JPH01232143A - Air-fuel ratio control device for internal combustion engine - Google Patents

Abstract

PURPOSE:To contrive the improvement of safety by stopping electrification to a heater decided to be abnormal unless an oxygen concentration detecting element increases its temperature to not less than the predetermined value even after the predetermined time electrifying the heater. CONSTITUTION:A CPU16, when it detects an engine for its cold start by a signal or the like of a water temperature sensor 2, electrifies a heater in an air-fuel ratio sensor 8 from a voltage stabilizer circuit 14. A temperature increases, when an oxygen concentration detecting element is activated, a voltage signal in accordance with oxygen concentration is output from an air fuel ratio control circuit 13, and a feedback control of air-fuel ratio in accordance with this air-fuel ratio signal is performed. Here even after the predetermined time from electrification of the heater, when an element temperature, detected by a built-in temperature sensor in the air-fuel ratio sensor 8 and an amplifier, is not increased to the predetermined temperature or more, the CPU16 detects the heater to be in abnormality, stopping the electrification to the heater while turning on an indicator lamp informing the abnormality. In this way, the improvement of safety can be contrived.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] This invention relates to an air-fuel ratio control device for an internal combustion engine.

[Conventional technology]

Internal combustion engines, especially vehicle engines that use three-way catalysts to purify exhaust gas, must maintain the air-fuel ratio of the exhaust gas strictly at the stoichiometric air-fuel ratio, and currently the output rapidly increases at the stoichiometric air-fuel ratio. An air-fuel ratio control device that performs feedback control using an air-fuel ratio sensor that changes the air-fuel ratio so that the air-fuel ratio becomes close to the stoichiometric air-fuel ratio has been put into practical use.

However, the above-mentioned air-fuel ratio control device has a drawback that the range of control is narrow because the air-fuel ratio sensor can only measure the stoichiometric air-fuel ratio. Therefore, attempts have been made to control the air-fuel ratio using an air-fuel ratio sensor that can continuously measure the air-fuel ratio from the lean side to the rich side according to not only the stoichiometric air-fuel ratio but also a specific component of the exhaust gas. This air-fuel ratio sensor includes an oxygen concentration detection element made of an ion-conducting solid electrolyte and a heater that activates the element.

In the air-fuel ratio control device described above, the air-fuel ratio sensor does not operate normally unless the oxygen concentration detection element of the air-fuel ratio sensor is heated by a heater and maintained at a predetermined temperature.

[Problem to be solved by the invention]

However, in the conventional apparatus described above, abnormalities such as disconnections and short circuits may occur in the heater (including connectors, electric wires, etc.), and there is no means for detecting heater abnormalities in such cases. Therefore, not only was there a lack of safety, but also a large amount of power was wasted in the event of a short circuit.

This invention was made to solve the above-mentioned problems, and its purpose is to obtain an air-fuel ratio control device for an internal combustion engine that can reduce power consumption and improve system safety. .

[Means to solve the problem]

The air-fuel ratio control device for an internal combustion engine according to the present invention includes a temperature detection means for detecting the temperature of an oxygen concentration detection element of an air-fuel ratio sensor, and a temperature of the oxygen concentration detection element that reaches a predetermined temperature or more after a predetermined time elapses after the heater is energized. The heater abnormality detecting means detects an abnormality in the heater when the heater is abnormal, and the heater energization stopping means stops energization to the heater in the event of an abnormality in the heater.

[For production]

The temperature detection means in this invention detects the temperature of the oxygen concentration detection element of the air-fuel ratio sensor. The heater abnormality detection means detects a heater abnormality when the element temperature does not exceed a predetermined temperature even after a predetermined period of time has elapsed after the heater was energized. The heater energization stopping means stops energization to the heater when an abnormality occurs in the heater.

〔Example〕

In Fig. 2, 1 is an engine, 2 is a water temperature sensor that detects the cooling water temperature of the engine 1, 3 is a crank angle sensor that detects the engine speed, 4 is an injector (fuel supply device), 5 is a throttle valve, and 6 is a This is a pressure sensor that measures the absolute pressure of the intake system.

An air-fuel ratio sensor 8 is disposed in the exhaust pipe 7 and detects the air-fuel ratio based on a specific component in the exhaust gas, and includes an oxygen concentration detection element and a heater that heats the element to a predetermined value. 9 is an intake air temperature sensor that measures intake air temperature; 10 is each sensor 2;
, 3, 6, 8.9, and controls the injector 4. The control circuit is composed of a microcomputer. 11 is electric power B (battery).

The device shown in Figure 2 is a so-called DJ system device,
The basic injection pulse time is calculated based on at least the output value of the pressure sensor 6 and the rotation speed information obtained from the crank angle sensor 3, and correction is performed using the outputs of the water temperature sensor 2 and intake temperature sensor 9, transient correction, and air-fuel ratio sensor 8. Feedback correction and the like are performed to determine the fuel injection pulse time.

FIG. 3 is a block diagram showing details of the control circuit 10,
16 is a CPU that performs calculations and control; 17 is a ROM with a built-in program; 1 is a RAM that temporarily stores data; 19 is a RAM that is always energized and stores data; 12 is an A/D converter. 13 is an air-fuel ratio sensor control circuit that controls the output of the air-fuel ratio sensor 8 so as to obtain an output proportional to the air-fuel ratio; 14 is a constant voltage applied to the heater for heating the oxygen concentration sensor built in the air-fuel ratio sensor 8; 15 is an I10 device (input/output device), 20 is a pass line connecting each component, 21 is an air-fuel ratio sensor 8
A temperature sensor amplifier 30 detects the temperature of the oxygen concentration detection element 30, which receives the output of the I10 device 15 and is an indicator lamp that informs the driver of a heater abnormality. Water temperature sensor 2
, the output of the air-fuel ratio sensor via the pressure sensor 6, amplifier 21, intake temperature sensor 9 and air-fuel ratio sensor control circuit 13 is input to the A/D converter 12, and the output of the crank angle sensor 3 is input to the I10 unit 15. Sent. Injector 4 is I10
It receives input from the CPU 16 via the device 15. Further, the constant voltage circuit 14 receives the output from the battery power source 11 and outputs it to the heater of the air-fuel ratio sensor 8 and the like. The indicator lamp 30 also receives the output from the I10 device 15 and indicates a heater abnormality.

The first part is a specific configuration diagram of the main parts of the device of the present invention. It is composed of a heater 24 that heats the oxygen concentration detection element consisting of an oxygen concentration battery section 23, a temperature sensor 26 that measures the temperature of the oxygen concentration detection element, and a sensor case 25 that supports these on the wall of the exhaust pipe 7. Ru. Temperature sensor 26 is formed by embedding a thermocouple in ceramic. The air-fuel ratio sensor control circuit 13 includes an operational amplifier 27, a voltage-current converter 28, a current-voltage converter 29, and the like.

Next, the operation of the configuration shown in FIGS. 1 and 3 will be explained. The oxygen concentration battery section 23 generates an electromotive force according to the difference in oxygen concentration between the atmosphere and the exhaust gas, and this electromotive force is compared with a reference voltage in an operational amplifier 27, and a voltage-current converter 28 is activated according to the difference. The pump current IF is supplied to the oxygen pump section 2 through
2.

This pump current 1. is converted into a voltage by the current-voltage converter 29 and output to the A/D converter 12 as an air-fuel ratio signal. The output characteristics are shown in FIG. Further, the temperature of the oxygen concentration detection element is measured by a temperature sensor 26 and inputted to the A/D converter 12 via the amplifier 21.

FIG. 4 shows a flowchart of the processing executed according to the program stored in the ROM 17, in which step 100
In step 101, the engine speed is read from the output of the crank angle sensor 3. In step 101, the intake pipe pressure is read from the output of the pressure sensor 6. In step 102, the cooling water temperature from the output of the water temperature sensor 2 and the output of the intake air temperature sensor 9 are read. Read the intake temperature. In step 103, a basic fuel injection pulse width is calculated from the engine speed and intake pipe pressure, and step 1
In 04, this is corrected by the water temperature and intake air temperature. In step 105, it is determined whether energization of the heater 24 has started. If it has not been started, a counter value T0 is set in a counter T at step 106. This counter value T
0 is subtracted by one in the routine shown in FIG. 5, which is executed at regular intervals. If the heater 24 has started to be energized, the process advances to step 107. In step 107, it is determined whether or not the count value is 0. If the count value is 0, the predetermined energization time has elapsed, so in step 108, the heater temperature tM is read from the output of the temperature sensor 26, and in step 109, the heater temperature tM is read from the output of the temperature sensor 26. , I is lower than a predetermined temperature t11. If it is smaller, it is determined that the heater 24 is abnormal, the heater 24 is turned off in step 110, and the indicator lamp 30 is turned on in step 111. In step 112, the injector 4 is driven in an open loop using the fuel injection pulse width obtained in step 104. or,
Even if the counter T is not O in step 107, the injector 4 is driven in an open loop with the pulse width obtained in step 104 in step 112. This is because since the energization time of the heater 24 has not reached the predetermined time, it is determined that the oxygen concentration detection element of the air-fuel ratio sensor 8 is not sufficiently heated. In step 109, the heater temperature is 1. is the predetermined value 1. If the temperature exceeds the above, it is determined that the heater 24 is normal, and in step 113, the air-fuel ratio sensor 8
In step 114, a target air-fuel ratio is calculated according to the operating state of the engine. In step 115, a correction coefficient for the fuel injection pulse width is calculated based on the deviation between the target air-fuel ratio and the actual air-fuel ratio, in step 116, the pulse width is corrected using this correction coefficient, and in step 112, the injector 4 is adjusted based on the corrected pulse width. Feedback control.

[Effects of the Invention] As described above, according to the present invention, when the temperature of the oxygen concentration detection element does not exceed the predetermined time after the heater is energized and the temperature of the oxygen concentration detection element does not exceed the predetermined time, an abnormality in the heater is detected and the heater is not energized. This makes it possible to improve safety and reduce power consumption in the event of a short circuit.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of the main parts of the device of this invention, FIG. 2 is a diagram of the overall structure of the device of this invention, FIG. 3 is a block diagram of a control circuit according to the invention, and FIGS. 4 and 5 are diagrams of the device of this invention. A flowchart showing the operation, and FIG. 6 is an output characteristic diagram of the air-fuel ratio sensor. DESCRIPTION OF SYMBOLS 1... Engine, 2... Water temperature sensor, 3... Crank angle sensor, 4... Injector, 6... Pressure sensor, 8... Air-fuel ratio sensor, 9... Intake temperature sensor,
DESCRIPTION OF SYMBOLS 10... Control circuit, 11... Power supply, 13... Air-fuel ratio sensor control circuit, 22... Oxygen pump part, 23...
- Oxygen concentration battery section, 24... Heater, 26... Temperature sensor. Note that the same reference numerals in the figures indicate the same or equivalent parts.

Claims (1)

[Claims] An internal combustion system that detects the air-fuel ratio according to specific components in exhaust gas using an air-fuel ratio sensor that has an oxygen concentration detection element and a heater that heats the element to a predetermined temperature, and performs feedback control of the fuel supply device to maintain the predetermined air-fuel ratio. In an engine air-fuel ratio control device, there is a temperature detection means for detecting the temperature of an oxygen concentration detection element, and a heater abnormality for detecting a heater abnormality when the temperature of the oxygen concentration detection element does not exceed a predetermined temperature after a predetermined period of time has passed after the heater is energized. An air-fuel ratio control device for an internal combustion engine, comprising a detection means and a heater energization stopping means for stopping energization to the heater in the event of a heater abnormality.