JP2017044637A - Flow sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide, as a thermal flow sensor, a flow sensor capable of having a detection range of a flow rate of a fluid widened and obtaining detection characteristics with excellent linearity.SOLUTION: A sensor chip 1 comprises a heating part RH and resistance bridges BG1, BG2. Two linear parts of the heating part RH are arranged orthogonally to an X direction in which a fluid flows. Similarly, resistors of the resistance bridges BG1, BG2 are arranged orthogonally to the X direction. Two resistors each are arranged on an upstream and a downstream side, and connected in a bridge shape. As a heated fluid flows, a difference in temperature distribution is generated between the upstream and downstream sides according to the flow rate, and becomes larger with the distance therebetween. Consequently, the resistance bridge BG2 close to the heating part RH performs detection when the flow rate is high so as to obtain high precision.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a flow sensor.

  The flow sensor for detecting the flow rate of fluid is, for example, a sensor chip having a structure in which a resistance heating unit is provided on a silicon chip, resistors are arranged at equal distances on both sides of the heating unit, and these resistors are bridge-connected. There is something with. In such a flow sensor, when the fluid in the vicinity is heated by the heating unit and the temperature is detected by the resistance bridge, the fluid flows and the heated portion moves, so that the output of the resistance bridge varies. By detecting this, the flow rate of the fluid is detected.

  However, when the flow rate of the fluid is increased, the heated fluid moves quickly at the bridge resistance position located on the upstream side, and thus the temperature of the fluid is significantly reduced. That is, since the amount of change in the upstream resistance value due to the change in flow rate is small in the high flow rate region, the change in output voltage due to the bridge resistance is also small. As a result, when the flow rate is high, there is a problem that the sensitivity of the flow rate that can be detected by the resistance bridge for temperature measurement is lowered.

  In recent years, intelligent signal processing of sensors has been promoted. There is a growing demand for a sensor signal that can be corrected to a straight line and output so that the signal detected by the sensor can be easily handled by a control process of an ECU (Electronic Control Unit).

  Therefore, in order to output the curve characteristic of the flow rate of the thermal flow sensor as a linearized signal, it is necessary to perform broken line correction as a process for correcting the sensor signal as a linearized signal. However, this causes a problem that the memory capacity for broken line correction increases.

JP 2012-137388 A

  The present invention has been made in consideration of the above circumstances, and its purpose is to provide a fluid flow rate detection range that is wide and accurate in a sensor that detects the flow rate by heating the fluid, and is linear. It is an object of the present invention to provide a flow sensor capable of obtaining good detection characteristics.

  The flow sensor according to claim 1 is a resistance bridge for temperature measurement having a heating part provided in a fluid flow path and a pair of resistors provided on both sides of the heating part in a direction along the flow path. A plurality of resistance bridges provided so that an arrangement interval between the heating unit and the resistor is different; and the fluid in the flow path is heated by the heating unit, and any one of the plurality of resistance bridges And a detector that detects the flow rate of the fluid based on the output signal.

  By adopting the above configuration, the fluid in the flow path heated by the heating unit is not flowing, that is, in a state where the flow rate is zero, in any direction along the flow path centering on the heating unit. Since the fluid is heated under the same conditions, the upstream side and the downstream side have the same temperature distribution. Thereby, since the resistor of the resistance bridge is exposed to the same temperature condition on both sides of the heating unit, the output voltage is not changed and the flow rate of zero is detected.

  In the state in which the fluid is flowing in the flow path, the fluid in the flow path heated by the heating unit moves from the upstream side to the downstream side, so that the downstream resistor has a temperature higher than that of the upstream resistor. Becomes higher. The output level of the detection signal of the resistance bridge changes according to the degree of this temperature change. The flow rate of the fluid can be detected from the amount of change in the output level.

  However, the temperature of the fluid in the flow path heated by the heating unit is high near the heating unit and rapidly decreases as the distance increases. For this reason, when the flow rate is low, the temperature at a position away from the heating unit changes greatly, and when the flow rate is high, the temperature near the heating unit also changes greatly. At this time, the temperature change at the position away from the heating unit can be obtained larger than the change at the close position, and the detection level change by the resistance bridge can be obtained largely.

  In addition, at a high flow rate, the temperature at a position away from the heating unit is a region where the change is small on both the upstream side and the downstream side, so the change amount according to the flow rate is small, and the detection level changes due to the resistance bridge. Get smaller. Even in this case, the temperature change at the position close to the heating unit can be obtained larger than the change at the remote position.

  Therefore, when the flow rate of the fluid in the flow path is low, the flow rate is detected by a resistance bridge located away from the heating unit, and when the flow rate becomes high, the flow rate is detected by a resistance bridge located near the heating unit. The detection operation can be performed accurately with a large level change. As a result, by performing detection operation by switching a plurality of resistance bridges, the range in which the flow rate can be detected can be expanded, and detection can be performed with high accuracy using a range in which the change in the detection level of each resistance bridge is large. become able to.

Schematic plan view of the sensor chip showing the first embodiment Schematic vertical side view of sensor chip Electrical configuration of flow sensor Action explanatory drawing, (a) The figure which shows the relationship between position and temperature, (b) Corresponding sectional drawing The figure which shows the relation of the detection signal level of the resistance bridge to the flow rate The figure which shows the relationship of the detection signal level with respect to the flow rate by the detection circuit Electrical configuration diagram showing the second embodiment Schematic plan view of a sensor chip showing a third embodiment The figure which shows the relationship of the detection signal level with respect to the flow rate by the detection circuit Schematic plan view of a sensor chip showing a fourth embodiment

(First embodiment)
Hereinafter, a first embodiment of the present invention will be described with reference to FIGS. In this embodiment, for example, the sensor chip 1 of the flow rate sensor is provided in an intake path that is a flow path in order to measure an intake amount of a gas such as air that is a fluid. In general, the detection part of the sensor chip 1 is arranged so as to be exposed to the flow path, and the flow rate is detected by utilizing a phenomenon that is cooled by the flow of air as a fluid.

  1 and 2 schematically show the configuration of the sensor chip 1. First, as shown in FIG. 2, the sensor chip 1 is built on a semiconductor substrate 2 such as a silicon substrate. A concave portion 2 a serving as a cavity is formed on the back surface side of the semiconductor substrate 2. The cross section of the recess 2a is formed in a trapezoidal shape by silicon etching or the like. Thin-film silicon is formed as a diaphragm 2b in the portion of the semiconductor substrate 2 where the recess 2a is formed.

  In the diaphragm 2b, an element part 3a is set, and a heating part RH and resistance bridges BG1 and BG2 formed by introducing impurities into a predetermined pattern region in the silicon substrate are formed. A lead portion 3b is provided adjacent to the element portion 3a on the silicon substrate 2 at a position away from the diaphragm 2b. The resistance pattern of the element part 3a is connected and electrically connected in the lead part 3b as described later.

  FIG. 1 shows a planar pattern of the heating unit RH and the resistance bridges BG1 and BG2 which are detection parts of the sensor chip 1. Assuming the case where the sensor chip 1 is arranged in a flow path serving as a measurement site, the left side in the figure is the upstream side where the fluid flows, the right side is the downstream side where the fluid flows, and the direction of the flow path is described as the X direction. In the central portion (X = 0) of the element portion 3a, two linear patterns orthogonal to the X-axis direction and a heating portion RH having an H shape formed by connecting these at an intermediate position are arranged.

  The resistance bridge BG1 includes four linear resistors R1u1, R1u2, R1d1, and R1d2 arranged in a direction orthogonal to the X axis, and is configured by bridge connection. The resistors R1u1 and R1u2 are arranged on the upstream side of the heating unit RH, and the resistors R1d1 and R1d2 are arranged on the downstream side of the heating unit RH.

  The upstream side resistors R1u1 and R1u2 are arranged from one side (upward direction in FIG. 1) to the other side (downward direction in FIG. 1) in the direction orthogonal to the X axis, and the two on the other side are collectively upstream. Is formed in a folded pattern so as to return to one side. The resistors R1d1 and R1d2 are formed in a folded pattern that is arranged from one side to the other side in the direction orthogonal to the X-axis, and that the two on the other side are collectively returned from the upstream side to the one side. .

  The distance between the center position of the heating unit RH and the center position of the resistors R1u1 and R1u2 is set to a, for example. Similarly, the distance between the center position of the heating part RH and the center position of the resistors R1d1 and R1d2 is also set to a.

  The resistors R1u1 and R1d1 are connected by a connecting resistor R1j1 in the lead portion 3b. The resistors R1u2 and R1d2 are connected by a connecting resistor R1j2 in the lead portion 3b. The connecting end of the resistor R1d1 opposite to the resistor R1j1 is connected to the positive terminal A1 of the first resistor bridge BG1 together with the connecting end of the resistor R1u2 opposite to the resistor R1j2. The connection end of the resistor R1d2 opposite to the resistor R1j2 is connected to the negative terminal B1 of the first resistor bridge BG1 together with the connection end of the resistor R1u1 opposite to the resistor R1j1. The central portion of the resistor R1j1 is connected to the detection terminal C1 of the first resistance bridge BG1. The central portion of the resistor R1j2 is connected to the detection terminal D1 of the first resistance bridge BG1.

  The resistance bridge BG2 includes four linear resistors R2u1, R2u2, R2d1, and R2d2 arranged in a direction perpendicular to the X axis, and is configured by bridge connection. The resistors R2u1 and R2u2 are disposed on the upstream side of the heating unit RH, and the resistors R2d1 and R2d2 are disposed on the downstream side of the heating unit RH.

  The upstream side resistors R2u1 and R2u2 are arranged in a folded pattern that is arranged from one side to the other side in the direction orthogonal to the X-axis, and that the two on the other side are collectively returned from the upstream side to the one side. Yes. Further, the resistors R2d1 and R2d2 are formed in a folded pattern that is arranged from one side to the other side in the direction orthogonal to the X axis, and that the two are collectively returned from the upstream side to the one side on the other side. .

  The distance between the center position of the heating unit RH and the center position of the resistors R2u1 and R2u2 is set to b, for example. Similarly, the distance between the center position of the heating part RH and the center position of the resistors R2d1, R2d2 is also set to b. In this case, the arrangement interval b of the second resistance bridge BG2 is set to be shorter than the arrangement interval a of the first resistance bridge BG1.

  The resistors R2u1 and R2d1 are connected by a connecting resistor R2j1 in the lead portion 3b. The resistors R2u2 and R2d2 are connected by a connecting resistor R2j2 in the lead portion 3b. The connecting end of the resistor R2d1 opposite to the resistor R2j1 is connected to the positive terminal A2 of the second resistor bridge BG2 together with the connecting end of the resistor R2u2 opposite to the resistor R2j2. The connecting end of the resistor R2d2 opposite to the resistor R2j2 is connected to the negative terminal B2 of the second resistor bridge BG2 together with the connecting end of the resistor R2u1 opposite to the resistor R2j1. The central portion of the resistor R2j1 is connected to the detection terminal C2 of the second resistance bridge BG2. The central portion of the resistor R2j2 is connected to the detection terminal D2 of the second resistance bridge BG2.

  One terminal of the heating unit RH is connected to the terminal H, and the other terminal is provided so as to be connected to the ground terminal GND although not shown. When the heating unit RH is energized between both terminals, the temperature of the resistor rises due to the current at that time, thereby heating a fluid such as gas or liquid in the vicinity of the heating unit RH.

  In addition, in FIG. 2, the arrangement | positioning state of above-described heating part RH and two resistance bridges BG1 and BG2 is shown simply as a cross-sectional structure of the sensor chip 1. FIG. The heating unit RH shows a resistor having two linear patterns as a single resistor pattern, and the two resistance bridges BG1 and BG2 have two resistors on the upstream side and the downstream side, respectively. The state in which each two are formed in a folded pattern is indicated by a single resistor pattern.

  Next, the configuration of the detection circuit 4 for detecting the flow rate by connecting the sensor chip 1 will be described with reference to FIG. The detection circuit 4 is configured by, for example, a semiconductor integrated circuit different from the sensor chip 1. The detection circuit 4 includes input terminals T1 to T8. The detection circuit 4 includes a selection switch 5, an amplifier 6, an AD conversion circuit 7, and a digital processing circuit 8, and is supplied with power from a DC power supply VD. The selection switch 5 includes eight switches S1 to S8. The switches S1 to S8 are constituted by semiconductor switching elements such as MOSFETs. The digital processing circuit 8 is provided with a control unit 8a that performs signal processing for flow rate detection. The switches S1 to S8 of the selection switch 5 are on / off controlled by the control unit 8a.

  The input terminals T1 to T8 are connected to the respective terminals of the sensor chip 1. The input terminal T1 is connected to the positive terminals A1 and A2 of the resistance bridges BG1 and BG2 and one terminal of the heating unit RH. The detection terminals D1 and C1 of the resistance bridge BG1 are connected to the input terminals T2 and T3, respectively. The negative terminal B1 of the resistance bridge BG1 is connected to the input terminal T4. The detection terminals D2 and C2 of the resistance bridge BG2 are connected to the input terminals T5 and T6, respectively. The negative terminal B2 of the resistance bridge BG2 is connected to the input terminal T7. The other terminal of the heating unit RH is connected to the input terminal T8.

  In the detection circuit 4, the input terminal T 1 is connected to the power supply terminal VD via the switch S 1 of the selection switch 5. The input terminals T2 and T5 are connected to one input terminal of the amplifier 6 via switches S2 and S5, respectively. The input terminals T3 and T6 are connected to the other input terminal of the amplifier 6 via switches S3 and S6, respectively. The input terminals T4, T7, T8 are connected to the ground GND via switches S4, S7, S8, respectively.

  The amplifier 6 amplifies and outputs a difference between signals input to the two input terminals. The AD conversion circuit 7 converts an input analog signal into a digital signal and inputs the digital signal to the control unit 8 a of the digital processing circuit 8. The control unit 8a performs switching control of the selection switch 5 to acquire a detection signal from the resistance bridge BG1 or BG2, and inputs the detection signal as a digital signal via the AD conversion circuit 7, thereby determining the flow rate of the fluid in the flow path. Perform detection processing.

Next, the operation of the above configuration will be described with reference to FIGS.
First, the principle that the fluid flow rate can be detected in a wide detection range according to the present embodiment will be described with reference to FIG. FIG. 4B shows a portion corresponding to the cross-sectional configuration of FIG. 2, and schematically shows the state of the fluid heated by the heating unit RH while the fluid is moving through the flow path. By energizing the heating unit RH, Joule heat is generated in the resistor, and this heats the fluid in the flow path. At this time, since the fluid flows from the left side to the right side in the drawing (X direction), the fluid is heated by heat radiated concentrically (actually concentric cylinder) around the heating unit RH. , Shift to the right side due to the movement of fluid. The displacement of the position of the fluid having the same heat becomes larger as the position is farther from the heating unit RH.

  In the state where the fluid flows in the X direction as described above, the heat distribution state of the fluid changes according to the flow rate. In FIG. 4A, the heat distribution in a state where the flow rate is zero (flow rate F = 0 [g / s]) is shown by a short broken line f0, and the flow rate is low (flow rate F = F1 [g / s] by a long broken line f1. s]), and the solid line f2 shows the heat distribution in a high flow rate state (flow rate F = F2 (> F1) [g / s]).

  As described above, in the state where the fluid is flowing in the flow path, the temperature distribution varies according to the flow rate. At the position (0) of the heating unit RH, the temperature of the fluid is constantly heated, but at the upstream side (X = −a), the fluid heated by the heating unit Rh is pushed back to the upstream side, whereby the temperature distribution f0. The temperature distribution f1 or f2 is obtained by compressing the shape in the X direction according to the flow rate. Further, on the downstream side (X = a), the fluid heated by the heating unit Rh is caused to flow downstream, so that the temperature distribution f1 or f2 is obtained by extending the shape of the temperature distribution f0 in the X direction according to the flow rate. .

  In the flow rate detection by the resistance bridges BG1 and BG2, the change in temperature from the above-described temperature distribution f0 to f1 and f2 is detected as a change in resistance value of the resistor. For example, in the resistance bridge BG1 in which the resistors are arranged outside (X = −a, X = a) with the heating unit RH as the center, the temperature is increased in the upstream portions (X = −a) of the resistors R1u1 and R1u2. The temperature falls and the temperature rises at the portions of the resistors R1d1 and R1d2 on the downstream side (X = a).

  Since the resistance values of the resistors R1u1, R1u2, R1d1, and R1d2 change according to the temperature, a difference in resistance value according to the temperature difference ΔTa between the upstream side and the downstream side is obtained as a detection output of the resistance bridge BG1. The resistance bridge BG1 obtains a detection signal corresponding to the temperature difference ΔTa (F1) when the flow rate is F1, and obtains a detection signal corresponding to the temperature difference ΔTa (F2) when the flow rate is F2.

  As the flow rate F increases from F1 to F2, as described above, the temperature distribution of the fluid heated by the heating unit RH changes from f1 to f2, but the upstream side, that is, the position in the X direction − In a, the decrease in temperature when the temperature distribution f1 changes to f2 is reduced. Further, at the downstream side, that is, the position a in the X direction, the temperature rise when the temperature distribution f1 changes to f2 is small.

  As a result, in the resistance bridge BG1, the detection signal can be obtained as a signal having a large change in the region where the flow rate F is low. However, when the flow rate F is high, the change in the detection signal is small and the substantial detection sensitivity is lowered. FIG. 5 shows the relationship between the fluid flow rate F and the level of the detection signal. In FIG. 5, the state in which the fluid flows in the X direction is the forward flow (FF), and the state in which the fluid flows in the opposite X direction is the backward flow (BF). As can be seen from the figure, the change in the level of the detection signal decreases as the flow rate F increases.

  On the other hand, in the resistance bridge BG2, the four resistors are located inside (X = −b, X = b) from the arrangement position of the resistors in the resistor bridge BG1. As a result, in the resistance bridge BG2, the detection signal does not change much in the region where the flow rate F is low, but when the flow rate F increases, the change in the detection signal increases. In other words, the substantial detection sensitivity increases when the flow rate F is higher than when the flow rate F is low.

  As shown in FIG. 4A, in the state where the fluid flows at the flow rate F1 or F2, the resistance bridge BG1 with the distance X = a and X = −a, the resistance with the distance X = b and X = −b. The temperature differences ΔTa (F1), ΔTa (F2), ΔTb (F1), and ΔTb (F2) detected by the bridge BG2 are as follows.

  The temperature difference ΔTa (F1) is a temperature difference that the temperature distribution f1 indicates at the downstream position (X = −a) and the upstream position (X = a) of the resistance bridge BG1. The temperature difference ΔTa (F2) is a temperature difference that the temperature distribution f2 indicates at each of the downstream position (X = −a) and the upstream position (X = a) of the resistance bridge 1. Similarly, the temperature differences ΔTb (F1) and ΔTb (F2) indicate the temperature distributions f1 and f2 at the temperatures indicated by the downstream position (X = −b) and the upstream position (X = b) of the resistance bridge BG2, respectively. It is a difference.

  As can be seen from the value of the temperature difference, in the resistance bridge BG1, the temperature difference ΔTa (F1) when the flow rate F0 changes to the flow rate F1 is large, but the temperature difference when the flow rate F1 changes to the flow rate F2. ΔTa (F2) is small. On the other hand, in the resistance bridge BG2, the temperature difference ΔTb (F1) when the flow rate F0 changes to the flow rate F1 is small, but the temperature difference ΔTa (F2) when the flow rate F1 changes to the flow rate F2 is large. .

  Therefore, when the flow rate F2 is large, the level of the detection signal of the resistance bridge BG2 close to the heating unit RH can be increased, so that the detection accuracy can be increased. FIG. 6 shows the characteristics of the detection signal level S when the flow rate detection is detected by the resistance bridge BG1 in the low flow rate region such as the flow rates F0 to F1, and the flow rate detection is performed by the resistance bridge BG2 in the high flow rate region such as the flow rate F2. Is shown. In this case, the flow rate at the boundary between the low flow rate region and the high flow rate region is Fx.

  As can be seen from the characteristics of FIG. 6, in the high flow rate region larger than the flow rate Fx, for example, when the flow rate Fs changes to Fr, the detection signal of the resistance bridge BG2 with respect to the difference ΔS1 of the detection signal S of the resistance bridge BG1. It can be seen that a large difference ΔS2 between S can be obtained. Note that data indicating the correspondence relationship of the detection signal S with respect to the fluid flow rate F illustrated in FIG. 6 is stored in advance in the storage unit of the control unit 8a.

  Next, the detection operation in the configuration of the present embodiment will be described. In this embodiment, when performing the detection operation, first, the control unit 8a is set so that the switches S1 to S4 of the selection switch 5 are turned on and the detection signal of the resistance bridge BG1 is input. The control unit 8a turns on and off the switch S8 of the selection switch 5 to energize the heating unit RH and control it to a predetermined temperature.

  In the state where the fluid is flowing in the X direction in the flow path, a temperature difference is generated between the positions X = −a and X = a. Therefore, the resistance values of the upstream resistors R1u1 and R1u2 are lowered, and the downstream side The resistance values of the resistors R1d1 and R1d2 are increased. Since the voltage VD is applied between the positive terminal A1 and the negative terminal B1 of the resistance bridge BG1, a potential difference is generated between the detection terminals C1 and D1. This potential difference is input to the amplifier 6 as the detection signal S.

  The detection signal S is amplified by the amplifier 6, converted into a digital signal by the AD conversion circuit 7, and input to the control unit 8a. In the control unit 8a, the flow rate F is calculated from the relationship between the detection signal level S and the fluid flow rate F shown in FIG. At this time, if the detected flow rate F is in the low flow rate region, the detected flow rate F at that time is output.

  When the detected flow rate F is in the high flow rate region, the detection signal from the resistance bridge BG1 is not used, and the control unit 8a turns off the switches S2 to S4 of the selection switch 5 and switches S5 to S7 instead. Turn on. Thereby, the power supply to the resistance bridge BG1 is stopped, and the voltage VD is applied between the positive terminal A2 and the negative terminal B2 of the resistance bridge BG2.

  In this state, the control unit 8a turns on and off the switch S8 of the selection switch 5 to energize the heating unit RH and control it to a predetermined temperature. In the state where the fluid flows in the X direction in the flow path, a temperature difference is generated between the positions X = −b and X = b as described above, and the resistance values of the upstream side resistors R2u1 and R2u2 decrease. The resistance values of the resistors R2d1 and R2d2 on the downstream side are increased. Thereby, a potential difference is generated between the detection terminals C2 and D2 of the resistance bridge BG2. This potential difference is input to the amplifier 6 as the detection signal S.

  The detection signal S is amplified by the amplifier 6, converted into a digital signal by the AD conversion circuit 7, and input to the control unit 8a. The control unit 8a calculates and outputs the flow rate F in the high flow rate region detected by the resistance bridge BG2 from the relationship between the detection signal level S and the fluid flow rate F shown in FIG.

  According to the present embodiment, with respect to the position X = −a, X = a in the X direction where the resistor of the resistance bridge BG1 is disposed, the position X = −b, X = A resistance bridge BG2 in which a resistor is arranged in b is provided. The control unit 8a detects using the resistance bridge BG1 in the low flow rate region where the flow rate is low, and detects using the resistance bridge BG2 in the high flow rate region where the flow rate is high.

  Accordingly, by performing detection operation by switching the two resistance bridges BG1 and BG2 with the selection switch 5, the range in which the flow rate can be detected can be expanded, and the change in the detection level of each resistance bridge BG1 and BG2 is large. It becomes possible to detect accurately using the range.

  Further, as described above, by selecting the resistance bridge BG1 or BG2 according to the flow rate detection range, the portion deviating from the linearity in the characteristics of the flow rate and the detection signal is reduced. It becomes easy to correct. Further, since the straight line correction is simplified, the memory capacity for correction as the storage unit can be reduced, which can contribute to reducing the chip area of the IC including the control unit 8a.

  In the above embodiment, the flow rate is first detected using the resistance bridge BG1, and when the flow rate is out of the low flow rate region, the resistance bridge BG2 is switched. However, the flow rate is first set using the resistance bridge BG2. If it is detected and deviated from the high flow rate region, the detection operation can be performed by setting to switch to the resistance bridge BG1.

  In the above embodiment, the configuration using two resistance bridges BG1 and BG2 is shown. However, as a configuration using three or more resistance bridges, a low flow rate region, an intermediate flow rate region (set one or more regions), and a high flow rate region. It can also be detected separately.

(Second Embodiment)
FIG. 7 shows the second embodiment. Hereinafter, parts different from the first embodiment will be described. In this embodiment, as the sensor chip 1a, temperature detection resistors Rt1 and Rt2 are provided in the vicinity of the resistance bridges BG1 and BG2. Resistors for temperature detection Rt1 and Rt2 are spares for detecting a rough flow rate when the temperature fluctuates in a state where the fluid flows in the flow path while the heating unit RH is energized and heated to a constant temperature. It functions as a component of the detection unit. The temperature detection resistors Rt1 and Rt2 have one terminal connected to the input terminal T1 of the detection circuit 4a and the other terminal connected to the input terminals Ta and Tb, respectively.

  In the detection circuit 4a, the selection switch 5a includes switches Sa and Sb in addition to the switches S1 to S8. The input terminal Ta is connected to the ground GND through the switch Sa and the resistor 9a. The input terminal Tb is connected to the ground GND through the switch Sb and the resistor 9b. A common connection point between the switch Sa and the resistor 9 a and a common connection point between the switch Sb and the resistor 9 b are connected to one input terminal of the amplifier 10.

  The comparison reference voltage Vref is input to the other input terminal of the amplifier 10. The comparison reference voltage Vref provides a voltage for determining which of the resistance bridges BG1 or BG2 is used for the flow rate measurement. The output signal of the amplifier 10 is input to the control unit 8b via the AD conversion circuit 11. In the above configuration, the temperature detection resistors Rt1 and Rt2, the resistors 9a and 9b, the amplifier 10, and the AD converter circuit 11 constitute a preliminary detection unit.

  Next, the operation of the above configuration will be described. Here, the approximate flow rate of the fluid flowing through the flow path is detected using the temperature detection resistors Rt1 and Rt2, and from which the detected approximate flow rate is set, which resistance bridge BG1 or BG2 is used is set. The operation will be described.

  With the fluid flowing in the flow path, a rough flow rate can be detected depending on the degree of temperature difference between the state before heating by the heating unit RH and the state of heating. At this time, by detecting the temperature detection resistor Rt1 of the resistance bridge BG1 and the temperature detection resistor Rt2 of the resistance bridge BG2, a rough flow rate is detected to determine whether the flow rate is low or high. Can do.

  As a result, the flow rate is accurately detected by the resistance bridge BG1 or BG2 corresponding to the obtained flow rate F region. In this case, when the flow rate F is in the low flow rate region, the switches S1 to S4, S8, and Sa of the selection switch 5a are turned on to use the resistance bridge BG1. Further, when the flow rate F is in the high flow rate region, the switches S1, S5 to S8, and Sb are turned on to use the resistance bridge BG2. In the heating by the heating unit RH, the control unit 8b controls the switch S8 to be on and off so as to reach a predetermined temperature.

According to the second embodiment as described above, the temperature detection resistors Rt1 and Rt2 are provided in the sensor chip 1a, and the resistor bridges BG1 and BG2 to be used after the approximate flow rate is detected is determined. Therefore, the same effect as the first embodiment can be obtained.
In the above-described embodiment, the configuration using two resistance bridges BG1 and BG2 is shown. However, in this embodiment, a configuration using three or more resistance bridges may be used.

(Third embodiment)
FIG. 8 and FIG. 9 show the third embodiment, and the following description will be focused on differences from the first embodiment. In this embodiment, the sensor chip 20 is used in place of the sensor chip 1. The sensor chip 20 includes three or more and n (n is an integer of 3 or more) resistance bridges BG1 to BGn. Further, in this sensor chip 20, the heating part RH has a small circular pattern, and the resistance bridges BG1 to BGn are arranged in a concentric arc shape with the heating part RH as the center.

  Hereinafter, the detailed configuration of the sensor chip 20 will be described with reference to FIG. A heating part RHa is arranged in the central part (X = 0) of the element part 3a. The heating unit RHa includes an arcuate part obtained by cutting a part of a small circle having a predetermined radius with respect to the center position O, and two connecting parts that are led from both ends of the arcuate part to the lead part 3b. In the heating by the heating part RHa, heat is transmitted to a concentric spherical surface that spreads radially around the arc-shaped part.

  The resistance bridges BG1 to BGn are arranged and formed like BG1, BG2,..., BGn in order from the inner side near the heating unit RHa. Each resistance bridge BG1 to BGn includes four resistors Rxu1, Rxu2, Rxd1 and Rxd2 (x is 1 to n), and each is bridge-connected in the same manner as described above. The resistors Rxu1 and Rxu2 are disposed on the upstream side of the heating unit RH, and the resistors Rxd1 and Rxd2 are disposed on the downstream side of the heating unit RHa.

  The upstream-side resistors Rxu1 and Rxu2 are formed in an arc shape concentric with the center O so as to surround the arc-shaped portion of the heating portion RHa on the upstream side, and are linearly connected on the lead portion 3b side. And is formed in a double arc shape so as to be folded back on the opposite side to the lead portion 3b. In this case, the resistor Rxu1 is disposed on the outer side and the resistor Rxu2 is disposed on the inner side.

  Similarly, the downstream-side resistors Rxd1 and Rxd2 are formed in a concentric arc shape with respect to the center O so as to surround the arc-shaped portion of the heating portion RHa on the downstream side, and are linear on the lead portion 3b side. Are formed in a circular arc shape that is doubled so as to be folded back on the opposite side to the lead portion 3b. In this case, the resistor Rxd1 is located outside and the resistor Rxd2 is located inside.

  Each of the resistance bridges BG1 to BGn is set to a distance a1 to an so that the central position O of the heating unit RHa and the arcuate portions of the resistors Rxu1 and Rxu2 are separated at a predetermined interval, for example. Similarly, the distance between the central position O of the heating part RHa and the arcuate parts of the resistors Rxd1 and Rxd2 is also set to the distances a1 to an equal to the arrangement of the resistors Rxu1 and Rxu2.

  In each resistance bridge BGx (x is 1 to n), the resistors Rxu1 and Rxd1 are connected by a connecting resistor Rxj1 in the lead portion 3b. The resistors Rxu2 and Rxd2 are connected by a connecting resistor Rxj2 in the lead portion 3b. The connection end of the resistor Rxd1 opposite to the resistor Rxj1 is connected to the positive terminal Ax of the resistor bridge BGx together with the connection end of the resistor Rxu2 opposite to the resistor Rxj2.

  The connection end of the resistor Rxd2 opposite to the resistor Rxj2 is connected to the negative terminal Bx of the resistor bridge BGx together with the connection end of the resistor Rxu1 opposite to the resistor Rxj1. The central portion of the resistor Rxj1 is connected to the detection terminal Cx of the resistor bridge BGx. The central portion of the resistor R1j2 is connected to the detection terminal Dx of the resistor bridge BGx.

  One terminal of the heating unit RH is connected to the terminal H, and the other terminal is provided so as to be connected to the ground terminal GND although not shown. When the heating unit RHa is energized between both terminals, the temperature of the resistor rises due to the current at that time, thereby heating the fluid in the vicinity of the heating unit RHa.

  Next, the operation of the above configuration will be described with reference to FIG. In this embodiment, since three or more resistance bridges BG1 to BGn are provided, the flow rate detection range can be set separately as in the first embodiment. In this case, as shown in FIG. 9, the resistance bridge BG1 located on the innermost side is the detection range [1] with the highest flow rate, and the resistance bridge BG2 located on the outer side is the detection range [2] with the next highest flow rate. Thereafter, similarly, the lower detection ranges [3] to [n] are sequentially set in the same manner. The detection ranges [1] to [n] are divided by flow rates Fx1 to Fxn−1, respectively.

  In this way, by dividing the detection range of the fluid flow rate into n by the n resistance bridges BG1 to BGn, the detection signal S is obtained with respect to the value of the fluid flow rate F as shown in FIG. It can be obtained as a substantially proportional signal.

  In addition, when heating by the heating unit RHa, the fluid is heated in a state close to a point heat source, and is detected by a resistor that forms an arc with respect to the heat spreading in a hemispherical shape. Even when it does not flow linearly, the flow rate can be detected with high accuracy. Further, since the fluid is heated in a state close to a point heat source, temperature control can be facilitated.

  According to the third embodiment, the sensor chip 20 has a configuration in which the heating unit RHa is arranged in a small circular arc shape and the three or more resistance bridges BG1 to BGn are provided. The resistor of BGn was set in a circular arc shape so as to surround the heating part RHa.

  Thereby, the heating part RHa can be handled as a point heat source, and by providing the resistance bridges BG1 to BGn in an arc shape, an accurate flow rate can be detected without being affected by a change in the flow of the fluid. Further, by providing three or more resistance bridges BG1 to BGn, the detection range of the flow rate of the fluid can be further divided and set, thereby further improving the linearity in the characteristics of the flow rate and the detection signal. .

(Fourth embodiment)
FIG. 10 shows the fourth embodiment. Hereinafter, parts different from the first embodiment will be described. In this embodiment, the sensor chip 30 includes the resistance bridges BG1 and BG2 of the sensor chip 1 of the first embodiment, and the heating unit RH is provided with the heating unit RH having the arc shape shown in the third embodiment. Yes.

  Also according to the fourth embodiment, it is possible to obtain the same effect as that of the first embodiment. Moreover, since the heating part RHa having an arc shape is provided, heating without uneven heating can be performed as a point heat source during heating.

(Other embodiments)
In addition, this invention is not limited only to one embodiment mentioned above, It can apply to various embodiment in the range which does not deviate from the summary, For example, it can deform | transform or expand as follows. .

  In the said 1st Embodiment, although the thing of an H type pattern is employ | adopted as the heating part RH, it can also be set as the pattern by which a connection part is arrange | positioned at the edge part of two resistors. A pattern using a single resistor can also be used.

  In the second embodiment, the temperature detection resistors Rt1 and Rt2 for detecting a rough flow rate are provided exclusively, but instead of this, the detection terminals C1 and C1 of the resistor bridge BG1 (or resistor bridge BG2) are provided. The preliminary detection unit can also be configured by using D1 as an open state and using between the positive electrode terminal A1 and the negative electrode terminal B1 as one resistor.

  In the third embodiment, the heating part RHa having an arc shape and the resistance bridges BG1 to BGn are used. However, the resistance bridge BG1 including the linear resistor used in the first embodiment is similarly configured to n. It can also be set as the structure which arranges.

In each of the above embodiments, it is assumed that the fluid flowing through the flow path flows in the X direction. it can.
Examples of the fluid include gases such as air and various gases, and liquids such as water, fuel, and chemicals.

  In the drawings, 1, 20 and 30 are sensor chips, 4 and 4a are detection circuits, 5 and 5a are selection switches, S1 to S8, Sa and Sb are switches, 6, 10 are amplifiers, 7 and 11 are AD conversion circuits, 8 is a digital processing circuit, 8a and 8b are control units, BG1 to BGn are resistance bridges, RH and RHa are heating units, Rxu1 and Rxu2 (x is an integer from 1 to n) are upstream resistors, Rxd1 and Rxd2 ( x is an integer of 1 to n) is a downstream resistor.

Claims (7)

A heating unit (RH, RHa) provided in a fluid flow path;
A resistance bridge for temperature measurement having a pair of resistors (Rxu1, Rxu2, Rxd1, Rxd2 (x is an integer of 1 to n)) provided on both sides in the direction along the flow path of the heating unit, A plurality of resistance bridges (BG1, BG2, BG1 to BGn) provided so that arrangement intervals (X = a, b, a1 to an) of the heating unit and the resistors are different;
And a detection unit (4, 4a) that heats the fluid in the flow path by the heating unit and detects a flow rate of the fluid based on an output signal of any of the plurality of resistance bridges. Flow rate sensor. The flow sensor according to claim 1,
The detection unit (4, 4a) uses a detection signal of the plurality of resistance bridges having a small arrangement interval of the resistor relative to the heating unit for detection when the flow rate is high, and detects a large arrangement interval. A flow sensor characterized in that a signal is used for detection when the flow rate is low. The flow sensor according to claim 1 or 2,
The heating unit (RH) is configured such that the heat generating unit is composed of two straight portions and a portion connecting them, and the two straight portions are orthogonal to the direction along the flow path.
The resistance bridge (BG1, BG2) is a flow sensor characterized in that the resistor is formed in a straight line and is arranged so as to be orthogonal to a direction along the flow path. The flow sensor according to claim 1 or 2,
The heating part (RHa) is formed in a circular shape or an arc shape,
The flow rate sensor, wherein the plurality of resistance bridges (BG1 to BGn) are formed in an arc shape in which the resistor surrounds a heat generating portion of the heating portion. The flow sensor according to claim 1 or 2,
The heating part (RHa) is formed in a circular shape or an arc shape,
The resistance bridge (BG1, BG2) is a flow sensor characterized in that the resistor is formed in a straight line and is arranged so as to be orthogonal to a direction along the flow path. The flow sensor according to any one of claims 1 to 5,
A selection switch (5, 5a) for selectively inputting detection signals of the plurality of resistance bridges;
The detection unit (4, 4a) includes a signal processing unit (8), detects a flow rate of the fluid from a detection signal of a resistance bridge preselected by the selection switch among the plurality of resistance bridges, and When the flow rate detected by the resistance bridge deviates, the flow rate of the fluid is detected by the signal processing unit after switching to the corresponding resistance flow rate bridge by the selection switch. The flow sensor according to any one of claims 1 to 5,
Provided with a preliminary detection unit for detecting a signal corresponding to the temperature from the voltage between the power supply terminals of the resistance bridge or the voltage for temperature measurement with the reference resistance (9a, 9b) interposed in the power supply path,
The detection unit (4a) heats the fluid in the flow path by the heating unit, detects a flow level of the fluid based on a signal detected by the preliminary detection unit, and includes a plurality of resistance bridges. A flow rate sensor for detecting a flow rate of the fluid by selecting a detection signal of a resistance bridge corresponding to the flow rate level.

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