JP2004076706A - Variable valve mechanism control system for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent a rough idling in the high-temperature starting of an engine. <P>SOLUTION: The engine 1 comprises intake port fuel injection valves 9a-9d, intake valves 11a-11d consisting of solenoid drive valves, exhaust valves 13a-13d, and a throttle valve 7 having an actuator 7a. An electronic control unit (ECU) 30 determines whether the engine is started at high temperature or not based on the engine cooling water temperature detected by a cooling water temperature sensor 39, fully opens the throttle valve in the high-temperature starting, and also advances the closing timing of each intake valve more than the bottom dead center of intake stroke to reduce the intake air quantity of a cylinder. Accordingly, since the pressure of the intake ports can be raised to the vicinity of the atmospheric pressure while suppressing the rise of the engine rotating speed, the rough idling by vacuum boiling of fuel in a fuel injection valve in the high-temperature starting can be prevented. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a variable valve mechanism control device for an internal combustion engine.
[0002]
[Prior art]
In an engine equipped with a fuel injection valve that injects fuel into the engine intake port, when starting the engine from a high temperature state, sufficient fuel may not be supplied to the cylinders, causing unstable idling speed or engine stall. It is known that there is.
[0003]
Normally, when the engine is started, the engine is operated with no load, and the throttle valve in the intake passage is fully closed to reduce the amount of intake air. For this reason, when the engine is started, a large negative pressure is generated in the intake port of each cylinder of the engine, and the pressure decreases.
[0004]
However, when the engine is started in a high temperature state, the fuel that stays in the fuel injection valve during stoppage and receives heat from the surroundings and becomes high temperature is injected from the fuel injection valve. This hot fuel is pressurized to the fuel injection pressure before the engine is started (that is, when the fuel injection valve is closed), so that no boiling occurs in the fuel injection valve.
[0005]
However, when the fuel injection valve is opened for fuel injection at the time of starting the engine at a high temperature, the pressure near the injection hole of the fuel injection valve rapidly decreases. In this case, when the fuel pressure in the vicinity of the injection hole drops below the fuel vapor pressure, the fuel evaporates instantaneously in the vicinity of the injection hole to generate bubbles, so-called reduced-pressure boiling occurs.
[0006]
When the depressurized boiling occurs in the fuel injection valve, a large amount of air bubbles are mixed in the fuel, so that the fuel amount actually injected into the intake port is substantially reduced even if the fuel injection valve opening time is the same. For this reason, when the fuel is decompressed and boiled in the fuel injection valve, the combustion air-fuel ratio of the engine becomes lean, the combustion of the engine becomes unstable, and a problem such as rough idle where the idling speed is not stable occurs.
[0007]
In order to prevent the occurrence of reduced-pressure boiling in the fuel injection valve, it is effective to increase the pressure of the intake port. Normally, when the engine is started, the engine is operated in a no-load (idle) state, so that the throttle valve is fully closed, and the intake port pressure is lower than the atmospheric pressure and is considerably lower than the vapor pressure of the high-temperature fuel. When the port pressure is increased to, for example, near the atmospheric pressure, the reduced pressure boiling in the fuel injection valve does not occur even at the time of the high temperature start.
For this reason, a control device has been devised in which the intake port pressure is increased at the time of engine high temperature start to prevent rough idle.
[0008]
An example of this type of control device is described in, for example, JP-A-8-200125.
The device disclosed in the publication relates to an engine provided with an idle speed control device, and operates a load driven by the engine (for example, a mechanical supercharger) for a predetermined period when the engine is started at a high temperature. When the driving load increases, the engine idle speed decreases, so the idle speed control device opens the idle control valve and increases the intake air amount of the engine. As a result, at the time of high temperature start, the intake port pressure increases, and the occurrence of rough idle or the like due to reduced pressure boiling at the fuel injection valve is prevented while maintaining the engine idle speed at the set speed.
[0009]
[Problems to be solved by the invention]
By the way, in the internal combustion engine, a variable valve mechanism that changes a valve opening characteristic value (a valve opening / closing timing, a valve opening period, a valve lift amount, etc.) of an intake valve or an exhaust valve is known. However, conventionally, in an engine equipped with such a variable valve operating mechanism, no attempt has been made to solve a problem such as rough idle at the time of high-temperature starting using the variable valve operating mechanism. There was a problem that it was hard to say that it was fully utilized.
An object of the present invention is to provide a control device for a variable valve mechanism of an internal combustion engine which can prevent a problem such as rough idle at the time of high temperature starting of the engine by using the characteristics of the variable valve mechanism in view of the above problems. And
[0010]
[Means for Solving the Problems]
According to the first aspect of the present invention, there is provided a control device for a variable valve mechanism of an internal combustion engine that changes a valve opening characteristic value of an intake valve or an exhaust valve, wherein the intake valve or the exhaust valve is activated when the engine is started at a high temperature. A variable valve mechanism control device for an internal combustion engine that increases an intake pipe pressure by changing at least one valve opening characteristic value is provided.
[0011]
That is, in the first aspect of the present invention, the variable valve mechanism is used to increase the intake pipe pressure by changing either one of the intake valve and the exhaust valve using the variable valve mechanism. It is possible to solve problems such as rough idle.
[0012]
According to the invention described in claim 2, when the engine is started at a high temperature, the opening degree of the throttle valve arranged in the intake passage is increased, and the valve opening characteristic value of at least one of the intake valve and the exhaust valve is changed. A variable valve mechanism control apparatus for an internal combustion engine according to claim 1, which increases the intake pipe pressure.
[0013]
That is, in the invention of claim 2, the engine is provided with a variable valve mechanism capable of changing the valve opening characteristics of the intake valve or the exhaust valve. For example, valve opening characteristic values such as valve opening / closing timing, valve opening period, and valve lift amount are closely related to the amount of air taken into the cylinder, and one or more of these valve opening characteristic values are determined. By changing the amount, the amount of intake air can be changed.
For this reason, if the engine intake air amount is changed by changing the valve opening characteristic value of the intake valve or the exhaust valve by the variable valve mechanism, the intake air amount is controlled without using the intake throttle (throttle valve). That is, a so-called non-throttle operation can be performed.
[0014]
In the present invention, the non-throttle operation is performed while increasing the throttle valve opening (for example, maintaining the throttle valve fully open) when the engine is started at a high temperature. For this reason, a negative pressure is not generated in the intake port, and the pressure near the substantially atmospheric pressure can be maintained.
[0015]
As the variable valve mechanism of the present invention, any type can be used as long as it can change the valve opening characteristic value.For example, each valve is provided with an individual electromagnetic actuator, An electromagnetically driven valve or the like that can individually set the valve opening timing and the valve closing timing can also be used.
[0016]
According to the invention described in claim 3, the closing timing of the intake valve is changed as the valve opening characteristic value, and the closing timing of the intake valve is advanced from the bottom dead center of the cylinder intake stroke. Item 2. A variable valve mechanism control device for an internal combustion engine according to item 2 is provided.
[0017]
That is, in the invention of claim 3, the closing timing of the intake valve is controlled as the valve opening characteristic value. The intake valve normally opens near the top dead center of the intake stroke and closes after the bottom dead center. However, if the valve closing timing is advanced while the valve opening timing of the intake valve is fixed, the valve opening period of the intake valve is shortened and the amount of air flowing into the cylinder decreases.
[0018]
In the present invention, the amount of air flowing into the cylinder is adjusted by advancing the closing timing of the intake valve. The actual amount of advance of the valve closing timing varies depending on the type of engine and the like.For example, if the throttle valve is fully opened, the intake port pressure becomes almost atmospheric pressure. In order to maintain the idling speed only by shortening the valve period, it is preferable that the valve closing timing is advanced considerably from the bottom dead center, and the intake valve is opened only near the top dead center of the intake stroke.
[0019]
According to the invention described in claim 4, the valve opening timing of the exhaust valve is changed as the valve opening characteristic value, and the exhaust valve opening timing is retarded from the bottom dead center of the exhaust stroke when the intake pipe pressure increases. A variable valve mechanism control device for an internal combustion engine according to any one of claims 1 to 3 is provided.
[0020]
That is, in the invention of claim 4, the opening timing of the exhaust valve is used as the valve characteristic value, and the opening timing of the exhaust valve is retarded from the bottom dead center of the exhaust stroke. Normally, the exhaust valve opens just before the bottom dead center of the exhaust stroke and closes near the top dead center. If the exhaust valve opening timing is retarded from the bottom dead center of the exhaust stroke, the burned gas in the cylinder is compressed by the piston because the exhaust valve is closed even after the piston starts rising. For this reason, the compression work of the cylinder increases in the early stage of the exhaust stroke, and the output torque of the engine decreases. As a result, even when the engine intake air amount increases due to an increase in the intake port pressure, an increase in the output torque is suppressed, and an excessive increase in the engine speed is prevented.
[0021]
The output torque is suppressed by retarding the opening timing of the exhaust valve, for example, when the intake air amount cannot be sufficiently reduced by adjusting the intake air amount by advancing the closing timing of the intake valve. Is particularly effective.
[0022]
According to the invention described in claim 5, an intake valve or an exhaust valve of an internal combustion engine including a throttle valve disposed in an intake passage and a fuel injection valve for injecting fuel into an intake passage downstream of the throttle valve. A variable valve actuation mechanism control device for changing the valve opening characteristic value of the throttle valve downstream of the throttle valve by changing at least one of an intake valve and an exhaust valve during engine high temperature start. A variable valve mechanism for an internal combustion engine that increases a passage pressure is provided.
[0023]
In other words, the invention described in claim 5 utilizes a variable valve mechanism to reduce the possibility that the fuel injection valve that injects fuel to the downstream side of the throttle valve will be decompressed and boiled to cause problems such as rough idle at the time of high-temperature start of the engine. Can be prevented.
[0024]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
FIG. 1 is a diagram illustrating a schematic configuration of an embodiment when the present invention is applied to a four-cylinder gasoline engine for a vehicle.
[0025]
In FIG. 1, reference numeral 1 denotes an engine body, 3 denotes an intake passage of the engine 1, and 3a denotes a surge tank connected to intake ports of each cylinder via intake manifolds 4a to 4d.
A throttle valve 7 for controlling the amount of intake air flowing through the intake passage 3 is provided on the intake passage 3. In the present embodiment, the throttle valve 7 is a so-called electronically controlled throttle valve that includes an independent actuator 7a such as a stepper motor and can operate independently of the driver's operation amount of an accelerator pedal (not shown).
[0026]
On the intake manifolds 4a to 4d, fuel injection valves 9a to 9d for injecting fuel to the intake ports of the respective cylinders are provided.
FIG. 1 shows an exhaust manifold 5a that connects the exhaust passage 5 of the engine to the exhaust port of each cylinder.
[0027]
In FIG. 1, reference numerals 11a to 11d denote intake valves provided in each cylinder, and reference numerals 13a to 13d denote exhaust valves. In the present embodiment, the intake valves 11a to 11d (hereinafter collectively referred to as the intake valve 11) and the exhaust valves 13a to 13d (hereinafter collectively referred to as the exhaust valve 13) are driven by individual electromagnetic actuators, and can be freely opened and closed. It is an electromagnetically driven valve that can be set. The electromagnetically driven valve will be described later in detail.
[0028]
In FIG. 1, reference numeral 30 denotes an electronic control unit (ECU) of the engine 1. In the present embodiment, the ECU 30 is a microcomputer having a known configuration in which a RAM, a ROM, and a CPU are connected by a bidirectional bus. In addition to the basic control for controlling the ignition timing, the fuel injection amount, the injection timing, and the like of the engine 1, the ECU 30 includes: In the present embodiment, a variable valve mechanism control operation at the time of high-temperature start described below is performed.
[0029]
For these controls, the output port of the ECU 30 is connected to the actuator 7a of the throttle valve 7 via the drive circuit 17, and controls the throttle valve opening. In this embodiment, the ECU 30 determines the throttle valve opening based on a predetermined relationship using an accelerator opening detected by an accelerator opening sensor 33 described later and the engine speed, and drives the actuator 7a to control the throttle valve. Controls valve opening. An output port of the ECU 30 is connected to each of the fuel injection valves 9a to 9d via a fuel injection circuit 19, and controls the fuel injection amount and the injection timing from each fuel injection valve, and also via a drive circuit 15. Connected to the intake valve 11 and the exhaust valve 13 of each cylinder to control the opening and closing operation of each valve.
[0030]
An output of an air-fuel ratio sensor 31 that detects an air-fuel ratio of exhaust gas (that is, a combustion air-fuel ratio of the engine) disposed in the exhaust passage 5 of the engine 1 is supplied to an input port of the ECU 30 via an AD converter (not shown). In addition to the input, the accelerator pedal depression amount (accelerator opening) of the driver is input from an accelerator opening sensor 33 provided near an accelerator pedal (not shown) via an AD converter (not shown). .
[0031]
Reference numeral 35 in FIG. 1 denotes a crank angle sensor. The crank angle sensor 35 is disposed in the vicinity of the crankshaft, and outputs a reference pulse for each predetermined reference rotation position of the crankshaft (for example, compression top dead center of a specific cylinder) and a crank rotation angle pulse for each constant crankshaft rotation angle. appear. The ECU 30 calculates the crank rotation speed (rotation speed) from the frequency of the crank rotation angle pulse signal input from the crank angle sensor 30, and based on the number of crank rotation angle pulses after the input of the reference pulse, the current rotation position of the crankshaft. (Crank angle) is calculated.
[0032]
Further, an input port of the ECU 30 receives a signal corresponding to an actual throttle valve opening from a throttle opening sensor 37 provided near the throttle valve 7 and a cooling water temperature sensor 39 provided in the engine cooling water passage. A signal corresponding to the engine cooling water temperature is input via an AD converter (not shown).
[0033]
Next, the starting control of the present invention will be described.
Normally, the starting fuel injection amount is set such that the engine combustion air-fuel ratio becomes rich in consideration of fuel that adheres to the intake port wall surface and is not supplied to the combustion chamber when the engine is started.
However, when the engine is restarted in a short time after the previous stop, the engine is started in a state where the engine temperature is considerably high. In this case, the fuel that has stayed in the fuel injection valve or the fuel pipe close to the engine during the stop of the engine becomes hot due to the heat of the engine, and the vapor pressure of the fuel also increases in accordance with the temperature. . In this state, when the fuel injection valve is opened and fuel injection is performed, the fuel pressure near the injection hole in the fuel injection valve rapidly decreases. The fuel pressure in the vicinity of the injection hole at the time of this fuel injection becomes lower as the pressure at the intake port becomes lower. When the fuel pressure becomes lower than the vapor pressure of the fuel, reduced pressure boiling occurs in which the fuel boils rapidly near the injection hole.
[0034]
Normally, the throttle valve is maintained in a fully closed state at the time of starting the engine or during idle operation after the start of the engine, so that the intake port pressure falls to or below the atmospheric pressure. During a cold start of the engine, the fuel temperature is low and the vapor pressure of the fuel is low, so that even if the intake port pressure is reduced, reduced pressure boiling does not occur. However, when the engine is started at a high temperature, the fuel temperature is high and the vapor pressure is also increasing. Therefore, when the intake port pressure decreases, decompression boiling occurs near the injection hole of the fuel injection valve, and fuel containing a large amount of air bubbles mixed from the fuel injection valve. It will be injected.
[0035]
For this reason, when depressurized boiling occurs, even if the injection time of the fuel injection valve is the same, the amount of fuel actually injected is reduced by the amount of the mixed air bubbles. When the engine is idling, the combustion air-fuel ratio of the engine becomes lean. For this reason, when the engine is started at a high temperature, combustion is not stabilized, and the idle speed fluctuates. In extreme cases, engine stall occurs, that is, so-called rough idle occurs.
[0036]
In this embodiment, a variable valve mechanism including the electromagnetically driven valves 11a to 11d and 13a to 13d is provided, and the occurrence of rough idle is prevented by a method described later using the variable valve mechanism.
[0037]
Next, the structure of the electromagnetically driven valve of the present embodiment will be described with reference to FIG.
FIG. 2 is a cross-sectional view schematically illustrating a configuration of an embodiment of the electromagnetically driven valve.
In FIG. 2, reference numeral 10 indicates the entire electromagnetically driven valve. In the present embodiment, both the intake valve and the exhaust valve of each cylinder of the internal combustion engine have an electromagnetically driven valve of the type shown in FIG. 2, respectively.
[0038]
2, reference numeral 54 denotes a valve body of an intake valve (or exhaust valve) of the internal combustion engine, and 54a denotes a valve shaft. A disk-shaped armature 53 made of a magnetic material is fixed to the upper part of the valve shaft 54a. Further, on both sides of the armature 53, electromagnetic actuators 51 and 52 facing each other with a predetermined clearance from the armature 53 are arranged. The electromagnetic actuators 51 and 52 include electromagnetic coils 51a and 52a and cores 51b and 52b, respectively, and energize the electromagnetic coils 51a and 52a to attract the armature 53 and cause the valve 54 to open and close. In the example of FIG. 2, the electromagnetic actuator 51 functions for a valve closing operation, and the electromagnetic actuator 52 functions for a valve opening operation.
[0039]
Further, springs 55 and 56 for urging the armature 53 in directions facing each other are provided on a casing 57 that houses the electromagnetic actuators 51 and 52 and the valve body 54 and the armature 53. When power is not supplied to either of the electromagnetic actuators 51 and 52 when the engine is stopped or the like, the valve element 54 is held at an intermediate position between the fully open position and the fully closed position by the urging force of the springs 55 and 56. Is done.
[0040]
In this embodiment, the ECU 30 alternately alternates between the valve closing actuator 51 and the valve opening actuator 52 of the electromagnetically driven valve 10 of each cylinder through the drive circuit 15 at every predetermined crank angle according to the stroke cycle of each cylinder. Energize. As a result, the intake and exhaust valves of each cylinder are driven to open and close at the determined valve timing.
[0041]
In FIG. 2, reference numeral 61 a denotes a disk-shaped lift detection target attached to the upper part of the valve shaft of the valve element 54, and 61 denotes a lift sensor arranged at a position facing the target 61 a at the upper part of the housing of the electromagnetically driven valve 10. The lift sensor 61 is composed of, for example, an eddy current displacement sensor, and supplies a voltage signal corresponding to the displacement of the target 61a, that is, the lift amount of the valve body 54, to the ECU 30.
[0042]
The ECU 30 controls the valve timing and the valve opening time of the intake and exhaust valves of each cylinder of the engine according to the engine operating state by controlling the energization timing and period of the actuator of each electromagnetically driven valve 10. In addition, high-temperature start control is performed to prevent rough idle during high-temperature start of the engine.
[0043]
Next, a description will be given of a high-temperature start control by the variable valve mechanism control of the present embodiment.
In the present embodiment, since the electromagnetically driven valve is used as the variable valve mechanism, the opening and closing timing of the intake and exhaust valves can be freely set. In the present embodiment, optimal values are set in advance for the valve opening timing and the valve closing timing of the intake valve 11 and the exhaust valve 13 in accordance with the engine operating conditions (the engine speed and the accelerator opening). A two-dimensional numerical table using the engine speed and the accelerator opening is stored in the ROM of the ECU 30. During the operation of the engine, the ECU 30 reads the optimal opening / closing timing from the numerical table stored in the ROM based on the engine speed and the accelerator opening, and controls the opening / closing timing of the intake valve 11 and the exhaust valve 11 to the above-mentioned optimal value. are doing.
[0044]
The optimal opening / closing timing of the intake / exhaust valve is set for the purpose of maintaining, for example, the residual burned gas (internal EGR gas) in the cylinder and the intake charging efficiency in an optimal state according to the operating state of the engine. The intake air amount is adjusted by controlling the opening of the throttle valve 7.
[0045]
FIG. 3 is a diagram showing the opening / closing timing of the intake valve during normal idle operation.
In FIG. 3, TDC indicates the top dead center of the intake stroke, and BDC indicates the bottom dead center of the intake stroke. During normal operation (operation not during high-temperature start-up), as shown by the solid line in FIG. 3, the intake valve opens near the top dead center TDC (FIG. 3, IO) and closes after the bottom dead center BDC (FIG. 3). (FIG. 3, IC). At this normal valve timing, the intake valve 11 is open over almost the entire intake stroke. Therefore, in order to maintain the idle speed by restricting the intake air amount and suppressing an increase in the rotational speed, the throttle valve during idling is operated. 7 is maintained almost fully closed.
For this reason, at normal times, the intake port pressure is considerably lower than the atmospheric pressure, and at the time of a high temperature start, as described above, the fuel is likely to be decompressed and boiled in the fuel injection valve, which causes rough idle and the like. Has become.
[0046]
In the present embodiment, at the time of the high temperature start, the throttle valve 7 is kept in the fully open state, and the intake air amount is not controlled by the intake throttle. Instead, as shown by a dotted line in FIG. The amount of air sucked into the cylinder is limited by advancing it to a time earlier than the dead center BDC. The advance amount (α in FIG. 3) greatly varies depending on the engine type, the size and number of valves, etc., so it is preferable to determine the details by experiments. However, the throttle valve 7 is fully opened and the intake port is substantially at atmospheric pressure. In order to suppress the increase in the idling speed while maintaining the intake air speed, it is necessary to considerably reduce the intake air amount, and as shown by IC 'in FIG. 3, the intake valve closing timing is advanced considerably to near the top dead center. It is necessary to shorten the opening period of the intake valve.
[0047]
As described above, by advancing only the closing timing of the intake valve earlier than the bottom dead center, the intake valve opens only for a short period near the intake top dead center TDC. In the vicinity, since the descending speed of the piston with respect to the change in the crank angle is small, the inflow speed of the intake air into the cylinder is relatively small. Therefore, by advancing the valve closing timing and opening the intake valve only near the top dead center, the amount of intake air can be effectively reduced. As described above, while increasing the opening degree of the throttle valve 7 to increase the intake port pressure to near the atmospheric pressure, the intake air amount is reduced by advancing the intake valve closing timing, thereby suppressing an increase in the idle speed. Meanwhile, it is possible to prevent the occurrence of rough idle due to the reduced pressure boiling of the fuel at the time of the high temperature start.
[0048]
In the present embodiment, the throttle valve is kept fully open at the time of high-temperature start. For example, even when the throttle valve is kept closed to a certain degree or fully closed, the closing timing of the intake valve is kept constant. Is advanced, the intake air amount in the cylinder is reduced, so that the intake port pressure rises more than during normal idle operation. For this reason, it is possible to prevent the occurrence of rough idle due to the reduced pressure boiling of the fuel at the time of a high temperature start even if the throttle valve is not necessarily kept fully open.
[0049]
Next, the high temperature start control of the exhaust valve 13 will be described.
In the present embodiment, the intake air amount is reduced by advancing the closing timing of the intake valve as described above. However, the closing timing of the intake valve depends on the type of engine, the size and number of the intake valves, and the like. It may not be possible to sufficiently reduce the amount of intake air while maintaining the intake port near the atmospheric pressure only by the advance angle of. In such a case, in addition to the advance of the closing timing of the intake valve, the opening of the throttle valve 7 is made smaller than the full opening to reduce the intake port pressure within a range where depressurized boiling does not occur. May be reduced.
However, in the case where the intake port pressure cannot be increased to such an extent that the reduced pressure boiling can be suppressed while maintaining the idle speed even if the advance of the intake valve closing timing and the reduction of the opening of the throttle valve 7 are performed. Instead of the advance of the intake valve closing timing, or in addition to the advance of the intake valve closing timing, the exhaust valve opening timing described below may be retarded.
[0050]
FIG. 4 is a view similar to FIG. 3, showing the exhaust valve opening / closing timing during normal idle operation and the exhaust valve opening / closing timing during high-temperature startup in the present embodiment. In FIG. 4, BDC indicates the bottom dead center of the exhaust stroke which is the start point of the exhaust stroke, and TDC indicates the top dead center of the exhaust stroke (same as the top dead center of the intake stroke) which is the end point of the exhaust stroke (that is, the start point of the intake stroke). During normal idle operation, the exhaust valve 13 opens slightly earlier than the bottom dead center BDC as shown by the solid line in FIG. 4 (EO in FIG. 4) and closes near the top dead center (FIG. 4, EC) ).
[0051]
On the other hand, at the time of the high temperature start, only the valve opening timing of the exhaust valve is delayed until the timing later than the BDC (EO ′ in FIG. 4) as shown by the dotted line in FIG. By maintaining the exhaust valve closed until later than the bottom dead center, the burned gas is compressed in the cylinder by the rise of the piston, and the output loss due to the compression work increases.
[0052]
Thus, even when the intake air amount cannot be reduced sufficiently and the cylinder output torque increases when the intake port pressure is maintained near the atmospheric pressure, the increase in the output torque can be offset by the output loss due to the compression work. Therefore, it is possible to prevent an increase in the engine speed and increase the intake port pressure while maintaining the idle speed, thereby preventing the occurrence of rough idle.
[0053]
FIG. 5 is a flowchart specifically illustrating the high-temperature start control operation of the present embodiment. This operation is performed as a routine that is repeatedly executed by the ECU 30 at regular intervals.
In the operation of FIG. 5, first, at step 501, it is determined whether or not the engine has been started at a high temperature. The determination as to whether or not the engine has been started at a high temperature is made based on whether or not the coolant temperature at the time of engine startup detected by the coolant temperature sensor 39 is equal to or higher than a predetermined value.
[0054]
If the engine has not been started at a high temperature in step 501, there is no possibility that rough idle will occur due to reduced pressure boiling of the fuel. Do. In the normal control of the variable valve mechanism, the opening / closing timing of the intake valve and the exhaust valve is set to the timing shown by the solid line in FIGS. 3 and 4, and the throttle valve is kept fully closed.
[0055]
If the engine is started at a high temperature in step 501, that is, if the cooling water temperature at the time of starting the engine is equal to or higher than a predetermined value, it is next determined in step 503 whether a predetermined time has elapsed after the engine was started. If the predetermined time has not elapsed, the routine proceeds to step 509, where the high temperature start control using the above-described variable valve mechanism is performed. That is, in this case, the opening and closing timings of the intake valve and the exhaust valve are set to the timings shown by the dotted lines in FIGS. 3 and 4, and the throttle valve 7 is kept fully open. As a result, the intake port pressure is increased to near the atmospheric pressure while maintaining the idle speed, so that rough idle due to reduced pressure boiling of the fuel is prevented.
[0056]
In the present embodiment, if the predetermined time has elapsed (step 503), the high-temperature start control of the variable valve mechanism is ended in principle and returns to the normal control (step 507). If the value of the fuel ratio feedback correction coefficient FAF is equal to or greater than a predetermined value (for example, 1.05), the high temperature start control in step 509 is performed even if the predetermined time has elapsed in step 503.
[0057]
That is, in the present embodiment, the control at the time of high-temperature start of the variable valve mechanism is performed until a predetermined time elapses after the high-temperature start of the engine, and the pressure of the intake port is maintained near the atmospheric pressure to prevent the decompression boiling of the fuel. In this case, it is determined in step 505 whether or not the reduced pressure boiling of the fuel has occurred due to the termination of the high temperature start control of the variable valve mechanism after the elapse of a predetermined time. In step 509 again, the high temperature start control of the variable valve mechanism is restarted.
[0058]
As described above, decompression boiling of fuel at the time of high temperature start occurs because fuel whose temperature has risen due to stagnation in a fuel injection valve or a pipe while the engine is stopped is injected into a low pressure intake port. If all the high-temperature fuel near the injection valve is injected and the low-temperature fuel supplied from the tank is injected from the fuel injection valve, no decompression boiling occurs.
[0059]
In the present embodiment, at the time of high-temperature start, when a time that can be determined that all of the high-temperature fuel in the fuel injection valve or the pipe has been injected has elapsed, the high-temperature start control of the variable valve mechanism is stopped and the control is returned to the normal control. However, since the time until all the high-temperature fuel is injected fluctuates depending on various conditions, even when the high-temperature start-up control is stopped, when it is determined that the fuel is decompressed and boiled under reduced pressure. The control at high-temperature start is immediately restarted.
[0060]
The air-fuel ratio feedback control correction coefficient FAF in step 505 in FIG. 5 is a correction coefficient calculated based on the output of the exhaust air-fuel ratio sensor 31 of the engine 1. As described above, in the present embodiment, the fuel injection amount (basic fuel injection amount) of the engine is set by the ECU 30 from a predetermined relationship based on the operating state of the engine (for example, engine speed and accelerator opening). In the present embodiment, the ECU 30 corrects the calculated basic fuel injection amount based on the output of the air-fuel ratio sensor 31 such that the exhaust air-fuel ratio becomes the target air-fuel ratio (for example, the stoichiometric air-fuel ratio). For example, when the air-fuel ratio detected by the air-fuel ratio sensor 31 is β times the target air-fuel ratio, the basic fuel injection amount needs to be β times to match the target air-fuel ratio. In this case, the value of the air-fuel ratio correction coefficient FAF is set to β, and the actual fuel injection amount is a value obtained by multiplying the basic fuel injection amount by the coefficient β.
[0061]
Now, when the target air-fuel ratio is the stoichiometric air-fuel ratio, when the value of FAF is larger than 1, the actual air-fuel ratio is leaner than the stoichiometric air-fuel ratio. Become. As described above, when the fuel is boiled under reduced pressure, the amount of fuel actually injected is reduced by the amount of generated bubbles. Therefore, when boiling under reduced pressure occurs, the air-fuel ratio detected by the air-fuel ratio sensor 31 becomes lean, and in the air-fuel ratio control separately executed by the ECU 30, the air-fuel ratio feedback correction coefficient FAF is increased to obtain the target air-fuel ratio. .
[0062]
In this embodiment, when the FAF increases to reach a predetermined value β (for example, about 1.05) in step 505 of FIG. 5, that is, when the actual air-fuel ratio becomes β times the target air-fuel ratio (for example, 1. In the case where the fuel injection amount becomes lean up to 05 times), it is determined that the fuel injection amount has decreased due to the reduced pressure boiling of the fuel, and the high temperature start control of the variable valve mechanism is restarted.
As described above, by executing the control operation of FIG. 5, it is possible to prevent the occurrence of rough idle or the like using the variable valve mechanism.
[0063]
In the above-described embodiment, the case where an electromagnetically driven valve provided with an individual electromagnetic actuator for each valve is used as the variable valve mechanism. However, another type, for example, a variable valve having a valve driving camshaft. Similar control is possible when a mechanism is used.
[0064]
For example, as an example, a type in which the intake valve is driven by using a three-dimensional cam whose cam lift continuously changes in the camshaft axis direction and the camshaft is moved in the axial direction to change the valve lift amount of the intake valve is possible. When the variable valve mechanism is used, it is possible to increase the intake port pressure while reducing the intake air amount of the cylinder by reducing the valve lift amount at the time of high temperature start.
[0065]
By the way, in the above-described embodiment, the variable valve mechanism using the electromagnetically driven valve is used. However, in the variable valve mechanism using the electromagnetically driven valve, it is necessary to initialize each electromagnetically driven valve when the engine is started.
As described with reference to FIG. 2, when the engine is stopped, that is, when neither the electromagnetic actuators 51 and 52 of the electromagnetically driven valve 10 are energized, the valve body is biased by the springs 55 and 56. Numeral 54 is held between the fully open position and the fully closed position (half open position). In order to enable the opening and closing operation of the valve from this state, it is necessary to perform a process of energizing the valve closing electromagnetic actuator 51 to draw all the intake valves and exhaust valves to the fully closed position. In the present embodiment, this processing is referred to as initialization processing. In the initialization processing, a drive current larger than a normal valve closing operation is applied to move the valve body that is stationary at the intermediate position. Need to be supplied to
[0066]
Normally, it is difficult to initialize all of the intake and exhaust valves at the same time due to the restriction of the power supply, and only two valves can be initialized at a time at most. However, if two valves are initialized at a time and the engine is started after all the valves have been initialized, it takes a long time to start the engine.
Therefore, in the present embodiment, as described below, the initialization of the intake valve and the exhaust valve of each cylinder is sequentially performed according to the ignition order, and the combustion is sequentially started from the cylinder whose initialization is completed. The engine start time when using an electromagnetically driven valve is shortened.
[0067]
In order to complete the preparation for starting combustion in each cylinder, the intake valve and the exhaust valve need to satisfy the following conditions.
(1) The intake valve is closed before starting fuel injection to the intake port.
(2) The exhaust valve is closed before the intake valve is opened during the intake stroke.
[0068]
The above conditions (1) and (2) are for preventing afterfire.
That is, the condition of (1) is that if fuel is injected into the intake port in a state where the intake valve is not closed, the injected fuel flows through the cylinder if the exhaust valve is not closed. This is because fuel may burn through the exhaust port when hot exhaust gas is discharged to the exhaust port after the start of combustion, and after-fire may occur. In this case, if the intake valve is closed before the start of fuel injection, the exhaust valve does not have to be closed.
[0069]
Also, the condition (2) is that if the exhaust valve is opened when the intake stroke is started, the air-fuel mixture sucked into the cylinder flows out to the exhaust port, and the likelihood of afterfire occurring as described above. Because there is.
Therefore, in the present embodiment, first, the intake valve of the cylinder is initialized and closed before fuel injection is started, and the exhaust valve of the same cylinder is initialized before the intake stroke is started after fuel injection. Then, by closing the valve, combustion is started in the cylinder in order along the ignition sequence.
[0070]
FIG. 6 is a flowchart illustrating the initialization of the electromagnetically driven valve at the time of starting the engine according to the present embodiment. As described with reference to FIG. 1, a four-cylinder engine is used in the present embodiment, and the ignition order is the cylinder order of 1-3-4-2.
[0071]
In the figure, # 1 to # 4 indicate cylinder numbers, respectively, and the point indicated by TDC1 is the compression top dead center of the # 1 cylinder. In this embodiment, the crank angle (CA) is represented on the basis of this point, and one cycle of the engine is set to 720 ° CA for convenience. In FIG. 2, (expansion), (discharge), (suction), and (pressure) indicate an expansion stroke, an exhaust stroke, an intake stroke, and a compression stroke of each cylinder, respectively.
[0072]
In FIG. 6, when cranking of the engine is started and the compression top dead center of # 1 is detected by the crank angle sensor 35, first in the present embodiment, during the expansion stroke (0 ° CA to 180 ° CA), The intake valve of the # 1 cylinder is initialized (FIG. 6, I-1). Thus, at the time when the fuel injection is performed at # 1 (the exhaust stroke, the timing indicated by IJ-1 in FIG. 6), the # 1 cylinder is used. The initialization of the intake valve is completed, and the intake valve is kept in a closed state.
[0073]
Further, during this exhaust stroke (180 ° CA to 360 ° CA), the exhaust valve E-1 of the # 1 cylinder is initialized, and the ignition timing of the intake valve I- of the # 3 cylinder following the # 1 cylinder is set. 3 are initialized at the same time. Thus, when the intake valve is opened (IS-1) in the intake stroke of the # 1 cylinder, the exhaust valve E-1 is kept closed, and the fuel injection (IJ-3) is performed in the # 3 cylinder. When started, the intake valve I-3 is also closed. As a result, the # 1 cylinder normally opens and closes the intake valve and the exhaust valve thereafter. Thereafter, the exhaust valve E-3 of the # 3 cylinder and the intake valve I-4 of the # 4 cylinder, the exhaust valve E-4 of the # 4 cylinder and the intake valve I-2 of the # 2 cylinder are simultaneously and sequentially initialized.
[0074]
By simultaneously and sequentially initializing the exhaust valve of a certain cylinder and the intake valve of the cylinder whose ignition sequence is next to the cylinder as described above, during one cycle of the engine (0 ° CA to 720 ° CA). In this case, the intake valves and the exhaust valves of all the cylinders are initialized, and at the same time, the combustion is started in all the cylinders, so that a normal operation can be performed.
[0075]
In this embodiment, since a four-cylinder engine is used, the initialization of each valve needs to be completed within the period of 180 ° CA. However, assuming that the cranking rotational speed is 200 rpm, 180 ° CA The time required for rotation is 150 ms. In the case of six cylinders and eight cylinders, the periods for completing the initialization are 150 ° CA and 120 ° CA, respectively, and the time required for this rotation is 125 ms and 100 ms, respectively.
On the other hand, since the time required for initializing the electromagnetically driven valve is about 60 ms, in this embodiment, each valve can be initialized with a sufficient margin in any case.
[0076]
Although the above description has been given of an engine that performs intake port injection, for example, an engine that includes an in-cylinder fuel injection valve that directly injects fuel into a combustion chamber and that can start by performing fuel injection during an intake stroke or a compression stroke is described. It is also possible to simultaneously initialize the intake valve and the exhaust valve of each cylinder by the start of the intake stroke.
[0077]
【The invention's effect】
According to the invention described in each claim, a common effect is achieved in which the problem such as rough idle at the time of starting the engine at a high temperature can be prevented by using the variable valve mechanism.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating a schematic configuration of an embodiment in which the present invention is applied to a four-cylinder engine for an automobile.
FIG. 2 is a cross-sectional view illustrating a schematic structure of an electromagnetically driven valve.
FIG. 3 is a diagram showing opening / closing timing of an intake valve at the time of engine start.
FIG. 4 is a diagram showing opening / closing timing of an exhaust valve at the time of engine start.
FIG. 5 is a flowchart for explaining an engine start control operation of the variable valve mechanism.
FIG. 6 is a diagram illustrating an initialization timing of the electromagnetically driven valve at the time of starting the engine.
[Explanation of symbols]
1. Internal combustion engine body
3. Intake passage
5. Exhaust passage
7 ... Throttle valve
10. Electromagnetically driven valve
11a-11d ... intake valve
13a to 13d ... exhaust valve
30 ... ECU
31 ... Exhaust air-fuel ratio sensor

Claims (5)

A control device for a variable valve mechanism of an internal combustion engine that changes a valve opening characteristic value of an intake valve or an exhaust valve,
A variable valve mechanism control device for an internal combustion engine that increases the intake pipe pressure by changing a valve opening characteristic value of at least one of an intake valve and an exhaust valve when the engine is started at a high temperature. 2. The engine according to claim 1, further comprising, at the time of starting the engine at a high temperature, increasing the opening degree of the throttle valve arranged in the intake passage and changing the valve opening characteristic value of at least one of the intake valve and the exhaust valve to increase the intake pipe pressure. Variable valve mechanism control device for an internal combustion engine. 3. The variable valve actuation valve for an internal combustion engine according to claim 1, wherein the closing timing of the intake valve is changed as the valve opening characteristic value, and the closing timing of the intake valve is advanced from a bottom dead center of a cylinder intake stroke. Mechanism control device. 4. The exhaust valve according to claim 1, wherein a valve opening timing of the exhaust valve is changed as the valve opening characteristic value, and the exhaust valve opening timing is retarded from a bottom dead center of an exhaust stroke when the intake pipe pressure increases. 12. The variable valve mechanism control device for an internal combustion engine according to claim 10. Variable operation for changing a valve opening characteristic value of an intake valve or an exhaust valve of an internal combustion engine having a throttle valve disposed in an intake passage and a fuel injection valve for injecting fuel into an intake passage downstream of the throttle valve. A control device for a valve mechanism,
A variable valve mechanism for an internal combustion engine, which changes a valve opening characteristic value of at least one of an intake valve and an exhaust valve to increase an intake passage pressure downstream of the throttle valve when the engine is started at a high temperature.

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