JP2012159003A - Method for controlling internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce shock due to torque fluctuation upon returning from fuel cut, and also to suppress NOx discharging amount after returning from the fuel cut.SOLUTION: A method for controlling the internal combustion engine mounted on a vehicle includes: stopping fuel supply to the internal combustion engine during the deceleration operation of the internal combustion engine; delaying ignition timing when the stopped fuel supply is restarted; and advancing the ignition timing after the fuel supply is restarted; wherein the speed for advancing the ignition timing after restarting the fuel supply is made slower the longer the time stopping the fuel supply.

Description

  The present invention relates to a control method for an internal combustion engine that controls ignition timing so as to control torque when fuel supply is resumed after fuel supply is interrupted.

  Conventionally, for example, an engine mounted on an automobile is a so-called fuel cut control that temporarily stops fuel supply when a predetermined deceleration operation condition, for example, a throttle valve is fully closed and the engine speed is equal to or higher than a predetermined speed. To implement. In such fuel cut control, when the engine speed falls below the return speed, the fuel supply is resumed (hereinafter referred to as fuel cut return), and the engine is controlled not to stop. In parallel with such fuel supply control, in order to suppress torque fluctuation (shock) that occurs at the time of fuel cut return, the ignition timing is retarded at the time of fuel cut return to reduce the increase in torque. It is known to implement a control that cancels out.

  For example, in the one described in Patent Document 1, in the case where the control is performed to retard the ignition timing at the time of fuel cut return and reduce the fluctuation of torque at the time of fuel cut return, when acceleration greater than a predetermined value is detected, Control to stop the retard of ignition timing. As described above, the engine is controlled so as to satisfy the requested acceleration by reducing the fluctuation of the torque when returning from the fuel cut and stopping the retard of the ignition timing when the acceleration greater than a predetermined value is detected. Is.

  By the way, when the fuel cut is restored, the exhaust gas does not flow into the catalyst during the fuel cut control, so the air-fuel ratio in the catalyst is in a lean state. In such a situation, when the retard of the ignition timing is stopped, that is, when the retarded ignition timing is returned early when the fuel cut is restored, NOx (nitrogen oxide) is discharged without being reduced by the catalyst. Sometimes. In particular, in the acceleration state, a large amount of NOx is discharged, but the oxygen concentration is high because the inside of the catalyst is in a lean state, and NOx may not be purified.

JP-A-3-271543

  Therefore, the present invention focuses on the above points and aims to reduce the NOx emission amount at the time of fuel cut return.

That is, according to the method for controlling an internal combustion engine of the present invention, in an internal combustion engine mounted on a vehicle, the fuel supply to the internal combustion engine is stopped during the deceleration operation of the internal combustion engine, and the ignition timing is delayed when the stopped fuel supply is restarted. A control method for an internal combustion engine in which the ignition timing is advanced after resumption of fuel supply,
It is characterized in that the speed at which the ignition timing is advanced after the resumption of fuel supply is delayed as the fuel supply is stopped longer.

  According to such a configuration, the ignition timing is retarded at the time of fuel cut return, and the ignition timing is advanced after the fuel cut return, thereby suppressing torque fluctuations at the time of fuel cut return, and after the fuel cut return. By slowing the speed at which the ignition timing is advanced, the longer the fuel cut is performed, the slower the oxygen stored in the catalyst during the fuel cut is consumed while the ignition timing is retarded. , NOx emission is suppressed.

  In order to compensate for the torque when the acceleration request is generated, it is determined whether or not there is an acceleration request when resuming the fuel supply or during the advance of the ignition timing. It is preferable to correct the intake air amount after the supply is resumed.

  The present invention is configured as described above, and can suppress a shock caused by a fluctuation in torque at the time of fuel cut return, and can be easily discharged at the time of fuel cut return due to the atmosphere in the catalyst during fuel cut. Can be suppressed.

BRIEF DESCRIPTION OF THE DRAWINGS Schematic structure explanatory drawing of the engine of embodiment of this invention. The flowchart which shows the control procedure of the embodiment. Action | operation explanatory drawing of the same embodiment. Action | operation explanatory drawing of the same embodiment.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

A multi-cylinder engine 100 schematically showing the structure of one cylinder in FIG. 1 is for an automobile, and the intake system 1 is provided with a throttle valve 11 of a so-called electronic throttle which is opened and closed by an electric motor. An intake manifold 12 is disposed downstream of the throttle valve 11. The intake manifold 12 includes a surge tank 13 and a manifold portion 14 extending from the surge tank 13 to the intake port of each cylinder. A fuel injection valve 3 is provided in the vicinity of the end of the intake manifold 12 on the cylinder head 22 side, and this fuel injection valve 3 is controlled by the electronic control unit 4. The cylinder head 22 is provided with an intake valve 21. Further, the exhaust system 5 is provided with an O ₂ sensor 51 for measuring the oxygen concentration in the exhaust gas discharged from the combustion chamber 23 through the exhaust valve 24 in a pipe line leading to a not-shown mafuran. It is attached at a position upstream of the three-way catalyst 52. As the engine itself, those widely known in this field can be used.

The electronic control device 4 is mainly configured by a microcomputer system including a central processing unit 41, a storage device 42, an input interface 43, and an output interface 44. The central processing unit 41 controls the operation of the engine 100 by executing a control program stored in the storage device 42. The input interface 43 includes an intake pressure signal a output from an intake pressure sensor 71 that detects the pressure in the surge tank 13, that is, an intake pipe pressure, and an engine speed that is output from an engine speed sensor 72 that detects the engine speed. Signal b, vehicle speed signal c output from the vehicle speed sensor 73 for detecting the vehicle speed, IDL signal d output from the idle switch 74 for detecting the open / closed state of the throttle valve 11, and the engine 100 as the temperature of the engine 100 The water temperature signal e output from the water temperature sensor 75 for detecting the cooling water temperature, the air-fuel ratio signal h output from the O ₂ sensor 51, and the like are input. Further, the output interface 44 outputs a drive signal n corresponding to the calculated fuel injection time to the fuel injection valve 3, an ignition signal m to the ignition plug 8, and the like.

  The electronic control unit 4 determines the opening time of the fuel injection valve 3 by using the intake pressure signal a output from the intake pressure sensor 71 and the rotation speed signal b output from the rotation speed sensor 72 as main information. A fuel injection control program for controlling the fuel injection valve 3 to inject fuel corresponding to the load from the fuel injection valve 3 into the intake system 1 is stored. Also, a fuel cut control program for executing a fuel cut that stops fuel supply in response to the establishment of a predetermined condition such as when the engine speed is equal to or higher than a predetermined speed during deceleration traveling when the throttle valve 11 is fully closed; In addition, a fuel cut return control program to be executed in an operation state in which the engine speed is equal to or lower than the fuel cut return speed (hereinafter referred to as the return speed) during execution of the fuel cut control is stored.

  The fuel cut return control program of this embodiment retards the ignition timing at the time of fuel cut return, and sequentially advances the ignition timing after the fuel cut return, the speed at which the ignition timing after the fuel cut return is advanced, The longer the fuel cut time is, the slower it will be. When restarting the fuel supply or when the ignition timing is advanced, determine whether there is an acceleration request. If it is determined that there is an acceleration request, restart the fuel supply. Later, the intake air amount is corrected to be increased.

  Below, the control procedure is shown in FIG. 2, and the entire fuel cut return control program will be described. The following description is for an operating state where the engine speed is equal to or lower than the fuel cut return rotational speed in a state where the fuel cut is performed and the engine rotational speed is decreasing. In this fuel cut return control program, the speed at which the ignition timing is advanced is controlled based on the fuel cut time as described above. Therefore, the elapsed time from the fuel cut start to the fuel cut return (hereinafter referred to as fuel cut) (Referred to as time).

  First, in step S1, it is determined whether or not the engine speed has become equal to or lower than the return speed. If it is determined in step S1 that the engine speed has become equal to or lower than the return speed, the ignition timing is retarded in step S2. The return rotational speed and the retard amount of the ignition timing can be set with those well known in the art.

  In step S3, the ignition timing retarded when returning from the fuel cut is sequentially advanced at the advance speed set based on the measured fuel cut time. As shown in FIG. 3, the progressive advancement means that the amount of retardation is continuously reduced at the set speed as time passes, and as shown in FIG. 4, the advance is retarded at the initial stage of advancement control. Including those that maintain the state for a predetermined time and then decrease the retardation amount continuously with time at a set speed. 3 includes those that advance in a staircase manner (decrease the amount of retardation) with a predetermined amount of advancement.

  In this case, the advance angle speed, in other words, the retard amount correction amount for reducing the retard amount within the unit time or the advance amount per unit time is set to be slower as the fuel cut is performed longer. In other words, the longer the fuel cut time, the leaner the air-fuel ratio in the three-way catalyst 52, that is, a larger amount of oxygen is stored. For this reason, NOx contained in the exhaust gas at the time of fuel cut return and after return may be discharged without being purified, so that combustion is sequentially improved by advancing the ignition timing after the fuel cut return. Thus, the amount of oxygen stored in the three-way catalyst 52 is reduced, and NOx emission is suppressed. Therefore, the advance speed is determined by advancing the ignition timing to a limit value at which NOx is not discharged.

  Thereafter, in step S4, it is determined whether or not there is an acceleration request due to depression of the accelerator pedal in the driving state after the fuel cut is restored.

  In step S5, the throttle valve is opened to correct the intake air amount. The amount of increase in the intake air amount corresponds to the degree of depression of the accelerator pedal, and is set to an amount that generates sufficient torque to satisfy the acceleration request in a state where the ignition timing is retarded.

  In such a configuration, when the engine speed is equal to or lower than the return speed when the vehicle is decelerated (“Yes” in step S1), the ignition timing is retarded when the fuel cut is returned to alleviate the shock due to torque fluctuation. Thereafter, after the fuel cut is restored, the retarded ignition timing is sequentially advanced at the advance speed set based on the measured fuel cut time (step S3), whereby the three-way catalyst 52 is occluded. Control is performed so that NOx is not discharged even in a state where a large amount of oxygen is released. If there is an acceleration request while executing the ignition timing control for suppressing the NOx emission amount in this way (“Yes” in step S4), the intake air amount is corrected to be increased (step S5). Secure the torque corresponding to the acceleration request.

  Thus, when the fuel cut is restored, the ignition timing is retarded, so that the torque difference between the fuel cut and the fuel cut return can be suppressed, and the ignition timing is sequentially advanced after the fuel cut is restored. Can be suppressed.

  And if there is an acceleration request while the ignition timing is advanced after returning from the fuel cut, the torque is increased by increasing the intake air amount, so that the ignition timing is kept retarded. be able to. For this reason, the ignition timing is not advanced to before the top dead center, and it is possible to suppress an increase in NOx due to the rapid improvement of the combustion state.

  The present invention is not limited to the above embodiment.

  In the above-described embodiment, the description is made of determining whether or not there is an acceleration request after returning from the fuel cut, but it is determined whether or not there is an acceleration request at the time of returning from the fuel cut, that is, almost simultaneously with the fuel cut return. In some cases, control may be made so that the intake air amount is corrected to be increased in the operation state after the subsequent fuel cut recovery.

  The description has been given of the correction for increasing the intake air amount by increasing the opening of the throttle valve 11. However, in the case of a throttle valve that opens and closes in response to the accelerator pedal, a bypass that bypasses the throttle valve is provided. The amount of intake air that is increased is controlled by an idle speed control device that includes a passage and a flow rate control valve that is provided in the bypass passage and controls the air flow rate.

  In addition, the specific configuration of each part is not limited to the above embodiment, and various modifications can be made without departing from the spirit of the present invention.

DESCRIPTION OF SYMBOLS 1 ... Intake system 11 ... Throttle valve 4 ... Electronic control unit 8 ... Spark plug 52 ... Three-way catalyst

Claims (2)

In an internal combustion engine mounted on a vehicle, the fuel supply to the internal combustion engine is stopped during the deceleration operation of the internal combustion engine, the ignition timing is retarded when restarting the stopped fuel supply, and the ignition timing is advanced after restarting the fuel supply. An internal combustion engine control method comprising:
A control method for an internal combustion engine, in which the speed at which the ignition timing is advanced after resumption of fuel supply is delayed as the fuel supply is stopped for a longer time. Determine if there is a request for acceleration when resuming fuel supply or when the ignition timing is advanced,
2. The control method for an internal combustion engine according to claim 1, wherein when it is determined that there is an acceleration request, the intake air amount is corrected to be increased after the fuel supply is resumed.

Images