JPS5859330A - Air-fuel ratio control method for internal-combustion engine - Google Patents

Abstract

PURPOSE:To compensate for the delay in response of a lean sensor when an objective value is changed, in the case the air-fuel ratio is controlled to meet the objective value based on the detected value of the lean sensor which generates an output signal that is proportional to the oxygen concentration. CONSTITUTION:An electronic control unit receives the detected values of a negative pressure sensor for an air intake pipe, an engine speed sensor, and the lean sensor which generates an output signal proportional to the oxygen concentration, and executes setting of the objective air-fuel ratio, computation of the corresponding objective output value V0 of the lean sensor, and computation of a basic fuel injecting quantity in steps 50-52. The present and previous objective values V0 and V1 are compared in a step 54. When the result is changed, an objective value change flag is made a 1. Then a correcting coefficient (f) is added or subtracted by gamma and delta which are larger than an ordinary fuel increasing rate alpha and a decreasing rate beta, in response to the value of (V0-V1), until the abolute value of the difference between the present and previous output values V and V2 of the lean sensor exceeds a specified value Q in a step 61.

Description

[Detailed description of the invention] The present invention relates to an air-fuel ratio control method for an internal combustion engine.

As an oxygen concentration detector capable of detecting the oxygen concentration in a gas, for example, an oxygen concentration detector using an oxygen ion conductive solid electrolyte such as zirconia is described in Japanese Patent Application Laid-Open No. 52-72286. is publicly known. In this oxygen concentration sensor, a thin film representing an anode is coated on one surface of a zirconia plate, a thin film representing an anode is coated on the other surface of the zirconia plate, and a voltage is applied between the cathode and the anode. When the oxygen molecules that come into contact with the cathode and are given electrons pass through the zirconia plate and then release electrons at the anode, a current is generated that flows from the anode to the electrode, and this current passes through the zirconia plate. The oxygen concentration can be determined from this current value because it is proportional to the number of oxygen molecules that are in contact with the cathode, that is, the partial pressure of oxygen in the gas that contacts the cathode. Therefore, if this oxygen concentration detector is installed in the engine exhaust passage, the oxygen concentration in the exhaust passage can be detected, and therefore the air-fuel ratio of the air-fuel mixture supplied into the engine cylinder can be known. Since this oxygen concentration detector detects the oxygen concentration in the exhaust passage, it functions as a detector when the air-fuel mixture supplied to the engine cylinder is a lean mixture. This type of oxygen concentration detector will hereinafter be referred to as ``Lee/Se/S''.

One method of controlling the air-fuel ratio using such a lean sensor is to directly control the fuel injection time based on the output signal of the lean sensor so that the air-fuel ratio becomes a predetermined air-fuel ratio. As a method, the fuel injection amount is determined according to the engine speed and intake pipe negative pressure, or according to the output signal of the air flow meter, and the deviation from this set injection amount is determined based on the output signal of the lean sensor. There are ways to control it. In either case, there is no particular problem if the target air-fuel ratio, that is, the target output voltage value of the lean sensor, is held constant, but if the target output voltage value changes suddenly, the output of the lean sensor There is a period in which the signal is unable to follow this and the air-fuel ratio deviates significantly from the target air-fuel ratio during this period.

As described above, the present invention provides an air-fuel ratio control method for an internal combustion engine that allows the air-fuel ratio to follow the pull even if the target air-fuel ratio, that is, the target output value of the lean sensor changes rapidly. be.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

Referring to FIG. 1, 1 is the engine body, 2 is the cylinder block, 3 is the piston that reciprocates within the cylinder cylinder z, 4 is the cylinder head fixed on the cylinder block 2, and 5 is the piston 3. A combustion chamber formed between the cylinder heads 4, a spark plug 6 disposed within the combustion IK device,
7 is an intake/-), 8 is an intake valve, 9 is an exhaust port, 1O is an exhaust valve, the intake I- and TOF are connected to a common surge tank 12 via a branch pipe, 11to 9
is connected to the exhaust manifold l'13. Each branch pipe 11 is provided with a fuel injection valve 15 that is controlled by an output signal from an electronic control unit x<h, and these fuel injection valves 15
Fuel is injected from the corresponding intake air /-)7.

The surge tank 12 is connected to an air cleaner (not shown) via an intake pipe 16, and a throttle valve 17 connected to an accelerator pedal is disposed within the intake pipe 16. A negative pressure sensor 18 is installed inside the surge tank 12 , and the negative pressure sensor 18 and rotational speed sensor 19 are connected to the electronic control unit 14 . On the other hand, a lean sensor 20 is attached to the exhaust manifold 13, and this lean sensor 20 is connected to the electronic control unit 14. Lean Senna 20
For example, as shown in FIG. 2, the device includes a cag-shaped oxygen ion conductive solid electrolyte 21 made of norconia, and a porous ceramic 22 whose outer peripheral surface is brazed. Placed. Further, a platinum thin film for an anode and a platinum thin film for a cathode are coated on the inner peripheral surface and the outer peripheral surface of the oxygen ion conductive solid electrolyte 21, respectively, and are connected to the platinum thin films.
A voltage is applied between 4. Oxygen molecular beams in the exhaust gas pass through the porous ceramic 22 by diffusion and reach the cathode platinum thin film of the oxygen ion conductive solid electrolyte 21, where they are given electrons and the oxygen molecules become oxygen ion conductive. passing through the solid electrolyte 21 and coming into contact with the anode platinum thin film of the oxygen ion conductive solid electrolyte 21 to emit electrons;
More current is generated.

FIG. 5 shows the relationship between the oxygen concentration p (-weight/cents) in the exhaust gas and the generated current A (mA). It can be seen that the generated current is approximately proportional to the oxygen deficiency as shown by the elongated line in the M5 diagram. In addition, oxygen 111 in the exhaust gas
If the air-fuel ratio is known, the air-fuel ratio supplied to the engine cylinder can be determined, and this air-fuel ratio is shown on the horizontal axis in FIG. Therefore #&
It can be seen from FIG. 5 that if the generated current is known, the air-fuel ratio of the air-fuel mixture supplied into the engine cylinder can be detected.

FIG. 3 shows the electronic control unit 14. Referring to FIG. 3, the electronic control unit 14 consists of a digital computer and is a microprocessor that performs various calculation processes.
q (MPU) 30, random access memory (RAM)
) 31, a read-only memory (ROM) 32 in which a control programmable controller, calculation constants, etc. are stored in advance, an input port 33, and an output port 34 are interconnected via a bidirectional node 35. To the east, electronic control unit 1
A clock generator 36 for generating various clock signals is provided within the circuit 4. As shown in FIG. 3, the negative pressure sensor 18 is connected to the input port 33 via a converter 37 and an AD converter 38. The negative pressure sensor 18 generates an output voltage proportional to the negative pressure generated in the surge tank 12, that is, the intake pipe negative pressure P, and this output voltage is converted into a corresponding binary number by the AD converter 38. is input to the MPU 30 via the input port 33 and the node 35. On the other hand, the rotation speed sensor 19 is connected to an input port 33 via a buffer 39. This rotation speed sensor 1
9 generates a signal every time the engine crankshaft rotates by a predetermined crank angle, and this signal is connected to the input port 3.
3 and a path 35 to the MPU 30.

The MPU 36 calculates the engine speed from the output of the rotation speed sensor 19. In addition, the lean sensor 20 is connected to a current-voltage converter 40. It is connected to the input port 33 via an amplifier 41 and an AD converter 42. lean sensor 20
The generated current is converted into a corresponding voltage in the current-voltage converter 40, and then this voltage is converted into a corresponding binary number in the AD converter 42, and this binary number is input to the input port 3.
3 and a path 35 to the MPU 30.

The relationship shown by the solid line in FIG. 5 is stored in advance in the ROM 32, but in this case, the vertical axis in FIG. The relationship between voltage V and oxygen concentration P is stored in the form of a data table or function.

The output port 34 is provided to output data for operating the fuel injection valve 15.
Binary data is written to No.4 from IIIPU 30 via No.4 bus 35. Each output terminal of the output port 34 is connected to a corresponding input terminal of the down counter 43. This down counter 43 is provided to convert the binary data written from the MPU 30 into the corresponding time length, and this down counter 43 counts down the data sent from the output port 34. It starts with a clock signal from the clock generator 36, completes counting when the count value reaches 0, and generates a count completion signal at the output terminal.

S-R Fri! The reset input terminal R of the 5-R7 rig float f44 is connected to the output terminal of the down counter 43, and the set input terminal S of the 5-R7 rig float f44 is connected to the clock generator 36.
is incremented by the clock signal of the clock generator 36 at the same time as the down count starts, and is reset by the count completion signal of the down counter 43 when the down count is completed. Therefore, the output terminal Q of the S-R Fritz f70tz7''44 is at a high level while the down count is being performed.
! : Nari. The output terminal Q of the 8-R frig float 7'' 44 is connected to the fuel injection valve 15 via the power amplification circuit 45, so that the fuel injection valve 15 is connected to the down counter 43.
It can be seen that the village is attacked while the number is counting down.

Next, the operation of the air-fuel ratio control device according to the present invention will be explained with reference to FIG. Referring to FIG. 4, first, in step 50, the negative pressure sensor 18 and the rotation speed sensor 19 are connected to each other.
The target air-fuel ratio is set from the output signal. This target air-fuel ratio is stored in advance in the ROM 32 as a function of the intake pipe negative pressure P and the engine speed N, as shown in FIG. 7, for example. The numerical values in FIG. 7 indicate the air-fuel ratio. Therefore, in step 50, the target air-fuel ratio is calculated from the relationship shown in FIG. A target output voltage value v0 of 20 is calculated, and then in step 52 a basic fuel injection time τ. is calculated. This basic fuel injection time τ6 is the time required to form a mixture with an air-fuel ratio as shown in FIG. 7, and is the basic fuel injection time τ. is stored in advance in the 10M32 in the form of a mag as a function of the intake pipe negative pressure P and the engine speed N, as shown in FIG. Note that this basic fuel injection time T0 is constant within a predetermined engine speed range and intake pipe negative pressure range, so even if the engine speed or intake pipe negative pressure changes slightly, the basic fuel injection time τ remains constant. . does not change (0) Next, in Stella f53, it is determined whether or not a target value change flag, which is set when the target air-fuel ratio changes, is set, and if the target value change flag is not set (1), the process proceeds to step 54.・Stella f5
4, it is determined whether the target output voltage value v0 of the lean sensor 20 in the current processing cycle is equal to the target output voltage value V in the previous processing cycle, and vo is V.

If the target air-fuel ratio is not equal to , that is, if the target air-fuel ratio has not changed, the process proceeds to step 55. In Stella 7'55, the current output voltage value V of the lean sensor 20 is the target voltage 111vo.
It is determined whether or not it is smaller than .

When Stella f5 & determines that the current output voltage value V is not smaller than the target voltage value v0, Stella f56
, a constant value α is added to the correction coefficient t, and the addition result is set as f, and then atr is added to the correction coefficient fst. On the other hand, when the current output voltage value V is determined to be smaller than the target voltage value v0 in the STETSUNO 55, the constant value I is subtracted from the correction coefficient f in the STELLA f5B, and the subtraction result is set as f, and then step 57 In step 57, the basic fuel injection time T0 is multiplied by the correction coefficient 1 to calculate the fuel injection time T, and fuel is injected from the fuel injection valve 15 for a time corresponding to this fuel injection time i. FIG. 6 shows the oxidation of the output voltage V of the lean sensor 20 and the correction coefficient f.As shown in the sections T and Tb of FIG. When the air-fuel ratio becomes larger than the target air-fuel ratio, the correction coefficient f is increased by α, so that the fuel injection amount is increased, and the output voltage V of the sensor 20 becomes the target voltage value. When v0 also becomes smaller, that is, when the air-fuel ratio becomes smaller than the target air-fuel ratio, the fuel injection amount is decreased in a rounded manner in which the correction coefficient 1 is decreased by β.

On the other hand, when the target air-fuel ratio changes (provided that the basic fuel injection time τ6 does not change at this time), the Stellar f in Fig. 4
At step 54, it is determined that vo is not equal to V, so the process goes to Stella 7"59. At this time, the time Te in FIG.
It is indicated by. In Stella 7”59, target value change flag 59
is set and then in step 60 the current target voltage value V. The target voltage value V in the previous l processing cycle from
, is subtracted, and the subtraction result is set as ΔV. Therefore, if the target air-fuel ratio becomes large, ΔV becomes positive, and if the target air-fuel ratio becomes small, ΔV becomes negative. Next, Stella 7''61 subtracts the output voltage v2 of the lean sensor 20 in the previous processing cycle from the current output voltage V of the lean sensor 20, and determines whether the absolute value of the subtraction result is smaller than a predetermined constant value Q. In other words, the left side By-v21 of step 61 represents the rate of change of the output voltage of the lean sensor 20. Therefore, in step 61, the lean sensor 2
It is determined whether the rate of change of the output voltage of 0 is smaller than a predetermined rate of change Q. As can be seen from FIG. 6, even if the target air-fuel ratio changes at time Tc, the output voltage of the lean sensor 20 does not change rapidly during the interval Td. Therefore, within section T4 in FIG. 6, the process proceeds to step 62, where it is determined whether ΔV obtained at step 60 is positive or not.

When it is determined in Stellar f62 that ΔV is positive, proceed to Stellar f63 and calculate δ from the correction coefficient f,
Let the subtraction result be f. On the other hand, if it is determined in Stellar f62 that 4v is not positive, the process proceeds to Stellar f64, where correction coefficient fKr is added, and the addition result is set as f. a of step 63 is much larger than l of Stellar 7'S8, and r of Stellar f64 is much larger than α of Stellar f56. Therefore, as shown in FIG. 6, the correction coefficient f is When the fuel injection time reaches 0 and then time T, the output voltage of the lean sensor 20 rises in response to the change in the target air-fuel ratio. It is determined that the rate of change of the output voltage of the lean sensor 20, 1v-v, is not smaller than the predetermined rate of change q,
As a result, proceed to Stella f65, lower the target value change flag, and then proceed to Step 55. Therefore, from then on, ↓1 step f5
In Step 6 or Step 58, α is added to the correction coefficient f, or β is subtracted from the correction coefficient f.

In addition, in the above-mentioned embodiment, r at steps 63 and 64
, δ have been explained as constant values, but these γ and δ are
As shown in the figure, the variation rate lΔv1 of the target air-fuel ratio, that is, Iv
It can also be increased as ov,l increases.

As described above, according to the present invention, the response delay of the lean sensor is reduced by forcibly and rapidly increasing or decreasing the basic fuel injection interval correction coefficient when the target air-fuel ratio changes. In this way, the air-fuel ratio can be made to match the target air-fuel ratio immediately. 1 more
The correction coefficient is adjusted to the target correction coefficient value by stopping the rapid increasing or decreasing action of the correction coefficient when the rate of change of the output voltage of the lean sensor exceeds a predetermined rate of change. Overshading or undersheeting can be prevented, and this can be further improved by changing the rate of increase and decrease of the overshading or undersheeting correction coefficient according to the rate of change in the target air-fuel ratio. can be prevented.

[Brief explanation of the drawing]

Fig. 1 is a side sectional view of the internal combustion engine according to the present invention, Fig. 2 is a side sectional view of the lean sensor, Fig. 3 is a circuit diagram of the electronic M# unit, and Fig. 4 explains the operation of the air-fuel ratio control device. Figure 5 is a diagram showing the relationship between lean sensor output and oxygen concentration. Figure 6 is a diagram showing changes in the correction coefficient. Figure 7 is a diagram showing the target and air-fuel ratio. FIG. 6 is a diagram showing the relationship between the rate of change of the air-fuel ratio and the addition term and subtraction ring of the correction coefficient. 12...Surge tank, 13...Exhaust manifold,
14...electronic control unit), 15-...fuel injection valve,
17...Throttle valve, 1g...Negative pressure sensor, 19
...Rotation speed sensor, 20...Leansen! .

Claims (1)

[Claims] 1. A lean sensor is attached to the engine exhaust passage to generate an output signal proportional to the oxygen concentration in the lean exhaust passage, and the amount of fuel supplied to the engine cylinder based on the output signal of the lean sensor is installed. In the air-fuel ratio control method for an internal combustion engine, the fuel amount is increased at a predetermined increase rate when the output voltage of the lean sensor becomes equal to or higher than the target output voltage, and the lean sensor output voltage is increased by a predetermined increase rate. When the target output voltage becomes lower than the target output voltage, the fuel amount is decreased at a predetermined reduction rate, and when the target output voltage changes to another target output voltage, the increase rate and the rate of increase of the fuel amount are reduced. A method for controlling the air-fuel ratio of an internal combustion engine. 2. In the fuel ratio control method for an internal combustion engine recited in claim No. A method for controlling an air-fuel ratio of an internal combustion engine to stop the increasing effect of the rate and the rate of decrease.