 that does not include gasoline). In addition, E100 here includes ethanol containing about 5% of moisture without being sufficiently removed in the ethanol purification process. However, the technique disclosed here is not limited to FFV based on the use of E25 to E100, but for example, E0 (that is, gasoline alone and does not include ethanol) to E85 (that is, gasoline concentration 15%, ethanol concentration 85%). ) Can also be applied to FFV used by a fuel whose ethanol concentration varies within the range.

  Although not shown in the figure, this vehicle has only a fuel tank (that is, a main tank) for storing the above-mentioned fuel. Like a conventional FFV, a fuel having a high gasoline concentration is separated from the main tank. It is characterized by not having a sub-tank for storing. The FFV is based on a gasoline specification vehicle to which only gasoline is supplied, and most of the configuration is shared between the two specifications.

  The engine 1 includes a cylinder block 12 and a cylinder head 13 mounted thereon, and a cylinder 11 is formed inside the block 12. As is well known, a crankshaft 14 is rotatably supported on the cylinder block 12 by a journal, a bearing or the like, and this crankshaft 14 is connected to a piston 15 via a connecting rod 16.

  Two inclined surfaces extending from the substantially central portion to the vicinity of the lower end surface of the cylinder head 13 are formed on the ceiling portion of each cylinder 11, and the inclined surfaces form a roof-like shape on which they are placed. It is a so-called pent roof type.

  The piston 15 is slidably inserted into each cylinder 11, and defines a combustion chamber 17 together with the cylinder 11 and the cylinder head 13. The top surface of the piston 15 is formed in a trapezoidal shape that protrudes from the peripheral portion toward the center portion so as to correspond to the pent roof type shape of the ceiling surface of the cylinder 11 described above. The combustion chamber volume when the compression top dead center is reached is reduced to achieve a high geometric compression ratio of 12 or more. On the top surface of the piston 15, a cavity 151 that is recessed in a substantially spherical shape is formed at the approximate center position. The cavity 151 is disposed so as to be opposed to the spark plug 51 disposed at the center of the cylinder 11, thereby shortening the combustion period. That is, as described above, in the high compression ratio engine 1, the top surface of the piston 15 is raised, and when the piston 15 reaches the compression top dead center, the top surface of the piston 15 and the ceiling surface of the cylinder 11 are used. The interval between and is extremely narrow. For this reason, when the cavity 151 is not formed, the initial flame interferes with the top surface of the piston 15 and the cooling loss increases, flame propagation is inhibited and the combustion speed is delayed. On the other hand, the cavity 151 avoids the interference of the initial flame and does not hinder its growth, so that the flame propagation becomes faster and the combustion period can be shortened. This is advantageous in suppressing knocking in a fuel with a high gasoline concentration, and contributes to an improvement in torque due to the advance of the ignition timing.

  For each cylinder 11, an intake port 18 and an exhaust port 19 are formed in the cylinder head 13, and each communicates with the combustion chamber 17. The intake valve 21 and the exhaust valve 22 are arranged so that the intake port 18 and the exhaust port 19 can be shut off (closed) from the combustion chamber 17, respectively. The intake valve 21 is driven by the intake valve drive mechanism 30 and the exhaust valve 22 is driven by the exhaust valve drive mechanism 40, thereby reciprocating at a predetermined timing to open and close the intake port 18 and the exhaust port 19.

  The intake valve drive mechanism 30 and the exhaust valve drive mechanism 40 have an intake camshaft 31 and an exhaust camshaft 41, respectively. The camshafts 31 and 41 are connected to the crankshaft 14 via a power transmission mechanism such as a known chain / sprocket mechanism. As is well known, the power transmission mechanism rotates the camshafts 31 and 41 once while the crankshaft 14 rotates twice.

  The intake valve drive mechanism 30 includes an intake valve timing variable mechanism 32 that can change the opening / closing timing of the intake valve 21, and the exhaust valve drive mechanism 40 can change the exhaust valve timing that can change the opening / closing timing of the exhaust valve 22. A mechanism 42 is included. In this embodiment, the intake valve timing variable mechanism 32 is a hydraulic, mechanical, or electric variable phase mechanism (Variable Valve Timing) that can continuously change the phase of the intake camshaft 31 within a predetermined angle range. The exhaust valve timing variable mechanism 42 is configured by a hydraulic, mechanical, or electric phase variable mechanism that can continuously change the phase of the exhaust camshaft 41 within a predetermined angle range. Yes. The intake valve timing variable mechanism 32 can adjust the effective compression ratio by changing the closing timing of the intake valve 21. The effective compression ratio is the ratio between the combustion chamber volume when the intake valve is closed and the combustion chamber volume when the piston 15 is at top dead center.

  The spark plug 51 is attached to the cylinder head 13 by a known structure such as a screw, for example. The electrode of the spark plug 51 faces the ceiling of the combustion chamber 17 at the approximate center of the cylinder 11. The ignition system 52 receives a control signal from the engine controller 100 and energizes the spark plug 51 so that a spark is generated at a desired ignition timing.

  The fuel injection valve 53 has a known structure, for example, using a bracket. In this embodiment, the fuel injection valve 53 is attached to one side (the intake side in the illustrated example) of the cylinder head 13. The engine 1 is a so-called direct injection engine in which fuel is directly injected into the cylinder 11. The tip of the fuel injection valve 53 faces the inside of the combustion chamber 17 in the vertical direction below the intake port 18 and in the horizontal direction at the center of the cylinder 11. However, the arrangement of the fuel injection valve 53 is not limited to this. In this example, the fuel injection valve 53 is a multi-hole (for example, six-hole) fuel injection valve (Multi Hole Injector: MHI). Although the direction of each nozzle hole is not shown in the drawing, the tip of the nozzle shaft is widened so that fuel can be injected into the entire cylinder 11. The advantage of MHI is that the diameter of one nozzle hole is small because of the multiple nozzle holes, the fuel can be injected at a relatively high pressure, and the fuel can be injected into the entire cylinder 11 so that the fuel can be injected. This increases the fuel efficiency and promotes fuel vaporization and atomization. Therefore, when fuel is injected during the intake stroke, it is advantageous in terms of fuel mixing performance and acceleration of vaporization / atomization using the intake air flow in the cylinder 11, while fuel is injected during the compression stroke. In this case, it is advantageous in terms of gas cooling in the cylinder 11 by promoting vaporization and atomization of the fuel. The fuel injection valve 53 is not limited to MHI.

  Although illustration of the structure of the fuel supply system 54 is omitted, a high-pressure pump that boosts the fuel and supplies the fuel to the fuel injection valve 53, a pipe, a hose, and the like that send fuel from the fuel tank to the high-pressure pump, And an electric circuit for driving the fuel injection valve 53. The high pressure pump is driven by the engine 1 in this example. Specifically, the high-pressure pump is attached to the camshaft. The high pressure pump may be an electric pump. The high-pressure pump is, for example, a plunger-type pump, and the plunger of the high-pressure pump pushes out fuel four times per camshaft rotation by a pump cam provided on the camshaft. This high-pressure pump is a relatively small-capacity pump here, which is the same as a gasoline specification vehicle. When the fuel injection valve 53 is a multi-injection type, the fuel injection pressure is set to be relatively high in order to inject fuel from a minute injection port. The maximum fuel pressure is, for example, 20 MPa. The electric circuit receives a control signal from the engine controller 100 and operates the fuel injection valve 53 to inject a desired amount of fuel into the combustion chamber 17 at a predetermined timing. Here, the fuel supply system 54 sets the fuel pressure higher as the engine speed increases. This is because as the engine speed increases, the amount of fuel injected into the cylinder 11 also increases, but the fuel pressure increases, which is advantageous for fuel vaporization and atomization, and the fuel injection valve 53 There is an advantage that the pulse width related to fuel injection is made as short as possible. As described above, an alcohol-containing fuel having an arbitrary ethanol concentration from E25 to E100 is stored in the fuel tank.

  The intake port 18 communicates with the surge tank 55 a through an intake path 55 b in the intake manifold 55. An intake air flow from an air cleaner (not shown) passes through the throttle body 56 and is supplied to the surge tank 55a. A throttle valve 57 is disposed on the throttle body 56. The throttle valve 57 throttles the intake air flow toward the surge tank 55a and adjusts the flow rate as is well known. The throttle actuator 58 receives the control signal from the engine controller 100 and adjusts the opening degree of the throttle valve 57.

  The exhaust port 19 communicates with a passage in the exhaust pipe as is well known by an exhaust path in the exhaust manifold 60. The exhaust manifold 60 is not shown, but the branch exhaust passages connected to the exhaust ports 19 of the cylinders 11 are gathered by the first gathering parts among the cylinders whose exhaust order is not adjacent to each other, and each first gathering part The downstream intermediate exhaust passages are gathered at the second gathering portion. That is, a so-called 4-2-1 layout is adopted for the exhaust manifold 60 of the engine 1. Further, at least one catalyst device 43 for purifying exhaust gas is interposed in the middle of the exhaust passage. The catalyst device 43 includes, for example, a three-way catalyst.

  The engine 1 is also provided with a starter motor 20 for performing cranking at the time of starting.

  The engine controller 100 is a controller based on a well-known microcomputer, and includes a central processing unit (CPU) that executes a program, a memory that is configured by, for example, RAM and ROM, and stores a program and data, And an input / output (I / O) bus for inputting and outputting signals.

The engine controller 100 includes an intake air flow rate and an intake air temperature from the air flow sensor 71, an intake manifold pressure from the intake pressure sensor 72, a crank angle pulse signal from the crank angle sensor 73, an engine water temperature from the water temperature sensor 78, and an exhaust passage. Various inputs such as the oxygen concentration in the exhaust gas are received from the linear O ₂ sensor 79 attached to the sensor. The engine controller 100 calculates the engine speed based on, for example, a crank angle pulse signal. The engine controller 100 also receives an accelerator opening signal from an accelerator opening sensor 75 that detects the amount of depression of the accelerator pedal. Further, a vehicle speed signal from a vehicle speed sensor 76 that detects the rotational speed of the output shaft of the transmission is input to the engine controller 100. In addition, a knock sensor 77 including an acceleration sensor that converts the vibration of the cylinder block 12 into a voltage signal and outputs it is attached to the cylinder block 12, and the output signal is also input to the engine controller 100.

  The engine controller 100 calculates the following control parameters of the engine 1 based on the input as described above. For example, a desired throttle opening signal, fuel injection pulse, ignition signal, valve phase angle signal, etc. The engine controller 100 outputs these signals to the throttle actuator 58, the fuel supply system 54, the ignition system 52, the intake and exhaust valve timing variable mechanisms 32 and 42, and the like. The engine controller 100 also outputs a drive signal to the starter motor 20 when the engine 1 is started.

Here, as a configuration unique to the FFV engine system, the engine controller 100 estimates the ethanol concentration of the fuel injected by the fuel injection valve 53 based on the detection result of the linear O ₂ sensor 79. The theoretical air fuel ratio (9.0) of ethanol is smaller than the theoretical air fuel ratio (14.7) of gasoline. The higher the ethanol concentration of the fuel, the richer the theoretical air fuel ratio (that is, the smaller the theoretical air fuel ratio). Therefore, under the condition that the engine is operated at the stoichiometric air-fuel ratio, when there is unburned oxygen in the exhaust gas, it can be determined that the ethanol concentration of the fuel was higher than expected. . Specifically, since the ethanol concentration of the fuel injected by the fuel injection valve 53, in other words, the ethanol concentration of the fuel stored in the fuel tank may change due to refueling, the engine controller 100 First, the fuel supply determination is performed based on the detection value of the level gauge sensor of the fuel tank. If it is determined that the fuel supply has been performed, the ethanol concentration of the fuel is estimated. From the signal output from the linear O ₂ sensor 79, the engine controller 100 determines that there is a lot of gasoline in the fuel when the air-fuel ratio is lean, and determines that there is a lot of ethanol in the fuel when the air-fuel ratio is rich. Thus, the ethanol concentration in the fuel is estimated. Instead of estimating the ethanol concentration of the fuel, a sensor that detects the ethanol concentration of the fuel may be provided. The estimated ethanol concentration is used for fuel injection control.

The engine controller 100 further calculates the vaporization rate of the fuel supplied into the cylinder 11 based on the detection result of the linear O ₂ sensor 79. The vaporization rate is defined by the weight ratio of the amount of fuel that contributes to combustion with respect to the amount of fuel supplied into the cylinder 11 (in other words, the amount of fuel injected by the fuel injection valve 53). The engine controller 100 calculates the weight of the fuel amount contributing to combustion based on the air-fuel ratio of the air-fuel mixture and the detected value of the linear O ₂ sensor, and calculates the calculated fuel weight and the fuel injection of the fuel injection valve 53. The vaporization rate is calculated based on the amount.

(Setting of fuel injection amount)
This engine system is a system mounted on the FFV as described above, and the engine 1 is supplied with alcohol-containing fuel having any mixing ratio from E25 to E100. Here, FIG. 2 is a diagram comparing the gasification characteristics of gasoline and ethanol. In addition, FIG. 2 has shown the change of the distillation amount (%) of each of gasoline and ethanol with respect to the temperature change under 1 atmosphere. Since gasoline is a multi-component fuel, it evaporates according to the boiling point of each component. The amount of gasoline distilled will vary approximately linearly with changes in temperature. That is, some components of the gasoline are vaporized even when the temperature state of the engine 1 is relatively low, and a combustible air-fuel mixture can be formed.

  On the other hand, since ethanol is a single component fuel, the distillation amount becomes 0% at a specific temperature (that is, 78 ° C. which is the boiling point of ethanol) or less, whereas when the specific temperature is exceeded, the distillation amount is 100%. %become. Thus, when gasoline and ethanol are compared, there is a state in which the amount of ethanol distilled is lower than the amount of gasoline distilled below a specific temperature, while the amount of ethanol distilled exceeds the specified temperature. Is higher than the amount of gasoline distilled. Therefore, in a low temperature state where the temperature state of the engine 1 is a predetermined temperature or lower (for example, the water temperature is less than about 30 ° C.), the fuel containing ethanol has a lower vaporization rate than gasoline. Thus, when the engine 1 is in a low temperature state, the lower the temperature state of the engine 1 and the higher the ethanol concentration of the fuel, the lower the fuel vaporization rate.

  As described above, since the fuel vaporization rate varies depending on the temperature state of the engine 1 and the ethanol concentration of the fuel, the engine controller 100 can set the engine load, the alcohol concentration, and the like so as to obtain a target vaporized fuel amount. The fuel amount increase correction according to the fuel vaporization rate is performed on the base fuel amount set according to the above. That is, the amount of fuel injected by the fuel injection valve 53 is increased as the fuel vaporization rate is lower.

(Engine control at high load and high speed)
When the operation state of the engine 1 is in a high load / high rotation region as shown by hatching in the operation region shown in FIG. 3, from the viewpoint of reliability of the engine 1 and / or prevention of overheating of the catalyst device 43, The air-fuel ratio of the air-fuel mixture is made richer than the stoichiometric air-fuel ratio, and the combustion temperature is lowered using the latent heat of vaporization of the fuel. Here, the high load range is a high load range including a fully open load, and the high rotation range is virtually the operation range of the engine 1 in the low speed range and the high rotation range in the rotational speed direction. This is a high rotation range when divided into two. Further, the air-fuel ratio here is richer than the power air-fuel ratio (for example, equivalent ratio φ = 1.2) at which the torque of the engine 1 is the highest (for example, equivalent ratio φ = 1.4). Such an air-fuel ratio is also called overrich).

  Therefore, when the operating state of the engine 1 is in the high load / high rotation region, the air / fuel ratio is overriched to increase the amount of fuel required, and the theoretical air / fuel ratio of ethanol is greater than that of gasoline. Since the value of the air-fuel ratio is small, the higher the ethanol concentration of the fuel, the greater the amount of fuel to be injected. Furthermore, when the temperature state of the engine 1 is a low temperature state of a predetermined temperature or lower (for example, 30 ° C. or lower), Concentrated fuel has a low fuel vaporization rate and a large increase correction value. As a result, the amount of fuel injected by the fuel injection valve 53 can be extremely large.

  FIG. 4 is a diagram illustrating a fuel injection period in a low temperature state (for example, the engine water temperature is about 10 to 30 ° C.) and at a high load and a high rotation speed. FIG. 4 shows the fuel injection period for each of the three types of fuel (ie, E95, E85, and E75) having different ethanol concentrations in the fuel. The fuel pressures are all set to the maximum fuel pressure (for example, 20 MPa).

  First, at E75, since the fuel injection amount increases as described above, after the fuel injection is started at the beginning of the intake stroke, the fuel injection is continued until the end of the middle stage of the compression stroke. After completion of fuel injection, ignition is performed near the compression top dead center.

  In E85 having a higher ethanol concentration than E75, since the ethanol concentration is relatively high, the fuel injection amount increases, and the increase correction amount increases as the vaporization rate decreases. Therefore, the fuel injection amount increases compared to E75. As a result, as in E75, assuming that fuel injection is started at the beginning of the intake stroke, the injection end timing is delayed from E75 in E85, as indicated by a one-dot chain line in FIG. This is disadvantageous in shortening the period from the end of fuel injection to ignition and ensuring the fuel vaporization time before ignition.

  Further, in E95 having an ethanol concentration higher than that of E85, the fuel injection amount is further increased, so that the injection end timing is further delayed as shown by a one-dot chain line in FIG. As a result, the period from the end of fuel injection to ignition is further shortened.

  On the other hand, the higher the ethanol concentration in the fuel, the easier it is to lower the vaporization rate, so it is desirable to secure a longer vaporization time. However, as described above, the higher the ethanol concentration, the shorter the fuel vaporization time before ignition. Therefore, the ignitability and / or combustion stability of the air-fuel mixture will be reduced. Further, the shortening of the vaporization time increases the amount of droplet fuel remaining in the cylinder 11 without being vaporized, which further worsens the fuel vaporization. Further, the unburned fuel is supplied to the catalyst device 43 and burned after in the catalyst device 43, so that the catalyst device 43 may be overheated.

  Therefore, in this engine system, when the engine 1 is at a low temperature and the engine 1 is in a high load / high rotation operation region, the ethanol concentration is determined according to the ethanol concentration in the fuel as shown by the solid line in FIG. The higher the fuel injection period, the shorter the fuel injection period (see “EOI” in the figure). Specifically, the injection period is shortened by reducing the fuel injection amount. By doing so, as indicated by the white arrow in FIG. 4, the period from the end of fuel injection to ignition becomes longer as the ethanol concentration is higher. In this way, it is possible to ensure the necessary vaporization time whether the ethanol concentration in the fuel is high or low, and the ignitability and / or combustion stability of the air-fuel mixture can be maintained regardless of the ethanol concentration in the fuel. Secured. In addition, by reducing the fuel injection amount, it is possible to reduce the amount of fuel remaining in the cylinder 11 as droplets without being vaporized, thereby suppressing or avoiding deterioration of fuel vaporization. This also improves the ignitability and / or combustion stability of the mixture. Further, the amount of unburned fuel discharged is suppressed, and afterburning in the catalyst device 43 is suppressed. As a result, overheating of the catalyst device 43 is also suppressed.

  Here, the one-dot chain line shown in FIG. 4 is the fuel injection amount (fuel injection period) set so that the air-fuel mixture becomes over-rich based on the operating state of the engine 1 and the fuel vaporization rate as described above. Thus, by reducing the fuel injection amount thus set, the air-fuel ratio of the air-fuel mixture is changed to the lean side. Specifically, the air-fuel ratio of the air-fuel mixture approaches the power air-fuel ratio. As described above, in the high load / high rotation operation region, the air-fuel ratio of the air-fuel mixture is originally set to overrich from the viewpoint of reliability of the engine 1 and prevention of overheating of the catalyst device 43, as described above. Even if the fuel injection amount is reduced, the air-fuel ratio of the air-fuel mixture does not become leaner than the stoichiometric air-fuel ratio. That is, the exhaust emission performance is not deteriorated.

  Note that the line indicated by a two-dot chain line in FIG. 4 is the maximum fuel injection amount determined from the performance limit of the high-pressure pump (that is, the longest fuel injection period at the maximum fuel pressure). As described above, the high-pressure pump is a relatively small-capacity pump that is the same as a gasoline specification vehicle. On the other hand, in FFV, the theoretical air-fuel ratio of ethanol is different from the theoretical air-fuel ratio of gasoline. Due to the low vaporization rate, the fuel injection amount increases depending on the state of the engine 1 and the fuel properties. Therefore, the fuel injection amount set according to the operating state of the engine 1 may exceed the maximum fuel injection amount (in the example of FIG. 4, the maximum fuel injection amount is exceeded at E95). ).

  On the other hand, in the control for reducing the fuel injection amount according to the ethanol concentration described above, the fuel injection amount set according to the operating state of the engine 1 is the maximum fuel injection as shown for E85 in the example of FIG. Even when the amount is not exceeded, this is performed from the viewpoint of ensuring a sufficiently long vaporization time between the end of fuel injection and ignition.

  Here, as described above, as a result of reducing the fuel injection amount, when the air-fuel ratio of the air-fuel mixture approaches from the overrich to the power air-fuel ratio, the combustion temperature and the exhaust gas temperature increase, There is a possibility that the reliability is lowered and the catalyst device 43 is overheated. Therefore, when the temperature of the catalyst device 43 is equal to or higher than a predetermined temperature and it is desired to avoid a temperature increase beyond that, the air-fuel mixture is emptied by reducing the fuel injection amount and reducing the charging efficiency of the engine 1 at the same time. The fuel ratio is kept richer than the power air-fuel ratio. As a result, overheating of the catalyst device 43 can be avoided, and the reliability of the engine 1 is ensured. However, the torque of the engine 1 decreases as much as the charging efficiency decreases.

  FIG. 5 shows an example of a flowchart executed by the engine controller 100 in connection with the adjustment control of the fuel injection amount and the charging efficiency at a low temperature and in a high load / high rotation range. First, in step S51 after the start, various signals are read, and at least the fuel injection amount, the fuel pressure, and the charging efficiency are set based on the operating state of the engine 1, the fuel vaporization rate, and the like.

  In the following step S52, it is determined whether or not the temperature state of the engine 1 is a predetermined low temperature state and the operating state of the engine 1 is in a predetermined high load / high rotation region. When the determination in step S52 is YES, the process proceeds to step S53, while when NO, the flow returns.

  In step S53, the fuel injection amount set in step S51 is limited (reduced) according to the ethanol concentration of the fuel. When the fuel ethanol concentration is low, the fuel injection amount may not be reduced. In step S53, the higher the ethanol concentration in the fuel, the more advanced the fuel injection end timing.

  In a succeeding step S54, the temperature state of the catalyst device 43 is determined, and it is determined whether or not it is necessary to suppress the temperature increase of the catalyst device 43. When the determination in step S54 is YES, the process proceeds to step S55.

  On the other hand, when the determination in step S54 is NO, the flow returns without moving to step S55. In this case, only the fuel injection amount is reduced, and the charging efficiency is not reduced. As a result, the air-fuel ratio of the air-fuel mixture approaches the power air-fuel ratio from overrich, but since the temperature state of the catalyst device 43 is relatively low, a slight temperature increase of the catalyst device 43 is allowed. In this case, the torque of the engine 1 is not reduced.

  In step S55, the charging efficiency is lowered so as to correspond to the fuel injection amount reduced in step S53. This maintains the air-fuel ratio of the air-fuel mixture in a richer state than the power air-fuel ratio. The charging efficiency of the engine 1 is reduced by delaying the closing timing of the intake valve 21 to a predetermined timing of intake bottom dead center shift by the variable intake valve timing mechanism 32. Such slow closing control of intake air has the advantage of reducing the charging efficiency of the engine 1 without increasing pump loss. In addition to the intake closing control, the charging efficiency may be reduced by, for example, reducing the opening of the throttle valve 57.

  In the above configuration, only the so-called direct injection fuel injection valve 53 for injecting fuel into the cylinder 11 is provided. In addition to the fuel injection valve 53, a fuel injection valve for injecting fuel into the intake port is provided. May be further provided.

1 Engine (Engine body)
11 Cylinder 100 Engine controller 21 Intake valve 32 Intake valve timing variable mechanism (variable valve mechanism)
43 catalyst device 53 fuel injection valve (fuel supply mechanism)
54 Fuel supply system (fuel supply mechanism)

Claims (4)

An engine body configured to be supplied with fuel containing alcohol having a lower vaporization rate than gasoline under conditions of a specific temperature or lower;
A fuel supply mechanism having a fuel injection valve for injecting the fuel, and configured to supply the fuel injected by the fuel injection valve into a cylinder of the engine body; and
A controller configured to operate the engine body through control of at least the fuel supply mechanism,
The controller compresses the fuel injection started during the intake stroke when the temperature of the engine body is below a predetermined temperature and the operating state of the engine body is in a predetermined high load / high rotation range. Inject the fuel so that it ends during the stroke,
The controller is also a control device for a spark ignition engine that shortens the fuel injection period so that the fuel injection end timing is advanced as the concentration of the alcohol in the fuel is higher. The control device for a spark ignition engine according to claim 1,
A catalyst device connected to the exhaust side of the engine body and configured to purify exhaust gas discharged from the engine body;
When the temperature of the catalyst device is equal to or higher than a predetermined temperature, the controller decreases the fuel injection amount so that the higher the alcohol concentration in the fuel is, the more the fuel injection end timing is advanced. At the same time, a control device for a spark ignition engine that lowers the charging efficiency of the engine body so as to correspond to the decrease in the fuel injection amount. The control device for the spark ignition engine according to claim 2,
A variable valve mechanism that is provided in the engine body and configured to be able to change the opening and closing timing of the intake valve;
The controller is a control device for a spark ignition engine that reduces the charging efficiency by setting the closing timing of the intake valve to a predetermined timing after intake bottom dead center through the variable valve mechanism. In the control device for the spark ignition engine according to any one of claims 1 to 3,
The fuel supply mechanism further includes a fuel pump that increases the pressure of the fuel injected by the fuel injection valve,
The controller sets an injection amount of the fuel to be injected by the fuel injection valve based on at least an operation state of the engine body and a fuel vaporization rate;
The controller is a spark ignition type that reduces the injection amount according to the concentration of the alcohol in the fuel even when the set injection amount is smaller than the maximum injection amount determined by the performance limit of the fuel pump. Engine control device.

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