JPS63129152A - Abnormality detector for hot-wire air flow meter - Google Patents

Abstract

PURPOSE:To improve decision accuracy of abnormality and to perform a backup function, by providing a temperature compensating cold wire of a hot-wire air flow meter and setting another cold wire to a position, where no wetness or the like by water in an intake system is generated, for the temperature compensating cold wire so that the abnormality is decided by output levels of both the above described wires. CONSTITUTION:A hot-wire air flow meter 10, if it generates wetness or the like by water, large changes a resistance value of a cold wire 14 in the flow meter generating a difference between the cold wire 14 and another cold wire 20, and this causes abnormality to be immediately decided. And a backup function in this case obtains an intake amount of air by using a map or the like through an engine speed and a throttle valve opening so as to normally inject fuel.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to an abnormality detection device for a hot wire air flow meter used in an electronic fuel injection tJ4 device for a vehicle engine. This concerns self-diagnosis and backup.

In recent years, in electronic fuel injection IJJ devices, a hot wire type current meter has been used instead of a flap type as a sensor for measuring the amount of intake air. This hot wire type has the advantages of avoiding pulsating waves in the intake system because it does not create resistance to the intake air, and is compact.
Because the cold wire for temperature compensation is installed directly in the airflow, breakdowns and malfunctions may occur.

One of the reasons is that when the wire A1 becomes wet, the value of the wire resistance decreases significantly due to cooling, so that the value of the amount of intake air determined by the flowmeter output becomes larger than the value of the actual amount of intake air. Then, by injecting fuel according to the amount of intake air determined by the flowmeter output, the air-fuel mixture becomes over-enriched, causing engine malfunction and deterioration of emissions. Therefore, it is necessary to install a backup system in advance as a countermeasure against such abnormalities.

[Prior Art] Conventionally, there is a prior art technique disclosed in Japanese Patent Application Laid-open No. 57-131832, for example, regarding countermeasures against abnormalities in the above-mentioned hot wire air flow meter. Here, it is shown that failure or malfunction is determined by detecting that the output level of the flowmeter has reached an abnormal value, and in this case, air flow agitation is detected using the suction pipe negative pressure.

[Problems to be Solved by the Invention] By the way, in the configuration of the prior art described above, since the determination is made only based on the output level of the flowmeter, the abnormality determination level becomes extremely large when various situations are taken into consideration. . Therefore, the accuracy of the judgment is poor, and the backup may not function if there is a slight abnormality.

Next, since the suction pipe negative pressure is used as a backup,
There are problems such as the need for a highly accurate negative pressure detector.

The present invention has been made in view of the above points, and is designed to improve the accuracy of abnormality determination and to easily and reliably perform backup air volume detection using existing sensor signals. The purpose is to provide a detection device.

[Means for Solving the Problems 1] In order to achieve the above object, the present invention provides a cold wire for temperature compensation of a hot-wire air flow meter, in which another cold wire is installed at a location where the intake system will not become wet with water. A backup function is provided by determining abnormalities based on the output levels of both cold wires. The backup function is configured to determine the amount of intake air based on the engine speed and throttle valve opening.

[Function] Based on the above configuration, when the hot wire air flow meter gets wet, the resistance value of the cold wire becomes thick (changes, causing a gap between it and other cold wires 7, Immediately determine the abnormality.And in this case, for backup,
The amount of intake air is determined using a map or the like based on the engine speed and throttle valve opening, and the fuel is injected normally.

Thus, in the present invention, it is possible to determine an abnormality with high accuracy from the output levels of the hot wire air flow meter and other cold wires, and to perform an accurate backup function.

[Example] Embodiments of the present invention will be described below based on the drawings.

Referring to FIG. 1, an electronic fuel injection engine will be briefly described. An air cleaner 1 communicates with a throttle chamber 3 via an intake pipe 2, and the throttle chamber 3 communicates with an engine body 5 via an intake manifold 4. A multi-point injector 7 is provided downstream of the throttle valve 6, and a three-way catalytic converter 9 for purifying exhaust gas is provided in the exhaust pipe 8.

As a control system, a hot wire air flow meter 10 is provided immediately downstream of the air cleaner 1, and this hot wire air flow meter 10 has a bypass 12 for the main nozzle 11, and a hot wire 13 and a cold wire 14 are connected to the bypass 12. will be exposed and installed. The control unit 15 utilizes the fact that when the hot wire 13 is heated by passing a current through it, the resistance value changes due to cooling by the air flow, and a bridge circuit is configured with both wires 13 and 14, so that the air flow velocity, that is, the mass flow ff1
Calculate Q.

Air mQ of such air flow meter 10, crank angle sensor 1
6 engine speed N, throttle opening sensor 17 and 0
The signals from the two sensors 18 are input to the control unit 19.

A fuel injection signal is then output from the control unit 19 to the injector 7 to inject a predetermined amount of fuel.

On the other hand, as a countermeasure against abnormalities in the air flow meter 10, another temperature compensation cold wire 720 is installed inside the air cleaner 1 at a position where there is no risk of water getting wet.

The output signals of this cold wire 20 and the cold wire 14 of the air flow meter 10 are input to the control unit 19 for self-diagnosis of abnormalities and backup functions.

In FIG. 2, the control unit 19 will be explained.

First, the fuel injection control system will be explained. It has an engine rotation speed input section 21 from the crank angle sensor 16 and an air input section 22 from the air flow meter 10, and these signals N,
Q is input to the basic injection pulse width calculation section 23, and the pulse width Tp is determined based on Q/N.

The pulse width Tp, throttle opening θ, O2 sensor signal, and correction signal are input to the fuel injection pulse width controller 24 to determine the final pulse width T1, and the drive unit 25 generates a fuel injection signal according to the pulse width T1. Output.

On the other hand, the abnormality countermeasure control system has a resistance value calculating section 26,27 into which the signal of the cold wire 14. When the output difference between ti11 and R11Rt exceeds a certain value α, that is, when IRI−R11≧α, it is determined that the sensor is wet. The air amount setting unit 29 is provided with a map of air fltQ'' depending on engine speed N and throttle opening θ.
′ is searched and output. Further, a switching section 30 is provided on the output side of the air amount input section 22, and is configured to switch between Q and Q' based on the determination result of the water wetness determining section 28.

Next, the operation of the abnormal lightning detection device configured as described above will be explained. First, when the air flow meter 10 is normal, the transient conditions of the #A degree compensation cold wire 14 and the other cold wires 20 are the same.

Therefore, the resistance values R1 and Rz determined by the resistance value calculation unit 26.27 become 1Rt−R11<α, and the water wetness determination unit 28 determines that the resistance values are normal, and the switching unit 30 switches the input unit 22 from the air. Switch to input IIQ. Therefore, the optimal fuel injection amount is determined by the fuel injection pulse width calculation section 24 based on the air flQ from the air flow meter 10, the engine speed N, and other correction signals, and fuel is injected from the injector 7 based on this.

On the other hand, when the air flow meter 10 gets wet, the water adheres to the temperature compensation cord wire 14 and is cooled by the latent heat of vaporization, so that the resistance value R1 of the resistance value calculation unit 26 is determined to indicate that there is no water leakage. The value is smaller than normal. Therefore, a large output difference occurs between the resistance value R1 of the other cold wire 2° that is not wet, and the resistance 1 series Rz, Rz is lR1-R2+≧
α, so that the water-wetting determination unit 28 determines that the water is wet. In this case, the air ff1Q' determined by the map search using the engine speed N and throttle opening θ in the air amount setting section 29 is input from the switching section 30 to the basic injection pulse width calculation section 23, so that the backup function is performed. become. In this way, the erroneous measurement value of the air amount Q by the air flow meter 10 is canceled, and the fuel injection 1ffi becomes suitable for the engine operating conditions.

When the water wetness is resolved and the water wetness determination unit 28 determines that the air is normal, the switching unit 30 again takes in the air 1iQ signal from the air flow meter 10 and returns to the original state.

The present invention has been described above in the case where the present invention is applied to troubles related to water leakage of hot wire air flowmeters, but it can be similarly applied to troubles other than water leaks.

[Effects of the Invention] As described above, according to the present invention, in abnormality determination of a hot wire air flow meter, a cold wire for transient compensation that changes only depending on the air temperature is used, and other cold wires of the same type are used. Since the determination is made by comparing with the wire, it is possible to quickly determine abnormality with high accuracy.

In addition, this determination allows for accurate backup 1M, thereby preventing engine malfunction and deterioration of emissions.

With the backup function, engine speed and throttle w
Since the air volume is set by ri, control becomes easier.
A dedicated sensor such as a negative pressure detector becomes unnecessary.

[Brief explanation of the drawing]

FIG. 1 is an overall configuration diagram showing an embodiment of an abnormality detection device of the present invention, and FIG. 2 is a block diagram of a control system. 10... Hot wire air flow meter, 14.20... Cold wire, 19... Control unit, 26.27...
Resistance value calculation section, 28...Water wetness determination section, 29...Air amount setting section, 3o...Switching section.

Claims (2)

[Claims] (1) In addition to the temperature compensation cold wire of the hot-wire air flowmeter, install another cold wire in a place where the intake system will not get wet, and determine whether there is an abnormality based on the output level of both cold wires. , an abnormality detection device for hot wire air flowmeters with backup function. (2) In the backup function, an abnormality detection device for a hot wire type air dragon meter according to claim 1, in which the amount of intake air is determined based on the engine speed and the throttle valve opening.