JP2017150419A - Engine and vehicle including the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To properly self-ignite air fuel mixture without lowering an in-cylinder temperature.SOLUTION: An engine 1 is a premixed compression ignition type engine that includes a fuel injection device 11 configured to directly inject fuel into a cylinder, and compresses air fuel mixture, obtained by mixing air and fuel, in the cylinder to perform self-ignition. The engine, in a premixed compression ignition region H where premixed compression ignition can be performed on the basis of a predetermined engine rotational frequency and a required engine load, injects fuel in a negative valve overlap period Twhere a suction valve and an exhaust valve are closed.SELECTED DRAWING: Figure 4

Description

  The present invention relates to an engine and a vehicle including the same, and more particularly to a premixed compression ignition type engine and a vehicle including the same.

  In recent engines, a premixed compression ignition type gasoline engine has been studied for the purpose of further improving fuel consumption (see, for example, Patent Document 1). The engine described in Patent Document 1 is a direct-injection engine that directly injects fuel into a cylinder, and does not use spark ignition (SI: Spark Ignition) with an ignition plug and an ignition plug. It is configured to be switchable between premixed compression ignition (HCCI) in which the mixed gas mixture is compressed and self-ignited.

  In Patent Document 1, premixed compression ignition is performed in an operation region (HCCI region) where the engine speed and engine load are relatively small, and SI ignition is performed in an operation region (SI region) where the engine load is relatively large. That is, SI ignition and premixed compression ignition are switched according to the engine speed and engine load.

JP 2010-236467 A

  By the way, the operation region (combustion region) in which the above-described premixed compression ignition can be realized is limited, and it is very difficult to control the premixed compression ignition. For example, it is conceivable that when the fuel is injected into the cylinder, the in-cylinder temperature decreases, and as a result, the temperature necessary for self-ignition of the air-fuel mixture cannot be obtained and misfire occurs.

  The present invention has been made in view of such points, and an object thereof is to provide an engine capable of appropriately self-igniting an air-fuel mixture without lowering the in-cylinder temperature and a vehicle including the same. .

  The engine according to the present invention is a premixed compression ignition type engine that includes a fuel injection device that directly injects fuel into a cylinder, compresses the air-fuel mixture mixed in the cylinder, and self-ignites. In a premixed compression ignition region where premixed compression ignition is possible based on a predetermined engine speed and engine load, fuel is injected during a negative valve overlap period in which both the intake valve and the exhaust valve are closed .

  According to this configuration, the in-cylinder temperature before combustion can be increased by injecting fuel during the negative valve overlap period. Therefore, the temperature necessary for the self-ignition of the air-fuel mixture can be secured, and the air-fuel mixture can be appropriately self-ignited without causing misfire.

  In the engine according to the present invention, the premixed compression ignition region can be premixed compression ignition in a first premixed compression ignition region and a region having a higher load than the first premixed compression ignition region. And a second premixed compression ignition region, and in the second premixed compression ignition region, fuel is preferably injected during an intake stroke. According to this configuration, by injecting the fuel during the intake stroke, it is possible to ensure the time until the air and the fuel are mixed before the mixture starts to combust. As a result, the air-fuel mixture homogenized in the cylinder can be combusted, and combustion with high combustion efficiency can be performed.

  In the engine according to the present invention, the premixed compression ignition region may further include a third premixed compression ignition region capable of performing premixed compression ignition in a region having a higher load than the second premixed compression ignition region. And in the third premixed compression ignition region, it is preferable to inject the fuel at least twice before the start of combustion during the compression stroke. According to this configuration, the air-fuel mixture is uneven by injecting the fuel into a plurality of times. As a result, stratified combustion can be performed and combustion can be slowed down. Therefore, even when the engine load is relatively high, premixed compression ignition of the air-fuel mixture becomes possible, and further improvement in fuel consumption is realized. In addition, by stratified combustion of the air-fuel mixture, the air-fuel mixture can be combusted as a whole efficiently, and deterioration of exhaust gas performance can be prevented.

  Further, the engine according to the present invention is configured to be able to switch between spark ignition of the air-fuel mixture using the spark of the ignition device and premixed compression ignition, and when switching from premixed compression ignition to spark ignition, a negative valve Preferably, the overlap period is set to zero and spark ignition by the ignition device is started. According to this configuration, by eliminating the negative valve overlap period, it is possible to prevent sudden torque fluctuations without increasing the engine load, and it is possible to smoothly switch from premixed compression ignition to spark ignition. .

  In the engine according to the present invention, when the premixed compression ignition is switched to the spark ignition, when the first premixed compression ignition region shifts to the spark ignition, the second and third premixed compression are performed. It is preferable to pass through the third premixed compression ignition region when the second premixed compression ignition region is shifted to spark ignition through the ignition region. According to this configuration, since the engine load increases stepwise, a sudden torque fluctuation can be prevented, and the premixed compression ignition can be smoothly switched to the spark ignition.

  The vehicle according to the present invention preferably includes the above-described engine. According to this configuration, it is possible to enjoy the operational effects of the engine described above in the vehicle.

  According to the present invention, by injecting fuel during the negative valve overlap period, the air-fuel mixture can be appropriately self-ignited without reducing the in-cylinder temperature.

It is a conceptual diagram of the engine which concerns on this Embodiment. It is a figure which shows the combustion map of the engine which concerns on this Embodiment. In the engine which concerns on this Embodiment, it is a figure which shows the opening / closing timing of the intake valve and exhaust valve with respect to engine load. In the engine which concerns on this Embodiment, it is a graph which shows the fuel-injection timing with respect to engine load. It is a figure which shows the control flow of the engine which concerns on this Embodiment. It is a figure which shows the control flow of the engine which concerns on this Embodiment. It is a figure which shows the control flow of the engine which concerns on this Embodiment. In the engine which concerns on this Embodiment, it is a figure which shows the supercharging pressure with respect to engine load, and an EGR valve opening degree.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the following, an example in which the engine according to the present invention is applied to a four-wheeled vehicle will be described, but the application target is not limited to this and can be changed. For example, the engine according to the present invention may be applied to other types of vehicles (for example, motorcycles). In the following drawings, a part of the configuration is omitted for convenience of explanation.

  A schematic configuration of an engine according to the present embodiment will be described with reference to FIG. FIG. 1 is a conceptual diagram of an engine according to the present embodiment. In the present embodiment, it is assumed that a configuration (for example, a crank sensor or the like) that is normally provided in an automobile is provided, and description thereof is omitted.

  The engine 1 according to the present embodiment self-compresses an air-fuel mixture that is premixed with air and fuel without using an ignition device (SI: Spark Ignition) and an ignition device. It is configured to be able to switch between premixed compression ignition (HCCI) to be ignited. The engine 1 is, for example, an in-line multi-cylinder (four cylinders in the present embodiment) gasoline engine.

  The engine 1 includes a fuel injection device 11 that directly injects fuel into each cylinder of the cylinder block 10. An in-cylinder pressure sensor 12 that detects the pressure in the cylinder is provided in each cylinder. Further, the engine 1 is provided with a valve gear 13 provided with a variable valve timing mechanism (not shown). Although details will be described later, the valve gear 13 adjusts a valve overlap period, which will be described later, by changing the opening and closing timings of the intake valve and the exhaust valve (both not shown) according to the engine load and the engine speed.

  An intake pipe 15 is connected to the intake side of the engine 1 via an intake manifold 14. The intake pipe 15 is provided with a throttle valve 16, a supercharger 17 (compressor 17 b), and an intercooler 18 from the upstream side. On the other hand, an exhaust pipe 20 is connected to the exhaust side of the engine 1 via an exhaust manifold 19. The exhaust pipe 20 is provided with a LAF sensor 21, a supercharger 17 (turbine 17a), and a catalyst device 22 from the upstream side.

  The fuel injection device 11 is composed of a direct injection injector, and injects fuel into the cylinder in accordance with a command from the ECU 26 described later. The in-cylinder pressure sensor 12 is, for example, a piezo-type pressure sensor provided with a piezoelectric element, and outputs a voltage signal corresponding to the in-cylinder combustion pressure. The voltage signal is output to the ECU 26. The throttle valve 16 is a valve body that adjusts the opening according to the driver's accelerator operation. The flow rate of the intake air is adjusted by adjusting the opening of the throttle valve 16.

  The supercharger 17 is a turbocharger that drives the compressor 17b by turning the turbine 17a with the pressure of the exhaust gas, and compresses the intake air by the compressor 17b. Specifically, in the supercharger 17, a turbine 17a provided on the exhaust pipe 20 side and a compressor 17b provided on the intake pipe 15 side are coaxially connected by a turbo shaft 17c. The intercooler 18 cools the intake air compressed by the supercharger 17.

  A LAF sensor 21 (Linear Air-fuel Ratio Sensor) detects the air-fuel ratio from the oxygen concentration in the exhaust gas. The LAF sensor 21 is composed of, for example, a zirconia oxygen sensor, and detects the air-fuel ratio from a current value that changes according to the oxygen concentration. The air-fuel ratio is output to the ECU 26. The catalyst device 22 purifies exhaust gas, and is composed of, for example, a three-way catalyst. The catalytic device 22 converts pollutants (carbon monoxide, hydrocarbons, nitrogen oxides, etc.) in the exhaust gas into harmless substances (carbon dioxide, water, nitrogen, etc.).

  Further, the engine 1 according to the present embodiment employs an EGR system (Exhaust Gas Recirculation system) in which a part of the exhaust gas is returned to the intake side and recombusted. Specifically, the exhaust pipe 20 on the downstream side of the catalyst device 22 and the intake pipe 15 on the downstream side of the throttle valve 16 are connected by a pipe 23. The piping 23 is provided with an EGR cooler 24 for cooling the exhaust gas and an EGR valve 25 for adjusting the intake amount of the exhaust gas in order from the exhaust side.

  In addition to the above configuration, the engine 1 includes an ECU 26 that performs overall control of various operations in the engine 1. The ECU 26 includes a processor that executes various processes in the engine 1, a memory, and the like. The memory is configured by a storage medium such as a ROM (Read Only Memory) or a RAM (Random Access Memory) according to the application. The memory stores a control program for controlling each part of the engine 1.

  In particular, the ECU 26 stores a combustion map (see FIG. 2) based on the engine load and the engine speed in a memory. This combustion map includes a spark ignition region (SI region described later) that can be ignited using an ignition device, and a premixed compression ignition region (HCCI region described later) that allows premixed compression ignition. . Although details will be described later, the ECU 26 calculates the engine load required from the driver's accelerator operation, and based on the engine speed detected from a crank sensor (not shown) and the engine load, spark ignition is performed from the combustion map described above. And various operations of the engine 1 are controlled so as to switch between premixed compression ignition.

  In the engine 1 configured as described above, the opening degree of the throttle valve 16 is adjusted in accordance with the driver's accelerator operation, and clean intake air via an air cleaner (not shown) is introduced into the supercharger 17. In the supercharger 17, the intake air is compressed, and the intake air is cooled by the intercooler 18 and then supplied into the cylinder. In the cylinder, fuel is injected at a predetermined timing, and intake air and fuel are mixed. At this time, the air-fuel mixture is combusted by spark ignition by the ignition device or premixed compression self-ignition. Exhaust gas after combustion is discharged from the exhaust manifold 19 through the exhaust pipe 20 and the catalyst device 22.

  By the way, in a premixed compression ignition type engine that has been studied conventionally, in order to realize HCCI operation over a wide range of engine loads, the timing of fuel injection and the number of fuel injections are changed according to the engine load. The operation of the engine is controlled. For example, in a region where the engine load is relatively low, fuel is supplied into the cylinder by one-stage direct injection and the air-fuel mixture is self-ignited. On the other hand, in a region where the engine load is relatively high, noise and the pressure increase in the cylinder caused by the air-fuel mixture burning all at once affect the engine strength. We are trying to slow down.

  However, in the above-described low load region, the in-cylinder temperature decreases as the engine load decreases, and there is a problem that the temperature necessary for self-ignition of the air-fuel mixture is not ensured and misfire occurs. Further, in the high load region, the fuel injected for the first time is mixed with fresh air until it reaches combustion and becomes uniform. For this reason, there is a problem that a desired stratification degree cannot be obtained and it is difficult to appropriately slow down the combustion of the air-fuel mixture. Further, the fuel injected after the second time is burned without being sufficiently evaporated, which may cause an increase in PM (Particulate Matter) emission.

Therefore, the engine 1 according to the present embodiment includes a plurality of (three in the present embodiment) regions H _{1 to} H based on the engine load and the engine speed based on the region in which HCCI operation can be performed (region H described later). _The fuel is divided into _three (see FIG. 2), and control is performed to change the fuel injection timing and the number of injections for each of the regions H _{1 to} H ₃ .

For example, in the region H _{1 where the} engine load is relatively small, fuel is injected during the negative valve overlap period T _N (see FIG. 3) in which both the intake valve and the exhaust valve are closed. Thereby, in addition to the combustion heat in the previous cycle, the in-cylinder temperature can be raised. Therefore, the temperature required for the self-ignition of the air-fuel mixture can be secured, and the air-fuel mixture can be appropriately self-ignited without causing misfire.

Also, the larger area H ₃ relatively engine load, to inject fuel at least two times before the combustion before the start of the compression stroke. As described above, by injecting the fuel into a plurality of times, the air-fuel mixture becomes uneven, and stratified combustion can be performed. As a result, combustion can be slowed and deterioration of exhaust gas performance can be prevented.

  Next, a combustion map of the engine according to the present embodiment will be described with reference to FIG. FIG. 2 is a diagram showing a combustion map of the engine according to the present embodiment.

  As shown in FIG. 2, in the combustion map, the horizontal axis represents the engine speed and the vertical axis represents the engine load. In this combustion map, a spark ignition that can be ignited using an ignition device with a predetermined engine speed N (hereinafter simply referred to as the speed N) and engine load L (hereinafter simply referred to as the load L) as boundaries. Region S (SI region, hereinafter simply referred to as region S) and premixed compression ignition region H (HCCI region, hereinafter simply referred to as region H) capable of premixed compression ignition are set.

  Specifically, a region where the engine speed is equal to or lower than a predetermined speed N and the engine load is equal to or lower than the predetermined load L is a region H. In the region H, premixed compression ignition is performed in which the air-fuel mixture is compressed and ignited for combustion without using an ignition device. On the other hand, the region S is an area where the engine speed is larger than the predetermined speed N or the engine load is larger than the predetermined load L. In the region S, the air-fuel mixture is ignited by normal spark ignition using an ignition device. These regions H and S are further divided into regions.

The region H is divided into _three regions H _{1 to} H ₃ for each engine load, and the region H ₁ (first HCCI region), region H ₂ (second HCCI region), region, in order from the lowest engine load. H ₃ (third HCCI region). Here, the engine speed and the engine load, which are the boundary values of the regions H _{1 to} H ₃ on the combustion map, are referred to as a speed N ₁ and loads L ₁ and L ₂ , respectively. Rotational speed N ₁ is set to be smaller than the predetermined rotational speed N. Load L ₁ is set smaller than the predetermined load L and the load L _2, the load L ₂ is smaller than the predetermined load L.

Region H ₁ is on the combustion map, engine speed engine load below the rotation speed N ₁ indicates a predetermined load L ₁ following areas. In the area H _1, and during the intake stroke negative valve overlap period T _{N (see} FIG. 4) described later, the fuel is injected. Region H _2, in the combustion map, above the area H _1, and the engine load the engine speed is below a predetermined rotational speed N indicates the load L ₂ following areas. In the region H _2, fuel is injected once during an intake stroke. Region H _3, in the combustion maps, a high load than the region H _2, engine speed and engine load below a predetermined rotational speed N indicates the following areas predetermined load L. In the region H _3, at least twice the fuel is injected to the combustion before the start of the compression stroke.

The region S is divided into three regions S _S , S _L and S _R according to the concentration of the air-fuel mixture. Region S _S is a stoichiometric SI region combustion of the mixture based on the stoichiometric air-fuel ratio is performed. Region S _S, the engine load is set to a predetermined load L larger area. Area S _L is a lean SI region combustion of the mixture at a density lower than the stoichiometric air-fuel ratio is performed. The region _SL is set to a region where the engine speed is greater than the predetermined speed N. Region S _R is a rich SI region combustion of the mixture at a high grayscale level than the stoichiometric air-fuel ratio is performed. Region S _R is set from the region S _S in a region of high load and high rotation side.

  In the present embodiment, the fuel injection timing, the number of injections, the opening / closing timings of the intake valve and the exhaust valve, and the like are controlled based on this combustion map. Thus, by dividing the combustion map into a plurality of regions, it is possible to switch the combustion method as appropriate according to the state of the engine. Control of fuel injection timing and the like in each region will be described later.

  Next, the opening / closing timing of the intake valve and the exhaust valve with respect to the engine load will be described with reference to FIG. FIG. 3 is a diagram showing opening / closing timings of the intake valve and the exhaust valve with respect to the engine load in the engine according to the present embodiment. In FIG. 3, the horizontal axis indicates the engine load, and the vertical axis indicates time. Further, BDC on the vertical axis in FIG. 3 indicates the bottom dead center of the crankshaft, and TDC indicates the top dead center of the crankshaft.

  As described above, in the present embodiment, the valve gear 13 (see FIG. 1) is configured to adjust the opening / closing timings of the intake valve and the exhaust valve according to the engine load and the engine speed. In FIG. 3, the portion indicated by the solid line indicates the opening / closing timing of the intake valve, and the portion indicated by the alternate long and short dash line indicates the opening / closing timing of the exhaust valve.

  Specifically, IVO (Intake Valve Open) indicates the opening timing of the intake valve, and IVC (Intake Valve Close) indicates the timing of closing the intake valve. On the other hand, EVO (Exhaust Valve Open) indicates the timing for opening the exhaust valve, and EVC (Exhaust Valve Close) indicates the timing for closing the exhaust valve.

In particular, before and after TDC from the exhaust stroke to the intake stroke, a positive valve overlap period T _P indicating a state in which both the intake valve and the exhaust valve are opened, or a state in which both the intake valve and the exhaust valve are closed is illustrated. A negative valve overlap period _TN is set. In FIG. 3, for convenience of explanation, these valve overlap periods T _P and T _N are indicated by hatching.

  Normally, in the SI combustion by the ignition device, the positive valve overlap period described above is provided in order to increase the charging efficiency of the intake air. However, in HCCI combustion, if both the intake valve and the exhaust valve are opened, the in-cylinder temperature is lowered. Therefore, a negative valve overlap period is provided to prevent the in-cylinder temperature from being lowered.

Specifically, the present embodiment is configured to change the valve overlap periods T _P and T _N according to the engine load. As shown in FIG. 3, as the engine load becomes higher toward the area H ₁ in the region H _3, the valve timing is adjusted so negative valve overlap period T _N becomes shorter. Then, in the boundary portion of the transition from region H (region H ₃₎ in the region S, the negative valve overlap period T _N becomes zero. Further the engine load is high, the valve timing so as to gradually positive valve overlap period T _P becomes longer be adjusted.

  Next, the fuel injection timing and the like in each region of the combustion map will be described with reference to FIG. FIG. 4 is a graph showing the fuel injection timing with respect to the engine load in the engine according to the present embodiment. Note that the horizontal and vertical axes in FIG. 4 are the same as those in FIG. Further, in FIG. 4, for the convenience of explanation, the time during which fuel injection is performed is indicated by dot hatching.

As shown in FIG. 4, in the area H _1, after being once fuel injection in negative valve overlap period T _N, in front of the BDC during the intake stroke, once again fuel is injected. Thus, by injecting fuel in the negative valve overlap period _TN , the in-cylinder temperature before combustion can be increased in addition to the combustion heat of the previous cycle. As a result, the temperature necessary for the self-ignition of the air-fuel mixture can be secured, and self-ignition can be promoted while preventing misfire.

In particular, the region H ₁ where the engine load is low is a region in which the air-fuel mixture is difficult to self-ignite, and the fuel can be easily injected during the negative overlap period _TN to facilitate self-ignition, so that the HCCI operation can be performed as a whole. The region H can be enlarged. As a result, further improvement in fuel consumption can be realized. The fuel injection amount in the negative valve overlap period _TN is preferably adjusted to 50% or less of the fuel injected before the next combustion.

In the region H _2, fuel is injected once during an intake stroke. Specifically, in regions H _2, along with the injection time of the fuel as the engine load becomes higher becomes longer, the fuel injection timing is adjusted so as to approach just before (IVC) beginning of the compression stroke. Thus, in the region H _2, by injecting fuel during the intake stroke, until the air-fuel mixture starts combustion, it is possible to secure the time until the mixed air and fuel. As a result, the air-fuel mixture homogenized in the cylinder can be combusted, and combustion with high combustion efficiency can be performed.

In the region H _3, at least twice and before start of combustion during the compression stroke (FIG. 4, 2 times) the fuel is injected. Specifically, in the region H _3, as the engine load increases, the fuel injection timing is delayed. In the region H _3, it is uneven mixture by injecting fuel a plurality of times. As a result, stratified combustion can be performed and combustion can be slowed down. Therefore, relatively the engine load even at high region H _3, it is possible to HCCI operation, further improvement in fuel efficiency is achieved. In addition, by stratified combustion of the air-fuel mixture, the air-fuel mixture can be combusted as a whole efficiently, and deterioration of exhaust gas performance can be prevented.

  In the region S, fuel injection is performed in a relatively longer period than in the region H before and after the IVC timing. Further, the timing of fuel injection is gradually advanced as the IVC timing is gradually advanced as the engine load increases. In the region S, ignition is performed by an ignition device (not shown) after fuel injection.

As described above, in the present embodiment, by adjusting the fuel injection timing and the number of injections according to the engine load, the combustion system (regions H _{1 to} H ₃ , region H to region S is adjusted according to the state of the engine. ) Can be switched.

In particular, when switching from premixed compression ignition to spark ignition, that is, when shifting from the region H (region H ₃ ) to the region S, the negative valve overlap period _{TN is set} to zero and the ignition device is used. Start spark ignition. Thus, by eliminating the negative valve overlap period _TN , it is possible to prevent sudden torque fluctuations without increasing the engine load, and it is possible to smoothly switch from premixed compression ignition to spark ignition. .

Also, when moving from the region H ₁ in the region S, instead of the flow directly goes to area S, it is preferable that the transition from through the region H2, H3 in the area S. Similarly, when moving from the region H ₂ in the region S, instead of the flow directly goes to area S, it is preferable that the transition from through the region H3 to the area S. In these cases, the engine load increases stepwise, and the negative valve overlap period _TN decreases stepwise. For this reason, similar to the above, rapid torque fluctuation can be prevented, and it is possible to smoothly switch from premixed compression ignition to spark ignition.

  Next, an engine control flow according to the present embodiment will be described with reference to FIGS. 5 to 7 are diagrams showing a control flow of the engine according to the present embodiment. Specifically, FIG. 5 shows a control flow until selecting spark ignition or premixed compression ignition, FIG. 6 shows a control flow in the case of premixed compression ignition, and FIG. 7 shows a control flow in the case of spark ignition. Is shown. In the control flow shown below, unless otherwise specified, the operation (determination) subject is the ECU.

  As shown in FIG. 5, when the control is started, first, the required engine load and the engine speed are calculated (step ST101). In the engine 1 (see FIG. 1), the amount of intake air supplied into the cylinder is adjusted according to the accelerator opening, and the in-cylinder pressure changes and the engine speed also changes. In this case, the required engine load is calculated from the accelerator opening, and the engine speed is calculated from the output value of a crank sensor (not shown).

  Next, the engine water temperature is measured (step ST102), and the combustion map is read (step ST103). Then, it is determined whether the engine water temperature is equal to or higher than the threshold and whether the state of the engine 1 belongs to the HCCI region (region H: see FIG. 2) (step ST104).

If the engine water temperature is equal to or higher than the threshold value and the state of the engine 1 belongs to the region H (step ST104: YES), as shown in FIG. 6, does it belong to the first HCCI region (region H ₁ : see FIG. 2)? It is determined whether or not (step ST201). If you belong to the region _{H 1} (step ST201: YES), after injecting the fuel with a negative valve overlap period _{T N,} are again fuel in the intake stroke is injected (step ST 202), the control is ended.

If it does not belong to the area _{H 1} (step ST 201: NO), the 2HCCI region: whether belongs to (region _{H 2} see FIG. 2) is determined (step ST 203). If you belong to the region _{H 2} (step ST203: YES), the fuel in the intake stroke is injected (step ST 204), the control is ended.

If it does not belong to the region _{H 2} (step ST 203: NO), the 3HCCI area: is determined to belong to (region _{H 3} see Figure 2), at least two times fuel is injected before the start of combustion during the compression stroke (Step ST205). Then, it is determined whether or not the last fuel injection has been completed before the start of combustion of the air-fuel mixture (step ST206).

  When the last fuel injection is finished before the start of combustion of the air-fuel mixture (step ST206: YES), the control is finished. On the other hand, when the last fuel injection is not completed before the start of combustion of the air-fuel mixture (step ST206: NO), a flag for advancing the fuel injection timing of the next cycle is set (step ST207), and the control ends.

  In step ST104, when the engine water temperature is lower than the threshold value or the state of the engine 1 does not belong to the region H (step ST104: NO), as shown in FIG. 7, as shown in FIG. It is determined whether or not the temperature of the feeder 17 (turbine 17a: see FIG. 1) is equal to or lower than a threshold value (step ST301). Note that the temperature of the catalyst device 22 or the turbine 17a is measured by a thermometer (not shown). The temperatures of the catalyst device 22 and the turbine 17a may be obtained from map data stored in the ECU 26 based on the driving state (fuel injection amount, etc.) of the engine 1.

When the temperature of the catalyst device 22 or the turbine 17a is equal to or lower than the threshold value (step ST301: YES), the NOx concentration in the exhaust gas is equal to or lower than the threshold value, and the state of the engine 1 is a lean SI region (region S _L : FIG. 2). It is determined whether it belongs to (see ST302).

  Note that the NOx concentration (NOx emission amount) in the exhaust gas can be detected by using a NOx sensor (not shown) provided downstream of the engine 1. Further, the NOx emission amount may be obtained in advance based on the driving condition of the engine 1 and stored in the ECU 26 as map data, and the map data may be referred to.

NOx concentration in the exhaust gas is equal to or less than the threshold value, if the state of the engine 1 belongs to the area S _L (step ST 302: YES), the condition of the lean SI region, combust a mixture of thinner than the stoichiometric air-fuel ratio Concentration Thus, the fuel injection and ignition control is performed (step ST303), and the control ends.

Greater than the NOx concentration in the exhaust gas threshold, or if the state of the engine 1 does not belong to the area _{S L} (step ST 302: NO), the state of the engine 1 stoichiometric SI region: (a region _{S S} see Figure 2) It is determined that it belongs. In this case, fuel injection and ignition control are performed so that the stoichiometric air-fuel ratio mixture is burned under the stoichiometric SI region conditions (step ST304), and the control ends.

In step ST301, if the temperature of the catalyst device 22 or the turbine 17a is higher than the threshold value (step ST301: NO), the engine 1 is in the rich SI region (region S _R : see FIG. 2) assuming that the engine load is large. It is determined that it belongs. In this case, fuel injection and ignition control are performed so that the air-fuel mixture is burned at a concentration higher than the stoichiometric air-fuel ratio under the conditions of the rich SI region (step ST305), and the control ends.

As described above, according to the present embodiment, the in-cylinder temperature before combustion can be increased by injecting fuel during the negative valve overlap period _TN . Therefore, the temperature necessary for the self-ignition of the air-fuel mixture can be secured, and the air-fuel mixture can be appropriately self-ignited without causing misfire.

  In addition, this invention is not limited to the said embodiment, It can change and implement variously. In the above-described embodiment, the size, shape, and the like illustrated in the accompanying drawings are not limited to this, and can be appropriately changed within a range in which the effect of the present invention is exhibited. In addition, various modifications can be made without departing from the scope of the object of the present invention.

Further, in the above-described embodiment, the region H _3, it is configured to inject the two fuel before combustion starts during the compression stroke is not limited to this configuration. For example, the fuel may be injected three or more times before the start of combustion during the compression stroke.

  In the above-described embodiment, the in-cylinder pressure is detected by the in-cylinder pressure sensor 12, but the present invention is not limited to this configuration. The increase amount of the in-cylinder pressure and the in-cylinder pressure may be calculated from the driving state of the engine 1. For example, it is conceivable to calculate the amount of increase in the in-cylinder pressure as the amount of change in the in-cylinder pressure with respect to time or crank angle.

In the above-described embodiment, the ignition device is not used in the region H. However, the present invention is not limited to this configuration. For example, in the engine load is relatively small area H _1, may be carried out ignition assist by the ignition device.

In the above-described embodiment, in the regions H ₂ , H ₃ and the region S, it is possible to perform supercharging by the supercharger 17 and introduction of EGR. FIG. 8 is a diagram showing the supercharging pressure and the EGR valve opening with respect to the engine load in the engine according to the present embodiment. FIG. 8A shows the supercharging pressure with respect to the engine load, and FIG. 8B shows the EGR valve opening degree with respect to the engine load. In FIG. 8, the horizontal axis represents the engine load, the vertical axis in FIG. 8A represents the supercharging pressure, and the vertical axis in FIG. 8B represents the EGR valve opening.

As shown in FIG. 8A, boost pressure is relatively low in the region H _1, is higher as the distance from the region H ₂ in the region H _3. In the region S, the supercharging pressure is maintained at a high level. As shown in FIG. 8B, EGR valve opening is relatively small in area _{H 1,} is larger as the distance from the region _{H 2} in the region _{H 3.} In the region S, the EGR valve opening is reduced as the engine load increases. In this case, particularly in the region H ₃ , in addition to slowing the combustion of the air-fuel mixture by multiple injections during the compression stroke, supercharging by the supercharger 17 and introduction of EGR will further slow down the combustion of the air-fuel mixture. Is possible.

  As described above, the present invention has the effect that the air-fuel mixture can be appropriately self-ignited without lowering the in-cylinder temperature. In particular, the present invention includes a premixed compression ignition type engine and the same. Useful for vehicles.

1 Engine 11 Fuel injection device 26 ECU
H HCCI region (premixed compression ignition region)
H ₁ first HCCI region (first premixed compression ignition region)
H2 _second HCCI region (second premixed compression ignition region)
H _{3 3rd} HCCI region (third premixed compression ignition region)
S SI area (spark ignition area)
S _S stoichiometric SI region S _L lean SI range S _R-rich SI region T _N negative valve overlap period T _P positive valve overlap period

Claims (6)

A premixed compression ignition type engine that includes a fuel injection device that directly injects fuel into a cylinder, compresses the mixture of air and fuel in the cylinder, and self-ignites.
In a premixed compression ignition region where premixed compression ignition is possible based on a predetermined engine speed and engine load, fuel is injected during a negative valve overlap period in which both the intake valve and the exhaust valve are closed engine. The premixed compression ignition region includes a first premixed compression ignition region and a second premixed compression ignition region capable of premixed compression ignition in a region having a higher load than the first premixed compression ignition region. Have
The engine according to claim 1, wherein fuel is injected during an intake stroke in the second premixed compression ignition region. The premixed compression ignition region further includes a third premixed compression ignition region capable of premixed compression ignition in a region having a higher load than the second premixed compression ignition region,
3. The engine according to claim 2, wherein in the third premixed compression ignition region, fuel is injected at least twice before the start of combustion during the compression stroke. It is configured to be able to switch between spark ignition of the air-fuel mixture using the spark of the ignition device and premixed compression ignition,
4. When switching from premix compression ignition to spark ignition, the negative valve overlap period is made zero and spark ignition by the ignition device is started. 5. Engine.   When switching from premixed compression ignition to spark ignition, when shifting from the first premixed compression ignition region to spark ignition, the second and third premixed compression ignition regions pass through the second premixed compression ignition region, 5. The engine according to claim 4, wherein when the premixed compression ignition region shifts to spark ignition, the engine passes through the third premixed compression ignition region.   A vehicle comprising the engine according to any one of claims 1 to 5.

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