JP2690655B2 - Thermal air flow meter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal air flow meter for detecting the intake air flow rate of, for example, an engine.

[0002]

2. Description of the Related Art Conventionally, as a heat type air flow meter, there is known a heat generating resistor for measuring an air flow rate in which a film type resistor is formed on a plate-shaped base such as ceramic or metal.

This type of heat generating resistor generally has a heat generating resistor arranged in an air passage in a cantilever structure. Further, as disclosed in, for example, JP-A-62-36521,
As a heat escape measure for preventing a decrease in responsiveness, a heat insulating member may be interposed between the heat generating resistor and the holding member,
As disclosed in Japanese Laid-Open Patent Publication No. 226016, there has been proposed one in which a heating resistor is supported by a supporting element protruding into an air passage in order to prevent damage due to a drop or a collision impact.

[0004]

As described above, in the thermal type air flow meter using the plate-shaped heating resistor, the total length of the heating resistor is increased when the variation in response and output characteristics is improved. It is a general method to form a thin plate to have a cantilever structure.

However, if the supporting method of the heating resistor is simply a cantilever structure, there is a limit to the degree of freedom in terms of overall length, plate thickness, etc. in order to secure mechanical strength. Therefore, it is necessary to consider vibration resistance for transmission, and there is a dimensional limitation for that.

The present invention has been made in view of the above points, and an object thereof is to increase the degree of freedom of a heating resistor to maintain good responsiveness and output characteristics, and at the same time, have a cantilever structure of a cantilever structure. To provide an air flow meter.

Another object is to provide a cantilever type thermal air flow meter which improves response and detection accuracy without using the heat insulating member as described above.

[0008]

In order to achieve the above object, the present invention basically proposes the following problem solving means.

[0009] One is a thermal air flow meter provided with a heating resistor arranged in an air passage for measuring an air flow rate, and a control module for controlling a current flowing through the heating resistor and outputting a detection signal. In the above, the heating resistor is formed by forming a film type resistor on the surface of a plate-shaped base, and the supporting member that cantilevers the heating resistor is a reinforcing member that applies the vicinity of the supported portion of the heating resistor. Is provided, and the length and thickness of the heating resistor protruding from the reinforcing member are set so that the natural frequency of the heating resistor is higher than the vibration range generated by the automobile engine. To solve the problem).

The other is that at least one surface of the heating resistor similar to the first problem solving means except the film type resistor has a film-shaped organic substance (synthesized) on the entire surface or in the vicinity of the supported portion of the heating resistor. The one coated with a resin is proposed (this is the second means for solving the problem).

Another is to propose a reinforcing member similar to the first problem solving means, which is provided with a heating resistor for suppressing heat escaping from the heating resistor for measuring the air flow rate. (3) means for solving the problems).

[0012]

Operation of the first problem-solving means: Since the reinforcing member is applied to the heating resistor, the mechanical strength of the heating resistor is strengthened even if it has a cantilever structure, but the heat generation which is the base of the heating resistor. When the heating resistor vibrates, the boundary between the resistor and the reinforcing member serves as a fulcrum, so that fatigue over time easily occurs.

However, in the present invention, the length and thickness from the tip of the heating resistor to the tip of the reinforcing member are set so as to be higher than the vibration range generated in the automobile engine. It does not resonate due to vibration and enhances vibration resistance, and prevents the above-mentioned vibration from causing fatigue over time and eventually breaking. Note that the natural frequency of the heating resistor becomes higher as the length becomes shorter and the thickness becomes thicker (the detailed calculation formula is shown in the embodiment).
In order to maintain good responsiveness and output characteristics, the degree of freedom in design such as lengthening the heating resistor to some extent is required. The present invention can satisfy this condition for the following reasons.

That is, since the heating resistor has a cantilever structure via the reinforcing member, the length of the heating resistor is apparently
Since the length from the resistor tip to the reinforcing portion tip is short, it is easy to design a high natural frequency, while the actual length of the heating resistor is from the support member tip to the heating resistor tip (in other words, to the reinforcing member). The actual length expands the degree of freedom because it can be set to the applied part).

Operation of the second means for solving the problems: When a method of coating at least one surface of the heating resistor (the surface excluding the portion having the membrane resistance) with an organic substance is used as the reinforcing member, the reinforcing member generates heat resistance. It becomes a part of the thickness of the body and raises the natural frequency of the heating resistor above the engine vibration range. Further, since the reinforcing member has elasticity, even when the heating resistor is made of a brittle material, the reinforcing member has a cushioning function to improve vibration resistance and shock resistance.

Function of the third problem-solving means: By appropriately heating the reinforcing member, the temperature difference between the heating resistor and the reinforcing member is reduced, and the heat generated by the heating resistor is applied to the reinforcing member. At the same time as blocking the conduction, since the reinforcing member and the supporting member are adjacent to each other, the thermal conduction to the supporting member can also be blocked.
Improves responsiveness and detection accuracy.

[0017]

BRIEF DESCRIPTION OF THE DRAWINGS FIG.

FIG. 1A is a front view of a thermal air flow meter according to a first embodiment of the present invention, FIG. 1B is a perspective view showing a cantilever structure of a heating resistor used in the same, and FIG. It is sectional drawing of the heating resistor.

As shown in FIG. 1 (a), the body 1 of the thermal air flow meter has an air passage (main passage) 5 for flowing the air supplied to the engine of the automobile and an air passage for measuring the air flow rate. A sub passage 6 is provided, and a heating resistor 3 for detecting an air flow rate and a temperature sensing resistor 4 for temperature compensation for detecting an air temperature are arranged in the sub passage 6.

The signals detected by the heat-generating resistor 3 and the temperature-sensitive resistor 4 are input to the control module 2 provided on the outer periphery of the body 1 so as to output an electric signal corresponding to the air flow rate.

The heating resistor 3 is formed by depositing a film type resistor (resistance pattern) 9 on the surface of a rectangular plate-shaped base 8 made of ceramic (alumina dielectric) as shown in FIG. 1B. The heating resistor 3 is supported by the supporting member 10 made of synthetic resin in a cantilever structure.

Reference numeral 7 denotes a glass reinforcing member, which is a heating resistor 3
7'is formed to match the width and the plate thickness of the heating resistor 3, and the vicinity of the supported portion of the heating resistor 3 is fitted into and joined to the groove 7 '. The vicinity of the location is configured to be applied by the reinforcing member 7 made of glass. The heating resistor 3 and the reinforcing member 7 combined in this manner are embedded in the supporting member 10 by being embedded in the step of molding the supporting member 10 made of synthetic resin.

A conductor pattern 11 is formed on the support member 10 by copper plating and constitutes a part of the control module 2. The conductor pattern 11 is electrically connected to the heating resistor 9 via the flexible wire 12. Here, the control module 2 includes a heating resistor 3 (membrane type resistor 9).
The heating current is controlled to flow through the heating resistor so that the temperature difference between the temperature sensing resistor 4 and the temperature sensing resistor 4 becomes constant.

The reinforcing member 7 in this embodiment reinforces the heating resistor 3 that is cantilevered. Further, the apparent length of the heating resistor 3 is shortened so that its natural frequency is the vibration of the automobile engine. Care is taken to make it easier to set higher than the range.

Here, the vibration f of the simple cantilever bar is
Young's modulus, second moment of area, specific gravity, sectional area, length, and plate thickness of the rod are E, T, ρ, A, 1, and h, respectively, and the circular constant, vibration coefficient, and gravitational acceleration are π, λ, respectively. If g, then it is expressed by the following equation.

[0026]

(Equation 1)

When a ceramic plate (alumina) is used for the cantilever, T = 3.47 × 10 ⁶ kgf / cm ² , ρ
= 3.8 × 1/10 ³ kg / cm ³ . Further, the vibration coefficient λ becomes 1.875 in the cantilever first-order mode, and by substituting these and g = 981 cm / s ² , the vibration frequency f ≧
The plate thickness h of 1000 Hz and Δl (where Δl is shown in FIG.
As shown in FIG. 2, the distance from the tip of the reinforcing member 7 to the tip of the heating resistor 3 is Δl = l ₁ −l ₂ ) in FIG.

[0028]

(Equation 2)

From the above, as parameters for determining the vibration frequency f, there are Δl and plate thickness h. In general, an automobile engine has a rotation speed of 6000r when considering up to the fifth high frequency.
It produces a vibration of about 1000 Hz at pm. Therefore,
If the natural frequency of the heat generating resistor 3 is 1000 Hz or less, the heat generating resistor 3 may be damaged due to resonance with the automobile engine. Therefore, in the present embodiment, the natural frequency of the heating resistor 3 is set to 1000 Hz or higher, and for example, Δl and h that satisfy this are as shown in the following table from the above equations. The characteristic as shown in FIG. 3 is obtained, and the shaded portion is the region where the natural frequency is 1000 Hz.

[0030]

[Table 1]

In this embodiment, the heating resistor 3 has a width of 3.0 m.
The length is 10 mm and the thickness is 0.15 mm.

According to this embodiment, since the reinforcing member 7 is applied to the heating resistor 3, the mechanical strength of the heating resistor 3 is strengthened even if it has a cantilever structure, and the heating resistor 3 is affected by engine vibration. Vibration resistance is enhanced without resonance, fatigue over time due to the above-described vibration is suppressed, and damage to the heating resistor 3 due to vibration is prevented. In addition, since the length of the heating resistor 3 apparently extends from the tip of the resistor 3 to the tip of the reinforcing member 7, it is easy to design a high natural frequency, and in addition, the actual length l ₁ of the heating resistor 3 is increased. Can extend from the tip of the supporting member 10 to the tip of the heat generating resistor 3, so that the degree of freedom in length can be widened, and the responsiveness and output characteristics of the heat generating resistor can be kept good.

FIG. 4 is a partial perspective view showing a second embodiment of the present invention. The same reference numerals as those used in the first embodiment denote the same or common elements (note that the reference numerals in other drawings are also the same. is there).

In this embodiment, the reinforcing member 7 for the heating resistor 3 is formed in a frame shape in which the surface of the heating resistor 3 on which the film resistor 9 is formed and the opposite surface and the four side surfaces are applied. Become. With such a reinforcing structure, when the heating resistor 3 receives vibration, the natural frequency can be reliably increased, and the vibration resistance can be further improved.

FIG. 5 shows a reinforcing member 7 according to a third embodiment of the present invention.
Is a plate-shaped member or a rod-shaped member, and the reinforcing member 7 is provided in a rib shape on the surface of the heating resistor 3 opposite to the surface on which the film resistor 9 is formed. According to this embodiment, the same effect as that of the first embodiment can be obtained, and since the reinforcing member 7 has a simple structure,
Manufacturing costs can also be reduced.

FIG. 6 shows a reinforcing member 7 according to a fourth embodiment of the present invention.
Is formed of a plate-shaped member, and is laminated on the surface of the heating resistor 3 opposite to the surface on which the film resistor 9 is formed. According to this embodiment, in addition to the same effect as the third embodiment,
Since the entire heating resistor 3 is reinforced in the width direction, there is an advantage that the force that the heating resistor 3 receives from the reinforcing member 7 due to vibration can be dispersed.

FIG. 7 shows a fifth embodiment of the present invention, which is a reinforcing member 7.
Is formed by an L-shaped plate member, and this is bonded to the surface of the heating resistor 3 opposite to the surface on which the film resistor 9 is formed. According to the present embodiment, the stress exerted on the reinforcing member 7 due to vibration is dispersed due to the L-shaped shape effect.
Even if the thickness is reduced, the same effect as the third embodiment can be sufficiently obtained.

FIG. 8 shows a sixth embodiment of the present invention. The reinforcing member in the present embodiment is formed of a film-shaped organic material 7a unlike the above-described embodiments, and this reinforcing member 7a is formed on the entire surface opposite to the surface on which the film resistor 9 of the heating resistor 3 is formed. The structure is covered over.

According to the present embodiment, the reinforcing member 7a becomes a part of the thickness of the heating resistor 3 to increase the natural frequency of the heating resistor above the engine vibration range. When the heating resistor 3 formed of a brittle material receives an impact force, the reinforcing member 7a
Acts as a cushioning material, which has the effect of improving the shock resistance of the thermal air flow meter.

FIG. 9 shows a seventh embodiment of the present invention, in which the reinforcing member 7 is integrally formed by molding using the same material as the supporting member 10. According to this embodiment, the material cost and the processing cost of the reinforcing member 7 can be reduced.

FIG. 10 shows an eighth embodiment of the present invention, in which the reinforcing member 7 is made of a metal material and is bonded to the surface of the heating resistor 3 opposite to the side where the film type resistor 9 is formed to have a low thermal conductivity. It is a structure in which members 13 are attached to each other. According to this example, the moldability of the reinforcing member 7 is good, and the reinforcing member 7
Even if a metal material is used for the above, the heat dissipation of the heat generating resistor 3 can be suppressed by the heat insulating effect of the adhesive member 13, and the deterioration of the sensor responsiveness can also be prevented.

FIG. 11 shows a ninth embodiment of the present invention, in which the reinforcing member 7 is made of a ceramic material having a low thermal conductivity, and in addition to vibration resistance, the heat insulating effect of the ceramic material prevents a decrease in responsiveness. it can.

FIG. 12 shows a tenth embodiment of the present invention, in which (a) is a view of the support structure of the heating resistor as seen from the back side, and (b) is a sectional view taken along the line AA. In the present embodiment, the heat generating resistor 14 for suppressing heat escaping from the heat generating resistor 3 is provided on the surface of the reinforcing member 7 which is not in contact with the heat generating resistor 3. The heat generating resistor 14 is formed on the surface of the reinforcing member 7 opposite to the joint surface of the heat generating resistor 3 by a film type resistor.

FIG. 13 shows an example of a drive circuit for the thermal air flow meter of this embodiment. In the figure, the power transistor Tr1,
Resistances Rh1 (heating resistor 3), R1, R2, R3, Rc
(Temperature compensation resistor 4), R7, operational amplifier OP1, OP2
Is a component of a heating current control circuit for measuring the air flow rate, reference numeral 17 is a drive circuit of the heating resistor 14 provided in the reinforcing member 7, and the circuit 17 shares the power supply with the air flow rate measurement circuit, the resistor R11 and the zener. Diode ZD1, resistor R1
2, 13 and the operational amplifier OP3 constitute a constant voltage circuit, and the constant voltage circuit 17 has an output stage with a heating resistor 14 (Rh
2) is electrically connected and a constant voltage is constantly applied to the heating resistor 14
Is applied to heat the reinforcing member 7.

In this case, the amount of heat applied to the reinforcing member 7 via the heating resistor 14 is such that the temperature gradient between the heating resistor 3 and the reinforcing member 7 is reduced.

FIG. 14 shows comparative data when the heating resistor 14 is provided on the reinforcing member 7 and when it is not provided.

The surface temperature distribution of the heating resistor 3 is as shown by the dotted line when the heating resistor (hereinafter referred to as a heating portion) 14 is not added to the reinforcing member 7. Air flow rate Q = 10kg / h
At this time, the difference between the temperature T ₂ of the l ₀ part and the support member 10 is the amount of heat escape. When the heating portion 14 is added to the reinforcing member, the surface temperature distribution becomes as shown by the solid line. Thereby, the reinforcing member 7
Since the temperature gradient between the heating resistor 3 and the heating resistor 3 is small, the amount of heat escaped to the support member 10 is small. Also, the heating resistor 3
If the temperature T1 at the l ₂ position is set among the maximum heat generation temperatures of 1, the characteristic influence degree due to heat conduction to the heat generating resistor 3 is small even when the air flow rate increases.

According to this embodiment, it is possible to suppress the escape of heat from the heating resistor 3 to improve the sensor responsiveness and further improve the weighing accuracy.

FIG. 15 shows an eleventh embodiment of the present invention. In this embodiment, the heating temperature sensing resistor 18 is provided in parallel with the heating unit 14. 15 is a conductive pattern, 16
Is a wire. FIG. 16 shows the control circuit 17 '.

A heating resistor Rh3 serving as the heating unit 14, a heating temperature sensing resistor 18 (Rs1), and resistors R14 and R15.
A bridge circuit is configured by the above, and the reinforcing member 7 is heated to a constant temperature via the bridge circuit, the operational amplifier OP4, and the power transistor Tr2 to reduce the temperature gradient with the heating resistor 3, and thus, with high accuracy. It is possible to control heating to prevent heat escape.

The control circuit of the heating unit 14 may be set so that the current value (heating temperature) changes according to the temperature of the heating resistor 3 for measuring the air flow rate. Prevention can be performed more accurately.

[0052]

According to the first and second means for solving the problems, the sensor response and the output characteristic are favorably maintained, and the vibration generated by the automobile engine is reinforced while the mechanical strength of the heating resistor used for this is reinforced. Since the resonance can be reliably prevented, it is possible to provide a thermal air flow meter having excellent vibration resistance.

According to the third means for solving the problem, the heat escaping from the heat generating resistor to the reinforcing member and the supporting member can be suppressed, so that the heat generated in the heat generating resistor is surely transferred to the air flow, so that the responsiveness is improved. It is also possible to provide a highly accurate thermal air flow meter.

[Brief description of the drawings]

FIG. 1 is a front view of a thermal type air flow meter according to a first embodiment of the present invention and a perspective view showing a supporting structure of a heating resistor used in the same.

FIG. 2 is a sectional view of a main part of the above embodiment.

FIG. 3 is a characteristic diagram showing the relationship between the length Δl, the thickness h, and the natural frequency of the heating resistor used in the above embodiment.

FIG. 4 is a perspective view of an essential part showing a second embodiment of the present invention.

FIG. 5 is a perspective view of an essential part showing a third embodiment of the present invention.

FIG. 6 is a front view of a main portion showing a fourth embodiment of the present invention.

FIG. 7 is a front view of an essential part showing a fifth embodiment of the present invention.

FIG. 8 is a perspective view of essential parts showing a sixth embodiment of the present invention.

FIG. 9 is a cross-sectional view of essential parts showing a seventh embodiment of the present invention.

FIG. 10 is a sectional view of an essential part showing an eighth embodiment of the present invention.

FIG. 11 is a cross-sectional view of essential parts showing a ninth embodiment of the present invention.

FIG. 12 is a rear view of a main part and a sectional view of the main part showing a tenth embodiment of the present invention.

FIG. 13 is an explanatory diagram showing a drive circuit of a tenth embodiment.

FIG. 14 is a temperature distribution characteristic diagram of a heating resistor for explaining the effect of the tenth embodiment.

FIG. 15 is a rear view of the essential parts showing the eleventh embodiment of the present invention.

FIG. 16 is an explanatory diagram showing a drive circuit for heating resistance of a reinforcing member of an eleventh embodiment.

[Explanation of symbols]

1 ... Body, 2 ... Control module, 3 ... Heating resistor, 4
... Temperature compensation resistance (temperature sensitive resistor), 5 ... Main air passage, 6 ...
Sub air passage, 7 ... Reinforcing member, 7a ... Reinforcing member (covering member), 8 ... Base, 9 ... Thin film resistance (heating resistance), 10 ...
Support member, 14 ... Exothermic resistance for heating reinforcing member, 17, 1
7 '... Drive circuit for heating the reinforcing member.

 ─────────────────────────────────────────────────── ─── Continuation of front page Examiner Yoshitaka Harita (56) References JP-A-61-186819 (JP, A) JP-A-62-36521 (JP, A) JP-A-2-249921 (JP, A) Special Features Kaihei 4-122818 (JP, A) JP-A-2-226016 (JP, A) JP-A-1-318923 (JP, A)

Claims (8)

(57) [Claims] 1. A thermal air flow meter comprising: a heating resistor arranged in an air passage for measuring an air flow rate; and a control module for controlling a current flowing through the heating resistor and outputting a detection signal. The heating resistor is formed by forming a film type resistor on the surface of a plate-shaped base, and a supporting member that cantilevers the heating resistor is
A reinforcing member is provided that applies the vicinity of the supported portion of the heating resistor, and the length of the heating resistor protruding from the reinforcing member,
A thermal air flow meter, wherein the thickness is set so that the natural frequency of the heating resistor is higher than the vibration range generated in an automobile engine. 2. The thermal air flow meter according to claim 1, wherein the reinforcing member is made of a material having a low thermal conductivity. 3. A thermal type air flow meter, comprising: a heating resistor arranged in an air passage for measuring an air flow rate; and a control module for controlling a current flowing through the heating resistor and outputting a detection signal. The heating resistor is formed by forming a film type resistor on the surface of a plate-shaped base, and a supporting member that cantilevers the heating resistor is
A reinforcing member is provided that applies the vicinity of the supported portion of the heating resistor, and the reinforcing member is provided with a heating resistor for suppressing heat escaping from the heating resistor for measuring the air flow rate. A thermal air flow meter. 4. A thermal type air flow meter, comprising: a heating resistor arranged in an air passage for measuring an air flow rate; and a control module for controlling a current flowing through the heating resistor and outputting a detection signal. The heating resistor is formed by forming a film type resistor on the surface of a plate-shaped base, and a supporting member that cantilevers the heating resistor is
A reinforcing member is provided that applies the vicinity of the supported portion of the heating resistor, and the length of the heating resistor protruding from the reinforcing member,
The thickness is set so that the natural frequency of the heat generating resistor is higher than the vibration range generated in the automobile engine, and the reinforcing member suppresses heat escaping from the heat generating resistor for measuring the air flow rate. A heat type air flow meter, which is provided with a heat generation resistance of. 5. The heating resistor provided in the reinforcing member according to claim 3 or 4, is electrically connected to a constant voltage circuit provided in the control module to heat the reinforcing member to a constant temperature. A thermal air flow meter, characterized in that it is set to. 6. The heat generating resistor according to claim 3 or 4, wherein the heat generating resistor provided in the reinforcing member is electrically connected to a current control circuit provided in the control module to measure the air flow rate. Current value (heating temperature) according to body temperature
The thermal air flow meter is characterized in that it is set to change. 7. The thermal air flow meter according to claim 1, wherein the reinforcing member is made of a ceramic material or a metal material. 8. A thermal type air flow meter comprising a heating resistor arranged in an air passage for measuring an air flow rate, and a control module for controlling a current flowing through the heating resistor and outputting a detection signal, The heating resistor is formed by forming a film resistor on the surface of a plate-shaped base, and the heating resistor has a cantilever structure, and at least one surface of the heating resistor excluding the film resistor has the entire surface thereof. Alternatively, the thermal air flow meter is characterized in that the heating resistor is supported by a film-shaped organic substance in the vicinity of the supported portion.