JP5593827B2 - Control device for spark ignition engine - Google Patents

Description

  The technology disclosed herein relates to a control device for a spark ignition engine configured to compress an air-fuel mixture in a cylinder and burn it by self-ignition.

  In recent years, in order to further improve fuel economy and clean exhaust of a spark ignition gasoline engine, a combustion mode in which the air-fuel mixture in the cylinder is compressed and burned by self-ignition has been proposed. In general, premixed compression ignition combustion Hereinafter, it is known by the name HCCI (Homogeneous-Charge Compression-Ignition) combustion. In this combustion mode, unlike general spark ignition combustion (hereinafter also referred to as SI (Spark Ignition) combustion), the premixed gas is self-ignited at a large number of points in the cylinder and starts combustion. Therefore, the thermal efficiency is extremely high and the emission property is also excellent.

  However, when the engine is in a relatively low load and low speed operation region, the temperature of the premixed gas may not rise to the self-ignition temperature even near the compression top dead center (TDC). In the gasoline engine described in Patent Document 1 or 2, a negative overlap period for closing both the intake valve and the exhaust valve from the exhaust stroke to the intake stroke of the cylinder is provided, and a large amount of burned gas remains (in other words, By increasing the internal EGR amount), the temperature in the cylinder is increased.

JP 2007-132319 A JP 2007-85241 A

  As described above, in order to perform HCCI combustion, the compression end temperature must satisfy the self-ignition condition. For example, during the period until the engine warm-up is completed, such as during cold start, the temperature difference between the cylinder temperature and the wall surface temperature in the cylinder is large, and the amount of heat released to the wall surface increases. The end temperature naturally does not satisfy the autoignition conditions. For this reason, when the engine is not warmed up, HCCI combustion cannot be performed, and SI combustion must be performed. However, in order to improve fuel consumption and purify exhaust, it is desirable to complete engine warm-up early and to perform HCCI combustion early.

  The technology disclosed herein has been made in view of such a point, and an object of the technology is to quickly complete engine warm-up in a spark ignition engine capable of performing HCCI combustion, and to perform HCCI combustion. Is to enable early execution.

  The technology disclosed herein performs pre-fuel injection by injecting fuel around a spark plug by a fuel injection valve and closing the intake valve from the viewpoint of promoting warm-up of the engine when the engine is not warmed up. Early spark ignition combustion (pre-SI combustion) was performed by performing spark ignition on the air-fuel mixture around the spark plug in the first half of the subsequent compression stroke. Such early spark ignition combustion compresses the gas in the cylinder that has become hot due to the combustion, so the amount of heat released to the wall surface in the cylinder is increased to increase the cooling loss and the engine warm-up. Promote. At the same time, the early spark ignition combustion also contributes to an increase in the compression end temperature. As a result, the compression end temperature can satisfy the self-ignition condition even when the engine is not warmed up, so the premixed gas formed in the cylinder by the main fuel injection different from the pre-fuel injection is Compression ignition combustion (main HCCI combustion) is performed in the vicinity of the compression top dead center after the spark ignition combustion.

  Specifically, a control device for a spark ignition engine disclosed herein includes a spark ignition engine to which fuel containing gasoline is supplied, and a fuel supply including a fuel injection valve that injects the fuel into a cylinder of the engine. And control means for controlling the operation of the spark ignition type gasoline engine through control of the fuel supply means and the spark plug. The means switches between an SI combustion mode in which the air-fuel mixture in the cylinder is spark-ignited by the spark plug and an HCCI combustion mode in which the air-fuel mixture in the cylinder is subjected to compression ignition combustion in accordance with an operating region of the engine.

Then, the control means further comprises, at the start of the engine, when a predetermined condition is satisfied, before the operation mode to reduce the activity of the catalyst, after completion of the operation mode, the engine is warming up is completed when the not warmed up yet, the execution vital pre fuel injection for injecting fuel around the spark plug by the fuel injection valve, the spark plug about by the spark plug in the compression stroke first half after the intake valve is closed The spark-ignition combustion is performed by performing spark ignition on the air-fuel mixture, and the pre-air-fuel mixture formed in the cylinder by the main fuel injection different from the pre-fuel injection is compressed after the spark ignition combustion. Compressive ignition combustion near the dead center.

  Here, the “unwarmed state” may be defined as a state in which, for example, the compression end temperature does not satisfy the self-ignition condition and HCCI combustion cannot be performed.

  Further, the combustion mode may be switched so that, for example, the SI combustion mode is set in the operation region of relatively high rotation and high load, and the HCCI combustion mode is set in the operation region of relatively low rotation and low load.

  According to the above configuration, when the engine is not warmed up, pre-fuel injection is performed to inject fuel around the spark plug, and spark ignition is performed by the spark plug in the first half of the compression stroke after the intake valve is closed. Spark ignition combustion, that is, pre-SI combustion is performed. Here, the timing of the pre-fuel injection is not particularly defined, and the pre-fuel injection may be executed at a timing at which an air-fuel mixture can be formed around the spark plug in the timing of the spark ignition executed in the first half of the compression stroke. .

  Such early spark ignition combustion, as described above, compresses the gas in the cylinder that has become hot due to combustion, and therefore increases the heat dissipation to the wall surface in the cylinder and increases the cooling loss of the engine. . That is, it is advantageous in promoting the warming up of the engine, and as a result, the time until the warming up of the engine is completed is shortened, and the engine can be shifted to the HCCI combustion mode at an early stage.

  Moreover, since the early pre-SI combustion described above also contributes to an increase in the compression end temperature, the compression end temperature can satisfy the self-ignition condition. Therefore, in the above-described configuration, the premixed gas formed in the cylinder by executing main fuel injection different from the pre-fuel injection causes compression ignition combustion instead of spark ignition combustion. That is, main HCCI combustion is performed. Here, the timing of the main fuel injection is not particularly limited, and may be executed at an appropriate timing so that the compression ignition combustion is performed near the compression top dead center, for example, MBT. The pre-SI combustion not only promotes warming up of the engine but also assists the subsequent main HCCI combustion, enabling compression ignition combustion (HCCI combustion) even when the engine is not warmed up. Thus, HCCI combustion can be started at an early stage.

  Since HCCI combustion is performed with non-throttling or less throttling, the pumping loss is reduced, so fuel efficiency is improved compared to performing SI combustion with throttling when the engine is not warmed up. It can improve.

The control means sets the amount of fuel supplied into the cylinder by the pre-fuel injection to be smaller than the amount of fuel supplied into the cylinder by the main fuel injection, and the cylinder through the two fuel injections. The total amount of fuel supplied into the engine is set so that the excess air ratio λ is 1 or more, and the control means supplies the cylinder with the pre-fuel injection as the engine load increases. The amount of fuel may be reduced, and the amount of fuel supplied into the cylinder by the main fuel injection may be increased .

  That is, since the pre-SI combustion by the pre-fuel injection and spark ignition is performed in the first half of the compression stroke, reverse torque can be generated. For this reason, in order to reduce the generated reverse torque as much as possible, it is desirable to set the amount of fuel supplied by pre-fuel injection to be smaller than the amount of fuel supplied by main fuel injection.

  In order to execute main HCCI combustion, from the viewpoint of thermal efficiency, it is preferable to set the total fuel amount supplied by both the pre-fuel injection and the main fuel injection so that the excess air ratio λ is larger than 1. From the viewpoint of completing the engine warm-up earlier, the total fuel amount is set so that the excess air ratio λ becomes 1, in other words, the amount of fuel supplied by pre-fuel injection is increased as much as possible. It is preferable to increase the engine cooling loss. Also, setting the total fuel amount so that the excess air ratio λ is 1 can be advantageous from the viewpoint of exhaust emission.

  The control means performs both the pre-fuel injection and the main fuel injection through the fuel injection valve, completes the pre-fuel injection in the first half of the compression stroke, and performs the main fuel injection in the second half of the compression stroke. It may be completed.

  Unlike this, the fuel supply means further includes a second fuel injection valve for injecting fuel into the intake port of the engine, and the control means performs the pre-fuel injection through the fuel injection valve, When performing the main fuel injection through the second fuel injection valve, the pre-fuel injection may be completed in the first half of the compression stroke, and the main fuel injection may be completed in the intake stroke before the compression stroke. Good.

  That is, when the main fuel injection is performed in the intake port through the second fuel injection valve, the main fuel injection is completed in the intake stroke, so that the fuel spray flows into the cylinder together with the intake air and the piston is lowered. Accordingly, it is widely dispersed in the cylinder with an increased volume to form a substantially uniform premixed gas. On the other hand, the pre-fuel injection is performed by injecting fuel around the spark plug in the first half of the compression stroke. In this case, by performing spark ignition with the spark plug, a relatively rich air-fuel mixture around the spark plug formed by the pre-fuel injection burns (pre-SI combustion), while substantially uniform in the cylinder. Since the premixed gas is in the first half of the compression stroke and is extremely diluted as a whole, the flame does not propagate. The substantially uniform premixed gas in the cylinder is subjected to compression ignition combustion near the compression top dead center after the spark ignition combustion (main HCCI combustion). For example, when the main fuel injection is performed in the intake port, the injection amount may be set so as to be in a lean state in which, for example, the in-cylinder excess air ratio λ is 2 or more.

  The engine may have a geometric compression ratio of 16 or more. That is, the above-described control is particularly effective when applied to an engine having a relatively high compression ratio with a geometric compression ratio of 16 or higher and at the same time a high expansion ratio.

  As described above, the control device for the spark ignition engine executes pre-fuel injection for injecting fuel around the spark plug and closes the intake valve in an unwarmed state before the warm-up of the engine is completed. By performing spark ignition combustion (pre-SI combustion) in the first half of the compression stroke after the valve, the engine is warmed up early by increasing the cooling loss of the engine, resulting in an HCCI combustion mode with excellent fuel efficiency and emissions. Can move early. In addition, by increasing the compression end temperature by early pre-SI combustion and making it possible to execute compression ignition combustion (main HCCI combustion) even when the engine is not warmed up, at least improvement in fuel consumption accompanying reduction in pumping loss To be advantageous.

It is the schematic which shows the structure of a spark ignition type gasoline engine and its control apparatus. (A) The figure which shows an example of the change of the catalyst temperature at the time of performing the warming-up promotion control which the said control apparatus performs, (b) The change of the catalyst temperature at the time of performing the conventional control, and an engine temperature It is a figure which shows an example. It is a timing chart which shows an example of the fuel-injection timing which concerns on warm-up promotion control, and a combustion timing, and a figure which illustrates the state in the cylinder at that time. It is a figure which shows self-ignition conditions and an example of the log | history of the temperature in a cylinder and pressure at the time of engine warm and cold. It is a figure which shows an example of the change of a cooling loss and an exhaust loss with respect to a combustion start time. It is a flowchart which concerns on especially warming-up promotion control which a control apparatus performs. It is an example of the compression end temperature map which concerns on the necessity of execution of warming-up promotion control. (A) It is an example of a characteristic concerning the setting of the base pre-injection amount and the base main injection amount. (B) and (c) are characteristic examples relating to the setting of correction coefficients for the pre-injection amount and the main injection amount, respectively. It is the schematic which shows the structure of the spark ignition type gasoline engine which concerns on another embodiment, and its control apparatus. The timing chart which shows an example of the fuel-injection timing and combustion timing which concern on the warming-up promotion control which the spark ignition type gasoline engine which concerns on the said another embodiment and its control apparatus perform, and the state in a cylinder at that time are illustrated FIG.

  Hereinafter, a control device for a spark ignition engine will be described with reference to the drawings. The following description of the preferred embodiment is merely exemplary in nature. FIG. 1 shows the overall configuration of a spark ignition engine and its control device according to this embodiment. In the figure, reference numeral 1 denotes a multi-cylinder gasoline engine mounted on a vehicle. The main body of the engine 1 has a cylinder head 4 disposed on a cylinder block 3 provided with a plurality of cylinders 2, 2,... (Only one is shown), and a piston 5 is fitted in each cylinder 2. A combustion chamber 6 is formed between the top surface of the cylinder head 4 and the bottom surface of the cylinder head 4. The piston 5 is connected to the crankshaft 7 by a connecting rod. Here, the engine 1 is an engine 1 capable of premixed compression ignition combustion (HCCI combustion), which will be described later in detail, and has a relatively high compression ratio with a geometric compression ratio of 16 or more, and at the same time The engine 1 has a relatively high expansion ratio.

  An intake port 9 and an exhaust port 10 are formed in the cylinder head 4 so as to open to the ceiling portion of the combustion chamber 6 for each cylinder 2. The intake port 9 opens on one side of the cylinder head 4, and the exhaust port 10 opens on the other side opposite to the cylinder head 4. The intake port 9 and the exhaust port 10 are opened and closed by an intake valve 11 and an exhaust valve 12, respectively. These intake and exhaust valves 11 and 12 are cams of a valve mechanism 13 disposed in the cylinder head 4. The shaft (not shown) is driven in synchronization with the rotation of the crankshaft 7.

  The valve mechanism 13 is abbreviated as a known mechanical phase variable mechanism 15 (hereinafter referred to as VVT (Variable Valve Timing)) capable of continuously changing the phase angle of the valve lift with respect to the crank rotation on the intake side and the exhaust side. The amount of intake air charged into the cylinder 2 and the amount of residual burned gas (internal EGR gas) can be adjusted by the operation thereof. A variable lift mechanism (CVVL (Continuous Variable Valve Lift) capable of continuously changing the valve lift amount may be provided together with the VVT 15, and the exhaust valve 12 is opened again in the intake stroke. A two-stage cam and a variable lift mechanism (VVL (Variable Valve Lift) with a lost motion mechanism for turning on and off the lift of the exhaust valve 12 in the intake stroke may be provided.

  In addition, a spark plug 16 is disposed with an electrode facing the ceiling of the combustion chamber 6 of each cylinder 2 and is energized by the ignition circuit 17 at a predetermined ignition timing. On the other hand, in this embodiment, a direct injection injector 18 that directly injects fuel is disposed in the cylinder 2 with the tip facing the intake side peripheral portion of the combustion chamber 6. For example, as conceptually shown in FIG. 3, the direct injection injector 18 is constituted by a multi-injection type fuel injection valve having a plurality of injection holes, and can inject fuel in the vicinity of the electrode of the spark plug 16. It is. That is, the engine 1 is configured as a so-called spray-guided direct injection engine 1. However, as will be described later, in the first half of the compression stroke, if the fuel spray can be supplied to the vicinity of the electrode of the spark plug 16, the configuration of the direct injection injector itself, the position of the direct injection injector, and the like are included. Any type of fuel injection may be employed. A fuel supply means is configured including the direct injection injector 18, a fuel supply line (not shown) connected to the direct injection injector 18, and a fuel pump.

  An intake passage 20 is connected to one side of the engine 1 so as to communicate with the intake port 9 of each cylinder 2. The intake passage 20 is for supplying fresh air to the combustion chamber 6 of each cylinder 2 of the engine 1, and the relatively downstream portion is an independent passage branched for each cylinder 2. The downstream end of each independent passage is connected to the intake port 9 of each cylinder 2. On the other hand, the relatively upstream portion is a common passage common to all cylinders, and in this common passage, an air cleaner 21 for filtering intake air and an electric throttle valve 22 in that order from the upstream side to the downstream side. , A compressor 611 of a turbocharger 61 described later, and an intercooler 23 for cooling the air compressed by the compressor 611 are arranged.

  On the other hand, an exhaust passage 30 for discharging burned gas (exhaust gas) from the combustion chamber 6 of each cylinder 2 is connected to the other side of the engine 1. The upstream portion of the exhaust passage 30 is constituted by an exhaust manifold having an independent passage that branches for each cylinder 2 and is connected to the outer end of the exhaust port 10 and a collecting portion where the independent passages gather. . On the downstream side of the exhaust manifold in the exhaust passage 30, a turbine 612 of the turbocharger 61 and a catalyst 31 for purifying harmful components in the exhaust are disposed in order from the upstream side to the downstream side. ing.

  A portion between the air cleaner 21 and the throttle valve 22 in the intake passage 20 and a portion between the turbine 612 of the turbocharger 61 and the catalyst 31 in the exhaust passage 30 allow a part of the exhaust gas to be taken into the intake passage. It is connected by an exhaust gas recirculation passage 40 for recirculating to 20. The exhaust gas recirculation passage 40 is provided with an exhaust gas recirculation valve 41 for adjusting the recirculation amount of the exhaust gas to the intake passage 20 and an EGR cooler 42 for cooling the exhaust gas.

  Here, the configuration of the turbocharger 61 will be briefly described. The turbocharger 61 includes a compressor 611 disposed between the throttle valve 22 and the intercooler 23 in the intake passage 20, and an exhaust gas. A turbine 612 disposed between the exhaust manifold in the passage 30 and the catalyst 31. An exhaust bypass passage 62 that bypasses the turbine 612 is also connected to the exhaust passage 30, and a wastegate valve 621 for adjusting the amount of exhaust flowing to the exhaust bypass passage 62 is disposed in the exhaust bypass passage 62. Has been.

  The spark ignition type gasoline engine 1 configured as described above is controlled by a power train control module (hereinafter referred to as PCM) 50 as a control means. The PCM 50 includes a CPU, a memory, a counter timer group, an interface, and a microprocessor having a path connecting these units. The PCM 50 includes an air flow sensor 51 that measures the air flow rate and the intake air temperature in the intake passage 20, a vehicle speed sensor 52 that detects the traveling speed of the vehicle, and an accelerator opening sensor that detects an operation amount (accelerator opening) of an accelerator pedal (not shown). 53, at least signals of a crank angle sensor 54 for detecting the rotation angle (crank angle) of the crankshaft 7 and an engine water temperature sensor 55 for detecting the temperature of engine cooling water are inputted, and various calculations are performed based on these signals. To determine the state of the engine 1 and the vehicle and control the VVT 15, the ignition circuit 17, the direct injection injector 18, the electric throttle valve 22, the exhaust gas recirculation valve 41, and the waste gate valve 621 accordingly. To do. Thus, the PCM 50 switches the combustion state of the engine 1 between HCCI combustion and SI combustion in accordance with the operation region of the engine 1.

  Specifically, in the operation region on the relatively low load and low rotation side, the premixed gas formed in the cylinder 2 is not directly ignited, but is compressed by the rise of the piston 5 and self-ignited. Execute the HCCI combustion mode. During the execution of the HCCI combustion mode, the throttle valve 22 is fully opened and the period from when the exhaust valve 12 is closed to when the intake valve 11 is opened during both the exhaust stroke and the intake stroke of the cylinder 2 (both the intake and exhaust valves 11 and 12). HCCI combustion is stabilized by increasing the temperature in the cylinder 2 with a large amount of internal EGR gas.

  Combustion by HCCI is considered to start combustion by pre-igniting the premixed gas substantially simultaneously at a number of locations in the combustion chamber 6 in the cylinder 2, as schematically shown in the lower right diagram of FIG. Therefore, the combustion period is shortened and the thermal efficiency is increased as compared with conventional combustion by flame propagation (Spark Ignition: SI combustion). In addition, since the combustion temperature is low, the production of nitrogen oxides is very low.

  On the other hand, HCCI combustion is realized in a fairly lean premixed gas or a premixed gas diluted with a large amount of EGR. In the operating region on the high rotation side, SI combustion is performed. At this time, the fuel injection amount is controlled so that the air-fuel ratio in the cylinder 2 becomes substantially the stoichiometric air-fuel ratio (excess air ratio λ = 1).

  The most characteristic control in the control device for the engine 1 disclosed herein is the control from the start of the engine 1 to the completion of warm-up. Hereinafter, the characteristic warm-up promotion control will be described with reference to the drawings. explain.

  FIG. 2B relates to the conventional control in the period from the start of the engine 1 to the completion of warm-up. When the AWS condition is satisfied at the start of the engine 1, particularly at the cold start, the engine 1 After the first explosion, the AWS operation mode for quickly raising the temperature of the catalyst 31 to a predetermined temperature is executed. AWS (Accelerated Warm-up System) is a system for increasing the amount of intake air when the engine 1 is started. Although not shown, the system is arranged on a bypass air passage that bypasses the throttle valve 22 and on the bypass air passage. At the time of cold start, the AWS valve is opened to increase the amount of intake air, and the ignition timing of the spark plug 16 is significantly retarded to retard the exhaust gas. The exhaust gas purification is promoted by increasing the temperature of the catalyst 31 to accelerate the activation of the catalyst 31. Therefore, SI combustion is executed in the AWS operation mode.

  In this AWS operation mode, as shown in FIG. 2B, when the catalyst temperature rapidly rises and reaches a predetermined temperature (for example, the activation temperature of the catalyst 31), the AWS operation mode is terminated, and then The SI combustion mode is executed.

  In the above-described AWS operation mode, although the exhaust loss can be increased to increase the catalyst temperature early by significantly retarding the ignition timing, the cooling loss is relatively reduced, so the engine temperature ( This is because the increase in the engine water temperature is suppressed by that amount, and the engine is not warmed up.

  For example, FIG. 4 shows the self-ignition condition in MBT in the relationship between the in-cylinder temperature Tx and the in-cylinder pressure Px when the engine speed is 1000 rpm and the excess air ratio λ = 2.4. HCCI combustion cannot be executed in the region on the left side of the dashed line in the figure because the auto-ignition condition is not satisfied, and HCCI combustion can be executed in the region on the right side because the auto-ignition condition is satisfied. Become. The solid line in the figure shows an example of the change history of the in-cylinder temperature and the in-cylinder pressure when the engine is warm, and the compression end temperature pressure (see the white circle in the figure) satisfies the self-ignition condition in MBT. Therefore, when the engine 1 is warm (for example, after the warm-up of the engine 1 is completed), HCCI combustion can be executed. On the other hand, when the engine 1 indicated by a broken line in the drawing is cold, the wall surface temperature (wall temperature) in the cylinder is low, and the temperature difference between the air-fuel mixture compressed in the cylinder and the wall temperature is the temperature of the engine 1. It becomes larger than the temperature difference between hours. As a result, the amount of heat released to the wall surface in the cylinder 2 increases, and the compression end temperature becomes lower than when the engine 1 is warm, and the self-ignition condition is not satisfied (see the black circle in the figure). Therefore, when the engine 1 is cold (in other words, in an unwarmed state), HCCI combustion cannot be executed.

  Therefore, in conventional control, SI combustion is performed during a period in which the engine 1 is not warmed up. In the SI combustion mode here, while setting the excess air ratio λ = 1, throttling is performed for load adjustment and the ignition timing is set to MBT or the engine 1 is slightly advanced (progressed to promote warm-up). Horn). Thus, in conventional control, pumping loss due to throttling is caused by executing SI combustion when the engine 1 is not warmed up in which HCCI combustion cannot be performed.

  Then, after the warm-up of the engine 1 is completed such that the engine water temperature reaches a predetermined temperature, HCCI combustion becomes possible, so that the operation mode is shifted to the normal operation mode. That is, as described above, the HCCI combustion mode and the SI combustion mode are switched according to the engine operating region. Among these, in the HCCI combustion mode, as described above, the throttle valve 22 is fully opened and the fuel injection amount is such that the excess air ratio λ in the cylinder 2 is 1 or more (the air-fuel ratio is lean). By being controlled, the efficiency is greatly improved in terms of fuel consumption, and it is also advantageous in terms of exhaust emission.

  In contrast to this conventional control, the control performed by the control device disclosed herein is to promote warm-up of the engine 1 during a period in which the engine 1 is not warmed up and cannot perform HCCI combustion. The warm-up promotion control (warm-up promotion mode) including the pre-combustion is executed. As will be described later in detail along with the execution of this warm-up promotion control, HCCI combustion can be performed even when the engine 1 is not warmed up. Combustion is not SI combustion but HCCI combustion. As a result, both the early transition to the normal operation mode (HCCI combustion mode) by shortening the warm-up time and the substantial expansion of the feasible period of the HCCI combustion mode have been realized, resulting in significant fuel efficiency improvements. Plan.

  Specifically, as shown in FIG. 3, in this warm-up promotion control, prior to main combustion, SI combustion is executed in the first half of the compression stroke (pre-SI combustion, see the lower left diagram in FIG. 3). This pre-SI combustion increases the cooling loss of the engine 1. For example, FIG. 5 shows the relationship between the cooling loss and the exhaust loss of the engine 1 with respect to the combustion start timing, and the cooling loss decreases as the combustion start timing becomes later (as it goes to the right in FIG. 5). On the other hand, exhaust loss increases. This is advantageous, for example, for raising the temperature of the catalyst 31, and corresponds to retarding the ignition timing in the AWS operation mode as described above. On the other hand, the earlier the combustion start timing is (the farther left it is in FIG. 5), the more the exhaust loss decreases, while the cooling loss increases. That is, since the gas in the cylinder 2 that has become high temperature due to early combustion is compressed, the amount of heat released to the wall surface in the cylinder 2 increases, and the cooling loss of the engine 1 increases. This is advantageous in promoting warm-up of the engine 1. Therefore, in warm-up promotion control, pre-SI combustion is performed in the first half of the compression stroke from the viewpoint of increasing the cooling loss by increasing the combustion start timing. Run. As a result, as shown in FIG. 2 (a), an increase in the temperature of the engine 1 (engine water temperature) is promoted compared to the conventional control (the gradient of the temperature change graph of the engine 1 becomes larger), and the engine 1 The time until the warm-up is completed is shortened compared to the conventional control. In other words, it is possible to quickly shift to the normal operation mode and quickly execute the HCCI combustion mode that is superior in terms of fuel consumption and exhaust emission.

  Moreover, since the early pre-SI combustion described above also contributes to an increase in the compression end temperature, the compression end temperature can satisfy the self-ignition condition. Therefore, in the warm-up promotion control, the premixed gas formed in the cylinder 2 by executing the main fuel injection different from the pre-fuel injection is burned in the vicinity of the MBT, not in the SI combustion but in the HCCI combustion (main HCCI combustion, (See the lower center and lower right in FIG. 3). Executing HCCI combustion even when the engine 1 is not warmed up is substantially equivalent to starting HCCI combustion at an early stage. As the main HCCI combustion is performed, the throttle valve 22 is basically fully opened during the warm-up promotion control period, so that the pumping loss is reduced. That is, the warm-up promotion control can improve the fuel efficiency at least by the reduction of the pumping loss as compared with the conventional control.

  Thus, the pre-SI combustion has not only a role of promoting warm-up of the engine 1 but also a role of assisting subsequent HCCI combustion. The warm-up promotion control is performed while the engine 1 is being executed while performing HCCI combustion. It can be said that the control promotes the warm-up of the engine.

  Next, control of the direct injection injector 18 and the spark plug 16 in the warm-up promotion control will be described with reference to FIG. First, fuel injection related to pre-SI combustion (pre-fuel injection) is performed by the direct injection injector 18, and the direct injection injector 18 injects fuel in the vicinity of the electrode of the spark plug 16, thereby A stratified mixture is formed in the vicinity of the electrode. In addition, in the pre-SI combustion, from the viewpoint of increasing the cooling loss, the combustion start timing is preferably set as early as possible in the first half of the compression stroke after the intake valve 11 is closed. Depending on the operating state (for example, compression end temperature, intake air amount, engine load, etc.), it may be changed and set as appropriate. The timing of the pre-fuel injection is appropriately set during the intake stroke or the compression stroke so that the pre-SI combustion can be performed at a desired timing in the first half of the compression stroke. As an example, the pre-fuel injection timing may be set immediately after the intake valve 11 is closed, for example. Thus, the spark plug 16 performs spark ignition on the stratified air-fuel mixture around the spark plug 16 at a predetermined timing to perform ignition combustion, thereby executing pre-SI combustion.

  Next, fuel injection (main fuel injection) related to main HCCI combustion is also performed by the direct injection injector 18. In this embodiment, the main fuel injection timing is set in the second half of the compression stroke after the completion of the pre-SI combustion. The timing of the main fuel injection may be set as appropriate so that the main HCCI combustion can be performed at a desired timing (for example, MBT), and the operation state of the engine 1 (for example, the compression end temperature, the intake air amount, the engine load, etc.). Accordingly, it may be changed and set as appropriate. By performing main fuel injection at a predetermined timing by the direct injection injector 18, a substantially uniform premixed gas is formed in the cylinder 2, and the premixed gas is compressed and ignited near the compression top dead center. The main HCCI combustion is executed.

  Next, the control at the time of starting the engine 1 executed by the PCM 50 will be described with reference to the flowchart of FIG. This flowchart starts after the first explosion of the engine 1, and here, it is assumed that the execution condition of the AWS is satisfied. First, in step S61 after the start, it is determined that the AWS operation mode is being executed, and the accumulated AWS execution time (that is, the execution duration time of the AWS operation mode up to the present time) is read. In the subsequent step S62, the accumulated AWS execution time is predetermined. It is determined whether or not it is greater than or equal to the value. When the predetermined value is not satisfied, that is, when the AWS operation mode is continued, the process proceeds to step S63 and the AWS operation mode is continued. On the other hand, when the AWS integration time is equal to or greater than the predetermined value and the AWS operation mode is terminated, the process proceeds to step S64. The predetermined value in step S62 is changed according to, for example, the engine water temperature or the outside air temperature.

  In step S64, which is shifted to end the AWS operation mode, the accelerator opening and the engine speed are read from the accelerator opening sensor 53 and the crank angle sensor 54, and in the subsequent step S65, the intake air is taken in based on the signal from the air flow sensor 51. Deriving the quantity. A CPS (Cylinder Pressure Sensor) that detects the pressure in the cylinder 2 may be attached, and the intake amount may be derived using the detected value of the CPS. In step S66, the engine water temperature and the intake air temperature are read from the water temperature sensor 55 and the air flow sensor 51, respectively, and the compression end temperature is calculated from the compression end temperature map that is preset and stored in the PCM 50. The compression end temperature map is set as shown in FIG. 7, for example, and the compression end temperature with respect to the engine water temperature and the intake air temperature is set. Based on this compression end temperature, can the normal end operation mode in which the compression end temperature satisfies the self-ignition condition and HCCI combustion can be executed (is a relatively upper right region in the figure), compression end temperature? It is possible to determine whether the warm-up acceleration mode in which the pressure does not satisfy the self-ignition condition and HCCI combustion cannot be performed (is a relatively lower left region in the figure). In step S67, it is determined whether or not it is possible to shift to the normal operation mode based on the calculated compression end temperature. When the transition is possible (when YES), the process proceeds to step S616, while the transition is impossible. If (NO), the process proceeds to step S68. Here, the compression end temperature is calculated using the compression end temperature map, but the compression end temperature may be calculated from the engine water temperature and the intake air temperature by modeling, for example.

  After step S68, since the engine 1 is not warmed up, the warm-up promotion mode for promoting warm-up of the engine 1 is executed. Specifically, in step S69, a base pre-injection amount and a main injection amount are set. The base pre-injection amount and the base main injection amount may be set as shown in FIG. 8A, for example. Here, the base pre-injection amount and the base main injection amount are constant regardless of the compression end temperature. Is set. Note that the base pre-injection amount and the base main injection amount may be changed according to the compression end temperature. Although details will be described later, after the warm-up of the engine 1 is completed, as shown in the figure, the execution of the pre-SI combustion is completed, so the base pre-injection amount is set to 0 (zero). On the other hand, since the pre-SI combustion performed in the warm-up promotion mode is executed in the first half of the compression stroke, it becomes a reverse torque. Therefore, the base main injection amount is the reverse torque before the warm-up of the engine 1 is completed. Is set relatively large in consideration of the occurrence of On the other hand, after the warm-up of the engine 1 is completed, the execution of the pre-SI combustion is terminated and no reverse torque is generated. Therefore, the base main injection amount (when the engine 1 is warmed up and the mode is shifted to the HCCI combustion mode). Is set to be smaller than that before the warm-up of the engine 1 is completed, as shown in FIG.

  Here, in the warm-up promotion mode, the total amount of the pre-injection amount and the main injection amount is set such that the excess air ratio in the cylinder 2 is λ = 1. This is to increase the cooling loss of the engine 1 to promote the warm-up of the engine 1 and complete the warm-up of the engine 1 at an early stage. That is, since the main HCCI combustion is performed, the total amount of the pre-injection amount and the main injection amount may be set so that the excess air ratio λ is larger than 1 from the viewpoint of thermal efficiency. However, in this case, since the pre-injection amount relatively decreases, an increase in the cooling loss of the engine 1 is suppressed, and there is a possibility that the time until the engine 1 is warmed up becomes longer. Therefore, in the warm-up promotion mode, if the highest priority is to complete the warm-up of the engine 1 at an early stage, the total amount of the pre-injection amount and the main injection amount is expressed as λ = 1. It is desirable to set so that Further, since the warm-up promotion control is executed after the activation of the catalyst 31 after the end of the AWS operation mode, setting the excess air ratio in the cylinder 2 to be λ = 1 is It can also be advantageous in terms of emissions.

  Further, the pre-injection amount may be limited to, for example, 1/3 or less of the main injection amount so that the above-described reverse torque does not become too large.

  In the subsequent step S610, the pre-injection amount correction coefficients (1) and (2) and the main injection amount correction coefficients (1) and (2) are set in accordance with the operating state of the engine 1, respectively. Specifically, as shown in FIG. 8B, a correction coefficient (1) for the pre-injection amount and a correction coefficient (1) for the main injection amount are set according to the intake air amount. As described above, in the warm-up promotion mode, the total amount of the pre-injection amount and the main injection amount is set so that the excess air ratio in the cylinder 2 becomes λ = 1, so that the pre-injection amount increases as the intake air amount increases. It is necessary to increase the injection amount and the main injection amount. Therefore, the pre-injection amount correction coefficient (1) and the main injection amount correction coefficient (1) are respectively set so that the pre-injection amount and the main injection amount are increased in accordance with the increase in the intake air amount.

  Further, as shown in FIG. 8C, the pre-injection amount correction coefficient (2) and the main injection amount correction coefficient (2) are set according to the engine load (accelerator opening). That is, as the engine load increases, the main injection amount is increased because of the need to increase the engine torque generated by the main HCCI combustion. On the other hand, as described above, in the warm-up promotion mode, since the total amount of the pre-injection amount and the main injection amount is set to be the excess air ratio λ = 1, the pre-injection amount is increased as the main injection amount is increased. Reduced weight. Accordingly, the pre-injection amount correction coefficient (2) is set so that the pre-injection amount decreases as the engine load increases, and the main injection amount correction coefficient (2) increases as the engine load increases. The injection amount is set to increase.

  Thus, if the correction coefficients (1) and (2) for the pre-injection amount and the main injection amount are set, the base pre-injection amount is corrected to, for example, the base pre-injection amount in accordance with the set correction coefficients (1) and (2) in step S611. The correction is performed by multiplying the coefficients (1) and (2). In step S612, the base main injection amount is corrected, for example, to the base pre-injection amount according to the set correction coefficients (1) and (2). ) Is corrected.

  In step S613, according to the set pre-injection amount, as described above, pre-fuel injection is executed at a predetermined timing, and in step S614, spark ignition by the spark plug 16 is executed at a predetermined timing. Thus, pre-SI combustion is performed. On the other hand, in step S615, main fuel injection is executed at a predetermined timing according to the set main injection amount, and the premixed gas formed in the cylinder 2 by this is compressed ignition combustion (main HCCI combustion) in the vicinity of MBT. (See also FIG. 3).

  If the warm-up of the engine 1 is promoted by the execution of the warm-up promotion mode and the warm-up is completed, it is determined in step S67 that it is possible to shift to the normal operation mode. Therefore, the process proceeds to step S616. Then, the normal operation mode for switching between the HCCI combustion mode and the SI combustion mode is executed in accordance with the operation region of the engine 1.

  Here, the order of each step in the flow of FIG. 6 is for convenience of explanation, and the order of changing the order as appropriate, or performing the execution of each step in parallel in time, etc. Of course it is possible.

  As described above, in the above-described configuration, in the non-warm-up state of the engine 1, particularly in the period after the end of the AWS operation mode and before the warm-up of the engine 1 is completed, the warm-up that performs both pre-SI combustion and main HCCI combustion Run promotion mode. By performing the pre-SI combustion in the first half of the compression stroke, the cooling loss of the engine 1 increases as shown in FIG. 5, and warming up of the engine 1 can be promoted. As illustrated in FIG. 2A, in the AWS operation mode, the ignition timing is retarded to increase the exhaust loss, so that the catalyst temperature rise is promoted while the engine 1 temperature rise is relatively high. On the other hand, in the warm-up promotion mode, the cooling loss of the engine 1 is increased, so that the temperature rise of the engine 1 becomes steeper than that in the AWS operation mode. Warm-up is promoted. As a result, the warm-up of the engine 1 can be completed early and the warm-up time can be shortened as compared with the conventional control that does not execute such pre-SI combustion (see (b) of the figure).

  Moreover, since execution of pre-SI combustion also contributes to increasing the compression end temperature, HCCI combustion can be performed even when the engine 1 is in an unwarmed state. Thus, in the warm-up promotion mode, by performing HCCI combustion as the main combustion, the throttle valve 22 can be fully opened to reduce the pumping loss. In particular, in the conventional control, SI combustion with throttling is executed during the period until the warm-up of the engine 1 is completed, and a pumping loss is generated. Will be advantageous. In addition, by performing main HCCI combustion, it is advantageous also in terms of exhaust emission.

  Therefore, by promoting warm-up of the engine 1, it is possible to shift to the normal operation mode at an early stage and to execute the HCCI combustion mode at an early stage, and to enable execution of HCCI combustion during the warm-up of the engine 1. Can be combined to improve fuel efficiency significantly.

  For example, as shown in FIG. 9, in addition to the direct injection injector 18, a port injector (second fuel injection valve) 19 is disposed so as to inject fuel toward the intake port 9, and the main HCCI. The main fuel injection for combustion may be executed by the port injector 19. In this case, as shown in FIG. 10, the timing of the main fuel injection by the port injector 19 may be completed in the intake stroke before the compression stroke in which the pre-fuel injection is performed. By doing so, the injected fuel spray flows into the cylinder 2 together with the intake air, and is widely dispersed in the cylinder 2 whose volume increases as the piston 5 descends to form a substantially uniform premixed gas (see FIG. (See also the lower left figure of 10). For example, in the flow shown in FIG. 6, step S615 is executed before step S613.

  In this case, a stratified mixture is formed in the vicinity of the electrode of the spark plug 16 by the pre-fuel injection in the cylinder 2 in which a substantially uniform pre-mixture is already formed, and the spark plug 16 As a result, the air-fuel mixture is sparked and pre-SI combustion is performed. At this time, since the pre-SI combustion is executed in the first half of the compression stroke, the premixed gas in the cylinder 2 is extremely lean as a whole at this timing, so the flame does not propagate, The substantially uniform premixed gas in the cylinder 2 is combusted in the vicinity of the compression top dead center after the pre-SI combustion. The main injection amount by the port injector 19 may be set so that, for example, the in-cylinder excess air ratio λ is 2 or more.

  Even when the main fuel injection is performed by the direct injection injector 18, the timing of the main fuel injection may be completed in the intake stroke before the compression stroke in which the pre-fuel injection is performed. By doing so, as in the case where the main fuel injection is executed by the port injector 19 described above, the injected fuel spray is widely dispersed in the cylinder 2 whose volume increases as the piston 5 descends, and is substantially uniform. A premixture may be formed.

  As described above, the spark ignition engine control device disclosed herein is useful in terms of improving the fuel efficiency of an automobile.

1 Spark Ignition Engine 16 Spark Plug 18 Direct Injection Injector (Fuel Injection Valve)
19 Port injector (second fuel injection valve)
2-cylinder 50 PCM (control means)
9 Intake port

Claims (5)

A spark ignition engine supplied with fuel containing gasoline,
Fuel supply means including a fuel injection valve for injecting the fuel into a cylinder of the engine;
A spark plug for spark ignition of the air-fuel mixture in the cylinder;
Through the control of the fuel supply means and the ignition plug, and a control unit for controlling the operation of the pre disappeared engine, a,
The control means includes an SI combustion mode in which an air-fuel mixture in the cylinder is spark-ignited by the spark plug according to an operating region of the engine, and an HCCI combustion mode in which the air-fuel mixture in the cylinder is subjected to compression ignition combustion. switching,
The control means further sets an operation mode for activating the catalyst when a predetermined condition is satisfied at the start of the engine,
After completion of the operation mode, the engine is, when not warmed up yet before the warm-up is complete, perform vital pre fuel injection for injecting fuel around the spark plug by the fuel injection valve, an intake Spark ignition combustion is performed by performing spark ignition on the air-fuel mixture around the spark plug by the spark plug in the first half of the compression stroke after the valve is closed, and the cylinder is performed by main fuel injection different from the pre-fuel injection. A control device for a spark ignition type engine, wherein a premixed gas formed inside is subjected to compression ignition combustion near the compression top dead center after the spark ignition combustion. The control device for a spark ignition engine according to claim 1,
The control means sets the amount of fuel supplied into the cylinder by the pre-fuel injection to be smaller than the amount of fuel supplied into the cylinder by the main fuel injection, and the cylinder through the two fuel injections. The total amount of fuel to be supplied in the interior is set so that the excess air ratio λ is 1 or more ,
The control means also reduces the amount of fuel supplied into the cylinder by the pre-fuel injection and increases the amount of fuel supplied into the cylinder by the main fuel injection in response to an increase in the engine load. Control device for spark ignition engine. The control device for a spark ignition engine according to claim 1,
The control means performs both the pre-fuel injection and the main fuel injection through the fuel injection valve, completes the pre-fuel injection in the first half of the compression stroke, and performs the main fuel injection in the second half of the compression stroke. Control device for the spark ignition engine to be completed. The control device for a spark ignition engine according to claim 1,
The fuel supply means further includes a second fuel injection valve that injects fuel into an intake port of the engine,
The control means performs the pre-fuel injection through the fuel injection valve, performs the main fuel injection through the second fuel injection valve, and completes the pre-fuel injection in the first half of the compression stroke. A control device for a spark ignition engine that executes main fuel injection at least in an intake stroke before the compression stroke. The control device for a spark ignition engine according to claim 1,
The engine is a spark ignition engine control device having a geometric compression ratio of 16 or more.

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