JP2010203366A - Control device for compression ignition type internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a control device for a compression ignition type internal combustion engine capable of maintaining excellent drivability by preventing an increase in NOx and the noise even if the intake pressure is low. <P>SOLUTION: An engine control system is constructed for a four-cylinder engine as a vehicular engine, and the fuel injection control or the like is executed by an ECU 60 as the center. The ECU 60 detects the intake pressure (S1), and decides the target ignition timing based on the detected intake pressure (S2). A control map wherein the intake pressure and the target ignition timing correspond to each other is housed in a ROM. The control map of this embodiment is set so that the target ignition timing is delayed as the intake pressure is lowered and that the injected fuel is burned at the same pressure grade as the pressure grade before the intake pressure is lowered. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a control device for a compression ignition type internal combustion engine.

  Conventionally, the NOx occlusion reduction catalyst that occludes the exhausted NOx during lean combustion and performs rich combustion when the occluded NOx exceeds a predetermined value to purge the occluded NOx and maintain the NOx purification rate. Has been proposed (see Patent Documents 1 and 2).

Japanese Patent No. 2658756 Japanese Patent No. 3427731

  A schematic diagram of the engine intake system is shown in FIG. The intake pipe 101 is a pipe for sending intake air from the outside to the intake port of the engine, and includes an EGR pipe 102 that recirculates a part of the exhaust gas as EGR gas, a throttle valve 103, and the like. In the engine intake air, a pressure difference ΔP is generated between the upstream pressure Pa on the outside side and the downstream pressure Pb on the engine side due to the throttle valve throttle.

  When performing rich combustion, if air (oxygen) commensurate with the amount of fuel is not sucked into the combustion chamber, the combustion will be incomplete and torque will not be maintained. It is necessary to obtain an amount of air (oxygen) commensurate with However, when the intake pressure is low, such as at high altitudes, the upstream pressure Pa is reduced. As a result, the pressure difference ΔP becomes small, and supercharging by the supercharger may not be in time, and the intake amount may decrease.

In order to maintain the pressure difference ΔP at the same level as in the normal case (lowland), it is necessary to lower the downstream pressure Pb of the throttle valve. To that end, it is conceivable to reduce the amount of EGR gas. However, if the amount of recirculated EGR gas is reduced, the concentration of O ₂ in the intake air in the combustion chamber increases, and combustion is activated.

FIG. 7 is a graph showing the relationship between the crank angle and the heat generation rate at high altitude (low intake pressure state) and normal time. In high altitude, that is, in a state where the O ₂ concentration in the intake air in the combustion chamber increases as a result of reducing the amount of EGR gas because the intake pressure is low, combustion occurs rapidly, so the heat generation rate rises rapidly. Therefore, at high altitude, a pressure gradient (indicating the amount of change in the cylinder pressure relative to the amount of change in the crank angle as compared with the normal time, that is, the state where the intake pressure is higher and the EGR gas amount is relatively large) dP / dθ, hereinafter simply referred to as pressure gradient).

  When the pressure gradient becomes large in this way, there is a problem that NOx increases or combustion noise increases. On the other hand, when the injection pressure is lowered in order to reduce combustion noise, there is a problem that the fuel injection amount is reduced, smoke is generated, and torque cannot be maintained.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to control a compression ignition internal combustion engine that prevents an increase in NOx and noise even when the intake pressure is low and maintains good drivability. Is to provide.

  The invention according to claim 1, which has been made to solve the above-described problem, includes an EGR means for recirculating a part of the exhaust gas taken out from the exhaust passage as EGR gas to the intake passage, and injects and supplies fuel into the combustion chamber. And a control device for a compression ignition type internal combustion engine. The control device also includes an intake pressure detection means for detecting the intake pressure in the intake passage.

The EGR rate is changed according to the detected intake pressure, and the fuel injection timing is shifted to the retarded side according to the detected degree of decrease in the intake pressure.
With the control device configured as described above, when the intake pressure in the intake passage decreases, the EGR rate is reduced to ensure the intake amount and to delay the fuel injection timing.

  Normally, fuel injection is performed so that the piston is ignited at a timing near the top dead center. This is because the temperature and pressure in the combustion chamber are highest at the timing when the piston is near the top dead center, and the fuel is most easily combusted. For this reason, if the fuel injection is shifted to the retarded side, the temperature and pressure in the combustion chamber are lowered from the top dead center, and the combustion activity is lowered.

Therefore, even if the EGR rate is decreased to prevent the intake air amount from decreasing due to a decrease in the intake pressure and the O ₂ concentration in the intake air is increased, the activation of the combustion is thereby controlled by the combustion timing. It can be canceled by suppressing the combustion activity by shifting to the retarded side. As a result, since rapid combustion can be prevented and the pressure gradient in the cylinder can be reduced, NOx and noise can be reduced without limiting the fuel injection amount and lowering the torque.

Thus, with the above control device, even when the intake pressure is low, increases in NOx and noise can be prevented and good drivability can be maintained.
The invention according to claim 2 is the control apparatus for the compression ignition type internal combustion engine according to claim 1, wherein the pressure gradient when the intake pressure is the first pressure and the intake pressure is higher than the first pressure. The fuel injection timing is shifted so that the pressure gradient in the case of the low second pressure is closer than that in the case where the fuel injection timing is not shifted.

  With the control device configured as described above, even if the intake pressure decreases, the pressure gradient that is the change amount of the in-cylinder pressure with respect to the change amount of the crank angle is set to a pressure gradient close to that before the intake pressure decreases. Therefore, noise can be reduced to the same extent as before the intake pressure decreases.

  A third aspect of the present invention is a control apparatus for a compression ignition type internal combustion engine according to the first or second aspect of the present invention, which has a control map or a relational expression showing the relationship between the intake pressure and the fuel injection timing. The fuel injection timing is set based on the detected intake pressure and the control map or the relational expression.

  With the control device configured as described above, an appropriate fuel injection timing can be determined based on a control map or a relational expression. Note that the control map and the relational expression are created in advance so as to have appropriate values through experiments or the like.

  According to a fourth aspect of the present invention, there is provided the control device for a compression ignition type internal combustion engine according to any one of the first to third aspects, wherein the setting of the fuel injection timing according to the degree of decrease in the intake pressure is made rich. It is performed at the time of combustion.

  With the control device configured as described above, the above-described fuel injection timing control is performed only at the time of rich combustion that requires sufficient intake air and easily generates noise due to an increase in oxygen concentration. Therefore, it is possible to effectively suppress noise during rich combustion in which combustion is activated and noise is generated when the intake pressure decreases.

Block diagram showing the engine control system Flow chart of fuel injection timing control routine Control map showing fuel injection timing Graph showing the relationship between crank angle, injection pulse and heat generation rate Graph showing the relationship between crank angle and in-cylinder pressure Conceptual diagram showing the structure of the intake system Graph showing the relationship between conventional crank angle and heat generation rate

Embodiments of the present invention will be described below with reference to the drawings.
(1) Overall Configuration An embodiment embodying the present invention will be described below with reference to the drawings. The engine control system 1 targets a four-cylinder diesel engine as a vehicle engine, for example, and performs fuel injection control and the like with an electronic control unit (hereinafter referred to as ECU) as a center. First, an overall schematic configuration diagram of the engine control system will be described with reference to FIG. In FIG. 1, only one cylinder is shown as a representative.

  In the engine 10 shown in FIG. 1, the intake pipe 11 is provided with a throttle valve 12 whose opening is adjusted by an actuator such as a DC motor, and a throttle opening sensor 13 for detecting the throttle opening. Although not shown, the intake pipe 11 is branched downstream of the EGR valve 36 and connected to the intake port of each cylinder of the engine 10.

An intake pressure sensor 14 is attached to the intake pipe 11 to detect the intake pressure in the intake pipe 11 and output it to the ECU 60.
The engine 10 is provided with an injector 15 for each cylinder. The injector 15 is connected to a common rail 16 common to each cylinder, and a high-pressure pump 17 is connected to the common rail 16. When the high-pressure pump 17 is driven, fuel is pumped up from a fuel tank (not shown), and high-pressure fuel is continuously accumulated in the common rail 16. The common rail 16 is provided with a common rail pressure sensor 18 that detects the fuel pressure in the common rail 16.

  An intake valve 21 and an exhaust valve 22 are provided at an intake port and an exhaust port of the engine 10, respectively. The intake air is introduced into the combustion chamber 23 by the opening operation of the intake valve 21 and is combusted together with the fuel injected and supplied from the injector 15. The exhaust gas after combustion is discharged to the exhaust pipe 31 by opening the exhaust valve 22.

A diesel particulate filter (DPF) 32 that collects PM (particulate matter) contained in the exhaust gas and a lean NOx trap (LNT) 33 are provided downstream of the exhaust pipe 31. The LNT 33 stores the exhausted NOx during lean combustion, and performs rich combustion when the stored NOx exceeds a predetermined value, thereby purging the stored NOx and re-storing the exhausted NOx. Make it possible. Further, NOx undergoes a reduction reaction with HC and CO in the exhaust when released, and is reduced to O ₂ and N ₂ .

  The engine 10 is provided with an exhaust gas recirculation device (EGR device) for recirculating a part of the exhaust gas as EGR gas to the intake system. That is, an EGR pipe 34 is provided between the downstream portion of the throttle valve 12 of the intake pipe 11 and the exhaust pipe 31. The EGR pipe 34 is provided with an EGR cooler 35 that cools the EGR gas that is circulated, and an EGR valve 36 that adjusts the EGR gas ring flow rate is provided at a connection portion between the EGR pipe 34 and the intake pipe 11. By circulating the EGR gas to the intake system, the combustion temperature is lowered and the generation of NOx is suppressed. The opening degree control of the EGR valve 36 is executed by the ECU 60 based on the engine operating state such as the engine load and the engine speed.

  An in-cylinder pressure sensor 51 that detects the pressure in the combustion chamber 23 is installed in the combustion chamber 23 of the engine 10. In addition, the engine control system includes an air-fuel ratio sensor 52 that detects the oxygen concentration of exhaust gas, and a crank angle sensor 53 that outputs a rectangular crank angle signal at every predetermined crank angle of the engine 10 (for example, at a cycle of 30 ° CA). Further, an accelerator opening sensor 54 for detecting an accelerator operation amount (accelerator opening) by the driver is provided.

  As is well known, the ECU 60 is composed mainly of a microcomputer composed of a CPU, ROM, RAM, etc., and executes various control programs stored in the ROM, thereby injecting fuel according to the engine operating state each time. Various controls of the engine 10 such as control are performed. The ECU 60 includes the throttle opening sensor 13, the intake pressure sensor 14, the common rail pressure sensor 18, the in-cylinder pressure sensor 51, the air-fuel ratio sensor 52, the crank angle sensor 53, and the accelerator opening sensor that are described above as information representing the engine operating state. Each detection signal from 54 etc. is inputted.

  Further, the ECU 60 acquires the ignition timing in the combustion chamber 23 based on the detection signal from the in-cylinder pressure sensor 51. Specifically, the in-cylinder volume that changes every time the piston moves up and down is obtained based on the detection signal from the crank angle sensor 53, and the heat generation rate is calculated from the in-cylinder volume and the in-cylinder pressure obtained from the in-cylinder pressure sensor 51. calculate. Then, the timing at which the heat generation rate exceeds a predetermined reference value is acquired as the ignition timing.

Further, the ECU 60 performs rich combustion in order to purge NOx stored in the LNT 33. Then, the following combustion injection timing control is executed so that the torque can be maintained even when rich combustion is performed when the intake pressure is low.
(2) Control during rich combustion under low intake pressure conditions (2.1) EGR rate control When the intake pressure is low, such as at high altitudes, the upstream pressure Pa decreases as shown in FIG. As a result, the intake air amount decreases. When the ECU 60 detects a decrease in the intake pressure from the output value of the intake pressure sensor 14, the EGR rate is decreased and the EGR gas amount is decreased, thereby reducing the downstream pressure of the throttle valve, and the pressure difference ΔP is equal to the normal case. The control to maintain is executed.
(2.2) Fuel Injection Timing Control A flowchart of a fuel injection timing control routine executed by the ECU 60 of the engine 10 is shown in FIG. The fuel injection timing control routine is executed at predetermined intervals, but the calculated fuel injection timing is applied only when rich combustion is performed when the intake pressure is low. During lean combustion, fuel injection is controlled in the same manner as in normal times regardless of the intake pressure. In FIG. 2, S indicates a step.

The ECU 60 first detects the intake pressure (S1). Here, the intake pressure in the intake pipe 11 is acquired from the output signal of the intake pressure sensor 14.
As another routine, the fuel injection amount required for rich combustion is set based on the accelerator opening and the engine speed. Further, the EGR gas amount is set with reference to the calculated fuel injection amount and the detected intake pressure.

Subsequently, the target ignition timing is determined (S2).
As shown in FIG. 3, the ROM stores a control map in which intake pressure and target ignition timing are associated with each other. The control map of the present embodiment is set so that the target ignition timing is delayed as the intake pressure decreases, and the injected fuel burns with the same combustion waveform as before the intake pressure decreases. A plurality of control maps are stored so that they can be appropriately changed according to the fuel injection amount, and an appropriate map is selected according to the fuel injection amount determined in the processing of another routine.

  Note that the corresponding fuel injection timing is preset for the target ignition timing determined by the control map, and the ECU 60 operates the injector 15 and the like so as to inject fuel at the fuel injection timing.

Next, the ignition timing is detected (S3). Here, the ignition timing of the combustion performed immediately before is detected based on the detection signal output from the in-cylinder pressure sensor 51.
Next, the ignition timing detected in S3 or S5 described later is compared with the target ignition timing, and the fuel injection timing is changed to match the target ignition timing (S4). Specifically, the ignition timing detected in S3 is compared with the target ignition timing determined from the control map of FIG. 3, and if the ignition timing detected in S3 is earlier, the output timing of the injection pulse is retarded, If the ignition timing is late, the output timing of the injection pulse is advanced.

  Then, it is determined whether or not the ignition timing detected in S3 is the target ignition timing (S5). If the ignition timing is not within a predetermined range that can be regarded as equivalent to the target ignition timing (S5: NO), the process returns to S3, and the ignition timing is detected again.

On the other hand, if the detected ignition timing is within a predetermined range from the target ignition timing (S5: YES), this process ends.
(3) Action and Effect FIG. 4 is a graph showing the relationship between the injection pulse, the heat generation rate, and the crank angle. When the intake pressure is a normal value, a pulse signal is output to the drive circuit of the injector 15 at the timing A in the figure in accordance with the timing when the crank angle becomes TDC (top dead center) to cause fuel injection ( Injection pulse 1). As a result, a combustion waveform having a heat generation rate of 1 in the figure is formed at the normal time when the intake pressure is a normal value.

  By the way, when performing rich combustion under conditions of low intake pressure such as during high altitude traveling, it is necessary to supply the same amount of air to the engine as the normal amount of air in order to maintain the torque. It is necessary to maintain the differential pressure before and after the throttle valve 20 at the same value as in normal times.

  In the engine control system 1 of the present invention, when the pressure upstream of the throttle valve 20 (intake pressure) decreases, the above-described differential pressure is maintained by performing control to reduce the recirculation amount of EGR gas on the downstream side. In the case of an engine equipped with a VNT (variable nozzle turbo), it is possible to increase the intake pressure to a normal value. However, if the turbo function cannot be fully exhibited, such as when the engine speed is low. As described above, it is necessary to reduce the amount of EGR gas.

If the amount of EGR gas is reduced, the O ₂ concentration of the air sucked into the combustion chamber 23 increases, so that combustion becomes active as it is, and the heat generation rate rises rapidly. However, in the engine control system 1 of the present invention, since the output timing of the injection pulse is delayed as indicated by B in FIG. 4, the injected fuel has a crank angle delayed from TDC, and the temperature in the combustion chamber 23, Combustion is performed in a state where the pressure is reduced, and the activity of combustion is reduced.

As a result, even if the O ₂ concentration in the intake air is increased due to the decrease in the EGR rate, the activation of combustion caused by this will be canceled out by the decrease in activity caused by shifting the combustion timing to the retarded side. As in the case of heat generation rate 2 in FIG. 4, the timing is delayed from the normal heat generation rate 1 as in the case of heat generation rate 1 (to be precise, the noise is adjusted in order to move to the retarded side. (It is necessary to make the combustion slightly more active than the time).

  FIG. 5 is a graph showing changes in the cylinder pressure with respect to the crank angle. The in-cylinder pressure corresponding to the heat generation rate 1 in FIG. 4 in a normal state has a waveform like the in-cylinder pressure 1 in FIG. In the engine control system 1 of the present invention, the in-cylinder pressure has a waveform like the in-cylinder pressure 2 because the timing at which the heat generation rate increases is slower than normal. At this time, the pressure gradient (dP / dθ) indicating the change amount of the in-cylinder pressure with respect to the change amount of the crank angle is the same value for the in-cylinder pressure 1 and the in-cylinder pressure 2, thereby suppressing an increase in combustion noise. it can.

  Therefore, even when the intake pressure is low, such as at high altitudes, it is possible to maintain good drivability and prevent an increase in noise without performing control to reduce the fuel injection pressure and the fuel injection amount.

  Further, with the engine control system 1 having the above-described configuration, the fuel injection timing control described above is performed only at the time of rich combustion that requires sufficient intake and is likely to generate NOx and noise due to an increase in oxygen concentration. And noise can be prevented.

On the other hand, in the conventional configuration in which the fuel injection timing control is not performed as in the engine control system 1 of the present invention, when the intake pressure is lowered due to high altitude traveling, if the EGR rate is decreased to reduce the amount of reflux EGR gas, Since the O ₂ concentration in the air increases, combustion becomes active and the heat generation rate rises abruptly. As a result, a combustion waveform like the heat generation rate 3 in FIG. 4 is formed.

The in-cylinder pressure at this time rapidly increases due to the influence of the heat generation rate that suddenly increases, as shown by the in-cylinder pressure 3 in FIG. . Therefore, NOx and combustion noise increase by increasing the pressure gradient in this way.
(4) Modifications The embodiment of the present invention has been described above. However, the present invention is not limited to the above embodiment, and can take various forms as long as it belongs to the technical scope of the present invention. Needless to say.

  For example, in the above-described embodiment, the configuration in which the ignition timing is used as an index indicating the combustion timing is exemplified, but other indexes may be used. For example, a combustion mass ratio 50 period (MFB50: Mass Fraction Burned 50) at which the combustion mass ratio in the cylinder becomes 50% of the whole in one combustion cycle is detected based on the in-cylinder pressure of the combustion chamber 23, and that timing is detected. It may be used as The MFB 50 integrates the combustion mass of one combustion cycle based on the in-cylinder pressure, and detects it as a combustion timing that is 50% of the total combustion mass.

  In the above embodiment, the fuel injection timing is determined using the control map shown in FIG. 3 used for the fuel injection timing control. However, the control map and a predetermined relational expression are used to determine the detected intake pressure. The retard amount of the fuel injection timing may be calculated, and the retard amount may be added to the fuel injection timing derived from the control map that does not take the intake pressure into consideration, and the fuel injection may be executed.

DESCRIPTION OF SYMBOLS 1 ... Engine control system, 10 ... Engine, 11 ... Intake pipe, 12 ... Throttle valve, 13 ... Throttle opening sensor, 14 ... Intake pressure sensor, 15 ... Injector, 16 ... Common rail, 17 ... High pressure pump, 18 ... Common rail pressure Sensor, 21 ... Intake valve, 22 ... Exhaust valve, 23 ... Combustion chamber, 31 ... Exhaust pipe, 32 ... DPF, 33 ... LNT, 34 ... EGR pipe, 35 ... EGR cooler, 36 ... EGR valve, 51 ... In-cylinder pressure sensor 52 ... Air-fuel ratio sensor, 53 ... Crank angle sensor, 54 ... Accelerator opening sensor

Claims (4)

A control device for a compression ignition internal combustion engine, comprising: EGR recirculation means for recirculating a part of exhaust gas taken out from an exhaust passage as EGR gas to an intake passage; and fuel injection means for injecting and supplying fuel into a combustion chamber. ,
Intake pressure detecting means for detecting intake pressure in the intake passage;
EGR control means for changing the EGR rate by the EGR recirculation means according to the intake pressure detected by the intake pressure detection means;
A control device for a compression ignition type internal combustion engine, comprising: fuel injection timing setting means for shifting the fuel injection timing to a retarded side in accordance with the degree of decrease in the intake pressure detected by the intake pressure detection means . The fuel injection timing setting means shifts the fuel injection timing between a pressure gradient when the intake pressure is the first pressure and a pressure gradient when the intake pressure is the second pressure lower than the first pressure. 2. The control device for a compression ignition type internal combustion engine according to claim 1, wherein the fuel injection timing is shifted so as to be close to that in the case where there is not. The fuel injection timing setting means has a control map or a relational expression showing the relationship between the intake pressure and the fuel injection timing, and the intake pressure detected by the intake pressure detecting means and the control map or the relational expression. The fuel injection timing is set based on the following. The control apparatus for a compression ignition type internal combustion engine according to claim 1 or 2. The compression ignition type according to any one of claims 1 to 3, wherein the fuel injection timing setting means sets the fuel injection timing according to the degree of decrease in the intake pressure during rich combustion. Control device for internal combustion engine.

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