JPS6014908Y2 - Intake air amount detection device for internal combustion engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an intake air amount detection device used in a fuel injection device of an internal combustion engine, and more particularly to a fail-safe mechanism in case of a malfunction.

In conventional electronically controlled fuel injection devices, an air flow sensor is usually used to detect the amount of intake air (air flow rate per unit time, hereinafter the same).

However, air flow sensors output an analog voltage signal proportional to the amount of intake air, so as signal processing methods have recently shifted to digital methods using microcomputers, the analog voltage signal can be converted into a digital signal. Therefore, the problem arises that the arithmetic circuit becomes complicated.

Furthermore, since the airflow sensor measures the amount of movement of the flap, it increases intake resistance and is relatively large, which poses a problem in terms of space utilization in the engine compartment.

In order to solve the above problems, it is conceivable to use a sensor that outputs a signal with a frequency proportional to the intake air amount, such as a Karman vortex flowmeter, as the intake air amount detection device.

However, since Karman vortex flowmeters have traditionally been used primarily as measuring instruments, no consideration has been given to a fail-safe mechanism in the event of a failure.

Therefore, when used as an intake air amount detection device for a fuel injection device of a vehicle, if the device were to fail, there was a risk that the engine would stop or operate abnormally, posing a practical problem.

The present invention has been made in view of the above points, and an object of the present invention is to provide an intake air amount detection device that detects failure of a flow meter and issues an alarm, and also outputs a pseudo signal equivalent to a predetermined flow rate even in the event of failure. With the goal.

The present invention will be explained in detail below based on the drawings.

FIG. 1 is a sectional view of an example of a Karman vortex flowmeter used in the present invention.

In FIG. 1, 1 is an air flow tube, 2 is a prismatic or cylindrical vortex generator, 3 is a through hole provided in the vortex generator 2 and perpendicular to the direction of the air flow, and 4 is a through hole provided in the through hole 3. heated wire (
electrical resistance wires), 5 and 6 are Karman vortices.

The generation period of the above-mentioned Karman vortices is determined according to the flow velocity of the air, and the higher the flow velocity, the shorter the generation period.

Furthermore, each time one Karman vortex is generated, air flows through the through hole 3 and takes away heat from the heating wire 4, so the resistance value of the heating wire 4 changes every time a Karman vortex is generated.

By detecting this change, it is possible to detect the generation period of the Karman vortex, that is, the air flow rate.

Next, FIG. 2 is a diagram showing an embodiment of the present invention.

Moreover, FIG. 3 is a signal waveform diagram of the circuit of FIG. 2, and a to f
2 shows signal waveforms at locations designated by the same reference numerals in FIG.

In FIG. 2, R1 is the resistance of the heating wire 4 of FIG. 1, and three resistors B□ to R3 constitute a bridge circuit.

When the unbalanced voltage between the M point and the N point of this bridge circuit is amplified by the differential amplifier 8, a waveform like the signal a is obtained.

The frequency of this signal a is proportional to the air flow rate.

Next, the signal a is applied to the AC amplifier 9 to create a signal of only the AC component, and this is applied to the waveform shaping circuit 10 to obtain a pulse signal C with a frequency proportional to the air flow rate.

On the other hand, the comparator 13 compares the voltage at point M and the reference voltage Vs, and outputs a high level signal when the reference voltage Vs is smaller.

This reference voltage Vs is set to a value slightly lower than the voltage Vo of the power supply 8 of the bridge circuit.

Under normal conditions, the voltage at point M is the power supply voltage Vo and the resistance R□
and R1, which is a value lower than the reference voltage Vs, and the signal d of the comparator 13 becomes a low level.

Therefore, the AND gate 15 is closed and its signal e is at a low level.

Therefore, under normal conditions, the pulse signal C is outputted from the output terminal 12 via the OR gate 11 as the air amount signal f.

Next, when the heating wire shown in FIG. 1 is disconnected, the resistance Rt becomes infinite.

Therefore, the voltage at point M becomes equal to the power supply voltage Vo and is larger than the reference voltage Vs, so the signal d becomes high level.
AND Gate 15 opens.

When AND gate 15 opens, a pseudo signal of a predetermined frequency output from oscillator 14 is output as signal e.

At this time, since the pulse signal c is at a low level, the above signal e is outputted from the output terminal 12 via the OR gate 11 as the air amount signal f.

The frequency of the pseudo signal output from the oscillator 14 is set to a value that allows the driver to notice an abnormality without the engine stopping, for example, a frequency corresponding to the amount of intake air when the engine speed is slightly higher than when idling. Set it.

Further, when the signal d of the comparator 13 becomes high level, the transistor Q1 is turned on and the lambre is turned on to warn of the occurrence of an abnormality.

Although the above-mentioned embodiments have been exemplified using a Karman vortex flow meter, the present invention can also be applied to a case where a hot wire anemometer or the like is used.

In that case, a digital signal or an analog signal is appropriately used as the pseudo signal depending on the output of the flowmeter used.

As explained above, according to the present invention, when a flowmeter fails, it outputs a pseudo signal corresponding to a predetermined flow rate.
There is no fear that the engine will stop, and in the event of a breakdown, the vehicle can be moved to the nearest safe place or repair shop by itself, so the safety and usability of vehicle operation can be improved.

Furthermore, by applying the present invention, it has become possible to put the Karman vortex flowmeter, which has excellent characteristics as a flowmeter, into practical use as an intake air indicator for a vehicle fuel injection system.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of an example of a Karman vortex flowmeter used in the present invention, FIG. 2 is a diagram of an embodiment of the present invention, and FIG. 3 is a signal waveform diagram of the circuit of FIG. 2. Explanation of symbols, 1... Air flow tube, 2...
Vortex generator, 3... Through hole, 4... Heating wire, 5, 6... Karman vortex, 7... Power supply, 8... ... Differential amplifier, 9 ... AC amplifier, 10 ... Waveform shaping circuit, 11 ...
・OR gate, 12... Output terminal, 13...
... Comparator, 14 ... Oscillator, 15 ...
...and gate.

Claims (1)

[Claims for Utility Model Registration] 1. In an intake air amount detection device used in a fuel control device that controls the fuel supply amount using the intake air amount of an internal combustion engine as one of the parameters, the resistance of a heating wire provided in the air flow a flow meter that takes out a change in current or a change in current as a signal; a first circuit that detects a break in the heating wire from an abnormality in the signal; An intake air amount detection device for an internal combustion engine, comprising a second circuit that outputs a pseudo signal. 2 A Karman vortex flow meter with a heating wire as a detection element is used as the flowmeter, and the first circuit is disconnected when the unbalance voltage of the bridge circuit with the heating wire on one side exceeds a predetermined value. An intake air amount detection device for an internal combustion engine according to claim 1, characterized in that the device uses a circuit for determining the amount of air taken into an internal combustion engine.