JP2014206143A - Spark ignition type engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve combustion stability in an engine to which an exotic fuel with an evaporation rate lower than that of gasoline under a temperature condition lower than a specific temperature, is fed.SOLUTION: The engine 1 includes: an oil storage part 23a that is communicated to a crankcase 12a and stores engine oil; a PCV hose 59 for leading a blow-by gas from the crankcase 12a to a surge tank 55a; and an engine controller 100. The engine controller 100 increases an effective compression ratio of the engine 1 when the amount of ethanol that is evaporated in the oil storage part 23a and flows into the surge tank 55a via the PCV hose 59 is large, relative to when the amount of ethanol that flows into the surge tank 55a via the PCV hose 59 is small.

Description

  The technology disclosed herein relates to a spark ignition engine.

  In recent years, biofuels have attracted attention from the viewpoint of environmental issues such as global warming, and gasoline and bioethanol, for example bioethanol, are mixed at any mixing ratio from E25, which is 25% ethanol mixed with gasoline, to E100, which is 100% ethanol. FFVs (Flexible Fuel Vehicles) that can travel with the fuel thus produced have been put into practical use.

  Since ethanol and gasoline have different vaporization characteristics, FFV requires control in consideration of the vaporization characteristics of ethanol. Specifically, ethanol has a lower vaporization rate than gasoline at low temperatures. Therefore, the higher the ethanol concentration, the worse the fuel vaporization performance and the lower the combustion stability. This problem is particularly serious when using E100 containing water (for example, E100 containing about 5% of water) whose water has not been sufficiently removed during the ethanol purification process.

  For example, the FFV disclosed in Patent Document 1 has a sub-tank that stores fuel with high gasoline concentration and excellent fuel vaporization performance, separately from a main tank that stores fuel supplied to an engine during normal traveling. Provided. When starting the engine or idling, fuel with a high gasoline concentration is supplied from the sub tank to the engine to improve startability and stability during idling.

  Further, the FFV disclosed in Patent Document 2 increases the fuel pressure of the fuel injected into the cylinder as the operating condition is such that the fuel is less likely to vaporize. This refines the fuel and promotes vaporization.

JP 2010-133288 A JP 2010-037968 A

  Thus, in an engine that is supplied with special fuel having a lower vaporization rate than gasoline under conditions below a specific temperature, the fuel supplied to the combustion chamber is not available under operating conditions that are disadvantageous to vaporization, such as during cold weather. May remain in a burning and liquid state. This unburned fuel drops from the combustion chamber to the crank chamber and is mixed into the engine oil in the oil pan.

  The special fuel in the oil pan is difficult to vaporize at low temperatures and remains mixed in the engine oil, but when the temperature of the special fuel exceeds its boiling point, the special fuel evaporates all at once. At that time, the special fuel contains the surrounding engine oil in a state of being atomized.

  Thus, the evaporated special fuel is guided from the crank chamber to the intake passage through the blow-by passage, and finally introduced into the combustion chamber.

  In other words, in an engine supplied with a special fuel having a lower vaporization rate than gasoline under a specific temperature or lower, engine oil is introduced into the combustion chamber via the special fuel evaporated in the crank chamber. Engine oil is not preferable from the viewpoint of combustion stability.

  The technology disclosed herein has been made in view of such a point, and the purpose thereof is to stabilize combustion in an engine supplied with special fuel having a lower evaporation rate than gasoline under a specific temperature or lower. It is to improve the performance.

  The technology disclosed herein communicates with an engine body configured to be supplied with a fuel containing a special fuel having a lower vaporization rate than gasoline under a specific temperature or lower, and a crank chamber of the engine body. A spark ignition engine comprising: a storage unit for storing engine oil; a blow-by passage for guiding blow-by gas in the crank chamber to an intake passage provided in the engine body; and a control unit for controlling operation of the engine body. When the special fuel evaporates in the reservoir and flows into the intake passage via the blow-by passage is large, the special fuel flowing into the intake passage via the blow-by passage is the target. It is assumed that the effective compression ratio of the engine body is increased as compared with the case where the amount is small.

  Here, the “special fuel having a lower vaporization rate than gasoline under a state of a specific temperature or less” is, for example, a single component fuel, and specifically, an alcohol such as ethanol or methanol can be exemplified. As a specific example of the alcohol, a biological alcohol such as bioethanol made from sugar cane may be used.

  The “fuel containing special fuel” includes both a fuel obtained by mixing a special fuel and other substances (for example, gasoline) and a fuel containing only a special fuel. When special fuel is ethanol, “fuel containing special fuel” is, for example, gasoline and ethanol mixed in any mixing ratio, from E25 where gasoline is mixed with 25% to E100 where ethanol is 100%. Fuel may be included. This “fuel including special fuel” may include combustion in which special fuel and water are mixed. Therefore, E100 containing about 5% of water is also included in the “fuel including special fuel”.

  According to this configuration, when the amount of special fuel that evaporates in the reservoir and flows into the intake passage via the blow-by passage is larger than that when the special fuel that flows into the intake passage via the blow-by passage is less, The effective compression ratio is increased. When there is much special fuel that evaporates in the reservoir and flows into the intake passage via the blow-by passage, more engine oil is introduced into the combustion chamber via the special fuel. In such a case, since the effective compression ratio is increased, the cylinder pressure and temperature in the compression stroke increase. As a result, deterioration of combustion stability can be suppressed even when a large amount of engine oil is introduced into the combustion chamber.

  On the other hand, when the amount of special fuel flowing into the intake passage via the blow-by passage is small, the effective compression ratio is low. Thereby, pump loss can be reduced and fuel consumption can be improved.

  The spark ignition engine further includes an intake valve that opens and closes an intake port provided in the engine body, and the control unit determines when the intake valve is closed at a partial load equal to or lower than a predetermined load. When the amount of the special fuel flowing into the intake passage through the blow-by passage is large, the time is set later than the point, compared with the case where the amount of the special fuel flowing into the intake passage through the blow-by passage is small. Thus, the closing timing of the intake valve may be close to the intake bottom dead center.

  Here, “partial load equal to or less than a predetermined load” means, for example, a load other than a high load including a fully open load, and when the engine load region is divided, a high load region including a fully open load is determined. Also means when the engine main body is operating at least in the low load region. For example, “at the time of partial load equal to or less than a predetermined load” may be when the engine main body is in an operating state in a low load region when the engine load region is divided into a low load region and a high load region. Then, the engine load region may be, for example, when the engine main body is operating in a low / medium load region obtained by dividing the engine load region into a low load region, a medium load region, and a high load region.

  According to this configuration, the effective compression ratio can be increased by bringing the closing timing of the intake valve closer to the intake bottom dead center from the delayed closing timing. According to this configuration, the adjustment of the effective compression ratio can be easily realized, and the adjustment of the effective compression ratio can be realized even in a relatively high speed operation region.

  That is, the effective compression ratio can be adjusted only by adjusting the closing timing of the intake valve, compared to a configuration in which the effective compression ratio is mechanically variable by connecting the crankshaft and the connecting rod via a link mechanism. Therefore, it is possible to easily increase the effective compression ratio with good responsiveness. In addition, the increase in the effective compression ratio may be such that the closing timing of the intake valve is set to an early closing timing, and then the closing timing is brought closer to the intake bottom dead center. However, in the high-speed operation range, the influence of the intake inertia is large, and if the valve closing timing is too short, the amount of air charged into the cylinder will decrease, so the valve closing timing of the intake valve should be set to early closing. Is unsuitable. On the other hand, when the closing timing of the intake valve is set to the late closing timing, the period of sucking air can be made as long as possible even in the high rotation operation region. That is, if the configuration is such that the closing timing of the intake valve is set to the late closing timing, the effective compression ratio can be adjusted while performing an appropriate operation even in the high-rotation operation region.

  Further, since the required output is not large at the time of partial load, there is no problem even if the effective compression ratio is lowered by closing the intake valve late. In other words, when the output is not so required, the effective compression ratio is reduced to reduce the pump loss. On the other hand, when there is a lot of engine oil flowing in with the evaporated special fuel, the effective compression ratio is improved to improve the combustion stability. . Thereby, the overall fuel efficiency can be improved.

  According to the spark ignition engine, combustion stability can be improved.

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 graph which shows the change of the valve closing timing of an intake valve with respect to engine water temperature. It is a graph which shows the change of the deficiency rate of oxygen concentration with respect to the driving cycle of an engine. It is a graph which shows the change of the effective compression ratio with respect to the evaporation amount of ethanol.

  Hereinafter, exemplary embodiments will be described in detail with reference to the drawings.

  Hereinafter, an embodiment of a direct injection engine will be described based on 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. This engine system includes a high compression ratio engine 1 having a geometric compression ratio of 12 to 20 (for example, 14).

  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% (ie, E25) to 100% (ie, E100) of ethanol. Although not shown in the figure, this vehicle has only the fuel (main tank) for storing the fuel, and stores a fuel having a high gasoline concentration separately from the main tank, like the conventional FFV. Does not have a sub tank. However, a sub tank may be provided.

  The engine 1 includes a cylinder block 12, a cylinder head 13 placed on the cylinder block 12, and an oil pan 23 provided below the cylinder block 12. 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. A crank chamber 12 a is formed by the lower part of the cylinder block 12 and the oil pan 23. An oil reservoir 23a for storing engine oil is formed inside the oil pan 23. The oil reservoir 23a and the crank chamber 12a communicate with each other. The oil reservoir 23a is an example of a reservoir.

  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 a so-called roof shape is formed in which these inclined surfaces are put against each other. It is a 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 constituted by an electric phase variable mechanism (Variable Valve Timing: VVT) capable of continuously changing the phase of the intake camshaft 31 within a predetermined angle range, The variable valve timing mechanism 42 is an electric phase variable mechanism capable of continuously changing the phase of the exhaust camshaft 41 within a predetermined angle range. 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 VVT may be a hydraulic type or a mechanical type.

  The spark plug 51 is attached to the cylinder head 13 by a known structure such as a screw. 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 that directly injects fuel into the cylinder 11, and the tip of the fuel injection valve 53 is located below the intake port 18 in the vertical direction and in the cylinder 11 in the horizontal direction. It is located in the center and faces the combustion chamber 17. 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.

  The fuel supply system 54 includes a high-pressure pump (fuel pump) that boosts the fuel and supplies the fuel to the fuel injection valve 53, piping and hoses that supply fuel from the fuel tank to the high-pressure pump, and the fuel injection valve 53. And an electric circuit to be driven. The fuel pump is driven by the engine 1 in this example. The fuel pump may be an electric pump. 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 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 in the throttle body 56, and 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.

  A downstream end of a PCV (Positive Crankcase Ventilation) hose 59 is connected to the surge tank 55a. The upstream end of the PCV hose 59 is connected to the engine block 12 via a PCV valve 59a. The PCV hose 59 communicates with the crank chamber 12 a of the engine block 12. The PCV valve 59a allows inflow of blow-by gas from the crank chamber 12a to the PCV hose 59, while preventing inflow of gas from the PCV hose 59 to the crank chamber 12a. Thus, the blow-by gas in the crank chamber 12a flows into the surge tank 55a through the PCV hose 59. The PCV hose 59 is an example of a blow-by passage. The surge tank 55a is an example of an intake passage.

The exhaust port 19 communicates with a passage in the exhaust pipe 61 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. The exhaust pipe 61 is provided with a linear O ₂ sensor 79. The linear O ₂ sensor 79 detects the air-fuel ratio of the air-fuel mixture based on the oxygen concentration in the exhaust gas.

  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 is an example of a control unit.

  The control unit may be realized by hard logic. The control unit may be composed of one element or may be physically composed of a plurality of elements. When configured by a plurality of elements, one control may be realized by a plurality of elements.

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 a linear O ₂ sensor. Various inputs such as air-fuel ratio from 79 are received. 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, and the higher the ethanol concentration of the fuel, the richer the theoretical air-fuel ratio. When there is unburned oxygen in the exhaust gas under the operating conditions, it can be determined that the ethanol concentration of the fuel is higher than expected. Using this fact, the engine controller 100 estimates the ethanol concentration of the fuel based on the oxygen concentration in the exhaust gas detected by the linear O ₂ sensor 79. Instead of estimating the ethanol concentration of the fuel, a sensor that detects the ethanol concentration of the fuel may be provided.

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 that has contributed to combustion based on the air-fuel ratio of the air-fuel mixture and the detection value of the linear O ₂ sensor 79, and calculates the calculated fuel weight and the fuel injection of the fuel injection valve 53. The vaporization rate is calculated from the 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, the gasoline can be vaporized even when the temperature state of the engine 1 is relatively low to form a combustible mixture.

  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, below the specified temperature, the amount of ethanol distilled is lower than the amount of gasoline distilled. On the other hand, when the specified temperature is exceeded, the amount of ethanol distilled is less than that of gasoline. It becomes higher than the amount of distillation. Therefore, in a cold state where the temperature state of the engine 1 is a predetermined temperature or lower (for example, the water temperature is about 20 ° C. or lower), the fuel containing ethanol has a lower vaporization rate than gasoline. Thus, when the engine 1 is in a cold 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, the fuel vaporization rate changes depending on the temperature state of the engine 1 and the ethanol concentration of the fuel. Therefore, the engine controller 100 can obtain the target vaporized fuel amount in accordance with the engine load or the like. A fuel amount increase correction is performed on the set base fuel amount in accordance with the fuel vaporization rate. That is, as the fuel vaporization rate is lower, the amount of fuel injected by the fuel injection valve 53 is increased.

  The engine controller 100 adjusts the effective compression ratio of the engine 1 according to the temperature of the engine 1 particularly in the partial load operation region. The engine controller 100 determines the temperature of the engine 1 based on the engine water temperature. FIG. 3 is a diagram showing the relationship of the closing timing of the intake valve 21 with respect to the engine water temperature. The engine controller 100 sets the closing timing of the intake valve 21 to a timing later than the intake bottom dead center. The lower the engine water temperature, that is, the lower the temperature of the engine 1, the more the intake valve 21 is closed. The timing is advanced. More specifically, the engine controller 100 advances the valve closing timing of the intake valve 21 stepwise as the engine water temperature decreases. By advancing the valve closing timing of the intake valve 21, the effective compression ratio increases, and the pressure and temperature in the cylinder 11 during the compression stroke increase. As described above, the lower the temperature of the engine 1, the lower the ethanol vaporization rate and the worse the combustion stability. On the other hand, the combustion stability can be improved by increasing the effective compression ratio as the engine water temperature is lower, that is, as the temperature of the engine 1 is lower. In addition, since the temperature in the cylinder 11 is increased by increasing the effective compression ratio, the vaporization of ethanol can be promoted. In this respect as well, the combustion stability can be improved. On the other hand, when the engine water temperature is high, the closing timing of the intake valve 21 is set relatively late, and the effective compression ratio is low. In the partial load operation region, since a very large output is not required, the effective compression ratio can be lowered, thereby reducing pump loss and improving fuel efficiency.

  In addition, the engine controller 100 adjusts the effective compression ratio of the engine 1 according to the amount of ethanol that evaporates in the crank chamber 12a and flows into the surge tank 55a via the PCV hose 59.

  Specifically, under conditions where the vaporization rate is low as in the cold state, some ethanol remains in the combustion chamber 17 in a liquid state without being vaporized. Since liquid ethanol is difficult to burn, most of the liquid ethanol remains in the combustion chamber 17 unburned. The remaining ethanol is dropped into the crank chamber 12a and mixed into the engine oil in the oil pan 23. When the temperature of the engine oil is relatively low, since the temperature of ethanol does not reach the boiling point, it exists in the engine oil as a liquid. However, when the temperature of the engine oil rises according to the operation of the engine 1 and the temperature of ethanol reaches the boiling point, the ethanol evaporates all at once. This evaporated ethanol (hereinafter also referred to as “evaporated ethanol”) contains the surrounding engine oil in a finely divided state. The evaporated ethanol flows out from the crank chamber 12a through the PCV hose 59 as blow-by gas and flows into the surge tank 55a. Thereafter, ethanol is supplied to the combustion chamber 17 via the intake manifold 55. Thus, the atomized engine oil is introduced into the combustion chamber 17 through the evaporated ethanol. Since engine oil is not preferable from the viewpoint of combustion stability, combustion stability deteriorates as the amount of engine oil increases. The amount of engine oil introduced into the combustion chamber 17 increases as the amount of evaporated ethanol flowing into the surge tank 55a via the PCV hose 59 increases.

In contrast, the engine controller 100 increases the effective compression ratio of the engine 1 as the amount of evaporated ethanol flowing into the surge tank 55a via the PCV hose 59 increases. Specifically, the engine controller 100 increases the effective compression ratio of the engine 1 when the amount of evaporated ethanol flowing into the surge tank 55a via the PCV hose 59 becomes a predetermined value or more. The engine controller 100 determines whether the amount of evaporated ethanol flowing into the surge tank 55a via the PCV hose 59 is equal to or greater than a predetermined value based on the oxygen concentration from the linear O ₂ sensor 79. That is, the engine controller 100 operates the engine 1 with the air amount, air-fuel ratio, and fuel amount according to the output request. In this state, when the evaporated ethanol in the crank chamber 12a is introduced into the combustion chamber 17, the amount of fuel in the combustion chamber 17 becomes larger than the desired amount of fuel, and the combustion chamber 17 becomes deficient in oxygen. As a result, the linear O ₂ sensor 79 outputs an output value indicating that the air-fuel ratio is on the rich side, that is, the oxygen concentration is insufficient. The engine controller 100 increases the effective compression ratio of the engine 1 when the oxygen concentration deficiency rate exceeds a predetermined value.

  FIG. 4 shows the change in the oxygen concentration deficiency with respect to the engine operating cycle. Here, the oxygen concentration deficiency rate is the ratio of the oxygen concentration deficient to the oxygen concentration realizing the stoichiometric air-fuel ratio. For example, if the operation of the engine 1 is started from a state where ethanol is mixed in the oil pan 23, the ethanol in the engine oil does not evaporate so much until the temperature of the engine oil rises as shown in FIG. Therefore, the oxygen concentration is close to the target value. When engine oil continues to run for a while and the engine oil rises, ethanol starts to evaporate, and the evaporated ethanol is introduced into the combustion chamber 17 via the PCV hose 59, the surge tank 55a, and the intake passage 55b. As a result, the oxygen concentration becomes insufficient. As the evaporated ethanol increases, the oxygen concentration deficiency gradually increases. When all the ethanol in the engine oil is evaporated, the amount of evaporated ethanol introduced into the combustion chamber 17 is also gradually reduced, and the oxygen concentration deficiency rate is gradually reduced. Eventually, the oxygen concentration matches the target value.

  Here, the engine controller 100 increases the effective compression ratio by advancing the closing timing of the intake valve 21 when the oxygen concentration deficiency rate exceeds a predetermined value. A large oxygen concentration deficiency indicates a large amount of evaporated ethanol. That is, the engine controller 100 adjusts the effective compression ratio according to the amount of ethanol evaporation, as shown in FIG. Specifically, the engine controller 100 increases the effective compression ratio when the ethanol evaporation amount exceeds a predetermined value. Since ethanol evaporates when the temperature of the engine 1 is high, as seen in FIG. 1, the valve closing timing of the intake valve 21 is advanced in a region where the engine water temperature is high and the closing timing of the intake valve 21 is set to the latest. It is adjusted to the corner side (see the broken line in FIG. 1). The engine controller 100 adjusts the closing timing of the intake valve 21 to the retard side to lower the effective compression ratio when the oxygen concentration deficiency rate is less than a predetermined value.

  Since evaporated ethanol contains engine oil, an increase in the amount of evaporated ethanol in the combustion chamber 17 means an increase in the amount of engine oil in the combustion chamber 17 and, in turn, deterioration in combustion stability. means. On the other hand, since the effective compression ratio is set high when the amount of evaporated ethanol introduced into the combustion chamber 17 is large, it is possible to suppress deterioration in combustion stability due to an increase in engine oil.

  On the other hand, when the amount of evaporated ethanol introduced into the combustion chamber 17 is small, the introduction of engine oil into the combustion chamber 17 is also small. Therefore, by reducing the effective compression ratio, the pump loss is reduced and the fuel efficiency is improved. be able to.

  Therefore, according to the embodiment, the engine 1 is configured to be supplied with a special fuel having a lower vaporization rate than gasoline under the condition of a specific temperature or lower, specifically, a fuel containing ethanol. The engine 1 communicates with the crank chamber 12a, and stores an oil reservoir 23a that stores engine oil, a PCV hose 59 that guides the blow-by gas in the crank chamber 12a to the surge tank 55a, and an engine controller that controls the operation of the engine 1. 100. The engine controller 100 evaporates in the oil reservoir 23a, and when there is a large amount of ethanol flowing into the surge tank 55a via the PCV hose 59, the ethanol flowing into the surge tank 55a via the PCV hose 59 The effective compression ratio of the engine 1 is made higher than when it is small.

  According to this configuration, the ethanol that remains unburned in the combustion chamber 17 and remains in a liquid state is dropped into the crank chamber 12a and mixed into the engine oil in the oil reservoir 23a. Ethanol mixed in the engine oil evaporates as the temperature rises and fills the crank chamber 21. When the ethanol evaporates, the surrounding engine oil is contained in a finely divided state. The evaporated ethanol in the crank chamber 12a flows into the surge tank 55a through the PCV hose 59 as blow-by gas. Thereafter, the evaporated ethanol is introduced into the combustion chamber 17 via the intake passage 55b. Since a large amount of evaporated ethanol introduced into the combustion chamber 17 means that a lot of atomized engine oil is introduced into the combustion chamber 17, the effective compression ratio of the engine 1 is increased in such a case. Even under operating conditions that are unfavorable for combustion stability because of a large amount of atomized engine oil, deterioration of combustion stability can be suppressed by increasing the effective compression ratio.

  On the other hand, when less evaporated ethanol is introduced into the combustion chamber 17, less engine oil is introduced into the combustion chamber 17. Therefore, even if the effective compression ratio is lowered, the influence on the combustion stability is small. Furthermore, since the required output is small in the partial load operation region, there is no problem even if the effective compression ratio is lowered. Rather, by reducing the effective compression ratio, it is possible to reduce pump loss and improve fuel efficiency.

  The engine 1 further includes an intake valve 21 that opens and closes the intake port 18, and the engine controller 100 sets the closing timing of the intake valve 21 later than the intake bottom dead center at the time of partial load equal to or lower than a predetermined load. When the amount of ethanol flowing into the surge tank 55a via the PCV hose 59 is large, the intake air is less than when the amount of ethanol flowing into the surge tank 55a via the PCV hose 59 is small. The valve closing timing of the valve 21 is brought close to the intake bottom dead center.

  That is, increasing the effective compression ratio described above is realized by bringing the closing timing of the intake valve 21 closer to the intake bottom dead center.

  Advancing the closing timing of the intake valve 21 makes it possible to adjust the effective compression ratio easily and with high responsiveness, compared to a configuration in which the effective compression ratio of the engine 1 is mechanically changed by the configuration of the crank rod and connecting rod. can do.

  Further, by adjusting the valve closing timing of the intake valve 21 in the region after the intake bottom dead center, it is possible to adjust the effective compression ratio while realizing appropriate operation even in the high rotation operation region. it can. In other words, if the closing timing of the intake valve 21 is set earlier than the intake bottom dead center, the period during which the intake valve 21 is opened is shortened, and in a high-speed operation region where the influence of intake inertia is large, It becomes difficult to fully fill. In contrast, when the closing timing of the intake valve 21 is adjusted in a region behind the intake bottom dead center, the period during which the intake valve 21 is open can be lengthened, and the period during which intake air is sucked is ensured. be able to.

  As described above, when a large amount of evaporated ethanol is introduced into the combustion chamber 17, the valve closing timing of the intake valve 21 can be advanced to improve combustion stability, and the evaporated ethanol introduced into the combustion chamber 17 can be increased. When the number is low, the closing timing of the intake valve 21 can be closed late to improve fuel efficiency.

<< Other Embodiments >>
As described above, the embodiment has been described as an example of the technique disclosed in the present application. However, the technology in the present disclosure is not limited to this, and can also be applied to an embodiment in which changes, replacements, additions, omissions, and the like are appropriately performed. Moreover, it is also possible to combine each component demonstrated by the said embodiment and it can also be set as new embodiment. In addition, among the components described in the accompanying drawings and detailed description, not only the components essential for solving the problem, but also the components not essential for solving the problem in order to exemplify the above technique. May also be included. Therefore, it should not be immediately recognized that these non-essential components are essential as those non-essential components are described in the accompanying drawings and detailed description.

  About the said embodiment, it is good also as following structures.

  Although the above-described configuration is FFV, the technology disclosed herein can be widely applied to vehicles equipped with an engine to which fuel containing alcohol is supplied, even if not FFV.

  In the above embodiment, an example in which ethanol is used as the special fuel has been described. However, the special fuel may be a substance other than that. For example, the special fuel may be an alcohol such as methanol, or an oil such as edible oil or industrial oil. The fuel mixed with the special fuel is not limited to gasoline.

In the embodiment, it is determined whether the amount of evaporated ethanol flowing into the surge tank 55a via the PCV hose 59 is greater than or equal to a predetermined value based on the oxygen concentration from the linear O ₂ sensor 79. However, the determination of the amount of evaporated ethanol flowing through the PCV hose 59 is not limited to the determination based on the oxygen concentration from the linear O ₂ sensor 79.

  In the above embodiment, when the oxygen concentration deficiency rate exceeds a predetermined value, that is, when the amount of evaporated ethanol flowing into the surge tank 55a via the PCV hose 59 exceeds a predetermined value, the effective compression ratio of the engine 1 is uniformly set. To a predetermined value. However, the present invention is not limited to this, and the effective compression ratio of the engine 1 may be changed according to the amount of evaporated ethanol flowing into the surge tank 55a via the PCV hose 59. That is, as the amount of evaporated ethanol flowing into the surge tank 55a via the PCV hose 59 increases, the effective compression ratio of the engine 1 increases, that is, the advance amount of the closing timing of the intake valve 21 set to be closed slowly. May be increased.

  As described above, the technology disclosed herein is useful for an engine that is supplied with a special fuel having a lower vaporization rate than gasoline under a condition below a specific temperature.

1 Engine (Engine body)
12a Crank chamber 18 Intake port 21 Intake valve 23a Oil reservoir (reservoir)
55a Surge tank (intake passage)
59 PCV hose (blow-by passage)
100 Engine controller (control unit)

Claims (2)

An engine body configured to be supplied with a fuel including a special fuel having a lower vaporization rate than gasoline under a state of a specific temperature or lower;
A storage section that communicates with a crank chamber of the engine body and stores engine oil;
A blow-by passage for guiding the blow-by gas in the crank chamber to an intake passage provided in the engine body;
A control unit for controlling the operation of the engine body,
When the special fuel evaporates in the reservoir and flows into the intake passage via the blow-by passage is large, when the special fuel flows into the intake passage through the blow-by passage is small A spark ignition engine that increases the effective compression ratio of the engine body. The spark ignition engine according to claim 1,
An intake valve that opens and closes an intake port provided in the engine body;
The control unit sets the closing timing of the intake valve to a timing later than the intake bottom dead center at a partial load equal to or less than a predetermined load, and the special fuel that flows into the intake passage via the blow-by passage A spark ignition engine in which the closing timing of the intake valve is brought closer to the intake bottom dead center when there is a large amount of fuel than when the special fuel flows into the intake passage through the blow-by passage is small.

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