JPH10252511A - Control device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress discharging of unburned fuel when an engine is started, in the internal combustion engine provided with a valve drive mechanism capa ble of opening/closing an intake/exhaust valve in arbitrary timing. SOLUTION: In a valve drive mechanism 20A, 20B, an intake/exhaust valve 11, 12 of an engine 1 is open/close driven. In an ECU 50, action of the valve drive mechanism 20A, 20B is controlled, open/close timing of the intake/exhaust valve 11, 12 is variably adjusted. In the case thus provided, the ECU 50 decides whether fuel in a cylinder of the engine 1 makes complete combustion or not, when a fact of incomplete combustion is decided, opening action of the intake/ exhaust valve 11, 12 is ceased in a fixed period, after complete combustion is confirmed, opening action of the intake/exhaust valve 11, 12 as ordinary is permitted. Here, at incomplete combustion time, a compression/expansion stroke is overlapped to be executed, also ignition of fuel is executed at each time. That is, in place of ordinary 4-cycle operation, 6-cycle operation of (suction + compression + expansion + recompression + reexpansion + exhaust) is executed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a four-cycle internal combustion engine having a valve drive mechanism capable of opening and closing an intake valve and an exhaust valve at any time and repeatedly performing four strokes of intake, compression, expansion and exhaust. The present invention relates to a control device which is applied, and particularly controls a combustion state at the time of starting the engine.

[0002]

2. Description of the Related Art In a general internal combustion engine, the rotation of a crankshaft is transmitted to an intake camshaft and an exhaust camshaft via timing means such as a belt or a chain. The intake valve and the exhaust valve are opened and closed by rotation of the camshaft. However, in such a configuration,
At the time of cranking by the starter motor, even if the fuel is ignited, if the in-cylinder pressure due to compression is not sufficiently increased, the flame does not sufficiently propagate and the combustion becomes slow. Therefore, there is a problem in that the combustion is continued until the exhaust valve is opened, then the flame is extinguished, and a large amount of unburned fuel (unburned HC) is discharged. Furthermore, if fuel injection is continued even during such an unstable state of starting the engine, a large amount of fuel remains on the intake port or cylinder as adhering to the wall surface or as floating droplets. These remaining fuels are vaporized at the time of compression after the initial explosion, and are liquefied at a stretch by blowdown to wet the spark plug. As a result, poor ignition due to plug smoldering may occur, leading to inability to start.

[0003] Under such circumstances, as a method of solving the above problem, there has been proposed a control device for an internal combustion engine provided with a valve drive mechanism capable of opening and closing an intake valve and an exhaust valve at an arbitrary timing (for example, Japanese Patent Application Laid-Open No. HEI 9-102572). 2-26730
No. 8). In such a device, the opening and closing operations of the intake valve and the exhaust valve are not performed by being linked to the rotation of the camshaft, but can be performed at an arbitrary timing and in an arbitrary cycle regardless of the rotation of the crankshaft. I was able to do it.

[0004]

However, in the above-mentioned conventional apparatus, although it is possible to open and close the intake and exhaust valves at an arbitrary timing, there is no disclosure concerning valve control at the time of starting the engine. At the time of starting, unburned fuel (unburned HC) may be discharged to the outside.

The present invention has been made in view of the above problems, and an object of the present invention is to provide an internal combustion engine having a valve drive mechanism capable of opening and closing intake and exhaust valves at any time. An object of the present invention is to provide a control device for an internal combustion engine that can suppress emission of unburned fuel at the time of starting.

[0006]

According to the first aspect of the present invention, a control command is given to a valve drive mechanism to control the opening and closing operations of an intake valve and an exhaust valve. Valve operation control means, complete combustion determination means for determining whether or not fuel is completely combusted in the cylinder of the internal combustion engine, at least when the complete combustion determination means determines that incomplete combustion has occurred, Valve operating means for suspending the opening operation of the exhaust valve by the valve operation control means within a certain period of time and allowing normal opening operation of the exhaust valve after confirming complete combustion.

In short, for example, when the internal combustion engine is started at a low temperature, the combustion of the fuel may be in an incomplete combustion state. In this state, if the opening and closing operation of the exhaust valve is performed according to a normal process, the unburned fuel (unburned fuel) HC) may be emitted. On the other hand, according to the configuration described above, it is possible to suppress the discharge of unburned fuel at the time of starting the engine by keeping the exhaust valve closed for a predetermined period during incomplete combustion.

In the first aspect of the present invention, it is desirable that the following second and third aspects of the present invention are implemented together. In the invention described in claim 2, when it is determined that incomplete combustion is occurring, the opening operation of the intake and exhaust valves by the valve operation control means is stopped, and the compression and expansion strokes are performed repeatedly. I have to. According to the third aspect of the invention, when the compression and expansion strokes are repeatedly performed, the ignition of the fuel is performed each time.

According to the second and third aspects of the present invention, instead of the normal four-cycle operation of "intake + compression + expansion + exhaust", the operation of "intake + compression + expansion + recompression + reexpansion + exhaust" is performed. 6
Cycle operation becomes possible. Thus, the combustion of the unburned fuel is repeated during incomplete combustion, and the complete combustion of the unburned fuel is promoted.

According to the present invention, it is determined whether or not to suspend the opening operation of the exhaust valve by the valve operating means based on the engine operating state. The operation of the exhaust valve is controlled as usual without suspending the operation. In this case, more specifically, as described in claim 5, it is preferable not to suspend the opening operation of the exhaust valve in the extremely low speed range or the extremely low temperature range of the internal combustion engine.

That is, during the low temperature start of the engine, if the opening operation of the exhaust valve is paused as described above, or if the six-cycle operation is performed by overlapping the compression and expansion strokes, the emission of unburned fuel is suppressed. As described above, such control may cause a disadvantage that the start time is lengthened when the internal combustion engine is under a predetermined operating state. Incidentally, the operating state of the engine in which such inconveniences may occur is, for example, a case where the engine speed (rotation speed at the time of cranking) is in an extremely low speed range of 100 rpm or less, or a case where the cooling water temperature is 0 ° C. or less. For example, this corresponds to a state where the battery load becomes excessive (a state where the starter current decreases). Therefore, in the above-mentioned operation state, in order to give priority to shortening the starting time, the six-cycle operation is prohibited and the normal four-cycle operation is performed.

Such a configuration serves as a criterion for determining whether to give priority to an incomplete combustion cylinder or a complete combustion cylinder when there is an incomplete combustion cylinder even in one cylinder in a multi-cylinder internal combustion engine. . At this time, if the incompletely burned cylinder is prioritized, the emission of unburned fuel is suppressed, while if the completely burned cylinder is prioritized, the starting time is reduced.

Furthermore, in the invention described in claim 6, the complete combustion determination means performs complete combustion based on the magnitude relationship between the required time of the compression stroke and the required time of the expansion stroke at the time of cranking by the starter motor. It is determined whether or not. That is, during complete combustion, the rotation speed of cranking increases during the expansion stroke as compared to the compression stroke, whereas during incomplete combustion (during misfire), there is almost no change in rotation speed between the compression stroke and the expansion stroke. . Therefore, the combustion state can be easily determined by comparing the time required for the compression stroke with the time required for the expansion stroke. As parameters for determining complete combustion,
Changes in the current flowing through the starter motor (starter current), battery voltage, in-cylinder pressure, and the like during cranking may be used, and the combustion state can be easily determined using these parameters.

On the other hand, in order to further suppress the emission of unburned fuel (HC) as described above, it is necessary to improve the engine startability. Therefore, in claims 7 to 9 described below, the injected fuel is atomized by the injector, thereby improving the engine startability. In the invention described in claim 7, at the time of starting the engine, the valve operation control means delays the opening timing of the intake valve from the normal timing. In the invention described in claim 8, at the time of starting the engine, the valve operation control means advances the closing timing of the exhaust valve more than the normal timing. According to the ninth aspect of the invention, after the starter motor starts cranking, the valve operation control means opens the intake valve first and then opens the exhaust valve.

According to the tenth aspect of the present invention, the number of revolutions at the time of cranking by the starter motor is detected, and the valve operation control means is provided until the detected number of revolutions at the time of cranking reaches a predetermined rotation range. (For example, both valves are opened or closed). In this case, the pump loss is reduced and the load on the starter motor can be reduced by not opening and closing the intake and exhaust valves until the cranking rotation speed increases. At this time, fuel injection and ignition are also stopped. Then, after the compression pressure is increased to the cranking speed at which the compression pressure becomes sufficient, the valves are opened and closed in the order of the exhaust side → the intake side.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION

(First Embodiment) Hereinafter, a first embodiment of the present invention will be described.
An embodiment will be described with reference to the drawings. In the present embodiment, the present invention is embodied in a four-cylinder gasoline injection type four-stroke engine, and its main configuration is that a hydraulic actuator drives an intake valve and an exhaust valve of the engine to open and close. A valve driving mechanism (camless valve driving mechanism) and an electronic control unit (hereinafter referred to as EC) for variably adjusting the opening / closing timing (valve timing) of intake and exhaust valves by controlling the operation of the valve driving mechanism.
U). The engine is configured to inject and supply fuel to an intake port, and has two valves on each of an intake side and an exhaust side (a total of four valves for each cylinder). The details will be described below.

FIG. 1 is a configuration diagram schematically showing an engine cross section and an engine control system according to the present embodiment. In FIG. 1, a cylinder 3 is formed in a cylinder block 2 of an engine 1.
Inside, a piston 4 connected to a crankshaft (not shown) is disposed so as to be able to reciprocate up and down in the figure. The piston 4 is connected to a crankshaft (not shown) via a connecting rod 5. The cylinder head 7 has an intake port 8 and an exhaust port 9 which communicate with the combustion chamber 6 above the piston. The intake port 8 is provided with an electromagnetically driven injector 10. The injector 10 controls the intake port 8 based on an injection control signal from the ECU 50.
Inject fuel into

Further, an intake valve 11 and an exhaust valve 12 are disposed in the cylinder head 7. The combustion chamber 6 and the ports 8,
9 is communicated or closed (intermittent). The combustion chamber 6 is substantially closed when the intake valve 11 and the exhaust valve 12 are both closed.
In the combustion chamber 6, an ignition plug 43 that ignites based on an ignition control signal from the ECU 50 is provided.

The valve drive mechanisms 20A and 20B are disposed above the cylinder head 7, and control the opening and closing operations of the intake valve 11 and the exhaust valve 12 in response to a control signal from the ECU 50. The valve drive mechanisms 20A, 20A
The detailed configuration of B will be described later.

The starter motor 44 is used to apply an initial rotation to the engine 1 to perform cranking.
It is driven to rotate by the power supply from. Incidentally, a starter current and a battery voltage flowing when the starter motor 44 is driven are detected as needed and input to the ECU 50.

The ECU 50 mainly includes a CPU for executing various control programs and a well-known microcomputer having a memory for storing control data, maps, and the like. A water temperature signal (Tw), an intake air temperature signal (Tin) detected by the intake air temperature sensor 52, a crank angle signal (Ne) detected by the crank angle sensor 53, and the like are input. And
Based on these input signals, control of fuel injection by the injector 10 and ignition control by the spark plug 43 are performed. In particular, at the time of starting the engine, the ECU 50 calculates an optimal fuel injection amount according to the cranking rotation speed, the engine water temperature, and the intake air temperature, and injects fuel from the injector 10 in synchronization with the opening timing of the intake valve 11. Further, an expected in-cylinder pressure is calculated from the cranking speed and the valve timing, and ignition is performed at a time when the thermal efficiency becomes the best while taking the combustion delay into account.

Further, the ECU 50 corresponds to valve operation control means for outputting a control command to the valve drive mechanisms 20A, 20B, and based on the various signals described above, the intake valve 11 and the exhaust valve by the valve drive mechanisms 20A, 20B. The opening and closing timing of the valve 12 is controlled. At this time, during normal operation of the engine 1, the opening and closing of the intake and exhaust valves 11, 12 are controlled in accordance with the engine speed and the engine load.
When the engine 1 is started at a low temperature, the opening and closing of the intake and exhaust valves 11 and 12 are controlled according to the fuel combustion state during the cranking period.

Next, referring to FIG.
The configuration of A, 20B and its peripheral parts will be described. However,
FIG. 2 shows only the configuration of the intake-side valve drive mechanism 20A, and FIG. 2 shows a pair of left and right intake valves 11.

In FIG. 2, a spring retainer 13 is attached to an upper end of the intake valve 11, and the intake valve 11 is provided between the spring retainer 13 and the cylinder head 7 in a valve closing direction (upward in the figure). A valve spring 14 for biasing is provided. The pair of left and right intake valves 11 is connected by a valve bridge 15 so as to be integrally operated. A plunger 16 that reciprocates vertically in the figure is connected to the upper surface of the valve bridge 15,
When the plunger 16 moves downward, the intake valve 1
1 is opened (the state shown in the figure) and moves upward, whereby the intake valve 11 is closed. The operation of the plunger 16 depends on the hydraulic pressure of the hydraulic chamber 17 formed on the upper surface thereof (the valve driving mechanism 20A).
Is controlled in accordance with the operating hydraulic pressure of the motor), the details of which will be described later. Reference numeral 18 denotes the intake valve 1
1 is an adjustment screw for finely adjusting the operation position.

On the other hand, in the valve drive mechanism 20A, a circular hole 22 extending in the left-right direction in the figure is formed in a housing 21 fixed to a part of the cylinder head 7, and the hole 22 is provided with a spool type. A directional control valve (hereinafter, referred to as a directional control valve) 23 is provided. Direction control valve 23
Are roughly divided into a cylindrical sleeve 24 and a sleeve 24.
The sleeve 24 is fixed by a lid 33 screwed in the vicinity of the opening of the circular hole 22. Hydraulic ports 26a, 26b, 26c are formed in an annular shape on the outer peripheral surface of the sleeve 24, and these hydraulic ports 26a, 26b, 26c are respectively provided with communication passages 27a, 27b,
It communicates with the inner peripheral surface of the sleeve via 27c.

The housing 21 has a hydraulic pump 4
A suction port 28 for sucking high-pressure oil supplied from 1 into the direction control valve 23 and a discharge port 29 for discharging high-pressure oil from the direction control valve 23 to the drain tank 42 are provided. Here, the hydraulic pump 41 pumps up the hydraulic oil from the drain tank 42, raises the pressure to about 12 MPa, and supplies it to the directional control valve 23. The suction port 28 communicates with the hydraulic port 26a via a passage 30, and the discharge port 29 communicates with the hydraulic port 26c via a passage 31. The hydraulic chamber 17 communicates with the hydraulic port 26b via a passage 32.

A housing chamber 35 is provided inside the housing 21.
A piston 36 that slides on the inner peripheral surface of the housing chamber 35 is provided in the housing chamber 35. In the piston 36, a piezo stack 37 that extends when voltage is applied is disposed. The piezo stack 37 is formed by laminating a large number of PZTs (lead zirconate titanate) as piezoelectric elements, and has a pair of electrodes 38a and 38b attached to one end thereof. Electrodes 38a, 3
A predetermined voltage is applied to 8b via the driver 55 based on a control command from the ECU 50. On the other hand, a disc spring 39 provided on the left side of the piston 36 applies a force in the contracting direction to the piezo stack 37. FIG. 2 shows a state where a voltage is applied to the piezo stack 37, and shows a state where the piezo stack 37 is extended and the piston 36 moves to the left in the drawing.

Next, the operation of the valve drive mechanism 20A will be described with reference to FIG.
It will be described according to. Here, FIG. 3A shows a state where a voltage is applied to the piezo stack 37. That is, when a voltage is applied, the piezo stack 37 is extended, and the piston 36 moves leftward in the figure against the spring force of the disc spring 39, whereby the spool 25 is pushed leftward.
At this time, the high-pressure oil sucked into the suction port 28 flows as shown by a broken line arrow in the drawing and is supplied into the hydraulic chamber 17, and the intake valve 11 is opened.

FIG. 3B shows a state in which no voltage is applied to the piezo stack 37. That is, in the state where the voltage application to the piezo stack 37 is released, the piston 25 is urged rightward in the figure by the spring force of the disc spring 39, so that the spool 25 is drawn rightward. At this time, the hydraulic oil in the hydraulic chamber 17 flows as indicated by the dashed arrow in the figure and is discharged to the discharge port 29 (returned to the drain tank 42), and the intake valve 11 is closed. Note that the above-described voltage application operation is controlled based on a control signal from the ECU 50.

As described above, in the valve drive mechanism 20A of the present embodiment, the plunger 16 and the hydraulic chamber 17 constitute a hydraulic cylinder for driving the intake valve 11, and the hydraulic control valve for interrupting the supply of hydraulic pressure to the hydraulic cylinder. Is constituted by a hydraulic pump 41 and a direction control valve 23. By using such a configuration, the opening / closing timing of the intake valve 11 can be freely controlled, and the intake characteristics of the engine 1 can be changed. Further, only the opening timing of the intake valve 11 can be changed without changing the closing timing of the intake valve 11 (conversely, only the valve closing timing can be changed).

Although the illustration and detailed description of the exhaust-side valve drive mechanism 20B are omitted, the exhaust-side valve drive mechanism 20B has substantially the same configuration as the above-described intake-side valve drive mechanism 20A. After all ECU5
The opening and closing are performed based on the control of the valve drive mechanism 20B by 0.

Next, the operation of this embodiment will be described. Here, in the present embodiment, when the engine 1 is started at a low temperature, the intake and exhaust valves 1
It is characterized by controlling the opening and closing operation of 1, 12
The outline will be described with reference to FIGS. In each of FIGS. 6 to 8, BDC shown on the horizontal axis indicates the piston bottom dead center of the engine 1, TDC indicates the piston top dead center, and the vertical axis indicates the valve lift amount.

FIG. 6 is a time chart showing the operation of the engine 1 in the normal mode corresponding to each of the steps of "exhaust", "intake", "compression", and "expansion". As shown in the figure, the exhaust valve 12 is opened during a period immediately before BDC and immediately after TDC in the exhaust stroke, and the intake valve 11 is opened during a period immediately before TDC and immediately after BDC in the intake stroke. Further, the fuel injection by the injector 10 is performed at an early stage of the intake stroke, and the injected fuel is ignited by the ignition plug 43 immediately before the compression TDC.
That is, in the normal mode shown in FIG. 6, the opening and closing operations of the intake and exhaust valves 11, 12 are controlled according to the four-cycle operation of the engine 1, and the fuel injection and ignition operations are controlled (hereinafter, this normal mode). Is also referred to as “four-cycle operation mode”). Although the valve lift operation of the present embodiment is realized by the hydraulic valve drive mechanisms 20A and 20B, it substantially matches the profile of a cam drive type that performs a lift operation with the rotation of the cam shaft.

In FIG. 7, the normal mode (4
The compression and expansion strokes are repeated twice as compared with the cycle operation mode). That is, this means that after the fuel injection, the intake and exhaust strokes (opening of the intake and exhaust valves 11, 12) after the compression and expansion strokes are performed once,
This means that the operation is stopped, and a six-cycle operation of “exhaust → intake → compression → expansion → compression → expansion” is performed as a whole (this is referred to as “six-cycle operation mode”). In this case, the compression and expansion strokes are 2 for one fuel injection.
This is repeated twice, and the ignition is performed each time near the two compression TDCs within the crank angle of 1080 degrees, thereby promoting the complete combustion of the in-cylinder fuel.

Further, in FIG. 8, the four-cycle operation is performed in the same manner as in the normal mode in FIG. 6, except that the opening timing of the intake valve 11 is delayed from TDC in FIG. (However, the opening / closing timing of the exhaust valve 12 is normal). In this case, by opening the intake valve 11 after the inside of the cylinder has a negative pressure, the flow velocity of the intake air is increased, and the fuel spray is guided into the cylinder (inside the combustion chamber 6) by the intake flow. Thereby, atomization of the injected fuel by the injector 10 is promoted. In the following description,
Such an operation mode is referred to as a “fuel atomization mode”.

FIG. 4 is a flowchart showing a valve control routine at the time of starting the engine according to the present embodiment. The routine is started by the ECU 50 in response to an ON operation of an ignition key.

Referring to FIG. 4, the ECU 50 first determines in step 101 whether the start completion flag XF1 is set to "1". This start completion flag XF1
Is initialized to “0” with the start of this routine, and is set to “1” when the following start completion condition is satisfied. That is, in step 102, the engine speed N detected by the crank angle sensor 53
It is determined whether or not e is equal to or higher than a predetermined rotation speed (400 rpm in the present embodiment). In the next step 103, the engine water temperature Tw detected by the water temperature sensor 51 is set to a predetermined temperature (40 in the present embodiment). ° C) or more. If any of steps 102 and 103 (start completion condition) is satisfied, the ECU 50 determines that the engine 1 has been warmed up and the start has been completed, and
At step 04, "1" is set to a start completion flag XF1. When the flag XF1 is set in this manner, the intake and exhaust valves 11, 12 are not driven by valve control at the time of low-temperature start described later, but are driven by well-known valve control during normal operation ( For example, based on the engine speed Ne and the engine load, the intake and exhaust valves 1
1, 12 are controlled).

On the other hand, before the start is completed (XF1 =
0), if both of the steps 102 and 103 are not satisfied (when Ne <400 rpm and Tw <40 ° C.), the ECU 50 proceeds to step 105 and sets the engine speed Ne to a predetermined engine speed (this embodiment). Then, 60 rp
m) It is determined whether or not it is not less than. At this time, when the engine is cold in winter or when the voltage of the battery 45 is low, a negative determination is made in step 105 (Ne <60 rpm), and EC
U50 proceeds to step 106.

In step 106, the ECU 50 controls the intake and exhaust valves 11, 12 according to the fuel atomization mode described above.
(See FIG. 8). That is, the opening timing of the intake valve 11 is controlled to the delay side, and the injector 10
Atomization of the injected fuel by the fuel is promoted. Further, the ECU 50 sets “1” to the four-cycle operation flag XF2 in the following step 107. The four-cycle operation flag XF2 indicates that the engine 1 is “four-cycle operation”
Or, when XF2 = 1, it is determined that four-cycle operation is being performed, and the crank angle is set within 720 degrees based on a control program (not shown). The fuel injection and the ignition are performed once each, and when XF2 = 0, it is determined that the six-cycle operation is being performed, and the fuel injection and the two ignitions are performed within the crank angle of 1080 degrees. (See FIGS. 6 to 8). Step 10 above
The processing of steps 6 and 107 is repeatedly executed until Ne ≧ 60 rpm and the determination in step 105 is affirmative.

When the determination in step 105 is affirmative,
The ECU 50 proceeds to step 108 in FIG. 5 and determines whether or not a condition for stopping the opening operation of the intake and exhaust valves 11 and 12 (valve stop condition) is satisfied. Here, the valve stop condition is determined by, for example, a map shown in FIG. 9. If the engine state at that time is in a permission area (shaded area in FIG. 9), the intake and exhaust valves 11 and 12 are used. The opening operation of the intake and exhaust valves 11 and 12 is prohibited if the operation is in a prohibited area other than the permission area.

If the determination in step 108 is negative, E
The CU 50 proceeds to step 109, and performs the intake and exhaust valves 1 according to the above-described normal mode (four-cycle operation mode).
Opening / closing control of the first and the second 12 (see FIG. 6). Also, EC
U50 sets “1” to the four-cycle operation flag XF2 in the subsequent step 110, and then sets in step 10 in FIG.
Return to 1. That is, as shown in FIG. 9, the engine 1 is operated under a low rotation condition or a low temperature condition (an area other than the hatched area in the figure).
Then, quick warm-up by promoting combustion is demanded. Therefore, in such a case, the valve control in the four-cycle operation mode has priority over the valve control in the six-cycle operation mode.

On the other hand, if the determination in step 108 is affirmative, the ECU 50 reads the time required for the compression stroke in step 111 (hereinafter referred to as the compression time t1), and in step 112, the time required for the expansion stroke. (Hereinafter referred to as expansion time t2). The compression time t1 and the expansion time t2 are calculated based on the detection result of the crank angle sensor 53.

Further, the ECU 50 calculates the time ratio (t1 / t2) between the read compression time t1 and the expansion time t2 in step 113, and in the following step 114, calculates the combustion at that time based on the time ratio (t1 / t2). It is determined whether or not is in a complete combustion state. In this case, FIG.
As shown in (b), if the combustion state is complete, the compression time t
1, the expansion time t2 becomes shorter (t1 / t2>
1) In the case of incomplete combustion, the compression time t1 and the expansion time t2 substantially match (t1 / t2 ≒ 1). Therefore, EC
U50 is regarded as a complete combustion state if t1 / t2> 1, and is regarded as an incomplete combustion state if t1 / t2 ≒ 1.
Here, whether or not complete combustion may be determined simply based on the magnitude relationship between the compression time t1 and the expansion time t2.

If it is determined in step 114 that the combustion state is complete, the ECU 50 proceeds to step 109,
The opening and closing of the intake and exhaust valves 11 and 12 are controlled in accordance with the above-described normal mode (four-cycle operation mode) (see FIG. 6).
reference). Further, the ECU 50 proceeds to step 110 to
“1” is set to the cycle operation flag XF2, and thereafter, the process returns to step 101 of FIG.

If it is determined in step 114 that the combustion state is incomplete, the ECU 50 proceeds to step 115.
To control the opening and closing of the intake and exhaust valves 11 and 12 in accordance with the above-described six-cycle operation mode (see FIG. 7). Further, the ECU 50 clears the four-cycle operation flag XF2 to “0” in the subsequent step 116, and thereafter returns to step 101 in FIG.

In the present embodiment, the processing of steps 111 to 114 in FIG. 5 corresponds to complete combustion determination means described in the claims, and the processing of step 115 corresponds to valve operation means.

According to the present embodiment described in detail above, the following effects can be obtained. (A) In the present embodiment, the inside of the cylinder of the engine 1 (the combustion chamber 6
It is determined whether or not the fuel is completely burned in (in), and if it is determined that the fuel is incompletely burned, the opening operation of the intake and exhaust valves 11 and 12 is stopped within a predetermined period to stop the complete combustion. After the determination, the normal opening operation of the intake and exhaust valves 11 and 12 is allowed. In short, for example, when the engine 1 is started at a low temperature, an incomplete combustion state may occur. If the opening and closing operations of the intake and exhaust valves 11 and 12 are performed in a normal stroke under this state, unburned fuel (HC)
May be discharged. However, according to this configuration, it is possible to suppress the discharge of unburned fuel when the engine is started by maintaining the intake and exhaust valves 11 and 12 in the closed state during incomplete combustion.

(B) If it is determined that the combustion is incomplete, the opening operation of the intake and exhaust valves 11 and 12 is stopped, and the compression and expansion strokes are repeatedly performed, and the ignition of the fuel is performed. Was performed each time. According to this configuration, a six-cycle operation of “intake + compression + expansion + recompression + re-expansion + exhaust” can be performed instead of the normal four-cycle operation of “intake + compression + expansion + exhaust”. Thus, the combustion of the unburned fuel is repeated during incomplete combustion, and the complete combustion of the unburned fuel is promoted.

(C) Since the valve system, the fuel injection system, and the ignition system are controlled in association with each other by the flag operation (operation of the four-cycle operation flag XF2), these controls can be performed comprehensively.

(D) It is determined whether or not to suspend the opening operation of the intake and exhaust valves 11 and 12 based on the engine operating state (step 108 in FIG. 5). The opening and closing of the intake and exhaust valves 11 and 12 are controlled as usual without suspending the opening operation. That is, the six-cycle operation is prohibited, and the normal four-cycle operation is performed. More specifically, in the extremely low speed range or the extremely low temperature range of the engine 1, the opening operation of the intake and exhaust valves 11, 12 is not stopped (the map in FIG. 9). In this case, in a state in which the battery load becomes excessive (a state in which the starter current decreases), it is possible to give priority to shortening the start-up time over suppressing discharge of unburned fuel.

(E) Further, it is determined whether or not the combustion is complete, based on the magnitude relationship between the required time for the compression stroke and the required time for the expansion stroke during cranking by the starter motor 44. In this case, the combustion state can be easily determined.

(F) The opening timing of the intake valve 11 is delayed from the normal timing (step 10 in FIG. 4).
6). That is, in order to further suppress the discharge of unburned fuel, it is necessary to improve the engine startability. Therefore,
By controlling the opening timing of the intake valve 11, the injector 10
The atomization of the injected fuel is attempted. in this case,
It is possible to suppress the emission of the unburned fuel and improve the engine startability.

The embodiment of the present invention can be realized in the following modes other than the above. In the above-described embodiment, the control is performed such that the opening operation of both the intake side and exhaust side valves 11 and 12 is stopped when incomplete combustion occurs at the time of low temperature start of the engine. However, this configuration may be changed. That is, if only at least the opening operation of the exhaust valve 12 is stopped, the effect of suppressing the discharge of unburned fuel can be obtained.

In the above embodiment, the compression and expansion strokes (and ignition) are performed one extra time at a time of incomplete combustion at the time of starting the engine at a low temperature, thereby realizing six-cycle operation of the engine 1. , The compression and expansion strokes (and ignition) may be performed two extra times to realize eight-cycle operation of the engine 1 (intake + compression + expansion +
The process of re-compression + re-expansion + re-compression + re-expansion + exhaust is performed). Further, the six-cycle operation and the eight-cycle operation may be selectively performed according to the engine operating state. In short, any configuration may be used as long as the intake and exhaust strokes are stopped within a certain period so as to suppress the discharge of unburned fuel in the cylinder and promote the combustion of the unburned fuel.

In a multi-cylinder engine (for example, a four-cylinder engine as in the above-described embodiment), if even one cylinder has an incomplete combustion cylinder, the incomplete combustion cylinder is given priority.
Alternatively, it may be determined whether to give priority to the complete combustion cylinder. If the incomplete combustion cylinder is to be prioritized, the six-cycle operation may be performed. If the complete combustion cylinder is to be prioritized, the four-cycle operation may be performed. At this time, if the incompletely burned cylinder is prioritized, the emission of unburned fuel is suppressed, while if the completely burned cylinder is prioritized, the starting time is reduced.

The valve control in the fuel atomization mode disclosed in the above embodiment may be embodied as shown in the following FIG. 11 or FIG. When the engine 1 is started at a low temperature, as shown in FIG. 11, the closing timing of the exhaust valve 12 is advanced from the normal timing, and after the exhaust valve 12 is closed, the inside of the cylinder (the inside of the combustion chamber 6) is compressed. The intake valve 11 is opened. In this case, the intake gas in the cylinder is blown back to the intake port 8, and the fuel spray is atomized. After the cranking by the starter motor 44 is started, as shown in FIG. 12, the intake valve 11 is first opened, and then the exhaust valve 12 is opened. in this case,
In the initial stage of the opening operation of the intake valve 11, the cylinder pressure is greater than the intake pipe pressure. Therefore, the intake gas in the cylinder is blown back to the intake port 8, and if the fuel is injected in synchronization with this timing, the fuel spray is atomized. You. In such a case, in particular, the amount of unburned fuel discharged is the shortest and the time required for starting is short in consideration of the cranking speed, intake air temperature, engine water temperature (cylinder wall temperature), battery voltage, and the like. The fuel injection is started at the same time as moving the intake valve 11 first without opening the exhaust valve 12 until the ranking rotation speed is reached. And
“Compression → ignition → explosion” is detected from the variation range of the cranking rotation speed, and the exhaust valve 12 is opened only when an explosion occurs. Further, when the explosion is insufficient, it is preferable to recompress and ignite without opening the exhaust valve 12, thereby completely terminating the combustion.

Here, step 1 in FIG.
The determination process of the engine speed Ne of 05 may be abolished, and the valve control in the fuel atomization mode may be always performed when the engine 1 is started at a low temperature. In this case, the valve control in the fuel atomization mode and the valve control in the six-cycle operation mode are performed in combination. On the other hand, it is also possible to embody the above-described process for atomizing the fuel without performing any process. Even in such a case, a process such as stopping the opening operation of the intake and exhaust valves 11 and 12 is performed. As a result, emission of unburned fuel can be suppressed.

Also, during incomplete combustion, the exhaust valve 12
May be delayed so that exhaust is performed after combustion is completely completed. That is, if the exhaust valve 12 is opened while the combustion is slow in the expansion stroke, the in-cylinder pressure drops sharply, which may extinguish the flame and discharge a large amount of unburned gas. The above problem can be prevented by delaying the opening timing of the valve 12.

Further, the rotation speed at the time of cranking by the starter motor 44 is detected, and the opening and closing operations of the exhaust and intake valves 11 and 12 are performed until the detected rotation speed at the time of cranking reaches a predetermined rotation range. Pause (eg, both valves open or closed). in this case,
By not opening and closing the intake and exhaust valves 11 and 12 until the cranking speed increases, the pump loss is reduced and the load on the starter motor 44 can be reduced.
At this time, fuel injection and ignition are also stopped. And
After the compression pressure has increased to the cranking speed at which the compression pressure becomes sufficient, the opening and closing operation of the exhaust valve 12 and the intake valve 12 may be performed in this order.

In the above embodiment, the compression time t1 and the expansion time t2 in the valve control routine of FIGS.
Although it is determined whether or not the engine 1 is completely combusted by using the time ratio of the above, this configuration may be changed. That is, as shown in FIGS. 10A and 10B, when the complete combustion is compared with the incomplete combustion, the peak value of the starter current is different. While it gradually decreases, the peak value of the starter current is maintained at a substantially constant value during incomplete combustion. Therefore, it is possible to determine the complete combustion state based on the peak value of the starter current.

Further, as a parameter for determining complete combustion, a change state of a current (starter current) flowing through the starter motor 44 at the time of cranking, a battery voltage, an in-cylinder pressure, or the like may be used. The combustion state can be determined. That is, as shown in FIG. 13, when the combustion shifts from incomplete combustion at the beginning of cranking to complete combustion, the cranking speed increases, the load on the starter motor 44 is reduced, and the starter current decreases. Also, by reducing the load on the starter motor 44, the battery 4
5, the power consumption decreases and the battery voltage increases. Therefore, it is possible to determine whether or not complete combustion has been reached from these changes in the starter current and the battery voltage. Further, although not shown, comparing the in-cylinder pressure at the time of complete combustion and at the time of incomplete combustion, the former in-cylinder pressure is higher, so that it is possible to determine the combustion state by this parameter (in-cylinder pressure). Become.

In the above embodiment, the hydraulically driven valve drive mechanisms 20A and 20B are disclosed as actuators for opening and closing the intake and exhaust valves 11 and 12. However, instead of this, a pneumatic drive type or an electromagnetic drive type is used. May be used.

Further, the control device of the present invention may be applied to a diesel engine. In such a case, the effect of suppressing the discharge of unburned fuel from the engine can be obtained.

[Brief description of the drawings]

FIG. 1 is a configuration diagram schematically showing an engine control system according to an embodiment of the invention.

FIG. 2 is a cross-sectional view showing a configuration of a valve driving mechanism and a peripheral portion thereof.

FIG. 3 is a sectional view for explaining the operation of the direction control valve.

FIG. 4 is a flowchart showing a valve control routine.

FIG. 5 is a flowchart showing a valve control routine continued from FIG. 4;

FIG. 6 is a time chart for explaining a valve control operation in a normal mode (four-cycle operation mode).

FIG. 7 is a time chart for explaining a valve control operation in a six-cycle operation mode.

FIG. 8 is a time chart for explaining a valve control operation in a fuel atomization mode.

FIG. 9 is a map showing a permission area for suspending a valve opening operation.

FIG. 10 is a time chart showing a difference in required time of a compression and expansion stroke and a difference in a starter current waveform between complete combustion and incomplete combustion.

FIG. 11 is a time chart for explaining a valve control operation in a fuel atomization mode.

FIG. 12 is a time chart for explaining a valve control operation in a fuel atomization mode.

FIG. 13 is a time chart showing transitions of a starter current, a battery voltage, an engine speed, and an intake air amount when the engine is started.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Engine (internal combustion engine), 10 ... Injector, 11
... intake valve, 12 ... exhaust valve, 20A, 20B ... valve drive mechanism, 43 ... spark plug, 44 ... starter motor, 45 ... battery, 50 ... valve operation control means, complete combustion judgment means, ECU constituting valve operation means (Electronic control device).

Claims (10)

[Claims] 1. A control device applied to an internal combustion engine having a valve drive mechanism capable of opening and closing an intake valve and an exhaust valve at an arbitrary time, and particularly controlling a combustion state at the time of engine start. A valve operation control unit that gives a control command to control the opening and closing operation of the intake valve and the exhaust valve; a complete combustion determination unit that determines whether fuel is completely burned in a cylinder of the internal combustion engine; When the complete combustion determination means determines that incomplete combustion has occurred, at least the opening operation of the exhaust valve by the valve operation control means is stopped within a certain period of time, and after confirming complete combustion, the normal opening operation of the exhaust valve is performed. A control device for an internal combustion engine, comprising: a valve operating means for permitting pressure. 2. When the incomplete combustion is judged by the complete combustion judging means, the opening operation of the intake and exhaust valves by the valve operation control means is stopped, and the compression and expansion strokes are repeated. The control device for an internal combustion engine according to claim 1, wherein the control is performed. 3. The control device for an internal combustion engine according to claim 2, wherein ignition of fuel is performed each time the compression and expansion strokes are performed in an overlapping manner. And determining whether or not to suspend the opening operation of the exhaust valve by the valve operating means based on an engine operating state. The control device for an internal combustion engine according to any one of claims 1 to 3, wherein opening and closing of the exhaust valve is controlled as described. 5. The control device for an internal combustion engine according to claim 4, wherein the opening operation of said exhaust valve is not stopped in an extremely low speed range or a very low temperature range of said internal combustion engine. . 6. The complete combustion determining means determines whether or not complete combustion is performed based on a magnitude relationship between a required time for a compression stroke and a required time for an expansion stroke during cranking by a starter motor. A control device for an internal combustion engine according to any one of claims 1 to 5. 7. The control device for an internal combustion engine according to claim 1, wherein at the time of starting the engine, the valve operation control means delays the opening timing of the intake valve from a normal timing. 8. The control device for an internal combustion engine according to claim 1, wherein at the time of starting the engine, the valve operation control means advances the closing timing of the exhaust valve beyond a normal timing. 9. The apparatus according to claim 1, wherein after starting cranking by the starter motor, the valve operation control means opens the intake valve first and then opens the exhaust valve. Control device for internal combustion engine. 10. An exhaust / intake valve opening / closing operation by said valve operation control means until a rotation speed at the time of cranking by a starter motor reaches a predetermined rotation range. 2. The control device for an internal combustion engine according to claim 1, wherein the control is stopped.