JP5739799B2 - Control device for compression ignition internal combustion engine - Google Patents

Description

  The present invention relates to a control device for a compression ignition internal combustion engine. More specifically, a premixed gas obtained by mixing fuel and air is supplied to a combustion chamber, and this is self-ignited under a high compression ratio. The present invention relates to an improvement in a control device for a premixed compression self-ignition internal combustion engine that achieves thermal efficiency.

  A premixed compression self-ignition internal combustion engine, for example, as disclosed in Patent Document 1, is a compression ignition operation (HCCI (Homogeneous Charge Compression) for premixed compression ignition combustion of an air-fuel mixture (premixed gas) supplied to a combustion chamber. Ignition)). In such an internal combustion engine, the pre-mixed gas is compressed under a high compression ratio (higher than the compression ratio of a normal spark ignition type internal combustion engine), and thus self-ignition is performed simultaneously at multiple points. There is an advantage that the flame can be propagated quickly and the combustion is completed in a short time, thereby improving the thermal efficiency and reducing the NOx emission while improving the fuel efficiency.

  As described above, since the compression ignition operation is a method of self-igniting the air-fuel mixture, the amount of air supplied to the combustion chamber, the amount of fuel, etc. are precisely controlled according to the operating state of the engine to appropriately control the combustion timing. There is a need. Therefore, in the technique described in Patent Document 1, the compression ignition operation is performed by attaching a sensor to the cylinder, directly detecting the in-cylinder pressure, and performing feedback control of the combustion timing based on the detected in-cylinder pressure. To continue stably.

JP 2005-69097 A

  However, when configured as in the technique described in Patent Document 1, a sensor for detecting the in-cylinder pressure, a high-speed processing CPU for executing feedback control, and the like are required, resulting in inconvenience that the structure is complicated.

  Accordingly, an object of the present invention is to provide a control device for a compression ignition internal combustion engine that solves the above-described problems and appropriately controls the combustion timing with a simple configuration, and thus stably continues the compression ignition operation. There is to do.

In order to solve the above-described problem, in claim 1, an injector is provided in an intake port of a compression ignition internal combustion engine to inject fuel, and air supplied via the intake port and the injector In a control apparatus for a compression ignition internal combustion engine that performs a compression ignition operation in which an air- fuel mixture with fuel to be injected is premixed in the intake port and then compression ignition combustion is performed in a combustion chamber, the operation during the compression ignition operation of the engine A basic fuel supply amount calculating means for calculating a basic fuel supply amount for the compression ignition operation based on a state; an intake air temperature detecting means for detecting an intake air temperature; a NOx amount detecting means for detecting a NOx amount in exhaust; together and a basic fuel supply quantity correcting means for correcting the basic fuel supply amount the calculated on the basis of the detected intake air temperature and the NOx amount, the basic fuel supply quantity corrected hand , The estimated in-cylinder pressure change rate of the engine based on the detected intake air temperature and the amount of NOx, and as configured to correct the basic fuel supply quantity based on the estimated in-cylinder pressure change rate.

In the control apparatus for a compression ignition internal combustion engine according to claim 2 , the basic fuel supply amount correction means corrects the basic fuel supply amount to be increased when the estimated in-cylinder pressure change rate is a predetermined value or less. On the other hand, the basic fuel supply amount is corrected to decrease when the estimated in-cylinder pressure change rate is larger than the predetermined value.

  In the control apparatus for the compression ignition internal combustion engine according to claim 1, the basic fuel supply amount of the compression ignition operation is calculated based on the operation state at the time of the compression ignition operation of the compression ignition internal combustion engine, and the intake air temperature and the exhaust gas And the basic fuel supply amount calculated based on the detected intake air temperature and the NOx amount is corrected, so that the combustion timing can be appropriately controlled with a simple configuration, Therefore, the compression ignition operation can be continued stably. In addition, the in-cylinder pressure sensor and high-speed CPU used in Patent Document 1 can be eliminated, which is advantageous in terms of cost.

The basic fuel supply amount correcting means estimates the in-cylinder pressure change rate of the engine based on the detected intake air temperature and the NOx amount, that is, the in-cylinder pressure change rate correlated with the combustion speed in the cylinder is taken as the intake air temperature. It estimated based on the NOx amount, since it is configured to correct the basic fuel supply quantity based on the estimated in-cylinder pressure change rate, can better control the combustion timing, thus the compression ignition operation more stably Can continue.

In the control apparatus for the compression ignition internal combustion engine according to claim 2 , the basic fuel supply amount correction means increases and corrects the basic fuel supply amount when the estimated in-cylinder pressure change rate is equal to or less than a predetermined value (specifically, The basic fuel supply amount is increased and corrected to increase the in-cylinder pressure change rate. On the other hand, when the estimated in-cylinder pressure change rate is larger than a predetermined value, the basic fuel supply amount is corrected to decrease (specifically, In addition to the effect described in claim 2, for example, the compression ignition operation can be reliably and stably continued in addition to the effect described in claim 2. The value can be set to a value, and the in-cylinder pressure change rate can be held at the predetermined value. As a result, the combustion timing can be more appropriately controlled, and therefore the compression ignition operation can be continued stably and reliably.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram showing an overall control apparatus for a compression ignition internal combustion engine according to an embodiment of the present invention. 2 is a graph showing two valve timing (and lift amount) characteristics that are switched (set) by the variable valve mechanism of the apparatus shown in FIG. 1. It is a block diagram which shows the structure of control of the fuel supply amount at the time of the compression ignition driving | operation of a compression ignition internal combustion engine among operation | movement of the electronic control unit shown in FIG. 2 is a flowchart showing a fuel supply amount control operation of a compression ignition internal combustion engine by an electronic control unit shown in FIG. 2 is a graph showing the characteristics of the in-cylinder pressure change rate with respect to the NOx concentration of the compression ignition internal combustion engine shown in FIG. 1. It is a graph which shows the characteristic of the in-cylinder pressure change rate with respect to the correction value c of the compression ignition internal combustion engine shown in FIG.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, an embodiment for implementing a control apparatus for a compression ignition internal combustion engine according to the invention will be described with reference to the accompanying drawings.

  FIG. 1 is a schematic diagram generally showing a control apparatus for a compression ignition internal combustion engine according to an embodiment of the present invention.

  In FIG. 1, reference numeral 10 denotes a water-cooled four-cycle single-cylinder OHV type compression ignition internal combustion engine (a premixed compression self-ignition internal combustion engine) that uses city gas (or LP gas; hereinafter simply referred to as “gas”) as fuel. (Hereinafter referred to as “engine”). The engine 10 is a general-purpose internal combustion engine used as, for example, a generator, an agricultural machine, a drive source for a cogeneration system, and the like, and has a displacement of, for example, 163 cc.

  In the engine 10, the air drawn from an air cleaner (not shown) and passing through the intake pipe (intake system) 12 is adjusted in flow rate by the throttle valve 14 and flows into the combustion chamber 20 when the intake valve 16 is opened. .

  An injector (gas injector) 22 is disposed near the intake port in front of the intake valve 16. Gas fuel is pumped to the injector 22 from a fuel supply source via a fuel supply pipe (both not shown) and connected to an electronic control unit (hereinafter referred to as “ECU”) 26 through a drive circuit 24. Is done. When a drive signal indicating the valve opening time is supplied from the ECU 26 to the drive circuit 24, the injector 22 opens, and gas fuel corresponding to the valve opening time is injected into the intake port. The injected gaseous fuel flows into the combustion chamber 20 while mixing with the air that flows in to form an air-fuel mixture (pre-air mixture).

  A spark plug (ignition means) 28 is disposed in the vicinity of the combustion chamber 20. The spark plug 28 is connected to the ECU 26 via an ignition device 30 such as an igniter. When an ignition signal is supplied from the ECU 26 to the ignition device 30, a spark discharge is generated between the electrodes facing the combustion chamber 20. Thus, the air-fuel mixture is ignited and burned, and the piston 34 slidably accommodated in the cylinder 32 is driven downward.

  The air-fuel mixture is also burned by compression ignition. That is, the engine 10 performs a compression ignition operation in which the air-fuel mixture is premixed compression ignition combustion according to the operating state and a spark ignition operation (SI (Spark Ignition) operation) in which the air-fuel mixture is combusted by spark ignition via the spark plug 28. Any one is performed, in other words, the operation is switched between the compression ignition operation and the spark ignition operation (premixing), and the engine is configured as a compression ignition internal combustion engine. Specifically, for example, the spark ignition operation is performed when the engine 10 is started or warmed up, and the compression ignition operation is performed when the engine 10 is in the rated operation region after warming up.

  The exhaust gas generated by the combustion flows through the exhaust pipe (exhaust system) 40 when the exhaust valve 36 is opened. In the middle of the exhaust pipe 40, a catalyst device 42 made of an exhaust purification catalyst (specifically, an oxidation catalyst) is disposed. When the catalyst device 42 is in an active state, the exhaust gas is purified by removing harmful components such as HC (hydrocarbon) and CO (carbon monoxide), and is released to the atmosphere outside the engine.

  A crank angle sensor (shown as “ENG rotation speed sensor” in the figure) 44 is disposed near the crankshaft (not shown) of the engine 10, and a TDC signal indicating a TDC (top dead center) or a crank angle in the vicinity thereof. And a crank angle signal obtained by subdividing the TDC signal. Those outputs are input to the ECU 26.

  The ECU 26 includes a microcomputer and includes a CPU, a ROM, a RAM, and the like. The ECU 26 calculates (detects) the engine speed NE by counting the crank angle signal among the input signals.

  The throttle valve 14 is connected to an electric motor (for example, a stepping motor or actuator) 46. The electric motor 46 is connected to the ECU 26. The ECU 26 drives the electric motor 46 based on the output of each sensor that is input, and controls the opening TH of the throttle valve 14. That is, the operation of the throttle valve 14 is controlled by a DBW (Drive By Wire) method.

  A throttle opening sensor 50 is disposed in the vicinity of the throttle valve 14 and generates an output indicating the throttle opening TH. An intake air temperature sensor (intake air temperature detecting means) 52 is provided downstream of the throttle valve 14 in the intake pipe 12. The intake air temperature sensor 52 outputs a signal indicating the temperature of intake air flowing through the downstream side of the throttle valve 14 (that is, the intake air temperature of the engine 10) Tin.

  A wide area air-fuel ratio sensor 56 is disposed upstream of the catalyst device 42 in the exhaust pipe 40, and a NOx sensor (NOx amount detection means) 60 is disposed downstream of the catalyst device 42. The wide area air-fuel ratio sensor 56 outputs a signal proportional to the oxygen concentration (ie, air-fuel ratio) of the exhaust gas, and the NOx sensor 60 outputs a signal indicating the amount of NOx (exactly NOx concentration) in the exhaust gas. Further, the catalyst device 42 is provided with a catalyst temperature sensor 62, which generates an output indicating the temperature Tc of the exhaust purification catalyst. The outputs of these sensor groups are also input to the ECU 26.

  The intake valve 16 and the exhaust valve 36 described above are connected to a variable valve mechanism 64. Although the detailed illustration of the variable valve mechanism 64 is omitted, for example, the variable valve mechanism 64 has a structure disclosed in Japanese Patent Application Laid-Open No. 2010-65565 previously proposed by the present applicant. Specifically, four cams of a first and a second intake cam and a first and a second exhaust cam are arranged adjacent to each other on a valve camshaft (camshaft). The intake lifter is in sliding contact with the first and second exhaust cams. The intake lifter and the exhaust lifter are each connected to a rocker arm via a push rod.

  During the spark ignition operation of the engine 10, by appropriately controlling the operation of an electromagnetic actuator, a control rod and the like connected to each cam, the intake lifter, the intake-side push rod and the rocker arm are controlled by the rotation operation of the first intake cam. And the intake valve 16 is driven with a valve timing (and lift amount) characteristic determined by the first intake cam.

  On the other hand, during the compression ignition operation of the engine 10, the intake lifter, the intake-side push rod and the rocker arm are operated by the rotation operation of the second intake cam, and the valve timing (and lift amount) characteristics determined by the second intake cam. Then, the intake valve 16 is driven. The exhaust valve 36 is also configured to operate in the same manner.

  The characteristic is shown by a solid line in FIG. 2 (16 for the intake valve 16 and 36 for the exhaust valve 36). During the compression ignition operation, the valve timing (and lift amount) is set to the characteristics shown by the solid line in FIG. Specifically, the closing timing of the exhaust valve 36 is advanced, and the opening timing of the intake valve 16 is retarded (at the crank angle). As a result, a predetermined amount of exhaust gas remains in the cylinder to increase the temperature of the air-fuel mixture (in-cylinder gas temperature), thereby enabling the compression ignition operation.

  On the other hand, during the spark ignition operation, the valve timing (and the lift amount) is set to a characteristic indicated by a broken line in FIG. Specifically, the closing timing of the exhaust valve 36 and the opening timing of the intake valve 16 are both changed to near the piston top dead center. As a result, the closing of the exhaust valve 36 is retarded and the amount of gas discharged in the combustion chamber increases, while the opening of the intake valve 16 is advanced and the inflow of intake air is accelerated, so that the exhaust gas is combusted. It is sent to the exhaust system without remaining in the chamber.

  Returning to the description of FIG. 1, the variable valve mechanism 64 is connected to the ECU 26 via the control circuit 66. The ECU 26 controls the operation of the variable valve mechanism 64 (more precisely, the electromagnetic actuator) through the control circuit 66, and sets the valve timing (and lift amount) of the intake valve 16 and the exhaust valve 36 to one of the above two characteristics. Set (change).

  Thus, the intake valve 16 and the exhaust valve 36 of the engine 10 can be freely opened and closed at any time (valve timing and lift amount) by the variable valve mechanism 64, and the operation of the engine 10 is controlled by the variable valve mechanism. Switching between the spark ignition operation and the compression ignition operation is performed by controlling the operation of 64.

  FIG. 3 is a block diagram showing the configuration of the fuel supply amount control during the compression ignition operation of the engine 10 among the operations of the ECU 26.

  As shown in FIG. 3, the outputs of the sensors 44, 50, 52, 60 described above are input to the ECU 26. The ECU 26 controls the amount of fuel supplied to the combustion chamber 20 by controlling the operation of the electric motor 46 of the injector 22 and the throttle valve 14 based on the inputs from these sensors.

  FIG. 4 is a flowchart showing the fuel supply amount control operation of the engine 10 by the ECU 26. The illustrated program is executed at a predetermined crank angle, for example.

  As shown in FIG. 4, first, in S (step) 10, the operation state during the compression ignition operation of the engine 10 is detected. Specifically, the engine speed NE is determined based on the output of the crank angle sensor 44. The degree TH is detected (calculated) based on the output of the throttle opening sensor 50.

  Next, in S12, the basic fuel supply amount is calculated based on the detected operating state of the engine 10. Specifically, a basic fuel supply amount is calculated by searching a map stored in the ROM based on the engine speed NE, the throttle opening TH, and the like.

  Next, the routine proceeds to S14, where the intake air temperature Tin [° C.] is detected (calculated) based on the output of the intake air temperature sensor 52, and the routine proceeds to S16, where the NOx amount (NOx concentration [ppm] to be precise) is calculated from the output of the NOx sensor 60. Is detected (calculated).

  Proceeding to S18, the in-cylinder pressure change rate dP / dθ [kPa / deg] of the engine 10 is estimated based on the detected intake air temperature Tin and NOx concentration. Here, estimation of the in-cylinder pressure change rate dP / dθ will be described with reference to FIGS.

  The in-cylinder pressure change rate dP / dθ is an in-cylinder pressure change amount per unit crank angle of the engine 10 and is a value correlated with the combustion speed in the cylinder. Specifically, when the in-cylinder pressure change rate dP / dθ increases, the combustion speed in the cylinder also increases, while when the in-cylinder pressure change rate dP / dθ decreases, the combustion speed decreases. Note that the in-cylinder pressure change rate dP / dθ is also proportional to the noise accompanying combustion in the cylinder, and the noise increases as the in-cylinder pressure change rate dP / dθ increases.

  Since the engine 10 is a general-purpose internal combustion engine used as a drive source for a generator or the like as described above, the in-cylinder pressure change rate dP / dθ is a certain value (for example, a value at which the fuel efficiency is relatively high). It is desirable to be controlled so as to change at Therefore, the inventor paid attention to the intake air temperature Tin and the NOx concentration, and examined the relationship between the in-cylinder pressure change rate dP / dθ and the NOx concentration through three conditions under the intake air temperature Tin of 50, 70, and 100 [° C.]. However, as shown in FIG. 5, it was found that the rising position of the graph of the in-cylinder pressure change rate dP / dθ with respect to the NOx concentration is almost the same, although it slightly changes depending on the intake air temperature Tin.

Therefore, if the graph shown in FIG. 5 is corrected using the intake air temperature Tin and a constant (correction coefficient), the in-cylinder pressure change rate dP / dθ can be expressed by a linear function graph as shown in FIG. Specifically, the graph of FIG. 6 can be obtained by calculating the correction value c by the following equation (1) and taking the calculated correction value c on the horizontal axis of the graph.
Correction value c = a (intake air temperature−b) × NOx concentration (1)
The values a and b in the equation are constants (correction coefficients) obtained through experiments.

  Therefore, a map having the characteristics shown in FIG. 6 is stored in the ROM in advance, the correction value c is calculated from the detected intake air temperature Tin and NOx concentration, and the map is searched based on the calculated correction value c. Thus, the in-cylinder pressure change rate dP / dθ can be estimated without detecting the in-cylinder pressure with a sensor or the like.

  Returning to the description of FIG. 4, the process then proceeds to S20, in which it is determined whether the in-cylinder pressure change rate dP / dθ estimated in S18 is greater than a predetermined value. This predetermined value is set to a value such as 800 [kPa / deg] that is relatively high in fuel efficiency, has an appropriate combustion timing (combustion speed), and can reliably and stably continue the compression ignition operation.

  When the result in S20 is negative, that is, when the in-cylinder pressure change rate dP / dθ is equal to or smaller than a predetermined value, the process proceeds to S22, and correction is performed to increase the basic fuel supply amount calculated in S12 by a predetermined amount. Next, the process proceeds to S24, in which the fuel supply amount is controlled so that the increase-corrected basic fuel supply amount is obtained. Specifically, the operation of the electric motor 46 of the injector 22 and the throttle valve 14 is controlled. As a result, the in-cylinder pressure change rate dP / dθ increases and approaches a predetermined value.

  On the other hand, when the result in S20 is affirmative, the process proceeds to S26, in which correction is performed to decrease the basic fuel supply amount by a predetermined amount, and then the process proceeds to S24 to execute the above-described processing. The fuel supply amount is controlled so that As a result, the in-cylinder pressure change rate dP / dθ decreases and approaches a predetermined value.

  As described above, in S22 and S26, the basic fuel supply amount calculated based on the detected intake air temperature Tin and NOx concentration is corrected, so that the in-cylinder pressure change rate dP / dθ is held near a predetermined value. Therefore, the compression ignition operation is stably continued.

As described above, the embodiment of the present invention includes the injector (gas injector) 22 that is provided in the intake port of the compression ignition internal combustion engine (engine) 10 and injects fuel, and is supplied through the intake port. In a control apparatus for a compression ignition internal combustion engine in which a mixture of air to be injected and fuel injected from the injector 22 is premixed in the intake port and then compression ignition operation is performed in the combustion chamber 20, the compression ignition of the engine 10 is performed. Basic fuel supply amount calculation means (ECU 26. S12) for calculating the basic fuel supply amount of the compression ignition operation based on the operation state at the time of operation, and intake air temperature detection means (intake air temperature sensor 52, S12) for detecting the intake air temperature Tin ECU 26. S14), NOx amount detection means (NOx sensor 60, ECU 26. S16) for detecting the NOx amount (NOx concentration) in the exhaust gas, Was composed as and a basic fuel supply amount correcting means (ECU26.S18~S26) for correcting the basic fuel supply amount the calculated on the basis of the detected intake air temperature Tin and the NOx amount.

  Thereby, although it is a simple structure, a combustion timing can be controlled appropriately and compression ignition operation can be continued stably. In addition, the in-cylinder pressure sensor and high-speed CPU used in Patent Document 1 can be eliminated, which is advantageous in terms of cost.

  The basic fuel supply amount correcting means estimates the in-cylinder pressure change rate dP / dθ of the engine 10 based on the detected intake air temperature Tin and the NOx amount (S18), and the estimated in-cylinder pressure change rate. (S20 to S26), the combustion timing can be controlled more appropriately, and the compression ignition operation can be continued more stably.

  Further, the basic fuel supply amount correction means increases the basic fuel supply amount when the estimated in-cylinder pressure change rate dP / dθ is equal to or less than a predetermined value (specifically, increases the basic fuel supply amount). (S20, S22) On the other hand, when the estimated in-cylinder pressure change rate dP / dθ is larger than the predetermined value, the basic fuel supply amount is corrected to decrease ( Specifically, since the basic fuel supply amount is corrected to decrease and the in-cylinder pressure change rate dP / dθ is decreased) (S20, S26), the predetermined value, for example, the compression ignition operation is reliably and stably continued. It is possible to set the value to such a value that the in-cylinder pressure change rate dP / dθ can be held at the predetermined value. As a result, the combustion timing can be more appropriately controlled, and therefore the compression ignition operation can be continued stably and reliably.

  In the above description, the in-cylinder pressure change rate dP / dθ is estimated from the intake air temperature Tin and the amount of NOx, but the cooling water temperature of the engine 10, the engine speed NE, and the throttle opening TH The in-cylinder pressure change rate dP / dθ may be estimated by adding the above. Moreover, although the predetermined value, the displacement of the engine 10 and the like are shown as specific values, they are merely examples and are not limited.

  10 engine (compression ignition internal combustion engine), 20 combustion chamber, 26 ECU (electronic control unit), 28 spark plug, 52 intake air temperature sensor (intake air temperature detecting means), 60 NOx sensor (NOx amount detecting means)

Claims (2)

An injector is provided at an intake port of a compression ignition internal combustion engine and injects fuel, and an air-fuel mixture of air supplied through the intake port and fuel injected from the injector is premixed in the intake port. In a control apparatus for a compression ignition internal combustion engine that performs a compression ignition operation in which compression ignition combustion is performed in a combustion chamber, a basic fuel supply amount for the compression ignition operation is calculated based on an operation state at the time of the compression ignition operation of the engine Fuel supply amount calculation means, intake air temperature detection means for detecting intake air temperature, NOx amount detection means for detecting NOx amount in exhaust, and the calculated basic fuel based on the detected intake temperature and NOx amount Rutotomoni a basic fuel supply quantity correcting means for correcting the supply amount, the basic fuel supply quantity correcting means, before based on the intake air temperature and the NOx amount which the detected Estimating the in-cylinder pressure change rate of the engine, the control apparatus for a compression ignition internal combustion engine, characterized by correcting the basic fuel supply quantity based on the estimated in-cylinder pressure change rate. The basic fuel supply amount correction means corrects the basic fuel supply amount to be increased when the estimated in-cylinder pressure change rate is equal to or less than a predetermined value, while the estimated in-cylinder pressure change rate is greater than the predetermined value. the control device of a compression ignition internal combustion engine according to claim 1, wherein the reducing correcting the basic fuel supply quantity.

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