JP2004100497A - Automatic stop/automatic restart device for engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce/eliminate overshoot of an engine immediately after automatic start of the engine. <P>SOLUTION: When an automatic stop request of the engine is detected (S1), firstly an EGR control valve is opened to introduce exhaust gas in an exhaust passage by a required flow rate into an intake passage (S2). Secondly, the engine is stopped (S3) and the EGR control valve is closed (S4), and the exhaust gas is retained in the intake passage until the automatic restart of the engine is performed according to automatic stop request of the engine. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an idle stop vehicle that automatically stops the engine when the vehicle is temporarily stopped such as at an intersection, and in particular, a technique for reducing an overshoot of the engine speed that occurs immediately after the automatic restart of the engine after the automatic stop of the engine. About.
[0002]
[Prior art]
In recent years, an automatic engine stop / restart device that automatically stops the engine when the vehicle is stopped, such as at an intersection, and automatically restarts the engine by cranking the engine with a motor generator when the vehicle starts thereafter. Are known.
[0003]
In such a device, when the engine is automatically restarted in a state where the select lever of the automatic transmission is in the drive (D) position, that is, in a state where the driving force in the forward direction of the engine can be transmitted to the axle, Since the negative pressure in the intake passage is small (close to the atmospheric pressure) and the intake amount of fresh air is large, the engine speed rapidly increases immediately after the automatic restart of the engine, that is, immediately after the fuel is ignited. It is easy to cause overshoot. Such an overshoot may give an occupant an unpleasant feeling of acceleration or the like, and countermeasures have been desired.
[0004]
In order to suppress such overshoot immediately after the automatic restart of the engine, Patent Literature 1 discloses a technique in which a motor generator performs a power generation operation after a complete explosion of the start of the engine.
[0005]
[Patent Document 1]
JP 2000-205003 A
[Problems to be solved by the invention]
However, in order to suppress the overshoot by the power generation operation of the motor generator, it is required that the motor generator has a sufficient rating and that the motor generator be controlled with high accuracy, which leads to an increase in cost. I will invite you.
[0007]
The present invention has been made in view of such a problem, and has a simple configuration that does not lead to an increase in cost and complexity of control, and is effective in overshooting the engine speed immediately after the automatic restart of the engine. It is a main object of the present invention to provide a new automatic stop / restart device for an engine which can be reduced or eliminated.
[0008]
[Means for Solving the Problems]
An automatic stop / restart apparatus for an engine according to the present invention is capable of automatically stopping and restarting an engine and has means for detecting a request for automatic engine stop. When the engine automatic stop request is detected, before the engine is automatically stopped, exhaust gas introduction means for introducing exhaust gas into the intake passage, and the exhaust gas in the intake passage until the engine is automatically restarted. And exhaust gas holding means for holding the exhaust gas.
[0009]
【The invention's effect】
According to the present invention, the flammable gas used for combustion immediately after the automatic restart of the engine is introduced by introducing the exhaust gas into the intake passage immediately before the automatic stop of the engine and holding the exhaust gas until the automatic restart of the engine. The amount of air decreases, and the overshoot of the engine immediately after the automatic restart can be effectively reduced or eliminated.
[0010]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the present invention will be described in detail with reference to the illustrated embodiments. FIG. 1 is a schematic configuration diagram showing an engine to which an automatic stop / automatic restart device according to the present invention is applied. The engine 10 is provided with an exhaust gas recirculation device that recirculates the exhaust gas in the exhaust passage 12 to the intake passage 14 in order to improve exhaust gas and improve fuel efficiency by reducing NOx. The exhaust gas recirculation device includes an EGR passage 18 connecting the exhaust passage 12 and a downstream portion 14a of the throttle 16 of the intake passage 14, an EGR control valve 20 provided in the middle of the EGR passage 18, and opening and closing the passage. And an EGR control solenoid 22 for driving the EGR control valve 20.
[0011]
The control unit 24 includes an air flow meter 26 that measures the amount of fresh air that passes through the air cleaner 25, a throttle opening sensor 28 that detects the opening of the throttle 16, a water temperature sensor 30 that detects a cooling water temperature of the engine 10, In addition to detection signals from a rotation speed sensor 32 for detecting an engine speed, a phase sensor 34 for detecting a cam phase, and the like, a vehicle speed signal, a start signal by a key switch, and the like are input. The control unit 24 outputs a control signal to the EGR control valve 20 based on these detection signals, controls its operation, and outputs a control signal to the fuel injection valve 36 to control the injection amount and the injection timing. And general engine control. The EGR control valve 20 is generally opened in a normal engine operating state, and is closed in consideration of startability and drivability only at the time of starting, idling, low-speed running, and the like.
[0012]
Although not shown, the vehicle includes a motor generator that drives the engine 10. When the vehicle is temporarily stopped such as when waiting for a traffic light, the engine 10 is automatically stopped, and when the vehicle is subsequently started, the engine 10 is driven by the motor generator to automatically restart the engine.
[0013]
FIG. 2 is a flowchart showing a control flow according to the present embodiment, which is stored and executed by the control unit 24 described above. In S (step) 1, it is determined whether an automatic engine stop request has been detected. Specifically, the vehicle speed is almost 0, that is, the vehicle is stopped, the brake pedal is depressed, and the storage amount (SOC) of the battery that supplies power to the motor generator is sufficiently left; and When the driving force of the engine 10 can be transmitted to the axle, specifically, when the select lever of the automatic transmission is in a driving position such as the D range, an automatic stop request is output, and the determination in S1 is affirmed. You.
[0014]
When the request to automatically stop the engine is detected, the process proceeds to S2, and the exhaust gas in the exhaust passage 12 is introduced into the throttle downstream 14a of the intake passage 14 (exhaust gas introducing means). Specifically, the EGR control valve 20 is opened according to the required flow rate of the exhaust gas to be introduced into the throttle downstream 14a, and the opening degree and the valve opening time are controlled. The required flow rate may be a fixed value set in advance, or may be calculated each time according to the operation state. However, the required flow rate is set so that the engine can burn stably at least immediately after the automatic restart of the engine. In other words, the proportion of fresh air introduced into the combustion chamber is secured to the extent that stable combustion is possible.
[0015]
When the exhaust gas corresponding to the required flow rate is introduced into the throttle passage 14a in the intake passage 12, the process proceeds to S3, in which fuel injection is prohibited, and the engine is automatically stopped. At S4, the EGR control valve 20 is closed to prevent fresh air from flowing from the exhaust passage 12 to the throttle downstream 14a. In addition, the throttle 16 is also fully closed, whereby the exhaust gas introduced into the intake passage 14 downstream of the throttle 14a is satisfactorily contained, and is held in the throttle downstream 14a (exhaust gas holding means). .
[0016]
In S5, it is determined whether an automatic restart request of the engine has been detected. For example, when the release of the brake pedal, the depression of the accelerator pedal, etc. are detected, an engine automatic restart request is output, and the determination in S5 is affirmed.
[0017]
When the engine automatic restart request is detected, the process proceeds to S6, where the engine is automatically restarted. Specifically, the engine 10 is cranked by the motor generator, and when the engine speed reaches a predetermined idle speed, fuel injection is restarted to restart the engine. At this time, the fuel injection amount is reduced and corrected in accordance with the amount of exhaust gas introduced into the downstream of the throttle 14a, that is, the required flow rate. Specifically, the fuel injection amount is reduced substantially in proportion to the required flow rate.
[0018]
FIG. 3 shows engine speed characteristics at the time of automatic engine restart. In the figure, the broken line A represents the control according to the present embodiment, that is, the characteristic when the above-described routine of FIG. 2 is performed, and the solid line B represents the characteristic when the control according to the present embodiment is not performed. I have.
[0019]
As in the present embodiment, when exhaust gas is introduced into the downstream of the throttle 14a of the intake passage 14 and the exhaust gas is held until the automatic restart of the engine, the engine rotational speed immediately after the automatic restart is exceeded. Shooting is sufficiently suppressed (ΔNe). For this reason, giving an uncomfortable feeling of acceleration etc. to the occupant due to the overshoot is reduced or eliminated.
[0020]
The reason for this is that immediately after the automatic restart of the engine, although the negative pressure is low and the volume of air introduced into the combustion chamber is large, the new exhaust gas introduced into the combustion chamber by introducing and holding exhaust gas downstream of the throttle 14a. Since the proportion of air decreases and the amount of combustible air substantially decreases, the overshoot of the engine speed is suppressed.
[0021]
Further, since the fuel injection amount is reduced according to the required flow rate of the exhaust gas to be introduced, unburned gas is not excessively discharged. Further, since the required flow rate of the exhaust gas is set in consideration of the combustion stability immediately after the automatic restart, there is no possibility that the combustion becomes unstable immediately after the automatic restart.
[0022]
Since the exhaust gas is introduced and held using the EGR control valve 20 of the exhaust gas purification device that is widely used in many vehicles, the complexity of the device and control and the increase in cost due to this are reduced. I will not invite you.
[0023]
Further, preferably, the pressure in the intake passage is directly detected by using a pressure sensor or the like, or is estimated based on a throttle opening, an intake air amount, and the like, and the required flow rate is adjusted based on the pressure. Thus, the required flow rate can be set with higher accuracy.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram showing an engine to which an automatic stop / automatic restart device according to the present invention is applied.
FIG. 2 is a flowchart showing a flow of automatic restart control according to an embodiment of the present invention.
FIG. 3 is a characteristic diagram showing a change in engine speed immediately after automatic restart of the engine.
[Explanation of symbols]
10 Engine 12 Exhaust passage 14 Intake passage 20 EGR control valve (exhaust gas introduction means / exhaust gas holding means)

Claims (5)

In an automatic engine stop and automatic restart device capable of automatically stopping and automatically restarting an engine and having a means for detecting an engine automatic stop request,
Exhaust gas introducing means for introducing exhaust gas into an intake passage before automatically stopping the engine when detecting the request for automatically stopping the engine;
An exhaust gas holding means for holding the exhaust gas in the intake passage until the engine is automatically restarted. Required flow rate setting means for setting a required flow rate of exhaust gas introduced into the intake passage by the exhaust gas introducing means,
2. The automatic engine stop / restart system according to claim 1, further comprising means for reducing the amount of fuel injection immediately after the automatic restart of the engine in accordance with the required flow rate. 3. The automatic engine stop / restart apparatus according to claim 2, wherein the required flow rate setting means sets the required flow rate so that stable combustion can be obtained at least immediately after the automatic restart of the engine. Having means for detecting or estimating the pressure in the intake passage,
4. The automatic engine stop / restart device according to claim 2, wherein the required flow rate setting means adjusts the required flow rate according to a pressure in the intake passage. 5. An exhaust gas recirculation device for recirculating exhaust gas in an exhaust passage into an intake passage during operation of an engine, wherein the exhaust gas recirculation device also serves as the exhaust gas introducing means. Automatic stop / restart device for the engine.

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