JP4765699B2 - Reciprocating internal combustion engine control method - Google Patents

Description

  The present invention relates to a reciprocating internal combustion engine including a variable compression ratio mechanism capable of changing a nominal compression ratio.

In a reciprocating internal combustion engine, when starting and running in a high altitude where the air density is low and the atmospheric pressure is low, the intake charge amount of the combustion chamber, that is, the compressed air density is insufficient, leading to a reduction in engine output and combustion stability. There is a problem. Therefore, in Patent Document 1, when the atmospheric pressure is low, such as when traveling at a low temperature and high altitude, the valve overlap amount of the intake / exhaust valves is increased by the variable valve timing mechanism in order to eliminate the engine output shortage. Correction to the side. Further, in Patent Document 2, torque shock at the time of switching is avoided by switching the valve timing of the intake valve at a timing at which the flow velocity of the intake air passing through the throttle valve does not change, and the valve timing is switched as the air density is lower. The switching intake charge amount is corrected to the lower side.
JP-A-10-141098 Japanese Patent Laid-Open No. 5-44503

  However, if the valve overlap is increased when the atmospheric pressure is low and the air density is low as in the above-described Patent Document 1, starting performance may be reduced due to an increase in the in-cylinder residual gas. Further, although the technique of Patent Document 2 can reduce the torque shock at the time of switching the valve timing regardless of the difference in air density between the flat ground and the high ground, it can be adapted to the air density such as insufficient engine output at the high ground where the air density is low. It is not possible to reduce fluctuations in engine output (torque). In particular, when starting an engine at a high altitude where the air density and atmospheric pressure are low, the combustion pressure torque decreases due to the decrease in compressed air density, and the influence of negative work such as mechanical friction increases, resulting in a longer complete explosion time. Therefore, it has become difficult to obtain good starting stability, and countermeasures have been desired.

The present invention has been made in view of such problems, and is a control method for a reciprocating internal combustion engine including a variable compression ratio mechanism that changes the nominal compression ratio of the reciprocating internal combustion engine, and an ignition switch is provided. A first step for determining whether or not the ignition switch is on; a second step for detecting an atmospheric pressure after the ignition switch is determined to be on in the first step; and a detection in the second step. A third step of setting a target compression ratio based on the atmospheric pressure, a fourth step of driving and controlling the variable compression ratio mechanism toward the target compression ratio set in the third step, A fifth step of determining whether or not the actual compression ratio has reached the target compression ratio by drive control in step 4, and after determining that the actual compression ratio has reached the target compression ratio in the fifth step Whether the starter switch is on And a seventh step of starting cranking after it is determined that the starter switch is turned on in the sixth step, and the starter switch is not turned on in the sixth step. If it is determined, the process is returned to the second step .

  As is well known, the “nominal compression ratio” is a geometric compression ratio defined by the ratio of the sum of the clearance volume of the combustion chamber and the piston stroke volume and the clearance volume, and the effective compression ratio. Unlike the intake / exhaust valve opening / closing timing, it does not change.

  According to the present invention, the variable compression ratio mechanism that can change the nominal compression ratio of a reciprocating internal combustion engine is used, and the target compression ratio is corrected according to the air density (atmospheric pressure), thereby reducing the air density. Variations in the compressed air density in the combustion chamber due to this can be reduced / eliminated, and consequently fluctuations in engine output can be reduced / prevented. Therefore, for example, even when starting at a high altitude with a low air density, it is possible to ensure combustion stability and improve engine startability. In addition, since the nominal compression ratio is manipulated by a variable compression ratio mechanism, for example, an increase in pump loss or combustion stability associated with a change in valve timing is achieved, compared to a case where an effective compression ratio is manipulated using a variable valve timing mechanism. There is no trade-off demerit such as loss of performance.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a system configuration diagram of a control device for a reciprocating internal combustion engine according to an embodiment of the present invention. Here, as a variable compression ratio mechanism that makes the nominal compression ratio of the reciprocating internal combustion engine variable, a variable using a multi-link piston-crank mechanism in which the piston 3 and the crank pin 8 of the crankshaft 7 are linked by a plurality of links. A compression ratio mechanism 21 is shown. The variable compression ratio mechanism 21 is known as disclosed in Japanese Patent Application Laid-Open No. 2003-90409 and the like, and only a brief description will be given here.

  The variable compression ratio mechanism 21 includes an upper link 5 having one end connected to a piston 3 sliding in the cylinder 2 of the cylinder block 1 via a piston pin 4, and a connection pin 6 connected to the other end of the upper link 5. The lower link 9 is rotatably connected to the crankpin 8 of the crankshaft 7 and one end is connected to the lower link 9 via the connection pin 10 in order to limit the degree of freedom of the lower link 9. A control link 11 connected to the cylinder block 1 so that the other end is swingably supported. The swing support position of the control link 11 is an eccentric cam portion of the control shaft 12 (control eccentric shaft). Part) 13 is variably controlled by 13. The control shaft 12 is disposed in parallel with the crankshaft 7 and is supported on the cylinder block 1 so as to be swingable. The rotational position of the control shaft 12 is changed and held by a hydraulic or electric actuator 22.

  By changing the rotational position of the control shaft 12, the motion restraint condition of the lower link 9 by the control link 11 changes, and the nominal compression ratio ε changes continuously with the stroke displacement of the piston 3. According to such a variable compression ratio mechanism 21, in addition to being able to change the nominal compression ratio continuously and steplessly according to the engine operating state, the piston stroke characteristic itself is brought close to a preferable characteristic, for example, a characteristic close to simple vibration. Can do. Further, by connecting the control link 11 to the lower link 9, the control shaft 12 can be disposed obliquely below the crankshaft 7 having a relatively large space, and the engine mountability is excellent.

  The engine control unit 20 has a function of storing and executing various control processes. The engine control unit 20 outputs a control signal corresponding to a target compression ratio tε described later to the actuator 22, and the variable compression ratio mechanism 21 to the target compression ratio tε. Drive control toward. This compression ratio control is performed based on engine operating conditions. Typically, the compression ratio control is performed toward the low compression ratio side so as to avoid knocking as the engine load increases. Further, as one of various sensors for detecting the engine operating state, an atmospheric pressure sensor 23 for detecting atmospheric pressure is provided in this embodiment. The atmospheric pressure sensor 23 is installed in the vicinity of the canister, for example.

  FIG. 2 is a flowchart showing the flow of control when the engine is started according to this embodiment. When the ignition switch (IGNSW) is turned on (ON), the process proceeds from step S1 to step S2, and the atmospheric pressure detected by the atmospheric pressure sensor 23 is read. In step S3, the target compression ratio tε is set (corrected) based on the atmospheric pressure. Specifically, tε is set using a control map (table) showing a correlation with a preset atmospheric pressure-target compression ratio tε as shown in FIG. As shown in FIG. 3, the reference compression ratio tε0, which is the target compression ratio for starting at standard atmospheric pressure, is corrected toward the lower side as the atmospheric pressure increases, and the lower the atmospheric pressure, the higher the atmospheric pressure. The target compression ratio tε is corrected to the increase side.

  Referring to FIG. 2 again, in step S4, drive control of the variable compression ratio mechanism 21 toward the target compression ratio tε set in step S3 is performed. In step S5, it is determined whether the target compression ratio tε has been controlled, that is, whether the compression ratio operation by the variable compression ratio mechanism 21 toward tε has been completed. This determination may be performed using, for example, a sensor that detects the angle of the control shaft 12, or may be determined more simply based on whether a predetermined time has elapsed.

  If it is determined that the operation to the target compression ratio tε is completed, the process proceeds from step S5 to step S6, and it is determined whether the starter switch (STSW) is on. When the starter switch is turned on, the process proceeds from step S6 to step S7, and cranking, that is, engine start is started.

  FIG. 5 shows a time chart at the time of high altitude start according to the present embodiment. As shown in the figure, at the time T0 when the ignition switch is switched from OFF to ON, in a situation where the atmospheric pressure is lower than the standard atmospheric pressure and the air density is low, prior to the start of engine start by cranking (T1), The target compression ratio tε is corrected to the increase side with respect to the reference target compression ratio tε0, and the variable compression ratio mechanism 21 is driven and controlled toward the target compression ratio tε. After the control to the target compression ratio tε is completed, cranking, that is, engine start is started by turning on the starter switch (T1).

  Here, the starting fuel increase amount (fuel injection amount) until the completion of engine start (T2) is set (corrected) according to the atmospheric pressure. Specifically, as shown in FIG. 4, fuel vaporization is promoted as the atmospheric pressure is lower than the reference fuel increase TP0 for starting, which is a reference in the state of standard atmospheric pressure. The fuel increase is corrected to the lower side by the amount of decrease. As a result, it is possible to improve fuel consumption, purify exhaust, and the like. Further, as shown in FIG. 5, the starting ignition timing until the completion of engine starting (T2) is corrected to the retarded side as compared to when the atmospheric pressure is in the standard state in order to improve the combustion stability. The

  As described above, in this embodiment, by correcting the target compression ratio tε according to the atmospheric pressure, the variation in the compressed air density in the combustion chamber due to the magnitude of the atmospheric pressure is reduced / eliminated, and the fluctuation of the engine output is consequently reduced. It can be reduced / prevented. In particular, when starting at a high altitude where the atmospheric pressure is low, the target compression ratio tε is corrected to increase according to the detection signal of the atmospheric pressure sensor 23, so that a compressed air density substantially equal to the standard atmospheric pressure state is ensured. It is possible to solve the shortage of engine output. For this reason, the combustion stability at the time of starting at high altitude is improved, and the starting time is sufficiently shortened (Δα) as compared with the case where the target compression ratio tε is not corrected as shown by the broken line in FIG. The start response can be improved.

  Further, since the operation toward the target compression ratio tε is performed prior to the start of engine start (cranking), cranking may start before the actual compression ratio is converted to the target compression ratio tε. The starting stability is further improved. Moreover, since the nominal compression ratio is manipulated by the variable compression ratio mechanism 21, for example, an increase in pump loss or combustion due to a change in the valve timing is compared with that in which the effective compression ratio is manipulated using a variable valve timing mechanism. There is no trade-off disadvantage such as a decrease in stability.

  An example of control in which such setting / correction control of the target compression ratio tε is also applied during normal engine operation is shown in FIG. This routine is repeatedly executed at predetermined intervals by the engine control unit 20n. In step S11, the atmospheric pressure detected by the atmospheric pressure sensor 23 is read. In step S12, the engine required load set mainly based on the accelerator opening APO is read. In step S13, the target compression ratio tε is set (corrected) based on the required load and the atmospheric pressure with reference to a preset control map as shown in FIG. The variable compression ratio mechanism 21 is driven and controlled toward the target compression ratio tε set in this way.

  As shown in FIG. 7, the target compression ratio tε is basically set to be lower for avoiding knocking as the required load becomes higher, and to be set higher for improving the charging efficiency as the required load becomes lower. The target compression ratio tε is corrected to the lower side as the atmospheric pressure becomes higher than the standard state so as to obtain a compressed air density equivalent to the standard state at the standard atmospheric pressure, and to the higher side as the atmospheric pressure becomes lower. It is corrected. Therefore, similarly to the above-described engine start, regardless of the atmospheric pressure state, a compressed air density equivalent to the standard state can be secured, and fluctuations in the engine output due to a difference in atmospheric pressure can be suppressed.

  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 case of a reciprocating internal combustion engine equipped with a supercharger, the target compression ratio may be corrected in consideration of changes in air density due to supercharging.

1 is a system configuration diagram showing a control device for a reciprocating internal combustion engine according to an embodiment of the present invention. The flowchart which shows the flow of control at the time of the engine starting which concerns on a present Example. The control map used for setting the target compression ratio in the routine of FIG. The characteristic view which shows an example of the setting of the fuel increase amount for starting. The time chart at the time of the highland start which concerns on a present Example. The flowchart which shows the flow of the setting process of the target compression ratio in the engine driving | operation which concerns on a present Example. 7 is a control map used for setting a target compression ratio in the routine of FIG.

Explanation of symbols

20 ... Engine control unit 21 ... Variable compression ratio mechanism 23 ... Atmospheric pressure sensor (air density detecting means)

Claims (1)

A control method for a reciprocating internal combustion engine comprising a variable compression ratio mechanism for changing a nominal compression ratio of the reciprocating internal combustion engine,
A first step of determining whether an ignition switch is on;
A second step of detecting atmospheric pressure after it is determined in the first step that the ignition switch is on;
A third step of setting a target compression ratio based on the atmospheric pressure detected in the second step;
A fourth step of driving and controlling the variable compression ratio mechanism toward the target compression ratio set in the third step;
A fifth step of determining whether or not the actual compression ratio has reached the target compression ratio by the drive control of the fourth step;
A sixth step of determining whether or not the starter switch is on after it is determined that the actual compression ratio has reached the target compression ratio in the fifth step;
A seventh step of starting cranking after it is determined in the sixth step that the starter switch is on;
Consists, when the starter switch in the sixth step is determined to be not ON, the control method of the reciprocating internal combustion engine, characterized in that the process returns to the second step.

Images