JP4182888B2 - Engine control device - Google Patents

Description

  The present invention relates to an engine control device.

Conventionally, as disclosed in Patent Document 1, the valve operating angle of the intake valve is reduced and the valve of the intake valve is reduced when the engine is started and when the engine is first idle (within a predetermined time after the engine is started). By delaying the timing (center phase of the valve operating angle), the intake valve opening timing is greatly delayed, and the negative pressure in the cylinder is developed until the intake valve opens, thereby increasing the intake flow velocity and atomizing the fuel Is known to promote. At the same time, by injecting fuel during the intake stroke (when the intake valve is lifted), the fuel is injected into the high-velocity intake flow to reduce the fuel wall flow in the cylinder, thereby reducing emissions. It is also known to improve.
JP 2003-3872 A

  However, in the technique described in Patent Document 1, the intake valve closing timing is delayed by reducing the valve operating angle of the intake valve for a predetermined time after the engine is started. For example, in the case of a direct injection engine However, although the atomization can be achieved by increasing the fuel pressure after the complete explosion, in spite of this atomization, delaying the intake valve opening timing uniformly causes a decrease in output due to an increase in pump loss, resulting in improved fuel efficiency. There was a problem of getting worse.

  An object of the present invention is to solve such conventional problems.

For this reason, in the present invention, the intake valve opening timing is delayed from the top dead center to the exhaust valve closing timing after the engine is started, and the fuel injection timing is set after the intake valve opening timing. It is delayed from the first half of the intake stroke, and when the fuel pressure exceeds a predetermined value, the intake valve opening timing is returned to the earlier side, and the fuel injection timing is returned to the first half of the intake stroke.

  According to the present invention, when the engine is started, the intake valve opening timing is delayed after top dead center and after the exhaust valve closing timing, so that the intake pressure is reduced by sucking in at a time after the negative pressure in the combustion chamber develops. The fuel atomization can be promoted and the emission (particularly the HC emission amount) can be improved. When the fuel pressure supplied to the fuel injection valve by the fuel pump rises, the fuel can be atomized. Therefore, when the fuel pressure exceeds a predetermined value, the intake valve opening timing is returned to the earlier side. As a result, the pump loss can be improved, and the output and fuel consumption can be improved.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a system diagram of an engine (direct injection spark ignition type internal combustion engine) showing an embodiment of the present invention.
In the intake passage 2 of the engine 1, an electric throttle valve 3 for controlling the intake air amount is installed. The opening degree of the electric throttle valve 3 is controlled by a step motor or the like that is operated by a signal from an engine control unit (hereinafter referred to as ECU) 20. Air that is controlled by the electric throttle valve 3 is taken into the combustion chamber 5 of the engine 1 through the intake valve 4.

  The intake valve 4 includes, as a variable valve operating device, a valve operating angle and lift amount variable device (VEL solenoid 49) capable of continuously changing the valve operating angle (open period) and the lift amount of the intake valve 4, and A variable valve timing device (VTC solenoid 51) capable of continuously changing the valve timing (center phase of the valve operating angle) of the intake valve 4 is provided. Details will be described later.

A fuel injection valve 7 is installed in the combustion chamber 5 of the engine 1 together with a spark plug 6.
The fuel supply system to the fuel injection valve 7 will be described. Fuel in the fuel tank 8 is sucked by a low-pressure fuel pump 9 driven by an electric motor, and low-pressure fuel discharged from the low-pressure fuel pump 9 is driven by the engine. The high pressure fuel pump 10 is supplied. The pressure of the fuel discharged from the low-pressure fuel pump 9 and supplied to the high-pressure fuel pump 10 is adjusted to a predetermined low pressure by a low-pressure pressure regulator 11 interposed in a return passage returning to the fuel tank 8. The high-pressure fuel discharged from the high-pressure fuel pump 10 is supplied to the fuel injection valve 7, and the fuel pressure is set to a predetermined high pressure by the high-pressure pressure regulator 12 interposed in the return passage returning to the suction side of the high-pressure fuel pump 10. Adjusted.

The fuel injection valve 7 is energized to the solenoid by an injection pulse signal output from the ECU 20 in the intake stroke or the compression stroke in synchronization with the engine rotation, and is opened to adjust the fuel in the combustion chamber 5 to a predetermined pressure. Is supposed to be injected.
The fuel injected into the combustion chamber 5 forms an air-fuel mixture, which is ignited by the spark plug 6 and burned. The exhaust gas after combustion is discharged to the exhaust passage 14 via the exhaust valve 13. An exhaust purification catalyst 15 is provided in the exhaust passage 14.

  The ECU 20 includes an accelerator opening Apo detected by an accelerator pedal sensor 21, an engine speed Ne detected by a crank angle sensor 22, an intake air amount Qa detected by an air flow meter 23, and an engine detected by a water temperature sensor 24. The coolant temperature (water temperature) Tw, the fuel pressure (fuel pressure) Pf from the high-pressure fuel pump 10 detected by the fuel pressure sensor 25 as the fuel pressure detection means to the fuel injection valve 7 and the like are input. In addition, a signal is also input from an engine key switch 26 having an ignition switch and a start switch.

The ECU 20 controls the opening degree of the electric throttle valve 3, the fuel injection timing and fuel injection amount of the fuel injection valve 7, the ignition timing of the spark plug 6, and the like based on the engine operating conditions detected from these input signals. .
The engine operation mode includes a stratified operation mode and a homogeneous operation mode. In the stratified operation mode, fuel is injected in the latter half of the compression stroke and stratified around the spark plug 6 in the combustion chamber 5. By forming the air-fuel mixture, stratified combustion is performed at a very lean air-fuel ratio (A / F = 30 to 40) as a whole. On the other hand, in the homogeneous operation mode, fuel injection is performed in the intake stroke, and a homogeneous air-fuel mixture is formed in the entire combustion chamber 5 so that the stoichiometric or lean air-fuel ratio (A / F = 20 to 30) is achieved. Make homogeneous combustion. Note that the control at the time of starting and immediately after the starting according to the present invention is performed in the homogeneous operation mode.

Next, the variable valve operating apparatus for the intake valve 4 will be described with reference to FIGS.
Above the valve lifter 40 at the end of the intake valve 4 (two are provided for each cylinder), a camshaft 41 that is driven to rotate around the shaft in conjunction with a crankshaft (not shown) extends in the cylinder row direction. ing. On the outer periphery of the cam shaft 41, a swing cam 42 is fitted so as to be swingable corresponding to the intake valve 4, and the swing cam 42 abuts against the valve lifter 40 to press it. The intake valve 4 is driven to open and close against the spring force of a valve spring (not shown).

Here, between the cam shaft 41 and the swing cam 42, the posture of the link that mechanically links both 41 and 42 is changed, and the valve operating angle (open period) and the lift amount of the intake valve 4 are continuously set. A valve operating angle and lift amount variable device (VEL device) that can be variably controlled is provided.
The VEL device includes a drive cam 43 that is eccentrically provided on the cam shaft 41 and rotates integrally with the cam shaft 41, a ring-shaped link 44 that is fitted on the outer periphery of the drive cam 43 so as to be relatively rotatable, and a cam shaft 41. A control shaft 45 extending substantially parallel to the cylinder row direction, a control cam 46 provided eccentrically with respect to the control shaft 45 and rotating integrally with the control shaft 45, and rotatable relative to the outer periphery of the control cam 46 And a rocker arm 47 whose one end is rotatably connected to the tip of the ring-shaped link 44, and is rotatably connected to the other end of the rocker arm 47 and the tip of the swing cam 42. 42 has a rod-like link 48 that mechanically cooperates.

  The cam shaft 41 and the control shaft 45 are rotatably supported on the cylinder head side of the engine via a bearing bracket. One end of the control shaft 45 is connected to the output end of an actuator (VEL solenoid) 49 for changing the valve operating angle, and the control shaft 45 is driven to rotate around the shaft within a predetermined control angle range by the VEL solenoid 49. And at a predetermined rotational phase.

With such a configuration, when the cam shaft 41 rotates in conjunction with the crankshaft, the ring-shaped link 44 substantially translates via the drive cam 43, and the rocker arm 47 swings around the control cam 46, The swing cam 42 swings through the rod-shaped link 48, and the intake valve 4 is driven to open and close.
Further, by rotating the control shaft 45 by the VEL solenoid 49, the center position of the control cam 46, which is the rocking center of the rocker arm 47, is changed, and the posture of each link 44, 48, etc. is changed, and the rocking cam The swing angle range of 42 changes. As a result, the valve operating angle and the lift amount continuously change while the central phase of the valve operating angle remains substantially constant. More specifically, the valve operating angle and the lift amount are increased by rotating the control shaft 45 in one direction, and the valve operating angle and the lift amount are decreased by rotating in the other direction. Yes.

Therefore, by duty-controlling the energization amount of the VEL solenoid 49 with a signal from the ECU 20, the rotation phase of the control shaft 45 can be changed, and the valve operating angle and the lift amount of the intake valve 4 can be changed. Thus, a valve operating angle and lift amount variable device (VEL device) is configured.
On the other hand, the camshaft 41 is driven by the rotation of the crankshaft being input to the sprocket 50 by a timing belt, and a rotary solenoid (VTC solenoid) capable of controlling the rotational phase between the sprocket 50 and the camshaft 41. ) 51 is installed.

Therefore, the rotational phase between the crankshaft and the camshaft 41 is changed by duty-controlling the energization amount of the VTC solenoid 51 with a signal from the ECU 20 to change the valve timing of the intake valve 4 (the central phase of the valve operating angle). Thus, a variable valve timing device (VTC device) is configured.
Next, the control at the start and immediately after the start according to the present invention will be described.

FIG. 4 is a flowchart of the control executed by the ECU 20 and immediately after the start. A time chart in this case is shown in FIG.
When the ignition switch is turned on (t1 in FIG. 5), the flow in FIG. 4 starts.
In S1, the fuel pressure Pf detected by the fuel pressure sensor 25 is read, and it is determined whether or not the fuel pressure Pf exceeds a predetermined value (threshold value SL) that enables atomization of the injected fuel. This is because the high pressure fuel pump 10 is stopped before starting, but the fuel pressure Pf may still be high if the time since the previous engine stop is short.

  If the fuel pressure Pf is less than or equal to the predetermined value, the process proceeds to S2, where the VEL device is driven so as to have a small operating angle and a low lift amount with respect to the normal operation state, and at the same time, the VTC device is in the normal operation state. In contrast, it is driven so as to be in a retarded state. Specifically, referring to the valve lift characteristic diagram of FIG. 6, the intake valve lift characteristic a during normal operation, which is set to have a valve overlap with the exhaust valve lift characteristic, has a small operating angle. By making the lift amount low and delaying the center phase of the operating angle, the intake valve opening timing is fixed after the top dead center (TDC) and the exhaust valve closing timing while the intake valve closing timing is fixed near the bottom dead center (BDC). The lift characteristic b is delayed thereafter. This is before starting but taking into account the operational delay of the VEL device and the VTC device so as to be in a predetermined state before starting (t1 → t2 in FIG. 5).

When the fuel pressure Pf exceeds the predetermined value, the process proceeds to S3, where the VEL device is driven and held in the normal operation state (large operating angle and high lift amount), and at the same time, the VTC device is in the normal operation state ( Drive and hold in the advanced angle state.
In S4, it is determined whether or not the start switch is turned on. If it is turned off, the process returns to S1.

When the start switch is turned on (t3 in FIG. 5), the starter motor is driven and cranking is performed while the start switch is turned on.
In S5, as in S1, the fuel pressure Pf detected by the fuel pressure sensor 25 is read, and it is determined whether or not the fuel pressure Pf exceeds a predetermined value (threshold value SL) that allows atomization of the injected fuel.
If the fuel pressure Pf is less than or equal to the predetermined value, the process proceeds to S6, where the VEL device is driven and held at a small operating angle and low lift with respect to the normal operation state, and at the same time, the VTC device is set to the normal operation state. Drive and hold in a retarded state. In S7, as shown in FIG. 6, the fuel injection timing is retarded from the fuel injection timing a in the first half of the intake stroke during normal operation, and the bottom dead center (BDC) after the intake valve closing timing. The fuel injection timing b in the vicinity is set. Specifically, as shown in a table of the fuel injection timing with respect to the valve operating angle of the intake valve in FIG. 7, the fuel injection timing is set according to the valve operating angle of the intake valve, and the smaller the actual valve operating angle is, The fuel injection timing is delayed so that the fuel injection timing is always after the intake valve opening timing, and the fuel injection timing is in the vicinity of bottom dead center (BDC) with the final minimum valve operating angle. Then, the process returns to S5.

When the fuel pressure Pf exceeds a predetermined value, that is, the discharge amount by the high-pressure fuel pump 10 increases due to the increase in the engine speed after starting, the fuel pressure Pf is a predetermined value at which atomized fuel can be atomized. If exceeded, the process proceeds to S8.
In S8, the VEL device is driven and held in the normal operation state (large operating angle and high lift amount), and at the same time, the VTC device is driven and held in the normal operation state (advance angle state). In S9, the fuel injection timing is set to the fuel injection timing (advanced state) in the first half of the intake stroke during normal operation. Also in this case, since there is an operation delay in the VEL device and the VTC device (t4 → t5 in FIG. 5), the fuel injection timing is set according to the valve operating angle and advanced according to the increase of the valve operating angle ( (See FIG. 7). Thereafter, normal control is performed.

  Therefore, when the fuel pressure Pf at the start and immediately after the start is low at the normal start, the intake valve is opened by reducing the operating angle of the intake valve by the VEL device and delaying the valve timing of the intake valve by the VTC device. Delay the timing after top dead center and after exhaust valve closing timing. As a result, the negative pressure in the cylinder is developed until the intake valve is opened, and when the intake valve is opened, the intake air flow rate can be increased by sucking in at a stroke. The contact energy increases (turbulence in the cylinder becomes stronger), fuel atomization can be promoted, and emissions (particularly HC emissions) can be improved. Further, in the VEL device, the lift amount decreases simultaneously with the decrease of the valve operating angle, which also contributes to the improvement of the intake flow velocity.

  Moreover, by reducing the operating angle of the intake valve with the VEL device and delaying the valve timing of the intake valve with the VTC device, the intake valve open timing can be delayed while the intake valve close timing is fixed, and the intake valve close By fixing the timing, it is possible to avoid the influence on the compression stroke and maintain the combustion performance. In particular, by fixing the intake valve close timing near the bottom dead center, by sealing the cylinder in the state of the maximum flow velocity obtained at the bottom dead center, to strengthen the in-cylinder flow after the transition to the compression stroke, Mixing with the injected fuel can be promoted.

  In addition, by delaying the intake valve opening timing and delaying the fuel injection timing, fuel injection is performed after the intake valve opening timing, and fuel is injected into the high-velocity intake flow to further atomize the fuel. Can be promoted. In particular, by setting the fuel injection timing in the vicinity of the bottom dead center, fuel injection can be performed at a maximum flow velocity, and fuel atomization can be promoted. However, since the in-cylinder flow is maintained for a certain period even after the transition to the compression stroke, the fuel injection timing may be shifted to the compression stroke as long as it is in the vicinity of the bottom dead center.

  On the other hand, if the discharge amount of the high-pressure fuel pump increases due to the increase in the engine speed after starting and the fuel pressure exceeds a predetermined value (threshold value SL), the fuel can be atomized by increasing the fuel pressure. . Therefore, at this time, the valve operating angle of the intake valve is returned to the normal large state by the VEL device, and the valve timing of the intake valve is returned to the normal early state by the VTC device (t4 → t5 in FIG. 5). Thus, the intake valve opening timing is returned to the normal early state (position slightly advanced from the top dead center) while the intake valve closing timing is fixed. By doing in this way, a pump loss can be improved and an output and fuel consumption can be improved. At the same time, the fuel injection timing is advanced and returned to the first half of the intake stroke, whereby an appropriate fuel injection timing can be obtained.

  In the above embodiment, the intake valve opening timing is delayed from the top dead center and the exhaust valve closing timing by reducing the valve operating angle of the intake valve and delaying the valve timing, thereby increasing the intake flow velocity. However, if the intake valve opening timing can be sufficiently delayed, the intake valve opening timing may be delayed only by reducing the intake valve operating angle by the VEL device, or the intake valve opening timing by the VTC device. Alternatively, the intake valve opening timing may be delayed only by delaying the valve timing. However, it is desirable to use both in combination from the viewpoint of fixing the intake valve closing timing at a desired position.

  In addition, although there is no particular reference to the target value (target fuel pressure) of the fuel pressure at the start and immediately after the start, in a direct injection engine that directly injects fuel into the cylinder, the intake stroke injection and the compression stroke injection are performed by a high pressure pressure regulator Since the target fuel pressure can be switched depending on the time, when atomizing the fuel by increasing the fuel pressure, the target fuel pressure may be set higher than the target fuel pressure during normal intake stroke injection.

Engine system diagram showing an embodiment of the present invention Configuration diagram of variable valve gear Cross-sectional view of the main part of FIG. Flow chart of control at start and immediately after start Time chart of control at start and immediately after start Valve lift characteristics Characteristics of fuel injection timing

Explanation of symbols

1 engine
2 Intake passage
3 Electric throttle valve
4 Intake valve
5 Combustion chamber
6 Spark plug
7 Fuel injection valve
8 Fuel tank
9 Low pressure fuel pump
10 High-pressure fuel pump
13 Exhaust valve
20 ECU
25 Fuel pressure sensor
49 VEL solenoid
51 VTC solenoid

Claims (9)

A variable valve operating device capable of changing a lift characteristic of the intake valve; and a fuel pressure detecting means for detecting a fuel pressure supplied to the fuel injection valve by a fuel pump. The fuel is detected by the fuel pressure detecting means by delaying the intake valve opening timing after top dead center and exhaust valve closing timing by the device , and delaying the fuel injection timing from the first half of the intake stroke so as to be after the intake valve opening timing. An engine control device , wherein when the pressure exceeds a predetermined value, the intake valve opening timing is returned to the earlier side, and the fuel injection timing is returned to the first half of the intake stroke . The variable valve operating device includes a valve operating angle variable device capable of changing the valve operating angle of the intake valve,
2. The engine control device according to claim 1, wherein the intake valve opening timing is delayed by reducing the valve operation angle of the intake valve by the valve operation angle varying device. As the variable valve operating device, provided with a valve timing variable device capable of changing the valve timing of the intake valve,
The engine control device according to claim 1, wherein the intake valve opening timing is delayed by delaying the valve timing of the intake valve by the variable valve timing device. The variable valve operating device includes a valve operating angle variable device that can change the valve operating angle of the intake valve, and a valve timing variable device that can change the valve timing of the intake valve,
The intake valve opening timing is delayed by reducing the valve operating angle of the intake valve by the valve operating angle variable device and delaying the valve timing of the intake valve by the valve timing variable device. Engine control device. By reducing the valve operating angle of the intake valve by the valve operating angle varying device and delaying the valve timing of the intake valve by the valve timing varying device, the intake valve opening timing is delayed while the intake valve closing timing is fixed. The engine control device according to claim 4. 6. The engine control device according to claim 5, wherein the intake valve closing timing is fixed at a bottom dead center . The engine control device according to any one of claims 1 to 6, wherein the fuel injection timing is delayed at the same time as the intake valve opening timing is delayed. 8. The engine control apparatus according to claim 7, wherein the fuel injection timing for delaying is set at a bottom dead center . 5. The valve operating angle variable device according to claim 2, wherein the valve operating angle and the lift amount of the intake valve are changed, and the lift amount is decreased simultaneously with the decrease of the valve operating angle. Engine control device.

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