JP2009243295A - Engine intake valve control method and device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce variation in the torque or air-fuel ratio of an engine in which a negative overlap (NVO) period is provided for intake/exhaust air during HCCI combustion, while suppressing a variation in the filling efficiency during change-over with SI combustion. <P>SOLUTION: During changing over the combustion condition of an engine 1 between a HCCI mode and a SI mode, when an operation timing for an intake valve 11 is changed so that its closing timing passes through a predetermined timing α for maximizing filling efficiency with the inertia of an intake air flow, a temporary increase of the filling efficiency is suppressed by adjusting a lift amount or a valve opening timing. This sufficiently reduces a variation in the torque or air-fuel ratio during a change-over transitional period. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a control technique for compressing a premixed gas in a cylinder of an engine and burning it by self-ignition, and in particular, a negative pressure that closes both intake and exhaust valves in an exhaust stroke or an intake stroke of a cylinder in a predetermined operating range. It relates to what provided the overlap period.

  In recent years, in order to further improve the fuel consumption of the engine and to clean the exhaust, a combustion mode in which the premixed gas in the cylinder is compressed and burned by self-ignition has been proposed, and generally the premixed compression ignition combustion (Premixed Charge Compression Ignition: PCCI, Homogeneous Charge Compression Ignition: HCCI, hereinafter collectively referred to as HCCI combustion). In such combustion by self-ignition, unlike the conventional spark ignition combustion (hereinafter referred to as SI combustion), the premixed gas is self-ignited at a large number of locations in the cylinder and starts combustion. As a result, the thermal efficiency is extremely high.

  In addition, even if the lean lean premixed gas that cannot achieve conventional SI combustion or the premixed gas diluted by a large amount of EGR is used, self-ignition occurs if the temperature in the cylinder compressed by the piston becomes higher than a predetermined level. Thus, although the combustion period itself is short, it does not become intense combustion, so that the generation of nitrogen oxides is remarkably reduced.

  However, since there is a possibility that the temperature of the premixed gas does not reach the self-ignition temperature even in the vicinity of the compression top dead center (TDC) in the operation region on the low load side, the intake valve has been conventionally operated from the exhaust stroke of the cylinder to the intake stroke. In addition, a negative overlap (NVO) period that closes both the exhaust valve and the exhaust valve is provided to increase the temperature in the cylinder by allowing high-temperature burned gas to remain (hereinafter also referred to as internal EGR). It has been broken.

  On the other hand, in the operating region on the high load side, stable HCCI combustion cannot be realized and SI combustion is performed. However, at this time, there must be a large amount of internal EGR gas as in HCCI combustion. When switching between, the overlap state of the intake / exhaust valve must be changed to greatly change the internal EGR gas amount, which may cause a sudden torque fluctuation (torque step).

With regard to this point, in the engine described in Patent Document 1, for example, when switching from SI combustion to HCCI combustion, first, SI combustion of a lean air-fuel mixture with a lean air-fuel ratio is performed, and then the air-fuel mixture is stratified around the spark plug. SI is burned. That is, the torque step is suppressed by increasing the intake air amount in advance before the transition from SI combustion to HCCI combustion and making the air-fuel ratio as lean as possible.
Japanese Patent Laid-Open No. 2007-16665

  By the way, in general, an intake valve of an engine is opened at an appropriate time before the top dead center (TDC) of a cylinder in consideration of an overlap with an exhaust valve, and is charged in consideration of charging efficiency due to the inertia of the intake flow. Although it is set to close after the dead center (BDC), in the case of providing a variable mechanism for changing the lift amount and the operation timing, the intake valve is connected to the intake valve on the relatively low load side of the operation region where SI combustion is performed. In many cases, it closes earlier (on the advance side) than a predetermined time when the charging efficiency is the highest due to the inertia of.

  On the other hand, during HCCI combustion, the operation timing of the intake valve is largely changed to the retard side as a whole in order to provide an NVO period, and the lift amount or the valve opening period increases, so the closing timing is In many cases, the angle is behind the predetermined time. For this reason, when switching between HCCI combustion and SI combustion, the closing timing of the intake valve, which changes to either the advance side or the retard side, passes the predetermined time, and at this time In particular, the charging efficiency may be increased, and the engine torque and the air-fuel ratio may be changed.

  In view of such points, an object of the present invention is to close the intake valve closing timing that is changed to the advance side or the retard side when switching between HCCI combustion (self-ignition mode) and SI combustion (spark ignition mode). Is to suppress a temporary increase in charging efficiency when passing through the predetermined time and to mitigate fluctuations in torque and air-fuel ratio.

  In order to achieve the above object, according to the present invention, when the intake valve closing timing passes a predetermined intake valve closing timing when the combustion mode of the engine is switched, the lift amount or the valve opening period is temporarily adjusted. An increase in filling efficiency is suppressed.

  Specifically, the invention of claim 1 is provided with a variable mechanism capable of changing the operation timing and lift amount or valve opening period of the intake valve and the exhaust valve, and both the intake valve and the exhaust valve in the exhaust stroke or the intake stroke of the cylinder. A self-ignition mode in which a closed negative overlap period is provided to allow the burned gas to remain and the pre-mixture is self-ignited after the later stage of the compression stroke; and a spark ignition mode in which the mixture in the cylinder is ignited. The target is an intake valve control method for an engine that is switched to either one.

  Then, when the mode is switched between the self-ignition mode and the spark ignition mode, the lift mechanism or the valve opening amount is changed while the closing timing of the intake valve is changed to either the advance side or the retard side by the variable mechanism. The first step of changing the period so that the charging efficiency of the intake air becomes low, and the closing mechanism of the intake valve is changed to the one by the variable mechanism so that the charging efficiency is increased in the lift amount or the valve opening period. And a second step of changing to

  According to the above method, first, if the engine is in the self-ignition mode, both the intake valve and the exhaust valve are closed during a predetermined period (NVO period) in the exhaust stroke or the intake stroke of the cylinder, and a large amount of burned fuel is generated in the cylinder. Gas (internal EGR gas) remains, thereby increasing the temperature state of the cylinder and realizing stable HCCI combustion. On the other hand, if the engine is in the spark ignition mode, the intake and exhaust valves are controlled to have a predetermined overlap.

  When the two combustion modes are switched, for example, when switching from the self-ignition mode to the spark ignition mode, the operation timing of the intake valve is changed to the advance side by the variable mechanism, and the closing timing is changed to the above-mentioned predetermined timing ( When the intake valve closes at this time, the lift amount or the valve opening period is changed so that the charging efficiency becomes low. (First step) On the other hand, when the time is away from the timing, the lift amount or the valve opening period is changed so as to increase the charging efficiency (second step), thereby suppressing a temporary increase in the charging efficiency. .

  Preferably, in the first step, the lift amount or the valve opening period is decreased as the closing timing is approached until a predetermined intake valve closing timing at which the charging efficiency becomes the highest due to the inertia of the intake air flow, In the second step, the lift amount or the valve opening period is increased as the predetermined intake valve closing timing passes and leaves. In this way, even when the intake valve closing timing passes the predetermined timing when switching the combustion mode, the charging efficiency can be changed at a substantially constant rate, and fluctuations in torque and air-fuel ratio can be eliminated. You can also.

  In particular, in the case of switching from the self-ignition mode to the spark ignition mode, the closing timing of the intake valve is advanced by the variable mechanism in the first step, while the opening timing is decreased without changing the opening timing. (Claim 3). In the case of switching from the self-ignition mode to the spark ignition mode, the operation timing of the intake valve is changed to the advance side as a whole, so the change to the opposite retard side for both the open timing and the close timing It is because it is preferable not to generate.

  From another point of view, the present invention is provided with a variable mechanism that can change the lift amount or valve opening period and timing of the intake valve and the exhaust valve, and is a negative mechanism that closes both the intake valve and the exhaust valve in the exhaust stroke or intake stroke of the cylinder. Any one of a self-ignition mode in which the burned gas is left by providing an overlap period and self-ignition of the premixture in the later stage of the compression stroke and a spark ignition mode in which the mixture in the cylinder is ignited The intake valve control device for an engine is configured to switch to a self-ignition mode and a spark ignition mode, and when the mode is switched between the self-ignition mode and the spark ignition mode, the operation timing of the intake valve is changed by the variable mechanism, and charging is performed according to the inertia of the intake flow An operation timing control means for changing the closing timing of the intake valve to either the advance side or the retard side so as to pass a predetermined timing when the efficiency becomes the highest, and at the time of the mode switching When the closing timing of the air valve approaches the predetermined time, the lift amount or the valve opening period is decreased accordingly, while when the valve passes through the predetermined time and leaves the predetermined time, the lift amount or the valve opening period is increased accordingly. And a lift control means to be provided (invention of claim 4).

  According to such a control apparatus, the intake valve control method according to the first and second aspects of the invention can be easily executed, and the operation of the invention can be obtained easily and reliably. When the lift control means switches the mode from the self-ignition mode to the spark ignition mode, the valve opening period is set so that the opening timing does not change when the closing timing of the intake valve advances and approaches a predetermined timing. (5), the operation of the invention according to claim 3 described above can be obtained.

  In the intake valve control method and the like according to the above-described invention, the variable mechanism changes both the lift amount and the valve opening period of the intake valve in association with each other. This is particularly effective when it cannot be freely changed (claim 6).

  As described above, according to the intake valve control method and the like according to the present invention, when the combustion state of the engine is switched between the self-ignition mode and the spark ignition mode, the closing timing is changed along with the change of the operation timing of the intake valve. However, when passing the predetermined time when the charging efficiency becomes the highest due to the inertia of the intake air flow, by adjusting the lift amount etc. corresponding to this, the temporary increase in the charging efficiency is suppressed, so the mode switching The fluctuations in torque and air-fuel ratio during the transition can be sufficiently mitigated.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. It should be noted that the following description of the preferred embodiment is merely illustrative in nature, and is not intended to limit the present invention, its application, or its use.

(overall structure)
FIG. 1 shows an overall configuration of an engine control apparatus A according to the present invention, and reference numeral 1 denotes a multi-cylinder gasoline engine mounted on a vehicle. The main body of the engine 1 has a cylinder head 4 disposed on a cylinder block 3 provided with a plurality of cylinders 2, 2,... (Only one is shown), and a piston 5 is fitted in each cylinder 2. A combustion chamber 6 is formed between the top surface of the cylinder head 4 and the lower surface of the cylinder head 4. The piston 5 is connected to the crankshaft 7 by a connecting rod, and a crank angle sensor 8 for detecting the rotation angle (crank angle) is disposed on one end side of the crankshaft 7.

  An intake port 9 and an exhaust port 10 are formed in the cylinder head 4 so as to open to the ceiling portion of the combustion chamber 6 for each cylinder 2. The intake port 9 extends obliquely upward from the ceiling of the combustion chamber 6 and opens on one side of the cylinder head 4, and the exhaust port 10 opens on the other side opposite to the cylinder head 4. The intake port 9 and the exhaust port 10 are opened and closed by an intake valve 11 and an exhaust valve 12, respectively. These intake and exhaust valves 11 and 12 are cams of a valve mechanism 13 disposed in the cylinder head 4. The shaft (not shown) is driven in synchronism with the rotation of the crankshaft 7.

  The valve mechanism 13 includes a known variable lift mechanism 14 (hereinafter abbreviated as VVL) capable of continuously changing the valve lift amount on the intake side and the exhaust side, and a phase angle of the valve lift with respect to crank rotation. And a known phase variable mechanism 15 (hereinafter abbreviated as VVT) that can be continuously changed are incorporated, and the lift characteristics of the intake and exhaust valves 11 and 12 are changed by their operation to It is possible to adjust the amount of intake air and the amount of residual burnt gas (internal EGR gas). A detailed description of the configurations of the VVL 14 and VVT 15 is omitted.

  In addition, a spark plug 16 is disposed with an electrode facing the ceiling of the combustion chamber 6 of each cylinder 2 and is energized by the ignition circuit 17 at a predetermined ignition timing. On the other hand, an injector 18 (fuel injection valve) that directly injects fuel into the cylinder 2 with the tip facing the peripheral edge of the intake side of the combustion chamber 6 is disposed. When fuel is injected by the injector 18 in the intake stroke of the cylinder 2, the fuel spray is mixed with the intake air and is widely dispersed in the cylinder 2 whose volume is increased as the piston 5 is lowered. A mixture is formed.

  In the figure, an intake system is disposed on one side of the cylinder head 4 located on the right side of the engine 1, and an intake passage 20 communicates with the intake port 9 of each cylinder 2. The intake passage 20 is for supplying air filtered by an air cleaner (not shown) to the combustion chamber 6 of each cylinder 2 of the engine 1, and an electric throttle is provided in the common passage upstream of the surge tank 21. A valve 22 is provided. The intake passage 20 is branched for each cylinder 2 downstream of the surge tank 21 and communicates with the intake port 9.

  On the other hand, an exhaust system is disposed on the other side of the cylinder head 4, and an exhaust passage 25 (exhaust manifold) branched for each cylinder 2 is connected to the exhaust port 10 of each cylinder 2. A sensor 26 for detecting the oxygen concentration in the exhaust gas is disposed at the collection portion of the exhaust manifold. Further, a catalyst 27 for purifying harmful components in the exhaust is disposed downstream of the exhaust manifold.

  In order to control the operation of the engine 1 configured as described above, a powertrain control module 30 (hereinafter referred to as PCM) is provided. As is well known, this includes a CPU, a memory, an I / O interface circuit, and the like. As shown in FIG. 2, a signal from the crank angle sensor 8 or the like is input, and the flow rate of air in the intake passage 20 is controlled. A signal from the airflow sensor 31 to be measured, a signal from an accelerator opening sensor 32 that detects an operation amount (accelerator opening) of an accelerator pedal (not shown), a signal from a vehicle speed sensor 33 that detects the traveling speed of the vehicle, Accept at least.

  Then, the PCM 30 determines the operating state of the engine 1 (for example, the load state and the engine speed) based on signals from the various sensors, and in accordance with this, the VVL 14, VVT 15, ignition circuit 17, injector 18, etc. At least control. That is, the PCM 30 adjusts the lift amount and working angle of the intake and exhaust valves 11 and 12 mainly by the operation of the VVL 14 and adjusts the opening / closing operation timing of the intake and exhaust valves 11 and 12 mainly by the operation of the VVT 15. The amount of intake air charged into the cylinder 2 and the amount of internal EGR gas are controlled.

  More specifically, as shown in FIG. 3 for an example of the intake valve 11, the VVL 14 of this embodiment is configured to increase the lift amount, that is, the operating angle, that is, the crank angle period from the opening timing to the closing timing of the intake valve 11. (Hereinafter referred to as a valve opening period, not including the buffer section) is also increased. In the example shown in the figure, the smaller the lift amount or the valve opening period of the intake valve 11 is, the more the valve opening period is advanced, and the angle is retarded as the lift amount increases. As a result, the opening timing of the intake valve 11 becomes substantially constant regardless of changes in the lift amount and the like, and only the closing timing changes to the advance side or the retard side.

  In other words, according to the VVL 14 of this embodiment, when the lift amount is small, the intake valve 11 has a so-called early closing characteristic that is advantageous for improving fuel efficiency, and the valve opening period increases as the lift amount increases. The closing time is delayed. Such a change in the closing timing is preferable for increasing the charging efficiency by the inertia of the intake air flow and ensuring the engine output. In addition, the amount of intake air charged into the cylinder 2 can be changed over a wide range by controlling the VVL 14 in this way, so the engine 1 of this embodiment controls the output regardless of the throttle valve 22.

  In addition to the structural characteristics of the VVL 14, the PCM 30 changes the operation timing of the intake valve 11 in a wider range by the operation of the VVT 15. That is, as will be described in detail below, when HCCI combustion is performed, the operation timing of the intake valve 11 is significantly retarded, and similarly, the operation timing of the exhaust valve 12 is advanced, and the exhaust stroke of the cylinder 2 is changed to the intake stroke. (Negative Valve Ovealap: NVO) period in which both intake and exhaust valves 11 and 12 are closed (refer to FIG. 5 (a)), so that a large amount of burned gas (internal EGR gas) is stored in the cylinder 2. It is made to remain in.

  Further, the PCM 30 operates the injector 18 at a predetermined timing to switch the air-fuel ratio in the cylinder 2 and the state of air-fuel mixture formation, and also changes the state of ignition by the spark plug 16 so as to change the internal EGR as described above. Along with a significant change in the gas amount, the combustion state of the engine 1 is switched to either HCCI combustion (self-ignition mode) or SI combustion (spark ignition mode) described below.

(Outline of engine control)
Specifically, as shown in an example of the control map in FIG. 4, in the operation region (H) on the relatively low load and low rotation side, ignition is basically performed on the premixed gas formed in the cylinder 2. Instead, the piston 5 is compressed and self-ignited by raising the piston 5. At this time, as shown in FIG. 5 (a), an NVO period is provided from the exhaust stroke to the intake stroke of the cylinder 2, the temperature in the cylinder 2 is increased by a large amount of internal EGR gas, and the intake stroke of the cylinder 2 is mainly used. Then, the fuel is injected by the injector 18 and sufficiently mixed with intake air and internal EGR gas to form a substantially uniform premixed gas and burned. In addition, in order to control the self-ignition timing more precisely, auxiliary ignition may be performed.

  Such self-ignition due to compression of the premixed gas is conventionally known and is generally called premixed compression ignition combustion (HCCI combustion). When the premixed gas formed in the combustion chamber 6 in the cylinder 2 is compressed, the self-ignition temperature is reached almost simultaneously at a number of locations in the combustion chamber 6, and the premixed gas is self-ignited almost simultaneously and burns. The combustion period is shortened and the thermal efficiency is increased as compared with the more general flame propagation combustion (SI combustion).

  In addition, HCCI combustion in which the premixed gas self-ignites can be realized even with a very lean premixed gas that is difficult to realize SI combustion or a premixed gas diluted with a large amount of internal EGR gas. As described above, since the combustion temperature is low even if the combustion period is short, the production of nitrogen oxides is very small. In other words, a pre-mixed gas that is not so lean or a pre-mixed gas with a low degree of dilution causes the timing of self-ignition to be too early and causes so-called knocking.

  In other words, HCCI combustion is realized by a very lean premixed gas or a premixed gas diluted by a large amount of EGR, and a very high output cannot be obtained, so the above control map (FIG. 4) is used. As shown, SI combustion is performed in the operation region (S) on the relatively high load side or high rotation side as before (hereinafter, the operation region (H) is referred to as the HCCI region, and the operation region (S)). Is called the SI region).

  According to the illustrated control map, HCCI combustion is not performed in an extremely low load region including idle, but this is not restrictive. Further, in the example of the figure, the HCCI region (H) and the SI region (S) adjacent to the high load side are divided by a boundary inclined so that the load becomes higher as the rotation speed is lower. Although not shown, hysteresis is set at this boundary to prevent control hunting.

−Mode switching−
By the way, in general, during SI combustion, the intake valve 11 is opened before the top dead center (TDC), and the lift amount and the valve opening period as shown in FIG. Therefore, on the low load side of the SI region (S) close to the boundary with the HCCI region (H), the lift amount and the valve opening period of the intake valve 11 are too large as shown in FIG. Without it, it closes earlier (in advance) than the bottom dead center (BDC) of inspiration.

  On the other hand, as described above, in the HCCI region (H), the operation timing (In) of the intake valve 11 is retarded and the operation timing (Ex) of the exhaust valve 12 is advanced as shown in FIG. Thus, the NVO period is provided, and the lift amount and the valve opening period are relatively large on the high load side close to the boundary with the SI region (S). Therefore, the closing timing of the intake valve 11 is retarded relative to the BDC. In many cases, it is more retarded than a predetermined closing time α at which the charging efficiency is highest due to the inertia of the intake air flow.

  For details on the predetermined closing timing α, as is well known in the art, in the intake stroke of the cylinder of the engine, the flow of the intake air that is drawn in by the lowering of the piston continues until after BDC due to its inertia, so the piston starts to rise. After that, if the intake valve is kept open and closed at a predetermined time α immediately before the intake flow disappears and the blowback occurs, the charging efficiency becomes the highest. Since the closing timing α varies depending on the magnitude of the inertia of the intake air flow, the higher the load side and the higher the rotation speed side, the higher the flow rate and the higher the flow velocity, the more retarded side α becomes.

  The combustion mode of the engine 1 is between the HCCI mode in which the intake valve 11 is closed on the retard side with respect to the predetermined timing α and the SI mode in which the intake valve 11 is closed on the advance side with respect to the timing α. At the time of switching, the closing timing of the intake valve 11 passes the predetermined timing α, and at this time, the charging efficiency is temporarily increased, which may cause fluctuations in engine torque and air-fuel ratio.

  That is, for example, when shifting from the HCCI mode to the SI mode as shown in FIGS. 5A to 5D, the state after the transition shown in FIG. 5D (the broken lines in FIGS. 5B and 5C are also shown). As shown in FIG. 6 (a), the entire operation timing of the intake valve 11 is advanced, and the lift amount and the opening / closing period are slightly reduced. When the timing is advanced and the lift amount or the like is uniformly reduced as shown by the broken line in FIG. 5B, when the intake valve 11 closes the predetermined timing α, the amount of decrease in the lift amount is reduced. Even if it is subtracted, the filling efficiency ce temporarily increases as shown by the broken line in FIG.

  Due to such fluctuations in the charging efficiency ce, the air-fuel ratio temporarily fluctuates to the lean side as shown by the dotted line in FIG. 6 (e), resulting in small torque fluctuations and worsening emissions. If the fuel injection amount is increased corresponding to the increase in efficiency ce, it is inevitable that a large torque fluctuation occurs.

  Therefore, in this embodiment, as will be described in detail below, the closing timing of the intake valve 11 that is changed to either the advance side or the retard side at the time of mode switching as described above is the predetermined time α. By adjusting the lift amount or the like in association with passing (hereinafter also referred to as a predetermined intake valve closing timing α), the above-described fluctuation in the charging efficiency is suppressed.

(Specific control procedure)
A specific control procedure at the time of mode switching will be described below with reference to FIGS. 9 and 10 in addition to FIGS. First, in step S1 after the start in FIG. 7, signals from the crank angle sensor 8, the airflow sensor 31, the accelerator opening sensor 32, the vehicle speed sensor 33, and the like are input, and in the subsequent step S2, the operating range of the engine 1 is determined. . That is, the engine speed is calculated based on the signal from the crank angle sensor 8, and the internal EGR amount is taken into account based on, for example, the vehicle speed and the accelerator opening, or on the basis of the signal from the airflow sensor 31 and the engine speed. The required torque (load state) to 1 is calculated. Based on the engine speed and the required torque thus obtained, it is determined whether the vehicle is in the HCCI region (H) or the SI region (S) with reference to the control map of FIG.

  Subsequently, in step S3, it is determined whether or not the mode is being switched. This is defined by, for example, the timer count of the PCM 30 when the operation region determined in step S2 changes between the HCCI region (H) and the SI region (S) across the boundary of the map of FIG. Until the predetermined time elapses, it is determined that switching is in progress (YES), and otherwise, it is determined that switching is not being performed (NO). If it is not switched, the process returns. On the other hand, if it is switched, the process proceeds to step S4. Here, it is determined whether or not the mode is switched from the HCCI mode to the SI mode based on the determination result in step S2.

  If the determination is NO and switching from the SI mode to the HCCI mode is in progress, the process proceeds to step S13 to be described later. If the determination is YES, the process proceeds to steps S5 to S12 to switch the mode from HCCI to SI. The intake valve 11 is controlled. That is, first, based on the current load and rotation speed of the engine 1, a predetermined intake valve closing timing α is read from a preset map (step S5). It is determined whether the closing timing is on the retard side (step S6).

  If the determination is YES and the closing timing of the intake valve 11 is currently retarded from the predetermined timing α, the closing timing of the intake valve 11 that advances with the switching to the SI mode passes the predetermined timing α. Therefore, a control signal is output in step S7, and the operation timing, lift amount, and opening / closing period of the intake valve 11 are changed by the operation of the VVL 14 and VVT 15. Specifically, as indicated by a solid line in FIG. 6A, the VVT 15 is not operated for a while (time t1 to t2) from the start of mode switching, and the lift amount and valve opening of the intake valve 11 are activated by the operation of VVL14. Decrease period. As a result, the opening timing of the intake valve 11 hardly changes as shown in FIG. 5B, and only the closing timing advances as the valve opening period decreases.

  That is, as the closing timing of the intake valve 11 is advanced and approaches the predetermined timing α, the lift amount and the like rapidly decrease with this, and filling as indicated by the dotted line in FIG. The fluctuation of the efficiency ce is cancelled, and the charging efficiency ce decreases at a substantially constant rate as indicated by the solid line in FIG. In addition, before and after switching from the HCCI mode to the SI mode, the operation timing of the intake valve 11 changes to the advance side as a whole. Therefore, even if the valve opening period is reduced as described above, the opening timing is retarded. It can be said that it is preferable for control not to change to the side.

  Then, in step S8, it is determined whether or not the closing timing of the intake valve 11 has passed the predetermined time α. Until it passes (NO), the process returns to step S7, while if it passes (YES), the process proceeds to step S9. The operation timing is advanced by the VVT 15 as shown in FIG. 5C and FIG. 6A, and the lift amount and the opening / closing period are increased by the VVL 14 as shown in FIG. 6B. At this time, as shown in FIG. 5 (c), the closing timing of the intake valve 11 is advanced to move away from the predetermined timing α, so that the charging efficiency is suddenly lowered. Therefore, as shown by the solid line in FIG. 6C, the filling efficiency ce continues to decrease at the same substantially constant rate as described above.

  In this way, it is determined in step S10 whether or not the operation timing, lift amount, and valve opening period of the intake valve 11 have been changed, and these have become control target values in the SI mode after mode switching. While this determination is NO, the process returns to step S9, and if the determination is YES, that is, if the lift amount of the intake valve 11 is in a state suitable for the SI mode, the process returns to completion (time t3 in FIG. 6). ).

  If NO is determined in step S6, the closing timing of the intake valve 11 before the mode switching is on the advance side with respect to the predetermined timing α, and does not pass through at the time of switching, so the process proceeds to step S11. In step S12, the operation timing of the intake valve 11 is advanced until it is determined that the switching is completed, and the lift amount and the opening / closing period are decreased.

  Next, when the engine 1 is switched from the SI mode to the HCCI mode, NO is determined in step S4, and the process proceeds to steps S13 to S18 shown in the flow of FIG. 8 to control the intake valve 11 for mode switching. . That is, in step S13, as in step S5, a predetermined intake valve closing timing α corresponding to the current load and speed of the engine 1 is read, and in subsequent step S14, the closing timing of the intake valve 11 in the HCCI mode after switching is read. Is determined to be retarded from the predetermined time α.

  If this determination is YES and the closing timing of the intake valve 11 after the mode switching is on the retard side of the predetermined timing α, as shown in FIGS. 9A to 9D along with the switching to the HCCI mode. The retarded closing timing of the intake valve 11 passes a predetermined intake valve closing timing α. Therefore, in step S15, the entire operation timing of the intake valve 11 is retarded by the VVT 15 as shown in FIG. 10 (a), and the lift amount and the opening / closing period of the intake valve 11 are increased by the VVL 14 as shown in FIG. 10 (b). (Time t1).

  Then, when the closing timing of the intake valve 11 is retarded by the operation of both VVL 14 and VVT 15 and rapidly approaches the predetermined timing α, the charging efficiency ce rapidly increases as shown in FIG. Then, when it becomes a value suitable for the HCCI mode after switching, the lift amount and the valve opening period of the intake valve 11 are decreased as shown in FIG. 9B and FIG. Prevent efficiency ce from rising. That is, as the closing timing of the intake valve 11 approaches the predetermined timing α, the lift amount and the valve opening period can be reduced, and fluctuations in the charging efficiency ce as shown by the dotted line in FIG.

  Then, in step S16, it is determined whether or not the closing timing of the intake valve 11 has passed the predetermined time α. Until it passes (NO), the process returns to step S13, but if it passes (YES), the process proceeds to step S17. As shown in FIGS. 9 (c) and 10 (b), the lift amount and the opening / closing period are increased as the operation timing of the intake valve 11 is delayed. The closing timing of the intake valve 11 also changes to the retard side even with this increase in the opening / closing period, but the charging efficiency is maintained substantially constant by increasing the lift amount and the opening / closing period (time t2 to t3).

  Thus, the operation timing, lift amount and valve opening period of the intake valve 11 are changed, and it is determined in step S18 whether or not they have become control target values in the HCCI mode after mode switching. During NO, the process returns to step S17, and if the determination is YES, the state is suitable for the SI mode, and the process returns upon completion of switching (time t3 in FIG. 10). If it is determined as NO in step S14, the closing timing of the intake valve 11 does not pass the predetermined timing α when the mode is switched, and the process immediately proceeds to steps S17 and S18.

  Step S7 in FIG. 7 and step S15 in FIG. 8 are respectively performed while changing the closing timing of the intake valve 11 to either the advance side or the retard side by the VVT 15 at the time of mode switching. This corresponds to the first step of reducing the lift amount and the valve opening period by the VVL 14 as the intake valve closing timing α approaches.

  Further, in steps S9 and S17, respectively, when the mode is changed, the closing timing of the intake valve 11 is changed to the one by the VVT 15 while passing through the predetermined intake valve closing timing α and away from it. This corresponds to the second step of increasing the lift amount and the valve opening period by the VVL 14.

  The control described above is realized by the CPU executing a control program stored electronically in the memory of the PCM 30. In this sense, the PCM 30 controls the VVT 15 at the time of mode switching. The operation timing control means for changing the closing timing of the intake valve 11 to either the advance side or the retard side so as to pass the predetermined timing α, and at that time, the closing timing of the intake valve 11 is set to the predetermined timing α. A lift control means for decreasing the lift amount or the valve opening period as it approaches and increasing the lift amount or the valve opening period as it moves away from the time α is provided in the form of a software program.

  Therefore, according to the engine control apparatus A according to this embodiment, first, when the engine 1 is in the HCCI region (H) on the relatively low load side, the so-called negative overlap ( NVO) period is provided, and self-ignition due to compression of the premixed gas can be promoted by increasing the temperature in the cylinder 2 with a large amount of internal EGR gas. On the other hand, in the SI region (S) on the relatively high load side, a sufficient output can be ensured by conventional general SI combustion.

  When the engine 1 shifts between the HCCI region (H) and the SI region (S) and the combustion mode is switched, the operation timing or lift amount of the intake valve 11 is changed by the operation of the VVL 14 or VVT 15. As the engine is closed, when the closing timing passes the predetermined intake valve closing timing α, the amount of lift etc. is temporarily reduced to sufficiently suppress fluctuations in charging efficiency, The fluctuation of the air-fuel ratio can be almost eliminated.

  In addition, in this embodiment, as shown in FIG. 5B and FIG. 6A, when the control mode is switched from the HCCI mode to the SI mode for a while (time t1 to t2), The opening time is hardly changed, the lift amount and the valve opening period are decreased, and only the closing time is advanced, thereby simplifying the control.

(Other embodiments)
The configuration of the present invention is not limited to the above-described embodiment, and includes various other configurations. That is, in the above-described embodiment, the NVO period is provided for the operation of the intake and exhaust valves 11 and 12 in the entire HCCI region (H) on the relatively low load side, but the present invention is not limited to this, and the HCCI region (H ), The NVO period may be provided only on the low load side.

  In the above embodiment, the opening timing of the intake valve 11 is hardly changed for a while when switching from the HCCI mode to the SI mode, and only the closing timing is advanced. Such a period may not be provided.

  In addition, the VVL 14 of the above embodiment has a structure in which the valve opening period increases and the operation timing is retarded as the lift amount increases. However, the present invention is not limited to this, and the lift amount and the valve opening period are not limited. The operating time may not change even if it changes, or the valve opening period and operating time may not change even if the lift amount changes.

  Furthermore, in the above-described embodiment, the lift characteristics of the intake valve 11 are continuously changed by the operation of the VVL 14 and VVT 15, but the present invention is not limited to this. For example, the intake valve 11 is individually opened and closed by an actuator. A simple valve mechanism may be used.

  As described above, the present invention can sufficiently reduce fluctuations in torque and air-fuel ratio at the time of mode switching in an engine that switches between the HCCI mode and the SI mode, and is suitable for automobiles. is there.

1 is a diagram illustrating an overall configuration of an intake valve control device according to an embodiment of the present invention. It is a block diagram which shows the outline of control. It is explanatory drawing which shows the change of the lift characteristic of an intake valve. It is explanatory drawing which shows an example of the control map which switches combustion mode. It is explanatory drawing which shows the change of the lift characteristic of an intake valve when switching from HCCI mode to SI mode. It is a time chart which shows the change of the operation timing of the intake valve, the lift amount, the charging efficiency, the EGR rate, and the air-fuel ratio when the mode is switched. It is a flowchart figure which shows the control procedure of an intake valve when switching from HCCI mode to SI mode. FIG. 8 is a diagram corresponding to FIG. 7 when switching from the SI mode to the HCCI mode. FIG. 6 is a diagram corresponding to FIG. 5 when switching from the SI mode to the HCCI mode. FIG. 7 is a diagram corresponding to FIG. 6 when switching from the SI mode to the HCCI mode.

Explanation of symbols

A Engine control device (Intake valve control device)
1 Engine 2 Cylinder 11 Intake valve 12 Exhaust valve 14 VVL (variable mechanism)
15 VVT (variable mechanism)
30 PCM (operation timing control means, lift control means)

Claims (6)

A variable mechanism that can change the operation timing and lift amount or valve opening period of the intake valve and exhaust valve is provided, and a negative overlap period that closes both the intake valve and the exhaust valve in the exhaust stroke or intake stroke of the cylinder is provided. Intake of the engine that switches between the self-ignition mode in which the fuel gas remains and the pre-mixed gas is self-ignited in the later stage of the compression stroke and the spark ignition mode in which the air-fuel mixture in the cylinder is ignited A valve control method comprising:
When the mode is switched between the self-ignition mode and the spark ignition mode, the lift amount or the valve opening period is changed while changing the closing timing of the intake valve to either the advance side or the retard side by the variable mechanism. A first step of changing the charging efficiency of the intake air to be low;
A second step of changing the lift amount or the valve opening period so as to increase the charging efficiency while changing the closing timing of the intake valve to the one by the variable mechanism when the mode is switched;
An engine intake valve control method comprising: In the first step, the lift amount or the valve opening period is decreased as the closing timing is approached until the predetermined intake valve closing timing at which the charging efficiency becomes the highest due to the inertia of the intake flow,
2. The engine intake valve control method according to claim 1, wherein in the second step, the lift amount or the valve opening period is increased as the predetermined intake valve closing timing passes and leaves.   In the case of mode switching from the self-ignition mode to the spark ignition mode, in the first step, the closing mechanism of the intake valve is advanced by the variable mechanism, while the valve opening period is decreased without changing the opening timing. The engine intake valve control method according to claim 2, wherein: A variable mechanism that can change the operation timing and lift amount or valve opening period of the intake valve and exhaust valve is provided, and a negative overlap period that closes both the intake valve and the exhaust valve in the exhaust stroke or intake stroke of the cylinder is provided. Intake of the engine that switches between the self-ignition mode in which the fuel gas remains and the pre-mixed gas is self-ignited in the later stage of the compression stroke and the spark ignition mode in which the air-fuel mixture in the cylinder is ignited A valve control device,
When the mode is switched between the self-ignition mode and the spark ignition mode, at least the closing timing of the intake valve is changed to either the advance side or the retard side by the variable mechanism, and the charging efficiency is increased by the inertia of the intake flow. An operation timing control means for passing a predetermined timing that is the highest,
When the closing timing of the intake valve approaches the predetermined time at the time of the mode switching, the lift amount or the valve opening period is decreased accordingly, and when the predetermined time passes and leaves, the lift amount is accordingly increased. Or lift control means for increasing the valve opening period;
An intake valve control device for an engine, comprising:   When the mode is switched from the self-ignition mode to the spark ignition mode, the lift control means sets a valve opening period so that the opening timing does not change when the closing timing of the intake valve advances and approaches the predetermined timing. 5. The engine intake valve control device according to claim 4, wherein the intake valve control device is reduced.   The variable mechanism changes both the lift amount and the valve opening period of the intake valve so that the valve opening period increases as the lift amount increases while the valve opening period also decreases as the lift amount decreases. The intake valve control device for an engine according to any one of claims 4 and 5.

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