JP2012026395A - Control device of internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve starting performance at a low temperature start of an engine while requests such as reduction in exhaust emission, the saving of fuel cost, and the reduction of cost can be satisfied.SOLUTION: At starting an engine, variable valve timing devices 32, 33 are controlled so that a NVO period (negative valve overlap period) in which both an exhaust valve 31 and an intake valve 30 are brought into closed states may be provided; and, pre-combustion control in which pre-injection in which fuel is injected into the cylinder during the NVO period and pre-ignition in which an air-fuel mixture by pre-injection is ignited are executed, and the air-fuel mixture by pre-ignition is burned. Furthermore, main combustion control is executed in which main injection in which fuel is injected after the execution of pre-injection and main ignition in which the air-fuel mixture by the main injection is ignited are executed, and the air-fuel mixture by the main injection is burned. Thereby, a temperature in the cylinder is raised by the combustion heat of pre-combustion (combustion of air-fuel mixture by pre-injection), the vaporization of injected fuel of the main injection is promoted effectively.

Description

  The present invention relates to a control device for an internal combustion engine having a function of injecting fuel into a cylinder during a negative valve overlap period of the internal combustion engine.

  In recent years, in an internal combustion engine mounted on a vehicle, for example, as described in Patent Document 1 (Japanese Patent No. 3525737) and Patent Document 2 (Japanese Patent No. 4005941), from the latter half of the exhaust stroke of the internal combustion engine. During the negative valve overlap period, the variable valve device (eg, variable valve timing device) is controlled to provide a negative valve overlap period in which both the exhaust valve and the intake valve are closed in the first half of the intake stroke. In some cases, the fuel is injected into the cylinder to inject the fuel into the high-temperature combustion gas remaining in the cylinder to promote the vaporization of the injected fuel.

Japanese Patent No. 3525737 Japanese Patent No. 4005941

  By the way, when the internal combustion engine is started at a low temperature, it is difficult for the fuel to vaporize. Therefore, in order to improve the startability, the fuel injection amount is increased more than usual, and the amount of fuel vaporized (the amount of fuel contributing to combustion) is reduced. In this case, exhaust emission and fuel consumption may be deteriorated.

  In order to improve startability at low temperature starting, in the case of a system using low boiling point fuel, a tank for storing low boiling point fuel is provided, or a low boiling point fuel (from low fuel) Since it is necessary to provide a separation device for separating the boiling point component), it is not possible to satisfy the demand for cost reduction, which is an important technical problem in recent years.

  Further, the techniques of Patent Documents 1 and 2 both promote the vaporization of the injected fuel by the heat of the combustion gas remaining in the cylinder by injecting the fuel into the cylinder during the negative valve overlap period. However, when the internal combustion engine is started, combustion gas is not generated until the first explosion starts. Therefore, simply injecting fuel into the cylinder during the negative valve overlap period effectively vaporizes the injected fuel. Therefore, the startability at the low temperature start cannot be sufficiently improved.

  Therefore, the problem to be solved by the present invention is to control the internal combustion engine which can improve the startability at the time of low temperature start of the internal combustion engine and can satisfy the demands of reducing exhaust emission, reducing fuel consumption and reducing cost. To provide an apparatus.

  In order to solve the above problems, the invention according to claim 1 includes a variable valve device that changes a valve opening / closing characteristic (for example, valve timing or lift amount) of at least one of an intake valve and an exhaust valve of an internal combustion engine. In the control device for an internal combustion engine, the variable valve device is controlled so as to provide a negative valve overlap period in which both the exhaust valve and the intake valve are closed from the latter half of the exhaust stroke to the first half of the intake stroke when the internal combustion engine is started. Pre-combustion control for performing pre-injection for injecting fuel into the cylinder during the negative valve overlap period and pre-ignition for igniting the air-fuel mixture by the pre-injection to burn the air-fuel mixture by the pre-injection And the main injection for injecting fuel in the intake stroke or the compression stroke after the pre-injection is performed, and the air-fuel mixture by the main injection It is obtained by a configuration having a combustion control means for running the main spark to fire implementing a main combustion control burning an air-fuel mixture by the main injection.

  In this configuration, since the in-cylinder temperature can be raised by the combustion heat of pre-combustion (fuel mixture combustion by pre-injection) at the time of starting the internal combustion engine, the main injected fuel ( It is possible to effectively promote vaporization of the injected fuel of the main injection. In this case, since the main injection fuel can be vaporized by the combustion heat of the pre-combustion before the first explosion of the main injection fuel starts, vaporization can be promoted from the first main injection fuel of each cylinder. . This makes it possible to stabilize the combustion state of main combustion (fuel mixture combustion by main injection) at an early stage even at a low temperature start, improving the startability at a low temperature start and reducing exhaust emissions and fuel consumption. Can meet the demand. In addition, since it is not necessary to newly provide parts or devices for improving the startability, it is possible to satisfy the demand for cost reduction, which is an important technical problem in recent years.

  In this case, it is preferable to perform the pre-injection in the first half of the negative valve overlap period. In this way, pre-ignition is performed in a state where the air-fuel mixture by pre-injection is compressed to a high pressure (a state in which combustion is easy) due to the piston rising in the first half of the negative valve overlap period (that is, the second half of the exhaust stroke). And the air-fuel mixture obtained by the pre-injection can be reliably burned.

  Further, as in claim 3, when the pre-injection is executed, if the required injection amount of the pre-injection is more than twice the minimum injection amount that can be injected by the fuel injection valve, the required injection amount of the pre-injection The fuel may be divided and injected several times. In this way, it is possible to inject the fuel corresponding to the required injection amount of the pre-injection little by little, and to promote the vaporization of the pre-injected fuel (pre-injected injected fuel). Can be burned.

  Further, as in claim 4, the injection timing of the pre-injection may be set based on at least one of the engine temperature, the engine speed, and the exhaust temperature. In this way, it is possible to set the pre-injection time to an appropriate value by changing the pre-injection time (the pre-injection time) according to the engine temperature, the engine speed, and the exhaust temperature. In this case, for example, the pre-injection timing is advanced as the engine temperature or the exhaust gas temperature decreases. As a result, in response to the fact that the fuel becomes harder to vaporize as the engine temperature and exhaust temperature become lower, the pre-injection timing is advanced, the time from pre-injection to pre-ignition is lengthened, and the pre-injected fuel is vaporized. You can earn time to do.

  Further, as in claim 5, pre-ignition may be executed after top dead center after top injection or after top dead center. In this way, compared with the case where pre-ignition is performed before top dead center, the peak timing of the combustion temperature of pre-combustion can be retarded and the vaporization promotion effect of the main injection fuel can be enhanced.

  Further, the ignition timing of the pre-ignition may be set based on at least one of the engine temperature and the intake air temperature. In this way, it is possible to set the pre-ignition timing to an appropriate value by changing the pre-ignition timing (pre-ignition ignition timing) according to the engine temperature or the intake air temperature. In this case, for example, the pre-ignition timing is retarded as the engine temperature or the intake air temperature decreases. As a result, the pre-ignition timing is retarded and the time from pre-injection to pre-ignition is increased, and the pre-injected fuel is vaporized in response to the fact that the fuel becomes harder to vaporize as the engine temperature and intake air temperature become lower. Time can be earned, and the peak timing of the pre-combustion combustion temperature can be retarded to enhance the effect of promoting the vaporization of the main injection fuel.

  Further, as in claim 7, the length of the negative valve overlap period may be set based on at least one of the engine temperature and the intake air temperature. In this way, the length of the negative valve overlap period can be set to an appropriate value by changing the length of the negative valve overlap period in accordance with the engine temperature or the intake air temperature. In this case, for example, the negative valve overlap period is lengthened as the engine temperature or the intake air temperature decreases. Accordingly, in response to the fact that the fuel becomes harder to vaporize as the engine temperature and intake air temperature become lower, the negative valve overlap period is lengthened, and the advance amount of the pre-injection timing and the retard amount of the pre-ignition timing are reduced. It becomes possible to enlarge.

  In the present invention, the pre-combustion control may be performed only at the time of starting the internal combustion engine (before the completion of the start). However, the present invention is not limited to this. May perform pre-combustion control. In this way, the vaporization of the main injection fuel can be promoted by pre-combustion until a predetermined period has elapsed even after the internal combustion engine is started.

FIG. 1 is a diagram showing a schematic configuration of an engine control system in one embodiment of the present invention. FIG. 2 is a diagram for explaining a method for setting the NVO period by the variable valve timing device. FIG. 3 is a time chart for explaining pre-combustion control and main combustion control. FIG. 4 is a diagram for explaining pre-combustion control and main combustion control. FIG. 5 is a flowchart for explaining the flow of processing of the combustion control routine. FIG. 6 is a diagram for explaining a method for setting the NVO period by the variable valve lift device.

Hereinafter, an embodiment embodying a mode for carrying out the present invention will be described.
First, a schematic configuration of the engine control system will be described with reference to FIG.
An air cleaner 13 is provided at the most upstream portion of the intake pipe 12 of the engine 11 that is an internal combustion engine, and an air flow meter 14 that detects the intake air amount is provided downstream of the air cleaner 13. A throttle valve 16 whose opening is adjusted by a motor 15 and a throttle opening sensor 17 for detecting the opening (throttle opening) of the throttle valve 16 are provided on the downstream side of the air flow meter 14.

  Further, a surge tank 18 is provided on the downstream side of the throttle valve 16, and an intake pipe pressure sensor 19 for detecting the intake pipe pressure is provided in the surge tank 18. The surge tank 18 is provided with an intake manifold 20 that introduces air into each cylinder of the engine 11, and each cylinder of the engine 11 is provided with a fuel injection valve 21 that directly injects fuel into the cylinder. Yes. An ignition plug 22 is attached to the cylinder head of the engine 11 for each cylinder, and the air-fuel mixture in the cylinder is ignited by spark discharge of the ignition plug 22 of each cylinder.

  Further, the engine 11 includes an intake side variable valve timing device 32 (variable valve device) for changing the valve timing (opening / closing timing) of the intake valve 30 and an exhaust side variable valve timing for changing the valve timing of the exhaust valve 31. A device 33 (variable valve device) is provided. Each of the variable valve timing devices 32 and 33 is an electric variable valve timing device capable of controlling the valve timing from when the engine is started (during cranking). A hydraulically driven variable valve timing device may be used as long as the valve timing can be controlled from the start of the engine.

  On the other hand, the exhaust pipe 23 of the engine 11 is provided with an exhaust gas sensor 24 (air-fuel ratio sensor, oxygen sensor, etc.) for detecting the air-fuel ratio or rich / lean of the exhaust gas. A catalyst 25 such as a three-way catalyst for purifying gas is provided.

  A cooling water temperature sensor 26 that detects the cooling water temperature and a knock sensor 27 that detects knocking are attached to the cylinder block of the engine 11. A crank angle sensor 29 that outputs a pulse signal every time the crankshaft 28 rotates by a predetermined crank angle is attached to the outer peripheral side of the crankshaft 28, and the crank angle and the engine are determined based on the output signal of the crank angle sensor 29. The rotation speed is detected.

  Outputs of these various sensors are input to an electronic control circuit (hereinafter referred to as “ECU”) 34. The ECU 34 is mainly composed of a microcomputer, and executes various engine control programs stored in a built-in ROM (storage medium) to thereby determine the fuel injection amount and the ignition timing according to the engine operating state. The throttle opening (intake air amount) and the like are controlled.

  Further, the ECU 34 executes a combustion control routine shown in FIG. 5 to be described later, so that when the engine is started, first, the exhaust valve 31 and the intake valve 30 are both closed from the latter half of the exhaust stroke to the first half of the intake stroke. The variable valve timing devices 32 and 33 on the intake side and the exhaust side are controlled so as to provide a valve overlap period (hereinafter referred to as “NVO”). Specifically, as shown in FIG. 2, the exhaust valve timing (exhaust valve) is set so that the valve closing timing of the exhaust valve 31 is advanced from TDC (top dead center) by the variable valve timing device 33 on the exhaust side. 31 and the intake valve timing (the valve timing of the intake valve 30) is controlled by the variable valve timing device 32 on the intake side so that the opening timing of the intake valve 30 is retarded from the TDC. Thus, an NVO period is provided.

  As shown in FIGS. 3 and 4, pre-injection [see FIG. 4 (a)] for injecting fuel into the cylinder during the NVO period at the time of starting the engine is performed, and the air-fuel mixture by this pre-injection is ignited. Pre-ignition [see FIG. 4 (b)] is executed, and pre-combustion control is performed to combust the air-fuel mixture by pre-injection. Further, main injection for injecting fuel in the intake stroke or compression stroke after execution of pre-injection (see FIG. 4C) is performed, and main ignition for igniting the air-fuel mixture by the main injection [FIG. 4E] The main combustion control for burning the air-fuel mixture by the main injection is performed.

  Thus, when the engine is started, the in-cylinder temperature can be raised by the combustion heat of pre-combustion (fuel mixture combustion by pre-injection). Even if the injected fuel) adheres to the piston 35, the inner wall surface of the cylinder, etc., the vaporization of the fuel can be effectively promoted [see FIG. 4 (d)]. In this case, since the main injection fuel can be vaporized by the combustion heat of the pre-combustion before the first explosion of the main injection fuel starts, vaporization can be promoted from the first main injection fuel of each cylinder. .

  In this embodiment, pre-injection is executed in the first half of the NVO period. Thereby, pre-ignition is executed in a state where the air-fuel mixture by pre-injection is compressed to a high pressure (a state in which combustion is easy) by the rise of the piston 35 in the first half of the NVO period (that is, the second half of the exhaust stroke). Ensure that the air-fuel mixture burns.

  Furthermore, pre-ignition is performed after TDC after execution of pre-injection or after TDC. Thereby, compared with the case where pre-ignition is performed before TDC, the peak timing of the combustion temperature of pre-combustion is retarded, and the vaporization promotion effect of the main injection fuel is enhanced.

Hereinafter, the processing content of the combustion control routine of FIG. 5 executed by the ECU 34 will be described.
The combustion control routine shown in FIG. 5 is repeatedly executed at a predetermined cycle while the ECU 34 is turned on, and serves as a combustion control means in the claims. When this routine is started, first, at step 101, it is determined whether or not it is a start time (before the start completion determination), for example, based on whether or not the engine speed has exceeded a predetermined complete explosion determination value.

  If it is determined in this step 101 that the engine is being started (before the start completion determination), the process proceeds to step 102 where the target exhaust valve timing is set so that the closing timing of the exhaust valve 31 is on the more advanced side than TDC. Is set to control the exhaust side variable valve timing device 33 so that the actual exhaust valve timing coincides with the target exhaust valve timing, and the opening timing of the intake valve 30 is also set to the retarded side. An NVO period is provided by setting the target intake valve timing and controlling the intake side variable valve timing device 32 so that the actual intake valve timing matches the target intake valve timing.

  At this time, for example, the length of the NVO period (that is, the length of the period from the closing timing of the exhaust valve 31 to the opening timing of the intake valve 30) according to the coolant temperature (substitute information of the engine temperature) is represented by a map or formula Thus, the length of the NVO period is changed according to the engine temperature, and the length of the NVO period is set to an appropriate value. In this case, the NVO period length map or mathematical expression is set such that, for example, the NVO period is lengthened as the coolant temperature (engine temperature substitute information) decreases. Accordingly, it is possible to increase the advance amount of the pre-injection timing and the retard amount of the pre-ignition timing in response to the fact that the fuel is less likely to vaporize as the engine temperature becomes lower. .

  Instead of the cooling water temperature, the length of the NVO period may be set by a map or a mathematical formula according to the intake air temperature, or the length of the NVO period may be set by a map or a mathematical formula according to the cooling water temperature and the intake air temperature. It may be set by, for example.

  Thereafter, the process proceeds to step 103, where the required injection amount for pre-injection and the required injection amount for main injection are set based on the engine operating state. At this time, for example, the required injection amount at start (= required injection amount of pre-injection + required injection amount of main injection) per cylinder is calculated according to the coolant temperature (replacement information of engine temperature) using a map or a mathematical formula. At the same time, after calculating the required injection amount for pre-injection according to the cooling water temperature using a map or a mathematical formula, the required injection amount for main injection (= (Required injection amount at start-up per cylinder-required injection amount of pre-injection)).

  Thereafter, the routine proceeds to step 104, where a pre-injection timing (pre-injection injection timing) and a main injection timing (main injection timing) are set based on the engine operating state. At this time, the pre-injection timing is set in the first half of the NVO period (advanced side with respect to TDC). For example, the pre-injection timing is set by a map or a mathematical formula according to the coolant temperature (engine temperature substitute information). Thus, the pre-injection time is changed according to the engine temperature, and the pre-injection time is set to an appropriate value. In this case, the pre-injection timing map or mathematical expression is set so that the pre-injection timing is advanced as the coolant temperature (engine temperature substitute information) decreases, for example. Accordingly, in response to the fact that the fuel becomes harder to vaporize as the engine temperature becomes lower, the pre-injection timing is advanced, the time from pre-injection to pre-ignition is lengthened, and the time for the pre-injected fuel to evaporate is increased. You can earn.

  Instead of the cooling water temperature, the pre-injection timing is set according to the intake air temperature or the exhaust gas temperature by a map or a mathematical formula, or the pre-injection timing is set according to the engine speed by a map or a mathematical formula. You may make it do. Further, the pre-injection timing may be set by a map or a mathematical formula according to two or more of the cooling water temperature, the intake air temperature, the exhaust gas temperature, and the engine speed.

  After this, the routine proceeds to step 105, where a pre-ignition timing (pre-ignition ignition timing) and a main ignition timing (main ignition timing) are set based on the engine operating state. At this time, the pre-ignition timing is set at TDC or after TDC. For example, the pre-ignition timing is set according to the engine temperature by setting the pre-ignition timing by a map or a mathematical formula according to the cooling water temperature (engine temperature substitute information). The pre-ignition timing is set to an appropriate value by changing the ignition timing. In this case, the pre-ignition timing map or mathematical expression is set so that, for example, the pre-ignition timing is retarded as the coolant temperature (engine temperature substitute information) decreases. Accordingly, in response to the fact that the fuel becomes harder to vaporize as the engine temperature becomes lower, the pre-ignition timing is retarded, the time from pre-injection to pre-ignition is lengthened, and the time for the pre-injected fuel to vaporize is increased. In addition to being able to earn, the peak timing of the pre-combustion combustion temperature can be retarded to enhance the effect of promoting the vaporization of the main injected fuel.

  In place of the cooling water temperature, the pre-ignition timing is set by a map or a mathematical expression according to the intake air temperature, or the pre-ignition timing is set by a map or a mathematical expression according to the cooling water temperature and the intake air temperature. You may do it.

  Thereafter, the routine proceeds to step 106, where it is determined whether the cylinder discrimination is completed based on the output signal of the crank angle sensor 29 and the output signal of the cam angle sensor (not shown), and it is determined that the cylinder discrimination is completed. The pre-fuel control is executed as follows. First, in Step 107, it is determined whether or not the crank angle detected by the crank angle sensor 29 has reached the pre-injection time. When it is determined that the crank angle has reached the pre-injection time, the process proceeds to Step 108. Pre-injection is executed to inject fuel for the required injection amount of pre-injection.

  Thereafter, the routine proceeds to step 109, where it is determined whether or not the crank angle detected by the crank angle sensor 29 has reached the pre-ignition timing. When it is determined that the crank angle has reached the pre-ignition timing, the routine proceeds to step 110. Advance and execute pre-ignition to ignite the air-fuel mixture by pre-injection. Thereby, the air-fuel mixture by the pre-injection is burned.

  If startability can be ensured without performing pre-combustion control (for example, when the cooling water temperature is equal to or higher than a predetermined value), the required injection amount for pre-injection is set to “0” and pre-injection and Pre-ignition may not be executed.

  Thereafter, the main combustion control is executed as follows. First, at step 111, it is determined whether or not the crank angle detected by the crank angle sensor 29 has reached the main injection timing, and when it is determined that the crank angle has reached the main injection timing, the routine proceeds to step 112, The main injection is executed to inject fuel for the required injection amount of the main injection.

  Thereafter, the routine proceeds to step 113, where it is determined whether or not the crank angle detected by the crank angle sensor 29 has reached the main ignition timing, and when it is determined that the crank angle has reached the main ignition timing, the routine proceeds to step 114. The main ignition is executed to ignite the air-fuel mixture by the main injection. Thereby, the air-fuel mixture by the main injection is burned.

  On the other hand, if it is determined in step 101 that it is not at the time of starting (that is, after starting), the routine proceeds to step 115, where valve timing control after starting (for example, during warm-up control) is executed. At this time, for example, the target exhaust valve timing and the target intake valve timing are set by a map or a mathematical formula based on the engine operating state (engine speed, load, cooling water temperature, etc.), and the actual exhaust valve timing is set to the target exhaust valve timing. The exhaust-side variable valve timing device 33 is controlled so as to match, and the intake-side variable valve timing device 32 is controlled so that the actual intake valve timing matches the target intake valve timing.

  Thereafter, the process proceeds to step 116, and the required injection amount after start-up (for example, during warm-up control) is set based on the engine operating state (engine speed, load, cooling water temperature, etc.) using a map or a mathematical expression. Thereafter, the process proceeds to step 117, and after setting the injection timing after start (for example, at the time of warm-up control) based on the engine operating state (engine speed, load, cooling water temperature, etc.) using a map or a mathematical formula, the process proceeds to step 118. Then, based on the engine operating state (engine speed, load, cooling water temperature, etc.), the ignition timing after startup (for example, during warm-up control) is set using a map or mathematical expression.

  Thereafter, the process proceeds to step 119, where it is determined whether the crank angle detected by the crank angle sensor 29 has reached the injection timing, and when it is determined that the crank angle has reached the injection timing, the process proceeds to step 120, Fuel injection is executed to inject fuel for the required injection amount.

  Thereafter, the routine proceeds to step 121, where it is determined whether or not the crank angle detected by the crank angle sensor 29 has reached the ignition timing, and when it is determined that the crank angle has reached the ignition timing, the routine proceeds to step 122, Ignition for igniting the mixture is executed to burn the mixture.

  In the present embodiment described above, the variable valve timing devices 32 and 33 are controlled so as to provide an NVO period when the engine is started, and during this NVO period, pre-injection for injecting fuel into the cylinder is executed and this pre-injection is performed. Since the pre-ignition control for igniting the air-fuel mixture is performed and the air-fuel mixture is combusted by pre-injection, the in-cylinder temperature can be increased by the combustion heat of the pre-combustion, and then When the main injection is executed, the vaporization of the main injection fuel can be effectively promoted. In this case, since the main injection fuel can be vaporized by the combustion heat of the pre-combustion before the first explosion of the main injection fuel starts, vaporization can be promoted from the first main injection fuel of each cylinder. . As a result, the combustion state of the main combustion can be stabilized at an early stage even at a low temperature start, and the requirements for exhaust emission reduction and fuel consumption reduction can be satisfied while improving the startability at the low temperature start. In addition, since it is not necessary to newly provide parts or devices for improving the startability, it is possible to satisfy the demand for cost reduction, which is an important technical problem in recent years.

  In this embodiment, since the pre-injection is executed in the first half of the NVO period, the air-fuel mixture by the pre-injection is compressed to a high pressure by the rise of the piston 35 in the first half of the NVO period (that is, the second half of the exhaust stroke). Thus, pre-ignition can be performed in a state where combustion is easy (a state in which combustion is easy), and the air-fuel mixture by pre-injection can be reliably burned.

  Further, in this embodiment, since pre-ignition is executed after TDC after execution of pre-injection or after TDC, the peak timing of the combustion temperature of pre-combustion is delayed compared to the case where pre-ignition is executed before TDC. The effect of promoting the vaporization of the main injection fuel can be enhanced.

  In the above embodiment, the variable valve timing devices 32 and 33 on the intake side and the exhaust side are controlled to provide the NVO period. However, the present invention is not limited to this, and for example, the lift amount of the intake valve is changed. In the case of a system including an intake side variable valve lift device and an exhaust side variable valve lift device that changes the lift amount of the exhaust valve, the intake side and exhaust side variable valve lift devices are controlled to control the NVO period. May be provided. Specifically, as shown in FIG. 6, the exhaust valve lift amount is controlled by the variable valve lift device on the exhaust side so that the closing timing of the exhaust valve is on the more advanced side than the TDC, and the intake side An NVO period is provided by controlling the lift amount of the intake valve so that the opening timing of the intake valve is retarded from the TDC by the variable valve lift device.

  In the above embodiment, the NVO period is provided by the variable valve timing devices 32 and 33 on both the intake side and the exhaust side. However, the present invention is not limited to this. For example, one of the intake side and the exhaust side is provided. The NVO period may be provided by a variable valve timing device, or the NVO period may be provided by one of the intake side and exhaust side variable valve lift devices.

  In the above embodiment, when the pre-injection is executed, the fuel for the required injection amount of the pre-injection is injected at a time. However, the present invention is not limited to this. For example, the required injection amount of the pre-injection is When the fuel injection valve 21 is at least twice the minimum injection amount that can be injected, the fuel for the required injection amount for pre-injection may be divided and injected multiple times (two or more times). If it does in this way, the fuel for the required injection quantity of pre-injection will be injected little by little, vaporization of pre-injection fuel can be accelerated | stimulated, and the air-fuel | gaseous mixture by pre-injection can be burned more reliably.

  Further, in the above embodiment, the length of the NVO period, the pre-injection timing, and the pre-ignition timing are set according to the cooling water temperature (engine temperature substitute information), etc., but the present invention is not limited to this. The calculation process may be simplified by setting at least one of the length of the NVO period, the pre-injection timing, and the pre-ignition timing as a fixed value set in advance.

  In the above embodiment, the pre-combustion control is performed only when the engine is started (before the start is completed). However, the present invention is not limited to this, and the pre-combustion control is performed for a predetermined period after the engine is started. Also good. In this way, vaporization of the main injection fuel can be promoted by pre-combustion until a predetermined period has elapsed even after the engine is started. At this time, a predetermined period during which the pre-combustion control is performed after the engine is started may be a fixed value set in advance, or may be set in accordance with a cooling water temperature (engine temperature substitute information), an engine speed, or the like. . Further, a period until the cooling water temperature or the engine rotation speed exceeds a predetermined value after the engine is started may be set as the predetermined period.

  Alternatively, the pre-combustion control may be executed only for a predetermined period when the engine is started. At this time, the predetermined period during which the pre-combustion control is performed at the time of starting the engine may be a fixed value set in advance, or may be set according to the cooling water temperature (engine temperature substitute information), the engine speed, or the like. .

  In addition, the present invention is not limited to the in-cylinder injection engine as shown in FIG. 1, and is a dual-injection engine having both a fuel injection valve for intake port injection and a fuel injection valve for in-cylinder injection. Can also be applied.

  DESCRIPTION OF SYMBOLS 11 ... Engine (internal combustion engine), 12 ... Intake pipe, 16 ... Throttle valve, 21 ... Fuel injection valve, 22 ... Spark plug, 23 ... Exhaust pipe, 26 ... Cooling water temperature sensor, 29 ... Crank angle sensor, 30 ... Intake valve , 31 ... exhaust valves, 32, 33 ... variable valve timing device (variable valve device), 34 ... ECU (combustion control means)

Claims (8)

In a control device for an internal combustion engine comprising a variable valve device that changes a valve opening / closing characteristic of at least one of an intake valve and an exhaust valve of the internal combustion engine,
The variable valve device is controlled to provide a negative valve overlap period in which both the exhaust valve and the intake valve are closed from the latter half of the exhaust stroke to the first half of the intake stroke when the internal combustion engine is started. Pre-injection for injecting fuel into the cylinder during the valve overlap period, and pre-ignition control for igniting the air-fuel mixture by the pre-injection to burn the air-fuel mixture by the pre-injection; Main combustion control for injecting fuel in the intake stroke or compression stroke after execution of injection, and executing main ignition for igniting the air-fuel mixture by the main injection to combust the air-fuel mixture by the main injection; A control device for an internal combustion engine, characterized by comprising combustion control means for carrying out.   The control apparatus for an internal combustion engine according to claim 1, wherein the combustion control means executes the pre-injection in the first half of the negative valve overlap period.   When the pre-injection executes the pre-injection, if the required injection amount of the pre-injection is more than twice the minimum injection amount that can be injected by the fuel injection valve, fuel for the required injection amount of the pre-injection 3. The control device for an internal combustion engine according to claim 1, wherein the fuel injection is divided into a plurality of times and injected.   The internal combustion engine according to any one of claims 1 to 3, wherein the combustion control means sets the injection timing of the pre-injection based on at least one of an engine temperature, an engine speed, and an exhaust temperature. Engine control device.   The control apparatus for an internal combustion engine according to any one of claims 1 to 4, wherein the combustion control means executes the pre-ignition after top dead center or after top dead center after execution of the pre-injection.   6. The control device for an internal combustion engine according to claim 1, wherein the combustion control means sets the ignition timing of the pre-ignition based on at least one of an engine temperature and an intake air temperature.   The internal combustion engine according to any one of claims 1 to 6, wherein the combustion control means sets the length of the negative valve overlap period based on at least one of an engine temperature and an intake air temperature. Control device.   8. The control apparatus for an internal combustion engine according to claim 1, wherein the combustion control means performs the pre-combustion control for a predetermined period after the internal combustion engine is started.

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