JP6172018B2 - Compression ignition engine starter - Google Patents

Description

  The technology disclosed herein relates to a starter for a compression ignition engine.

  Patent Document 1 describes a diesel engine that stops an engine when an automatic stop condition is satisfied and restarts the engine when a restart condition is satisfied. In this diesel engine, when the restart condition is satisfied, the piston position is in the middle of the compression stroke when the piston first reaches the compression top dead center after starting, that is, when the engine automatically stops. The first fuel injection is performed on a cylinder, and it is compressed and ignited. As a result, the engine can be restarted quickly. Further, in this diesel engine, it was determined that the first compression ignition could not be performed in the cylinder because the piston position of the compression stroke cylinder at the time of stop was located on the top dead center side and the effective compression ratio was lowered. In some cases, the first fuel injection is not performed to the compression stroke cylinder at the time of stop, but the first fuel injection is performed to the intake stroke cylinder at the time of stop when the piston reaches the compression top dead center, and compression ignition combustion is performed. .

JP 2009-62960 A

  Incidentally, there is known a compression ignition type engine configured to supply fuel containing gasoline into a cylinder and combust the mixture by compression ignition. In this compression ignition type engine, it is conceivable to set the geometric compression ratio high from the viewpoint of improving the stability of the compression ignition combustion.

  By setting the geometric compression ratio high, compression ignition combustion is possible even when the engine is started. When starting the compression ignition type engine, it is desirable to perform compression ignition near the compression top dead center. By doing so, a large torque is generated and the engine can be started quickly. For example, if fuel is injected into the cylinder during the period from the end of the compression stroke to the beginning of the expansion stroke, compression ignition occurs near the compression top dead center.

  By performing the first fuel injection and compression ignition combustion, the amount of gas leakage from the joint gap of the piston ring decreases when the engine speed increases. The compression ratio is relatively high. By increasing the effective compression ratio, the pressure and temperature in the cylinder when the piston reaches compression top dead center (that is, the compression end temperature and the compression end pressure) are relatively increased. Unlike spark ignition, compression ignition is greatly affected by the temperature and pressure environment in the cylinder, so the timing of the second fuel injection is the same as the timing of the first fuel injection. Then, the timing of compression ignition becomes relatively early, and there is a possibility that the pressure increase in the cylinder due to compression ignition combustion becomes steep. The pressure increase rate (dP / dθ) in the cylinder is a parameter that can be an index of engine combustion noise, and the pressure increase rate (dP / dθ) exceeds the limit value when the compression ignition engine is started. Also become.

  The problem of combustion noise at the time of starting the engine is not only when the compression ignition type engine is forcibly started, but becomes more prominent when restarting the engine that has been automatically stopped, as described in Patent Document 1. .

  That is, when the fuel is first injected into the stop compression stroke cylinder when the engine is restarted, the piston of the stop compression stroke cylinder is in the middle of the compression stroke, and the compression stroke up to the compression top dead center is relative. Therefore, the effective compression ratio is low. On the other hand, the stop-time intake stroke cylinder that injects the fuel next reaches the compression top dead center through the intake bottom dead center, so that the compression stroke is relatively long and the effective compression ratio becomes high. This, combined with the increase in the effective compression ratio accompanying the increase in engine speed described above, increases the pressure in the cylinder due to compression ignition combustion in the cylinder that injects fuel after the second restart when the engine is restarted. Tends to be steep.

  Further, since the engine is automatically started when the engine is restarted, the demand for sound becomes stricter than when the driver performs a starting operation, and the limit value of the pressure increase rate (dP / dθ) is more It can be even lower.

  The technology disclosed herein has been made in view of such a point, and the purpose thereof is to prevent combustion noise from increasing while enabling rapid start-up when the compression ignition engine is started. There is to do.

  The technology disclosed here is delayed by a predetermined crank angle with respect to the compression top dead center when the pressure increase in the cylinder due to compression ignition combustion becomes steep due to an increase in the effective compression ratio at the start of the compression ignition type engine. The fuel injection timing was delayed so that the compression ignition occurred.

  Specifically, the technology disclosed herein relates to a compression ignition engine starter, and the starter includes a multi-cylinder engine configured to have a plurality of cylinders into which pistons are respectively inserted, and in each cylinder. An injector configured to inject fuel containing gasoline, and injecting the fuel at a predetermined timing through the injector, and combusting an air-fuel mixture formed in the cylinder by compression ignition. And a control unit configured to operate the cylinder engine.

When the multi-cylinder engine is forcibly started by a driver's starting operation , the control unit sequentially injects fuel into the plurality of cylinders during a period from the end of the compression stroke to the initial stage of the expansion stroke, and mixing in the cylinder When the multi-cylinder engine is forcibly started, the control unit is configured to inject fuel into a cylinder that injects fuel first, and then injects fuel into a cylinder that injects fuel next. Is retarded so that compression ignition occurs with a delay of a predetermined crank angle with respect to the compression top dead center.

  Here, the “end of the compression stroke” may be an end when the compression stroke is divided into three equal parts of an initial period, a middle period, and an end period. In addition, the “expansion stroke initial stage” may be an initial stage when the expansion stroke is divided into three equal parts into three periods, an initial period, a middle period, and a final period.

  The fuel injection performed in “the period from the end of the compression stroke to the initial stage of the expansion stroke” is the main combustion that contributes most to the generation of torque, that is, the fuel injection for generating the largest amount of heat in one cycle. This fuel injection can be called main injection. “Performing fuel injection in the period from the end of the compression stroke to the initial stage of the expansion stroke” only needs to include fuel injection performed within the period. That is, main injection may be performed within the period, and fuel injection may be further performed outside the period. Further, a plurality of fuel injections including the main injection may be performed within the period.

According to the above configuration, when the multi-cylinder engine is forcibly started by the driver's starting operation, fuel is sequentially injected into the plurality of cylinders. During the period from the end of the compression stroke to the beginning of the expansion stroke, the air-fuel mixture formed by the fuel injected into the cylinder is burned by compression ignition. Compression ignition is a controlled self-ignition. The compression ignition combustion has a shorter combustion period and higher thermal efficiency than the spark ignition combustion, and is advantageous for generating a large torque, and enables a quick start of the compression ignition engine.

When the multi-cylinder engine is forcibly started, the control unit retards the injection timing to the cylinder that injects fuel next to the injection timing to inject the fuel to the cylinder that injects fuel first. That is, the injection timing when fuel is first injected is relatively early in the period from the end of the compression stroke to the beginning of the expansion stroke. Thereby, in the cylinder which injected the fuel first, compression ignition is carried out near compression top dead center, and it burns. The expansion energy generated by the compression ignition combustion is efficiently transmitted to the piston, which is advantageous for quick start of the multi-cylinder engine.

  The number of revolutions of the multi-cylinder engine is increased by the combustion by the first fuel injection, but the control unit injects fuel when the fuel is injected next (this fuel injection is a cylinder different from the first fuel injection). The timing is set to a relatively late timing from the end of the compression stroke to the initial stage of the expansion stroke. Thus, compression ignition is performed with a delay of a predetermined crank angle with respect to the compression top dead center. This compression ignition combustion is carried out at the timing when the degree of pressure decrease in the cylinder increases away from the compression top dead center even in the expansion stroke in which the pressure in the cylinder gradually decreases. Steepness is avoided.

  Here, as a result of "compression ignition with a delay of a predetermined crank angle with respect to compression top dead center", the combustion period of compression ignition combustion becomes a point when the pressure increase rate in the cylinder during motoring becomes a negative maximum value. You may make it overlap, or it may be made to overlap with the period (10 degrees-20 degrees CA after a compression top dead center) where the combustion center of compression ignition combustion has a large negative pressure increase rate. By doing so, it is possible to effectively reduce the pressure increase rate in the cylinder during the compression ignition combustion.

  In this way, during the second fuel injection in which the effective compression ratio is relatively high, an increase in the pressure increase rate (dP / dθ) in the cylinder due to compression ignition combustion is suppressed, and the combustion noise level is below the limit value. It becomes possible to fit in.

The control unit, wherein the forcible starting of the multi-cylinder engine, the air-fuel ratio A / F of the mixture, or, the weight ratio between the gas and the fuel in the cylinder G / F is forced start completion of the multi-cylinder engine The fuel injection amount may be adjusted so that it becomes richer than the A / F or G / F of the air-fuel mixture in the subsequent low-load steady operation state.

When the multi-cylinder engine is forcibly started, the A / F or G / F of the air-fuel mixture is made relatively rich, which is advantageous for stabilizing the compression ignition combustion and generating a large torque. This allows a quick start of the engine.

  On the other hand, when the A / F or G / F of the air-fuel mixture is made relatively rich, when the effective compression ratio becomes high, the pressure rise in the cylinder due to compression ignition combustion tends to become steep, As described above, an increase in combustion noise can be avoided by retarding the fuel injection timing and performing compression ignition combustion in the expansion stroke.

The control unit may set the excess air ratio λ of the air-fuel mixture to 1 when the multi-cylinder engine is forcibly started.

In this way, when the engine is forcibly started, it is advantageous for stabilization of compression ignition combustion and generation of a large torque, and a multi-cylinder engine can be started quickly. On the contrary, in the low load steady operation state (including the idle operation state) after the forced start of the engine is completed, the excess air ratio λ of the air-fuel mixture is made lean exceeding 1, thereby improving the thermal efficiency. It is done.

  The control unit may perform pre-stage injection with a smaller injection amount than the main injection before the main injection performed in the period from the end of the compression stroke to the initial stage of the expansion stroke for the cylinder into which fuel is injected next.

  Here, “pre-stage injection” is performed by injecting an amount of fuel in which the injected fuel undergoes an oxidation reaction without reaching a thermal flame reaction, thereby suppressing a decrease in temperature in the cylinder after compression top dead center, It may be defined as injection that keeps the temperature fluctuation in the cylinder within a predetermined temperature range. That is, as the expansion stroke proceeds, the temperature in the cylinder gradually decreases, and if the compression ignition timing is delayed too much after the compression top dead center, there is a risk of misfire. On the other hand, if the compression ignition timing is after the compression top dead center and close to the compression top dead center, the pressure in the cylinder is high, and the pressure rise due to compression ignition combustion becomes steep.

  The pre-stage injection compresses the fuel injected into the cylinder by the main injection by keeping the temperature fluctuation in the cylinder within a predetermined temperature range while suppressing the temperature drop in the cylinder after the compression top dead center. It is possible to stably perform compression ignition at a late timing after the top dead center (that is, at a timing delayed by a predetermined crank angle with respect to the compression top dead center). This is advantageous in avoiding a sharp increase in pressure due to compression ignition combustion.

  Here, the pre-stage injection also prevents the temperature in the cylinder from becoming too high. If the temperature in the cylinder becomes too high, the fuel injected into the cylinder may ignite locally before being sufficiently mixed with air, and soot may be generated. The pre-stage injection also suppresses soot generation.

  Here, the pre-stage injection may be, for example, an injection performed at a timing before the end of the compression stroke. Further, the pre-stage injection may be divided into a plurality of injections. The plurality of upstream injections may be a first injection performed at a timing before the end of the compression stroke and a second injection performed near the top dead center after the compression top dead center.

The control unit may set the injection timing so that the combustion center of gravity of the compression ignition combustion is after the compression top dead center when the multi-cylinder engine is forcibly started. In this way, at the time of the first fuel injection, the compression ignition combustion is performed at a timing close to the compression top dead center, thereby increasing the generated torque, which is advantageous for quick start of the multi-cylinder engine. Also, at the time of the next fuel injection, compression ignition combustion is performed at a timing away from the compression top dead center, which is advantageous for reducing combustion noise. The combustion center of gravity can be defined as a time when 50% of the fuel in the cylinder finishes burning (a time when the combustion mass ratio of the fuel becomes 50%).

  The compression ignition engine starter disclosed herein is also configured to inject a fuel containing gasoline into each cylinder and a multi-cylinder engine configured to have a plurality of cylinders into which pistons are respectively inserted. And a control unit configured to operate the multi-cylinder engine by injecting the fuel through the injector at a predetermined timing and combusting an air-fuel mixture formed in the cylinder by compression ignition, .

The control unit automatically stops the multi-cylinder engine when a predetermined automatic stop condition is satisfied, and expands sequentially from the end of the compression stroke to the plurality of cylinders when a predetermined restart condition is satisfied. The fuel injection is performed in the initial stage of the stroke, and the air-fuel mixture in the cylinder is compressed and ignited and combusted to restart the multi-cylinder engine, and the control unit compresses the engine when the multi-cylinder engine is restarted. When the first fuel injection to the stroke cylinder is performed, the injection timing to the stop intake stroke cylinder that injects the fuel next to the injection timing at which the fuel is first injected to the compression stroke cylinder at the time of stop is compressed top dead. The angle is retarded so that compression ignition occurs with a delay of a predetermined crank angle with respect to the point.

  In this case as well, the “end of the compression stroke” may be the end when the compression stroke is divided into three equal parts of the initial period, the middle period, and the final period. In addition, the “expansion stroke initial stage” may be an initial stage when the expansion stroke is divided into three equal parts into three periods, an initial period, a middle period, and a final period.

  The fuel injection performed in “the period from the end of the compression stroke to the initial stage of the expansion stroke” is the main combustion that contributes most to the generation of torque, that is, the fuel injection for generating the largest amount of heat in one cycle. It can be called main injection. To repeat, “performing fuel injection in the period from the end of the compression stroke to the initial stage of the expansion stroke” only needs to include fuel injection performed within the period. That is, main injection may be performed within the period, and fuel injection may be further performed outside the period. Further, a plurality of fuel injections including the main injection may be performed within the period.

According to the arrangement, a multi-cylinder engine has been stopped by a predetermined automatic stop condition is satisfied, when a predetermined restart condition is restarted by established, basically, with respect to the stop-state compression-stroke cylinder Then, the first fuel injection is performed and the compression ignition combustion is performed. The stop compression stroke cylinder is a cylinder where the piston first reaches compression top dead center due to cranking of the multi-cylinder engine, and the multi-cylinder engine is quickly restarted by performing the first compression ignition combustion in the cylinder. Is possible. The compression ignition combustion in the stop-time compression stroke cylinder by the first fuel injection is desirably performed near the compression top dead center from the viewpoint of generating a large torque.

  Following the first fuel injection for the stop-time compression stroke cylinder, the second fuel injection is performed for the stop-time intake stroke cylinder. Since the intake stroke cylinder at the time of stop is longer than the compression stroke cylinder at the time of stop, the effective compression ratio is also relatively high. Further, at the time of the second fuel injection, the effective compression ratio can be further increased by the increase in the engine speed. Therefore, in the stop-time intake stroke cylinder, the pressure rise due to the compression ignition combustion tends to be steep.

  Therefore, in the above-described configuration, the injection timing to the stop-time intake stroke cylinder is relatively retarded so that the compression ignition occurs with a delay of a predetermined crank angle with respect to the compression top dead center. As a result, as described above, the compression ignition combustion is performed at the timing when the degree of pressure decrease in the cylinder increases away from the compression top dead center, so that the pressure increase in the cylinder becomes steep. Is avoided. When restarting an engine having a severe requirement level for combustion noise, an increase in combustion noise is prevented while enabling quick start.

When the multi-cylinder engine is restarted, the control unit determines whether the air-fuel ratio A / F of the air-fuel mixture or the G / F, which is the weight ratio between the gas in the cylinder and the fuel, is completed. The fuel injection amount may be adjusted so that it becomes richer than the A / F or G / F of the air-fuel mixture in the subsequent low-load steady operation state.

The control unit may set the excess air ratio λ of the air-fuel mixture to 1 when the multi-cylinder engine is restarted.

The control unit may perform pre-stage injection with a smaller injection amount than the main injection before the main injection performed in the period from the end of the compression stroke to the initial stage of the expansion stroke for the cylinder into which fuel is injected next.

The control unit may set the injection timing so that the combustion center of gravity of the compression ignition combustion is after the compression top dead center when the multi-cylinder engine is restarted.

  When the multi-cylinder engine is restarted, the control unit performs initial fuel injection to the stop-time compression stroke cylinder when the piston position of the stop-time compression stroke cylinder is on the top dead center side with respect to a predetermined crank angle. Instead, the first fuel injection may be performed on the intake stroke cylinder at the time of stop, and the injection timing may be set so that the compression ignition is delayed by a predetermined period with respect to the compression top dead center.

  When the piston position of the compression stroke cylinder at the time of stop is relatively on the top dead center side, the compression stroke is shortened and the effective compression ratio is lowered, so that the compression end temperature and the compression end pressure are lowered. This reduces the stability of compression ignition of the fuel injected into the cylinder.

  Therefore, when the piston position of the compression stroke cylinder at the time of stop is on the top dead center side from the predetermined crank angle, the first fuel injection to the compression stroke cylinder at the time of stop is not performed when the multi-cylinder engine is restarted. The first fuel injection is performed in the intake stroke cylinder. As described above, the intake stroke cylinder at the time of stoppage has a long compression stroke and a high effective compression ratio, so that the problem of reduced stability of compression ignition is avoided. On the other hand, because the effective compression ratio of the stop-time intake stroke cylinder is high, the injection timing is delayed although it is the first fuel injection when the engine is restarted. In this way, the compression ignition combustion is performed stably, while avoiding a steep rise in pressure, an increase in combustion noise at the time of engine restart is prevented.

As described above, according to the compression ignition type engine starting device, when the multi-cylinder engine is forcibly started or restarted, the fuel is injected into the cylinder that injects fuel first. By delaying the injection timing when the fuel is next injected, it is possible to prevent the combustion noise from increasing while realizing a quick start of the engine.

It is the schematic which shows the structure of an engine. It is a block diagram which shows the structure which concerns on control of an engine. It is sectional drawing which shows the internal structure of an injector. It is the schematic which illustrated the short pulse high voltage which a high voltage controller outputs. It is the schematic which illustrates the map which concerns on the operation control of an engine. (A) is a figure which shows the injection form at the time of retarded self-ignition combustion, (B) is a figure which illustrates the temperature change in a cylinder. It is the schematic which illustrates the production | generation state of ozone in a cylinder. It is a control flow concerning engine restart. It is a figure which shows the relationship between the change of the piston position of a compression stroke cylinder at the time of a stop, and the change of the temperature in a cylinder. It is explanatory drawing which illustrates the fuel-injection timing of each cylinder when restarting an engine. It is a time chart which illustrates the change (upper figure) of the closing timing of an intake valve, and the change (lower figure) of an engine speed when restarting an engine.

  Hereinafter, embodiments will be described with reference to the drawings. The following description is exemplary.

(Overall configuration of engine system)
1 and 2 show a configuration of an engine system 1 according to the embodiment. The engine system 1 is a system mounted on a vehicle. The engine system 1 includes an engine 10, various actuators associated with the engine 10, various sensors, and an ECM (Engine Control Module) 100 that controls the actuators based on signals from the sensors.

  Although not shown, the crankshaft 15 of the engine 10 is connected to drive wheels via a transmission. The vehicle is propelled by the output of the engine 10 being transmitted to the drive wheels. The engine 10 includes a cylinder block 12 and a cylinder head 13 mounted thereon, and a plurality of cylinders 11 are formed inside the cylinder block 12 (only one is shown in FIG. 1). . The engine 10 is a multi-cylinder engine. Although not shown, a water jacket through which cooling water flows is formed inside the cylinder block 12 and the cylinder head 13. In each cylinder 11, a piston 16 connected to a crankshaft 15 via a connecting rod 14 is slidably fitted. The piston 16 divides the combustion chamber 17 together with the cylinder 11 and the cylinder head 13. The cylinder block 12, the cylinder head 13, the piston 16, and the like are made of a metal having electrical conductivity, such as an aluminum alloy, and are grounded.

  In the present embodiment, the ceiling surface 17a of the combustion chamber 17 (the lower surface of the cylinder head 13) is formed in a spherical shape bulging upward (that is, a dome shape). Corresponding to the shape, the top surface 16a of the piston 16 is also formed in a dome shape. A concave cavity 16 b is formed at the center of the top surface 16 a of the piston 16. In addition, the shape of the ceiling surface 17a and the top surface 16a of the piston 16 may be any shape as long as a high geometric compression ratio described later is possible. Both the top surface 16a (portion excluding the cavity 16b) may be configured as a surface perpendicular to the central axis of the cylinder 11, and the ceiling surface 17a has a triangular roof shape (so-called pent roof shape), The top surface 16a of the piston 16 may have a convex shape corresponding to the ceiling surface 17a.

  Although only one is shown in FIG. 1, two intake ports 18 are formed in the cylinder head 13 for each cylinder 11, and each communicates with the combustion chamber 17 by opening on the lower surface of the cylinder head 13. Similarly, two exhaust ports 19 are formed in the cylinder head 13 for each cylinder 11, and each communicates with the combustion chamber 17 by opening on the lower surface of the cylinder head 13.

  The cylinder head 13 is provided with an intake valve 21 and an exhaust valve 22 so that the intake port 18 and the exhaust port 19 can be shut off (closed) from the combustion chamber, respectively. The intake valve 21 is driven by an intake valve drive mechanism, and the exhaust valve 22 is driven by an exhaust valve drive mechanism. The intake valve 21 and the exhaust valve 22 reciprocate at a predetermined timing to open and close the intake port 18 and the exhaust port 19, respectively, and exchange gas in the cylinder 11. Although not shown, the intake valve drive mechanism and the exhaust valve drive mechanism each have an intake cam shaft and an exhaust cam shaft that are drivingly connected to the crankshaft 15, and these camshafts are synchronized with the rotation of the crankshaft 15. Then rotate. In this example, the intake valve driving mechanism and the exhaust valve driving mechanism are a hydraulic or electric variable phase mechanism (Variable Valve Timing: VVT) capable of continuously changing the phase of the intake camshaft within a predetermined angle range. 23 and 24 are included at least. The intake valve driving mechanism and / or the exhaust valve driving mechanism may be provided with a variable lift mechanism capable of changing the valve lift amount together with the VVTs 23 and 24. The lift variable mechanism may be a CVVL (Continuous Variable Valve Lift) capable of continuously changing the lift amount.

  The intake port 18 of each cylinder 11 communicates with the intake passage 30 via an intake manifold not explicitly shown in FIG. Similarly, the exhaust port 19 of each cylinder 11 communicates with the exhaust passage 40 via an exhaust manifold that is not clearly shown.

  A throttle valve 31 that adjusts the amount of intake air to each cylinder 11 is disposed in the intake passage 30. A portion of the intake passage 30 downstream of the throttle valve 31 and the exhaust passage 40 are connected by an EGR passage 51 for returning a part of the exhaust gas to the intake passage 30. The EGR passage 51 is provided with an EGR valve 52 for adjusting the recirculation amount of the exhaust gas to the intake passage 30 and a water-cooled EGR cooler 53 for cooling the exhaust gas. An EGR system 50 is configured including the EGR passage 51, the EGR valve 52, and the EGR cooler 53.

  Although not shown, a catalytic converter that purifies harmful components in the exhaust gas is disposed on the downstream side of the exhaust passage 40. The catalytic converter incorporates a three-way catalyst, for example, and has a function of purifying harmful components (HC, CO, NOx) contained in the exhaust gas passing through the exhaust passage.

  In the engine 10, an injector 6 that directly injects fuel into the cylinder 11 (inside the combustion chamber 17) is disposed on the central axis of the cylinder 11 in the cylinder head 13. The injector 6 is attached and fixed to the cylinder head 13 with a known structure such as using a bracket. The tip of the injector 6 faces the center of the ceiling surface 17 a of the combustion chamber 17.

  As shown in FIG. 3, the injector 6 is an outer valve-opening type injector having an outer valve 62 that opens and closes a nozzle port 61 that injects fuel into the cylinder 11. The nozzle port 61 is formed in a tapered shape whose diameter increases toward the distal end side at the distal end portion of the fuel pipe 63 extending along the central axis of the cylinder 11. The base end side end of the fuel pipe 63 is connected to a case 65 in which a piezo element 64 is disposed. The outer open valve 62 includes a valve main body 62a and a connecting portion 62b connected to the piezo element 64 from the valve main body 62a through the fuel pipe 63. A portion of the valve main body 62a on the connecting portion 62b side has substantially the same shape as the nozzle port 61, and when the portion is in contact (sitting) with the nozzle port 61, the nozzle port 61 is in a closed state. . At this time, the tip side portion of the valve main body 62 a is in a state of protruding to the outside of the fuel pipe 63.

  The piezo element 64 lifts the outer open valve 62 from a state where the nozzle port 61 is closed by pressing the outer open valve 62 toward the combustion chamber 17 in the central axis direction of the cylinder 11 by deformation due to application of voltage. Then, the nozzle port 61 is opened. At this time, fuel is injected from the nozzle port 61 into the cylinder 11 in a cone shape (specifically, a hollow cone shape) centered on the central axis of the cylinder 11. The taper angle of the cone is 90 ° to 100 ° in this embodiment (the taper angle of the inner hollow portion is about 70 °). When the application of voltage to the piezo element 64 is stopped, the piezo element 64 returns to the original state, and the outer opening valve 62 closes the nozzle port 61 again. At this time, the compression coil spring 66 disposed around the connecting portion 62 b in the case 65 facilitates the return of the piezo element 64.

  As the voltage applied to the piezo element 64 increases, the lift amount (hereinafter simply referred to as lift amount) of the outer open valve 62 from the state in which the nozzle port 61 is closed increases. The larger the lift amount, the larger the opening of the nozzle port 61, the greater the penetration of fuel spray injected from the nozzle port 61 into the cylinder 11, and the longer the fuel amount injected per unit time. And the particle size of the fuel spray becomes large. The response of the piezo element 64 is fast, and the later-described injection can be easily realized. However, the means for driving the outer valve 62 is not limited to the piezo element 64. In addition, the injector 6 is not limited to the outer valve opening type, and for example, a multi-hole injector may be employed.

  The fuel supply system 67 (see FIG. 2) includes an electric circuit for driving the outer opening valve 62 (piezo element 64) and a fuel supply system for supplying fuel to the injector 6. The ECM 100 outputs an injection signal having a voltage corresponding to the lift amount to the electric circuit at a predetermined timing, thereby operating the piezo element 64 and the outer opening valve 62 via the electric circuit, and a desired amount of fuel. Is injected into the cylinder 11. When the injection signal is not output (when the voltage of the injection signal is 0), the nozzle port 61 is closed by the outer opening valve 62. Thus, the operation of the piezo element 64 is controlled by the injection signal from the ECM 100. Thus, the ECM 100 controls the operation of the piezo element 64 to control the fuel injection from the nozzle port 61 of the injector 6 and the lift amount during the fuel injection.

  The fuel supply system is provided with a high-pressure fuel pump and a common rail (not shown). The high-pressure fuel pump is driven by the engine 10 and pumps the fuel supplied from the fuel tank via the low-pressure fuel pump to the common rail, and the common rail stores the pumped fuel at a predetermined fuel pressure. Then, when the injector 6 is operated (the outer opening valve 62 is lifted), the fuel stored in the common rail is injected from the nozzle port 61.

  Here, the fuel of the engine 10 is gasoline in the present embodiment, but may be gasoline containing bioethanol or the like, and any fuel as long as it is a fuel (liquid fuel) containing at least gasoline. Also good.

  A discharge plug 71 of the ozone generator 7 is disposed in the combustion chamber 17 of the engine 10. The discharge plug 71 is fixed to the cylinder head 13 by a known structure such as a screw. The distal end portion of the discharge plug 71 protrudes from the ceiling surface 17 a of the combustion chamber 17 and faces the combustion chamber 17. In FIG. 1, the distal end portion of the discharge plug 71 is drawn so as to be deviated from the relationship shown in the figure. (See also FIG. 7. Note that FIG. 1 and FIG. 7 are different in cross section). The discharge plug 71 has a rod-like electrode 71b whose periphery is electrically insulated by an insulator 71a. The electrode 71 b protrudes into the combustion chamber 17 in a state where it is electrically insulated from the cylinder head 13 and the cylinder block 12.

  The ozone generation unit 7 also has a high voltage controller 72 as shown in FIG. The high voltage controller 72 is electrically connected to the discharge plug 71, and applies a controlled pulsed high voltage to the electrode 71b so that an extremely short pulse discharge as described later occurs in the combustion chamber 17. It has a function to do. Specifically, as shown in FIG. 4, the voltage (short pulse high voltage) having a pulse width PW of 50 nanoseconds or less and a high voltage of 10 kV or more is intermittently applied to the electrode 71b for a predetermined period. Have. In addition, arrangement | positioning and structure of the ozone production | generation part 7 are not limited to this.

  The ECM 100 is a controller based on a well-known microcomputer. The ECM 100 is a central processing unit (CPU) that executes a program, a memory that includes, for example, a RAM or a ROM and stores a program and data, and an electric signal input. And an input / output (I / O) bus for outputting.

  The ECM 100 includes a vehicle speed sensor 81 for detecting the vehicle speed, an accelerator opening sensor 82 for detecting the accelerator opening, a brake sensor 83 for detecting on / off of the brake pedal, and a flow rate and temperature of fresh air flowing through the intake passage 30. An air flow sensor 84, a crank angle sensor 85 that outputs a crank angle pulse signal for detecting the rotation angle and rotation speed of the crankshaft 15, a cam angle sensor 86 that outputs a camshaft pulse signal for obtaining cylinder identification information, A water temperature sensor 87 that outputs the cooling water temperature of the engine 10, an oil temperature sensor 88 that outputs the oil temperature, and a battery sensor 89 that outputs the remaining amount of the on-vehicle battery (not shown) are connected.

  The ECM 100 determines the operating state of the engine 10 based on the signal from each sensor described above, and sets the control parameter of the engine 10 corresponding thereto. The ECM 100 sends signals corresponding to the control parameters to the throttle valve 31, the fuel supply system 67, the intake VVT 23, the exhaust VVT 24, the high voltage controller 72, the EGR valve 52, the starter motor 91 not shown in FIG. Output to.

(Engine structure)
Next, the configuration of the engine body will be described in more detail. The geometric compression ratio ε of the engine 10 is 20 or more and 40 or less. The geometric compression ratio ε is particularly preferably 25 or more and 35 or less. Since the engine 10 has a configuration in which the compression ratio = expansion ratio, the engine 10 has a relatively high expansion ratio as well as a high compression ratio. As will be described in detail later, the engine 10 is configured to burn the fuel injected into the cylinder 11 in the entire operation region by compression ignition, and the high geometric compression ratio is advantageous for stabilizing the compression ignition combustion. It is.

  The combustion chamber 17 is defined by the wall surface of the cylinder 11, the top surface of the piston 16, the lower surface (ceiling surface 17 a) of the cylinder head 13, and the valve head surfaces of the intake valve 21 and the exhaust valve 22. Yes. And in order to reduce a cooling loss, the combustion chamber 17 is thermally insulated by providing a heat insulation layer in each of these surfaces. A heat insulation layer may be provided in all of these section screens, and may be provided in a part of these section screens. Further, although it is not a wall surface that directly partitions the combustion chamber 17, a heat insulating layer may be provided on the port wall surface near the opening on the ceiling surface 17 a side of the combustion chamber 17 in the intake port 18 or the exhaust port 19.

  Since these heat insulation layers suppress that the heat of the combustion gas in the combustion chamber 17 is released through the section screen, the heat conductivity is set lower than that of the metal base material constituting the combustion chamber 17. .

  In addition, the heat insulation layer preferably has a volumetric specific heat smaller than that of the base material in order to reduce cooling loss. That is, it is preferable to reduce the heat capacity of the heat insulating layer so that the temperature of the section screen of the combustion chamber 17 changes following the fluctuation of the gas temperature in the combustion chamber 17.

The heat insulation layer may be formed, for example, by coating a ceramic material such as ZrO ₂ on the base material by plasma spraying. The ceramic material may contain a number of pores. If it does in this way, the heat conductivity and volume specific heat of a heat insulation layer can be made lower.

  In the present embodiment, in addition to the heat insulation structure of the combustion chamber, a heat insulation layer is formed by a gas layer in the cylinder 11 (that is, in the combustion chamber 17), so that the cooling loss is greatly reduced. .

  Specifically, the ECM 100 includes a nozzle port of the injector 6 after the compression stroke so that a gas layer containing fresh air is formed at the outer peripheral portion in the cylinder 11 of the engine 10 and an air-fuel mixture layer is formed at the center. In order to inject fuel into the cylinder 11 from 61, an injection signal is output to the electric circuit of the fuel supply system 67. That is, fuel is injected into the cylinder 11 by the injector 6 after the compression stroke, and the penetration of the fuel spray is suppressed to such a size (length) that the fuel spray does not reach the outer periphery of the cylinder 11. Stratification is realized in which an air-fuel mixture layer is formed at the center of the cylinder 11 and a gas layer containing fresh air is formed around the air-fuel mixture layer. This gas layer may be only fresh air, and may contain burned gas (EGR gas) in addition to fresh air. It should be noted that there is no problem even if a small amount of fuel is mixed in the gas layer, and the fuel layer may be leaner than the gas mixture layer so that the gas layer can serve as a heat insulating layer.

  If the fuel undergoes compression ignition combustion with the gas layer and the mixture layer formed as described above, the gas layer between the mixture layer and the wall surface of the cylinder 11 causes the flame of the mixture layer to Without contacting the wall surface, the gas layer serves as a heat insulating layer, and the release of heat from the wall surface of the cylinder 11 can be suppressed. As a result, the cooling loss can be greatly reduced.

  It should be noted that reducing the cooling loss only converts the reduced cooling loss into an exhaust loss and does not contribute much to the improvement in the illustrated thermal efficiency. The energy of the combustion gas corresponding to the reduced cooling loss is efficiently converted into mechanical work. That is, it can be said that the illustrated thermal efficiency is greatly improved in the engine 10 by adopting a configuration that reduces both the cooling loss and the exhaust loss.

(Engine fuel injection control)
The engine 10 performs compression ignition combustion of the fuel injected into the cylinder by the injector 6 in the entire operation region. More specifically, the engine 10 is a low load and medium load operating region in which the engine load is lower than a predetermined load (that is, a switching load) indicated by a solid line in FIG. The operation region A has a higher load side operation region than the normal operation region A, and includes a retard operation region B in which the compression ignition combustion is performed. As will be described later, the retard operation region B is divided into a region B1 and a region B2 with respect to high and low loads.

  In the normal operation region A, the fuel is compressed and ignited near the compression top dead center and burned. For example, the fuel injection start timing by the injector 6 is set during the compression stroke. In the normal operation region A, the ECM 100 adjusts the fuel amount, the fuel injection timing, and the fuel injection mode according to the engine speed, the engine load, and the effective compression ratio.

  In the normal operation region A, the excess air ratio λ in the entire cylinder is set to 2 or more, or the weight ratio G / F of the gas in the cylinder 11 to the fuel is set to 30 or more. Thereby, RawNOx can be reduced while achieving thermal insulation by the heat insulation layer and improving the illustrated thermal efficiency. From the viewpoint of reducing RawNOx, the excess air ratio λ ≧ 2.5 is even more preferable. Moreover, since the illustrated thermal efficiency peaks when the excess air ratio λ = 8, the range of the excess air ratio λ is preferably 2 ≦ λ ≦ 8 (more preferably 2.5 ≦ λ ≦ 8). In addition, since the lean air-fuel mixture sets the throttle valve 31 to the open side, it can contribute to the improvement of the illustrated thermal efficiency by reducing the gas exchange loss (pumping loss). The normal operation region A can be called a lean region because the excess air ratio λ is set to exceed 1.

  Thus, in the normal operation region A, the excess air ratio λ is set to 2 or more. However, when the load on the engine 10 increases and the amount of fuel increases, it may be difficult to set the excess air ratio λ to 2 or more. . Therefore, in this engine 10, the excess air ratio λ is set to 1 in the retard operation region B where the load of the engine 10 is relatively high. In the retard operation region B, it becomes possible to maintain good exhaust emission performance using a three-way catalyst. In this engine system 1, it is possible to omit the NOx purification catalyst. The retard operation region B can be called the λ = 1 region because the excess air ratio λ is 1.

  In the retard operation region B, as shown in FIG. 6, the in-cylinder temperature from the compression top dead center until the main-injected fuel is compressed and ignited is substantially maintained at the in-cylinder temperature at the compression top dead center. Pre-stage injection for generating heat and main injection for causing compression ignition combustion in the expansion stroke are performed. Hereinafter, the self-ignition combustion that retards the ignition timing while maintaining the in-cylinder temperature after the compression top dead center by the pre-stage injection is referred to as “retard self-ignition combustion”.

  In the pre-stage injection, the fuel is injected in an amount corresponding to the air-fuel ratio that causes the injected fuel to undergo partial oxidation reaction, and the in-cylinder temperature after the compression top dead center can be compressed and ignited for a predetermined period. It is for maintaining the temperature. In the pre-stage injection, although the fuel undergoes an oxidation reaction, it does not reach a thermal flame reaction, so that only an amount of heat that suppresses a decrease in the in-cylinder temperature after compression top dead center is generated. That is, the pre-stage injection is for maintaining the in-cylinder temperature after the compression top dead center while preventing the in-cylinder temperature from becoming too high. By this pre-stage injection, as shown in FIG. 6B, the air-fuel mixture after compression top dead center expands, that is, substantially isothermally expands in a state where the temperature change is suppressed within a predetermined temperature range. In this specification, this substantially isothermal expansion is simply referred to as “isothermal expansion”.

  The upper limit value of the predetermined temperature range is a temperature lower than the temperature at which the fuel from the main injection ignites before being mixed with the air in the cylinder. The lower limit value of the predetermined temperature range is a temperature higher than the in-cylinder temperature that decreases due to motoring. That is, the in-cylinder temperature from the compression top dead center to the occurrence of main combustion by the pre-injection is lower than the temperature at which the fuel from the main injection ignites before being mixed with the air in the cylinder, and at the compression top dead center. The in-cylinder temperature is maintained at a temperature higher than the temperature reduced by performing motoring. For example, the “predetermined temperature range” is 100 degrees. More specifically, the in-cylinder temperature from the compression top dead center until the main combustion occurs is maintained at 1000 to 1100K. However, the temperature width is not limited to 100 degrees. Any other value such as 90 degrees or 110 degrees may be used as long as it is a temperature range that prevents abnormal combustion of the fuel and enables retarded self-ignition combustion.

  Similarly, the in-cylinder temperature while the variation in the in-cylinder temperature is within a predetermined temperature range is not limited to 1000 to 1100K. Other values such as 950 to 1100K, 1000 to 1150K, and 1100 to 1200K may be used as long as the temperature is such that the abnormal combustion of the fuel is prevented and the retarded self-ignition combustion is possible.

  The main injection is an injection for generating main combustion that generates engine torque (combustion that generates the largest amount of heat in one cycle). In the main injection, the fuel is injected at a timing when the fuel is ignited while the variation in the in-cylinder temperature is within the predetermined temperature range in the expansion stroke. Furthermore, the injection timing of the main injection is a timing at which the combustion period of the main combustion overlaps with the point in time when the pressure increase rate in the cylinder 11 during motoring becomes a negative maximum value. Here, ignition means a point in time when the combustion mass ratio of the fuel becomes 10% or more. For example, the main injection is executed after the compression top dead center and during the expansion stroke (more specifically, the initial stage when the expansion stroke is divided into three equal parts in the initial, middle and final stages). Since the main injection causes main combustion that generates torque, it is necessary to inject fuel corresponding to the required torque. For example, in the main injection, it is preferable to inject 3/4 or more of the total injection amount including the injection amount by the pre-stage injection and the injection amount by the main injection.

  When the main combustion is retarded in this way, there is a limit to the period during which the retard can be performed. That is, as the expansion stroke proceeds, the in-cylinder temperature decreases as the volume in the cylinder 11 increases, and if the main combustion is retarded too much, misfire occurs. The lowering speed of the in-cylinder temperature in the expansion stroke is faster as the compression ratio is higher. Therefore, the higher the compression ratio, the shorter the retardable period. However, the period in which the main combustion can be retarded can be extended by maintaining the in-cylinder temperature after compression top dead center by the pre-stage injection.

  However, when increasing the in-cylinder temperature after compression top dead center, if the in-cylinder temperature is too high, the fuel injected by the main injection will ignite locally before mixing with the air in the cylinder, There is a risk of causing wrinkles. However, according to the pre-stage injection, the fluctuation of the in-cylinder temperature after the compression top dead center is suppressed within a predetermined temperature range, so that an excessive increase in the in-cylinder temperature is also suppressed. As a result, it is possible to suppress the occurrence of soot by locally igniting the fuel from the main injection.

  In the low load side region B1 in the retard operation region B, the first pre-injection and the main injection shown in FIG. This avoids an increase in combustion noise. The total injection amounts of the first pre-stage injection and the main injection are set so that the overall excess air ratio λ in the cylinder is 1.

  On the other hand, in the region B2 on the high load side in the retard operation region B, between the first pre-stage injection before the compression top dead center and the main injection after the compression top dead center shown in FIG. After performing the second pre-stage injection, the retarded self-ignition combustion is performed. In the high load side region B2, it is necessary to further retard the compression ignition combustion period than the low load side region B1 for the purpose of avoiding combustion noise. If there is a large delay from the compression top dead center, even if an attempt is made to maintain the temperature in the cylinder by the pre-stage combustion described above, the temperature may not be maintained and may be reduced, resulting in a misfire. In other words, the second pre-stage injection generates a quantity of heat for maintaining the in-cylinder temperature from the compression top dead center to the compression ignition of the main injection fuel substantially at the compression top dead center. Yes, thereby adjusting the temperature maintenance period.

  The second pre-stage injection also injects fuel by an amount that provides an air-fuel ratio that causes partial oxidation reaction of the injected fuel. The in-cylinder temperature after the compression top dead center is maintained for a predetermined period of time. It is for maintaining the temperature at which ignition is possible. In the second pre-stage injection, although the fuel undergoes an oxidation reaction but does not reach a hot flame reaction, only a quantity of heat that suppresses a decrease in the in-cylinder temperature after the compression top dead center is generated. The second pre-stage injection is for maintaining the in-cylinder temperature after the compression top dead center while preventing the in-cylinder temperature from becoming too high. By this second pre-stage injection, the temperature maintenance period after the compression top dead center becomes longer in the region B2 on the high load side than in the region B1 on the low load side.

  Thus, in the high load side region B2, the injection timing of the main injection is delayed from the injection timing in the low load side region B1. However, the timing of the main injection is the timing at which the fuel is ignited while the variation in the in-cylinder temperature is within the predetermined temperature range in the expansion stroke, and the combustion period of the main combustion is in the cylinder during motoring. This is the same timing as when the pressure increase rate reaches the maximum negative value. By relatively retarding the timing of the main injection, the compression ignition timing is delayed, and as a result, the compression ignition combustion period is retarded relative to the region B1 on the low load side. Thus, it is possible to avoid combustion noise even in the high load region B2.

  The injection amount of the second front-stage injection increases as the load on the engine 10 increases. As the load increases, the timing of the main injection needs to be delayed in order to delay the combustion period. Therefore, by increasing the injection amount of the second pre-stage injection, the period of maintaining the predetermined temperature after the compression top dead center is lengthened. To do. Thereby, although the injection start timing of the second front stage injection hardly changes with the load of the engine 10, the injection end timing becomes later as the load of the engine 10 becomes higher.

  The injection start timing of the main injection is gradually retarded as the load on the engine 10 increases. This corresponds to retarding the period of compression ignition combustion and delaying the injection end timing of the second pre-stage injection. The main injection that contributes to the engine torque increases as the load on the engine 10 increases.

  On the other hand, the first pre-stage injection is almost constant with respect to the load of the engine 10 over the entire retard operation region B in both the injection amount and the injection timing.

  Even in the high load side region B2, the total injection amount of the front injection, the second front injection, and the main injection is set so that the excess air ratio λ of the entire cylinder becomes 1. The injection amount by the first pre-stage injection is about 5% of the total injection quantity, and the injection quantity by the second pre-stage injection is about 15% of the total injection quantity. The injection amount of the main injection is about 80% of the total injection amount.

  The solid line in FIG. 6B shows an example of the temperature change in the cylinder 11 in the low load side region B1 where the first pre-stage injection and the main injection are performed. Further, the alternate long and short dash line in the figure shows an example of the temperature change in the cylinder 11 in the high-load region B2 where the first pre-stage injection, the second pre-stage injection, and the main injection are performed. As described above, the fuel injected into the cylinder 11 by the pre-stage injection adjusts the compression end temperature, and the fuel injected into the cylinder 11 by the second pre-stage injection after the compression top dead center is compressed by the partial oxidation reaction. The period for maintaining the temperature in the cylinder 11 after the top dead center in a predetermined range is further extended. The broken line indicates the temperature change in the cylinder 11 after compression top dead center during motoring. Thus, in each of the regions B1 and B2, the fuel injected into the cylinder 11 by the main injection is compressed and ignited at a predetermined timing and burned.

(Ozone generation in cylinder)
In the retard operation region B, as described above, the combustion period of the compression ignition combustion is retarded by performing at least the front injection and the main injection. Further, in the retard operation region B, the engine 10 directly generates ozone that induces self-ignition from the intake air in the combustion chamber 17 as necessary, thereby stabilizing the compression ignition combustion. By generating ozone directly in the combustion chamber 17, it is possible to improve ozone generation efficiency and energy utilization efficiency, proper mixing with intake air in the combustion chamber 17, improvement in control response, and the like.

  Specifically, since the cylinder head 13 and the cylinder block 12 forming the cylinder 11 are grounded, when a short pulse high voltage is applied to the electrode 71b, the inner surface of the cylinder 11 (specifically, The inner surface of the combustion chamber 17) and the electrode 71b constitute an anode and a cathode, and discharge occurs between them (the electrode 71b corresponds to the anode and the cylinder 11 corresponds to the cathode).

  Since the applied voltage is controlled to a predetermined short pulse high voltage, only the streamer discharge is generated in the combustion chamber 17. Therefore, there is no risk of sparks or heat. Since a dielectric is not interposed and is directly generated in the combustion chamber 17, high ozone generation efficiency and energy utilization efficiency can be obtained.

  The high voltage controller 72 operates in at least one of an intake stroke, a compression stroke, and an expansion stroke, and generates ozone in the cylinder 11. For example, a short pulse high voltage may be applied to the electrode 71b in synchronization with the intake valve 21 being opened and intake air being introduced into the combustion chamber 17. By doing so, inhalation (oxygen) is continuously supplied in the vicinity (discharge space) of the electrode 71b where discharge occurs, and the generated ozone and the intake air are switched.

  As a result, ozone can be generated almost without being affected by the saturation concentration of ozone, so that higher ozone generation efficiency and energy utilization efficiency can be obtained. Mixing of ozone and intake air is also promoted.

  Further, when the high voltage controller 72 generates ozone during the compression stroke or the expansion stroke, a short pulse high voltage may be applied to the electrode 71b in synchronization with the fuel injection by the injector 6. By doing so, as shown in FIG. 7, air flows in the sealed combustion chamber 17 due to the momentum of the injected fuel, whereby ozone and air are interchanged in the discharge space, and high ozone generation is achieved. Ozone is generated while maintaining efficiency. In addition, when generating ozone during a compression stroke or an expansion stroke, it is also possible to generate ozone without synchronizing with fuel injection.

  The fuel injected into the cylinder 11 by the main injection is given energy by ozone and is easily self-ignited and combusted. That is, ozone assists the compression ignition of fuel.

  According to the pre-stage injection (including the first and second pre-stage injections), the decrease in the in-cylinder temperature after the compression top dead center can be suppressed, so that the period during which the compression ignition combustion can be retarded can be extended. However, there is a limit even if the period of retarding can be extended. On the other hand, by generating ozone in the cylinder 11, even if the ignition timing is retarded until ignition is difficult or impossible without the supply of ozone, the fuel can be compressed and ignited. The supply of ozone makes it possible to extend the retard period when retarding compression ignition combustion.

  The supply of ozone may always be performed. By supplying ozone, it is possible to reduce the injection amount of the pre-stage injection. The supply of ozone may be performed only when the in-cylinder temperature after compression top dead center falls below a predetermined temperature. This predetermined temperature is a temperature at which the compression ignition combustion of the fuel can be performed without supplying ozone. That is, as described above, this is a temperature corresponding to the lower limit value when the in-cylinder temperature fluctuation from the compression top dead center until the fuel is ignited by the main injection is maintained within a predetermined temperature range by the pre-stage injection. That is, ozone may be supplied in a situation where self-ignition combustion of fuel by main injection is difficult only by maintaining the in-cylinder temperature after compression top dead center by pre-stage injection.

  The supply of ozone may be performed only in the region B2 on the high load side in the retard operation region B, or may be performed over the entire region of the retard operation region B.

  Further, the concentration of ozone generated by the ozone generator 7 may be increased as the load on the engine 10 is increased, for example. The higher the ozone concentration is, the stronger the compression ignition assist becomes, and the compression ignition becomes possible or the ignition timing is advanced even if the temperature in the cylinder 11 is low. On the other hand, increasing the ozone concentration is disadvantageous for fuel consumption deterioration and engine 10 corrosion. Therefore, the ozone concentration may be higher as the load on the engine 10 is higher so as to supply the minimum necessary ozone.

(Fuel injection control at engine restart)
From the viewpoint of improving fuel efficiency, the engine system 1 automatically stops the engine 10 when a predetermined automatic stop condition is satisfied, and restarts the engine 10 when the predetermined restart condition is satisfied (that is, It performs so-called idling stop control that automatically starts. In the engine system 1, compression ignition combustion is performed even when the engine 10 is restarted. Hereinafter, fuel injection control when the engine 10 is restarted will be described with reference to the flowchart of FIG.

  The flow in FIG. 8 starts after the restart condition is satisfied and the engine 10 is automatically stopped. Here, as the automatic stop condition, for example, the vehicle is in a stopped state, the opening degree of the accelerator pedal is zero (accelerator off), the brake pedal is depressed (brake on), and the engine 10 is cooled. Assume that the automatic stop condition is satisfied when a plurality of requirements such as the water temperature is equal to or higher than a predetermined value and the remaining battery level is equal to or higher than a predetermined value are satisfied.

  In step S1 after the start, based on output signals from various sensors and the like, the stop position of the piston 16, the outside air temperature, the atmospheric pressure, the cooling water temperature and the oil temperature of the engine 10, the brake depression amount, the accelerator depression amount, and the air conditioning device Reads on / off status, vehicle interior temperature, battery level, etc. These parameters relate to the restart condition of the engine 10 and the restart control of the engine 10.

  In a succeeding step S2, it is determined whether or not a restart condition is satisfied. The restart conditions are, for example, that the brake pedal has been released, that the accelerator pedal has been depressed, that the coolant temperature of the engine 10 has become less than a predetermined value, that the amount of decrease in the remaining battery capacity has exceeded an allowable value, Requirements such as the stop time of the engine 10 exceeding the upper limit time and the necessity of operating the air conditioner (that is, the difference between the vehicle interior temperature and the set temperature of the air conditioner exceeds a predetermined value) When at least one of the above is satisfied, it is determined that the restart condition is satisfied.

  When the determination in step S2 is NO, the flow is returned. On the other hand, when the determination in step S2 is YES (that is, when the restart condition is satisfied), the flow proceeds to step S3.

  In step S3, it is determined whether or not it is the first explosion when the restart of the engine 10 is started. Here, the explanation will be made assuming that it is the first explosion. The flow moves from step S3 to step S4.

  In step S4, it is determined whether or not the first compression ignition is possible. Here, the first compression ignition is a cylinder in which the piston first reaches the compression top dead center when the restart of the engine 10 is started by cranking when the engine 10 is automatically stopped. This cylinder is called a compression stroke cylinder at the time of stop), and fuel is injected and combustion is performed by compression ignition. When the engine 10 is restarted, the engine 10 is quickly restarted by injecting fuel into the stop-time compression stroke cylinder and performing compression ignition combustion. The determination in step S4 is to determine whether or not combustion is possible by compression ignition when fuel is injected into the stop compression stroke cylinder. Specifically, the determination is made based on the estimated temperature (compression end temperature (T1)) in the cylinder 11 when the piston of the compression stroke cylinder at the time of stop reaches the compression top dead center.

  The estimation of the compression end temperature (T1) is an estimation of the compression end temperature due to motoring. For example, the temperature increase due to the compression stroke from the stop position to the compression top dead center of the piston of the compression stroke cylinder at the time of stop. This is possible by multiplying (T0) by predetermined coefficients C1, C2, C3.

  The coefficient C1 is an outside air temperature coefficient. For example, when the outside air temperature is 20 ° C., C1 = 1.0, and below 20 ° C., the lower the temperature, the smaller the coefficient C1 (for example, 0 ° C., C1 = 0.95). When the temperature exceeds 20 ° C., the coefficient C1 is increased as the temperature increases (for example, C1 = 1.03 at 40 ° C.).

  The coefficient C2 is an external atmospheric pressure coefficient. For example, when the external air pressure is 1.0 atmospheric pressure, C2 = 1.0. If the atmospheric pressure is less than 1 atmospheric pressure, the lower the atmospheric pressure, the smaller the coefficient C2 (for example, 0.90 atmospheric pressure, C1 = 0.90) When the pressure exceeds 1 atm, the higher the atmospheric pressure, the larger the coefficient C2 (eg, 1.10 atm, C2 = 1.10).

  The coefficient C3 is an engine temperature coefficient. When the engine temperature (cooling water temperature and / or oil temperature) is 70 ° C., C3 = 1.0, and when the temperature is lower than 70 ° C., the coefficient C3 is decreased (for example, 40 ° C.). C3 = 0.97), when it exceeds 70 ° C., the higher the temperature, the larger the coefficient C4 (for example, at 100 ° C., C3 = 1.01).

  Thus, when the estimated compression end temperature (T1) is equal to or higher than the temperature at which the compression ignition combustion of the fuel is possible, the determination of step S4 is determined as YES, and the process proceeds to step S5, while the estimated compression end When the temperature (T1) is lower than the temperature at which compression ignition combustion of the fuel is possible, the determination in step S4 is determined as NO, and the process proceeds to step S10. For example, when the piston position of the compression stroke cylinder at the time of stop is on the top dead center side with respect to the predetermined crank angle, the compression stroke is shortened, so that the temperature rise (T0) due to the compression stroke is small. As a result, the determination in step S4 can be NO. On the other hand, when the piston position of the compression stroke cylinder at the time of stop is at a predetermined crank angle or lower dead center side than that, the compression stroke becomes longer, and the temperature rise (T0) due to the compression stroke becomes larger. As a result, the determination in step S4 can be YES.

  In step S5 and subsequent steps, when the engine 10 is restarted, fuel is injected into the compression stroke cylinder at the time of stop to perform compression ignition and combustion. On the other hand, in step S10, when the engine 10 is restarted, fuel is not injected into the compression stroke cylinder at the time of stop, but fuel is injected into the intake stroke cylinder at the time of stop where the piston reaches the compression top dead center. In this way, when the engine 10 is restarted on the basis of the estimated compression end temperature (T1), the cylinder to which fuel is first injected is switched, so that the compression ignition combustion is surely performed for the first injected fuel. .

  In step S5, based on the estimated compression end temperature (T2), the first fuel injection amount and the injection timing for the stop-time compression stroke cylinder are set. Unlike the estimated compression end temperature (T1) described above, the estimated compression end temperature (T2) is a compression end temperature estimated in consideration of fuel injection into the cylinder 11. In step S5, the fuel injection amount and the injection timing to the compression stroke cylinder at the time of stop are set so that the compression end temperature becomes a temperature at which compression ignition is possible.

  FIG. 9 illustrates the temperature change in the cylinder when the engine 10 is restarted in the compression stroke cylinder at the time of stop. As the piston 16 moves toward the compression top dead center by cranking (corresponding to the right to left in FIG. 9), the gas (generally air) in the cylinder 11 is compressed, and the temperature in the cylinder 11 gradually increases. To do. When the piston stop position of the compression stroke cylinder at the time of stop is located at P1, which is relatively at the bottom dead center side, the compression stroke to reach the top dead center is long and the effective compression ratio becomes high. For this reason, the temperature in the cylinder 11 changes from a solid line to a one-dot chain line, and the compression end temperature also increases (Temp1).

  When the engine 10 is restarted, fuel injection is performed in the compression stroke cylinder at the time of stopping until the piston 16 reaches top dead center. In the example of FIG. 9, it is assumed that fuel is injected into the compression stroke cylinder at the stop at a predetermined timing (F1). This injection timing corresponds to the end of the compression stroke. An air-fuel mixture is formed in the cylinder 11 by the fuel injection. The specific heat ratio of the air-fuel mixture is lower than the specific heat ratio of air before the fuel is injected. Therefore, after fuel injection, the temperature rise of the gas accompanying compression becomes moderate, and as a result, the actual compression end temperature becomes Temp2 as shown by the solid line in FIG. In the example of FIG. 9, when the piston position of the compression stroke cylinder at the time of stop is relatively at the bottom dead center side (P1), the compression end temperature Temp2 is as much as the compression stroke can be sufficiently secured. The temperature required for compression ignition is slightly exceeded. On the other hand, although illustration is omitted, when the fuel injection timing is further advanced, the amount of stroke for compressing the air-fuel mixture having a low specific heat ratio increases accordingly, so that the compression end temperature becomes lower than Temp2. As a result, the compression end temperature can be lower than the temperature required for compression ignition. This hinders the stabilization of compression ignition combustion. Conversely, when the fuel injection timing is further delayed, the stroke for compressing air having a high specific heat ratio is increased by that amount, so that the compression end temperature becomes higher than Temp2. As a result, the compression end temperature can greatly exceed the temperature required for compression ignition. This leads to a situation where the timing of compression ignition becomes too early.

  In step S5, based on the compression end temperature (T1) estimated in step S4, the compression end temperature (T2) when fuel for the required injection amount is injected at a predetermined timing in the latter half of the compression stroke is estimated. Here, the “predetermined (injection) timing in the second half of the compression stroke” is a timing at which the fuel injected into the cylinder 11 undergoes compression ignition at an optimal timing near the compression top dead center after a predetermined ignition delay. Further, the required injection amount is an injection amount such that the excess air ratio λ is 1. By setting the excess air ratio λ to 1 when the engine 10 is restarted, the stability of the compression ignition combustion is increased, and a large torque is generated so that the engine 10 can be restarted quickly.

  When the estimated compression end temperature (T2) exceeds the temperature required for compression ignition, the fuel injection amount is set to the required injection amount and the injection timing is set to the predetermined timing in step S5. By doing so, the expansion energy due to the compression ignition combustion is transmitted to the piston 16 most efficiently, and a large torque can be generated. What is necessary is just to set the temperature required for compression ignition suitably in 800-900K, for example.

  On the other hand, when the estimated compression end temperature (T2) is lower than the temperature necessary for compression ignition, the fuel injection timing is retarded from a predetermined timing. As a result, the amount of stroke for compressing air having a high specific heat ratio increases, and accordingly, the compression end temperature can be increased, and the temperature required for compression ignition can be exceeded. Here, if the fuel injection timing is delayed too much, ignition may occur without ensuring a sufficient time for the injected fuel and air to mix, and as a result, soot may be generated. Therefore, the fuel injection timing is limited by a preset delay angle limit.

  Further, when the estimated compression end temperature (T2) greatly exceeds the temperature required for compression ignition, there is a possibility that compression ignition will occur before reaching the compression top dead center. Therefore, the fuel injection timing is advanced from the predetermined timing. Thereby, since the stroke for compressing the air-fuel mixture having a low specific heat ratio is increased, the compression end temperature can be lowered by that amount, and it is prevented that the temperature required for compression ignition is greatly exceeded.

  Thus, when the piston position of the compression stroke cylinder at the time of stop is relatively located at the bottom dead center side, a sufficient compression stroke can be secured, so as shown by a white arrow in FIG. By appropriately changing the fuel injection timing, the compression end temperature can be adjusted so as to exceed the temperature required for compression ignition. When the piston position is on the top dead center side, the injection timing is retarded than when the piston is on the bottom dead center side. In step S5, the fuel injection timing is set so that the compression end temperature exceeds the temperature required for compression ignition. As a result, the injection timing is set at the end of the compression stroke.

  On the other hand, in the compression stroke cylinder at the time of stop, when the stop position of the piston 16 is relatively located on the top dead center side (see P2 in FIG. 9), the compression stroke is relatively short and effective. The compression ratio is relatively low. As a result, the temperature in the cylinder 11 during motoring changes from a solid line to a one-dot chain line in FIG. 9, and the compression end temperature becomes relatively low (Temp3). In this case, as described above, in order to increase the compression end temperature as much as possible, even if the fuel injection timing is delayed to, for example, a preset delay angle limit (see F2 in FIG. 9), the compression end temperature Temp4 is It is also possible for the temperature to be below that required for compression ignition. In this case, in step S5, the fuel injection timing is set to the retard limit.

  In this way, if the fuel injection amount and the fuel injection timing in the compression stroke cylinder at the time of stop are respectively set in step S5, it is determined in step S6 whether ozone generation is necessary based on the estimated compression end temperature (T3). The estimated compression end temperature (T3) is the compression end temperature in the stop-time compression stroke cylinder when fuel is injected in accordance with the fuel injection amount and fuel injection timing set in step S5. When the estimated compression end temperature (T3) is equal to or higher than the temperature necessary for compression ignition, it is determined that ozone generation is unnecessary. When the estimated compression end temperature (T3) is lower than the temperature necessary for compression ignition, it is determined that ozone generation is necessary. When it is determined in step S6 that ozone generation is necessary, the amount of ozone generated and generated by the ozone generator 7 based on the fuel injection amount, the fuel injection timing, the temperature difference between the compression end temperature and the temperature required for compression ignition, etc. Set each timing. In the example of FIG. 9, when the compression end temperature (T3) is Temp2, it is determined that generation of ozone is unnecessary. When the compression end temperature (T3) is Temp4, it is determined that ozone needs to be generated. That is, when the engine 10 is restarted, when the piston position of the compression stroke cylinder at the time of stop is at P2 on the top dead center side, the fuel injection timing F2 is set to be greater than the injection timing F1 at P1 on the bottom dead center side. Is also retarded, and ozone is generated in the stop-time compression stroke cylinder through the ozone generator 7.

  It should be noted that here, in consideration of improvement in fuel consumption, etc., the fuel injection timing is set so that the compression end temperature is increased as much as possible by adjusting the fuel injection timing in step S5 so that ozone generation is not performed as much as possible. On the other hand, ozone is generated only when the compression end temperature cannot be further increased due to the retardation limit.

  In contrast, in step S5, the fuel injection timing is temporarily set to a predetermined timing, the compression end temperature in that case is estimated, and the estimated compression end temperature and the temperature required for compression ignition are calculated. Based on the temperature difference, the ozone generation amount and the generation timing by the ozone generation unit 7 are set (including not generating ozone), and the fuel injection timing may be reset. .

  Further, the fuel injection timing may be set on the premise of the generation of ozone. For example, when the piston position of the stop compression stroke cylinder is at a predetermined position between the top dead center and the bottom dead center or on the top dead center side, ozone is generated in the stop compression stroke cylinder. The fuel injection timing may be set on the advance side of the delay limit of the fuel injection timing determined on the assumption that ozone is generated in the cylinder. The “predetermined position” here can be set as appropriate. For example, the center position between the top dead center and the bottom dead center may be used.

  In step S6, whether or not ozone generation is necessary is determined. However, ozone may be always generated when the engine 10 is restarted, and in step S6, the ozone generation amount may be set. That is, when the estimated compression end temperature is equal to or lower than a predetermined temperature (the predetermined temperature may be a temperature necessary for compression ignition or a temperature set based on the temperature), the amount of ozone generated When the estimated compression end temperature exceeds a predetermined temperature, the amount of ozone generated may be relatively reduced. The generation amount of ozone may be set according to the temperature difference between the estimated compression end temperature and the predetermined temperature (for example, so as to be proportional).

  In this way, if the fuel injection amount, the fuel injection timing, and the necessity of ozone generation are respectively set in steps S5 and S6, the starter motor 91 is driven and cranking of the engine 10 is started in step S7. In subsequent step S8, it is determined whether ozone generation is necessary. When ozone generation is necessary, the process proceeds to step S9, and fuel is injected into the stop-time compression stroke cylinder through the injector 6 at the set fuel injection amount and at the set injection timing. In the first compression ignition, fuel injection is performed at the end of the compression stroke. Along with this fuel injection, ozone is generated at a predetermined timing. As described above, since the ozone generator 7 can generate ozone in the sealed cylinder 11, it is advantageous in generating ozone in the stop-time compression stroke cylinder when the engine 10 is restarted. .

  On the other hand, when ozone generation is unnecessary, the process proceeds from step S8 to step S12, and fuel is injected into the stop-time compression stroke cylinder through the injector 6 at the set fuel injection amount and at the set injection timing. Also in this case, the fuel injection is performed at the end of the compression stroke.

  On the other hand, after it is determined in step S4 that the first compression ignition in the stop compression stroke cylinder cannot be performed, in step S10, the first compression of the second compression cylinder, that is, the intake stroke cylinder at the stop is first performed. The fuel injection amount and the injection timing at the time of injection are set based on the estimated compression end temperature (T4) of the stop-time intake stroke cylinder. The fuel injection amount is set so that the excess air ratio λ = 1 as in step S5. The estimated compression end temperature (T4) can be estimated in the same manner as the compression end temperature in the stop-time compression stroke cylinder estimated in step S4. However, unlike the stop-time compression stroke cylinder, the stop-time intake stroke cylinder can sufficiently secure the compression stroke, and the compression end temperature sufficiently exceeds the temperature required for ignition. On the other hand, in the intake stroke cylinder at the time of stop, the intake end heated by the radiant heat is compressed during the automatic stop of the engine. As a result, the compression end temperature tends to increase, and as a result, the fuel injection timing is advanced. Sometimes pre-ignition may occur. Further, since the timing of compression ignition becomes earlier, the pressure increase rate (dP / dθ) in the cylinder 11 may exceed the limit value.

  Therefore, in step S10, the fuel injection timing is retarded according to the estimated compression end temperature (T4). As a result of retarding the fuel injection timing as described above, the pre-stage injection and the main injection may be performed so as to achieve the above-described retarded self-ignition combustion. That is, in order to delay the fuel injection that contributes to the generation of engine torque (that is, main injection) after the compression top dead center, the first pre-stage injection or the first and second pre-stage injections are performed. The retarded self-ignition combustion in the intake stroke cylinder at the time of the second compression stop is the same control as the retarded self-ignition combustion after the second explosion described later.

  If the fuel injection amount and the injection timing for the stop-time intake stroke cylinder are respectively set in step S10, the starter motor 91 is driven and cranking of the engine 10 is started in the subsequent step S11. Then, in the subsequent step S12, fuel is injected into the stop-time intake stroke cylinder according to the fuel injection amount and injection timing set in step S10. In this case, fuel injection is performed in the period from the end of the compression stroke to the initial stage of the expansion stroke. Thereby, generation | occurrence | production of a pre-ignition and the pressure rise rate (dP / d (theta)) in the cylinder 11 exceeding a limit value are each avoided.

  In this way, if the first explosion combustion is performed in the stop-time compression stroke cylinder or the stop-time intake stroke cylinder, the flow shifts from step S3 to step S13.

  In step S13, fuel is injected at a predetermined fuel injection timing in a cylinder that performs combustion after the second explosion (that is, the second explosion becomes a stop-time intake stroke cylinder or a stop-time exhaust stroke cylinder). When the compression ignition combustion is performed, it is determined whether or not the pressure increase rate (dP / dθ) in the cylinder 11 exceeds the limit value. After the second explosion, the number of gas leaks from the joint gap of the piston ring is reduced and the effective compression ratio is increased by increasing the rotational speed of the engine 10. Further, particularly when the first explosion is performed in the compression stroke cylinder at the time of stop and the second explosion is performed in the intake stroke cylinder at the time of stop when the effective compression ratio is relatively low due to the relationship of the piston position, the intake stroke at the time of stop is performed. Since the compression stroke of the cylinder is relatively long, the effective compression ratio can be significantly increased. As a result, when fuel injection is performed at a predetermined fuel injection timing (for example, the same fuel injection timing as the first explosion), the compression ignition timing is advanced, and the pressure increase in the cylinder 11 due to the compression ignition combustion is steep. There is a case. Further, the earlier timing of compression ignition may cause an increase in Pmax and an increase in combustion temperature, resulting in a decrease in engine reliability and / or an increase in RawNOx.

  If it is determined in step S13 that dP / dθ does not exceed the limit value (that is, NO), the process proceeds to step S14, and if it exceeds the limit value (that is, YES), the process proceeds to step S15. Transition.

  In step S14, since the rate of increase in pressure in the cylinder 11 does not exceed the limit value, fuel injection is performed within the period from the end of the compression stroke to the initial stage of the expansion stroke so as to burn by compression ignition near the compression top dead center. Do. The fuel injection amount is set so that the excess air ratio λ is 1. As a result, even after the second bomb, a large torque is generated to enable quick restart. From the second explosion onward, the actual time with respect to the change in the crank angle is shortened as the rotational speed of the engine 10 gradually increases. Therefore, the time (ignition delay time) in which the fuel injected into the cylinder and air are mixed is shortened. This may cause wrinkles. Therefore, in step S14, it is preferable to inject the fuel at an appropriate timing that can ensure the ignition delay time.

  On the other hand, in step S15, since the pressure increase rate in the cylinder exceeds the limit range, the pre-stage injection and the main injection are performed so as to achieve the above-described retarded self-ignition combustion. Accordingly, the timing of fuel injection (that is, main injection) that contributes to the generation of torque is in the initial stage of the expansion stroke and is retarded with respect to the timing of fuel injection for the first explosion. By doing this, as described above, since compression ignition is performed after a predetermined crank angle with respect to the compression top dead center and combustion is performed, it is avoided that the pressure rise in the cylinder 11 becomes steep. It is possible to keep the rate of increase (dP / dθ) below the limit value. Further, an increase in Pmax and an increase in the combustion temperature are avoided, and it is possible to ensure engine reliability and suppress RawNOx. Further, since the main injection is performed in the expansion stroke period in which the pressure in the cylinder 11 gradually decreases, the engine speed increases after the second explosion and the real time for the change in the crank angle is shortened. Long ignition delay time can be secured. Thereby, generation | occurrence | production of soot is also suppressed. It should be noted that the fuel injection amount including the pre-stage injection and the main injection is set so that the excess air ratio λ is 1.

  In step S16 after steps S14 and S15, it is determined whether the engine speed NE has reached a predetermined value or less, that is, whether or not the complete explosion speed (for example, 500 rpm) has been reached. , Steps S13 to S15 are repeated. On the other hand, when the engine speed NE exceeds the predetermined value, the process proceeds to step S17, and the starter motor 91 is stopped assuming that the start of the engine 10 is completed. Since the engine 10 after the start is in the normal operation region A including the idle operation state (see FIG. 5), the excess air ratio λ is changed from λ = 1 while the engine 10 is restarted to λ ≧ Is changed to 2.

  FIG. 10 shows an example of fuel injection control when the engine 10 is restarted according to the flow of FIG. FIG. 10 shows the strokes of the first to fourth cylinders, and the crank angle advances from left to right. A square indicated by “F” in FIG. 10 indicates fuel injection, and a peak indicated by “H” indicates heat generation due to compression ignition combustion. Further, the vertical line at the left end of FIG. 10 corresponds to the piston position when the engine 10 is automatically stopped. In the example of FIG. 10, the third cylinder is the compression stroke cylinder at the stop, and the compression stroke cylinder at the stop. The first explosion combustion is possible (that is, the determination in step S4 is YES in the flow of FIG. 8).

  When the restart condition of the engine 10 is satisfied and cranking is started, a predetermined amount of fuel satisfying λ = 1 is injected into the third cylinder at a predetermined timing at the end of the compression stroke. Thereby, the third cylinder is ignited by compression near the compression top dead center. Since the effective compression ratio of the first-combustion combustion in the compression stroke cylinder when stopped is relatively low, the pressure increase rate (dP / dθ) in the cylinder 11 even if compression ignition is performed near the compression top dead center. Does not exceed the limit. On the other hand, by performing compression ignition near the compression top dead center and burning, the combustion center of gravity (the time when the combustion mass ratio becomes 50%) becomes near the compression top dead center, and the expansion energy due to compression ignition combustion is It is transmitted to the piston 16 efficiently, which is advantageous for quick start of the engine 10.

  Next, the intake stroke cylinder at the time when the piston 16 reaches the compression top dead center is the fourth cylinder. In the example of FIG. 10, the first pre-stage injection and the expansion stroke in the compression stroke are performed so that the retarded self-ignition combustion is performed. The initial main injection is performed. Thus, by controlling the fuel injection timing so that the compression ignition is delayed by a predetermined crank angle with respect to the compression top dead center, the pressure increase rate (dP / dθ) in the cylinder 11 is prevented from exceeding the limit value. To do. This delays the injection timing to the stop-time intake stroke cylinder to inject the fuel next to the fuel injection timing to the stop-time compression stroke cylinder to inject the fuel first. It is possible to prevent the pressure increase rate from becoming steep. The timing of the first pre-stage injection may be, for example, ATDC −90 ° to −30 ° CA, and the timing of the main injection may be, for example, ATDC 10 ° to 30 ° CA.

  The stop-time exhaust stroke cylinder that performs the third explosion combustion is the second cylinder. In the example of FIG. 10, the first pre-stage injection during the compression stroke and the main injection at the initial stage of the expansion stroke are performed for the second cylinder so that the retarded self-ignition combustion is performed. Here, since the number of leaks through the joint gap of the piston ring gradually decreases as the rotational speed of the engine 10 gradually increases from the start of the engine 10, it is 3 The effective compression ratio can be higher in the exhaust stroke cylinder at the time of stop that performs combustion of the explosion. Therefore, the injection timing of the main injection in the exhaust stroke cylinder at the time of the third explosion is such that the compression ignition combustion is slower in the exhaust stroke cylinder at the time of the third explosion stop than the intake stroke cylinder at the time of the second explosion stop. The injection timing of the main injection in the intake stroke cylinder at the time of the second explosion stop may be further retarded. By doing so, it is possible to further suppress an increase in combustion noise.

  The stop expansion stroke cylinder that performs the fourth explosion combustion is the first cylinder. As described above, in accordance with the further increase in the rotation speed of the engine 10 and the further increase in the effective compression ratio, the main injection is performed so that the compression ignition combustion is further delayed in the fourth expansion stop-time expansion stroke cylinder in the illustrated example. The injection timing is further retarded. Therefore, in the first cylinder that performs the fourth explosion combustion, the first front-stage injection and the second front-stage injection are performed. In this way, even if the injection timing of the main injection is further delayed, the compression ignition combustion can be stabilized. Further, the pressure increase rate (dP / dθ) of the cylinder 11 accompanying the compression ignition combustion is also suppressed from exceeding the limit value. Note that the timing of the second pre-stage injection may be, for example, ATDC 0 ° to 10 ° CA.

  Thus, in the example of FIG. 10, compression ignition combustion of the fourth explosion is performed in the first cylinder, and the restart of the engine 10 is completed. As is apparent from FIG. 10, the combustion center of gravity of the compression ignition combustion is set after the compression top dead center until the start is completed after the restart of the engine 10 is started.

  FIG. 10 shows an example of fuel injection control when the engine 10 is restarted. Each cylinder during the period from the start of restart to the completion of start according to the state in the cylinder 11 or the like. The fuel injection timing at 11 is changed as appropriate.

  Further, in the above example, the injection timing of the main injection is gradually delayed as the rotational speed of the engine 10 is increased through the restart of the engine 10, but the fuel injection timing after the second explosion (main injection timing) Timing) may be fixed at a timing delayed by a predetermined crank angle from the fuel injection timing of the first explosion, regardless of the increase in the rotational speed of the engine 10.

  In the flow of FIG. 8, ozone is generated in the cylinder 11 as necessary only during the combustion of the first explosion. However, in the combustion after the second explosion, ozone is generated in the cylinder 11 as necessary. May be generated.

(Intake control when engine restarts)
As described above, the effective compression ratio increases as the engine speed increases when the engine 10 is restarted. As a result, compression ignition combustion becomes steep, and the pressure increase rate (dP / dθ) in the cylinder 11 may exceed the limit value. In the engine system 1, when the engine 10 is restarted, the amount of intake air introduced into the cylinder 11 is temporarily reduced in addition to retarding the combustion period of compression ignition combustion by the fuel injection control described above. Thus, the effective compression ratio is prevented from increasing when the engine 10 is restarted. In the engine system 1, the intake air amount is reduced by so-called late intake closing, in which the intake valve 21 delays the closing timing of the intake valve 21 after the intake bottom dead center by the intake VVT 23. This is advantageous for improving fuel efficiency by reducing pumping loss. The intake air amount introduced into the cylinder 11 may be reduced by adjusting the opening of the throttle valve 31.

  FIG. 11 exemplifies a change in engine speed (lower diagram) and a change in valve closing timing of the intake valve 21 (upper diagram) when the engine 10 is restarted. The starter motor 91 is driven at time t1, and the restart of the engine 10 is started. When the restart of the engine 10 is started, the closing timing of the intake valve 21 is set to a predetermined timing relatively on the advance side. As a result, when the restart of the engine 10 is started, a large amount of intake air can be introduced into the cylinder 11, and a large torque is generated, which is advantageous in speeding up the restart of the engine 10.

  After the restart of the engine 10 is started, the closing timing of the intake valve 21 is changed to the retard side as the rotational speed of the engine 10 increases. In the example of FIG. 11, the valve closing timing is continuously changed in proportion to the increase in engine rotation after time t2 when the rotation speed of the engine 10 exceeds a predetermined rotation speed. Although not shown here, the closing timing of the intake valve 21 may be changed in stages in proportion to the increase in engine rotation. As the engine speed increases, the amount of gas leakage from the joint gap of the piston ring decreases, but the amount of intake air introduced into the cylinder 11 also decreases, so that an increase in the effective compression ratio is suppressed. The effective compression ratio is almost constant or increases gradually. Thereby, it becomes possible to control the timing of compression ignition, and it is suppressed that the timing of compression ignition becomes early in the period until the restart of the engine 10 is completed. As a result, it is avoided that the rate of pressure increase (dP / dθ) in the cylinder 11 due to compression ignition combustion is steep, and combustion noise is prevented from increasing when the engine 10 is restarted. On the other hand, the effective compression ratio can be maintained as high as possible by changing the valve closing timing in proportion to the increase in the engine speed. This is advantageous for quick start of the engine 10.

  Then, when the engine speed reaches the complete explosion speed at time t3 and the start of the engine 10 is completed, the closing timing of the intake valve 21 is advanced. Thereby, the intake air amount introduced into the cylinder 11 increases.

  The excess air ratio λ is set to 1 from the start of the engine 10 until the start is completed. As described above, this is advantageous in generating large torque, and realizes quick restart of the engine 10. On the other hand, when the restart of the engine 10 is completed and the operation state of the engine 10 shifts to the normal operation region A (including the idle operation state), the engine 10 sets the excess air ratio λ to λ> 1 (more precisely, As described above, a lean of λ ≧ 2) is set. Increasing the intake air amount introduced into the cylinder 11 by advancing the closing timing of the intake valve 21 after the start of the engine 10 is advantageous for leaning of the air-fuel mixture. The closing timing of the intake valve 21 after completion of the start is appropriately set according to the operating state of the engine 10.

  In this way, when restarting the engine 10 that has been automatically stopped, the combustion noise is suppressed from increasing while the restart is performed quickly. In particular, the restart (that is, automatic start) of the engine 10 is a start that does not depend on the start operation of the driver, and therefore, more severe suppression of combustion noise is required than during the forced start. Combining the delay of the injection timing with the reduction of the intake amount introduced into the cylinder 11 makes it possible to suppress combustion noise at a high level.

  Note that the technology disclosed herein can be applied not only when the engine 10 is restarted but also when the engine 10 is forcedly started due to the start operation of the driver. When the engine 10 is forcibly started, in order to wait for cylinder identification or a rise in fuel pressure, the starter motor 91 is driven to start cranking the engine 10 and then fuel is injected into the first compression cylinder. In this case, the fuel is first injected into the second or third compression cylinder. In that case, since the effective compression ratio of the cylinder that performs the first fuel injection becomes relatively high, the fuel injection timing may be delayed. The fuel injection timing may be delayed so that the compression ignition combustion is delayed by a predetermined period with respect to the compression top dead center. . In addition, for the cylinder that performs fuel injection next, the effective compression ratio increases as the engine speed increases, so the compression ignition combustion is performed with a delay of a predetermined period from the compression top dead center. What is necessary is just to delay injection timing rather than fuel injection timing.

  Further, the intake air amount reduction control shown in FIG. 11 can be omitted.

  In the above configuration, the present technology has been described by taking a naturally aspirated engine as an example, but the present technology can also be applied to an engine including a turbocharger.

  Accordingly, the compression ignition type engine starter (engine system 1) includes a multi-cylinder engine (engine 10) configured to have a plurality of cylinders 11 into which pistons 16 are respectively inserted, and gasoline in each cylinder 11. An injector 6 configured to inject the contained fuel; and the fuel is injected through the injector 6 at a predetermined timing, and an air-fuel mixture in the cylinder 11 formed thereby is combusted by compression ignition, whereby the engine And a control unit (ECM100) configured to operate the engine 10. When the engine 10 is started, the ECM100 sequentially supplies fuel to the plurality of cylinders 11 during a period from the end of the compression stroke to the beginning of the expansion stroke. In addition to performing injection, the air-fuel mixture in the cylinder 11 is combusted by compression ignition, and the ECM 100 At the time of starting the engine 10, the injection timing for the next fuel injection is delayed from the injection timing for the first fuel injection so that the compression ignition occurs with a delay of a predetermined crank angle with respect to the compression top dead center. Horn.

  The compression ignition engine starter (engine system 1) also includes a multi-cylinder engine (engine 10) configured to have a plurality of cylinders 11 into which pistons 16 are respectively inserted, and gasoline is contained in each cylinder 11. The engine 10 by injecting the fuel at a predetermined timing through the injector 6 and burning the air-fuel mixture in the cylinder 11 formed thereby by compression ignition. And a control unit (ECM100) configured to operate the engine 10. The ECM100 automatically stops the engine 10 when a predetermined automatic stop condition is satisfied, and when a predetermined restart condition is satisfied In addition, fuel is injected into the plurality of cylinders 11 sequentially from the end of the compression stroke to the initial stage of the expansion stroke, and the cylinder 1 The engine 10 is restarted by compressing and igniting the air-fuel mixture therein, and when the engine 10 is restarted, the ECM 100 is in response to the injection timing to the stop compression stroke cylinder that injects fuel first. Next, the injection timing to the stop-time intake stroke cylinder for injecting the fuel is retarded so that the compression ignition occurs with a delay of a predetermined crank angle with respect to the compression top dead center.

  Further, when the engine 10 is started, the ECM 100 is such that the A / F or G / F of the air-fuel mixture is higher than the A / F or G / F of the air-fuel mixture in the low-load steady operation state after the start of the engine 10 is completed. The fuel injection amount is adjusted so that the engine becomes rich.

  In particular, the ECM 100 sets the excess air ratio λ of the air-fuel mixture to 1 when the engine 10 is started.

  The ECM 100 performs the pre-stage injection with a smaller injection amount than the main injection before the main injection performed in the period from the end of the compression stroke to the initial stage of the expansion stroke for the cylinder 11 to be injected next.

  When the engine 10 is started, the ECM 100 sets the injection timing such that the combustion center of gravity of compression ignition combustion is after the compression top dead center.

  The ECM 100 does not perform the first fuel injection to the compression stroke cylinder at the stop when the piston position of the compression stroke cylinder at the stop is on the top dead center side with respect to a predetermined crank angle when the engine 10 is restarted. The first fuel injection is performed on the intake stroke cylinder at the time of stop, and the injection timing is set so that the compression ignition is delayed by a predetermined period with respect to the compression top dead center.

  According to this engine system 1, it is possible to prevent combustion noise from increasing while realizing quick start of the engine 10.

1 Engine system (starting device)
10 engine (multi-cylinder engine)
11 cylinder 16 piston 100 ECM (control part)
6 Injector

Claims (11)

A multi-cylinder engine configured to have a plurality of cylinders each having a piston inserted therein;
An injector configured to inject fuel containing gasoline into each cylinder;
A control unit configured to operate the multi-cylinder engine by injecting the fuel through the injector at a predetermined timing, and combusting an air-fuel mixture formed in the cylinder by compression ignition, and
When the multi-cylinder engine is forcibly started by a driver's starting operation , the controller sequentially injects fuel into the plurality of cylinders during a period from the end of the compression stroke to the initial stage of the expansion stroke, Burned by compression ignition,
When the multi-cylinder engine is forcibly started, the control unit sets the injection timing to the cylinder that injects fuel first and the injection timing to the cylinder that injects fuel next to the compression top dead center. A starter of a compression ignition type engine that retards the ignition so that the ignition is delayed by a predetermined crank angle. The starting device for a compression ignition engine according to claim 1 ,
The control unit, wherein the forcible starting of the multi-cylinder engine, the air-fuel ratio A / F of the mixture, or, the weight ratio between the gas and the fuel in the cylinder G / F is forced start completion of the multi-cylinder engine A starter for a compression ignition engine that adjusts the fuel injection amount so as to be richer than the A / F or G / F of the air-fuel mixture in the subsequent low-load steady operation state. The starting device for a compression ignition engine according to claim 2 ,
The control unit is a compression ignition type engine starter that sets the excess air ratio λ of the air-fuel mixture to 1 when the multi-cylinder engine is forcibly started. The starter for a compression ignition engine according to any one of claims 1 to 3 ,
For the cylinder that injects fuel next, the control unit performs a first stage injection with a smaller injection amount than the main injection before the main injection performed in the period from the end of the compression stroke to the beginning of the expansion stroke. Starter. The starting device for a compression ignition engine according to any one of claims 1 to 4 ,
The control unit is a starter for a compression ignition engine that sets an injection timing so that a combustion center of gravity of compression ignition combustion is after compression top dead center when the multi-cylinder engine is forcibly started. A multi-cylinder engine configured to have a plurality of cylinders each having a piston inserted therein;
An injector configured to inject fuel containing gasoline into each cylinder;
A control unit configured to operate the multi-cylinder engine by injecting the fuel through the injector at a predetermined timing, and combusting an air-fuel mixture formed in the cylinder by compression ignition, and
The control unit automatically stops the multi-cylinder engine when a predetermined automatic stop condition is satisfied, and sequentially starts the expansion stroke from the end of the compression stroke to the initial stage of the expansion stroke when the predetermined restart condition is satisfied. And restarting the multi-cylinder engine by subjecting the air-fuel mixture in the cylinder to compression ignition combustion.
When the multi-cylinder engine is restarted, the control unit performs the first fuel injection to the compression stroke cylinder at the time of stop, and then the fuel is injected to the injection timing at which the fuel is first injected into the compression stroke cylinder at the time of stop. A starter for a compression ignition engine that retards the injection timing to the intake stroke cylinder at the time of stopping the injection so that the compression ignition is delayed by a predetermined crank angle with respect to the compression top dead center. The starting device for a compression ignition engine according to claim 6 ,
The control unit, wherein the time of re-starting of the multi-cylinder engine, the air-fuel ratio A / F of the mixture, or, the weight ratio between the gas and the fuel in the cylinder G / F is re-start completion of the multi-cylinder engine A starter for a compression ignition engine that adjusts the fuel injection amount so as to be richer than the A / F or G / F of the air-fuel mixture in the subsequent low-load steady-state operation state. The starter for a compression ignition engine according to claim 7 ,
The control unit, wherein the time of re-starting of the multi-cylinder engine, the starting device of a compression ignition type engine that the air excess ratio of the mixture gas λ 1. The start device for a compression ignition engine according to any one of claims 6 to 8 ,
For the cylinder that injects fuel next, the control unit performs a first stage injection with a smaller injection amount than the main injection before the main injection performed in the period from the end of the compression stroke to the beginning of the expansion stroke. Starter. The start device for a compression ignition engine according to any one of claims 6 to 9 ,
The control unit, wherein the time of re-starting of the multi-cylinder engine, as the centroid of combustion compression ignition combustion is compression top dead center or later, the starting device of a compression ignition type engine for setting the injection timing. The starter for a compression ignition engine according to any one of claims 6 to 10 ,
When the multi-cylinder engine is restarted, the control unit performs initial fuel injection to the stop-time compression stroke cylinder when the piston position of the stop-time compression stroke cylinder is on the top dead center side with respect to a predetermined crank angle. Without starting, the first fuel injection is performed to the stop-time intake stroke cylinder, and the injection timing is set so that the compression timing is delayed by a predetermined period with respect to the compression top dead center. .

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