JP2010203311A - Control device for internal combustion engine - Google Patents

Abstract

A control device for an internal combustion engine capable of accurately detecting an air-fuel ratio of each cylinder of a multi-cylinder internal combustion engine.
In a control apparatus for a multi-cylinder internal combustion engine in which an air-fuel ratio sensor 126 is provided in an exhaust passage 125, an air-fuel ratio variation ΔA / F of each cylinder obtained in advance with respect to an output amplitude ΔPaek of the air-fuel ratio sensor is obtained. A storage means 11 storing a first characteristic expression indicating a relationship and a second characteristic expression having a sensitivity to variation in air-fuel ratio of each cylinder lower than that of the first characteristic expression; and determining an output amplitude from the output of the air-fuel ratio sensor; There is provided a variation detecting means 11 for obtaining an air-fuel ratio variation using the first air-fuel ratio characteristic equation.
[Selection] Figure 1

Description

  The present invention relates to a control device for an internal combustion engine.

As a technique for detecting the actual air-fuel ratio of each cylinder of a direct injection multi-cylinder engine with one air-fuel ratio sensor (including an oxygen sensor), taking into account the combustion interval of each cylinder and the delay time until it reaches the air-fuel ratio sensor, An apparatus that estimates an actual air-fuel ratio from an output change of an air-fuel ratio sensor corresponding to a sampling period of each cylinder is known (Patent Document 1).

JP 2000-220492 A

  However, if the response speed of the air-fuel ratio sensor is insufficient with respect to the sampling period of each cylinder, the detected value of the cylinder between the leanest cylinder and the richest cylinder becomes inaccurate due to the influence of the front and rear peak values.

The problem to be solved by the present invention is to provide a control device for an internal combustion engine that can accurately detect the air-fuel ratio of each cylinder of a multi-cylinder internal combustion engine.

The present invention obtains in advance at least two characteristic formulas having different sensitivities indicating the relationship of the air-fuel ratio variation of each cylinder with respect to the output amplitude of the air-fuel ratio sensor. The above problem is solved by using an equation.

  According to the present invention, since the air-fuel ratio variation is detected using the characteristic equation having high sensitivity of the two characteristic equations acquired in advance, the accurate air-fuel ratio can be detected regardless of the response speed of the air-fuel ratio sensor. .

1 is a block diagram showing a control device for an internal combustion engine to which an embodiment of the present invention is applied. It is a graph which shows an example of the output of the air fuel ratio sensor of FIG. It is a graph which shows the characteristic formula stored in the engine control unit of FIG. It is a graph which shows the type of the output of the air fuel ratio sensor observed when acquiring the characteristic formula of FIG. 2 is a graph showing an example of air-fuel ratio correction executed by the engine controller of FIG. 1. 2 is a graph showing a relationship with an operating angle by a variable valve mechanism in air-fuel ratio correction executed by the engine controller of FIG. 1. It is a flowchart which shows the control procedure performed with the engine controller of FIG.

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

  FIG. 1 is a block diagram showing a direct injection multi-cylinder engine EG to which an embodiment of the present invention is applied. An air filter 112 and an air flow meter 113 for detecting an intake air flow rate are provided in an intake passage 111 of the engine EG. A throttle valve 114 and a collector 115 for controlling the intake air flow rate are provided.

  The throttle valve 114 is provided with an actuator 116 such as a DC motor that adjusts the opening of the throttle valve 114. The throttle valve actuator 116 electronically controls the opening of the throttle valve 114 based on the drive signal from the engine control unit 11 so as to achieve the required torque calculated based on the driver's accelerator pedal operation amount and the like. Further, a throttle sensor 117 for detecting the opening degree of the throttle valve 114 is provided, and the detection signal is output to the engine control unit 1. The throttle sensor 117 can also function as an idle switch.

  The fuel injection valve 118 is provided facing the combustion chamber 123. The fuel injection valve 118 is driven to open by a drive pulse signal set in the engine control unit 11 and directly injects fuel, which is pumped from a fuel pump (not shown) and controlled to a predetermined pressure by a pressure regulator, into the cylinder.

  A space surrounded by the cylinder 119, the crown surface of the piston 120 that reciprocates within the cylinder, and the cylinder head provided with the intake valve 121 and the exhaust valve 122 constitutes a combustion chamber 123. The spark plug 124 is mounted facing the combustion chamber 123 of each cylinder, and ignites the intake air-fuel mixture based on an ignition signal from the engine control unit 11.

  On the other hand, the exhaust passage 125 is provided with an air-fuel ratio sensor 126 for detecting an exhaust gas by detecting a specific component in the exhaust gas, for example, oxygen concentration, and thus an air-fuel ratio of the intake air-fuel mixture. Is output. The air-fuel ratio sensor 126 may be an oxygen sensor that performs rich / lean output, or a wide-area air-fuel ratio sensor that linearly detects the air-fuel ratio over a wide area.

  The exhaust passage 125 is provided with an exhaust purification catalyst 127 for purifying the exhaust. The exhaust purification catalyst 127 oxidizes carbon monoxide CO and hydrocarbon HC in the exhaust in the vicinity of stoichiometric (theoretical air-fuel ratio, λ = 1, air weight / fuel weight = 14.7), and nitrogen oxide NOx. It is possible to use a three-way catalyst that can purify the exhaust gas by reducing the above, or an oxidation catalyst that oxidizes carbon monoxide CO and hydrocarbon HC in the exhaust gas.

  On the downstream side of the exhaust purification catalyst 127 in the exhaust passage 125, there is provided an oxygen sensor 128 that detects a specific component in the exhaust, for example, oxygen concentration, and outputs a rich / lean output, and the detection signal is output to the engine control unit 11. The Here, by correcting the air-fuel ratio feedback control based on the detection value of the air-fuel ratio sensor 126 based on the detection value of the oxygen sensor 128, so as to suppress a control error associated with the deterioration of the air-fuel ratio sensor 126 (so-called) Although the downstream oxygen sensor 128 is provided (for the adoption of a double air-fuel ratio sensor system), if it is only necessary to perform air-fuel ratio feedback control based on the detection value of the air-fuel ratio sensor 126, the oxygen sensor 128 is Can be omitted.

  In FIG. 1, reference numeral 129 denotes a muffler.

  The crankshaft 130 of the engine EG is provided with a crank angle sensor 131, and the engine control unit 11 counts a crank unit angle signal output from the crank angle sensor 131 in synchronization with the engine rotation for a predetermined time, or By measuring the cycle of the crank reference angle signal, the engine speed Ne can be detected.

  The cooling jacket 132 of the engine EG is provided with a water temperature sensor 133 facing the cooling jacket, detects the cooling water temperature Tw in the cooling jacket 131, and outputs this to the engine control unit 11.

  FIG. 2 is a graph showing an example of the output of the air-fuel ratio sensor 126 provided in the exhaust passage 125. The first cylinder (# 1) is provided by the air-fuel ratio sensor provided in one exhaust passage of the V-type six-cylinder engine. The air-fuel ratio (oxygen concentration) output signals of the third cylinder (# 3) and the fifth cylinder (# 5) are shown.

  As mentioned in the Background Art section, the air-fuel ratio sensor has a considerable response speed delay with respect to the sample period shown on the horizontal axis of the figure. did.

  FIG. 3 shows that an air-fuel ratio sensor 126 is provided in one exhaust passage 125 of the V-type six-cylinder engine and various operating conditions are set, so that three cylinders, that is, a first cylinder (# 1) and a third cylinder ( # 3) and the fifth cylinder (# 5) are intentionally caused to vary the air-fuel ratio, and the output amplitude ΔPeak (the length between the maximum output and the minimum output in FIG. 2) of the air-fuel ratio sensor 126 at that time is plotted. Is.

  According to this, as shown in FIGS. 4A and 4B, the type in which the air-fuel ratio of one of the three cylinders is different from the air-fuel ratio of the other two cylinders is the first type shown in FIG. According to the characteristic formula. On the other hand, the difference between the air-fuel ratios of the three cylinders approximates each other and is not extremely large, and gradually increases as shown in FIG. 10C or gradually decreases as shown in FIG. Such a type follows the second characteristic equation shown in FIG.

  That is, the cylinder # 3 between the lean cylinder # 1 and the rich cylinder # 5 as shown in FIG. 4A, or the lean cylinder # 1 and the rich cylinder # as shown in FIG. 4B. The detection value of cylinder # 5 between 3 and 3 tends to be inaccurate due to the influence of the front and rear peak values, but from the results of FIG. 3, the detected values are similar to those shown in FIGS. However, it has been found that the output amplitude ΔPeak of the air-fuel ratio sensor 126 is highly sensitive to the air-fuel ratio variation ΔA / F.

  Therefore, as shown in FIG. 3, if the relationship of the output amplitude ΔPeak of the air-fuel ratio sensor 126 to the air-fuel ratio variation ΔA / F between the cylinders of the internal combustion engine is obtained in advance by experiments and simulations and used as a control map, It is possible to accurately obtain the air-fuel ratio variation ΔA / F between the cylinders from the output amplitude ΔPeak of the fuel ratio sensor 126.

  Next, the control procedure will be described.

  FIG. 7 is a flowchart showing the control procedure of this example, and will be described as an internal combustion engine provided with a variable valve mechanism that makes the operating angle of the intake valve 121 variable. As the variable valve mechanism, a known mechanism that can continuously change the operating angle, lift amount, phase, and the like can be employed.

  In step S1, it is determined whether or not the detection of the cylinder-by-cylinder air-fuel ratio is permitted. For example, the idling switch is ON (in an idling state) or is not in an accelerating state, the engine speed is equal to or less than a predetermined value, the intake / exhaust valve operating angle is within a predetermined range, the air-fuel ratio λ control is being executed, the canister Permission can be issued when all of the conditions such as non-operation of fuel purge from No. and no misfire determination are satisfied.

  In step S2, as shown in FIG. 6, the variable valve mechanism is driven to set the operating angle of the intake valve 121 to the initial position. This initial position is a position where the operating angle is relatively large.

  In step S3, the signal from the air-fuel ratio sensor 126 is captured, and the output amplitude ΔPeak is calculated from the output waveform as shown in FIG.

  In step S4, the output amplitude ΔPeak calculated in step S3 is substituted into the first characteristic equation of FIG. 3 to calculate the air-fuel ratio variation ΔA / F between the cylinders.

  In step S5, it is determined whether or not ΔA / F calculated in step S4 is smaller than a predetermined threshold value α. If smaller, the process proceeds to step S10 without correcting the air-fuel ratio in steps S6 to S9.

  If ΔA / F is larger than the predetermined threshold value α in step S5, the process proceeds to step S6, and the output amplitude ΔPeak calculated in step S3 is substituted into the second characteristic equation shown in FIG. / F is calculated.

  In step S7, the cylinder to be corrected is determined from the ignition timing of the spark plug 124 and the output timing of the air-fuel ratio sensor 126.

  In step S8, a Δ pulse width corresponding to the fuel amount to be corrected is calculated for each cylinder from the calculated ΔA / F, and pulse correction is applied to each cylinder in step S9.

  At this time, as shown in FIG. 5, when the detected air-fuel ratio variation ΔA / F is on the lean side with respect to the target A / F, the change rate of the correction amount is increased, and the target A is shortened as quickly as possible. Control to reach / F. On the other hand, when the detected air-fuel ratio variation ΔA / F is on the rich side with respect to the target A / F, the change rate of the correction amount can be made relatively small to avoid overshooting on the lean side. desirable.

  6 completes the air-fuel ratio correction process at the initial position of the operating angle shown in FIG. 6. If the operating angle has not reached the target value in step S10, the process proceeds to step S11, and the second learning is shown in FIG. After reducing the operating angle as described above, the process returns to step S3 and the above processing is repeated.

  As described above, according to this example, the existing air-fuel ratio sensor 126 can be used as it is, and the air-fuel ratio variation for each cylinder can be accurately detected. As a result, combustion stability and catalyst conversion rate can be improved.

  In particular, since the variation in the air-fuel ratio is detected using the first characteristic equation in which the sensitivity of the variation in the air-fuel ratio of each cylinder with respect to the output amplitude ΔPaek is detected, it is possible to suppress the determination of the variation being too small.

  On the other hand, since the air-fuel ratio variation is corrected using the second characteristic equation that is low in sensitivity of the air-fuel ratio variation of each cylinder with respect to the output amplitude ΔPaek, overcorrection can be suppressed.

  Further, when the air-fuel ratio is corrected in step S9, when the detected air-fuel ratio variation ΔA / F is on the rich side from the correction target value, the change rate of the correction amount is set as compared with the case on the lean side. Set smaller. Thereby, since it does not overshoot to the lean side where the amount of air is small and combustion resistance is weak, misfire can be prevented.

  In addition, when the variable valve mechanism is provided, the air-fuel ratio determination for each cylinder is performed step by step from the larger operating angle. As a result, misfire can be prevented when starting from a minimum operating angle where the variation in air-fuel ratio is large.

  The engine control unit 11 of this example corresponds to a storage unit, a variation detection unit, and a variation correction unit of the present invention.

EG ... Engine (internal combustion engine)
DESCRIPTION OF SYMBOLS 11 ... Engine controller 111 ... Intake passage 112 ... Air filter 113 ... Air flow meter 114 ... Throttle valve 115 ... Collector 116 ... Throttle valve actuator 117 ... Throttle sensor 118 ... Fuel injection valve 119 ... Cylinder 120 ... Piston 121 ... Intake valve 122 ... Exhaust Valve 123 ... Combustion chamber 124 ... Spark plug 125 ... Exhaust passage 126 ... Air-fuel ratio sensor 127 ... Exhaust purification catalyst 128 ... Oxygen sensor 129 ... Muffler 130 ... Crankshaft 131 ... Crank angle sensor 132 ... Cooling jacket 133 ... Water temperature sensor 134 ... Temperature Sensor

Claims (6)

In a control device for a multi-cylinder internal combustion engine provided with an air-fuel ratio sensor in an exhaust passage,
A first characteristic equation indicating the relationship of the air-fuel ratio variation of each cylinder with respect to the output amplitude of the air-fuel ratio sensor acquired in advance, and a second characteristic equation in which the sensitivity to the air-fuel ratio variation of each cylinder is lower than the first characteristic equation Storage means for storing
A control apparatus for an internal combustion engine, comprising: variation detection means for obtaining an output amplitude from an output of the air-fuel ratio sensor and obtaining an air-fuel ratio variation using the first air-fuel ratio characteristic equation. The control apparatus for an internal combustion engine according to claim 1,
When the variation in air-fuel ratio by the variation detection means is larger than a predetermined threshold, the variation correction means further obtains the variation in air-fuel ratio by the second characteristic equation and obtains the correction amount of the air-fuel ratio according to the variation in air-fuel ratio. A control device for an internal combustion engine. The control device for an internal combustion engine according to claim 1 or 2,
The control apparatus for an internal combustion engine, wherein the first characteristic equation and the second characteristic equation correlate with the arrangement of the cylinders and the magnitude of variation in the air-fuel ratio. The control apparatus for an internal combustion engine according to any one of claims 1 to 3,
The variation correction unit sets the change rate of the correction amount to be smaller when the air-fuel ratio variation detected by the variation detection unit is richer than the correction target value compared to when the variation is on the lean side. Control device for internal combustion engine. In the control device for an internal combustion engine according to any one of claims 1 to 4,
The internal combustion engine includes a variable valve mechanism that varies an operating angle of at least one of an intake valve and an exhaust valve,
A control device for an internal combustion engine, comprising: control means for executing detection of the air-fuel ratio variation and correction of the air-fuel ratio variation while gradually changing the operating angle. The control apparatus for an internal combustion engine according to claim 5,
The control device for an internal combustion engine, wherein the control means is executed while gradually changing the operating angle from a larger one to a smaller one.

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