THERMAL TYPE FLOW SENSOR

Abstract

A thermal type flow sensor measures a flow rate of a fluid by means of a heat resistive element having a temperature dependency. The sensor is comprised of: plural heat resistive elements used for a flow rate measurement; and a driver circuit for controlling a current applied to these heat resistive elements to cause their heating. The driver circuit is configured to sense a resistance change of a lower-temperature side heat resistive element among the plural heat resistive elements and to control the current to be applied to the plural heat resistive elements in accordance with a sensed value of the lower-resistance's variation.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view showing a sensor element according to a first embodiment.

FIG. 2 is a cross-sectional view showing a sensor element according to the first embodiment.

FIG. 3 is a cross-sectional view showing a sensor element according to the first embodiment.

FIG. 4 is a driver circuit of the sensor element according to the first embodiment.

FIG. 5 is a temperature distribution of the sensor element according to the first embodiment.

FIG. 6 is a driver circuit of the sensor element according to the first embodiment.

FIG. 7 is a plan view showing the mounting formation of the sensor element according to the first embodiment.

FIG. 8 is a cross-sectional view showing the mounting formation of the sensor element according to the first embodiment.

FIG. 9 is a plan view showing the configuration of a temperature sensitive resistive element according to the first embodiment.

FIG. 10 is a driver circuit of the sensor element according to the first embodiment.

FIG. 11 is a driver circuit of the sensor element according to the first embodiment.

FIG. 12 is a plan view showing a sensor element according to a third embodiment.

FIG. 13 is a driver circuit of the sensor element according to the third embodiment.

FIG. 14 is a driver circuit of the sensor element according to the third embodiment.

FIG. 15 is a driver circuit of the sensor element according to the third embodiment.

FIG. 16 is a driver circuit of the sensor element according to the third embodiment.

FIG. 17 is a plan view showing a sensor element according to a fourth embodiment.

FIG. 18 is a driver circuit of the sensor element according to the fourth embodiment.

FIG. 19 is a driver circuit of the sensor element according to the fourth embodiment.

FIG. 20 is a driver circuit of the sensor element according to the fourth embodiment.

FIG. 21 is a driver circuit of the sensor element according to the fourth embodiment.

FIG. 22 is a plan view showing a sensor element according to a fifth embodiment.

FIG. 23 is a driver circuit of the sensor element according to the fifth embodiment.

FIG. 24 is a plan view showing a sensor element according to a sixth embodiment.

FIG. 25 is a layout diagram showing the sensor element according to the sixth embodiment.

FIG. 26 is a driver circuit of the sensor element according to a second embodiment.

Claims

1. A thermal type flow sensor for measuring a flow rate of a fluid by means of a heat resistive element having a temperature dependency; comprising: plural heat resistive elements used for a flow rate measurement; anda driver circuit for controlling a current applied to these heat resistive elements to cause their heating,wherein the driver circuit is configured to sense a resistance change of a lower-temperature side heat resistive element among the plural heat resistive elements and to control the current to be applied to the plural heat resistive elements in accordance with a sensed value of the lower-resistance's variation.

2. A thermal type flow sensor for measuring a flow rate of a fluid by means of a heat resistive element having a temperature dependency; comprising: plural heat resistive elements used for a flow rate measurement; anda driver circuit for controlling a current applied to these heat resistive elements to cause their heating,wherein the plural heat resistive elements are arranged in a flow passage of the fluid to be measured, andwherein the driver circuit is configured to sense a resistance change of an off-center heat resistive element in an arrangement of the plural heat resistive elements and to control the current to be applied to the plural heat resistive elements in accordance with a sensed value of the off-center resistance's change.

3. A thermal type flow sensor for measuring a flow rate of a fluid by means of a heat resistive element having a temperature dependency; comprising: a first series circuit including at least a first resistive element and a second resistive element;a second series circuit including at least a third resistive element and a fourth resistive element;a bridge circuit that connects the first series circuit and the second series circuit in parallel;a fifth resistive element that is connected in parallel to the bridge circuit; anda driver circuit that takes in a first intermediate voltage between the first resistive element and the second resistive element and a second intermediate voltage between the third resistive element and the fourth resistive element to control a current that flows in the first to fifth resistive elements in accordance with a difference between those intermediate voltages.

4. A thermal type flow sensor for measuring a flow rate of a fluid by means of a heat resistive element having a temperature dependency; comprising: a substrate having a thin-walled portion therein;a first series circuit including a first resistive element and a second resistive element;a second series circuit including a third resistive element and a fourth resistive element;a bridge circuit that connects the first series circuit and the second series circuit in parallel; anda fifth resistive element that is connected in parallel to the bridge circuit,wherein the first resistive element and the fifth resistive element are formed on the thin-walled portion of the substrate.

5. The thermal type flow sensor according to claim 4, wherein the fourth resistive element is also formed on the thin-walled portion of the substrate.

6. The thermal type flow sensor according to claim 4, wherein the third resistive element is also formed on the thin-walled portion of the substrate.

7. The thermal type flow sensor according to claim 3, wherein all of the first to fifth resistive elements are formed on the same substrate.

8. A thermal type flow sensor for measuring a flow rate of a fluid by means of a heat resistive element having a temperature dependency; comprising: a substrate having a thin-walled portion therein;a bridge circuit which is constituted by at least a first resistive element, a second resistive element, a third resistive element, and a fourth resistive element and that provided on the substrate;wherein those resistive elements are connected to each other by a pattern formation on the substrate to form the bridge circuit, and wherein the first resistive element is disposed on the thin-walled portion, and the second to fourth resistive elements are disposed so as to be close to each other outside the thin-walled portion of the substrate.

9. A thermal type flow sensor which measures a flow rate of a fluid by means of a heat resistive element having a temperature dependency and that is formed on a substrate; comprising: wherein the substrate is provided with a bridge circuit which is formed by connecting at least a first series circuit including a first resistive element and a second resistive element and a second series circuit including a third resistive element, a fourth resistive element, and a fifth resistive element, to each other in parallel;wherein the first to fifth elements are connected to each other by a patter formation on the substrate; andthe flow sensor further comprises an operational amplifier circuit that takes in a potential between the first resistive element and the second resistive element and a potential across the fourth resistive element, to output an electric signal based on both of the potentials.

10. A thermal type flow sensor for measuring a flow rate of a fluid by means of a heat resistive element having a temperature dependency and that is formed on a substrate; comprising: wherein the resistive element and an electric terminal pad for outputting an electric signal of the resistive element outside the substrate are formed on the substrate; and the resistive element is formed and connected at a position apart from the electric terminal pad by W/2 or longer when it is defined that a shorter side of the substrate is W, and a longer side thereof is L.

11. A thermal type flow sensor comprising a substrate having a thin-walled portion therein, an air flow measurement resistive element formed on the thin-walled portion, and an electric terminal pad for outputting an electric signal of the resistive element outside the substrate; wherein the thin-walled portion is formed at a position apart from the electric terminal pad by W/2 or longer when it is defined that a shorter side of the substrate is W, and a longer side thereof is L.

12. A thermal type flow sensor having a substrate, plural resistive elements having thermal dependencies respectively, an electric terminal pad for outputting an electric signal of a heat resistive element among the plural resistive elements outside the substrate; wherein a wall thickness removed-portion, which is formed by removing a part of the wall thickness of the substrate, is provided between the resistive element and the electric terminal pad on a substrate's one surface opposite to another substrate's surface on which the resistive element and the electric terminal pad are formed.

13. A thermal type flow sensor comprising a substrate having a thin-walled portion therein, an air flow measurement resistive element formed on the thin-walled portion, and an electric terminal pad for outputting an electric signal of the resistive element outside the substrate; wherein a recess portion is formed at a part of on a substrate's one surface opposite to another substrate's surface on which the resistive element and the electric terminal pad formed, and the recess portion is located between the resistive element and the electric terminal pad.

14. A thermal type flow sensor comprising: a flow rate measurement-sensor element which is made by forming plural resistive elements with a temperature dependency on a first substrate; anda second substrate for mounting the sensor element thereon,wherein the sensor element is adhered to the second substrate by using an adhesive partially coated on the first substrate; andwherein when defining a direction linking between each of the resistive elements and a position of the adhesive as a longitudinal direction, a pattern of the resistive elements are configured by a longitudinal resistive portions that allow a current to flow in the longitudinal direction and a lateral resistive portions that allow the current to flow in the lateral direction,wherein each resistance of the resistive elements is a combined resistance of a resistance R1 of the longitudinal resistive portions and a resistance Rt of the lateral resistive portions,wherein each of the resistive elements is formed in such a manner that a resistance ratio of R1 and Rt is substantially equal to Rt:R1=t:1 with respect to the piezoelectric resistance coefficient 1 of the longitudinal resistive portions and the piezoelectric resistance coefficient t of the lateral resistive portions, andwherein a recess portion where the thickness of the first substrate is partially removed is formed between the area of the resistive elements and the adhesive on the substrate.

15. A thermal type flow sensor having a substrate with a thin-walled portion and a heat resistive element formed on the thin-walled portion for the purpose of measuring a flow rate, wherein a wall-thickness of the substrate is partially removed so that a C-shaped, a U-shaped, or a L-shaped groove is formed so as to surround the thin-walled portion.