JP4779757B2 - Control device and control method for internal combustion engine - Google Patents

Description

  The present invention relates to control of an internal combustion engine provided with valve timing changing means.

In Patent Document 1, in a two-cycle multi-cylinder engine, a scavenging amount is obtained based on the crank chamber pressure, and a fuel injection amount is set based on the scavenging amount and A / F (air-fuel ratio). Patent Document 2 discloses a technique for adjusting a scavenging amount in two-cycle operation by controlling valve timing in an engine that can switch between four-cycle operation and two-cycle operation.
Japanese Patent Laid-Open No. 4-311636 JP 2004-204745 A

  In a four-cycle internal combustion engine, in the valve overlap period in which both the intake valve and the exhaust valve are open, the cylinder residual gas is increased by the fresh air from the intake passage as the amount of fresh air blown from the intake passage to the exhaust passage increases. The so-called scavenging action is pushed out to the exhaust passage, the amount of residual cylinder gas remaining in the cylinder is reduced, the knock resistance is improved, and the engine output (torque) can be improved. However, the above scavenging action largely depends on the intake pressure and exhaust pressure, and it is sufficient to change the valve overlap amount by simply changing the intake / exhaust valve timing based on the engine speed and engine load. If the valve overlap amount is increased in a situation where the exhaust pressure becomes transiently high, for example, in an acceleration transition period in an internal combustion engine equipped with a turbocharger, the scavenging action is not always obtained. In-cylinder residual gas may increase.

The present invention has been made in view of such problems, and includes valve timing changing means capable of changing a valve overlap amount at which both the intake valve and the exhaust valve are opened, and is provided from the intake passage to the exhaust passage. The new air blow-off amount is estimated, and the valve overlap amount is controlled to increase as the estimated new air blow-off amount increases .

  According to the present invention, by controlling the valve overlap amount in accordance with the amount of new air blown directly related to the scavenging action, the scavenging action by the valve overlap is effectively utilized to reduce the in-cylinder residual gas amount. In addition, the filling efficiency can be improved.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a system configuration diagram of an internal combustion engine according to an embodiment of the present invention. This internal combustion engine 10 is a four-cycle spark ignition type multi-cylinder reciprocating engine, and for each cylinder, a spark plug 7 for spark-igniting an air-fuel mixture in the combustion chamber and fuel is injected into the combustion chamber (or intake port). A fuel injection valve 6 is provided. In the intake passage 11, in order from the upstream side, an air flow meter 2 that measures the intake air amount, a compressor 1 </ b> A of the turbocharger 1, an intercooler 3 that cools the intake air (supercharge), and an intake air amount A throttle 4 to be adjusted is disposed. Further, the exhaust passage 12 is provided with a turbine 1B of the turbocharger 1 and an A / F sensor 5.

  The throttle 4 is electrically controlled so that the opening degree can be adjusted independently of the operation of the accelerator pedal by the driver. As is well known, the turbocharger 1 rotates the exhaust turbine 1B with exhaust energy to drive a compressor 1A connected coaxially to supercharge intake air. The A / F sensor 5 is a wide-range air-fuel ratio sensor that outputs a signal (current value) that is substantially proportional to the oxygen concentration in the exhaust, and can perform air-fuel ratio feedback control even during lean combustion where the air-fuel ratio is lean. It is often used in recent lean burn engines.

  The internal combustion engine is also provided with an intake valve timing changing mechanism 21 that can change the opening / closing timing of the intake valve and an exhaust valve timing changing mechanism 22 that can change the opening / closing timing of the exhaust valve. These valve timing changing mechanisms 21 and 22 change the phase of the camshaft with respect to the crankshaft as is well known. An intake cam angle sensor 23 for detecting the phase of the intake camshaft corresponding to the opening / closing timing of the intake valve and an exhaust cam angle sensor 24 for detecting the phase of the exhaust camshaft corresponding to the opening / closing timing of the exhaust valve are provided. It has been.

  A control unit (engine control module: ECM) 13 is a digital computer having a function of storing and executing various control processes. In addition to the A / F sensor 5, the air flow meter 2, and the cam angle sensors 23 and 24, Based on detection signals from various sensors such as the crank angle sensor 14, control signals are output to the throttle 4, the fuel injection valve 6, the spark plug 7, the valve timing changing mechanisms 21, 22, and the like to control their operations.

FIG. 2 is a flowchart showing the flow of estimation control of the fresh air blow-off amount S 2 by the control unit 1 3. In step S 1 1, the engine speed N e, the crank angle (C A) that is the rotational position of the crankshaft (or camshaft), the intake air amount, and the like are read based on the detection signals from the various sensors. In step S 1 2, the exhaust gas flow rate with respect to the crank angle C A is read based on the engine speed N e and the intake air amount. For example, a control map as shown in FIG. 3 preset for each engine speed N e and intake air amount is read.

In step S13, the delay time until the exhaust gas discharged from the combustion chamber reaches the A / F sensor 5 with reference to a preset control map as shown in FIG. 4 based on the engine speed Ne. Td (ms) is calculated. In step S14, the delay on the basis of time and Td and the engine speed Ne and the crank angle CA, the period in which only the exhaust valve is opened, i.e. non-overlapping from the exhaust valve opening timing EV O to the intake valve opening timing IVO ( (O / L) The sampling time (ms) of the period Ta and the period during which both the intake valve and the exhaust valve are opened, that is, the overlap (O / L) period Tb from the intake valve opening timing IVO to the exhaust valve closing timing EVC (CA) sampling time (ms) is set. As shown in FIG. 5, the sampling time becomes shorter as the engine speed Ne becomes higher.

  In step S15, the A / F sensor 5 detects the oxygen concentration Ca in the non-O / L period Ta and the oxygen concentration Cb in the O / L period Tb in consideration of the response delay time Td. . Ca is the oxygen concentration per unit time that is sequentially detected in the non-O / L period Ta, and Cb is the average oxygen concentration in the O / L period Tb. Since a large amount of oxygen remains in the unburned fresh air blown from the intake passage 11 to the exhaust passage 12, as shown in FIG. 6, in the O / L period Tb in which fresh air is contained in the exhaust gas, the non-burning fresh air The oxygen concentration temporarily becomes higher than the O / L period Ta, and the output signal from the A / F sensor 5 that is proportional to the oxygen concentration becomes locally higher. The present invention has been made paying attention to this point, and is based on the oxygen concentration of the O / L period Tb and the non-O / L period Ta as described later with a simple configuration using the existing A / F sensor 5. Thus, the fresh air blow-through amount S2 blown from the intake passage 11 to the exhaust passage 12 is accurately estimated.

In step S16, the dilution concentration Ck in the O / L period Tb is calculated by the following equation (1). The dilution concentration Ck corresponds to the ratio of the amount of fresh air blown from the intake passage 11 to the exhaust passage 12 during the O / L period Tb with respect to the amount of exhaust gas (flow rate) discharged from the combustion chamber to the exhaust passage 12.
Ck = (Cb / Ca) −1 (1)
In step S17, based on the dilution concentration Ck and the exhaust gas amount set in step S12, a new air blow-off amount S2 that blows from the intake passage 11 to the exhaust passage 12 in the O / L period Tb is calculated. Specifically, for each extremely short calculation interval (for example, a predetermined crank angle), the amount of fresh air blow-out per unit time is sequentially calculated (Ck × exhaust gas flow rate), and these are integrated to make one cycle per cylinder. It is possible to accurately obtain the fresh air blow-through amount S2 at (see FIG. 7).

Figure 8 is a flow chart showing the control contents of the valve overlap amount using fresh air blow amount S 2 of the present embodiment (period). This routine is stored by the control unit 13 and is repeatedly executed every extremely short period (predetermined crank angle).

  In step S21, engine operating conditions such as engine speed Ne, crank angle (or cam angle), intake / exhaust valve opening / closing timing (camshaft phase) are read. In step S22, the target phase of the intake camshaft by the intake valve timing mechanism 21, that is, the target intake valve, based on the engine speed (and the engine load), for example, using a preset control map as shown in FIG. An opening timing tIVO (and an intake valve closing timing) and a target phase of the exhaust camshaft by the exhaust valve timing mechanism 22, that is, a target exhaust valve closing timing tEVC (and an exhaust valve opening timing) are set. In step S23, a valve overlap period (amount) rO / L in which both the intake valve and the exhaust valve are open is calculated based on the detection signals of the cam angle sensors 23 and 24 described above. Further, the valve overlap request amount tO / L is set with reference to a preset control map as shown in FIG.

  In step S24, it is determined whether the rO / L (or tO / L) exceeds a predetermined determination value sO / L. If the determination value sO / L is not exceeded, it is determined that a good scavenging action due to valve overlap cannot be obtained, and this routine is terminated. If rO / L (or tO / L) exceeds the determination value sO / L, the process proceeds to step S25, and the fresh air blow-off amount S2 obtained by the routine of FIG. 2 is read. In step S26, it is determined whether the fresh air blow-through amount S2 exceeds a predetermined determination value Sh. If the fresh air blow-through amount S2 exceeds the determination value Sh, the process proceeds to step S27, and a change ΔS of the fresh air blow-through amount S2 is calculated. Specifically, the change ΔS is obtained from the difference (S2−S2old) between the current fresh air blow-through amount S2 and the fresh air blow-through amount S2old one cycle before. In step S28, it is determined whether the fresh air blow-off amount S2 is increasing or decreasing based on the ΔS. Specifically, it is determined whether ΔS is a positive value exceeding 0 (zero) or a negative value.

  When it is determined that ΔS is a positive value and the fresh air blow-off amount S2 is increasing, the process proceeds to step S29, and the valve overlap increase amount a is set. This increase amount “a” is a fixed value set in advance, and is a small value so that the valve overlap amount does not fluctuate rapidly. In step S30, it is determined whether the intake valve opening timing IVO can be advanced. That is, it is determined whether the actual IVO detected by the tIVO or the intake cam angle sensor 23 is a value excluding the most advanced value. If the advance of the IVO is possible, the process proceeds to step S31, and the target intake valve opening timing tIVO is corrected to the advance side by the increment a. If the advance of the IVO is impossible, the process proceeds to step S32, and the target exhaust valve closing timing tEVC is retarded by the amount of increase a or the amount of advance of the IVO subtracted from the amount of increase a. to correct.

  When ΔS is a negative value and the fresh air blow-off amount S2 is decreasing, the process proceeds from step S28 to step S33, the valve overlap decrease amount b is set, and the process proceeds to step S34. This decrease amount b is a fixed value set in advance, as in the case of the above increase amount, and is a small value so that the valve overlap amount does not fluctuate rapidly. Further, when the fresh air blow-through amount S2 does not exceed the predetermined determination value Sh, the process proceeds from step S26 to step S37, and the valve overlap amount decrease amount c is set so that the valve overlap amount becomes 0 (zero). Set and proceed to step S34. This reduction amount c is set based on the above rO / L or tO / L.

  In step S34, it is determined whether the exhaust valve closing timing EVC can be advanced. That is, it is determined whether the actual EVC detected by tEVC or the exhaust cam angle sensor 24 is a value excluding the most advanced value. If the advance of EVC is possible, the process proceeds to step S35, and the target exhaust valve closing timing tEVC is corrected to the advance side by the amount of decrease b. If it is determined in step S34 that advancement of EVC is impossible, the process proceeds to step S36, and the target intake air amount is obtained by subtracting the advancement amount of EVC from the reduction amount b or c or the reduction amount b or c. Correct the valve opening timing tIVO to the retard side.

  Next, the effect of the present embodiment will be described with reference to the time charts of FIGS.

As exaggeratedly shown in FIG. 12, when the change ΔS of the fresh air blow-off amount is in the increasing direction, the valve overlap amount is gradually increased by the above steps S29 to S32. On the other hand, as shown in FIG. 1 1, the change ΔS in the fresh air flowing amount S2 is in the decreasing direction, the above steps S33 to S36, the valve overlap amount is reduced. Therefore, the amount of fresh air blown directly related to the scavenging action can be increased with high accuracy, the scavenging action is utilized to the maximum to reduce the residual gas amount in the cylinder, and the knocking performance and engine output (torque) performance. Can be improved. Moreover, since the valve overlap amount is increased or decreased based on the fresh air blow-off amount S2 obtained every cycle, it is extremely excellent in responsiveness, and good controllability can be obtained even in a situation such as an acceleration transition period. it can.

  Further, as shown in FIG. 11, when the fresh air blow-off amount S2 becomes equal to or less than the determination value Sh, the scavenging effect due to the valve overlap can no longer be expected, and conversely, the in-cylinder residual gas amount is increased by the blowback from the exhaust passage. Although there is a possibility of increase, according to the present embodiment, the valve overlap amount is reduced to 0 (zero) by the processing of steps S37 and S34 to S36 described above. There is no fear.

Thus, when reducing the valve overlap, first, the advancement of the exhaust valve closing timing EVC is preferentially performed by the processing of steps S3 4 to S3 6 as shown in FIG. Only when the advance of the exhaust valve closing timing EVC is impossible, the intake valve opening timing IVO is retarded. For this reason, it is possible to effectively suppress a decrease in charging efficiency due to the retarding of the intake valve opening timing IVO. Conversely, when increasing the valve overlap, in step S3 0 to S3 2 processing described above, as shown in FIG. 12, first, the advance of the intake valve opening timing IVO is performed preferentially, Only when the intake valve opening timing IVO cannot be advanced, the exhaust valve closing timing EVC is retarded. Therefore, the effect of improving the charging efficiency due to the advancement of the intake valve opening timing IVO can be fully utilized.

  As described above, the present invention has been described based on the specific embodiments. However, the present invention is not limited to the above-described embodiments, and includes various modifications and changes without departing from the spirit of the present invention. . For example, in the above embodiment, the present invention is applied to an in-cylinder injection type internal combustion engine that injects fuel directly into the combustion chamber. However, the present invention is not limited to this, and a port injection type internal combustion engine that injects fuel into an intake port. It is also possible to apply the present invention. In this case, fresh air blown from the intake passage to the exhaust passage becomes the air-fuel mixture. Even in this case, the fresh air blow-off amount can be estimated based on the oxygen concentration detected by the air-fuel ratio sensor as in the above embodiment. Further, in the above embodiment, the air-fuel ratio sensor 5 is arranged on the upstream side (near the combustion chamber) of the exhaust turbine 1B in order to eliminate the influence of the exhaust turbine 1B and increase the estimation accuracy of the fresh air blow-off amount. However, the installation position of the air-fuel ratio sensor is not limited to this, and may be arranged downstream of the exhaust turbine 1B, for example, when the estimation accuracy of the fresh air blow-off amount can be ensured.

1 is a system configuration diagram of an internal combustion engine to which one embodiment of the present invention is applied. The flowchart which shows the flow of estimation control of the fresh air blow-through amount of a present Example. The characteristic view which shows an example of the control map which shows the exhaust gas flow volume with respect to a crank angle. The characteristic view which shows an example of the control map which shows the relationship between an engine speed and response delay time. The characteristic view which shows an example of the control map which shows the relationship between an engine speed and sampling time. Explanatory drawing which shows the output change of the A / F sensor in a valve overlap period. Explanatory drawing which shows the output and exhaust gas flow volume of an A / F sensor. The flowchart which shows the flow of control of the valve overlap amount using the new air blow-through amount. The characteristic view which shows an example of the control map used for the setting of the target intake valve opening timing. The characteristic view which shows an example of the control map used for the setting of valve overlap requirement amount. The time chart for demonstrating the effect of a present Example. The time chart for demonstrating the effect of a present Example similarly .

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Turbocharger 5 ... Air-fuel ratio sensor (oxygen concentration detection means)
6 ... Fuel injection valve 7 ... Spark plug 11 ... Intake passage 12 ... Exhaust passage 13 ... Control unit 21 ... Intake valve timing changing mechanism (intake valve timing changing means)
22 ... Exhaust valve timing changing mechanism (exhaust valve timing changing means)
23 ... Intake cam angle sensor 24 ... Exhaust cam angle sensor

Claims (8)

A valve timing changing means capable of changing a valve overlap amount in which both the intake valve and the exhaust valve are opened; and
New air blow-through amount estimation means for estimating the amount of new air blow-through from the intake passage to the exhaust passage;
A control unit that controls the valve overlap amount to increase as the estimated amount of fresh air blown out increases,
A control apparatus for an internal combustion engine, comprising: The valve timing changing means has an intake valve timing changing means for changing the opening / closing timing of the intake valve, and an exhaust valve timing changing means for changing the opening / closing timing of the exhaust valve,
2. The control unit according to claim 1, wherein, when the valve overlap amount is decreased, the control unit prioritizes the advancement of the exhaust valve closing timing as compared with the retarding of the intake valve opening timing. Control device for internal combustion engine. The valve timing changing means has an intake valve timing changing means for changing the opening / closing timing of the intake valve, and an exhaust valve timing changing means for changing the opening / closing timing of the exhaust valve,
3. The control unit according to claim 1 or 2, wherein when the valve overlap amount is increased, the intake valve opening timing is advanced as compared with the retarding of the exhaust valve closing timing. The internal combustion engine control device described.   The control device for an internal combustion engine according to any one of claims 1 to 3, wherein the control unit sets the valve overlap amount to 0 when the fresh air blow-through amount is equal to or less than a predetermined determination value.   The controller determines whether the fresh air blow-through amount is increasing or decreasing, and increases the valve overlap amount when increasing, and decreases the valve overlap amount when decreasing. The control apparatus for an internal combustion engine according to any one of claims 1 to 4. Having oxygen concentration detecting means for detecting the oxygen concentration in the exhaust passage;
6. The control apparatus for an internal combustion engine according to claim 1, wherein the fresh air blow-off amount estimating means estimates a fresh air blow-off amount based on the oxygen concentration. An air-fuel ratio sensor for detecting the oxygen concentration in the exhaust passage;
A delay time calculating means for calculating a delay time until the exhaust gas discharged from the combustion chamber reaches the air-fuel ratio sensor based on the engine speed;
Based on the oxygen concentration in the exhaust passage detected by the air-fuel ratio sensor and the delay time detected by the delay time calculation means, oxygen in a non-overlap period in which only the exhaust valve opens during one cycle Oxygen concentration calculating means for calculating the concentration and the oxygen concentration in the overlap period in which both the intake valve and the exhaust valve are opened during one cycle;
Have
The fresh air blow-off amount estimating means sequentially estimates the fresh air blow-off amount in one cycle based on the oxygen concentration in the non-overlap period and the oxygen concentration in the overlap period. The control apparatus for an internal combustion engine according to claim 6. A control method for an internal combustion engine comprising valve timing changing means capable of changing a valve overlap amount in which both an intake valve and an exhaust valve are opened,
Estimate the amount of fresh air blown from the intake passage to the exhaust passage,
A control method for an internal combustion engine, wherein control is performed such that the valve overlap amount increases as the amount of fresh air blow-through increases.

Images