JP2008215143A - Start control device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a start control device for an internal combustion engine capable of ensuring startability by forming an air-fuel mixture with fuel sufficiently vaporized in a cylinder and quickly igniting and burning it in starting using an alcohol-containing fuel. <P>SOLUTION: This start control device for the internal combustion engine is provided with a fuel injection valve (fuel injection means) and a variable valve train controlling the lift of an intake valve (suction valve), and uses the alcohol-containing fuel in at least starting. The start control device is so configured that the lift of the intake valve (suction valve) is minimized while stopping fuel injection from the fuel injection valve (fuel injection means), for a predetermined time from the start of cranking. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a start control device for an internal combustion engine using an alcohol-containing fuel, and relates to a technique for improving start performance.

As an internal combustion engine using an alcohol-containing fuel, like the one described in Patent Document 1, when the alcohol concentration of the fuel is high, the valve overlap period of the intake and exhaust valves is increased by a variable valve mechanism to reduce the internal EGR amount. Some increase the accelerator depression amount to reduce the pumping loss and improve the fuel consumption.
JP-A-5-272364

  However, in the one described in Patent Document 1, the variable valve mechanism is not involved in improving the startability. That is, as in the normal mechanism, when starting, cranking is started and the intake valve is opened and closed so that the cylinder is cooled by low-temperature outside air intake, so that the fuel is not sufficiently vaporized in the cylinder. Since the alcohol-containing fuel has a low alcohol vaporization property, an ignitable air-fuel mixture cannot be stably formed, and the starting performance is deteriorated.

  The present invention has been made in view of the above-described conventional problems, and at the time of starting using an alcohol-containing fuel, a sufficiently vaporized mixture of fuel is formed in a cylinder and quickly ignited and burned. An object of the present invention is to provide a start control device for an internal combustion engine that can ensure start performance.

For this reason, the invention according to claim 1
A start control device for an internal combustion engine comprising a fuel injection means and a variable valve mechanism for controlling a lift amount of an intake valve, and using an alcohol-containing fuel at least at the start,
Control is performed to minimize the lift amount of the intake valve while stopping fuel injection of the fuel injection means for a predetermined time from the start of cranking.

The invention according to claim 2
It has a variable valve mechanism that controls the lift amount of the exhaust valve,
Control is performed to minimize the lift amount of the exhaust valve for a predetermined time from the start of cranking.
The invention according to claim 3
The minimum value of the lift amount of the intake valve or the minimum value of the lift amount of the intake valve and the exhaust valve is zero.

The invention according to claim 4
The control to minimize the lift amount of the intake valve or the exhaust valve while stopping the fuel injection of the fuel injection means is performed when the engine temperature is lower than a predetermined value or the alcohol concentration of the fuel is higher than a predetermined value. It is characterized by being.

According to the first aspect of the present invention, the cylinder does not suck in the cryogenic outside air through the intake port or minimizes the intake valve lift amount by minimizing the lift amount of the intake valve for a predetermined time from the start of cranking. Even a very small amount.
Here, when the exhaust valve is driven to open and close during the predetermined time in the same manner as in other operations, the cylinder sucks part of the exhaust gas in the exhaust port due to internal negative pressure when the exhaust valve is opened, When the piston is raised, the exhaust gas is caused to flow out to the exhaust port through the exhaust valve that is open. That is, the exhaust gas once discharged from the cylinder to the exhaust port is re-inhaled from the exhaust port to the cylinder, and the cylinder hardly inhales the cryogenic outside air through the exhaust port.

Alternatively, even when the lift amount of the exhaust valve is minimized during the predetermined time, since the flow of air in and out of the cylinder is further restricted, the cylinder hardly sucks in the cryogenic outside air through the exhaust port.
In this manner, since the cryogenic outside air is hardly sucked directly into the cylinder from either the intake port or the exhaust port for a predetermined time from the start of cranking, the cooling of the cylinder is suppressed. Then, the cylinder is effectively heated by the friction due to the piston motion or the gas flow friction at the valve head of the exhaust valve by the amount of the cooling suppression. Therefore, by setting the predetermined time to an appropriate length, after the predetermined time elapses, the cylinder rises in temperature to a state where the fuel can be sufficiently vaporized, and from this time, the intake valve and the exhaust valve are opened and closed. By starting the drive and fuel injection by the fuel injection means, a mixture in which the fuel is sufficiently vaporized is formed in the cylinder, and it is quickly ignited and burned to complete explosion. Thereby, the amount of unburned fuel discharged at the time of start-up can be greatly reduced, and fuel consumption can be improved.

According to the second aspect of the present invention, since the lift amount of both the intake valve and the exhaust valve is minimized for a predetermined time from the start of cranking, the flow of air in and out of the cylinder is further limited. As a result, cranking can be performed in a state where the heat insulation effect of the cylinder is enhanced, the warming-up efficiency of the cylinder is improved, and the engine can be started in a short time by shortening the predetermined time.
According to the third aspect of the present invention, the minimum value of the lift amount of the intake valve or the minimum value of the lift amount of the intake valve and the exhaust valve is set to zero, so that a predetermined time from the start of cranking is transferred to the cylinder. Therefore, it is possible to reliably suppress the intake of outside air at a very low temperature, further suppress the cooling of the cylinder, and further improve the starting performance.

  According to the fourth aspect of the present invention, a sufficiently vaporized fuel mixture is formed in the cylinder even under conditions where normal fuel is difficult to vaporize, such as when starting from a very low temperature or when using fuel with a high alcohol concentration. Thus, the ignition performance can be promptly ignited and the starting performance can be improved.

Hereinafter, embodiments of the present invention will be described.
In FIG. 1, air is sucked into the combustion chamber 3 of the internal combustion engine 1 through a throttle valve 4, an intake port 5, and an intake valve 7.
The combustion exhaust is discharged from the combustion chamber 3 through the exhaust valve 9 and the exhaust port 11, purified by a catalyst, and then released into the atmosphere.

The exhaust valve 9 is driven to open and close at a constant valve lift and valve operating angle by a cam pivotally supported on the exhaust camshaft.
On the other hand, the intake valve 7 is provided with a VEL mechanism 13 that continuously and variably controls the valve lift amount together with the operating angle as a variable valve mechanism.
The intake valve 7 may include a variable valve timing mechanism that continuously changes the valve timing by changing the phase of the valve operating angle with respect to the crank angle together with the VEL mechanism 13. Alternatively, other mechanisms that can maintain the intake valve 7 in a closed state may be provided instead.

An engine control unit (ECU) 15 incorporating a microcomputer controls the throttle valve 4 and the VEL mechanism 13 in accordance with the engine operating state.
The ECU 15 includes a water temperature sensor 17 that detects the coolant temperature Tw of the engine 1, a crank angle sensor (not shown) that extracts a crank angle signal from the crankshaft, and alcohol (fuel containing alcohol) that is connected to a fuel tank 19. A detection signal is input from an alcohol concentration sensor 21 or the like that detects the concentration C.

  Further, an electromagnetic fuel injection valve 23 is provided in the intake port 5 upstream of the intake valve 7 of each cylinder. When the fuel injection valve 23 is driven to open by an injection pulse signal from the ECU 15, An amount of fuel proportional to the injection pulse width (valve opening time) is injected. The fuel injection valve 23 and the fuel tank 19 are connected via a fuel passage 25, and the alcohol concentration sensor 21 is disposed in the middle of the fuel passage 25.

Here, control of fuel injection and valve lift at the start by the ECU 15 will be described with reference to the flowchart of FIG.
The routine shown in the flowchart of FIG. 2 is executed when the engine 1 is started. The start time is, for example, cranking when the key switch is operated to the START position.

First, in step S1, cranking of the engine 1 is started.
Next, in step S2, the cooling water temperature Tw detected by the water temperature sensor 17 is read.
In step S3, the alcohol concentration sensor 21 detects the alcohol concentration C of the fuel.

In step S4, it is determined whether the cooling water temperature Tw is less than a predetermined value A or the alcohol concentration C is a predetermined value B or more.
If it is determined in step S4 that none of the above conditions is satisfied, it is determined that the cylinder temperature increase control according to the present invention is not necessary, and the process proceeds to step S5, while opening and closing the intake valve 7 and the exhaust valve 9 Cranking is performed while fuel is injected into the intake port 5 by the fuel injection valve 23, and the routine is terminated.

On the other hand, if it is determined in step S4 that any one of the above conditions is met, the process proceeds to step S6, where fuel injection is performed while maintaining the lift amount of the intake valve 7 to zero (minimum value), that is, in the closed state. The fuel injection of the valve 23 is stopped, cranking is performed, and the process proceeds to step S7. The exhaust valve 9 is opened and closed during the cranking.
In step S7, it is determined whether time t (predetermined time) has elapsed since the start of cranking. The time t may be a fixed value for simplicity, but may be variably set based on the cooling water temperature Tw at the time of starting, the alcohol concentration C, and the like.

If it is determined in step S7 that time t has not elapsed since the start of cranking, the process returns to step S6, and steps S6 and S7 are circulated until it is determined that time t has elapsed.
On the other hand, if it is determined in step S7 that the time t has elapsed from the start of cranking, the process proceeds to step S8, and the opening / closing drive of the intake valve 7 and the fuel injection to the intake port 5 of the fuel injection valve 23 are permitted. And the routine ends.

According to the present embodiment, the lift amount of the intake valve 7 is made zero until the time t elapses from the start of cranking, so that the cylinder does not suck in the cryogenic outside air via the intake port 5.
Further, the cylinder sucks a part of the exhaust gas in the exhaust port 11 due to the internal negative pressure when the exhaust valve 9 is opened, and flows out the exhaust gas to the exhaust port 11 through the open exhaust valve 9 when the piston is raised. Let That is, the exhaust once discharged from the cylinder to the exhaust port 11 is re-inhaled from the exhaust port 11 into the cylinder. In other words, only the same air in and out of the cylinder / exhaust port 11 is repeatedly repeated, and the cryogenic outside air is hardly taken into the cylinder directly from either the intake port 5 or the exhaust port 11. For this reason, the amount of cooling of the cylinder by the fresh air is extremely small as compared with the case where the cryogenic fresh air is sucked into the cylinder every intake stroke as in normal operation.

As described above, the cooling of the cylinder due to the intake of the low-temperature fresh air can be greatly reduced. As a result, the cylinder is effectively heated by the friction caused by the piston motion and the gas flow friction of the valve head of the exhaust valve 9. Therefore, by setting the time t to an appropriate length, the cylinder can be sufficiently vaporized after the time t has elapsed.
Then, after the elapse of time t, the opening / closing drive of the intake valve 7 and the fuel injection to the intake port 5 of the fuel injection valve 23 are started, so that at the time of starting from an extremely low temperature or when using a fuel with a high alcohol concentration Even so, a sufficiently vaporized fuel-air mixture can be formed in the cylinder and quickly ignited and combusted to improve the starting performance.

The fuel injection period of the fuel injection valve 23 after the elapse of the time t is preferably set to both the intake stroke and the exhaust stroke in one cycle, and each fuel injection amount in the intake stroke and the exhaust stroke is It is good to control according to the driving state.
The present invention is not limited to the above embodiment, and may be configured as follows.
First, the engine temperature (cylinder temperature) may be estimated based on the temperature of the lubricating oil, the temperature of the intake air, and the like in addition to the coolant temperature Tw.

In the above embodiment, the cranking period of step S6 is performed until the time t has elapsed from the start of cranking. Instead, the cooling water temperature Tw, the rate of increase of the cooling water temperature Tw, and the integration It may be until the time when the engine speed reaches a predetermined value.
Further, a variable valve mechanism may be provided on the exhaust valve 9 side, or another mechanism that can maintain the exhaust valve 9 in a closed state may be provided. As a result, the lift amount of both the intake valve 7 and the exhaust valve 9 is minimized, preferably zero, so that it is possible to completely eliminate the entry and exit of fresh air into the cylinder, and the heat insulation effect of the cylinder is enhanced. Cranking is possible, the temperature raising efficiency of the cylinder is improved, and the start can be performed in a short time by shortening the time t.

Moreover, in the said embodiment, although the fuel injection valve 23 was set as the structure which injects a fuel in the intake port 5, it is good also as a structure which injects a fuel directly in a cylinder.
Here, technical ideas other than the claims that can be grasped from the above embodiment will be described together with effects.
(A) In the internal combustion engine start control device according to any one of claims 1 to 4,
The fuel injection amount of the fuel injection valve in the intake stroke and the fuel injection amount of the fuel injection valve in the exhaust stroke can be adjusted within one cycle after the lapse of the predetermined time. Features.

According to the above invention, each fuel injection amount in the intake stroke and the exhaust stroke can be optimally controlled according to the operating state and the like.
(B) In the start control device for an internal combustion engine according to any one of claims 1 to 4, (a),
The engine temperature is estimated based on any one of cooling water, lubricating oil, and intake air.

According to the above invention, even when it is difficult to directly detect the engine temperature, the engine temperature can be estimated and detected based on any one of the temperature of cooling water, lubricating oil, and intake air.
(C) In the start control device for an internal combustion engine according to any one of claims 1 to 4, (A), (B),
The predetermined time is
Set when starting the engine,
Alternatively, the engine temperature, the rate of increase in engine temperature, and the value of any of the accumulated engine speed are monitored until the value reaches a predetermined value.
It is characterized by that.

According to the above invention, when the predetermined time set at the start of the engine has elapsed, or when any of the engine temperature, the rate of increase of the engine temperature, and the accumulated engine speed reaches a predetermined value, the cylinder is in a warm-up state. It can be estimated that
(D) In the start control device for an internal combustion engine according to any one of claims 1 to 4 and (a) to (c),
The fuel injection valve is disposed in the intake port.

According to the above invention, the fuel is injected into the intake port from the fuel injection valve, and flows into the cylinder together with the intake air when the intake valve is opened.
(E) In the start control device for an internal combustion engine according to any one of claims 1 to 4 and (a) to (c),
The fuel injection valve is configured to inject fuel directly into a cylinder.

According to the above invention, the fuel is directly injected into the cylinder from the fuel injection valve.
(F) In the start control device for an internal combustion engine according to any one of claims 1 to 4 and (a) to (e),
The alcohol-containing fuel is alcohol-containing gasoline.
According to the above invention, the starting performance of an internal combustion engine using alcohol-containing gasoline as fuel can be improved.

The figure which shows the system configuration | structure of embodiment of this invention. The flowchart which shows control of the valve lift and fuel injection at the time of the start by ECU which concerns on embodiment of this invention

Explanation of symbols

1 Internal combustion engine 7 Intake valve 9 Exhaust valve 13 VEL mechanism 17 Water temperature sensor 21 Alcohol concentration sensor 23 Fuel injection valve

Claims (4)

A start control device for an internal combustion engine comprising a fuel injection means and a variable valve mechanism for controlling a lift amount of an intake valve, and using an alcohol-containing fuel at least at the start,
A start control device for an internal combustion engine, characterized in that control is performed to minimize the lift amount of the intake valve while stopping fuel injection of the fuel injection means for a predetermined time from the start of cranking. It has a variable valve mechanism that controls the lift amount of the exhaust valve,
2. The start control device for an internal combustion engine according to claim 1, wherein control is performed such that a lift amount of the exhaust valve is minimized for a predetermined time from the start of cranking.   The start control device for an internal combustion engine according to claim 1 or 2, wherein a minimum value of the lift amount of the intake valve or a minimum value of the lift amount of the intake valve and the exhaust valve is zero. .   The control to minimize the lift amount of the intake valve or the exhaust valve while stopping the fuel injection of the fuel injection means is performed when the engine temperature is lower than a predetermined value or the alcohol concentration of the fuel is higher than a predetermined value. The start control device for an internal combustion engine according to any one of claims 1 to 3, wherein

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