JP4998400B2 - Start control device for internal combustion engine - Google Patents

Description

  The present invention relates to an internal combustion engine start control device, and more particularly to a start control device suitable as a device for controlling the start of an internal combustion engine having functions of automatic stop and automatic start.

  Patent Document 1 discloses a system that automatically stops and automatically restarts an internal combustion engine during operation of a vehicle system. In eco-run vehicles and hybrid vehicles, it is not uncommon for the internal combustion engine to be automatically stopped or automatically started with the internal combustion engine sufficiently warmed up.

  The mixed gas sucked into the cylinder is more likely to self-ignite as the gas temperature increases. For this reason, when the internal combustion engine is automatically restarted, self-ignition of the in-cylinder gas is more likely to occur than during a normal start in a cold state.

  The system disclosed in Patent Document 1 performs control different from that during cold start in order to prevent self-ignition of fuel during restart at a high temperature. Specifically, this system reduces the actual compression ratio of the internal combustion engine by delaying the closing timing of the intake valve when restarting at a high temperature. If the actual compression ratio in the cylinder is lowered, an increase in gas temperature in the compression stroke is suppressed and self-ignition is unlikely to occur. For this reason, lowering the actual compression ratio at the time of high temperature restart is effective in preventing self-ignition of fuel.

  Further, Patent Document 1 discloses increasing the fuel injection amount as a technique for preventing self-ignition during high-temperature restart. As the fuel injection amount increases, the increase in in-cylinder temperature during the compression stroke is suppressed by increasing the latent heat of vaporization of the fuel. Fuel self-ignition is less likely to occur as the in-cylinder temperature is lower. For this reason, increasing the fuel injection amount at high temperature restart is also an effective technique for preventing self-ignition of fuel.

JP 2007-120448 A JP 2001-173488 A JP 2005-69049 A

  By the way, when the internal combustion engine is automatically restarted, the state of the internal combustion engine at the time of the restart is not always constant. For example, the piston positions of the individual cylinders are left to the outcome when the internal combustion engine is stopped, and are not always constant. Also, the temperature of the internal combustion engine at the time of restart varies depending on the engine temperature at the time of stop, the environmental temperature during the stop, and the duration of the stop, and is not always constant.

  Fuel self-ignition occurs when the temperature of the in-cylinder gas rises to the self-ignition generation temperature during the compression stroke. As the in-cylinder gas temperature in the stage before the start of compression increases, the temperature of the in-cylinder gas easily reaches the self-ignition generation temperature in the course of the compression stroke. For this reason, when the restart of the internal combustion engine is requested in an environment where the in-cylinder gas temperature is high before the compression starts, the self-ignition of the fuel is suppressed as compared with the case where the restart is requested in an environment where the temperature is low. It is likely to occur.

  When the restart of the internal combustion engine is requested, the system disclosed in Patent Document 1 determines whether or not it is in a high temperature environment that needs to suppress self-ignition, and when the determination is affirmed, Delay the closing timing of the intake valve (reduce the actual compression ratio) and increase the fuel injection amount. However, this system always reduces the actual compression ratio and increases the fuel injection amount under certain conditions without considering the state of the internal combustion engine in a high temperature environment.

  That is, in the system of Patent Document 1, even when the internal combustion engine is in a state where it is relatively difficult to generate self-ignition, if the determination of the high temperature environment is affirmative, the actual compression ratio is always assumed assuming the worst state. Is reduced and the fuel injection amount is increased. In this regard, the conventional system described above improves the fuel efficiency of the internal combustion engine by unnecessarily reducing the actual compression ratio or unnecessarily increasing the fuel injection amount when the internal combustion engine is automatically restarted. It had the aspect that it might be lowered.

  The present invention has been made to solve the above-described problems, and is an internal combustion engine that can effectively suppress self-ignition during restart without unnecessarily reducing the fuel efficiency of the internal combustion engine. An object is to provide a start control device.

In order to achieve the above object, a first invention is a start control device for an internal combustion engine,
Stop position detecting means for detecting the piston stop position;
Cylinder temperature detecting means for detecting the cylinder temperature;
Limit injection amount rule storage means for storing a limit injection amount rule established between the piston stop position and the cylinder temperature and a limit fuel injection amount that does not cause self-ignition combustion at the time of restart;
Limit injection amount calculation means for calculating the limit fuel injection amount by applying the detection value of the piston stop position and the detection value of the cylinder temperature to the limit injection amount rule;
Injection amount control means for controlling the fuel injection amount at the time of restart to an injection amount corresponding to the calculated value of the limit fuel injection amount , and
The limit injection amount rule is:
A pre-compression temperature rule established between the piston stop position and the cylinder temperature, and a pre-compression cylinder gas temperature that is a cylinder gas temperature immediately before the start of compression;
An injection amount conversion rule established between the in-cylinder gas temperature before compression and the limit fuel injection amount, and
The limit injection amount calculating means includes
Means for applying the detection value of the piston stop position and the detection value of the cylinder temperature to the pre-compression temperature rule, and calculating a pre-compression cylinder gas temperature at restart;
By applying the calculated value of the pre-compression cylinder gas temperature in the injection amount conversion rule, it means for calculating the limit fuel injection amount, characterized by Rukoto equipped with.

The second invention is the first invention, wherein
A variable valve mechanism that changes the closing timing of the intake valve;
A valve closing timing detecting means for detecting the valve closing timing of the intake valve,
The limit injection amount storage means stores a plurality of limit injection amount rules established under each of a plurality of valve closing timings of the intake valve,
The limit injection amount calculating means applies the detection value of the piston stop position, the detection value of the cylinder temperature, and the detection value of the valve closing timing to the plurality of limit injection amount rules, thereby limiting the limit fuel injection amount. Is calculated.

A third aspect of the present invention is the first or second inventions in Oite,
A start control device for an internal combustion engine having a plurality of cylinders,
When restarting the internal combustion engine, the first explosion cylinder detection means for detecting the first explosion cylinder capable of causing ignition combustion first among the plurality of cylinders,
The limit injection amount calculation means calculates the limit fuel injection amount based on a piston stop position of the initial explosion cylinder,
The injection amount control means controls the fuel injection amount to an injection amount corresponding to the calculated value of the limit fuel injection amount at the time of the first fuel injection to the first explosion cylinder when the internal combustion engine is restarted. Features.

According to the first aspect, when the restart of the internal combustion engine is requested, the limit fuel injection amount that does not cause the self-ignition combustion can be calculated based on the piston stop position and the cylinder temperature. Further, according to the present invention, the internal combustion engine can be restarted with the limit fuel injection amount. For this reason, according to the present invention, the internal combustion engine can be restarted without causing self-ignition with the minimum fuel injection amount according to the situation at the time of restart.
Further, according to the present invention, it is possible to calculate the in-cylinder gas temperature before compression based on the piston stop position and the cylinder temperature when the internal combustion engine is requested to restart. Furthermore, according to the present invention, the limit fuel injection amount can be calculated based on the calculated value of the in-cylinder gas temperature before compression.

  According to the second invention, when the restart of the internal combustion engine is requested, it is possible to calculate the optimum limit injection amount according to the piston stop position, the cylinder temperature, and the intake valve closing timing. Therefore, according to the present invention, even in a system in which the closing timing of the intake valve when the internal combustion engine is stopped varies depending on the function of the variable valve mechanism, self-ignition at the time of restart is performed with the minimum fuel injection amount. It can be effectively prevented.

According to the third aspect of the present invention, the limit fuel injection amount can be injected at the time of the first fuel injection to the first explosion cylinder capable of causing ignition combustion first among the plurality of cylinders. For this reason, according to the present invention, the internal combustion engine can be restarted with the minimum fuel injection amount without causing self-ignition most rapidly after the restart request is generated.

Embodiment 1 FIG.
[Configuration of the embodiment]
FIG. 1 is a diagram for explaining the configuration of the first embodiment of the present invention. As shown in FIG. 1, the system of the present embodiment includes an internal combustion engine 10. It is assumed that the internal combustion engine 10 is mounted on an eco-run vehicle or a hybrid vehicle. In these vehicles, when it is determined that the operation of the internal combustion engine 10 is unnecessary during operation of the vehicle system, the internal combustion engine 10 is automatically stopped. Thereafter, when the internal combustion engine 10 needs to be operated, the internal combustion engine 10 is automatically restarted. For this reason, in this embodiment, the internal combustion engine 10 shall be automatically stopped and automatically restarted as necessary.

  An intake passage 12 and an exhaust passage 14 communicate with the internal combustion engine 10. The combustion chamber 16 of the internal combustion engine 10 communicates with the intake passage 12 as the intake valve 18 opens and closes. A variable valve mechanism 20 is connected to the intake valve 18. The variable valve mechanism 20 can open and close the intake valve 18 in conjunction with the crank angle of the internal combustion engine 10 and change at least the closing timing of the intake valve 18. The variable valve mechanism 20 has a built-in position sensor that generates an output corresponding to the closing timing of the intake valve 18.

  In the present embodiment, the variable valve mechanism 20 is driven by a hydraulic pressure generated during operation of the internal combustion engine 10, and the valve opening characteristic of the intake valve 12 cannot be changed while the internal combustion engine 10 is stopped. . In the present embodiment, the variable valve mechanism 20 has a function of returning the closing timing of the intake valve 12 to a predetermined starting timing when the internal combustion engine 10 is stopped.

  The combustion chamber 16 of the internal combustion engine 10 communicates with the exhaust passage 14 as the exhaust valve 22 is opened and closed. A variable valve mechanism 24 is connected to the exhaust valve 22. The variable valve mechanism 24 can appropriately change the valve opening characteristic of the exhaust valve 22 using the hydraulic pressure of the internal combustion engine 10.

  An atmospheric pressure sensor 26 is provided in the intake passage 12 of the internal combustion engine 10. A throttle valve 28 is disposed downstream of the atmospheric pressure sensor 26. Further, a fuel injection valve 30 is assembled downstream of the throttle valve 28.

  The fuel injection valve 30 is supplied with fuel of a predetermined pressure from a fuel pump (not shown), and injects an amount of fuel corresponding to the valve opening time TAU. Therefore, the fuel injection amount for the internal combustion engine 10 can be controlled by the valve opening time TAU of the fuel injection valve 20.

  The internal combustion engine 10 has a piston 32 disposed in the cylinder. The position of the piston 32 can be detected by a crank angle sensor 34. The crank angle sensor 34 can detect the crank angle by a 720 ° CA (Crank Angle) system. Therefore, according to the output of the crank angle sensor 34, the position of the piston 32 can be detected by distinguishing between the intake stroke and the explosion stroke, and distinguishing between the exhaust stroke and the compression stroke.

  Further, a water temperature sensor 36 is assembled in the internal combustion engine 10. According to the water temperature sensor 36, the cooling water temperature THW of the internal combustion engine 10 can be detected. The various sensors and actuators described above are electrically connected to an ECU (Electronic Control Unit) 40. Therefore, the ECU 40 can detect the closing timing, the crank angle, the coolant temperature THW, and the like of the intake valve 18. Further, the ECU 40 can drive the variable valve mechanisms 20 and 24 and the fuel injection valve 30.

[Operation of Embodiment 1]
(Operational features)
The operation of the system according to this embodiment will be described below with reference to FIGS.
Fig. 2 shows the crank angle in the intake stroke, that is, the crank angle after the intake top dead center (intake ATDC, After Top Dead Center) and the intake bottom dead center (intake BDC, Bottom Dead Center). It shows the relationship with the amount of fresh air (intake volume). According to the relationship shown in FIG. 2, for example, it can be seen that the intake amount of fresh air generated in the process in which the piston 32 moves from the intake top dead center (Intake TDC, After Top Dead Center) to the intake BDC is about 450 cc. When the piston is located at intake ATDC 60 ° CA, about 150 cc of gas is already present in the cylinder, and then about 300 cc of fresh air is sucked in the process of moving the piston 32 to the intake BDC. I understand that

  The relationship shown in FIG. 2 can be specified for the type of the internal combustion engine 10. If this relationship is known with respect to the internal combustion engine 10, it is possible to detect at what ratio fresh air and residual gas are present in the cylinder at the time of restart, as will be described below. . That is, if the piston 32 is stopped at the position of, for example, intake ATDC 60 ° CA prior to restart, the ratio of fresh air (300 cc) to residual gas (150 cc) is 2: 1 during the restart. Can be detected.

  When the internal combustion engine 10 is started, the closing timing of the intake valve 18 is set to an appropriate crank angle within the compression stroke, that is, an appropriate crank angle after the intake bottom dead center (intake ABDC). ing. For this reason, after the piston 32 passes through the intake BDC, the in-cylinder gas flows backward into the intake passage 12 until the intake valve 18 is closed. During this time, the ratio of fresh air and residual gas in the cylinder does not change. Therefore, the gas ratio at the time when the intake valve 18 is closed becomes 2: 1, which is the same as the ratio in the intake BDC.

  When the internal combustion engine 10 is restarted, the gas existing in the cylinder when the intake valve 18 is closed for the first time after the restart is started is used for the first explosion. Hereinafter, this gas is referred to as “first explosion gas”. That is, when the internal combustion engine 10 is restarted, the initial explosion gas is confined in the cylinder when the intake valve 18 is closed for the first time, and thereafter, the compression of the initial explosion gas proceeds as the crank angle increases. In this process, the temperature of the initial explosion gas rises, and when the temperature reaches the self-ignition generation temperature, fuel self-ignition occurs in the cylinder. Hereinafter, the in-cylinder gas temperature immediately before the initial explosion gas starts to be compressed is referred to as “in-cylinder gas temperature before compression”.

  The in-cylinder gas temperature before compression is an important factor that determines whether self-ignition occurs in the initial explosion gas. In other words, if the in-cylinder gas temperature is high, the in-cylinder gas temperature easily reaches the self-ignition generation temperature in the course of compression, while if the in-cylinder gas temperature is low, the in-cylinder gas temperature is It is difficult to reach the self-ignition temperature. For this reason, it is effective to detect the in-cylinder gas temperature as a premise for preventing the self-ignition of the first explosion gas.

  Since the residual gas in the cylinder continues to be heated in the cylinder while the internal combustion engine 10 is stopped, the temperature becomes higher than that of fresh air. The in-cylinder gas temperature before compression is a temperature realized as a result of mixing these two kinds of gases, and is therefore mainly composed of three elements: fresh air temperature, residual gas temperature, and fresh air to residual gas ratio. Determined by.

  Of these three elements, the temperature of fresh air and the temperature of residual gas are mainly temperatures corresponding to the temperature of the internal combustion engine 10 itself, that is, the cooling water temperature THW. On the other hand, as described with reference to FIG. 2, the ratio of fresh air to residual gas is determined almost uniquely according to the piston stop position at the time of restart. For this reason, the in-cylinder gas temperature before compression can be estimated based on the coolant temperature THW at the time of restart and the piston stop position.

  FIG. 3 shows the relationship between the stop position of the piston 32 and the in-cylinder gas temperature using the cooling water temperature THW as a parameter. Specifically, the curve shown at the lowest position in FIG. 3 shows the relationship established between the piston stop position and the pre-compression cylinder gas temperature when the coolant temperature THW is 60 °. A plurality of curves shown above this curve respectively show the relationship between the two that is established under a higher cooling water temperature THW.

  As the piston stop position approaches the intake BDC (ATDC 180 ° CA), the ratio of the residual gas to the initial explosion gas increases. For this reason, the in-cylinder gas temperature becomes higher as the piston stop position is closer to the intake BDC, as shown in FIG. Further, the higher the cooling water temperature THW, the higher the temperature of fresh air and the temperature of the residual gas. For this reason, as shown in FIG. 3, the in-cylinder gas temperature becomes higher as the cooling water temperature THW is higher.

  The relationship shown in FIG. 3 can be specified in advance for the internal combustion engine 10 experimentally or by simulation. If this relationship is known, it is possible to predict the in-cylinder gas temperature before compression of the initial explosion gas based on the piston stop position and the coolant temperature THW when restarting the internal combustion engine 10 is requested. It is.

  By the way, the internal combustion engine 10 of the present embodiment has a plurality of cylinders. If the internal combustion engine 10 is a four-cylinder engine, for example, when the internal combustion engine 10 is stopped, the piston 32 of one cylinder always has an intake TDC (intake ATDC 0 ° CA) and an intake BDC (intake ATDC 180 ° CA). That is, it stops within the crank angle region shown in FIG.

  When the piston 32 of the cylinder is stopped in the region indicated by “2TDC” in FIG. 3, that is, in the region from the intake ATDC 0 ° CA to the intake ATDC 120 ° CA, the piston 32 reaches the intake BDC. A certain amount of fresh air can be sucked into the cylinder from the intake port. On the other hand, when the piston 32 is stopped in the region indicated as “lean misfire region” in FIG. 3, that is, in the region from the intake ATDC 120 ° CA to the intake ATDC 180 ° CA, the piston 32 becomes the intake BDC. By the time, the gas in the intake port can hardly be sucked into the cylinder until it reaches.

  The fuel injection valve 30 of the internal combustion engine 10 injects fuel into the intake port. For this reason, in order to supply fuel into the cylinder, it is necessary that the gas in the intake port is sucked into the cylinder to some extent. That is, in order to cause combustion in a cylinder of a certain cylinder, it is necessary that the gas in the intake port is sucked into the cylinder to some extent before the piston 32 of that cylinder reaches the intake BDC.

  In the four-cylinder engine, the pistons 32 of the four cylinders sequentially reach the compression TDC every 180 ° CA. For example, when the piston 32 of the # 1 cylinder has stopped in the region of “2TDC” shown in FIG. 3, after the internal combustion engine 10 is started, the piston 32 of the # 1 cylinder reaches the intake BDC. A certain amount of fresh air and fuel can be sucked into the cylinder.

  When the # 1 cylinder piston 32 reaches the intake BDC, the # 2 cylinder piston 32 reaches the compression TDC. At this time, since the fuel is not supplied to the # 2 cylinder, the first explosion cannot be caused in this cylinder. In this case, among the four cylinders, the cylinder that can generate the first explosion earliest (hereinafter referred to as “first explosion cylinder”) is the # 1 cylinder that has already sucked fuel into the cylinder at this time. Become. Here, the # 1 cylinder is the cylinder that reaches the compression TDC second after the restart of the internal combustion engine 10 is started. Hereinafter, the start in which the cylinder that reaches the second compression TDC as the first explosion cylinder becomes the first explosion cylinder as in this case is referred to as “2TDC” start.

  When the # 1 cylinder piston 32 is stopped in the “lean misfire region” shown in FIG. 3, after the internal combustion engine 10 is started, the piston 32 reaches the intake BDC in the cylinder. Insufficient fuel can not be inhaled. For this reason, in this case, it is impossible to cause the internal combustion engine 10 to perform the initial explosion when the piston 32 of the # 1 cylinder reaches the compression TDC. That is, in this case, the # 1 cylinder cannot be the first explosion cylinder, and the # 4 cylinder that has stopped the piston 32 immediately before the intake TDC becomes the first explosion cylinder. Hereinafter, as in this case, the start in which the cylinder (# 4 cylinder) that reaches the third compression TDC after the start of the internal combustion engine 10 becomes the first explosion cylinder is referred to as “3TDC” start.

  The system of this embodiment is intended to prevent self-ignition in the first explosion cylinder. For this reason, when a restart request for the internal combustion engine 10 is generated, the ECU 40 first specifies the first explosion cylinder. Specifically, first, it is determined whether the piston 32 of any cylinder is stopped in the “2TDC” region shown in FIG. As a result, if it is found that the piston 32 of any of the cylinders is stopped in the “2TDC” region, the cylinder is set as the first explosion cylinder. In this case, 2TDC start is performed thereafter.

  On the other hand, when it is determined that the piston 32 of any cylinder does not stop in the “2TDC” region (that is, the piston 32 of the cylinder in the intake stroke stops in the “lean misfire region” shown in FIG. 3). The cylinder in which the piston 32 is stopped immediately before the intake TDC is the first explosion cylinder. In this case, 3TDC start is performed thereafter.

  In the case of 2TDC start, the piston 32 of the first explosion cylinder is stopped within the crank angle region shown in FIG. In this case, as described above, the pre-compression cylinder gas temperature can be calculated by applying the piston stop position and the coolant temperature THW to the relationship shown in FIG.

  On the other hand, in the case of 3TDC start, the piston 32 of the first explosion cylinder is stopped at a position (crank angle before ATDC 0 ° CA) deviated from the crank angle region shown in FIG. Therefore, in this case, the piston stop position of the first explosion cylinder cannot be directly applied to the relationship shown in FIG. However, the ratio of fresh air and residual gas in the initial explosion gas is the same when the piston 32 is stopped before the intake TDC and when the piston 32 is stopped at the intake TDC. For this reason, in the case of 3TDC start, assuming that the piston stop position is ATDC 0 ° CA, the in-cylinder gas temperature before compression can be estimated from the relationship shown in FIG.

  In the system of this embodiment, as described above, when the internal combustion engine 10 is stopped, the variable valve mechanism 20 returns the valve closing timing of the intake valve 18 to a predetermined start timing. For this reason, the internal combustion engine 10 is always started in a state where the closing timing of the intake valve 18 is controlled to the starting timing.

  The in-cylinder gas amount at the time of start-up, that is, the volume of the initial explosion gas before compression, is almost uniquely determined by the closing timing of the intake valve 18. That is, in the internal combustion engine 10, the actual compression ratio ε of the first explosion cylinder is almost uniquely determined by the closing timing of the intake valve 18 of the cylinder. Therefore, in the present embodiment, the internal combustion engine 10 is always started under a substantially constant actual compression ratio.

  In-cylinder gas self-ignition occurs when the in-cylinder gas temperature during the compression stroke reaches the self-ignition generation temperature. On the other hand, the in-cylinder gas arrival temperature during the compression process is greatly affected by three factors: (1) actual compression ratio ε, (2) in-cylinder gas temperature before compression, and (3) in-cylinder fuel amount. In the present embodiment, since the actual compression ratio ε at the time of starting is fixed, the in-cylinder gas arrival temperature is mainly determined by two elements of the in-cylinder gas temperature and the in-cylinder fuel amount. That is, in the present embodiment, whether or not self-ignition occurs in the cylinder is almost determined by two factors of the in-cylinder gas temperature and the fuel injection amount for the first explosion cylinder.

  FIG. 4 shows a region where auto-ignition combustion occurs under the actual compression ratio ε at the start time and a region where ignition combustion occurs. The fuel injection time TAU for the first explosion cylinder and the in-cylinder gas temperature before compression are two elements. FIG. A curve indicated by a solid line in FIG. 4 is a boundary line that divides these two regions. In FIG. 4, the region above the boundary line is a region where autoignition combustion occurs, while the region below the boundary line is a region where ignition fuel is generated.

  The in-cylinder gas arrival temperature becomes higher as the in-cylinder gas temperature before compression is higher. For this reason, as shown in FIG. 4, if the fuel injection time TAU is the same, the region where the in-cylinder gas temperature is high becomes the self-ignition combustion region, and the region where the temperature is low becomes the ignition combustion region.

  Further, the amount of fuel in the cylinder increases as the fuel injection time TAU increases. And as the amount of fuel in the cylinder increases, the suppression of temperature rise due to the latent heat of vaporization of the fuel becomes more prominent, and self-ignition hardly occurs. For this reason, as shown in FIG. 4, the boundary line between the self-ignition combustion region and the ignition combustion region is expanded to the higher temperature side as the fuel injection amount TAU is longer.

  The relationship shown in FIG. 4 can be specified in advance for the internal combustion engine 10. On the other hand, in the present embodiment, as described above, it is possible to estimate the in-cylinder gas temperature before compression of the cylinder based on the piston stop position of the first explosion cylinder and the coolant temperature THW at the time of restart ( (See FIG. 3). If the relationship shown in FIG. 4 is known and the in-cylinder in-cylinder gas temperature can be estimated, the shortest fuel injection time TAU that does not cause self-ignition under that condition can be calculated (in-compression cylinder) TAU riding on the boundary of Fig. 4 for the estimated gas temperature).

  Focusing on the fuel efficiency characteristics of the internal combustion engine 10, it is desirable that the fuel injection time TAU at the start is small as long as self-ignition does not occur. Therefore, when the internal combustion engine 10 is restarted, the system of this embodiment first estimates the in-cylinder gas temperature using the relationship shown in FIG. 3, and further uses the relationship shown in FIG. It was decided to set the shortest fuel injection time TAU that would not cause

(Specific processing)
FIG. 5 is a flowchart of processing executed by the ECU 40 in order to realize the above function. In the routine shown in FIG. 5, it is first determined whether or not the internal combustion engine 10 is stopped (step 100). As a result, when it is determined that the internal combustion engine 10 is not stopped, it is determined that it is not necessary to proceed with this routine, and the current process is completed.

  On the other hand, if it is determined that the internal combustion engine 10 is stopped, then the crank angle in the 720 ° CA system and the coolant temperature THW are read (step 102). The ECU 40 identifies the initial explosion cylinder at the time of restart based on the crank angle read here, and determines whether the restart is performed by 2TDC start or 3TDC start (see FIG. 3).

  Next, the in-cylinder gas temperature is estimated (step 104). The ECU 40 stores the relationship shown in FIG. Here, by applying the piston stop position (ATDC 0 ° CA if 3TDC start is selected) and the coolant temperature THW to the relationship, the pre-compression cylinder gas corresponding to the current situation is applied. The temperature is estimated.

  Next, the basic fuel injection amount for the first explosion cylinder is calculated (step 106). The ECU 40 stores the relationship shown in FIG. Here, the minimum fuel injection time TAUmin that does not cause self-ignition is calculated by applying the pre-compression cylinder interior gas temperature estimated by the processing of step 104 to the relationship.

  Next, the atmospheric pressure is detected based on the output of the atmospheric pressure sensor 26 (step 108). Next, an atmospheric correction coefficient is calculated based on the detected value of the atmospheric pressure (step 110).

  In the internal combustion engine 10 of the present embodiment, as described above, the actual compression ratio ε of the initial explosion cylinder is always constant. However, the amount of gas compressed in the cylinder increases and decreases under the influence of atmospheric pressure. For this reason, the in-cylinder pressure at the compression end decreases as the atmospheric pressure decreases. When the in-cylinder pressure decreases, fuel self-ignition hardly occurs. For this reason, the minimum fuel injection time TAUmin that does not cause self-ignition becomes shorter as the atmospheric pressure is lower. The ECU 40 stores the relationship between them, and in step 110, calculates the atmospheric correction coefficient according to the relationship.

  Next, the ECU 40 calculates the final fuel injection time TAU for the first-explosion cylinder by multiplying the basic fuel injection time TAUmin calculated in the above step 106 by the atmospheric correction coefficient calculated in the above step 110 (step 112).

  When the above processing is completed, the ECU 40 performs start permission flag processing (step 114). The processes in steps 100 to 114 are repeatedly executed while the internal combustion engine 10 is stopped. When a restart request for the internal combustion engine 10 is generated, a start process is performed based on the fuel injection time TAU calculated at that time.

  According to the above processing, when restart of the internal combustion engine 10 is requested, the minimum fuel injection amount that does not cause self-ignition is calculated based on the piston stop position of the first explosion cylinder and the coolant temperature THW. Can do. For this reason, according to the system of the present embodiment, it is possible to achieve excellent fuel efficiency characteristics while effectively preventing self-ignition during restart.

  In the first embodiment described above, first, the pre-compression cylinder gas temperature is calculated based on the piston stop position and the coolant temperature THW, and the basic fuel injection amount TAUB is calculated based on the calculated pre-compression cylinder gas temperature. However, the calculation procedure of the basic fuel injection amount TAUB is not limited to this. For example, a relationship established between the piston stop position, the coolant temperature THW, and the basic fuel injection amount TAUB is determined in advance, and the basic fuel injection amount TAUB is directly calculated based on the piston stop position and the coolant temperature THW. It is good to do.

  In Embodiment 1 described above, the internal combustion engine 10 includes the variable valve mechanism 20, but the configuration of the internal combustion engine 10 is not limited to this. That is, the drive mechanism of the intake valve 18 may be a mechanism although the valve closing timing cannot be changed.

In the first embodiment described above, the internal combustion engine 10 is mounted on an eco-run vehicle or a hybrid vehicle, and it is assumed that automatic stop and automatic restart are repeated. However, the present invention is based on such a premise. It is not limited. That is, the process of setting the minimum fuel injection amount that does not cause self-ignition from the piston stop position and the coolant temperature THW at the time of starting may be performed for a normal internal combustion engine that does not cause automatic stop or automatic restart. Good. This point
The same applies to other embodiments described below.

  In the first embodiment described above, the variable valve mechanism 20 returns the valve closing timing of the intake valve 18 to a predetermined start timing when the internal combustion engine 10 is stopped. However, the present invention is limited to this. It is not something. That is, the closing timing of the intake valve 18 when the internal combustion engine 10 is stopped, that is, the closing timing when the internal combustion engine 10 is restarted may not always be constant.

  The in-cylinder gas temperature at the compression end is mainly determined by the in-cylinder gas temperature before compression and the actual compression ratio ε. On the other hand, the actual compression ratio ε of the initial explosion cylinder changes according to the closing timing of the intake valve 18. For this reason, when the valve closing timing of the intake valve 18 changes, the in-cylinder gas temperature at the compression end becomes a different temperature even if the in-cylinder in-cylinder gas temperature is the same.

  The relationship shown in FIG. 4 is established when the actual compression ratio ε at the time of restart is always constant, and the cylinder gas temperature at the compression end is uniquely determined when the cylinder gas temperature before compression is determined. In other words, the relationship shown in FIG. 4 is a relationship that can be determined for each of the different actual compression ratios when the actual compression ratio ε varies. When the closing timing of the intake valve 18 is not constant when the internal combustion engine 10 is restarted, a relationship similar to that shown in FIG. 4 is determined for a plurality of actual compression ratios ε (valve closing timing). is required. In addition, if the actual compression ratio ε and the in-cylinder in-cylinder gas temperature at the time of restart are compared with each other, as in the case of the first embodiment, the minimum fuel injection amount that does not cause self-ignition Can be set.

  In the first embodiment described above, the crank angle sensor 34 corresponds to the “stop position detecting means” in the first invention, and the water temperature sensor 36 corresponds to the “cylinder temperature detecting means” in the first invention. is doing. Further, the ECU 40 stores the relationship shown in FIG. 3 and the relationship shown in FIG. 4, thereby realizing the “limit injection amount rule storage means” in the first invention. Further, the “limit injection amount calculating means” in the first aspect of the present invention is realized by the ECU 40 executing the processing of steps 102 to 106. Furthermore, the “injection amount control means” according to the first aspect of the present invention is realized by the ECU 40 performing the restart injection at the fuel injection amount calculated in step 112.

  In the first embodiment described above, the position sensor incorporated in the variable valve mechanism 20 corresponds to the valve closing timing detecting means in the second invention. Further, the ECU 40 stores the same relationship as shown in FIG. 4 defined for each of a plurality of actual compression ratios (closing timings of intake valves) together with the relationship shown in FIG. The “limit injection amount storage means” can be realized. Further, by causing the ECU 40 to calculate the basic fuel injection time TAUB in step 106 by fitting the pre-compression cylinder interior gas temperature and the closing timing of the intake valve 18 to a plurality of relationships similar to those shown in FIG. The “limit injection amount calculating means” in the second aspect of the invention can be realized.

In the first embodiment described above, the "pre-compression temperature rules" in the invention relationships of the first shown in FIG. 3, the "injection amount conversion rule" is the relationship shown in FIG. 4 in the first aspect of the present invention , Respectively. Further, ECU 40 is "by executing the process of step 104 is" means for calculating the pre-compression cylinder gas temperature "in the first invention, in the first embodiment is realized by executing the process of step 106 Each means for calculating the limit fuel injection amount is realized.

Further, in the first embodiment described above, the “first-explosion cylinder detecting means” in the third aspect of the present invention is realized by the ECU 40 specifying the initial-explosion cylinder based on the crank angle in step 102.

Embodiment 2. FIG.
[Configuration of Embodiment 2]
Next, a second embodiment of the present invention will be described with reference to FIGS.
The system of the present embodiment can be realized by causing the ECU 40 to execute a routine shown in FIG. 9 described later in the system configuration shown in FIG. However, in the present embodiment, the variable valve mechanism 20 of the intake valve 18 is an electric type or a stock pressure type, and operates while the internal combustion engine 10 is stopped, that is, operates before the internal combustion engine 10 is started. Shall be able to.

[Features of Embodiment 2]
In the system of the first embodiment described above, the fuel injection amount is controlled to the minimum amount that does not cause self-ignition under a predetermined actual compression ratio ε when the internal combustion engine 10 is started. In this case, the air-fuel ratio itself at the time of the first explosion may be a value enriched with respect to the target air-fuel ratio. In such a case, if the actual compression ratio ε is reduced prior to the first explosion, the minimum fuel injection amount that does not cause self-ignition can be reduced, and the enrichment of the air-fuel ratio can be suppressed. In other words, if the actual compression ratio ε at the first explosion is lowered to an appropriate value, it is possible to prevent the occurrence of self-ignition while maintaining the target air-fuel ratio.

  In order to improve the fuel consumption characteristics of the internal combustion engine 10, it is desirable that the fuel injection amount at the start is small. Therefore, in the present embodiment, when the internal combustion engine 10 is started in accordance with the principle described above, the actual compression ratio ε is self-ignited under the fuel injection amount while controlling the fuel injection amount to a value corresponding to the target air-fuel ratio. The valve closing timing of the intake valve 18 is controlled so as to be the highest value that does not cause the above.

[Control Principle of Second Embodiment]
FIG. 6 is a diagram showing a region in which self-ignition combustion occurs at a target air-fuel ratio and a region in which ignition combustion occurs, using the actual compression ratio ε and the in-cylinder gas temperature as parameters. Further, the broken line drawn at the boundary between these two regions indicates that the compression end temperature in the cylinder reaches the self-ignition generation temperature under the target air-fuel ratio (the actual compression ratio ε and the cylinder gas temperature before compression). Represents a set of combinations).

  The relationship shown in FIG. 6 can be specified for the internal combustion engine 10 experimentally or by simulation. On the other hand, as described in the first embodiment, when the internal combustion engine 10 is started, the in-cylinder gas temperature before compression can be estimated based on the piston stop position and the coolant temperature THW (see FIG. 3). If the pre-compression cylinder gas temperature at the start is applied to the relationship shown in FIG. 6, an upper limit value of the actual compression ratio ε that does not cause self-ignition (hereinafter referred to as “upper limit actual compression ratio εmax”) is detected. Is possible.

  That is, in the internal combustion engine 10, when a start request is generated, the in-cylinder gas temperature is estimated based on the piston position at the time of stop and the coolant temperature THW (see FIG. 3), and further based on the estimated temperature. Thus, the upper limit actual compression ratio εmax can be calculated (see FIG. 6). Here, since the in-cylinder gas temperature before compression and the upper limit actual compression ratio εmax have a one-to-one correspondence, the vertical axis shown in FIG. 3 can be converted into the upper limit actual compression ratio εmax. When the vertical axis shown in FIG. 3 is converted into the upper limit actual compression ratio εmax, it is possible to specify the relationship that is established between the combination of the piston stop position and the coolant temperature THW and the upper limit actual compression ratio εmax.

  FIG. 7 shows an example of the upper limit actual compression ratio map created by organizing the above relationships. In the present embodiment, the ECU 40 stores an upper limit actual compression ratio map that defines the upper limit actual compression ratio εmax using the piston stop position and the coolant temperature THW as parameters, as shown in FIG. Therefore, the ECU 40 directly calculates the upper limit actual compression ratio εmax that does not cause self-ignition under the target air-fuel ratio from the piston stop position and the cooling water temperature THW by referring to the map when the internal combustion engine 10 is started. can do.

  FIG. 8 shows the relationship established between the closing timing of the intake valve 18 (crank angle after intake bottom dead center) and the actual compression ratio ε of the first explosion cylinder. As shown in FIG. 8, the actual compression ratio ε of the initial explosion cylinder is uniquely determined by the closing timing of the intake valve 18. The ECU 40 stores the relationship shown in FIG. For this reason, when the upper limit actual compression ratio εmax is known, the ECU 40 can specify the valve closing timing for realizing the compression ratio εmax.

  The system of the present embodiment controls the closing timing of the intake valve 18 to a timing for realizing the upper limit actual compression ratio εmax prior to starting when a start request for the internal combustion engine 10 occurs. Thereafter, the internal combustion engine 10 is started with a fuel injection amount that achieves the target air-fuel ratio. According to such processing, ignition combustion of the mixed gas controlled to the target air-fuel ratio occurs in the first explosion cylinder, and an ideal first explosion can be obtained with the smallest amount of fuel.

[Specific Processing in Second Embodiment]
FIG. 9 is a flowchart of a routine executed by the ECU 40 in the present embodiment in order to realize the above function. 9, the same steps as those shown in FIG. 5 are given the same reference numerals, and the description thereof is omitted or simplified.

  In the routine shown in FIG. 9, after the piston stop position and the coolant temperature THW are read in step 102, they are applied to the upper limit actual compression ratio map (see FIG. 7) (step 120). As a result, under the current situation, an upper limit actual compression ratio εmax that does not cause self-ignition is calculated under the target air-fuel ratio.

  Next, the valve closing timing of the intake valve 18 that realizes the air-fuel ratio εmax is calculated by applying the upper limit actual compression ratio εmax to the map shown in FIG. 8 (step 122). Subsequently, the variable valve mechanism 20 is controlled so that the timing is set (step 124).

  Until the valve closing timing is set, the processing of steps 100 to 124 is repeatedly executed (step 126). When the setting is completed, the closing timing of the intake valve 18 and the atmospheric pressure are read (step 128).

  Next, the ECU 40 refers to the intake air amount map to calculate the initial explosion gas amount (step 130). FIG. 10 shows an intake air amount map stored in the ECU 40. In the internal combustion engine 10, the initial explosion gas amount used for the initial explosion is mainly determined by the closing timing of the intake valve 18. FIG. 10 is a map of the relationship established under the standard atmospheric pressure between them. In step 130, the amount of air given to the first explosion is calculated according to this map.

  Next, the ECU 40 calculates a basic fuel injection time TAUB for which the target air-fuel ratio is actually applied with respect to the initial explosion gas amount (step 132). Thereafter, when the final fuel injection time TAU is calculated by atmospheric pressure correction, the start of the internal combustion engine 10 is permitted (steps 110 to 114).

  According to the above processing, it is possible to cause the first explosion by ignition combustion in the cylinder while controlling the combustion gas of the first explosion cylinder to the target air-fuel ratio. Therefore, according to the system of the present embodiment, the internal combustion engine 10 can be restarted smoothly while realizing ideal emission characteristics and fuel consumption characteristics.

  In the second embodiment described above, the upper limit actual compression ratio map that directly determines the upper limit actual compression ratio εmax is used based on the piston stop position and the coolant temperature THW, but the present invention is limited to this. It is not a thing. That is, a map for determining the pre-compression cylinder gas temperature based on the piston stop position and the coolant temperature THW (see FIG. 3) and a map for determining the upper limit actual compression ratio εmax from the pre-compression cylinder gas temperature (see FIG. 6). Both may be stored in the ECU 40 and the upper limit actual compression ratio εmax may be obtained via the in-cylinder gas temperature before compression. This also applies to the third embodiment described below.

  In Embodiment 2 described above, after obtaining the upper limit actual compression ratio εmax, the valve closing timing corresponding to εmax is calculated with reference to the map shown in FIG. It is not limited to. That is, since the relationship shown in FIG. 8 is merely conversion, this relationship is incorporated into the relationship shown in FIG. 7 (or FIG. 6), and from the piston stop position and the cooling water temperature THW (or from the in-cylinder gas temperature), The valve closing timing of the intake valve 18 for which the upper limit actual compression ratio εmax is actually applied may be directly calculated. This also applies to the third embodiment described below.

Embodiment 3 FIG.
[Features of Embodiment 3]
Next, a third embodiment of the present invention will be described with reference to FIGS.
The system of the present embodiment can be realized by causing the ECU 40 to execute a routine shown in FIG. 12 described later in place of the routine shown in FIG. 9 in the system of the second embodiment described above.

  The system of the second embodiment described above prevents the occurrence of self-ignition by moving the valve closing timing of the intake valve 18 while maintaining the target air-fuel ratio when the internal combustion engine 10 is started. This method is extremely effective in improving the emission characteristics and fuel efficiency characteristics at restart. However, according to the above method, the initial explosion gas amount inevitably varies. Since the output torque of the internal combustion engine 10 changes depending on the amount of gas combusted in the cylinder, if the initial explosion gas amount changes, the output torque at the time of the initial explosion also varies.

  By the way, the output torque of the internal combustion engine 10 can be increased or decreased by the actual compression ratio ignition timing. FIG. 11 shows how the output torque of the internal combustion engine 10 changes in accordance with the in-cylinder charging efficiency (actual compression ratio) and the ignition timing. Since the output torque of the internal combustion engine 10 is thus affected by both the charging efficiency (actual compression ratio) and the ignition timing, if the ignition timing is appropriately controlled in accordance with the change in the closing timing of the intake valve 18. It is possible to stabilize the output torque at the time of the first explosion by offsetting the torque change accompanying the fluctuation of the first explosion gas amount.

[Specific Processing of Embodiment 3]
FIG. 12 is a flowchart of a routine executed by the ECU 40 in the present embodiment. The routine shown in FIG. 12 is the same as the routine shown in FIG. 9 except that steps 140 to 144 are inserted between steps 112 and 114. In FIG. 12, the same steps as those shown in FIG. 9 are denoted by the same reference numerals, and the description thereof is omitted or simplified.

  That is, in the routine shown in FIG. 12, after the fuel injection time TAU for realizing the target air-fuel ratio is calculated in step 112, first, the ignition timing map is referred to (step 140). The ignition timing map is a map for determining a basic ignition timing based on the operating state of the internal combustion engine 10. Here, the basic ignition timing is set according to the map.

  Next, the closing timing of the intake valve 18 in the first explosion cylinder, that is, the intake closing timing calculated in step 122 is read (step 142). Next, the ignition timing of the first explosion cylinder is determined based on the valve closing timing (step 144).

  FIG. 13 shows an example of a corrected ignition timing map. The corrected ignition timing map defines the relationship between the closing timing of the intake valve 18 and the correction amount to be applied to the ignition timing in order to make the initial explosion torque constant. The ECU 40 stores this map. In step 144, first, the correction amount of the ignition timing is calculated according to the map. Then, the ignition timing of the first explosion cylinder is set by adding the correction amount to the basic ignition timing set in step 140.

  Thereafter, the ECU 40 completes the current processing cycle through the processing of step 114. According to the above processing, by appropriately setting the closing timing of the intake valve 18, the occurrence of self-ignition can be prevented while maintaining the target air-fuel ratio, and further, the initial timing can be improved by appropriately correcting the ignition timing. Torque variation can be suppressed. For this reason, according to the system of the present embodiment, the internal combustion engine 10 can be smoothly restarted while maintaining the drivability well in addition to the emission characteristics and the fuel consumption characteristics.

It is a figure for demonstrating the structure of Embodiment 1 of this invention. It is a figure which shows the relationship between the crank angle after an intake top dead center, and the quantity (intake volume) of the fresh air suck | inhaled in a cylinder by an intake bottom dead center. It is the figure which showed the relationship between the stop position of a piston and the in-cylinder gas temperature before compression using the cooling water temperature THW as a parameter. FIG. 2 is a diagram showing a region where auto-ignition combustion occurs under an actual compression ratio ε at the start time and a region where ignition combustion occurs, as two elements: the fuel injection time TAU for the first explosion cylinder and the in-cylinder gas temperature before compression. is there. It is a flowchart of the routine performed in Embodiment 1 of the present invention. It is the figure which showed the area | region where self-ignition combustion occurs under a target air fuel ratio, and the area | region where ignition combustion occurs, using two parameters, actual compression ratio (epsilon) and in-cylinder gas temperature. An example of the upper limit actual compression ratio map used in Embodiment 2 of the present invention will be shown. The relationship established between the valve closing timing of the intake valve and the actual compression ratio ε of the first explosion cylinder is shown. It is a flowchart of the routine performed in Embodiment 2 of this invention. An example of the intake air amount map used in Embodiment 2 of the present invention will be shown. This shows how the output torque of the internal combustion engine changes in accordance with the in-cylinder charging efficiency (actual compression ratio) and the ignition timing. It is a flowchart of the routine performed in Embodiment 3 of the present invention. An example of the correction | amendment ignition timing map used in Embodiment 3 of this invention is shown.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Internal combustion engine 18 Intake valve 20 Variable valve mechanism 34 Crank angle sensor 36 Water temperature sensor 40 ECU (Electronic Control Unit)

Claims (3)

Stop position detecting means for detecting the piston stop position;
Cylinder temperature detecting means for detecting the cylinder temperature;
Limit injection amount rule storage means for storing a limit injection amount rule established between the piston stop position and the cylinder temperature and a limit fuel injection amount that does not cause self-ignition combustion at the time of restart;
Limit injection amount calculation means for calculating the limit fuel injection amount by applying the detection value of the piston stop position and the detection value of the cylinder temperature to the limit injection amount rule;
Injection amount control means for controlling the fuel injection amount at the time of restart to an injection amount corresponding to the calculated value of the limit fuel injection amount , and
The limit injection amount rule is:
A pre-compression temperature rule established between the piston stop position and the cylinder temperature, and a pre-compression cylinder gas temperature that is a cylinder gas temperature immediately before the start of compression;
An injection amount conversion rule established between the in-cylinder gas temperature before compression and the limit fuel injection amount, and
The limit injection amount calculating means includes
Means for applying the detection value of the piston stop position and the detection value of the cylinder temperature to the pre-compression temperature rule, and calculating a pre-compression cylinder gas temperature at restart;
By applying the calculated value of the pre-compression cylinder gas temperature in the injection amount conversion rules, and start control system for the internal combustion engine, characterized in Rukoto and means for calculating the limit fuel injection amount. A variable valve mechanism that changes the closing timing of the intake valve;
A valve closing timing detecting means for detecting the valve closing timing of the intake valve,
The limit injection amount storage means stores a plurality of limit injection amount rules established under each of a plurality of valve closing timings of the intake valve,
The limit injection amount calculating means applies the detection value of the piston stop position, the detection value of the cylinder temperature, and the detection value of the valve closing timing to the plurality of limit injection amount rules, thereby limiting the limit fuel injection amount. The start control device for an internal combustion engine according to claim 1, wherein: A start control device for an internal combustion engine having a plurality of cylinders,
When restarting the internal combustion engine, the first explosion cylinder detection means for detecting the first explosion cylinder capable of causing ignition combustion first among the plurality of cylinders,
The limit injection amount calculation means calculates the limit fuel injection amount based on a piston stop position of the initial explosion cylinder,
The injection amount control means controls the fuel injection amount to an injection amount corresponding to the calculated value of the limit fuel injection amount at the time of the first fuel injection to the first explosion cylinder when the internal combustion engine is restarted. 3. The start control device for an internal combustion engine according to claim 1, wherein the start control device is an internal combustion engine.

Images