JP5018660B2 - Internal combustion engine start control system - Google Patents

Description

  The present invention relates to start control of an internal combustion engine capable of changing a compression ratio.

Conventionally, when starting an internal combustion engine, a technique has been proposed in which the compression ratio is lowered at the beginning of the start and the compression ratio is increased after the engine speed exceeds a predetermined value (see, for example, Patent Document 1).
JP 2002-276446 A JP 2007-146701 A JP 2003-328794 A JP 2005-30253 A JP 2004-92639 A

  An object of the present invention is to provide a technique capable of further improving drivability and emission at the time of starting an internal combustion engine capable of changing the compression ratio.

The present invention employs the following means in order to solve the above-described problems. That is, the present invention provides an internal combustion engine start control system capable of changing a compression ratio.
Low compression means for reducing the compression ratio during a period from the start of the internal combustion engine until the engine speed exceeds a predetermined complete explosion determination value;
A calculation means for calculating a rising speed of the engine speed during the period;
When the ascending speed calculated by the calculating means is below a predetermined lower limit value, correcting means for increasing the compression ratio from the compression ratio set by the low compression means;
I was prepared to.

  The complete explosion determination value here is a value corresponding to the engine speed when the fuel is combusted in all the cylinders of the internal combustion engine or the idle speed (first idle speed) after the start of the internal combustion engine is completed.

  As a method for starting an internal combustion engine capable of changing the compression ratio, the method described in Patent Document 1 is known. According to this method, the compression ratio is set low during the period from the start of cranking until the engine speed reaches the target cranking speed, and after the engine speed exceeds the target cranking speed, the compression ratio is high. Is set. The target cranking speed here is an engine speed (for example, about 200 rpm) at which the starter motor can stably rotate the engine output shaft (crankshaft).

  If the compression ratio of the internal combustion engine is lowered during the period from the start of cranking until the engine speed reaches the target cranking speed, the load applied to the starter motor is reduced. As a result, the starter motor has an advantage that the engine speed can be increased to the target cranking speed at an early stage.

  On the other hand, if the compression ratio is increased after the engine speed reaches the target cranking speed, the compression end temperature (the temperature in the cylinder when the piston is located at the compression top dead center) increases, so the fuel vaporization occurs. -There are advantages that atomization is promoted and the ignitability of fuel is enhanced.

  By the way, if the compression ratio is inadvertently increased after the engine speed reaches the target cranking speed, knocking may occur. That is, the amount of fuel supplied into the cylinder when the internal combustion engine is started is comparable to the amount of fuel when the internal combustion engine is operating at a high load. For this reason, when the octane number of the fuel is lower than the assumed value or when the intake air temperature at the start is high, knocking is likely to occur due to the increase in the compression ratio.

  Therefore, the internal combustion engine start control system according to the present invention sets the compression ratio to be low during the period from the start of the internal combustion engine (start of cranking) until the engine speed exceeds the complete explosion determination value. The compression ratio at that time may be constant, but from the start of cranking until the engine speed reaches the target cranking speed, the compression ratio is lowered as much as possible mechanically, and the engine speed is set to the target crank speed. After reaching the ranking rotational speed, the compression ratio may be lowered within a range in which fuel ignitability can be secured.

  If the compression ratio is kept low after the engine speed reaches the target cranking speed (especially after the first explosion), the fuel octane number is higher than the expected value or the intake air temperature at startup is low. For example, the start period may be prolonged or the internal combustion engine may stop (engine stall).

  On the other hand, the internal combustion engine start control system of the present invention has a predetermined lower limit for the increase speed of the engine speed during the period from the start of the internal combustion engine until the engine speed exceeds the complete explosion determination value. If it falls below, the compression ratio is made higher than the previous compression ratio. That is, the internal combustion engine start control system according to the present invention provides a compression ratio only when the increase speed of the engine speed falls below the lower limit value during the period from the start of the start of the internal combustion engine until the engine speed exceeds the complete explosion determination value. I tried to increase.

  According to this invention, it is possible to suppress the occurrence of knocking while suppressing an increase in the starting period and deterioration of emissions. As a result, it is possible to further improve the drivability and emission at the start.

  By the way, when the fuel burns (complete explosion) in all the cylinders of the internal combustion engine, the engine speed temporarily rises (blows up) to the complete explosion determination value or more. That is, when the internal combustion engine has completed a complete explosion, the engine speed first rises to a complete explosion determination value or more. Subsequently, the engine speed decreases after reaching the peak value. Thereafter, the engine speed converges to a steady state (for example, the first idle speed).

  In the above-described blowing process, the behavior of the fuel adhering to the wall surface (fuel adhering to the intake port, the cylinder bore wall surface, the piston, etc.) becomes unstable. For example, during the period in which the engine speed increases (hereinafter referred to as “rotational increase period”), the wall surface adhering fuel may rapidly decrease. In such a case, the air-fuel ratio during a period in which the engine speed decreases from the peak value (hereinafter referred to as “rotation reduction period”) becomes excessively high, and the internal combustion engine may misfire.

  On the other hand, a method for increasing the fuel injection amount during the rotation reduction period can be considered. However, since it is difficult to accurately specify the amount of decrease in the wall-attached fuel, there is a risk that the fuel injection amount will be excessive or insufficient.

  Therefore, the internal combustion engine start control system according to the present invention further includes high compression means for making the compression ratio after the engine speed exceeds the complete explosion determination value higher than the compression ratio before that. Good.

According to the high compression means described above, the compression ratio when the engine speed increases, preferably the compression ratio during the rotation reduction period, is higher than the previous compression ratio. As a result, the compression end temperature rises, making it difficult for the internal combustion engine to misfire. Accordingly, misfire of the internal combustion engine can be avoided even when the air-fuel ratio during the rotation reduction period is significantly increased.

  According to the knowledge of the inventor of the present application, the behavior of the wall surface adhering fuel amount during the rotation increasing period and / or the rotation decreasing period becomes more unstable as the peak value becomes higher. Therefore, the high compression means may increase the compression ratio in the rotation reduction period as the peak value increases.

  In the present invention, the compression ratio of the internal combustion engine includes a combustion chamber volume (volume in the cylinder when the piston is located at the top dead center) and a volume inside the cylinder when the piston is located at the bottom dead center. And a method of changing the ratio (effective compression ratio) between the combustion chamber volume and the volume in the cylinder when the intake valve is closed.

  ADVANTAGE OF THE INVENTION According to this invention, at the time of the start of the internal combustion engine which can change a compression ratio, the drivability and emission at the time of start can be improved further.

  Hereinafter, specific embodiments of the present invention will be described with reference to the drawings. The dimensions, materials, shapes, relative arrangements, and the like of the components described in the present embodiment are not intended to limit the technical scope of the invention to those unless otherwise specified.

  FIG. 1 is a diagram showing a schematic configuration of an internal combustion engine to which the present invention is applied. An internal combustion engine 1 shown in FIG. 1 is a four-stroke cycle spark ignition type internal combustion engine (gasoline engine) having a plurality of cylinders 2.

  The cylinder 2 of the internal combustion engine 1 is connected to the intake passage 30 through the intake port 3 and is connected to the exhaust passage 40 through the exhaust port 4.

  The intake port 3 is provided with a fuel injection valve 5 that injects fuel into the cylinder 2. The intake passage 30 is provided with a throttle valve 6 that controls the amount of air flowing through the intake passage 30. An intake pressure sensor 7 that measures the pressure (intake pressure) in the intake passage 30 is provided in the intake passage 30 downstream of the throttle valve 6. An air flow meter 8 that measures the amount of air flowing through the intake passage 30 is provided in the intake passage 30 upstream of the throttle valve 6.

  On the other hand, an exhaust purification device 9 is disposed in the exhaust passage 40. The exhaust purification device 9 includes a three-way catalyst, an NOx storage reduction catalyst, and the like, and purifies exhaust when it is in a predetermined activation temperature range.

  Further, the internal combustion engine 1 is provided with an intake valve 10 that opens and closes an open end of the intake port 3 facing the cylinder 2 and an exhaust valve 11 that opens and closes an open end of the exhaust port 4 facing the cylinder 2. The intake valve 10 and the exhaust valve 11 are driven to open and close by an intake camshaft 12 and an exhaust camshaft 13, respectively.

  A spark plug 14 for igniting the air-fuel mixture in the cylinder 2 is disposed at the upper part of the cylinder 2. A piston 15 is slidably inserted into the cylinder 2. The piston 15 is connected to the crankshaft 17 via a connecting rod 16.

A crank position sensor 18 that detects a rotation angle of the crankshaft 17 is disposed in the vicinity of the crankshaft 17. Furthermore, a water temperature sensor 19 for measuring the temperature of the cooling water circulating through the internal combustion engine 1 is attached to the internal combustion engine 1.

  The internal combustion engine 1 is provided with a variable compression ratio mechanism 21. The variable compression ratio mechanism 21 is a mechanism that changes the mechanical compression ratio or the effective compression ratio of the internal combustion engine 1. As such a variable compression ratio mechanism 21, (1) a mechanism that changes the mechanical compression ratio of the internal combustion engine 1 by changing the relative position between the crankcase and the cylinder block, and (2) the length of the connecting rod is changed. By doing so, a mechanism for changing the mechanical compression ratio of the internal combustion engine 1 or (3) a mechanism for changing the closing timing of the intake valve (variable valve mechanism) can be exemplified.

  The internal combustion engine 1 configured as described above is provided with an ECU 20. The ECU 20 is an electronic control unit that includes a CPU, a ROM, a RAM, and the like. The ECU 20 is electrically connected to various sensors such as the intake pressure sensor 7, the air flow meter 8, the crank position sensor 18, and the water temperature sensor 19 described above, and can input measurement values of the various sensors.

  The ECU 20 electrically controls the fuel injection valve 5, the throttle valve 6, the spark plug 14, and the variable compression ratio mechanism 21 based on the measured values of the various sensors described above. For example, the ECU 20 executes known control such as fuel injection control and ignition control, and also executes start-up control that is the gist of the present invention.

  Hereinafter, start control in the present embodiment will be described.

  FIG. 2 is a graph showing changes in the engine speed Ne when the internal combustion engine 1 is started. In FIG. 2, when cranking is started (starter motor is operated) (t1 in FIG. 2), the engine speed Ne increases and reaches the target cranking speed Necrank (t2 in FIG. 2).

  If the first explosion occurs in any of the cylinders 2 when the internal combustion engine 1 is rotating at the target cranking speed Necrank (t3 in FIG. 2), the engine speed Ne increases rapidly. When the engine speed Ne increases rapidly, fuel vaporization and atomization are promoted and the in-cylinder pressure and in-cylinder temperature increase, so that the fuel is combusted also in the other cylinders 2.

  When the fuel is combusted (complete explosion) in all the cylinders 2 of the internal combustion engine 1, the engine speed Ne exceeds the complete explosion determination value Nebase and blows up. When the engine speed Ne rises, the ECU 20 performs fuel injection amount reduction correction, ignition timing retardation correction, and the like. Therefore, the engine speed Ne decreases after reaching the peak value Nemax (t4 in FIG. 2). Then, the engine speed Ne converges on the first idle engine speed (equivalent to the complete explosion determination value Nebase in the example shown in FIG. 2) (t5 in FIG. 2).

  In the process as shown in FIG. 2, the ECU 20 controls the variable compression ratio mechanism 21 as follows. First, in the cranking period (period from t1 to t3 in FIG. 2), the ECU 20 controls the variable compression ratio mechanism 21 so that the compression ratio becomes a predetermined minimum compression ratio.

  The minimum compression ratio described above may be the minimum compression ratio that can be realized by the variable compression ratio mechanism 21. However, since the first explosion may be difficult to occur, the compression ratio after the engine speed Ne reaches the target cranking speed Necrank (after t2 in FIG. 2) is slightly higher than the minimum compression ratio. You may do it. The compression ratio at that time is the lowest compression ratio within a range in which the ignitability of the fuel (air-fuel mixture) can be ensured, and is preferably experimentally obtained in advance.

  Thus, if the compression ratio is lowered during the period from t1 to t3 in FIG. 2, the load on the starter motor is reduced. As a result, the engine speed Ne quickly reaches the target cranking speed Necrank.

  Next, in the period from the first explosion occurrence until the engine speed Ne reaches the peak value Nemax (the period from t3 to t4 in FIG. 2), the ECU 20 is similar to the period from t2 to t3 described above. Set the compression ratio low. A period from t3 to t4 in FIG. 2 is a period in which a comparable amount of fuel is supplied into the cylinder 2 during high load operation, and the in-cylinder pressure and the in-cylinder temperature rapidly increase. For this reason, if the compression ratio in the period is inadvertently increased, knocking may occur. On the other hand, if the compression ratio in the period is kept low, occurrence of knocking can be avoided.

  However, when the intake air temperature is very low, or when the octane number of the fuel is higher than the expected value, the ignition performance of the fuel may be deteriorated due to a decrease in the compression ratio. In such a case, the internal combustion engine 1 may stop after the first explosion occurs, or the discharge amount of unburned fuel components may increase.

  Therefore, the ECU 20 increases the compression ratio only when the increase speed of the engine speed Ne falls below the lower limit during the period from t3 to t4.

  Specifically, the ECU 20 first calculates the increasing speed of the engine speed Ne (the increasing amount ΔNe of the engine speed Ne per unit time) based on the measured value of the crank position sensor 18. This calculation process is periodically repeated in the period from t3 to t4.

  Subsequently, the ECU 20 determines whether or not the increase speed ΔNe of the engine speed Ne is smaller than a predetermined lower limit value ΔNemin. The lower limit value ΔNemin corresponds to the lowest value that the increase speed ΔNe of the engine speed Ne can take when the internal combustion engine 1 is started using fuel having a specified octane number, and has been experimentally determined in advance.

  When the increase speed ΔNe of the engine speed Ne is smaller than the lower limit value ΔNemin, the ECU 20 calculates a new target compression ratio by adding a predetermined amount to the previous compression ratio. Then, the ECU 20 controls the variable compression ratio mechanism 21 according to the target compression ratio. The above-mentioned predetermined amount may be a fixed value, but as the difference (ΔNemin−ΔNe) between the increase speed ΔNe of the engine speed Ne and the lower limit value ΔNemin increases and / or the intake air temperature. It may be increased as the value becomes lower.

  When the compression ratio in the period from t3 to t4 is determined in this way, it is possible to avoid the occurrence of knocking while suppressing an increase in the starting period and deterioration of emissions. As a result, it is possible to improve drivability and emission when starting the internal combustion engine 1.

  Note that the ECU 20 may increase the compression ratio ε over time during the period from t3 to t4, regardless of the increase speed ΔNe of the engine speed Ne. In this case as well, it is possible to avoid the occurrence of knocking while suppressing an increase in the starting period and deterioration of emissions.

  In the period (the period from t4 to t5 in FIG. 2) until the engine speed Ne reaches the peak value Nemax and converges to the first idle speed, the ECU 20 starts from the period from t3 to t4 described above. Also increase the compression ratio.

  When the engine revolution speed Ne as described above occurs, the behavior of the fuel adhering to the wall surface (fuel adhering to the intake port, cylinder bore wall surface, piston, etc.) becomes unstable. For example, the fuel adhering to the wall surface may suddenly decrease during the rotation increase period (the period from t3 to t4) until the engine speed Ne reaches the peak value Nemax.

  In such a case, there is a possibility that the inside of the cylinder 2 will be in an excessive air state during the rotation reduction period (period from t4 to t5) until the engine speed Ne decreases from the peak value Nemax to the first idle speed Nebase. There is. If the air in the cylinder 2 becomes excessive during the rotation reduction period, the internal combustion engine 1 may misfire and the engine speed Ne may decrease excessively.

  Therefore, the ECU 20 controls the variable compression ratio mechanism 21 so that the compression ratio during the rotation reduction period is higher than the compression ratio during the rotation increase period. If the compression ratio during the rotation reduction period is increased in this way, the occurrence of misfire can be avoided even if the inside of the cylinder 2 falls into an excessive air state. As a result, an excessive decrease in the engine speed Ne is suppressed, so that deterioration in drivability can be suppressed.

  Hereinafter, the procedure for setting the compression ratio when the internal combustion engine 1 is started will be described with reference to FIG. FIG. 3 is a flowchart showing a compression ratio control routine when the internal combustion engine 1 is started. This routine is stored in advance in the ROM of the ECU 20.

  In the compression ratio control routine of FIG. 3, the ECU 20 first determines in S101 whether or not the internal combustion engine 1 is in the starting period, in other words, whether or not the starter switch is on. If a negative determination is made in S101, the ECU 20 ends the execution of this routine. On the other hand, if an affirmative determination is made in S101, the ECU 20 proceeds to S102.

  In S102, the ECU 20 determines whether or not the engine speed Ne is higher than the target cranking speed Necrank. That is, it is determined whether or not the internal combustion engine 1 is in a state after the first explosion.

  If a negative determination is made in S102 (Ne ≦ Nerank), the ECU 20 proceeds to S103 and sets the target compression ratio ε to the low compression ratio εlow. As the low compression ratio εlow, the above-described minimum compression ratio can be used. The ECU 20 returns to S102 after executing the process of S103.

  If an affirmative determination is made in S102 (Ne> Nerank), the ECU 20 proceeds to S104 and calculates an increase speed ΔNe of the engine speed Ne.

  Subsequently, the ECU 20 proceeds to S105, and determines whether or not the increasing speed ΔNe calculated in S104 is equal to or higher than the lower limit value ΔNemin.

  If a negative determination is made in S105 (ΔNe <ΔNemin), the ECU 20 proceeds to S106, and calculates a new target compression ratio ε by adding a predetermined amount Δε to the low compression ratio εlow. Then, the ECU 20 controls the variable compression ratio mechanism 21 according to the target compression ratio ε. In this case, since the ignitability of the fuel is improved, the stop of the internal combustion engine 1 and the increase in the discharge amount of unburned fuel components are suppressed. The ECU 20 returns to S104 after executing the process of S106.

  On the other hand, when an affirmative determination is made in S105 (ΔNe ≧ ΔNemin), the ECU 20 proceeds to S107. In S107, the ECU 20 determines whether or not the engine speed Ne is equal to or greater than the complete explosion determination value Nebase, in other words, whether or not the internal combustion engine 1 has been completely exploded.

  If a negative determination is made in S107 (Ne <Nebase), the ECU 20 returns to S104 described above. On the other hand, when an affirmative determination is made in S107 (Ne ≧ Nebase), the ECU 20 proceeds to S108.

  In S108, the ECU 20 determines whether or not the peak value Nemax of the engine speed Ne is detected. That is, it is determined whether or not the amount of change in the engine speed Ne per unit time has changed from a positive value to a negative value.

  If a negative determination is made in S108, the ECU 20 repeatedly executes the process of S108 until the peak value Nemax of the engine speed Ne is detected. On the other hand, if a positive determination is made in S108, the ECU 20 proceeds to S109.

  In S109, the ECU 20 sets the target compression ratio ε to the high compression ratio εhigh. At this time, the high compression ratio εhigh is set higher as the peak value Nemax increases. Thus, when the compression ratio in the rotation reduction period is increased, it is possible to suppress the occurrence of misfire even if the inside of the cylinder 2 falls into an excessive air state.

  The ECU 20 proceeds to S110 after executing the process of S109. In S110, the ECU 20 determines whether or not the engine rotational speed Ne is equal to the first idle rotational speed Neidl, in other words, whether or not the engine rotational speed Ne has converged to the first idle rotational speed Neidl.

  If a negative determination is made in S110 (Ne ≠ Neidl), the ECU 20 returns to S109 described above. On the other hand, when an affirmative determination is made in S110 (Ne = Neidl), the ECU 20 ends the execution of this routine. After completing the execution of this routine, the ECU 20 may lower the target compression ratio ε from the above-described high compression ratio εhigh in order to activate the exhaust purification device 9 at an early stage.

  As described above, the ECU 20 executes the compression ratio control routine of FIG. 3 to realize the low compression means, calculation means, correction means, high compression means, and detection means according to the present invention. As a result, drivability and emissions can be improved when the internal combustion engine 1 is started.

  In this embodiment, the internal combustion engine in which the fuel injection valve is disposed in the intake port is taken as an example. However, the fuel injection valve is disposed in the cylinder (that is, disposed in a position where fuel can be directly injected into the cylinder). Of course, it may be an internal combustion engine.

1 is a diagram showing a schematic configuration of an internal combustion engine to which the present invention is applied. It is a figure which shows the change of the engine speed at the time of start-up of an internal combustion engine. 3 is a flowchart showing a compression ratio control routine at the start of the internal combustion engine.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine 2 ... Cylinder 3 ... Intake port 4 ... Exhaust port 5 ... Fuel injection valve 6 ... Throttle valve 7. ....... Intake pressure sensor 8 ... Air flow meter 9 ... Exhaust gas purification device 14 ... Spark plug 15 ... Piston 16 ... Connecting rod 17 ... Crank Shaft 18 ... Crank position sensor 19 ... Water temperature sensor 20 ... ECU
21 ... Variable compression ratio mechanism 30 ... Intake passage 31 ... Air flow control valve 40 ... Exhaust passage

Claims (3)

In an internal combustion engine start control system capable of changing the compression ratio,
Low compression means for reducing the compression ratio during the period from the start of the internal combustion engine until the engine speed exceeds a predetermined complete explosion determination value;
A calculation means for calculating a rising speed of the engine speed during the period;
When the ascending speed calculated by the calculating means is below a predetermined lower limit value, correcting means for increasing the compression ratio from the compression ratio set by the low compression means;
A start control system for an internal combustion engine, comprising:   2. An internal combustion engine start control system according to claim 1, further comprising high compression means for making the compression ratio after the engine speed exceeds the complete explosion determination value higher than the compression ratio before that. In Claim 2, further comprising a detecting means for detecting a peak value reached after the engine speed exceeds the complete explosion determination value,
The internal combustion engine start control system, wherein the high compression means increases the compression ratio as the peak value detected by the detection means increases.

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