JPH01227833A - Air-fuel ratio control device - Google Patents

Abstract

PURPOSE:To enable control of an air-fuel ratio with high accuracy by comparing an offset voltage with a voltage on a control unit side at a stoichiometric point under fuel cut control so as to obtain individual differences or the like of an air-fuel ratio sensor, and amending a measured value. CONSTITUTION:It is judged whether fuel is cut or not in a control unit 12 under the operation of an engine. When the fuel is cut, a switch mechanism 15 is switched off, and an offset voltage Vo set by a sensor controller 14 is measured. A voltage value (reference voltage) at a stoichiometric point (theoretical air-fuel ratio) is computed from an air-fuel ratio value of a map using a preset voltage as a parameter, and the reference voltage is compared with the offset voltage to obtain an offset voltage difference V. When the fuel is not cut and the switch mechanism 15 is switched on, an output voltage of an air-fuel ratio sensor 11 is measured, the measured voltage is amended with the difference V, and the air-fuel ratio corresponding to the amended voltage is retrieved on the map.

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to an air-fuel ratio control tIIl device for an automobile engine.

[Conventional technology]

Conventionally, the O1 sensor used for air-fuel ratio control is
It was only possible to determine whether the air-fuel ratio was richer or leaner than the stoichiometric air-fuel ratio.
Wide-range air-fuel ratio sensors that can continuously detect air-fuel ratios over a very wide range of 2-25 have come into use. Here, due to the principle of the sensor, the output is obtained as a current, so the interface of the control unit has 1! A signal is required that is obtained by converting the voltage by a current/voltage converter into a digital signal by an A/D converter. Furthermore, since the direction of current is different between the rich side and the lean side, an offset voltage is applied to the output of this current/voltage converter in advance, and then analog-to-digital conversion is performed.

[Problem to be solved by the invention]

The problem here is that the control unit stores the relationship between the output voltage and the air-fuel ratio as a map, and reads out the air-fuel ratio based on the given voltage value. This means that it is actually difficult to select and set so as to eliminate individual errors and errors on the interface circuit. That is, even this small error becomes a problem when feedback control is performed near the stoichiometric air-fuel ratio using the air-fuel ratio sensor. The present invention has been made based on the above-mentioned circumstances, and the error in the offset voltage is checked using the period during fuel cut, and during feedback control of the actual air-fuel ratio, the air-fuel ratio is determined based on the above-determined error. Air-fuel ratio control lfF! This is what we are trying to provide. [Means for Solving Problem 311] Therefore, in the present invention, the output current of the air-fuel ratio sensor is
A switch means for turning off the output of the air-fuel ratio sensor during fuel cut, and an OFF state of the switch means, in which the voltage is converted by a voltage converter and an offset voltage is added to the voltage value to provide a measured value to the control unit. , comprising an error measuring means for measuring the offset voltage and calculating an error with the voltage corresponding to the stoichiometric point on the control unit side, and a correcting means for correcting the measured value that is susceptible to the error when the switch means is on. ing.

[For production]

Therefore, individual errors in the sensor, errors in the interface circuit of the control unit, etc. can be obtained by comparing the offset voltage during fuel cut with the voltage on the control unit side at the stoichiometry point, and the measured value can be calculated using these errors. It can be corrected. Therefore, feedback control of the air-fuel ratio can be accurately controlled near the stoichiometric air-fuel ratio.

【Example】

Hereinafter, one embodiment of the present invention will be specifically described with reference to the drawings. In FIG. 1, reference numeral 1 is an engine, and its intake system 2 is provided with a throttle valve 3, upstream of which is provided a hot wire type air flow meter 4, and downstream thereof is provided with a throttle chamber 5. It is being An injector 6 is provided near each intake boat of the intake manifold downstream of the throttle chamber 5. Further, the throttle valve 3 has a throttle opening sensor 7, the engine 1 has a water temperature sensor) J-8, and a crank angle sensor 9, and the exhaust system 10 of the engine 1 has a wide range air-fuel ratio sensor 11. (The wide range air-fuel ratio sensor 11 has current characteristics as shown in FIG. 5). And each of the above sensors 7.8
．． 9 and 11. A detection signal from the air flow meter 4 is supplied to a control unit 12. The control unit 12 outputs appropriate IQIn signals to the injector 6, ignition coil 13, etc. as a result of calculations based on the detection signals from the sensors. The control unit 12 is particularly connected to the air-fuel ratio sensor 11 in a configuration as shown in FIG. Here, the air-fuel ratio sensor 11 is connected to an external sensor controller 14, and the output signal (Il flow) of the air-fuel ratio sensor 11 is provided to the switching voltage converter 6116 via the switch mechanism 15. Here, a voltage corresponding to the above output signal is outputted and supplied to the analog-to-digital converter 17. And the above analog
The output signal of the digital converter 17 is 1. [Introduced into the control unit 12.] That is, the control unit 12 has an input interface 12a, an output interface 12b, a data bus 12c, and a ROM1.
2d, RAM 12e, CPU 12f, etc. are prepared, and constitute one microcomputer. The signal output system for air-fuel ratio control is configured as a control system as shown in FIG. That is, when the fuel injection by the injector 6 is interrupted, a signal to switch off the switch mechanism 15 is output from the control unit 12, but at the same time, an offset signal is output to the switch mechanism 15 to measure the offset voltage Vo set by the sensor controller 14. A voltage measuring means 18, a reference voltage calculating means 19 that calculates a voltage value at a stoichiometric point (]!I! stoichiometric air-fuel ratio) from the air-fuel ratio value of a map using a voltage preset in the ROM 12d as a parameter; The error measuring means 20 which compares the reference voltage Vs read out by the calculation means 19 and the offset voltage Vo to obtain the difference value (error) ΔV=Vo−Vs and the switch mechanism 15 are turned on, and fuel injection is started. When the time comes, the air-fuel ratio sensor 11 corrects the output signal from the air-fuel ratio sensor 11 using the difference value ΔV (that is, V-ΔV). As shown in FIG. 4, the control unit 12 first determines in step 5101 whether or not the fuel is being cut, and if the fuel is being cut, the process proceeds to step 8102 and the switch mechanism is activated. 15 off,
In step 5103, offset voltage VO is measured. Then, in step 5104, the voltage VS at the stoichiometric point in the map is calculated, and in step 5105, the offset voltage error ΔV=V. -Measure Vs. Then, the process returns to step 5101, but if it is determined in step 5101 that the fuel is not being cut, the process proceeds to step 8106, the switch mechanism 15 is turned on, and the output voltage V of the sensor 11 is measured in step 5107. Next, in step 8108, the voltage error Δ
(2) is used to calculate v=■-Δ■, and in step 5109, V is used as the measured voltage and checked against the map to determine the corresponding air-fuel ratio.

【Effect of the invention】

The present invention has been described in detail above, and individual errors in the sensor, errors in the interface circuit of the control unit, etc. are determined by comparing the offset voltage during fuel cut with the voltage on the control unit side at the stoichiometric point. The measured value can be corrected using this error. Therefore, in the air-fuel ratio feedback 1li11ra, accurate control can be performed near the stoichiometric air-fuel ratio.

[Brief explanation of the drawing]

Fig. 1 is a schematic configuration diagram showing an embodiment of the present invention, Fig. 2 is a block diagram showing a circuit configuration for incorporating the output of the air-fuel ratio sensor into the control unit, and Fig. 3 is a block diagram showing the circuit configuration for inputting the output of the air-fuel ratio sensor into the control unit. FIG. 4 is a block diagram showing a circuit configuration for correcting the relationship 1111a, FIG. 4 is a flowchart for calculating the air-fuel ratio, and FIG. 5 is a characteristic line diagram of the air-fuel ratio sensor. 6... Injector, 11... Air-fuel ratio sensor, 12
...Control unit, 15...Switch mechanism, 16...Current/voltage converter, 20...Error: [m
Means, 21...Correction means. Patent Attorney Susumu Murai Figure 4 Figure 5

Claims (1)

[Claims] Convert the output current of the air-fuel ratio sensor with a current/voltage converter,
In a device that adds an offset voltage to the voltage value to provide a measured value to the control unit, a switch means for turning off the output of the air-fuel ratio sensor during fuel cut, and an offset voltage is measured when the switch means is in the OFF state. , an air-fuel ratio control comprising: an error measuring means for calculating an error with a voltage corresponding to a stoichiometric point on the control unit side; and a correcting means for correcting the measured value based on the error when the switch means is in the on state. Device.