JPS60230019A - Gas flow rate detector - Google Patents

Abstract

PURPOSE:To detect accurately and sensitively a flow rate to the variation in flow rate by arranging thin flat plate type detecting elements for the flow rate and gas temperature in a gas flow passage. CONSTITUTION:When the thin flat plate type flow rate detecting element 4 and thin flat plate type gas temperature detecting element 5 are arranged in the gas flow passage 2, the element 4 is arranged extending in parallel to the axial line X of the flow passage 2 and along a line X. Further, the element 5 is aranged in parallel to the line X slantingly below the upstream side of the element in the direction F of the gas flow. Consequently, the gas flow disturbed by the lead wire 10 of the element 5 never reaches the element 4.

Description

[Detailed description of the invention] Industrial applications The present invention relates to a gas flow rate detection device.

BACKGROUND OF THE INVENTION A gas flow rate detection device applying the principle of a hot wire anemometer to detect a gas flow rate, for example, the intake air amount of an internal combustion engine, is known as described in Japanese Patent Laid-Open No. 103421/1983. In this gas flow rate detection device, a flat support carrying a self-heating measuring resistor is arranged on the axis of the gas flow path, and a flat supporting body carrying a compensation resistor is arranged straight ahead of the measuring resistor supporting body. Then, the heating current supplied to the measuring resistor is adjusted so that the temperature difference between the measuring resistor and the compensation resistor is equal, and the gas flow rate is detected from the current value required to heat the measuring resistor. .

However, in this gas flow detection device, first of all, the compensating resistance support is arranged directly in front of the measuring resistance support, so that the gas flow disturbed by the compensating resistance support flows over the measuring resistance surface of the measuring resistance support. . As a result, the degree of cooling of the measuring resistor changes depending on the degree of turbulence, so the current value supplied to the measuring resistor does not correspond accurately to the gas flow velocity (
Therefore, there is a problem that the gas flow velocity cannot be detected accurately.

Secondly, in this gas flow rate detection device, the measurement resistor also serves as a heater, so there is a problem that the gas flow rate cannot be detected accurately. The characteristics required of a measuring resistor are sensitivity to temperature changes, that is, a large temperature coefficient of resistance.

However, if the temperature coefficient of the resistor is increased, the change in resistance value due to temperature changes will increase, and the heating current value supplied to the measuring resistor, that is, the output signal of the gas flow rate detection device, will include ripples due to the sensitivity. The so-called signal-to-noise ratio (S/N ratio) decreases.Therefore, a resistor with a large temperature coefficient of resistance cannot be used as a measuring resistor, and thus good sensitivity to changes in flow velocity cannot be obtained. There's a problem.

OBJECTS OF THE INVENTION An object of the present invention is to provide a gas flow rate detection device that is sensitive to changes in flow velocity and can accurately detect flow velocity.

Structure of the Invention The structure of the present invention is such that a thin flat plate-shaped flow velocity detection element and a thin flat plate-shaped gas temperature detection element are arranged in parallel to the axis of the gas flow passage. Flow velocity detection element and gas temperature detection as seen along the flow velocity detection element 1 The gas temperature detection element is arranged diagonally upstream of the flow velocity detection element so that the projected images of the output element do not overlap with each other.

Example 2 Referring to FIGS. 1 and 2, 1 is a gas flow pipe, 2
Reference numeral 3 indicates a gas flow passage, and 3 indicates a detection element holder made of a non-conductive and heat-insulating synthetic resin material.

When the present invention is applied to an internal combustion engine, the gas flow passage 2 represents an intake passage or a bypass passage that connects a venturi formed in the intake passage and an intake passage upstream of the venturi. As shown in FIGS. 1 and 2, the gas flow passage 2
Inside, a thin flat plate-shaped flow velocity detection element 4 and a thin flat plate-shaped gas temperature detection element 5 are arranged. The flow velocity detection element 4 is arranged on the axis X of the gas flow passage 2 so as to extend along the axis X. However, this flow velocity detection element 4
does not necessarily need to be placed on the axis X, and can be placed at a distance from the axis X, but even in this case, the flow velocity detection element 4 must be placed parallel to the axis X. 8 for temperature measurement 8 5 is located diagonally upstream of the flow velocity detection element 4 with respect to the gas flow direction indicated by arrow F, and is aligned with axis X.
is placed parallel to. That is, the gas temperature detection element 5 is arranged at a distance from the flow velocity detection element 4 in the axis X direction, and as shown in FIG. It is arranged so that the projected image 5a of the gas temperature detection element 5 does not overlap with each other. The flow velocity detection element 4 and the gas temperature detection element 5 need only be arranged so that their projected images 4a and 5a do not overlap each other, so the flow velocity detection element 4 and the gas temperature detection element 5 are not necessarily arranged in parallel. For example, the projected image 4a
, 5a may be arranged at right angles to each other.

FIG. 3 shows an enlarged plan view of the flow rate detection element 4 and the gas temperature detection element 5. Referring to FIG. 3, the flow velocity detecting element 4 consists of a thin flat base 6 made of a silicon wafer chip, and a thin film heating resistor R is disposed on the surface of the base 6.
H and a heat-sensitive resistor R2 are formed. The heating resistor R8 is used only to heat the heat-sensitive resistor Rt, and therefore the heating resistor RH is made of a material with an extremely small temperature coefficient of resistance. On the other hand, the heat-sensitive resistor R2 is used only for detecting changes in resistance, and therefore, the heat-sensitive resistor R2 is made of a material with an extremely large temperature coefficient of resistance.

The heat generated by the heating resistor R□ is transferred to the heat-sensitive resistor R2 by thermal conduction through the base 6 on the one hand, and is transferred to the heat-sensitive resistor R2 by heat transfer by the gas flow on the other hand. Therefore, in order to ensure heat transfer by heat transfer, the heating resistor R11 is placed upstream of the heat sensitive resistor R2. The thin strip lead terminal 7 of the heating resistor RH and the thin strip lead terminal 8 of the heat sensitive resistor R2 are fixed to the detection element holder 3 as shown in FIGS. It is supported by lead terminals 7 and 8. On the other hand, as shown in FIG. 3, the gas temperature detection element 5 also consists of a thin plate-shaped base 9 made of a silicon wafer chip, and a thin film heat-sensitive resistor R1 is disposed on the surface of the base 9.
is formed. This heat-sensitive resistor R1 is made of a material with a large temperature coefficient of resistance. The thin strip-shaped lead terminal 10 of the heat-sensitive resistor R is fixed to the detection element holder 3 as shown in FIGS. 1 and 2, and therefore the gas temperature detection element 5
is supported by these lead terminals 10.

FIG. 4 shows a cross-sectional view of the flow velocity detection element 4. Referring to FIG. 4, an insulating layer 11 made of SiO□ is formed on a substrate 6 made of silicon, and a thin film heating resistor RH and a thin film heat sensitive resistor R2 are formed on this insulating layer 11. These heating resistor RH and heat sensitive resistor R2 are further
is covered with a protective layer 12 consisting of . The gas temperature detecting element 5 also has the same cross-sectional structure as the flow rate detecting element 4, and therefore the description of the cross-sectional structure of the gas temperature detecting element 5 will be omitted.

FIG. 5 shows a detection circuit for the flow rate detection element 4 and the gas temperature detection element 5 shown in FIG. Referring to FIG. 5, one end of the heating resistor R is grounded via a fixed resistor R8, and the other end of the heating resistor RH is connected to the emitter of the transistor Tr. These fixed resistors rl+r2 and heat-sensitive resistors R+, Rt
A bridge circuit is formed. Fixed resistance rl+rf
The connection point P of fi is connected to one input terminal of the comparator C, and the connection point Q of the heat sensitive resistors Rt and Rz is connected to the other input terminal of the comparator C. Further, the output terminal of the comparator C is connected to the base of the transistor T. As mentioned above, the heat-sensitive resistors R+ and Rz are made of a material with a large temperature coefficient of resistance, and the heat-sensitive resistor R2
The heat-sensitive resistors R,, R,, r, , r so that the voltages at the connection points P and Q become equal when the temperature of the heat-sensitive resistor R1 is higher than the temperature of the heat-sensitive resistor R1 by a constant temperature Δt.

The resistance value is determined. Therefore, the heat-sensitive resistor R+.

When the temperature difference of R1 becomes smaller than Δt, the voltage at the connection point Q becomes higher than the voltage at the connection point P, and as a result, the output voltage of the comparator C becomes a high level.

When the output voltage of the comparator C becomes a high level, the transistor Tr is turned on, and power is supplied to the heating resistor Ri+, so that the temperature of the heat-sensitive resistor R2 rises. Next, when the temperature difference between the heat-sensitive resistors R1 and Rz becomes equal to Δt, the output voltage of the comparator C becomes a low level, and as a result, the transistor Tr is turned off, so that the supply of power to the heating resistor RH is stopped. By controlling the supply of power to the heating resistor R, in this way, the sensitive resistor R+,
The temperature difference Δt of Rz is kept constant.

On the other hand, when a platinum wire with a diameter d is placed in a fluid with a flow velocity ν and the platinum wire is heated, the amount of heat H carried away by the fluid is expressed by the following equation of V and King.

H=KT+■RoroCτ- ['7T Where: Thermal conductivity of the fluid Cv: Specific heat of constant volume of the fluid ρ: Original fluid density T: Temperature difference between the temperature of the platinum wire and the temperature of the fluid This formula is used in the present invention. When applied to the temperature difference T, the temperature difference T
,,R, is equal to the temperature difference Δt. In addition, in order to keep the temperature difference Δt between the heat-sensitive resistors R+ and Rz constant, it is necessary to add a heat amount equal to the heat amount H carried away by the fluid to the heat-sensitive resistor R2. The amount of heat generated is equal to i''R/J. Here, i is the current value flowing through the heating resistor RH, R is the resistance value of the heating resistor R9, and J is the work equivalent of heat. Therefore, as the heating resistor RH, the resistance If a resistor with an extremely small temperature coefficient is used, the above equation can be easily expressed as follows.

i ” = B f [T+ Nikode B and C are constants determined from the type of fluid and the resistance value of the heating resistor RH.

Therefore, it can be seen from this equation that the velocity ν of the fluid can be detected by detecting the current flowing through the heating resistor R. In the embodiment shown in FIG. 5, the current flowing through the heating resistor R1 is detected by detecting the voltage at one end of the resistor R8 using a detector. Therefore, this detector can detect the flow velocity of the gas flowing within the gas flow passage 2, and therefore the amount of gas flowing within the gas flow passage 2.

As shown in FIGS. 1 and 2, the gas temperature detection element 5 and its lead terminal 10 do not reach the flow rate detection RH and the heat-sensitive resistor R2, and the gas temperature detection element 5 does not reach the flow rate detection element 4.
Since the heating resistor R1l is disposed upstream of the heating resistor R1l, the heat generated by the heating resistor R1l is not transferred to the gas temperature detecting element 5, and the gas temperature detecting element 5 is spaced apart from the flow velocity detecting element 4 in the axis X direction. Since they are arranged apart from each other, the radiant heat emitted from the bottom surface of the flow rate detection element 4 does not reach the gas temperature detection element 5. Therefore, the heat-sensitive resistor Rt of the gas temperature detection element 5 is accurately proportional to the gas salt. Resistance changes. Therefore, the gas flow rate can be accurately detected by the flow rate detection element 4 and the gas temperature detection element 5. In addition, the heat-sensitive resistor R2
Since a so-called indirect heating method is adopted in which the heat-sensitive resistor R2 and the heating resistor RH are separately provided, the temperature coefficient of resistance of the heat-sensitive resistor R2 can be increased (in this way, the gas flow velocity can be detected with greater sensitivity). be able to.

Another embodiment is shown in FIGS. 6 and 7. In this embodiment as well, the gas temperature detection element 5 is arranged diagonally upstream of the flow velocity detection element 4, as in the embodiments shown in FIGS. 1 and 2. However, in this embodiment, the flow rate detection element 4 and the gas temperature detection element 5 have corresponding lead terminals 7;8.
The surface of the base 6, on which the heating resistor Rn and the heat-sensitive resistor R2 are formed, and the surface of the base 9, on which the heat-sensitive resistor R3 is formed, face outward in opposite directions. This differs from the embodiments shown in FIGS. 1 and 2 in this respect.

Effects of the Invention By arranging the gas temperature detection element diagonally upstream of the flow velocity detection element, the gas flow disturbed by the gas temperature detection element does not reach the flow velocity detection element, thus reducing the gas flow velocity. Can be detected accurately. Furthermore, by employing an indirect heating method, the gas flow velocity can be detected with high sensitivity.

[Brief explanation of drawings]

2... Gas flow path, 4... Flow velocity detection element, 5...
... Gas temperature detection element, 6.9... Base, 47, 8.
10...Lead terminal, RM...Heating resistor, R+
, Rt...thermal resistor. Figure 6 ■ ■ Figure 8 7171 Operation area

Claims (1)

[Claims] A thin plate-shaped flow velocity detection element and a thin plate-shaped gas temperature detection element are arranged in parallel to the axis of the gas flow passage, and the flow velocity is detected along the axis of the gas flow passage. A gas flow rate detection device in which a gas temperature detection element is arranged diagonally upstream of a flow rate detection element so that the projected images of the gas temperature detection element and the gas temperature detection element do not overlap with each other.