JPS6273124A - Heat type flow rate detector - Google Patents

Abstract

PURPOSE:To detect reverse flowing in the operating region of an engine in a low rotary-output zone, by arranging two heating resistors so as to face each other along a flow, and detecting the reverse flow based on the magnitude of an electric signal corresponding to the flow rate. CONSTITUTION:A first heating resistor 1 is a heat sensitive element obtained by forming a platinum thin film on a cylindrical ceramic bobbin. A second heating resistor 2 has the same characteristics and the same configuration. The resistors 1 and 2 are both arranged approximately vertically with respect to the direction of a flow 5. Temperature compensating resistors 3 and 4 are further provided. The calorific values of the two heating resistors 1 and 2 are compared 10 and the forward or reverse direction of the flow 5 is judged. The heating resistors having the same configuration and the same characteristics are used and controlled at the same heating temperature by amplifiers 7 and transistors 6. The calorific value in the first heating resistor 1 or the second heating resistor 2 is measured and the flow rate is obtained. By comparing the calorific values of both resistors, the flowing direction can be detected at the same time.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a thermal flow rate detector used, for example, to measure intake nitrogen gas introduced into a cylinder of an engine.

[Conventional technology] Is there an engine control function recently? For the purpose of improving the performance, a microcomputer is used to perform comprehensive old control of the Nen Engine.
3) Intake air #L view is a representative parameter.

Conventionally, it has been possible to reduce costs by using a so-called hot-ray weighted sensor as a sensor for increasing the amount of intake air into the engine, and the nonlinearity of its output characteristics has the characteristic of completely equalizing relative errors and allowing a wide dynamic range. known to be desirable.

[Problem that the invention seeks to solve]

The hot wire flow sensor described above operates accurately and has a satisfactory function for detecting the intake air flow rate during steady engine running and cruising. In the low rotational output zone of a small engine, there are no problems. That is, in this simple example, the amount of air sucked into the engine pulsates over time, resulting in the strange pulsating waveform shown in FIG. Also, the movement of the airflow is different when the intake and exhaust valves of the engine overlap and when only the intake valve is open, and when the intake and exhaust valves overlap, the intake pipe side is As a result, the pressure increases, and an air flow in the opposite direction is generated, as shown by the line in FIG.

This phenomenon occurs in different forms, such as the shape of the engine's combustion chamber, the shape of the intake and exhaust pipes, and the shape of the air cleaner.
00 rpm) and negative suction pressure of 100 mmH9 or less. For such backflow pulsating flow, the output of the conventional hot wire flow rate sensor becomes a J-shaped waveform as shown in Figure 4, and since there is no way to detect the entire backflow, it is difficult to detect the true amount of air. I can't. In other words, the air flow rate signal is configured so that it can only receive a signal in one direction (9W), regardless of whether it is in one direction or in the opposite direction, so during a pulse with full blowback, the intake air amount can be measured accurately. Problems that can't be done are rare.

This invention has a total of 711 problems as mentioned above!1. The overall purpose is to obtain a thermal flow rate detector that can detect all the backflow that occurs during pulsation, eliminate calibration errors due to backflow, and perform accurate flow rate detection.

[Ninth method to solve all problems A]

The thermal flow rate detector related to this light QJj is installed in the fluid passage, and a VC second heating resistor is disposed opposite the first heating resistor in the wave flow of the first heating resistor, 1 of each heating resistor! In addition to controlling the output current, it is equipped with a nine-output drive circuit and a ratio device to compare both output currents.

[Effect]

In the thermal flow rate detector according to the present invention, the magnitude relationship of the average heat transfer coefficients between the two heating resistors and the fluid is reversed depending on the flow direction.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings. 1st
In the figure, 1 is a first heat-generating resistor, which is a temperature-sensitive element formed entirely of a platinum thin film on a cylindrical ceramic bobbin, and 2 is a first heat-generating resistor.
A second heating resistor having the same characteristics and the same shape as the heating resistor 1 is disposed close to the downstream side so as to face the first heating resistor 1. 3 and 4 are temperature compensation resistors.

Each resistor is arranged substantially perpendicular to the direction of flow 5.

General 1. Conditions of error, 2. Calorific value P of the heating resistor
is given by the following equation.

P"hm"s'(THTa, :i "Pa""
(1) Here, hm; average heat transfer coefficient S between the heating resistor and the fluid; surface area TH of the heating resistor; temperature Ta of the heating resistor; S fluid temperature Po: amount of heat generated when the flow rate is zero; The average heat transfer coefficient hm is the mainstream velocity tlQ
It is expressed as a function of

hm=C-uo"" (2) where C and n are constants that depend on the physical properties of the fluid and the relative potential relationship of the two heating resistors.

Next, by substituting equation (2) into equation 't (1), P-Cuo
nS(TH-Ta) 1Po... (3),
By controlling the temperature difference between the heating resistor and the fluid to keep it constant and measuring the total amount of heat generation P, the main speed UO can be found.

Now, regarding the first heating resistor 1 and the second heating resistor 2 (3
) formula, each amount of light P'' and P2 are the total number of feet CI, C! Close P+ = C+ ・uon &SI#
(, TRI Ta) -” Poi Fu Pz= Cz 1luon11sz(To2 Ta)
``Poz... (4) Given by: 2 heating resistors with the same shape and the same characteristics?Since two heating resistors are used, if the temperature difference between the heating resistor and the fluid is set equal, each The difference in the amount of light is given by the following equation.

P+ Pz=(CI Cz)・uon where A=
81CTHI Ta) = Sz (TH2Ta)
(5) Distance between the axes of the two heat generating resistors 'L L, total diameter d of the heat generating resistors, and UfCI+ Cz where the flow is in the forward direction in the range of 3≦L/d≦9. The size relationship of CI>CI
”... (6).

At the time of backflow, the relationship in equation (6) is reversed, and CI>Cz...-(7). Therefore, compare the amount of heat generated by the two heating resistors, and if Pz>P+, proceed in the forward direction of the flow9, P! <P
If IC+, it can be determined that the flow is in the opposite direction. Furthermore, since the two heating resistors have the same shape and characteristics, I
The relationship between the amount of heat generated by the first heating resistor and the main flow velocity in the E4 direction matches that of the second heating resistor in the opposite direction. So, in particular, when L/d≦9, is it better than in range 1 when L/d>9? This is because there is no difference in the flow behavior between the fj-side heating resistor and the downstream-side heating resistor, and the time difference between the two flow velocity detection points becomes a problem.

Therefore, using two heating resistors with the same shape and characteristics,
By controlling the heat generation temperature to be the same and measuring the heat generation amount in the first heating resistor 1 or the second heating resistor 2, the current t' can be determined, and at the same time, the heat generation in the sheet resistor (c) can be determined. By comparing the amounts, the flow direction can also be detected.

FIG. 2 shows a C* circuit of a heating resistor with a backflow detector. The circuit shown in Figure 2 has a wheat strike/bridge configuration consisting of each resistor: heating resistor 1 (straddle 2), temperature compensation resistor 3 (-i ta 4), and fixed resistor 9, and the midpoint Detection is performed by a differential amplifier circuit using a potential difference amplifier 7.The output of this amplifier 7 is input to the base of all transistors 60, and the potential at the midpoint of the bridge is always equal. Electrical bits are supplied through the bridge equilibrium condition 9, and the resistances fw and RH of the heating resistor, which is connected to the flow rate detection resistor, are expressed by the following equations.

Here, P+ + Rt r Rs : Resistance value of the fixed resistor Rc : Resistance value of the temperature compensation resistor Both Rn and Re show temperature dependence, and when the fluid temperature rises, the resistance value of Re also increases accordingly. is increased to compensate for the effect of increased fluid temperature.

Also, if the fluid temperature is constant, Rc is constant! l, RH
The amplifier γ operates to control the current flow to the bridge so that the value remains constant regardless of the magnitude of the flow rate. If the current flowing through the heating resistor is 'tI, then heat generation... (1
0) Therefore, by measuring this potential, the flow velocity uo and flow rate are determined.

Each of the heating resistors 1 and 2 is connected to the Wheatstone bridge circuit shown in FIG. 2, and flow rate signals a and b corresponding to the respective heat generation amounts P+ and Pz are output. These flow rate signals a and b are also connected to the input terminal of the voltage comparator 10, and when the first flow rate signal a is greater than the second flow rate signal, the output signal of the voltage comparator 10 is
9, when the second flow rate signal is larger than the first flow rate signal a, the above output becomes logic [L].

The electrical signals a, b, and c are omitted in the diagram, but are connected to a well-known microprocessor, and when the signal c is logic "H", it is detected that there is a reverse flow, and the second flow signal is generated. seek,
When the signal C is logic 1 to LJ, the amount of the forward direction θ can be determined.

In addition, in the above-mentioned Example "c", the ratio of the distance between the axes of the heating resistor and the outer diameter d of the heating resistor was shown in the range of -3≦L, /'d≦9, but 1 <iL/'d In the range <3, there is a difference in the uniform heat transfer coefficients of the two heating resistors, so it is possible to reverse the flow in the same way.

In addition, in the above implementation example, the entire flow f signal of the heating resistor on the upstream side is measured as a flowmeter signal, but the same effect as in the above embodiment can be obtained by calculating the total flow rate from the fklk signal of the heating resistor on the downstream side. play.

〔Effect of the invention〕

As described above, according to the present invention, the two heating resistors are disposed opposite to each other along the flow, and the configuration is such that all 19 backflows can be detected based on the magnitude relationship of the electric signal corresponding to the flow rate. Backflow that tends to occur in the engine's low rotational output zone? Even in the accompanying pulsating intake state, by correcting the flow rate by narrowing the reverse flow, the effect of accurately detecting the amount of intake air taken into the engine at the time of combustion is Δ).

[Brief explanation of drawings]

Fig. 1 is a configuration diagram showing an example of the flow rate detection section of a thermal flow rate detector according to one embodiment of the present invention ff1J, shown in purple, and Fig. 2 converts the signal from the heating resistor ρ into an electric signal corresponding to the flow TFC. In addition, a circuit diagram for detecting backflow, Fig. 3 is a diagram showing all the changes in intake air amount over time when intake pulsation is bad, and Fig. 4 (-S, a conventional thermal flow rate detector for the pulsating flow shown in Fig. 3). 1 is a diagram showing all flow rate signals of 1...first heating resistor, 2...second heating resistor, 3...first temperature compensation resistor, 4...first 2 Temperature compensation resistor, 5... Current, 6 φ... Transine, 7... φ - Amplifier, 8... Power supply, 9...
・Fixed resistor, 10... Voltage comparator.

Claims (3)

[Claims] (1) A first heating resistor installed in the fluid passage to sense the flow rate; and a first heating resistor disposed in the fluid passage downstream of the first heating resistor to sense the flow rate and facing the first heating resistor. A second heating resistor to sense, a drive circuit unit that controls the current of each heating resistor and takes out the output current of each heating resistor as a signal corresponding to the flow rate, and a comparison that receives the signal corresponding to each flow rate as input. A thermal flow rate detector characterized by comprising: (2) the first heating resistor and the second heating resistor have the same shape;
The thermal flow rate detector according to claim 1, which has the same characteristics. (3) The first and second heating resistors have the same cylindrical shape, and the ratio of the distance L between the axes of the two heating resistors to the diameter d of each heating resistor is within the range of 1 to 9. A thermal flow rate detector according to claim 1, characterized in that: