JPS5942699Y2 - Power control circuit for hot wire current meter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a power supply control circuit for a hot-wire anemometer that measures the flow velocity of a fluid by utilizing the resistance-temperature characteristics of a predetermined metal wire placed in the fluid.

A hot wire anemometer is one of the devices for measuring the flow velocity of a fluid.

This current meter uses a metal wire with a predetermined resistance-temperature characteristic, and when this metal wire is placed in a fluid and a predetermined current is passed through it, the metal wire, that is, the hot wire This method takes advantage of the property that the resistance value changes when cooled.

Hot wire anemometers have a structure in which a metal wire, or hot wire, is exposed in the fluid and is constantly in contact with high-speed fluid, so in order to accurately measure the flow velocity and prevent damage to the hot wire portion, It is necessary to keep the hot wire part clean at all times to prevent an increase in heat capacity and frictional resistance with the fluid.

For this purpose, an effective method is to increase the temperature of the hot wire portion at the end of the velocity measurement and burn off the foreign matter adhering to the hot wire portion to remove it.

In particular, when using a hot-wire current meter to measure the intake air flow rate of an internal combustion engine, there is a high probability that the intake air is contaminated with dust, etc., and foreign matter tends to adhere to the hot wire, so it is necessary to increase the reliability of flow velocity measurement. Therefore, it is necessary to burn off the foreign matter by passing a current through the hot wire as described above other than when the internal combustion engine is running, and in particular, it is necessary to run such a current immediately when the internal combustion engine is stopped, that is, immediately after the flow velocity has ended. is preferred.

An object of the present invention is to provide a power supply control circuit for a hot-wire anemometer that can temporarily supply a predetermined voltage to the hot-wire anemometer after the end of flow velocity measurement by the hot-wire anemometer.

The present invention will be described in detail below with reference to the drawings.

FIG. 1 shows a block diagram of an embodiment of a power supply control circuit for a hot-wire anemometer according to the present invention.

As shown in the figure, this hot wire anemometer power supply control circuit has a first switching circuit 2, a comparator 3, a second switching circuit 4, a charge/discharge circuit 5, and a feedback resistor 6, and has a predetermined value. The power supply is configured to output an output voltage VOUT to be supplied to the hot wire via the second switching circuit 4.

Further, from this power source, a system voltage VSY8 is outputted via a system switch 1 to drive parts other than the power supply control circuit for the hot-wire current meter, such as a starter device 9 in an internal combustion engine, an ignition device, a fuel supply device, etc. It looks like this.

One terminal of the first switching circuit 2 is grounded, and the other terminal is connected to the charging/discharging circuit 5. When a predetermined control voltage is input through the system switch 1, both terminals are brought into conduction. Ru.

The output of the charging/discharging circuit 5 is connected to a comparator 3, which also receives a predetermined reference voltage ref, and compares it with this reference voltage Vref. The output current is generated only when the output voltage is small.

The output current of the comparator 3 is input to a second switching circuit 4, which turns on and off the current supplied from the power supply to control the hot wire drive voltage VOUT.

In other words, only when an output current is generated in the comparator 3', the second switching circuit 4 is turned on and the hot wire drive voltage VOUT
occurs.

Further, this hot wire drive voltage VOUT is input to the charge/discharge circuit 5 via a feedback resistor 6 having a predetermined resistance value.

Next, the operation of this circuit will be explained.

First, when the system switch 1 is turned on, the system voltage supplied to each device is generated.
At the same time, this voltage turns on the first switching circuit 2, and the terminal to which the charge/discharge circuit 5 is connected is electrically connected to the single-power terminal, that is, the ground terminal, and the potential at this point is zero.

Therefore, when the charging/discharging circuit 5 is in the discharge state, the voltage input to the comparator 3 is smaller than the predetermined reference voltage Vref,
An output current flows from the comparator 3 to the second switching circuit.

Therefore, the second switching circuit is turned on and the hot wire drive voltage V 1 is generated.

This causes heat UT The linear current meter becomes operational.

At this time, the output current of the second switching circuit 4 is supplied to the charge/discharge circuit 5 via the feedback resistor 6, but since the feedback resistor 6 has a predetermined resistance value, the charge/discharge circuit 5 The potential at the input end of remains zero.

As long as the system switch 10 remains on, the system voltage Vs y s and the hot wire drive voltage 6d are supplied, and the hot wire type anemometer enters the operating state.

Next, when the system switch 1 is turned off, the system voltage is first turned off and the control voltage of the first switching circuit 2 becomes zero, so that the first switching circuit 2 is turned off.

As a result, the input terminal of the charging/discharging circuit 5 connected to the first switching circuit 2ttc is not grounded.

As a result, the hot wire driving voltage ■ is applied via the feedback resistor 6 connected to this part.

Current begins to be supplied by the UT.

This current gradually charges the capacitor C of the charging/discharging circuit 5, and the potential at the output end connected to the comparator 3 rises.

When the potential at this point rises and exceeds the reference voltage V r e f , the output current of the comparator 3 is turned off.

As a result, the second switching circuit is turned off, and the output voltage, that is, the hot wire drive voltage ■.

UT becomes zero, the heating state of the hot wire of the hot wire anemometer ends, and all devices come to a halt.

A time chart of the output voltage of this circuit in each of the above steps is shown in FIG.

As shown in this figure, at the time when the system switch 1 is turned on, that is, at time to, the system is
and hot wire drive voltage■.

UT occurs. In this case, there is a slight time lag from when the system switch 1 is turned on until the second switching circuit 4 is turned on and generates the hot wire drive voltage VOUT, but the second switching circuit is composed of a relay. In the case of a transistor, this time difference is on the order of several m8ee, but in the case of a transistor, it is as fast as several μsec.

The next time the system switch is turned on, that is, time 1.
, the system voltage VSYS becomes zero, but the hot wire drive voltage VOUT continues to occur.

That is, charging of the charging/discharging circuit 5 is started from this time t1, and only when the output potential of this circuit is delayed by a predetermined reference voltage VrefK, the second switching circuit is turned off and the supply of the hot wire drive voltage V is stopped. .

The time from UT tl to t2, that is, Δt, is the time during which voltage is applied to the hot wire after the flow velocity measurement by the hot wire current meter is completed.

The length of Δt can be arbitrarily set by changing the constant of the charging/discharging circuit 5.

When the flow state of the fluid to be measured in the hot wire anemometer is turned on and off by the device driven by the system voltage VSYS, the movement of the fluid around the hot wire stops at time t1.

Therefore, the heat generated in the hot wire by the hot wire drive current is not released, so the temperature of the hot wire increases, and the deposits can be burned off and removed.

After such a cleaning action is performed for a certain period of time, the driving voltage of the hot wire is turned off.

Since the power supply control circuit for a hot-wire anemometer according to the present invention operates as described above, it is particularly suitable for use in a hot-wire anemometer for measuring the intake air flow rate of an internal combustion engine.

Furthermore, in a device where the fluid flow does not stop at the time t1 when the system voltage Vsys becomes zero, the above purifying effect will not work, but in that case, the voltage Vi at the input terminal of the charging/discharging circuit 50 is A predetermined high-voltage power source is controlled by the hot wire, and a voltage from the high-voltage power source is applied to the hot wire between times t1 and t2 to heat the hot wire and exert a cleaning action.

Next, FIG. 3 shows an embodiment of the power supply control circuit for a hot-wire anemometer according to the present invention.

This circuit has the same configuration as the block diagram described above, and the operation of this circuit will be explained in detail.

The first switching circuit 2 consists of a transistor T1 and a bias resistor R1 when the system switch 1 is turned on.
A base current is supplied to this transistor T1 through
turns on and collector current flows.

A charging/discharging circuit 5 consisting of a variable resistor R and a capacitor +jC is connected to the collector of the transistor T1 via a diode D2.

Further, a resistor and a diode D3 are connected in parallel to the variable resistor R in order to increase the discharging speed of the charging/discharging circuit T.

Next, the comparator 3 is composed of transistors T2 and T3, and the output of the charging/discharging circuit 5 is inputted to the base of the transistor T2 via a resistor RI O,
A reference voltage ref given by resistors R14 and R15 is input to the base of 3.

Since these transistors T2 and T3 work differentially, T2
If T3 is off, T3 is on.

Further, the collector of the transistor T3 is connected to the base of the transistor T4 of the second switching circuit 4 via a resistor R□6.

Transistors T4 and T5 are Darlington connected and are turned on by the collector current of transistor T3, generating a power voltage .

With the above configuration, when the UT system switch 1 is turned on, each part operates in sequence and the transistor T5 is turned on, and the power supply voltage vcc supplied to the collector side of T5 is outputted to the emitter side, producing the output voltage VOUT. .

In addition, in order to speed up the rising speed at this time, it is recommended to connect the collector of the transistor T□ and the base of the transistor T4 with a resistor R7. In this case, the transistor T
A collector current of 1 can turn on transistors T4 and T5.

Next, when the system switch 1 is turned off, the base current of the transistor Tl is cut off, so that the transistor T1 is turned off.

At this time, a diode T is connected to the collector of the transistor T1.
The input terminal of the charging/discharging circuit connected through 2 is connected to the emitter of the transistor T5 of the second switching circuit 4 through the feedback resistor R'. A current flows and the potential of the + side terminal of the capacitor C rises.

Accordingly, the base potential of the transistor T2 of the comparator 3 gradually rises, and when it becomes higher than the base potential of the transistor T3, that is, Vref, the transistor T2 is turned on and the transistor T3 is turned off.

Therefore, since the collector current of the transistor T3 is connected, the transistors T4 and T of the second switching circuit 4 are connected.
5 is turned off and the output voltage ■.

UT gets zero.

With the above configuration, it is possible to turn off the second switching circuit 4 after a predetermined period of time has passed after the system switch 1 is turned off.

Further, when applying a voltage to the hot wire using a separate high voltage power source as described above, the control voltage Vi for this high voltage power source can be taken out from the collector portion of the transistor Tl via the resistor R5.

In the embodiment described above, the comparator 3 is constituted by individual transistors T2 and T3, but it is also possible to use an operational amplifier in this part.

[Brief explanation of drawings]

Fig. 1 is a block diagram of an embodiment of the hot-wire type flow velocity related power supply control circuit according to the present invention, Fig. 2 is a time chart showing the output voltage of the circuit illustrated in Fig. 1, and Fig. 3 is according to the present invention. FIG. 2 is a circuit diagram of an embodiment of a hot-wire type flow velocity-related power supply control circuit. Explanation of symbols of main parts: 1...System switch, 2...First switching circuit, 3...
... Comparator, 4 ... Second switching circuit, 5 ... Charge/discharge circuit, 6 ... Feedback resistor.

Claims (1)

[Scope of utility model registration request] a first switching circuit that is turned on when one power terminal is grounded and a predetermined braking voltage is input; a charging/discharging circuit coupled to the other power terminal of the first switching circuit; a comparator that compares the output voltage of the circuit with a predetermined reference voltage; and a second switching device that is switch-controlled by the output voltage of the comparator and outputs a voltage supplied from a predetermined power source to supply a driving voltage for the hot wire. 1. A power supply control circuit for a heat/wire current meter, comprising: a circuit; and a feedback resistor for guiding the output voltage of the second switching circuit to the charging/discharging circuit.