JP2853178B2 - Engine air-fuel ratio detector - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an air-fuel ratio detection device provided in an engine.

(Prior art and its problems) Some automobile engines and the like are provided with a sensor in which an output voltage changes proportionally in accordance with oxygen concentration in an exhaust passage, and feedback control of a fuel supply system to control an air-fuel ratio. .

For example, a slice level (reference voltage) S is set for the output voltage X of the sensor, and if X> S is determined by comparing the two voltages, it is determined that the target air-fuel ratio is on the rich side and the air-fuel ratio is shifted to the lean side. If X <S, on the contrary, the air-fuel ratio is shifted to the lean side (Reference material: "Automotive Engineering Complete Volume 10 Gasoline Engine" Showa Sankaido Co., Ltd.
October 1979, p. 264).

However, since the sensor is exposed to high-temperature exhaust gas during operation of the engine, the sensor is deteriorated by heat and lead in the exhaust gas, and the output characteristics of the sensor change with time.

If the deterioration of the sensor actually progresses with a long operation, a large deviation occurs in the air-fuel ratio supplied to the engine,
There was a problem of causing engine malfunction.

An object of the present invention is to provide an air-fuel ratio detection device provided with a fail-safe function for coping with sensor deterioration, focusing on such conventional problems.

(Means for Solving the Problems) In order to achieve the above object, according to the present invention, as shown in FIG. 1, a sensor 1 for generating an output corresponding to the oxygen concentration in the exhaust gas of the engine, In an air-fuel ratio detection device for an engine, comprising means 2 for determining the magnitude of the output of the sensor 1 to detect the air-fuel ratio of the engine,
Comparing means 3 for comparing the output of the sensor when the air is excessive and the output of the fuel when the fuel is excessive with a plurality of predetermined reference values, based on a predetermined calculation process based on the comparison result, And a slice level calculating means 4 for calculating a corresponding slice level.

(Operation) The self-diagnosis of the degree of deterioration of the sensor from the output value of the sensor and the setting of the slice level by predetermined arithmetic processing determined from the output value of the sensor can prevent the air-fuel ratio control from being greatly disturbed by the deterioration of the sensor. Avoidance can prevent NOx and CO emissions from deteriorating.

Since the slice level is set stepwise based on a plurality of reference values for the sensor output, there is an inconvenience that the slice level is unnecessarily changed due to temporary deterioration or slight deterioration due to a temperature change or the like. Can be avoided.

(Example) Hereinafter, an example of the present invention is described based on an accompanying drawing.

FIG. 2 is a system diagram of an air-fuel ratio control device for an automobile engine. In the figure, an oxygen sensor 26 is attached to an exhaust pipe 33, and a signal from this sensor is input to a control unit 40. The control unit 40 performs feedback control so as to obtain a target air-fuel ratio by increasing or decreasing the amount of fuel from the fuel injection valve 35 based on various operation variables. Here, the pulse width Ti corresponding to the fuel injection amount required per ignition cycle is basically calculated by Ti = Tp × COEF × α + Ts. Where Tp
Is the basic pulse width, α is the feedback amount calculated based on the deviation between the output X of the air-fuel ratio sensor 26 and the slice level S, COEF is the sum of various correction coefficients for improving specific operating conditions, and Ts is invalid. The pulse width. In the figure, 24 is an air amount sensor, 25 is a crank angle sensor, and 27 is a water temperature sensor.

FIG. 3 shows an experimental result of measuring the output characteristics of the oxygen sensor 26. The output value of a deteriorated sensor (broken line) is relatively lower than that of a new sensor (solid line). Also, the fourth
The figure shows an experimental result of measuring the degree to which the output response time of the oxygen sensor 26 changes according to the operation time.

Based on these characteristics, the control unit 40 performs a fail-safe function and a self-diagnosis function to cope with the deterioration of the oxygen sensor 26 of the present invention. To be corrected.

Xr is a rich output voltage of the oxygen sensor 26, Xl is a lean output voltage, and F (Xr, Xl) is a correction function of output characteristic change.
(Xr, Xl) when the correction function of the output response time change, the basic slice level S _{0 is, S 0 = (Xr + Xl} ) × [0.5-F (X
r, Xl) -G (Xr, Xl)].

Hysteresis when the K ₁ air-fuel ratio is changed from lean to rich, when the K ₂ from the rich and hysteresis when changing the lean slice level S ₁ at the time from lean to rich
Is S ₁ = S ₀ + K ₁ , the slice level S ₂ from rich to lean
Is calculated as S ₂ = S ₀ −K ₂ (K ₁ > 0, K ₂ >
0).

 The following is set as F (Xr, Xl).

F (Xr, Xl) = 0 F (Xr, Xl) = 3.3 × 10 ⁻¹ [0.9− (Xr + Xl)] F (Xr, Xl) = 5.0 × 10 ⁻² G (Xr, Xl) is as follows. Is set.

G (Xr, Xl) = 0 G (Xr, Xl) = 6.0 × 10 ⁻¹ [0.9− (Xr + Xl)] G (Xr, Xl) = 3.0 × 10 ⁻² The selection of the above function values is shown in FIG. As described above, the calculation is performed based on the sensor output value Xr + Xl, and when 0.9 ≦ Xr + Xl, F (Xr, X
l) = 0, and when 0.75 ≦ Xr + Xl <0.9, F (Xr, Xl) =
3.3 × and ^{10 -1 [0.9- (Xr + Xl} )], when Xr + Xl <0.75 is set to F (Xr, Xl) = 5,0 × 10 -2. Also, 0.9 ≦ Xr + Xl
, G (Xr, Xl) = 0 when 0.85 ≦ Xr + Xl <0.9, G (Xr, Xl) = 6.0 × 10 ⁻¹ [0.9− (Xr + Xl)], and Xr
When + Xl <0.85, G (Xr, Xl) = 3.0 × 10 ⁻² .

FIG. 6 shows a routine for performing self-diagnosis and fail-safe to cope with the deterioration of the oxygen sensor 26. This routine is periodically executed in the CPU.

First, in step 41, Xr and Xl are read, and in step 42, Xr and Xl are read.
The magnitude of + Xl is determined, and F (Xr, Xl) is selected.

That is, if D ₁ ≦ Xr + Xl, F (Xr, X
l) = 0, and if E ₁ ≦ Xr + Xl <D ₁ , at step 44 F
_{(Xr, Xl) = B 1} × [A 1 - (Xr + Xl)] and then, Xr + Xl <E ₁
F (Xr, Xl) in step 45 in the case of = a C _1.

Next, in step 46, the size of Xr + Xl is determined, and G (Xr, X
l) Select

That is, if D ₂ ≦ Xr + Xl, G (Xr, X
l) = 0, and if E ₂ ≦ Xr + Xl <D ₂
(Xr, Xl) = B ₂ × [A ₂ − (Xr + Xl)], and Xr + Xl <E ₂
For F in step 49 (Xr, Xl) = and C _2.

Proceeding to step 50, the basic slice level S ₀ is set to S ₀ =
It is calculated by (Xr + Xl) × [0.5−F (Xr, Xl) −G (Xr, Xl)].

Slice level S ₁ during the lean proceeds to step 51 S ₁
= Calculated as S ₀ + K _1, the slice level S ₂ in the rich proceeds to step 52 to calculate each as _{S 2 = S 0 -K 2 (} K 1> 0, K 2> 0).

As described above, the change in the output characteristic of the oxygen sensor 26 is diagnosed, and the slice level S ₀ is changed according to the change in the output characteristic.
By changing (S ₁ or S ₂ ) in stages, it is possible to prevent the air-fuel ratio control of the engine from being greatly disturbed toward the excess fuel side.

FIG. 7 shows experimental results obtained by measuring that the exhaust gas component of the engine changes with the deterioration of the oxygen sensor 26 in each of the conventional air-fuel ratio control and the air-fuel ratio control according to the present embodiment. Even if the oxygen sensor 26 deteriorates with a long operation, NO
Deterioration of x and CO emission emissions can be kept small.

As another embodiment, the degree of deterioration of the sensor is determined based on the time when the output of the sensor is on the rich side beyond the slice level and the time on the lean side beyond the slice level to improve the detection accuracy. Can also be measured.

(Effects of the Invention) As described above, according to the present invention, in the air-fuel ratio detecting device for an engine, comparing means for comparing the output of the sensor when the air is excessive and the output when the fuel is excessive with a plurality of predetermined reference values;
Slice level calculation means for calculating a slice level according to the sensor output based on a predetermined calculation process based on the comparison result is provided, so that the degree of deterioration of the sensor can be accurately detected by self-diagnosis. Thus, the slice level can be changed, whereby it is possible to prevent the air-fuel ratio control from being greatly disturbed due to long-time operation in an automobile engine or the like, and the NOx and CO emissions from deteriorating. In addition, since the slice level is changed stepwise based on a plurality of reference values according to the degree of deterioration of the sensor, the slice level is changed unnecessarily for temporary deterioration and characteristic changes of the sensor to reduce exhaust emissions. It is possible to avoid a problem that causes deterioration.

[Brief description of the drawings]

FIG. 1 is a diagram corresponding to claims of the present invention, FIG. 2 is a system diagram of a control system applied to the present invention in the embodiment, FIG. 3 is a characteristic diagram of a sensor output value, and FIG. 4 is a characteristic diagram of an output response time. , FIG. 5 is a diagram of slice level correction values, FIG. 6 is a flow chart showing the operation of this embodiment, and FIG. 7 is a diagram showing the operation. 1 ... sensor, 2 ... air-fuel ratio detecting means, 3 ... slice level calculating means, 4 ... switching means.

Claims (1)

(57) [Claims] 1. An engine air-fuel ratio detection system comprising: a sensor for generating an output corresponding to an oxygen concentration in exhaust gas of an engine; In the apparatus, comparing means for comparing the output of the sensor at the time of excess air and the output of the fuel excess at a time with a plurality of predetermined reference values, and the sensor based on a predetermined arithmetic processing according to the comparison result An air-fuel ratio detecting device for an engine, comprising: a slice level calculating means for calculating a slice level according to an output.