JP2017190736A - Controller of internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a controller of an internal combustion engine capable of avoiding excessive combustion suppression due to water injection and a risk of accident fire resulting from the excessive combustion suppression.SOLUTION: A controller of an internal combustion engine includes: an in-cylinder pressure sensor 30 configured to grasp in-cylinder pressure; a water tank 46 storing water; a pump 45 configured to pump water in the water tank 46 to a water injection injector 43; the water injection injector 43 configured to inject water into a combustion chamber 7 with valve opening; and an ECU 3 configured to, when SI combustion is switched to HCCI combustion, for a predetermined cycle number Y until fresh air flows into a cylinder and lean HCCI operation becomes stable, perform water injection so that a maximum in-cylinder pressure becomes a target maximum in-cylinder pressure.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a control device for an internal combustion engine.

  Conventionally, as a combustion mode of an internal combustion engine such as a gasoline engine, SI (Spark Ignition) combustion in which an air-fuel mixture is forcibly ignited by spark discharge from a spark plug has been widely used. Development of a gasoline engine that uses premixed compression self-ignition combustion, which introduces the burned gas and self-ignites the air-fuel mixture, as a combustion mode is underway. Here, the premixed compression self-ignition combustion is referred to as HCCI (Homogeneous Charge Compression Ignition) combustion.

  In an internal combustion engine having such an HCCI combustion function, a negative valve overlap that closes both the intake valve and the exhaust valve from the exhaust stroke to the intake stroke and seals the exhaust gas as internal EGR (Exhaust Gas Recirculation) gas in the combustion chamber. Some (NVO: Negative Valve Overlap) periods are provided, and the internal cylinder temperature, which is the temperature in the combustion chamber, is increased by internal EGR gas.

  In an internal combustion engine that switches between SI combustion and HCCI combustion, when switching from SI combustion to HCCI combustion, the amount of internal EGR is increased by increasing the NVO period. Immediately after switching from SI combustion to HCCI combustion, the temperature of the exhaust gas due to SI combustion is high, so the ignition timing at the start of HCCI combustion is earlier than the allowable value. By accelerating the ignition timing, the combustion temperature becomes high and the rate of pressure increase increases, resulting in an increase in vibration and noise.

  In Patent Document 1, when switching from spark ignition combustion to compression ignition combustion, the operation amount such as the internal EGR amount is corrected based on the exhaust temperature, and each operation amount is set when the exhaust temperature falls within a predetermined value. This is the set value for compression ignition combustion.

  Further, in Patent Document 2, when the operation is switched from the spark ignition operation to the self ignition operation, a predetermined gas after the combustion gas generated by the combustion based on the last spark ignition immediately before the operation switching starts to be discharged from the combustion chamber. A liquid such as water is jetted once or twice at the timing.

  The water to be sprayed is stored in a water tank in the vehicle, and is operated by a user filling the water or storing water condensed in an external EGR or exhaust pipe in the tank. The amount of water injection is determined by the engine load and the engine speed (see paragraph 0084).

JP 2007-247479 A JP 2006-17082 A

  However, in the thing of the above-mentioned patent document 1, when an internal combustion engine is drive | operated with high load, since internal EGR gas temperature is high, a sharp combustion generate | occur | produces at the time of the start of HCCI combustion. As a result, the maximum in-cylinder pressure increases, causing deterioration of combustion noise and increase in vibration.

  Moreover, in the thing of the above-mentioned patent document 2, in the situation where switching from SI combustion to HCCI combustion is frequently used, the amount of water in the water tank is insufficient, and water required for switching from SI combustion to HCCI combustion is required. The above-mentioned problem cannot be solved.

  On the other hand, in a situation where the cooling water temperature or intake air temperature of the internal combustion engine is low and HCCI combustion is difficult to occur, there is a risk of misfire due to water injection.

  Therefore, an object of the present invention is to provide a control device for an internal combustion engine that can avoid excessive combustion suppression by water injection and the risk of misfire resulting therefrom.

  In order to solve the above problems, the present invention is an internal combustion engine control device configured to be able to switch between spark ignition combustion and compression auto-ignition combustion, and an in-cylinder pressure sensor for detecting a pressure in a cylinder of the internal combustion engine, When switching from the spark ignition combustion to the compression ignition combustion, the maximum in-cylinder pressure in the cylinder becomes the target value until the amount of fresh air in the cylinder becomes an amount necessary for the compression ignition combustion. And a controller for injecting water into the cylinder.

  Thus, according to the present invention, it is possible to provide a control device for an internal combustion engine that can avoid excessive combustion suppression by water injection and the risk of misfire resulting therefrom.

FIG. 1 is a schematic configuration diagram of a control device for an internal combustion engine according to an embodiment of the present invention. FIG. 2 is a graph showing an example of a map for obtaining a target maximum in-cylinder pressure of the control device for an internal combustion engine according to the embodiment of the present invention. FIG. 3 is a graph showing an example of a map for obtaining the injection command time of the control apparatus for an internal combustion engine according to the embodiment of the present invention. FIG. 4 is a graph showing an example of an in-cylinder temperature prediction map before ignition of the control device for an internal combustion engine according to the embodiment of the present invention. FIG. 5 is a graph showing an example of a water injection amount map of the control device for an internal combustion engine according to the embodiment of the present invention. FIG. 6 is a flowchart showing a procedure of water injection control processing of the control device for an internal combustion engine according to the embodiment of the present invention. FIG. 7 is a flowchart showing a procedure of water injection amount determination logic of the control device for an internal combustion engine according to the embodiment of the present invention. FIG. 8 is a time chart showing the operation of the water injection injector by the water injection control process of the control device for the internal combustion engine according to the embodiment of the present invention. FIG. 9 is a time chart showing a change in the maximum in-cylinder pressure by the water injection control process of the control apparatus for an internal combustion engine according to the embodiment of the present invention.

  Hereinafter, an internal combustion engine control apparatus according to an embodiment of the present invention will be described in detail with reference to the drawings.

  In FIG. 1, a vehicle 1 equipped with an internal combustion engine control apparatus according to an embodiment of the present invention includes an internal combustion engine type engine 2 and an ECU (Electronic Control Unit) 3 as a control unit. .

  The engine 2 is formed with a cylinder 5 as a cylinder. The cylinder 5 houses a piston 6 that can reciprocate up and down in the cylinder 5. A combustion chamber 7 is provided in the upper part of the cylinder 5. The combustion chamber 7 is provided with an in-cylinder pressure sensor 30 for grasping the in-cylinder pressure that is the pressure inside the cylinder 5.

  The engine 2 is a so-called four-cycle gasoline engine that performs a series of four strokes including an intake stroke, a compression stroke, an expansion stroke, and an exhaust stroke while the piston 6 makes two reciprocations in the cylinder 5.

  The piston 6 is connected to the crankshaft via a connecting rod (not shown). The connecting rod converts the reciprocating motion of the piston 6 into the rotational motion of the crankshaft.

  The combustion chamber 7 is provided with a spark plug 8 and an injector 9. The spark plug 8 is disposed in the combustion chamber 7 with an electrode protruding, and the ignition timing is controlled by the ECU 3. The injector 9 is a so-called in-cylinder fuel injection valve that injects fuel supplied from a fuel tank (not shown) by a fuel pump into the combustion chamber 7.

  The engine 2 is provided with an intake port 11 and an exhaust port 21. The intake port 11 communicates the combustion chamber 7 with an intake passage 16a described later. The intake port 11 is provided with an intake valve 12.

  The intake valve 12 is opened and closed so as to communicate or block the intake passage 16a and the combustion chamber 7. The intake valve 12 is opened and closed by an intake side variable valve mechanism 13.

  As the intake side variable valve mechanism 13, for example, an electromagnetic variable valve mechanism that opens and closes the intake valve 12 by an electromagnetic actuator composed of an electromagnet and a spring can be used. Specifically, the intake side variable valve mechanism 13 opens the intake valve 12 that is normally urged in the valve closing direction by a spring by attracting a movable portion fixed to the intake valve 12 by excitation of an electromagnet. It is designed to move in the valve direction.

  The intake side variable valve mechanism 13 may be a hydraulic variable valve mechanism using a hydraulic actuator instead of the electromagnetic actuator. Further, as the intake side variable valve mechanism 13, a mechanical variable valve mechanism that can change the opening / closing timing of the intake valve 12 using cam members such as a main cam and a sub cam may be used.

  Further, the intake side variable valve mechanism 13 is configured such that, for example, the exciting current for the electromagnet is adjusted by the ECU 3 so that the lift amount of the intake valve 12 can be continuously changed with the opening / closing timing of the intake valve 12. It may be.

  An intake manifold 14 is connected to the intake port 11. A surge tank 15 is provided on the upstream side of the intake manifold 14 where the intake air flows.

  An intake pipe 16 is connected to the upstream side of the surge tank 15 in the intake direction. An intake passage 16 a communicating with the intake port 11 is formed in the intake pipe 16. An electronically controlled throttle valve 17 is provided in the intake passage 16a. The throttle valve 17 is electrically connected to the ECU 3.

  The throttle valve 17 is configured to adjust the intake air amount of the engine 2 by controlling the throttle opening degree according to a command signal from the ECU 3. The throttle valve 17 is provided with a throttle opening sensor 18 for detecting the throttle opening.

  On the other hand, the exhaust port 21 is provided with an exhaust valve 22. The exhaust valve 22 is opened and closed so as to communicate or block an exhaust passage 24a described later and the combustion chamber 7. The exhaust valve 22 is opened and closed by an exhaust side variable valve mechanism 23.

  Since the exhaust side variable valve mechanism 23 has the same configuration as the intake side variable valve mechanism 13 described above, detailed description thereof is omitted, but the excitation and deexcitation of the electromagnet is controlled by the ECU 3 so that the exhaust The opening / closing timing of the valve 22 is arbitrarily changed. The exhaust side variable valve mechanism 23 may be a hydraulic variable valve mechanism using a hydraulic actuator instead of the electromagnetic actuator. Further, as the exhaust-side variable valve mechanism 23, a mechanical variable valve mechanism that can change the opening / closing timing of the exhaust valve 22 using cam members such as a main cam and a sub cam may be used. Therefore, the ECU 3 can easily adjust the valve opening period of the exhaust valve 22.

  An exhaust pipe 24 is connected to the exhaust port 21. An exhaust passage 24 a communicating with the exhaust port 21 is formed in the exhaust pipe 24.

  The engine 2 is provided with an exhaust recirculation pipe 41 that communicates the intake passage 16a and the exhaust passage 24a. The exhaust gas recirculation pipe 41 is configured to perform EGR to recirculate part of the exhaust gas to the intake side. The exhaust gas recirculation pipe 41 is provided with an EGR valve 42 as an exhaust gas recirculation control valve for adjusting the exhaust gas recirculation amount.

  The EGR valve 42 is electrically connected to the ECU 3. The EGR valve 42 is configured to adjust the amount of exhaust gas recirculated to the intake side by controlling the valve opening according to a command signal from the ECU 3.

  The combustion chamber 7 is provided with a water injection injector 43. The water injection injector 43 is connected to a pump 45 through a water supply pipe 44. The pump 45 is connected to a water tank 46 that contains water. The water tank 46 is provided with a water amount sensor 47 that detects the amount of water in the water tank 46.

  The pump 45 pumps the water in the water tank 46 to the water injection injector 43. Thereby, the water injection injector 43 injects water into the combustion chamber 7 when the valve is opened in response to the drive signal from the ECU 3.

  The water tank 46 is connected to a filter 49 via a water supply pipe 48. The filter 49 is connected to the surge tank 15. As a result, the condensed water generated in the exhaust gas recirculation pipe 41 flows into the filter 49 through the surge tank 15, is filtered by the filter 49, and is stored in the water tank 46.

  The ECU 3 includes a computer unit that includes a central processing unit (CPU), a random access memory (RAM), a read only memory (ROM), a flash memory, an input port, and an output port.

  The ROM of the computer unit stores a program for causing the computer unit to function as the ECU 3 along with various control constants and various maps. That is, the computer unit functions as the ECU 3 when the CPU executes a program stored in the ROM.

  In addition to the throttle opening sensor 18, in-cylinder pressure sensor 30, and water amount sensor 47 described above, various sensors such as an accelerator opening sensor 31 and a crank angle sensor 32 are connected to the input port of the ECU 3.

  The accelerator opening sensor 31 detects an accelerator opening that is an opening of an accelerator pedal (not shown) operated by a driver when, for example, an acceleration is requested. The crank angle sensor 32 detects the rotation angle of the crankshaft. The ECU 3 calculates the engine speed based on the detection result input from the crank angle sensor 32.

  On the other hand, on the output side of the ECU 3, various controls such as the ignition plug 8, the injector 9, the intake side variable valve mechanism 13, the throttle valve 17, the exhaust side variable valve mechanism 23, the EGR valve 42, the water injection injector 43, etc. The object is connected.

  The ECU 3 switches between SI combustion and HCCI combustion according to the operating state of the engine 2. Specifically, the ECU 3 determines whether the operation region of the engine 2 is in the SI combustion region or the HCCI combustion region by referring to a combustion region map using the engine speed and the engine load as parameters. Based on the determination, whether to perform SI combustion or HCCI combustion is selected. The combustion region map is obtained in advance by experiments or the like and stored in the ROM of the ECU 3.

  The ECU 3 calculates the engine load as the engine load based on the accelerator opening input from the accelerator opening sensor 31 and the engine speed calculated from the detection result input from the crank angle sensor 32.

  In the HCCI mode in which the HCCI combustion is performed, the ECU 3 performs the valve timing of the intake valve 12 and the exhaust valve 22 for outputting the engine load requested by the driver based on the engine speed and the engine load, and the fuel injection by the injector 9. Determine the amount.

  Further, in the HCCI mode, the ECU 3 sets a blockage period (NVO period) during which both the intake valve 12 and the exhaust valve 22 are closed from the exhaust stroke to the intake stroke.

  When switching from SI combustion to HCCI combustion, the ECU 3 injects water into the combustion chamber 7 to lower the in-cylinder pressure to the target in-cylinder pressure to achieve stable lean HCCI combustion.

  The ECU 3 causes the water injection injector 43 to inject water into the combustion chamber 7 during a predetermined cycle after determining that the operation region of the engine 2 is the HCCI combustion region. The ECU 3 causes the water injection injector 43 to inject water into the combustion chamber 7 at a predetermined timing after the combustion gas resulting from the spark ignition combustion starts to be discharged from the combustion chamber 7.

  The predetermined cycle is the number of cycles until a large amount of fresh air flows into the cylinder due to an increase in the throttle opening due to the start of switching to HCCI combustion, resulting in a stable lean HCCI operation. In this cycle number, four strokes from the intake stroke to the exhaust stroke are defined as one cycle.

  For example, assuming that fresh air enters the cylinder at the same speed as the piston speed, the ECU 3 sets the distance from the throttle valve 17 to the intake valve 12 to L [m], the piston speed to v [m / s], and the engine speed. As Ne [rpm], the predetermined cycle number Y is calculated by the following formula 1.

  The predetermined timing is obtained in advance by experiments or the like and stored in the ROM of the ECU 3.

  Thereby, water injection can be performed during the predetermined number of cycles until stable lean HCCI operation is achieved, and the predetermined cycle can be uniquely determined according to the engine specifications and the engine speed.

  When the ECU 3 determines that the operation region of the engine 2 is the HCCI combustion region, if the water amount in the water tank 46 detected by the water amount sensor 47 is less than a predetermined amount set in advance, the ECU 3 does not perform HCCI combustion.

  As the predetermined amount of water in the water tank 46, for example, the amount of water injected into the combustion chamber 7 by the water injector 43 is stored, the average value of the water amount and the standard deviation σ are obtained, and 2σ is added to the average value. The value is a predetermined amount of water. That is, the variation in the amount of jet water for each switching when applied to the normal distribution is obtained, and the amount of water is not deficient at 95% of the switching times.

  Thereby, an increase in in-cylinder pressure due to switching from SI combustion to HCCI combustion under a situation where water injection is not possible can be suppressed.

  The ECU 3 calculates a target maximum in-cylinder pressure, which is a target maximum in-cylinder pressure when switching to HCCI combustion, based on the engine load and the engine speed when it is determined that the operation region of the engine 2 is the HCCI combustion region. To do.

  For example, the ECU 3 calculates the target maximum in-cylinder pressure using a map in which the target maximum in-cylinder pressure is determined from the engine load and the engine speed as shown in FIG. This map is obtained in advance by experiments or the like and stored in the ROM of the ECU 3. The target maximum in-cylinder pressure is set higher as the engine load is higher and higher as the engine speed is higher.

  The ECU 3 calculates the water injection amount of the first water injection based on the engine load and the engine speed when it is determined that the operation region of the engine 2 is the HCCI combustion region.

  For example, the ECU 3 obtains the injection command time from a map in which the injection command time to the water injection injector 43 is determined from the engine load and the engine speed as shown in FIG. This map is obtained in advance by experiments or the like and stored in the ROM of the ECU 3. The injection command time for water injection is set to be longer as the engine load is higher and the engine speed is lower.

  The reason why the injection command time is lengthened as the engine load is high is that the maximum in-cylinder pressure tends to increase because the fuel injection amount is large. The reason why the injection command time is increased as the engine speed is lower is that the time during which the air-fuel mixture is compressed is longer, so that combustion becomes steep and the maximum in-cylinder pressure tends to increase.

  The ECU 3 calculates the second and subsequent water injection amounts based on the engine load, the engine speed, the current value of the maximum in-cylinder pressure, and the target maximum in-cylinder pressure.

  The ECU 3 uses, for example, a pre-ignition cylinder temperature prediction map in which the pre-ignition in-cylinder temperature is determined from the engine load, the engine speed, and the maximum in-cylinder pressure as shown in FIG. The deviation between the temperature and the in-cylinder temperature before ignition due to the target maximum in-cylinder pressure is calculated. The pre-ignition in-cylinder temperature prediction map is obtained in advance by experiments or the like and stored in the ROM of the ECU 3. The in-cylinder temperature before ignition is set higher as the maximum in-cylinder pressure is higher.

  For example, the ECU 3 calculates the water injection amount by a water injection amount map in which the injection water amount is determined from the engine load, the engine speed, and the in-cylinder temperature deviation before ignition as shown in FIG. The water injection map corresponds to the temperature range in which the latent heat of vaporization of the injected water cools the in-cylinder gas, and can be obtained by calculation based on thermodynamics. The water injection amount map is stored in the ROM of the ECU 3.

  The ECU 3 calculates the injection command time of the water injection injector 43 based on the calculated water injection amount, and controls the water injection injector 43.

  If the current value of the maximum in-cylinder pressure is less than the target maximum in-cylinder pressure, the ECU 3 may determine that water injection is not necessary and may not perform water injection.

  Thereby, the excessive combustion suppression by water injection and the risk of the misfire resulting therefrom can be avoided.

  The ECU 3 determines that the operation region of the engine 2 is the HCCI combustion region and calculates the integrated water injection amount while continuing the water injection after starting the water injection. The ECU 3 stops water injection when the integrated water injection amount exceeds a predetermined integrated water injection amount obtained by multiplying the minimum in-cylinder volume by the adjustment coefficient X. The adjustment factor X corresponds to a safety factor and takes a value between zero and one. The adjustment coefficient X is preferably set to a value of about 0.8.

  Thereby, it is possible to switch from SI combustion using water injection to HCCI combustion while avoiding the risk of water hammer.

  A water injection control process performed by the control apparatus for an internal combustion engine according to the present embodiment configured as described above will be described with reference to FIGS. 6 and 7. Note that the water injection control process described below is started when the ECU 3 starts to operate, and is executed at a preset time interval.

  In step S1, the ECU 3 determines whether or not the engine load and the engine speed are within the HCCI operation region. When it is determined that it is not within the HCCI operation region, the ECU 3 ends the process.

  When it determines with it being in the HCCI driving | operation area | region, ECU3 determines whether the water quantity of the water tank 46 is more than predetermined amount in step S2. When it is determined that the amount of water in the water tank 46 is not equal to or greater than the predetermined amount, the ECU 3 ends the process.

  When it is determined that the amount of water in the water tank 46 is equal to or greater than the predetermined amount, in step S3, the ECU 3 calculates a target maximum in-cylinder pressure from the engine load and the engine speed. At this time, a flag indicating that the switching control from SI combustion to HCCI combustion has started may be turned on so that other processes can be identified.

In step S4, the ECU 3 advances the closing timing of the exhaust valve 22.
In step S5, the ECU 3 retards the opening timing of the intake valve 12.

  In this way, the ECU 3 provides an NVO period for capturing a large amount of residual gas required for HCCI operation in the cylinder.

  In step S6, the ECU 3 increases the throttle opening and starts shifting to lean HCCI operation.

  In step S7, the ECU 3 calculates an injection command time for the first water injection from the engine load and the engine speed.

  In step S8, the ECU 3 opens the water injection injector 43. In step S9, the ECU 3 waits for a timer based on the water injection command time. When the timer expires, the ECU 3 closes the water injection injector 43 in step S10.

  In step S11, the ECU 3 determines whether or not the accumulated water injection amount is less than a value obtained by multiplying the minimum in-cylinder volume by the adjustment coefficient X. When it is determined that the integrated water injection amount is not less than the value obtained by multiplying the minimum in-cylinder volume by the adjustment coefficient X, the ECU 3 advances the process to step S16.

  When it is determined that the integrated water injection amount is less than the value obtained by multiplying the minimum cylinder volume by the adjustment coefficient X, in step S12, the ECU 3 obtains the maximum cylinder pressure of the cycle in which water injection has been performed as the current maximum cylinder pressure. To do.

In step S13, the ECU 3 updates the injection command time calculated by the water injection amount determination logic shown in FIG. 7 as the injection command time for the next water injection.
In step S14, the ECU 3 stands by until the water injection timing of the next cycle.

  When the water injection timing of the next cycle comes, in step S15, the ECU 3 determines whether or not the water injection has been performed for a predetermined number of cycles Y. If it is determined that the water injection is not performed for the predetermined number of cycles Y, the ECU 3 returns to step S8 and continues the process.

  When it is determined that the water injection is performed for the predetermined number of cycles Y, the ECU 3 turns off the spark ignition by the spark plug 8 in step S16.

  In step S17, the ECU 3 resets the integrated water injection amount to zero and ends the process.

Next, the water injection amount determination logic will be described with reference to FIG.
In step S21, the ECU 3 calculates a pre-ignition in-cylinder temperature deviation using the pre-ignition in-cylinder temperature prediction map.

In step S22, the ECU 3 calculates the water injection amount using the water injection amount map.
In step S23, the ECU 3 calculates an injection command time for water injection from the water injection amount, and ends the process.

  The operation by such combustion stabilization processing will be described with reference to FIGS. As shown in FIG. 8, when it is determined that the engine load and the engine speed are within the HCCI operation region at T1, the closing timing of the exhaust valve 22 is advanced, and the opening timing of the intake valve 12 is retarded. , An NVO period is provided.

  At the same time, the throttle opening is opened and fresh air is introduced. Water injection is performed for a predetermined number of cycles Y until this fresh air flows into the cylinder and a stable lean HCCI operation is achieved.

  The injection command time for the first water injection is calculated based on the engine load and the engine speed.

The second and subsequent injection command times are calculated so that the maximum in-cylinder pressure becomes the target maximum in-cylinder pressure based on the maximum in-cylinder pressure and the target maximum in-cylinder pressure of the cycle in which water injection is performed.
As a result, as shown in FIG. 9, the internal EGR amount increases and the maximum in-cylinder pressure decreases.

  When water injection is performed for a predetermined number of cycles Y, the maximum in-cylinder pressure approaches the target maximum in-cylinder pressure, the internal EGR gas temperature decreases, and the A / F (air-fuel ratio) increases.

  When the water injection of the predetermined number of cycles Y is completed, the spark ignition by the spark plug 8 is turned off at T2, and the transition to the HCCI operation is completed.

  Thus, in the above-described embodiment, when switching from SI combustion to HCCI combustion, the maximum in-cylinder pressure is set to the target maximum for a predetermined number of cycles Y until the fresh air flows into the cylinder and becomes a stable lean HCCI operation. An ECU 3 is provided for injecting water so as to achieve in-cylinder pressure.

  Thereby, the excessive combustion suppression by water injection and the risk of the misfire resulting therefrom can be avoided. Further, water injection can be performed until a stable lean HCCI operation is achieved.

  Further, the ECU 3 does not switch from SI combustion to HCCI combustion when the amount of water in the water tank 46 is less than a predetermined value.

  Thereby, the amount of water in the water tank 46 is insufficient and water injection cannot be performed, and the risk that the maximum in-cylinder pressure increases can be avoided.

  Further, the ECU 3 stores the water injection amount at the time of switching from past SI combustion to HCCI combustion, and obtains a predetermined value from the average and standard deviation of past water injection amounts.

  Thereby, the predetermined value of the amount of water in the water tank 46 can be minimized, and switching from SI combustion to HCCI combustion can be made possible at many occasions.

  Moreover, ECU3 stops water injection, when the integrated water injection amount after starting switching from SI combustion to HCCI combustion becomes more than a fixed value.

  Thereby, water injection at the time of switching from SI combustion to HCCI combustion can be executed while avoiding the risk of water hammer.

  Further, the ECU 3 obtains the predetermined cycle number Y from the distance L from the throttle valve 17 to the intake valve 12, the piston speed v, and the engine speed Ne.

  Thus, the predetermined cycle number Y can be uniquely determined according to the engine specifications and the engine speed.

  In addition, in this embodiment, it showed about the time of the water injection at the time of switching from SI combustion to HCCI combustion, However, It can apply also in the combustion suppression at the time of rapid acceleration using water injection, and preignition suppression.

  While embodiments of the invention have been disclosed, it will be apparent to those skilled in the art that changes may be made without departing from the scope of the invention. All such modifications and equivalents are intended to be included in the following claims.

1 vehicle 2 engine (internal combustion engine)
3 ECU (control unit)
18 Throttle opening sensor 30 In-cylinder pressure sensor 31 Accelerator opening sensor 32 Crank angle sensor 43 Water injection injector 44 Water supply pipe 45 Pump 46 Water tank 47 Water amount sensor

Claims (4)

A control device for an internal combustion engine configured to be able to switch between spark ignition combustion and compression ignition combustion,
An in-cylinder pressure sensor for detecting a pressure in a cylinder of the internal combustion engine;
When switching from the spark ignition combustion to the compression ignition combustion, the maximum in-cylinder pressure in the cylinder becomes a target value until the amount of fresh air in the cylinder becomes an amount necessary for the compression ignition combustion. And a control unit for injecting water into the cylinder.   2. The control device for an internal combustion engine according to claim 1, wherein the control unit does not switch from the spark ignition combustion to the compression autoignition combustion when the amount of water used for the water injection is less than a predetermined amount. .   3. The control device for an internal combustion engine according to claim 2, wherein the control unit calculates the predetermined use amount based on a water amount of the water injection at the time of switching from the spark ignition combustion to the compression self-ignition combustion in the past.   The said control part stops the said water injection, when the integrated water injection amount at the time of the switching from the said spark ignition combustion to the said compression auto-ignition combustion becomes more than predetermined integrated water injection amount. The control device for an internal combustion engine according to any one of claims 1 to 3.

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