JP2001263104A - Variable valve control device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a variable valve control device which improves exhaust controlling performance, fuel efficiency, and fuel stability of an engine at the same time. SOLUTION: This variable valve control device controls an intake valve closing timing IVC according to an engine operating condition and sets a target residual gas ratio REGR. Effective intake volume VI (cylinder volume at IVC) calculated from IVC is multiplied with the target residual gas ratio REGR so as to calculate target residual gas volume VE (cylinder volume at the exhaust valve closing timing EVC). The target EVC is controlled by calculating from target residual gas volume VE. As a result, residual gas volume (internal EGR volume) is highly accurately controlled so that exhaust controlling performance, fuel efficiency, and fuel stability are improved at the same time.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a device for controlling an intake / exhaust valve (variable valve) of an engine, such as an electromagnetic drive type, whose opening and closing timing can be arbitrarily variably controlled. To control the closing timing of an intake valve and an exhaust valve as described above.

[0002]

2. Description of the Related Art In a conventional general engine, the intake air amount is controlled by the opening degree of a throttle valve. However, in recent years, an intake / exhaust valve of an electromagnetic drive type is provided, and the intake air amount is mainly controlled by controlling the closing timing of the intake valve. Has been proposed (see Japanese Patent Application Laid-Open No. 10-37727).

In this type of intake air amount control, when the throttle valve is not provided, the intake pressure is maintained at substantially the atmospheric pressure, and when the throttle valve is used together, the intake pressure corresponding to the throttle valve opening degree is increased. By controlling the volume of cylinder intake air according to the effective intake stroke determined by the closing timing of the valve, control can be performed to obtain a target air amount (required intake air amount) corresponding to the required torque.

[0004]

On the other hand, in a cam-driven variable valve, the exhaust valve is set to close before the piston reaches a top dead center, so that the residual gas amount (internal EGR amount) in the combustion chamber is set. To reduce NOx and pumping loss (see JP-A-62-13708).

However, this method cannot control the amount of residual gas with high precision, so that it has been difficult to achieve both a reduction in NOx and a reduction in pumping loss and stable combustion.

[0006] Also, none of the electromagnetically driven variable valves can control the residual gas amount with high accuracy.
The present invention has been made in view of such a conventional problem, and by controlling the closing timing of the intake valve and the closing timing of the exhaust valve in the variable valve, the residual gas amount is controlled with high accuracy, and the exhaust gas is controlled. It is an object of the present invention to achieve both improvement in purification performance and fuel efficiency and stable combustion.

[0007]

According to a first aspect of the present invention, there is provided a variable valve control apparatus capable of arbitrarily variably controlling the opening / closing timing of an intake / exhaust valve of an engine. A target residual gas ratio, which is a target ratio of the residual gas amount in the cylinder at the end of the exhaust stroke to the total gas amount in the cylinder at the end of the intake stroke, is set, and the intake valve is closed so as to achieve the target residual gas ratio. The timing and the closing timing of the exhaust valve are controlled.

According to the first aspect of the present invention, the closing timing of the intake valve and the closing timing of the exhaust valve are controlled so as to achieve the target residual gas rate set based on the operating state of the engine.

Thus, even when the intake air amount changes due to the control of the closing timing of the intake valve, the closing timing of the exhaust valve is controlled in relation to the closing timing of the intake valve so as to achieve the target residual gas rate. Therefore, the ratio between the amount of intake air and the amount of residual gas, that is, the internal EGR rate can be controlled to a desired value.
It is possible to achieve both a reduction in NOx and a reduction in pumping loss and stable combustion.

[0010] The invention according to claim 2 is to calculate a target residual gas amount by multiplying the total gas amount calculated based on the closing timing of the intake valve by the target residual gas rate. It is characterized in that the closing timing of the exhaust valve is set based on this.

According to the second aspect of the present invention, the total gas amount in the cylinder corresponding to the cylinder volume at the end of the intake stroke is calculated based on the closing timing of the intake valve. Is multiplied to calculate the target residual gas amount. Then, the closing timing of the exhaust valve can be calculated so that the residual gas amount determined by the cylinder volume at the closing timing of the exhaust valve matches the target residual gas amount.

Further, the invention according to claim 3 is characterized in that the total gas amount is calculated by multiplying the cylinder volume at the closing timing of the intake valve by the intake pressure in the intake passage.

According to the third aspect of the invention, the total gas amount in the cylinder at the end of the intake stroke is calculated by multiplying the cylinder volume at the closing timing of the intake valve by the intake pressure in the intake passage.

In this way, when the intake pressure is variably controlled by a throttle valve or the like, the total gas amount can be calculated with high accuracy in consideration of the intake pressure. Claim 4
The invention according to the invention calculates a target intake air volume and a target residual gas volume from a target intake air amount and a target residual gas rate set based on an operation state of the engine, and closes an intake valve based on the target intake air volume. The timing is set, and the closing timing of the exhaust valve is set based on the target residual gas volume.

According to the present invention, the target intake air amount and the target residual gas rate are set based on the operation state of the engine, and the target residual gas amount is multiplied by the target residual gas rate to obtain the target residual gas amount. Desired. Then, a target intake volume corresponding to a substantial intake stroke volume from the top dead center of the piston to the closing of the intake valve is calculated based on the target intake air amount. Also, the residual gas volume that can be variably controlled by the exhaust valve closing timing based on the target residual gas amount, that is, the residual gas volume remaining in the cylinder as the residual gas between the piston position and the piston top dead center position at the exhaust valve closing timing. The target residual gas volume corresponding to the volume of the stroke to be performed is calculated. Then, the closing timing of the intake valve is calculated based on the target intake volume,
The closing timing of the exhaust valve is calculated based on the target exhaust volume.

In this manner, in the so-called torque demand control for setting the target intake air amount corresponding to the target torque according to the driver's intention and performing the engine output control with high accuracy, the residual gas amount (internal EGR amount) The control of (1) is also performed with high accuracy, and the exhaust gas purifying performance and the fuel efficiency can be sufficiently improved while ensuring stable combustion.

The invention according to claim 5 is characterized in that the target intake volume and the target residual gas volume are calculated in consideration of the intake pressure in the intake passage.

According to the fifth aspect of the present invention, the target intake volume corresponding to the target intake air amount and the target residual gas volume corresponding to the target residual gas amount change in accordance with the intake pressure in the intake passage. A target intake volume and a target residual gas volume are calculated in consideration of the pressure.

In this way, when the intake pressure is variably controlled by the throttle valve or the like, the target intake volume and the target residual gas volume can be calculated with high accuracy in consideration of the intake pressure.

According to a sixth aspect of the present invention, the opening timing of the intake valve is set after the closing timing of the exhaust valve. Since the lap amount is eliminated, the intake air amount (the amount of fresh air that does not include residual gas) can be accurately calculated according to the opening / closing timing of the intake valve, and the intake air amount and residual gas amount can be accurately set to target values accordingly. The closing timing of the intake valve and the exhaust valve can be controlled as controlled.

[0021]

Embodiments of the present invention will be described below. FIG. 1 is a system diagram of an engine provided with a variable valve control device according to an embodiment of the present invention.

The combustion chamber 3 defined by the piston 2 of each cylinder of the engine 1 is provided with an electromagnetically driven intake valve 5 and an exhaust valve 6 so as to surround the ignition plug 4. 7 is an intake passage, and 8 is an exhaust passage.

FIG. 2 shows the basic structure of an electromagnetic drive device for the intake valve 5 and the exhaust valve 6 (which constitutes a variable valve together with the intake and exhaust valves). A plate-shaped mover 2 is mounted on a valve shaft 21 of a valve body 20.
2 is attached, and the mover 22 is
It is urged by 3 and 24 to the neutral position. A valve opening electromagnetic coil 25 is disposed below the movable element 22, and a valve closing electromagnetic coil 26 is disposed above the movable element 22.

Before the engine 1 is started, the valve-opening electromagnetic coil 25 and the valve-closing electromagnetic coil 26 are alternately energized to resonate the mover 22, and when the amplitude becomes sufficiently large, one of the electromagnetic The mover 22 is suction-held by the coil.

Thereafter, when the valve is opened from the valve closed state, the power supply to the upper valve closing electromagnetic coil 26 that is attracting the movable element 22 is stopped, and then the movable element 2 is biased by the spring 23.
The valve body 20 is lifted and opened by energizing the valve opening electromagnetic coil 25 and attracting the mover 22 from a position sufficiently approaching the lower valve opening electromagnetic coil 25 to move the valve element 20 downward. Let it go.

On the other hand, when the valve is closed from the open state,
After stopping the energization of the lower valve-opening electromagnetic coil 25 that is adsorbing 2, the movable element 22 is moved upward by the urging force of the spring 24, and is sufficiently close to the upper valve-closing electromagnetic coil 26. From there, the valve closing electromagnetic coil 26 is energized,
By adsorbing the mover 22, the valve body 20 is seated on the seat and closed.

Returning to FIG. 1, an air flow meter 14 for detecting the amount of intake air and a throttle valve 15 for electronically controlling the opening are provided in the intake passage 7, and an electromagnetic type is provided at an intake port for each cylinder. Fuel injection valve 9 is provided.

Here, the operations of the intake valve 5, the exhaust valve 6, the throttle valve 15, the fuel injection valve 9 and the spark plug 4 are controlled by a control unit 10, which is synchronized with the engine rotation. A crank angle sensor 11 that outputs a crank angle signal and thereby detects an engine rotation speed, and an accelerator pedal sensor 12 that detects an accelerator opening (depression amount of an accelerator pedal)
And so on, a signal is input.

The closing timing of the intake valve 5 is set based on the operating conditions of the engine such as the accelerator opening and the engine speed so that the intake air amount increases in accordance with the increase in the required engine output. The target residual gas rate is set so that an appropriate residual gas amount (internal EGR amount) is obtained in order to reduce exhaust emissions, in particular NOx emissions, and improve fuel efficiency by reducing pumping loss while ensuring flammability. The closing timing of the exhaust valve 6 is set so that the target residual gas ratio is satisfied in connection with the control of the closing timing of the intake valve 5.

The intake air amount is detected based on the values detected by the various sensors, and the fuel injection amount from the fuel injection valve 9 is controlled based on the intake air amount. Hereinafter, an embodiment of closing timing control of an intake valve and an exhaust valve according to the present invention will be described with reference to the drawings.

FIG. 3 shows a control block diagram of the simplest first embodiment. The target IVC setting unit performs a search from a table set in advance based on the operating conditions of the engine such as the accelerator opening and the engine speed so that the intake air amount increases in accordance with an increase in the engine required output. The target closing timing IVC of the intake valve 5 is set.

The IVC control unit controls the set intake valve 5
The electromagnetic drive device is driven to control the closing timing of the intake valve 5 so that the target closing timing IVC is obtained. Based on the set intake valve target closing timing IVC, the effective intake air amount calculation unit calculates the IVC, that is, the total gas amount in the cylinder at the end of the substantial intake stroke, that is, the effective intake air amount VI.
, The cylinder volume in the IVC is calculated. As shown in FIG. 4, the effective intake air amount VI is a target displacement which is a stroke volume from the top dead center of the piston to the closing of the intake valve at a combustion chamber volume Vc (constant value) when the piston is at the top dead center. Calculated as a value obtained by adding the intake volume Vs1, for example, IV
The target intake volume Vs1 is calculated by a search from a table as shown in FIG. 5 as a function of C, and is calculated by adding the target intake volume Vs1 to the combustion chamber volume Vc.

The target residual gas rate setting section includes an accelerator opening,
Based on engine operating conditions such as engine speed,
A target residual gas ratio (residual gas amount / total gas amount) REGR is set by searching from a table set in advance.
FIG. 6 shows a characteristic map of the target residual gas ratio REGR according to the engine torque and the engine rotation speed. As shown in the figure, the target residual gas rate REGR is set to be large in a low-medium rotation and low load region.

The target residual gas amount calculator calculates a target residual gas amount VE by multiplying the effective intake air amount VI by the target residual gas ratio REGR. The target EVC setting unit calculates a target closing timing EVC of the exhaust valve based on the target residual gas amount VE. Specifically, the stroke in which the combustion chamber volume Vc is subtracted from the target residual gas amount VE to remain in the cylinder as residual gas between the piston position and the piston top dead center position when the exhaust valve is closed. The target exhaust volume Vs2 corresponding to the volume of the exhaust valve is calculated, and the target closing timing EVC of the exhaust valve is set based on the target exhaust volume Vs2 by, for example, searching a table as shown in FIG.

The EVC control unit controls the closing timing of the exhaust valve 6 by driving the electromagnetic driving device so that the set target closing timing EVC of the exhaust valve is obtained. With this configuration, the closing timing of the exhaust valve 6 is controlled in relation to the closing timing of the intake valve 5 so as to achieve the target residual gas rate. Therefore, it is possible to achieve both the reduction of NOx and the reduction of pumping loss and stable combustion.

Next, a second embodiment will be described. In the second embodiment, the closing timing of the intake valve 5 and the exhaust valve 6 is controlled in consideration of the intake pressure downstream of the throttle valve 15. That is, under the operating condition in which the intake air amount is variably controlled according to the closing timing of the intake valve 5, when the throttle valve 15 is substantially fully opened and the intake pressure is substantially constant at atmospheric pressure, the exhaust pressure is also substantially atmospheric pressure. Therefore, it is not necessary to consider the intake pressure as in the first embodiment (the accuracy can be improved by correcting the exhaust pressure to a value slightly larger than the atmospheric pressure as described later), but the evaporative fuel In order to secure a negative pressure for purging and braking, the throttle valve 15 is throttled and controlled to a predetermined negative pressure, and then the intake air amount is changed according to the closing timing of the intake valve. It is necessary to control by detecting an intake pressure different from the exhaust pressure.

FIG. 8 is a control block diagram of the second embodiment. The effective intake air amount calculation unit calculates an effective intake air amount VI which is a volume value calculated in the same manner as in the first embodiment,
An effective intake air amount QI (= Pm · VI), which is a mass value, is calculated by multiplying the intake air pressure Pm downstream of the throttle valve. Here, the intake pressure Pm may be a target intake pressure set based on operating conditions of the engine, such as an accelerator opening and an engine speed, but may be determined by using an intake pressure detected by providing an intake pressure sensor. Is also good.

The target residual gas rate setting section sets the target residual gas rate REGR as in the first embodiment. The target residual gas amount calculation unit multiplies the effective intake air amount QI by the target residual gas ratio REGR to obtain a target residual gas amount Q which is a mass value.
Calculate E.

The target EVC setting section calculates the target closing timing EVC of the exhaust valve based on the target residual gas amount QE.
Specifically, after calculating the target residual gas volume Vs2 from the target residual gas amount QE according to the following equation, the table shown in FIG. 7 is searched to set the target closing timing EVC of the exhaust valve.

QE = REGR · QI = Pe · (Vs2 + Vc) Therefore, Vs2 = QE / Pe−Vc where Pe: exhaust pressure correction coefficient Here, the exhaust pressure correction coefficient Pe may be simply a constant. The accuracy can be further improved by using a coefficient set as a map shown in FIG. 11 for the coefficient for correcting the exhaust pressure and temperature depending on operating conditions such as the accelerator opening and the engine rotation speed.

The IVC control unit and the EVC control unit determine the target closing timing IVC of the intake valve 5 and the exhaust valve 6.
The electromagnetic drive device is driven to control the closing timing of the intake valve 5 and the closing timing of the exhaust valve 6 so that the target closing timing EVC is obtained.

Next, a third embodiment will be described. The third embodiment is applied to a so-called torque demand control in which a target torque is set based on a driver's operation intention and an intake air amount is controlled so as to obtain the target torque.

FIG. 9 is a control block diagram of the third embodiment. The target intake air amount setting section is used to determine the accelerator opening,
Based on engine operating conditions such as engine speed,
The target intake air amount Qc corresponding to the target torque is set by searching a preset table or the like.

The target residual gas rate setting section includes the first and second residual gas rate setting sections.
In the same manner as in the first embodiment, the target residual gas rate R
Set EGR.

The target intake pressure setting section sets a predetermined target intake pressure (negative pressure) Pm based on engine operating conditions such as accelerator opening and engine speed. The target intake volume calculation unit calculates a target intake volume Vs1 by the following equation based on the set target intake air amount Qc, target residual gas ratio REGR, and target intake pressure Pm.

QI = Pm · (Vs1 + Vc) Qc = (1-REGR) · QI = (1-REGR) · Pm · (Vs1 + Vc) Therefore, Vs1 = Qc / ｛Pm · (1-REG)
R)｝-Vc The target residual gas volume calculation unit calculates the set target intake air amount Qc, target residual gas rate REGR, and target intake pressure P
Based on m, the target residual gas volume Vs2 is calculated by the following equation.

QE = REGR · QI = REGR · Pm · (Vs1 + Vc) = Pe · (Vs2 + Vc) Therefore, Vs2 = Pm · REGR · (Vs1 + V
c) / Pe-Vc The target TH opening area calculation unit calculates the target throttle opening area ATH based on the set target intake air amount Qc and the target intake pressure Pm as follows.

First, the target intake pressure Pm and the atmospheric pressure Pa (= 7
An air amount / throttle opening area conversion coefficient RQ is calculated from a table as shown in FIG. 10 based on the ratio Pm / Pa to 60 mmHg). The characteristic of the coefficient RQ is that, in a region where the intake pressure is equal to or less than a predetermined value, a so-called sonic flow occurs and the intake air amount increases in proportion to the increase of the opening area regardless of the intake pressure change. Therefore, when the intake pressure increases more than a certain level, the intake air amount increases due to the increase of the intake pressure. Therefore, the coefficient RQ is decreased to decrease the opening area with the increase of the intake pressure, and further, the intake pressure is reduced. Increases, the intake air amount increases in accordance with the increase in the opening area irrespective of the change in intake pressure. Therefore, the coefficient RQ is kept constant.

Using the air amount / throttle opening area conversion coefficient RQ, a target throttle opening area ATH is calculated by the following equation. ATH = Qc · Ne · RQ The IVC control unit and the EVC control unit drive the electromagnetic drive device such that the set target closing timing IVC of the intake valve 5 and the target closing timing EVC of the exhaust valve 6 are obtained. Thus, the closing timing of the intake valve 5 and the closing timing of the exhaust valve 6 are controlled.

The target TH opening calculating section calculates the target throttle opening ETH by converting the target throttle opening area ATH into a target throttle opening ETC by searching a table or the like. The TH control unit controls the opening of the throttle valve 15 by driving the electronically controlled throttle device so as to achieve the target throttle opening ETC.

In this manner, in the torque demand control for performing the engine output control with high accuracy according to the driver's will, the control of the residual gas amount (internal EGR amount) is also performed with high accuracy, and stable combustion performance is obtained. , The exhaust purification performance and the fuel efficiency can be improved sufficiently.

In the first and second embodiments as well, the target intake air amount, the target residual gas amount, and the target intake pressure are determined in advance based on the accelerator opening, the engine speed, and the like. Therefore, if the target intake air amount, target residual gas amount, and target intake pressure are taken into consideration when setting the target closing timing of the intake valve, control that is close to torque demand control can be simplified. Can do it.

[Brief description of the drawings]

FIG. 1 is a system diagram of an engine including a variable valve control device according to an embodiment of the present invention.

FIG. 2 is a basic structural diagram of an electromagnetic drive device for intake and exhaust valves.

FIG. 3 is a control block diagram of closing timing control of an intake valve and an exhaust valve according to the first embodiment.

FIG. 4 is a view for explaining a target intake volume and a target exhaust volume in the embodiment.

FIG. 5 is a table characteristic diagram for obtaining a target intake volume from the above based on a target closing timing of the intake valve.

FIG. 6 is a table characteristic diagram for obtaining a target residual gas ratio from engine operating conditions.

FIG. 7 is a table characteristic diagram for obtaining a target closing timing of the exhaust valve from the above target exhaust volume.

FIG. 8 is a control block diagram of closing timing control of an intake valve and an exhaust valve according to a second embodiment.

FIG. 9 is a control block diagram of closing timing control of an intake valve and an exhaust valve according to a third embodiment.

FIG. 10 is a table characteristic diagram for calculating an air amount / throttle opening area conversion coefficient RQ used in the embodiment.

FIG. 11 is a map showing an exhaust pressure correction coefficient.

[Description of Signs] 1 Engine 5 Intake valve 6 Exhaust valve 9 Fuel injection valve 10 Control unit 11 Crank angle sensor 12 Accelerator pedal sensor 14 Air flow meter 15 Throttle valve

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Claims (6)

[Claims] A variable valve control device capable of arbitrarily variably controlling the opening / closing timing of an intake / exhaust valve of an engine, wherein an exhaust stroke is terminated based on a total gas amount in a cylinder at the end of an intake stroke based on an engine operating state. Setting a target residual gas ratio which is a target ratio of the residual gas amount in the cylinder at the time, and controlling a closing timing of the intake valve and a closing timing of the exhaust valve so as to achieve the target residual gas ratio. Variable valve control device. 2. A target residual gas amount is calculated by multiplying the total gas amount calculated based on a closing timing of an intake valve by the target residual gas rate, and a closing timing of an exhaust valve is determined based on the target residual gas amount. The control device for a variable valve according to claim 1, wherein the setting is performed. 3. The variable valve according to claim 1, wherein the total gas amount is calculated by multiplying a cylinder volume at a closing timing of the intake valve by an intake pressure in an intake passage. Control device. 4. A target intake air volume and a target residual gas volume are calculated from a target intake air amount and a target residual gas ratio set based on an operation state of the engine, and the intake valve is closed based on the target intake volume. The control apparatus for a variable valve according to claim 1, wherein the timing is set, and the closing timing of the exhaust valve is set based on the target residual gas volume. 5. The variable valve control device according to claim 4, wherein the target intake volume and the target residual gas volume are calculated in consideration of an intake pressure in an intake passage. 6. The variable valve control device according to claim 1, wherein the opening timing of the intake valve is set after the closing timing of the exhaust valve.