JP2010281215A - Method for controlling air-fuel ratio of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem that, in a variable valve timing mechanism controlled by a hydraulic fluid, for example, when the valve timing of an exhaust valve is controlled during transient operation such malfunctions that a delay in response is caused, an air-fuel ratio is made lean in deceleration, and the air-fuel ratio is shifted to a rich side can occur. <P>SOLUTION: The method for controlling the air-fuel ratio of an internal combustion engine controls an air-fuel ratio by detecting a difference between the target value of valve timing and the actually-measured value and varying a damping amount and an initial variation for fuel correction in correction control during a transient time according to the degree of the detected difference, in the case that the variable valve timing mechanism controls a valve overlap quantity when the exhaust valve and an intake valve are simultaneously opened according to an operating state in the internal combustion engine including the variable valve timing mechanism and a fuel injection valve supplying fuel through an intake port. The detected difference is compared with a predetermined value. As the result of comparison, when the detected difference is larger than a predetermined value, an initial variation for the fuel correction during the transient time is greatly corrected in comparison with a predetermined amount and the damping ratio of the damping amount is increased. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an air-fuel ratio control method for an intake port injection type internal combustion engine having a variable valve timing mechanism.

  2. Description of the Related Art Conventionally, in an internal combustion engine having a variable valve timing mechanism for changing the opening / closing timing of at least one of an exhaust valve and an intake valve and injecting fuel into an intake port, a part of the injected fuel is taken into an intake port or the like. It is known to adhere to surfaces such as inner wall surfaces in the system. Due to the presence of such adhered fuel, various air-fuel ratio controls are performed.

  For example, in the technique disclosed in Patent Document 1, the amount of direct fuel transported directly into the combustion chamber and the liquid transported to the combustion chamber from the liquid film formed on the surface of the intake system among the injected fuel. Calculate the amount of membrane transport, calculate the total amount of fuel transported to the combustion chamber based on both calculated, and control the fuel so that the total amount of fuel transport is an appropriate amount according to the operating conditions It is. In this Patent Document 1, the fuel is controlled by variably setting the ratio of the direct feed fuel amount and the liquid film transport amount in accordance with the control state of the variable valve timing mechanism.

JP 2006-63924 A

  By the way, the variable valve timing mechanism is generally controlled by the working oil, but in the case of performing such oil control, the valve timing of the exhaust valve or the intake valve is controlled during transient operation. In some cases, there may be a slight delay in response until the control signal is actually activated.

  When such a response delay occurs, the valve overlap amount when both the exhaust valve and the intake valve are temporarily opened may be different from the normal case. For this reason, the transport and vaporization conditions of the fuel are different, and the ratio between the direct transport amount and the liquid film transport amount is different from the normal amount.As a result, the air-fuel ratio becomes over-rich than usual during deceleration and then weaker than usual. There is a possibility that the engine becomes lean, becomes excessively lean at the time of acceleration, and then shifts to a slightly richer side than usual after that.

  Therefore, the present invention aims to eliminate such problems.

  That is, an air-fuel ratio control method for an internal combustion engine according to the present invention includes a variable valve timing mechanism that controls the valve timing of at least one of an exhaust valve and an intake valve, and a fuel injection valve that supplies fuel via an intake port. When the variable valve timing mechanism controls the valve overlap amount when the exhaust valve and the intake valve are opened simultaneously according to the operating state, the target value and actual measured value of the valve timing during transient operation An air-fuel ratio control method for an internal combustion engine, in which an air-fuel ratio is controlled in a variable manner according to the degree of deviation detected by detecting an initial change amount and an attenuation amount for fuel correction in transient correction control. If the detected deviation is compared with the predetermined value and the detected deviation is larger than the predetermined value, the initial change amount of the fuel correction at the time of transition is corrected to be larger than the predetermined amount. And characterized by increasing the attenuation rate of the attenuation.

  According to such a configuration, when it is detected that the deviation between the target value of the valve timing and the actual measurement value during the transient operation is larger than the predetermined value, the initial change amount and the attenuation ratio of the attenuation amount are increased. Even if there is a time delay before the actual valve timing, that is, the actual measurement value reaches the target value, the air-fuel ratio disturbance caused by the fuel adhering to the intake port due to the exhaust gas blow-back or vice versa to correct. As a result, it is possible to suppress a decrease in drivability during transient operation, that is, acceleration / deceleration.

  The present invention is configured as described above, and the exhaust gas is blown back even if there is a time delay until the actual valve timing, that is, the actually measured value reaches the target value during transient operation. Alternatively, the air-fuel ratio disturbance caused by the fuel adhering to the intake port can be corrected by the reverse phenomenon. As a result, it is possible to suppress a decrease in drivability during transient operation, that is, acceleration / deceleration.

BRIEF DESCRIPTION OF THE DRAWINGS Structure explanatory drawing which shows schematic structure of embodiment of this invention. The flowchart which shows the outline of the control procedure of the embodiment. Explanatory drawing at the time of the deceleration driving | operation of the embodiment. Explanatory drawing at the time of the acceleration driving | operation of the embodiment.

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

  A three-cylinder engine (hereinafter referred to as an engine) 100 schematically showing the configuration of one cylinder in FIG. 1 is mounted on, for example, an automobile. The engine 100 includes a variable valve timing mechanism 2 for changing the opening / closing timing of the exhaust valve 1. The variable valve timing mechanism 2 uses a so-called oscillating cylinder mechanism, and includes a rotor fixed to the intake camshaft 3, a housing fitted outside the rotor, and an electromagnetic for rotating the housing with respect to the rotor. An oil control valve 4 that is a four-way switching control valve, a pair of gears 6 and 7 that are attached to the housing and fixed to the exhaust camshaft 5 so as to mesh with each other, and attached to the end of the intake camshaft 3 The crank angle sensor 9 that outputs the crank angle signal b and the cylinder discrimination signal, and the exhaust cam angle signal c is output every time it is attached to the end of the exhaust cam shaft 5 and rotates 240 ° CA (crank angle). The cam angle sensor 10 is provided.

The intake system 11 of the engine 100 is provided with a throttle valve 12 that opens and closes in response to an accelerator pedal (not shown), and an intake manifold 14 that integrally has a surge tank 13 is attached downstream of the throttle valve 12. A fuel injection valve 16 is attached to the end of the intake manifold 14 on the intake port 15 side. The fuel injection valve 16 is controlled by an electronic control unit 17 described later, and injects fuel into the intake port 15. Reference numeral 18 denotes an intake valve. In this embodiment, the opening / closing timing is fixed. On the other hand, the exhaust system 20 of the engine 100 is configured by connecting a three-way catalyst 22 to an exhaust manifold 21, and an O ₂ sensor 23 for detecting an air-fuel ratio is attached to the exhaust manifold 21.

  In such a configuration, the valve timing (opening / closing timing) of the exhaust valve 1 is changed by the variable valve timing mechanism 2 being operated by the opening / closing timing signal output from the electronic control unit 17. In other words, when the variable valve timing mechanism 2 receives the opening / closing timing signal, the oil control valve 4 controls the direction and amount of hydraulic oil flowing into and out of the housing. As a result, the relative angle of the housing with respect to the rotor changes, and a desired rotational phase difference is generated between the intake camshaft 3 and the exhaust camshaft 5 to variably control the valve timing. That is, the opening / closing timing of the intake valve 18 and the opening / closing timing of the exhaust valve 1 are changed by changing the opening / closing timing of the exhaust valve 1 while always opening / closing the intake valve 18 with respect to the rotation of the crankshaft. The relative phase difference can be freely changed within a predetermined angle range.

  The electronic control unit 17 is mainly configured by a microcomputer system including a central processing unit 24, a storage device 25, an input interface 26, and an output interface 27. The central processing unit 24 controls the operation of the engine 100 by executing various programs described below that are stored in the storage device 25. Information necessary for operation control of the engine 100 is input to the central processing unit 24 via the input interface 26, and the central processing unit 24 controls the fuel control valve 16, the oil control valve 4, and the like. The signal is output via the output interface 27.

Specifically, the input interface 26 has an intake air pressure signal a output from the intake pressure sensor 30 for detecting the intake pressure of the air flowing into the intake manifold 14, and a crank angle signal output from the crank angle sensor 9. b, an exhaust cam angle signal c output from the cam angle sensor 10 for detecting the rotation angle of the exhaust camshaft 5, an IDL signal d output from the idle switch 31 for detecting the open / closed state of the throttle valve 12. A water temperature signal e output from the water temperature sensor 32 for detecting the coolant temperature of the engine 100, a voltage signal f output from the O ₂ sensor 23, and the like are input. On the other hand, the output interface 27 outputs a fuel injection signal g to the fuel control valve 16, an ignition signal h to the spark plug 28, an open / close timing signal k to the oil control valve 4 of the variable valve timing mechanism 2, and the like. Is done.

  In such a configuration, the electronic control unit 4 sets the intake air pressure signal a output from the intake pressure sensor 30 and the crank angle signal b output from the crank angle sensor 9 as main information according to the operating state. The fuel injection amount is calculated by correcting the basic fuel injection amount to be performed using various correction amounts including a transient correction amount described later, and the fuel injection time corresponding to the fuel injection amount, that is, the energization time for the fuel injection valve 16 The fuel injection valve 16 is controlled according to the determined energization time, and fuel is injected toward the intake port 15. Such fuel injection control itself may apply what is known in this field.

  The electronic control unit 4 also has a valve timing target value during transient operation when the variable valve timing mechanism 2 controls the valve overlap amount that the exhaust valve 1 and the intake valve 18 open simultaneously according to the operating state. When the air-fuel ratio is controlled by changing the initial change amount and attenuation amount for fuel correction in the transient correction control according to the detected degree of deviation, Air-fuel ratio control that compares a predetermined value and, if the detected deviation is larger than the predetermined value, corrects the initial change amount of the fuel correction at the time of transition larger than the predetermined amount and increases the attenuation rate of the attenuation amount The program is stored.

  Based on FIG. 2, the structure of the air-fuel ratio control program of this embodiment will be described. In the engine 100, the electronic control unit 4 controls the variable valve timing mechanism 2 in accordance with the operation state detected by the signals output from the various sensors described above, so that an appropriate valve overlap amount is obtained. By maintaining this, fuel vaporization is promoted. The air-fuel ratio program is executed at every calculation timing of the fuel injection amount when it is determined that the operating state of the engine 100 is a transient operation. The determination at the time of transient operation is performed based on, for example, the intake air pressure signal a. When the intake air pressure signal a becomes low, it is determined that the transient operation is a transient operation at deceleration, and when it becomes high, the transient operation at acceleration is determined. judge.

  First, in step S1, a deviation between the valve timing target value and the actual measurement value is detected. The actual measurement value is obtained based on the crank angle signal b output from the crank angle sensor 9 and the exhaust cam angle signal c output from the cam angle sensor 10. The target value is set according to the operating state at this time.

  In step S2, it is determined whether or not the detected deviation is larger than a predetermined value. Predetermined values conform to the fact that when the transition from steady operation to transient operation is abrupt, it takes time until the valve timing of the exhaust valve 1 actually reaches the target value, and the deviation becomes large. Set by. If it is determined that the deviation is greater than the predetermined value, the process proceeds to step S3.

  In step S3, an initial change amount that is a correction amount of the basic fuel injection amount in the transient correction control is set to be larger than a predetermined amount. The initial change amount is set as a change amount within a predetermined time from the time when the target value of the valve timing is switched. The predetermined amount of the initial change amount and the attenuation rate of the attenuation amount, which will be described later, are increased such that the absolute value thereof increases as the deviation between the target value of the valve timing and the actually measured value increases. (Cooling water temperature) is set as a parameter, for example, in an initial variation map and an attenuation rate map. In step S3, an initial change amount larger than the predetermined amount is set by, for example, multiplying a predetermined amount of the initial change amount by a coefficient.

  In step S4, the initial change amount is set by a predetermined amount corresponding to the operation region. Accordingly, the initial change amount in this case is smaller than that in step S3.

  In step S5, the basic fuel injection amount is corrected by the set initial change amount, and the air-fuel ratio when there is a deviation between the target value of the valve timing and the actual measurement value during transient operation is controlled. When the basic fuel injection amount is corrected, the initial change amount is added from the basic fuel injection amount in the case of the deceleration operation, and the initial change amount is subtracted in the acceleration operation to correct each.

  In step S6, it is determined whether or not the timing for switching between the initial change amount and the attenuation amount in the transient correction control has come. The switching timing is set by the elapsed time from the start of transient operation. Therefore, in step S6, it is determined that it is the switching timing when a predetermined elapsed time has elapsed from the start of the transient operation, and the process proceeds to step S7.

  In step S7, it is determined whether or not the valve timing deviation detected after the elapsed time is larger than a predetermined value. If it is determined that the deviation is greater than the predetermined value, the process proceeds to step S8.

  In step S8, as in the case of the initial change amount, based on the deviation at this time point, a predetermined value of the attenuation ratio of the attenuation amount is multiplied by a count to set an attenuation ratio larger than the predetermined ratio of the attenuation ratio. is there.

  On the other hand, in step S9, the attenuation ratio of the attenuation amount is set by a predetermined ratio corresponding to the operation region. In this case, the initial change amount in step S4 is smaller than that in step S8.

  In step S10, the basic fuel injection amount is corrected by the attenuation amount of the set attenuation ratio, and the air-fuel ratio when there is a deviation between the target value of the valve timing during transient operation and the actually measured value is controlled. Even in this case, when correcting the basic fuel injection amount, in the case of the deceleration operation, the attenuation amount of the attenuation ratio set from the basic fuel injection amount is added, and in the case of the acceleration operation, the same attenuation amount is added. Subtract and correct each. Specifically, in the case of the deceleration operation, the fuel injection amount is rapidly decreased according to the deceleration rate, and in the acceleration operation, on the contrary, the fuel injection amount is rapidly increased.

  In such a configuration, for example, when it is determined that the deviation between the detected valve timing target value and the actual measurement value is larger than the determination value during the transient operation of deceleration (steps S1 and S2), the initial change amount is set to be larger than the predetermined amount. That is, by correcting (decreasing) the basic fuel injection amount so that the fuel injection amount decreases, and increasing the attenuation rate of the attenuation amount after a predetermined elapsed time, the attenuation, that is, the decrease correction is suddenly lost. Correct the basic fuel injection amount. As a result, as shown in FIG. 3, in the fuel injection amount decrease correction during the deceleration transient operation, the liquid film fuel is reduced at the initial stage of correction by reducing the fuel injection amount early when the valve timing deviation is large. Thus, the air-fuel ratio is prevented from rapidly becoming richer, and thereafter the air-fuel ratio is stabilized by increasing the attenuation ratio of the attenuation amount.

  By controlling the air-fuel ratio in this way, the liquid film fuel adhering to the intake port 15 is blown off to the intake manifold 14 by blowing back during valve timing control during transient operation, so that the air-fuel ratio becomes leaner. Shock due to change can be suppressed. In FIG. 3, the solid line indicates the case where the deviation of the valve timing is large, and the alternate long and short dash line indicates the change in the respective air-fuel ratios when the deviation is smaller than the predetermined value (corresponding to step S4 and step S9). It is.

  Similarly, during acceleration acceleration operation, if it is determined that the difference between the detected valve timing target value and the actual measurement value is larger than the determination value (steps S1 and S2), the initial change amount is set larger than the predetermined amount. That is, the basic fuel injection amount is corrected (increased) so that the fuel injection amount increases, and after a predetermined elapsed time, the attenuation rate of the attenuation amount is increased so that the basic fuel injection amount suddenly attenuates or decreases. Correct. As a result, as shown in FIG. 4, in the increase correction of the fuel injection amount during the transient operation of acceleration, when the deviation of the valve timing is large, the fuel injection amount is increased early so that the air-fuel ratio is The lean side is prevented from being rapidly increased, and thereafter, the damping ratio of the attenuation amount is large, so that it rapidly changes to the rich side to stabilize the air-fuel ratio.

  By controlling the air-fuel ratio in this way, the blow-off due to the blowback during the valve timing control during the transient operation is reduced, and the liquid film fuel adhering to the intake port 15 flows into the combustion chamber 32 and is emptied. Shock caused by the change of the fuel ratio to the rich side can be suppressed. In FIG. 4, the solid line shows the change in the air-fuel ratio when the valve timing deviation is large, and the alternate long and short dash line shows the change in the air-fuel ratio when the deviation is smaller than the predetermined value (corresponding to step S4 and step S9). It is.

  In the above-described embodiment, the description has been given of the case where only the exhaust valve 1 can control the opening / closing timing, but the present invention may be applied to the one capable of controlling the valve timing of both the exhaust valve 1 and the intake valve. Good.

  In addition, the correction for increasing the attenuation ratio of the initial change amount and the attenuation amount has been described by multiplying each predetermined value by a coefficient. However, a constant is added or a value after correction is set by a map. It may be.

  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.

  As an application example of the present invention, there is one that is applied to an internal combustion engine of a type that includes a variable valve timing mechanism and injects fuel into an intake port.

DESCRIPTION OF SYMBOLS 1 ... Exhaust valve 2 ... Variable valve timing mechanism 15 ... Intake port 16 ... Fuel injection valve 17 ... Electronic control unit 18 ... Intake valve

Claims (1)

In an internal combustion engine including a variable valve timing mechanism that controls valve timing of at least one of an exhaust valve and an intake valve and a fuel injection valve that supplies fuel via an intake port, the variable valve timing mechanism is in an operating state. Accordingly, when controlling the valve overlap amount when the exhaust valve and the intake valve open simultaneously, the deviation between the target value of the valve timing during transient operation and the measured value is detected, and the fuel correction in the transient correction control is detected. An air-fuel ratio control method for an internal combustion engine, wherein the air-fuel ratio is controlled by varying the initial change amount and the attenuation amount in accordance with the detected degree of deviation,
Compare the detected deviation with a predetermined value,
An air-fuel ratio control method for an internal combustion engine, wherein, as a result of comparison, if the detected deviation is larger than a predetermined value, the initial change amount of fuel correction at the time of transition is corrected to be larger than a predetermined amount and the damping ratio of the damping amount is increased.

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