JPH0812095B2 - Intake air amount detector for internal combustion engine - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an intake air amount detection device for an internal combustion engine, and more particularly to a technique for improving output voltage characteristics at the start of energization.

<Prior Art> Conventionally, in an internal combustion engine equipped with an electronically controlled fuel injection device, as a flow rate measuring device used for measuring an intake air amount, there is a hot wire type flow meter as shown in FIG. (See, for example, Kaikai 64-50323).

That is, in the drawing, the heat ray resistance 1 and the heat ray resistance 1 as a heat generating resistor which is interposed in the intake passage and constitutes the sensor unit.
A bridge circuit is formed by the temperature compensating resistor 2, the flow rate adjusting resistor 3 and the output resistor 4 which are arranged in the same atmosphere as
The current supplied to this bridge circuit is the differential amplifier 5 and the power transistor 6 for inputting the potentials at points a and b in the figure.
Is controlled according to the change of the intake air flow rate.

Then, for example, if the intake air flow rate, that is, the intake air flow velocity increases, the cooling degree of the heat wire resistance 1 increases and the resistance value thereof tends to decrease, but at this time, the potential at the point a increases and the differential amplifier 5 Output is reduced. As a result, the collector current to the power transistor 6 increases and the supply current from the power source UB such as a battery to the bridge circuit increases, so that the heat generation amount of the heat wire resistor 1 can be increased and the resistance value can be kept constant. Controlled to keep on. Therefore, for example, the intake air flow rate can be read from the output voltage Vs of the output resistor 4.

<Problems to be Solved by the Invention> By the way, in a flow meter including a heating resistor such as a hot wire type flow meter as a sensor unit, constant resistance control is performed, and therefore, as shown in FIG. In addition, when the power is turned on (when the ignition switch is turned on), a large current flows until the heat wire resistance 1 reaches a constant temperature (power-on characteristic), and the following problems occur.

That is, when the ignition switch is OFF, the resistance value of the heat wire resistance 1 is small, so that the maximum voltage is applied to the bridge circuit until the power transistor 6 is in the saturation region when the ignition switch is ON. That is, the output voltage of the hot-wire flow meter suddenly rises, the temperature of the hot-wire resistance 1 which was approximately 20 to 30 ° C becomes 260 ° C, and the drive capability of the power transistor 6 becomes full at a certain output voltage.
The output voltage is slightly decreased by entering the saturation region of the power transistor 6, then becomes the active region of the power transistor 6, the output voltage is rapidly decreased, and the output voltage is gradually decreased at a certain output voltage point. Stabilizes to a constant output voltage.

Therefore, it takes about 8 to 10 seconds until the output voltage of the flow meter becomes constant after the ignition switch is turned on, that is, before the final reaching point a in the figure is reached.

When the hot-wire flow meter changes the output voltage as described above when the engine is started, detection is performed that is different from the actual intake air flow rate when the engine is started. Therefore, for example, when restarting during warm-up, when there is no increase correction due to water temperature, that is,
When the fuel injection amount is substantially determined according to the output of the hot wire type flow meter, the mixture ratio is shifted to the rich side as shown in FIG.

As a result, the mixing ratio at the start cannot be obtained properly,
There was a problem that startability deteriorates.

Note that, in FIG. 5, the portion b indicates the maximum cut portion of Tp (basic fuel injection amount).

Therefore, in view of the above conventional problems, the present invention,
By improving the power-on characteristics of a flow meter such as a hot wire type, the purpose is to optimize the mixing ratio at the start and improve the startability.

<Means for Solving the Problem> Therefore, the intake air amount detection device for an internal combustion engine of the present invention is configured such that a heating resistor which is interposed in the intake passage to form a sensor unit and the heating resistor in the same atmosphere. Intake air flow rate detection of an internal combustion engine in which a bridge circuit is formed by a temperature compensation resistance, a flow rate adjustment resistance and an output resistance, and the current supplied to the bridge circuit is controlled according to the change of the intake air flow rate. The apparatus is provided with a means for applying electric energy required as a pulse determined by a function of the battery voltage and time until the output voltage reaches the final reaching point after turning on the ignition switch.

<Operation> In such a configuration, by applying a pulse, a large current from a power source such as a battery flows to the bridge circuit instead of the constant resistance control. The voltage stabilizes instantly.

The pulse width of the above pulses may be determined as a function of only battery voltage and time.

In this way, the output voltage of the flowmeter stabilizes instantly when the ignition switch is turned on, and as a result, the time to reach the final reaching point can be shortened, so that the proper mixing ratio at engine startup can be obtained. It is possible to improve the property.

<Example> Hereinafter, an example of the present invention is described based on a drawing.

In FIG. 1, a hot-wire type flow meter as an intake air flow rate detecting device of the present invention includes a hot-wire resistor 1 as a heat-generating resistor which is interposed in an intake passage and constitutes a sensor unit, and the hot-wire resistor 1
A bridge circuit is formed by the temperature compensating resistor 2, the flow rate adjusting resistor 3 and the output resistor 4 which are arranged in the same atmosphere as
The current supplied to this bridge circuit is the differential amplifier 5 and the power transistor 6 for inputting the potentials at points a and b in the figure.
The configuration controlled by the change of the intake air flow rate by
It is the same as the conventional one.

In such a hot wire type flow meter, at the time of starting, instead of the conventional constant resistance control, the electric energy required from the output of the flow meter to the final reaching point after the ignition switch is NO is expressed by a function of battery voltage and time. Means are provided for applying as a pulse to be determined.

 Such means is configured as follows.

That is, in the figure, a transistor 7 is connected to the output terminal of the differential amplifier 5, and a predetermined pulse width T, that is, a pulse of a predetermined time is input to the transistor 7 from the microcomputer 9 of the control unit 8. .

Then, at the time of starting, the transistor 7 is turned on by inputting a pulse of a predetermined width to the transistor 7, and the output terminal voltage of the differential amplifier 5 becomes low level, which increases the collector current of the power transistor 6. A large current from the power source UB such as a battery instantly flows to the bridge circuit.

That is, since a large current from the power source UB such as a battery flows to the bridge circuit regardless of the differential of the power transistor 6, the heating current control by the pulse of FIG. 3 is different from the conventional heating current control of FIG. Therefore, the output voltage of the flow meter stabilizes instantly.

In this case, if equal to the S ₁ of FIG. 2 and S ₂ of FIG. 3 of this configuration is a conventional example, the electrical energy amount is equal.

Here, a method of determining the pulse width T of the pulse will be described.

That is, as a parameter of the amount of electric energy described above,
These include:

VB (battery voltage) Q (air flow rate) ta (ambient temperature) And the amount of temperature change of the heat wire resistance 20 ℃ (normal temperature) to 240 ℃
Considering the above, and considering the transition to the constant resistance control after starting, the influence of the ambient temperature ta can be eliminated.

That is, m · C (θ-ta), where m mass C specific heat θ heat wire temperature, and air flow rate Q is 0 kg / h at startup (before cranking).
You can think of it as (natural convection only).

Therefore, the pulse width of the electric energy may be determined as a function of only the battery voltage VB and the time (T), and the pulse width T may be determined by the following equation.

Here, the above Coef is the time set at the experimental level, and VB is the current, that is, the battery voltage when the ignition switch is ON.

As described above, at start-up, instead of the conventional constant resistance control, the electrical energy required for the output of the flowmeter to reach the final reaching point after turning on the ignition switch is determined by a function of battery voltage and time. As described above, since the output voltage of the flowmeter is instantly stabilized when the ignition switch is turned on and the time required to reach the final reaching point can be shortened, as shown in FIG. 5c. By performing such a mixture ratio control, the mixture ratio at the time of starting can be appropriately obtained, and the startability can be improved.

<Effect of the Invention> As described above, according to the present invention, the electric energy required for the output of the intake air flow rate detection device to reach the final reaching point from the ignition switch ON is determined by a function of the battery voltage and time. Since it is configured to be applied as a pulse, the output voltage of the flow meter is instantly stabilized when the ignition switch is turned on, the time to reach the final reaching point can be shortened, and a proper mixing ratio at start can be obtained. Therefore, it is very useful that the startability can be improved.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, FIGS. 2 and 3 are control characteristic diagrams of a conventional and the present invention, FIG. 4 is a circuit diagram showing a conventional example, and FIG. It is a characteristic view which shows a problem. 1 ... Heat ray resistance, 2 ... Temperature compensation resistance, 3 ... Flow rate adjustment resistance, 4 ... Output resistance, 5 ... Differential amplifier, 6 ... Power transistor, 7 ... Transistor, 8 ... Control unit, 9 ... Microcomputer

Claims (1)

[Claims] 1. A bridge circuit is formed by a heating resistor interposed in an intake passage to form a sensor unit, and a temperature compensation resistor, a flow rate adjusting resistor and an output resistor which are arranged in the same atmosphere as the heating resistor. Then, in the intake air amount detection device of the internal combustion engine, which controls the supply current to the bridge circuit according to the change of the intake air flow rate, until the output voltage reaches the final reaching point after turning on the ignition switch. An intake air amount detecting device for an internal combustion engine, comprising means for applying necessary electric energy as a pulse determined by a function of battery voltage and time.