JP4677844B2 - Engine valve timing control device - Google Patents

Description

  The present invention relates to a valve timing control device for an engine in which valve overlap between an intake valve and an exhaust valve is variable, and more particularly to control of valve overlap during warm-up after engine startup.

Patent Document 1 discloses a valve timing control device that stabilizes combustion by reducing a valve overlap at a low temperature start and increases a valve overlap at a high temperature start to reduce a pumping loss.
JP 2004-156511 A

As described above, in the control of the valve overlap at the time of the conventional cold start, the unique control is performed to increase the valve overlap as the temperature is higher. Therefore, there is a problem that sufficient combustion stability cannot be ensured and good startability cannot be obtained at extremely low temperatures.
The present invention has been made in view of the above problems, and an object of the present invention is to improve combustion stability in an extremely low temperature state by controlling valve overlap, thereby improving startability at an extremely low temperature.

For this reason, the valve timing control device for an engine according to the present invention provides a valve overlap as a plus lap when the engine temperature is very low, ie, lower than a predetermined temperature, during warm-up after engine startup, and when the engine temperature is equal to or higher than the predetermined temperature. Control is performed so that a minus lap is performed. If the engine is not warming up, normal control for advancing and retarding the valve timing according to the engine load and the rotational speed is performed .

According to such a configuration, the valve overlap is not reduced as the engine temperature becomes lower, but the valve overlap is controlled to a larger side when the engine temperature is lower than the predetermined temperature compared to when the engine temperature is higher than the predetermined temperature. To do.
Conventionally, in order to improve the combustion stability of the engine, it has been considered necessary to reduce the valve overlap and reduce the amount of residual gas in the combustion chamber.

However, in the extremely low temperature state, the fuel injected from the fuel injection valve adheres to the combustion chamber wall surface as droplets, resulting in deterioration of ignitability and unstable combustion. If the fuel vaporization is promoted by using the thermal energy, combustion stability in a cryogenic state can be improved.
Therefore, by controlling the valve overlap to the large side in the cryogenic state, the residual gas in the combustion chamber is increased to improve the combustion stability, and the starting performance at the cryogenic temperature is improved.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a system diagram of an engine in the embodiment.
The engine 1 shown in FIG. 1 is a gasoline engine, and the air that is metered by the intake throttle valve 2 is stored in the intake collector 3 and then the combustion chamber 10 of each cylinder via the intake manifold 4 and the intake valve 5. To be introduced.

Fuel (gasoline) is injected and supplied into the intake port 6 from the fuel injection valve 7 arranged in the intake port 6 of each cylinder at a predetermined timing synchronized with the engine rotation.
Here, an amount of fuel proportional to the valve opening time of the fuel injection valve 7 is injected, and the valve opening time (fuel injection amount) depends on the pulse width of the injection pulse signal output from the engine controller 31. The fuel injection timing is controlled by the output timing of the injection pulse signal.

While the engine controller 31 calculates the fuel injection amount (injection pulse width) based on the intake air flow rate detected by the air flow meter 32 and the engine speed calculated based on the signal from the crank angle sensor 33, Based on the signal from the cam sensor 34, the cylinder at the specific piston position is discriminated, and an injection pulse signal is output to each fuel injection valve 7.
The fuel injected into the intake port 6 is sucked into the combustion chamber 10 via the intake valve 5 and mixed with the intake air to generate an air-fuel mixture in the combustion chamber 10.

The air-fuel mixture is confined in the combustion chamber 10 by closing the intake valve 5, compressed by the rise of the piston 11, and ignited by the spark plug 12 (ignition device) to burn.
The gas pressure due to the combustion works to push down the piston 11, and the reciprocating motion of the piston 11 is converted into the rotational motion of the crankshaft 13.
The combusted gas (exhaust gas) is discharged to the exhaust passage 15 provided with the catalytic converters 16 and 17 when the exhaust valve 14 is opened.

The engine controller 31 determines the basic fuel injection amount from the fuel injection valve 7 according to the operating conditions, and detects the exhaust air-fuel ratio based on the signal from the air-fuel ratio sensor 18 provided upstream of the catalytic converter 16. The fuel injection amount is feedback-corrected so that the exhaust air-fuel ratio becomes the target air-fuel ratio.
The intake throttle valve 2 is opened and closed by a throttle actuator 21.

The engine controller 31 determines a target torque based on the opening of the accelerator pedal 36 detected by the accelerator sensor 35, determines a target air amount for realizing the target torque, and obtains the target air amount. The throttle actuator 21 (the opening degree of the intake throttle valve 2) is controlled.
Further, the engine 1 of the present embodiment has a variable valve timing mechanism (hereinafter referred to as “a valve phase mechanism”) that variably controls the rotational phase difference between the crankshaft 13 and the intake valve side camshaft 22 to advance or retard the valve timing of the intake valve 5. "VTC mechanism") 23.

As the VTC mechanism 23, various known mechanisms as disclosed in, for example, Japanese Patent Application Laid-Open Nos. 2004-156511 and 2003-003872 can be employed.
By advancing and retarding the valve timing of the intake valve 5 by the VTC mechanism 23, as shown in FIG. 3, the valve overlap is a period in which both the intake valve 5 and the exhaust valve 14 are open near the top dead center. Changes.

  The closing timing of the exhaust valve 14 is fixed near top dead center, while the opening timing of the intake valve 5 is advanced from the closing timing of the exhaust valve 14 by the advance / retard angle control by the VTC mechanism 23. It changes in a range from an angular position to an angular position delayed from the closing timing of the exhaust valve 14, and the valve overlap changes from a plus lap to a minus lap.

Here, the engine controller 31 adjusts the valve overlap by controlling the VTC mechanism 23 as shown in the flowchart of FIG. 2 during warm-up after the engine is started.
In the flowchart of FIG. 2, first, when the engine 1 is started (step S1), the process proceeds to step S2, and the coolant temperature Tw of the engine 1 is detected based on the detection signal from the water temperature sensor 37.

The cooling water temperature Tw is a state quantity representative of the temperature of the engine 1, and can be made to detect the intake air temperature instead of the cooling water temperature Tw. Further, the temperature or lubrication of the cylinder head or the cylinder block can be detected. Oil temperature etc. can be detected.
When the coolant temperature Tw is detected, the process proceeds to step S3, where it is determined whether the engine is warming up based on whether the coolant temperature Tw exceeds the warm-up determination value.

Here, if it is determined that the coolant temperature Tw is equal to or lower than the warm-up determination value and is warming up, the process proceeds to step S4, and the detected value of the coolant temperature Tw is lower than the set temperature (for example, 5 ° C.). It is determined whether or not the temperature is extremely low.
When the cooling water temperature Tw is in an extremely low temperature state lower than the set temperature, the process proceeds to step S5.

In step S5, the valve timing of the intake valve 5 is advanced by the VTC mechanism 23 so that the valve overlap becomes a plus lap state with a crank angle of about 4 deg as shown in FIG.
In the valve timing shown in FIG. 3A, the crank angle position (BTDC 4 deg) 4 deg before the closing timing EVC (piston top dead center TDC) of the exhaust valve 14 is set to the opening timing IVO of the intake valve 5, and the exhaust valve 14 Immediately before the closing timing EVC of 14 (the beginning of opening of the intake valve 5), a period in which both the intake valve 5 and the exhaust valve 14 are opened by 4 deg in crank angle is provided.

On the other hand, when the cooling water temperature Tw is equal to or higher than the set temperature and the engine is warming up but is not in an extremely low temperature state, the process proceeds to step S6.
In step S6, the valve timing of the intake valve 5 is retarded by the VTC mechanism 23, and as shown in FIG. 3B, after the exhaust valve 14 is closed and the crank angle is rotated by about 4 degrees, the intake valve 5 is Set to the minus wrap state that begins to open.

In the valve timing shown in FIG. 3B, the crank angle position (ATDC 4 deg) 4 deg later than the closing timing EVC (from the piston top dead center TDC) of the exhaust valve 14 is set as the opening timing IVO of the intake valve 5. This is a setting in which a period during which both the intake valve 5 and the exhaust valve 14 are open is not provided immediately before the closing timing EVC of the exhaust valve 14.
On the other hand, if it is determined in step S3 that the engine is not warming up, the process proceeds to step S7, and normal control for advancing / retarding the valve timing of the intake valve 5 is performed according to, for example, the engine load and / or the engine speed.

The exhaust performance of the engine 1 is greatly influenced by the unburned HC discharged at the time of starting. In order to reduce the unburned HC discharged into the atmosphere, a method of delaying the ignition timing and increasing the combustion period, There is a method in which the catalyst is activated early by increasing the temperature.
However, if the ignition timing is retarded, the combustion stability deteriorates, so the limit that can be retarded largely depends on the performance of engine combustion stability.

Conventionally, in order to improve the combustion stability of an engine, it has been considered necessary to reduce the valve overlap of the intake and exhaust valves to reduce the amount of residual gas in the combustion chamber.
That is, if the valve overlap is large and the amount of residual gas in the combustion chamber is large, the mixture concentration in the combustion chamber decreases, so the air-fuel ratio in the vicinity of the spark plug 12 becomes thin, the ignitability deteriorates, and the flame propagation slows down. The combustion period increases and the combustion becomes unstable.

However, it has been found that even when the engine is warming up, combustion stability is improved by increasing the valve overlap amount to increase the residual gas in an extremely low temperature state.
This is because, in an extremely low temperature state, the atomization of the fuel injected from the fuel injection valve 7 is alienated, and the fuel adheres to the combustion chamber wall surface as droplets, so that the ignitability deteriorates or the combustion becomes unstable. It becomes.

Therefore, in the present embodiment, by controlling the valve overlap to the large side in the cryogenic state, the residual gas in the combustion chamber is increased, and the vaporization of fuel is promoted by using the thermal energy of the residual gas. The fuel is prevented from adhering to the combustion chamber wall surface as droplets, and the combustion stability is improved.
After leaving the cryogenic state, the residual gas is reduced by using the valve overlap as a minus lap, thereby increasing the mixture concentration in the combustion chamber and ensuring the combustion stability of the engine.

  In the above-described embodiment, a plus lap is used if the temperature is extremely low, which is lower than the set temperature even during warm-up, and a minus lap is used in the warm-up state that is equal to or higher than the set temperature. Alternatively, the valve overlap may be decreased and changed in more stages, and the decrease in valve overlap is not limited to the change up to the minus lap, but the plus lap amount is reduced while maintaining the plus lap state. It may be changed.

  Further, instead of a variable valve timing mechanism (hereinafter referred to as “VTC mechanism”) 23 that variably controls the rotational phase difference between the crankshaft 13 and the intake valve side camshaft 22, a mechanism that opens and closes the intake and exhaust valves with electromagnetic force. Alternatively, the valve overlap can be changed by using a mechanism for switching the drive cam and a mechanism for continuously changing the lift amount and the operating angle.

  Further, a mechanism for changing the valve timing of the exhaust valve 14 is provided, and the valve overlap is controlled by changing the valve timing of the exhaust valve 14 or by changing the valve timings of both the intake valve 5 and the exhaust valve 14. be able to.

The system diagram of the engine in an embodiment. The flowchart which shows the valve overlap control at the time of warming-up in embodiment same as the above. The figure which shows the switching characteristic of the valve overlap in embodiment same as the above.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Engine, 2 ... Intake throttle valve, 5 ... Intake valve, 14 ... Exhaust valve, 23 ... Variable valve timing mechanism (VTC mechanism), 31 ... Engine controller, 37 ... Water temperature sensor

Claims (4)

In the engine valve timing control device that makes the valve overlap of the intake valve and the exhaust valve variable,
During engine warm-up after engine start-up, when the engine temperature is extremely low, which is less than a predetermined temperature , the valve overlap is controlled to be a plus lap, and when it is above the predetermined temperature, the minus lap is controlled.
An engine valve timing control device that performs normal control for advancing and retarding the valve timing in accordance with the engine load and rotation speed when the engine is not warming up . 2. The engine valve timing control apparatus according to claim 1, wherein when the temperature is equal to or higher than the predetermined temperature and a negative lap is set, the closing timing of the exhaust valve is controlled to be near the top dead center . 3. The engine valve timing control device according to claim 1, wherein the engine temperature is determined based on a cooling water temperature of the engine. 3. The engine valve timing control apparatus according to claim 1, wherein the engine temperature is determined based on an intake air temperature of the engine.

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