JP6156226B2 - Control device for compression ignition engine - Google Patents

Description

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

  A compression ignition engine is an engine that uses a combustion system (compression ignition combustion) that self-ignites an air-fuel mixture in a cylinder. In this case, unlike the system in which the air-fuel mixture is combusted by the flame ignited by the spark plug spreading and spreading, the air-fuel mixture is ignited simultaneously and frequently at various locations in the cylinder. Therefore, since the combustion period is shortened, fuel efficiency is expected to be improved by improving thermal efficiency.

  Patent Document 1 describes that in a control device for a compression ignition engine, fuel efficiency is improved by executing control (so-called fuel cut control) that interrupts fuel injection at the time of deceleration or the like. Yes.

Japanese Patent No. 4159918

  By the way, in the control device capable of executing the fuel cut control as described above, when the engine speed decreases to a predetermined value while the fuel cut control is being performed, there is no inconvenience such as engine stall. The fuel injection is restarted (returns naturally).

  However, when returning from the fuel cut control, the in-cylinder temperature is reduced during the fuel cut control and stable compression ignition combustion cannot be performed. Therefore, the control device described in Patent Document 1 uses the fuel cut control. Immediately after returning from the ignition, spark ignition combustion is performed, and after the in-cylinder temperature is increased, the combustion is switched to compression ignition combustion.

  However, performing spark ignition combustion at the time of return from the fuel cut control causes a reduction in exhaust emission performance, a deterioration in fuel consumption, and the like.

  The technology disclosed herein has been made in view of such a point, and the object thereof is to perform spark ignition combustion at the time of natural return from fuel cut control in a control device for a compression ignition engine. It is to stabilize the return due to compression ignition combustion.

The technology disclosed herein relates to a control device for a compression ignition engine. The control device includes an engine main body having a cylinder, fuel injection means for injecting an amount of fuel corresponding to the operating state of the engine main body into the cylinder at an injection timing corresponding to the operating state, and into the cylinder. A throttle valve for adjusting the amount of intake air of the engine, a control means for driving the engine main body by compressing and igniting the air-fuel mixture in the cylinder, and an ozone generating means for generating ozone in the cylinder. The fuel injection means has an injector for injecting fuel containing at least gasoline into the cylinder through an injection port at the tip thereof, and a fuel supply system for controlling an injection mode of the injector, and the injector Is configured to be able to change the opening of the injection port.

The control means performs fuel cut control for forcibly interrupting the operation of the fuel injection means when a predetermined condition is satisfied when the engine body is decelerated, and during the fuel cut control . Decreases the amount of intake air through the throttle valve, thereby setting the amount of intake air to a minimum amount corresponding to the inertial operation of the engine body.

The control means further restarts fuel injection by the fuel injection means when detecting that the engine speed has decreased to a predetermined value during execution of the fuel cut control. By controlling the fuel injection means and the ozone generation means, the main injection in which the opening of the injection port is changed so that the air-fuel mixture is unevenly distributed near the center of the combustion chamber in the cylinder is compressed. run since late vital, prior to the main injection, and executes a pre-stage injection for injecting a small amount of fuel than the main injection, in synchronization with the front stage injection produces ozone within the cylinder.

  According to this configuration, when the engine body is in steady operation, the control means executes main injection that injects an amount of fuel corresponding to the operating state of the engine body into the cylinder at a predetermined injection timing, Burn by compression ignition.

  The control means also executes fuel cut control when it is determined that a predetermined condition is satisfied during deceleration of the engine body. During the fuel cut control, combustion is not performed in the cylinder, so the engine body operates by inertia and the engine speed decreases monotonously. Thus, when the engine speed decreases to a predetermined value, the fuel injection is restarted (returns naturally) to prevent inconvenience such as engine stall. That is, an amount of fuel that can at least maintain the engine speed is injected.

  However, since the inside of the cylinder is cooled while the fuel cut control is being performed, the compression ignition combustion in the cylinder is not stable immediately after the restart of fuel injection. Therefore, when the control means naturally returns from the fuel cut control, prior to the main injection, the control means performs a front injection that injects a smaller amount of fuel than the main injection, and generates ozone in the cylinder in synchronization with the front injection. . Here, to synchronize the front-stage injection and the generation of ozone means to generate ozone in accordance with the timing at which the front-stage injection is executed, and the generation time of the ozone is higher than that of the main injection. Means close to the time. For example, at least a part of the period for performing the pre-injection and the period for generating ozone may overlap.

  By generating ozone in synchronization with the pre-injection, the ozone acts on the fuel injected by the pre-injection to activate the fuel. Further, a low temperature oxidation reaction of the fuel is induced, and the environment in the cylinder is changed to an environment in which the ignitability of the fuel is improved. Here, it is preferable that the injection amount of the pre-stage injection is set to a small amount such that the injected fuel does not ignite early.

  Due to the fuel activated in the cylinder and the in-cylinder environment with improved ignitability, the fuel injected into the cylinder is stably ignited and combusted by the main injection. In this way, compression ignition combustion is stabilized at the time of natural recovery from the fuel cut control in which the in-cylinder temperature decreases.

  The control means may execute the pre-injection during the intake stroke and execute the main injection after the latter half of the compression stroke.

  Here, the front injection may be performed in the first half of the intake stroke. The “first half of the intake stroke” means the first half when the intake stroke is divided into the first half and the second half.

  Further, “after the second half of the compression stroke” includes the second half when the compression stroke is divided into the first half and the second half, and the expansion stroke.

  According to this configuration, by executing the pre-stage injection during the intake stroke, it becomes possible to lengthen the time that the fuel injected by the pre-stage injection is activated by ozone, and to sufficiently oxidize at a low temperature. Therefore, it is advantageous in stabilizing the compression ignition of the fuel injected by the main injection executed after the latter half of the compression stroke.

The engine main body has a plurality of cylinders, and the control unit controls the fuel injection unit and the ozone generation unit to restart the fuel injection, and then each of the plurality of cylinders. It is good also as stopping the said front | former injection and the production | generation of the ozone after performing combustion once each .

  According to this configuration, if the fuel injection is resumed and combustion is performed, the temperature in the cylinder rises. As a result, ignitability can be ensured without performing front-stage injection and ozone generation. For example, after a predetermined number of cycles has elapsed after restarting fuel injection, or based on estimation of the temperature state in the cylinder, input from a temperature sensor provided in the cylinder, or the like, the temperature in the cylinder When it is determined that the fuel consumption has been sufficiently increased, by stopping the pre-injection and the generation of ozone, consumption of energy necessary for the generation of ozone is suppressed, which is advantageous in improving the fuel consumption.

  As described above, the control device for the compression ignition engine responds to the fact that the in-cylinder temperature decreases at the time of natural recovery from the fuel cut control. Since the generation of ozone is executed in synchronization with the injection, the compression ignition combustion can be stabilized.

It is the schematic which shows the structure of a compression ignition type engine. It is a block diagram concerning control of a compression ignition type engine. It is explanatory drawing which shows the production | generation of the ozone synchronized with the front | former stage injection in an intake stroke, and this front | former stage injection. It is explanatory drawing which shows the state which the fuel injected in the compression top dead center vicinity starts compression ignition. It is explanatory drawing explaining the driving | operation area | region of an engine. It is an example of the timing which performs fuel injection and ozone generation at the time of the natural return from fuel cut control, and the heat release rate accompanying combustion of the injected fuel.

Hereinafter, an embodiment of a control device for a compression ignition engine will be described with reference to the drawings. The description of the following embodiment is an example.
(Overall configuration of engine system)
FIGS. 1-2 has shown the structure of the engine system 1 which concerns on embodiment. The engine system 1 is a system mounted on a vehicle, and is based on an engine body (hereinafter simply referred to as an engine) 10, various actuators associated with the engine 10, various sensors, and signals from the sensors. A PCM (Powertrain Control Module) 100 as a control means for controlling the actuator is included.

  In the following, the main parts of the respective configurations of the engine 10 and various actuators and sensors associated with the engine 10 will be described. However, parts that employ well-known ones are not shown or described except for some parts. And

  The engine 10 is configured to be mounted on a vehicle such as an automobile, and is a compression ignition engine to which fuel including at least gasoline is supplied.

  As shown in FIG. 1, the engine 10 includes a cylinder block 11 and a cylinder head 12 mounted and fixed thereon. A plurality of cylinders (only one is shown in FIG. 1, but actually a plurality of cylinders are arranged in series) 13 are formed inside the cylinder block 11 and extend along the cylinder 13. Thus, the crankshaft 14 is rotatably supported. The crankshaft 14 is connected to the piston 16 via a connecting rod 15.

  The piston 16 is slidably fitted in each cylinder 13, and the combustion chamber 17 is defined by the top surface 16 a of the piston 16, the wall surface 13 a of the cylinder 13, and the lower surface 12 a of the cylinder head 12. It is partitioned. In this embodiment, the piston 16 has a top dead center where the top surface 16a of the piston 16 is closest to the lower surface 12a of the cylinder head 12 in the course of a series of cycles including an intake stroke, a compression stroke, an expansion stroke, and an exhaust stroke. TDC) and the top surface 16a of the piston 16 reciprocate between the bottom dead center (BDC) farthest from the lower surface 12a of the cylinder head 12. FIG. 1 schematically shows a state where the piston 16 is moving from the top dead center to the bottom dead center.

  The lower surface 12a of the cylinder head as the upper inner surface (upper surface) of the combustion chamber 17 is formed in a dome shape that bulges upward on the paper surface of FIG. 2, for example, as shown in FIG. Corresponding to this shape, the top surface 16a of the piston 16 is also formed in a dome shape. A disc-shaped recess is formed at the center of the top surface 16 a of the piston 16.

  The engine 10 includes a fuel supply device 20 as fuel supply means. The fuel supply device 20 includes an injector 21 and a fuel supply system 22. The injector 21 is attached to each combustion chamber 17 of the cylinder head 12 and directly injects fuel into each combustion chamber 17 (direct injection). The injector 21 is disposed such that the injection port at the tip thereof faces the inside of the combustion chamber 17 from the center portion of the lower surface 12 a of the cylinder head 12, and from the center portion to the inside of the combustion chamber 17. Gasoline is injected so that it spreads radially. As the injector 21, it is possible to employ an outer valve-opening type injector or a multi-hole type injector.

  In this embodiment, a piezo injector 21 that is configured using a piazo element and capable of advanced opening degree control of the injection port is used as the injector 21. Therefore, according to this configuration, even when the rotational speed of the engine 10 is very large, the injection amount per unit time, the injection timing, and the like can be controlled with high accuracy.

  The fuel supply system 22 for operating the injector 21 includes, for example, an electric circuit for changing the opening degree of the injector 21 and a fuel supply system for supplying fuel to the injector 21, and according to a control signal from the PCM 100. The operation of the fuel supply device 20 is controlled so that a predetermined amount of fuel is injected into the combustion chamber 17 at a predetermined timing.

  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.

  Here, an ozone generator 30 as ozone generating means is further provided on the lower surface 12a side of the cylinder head 12 (upper surface side of the combustion chamber 17). The ozone generator 30 is attached to the cylinder head 12 by a known structure such as screwing, and includes a discharge plug 31 and an ozone generation system 32.

  The distal end portion of the discharge plug 31 protrudes from the vicinity of the injection port of the injector 21 into the combustion chamber 17 and is provided with a rod-like electrode 31b whose periphery is electrically insulated by an insulator 31a. With this configuration, the electrode 31b protrudes into the combustion chamber 17 while being electrically insulated from the cylinder head 12, the cylinder block 11, and the like. The cylinder block 11, the cylinder head 12, the piston 16, and the like are grounded.

  The ozone generation system 32 has an electrical circuit corresponding to a high voltage, and generates ozone by applying a pulsed high voltage to the electrode 31b in accordance with a control signal from the PCM 100. The concentration of ozone generated in the combustion chamber 17 can be adjusted by appropriately changing the magnitude of the voltage, the application period, the pulse width, and the like.

  The cylinder head 12 also has an intake port 18 and an exhaust port 19 that are adjacent to the injector 21 for each cylinder 13, and each communicates with the combustion chamber 17. An intake valve 41 and an exhaust valve 42 are respectively disposed in the intake port 18 and the exhaust port 19 so that the opening can be closed from the combustion chamber 17 side. The intake valve 41 is driven by the intake valve drive mechanism, and the exhaust valve 42 is driven by the exhaust valve drive mechanism, thereby reciprocating at a predetermined timing to open and close the ports 18 and 19, and the gas in the combustion chamber 17. Exchange.

  The intake valve drive mechanism and the exhaust valve drive mechanism each have an intake camshaft and an exhaust camshaft. These camshafts are drivingly connected to the crankshaft 14 via a known power transmission mechanism, and rotate in conjunction with the rotation of the crankshaft 14. The intake valve driving mechanism and the exhaust valve driving mechanism are configured in a rocker arm type having a swing arm, for example.

  In this embodiment, at least the intake valve drive mechanism includes, for example, an electric valve phase variable mechanism (VVT) 43 that can change the phase of the intake camshaft and thus the opening / closing timing of the intake valve 41. Has been. In addition to the VVT 43, the intake valve drive mechanism further includes a continuously variable valve lift mechanism (Continuous Variable Valve Lift: CVVL) 44 that can continuously change the movement amount (valve lift amount) of the intake valve 41. ing. The VVT 43 and CVVL 44 adjust the opening / closing amount and opening / closing timing of the intake valve 41 so as to introduce a predetermined amount of gas into the combustion chamber 17 at a predetermined timing according to a control signal from the PCM 100.

  The intake port 18 of each combustion chamber 17 communicates with the intake passage 50 as shown in FIG. On the other hand, the exhaust port 19 of each combustion chamber 17 communicates with the exhaust passage 60.

  An air cleaner that filters air sucked from outside is disposed at the upstream end of the intake passage 50, while a surge tank 51 is disposed near the downstream end of the intake passage 50. The intake passage 50 further downstream than the surge tank 51 is an independent passage branched for each combustion chamber 17, and the downstream end of each independent passage is connected to the intake port 18 of each combustion chamber 17.

  Between the air cleaner and the surge tank 51 in the intake passage 50, a throttle valve 52 for adjusting the amount of intake air to each combustion chamber 17 is disposed, and a predetermined amount of fresh air is generated according to a control signal from the PCM 100. The opening / closing amount of the throttle valve 52 is adjusted so as to be introduced.

  The upstream portion of the exhaust passage 60 is configured to have an independent passage branched for each combustion chamber 17 and connected to the outer end of the exhaust port 19 and a collecting portion where the independent passages gather. An exhaust purification device that purifies harmful components in the exhaust gas is connected to the downstream side of the collecting portion in the exhaust passage 60. As the exhaust purification device, for example, a cylindrical case, For example, a three-way catalyst is provided in the flow path. For example, a muffler is connected to the further downstream side of the exhaust purification device, and the purified exhaust gas is discharged to the outside.

  A portion of the intake passage 50 between the surge tank 51 and the throttle valve 52 and a portion of the exhaust passage 60 on the upstream side of the exhaust purification device are used for returning a part of the exhaust gas to the intake passage 50. It is connected via a cooled EGR 70 as means. The cooled EGR 70 is configured to include an EGR passage 71 in which an EGR cooler 72 for cooling the exhaust gas with the engine coolant is disposed. The EGR passage 71 includes an exhaust gas to the intake passage 50 for the exhaust gas. An EGR valve 73 for adjusting the amount of reflux is provided. By adjusting the opening / closing amount of the EGR valve 73 in accordance with a control signal from the PCM 100, a predetermined EGR rate (a mass ratio of exhaust gas to all gases sucked into the cylinder 13) is realized in cooperation with the throttle valve 52. Is configured to do.

  The engine 10 has a high geometric compression ratio. The geometric compression ratio ε is, for example, 20 ≦ ε ≦ 40, preferably 25 ≦ ε ≦ 35. The engine 10 burns the fuel injected from the injector 21 into the combustion chamber 17 by compression ignition without ignition by the spark plug.

  Specifically, in this embodiment, the intake valve 41 closes the intake port 18 from 40 degrees before compression top dead center to about 180 degrees (BTDC 40 to 180 degrees).

  Then, in the compression stroke, the piston 16 moves upward in the drawing of FIG. 1 to compress the taken-in gas adiabatically. During the period from the intake stroke to the compression stroke, the injector 21 operates to inject fuel from the tip of the injector 21 so as to spread radially downward from the paper surface, for example, as shown in FIG. Thus, an air-fuel mixture in which gas and fuel are mixed is generated in the combustion chamber 17.

  Specifically, in the engine 10, when the fuel injection amount is relatively small, for example, when the engine load is relatively low, the air-fuel mixture is unevenly distributed near the central portion inside the combustion chamber 17 when the fuel is injected. The opening degree of the injector 21 is controlled. As an example, as shown in FIG. 4, when the piston 16 is located near the top dead center, the fuel injected from the injector 21 fits in a space defined by the recess of the piston 16 and the lower surface 12 a of the cylinder head. Is injected into.

  By being unevenly distributed in this way, a heat insulation layer (air heat insulation layer) consisting essentially of air can be interposed between the air-fuel mixture layer and the inner surfaces 11a, 12a, 16a that define the combustion chamber 17. Since the flame when the air-fuel mixture burns can be prevented from contacting the inner surfaces 11a, 12a, 16a of the combustion chamber 17, heat can be prevented from escaping to the outside through the inner surfaces 11a, 12a, 16a. This is advantageous in reducing the cooling loss and improving fuel consumption.

  The generated air-fuel mixture is self-ignited (compression ignition) as soon as it reaches the ignition point determined by the pressure of the gas, and burns. Specifically, as shown in FIG. 4, the ignition point is reached in the vicinity of the compression top dead center, and self-ignition occurs simultaneously and frequently at various locations in the combustion chamber 17. The ignited air-fuel mixture generates a quantity of heat having a predetermined height and width as the combustion progresses. In this embodiment, the combustion center of gravity at this time is set to be approximately 5 degrees (approximately 5 degrees ATDC) after passing through the compression top dead center in the first stage of the expansion stroke. Then, the gas rapidly expanded by the amount of heat pushes the piston 16 downward in FIG. 4 to rotate the crankshaft 14, and the torque generated by the rotation is output from the engine 10 as a driving force. The vehicle is propelled by transmitting the output from the engine 10 to driving wheels connected via a transmission.

  Thereafter, the exhaust valve 42 is operated to open the exhaust port 19, and the gas in the cylinder 13 is discharged from the port 19 as exhaust gas.

  A part of the gas discharged at this time flows into the surge tank 51 after being cooled via the EGR passage 71 according to the opening degree of the EGR valve 73. And it mixes with the fresh air newly introduced from the outside, is again introduced into the combustion chamber 17 from the intake port 18, and is reused as an air-fuel mixture. On the other hand, other discharged gas passes through the exhaust purification device and is exhausted to the outside.

  In the following, the main part of the configuration of the PCM 100 that controls the operation of the engine 10 configured to be driven in this way will be described, but the parts adopting well-known ones are not shown except for a part. To do.

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

  As shown in FIG. 2, the PCM 100 includes at least a vehicle speed sensor SW1 that detects a propulsion speed (vehicle speed) of the vehicle, an accelerator opening sensor SW2 that detects a depression amount (accelerator opening) of the accelerator pedal P, and an engine 10. An engine speed sensor SW3 for detecting the output speed (engine speed) is connected, and the detection value of each sensor is input to the PCM 100.

  The PCM 100 is also connected to an air flow sensor SW4 that is provided upstream of the intake passage 50 and detects the flow rate of fresh air flowing through the intake passage 50.

  The PCM 100 determines the state of the engine 10 and the vehicle based on the input from each sensor described above, and sets the control parameters of the engine 10 so that the corresponding fuel injection, intake, discharge, etc. are performed. Then, the PCM 100 outputs a control signal based on each set control parameter to the fuel supply system 22, the ozone generation system 32, the VVT 43, the CVVL 44, the throttle valve 52, the EGR valve 73, and the like to operate the engine 10.

  When the engine 10 is operated, the PCM 100 determines the air-fuel ratio (A / F), the intake air according to the engine load determined according to the depression amount (accelerator opening) of the accelerator pedal P and the engine speed of the engine 10. The amount, fuel injection amount, EGR rate, injection timing (timing for starting main injection from the injector 21), opening / closing timing of the intake valve 41, timing for starting application to the electrode 21b, etc. are set, and the set values are set. Actuate various actuators.

  As shown in FIG. 5, the engine load is divided into an operation region R1 higher than a predetermined load indicated by a solid line in the drawing and an operation region R2 on the lower load side.

  In this embodiment, the excess air ratio λ is set to 1 (that is, A / F is set to about 14.7) in the operation region R1 on the high load side. This operation region R1 is a region where a relatively large amount of fuel is combusted, and is hereinafter also referred to as a λ1 region. In the λ1 region, the injection start timing at which the injector 6 starts fuel injection (hereinafter, this injection start timing is also referred to as injection timing) is set from the end of the compression stroke to the beginning of the expansion stroke. Here, the end of the compression stroke corresponds to the initial stage when the compression stroke is divided into three equal parts of the initial stage, the middle stage, and the final stage. In the λ1 region, the fuel injection amount is relatively large and the air-fuel ratio of the air-fuel mixture is set to the stoichiometric air-fuel ratio, so that the pressure rise in the cylinder 13 due to compression ignition combustion becomes steep, and combustion noise is increased. There is a possibility of increasing. Therefore, in the λ1 region, by setting the fuel injection timing relatively late, the compression ignition timing is set within the expansion stroke away from the compression top dead center, thereby causing the compression ignition combustion within the cylinder 13. Set during the expansion stroke when the pressure drops. The fuel injection in the λ1 region may be performed all at once, or the main injection for generating main combustion (combustion that generates the largest amount of heat in one cycle) for generating engine torque, and before the main injection. It is also possible to divide into the pre-injection to be performed. In the λ1 region, the combustion injection start timing (this injection start timing corresponds to the injection start timing of the main injection) is set according to the operating state of the engine 10.

  On the other hand, in the operation region R2 on the low to medium load side, the excess air ratio λ in the combustion chamber 17 is set to, for example, 2.0 or more (that is, A / F is 30 or more). Hereinafter, the operation region R2 is also referred to as a lean region. The formation of the air heat insulating layer described above is mainly performed in this lean region. In the lean region, the start timing of the combustion injection by the injector 6 is set at the end of the compression stroke, for example. Thereby, the air-fuel mixture can be unevenly distributed in the vicinity of the central portion inside the combustion chamber 17. In the lean region, the fuel injection amount is relatively small and the air-fuel ratio of the air-fuel mixture is set to be leaner than the stoichiometric air-fuel ratio, so that an increase in pressure in the cylinder 13 due to compression ignition combustion is suppressed. Therefore, the fuel injection start timing is set relatively early in the lean region. The fuel injection in the lean region may be performed in a lump or in a divided manner. Even in the lean region, the fuel injection start timing is set according to the operating state of the engine 10.

  When a predetermined condition (fuel cut condition) is satisfied while the vehicle is decelerating, for example, the accelerator pedal P is not depressed (the accelerator opening is zero), and the PCM 100 has a predetermined engine speed. When it is determined that the engine speed is equal to or higher than the number of revolutions, fuel cut control for interrupting fuel injection into the combustion chamber 17 by the injector 21 is executed.

  While the fuel cut control is being executed, the engine 10 continues to operate due to inertia. At this time, since combustion does not occur in the combustion chamber 17, the temperature in the cylinder 13 gradually decreases. When the control is executed, the EGR rate decreases toward zero. However, the actual EGR rate is slightly after the fuel cut control is executed due to the exhaust gas remaining in the intake passage 50 and the EGR passage 71. It reaches zero with a delay.

  Then, when the fuel cut control is being executed, if the accelerator pedal P is depressed to re-accelerate or the engine speed falls below a predetermined speed, the PCM 100 ends the fuel cut control. Then restart the fuel injection.

  In particular, in the case of the natural return such as the latter, the A / F, the intake air amount, the fuel injection amount, the injection timing (also described as the injection timing or the injection start timing) so as to realize a predetermined operating state of the engine 10. The EGR rate and the like are set, and the engine 10 is operated based on the setting.

However, for several cycles immediately after resuming fuel injection, combustion has not been performed so far and exhaust gas does not exist. Therefore, as described later, the actual EGR rate is A certain delay is reached after a certain delay.
(Engine fuel injection control for natural recovery from fuel cut control)
The PCM 100 executes the pre-stage injection prior to the main injection in order to improve the ignitability of the air-fuel mixture in the combustion chamber 17 at the time of natural recovery from the fuel cut control, and synchronizes with the pre-stage injection. To generate ozone.

  Hereinafter, such control will be described in detail. In the example described here, as indicated by arrows A1 and A2 in FIG. 5, the fuel is being released while the accelerator pedal P is released and the vehicle is decelerating from the state of steady operation in the λ1 region. This is the behavior of the engine 10 until the fuel injection is resumed when the cut control is executed and then the engine speed falls below a predetermined speed.

  First, it is assumed that the engine 10 is in steady operation. That is, in this state, the accelerator opening is kept constant, and the operation region R1 (λ1 region) is selected based on the engine load set according to the accelerator opening. As described above, the EGR rate, the intake air amount, the fuel injection amount, and the injection timing are set by the PCM 100 so as to correspond to the operation region R1 according to the engine load and the engine speed. . For example, the injection timing is selected to be 5 degrees before compression top dead center.

  Next, it is assumed that in order to decelerate the vehicle, the depression of the accelerator pedal P is released, and the accelerator opening decreases monotonously. In this state, the fuel injection amount decreases as the accelerator opening decreases, and the intake air amount also decreases to keep the excess air ratio λ constant.

  When the PCM 100 determines that the engine speed is greater than or equal to a predetermined value when the accelerator opening decreases and reaches zero based on inputs from the rotation speed sensor SW2 and the accelerator opening sensor SW3, the fuel cut condition As a result, the fuel cut control is executed. The PCM 100 outputs a control signal so as to interrupt the combustion injection from the injector 21 into the combustion chamber 17.

  Further, as the vehicle decelerates, the operation region of the engine 10 shifts from the operation region R1 to the operation region R2 (lean region) as indicated by an arrow A1 in FIG. The engine load and engine speed of the engine 1 monotonously decrease along the arrow A1.

  While the fuel cut control is being performed, the engine 10 operates with inertia under a minimum intake air amount without combustion of fuel. During this period, the engine speed decreases monotonously along the arrow A2 in FIG.

  When it is determined that the engine speed has decreased to a predetermined value based on the input from the rotational speed sensor SW2, the PCM 100 determines that the natural recovery condition is satisfied, and performs fuel injection so as to maintain the engine speed at or above the predetermined value. Resume (perform natural recovery).

  The PCM 100 sets the A / F, the EGR rate, the intake air amount, the fuel injection amount, and the injection timing so that the fuel injection is resumed and the predetermined operation state of the engine 10 is obtained, and the setting is realized. The control signal is output to the EGR valve 73, the throttle valve 52, the fuel supply system 22, and the like. By this control signal, the intake air amount and the fuel injection amount start to increase, and the combustion of fuel resumes.

  When performing such a natural return, the PCM 100 executes the front stage injection in addition to the main injection that injects the fuel after the latter half of the compression stroke, for example, in the vicinity of the compression top dead center. The pre-stage injection is, for example, a quantity that is smaller than the main injection and does not ignite early in the period from the initial stage to the middle stage of the intake stroke when the intake stroke is divided into three parts of the initial stage, the middle stage, and the final stage. Inject fuel. Further, as shown in FIGS. 3 and 6, a control signal is output to the ozone generation system 32 so as to generate ozone in the combustion chamber 17 in synchronization with the pre-stage injection.

  By generating ozone in the cylinder 13 in synchronization with the front injection during the intake stroke, the ozone acts on the fuel injected by the front injection and activates the fuel. A low temperature oxidation reaction of the fuel is induced during the compression stroke, and the environment in the cylinder 13 becomes an environment in which the ignitability of the fuel is improved near the compression top dead center. In order to ensure a long time for the fuel by the front injection to be activated by ozone, the front injection is preferably performed in the first half of the intake stroke.

  Thus, compression ignition of the fuel supplied by the main injection performed near the compression top dead center is promoted. That is, compression ignition combustion is stabilized even immediately after the natural return and even when the temperature in the cylinder 13 is low.

  Further, the fuel supplied in the main injection forms an air-fuel mixture that is unevenly distributed near the center of the combustion chamber 17, and a gas layer containing the fuel supplied by the pre-stage injection is formed around it. This gas layer is lean because the pre-stage injection is small, and contributes to the reduction of the cooling loss as in the air heat insulation layer described above. Immediately after executing the natural recovery, the wall surface temperature in the cylinder 13 is low, so that the effect of reducing the cooling loss is also increased.

  While the natural return is being executed, the operating state of the engine 10 moves within the operating region R2 along the arrow A2 in FIG.

  When the PCM 100 performs the natural recovery, if the number of cycles determined according to the configuration of the engine 10 is executed, for example, once for each cylinder 13, the inside of each cylinder 13 is sufficiently warmed, and the pre-stage injection is performed. And even if it does not supply ozone, it determines with the stability of compression ignition combustion being securable, and complete | finishes the front | former injection accompanying the production | generation of ozone.

  As described above, when the PCM 100 spontaneously recovers from the fuel cut control, the fuel supply device 20 and the ozone generator 30 are operated prior to the main fuel injection in order to cope with a decrease in the temperature in the cylinder 13, and the upstream injection is performed. And generation of ozone in synchronization with the preceding injection. By generating ozone in accordance with the timing of executing the pre-injection, a low temperature oxidation reaction of the fuel injected by the pre-injection is induced, and the ignitability of the fuel is improved. If main injection is executed in such a situation, even if the inside of the cylinder 13 is at a low temperature, the fuel is stably compressed and ignited. In this way, the compression ignition combustion is stabilized even during the natural recovery from the fuel cut control in which the in-cylinder temperature decreases.

  The PCM 100 also performs pre-injection and generation of ozone synchronized with the pre-injection during a period from the initial stage of the intake stroke to the middle stage, so that the fuel injected by the pre-stage injection is sufficiently vaporized. Since the time for performing the low-temperature oxidation reaction induced by ozone can be made relatively long, it is advantageous in stabilizing the compression ignition by the main injection performed near the compression top dead center.

The PCM 100 also determines, for example, that the temperature in the cylinder 13 has sufficiently increased after a predetermined number of cycles have elapsed, and stops the front-stage injection and the generation of ozone synchronized with the front-stage injection. Consumption of the required fuel and electric power required for application to the electrode 31b is suppressed, which is advantageous in improving fuel consumption.
<Other embodiments>
Although the description has been given of the configuration in which the pre-injection in which the pre-injection with the generation of ozone is performed once for each cylinder 13 at the time of natural recovery, the configuration is not necessarily limited thereto. Depending on the configuration of the engine 10 or the like, the pre-injection may be performed twice or more, or a sensor for measuring the temperature of the inner wall surface of the cylinder 13 is provided, and the pre-injection is performed based on the signal from this sensor. You may comprise so that it may continue or complete | finish. Also, based on the input from various sensors, the transition of the temperature of the inner wall surface after the natural return is estimated, and based on the estimation, the number of times of performing the pre-injection accompanied by the generation of ozone is determined. Also good.

  The configurations of the intake passage 50 and the exhaust passage 60 can also be changed. For example, in the cooled EGR 70, a bypass passage for bypassing the EGR cooler 72 can be provided. In such a case, the temperature of the EGR gas and thus the ignitability of the air-fuel mixture can be controlled to a higher degree.

  The technology disclosed herein can also be applied to an engine with a turbocharger.

  The configuration including the CVVL 44 in the intake valve driving mechanism is not essential.

  As described above, in the control device for the compression ignition type engine, the compression ignition combustion can be stabilized at the time of natural return from the fuel cut control, and there is industrial applicability.

10 engine body 13 cylinder 100 PCM (control means)
20 Fuel supply device (fuel supply means)
30 Ozone generator (Ozone generating means)

Claims (2)

An engine body having a cylinder;
Fuel injection means for injecting an amount of fuel corresponding to the operating state of the engine body into the cylinder at an injection timing corresponding to the operating state;
A throttle valve for adjusting the amount of intake air into the cylinder;
Control means for driving the engine body by subjecting the air-fuel mixture in the cylinder to compression ignition combustion;
Ozone generating means for generating ozone in the cylinder,
The fuel injection means includes an injector that injects fuel containing at least gasoline into the cylinder through an injection port at a tip thereof, and a fuel supply system that controls an injection mode of the injector ,
The injector is configured to be able to change the opening of the injection port,
The control means performs fuel cut control for forcibly interrupting the operation of the fuel injection means when a predetermined condition is satisfied when the engine body is decelerated, and during the fuel cut control . Is configured to set the intake air amount to a minimum amount corresponding to the inertial operation of the engine body by reducing the intake air amount via the throttle valve,
The control means further restarts fuel injection by the fuel injection means when detecting that the engine speed has decreased to a predetermined value during execution of the fuel cut control. By controlling the fuel injection means and the ozone generation means, the main injection in which the opening of the injection port is changed so that the air-fuel mixture is unevenly distributed near the center of the combustion chamber in the cylinder is compressed. A compression ignition method that is executed after the second half and performs preceding injection that injects a smaller amount of fuel than the main injection, and generates ozone in the cylinder in synchronization with the preceding injection. Engine control device. The control apparatus for a compression ignition engine according to claim 1 ,
The engine body has a plurality of cylinders,
The control unit controls the fuel injection unit and the ozone generation unit to restart the fuel injection and then perform combustion once in each of the plurality of cylinders. A control device for a compression ignition engine that stops generation of ozone.

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