JPH01185416A - Thermal flowmeter for internal combustion engine - Google Patents

Abstract

PURPOSE:To accurately measure a suction amount of air by eliminating the detection error caused by the back flow of an air stream generated at the time of pulsation, by providing heat generating resistors each composed of a temp.-sensitive resistance film to a substrate on the upstream and downstream sides thereof. CONSTITUTION:A Wheatstone bridge is constituted of the heat generating resistor 11a on the upstream side, the temp. compensating resistor 12a on the upstream side and fixed resistors 13a, 14a, 15a and the potential difference between the middle point of the resistors 13a, 15a and the middle point of the resistors 14a, 11a is detected by a differential amplifier 16a. The signal from said amplifier 16a is inputted to the base of a transistor (Tr) 17a and closed loop control is performed so as to make the potentials at the middle points of the bridge equal. The current allowed to flow to the bridge is controlled by the amplifier 16a and the Tr 17a so as to make the resistance value of the resistor 11a constant regardless of a flow rate. By detecting the current flowing to the resistor 11a as the voltage drop in the resistor 14a, a flow rate of air can be calculated.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a thermal flowmeter for an internal combustion engine that measures intake air jjL of the internal combustion engine.

[Conventional technology]

As an air flow meter for measuring the amount of intake air in internal combustion engines of automobiles, this vane senses the dynamic pressure of the intake air flow with a movable vane and detects the amount of intake air from an electrical signal corresponding to the opening angle of this movable vane. Thermal type flowmeters have been the mainstream, but recently thermal type flowmeters, which have the advantages of small size and high response, have been put into practical use.

FIG. 5 is a plan view showing a flow rate detection section consisting of a thermal flowmeter heating resistor and a temperature compensation resistor in a conventional thermal flowmeter for internal combustion engines disclosed in, for example, Japanese Unexamined Patent Publication No. 56-7018. be. In the figure, reference numeral 1 denotes a thin substrate made of synthetic resin foil, and this substrate 1 is integrally connected to a reinforcing member 2 in terms of material.

The reinforcing plate 2 has holes 3 in the region of the resistors 11 and 12.

This hole 3 reduces the heat capacity and provides a flowmeter with a short response time. Heat generating resistor 11 and temperature compensation resistor 12
is made of nickel foil and is formed by conventional foil deposition and photoetching.

The heating resistor 11 is 1/lo smaller than the temperature compensation resistor 12.
It is designed to have the following resistance value.

The power supply takes place via the connection surfaces 5, 6. Reference numeral 4 denotes an intermediate bridge portion that prevents mutual thermal influence between the heating resistor 11 and the temperature compensating resistor 12.

In the measuring bridge circuit diagram of the flowmeter shown in FIG. 6, the heating resistor 11. Temperature compensation resistor 12 Fixed resistor 13 to 15
Whiston Pritzno is composed of: The output of the Whiston Pritzno is input to a differential amplifier 16, and the output of the differential amplifier 16 is input to the pace of a power transformer 17.

/#The emitter of the power transistor 17 is connected to the input terminal of the whistle transistor 17, and the collector is connected to the power supply.

In addition to the feedback circuit of the differential amplifier 16 and the nosewort transformer 17 in the flow rate measurement circuit configured as described above, the heating resistor 11 is designed so that the intake temperature is constantly raised to a constant temperature. It is configured.

At this time, the current flowing through the heat generating resistor is a function of the flow rate, so the intake air t is detected by the voltage drop across the resistor 14.Generally, a flat plate having a heat generating resistor 11 and a temperature compensation resistor 12 is used. The substrate 1 is arranged parallel to the flow direction of the intake air, and the temperature compensating resistor 12 is placed on the upstream side.

However, a signal substantially equivalent to the flow rate detection signal for one-way flow is also obtained for reverse flow, and conventional thermal flowmeters do not have reverse flow detection means.

In the case of a 4-cylinder engine, in the low rotation output zone,
Intake air pulsates over time, and during overlapping when both the intake valve and exhaust valve are open, air flows back to the intake side due to positive pressure on the exhaust side.

Under such a phenomenon, in the case of a conventional flowmeter, the sum of the flow rate in the reverse direction and the flow rate in the forward direction is detected as Makinto's air flow rate, resulting in a flow rate detection error equivalent to twice the flow rate in the reverse direction. will occur.

[Problem to be solved by the invention]

Conventional thermal flow rate needles for internal combustion engines do not have the above-mentioned backflow detection means, so when the flow in the intake nitrogen pipe is a pulsating flow accompanied by backflow, there is a problem in that a flow rate detection error occurs. .

This invention was made to solve the above-mentioned problems, and provides a thermal flow chamber rrt for an internal combustion engine that can eliminate detection errors caused by backflow of airflow that occurs during pulsation and can accurately measure the amount of intake air. The purpose is to

[Section fMt-Means for solving]

A thermal flow rate needle for an internal combustion engine according to the present invention includes a heating resistor made of a temperature-sensitive resistive film on the upstream and downstream sides of a flat substrate disposed in an intake passage so as to be parallel to the flow; A comparator is provided for electrically determining the amount of heat radiated from the heating resistor and detecting the flow direction of the intake air.

[Effect]

In this invention, the comparator electrically detects the difference in the amount of heat dissipated from each of the heating resistors on the upstream and downstream sides of the flat substrate, and the flow direction is determined. measure quantity.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings. 1st
In the figure, l is a planar substrate made of an electrically insulating material with high thermal conductivity such as ceramic;
There are two heating resistors 11a made of a thin platinum film on the surface of the
, llb are formed by scattering and photoetching.

The heating resistor 11a is formed at a position corresponding to the upstream side of the intake air, and the heating resistor 11b is formed at a position corresponding to the downstream side of the intake air, and a thin film of Attos or Sin is coated on the outer surface. Note that 5.6 is a connection surface between the heating resistors 11a and llb. Further, AI indicates the flow direction of intake air.

The temperature compensating resistor for detecting the intake air temperature is also constructed of similar grosses. The temperature coefficient of resistance of the temperature compensation resistor is the same as that of the heating resistor, and the resistance value is 50% that of the heating resistor.
It is designed to more than double.

FIG. 2 is a perspective view of the thermal flow needle for an internal combustion engine according to the present invention, in which 20 is a pair of support members formed in an "L" shape. This support member 20 is made of an insulating material and is installed parallel to the flow direction A1 of the intake air. A metalized wiring layer 21 is formed on the surface of this support member 200.

On the other hand, 11 is a general term for the heating resistors IIa and llb, and this heating resistor 11 and the temperature compensation resistor 1
2 is brazed onto the wiring layer 21 at its connection surfaces 5 and 6.

Next, a backflow detection method will be explained. The thermal balance equation between the heating resistor and the fluid is given by the following equation.

Q=h, , SΔT Where, Q: Amount of heat dissipated from the heating element, h, II: Average heat transfer coefficient, ΔT: Temperature difference between the heating resistor and the fluid, The heat transfer coefficient is the heat transfer coefficient to the substrate l of the heating resistor. along the streamwise distance N
x and the flow velocity U, for example, the average heat transfer coefficient ht of the heating resistor 11a on the upstream side, the heating resistor 11b on the downstream side
Letting the average heat transfer coefficient of h2 be given by the following equations.

However, j is the length of the heating resistor substrate 1 in the X direction
It is assumed that the heating resistor 11b on the downstream side is formed from 18mX=y to t. Further, A is a constant.

As is clear from the above equation, when the flow rate is constant, hl>ha
Therefore, there are two heating resistors 11a.

Assuming that the area S of 11b and the temperature difference ΔT are equal, the amount of heat radiated from the heating resistor is larger on the upstream side than on the downstream side. Therefore, the flow direction of the intake air can be detected based on the difference in the amount of heat dissipated from both the upstream heating resistor 11a and the downstream heating resistor 11b.

Next, the flow rate and flow direction detection circuit will be explained with reference to FIG. An upstream heating resistor 11a, an upstream temperature compensation resistor 12a, and a fixed resistor 13a.

14a and 15a constitute a Whiston bridge, and a differential amplifier 16a detects the potential difference between the midpoint between the fixed resistors 13a and 15a and the midpoint between the fixed resistor 14a and the heating resistor 11a.

The signal from this differential amplifier 16a is transferred to a transistor 17a.
closed-loop control is performed so that the potential at the midpoint of the above-mentioned Pritsuno is always equal.

The emitter of this transistor i-stor 17a is connected to the connection point between the temperature compensating resistor 12a and the heating resistor 11a, and its flap is connected to the power source.

Similarly, the heating resistor ttb on the downstream side, the temperature compensation resistor 12b on the downstream side, and the fixed resistor 13b.

14b, 15b, a differential amplifier 16b and a built-in transistor 17b constitute a closed loop control circuit.

From the Britsno equilibrium condition, the resistance value R of the heating resistor tta is
H is given by the following equation.

However, RK: resistance value of the temperature compensation resistor 12a, R1;
The resistance value of the fixed resistor 13a, R8; The resistance value of the fixed resistor 15a, R3r The resistance value of the fixed resistor 14a, The resistance value RH of the heating resistor 11a is also 100 at the intake air temperature.
Each Pritsuno midpoint fK is set so that the temperature is higher by ℃, and if the intake air temperature is constant, the resistance 11 Rx of the temperature compensation resistor 12a and the resistance value RH of the heating resistor 11a are constant, and this heating resistance The current applied to the differential amplifier 16a and the transistor 17a is controlled so that the resistance value RH of the body 11a remains constant regardless of the flow rate. Therefore, the current flowing through the heating resistor 11a is controlled by the fixed resistor 14a.
By detecting the voltage drop at , the air flow rate can be determined.

Since the amount of heat dissipated from the heating resistor 11a is equal to the amount of heat generated, the voltage drop Va at the fixed resistor 14a becomes a function of the dissipated heat tQa as shown in the following equation.

On the other hand, since the dissipated heat flQa is given in the form of a function of the flow rate, the air flow rate at the voltage drop va (hereinafter referred to as output voltage) can be detected.

Similar control is performed in the closed loop control circuit including the heating resistor 11b on the downstream side, and the voltage drop vb (hereinafter referred to as output voltage) at the fixed resistor 14b is equal to the dissipated heat 11Q.
It becomes a function of b.

If the circuit constants of both closed loop control circuits are designed to be the same, a difference in the average heat transfer coefficients of both heating resistors will appear in the output voltage Va and vb. In other words, in the case of forward flow, Va > Vb, and in the case of reverse flow, Va (■).Therefore, by inputting both output voltages to the comparator 18 and detecting the output of the comparator 18, the flow direction can be detected. can.

In the above embodiment, the heating resistor 11 and the temperature compensating resistor 12 are each formed on two substrates, but they may be formed on one substrate as shown in FIG. A hole 3 is provided in the center of the substrate 1 to avoid the influence of heat generated by the heating resistor.

Further, in the above embodiment, the case where two heating resistors are formed on the entire substrate of the heating resistor is explained, but the fourth heating resistor is formed on the entire substrate.
The same effect can be obtained by arranging two heat generating resistors in parallel on the upstream and downstream sides of the substrate l even in a part of the substrate as shown in the figure.

〔Effect of the invention〕

As explained above, this invention is configured such that two heating resistors are formed on the upstream and downstream sides of a flat substrate, and the flow direction can be detected from the difference in the amount of heat dissipated from the two heating resistors. This has the effect of obtaining highly accurate measurements of the intake air type of internal combustion engines that are accompanied by backflow.

[BRIEF DESCRIPTION OF THE DRAWINGS] Figure 5g1 is a plan view showing a heating resistor of a thermal flowmeter for an internal combustion engine according to an embodiment of the present invention, and Figure 2 shows a flow rate detection section of the thermal flowmeter of the same embodiment. FIG. 3 is a circuit diagram of the thermal flow meter according to the embodiment shown above, FIG. 4 is a plan view of a heating resistor in another embodiment of the thermal flow meter for an internal combustion engine according to the present invention, and FIG. 1 is a plan view showing a flow rate detection part in a conventional thermal flowmeter for internal combustion engines, and FIG. 6 is a circuit diagram of a conventional thermal flowmeter for internal combustion engines. , connection surface, 11. ll
a, llb...heating resistor, 12, 12a, 12b.
...Temperature compensation resistor, 12a to 15a, 12b to 15
b = fixed resistance, 16m, 16b - differential amplifier, 17a
. 17b...Transistor, 18...Comparator. In addition, in the figures, the same reference numerals indicate the same or equivalent parts.

Claims (1)

[Claims] A heating resistor made of a temperature-sensitive resistive film is formed on the upstream and downstream sides of a flat substrate disposed in the intake passage parallel to the flow of intake air, and each of the upstream and downstream sides A thermal flow meter for an internal combustion engine, comprising a comparator that electrically determines the difference in the amount of heat dissipated from the heating resistor and detects the flow direction of intake air.