JP2014231805A - Control device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a control device for an internal combustion engine that can secure transition from spark ignition combustion to compression ignition combustion for stable combustion and that can maintain good exhaust characteristics.SOLUTION: Fuel for spark combustion to increase a gas temperature TGAS in a combustion chamber is injected by a direct-injection fuel injection valve 6D and spark ignition is performed by an ignition plug 7. A lower limit value of spark fuel injection amount QTRG is set so that the gas temperature TGAS can be increased to a temperature TCIG enabling compression ignition by spark ignition combustion of the injected fuel. An upper limit value of the spark fuel injection amount QTRG is set so that NOx discharge amount MNOx is a predetermined upper limit value or less. The spark fuel injection amount QTRG [mm/st] is set to satisfy the following formula: V×8×10≤QTRG≤3.7/N, where V indicates exhaust amount [cc] per cylinder and N indicates the number of cylinders.

Description

  The present invention relates to a control device for an internal combustion engine, and more particularly to an operation in a compression ignition combustion mode that includes an in-cylinder fuel injection valve that injects fuel into a combustion chamber and an ignition plug and compresses and ignites an air-fuel mixture supplied into the combustion chamber. The present invention relates to a control device for a possible internal combustion engine.

  In Patent Document 1, an in-cylinder fuel injection valve for injecting fuel into a combustion chamber and an ignition plug are provided, and an air-fuel mixture supplied into the combustion chamber is locally combusted by ignition by the ignition plug, and an air-fuel mixture in the combustion chamber is obtained. There is shown a control device for an internal combustion engine that operates in a compression ignition combustion mode in which the temperature of the mixture is increased to compress and ignite the entire mixture. According to this device, for example, in the high load operation region of the engine, the operation in the spark ignition combustion mode by the spark plug is performed, and in the predetermined partial load operation region, the operation in the compression ignition combustion mode is performed.

JP 2002-161780 A

  In the apparatus shown in Patent Document 1, there is no specific disclosure about the amount of fuel injected by the in-cylinder fuel injection valve in order to generate local combustion, and compression ignition is performed from local first-stage spark ignition combustion. In order to make sure to shift to the second stage of combustion and always obtain stable combustion, a more specific study was necessary. Further, if the fuel injection amount is increased in order to obtain stable combustion, there is a detrimental effect that the NOx emission amount increases. Therefore, this point needs to be taken into consideration when setting the fuel injection amount.

  The present invention has been made by paying attention to the above-mentioned points, and is an internal combustion engine capable of stably shifting from spark ignition combustion to compression ignition combustion to achieve stable combustion and maintaining good exhaust characteristics. An object is to provide a control device.

In order to achieve the above object, the invention described in claim 1 includes port fuel injection means (6P) for injecting fuel into the intake port (2a), and in-cylinder fuel injection means (6D) for injecting fuel into the combustion chamber. An internal combustion engine control device comprising an ignition means (7) provided in the combustion chamber and capable of operating in a compression ignition combustion mode for compressing and igniting a mixture of fuel and air supplied into the combustion chamber; In the compression ignition combustion mode, the in-cylinder fuel injection means (6D) performs fuel injection in the vicinity of compression top dead center, and the injected fuel is ignited using the ignition means (7), thereby mixing the fuel. Combustion control means for raising the temperature of the gas (TGAS) and compressing and igniting the air-fuel mixture by the temperature rise is provided, and the fuel injection amount QTRG [mm] per stroke by the in-cylinder fuel injection means ³ / st] is set to satisfy the following formula (A):
V × 8 × 10 ⁻⁴ ≦ QTRG ≦ 3.7 / N (A)
Here, V is the displacement [cc] per cylinder, and N is the number of cylinders of the engine.

According to this configuration, by setting the fuel injection amount QTRG to a lower limit value (V × 8 × 10 ⁻⁴ ) or more, it is possible to generate a heat amount that realizes a reliable transition to compression ignition combustion, and an upper limit value ( 3.7 / N) or less, it is possible to suppress an increase in the amount of generated heat and an increase in the NOx emission amount. As a result, it is possible to achieve stable compression ignition combustion with a minimum fuel injection amount and maintain good exhaust characteristics, thereby obtaining an effect of improving fuel consumption.

  According to a second aspect of the present invention, in the control device for an internal combustion engine according to the first aspect, the lower limit value of the fuel injection amount QTRG is such that the in-cylinder gas temperature (TGAS) is 50 [° K depending on the amount of heat generated during combustion. ] It is set to rise.

  According to this configuration, it is possible to realize stable compression ignition combustion by increasing the in-cylinder gas temperature by 50 [° K].

According to a third aspect of the present invention, in the control device for an internal combustion engine according to the first or second aspect, a distance L [mm] between the in-cylinder fuel injection means and the ignition means is set by the following formula (B): Characterized by:
L = -7 * N + 61 (B).

  According to this configuration, since the distance L [mm] between the in-cylinder fuel injection means and the ignition means is set using the formula (B), the fuel injection amount QTRG is set to the upper limit value (3.7 / N) or less. Spark ignition combustion can be reliably generated while suppressing NOx emission.

It is a figure which shows the structure of the internal combustion engine concerning one Embodiment of this invention, and its control apparatus. It is a figure which shows arrangement | positioning of a fuel injection valve (6D, 6P). It is a figure which shows the engine operation area | region (HCCI) which performs compression ignition operation. It is a time chart which shows transition of the gas temperature (TGAS) in a combustion chamber in a compression stroke. It is a figure which shows the relationship between the exhaust amount V per cylinder, and the lower limit (QTRGMIN) of the direct injection fuel injection amount. It is a figure which shows the relationship between the emitted-heat amount (HQTRG) by spark ignition, and NOx generation amount (MNOx). It is a figure which shows the relationship between the number of cylinders (N) and the upper limit (QTRGMAX) of the direct injection fuel injection amount. It is a figure for demonstrating the setting method of the distance (L) of a cylinder fuel injection valve (6D) and a spark plug (7).

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a diagram showing a configuration of an internal combustion engine and its control device according to an embodiment of the present invention. In FIG. 1, an internal combustion engine (hereinafter simply referred to as “engine”) 1 having four cylinders includes an intake valve and an exhaust valve, a cam for driving them, and a valve operation characteristic variable mechanism 40. The variable valve operation characteristic mechanism 40 includes an intake valve lift variable mechanism that switches a valve lift amount (maximum lift amount) and an opening angle (valve opening period) of the intake valve between a high-speed operation characteristic and a low-speed operation characteristic; Exhaust valve lift amount variable mechanism that switches the valve lift amount (maximum lift amount) and opening angle (valve opening period) between high speed operation characteristics and low speed operation characteristics, and the crankshaft of the cam that drives the intake valve The intake valve operating phase variable mechanism that changes the operating phase of the intake valve by continuously changing the operating phase based on the rotation angle, and the cam that drives the exhaust valve, based on the crankshaft rotation angle It has an exhaust valve operating phase variable mechanism that changes the operating phase of the exhaust valve by changing the phase continuously.

  A throttle valve 3 is arranged in the intake passage 2 of the engine 1. An actuator 8 that drives the throttle valve 3 is connected to the throttle valve 3, and the operation of the actuator 8 is controlled by an electronic control unit (hereinafter referred to as “ECU”) 5.

  The engine 1 is provided for each cylinder slightly upstream of the intake valve of each cylinder, and a port fuel injection valve 6P that injects fuel into the intake port of the intake passage 2 and directly injects fuel into the combustion chamber of each cylinder. And an in-cylinder fuel injection valve 6D. Each injection valve 6P, 6D is connected to a fuel pump (not shown) and is electrically connected to the ECU 5, and the valve opening timing (fuel injection timing) and the valve opening time (fuel injection time) are controlled by signals from the ECU 5. Is done. The ignition plug 7 of each cylinder of the engine 1 is connected to the ECU 5, and the ECU 5 supplies an ignition signal to the ignition plug 7 to perform ignition timing control.

  An intake air amount sensor 11 that detects the intake air amount GAIR [g / sec] and an intake air temperature sensor 12 that detects the intake air temperature TA are provided on the upstream side of the throttle valve 3. The throttle valve 3 is connected to a throttle valve opening sensor 13 for detecting the throttle valve opening TH. An intake pressure sensor 14 for detecting the intake pressure PBA is attached downstream of the throttle valve 3, and an engine coolant temperature sensor 15 for detecting the engine coolant temperature TW is attached to the main body of the engine 1. An in-cylinder pressure sensor 16 for detecting a pressure (in-cylinder pressure) PCYL in the combustion chamber is provided in the combustion chamber of each cylinder of the engine 1. Further, an exhaust temperature sensor 18 for detecting the exhaust temperature TE is provided in the exhaust passage 4 of the engine 1. Detection signals from these sensors 11 to 16 and 18 are supplied to the ECU 5. The exhaust passage 4 is provided with an exhaust purification device (not shown).

  The ECU 5 is connected to a rotation angle parameter detection unit 17 that detects an angle parameter synchronized with the rotation of the engine 1. The rotation angle parameter detection unit 17 determines the rotation angle of a crankshaft (not shown) of the engine 1. Crank angle position sensor to detect, intake cam angle position sensor to detect the rotation angle of the intake cam shaft to which the cam that drives the intake valve of the engine 1 is fixed, and exhaust to which the cam that drives the exhaust valve of the engine 1 is fixed An exhaust cam angle position sensor that detects the rotation angle of the cam shaft is provided. A signal corresponding to the rotation angle of the crankshaft and the rotation angle of each camshaft is supplied to the ECU 5 by the rotation angle parameter detector 17. The crank angle position sensor includes a pulse (hereinafter referred to as “CRK pulse”) generated at every constant crank angle cycle (for example, a cycle of 6 degrees), a pulse for specifying a predetermined angular position of the crankshaft, and the start of the intake stroke of each cylinder. And a pulse generated at the top dead center (TDC) (hereinafter referred to as “TDC pulse”). These pulses are used for various timing controls such as fuel injection timing and ignition timing, and detection of engine speed (engine speed) NE. The intake cam angle position sensor and the exhaust cam angle position sensor output a pulse each time the intake cam shaft and the exhaust cam shaft rotate by a predetermined angle (for example, 1 degree). From the relative relationship between the output of the intake cam angle position sensor and the output from the crank angle position sensor, the operation phase of the intake valve is detected, and from the relative relationship between the output of the exhaust cam angle position sensor and the output from the crank angle position sensor The operating phase of the exhaust valve is detected.

  The ECU 5 includes an accelerator sensor 31 for detecting an accelerator pedal depression amount (hereinafter referred to as “accelerator pedal operation amount”) AP of a vehicle driven by the engine 1 and a vehicle speed sensor 32 for detecting a traveling speed (vehicle speed) VP of the vehicle. , And an atmospheric pressure sensor 33 for detecting the atmospheric pressure PA is connected. Detection signals of these sensors 31 to 33 are supplied to the ECU 5.

  The variable valve operation characteristic mechanism 40 includes a lift amount control actuator for switching the maximum lift amount and the opening angle (hereinafter simply referred to as “lift amount”) of the intake valve and the exhaust valve between the high speed operation characteristic and the low speed operation characteristic. And an operation phase control actuator for continuously changing the operation phases of the intake valve and the exhaust valve, and the operation of these control actuators is controlled by the ECU 5. As the valve operating characteristic variable mechanism 40, for example, a known valve operating mechanism disclosed in Japanese Patent No. 2619696, Japanese Patent Application Laid-Open No. 2008-106654, and the like can be used.

  Although not shown, an exhaust gas recirculation mechanism that recirculates part of the exhaust gas from the exhaust passage 4 to the intake passage 2 is provided.

  The ECU 5 shapes input signal waveforms from various sensors, corrects the voltage level to a predetermined level, converts an analog signal value into a digital signal value, etc., and a central processing unit (hereinafter referred to as “CPU”). In addition to a storage circuit that stores a calculation program executed by the CPU, a calculation result, and the like, an output circuit that supplies drive signals to various actuators, fuel injection valves 6P and 6D, and a spark plug 7 is provided.

  The CPU of the ECU 5 controls the opening degree of the throttle valve 3, the fuel injection control (control of the fuel injection timing and the fuel injection time by the fuel injection valves 6P and 6D), the ignition timing control, and the intake air according to the detection signal of the sensor. Controls the operating characteristics of valves and exhaust valves.

  FIG. 2 is a view for explaining the mounting positions of the port fuel injection valve 6P, the in-cylinder fuel injection valve 6D, and the spark plug 7. The port fuel injection valve 6P can inject fuel into the intake port 2a. The in-cylinder fuel injection valve 6D is disposed in the vicinity of the intake valve 21 and at a distance L from the spark plug 7, and the spark plug 7 is disposed in the cylinder 1a of the engine 1. It is arrange | positioned at the top. The in-cylinder fuel injection valve 6D has a single fuel injection hole at a position where fuel can be injected toward the spark plug 7 as indicated by a broken line in the drawing. The distance L is defined as the distance from the fuel injection hole to the discharge electrode of the spark plug 7.

  In the present embodiment, the operation in the compression ignition combustion mode described above and the operation in the normal spark ignition combustion mode are switched and executed according to the engine operating state. In the following description, the operation in the compression ignition combustion mode is referred to as “HCCI (Homogeneous Charge Compression Ignition) operation”, and the operation in the spark ignition combustion mode is referred to as “SI (Spark Ignition) operation”. In the HCCI operation, an operation is performed in which the temperature of the air-fuel mixture (cylinder gas) is raised by local combustion generated by spark ignition (hereinafter referred to as “fire type combustion”) to generate compression ignition combustion. Further, in the HCCI operation, control is performed to increase the in-cylinder gas temperature before spark ignition by setting the lift amount of the intake / exhaust valve to the low speed operation characteristic to increase the internal exhaust gas recirculation amount. By performing the HCCI operation, the combustion temperature can be lowered, and the emission amount of particulate matter and NOx can be reduced.

  FIG. 4 is a diagram showing an engine operation region defined by the engine speed NE and the required torque TRQ of the engine 1. The operation region in which the HCCI operation is performed is an operation region of a relatively low load and hatched. Is shown. The area other than the HCCI operation area is the SI operation area. The required torque TRQ is set so as to be substantially proportional to the accelerator pedal operation amount AP.

  In the HCCI operation, fuel injection by the in-cylinder fuel injection valve 6D and ignition by the spark plug 7 are performed so that fire type combustion is performed in the vicinity of the compression top dead center. The fuel injection amount (hereinafter referred to as “fire type fuel injection amount”) QTRG by the in-cylinder fuel injection valve 6D for performing the ignition type combustion is set to a value that can reliably generate the compression ignition combustion, and the required torque TRQ The fuel required accordingly is supplied by fuel injection by the port fuel injection valve 6P.

  The optimum setting method of the fire type fuel injection amount QTRG and the optimum setting method of the distance L (see FIG. 2) between the in-cylinder fuel injection valve 6D and the spark plug 7 related to the fire type fuel injection amount QTRG will be described below. .

  FIG. 4 is a time chart showing the transition of the gas temperature TGAS in the combustion chamber in the compression stroke (the horizontal axis is the crank angle CA, “0” corresponds to the compression top dead center), and the solid line shows the temperature rise characteristics due to compression. The broken line shows the temperature rise characteristic due to the heat generated by the fire type combustion. TCIG shown in FIG. 4 indicates the gas temperature TGAS at which the compression ignition is surely generated, and the compression ignition combustion is performed by setting the calorific value HQTRG by the fire type combustion so that the gas temperature TGAS becomes higher than the rising temperature DTRIS. Can be reliably generated. The CAIG shown in FIG. 4 corresponds to the compression ignition timing.

Therefore, in the present embodiment, the lower limit value QTRGMIN [mm ³ / st] of the fire type fuel injection amount QTRG that causes the fire type combustion is set by the following equation (1). [Mm ³ / st] is a unit indicating the fuel injection volume per stroke. In the present embodiment, since one injection is performed in the compression stroke, the volume of fuel injected by one injection is shown.
QTRGMIN = V × 8 × 10 ⁻⁴ (1)
Here, V is the displacement [cc] per cylinder.

  FIG. 5 is a diagram showing the relationship between the displacement V V and the lower limit value QTRGMIN obtained when the rising temperature DRTRISE is 50 ° K. By expressing the relationship shown in this diagram with a mathematical expression, the expression (1) is obtained. It is done.

  By setting the fire type fuel injection amount QTRG to be equal to or greater than the lower limit value QTRGMIN, compression ignition combustion can be stably generated at the ignition timing CAIG.

  Next, a method for setting the upper limit value QTRGMAX of the fire type fuel injection amount QTRG will be described. In the present embodiment, the upper limit value QTRGMAX is set so that the NOx emission amount MNOx [mg / sec] per unit time resulting from fire type combustion is equal to or less than the NOx emission amount upper limit value MNOxLH.

FIG. 6 is a diagram showing the relationship between the calorific value HQTRG [J] and NOx emission amount MNOx due to fire type combustion, and the NOx emission amount MNOx increases as the calorific value HQTRG increases. Since the current NOx emission amount upper limit value MNOxLH is 0.12 [mg / sec] in traveling in the JC08 mode, the calorific value HQTRG needs to be 25 [J] or less per cylinder as is apparent from FIG. There is. That is, since the engine as a whole needs to be 100 [J] or less, when the number of cylinders is N, the upper limit value QTRGMAX is given by the following equation (2). Equation (2) is obtained with a calorific value per 1 [mm ³ ] of fuel of 27.0 [J]. FIG. 7 illustrates the relationship of equation (2).
QTRGMAX = 3.7 / N (2)

From the above, by setting the fire type fuel injection amount QTRG so as to satisfy the following formula (3), the compression ignition combustion is stably generated and the NOx emission amount MNOx is suppressed to the NOx emission amount upper limit value MNOxLH or less. It becomes possible.
V × 8 × 10 ⁻⁴ ≦ QTRG ≦ 3.7 / N (3)

Next, a method for setting the distance L between the in-cylinder fuel injection valve 6D and the spark plug 7 will be described.
FIG. 8A is a diagram (four-cylinder engine) showing the relationship between the distance L and the heat generation amount HQTRG. As the distance L increases, it is necessary to increase the injection amount QTRG from the viewpoint of ensuring the penetration of the in-cylinder fuel injection valve 6D, so the heat generation amount HQTRG increases. The relationship shown in FIG. 8A can be expressed by the following formula (4).
HQTRG = 10 ⁻⁴ × L ⁴ −0.0084 × L ³ + 0.26 × L ²
−3.1 × L + 26.5 (4)

Further, as described above, it is necessary to satisfy the following formula (5) from the viewpoint of suppressing the NOx emission amount MNOx.
HQTRG ≦ 100 / N (5)
From the equations (4) and (5), the distance L needs to be set as shown by the following equation (6).
L ≦ −7 × N + 61 (6)

If the distance L is too short, ignition by spark ignition is difficult to occur, so it is desirable to set the upper limit value of the equation (6) as shown in the following equation (6a).
L = −7 × N + 61 (6a)

  FIG. 8B is a diagram showing the relationship between the distance L and the NOx emission amount MNOx. In a four-cylinder engine, the NOx emission amount MNOx is set to 33 [mm] calculated by the equation (6a). Can be confirmed to be 0.12 [mg / sec] or less.

As described above, in the present embodiment, by setting the fire type fuel injection amount QTRG to the lower limit value QTRGMIN (V × 8 × 10 ⁻⁴ ) or more, a temperature increase that realizes a reliable transition to compression ignition combustion is generated. By setting the upper limit value QTRGMAX (3.7 / N) or less, it is possible to suppress an increase in the amount of generated heat and an increase in the amount of NOx generated. As a result, it is possible to achieve stable compression ignition combustion with a minimum fuel injection amount and maintain good exhaust characteristics, thereby obtaining an effect of improving fuel consumption.

  Further, by setting the fire type fuel injection amount QTRG to be equal to or higher than the lower limit value QTRGMIN, the gas temperature TGAS in the combustion chamber is raised by 50 [° K], and stable compression ignition combustion can be realized.

  Further, since the distance L [mm] between the in-cylinder fuel injection valve 6D and the spark plug 7 is set using the equation (6a), the fuel injection amount QTRG is set to the upper limit value QTRGMAX (3.7 / N) or less. It is possible to reliably generate spark combustion by sparks while suppressing NOx emissions.

  In the present embodiment, the in-cylinder fuel injection valve 6D corresponds to the in-cylinder fuel injection means, the spark plug 7 corresponds to the ignition means, and the ECU 5 constitutes the combustion control means.

  The present invention is not limited to the embodiment described above, and various modifications can be made. For example, in the above-described embodiment, an example of a four-cylinder engine is shown. However, as indicated by N, the present invention can be applied regardless of the number of cylinders. The configuration of the present invention can also be applied to a marine vessel propulsion engine such as an outboard motor having a vertical crankshaft.

DESCRIPTION OF SYMBOLS 1 Internal combustion engine 2 Intake passage 2a Intake port 5 Electronic control unit (combustion control means)
6D In-cylinder fuel injection valve (in-cylinder fuel injection means)
6P port fuel injection valve 7 Spark plug (ignition means)

Claims (3)

Port fuel injection means for injecting fuel into the intake port, in-cylinder fuel injection means for injecting fuel into the combustion chamber, and ignition means provided in the combustion chamber, the fuel and air supplied to the combustion chamber In a control device for an internal combustion engine capable of operating in a compression ignition combustion mode for compressing and igniting an air-fuel mixture,
In the compression ignition combustion mode, fuel injection is performed in the vicinity of compression top dead center by the in-cylinder fuel injection means, and the injected fuel is ignited by using the ignition means to raise the temperature of the air-fuel mixture. A combustion control means for compressing and igniting the air-fuel mixture by the temperature rise,
A control device for an internal combustion engine, wherein the fuel injection amount QTRG [mm ³ / st] per stroke by the in-cylinder fuel injection means is set to satisfy the following formula:
V × 8 × 10 ⁻⁴ ≦ QTRG ≦ 3.7 / N
Here, V is the displacement [cc] per cylinder, and N is the number of cylinders of the engine.   2. The control device for an internal combustion engine according to claim 1, wherein the lower limit value of the fuel injection amount QTRG is set so that the in-cylinder gas temperature is increased by 50 [° K] according to the amount of heat generated during combustion. The control device for an internal combustion engine according to claim 1 or 2, wherein a distance L [mm] between the in-cylinder fuel injection means and the ignition means is set by the following equation:
L = −7 × N + 61.

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