JP2018172999A - Control device for premixed compression ignition engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize proper HCCI combustion in a wide load range in which both a soot (soot) generation amount and combustion noise are suppressed in a premixed compression ignition type engine. SOLUTION: When the engine is operated in a first operating region where the load is equal to or higher than a predetermined value, after the fuel injection by the fuel injection valve 11 is completed, the fuel is injected into the outer peripheral portion of the combustion chamber 10 before the fuel self-ignites. Water is jetted from the water jet valve 57 at a timing at which water can be unevenly distributed. When the engine is operating in the second operating region where the load is lower than in the first operating region, fuel is injected in the latter half of the compression stroke, and combustion by self-ignition ends after the fuel injection ends. The fuel injection valve 11 and the water injection valve 57 are controlled so that water is injected within the period up to. [Selection diagram] Figure 2

Description

  The present invention relates to an engine capable of premixed compression ignition combustion (HCCI combustion) in which fuel is self-ignited while being mixed with air.

  As an example of the premixed compression ignition type engine as described above, one disclosed in Patent Document 1 below is known. In the engine of this Patent Document 1, during operation in a predetermined premixed combustion region, a part of the exhaust gas discharged into the exhaust passage is introduced into the combustion chamber as EGR gas and is earlier than the compression top dead center. Control is performed to inject fuel into the combustion chamber at timing (for example, 60 to 70 ° CA before compression top dead center). In this way, by injecting fuel into the combustion chamber in which EGR gas, which is an inert gas, is present, the injected fuel can be self-ignited after a predetermined ignition delay, and soot (NO) and NOx It is said that proper combustion with a small amount of generation can be realized.

  Here, when the engine load increases, it is necessary to introduce a large amount of air (fresh air) into the combustion chamber in order to ensure a high output corresponding to the load. For this reason, in the high load region of the engine, a sufficient amount of EGR gas cannot be introduced into the combustion chamber, and there is a concern that self-ignition may be accelerated or combustion may be abrupt. On the other hand, for example, if a large turbocharger is applied to the engine, it is considered that both air and EGR gas can be sufficiently introduced into the combustion chamber. However, in this method, the pressure in the combustion chamber suddenly increases with combustion. There is a problem that a large noise is generated and a cooling loss increases with an increase in supercharging pressure. For this reason, it has been required to achieve both introduction of air (fresh air) and slowing of combustion without relying only on supercharging.

  As a method for meeting the above requirements, it is proposed to inject water directly into the combustion chamber. With this method, the required amount of water can be supplied into the cylinder without causing a shortage of air, so there is a possibility that combustion can be controlled to an extent that combustion noise is not excessive while ensuring sufficient output torque. is there.

  As an engine that employs water injection into the combustion chamber as described above, one disclosed in Patent Document 2 is known. The engine disclosed in Patent Document 2 includes a water injection valve at a side position on the intake side of a combustion chamber, for example, and water is injected obliquely downward from the water injection valve toward the combustion chamber. . During low load operation of the engine, water is injected from the water injection valve at a timing such that water adheres to the bottom surface of the cavity in the crown surface of the piston, and during high load operation of the engine, the combustion chamber above the cavity Water is injected from the water injection valve at a timing such that water is supplied to the center.

JP 2009-209809 A JP 2008-175078 A

  However, the technique disclosed in Patent Document 2 is directed to a spark ignition engine that uses a spark plug to forcibly ignite an air-fuel mixture, and does not target a premixed compression ignition engine. Although it is conceivable to apply the same water injection to a premixed compression ignition type engine, in such a case, the following problems are considered to occur.

  That is, as in Patent Document 2, when water is injected toward the center of the combustion chamber during high-load operation of the engine, the center that is likely to be hotter than the outer periphery of the combustion chamber is cooled by the injection water. There is a possibility that the temperature distribution in the combustion chamber is made uniform and most of the air-fuel mixture self-ignites at the same timing. In this case, since a large amount of fuel burns in a short period of time, there is a concern that a sudden pressure increase will occur and combustion noise will increase.

  Moreover, in the said patent document 2, although it is supposed that a cooling loss will be reduced by the water injection at the time of an engine low load driving | running, sufficient effect may not be acquired only by water injection.

  Specifically, in Patent Document 2, water injected during low-load operation of the engine adheres to the bottom surface of the cavity of the piston to form a water film, thereby suppressing combustion heat transfer (heat transfer) to the piston. The cooling loss is supposed to be reduced. However, in Patent Document 2, since the air-fuel mixture burns in the entire combustion chamber (that is, combustion occurs outside the cavity), when the water film is formed on the bottom surface of the cavity as described above, heat transfer to the piston is performed. The effect of suppressing is only limited. Of course, if the fuel is concentrated inside the cavity and the combustion region is limited to a small range, it is thought that the effect of suppressing the above-described heat transfer is enhanced. However, if the combustion region is limited unnecessarily, it is extremely fuel-rich locally. There is a problem that a large air-fuel mixture is formed and the amount of soot is increased.

  The present invention has been made in view of the above circumstances, and provides a control device for a compression ignition engine capable of realizing proper HCCI combustion in which both the amount of generated soot and combustion noise are suppressed in a wide load range. The purpose is to provide.

  In order to solve the above problems, the present invention relates to a fuel injection for injecting a fuel containing gasoline into a combustion chamber defined by a piston accommodated in a cylinder so as to be reciprocable, and a wall surface of the cylinder and the piston. An apparatus for controlling an engine capable of premixed compression ignition combustion, comprising a valve and a water injection valve for injecting water into a combustion chamber, wherein the fuel injected from the fuel injection valve is mixed with air and burned by self-ignition The fuel injection control unit for controlling the fuel injection amount and the injection timing from the fuel injection valve, and the water injection control unit for controlling the water injection amount and the injection timing from the water injection valve, When the engine is operated in the first operation region where the load is equal to or greater than a predetermined value, the water injection control unit causes the fuel injection so that water is unevenly distributed on the outer peripheral portion of the combustion chamber immediately before the fuel self-ignites. valve When the engine is operated in the second operation region where the load is lower than that in the first operation region, water is injected from the water injection valve at a predetermined timing after the fuel injection by the fuel injection is completed, and the fuel injection control unit And the water injection controller controls the fuel so that fuel is injected in the latter half of the compression stroke and water is injected within a period from the end of the fuel injection to the end of combustion by the self-ignition. The injection valve and the water injection valve are controlled (claim 1).

  According to the present invention, in the first operating region on the high load side, water injection that causes water to be unevenly distributed on the outer peripheral portion of the combustion chamber is performed before the start of combustion (self-ignition). When the outer periphery of the chamber is cooled by water, the temperature of the outer periphery is sufficiently lowered as compared with the center of the combustion chamber, which is likely to become high temperature, and the temperature difference between the center and the outer periphery of the combustion chamber is expanded. . As a result, a significant difference occurs in the fuel ignition timing between the central portion and the outer peripheral portion of the combustion chamber (the ignition timing at the outer peripheral portion is later than the ignition timing at the central portion), so that the progress of combustion proceeds. It becomes gentle, and it is possible to prevent the maximum value of the rate of increase in pressure (dp / dθ) in the combustion chamber from becoming excessive. In this way, by increasing the temperature difference in the combustion chamber and slowing down the combustion, even under high load conditions where the amount of fuel injection (ie, heat generation amount) is large and combustion tends to be sharp, combustion noise Can be suppressed to an appropriate level.

In the second operating region on the low load side, fuel injection is performed at a relatively late time in the second half of the compression stroke. Therefore, the fuel is self-ignited due to a synergistic effect with the small injection amount and weak fuel penetration. At a time before the fuel is obtained, the fuel is unevenly distributed only in a part of the combustion chamber. When the fuel self-ignites in such a state, the combustion region (region where the flame spreads) is limited to a relatively narrow range, so the area where the flame contacts the wall surface of the combustion chamber can be reduced, and the cooling loss is effectively reduced. Can be reduced. However, there is a possibility that an excessively rich air-fuel mixture may be formed in a region where the fuel is unevenly distributed, and there is a concern that the amount of soot generated increases accordingly. On the other hand, in the present invention, water is supplied to a high-temperature combustion chamber where combustion is continued and vaporized by water injection started immediately after compression top dead center, and the vaporized water contributes to the combustion reaction. As a result, the oxidization of carbon (C) is promoted (converted into CO ₂ or the like) by the strong oxidation action by the OH radical, so that the generation amount of soot is effectively reduced. Can be suppressed.

  Preferably, the water injection valve is provided so as to inject water radially from the vicinity of the center of the ceiling surface of the combustion chamber toward the piston, and when operating in the first operation region, the water injection control unit Injects water from the water injection valve during the period from the first period to the middle period of the compression stroke (claim 2).

  Thus, when water is injected radially from the vicinity of the center of the ceiling surface of the combustion chamber in the first to middle stages of the compression stroke, the injected water is directed to the outer peripheral portion of the crown surface of the piston or the peripheral wall of the cylinder. A state where water is unevenly distributed in the outer peripheral portion of the combustion chamber can be appropriately created by the jet water.

  Preferably, during operation in the second operation region, the water injection control unit controls the water injection valve so that water injection is started during a duration of combustion by the self-ignition (Claim 3). .

  According to this configuration, water can be appropriately supplied to the combustion chamber in which combustion is continuing, and the amount of soot generated is effectively increased by the action of increasing OH radicals brought about by the water (water vapor after vaporization). Can be suppressed.

  Preferably, each of the first operation region and the second operation region is set to a low speed region where the engine speed is less than a predetermined value.

  According to this configuration, it is possible to appropriately cope with these problems in a low speed region where combustion noise and soot problems are likely to become apparent. That is, in the low speed range where the amount of change in the crank angle per unit time is small, the combustion occurs in a high temperature and high pressure environment near the compression top dead center, and the combustion noise is larger than that in the high speed range. The amount of soot is likely to increase. On the other hand, in the above-described configuration, the above-described two types of water injection that lead to slowing of combustion or promotion of carbon oxidation are executed according to the load in a speed range where the rotational speed is less than a predetermined value. The amount of combustion noise and soot generation can be effectively suppressed by water injection.

  Preferably, the water injection valve injects water heated by heat exchange with the exhaust gas discharged from the combustion chamber.

  According to this configuration, it is possible to prevent the output torque from being lowered due to excessive cooling of the combustion chamber by the injected water. In particular, in the second operating region where the load is low, the time required for increasing the OH radicals (the time required for the injected water to vaporize and increase the OH radicals) is shortened by increasing the temperature of the jet water. In addition, the effect of suppressing soot can be further enhanced. In addition, since the water is heated using the heat of the exhaust gas, useless energy is not consumed for heating, and energy efficiency can be maintained satisfactorily.

  As described above, according to the compression ignition engine control apparatus of the present invention, appropriate HCCI combustion in which both the generation amount of soot and combustion noise are suppressed can be realized in a wide load range.

It is a figure showing the whole premixed compression ignition type engine composition concerning one embodiment of the present invention. It is sectional drawing of an engine main body. It is a block diagram which shows the control system of an engine. It is a map figure which shows the difference in control according to the driving | running condition of an engine. It is a time chart for demonstrating the aspect of the fuel injection and water injection in a low speed and high load area | region (1st operation area | region). It is a time chart for demonstrating the aspect of the fuel injection and water injection in a low speed and low load area | region (2nd driving | operation area | region). It is a time chart for demonstrating the aspect of fuel injection and water injection in a high-speed and high load area | region (3rd operation area | region). It is operation | movement explanatory drawing for demonstrating the effect | action by water injection in the said 1st driving | operation area | region. It is operation | movement explanatory drawing for demonstrating the effect | action by the water injection in the said 2nd driving | operation area | region. It is operation | movement explanatory drawing for demonstrating the effect | action by the water injection in the said 3rd driving | operation area | region. It is a state change figure of water for explaining the nature of supercritical water and subcritical water.

(1) Overall Configuration of Engine FIGS. 1 and 2 are views showing a preferred embodiment of a premixed compression ignition engine (hereinafter also simply referred to as an engine) to which the control device of the present invention is applied. The engine shown in the figure is a four-cycle gasoline engine mounted on a vehicle as a driving power source, and includes an in-line multi-cylinder engine main body 1 including four cylinders 2 arranged in a row, and an engine main body 1. An intake passage 20 through which intake air introduced into the engine flows, an exhaust passage 30 through which exhaust gas discharged from the engine body 1 flows, and an EGR device that recirculates part of the exhaust gas flowing through the exhaust passage 30 to the intake passage 20 40, and a water supply system 50 that supplies water extracted from the exhaust gas flowing through the exhaust passage 30 to each cylinder 2 of the engine body 1.

  As shown in FIG. 2, the engine body 1 includes a cylinder block 3 in which the cylinder 2 is formed, a cylinder head 4 attached to the upper surface of the cylinder block 3 so as to close the cylinder 2 from above, and each cylinder 2. And a piston 5 accommodated in a reciprocating manner.

  A combustion chamber 10 is defined above the piston 5. The combustion chamber 10 is supplied with fuel (a fuel mainly composed of gasoline) injected from a fuel injection valve 11 described later. The supplied fuel burns in the combustion chamber 10, and the piston 5 pushed down by the expansion force due to the combustion reciprocates in the vertical direction.

  Below the piston 5, a crankshaft 15 that is an output shaft of the engine body 1 is disposed. The crankshaft 15 is connected to the piston 5 via the connecting rod 14 and rotates around the central axis according to the reciprocating motion of the piston 5. The cylinder block 3 is provided with a crank angle sensor SN1 that detects a rotation angle (crank angle) and a rotation speed (engine rotation speed) of the crankshaft 15.

  A cavity 5 a is formed in the crown surface (upper surface) of the piston 5, with its central portion recessed on the opposite side (downward) from the cylinder head 4. The cavity 5a is formed to have a volume that occupies most of the combustion chamber 10 when the piston 5 rises to the top dead center.

  The cylinder head 4 has one fuel injection valve 11 for injecting fuel mainly composed of gasoline supplied from a fuel pump (not shown) into the combustion chamber 10 of each cylinder 2 for each cylinder 2 (four in total). ) Is provided. Each fuel injection valve 11 is provided so as to be adjacent to a water injection valve 57 to be described later in a slightly inclined posture with respect to the central axis of the cylinder 2. As shown in FIG. 1, a fuel rail 16 is provided above the fuel injection valve 11 to store the fuel supplied from the fuel pump in a pressure accumulation state. The fuel stored in the fuel rail 16 is supplied to each fuel injection valve 11 through the same number (four) of distribution pipes 17 as the fuel injection valves 11.

  The fuel injection valve 11 has a tip portion exposed to the combustion chamber 10 in the vicinity of the central axis of the cylinder 2 and can inject fuel radially through a plurality of injection holes (not shown) provided in the tip portion. Is possible. The tip of the fuel injection valve 11 is disposed at a position facing the cavity 5a of the piston 5 when the piston 5 is at the compression top dead center. Fuel is injected from the fuel injection valve 11 during the intake stroke or the compression stroke, and the injected fuel is mixed with air (intake air) introduced into the combustion chamber 10 and then, for example, in the vicinity of the compression top dead center. Ignite.

  That is, in the engine of the present embodiment, instead of spark ignition combustion (combustion in which an air-fuel mixture is forcibly ignited by spark ignition) generally employed when gasoline is used as a fuel, an air-fuel mixture of fuel and air is used as a piston. HCCI combustion (premixed compression ignition combustion) that is self-ignited in accordance with compression by 5 is performed in all operating regions of the engine. For this reason, the spark plug is basically unnecessary in the engine of the present embodiment, but spark ignition combustion is executed instead of HCCI combustion in a situation where self-ignition is difficult, for example, immediately after the engine is cold started. Even after warm-up, so-called spark assist may be executed to promote HCCI combustion, and a spark plug may be provided for such a purpose.

  In order to enable the HCCI combustion as described above, the compression ratio of each cylinder 2 is set higher in the engine of the present embodiment than in a general gasoline engine that employs spark ignition combustion. Specifically, in this embodiment, the geometric compression ratio of each cylinder 2, that is, the volume of the combustion chamber 10 when the piston 5 is at the top dead center and the combustion chamber 10 when the piston 5 is at the bottom dead center. The volume ratio is set to 16 to 35, more preferably 18 to 30.

  As shown in FIG. 2, the cylinder head 4 receives, for each cylinder 2, the intake port 6 for introducing the air supplied from the intake passage 20 into the combustion chamber 10 and the exhaust gas generated in the combustion chamber 10. An exhaust port 7 for leading to the exhaust passage 30, an intake valve 8 that opens and closes the opening of the intake port 6 on the combustion chamber 10 side, and an exhaust valve 9 that opens and closes the opening of the exhaust port 7 on the combustion chamber 10 side, respectively. Is provided.

  As shown in FIG. 1, the intake passage 20 includes a single tubular common intake pipe 22 and an intake manifold 21 formed to branch from the downstream end of the common intake pipe 22. Each branch pipe of the intake manifold 21 is connected to the engine body 1 (cylinder head 4) so as to communicate with the combustion chamber 10 of each cylinder 2 via the intake port 6, and the downstream end portion of the common intake pipe 22 is The manifolds of the branch pipes of the intake manifold 21 (the parts where the upstream ends of the branch pipes gather) are connected. In the present specification, the upstream (or downstream) in the intake passage 20 refers to the upstream (or downstream) in the flow direction of the intake air flowing through the intake passage 20.

  The common intake pipe 22 is provided with an air cleaner 25 for removing foreign substances contained in the intake air and an openable / closable throttle valve 27 for adjusting the flow rate of the intake air flowing through the common intake pipe 22 in this order from the upstream side. Yes. Furthermore, an air flow sensor SN2 that detects the flow rate of the intake air flowing through the common intake pipe 22 is provided on the downstream side of the throttle valve 27 in the common intake pipe 22.

  In the engine of this embodiment, since HCCI combustion is performed in all operating regions, the throttle valve 27 is basically maintained at an opening corresponding to full opening except during deceleration operation or when the engine is stopped. .

  The exhaust passage 30 includes a single tubular common exhaust pipe 32 and an exhaust manifold 31 formed so as to branch from the upstream end of the common exhaust pipe 32. Each branch pipe of the exhaust manifold 31 is connected to the engine body 1 (cylinder head 4) so as to communicate with the combustion chamber 10 of each cylinder 2 via the exhaust port 7, and an upstream end portion of the common exhaust pipe 32 is The exhaust manifold 31 is connected to the branch pipe assembly (the part where the downstream ends of the branch pipes gather together). In the present specification, upstream (or downstream) in the exhaust passage 30 means upstream (or downstream) in the flow direction of the exhaust gas flowing through the exhaust passage 30.

  In the common exhaust pipe 32, a catalyst device 35, a heat exchanger 54, and a condenser 51 are provided in this order from the upstream side.

  The catalyst device 35 is for purifying harmful components contained in the exhaust gas. For example, the catalyst device 35 has a built-in catalyst composed of any one or a combination of a three-way catalyst, an oxidation catalyst, and an NOx catalyst. In addition to such a catalyst, a filter for collecting PM contained in the exhaust gas may be included.

  The condenser 51 condenses water vapor contained in the exhaust gas, and the heat exchanger 54 raises the temperature of the condensed water generated by the condenser 51. The heat exchanger 54 and the condenser 51 are elements that constitute a part of the water supply system 50 (details will be described later).

  The EGR device 40 includes an EGR passage 41 that allows the common exhaust pipe 32 and the common intake pipe 22 to communicate with each other, and an EGR valve 42 and an EGR cooler 43 that are provided in the EGR passage 41.

  The EGR passage 41 connects a part of the common exhaust pipe 32 upstream of the catalyst device 35 and a part of the common intake pipe 22 downstream of the throttle valve 27. The EGR valve 42 is an open / close valve for adjusting the flow rate of exhaust gas (EGR gas) recirculated from the common exhaust pipe 32 to the common intake pipe 22 through the EGR passage 41. The EGR cooler 43 is a heat exchanger that cools the EGR gas flowing through the EGR passage 41 by heat exchange with a predetermined refrigerant (for example, engine coolant).

(2) Specific Configuration of Water Supply System As shown in FIG. 1, the water supply system 50 includes a condenser 51 and a heat exchanger 54 described above, a water tank 52 that stores the condensed water generated by the condenser 51, and A water supply pump 53 that pumps the condensed water stored in the water tank 52 toward the heat exchanger 54, and a high pressure and high pressure water that is pressurized by the water pump 53 and heated by the heat exchanger 54 while accumulating pressure. A pressure accumulation rail 56 that is stored in a state, and a water injection valve 57 that is provided one for each cylinder 2 (four in total) to supply water stored in the pressure accumulation rail 56 to the combustion chamber 10 of each cylinder 2. The first water pipe 61 connecting the condenser 51 and the water tank 52, the second water pipe 62 connecting the water tank 52 and the heat exchanger 54, and the first water pipe connecting the heat exchanger 54 and the pressure accumulation rail 56. 3 water piping 63 and pressure accumulation A plurality of (four) distribution pipes 64 connecting the rail 56 and each water injection valve 57 are provided.

  The condenser 51 is a heat exchanger for condensing water vapor contained in the exhaust gas flowing through the common exhaust pipe 32, and cools the exhaust gas by heat exchange with a predetermined refrigerant (for example, engine cooling water). Thus, the water vapor contained in the exhaust gas is condensed. The condensed water generated by the condenser 51 flows out downstream through the first water pipe 61 and is stored in the water tank 52.

  The water feed pump 53 is provided in the middle of the second water pipe 62 and feeds the condensed water stored in the water tank 52 toward the heat exchanger 54 while pressurizing the condensed water. In FIG. 1, a single pump 53 is illustrated as a water pump. However, the water pump is configured to feed water stored in the water tank 52 at a relatively low pressure, and water fed from the feed pump. A multi-stage pump combined with a high-pressure pump that pressurizes and raises the pressure to a desired pressure may be used.

  The heat exchanger 54 is provided so as to heat the water supplied from the water pump 53 by heat exchange with the exhaust gas before flowing into the condenser 51. Although not shown in detail, the heat exchanger 54 includes a small-diameter and long-shaped thin tube 54a inserted into a portion of the common exhaust pipe 32 positioned between the catalyst device 35 and the condenser 51, and the thin tube 54a. And a heat retaining case 54b provided so as to cover the common exhaust pipe 32 in the portion where the is inserted.

  The water heated by the heat exchanger 54 is sent to the downstream side through the third water pipe 63 and stored in the pressure accumulation rail 56. The pressure accumulation rail 56 is provided with a water pressure sensor SN3 that detects the pressure of the internal water.

  The water stored in the pressure accumulation rail 56 is heated to 100 ° C./2 MPa or more through the heating by the heat exchanger 54 and the pressurization by the water supply pump 53 as described above. Since the pressure is as high as 2 MPa or higher, water does not boil even when heated to 100 ° C. or higher, and maintains a liquid state. Then, the water stored in the pressure accumulation rail 56 in such a state is injected into the combustion chamber 10 of each cylinder 2 through the water injection valve 57 when necessary. That is, in this embodiment, water injected from the water injection valve 57 to the cylinder 2 is high-temperature / high-pressure liquid water having a temperature of 100 ° C. or higher and a pressure of 2 MPa or higher.

  The water injection valve 57 is attached to the cylinder head 4 in such a posture that its axial center substantially coincides with the central axis of the cylinder 2. The water injection valve 57 has a tip portion exposed to the combustion chamber 10 in the vicinity of the center of the ceiling surface of the combustion chamber 10 so as to face the cavity 5a of the piston 5 from directly above, and a plurality of nozzle holes provided in the tip portion. It is possible to spray water radially through (not shown).

(3) Engine Control System FIG. 3 is a block diagram showing the engine control system. The PCM 100 shown in this figure is a microprocessor for overall control of the engine, and includes a known CPU, ROM, RAM, and the like.

  Detection signals from various sensors are input to the PCM 100. For example, the PCM 100 is electrically connected to the above-described crank angle sensor SN1, air flow sensor SN2, and water pressure sensor SN3, and information detected by these sensors (that is, crank angle, in-cylinder pressure, intake air flow rate, water pressure). Etc.) are sequentially input to the PCM 100 as electrical signals.

  Further, the vehicle is provided with an accelerator sensor SN4 that detects an opening degree of an accelerator pedal (not shown) operated by a driver driving the vehicle, and a detection signal from the accelerator sensor SN4 is also input to the PCM 100. .

  The PCM 100 controls each part of the engine while executing various determinations and calculations based on input signals from the sensors. That is, the PCM 100 is electrically connected to the fuel injection valve 11, the throttle valve 27, the EGR valve 42, the water supply pump 53, the water injection valve 57, and the like. Outputs a control signal.

  As functional elements related to the control, the PCM 100 includes a fuel injection control unit 101, a water injection control unit 102, and an EGR control unit 103.

  The fuel injection control unit 101 is detected by the engine rotational speed detected by the crank angle sensor SN1, the engine load (requested torque) specified from the detected value (accelerator opening) of the accelerator sensor SN4, and the airflow sensor SN2. The fuel injection amount and injection timing from the fuel injection valve 11 are determined based on the intake flow rate, and the fuel injection valve 11 is controlled according to the determination.

  Based on the internal pressure of the pressure accumulation rail 56 (the pressure of water stored in the pressure accumulation rail 56) detected by the water pressure sensor SN3, the water injection control unit 102 holds the pressure at a required pressure (2 MPa) or more. Then, the water supply pump 53 is driven. Further, the water injection control unit 102 determines the water injection amount and the injection timing from the water injection valve 57 based on the engine load and the rotation speed, and controls the water injection valve 57 according to the determination.

  The EGR control unit 103 determines a target value (target EGR rate) of the EGR rate that is the ratio of EGR gas in the total gas amount in the combustion chamber 10 based on the engine load, the rotational speed, and the like, and the target EGR rate. The EGR valve 42 is controlled so that an amount of EGR gas corresponding to the above is introduced into the cylinder 2. As the target EGR rate, an EGR rate that achieves proper HCCI combustion is determined in advance for each engine operating condition. For example, the target EGR rate is reduced under operating conditions where the engine load is high (the fuel injection amount is large).

(4) Control according to operation conditions Next, the control of the fuel injection valve 11 and the water injection valve 57 by the PCM 100 (the fuel injection control unit 101 and the water injection control unit 102) will be described in detail.

  FIG. 4 is a map for explaining the difference in control according to the engine operating conditions (load / rotational speed). As shown in the figure, the engine operating region is roughly divided into four operating regions A1 to A4 depending on the control of the fuel injection valve 11 and the water injection valve 57. Assuming that the first operation region A1, the second operation region A2, the third operation region A3, and the fourth operation region A4, respectively, the first operation region A1 has a rotational speed that is less than a predetermined value Rx and a load that is greater than or equal to a predetermined value Lx. The second operation region A2 is a low-speed / low-load operation region in which the rotational speed is less than the predetermined value Rx and the load is less than the predetermined value Lx, and the third operation region A3. Is a high-speed / high-load operation region where the rotational speed is equal to or greater than the predetermined value Rx and the load is equal to or greater than the predetermined value Lx. The fourth operational region A4 is a rotational speed equal to or greater than the predetermined value Rx and the load is equal to the predetermined value Lx. This is a high-speed, low-load operating range that is less than The predetermined value Lx, which is the load threshold value, is shown as being constant regardless of the rotational speed in FIG. 4, but may be a value that changes according to the rotational speed. Similarly, the predetermined value Rx that is the threshold value of the rotation speed is illustrated as being constant regardless of the load in FIG. 4, but may be a value that changes according to the load.

  Among the operation regions A1 to A4 shown in FIG. 4, at least in the first, second, and third operation regions A1, A2, and A3, the fuel injection valve is controlled by the fuel injection control unit 101 and the water injection control unit 102. 11 and the water injection from the water injection valve 57 are both executed. Operations of the fuel injection valve 11 and the water injection valve 57 in the first, second, and third operation regions A1, A2, and A3 will be described in order in the following (a), (b), and (c).

  Here, in the following explanations (a) to (c), terms such as “early period”, “middle period”,... Of the intake stroke or compression stroke are used as terms for specifying the timing of fuel injection or water injection. This is based on the following assumptions. That is, in this specification, each period when an arbitrary stroke such as an intake stroke or a compression stroke is divided into three equal parts is defined as “first period”, “middle period”, and “late period” in order from the front. For this reason, for example, (i) the first half, (ii) the middle, and (iii) the second half of the compression stroke are (i) before compression top dead center (BTDC) 180 to 120 ° CA, and (ii) BTDC 120 to 60 °, respectively. CA, (iii) refers to each range of BTDC 60 to 0 ° CA. Similarly, in this specification, each period when an arbitrary stroke such as an intake stroke or a compression stroke is divided into two equal parts is defined as “first half” and “second half” in order from the front. For this reason, for example, (iv) first half and (v) second half of the compression stroke indicate ranges of (iv) BTDC 180 to 90 ° CA and (v) BTDC 90 to 0 ° CA, respectively.

(A) Control in the first operation region In the first operation region A1 of low speed and high load, as shown in FIG. 5, the fuel injection If1 from the fuel injection valve 11 is within the period from the middle stage to the latter stage of the intake stroke. And the water injection Iw1 from the water injection valve 57 is executed within the period from the first period to the middle period of the compression stroke.

  By performing the fuel injection If1 at the timing as described above (the middle stage to the latter stage of the intake stroke), the fuel distribution before ignition is sufficiently uniformized. That is, when fuel is injected from the fuel injection valve 11 during a period from the middle stage to the latter stage of the intake stroke, the injected fuel is vaporized and atomized while being agitated by intake air flow or the like, and compression top dead center (FIG. 5). Until the TDC) is uniformly dispersed in the combustion chamber 10.

  The amount of fuel injected by the fuel injection If1 is set to a relatively large value that meets the conditions of the first operating region A1 where the load is high. The injection pulse width of the fuel injection If1 (the valve opening period of the fuel injection valve 11) is increased or decreased according to the determined injection amount, and the pulse width is increased as the injection amount increases. The same applies to the water injection Iw1.

  The timing of the water injection Iw1 (from the first to the middle of the compression stroke) is determined with the intention that the water injected from the water injection valve 57 is unevenly distributed in the outer peripheral portion of the combustion chamber 10. That is, when water is injected from the water injection valve 57 within the period from the first period to the middle period of the compression stroke, the injected water is as shown in the lower diagram of FIG. 8 (FIG. 5 also shows the corresponding figure). (Schematically shown), which flies radially toward a region outside the cavity 5a on the crown surface of the piston 5 (hereinafter referred to as the outer peripheral portion of the crown surface) or toward the peripheral wall of the cylinder 2. The flying water evaporates after adhering to the outer peripheral part of the crown surface of the piston 5 or the peripheral wall of the cylinder 2, and as a result, as shown in the middle diagram of FIG. At this point, a relatively concentrated water (mainly water vapor) is present at the outer periphery of the combustion chamber 10, that is, the concentration of water present at the outer periphery of the combustion chamber 10 is higher than that at the center of the combustion chamber 10. And a sufficiently dark state is obtained. And as a result of the wall surface temperature and gas temperature of the outer peripheral part of the combustion chamber 10 decreasing due to the cooling effect of the water unevenly distributed on the outer peripheral part of the combustion chamber 10 in this way, the fuel immediately before self-ignition (near the compression top dead center) As the temperature distribution in the combustion chamber 10, a distribution as shown in the upper graph of FIG. 8 is obtained. In the upper graph, the solid line waveform indicates the temperature distribution when the water injection is performed, and the broken line waveform indicates the temperature distribution when the water injection is not performed. From the comparison between the two, the temperature (wall surface temperature and gas temperature) of the outer peripheral portion of the combustion chamber 10 intensively decreases due to the effect of the water injection Iw1, and the difference between the temperature of the outer peripheral portion and the temperature of the central portion increases. It is understood that

  As a cooling effect on the outer peripheral portion of the combustion chamber 10 by the injection water, a higher level is required as the amount of fuel injection is large and the combustion chamber 10 is likely to become high temperature. For this reason, the amount of water injection by the water injection Iw1 is generally set to a larger value as the load is higher in the first operation region A1.

(B) Control in the second operation region In the second operation region A2 of low speed and low load, as shown in FIG. 6, fuel injection If2 from the fuel injection valve 11 is executed in the latter half of the compression stroke, Water injection Iw2 from the injection valve 57 is executed immediately after the compression top dead center.

  Since the load in the second operation region A2 is lower than that in the first operation region A1, the fuel injection amount by the fuel injection If2 is set to a value smaller than the fuel injection If1 (FIG. 5) in the first operation region A1. . As described above, since the fuel injection amount is small in the second operation region A2, the penetration (penetration force) of the fuel injected from the fuel injection valve 11 is relatively weak.

  The timing of the fuel injection If2 (the second half of the compression stroke) is determined with the intention of containing the fuel injected from the fuel injection valve 11 in the cavity 5a of the piston 5. That is, when fuel is injected from the fuel injection valve 11 in the latter half of the compression stroke, the injected fuel is as shown in the lower diagram of FIG. 9 (FIG. 6 schematically shows the corresponding figure). It flies radially toward the inside of the cavity 5a of the piston 5. Most of the fuel that has flown into the cavity 5a stays inside the cavity 5a in combination with the small injection amount and weak fuel penetration. As a result, a state in which the concentration of the fuel existing inside the cavity 5a is sufficiently thicker than that outside the cavity 5a is obtained, and a locally rich air-fuel mixture is formed inside the cavity 5a. This rich air-fuel mixture reaches self-ignition without difficulty when the piston 5 reaches near the compression top dead center, and HCCI combustion is started.

  The timing of the water injection Iw2 (immediately after the compression top dead center) is determined with the intention of overlapping the water injection during the period of combustion (HCCI combustion) started near the compression top dead center as described above. More specifically, the timing of water injection Iw2 is set to a timing at which water injection starts after the time when combustion starts and water injection ends before the time when combustion ends. The water injected from the water injection valve 57 at such a timing flies radially toward the inside of the cavity 5a as shown in the upper diagram of FIG. At this time, since combustion has already occurred in the central portion of the combustion chamber 10 (mainly the internal space of the cavity 5a), the water injected by the water injection Iw2 is supplied into this combustion region.

(C) Control in the third operation region In the third operation region A3 of high speed and high load, as shown in FIG. 7, the fuel injection If3 from the fuel injection valve 11 is within the period from the middle stage to the latter stage of the intake stroke. The water injection Iw3 from the water injection valve 57 is executed at the latter stage of the compression stroke.

  Since the third operation region A3 is in the same load region as the first operation region A1, the fuel injection amount by the fuel injection If3 is substantially equal to the fuel injection If1 (FIG. 5) in the first operation region A1. However, since the rotation speed is higher in the third operation region A3 than in the first operation region A1 (in other words, the amount of change in the crank angle per unit time is large), the crank angle required to inject the same amount of fuel is the first. It becomes longer than in the case of one operation region A1. This is why the pulse width of the fuel injection If3 in the third operation region A3 is longer than the pulse width of the fuel injection If1 in the first operation region A1.

  The timing of the water injection Iw3 (the latter stage of the compression stroke) is determined with the intention of containing the water injected from the water injection valve 57 in the cavity 5a of the combustion chamber 10. That is, when water is injected from the water injection valve 57 in the latter stage of the compression stroke, the injection water is as shown in the lower diagram of FIG. 10 (FIG. 7 also shows a schematic diagram corresponding thereto). It flies radially toward the inside of the cavity 5a. The flying water evaporates after adhering to the wall surface of the cavity 5a. As a result, as shown in the middle diagram of FIG. 10, the center of the combustion chamber 10 is reached when the piston 5 rises to near the compression top dead center. A state in which relatively high concentration water (mainly water vapor) is present in the part, that is, a state in which the concentration of water existing in the central part of the combustion chamber 10 is sufficiently thicker than the outer peripheral part of the combustion chamber 10 is obtained. . As a result of the cooling effect of the water unevenly distributed in the central portion of the combustion chamber 10 as described above, the wall surface temperature and gas temperature of the central portion (cavity 5a) of the combustion chamber 10 decrease, and as a result, the fuel immediately before self-ignition (on compression) As the temperature distribution of the combustion chamber 10 in the vicinity of the dead point), a distribution as shown in the upper graph of FIG. 10 is obtained. Since the central portion of the combustion chamber 10 is likely to be hotter than the outer peripheral portion, the temperature difference between the central portion and the outer peripheral portion is reduced by decreasing the temperature of the central portion of the combustion chamber 10 as shown in the upper graph. To do.

  As a cooling effect for the central portion of the combustion chamber 10 by the injection water, a higher level is required as the amount of fuel injection is large and the combustion chamber 10 is likely to be at a high temperature. For this reason, the amount of water injected by the water injection Iw3 is generally set to a larger value as the load is higher in the third operation region A3.

(5) Operational Effects As described above, in this embodiment, when the engine is operated in the first operation region A1 of low speed and high load, fuel is injected from the fuel injection valve 11 during the intake stroke (fuel Thereafter, water is injected from the water injection valve 57 during the first to middle periods of the compression stroke in which water can be unevenly distributed in the outer peripheral portion of the combustion chamber 10 (water injection Iw1). On the other hand, when the engine is operating in the second operating region A2 of low speed and low load, fuel is injected from the fuel injection valve 11 in the latter half of the compression stroke (fuel injection If2), and then the injected fuel is self-generated. Water is injected from the water injection valve 57 immediately after the compression top dead center slightly delayed from ignition (water injection Iw2). According to such a configuration, there is an advantage that appropriate HCCI combustion in which both the generation amount of soot (soot) and combustion noise are suppressed can be realized in a wide load range.

  That is, in the above embodiment, in the first operating region A1 on the high load side, the water injection Iw1 that causes water to be unevenly distributed on the outer peripheral portion of the combustion chamber 10 is executed before the start of combustion (self-ignition), so the start of combustion Since the outer peripheral part of the combustion chamber 10 is cooled by water before, the temperature of the outer peripheral part is sufficiently lowered as compared with the central part of the combustion chamber 10 which tends to become high temperature. The temperature difference between and increases. As a result, a significant difference occurs in the fuel ignition timing between the central portion and the outer peripheral portion of the combustion chamber 10 (the ignition timing at the outer peripheral portion is later than the ignition timing at the central portion). It becomes possible to prevent the pressure rise rate (dp / dθ) in the combustion chamber 10 from becoming excessively large. In this way, by increasing the temperature difference of the combustion chamber 10 and slowing down the combustion, even under high load conditions where the amount of fuel injection (that is, the amount of heat generation) is large and the combustion tends to become steep, combustion occurs. Noise can be suppressed to an appropriate level.

Further, in the second operating region A2 on the low load side, the fuel injection If2 is executed at a relatively late time such as the latter half of the compression stroke, so that the fuel is generated due to a synergistic effect with a small injection amount and weak fuel penetration. At a point before self-ignition, a state where the fuel is unevenly distributed is obtained only in a part of the combustion chamber 10 (particularly, inside the cavity 5a). When the fuel self-ignites in such a state, the combustion region (region where the flame spreads) is limited to a relatively narrow range, so the area where the flame contacts the wall surface of the combustion chamber 10 can be reduced, and cooling loss is effectively reduced. Can be reduced. However, there is a possibility that an excessively rich air-fuel mixture may be formed in the region where the fuel is unevenly distributed (in the cavity 5a), and there is a concern that the amount of soot generated increases accordingly. On the other hand, in the above-described embodiment, water is supplied to the high-temperature combustion chamber 10 where the combustion is continuing and is vaporized by the water injection Iw2 that is started immediately after the compression top dead center, and the vaporized water is combusted. Since the effect of increasing OH radicals contributing to the reaction is brought about, the strong oxidation action by the OH radicals promotes the oxidation of carbon (C) (converted to CO ₂ or the like). As a result, the amount of soot generated is reduced. It can be effectively suppressed.

  Moreover, in the said embodiment, since water is radially injected toward the piston 5 from the water injection valve 57 provided in the center vicinity of the ceiling surface of the combustion chamber 10, at the time of the driving | operation in 1st operation area | region A1, water is injected. By injecting water during the period from the first period to the middle period of the compression stroke by the injection Iw1, the injected water is injected into the outer peripheral portion of the crown surface of the piston 5 (the outer surface of the cavity 5a) or the peripheral wall of the cylinder 2. A state in which water is unevenly distributed on the outer peripheral portion of the combustion chamber 10 can be appropriately created by the jet water.

  Further, in the above-described embodiment, during the operation in the second operation region A2, the water injection Iw2 is started and ended during the combustion continuation period due to self-ignition (that is, the period of the water injection Iw2 is completely included in the combustion period). Therefore, water can be properly supplied to the combustion chamber 10 in which combustion is continuing, and soot is increased by the action of increasing OH radicals brought about by the water (water vapor after vaporization). Can be effectively suppressed.

  Further, in the above embodiment, the first operation region A1 and the second operation region A2 in which the above-described control is performed are both set in the low speed region where the engine speed is less than the predetermined value Rx. These problems can be appropriately dealt with at low speeds where noise and soot problems are likely to manifest. That is, in the low speed range where the amount of change in the crank angle per unit time is small, the combustion occurs in a high temperature and high pressure environment near the compression top dead center, and the combustion noise is larger than that in the high speed range. The amount of soot is likely to increase. On the other hand, in the above embodiment, in the speed range where the rotational speed is less than the predetermined value Rx, the above-described two types of water injection (water injection Iw1 in the first operation region A1) leading to slowing of combustion or promotion of carbon oxidation. Alternatively, since the water injection Iw2) in the second operation region A2 is executed according to the load, the combustion noise and the soot generation amount can be effectively suppressed by these water injections Iw1 and Iw2.

  Moreover, in the said embodiment, since the high temperature water (100 degreeC or more water) heated by heat exchange with exhaust gas is injected from the water injection valve 57, the combustion chamber 10 is cooled too much by the injected water. As a result, the output torque can be prevented from decreasing. In particular, in the second operation region A2 of low speed and low load, the time required for increasing the OH radicals due to the high temperature of the jet water (required until the water jetted by the water jet Iw2 vaporizes and increases the OH radicals). (Time) is shortened, so that the effect of suppressing soot can be further enhanced. In addition, since the water is heated using the heat of the exhaust gas, useless energy is not consumed for heating, and energy efficiency can be maintained satisfactorily.

  Further, in the above embodiment, during operation in the high-speed / high-load third operation region A3, fuel is injected from the fuel injection valve 11 during the intake stroke (fuel injection If3), and thereafter, in the central portion of the combustion chamber 10 Since water is injected from the water injection valve 57 at a later stage of the compression stroke in which water can be unevenly distributed (water injection Iw3), the central portion of the combustion chamber 10 that is likely to be hotter than the outer peripheral portion of the combustion chamber 10 The temperature difference between the central portion and the outer peripheral portion of the combustion chamber 10 is reduced by being intensively cooled. As a result, there is no significant difference in the ignition timing at the center / outer periphery of the combustion chamber, and relatively steep combustion occurs in which a large amount of fuel burns in a short time. However, in the third operation region A3 where the rotational speed is higher than that in the first operation region A1, the amount of change in the crank angle per unit time is large, so the maximum value of the rate of pressure increase (dp / dθ) even if the combustion is sharpened. Is not so big. For this reason, even if the temperature of the combustion chamber 10 is made uniform in the third operation region A3 where the rotational speed is high as described above, the combustion noise is not particularly a problem, but rather a lot of fuel is burned in a short time. As a result, it is considered that combustion with low exhaust loss (high thermal efficiency) is realized. Moreover, although the center part of the combustion chamber 10 is a part which becomes easy to become especially high temperature on the conditions of high rotation and high load like 3rd operation area | region A3, the center part of the combustion chamber 10 in the said 3rd operation area | region A3. According to the above embodiment, in which the temperature of the combustion chamber 10 is directly cooled by the jet water, it is reliably avoided that the temperature of the central portion of the combustion chamber 10 is excessively increased, so that the cooling loss is reduced and the thermal efficiency of the engine is improved. be able to.

(6) Modification (a) First Modification In the above embodiment, the water injected from the water injection valve 57 into the combustion chamber 10 is a relatively high temperature having a temperature of 100 ° C. or higher and a pressure of 2 MPa or higher. Although high-pressure water was used, the temperature, pressure, and the like of the jet water can be changed as appropriate depending on which of the water jet contribution effects required in each of the operation regions A1, A2, A3 described above is important. .

  For example, water whose temperature and pressure have been increased to a so-called supercritical or subcritical state (that is, supercritical water or subcritical water) can be injected into the combustion chamber 10. Here, supercritical water is water having a temperature and pressure higher than the critical point of water, and subcritical water is water having properties close to supercritical water. FIG. 11 shows changes in the state of water accompanying changes in enthalpy (horizontal axis) and pressure (vertical axis). Supercritical water and subcritical water will be described with reference to FIG. The water can be defined as water contained in the region Z1 having a temperature and pressure higher than the critical point X of water, and the subcritical water can be defined as water contained in the region Z1a adjacent to the region Z1.

More specifically, in FIG. 11, LT is an isotherm, LD is an isodensity line, a numerical value following LT represents temperature (K), and a numerical value following LD represents density (kg / m ³ ). . The region Z2 represents a liquid region, the region Z3 represents a gas region, and the region Z4 represents a region where the liquid and the gas coexist. The region Z1 corresponding to supercritical water is a very high temperature / high pressure region that does not belong to any of these regions Z2, Z3, and Z4. In such a region Z1, water is in a special state having both liquid and gas properties (not applicable to any of the three phases of liquid, gas, and solid), that is, a supercritical state. Note that the temperature of the critical point X is 647 K (more precisely 647.3 K) and the pressure is 22 MPa (more precisely 22.12 MPa). Therefore, the supercritical water belonging to the region Z1 is 647 K (374 ° C.). It is the water which has the above temperature and the pressure of 22 Mpa or more. Further, the subcritical water belonging to the region Z1a is water having a temperature of 600 K or more and less than 647 K and a density of 250 kg / m ³ or more.

  When such supercritical water / subcritical water is injected into the combustion chamber 10, it is considered that a fuel efficiency improvement effect can be obtained by utilizing the rapid expansion work of water after injection. That is, as indicated by an arrow W1 in FIG. 11, supercritical water / subcritical water requires little enthalpy (latent heat) to change to gaseous water. On the other hand, the liquid water contained in the region Z2 requires a large enthalpy (latent heat) in order to change into a gas as indicated by an arrow W2. This means that injecting supercritical water / subcritical water can sufficiently reduce the temperature drop of the combustion chamber 10 due to absorption of latent heat of water, rather than injecting liquid water. Moreover, the supercritical water / subcritical water injected into the combustion chamber 10 works to push down the piston 5 by rapidly expanding in the combustion chamber 10. Therefore, when supercritical water / subcritical water having such a property is injected into the combustion chamber 10, there is a possibility that the fuel consumption can be improved by reducing the fuel injection amount by the work increment accompanying the injection.

  In particular, in the second operation region A2, since water is injected after the compression top dead center, it is considered that a sufficient fuel efficiency improvement effect can be obtained if supercritical water / subcritical water is used as the injection water. That is, when the supercritical water / subcritical water is injected after the compression stroke in the second operation region A2, the injected supercritical water / subcritical water expands rapidly during the expansion stroke, so that the piston 5 Since the pressure is pushed down, the fuel injection amount can be reduced by the amount corresponding to the push-down work (accordingly, increase in output torque). In addition, when supercritical water / subcritical water is generated using the heat of the exhaust gas, so-called exhaust heat recovery that converts the heat of the exhaust gas into output is achieved, so that a sufficient fuel economy improvement effect is obtained. It becomes possible.

  However, when supercritical water / subcritical water is used also in the first operation region A1 on the high load side, for example, the cooling effect by water injection expected in the first operation region A1 (that is, the outer peripheral portion of the combustion chamber 10 is The effect of cooling and slowing down combustion) is thought to decrease. However, even supercritical water / subcritical water is lower than the temperature of the combustion chamber 10 in the vicinity of the compression top dead center, so that a reasonable cooling effect can be expected. In addition, since water is an inert gas, it is considered that the same slowing effect can be obtained even when supercritical water / subcritical water is injected due to the effect of the uneven distribution of water as the inert gas. That is, when supercritical water / subcritical water is injected, a sufficient amount of water can be supplied to the outer peripheral portion of the combustion chamber 10 in a very short time, so that the concentration of the inert gas in the outer peripheral portion is sufficiently increased. The action caused mainly by the concentration difference makes it possible to slow down the combustion (although the cooling effect is reduced).

(B) Other Modifications In the above embodiment, the water injection valve 57 is a multi-injection type injection valve having a plurality of injection holes formed at the tip, but the water injection valve that can be used in the present invention. However, the present invention is not limited to this, and a so-called outward-opening type injection valve can be used as the water injection valve. The outward opening type injection valve includes, for example, a cylindrical valve body and a needle valve inserted into the valve body so as to be able to advance and retract. The distal end portion of the needle valve is accommodated in a state where the outer peripheral surface thereof can be in close contact with the inner peripheral surface of the distal end portion of the valve body. In such an outside-opening type injection valve, the needle valve is driven in the protruding direction when the valve is opened, so that a continuous ring-shaped slit is formed between the tip of the needle valve and the inner peripheral surface of the valve body. A nozzle port is formed, and water is sprayed in a cone shape through this nozzle port (such a cone-shaped water spray is also a mode in which water is sprayed radially). The same applies to the fuel injection valve 11 in which an outwardly opening type injection valve can be used.

  Further, in the above embodiment, in the first operating region A1 of low speed and high load, in order to create a state where water is unevenly distributed on the outer peripheral portion of the combustion chamber 10 immediately before the self-ignition of the fuel, Water is injected radially from the water injection valve 57 disposed near the center in the first to middle of the compression stroke (water injection Iw1). The timing of the water injection Iw1 in the first operation region A1 Any timing may be used as long as it can create a state in which water is unevenly distributed in the outer peripheral portion of the combustion chamber 10 immediately before self-ignition. For example, if the mounting position of the water injection valve 57 changes, the timing suitable for uneven distribution of water on the outer peripheral portion of the combustion chamber 10 can also change, so the timing of the water injection Iw1 depends on the mounting position of the water injection valve 57 and the like. May be adjusted accordingly. However, in any case, the water injection Iw1 in the first operation region A1 needs to be started after the fuel injection If1 by the fuel injection valve 11 is completed until the fuel self-ignites.

  Further, in the above-described embodiment, the fuel is injected from the fuel injection valve 11 in the middle or later stage of the intake stroke in the low speed / high load first operation area A1 (fuel injection If1). The timing of the fuel injection If1 at A1 may be any timing as long as the fuel is relatively uniformly dispersed in the combustion chamber 10 until the compression top dead center, and can be appropriately changed as long as the timing is reached. For example, the fuel injection If1 may be executed in the first half of the compression stroke. However, the timing of the fuel injection If1 in the first operation region A1 is set to be earlier than the timing of the fuel injection If2 in the second operation region A2. The same applies to the fuel injection If3 in the third operation region A3 with high speed and high load.

  Further, in the above-described embodiment, in the second operating region A2 of low speed and low load, the water injection Iw2 is started immediately after the compression top dead center and then ended, so that the period of the water injection Iw2 is within the combustion period. Although water was injected in such a manner as to be completely included, the timing of the water injection Iw2 in the second operation region A2 is that the action of increasing OH radicals by the water injected into the combustion chamber 10 (water vapor after vaporization). Any timing that extends during the combustion period may be used, and appropriate changes can be made as long as the timing is reached. However, for this purpose, the water injection Iw2 in the second operation region A2 needs to be started between the end of the fuel injection If2 and the end of combustion. Water injection Iw2 may end at the end of the combustion period, but water injected after combustion does not contribute to the suppression of soot, so water injection Iw2 also ends as soon as combustion ends. It is desirable to let them.

  Further, in the above-described embodiment, in the third operating region A3 of high speed and high load, in order to create a state in which water is unevenly distributed in the central portion of the combustion chamber 10 (inside the cavity 5a), immediately before the self-ignition of fuel, Although water is injected radially from the injection valve 57 in the latter half of the compression stroke (water injection Iw3), the timing of the water injection Iw3 in the third operation region A3 is the center of the combustion chamber 10 immediately before self-ignition. Any timing can be used as long as water can be unevenly distributed in the section, and appropriate changes can be made as long as the timing is reached. For example, depending on the scheduled timing of self-ignition, water may be injected at a timing such that a part or all of the period of the water injection Iw3 is included in the initial stage of the expansion stroke.

  Moreover, although the said embodiment demonstrated the example which applied this invention to the gasoline engine by which the HCCI combustion which compresses and self-ignites the mixture of gasoline and air is performed in all the operation areas, this invention is applied. Possible engines are not limited to such engines. For example, a gasoline engine in which HCCI combustion is performed in a part of the operation region and spark ignition combustion is performed in the remaining operation region, or an engine that causes HCCI combustion of fuel containing subcomponents (alcohol or the like) other than gasoline. The present invention is also applicable.

2 cylinder 5 piston 10 combustion chamber 11 fuel injection valve 57 water injection valve 101 fuel injection control unit 102 water injection control unit A1 first operation region A2 second operation region Lx (load) predetermined value Rx (rotational speed) predetermined value If1 Fuel injection (in the first operating region) If2 Fuel injection (in the second operating region) Iw1 Water injection (in the first operating region) Iw2 Water injection (in the second operating region)

Claims (5)

A piston reciprocally accommodated in the cylinder, a fuel injection valve that injects fuel containing gasoline into a combustion chamber defined by the cylinder wall and the piston, and a water injection valve that injects water into the combustion chamber A device for controlling an engine capable of premixed compression ignition combustion in which fuel injected from the fuel injection valve is mixed with air and combusted by self-ignition,
A fuel injection control unit for controlling the fuel injection amount and the injection timing from the fuel injection valve;
A water injection control unit that controls the injection amount and the injection timing of water from the water injection valve,
When the engine is operated in the first operation region where the load is equal to or greater than a predetermined value, the water injection control unit causes the fuel injection so that water is unevenly distributed on the outer peripheral portion of the combustion chamber immediately before the fuel self-ignites. Water is injected from the water injection valve at a predetermined timing after the fuel injection by the valve is completed,
When the engine is operated in the second operation region where the load is lower than that in the first operation region, the fuel injection control unit and the water injection control unit inject fuel in the latter half of the compression stroke, and The fuel injection valve and the water injection valve are controlled such that water is injected within a period from when the combustion is terminated by the self-ignition until the combustion ends by the self-ignition. Control device. The control device for a premixed compression ignition engine according to claim 1,
The water injection valve is provided so as to inject water radially from the vicinity of the center of the ceiling surface of the combustion chamber toward the piston,
During the operation in the first operation region, the water injection control unit causes water to be injected from the water injection valve within a period from the first period to the middle period of a compression stroke. Control device. In the control device of the premixed compression ignition type engine according to claim 1 or 2,
During the operation in the second operation region, the water injection control unit controls the water injection valve so that water injection is started during the duration of combustion by the self-ignition. Control device for compression ignition engine. In the control apparatus of the premixed compression ignition type engine according to any one of claims 1 to 3,
The control device for a premixed compression ignition type engine, wherein the first operation region and the second operation region are both set to a speed region on a low speed side where the rotational speed of the engine is less than a predetermined value. In the control device of the premixed compression ignition engine according to any one of claims 1 to 4,
The control apparatus for a premixed compression ignition engine, wherein the water injection valve is for injecting water heated by heat exchange with the exhaust gas discharged from the combustion chamber.

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