JP2636298B2 - Air-fuel ratio control device for multi-cylinder internal combustion engine - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an air-fuel ratio control device for a multi-cylinder internal combustion engine using a maximum in-cylinder pressure for each cylinder.

[Prior Art and Problems to be Solved by the Invention] Conventionally, in an engine equipped with an electronically controlled fuel injection device (EGI), first, in order to maintain an optimum air-fuel ratio in each operation region, first, The basic fuel injection amount of each operation region is obtained, and then the basic fuel injection amount is corrected by various correction terms corresponding to the parameters of the operating state of the engine, and the actual fuel injection amount is obtained by feedback control. A fuel ratio control device is provided.

The basic fuel injection amount Tp is obtained as a function of the intake air amount Q and the engine speed N. That is, Tp = K · Q / NK: coefficient.

The actual fuel injection amount Ti is given by: Ti = Tp · KA / F · KFB KA / F: Air-fuel ratio correction coefficient set based on engine speed, cooling water temperature, throttle opening, etc. KFB: Exhaust gas It is obtained from the air-fuel ratio feedback correction amount obtained from the oxygen concentration.

The intake air amount Q is detected by an air flow meter disposed immediately downstream of the air cleaner or an intake air amount sensor such as an intake negative pressure sensor provided in an air chamber downstream of the throttle valve. Further, the air-fuel ratio feedback correction amount KFB is detected by an exhaust sensor exposed in the exhaust passage.

By the way, in general, in a multi-cylinder internal combustion engine, (1) the amount of air taken into each cylinder differs due to complicated intake pipe shape or interference between the taken-in air and the like.

(2) The combustion temperature is slightly different for each cylinder due to the influence of the cooling path of each cylinder.

(3) Production variations occur in the combustion chamber volume, piston shape, and the like of each cylinder.

(4) The air-fuel ratio is slightly different for each cylinder due to a difference in fuel injection amount due to an accuracy error of the injector.

Despite the problems described above, the conventional combustion control at the stoichiometric air-fuel ratio did not significantly affect the driving performance.

However, in recent high-performance engines that tend to have high output and low fuel consumption, even a slight variation in the air-fuel ratio of each cylinder as in the past has had a large effect on the output fluctuation of each cylinder, resulting in energy loss. Spawn.

As a result, not only does the total output of the engine decrease, but also the output becomes unstable, which causes problems such as promoting vibration and poor controllability of the air-fuel ratio.

Further, in order to eliminate variations in output due to variations in components, for example, a pressure in a combustion chamber is detected by using an in-cylinder pressure sensor as disclosed in Japanese Patent Application Laid-Open No. Sho 60-13943, and the combustion is measured. Some control the fuel injection amount by pressure. However, in the above publication, in an operating region where feedback control is not performed in a transient state such as when the throttle valve is fully opened, closed loop control is formed using the combustion pressure (indicated average effective pressure) in the combustion chamber, and the fuel injection amount is reduced. The control is intended to eliminate the variation in the output, and has not yet eliminated the variation in the air-fuel ratio between the cylinders in the region where the feedback control is performed, which causes a problem of deteriorating the exhaust emission.

[Object of the Invention] The present invention has been made in view of the above circumstances, and not only can the total output of an engine be improved and stable output characteristics can be obtained, but also fuel consumption can be reduced.
It is an object of the present invention to provide an air-fuel ratio control device for a multi-cylinder internal combustion engine capable of reducing emissions.

[Means and Actions for Solving the Problems] An air-fuel ratio control apparatus for a multi-cylinder internal combustion engine according to the present invention calculates a basic fuel injection amount based on an output signal from an intake air amount sensor and an output signal from a rotation speed sensor. A basic fuel injection amount calculating unit, a feedback correction amount calculating unit that calculates a feedback correction amount of a reference cylinder based on an output signal from an exhaust sensor facing an exhaust passage of a specific reference cylinder; A reference fuel injection amount calculating unit for calculating a fuel injection amount to a reference cylinder from an output signal from the amount calculating unit and an output signal from the feedback correction amount calculating unit;
A cylinder-by-cylinder pressure maximum value calculation unit that takes in the output signal of the in-cylinder pressure sensor disposed in each cylinder and calculates the maximum value of the in-cylinder pressure for each cylinder; and the in-cylinder pressure maximum value of the reference cylinder and the An in-cylinder pressure comparison operation unit that performs an operation to compare the in-cylinder pressure maximum value, and a fuel injection in which an output signal from the in-cylinder pressure comparison operation unit is taken and the in-cylinder pressure maximum value of each cylinder becomes the in-cylinder pressure maximum value of the reference cylinder. A cylinder-by-cylinder fuel injection correction unit that calculates the amount for each cylinder, and controls the air-fuel ratio of each cylinder based on the output signal from each in-cylinder pressure sensor to eliminate inter-cylinder variations in the air-fuel ratio.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. 1 shows an embodiment of the present invention, FIG. 1 is a schematic view of a main part of an engine, FIG. 2 is a schematic plan view of an engine, and FIG.
FIG. 3 is a sectional view taken along the line III-III of FIG.
FIG. 5 is a block diagram of the air-fuel ratio control means, FIG. 6 is a block diagram of the air-fuel ratio control means, and FIG.
X), a correlation diagram showing the air-fuel ratio (A / F) on the horizontal axis, and FIG. 8 is a flowchart showing the operation procedure of the air-fuel ratio control means.

Reference numeral 1 in the figure denotes a four-cylinder horizontally opposed engine body, which is an example of a multi-cylinder internal combustion engine, and includes a cylinder block 2
Are divided into two banks (LH, RH) with the crankshaft 3 as the center.

Further, a water temperature sensor 24 is exposed to the water jacket, and each piston 4 inserted into each of the cylinders 2a, 2b, 2c, 2d provided in the LH bank and the RH bank of the cylinder block 2 is connected to the crankshaft 3. Are connected to each other via a connecting rod (not shown). Further, combustion chambers 6a, 6b, 6c and 6d are formed in portions of the cylinders 2a to 2d surrounded by the piston 4 and the cylinder heads 5a and 5b, respectively.

In addition, the cylinders 2a to 2 of the cylinder heads 5a and 5b
An in-cylinder pressure sensor 7 is mounted and fixed at a position corresponding to d via an adapter 8, and a tip end detection portion of the in-cylinder pressure sensor 7 faces each of the combustion chambers 6a to 6d. further,
An ignition plug 9 is mounted on each of the cylinder heads 5a and 5b in correspondence with each of the cylinders 2a to 2d. The in-cylinder pressure sensor 7 may be directly fixed to the cylinder heads 5a and 5b.

Further, the suction ports 1a communicating with the combustion chambers 6a to 6d, respectively.
In addition, injectors 10a, 10b, 10c, 10d are facing,
Further, the upstream side of each intake port 1a is located at the intake manifold.
The throttle chamber 14 is provided with a throttle valve 13 via the air passage 11, and the upstream side of the throttle chamber 14 is communicated with an air cleaner 17 via an intake pipe 15.

A suction negative pressure sensor 25, which is an example of an intake air amount sensor, is provided downstream of the throttle valve 13. The intake negative pressure sensor 25 measures the intake negative pressure generated downstream the throttle valve measured signal P _o output, the amount of intake air is indexed.

The crankshaft 3 has an engine speed N
And a rotational speed sensor 18 for detecting the crank angle Crθ. Reference numeral 19 denotes a throttle position sensor for detecting the throttle opening θ.

On the other hand, an exhaust sensor 22 faces the exhaust passage 12 of a specific cylinder of the engine body 1, and this cylinder is set as a reference cylinder. Reference numeral 23 denotes a catalytic converter.

Reference numeral 20 denotes an air-fuel ratio control unit.The central processing unit CPU 40, a read-on memory ROM 41, a random access memory RAM 42, an input port 44, and an output port 46 are connected by a system bus 43. Is connected to an A / D converter 45 for converting analog signals from the respective sensors from analog to digital and inputting them to the input port 44. Among the above sensors, the in-cylinder pressure sensor 7 to which the throttle position sensor 19, the water temperature sensor 24, the suction negative pressure sensor 25, and the charge amplifier 48 are connected is connected to the A / D converter 45, and the rotation speed sensor 18, the exhaust gas The sensor 22 is connected to the input port 44 through a waveform shaping circuit (not shown) provided as needed. The above output port 46
Are connected to the injector drive units 38a, 38b, 38c, 38d,
The injectors 10a to 10d are independently driven.

Further, the air-fuel ratio control means 20 includes a basic fuel injection amount calculation unit 30, an air-fuel ratio correction coefficient calculation unit 32, a feedback correction amount calculation unit 33, a reference fuel injection amount calculation unit 31, a cylinder-by-cylinder pressure maximum. It comprises a value calculation section 34, an in-cylinder pressure comparison calculation section 35, a cylinder-specific fuel injection correction section 36, an air-fuel ratio learning map 37, and injector drive sections 38a to 38d.

In the basic fuel injection amount calculating section 30, the suction negative pressure sensor 25
And indexing output signal P _o the intake air amount from the rotation speed sensor
A basic fuel injection amount (pulse width) Tp is calculated based on the output signal N indicating the engine speed from 18.

Further, the air-fuel ratio correction coefficient calculation unit 32 outputs the output signal N
The air-fuel ratio correction coefficient KA / F is calculated from the output signal Tw indicating the cooling water temperature from the water temperature sensor 24, the output signal θ indicating the throttle opening from the throttle position sensor 19, and the like.
On the other hand, the feedback correction amount calculation unit 33
The air-fuel ratio feedback correction amount KFB is calculated based on the output signal E indicating the air-fuel ratio feedback value from the controller.

The reference fuel injection amount calculation unit 31 calculates the actual fuel injection amount obtained by correcting the basic fuel injection amount Tp with the air-fuel ratio correction coefficient KA / F and the air-fuel ratio feedback correction amount KFB. Based on this, the injector driving unit 38a outputs the optimum fuel injection pulse width Ti suitable for the intake air amount to the injector 10a arranged in the reference cylinder. The above shows that the known feedback control is applied to the reference cylinder.

The cylinder-by-cylinder in-cylinder pressure maximum value calculation unit 34 calculates a pressure signal P in each cylinder from an in-cylinder pressure sensor 7 disposed in each cylinder,
Crθ corresponding to the crank angle from the rotational speed sensor 18, and by captures and suction pipe pressure signal P _o from the suction negative pressure sensor 25,
A maximum in-cylinder pressure value PMAX corresponding to the crank angle of each cylinder is detected. The absolute value of the in-cylinder pressure is corrected to a zero point by a signal from the suction negative pressure sensor 25.

Here, generally, as shown in FIG. 7, in the partial region, PMAX becomes the maximum at the stoichiometric air-fuel ratio (A / F = 1).
It is time for 4.7). In the operation region where the reference cylinder maintains the stoichiometric air-fuel ratio by feedback control, if the maximum cylinder pressure of the reference cylinder is PMAX _o , the maximum cylinder pressure PMAX of the other cylinder is set to the maximum cylinder pressure of the reference cylinder. Value PMAX
By controlling so as to approach _o , all cylinders approach the stoichiometric air-fuel ratio.

Based on the above, the in-cylinder pressure comparison calculation unit 35 compares and calculates the maximum in-cylinder pressure value PMAX _o of the reference cylinder and the maximum in-cylinder pressure value PMAX of each cylinder for each cylinder, and calculates the maximum in-cylinder pressure value PMAX _{o of the} reference cylinder.
Is output to the cylinder-by-cylinder fuel injection correction unit 36.

Based on the signal from the in-cylinder pressure comparison / calculation unit 35, the cylinder-by-cylinder fuel injection correction unit 36 sets the maximum in-cylinder pressure value PMAX of each cylinder to a predetermined allowable value with respect to the maximum in-cylinder pressure value PMAX _{o of} the reference cylinder. The fuel injection correction amount KLRN is increased or decreased so as to be equal, and given to the reference fuel injection amount from the reference fuel injection amount calculation unit 31 (Ti ′ = Ti · KLRN), and an injector drive unit provided independently for each cylinder A signal is output to each of 38b, 38c, 38d to drive the injectors 10b, 10c, 10d. Further, the air-fuel ratio learning map 37 storing the fuel injection correction amount KLRN is rewritten, and the fuel injection correction amount KLRN is subjected to learning control. The air-fuel ratio learning map 37 is specifically described above.
This is stored in the RAM 42.

By the above operation, the maximum value of the in-cylinder pressure of each cylinder other than the reference cylinder is controlled so as to be equal to the maximum value of the in-cylinder pressure of the reference cylinder. As is apparent from FIG. 7, all the cylinders are maintained at the stoichiometric air-fuel ratio. Variations in air-fuel ratio and output torque between cylinders are eliminated.

Next, the operation of controlling the air-fuel ratio of each cylinder by the air-fuel ratio control means will be described with reference to the flowchart of FIG.

When the engine is running and all cylinders are initially operated by the signal from the reference fuel injection amount calculation unit, the reference cylinder is detected by the exhaust sensor facing the exhaust passage of the reference cylinder.
When the operation range reaches the stoichiometric air-fuel ratio under the feedback control of O _{2, the} maximum cylinder pressure PMAXo of the reference cylinder is first detected in step 100 from the output signal of each cylinder pressure sensor. A maximum in-cylinder pressure value PMAX is detected for each cylinder. Then the difference ΔP = PMAX _o -PMAX the cylinder pressure maximum value PMAX _o is compared PMAX _o of the in-cylinder pressure maximum value PMAX and the reference cylinder of each cylinder is calculated stored at step 102. Next, at step 103, it is determined whether this ΔP is within the allowable value ΔPINIT, that is, whether each cylinder is within the fluctuation range of the air-fuel ratio allowed for the reference cylinder. ΔP ≦ ΔPINIT
Is determined to be within the allowable value, and the flow returns to step 100 again without correcting the fuel injection correction amount KLRN. On the other hand, ΔP> Δ
For a cylinder that is PINIT, it is first assumed that the air-fuel ratio is lean, and the fuel injection amount of the cylinder is X% of the reference fuel injection amount (for example, an amount stored in a map according to the magnitude of ΔP). ) Increase (KLRN + X). And step 10
The flow shifts to 5, and the maximum in-cylinder pressure value P'MAX of the cylinder is detected again. Then, the flow shifts to step 106. In step 106, similarly, the difference ΔP '= PM from the maximum in-cylinder pressure value PMAX _o of the reference cylinder.
AX ₀ −P′MAX is compared and calculated. The process further proceeds to step 107, where ΔP ′ is compared with ΔP stored in step 102,
If ΔP ≧ ΔP ′, the routine proceeds to step 108, where the fuel injection amount of the cylinder is further increased by X% (KLRN +
X). That is, 2X% increase from the reference fuel injection amount,
Move to step 110. Conversely, if ΔP <ΔP ′, the routine proceeds to step 109, where the fuel injection amount is reduced by Y% with respect to the reference fuel injection amount in order to correct the assumption that the air-fuel ratio in step 104 is lean (KLRN-Y). ). Here, as is clear from FIG. 7, it is appropriate that the decrease of Y% is Y = 3X%, including the amount which has already been increased by X% in step 104 and shifted to the rich side. In step 110, the fuel injection correction amount KLRN stored in the air-fuel ratio learning map is rewritten, and the program ends.

As described above, in this embodiment, the example in which the fuel injection amount for the cylinders other than the reference cylinder is corrected with respect to the reference fuel injection amount, which is the fuel injection amount for the reference cylinder, has been described, but the present invention is not limited to this. For example, correlation data between the maximum value of the in-cylinder pressure and the fuel injection amount obtained in advance based on an experiment or the like is stored as map data in the ROM in the air-fuel ratio control means, and the map data in the ROM is appropriately referred to. A method of determining the fuel injection amount is also conceivable.

[Effects of the Invention] As described above, according to the present invention, the maximum value of the in-cylinder pressure of all the cylinders is calculated, and the fuel injection is performed so that the maximum value of the in-cylinder pressure of each cylinder becomes the maximum value of the in-cylinder pressure of the reference cylinder. Since the amount is set, it is possible to control the variation of the air-fuel ratio of each cylinder,
As a result, vibration and energy loss are reduced, and not only the total output of the engine is improved and stable output characteristics are obtained, but also low fuel consumption can be realized and quietness is ensured. Excellent effects are achieved, such as reduction of emission.

[Brief description of the drawings]

BRIEF DESCRIPTION OF THE DRAWINGS The drawings show an embodiment of the present invention, FIG. 1 is a schematic view of an essential part of an engine, FIG. 2 is a schematic plan view of the engine, FIG. 3 is a sectional view taken along the line III-III of FIG. FIG. 3 is a sectional view taken along the line IV-IV of FIG. 3, FIG. 5 is a block diagram of the air-fuel ratio control means, FIG. 6 is a block diagram of the air-fuel ratio control means, and FIG. FIG. 8 is a flowchart showing the operation procedure of the air-fuel ratio control means, with the axis indicating the air-fuel ratio (A / F). 2 ... Cylinder block, 2a-2d ... Cylinder, 7 ... In-cylinder pressure sensor, 30 ... Basic fuel injection amount calculator, 31 ... Reference fuel injection amount calculator, 32 ... Air-fuel ratio correction coefficient calculator, 33 ……
Feedback correction amount calculation unit, 34: Maximum cylinder-internal cylinder pressure calculation unit, 35: Cylinder pressure comparison calculation unit, 36: Fuel injection correction unit for each cylinder, 37: Air-fuel ratio learning map, PMAX _o ... Reference cylinder pressure maximum of the cylinder, PMAX ...... cylinder pressure maximum value of each cylinder, N, Q, Crθ, Tw , θ, E, P o, P ...... output signal.

Claims (1)

(57) [Claims] A basic fuel injection amount calculation unit for calculating a basic fuel injection amount based on an output signal from an intake air amount sensor and an output signal from a rotation speed sensor, and an exhaust passage of a specific reference cylinder. A feedback correction amount calculator for calculating a feedback correction amount of the reference cylinder based on an output signal from the exhaust sensor; and a reference based on an output signal from the basic fuel injection amount calculator and an output signal from the feedback correction amount calculator. A reference fuel injection amount calculation unit for calculating a fuel injection amount to a cylinder, and a cylinder-by-cylinder pressure maximum for taking in an output signal of an in-cylinder pressure sensor disposed in each cylinder and calculating a maximum value of the in-cylinder pressure for each cylinder. A value calculation unit, an in-cylinder pressure comparison operation unit that compares and calculates an in-cylinder pressure maximum value of the reference cylinder and an in-cylinder pressure maximum value of each cylinder, and an output signal from the in-cylinder pressure comparison operation unit. Inside the cylinder Maximum air-fuel ratio control apparatus for a multi-cylinder internal combustion engine having a cylinder fuel injection correction unit in-cylinder pressure maximum value and becomes fuel injection quantity calculating for each cylinder of the reference cylinder.