JP4474308B2 - Flow sensor - Google Patents

Description

  The present invention relates to a flow rate sensor that measures a flow rate by using a heating resistor, for example, a flow rate sensor suitable for measuring an intake air flow rate of an internal combustion engine.

  2. Description of the Related Art Conventionally, a thermal sensor that is installed in an intake air passage of an internal combustion engine such as an automobile and measures an intake air flow rate has become mainstream because it can directly detect a mass flow rate. In such a thermal flow sensor, it is relatively easy to produce a flow measuring element for measuring a flow rate on a semiconductor substrate such as silicon (Si) using a semiconductor microfabrication technology, in a mass production method. It has been attracting attention in recent years because it is economical because it can be performed, and it can be driven at low power with a small size.

  A flow rate that measures the flow rate with high accuracy even in a state where intake pulsation occurs in the engine and air flow (back flow) from the engine toward the air cleaner occurs due to stricter exhaust regulations and improved fuel efficiency. Measuring devices are becoming necessary. In order to measure the air flow rate with high accuracy even in the engine state described above, a flow rate measuring device having a response speed and direction detection function capable of following the pulsation is necessary.

  As an example of means for achieving this, in a sensor manufactured by using a semiconductor microfabrication technique on a semiconductor substrate such as silicon (Si) described above, a thin film measurement region is formed, and a flow rate measuring resistor is formed in the thin film region. It is possible to speed up the thermal response by forming a body. The direction detection function can be achieved by a flow rate measuring resistor pattern. By having the direction detection means, it is possible to measure the air flow rate more accurately than the flow rate sensor that does not have the direction detection means in an operating state where an air flow (reverse flow) from the engine toward the air cleaner is generated. Become.

  In the past, intake pulsation increased at low engine speeds of four-cylinder engines, and backflow was often generated near the throttle fully open, but the valve opening / closing time corresponding to recent exhaust gas regulations, fuel efficiency reduction, etc. changed In an engine that performs complicated control such as generating pulsation and backflow at a high speed, the backflow tends to increase. Also, a pulsating flow including a reverse flow is generated even in a multi-cylinder engine having four or more cylinders. Therefore, the direction detection function is a very effective means. Further, by forming the resistor for detecting the flow rate on the thin film in this way, a high-speed thermal response can be obtained with respect to the flow rate change. In this way, when a flow sensor that responds at high speed is applied to automobile control, even if the flow rate changes suddenly, it is possible to respond to the change in the flow rate. It is possible to measure the air flow rate more accurately than a slow flow rate sensor.

  However, air flowing through the intake pipe of an automobile on which the flow sensor is mounted contains pollutants such as dust and oil contained in the atmosphere. Although most of the fouling substances are removed by the air cleaner, for example, fine particles of 15 μm or less pass through the air cleaner and reach the flow sensor. In addition, due to aging of the air cleaner, there is a possibility that the pollutant accumulated in the air cleaner reaches the flow sensor. Since the flow rate measuring element used in the present invention has the thin film portion as described above, a configuration in which these fouling substances do not easily collide is effective from the viewpoint of reliability. As a means for realizing this, in the flow sensor, a sub-passage that performs inertia separation so that the pollutant does not collide with the flow measuring element is effective. For example, a sub-passage that has a curved portion whose diameter gradually decreases upstream from the forward flow of the flow rate measuring element is effective as the sub-passage that removes the pollutant due to inertia.

JP 2003-83788 A

  As described above, the reliability of the secondary passage having a curved portion whose diameter gradually decreases upstream of the flow measuring element is very high, but the flow velocity of the secondary passage changes in the radial direction of the flow path. , The central flow rate will be faster. Therefore, when mass production is performed, variation in flow characteristics is not sufficient.

  In addition, since the flow rate measuring element described above has a flat plate structure, the flow rate is not stable if the flow on the surface of the flow rate measuring element is disturbed. It is desirable that the flow rate measuring element is mounted on some support by bonding or the like, and the relationship between the surface position of the flow rate measuring element and the surface position of the support is such that the flow is not disturbed. However, due to manufacturing variations, the surface position of the flow measuring element and the surface position of the support vary due to the thickness variation of the flow measuring element, the thickness variation of the support, and the thickness variation of the adhesive when bonded. Due to this variation, variations such as flow rate characteristics and temperature characteristics occur.

  Due to the above two problems, the conventional configuration has a problem that the manufacturing variation of the flow sensor becomes large at the time of mass production.

In order to achieve the above object, the flow sensor of the present invention has a flow measuring element in the sub-passage so that the flow direction of the air flowing into the sub-passage having the curved portions upstream and downstream is directed toward the flow measuring element. A constricted part is formed on the surface facing the flow measuring element in the vicinity, and this constricted shape swells the surface facing the flow meter element into a substantially fan shape, and tilts to the position where the distance of the surface facing the flow measuring element is the smallest. The inner circumference side is configured to be steeper than the outer circumference of the auxiliary passage.

  According to the present invention, it is possible to provide a flow sensor with high reliability and small manufacturing variation during mass production.

  A throttle shape is formed in the vicinity of the flow measuring element in the sub-passage so that the forward flow and the reverse flow flowing into the sub-passage having a curved portion whose diameter gradually decreases in the upstream direction toward the flow measuring element. The apex of is located downstream of the flow rate measuring element with respect to the forward flow.

  Embodiments of the present invention will be described below with reference to the drawings. First, each component used in the present invention will be described.

FIG. 3 is a plan pattern diagram of the flow rate measuring element 1, and FIG. 4 is a cross-sectional view of the flow rate measuring element 1. The flow rate measuring element 1 is manufactured by a semiconductor manufacturing technique. This will be described below. A silicon dioxide layer is thermally oxidized or CVD (Chemical Vapor) as an insulating layer 3 on a single crystal silicon substrate 2.
A silicon nitride layer is formed by a method such as CVD. Next, a polycrystalline silicon layer is formed by a method such as CVD, and phosphorus (P) is doped as an impurity by thermal diffusion or ion implantation in order to obtain a desired resistance value. Thereafter, the polycrystalline silicon layer is patterned to form the heating resistor 4, the intake air temperature detecting resistor 5, the upstream temperature sensitive resistors 6, 7, the downstream temperature sensitive resistors 8, 9, and the lead resistor 12. Next, a silicon nitride layer and a silicon dioxide layer are formed as the protective layer 13 by a method such as CVD. Thereafter, the protective layer 13 is patterned to remove the portion of the protective layer 13 where the electrode 14 is to be formed. Next, after forming an aluminum layer as an electrode material, patterning is performed by etching to form an electrode 14. Finally, in order to form the cavity 15, patterning is performed on the surface of the single crystal silicon substrate 2 where the heating resistor 4 is not formed. Thereafter, the cavity 15 is formed by anisotropic etching. By hollowing out in this way, the regions where the heating resistors 4, the upstream temperature sensitive resistors 6, 7 and the downstream temperature sensitive resistors 8, 9 are arranged become a thermally insulated thin film portion 16. . Since the above-mentioned silicon dioxide and polycrystalline silicon have compressive stress and silicon nitride has tensile stress, the thin film portion 16 having no deflection is formed by laminating these materials with an appropriate film thickness. It becomes possible. Finally, it is divided into chips by dicing. Further, the resistor can be formed of single crystal silicon by using a substrate in which two single crystal silicon substrates whose surfaces are oxidized are bonded to each other. In addition, if the adhesion is appropriate, a metal material such as platinum can be used as the resistor.

  FIG. 5 is a partial cross-sectional view of the flow rate sensor module 100 mounted with the flow rate measuring element 1 of the present invention attached to the intake pipe. FIG. 6 is a cross-sectional view of the flow sensor module 100 of the present invention. The support 20 on which the flow rate measuring element 1 is mounted is formed of a laminated substrate made of glass ceramic. As the support 20, it is also possible to employ a high-temperature fired ceramic, a metal plate, a plastic material, or the like. However, since it is desirable that the flow rate measuring element 1 be thermally insulated from surrounding members, it is effective to employ a glass ceramic laminated substrate having a low thermal conductivity. Further, by adopting the laminated substrate, it is possible to integrally form the circuit 21 for supplying power to the flow measuring element 1 and performing signal processing from the flow measuring element 1 on the support 20. Since the support 20 and the circuit 21 are integrated in this way, the number of parts and the number of bonding points can be reduced, which is advantageous in terms of cost and reliability. In addition, since the circuit 21 for controlling the flow rate measuring element 1 using the inner layer conductor of the multilayer substrate can be configured, the circuit 21 can be reduced in size, so that the flow sensor module 100 can be reduced in size. it can. The support 20 is formed with a recess 22 for accommodating the flow rate measuring element 1, and the flow rate measuring element 1 is bonded to the recess 22 with an epoxy or silicone adhesive. The electrode 14 of the flow rate measuring element 1 and the electrode of the support 20 are electrically connected by a connection line 23 such as a gold wire. This connecting portion is covered with an epoxy-based or silicone-based resin in order to prevent electrolytic corrosion due to contaminants and moisture contained in the intake air. The support 20 on which the flow rate measuring element 1 is mounted is mounted on the housing case 24 with a silicone-based adhesive 23. Further, the housing case 24 is inserted into the main passage 25.

  In FIG. 5, the air (forward flow 26) flowing from the air cleaner toward the engine in the main passage 25 travels from the inlet 41 to the outlet 42 of the sub-passage 40. In order to cope with the detection of the reverse flow, as shown in the present invention, it is effective that the inlet 41 is opened on the air cleaner side and the outlet 42 is opened on the engine side. In this case, since the flow path of the sub-passage needs to go around, the cross-sectional area of the sub-passage occupying the cross-sectional area of the main passage becomes large, and the pressure loss increases. In order to reduce this, a configuration in which the support 20 is embedded in the wall surface of the sub-passage 40 and is used as a part of the wall surface of the sub-passage 40 is effective.

  Next, the operation principle of the flow sensor module 100 will be described with reference to FIGS. The heating resistor 4 constitutes a bridge circuit 30 together with the intake air temperature detection resistor 5, the resistor 10, and the resistor 11. The resistor 10 and the resistor 11 are formed on the circuit 21 on the support 20 or the flow rate measuring element 1. The bridge circuit 30 is feedback-controlled so that the heating resistor 4 is higher than the intake air temperature detection resistor 5 by a certain temperature. Four temperature sensing resistors, upstream temperature sensing resistors 6 and 7 and downstream temperature sensing resistors 8 and 9, constitute a bridge circuit 31. A voltage Vref is applied to the bridge circuit 31. The upstream temperature sensitive resistors 6, 7 and the downstream temperature sensitive resistors 8, 9 are heated to a predetermined temperature by heat conduction and heat transfer from the heating resistor 4. In the windless state, ideally, the upstream side temperature sensitive resistors 6 and 7 and the downstream side temperature sensitive resistors 8 and 9 are heated equally, so that the temperature difference is substantially zero. Therefore, the contact 32 and the contact 33 have substantially the same potential.

  Here, when the forward flow 26 is generated, the upstream side temperature sensitive resistors 6 and 7 are cooled and the average temperature is lowered, so that the resistance value becomes small. Accordingly, a potential difference is generated between the contact 32 and the contact 33. On the other hand, in the case of the backflow 27 in FIG. 3, contrary to the above, the downstream side temperature sensitive resistor 7 is cooled more than the upstream side temperature sensitive resistor 6, so that again between the contacts 32 and 33. A potential difference occurs. Since this potential difference increases with the flow rate, the flow rate can be measured based on this potential difference. In addition, the direction can be determined depending on which potential of the contact 32 and the contact 33 is high. This potential difference is input to the arithmetic unit 34, and the arithmetic unit 34 outputs a predetermined voltage with respect to the air flow rate.

  The auxiliary passage 40 will be described with reference to FIGS. The sub passage 40 flows out from the outlet 42 after making a round so that the air flowing in from the inlet 41 vortexes. In order to obtain an inertial effect, the flow path from the inlet 41 to the flow rate measuring element 1 is composed of a curved portion that gradually decreases in diameter. With this configuration, as shown in FIG. 8, before the air flow passes through the spiral flow path and reaches the flow rate measuring element 1, fouling substances such as dust and moisture are pressed against the outer peripheral surface by the inertia effect. Then, it is discharged from the outlet 32 as it is. Therefore, the fouling substance cannot reach the surface of the flow measuring element 1. For example, even when particles of about 5 to 200 μm are continuously charged into the main passage 25, the flow rate measuring element is not destroyed. Even in the case of moisture, even if the main passage 25 is continuously charged, the flow rate measuring element is not destroyed.

  Here, the flow measuring element 1 is mounted on the support 20, but the thickness variation of the single crystal silicon substrate 2, the variation in the depth of the recess 22 of the support 20, and the flow measuring element 1 is bonded to the support 20. The surface position of the flow rate measuring element 1 and the surface position of the support 20 vary due to variations in the thickness of the adhesive. FIG. 9 shows the surface position relationship of the standard position, and FIG. 10 shows an example in which the surface position relationship varies. If the surface positional relationship varies as shown in FIG. 10, the flow on the surface of the flow rate measuring element is disturbed at the end of the flow rate measuring element 1, so that it greatly changes as shown in FIG. When a measuring element is provided on a plate-shaped surface and air flows parallel to the surface of the measuring element, the flow velocity is very small on the very surface of the measuring element. Therefore, as shown in FIG. 10, when the relationship between the surface position of the flow rate measuring element 1 and the surface position of the support 20 changes, a great change occurs in the flow direction of the flow rate measuring element surface. Due to this change, as shown in FIG. 13, a large characteristic change occurs compared to the flow rate characteristic at the standard mounting position.

FIG. 1 shows the shape of the throttle 43 in the auxiliary passage 40 of the present invention. As shown in the cross section of FIG. 2, the upstream of the flow rate measuring element 1 has a shape in which the flow path cross section gradually becomes smaller. With this configuration, as shown in FIG. 11, the flow strikes the flow rate measuring element 1 from an oblique direction. In this configuration, even if the surface position of the flow rate measuring element 1 and the surface position of the support 20 vary as shown in FIG. 12, they are hardly affected by this, so that the characteristic change hardly occurs as shown in FIG. 13. However, the configuration in which the flow is directed toward the flow rate measuring element 1 as shown in FIG. 11 is effective when applied to the auxiliary passage 40 having the inertia effect as shown in the present invention. If the air flow is directed toward the flow rate measuring element 1 in the passage where inertia separation is not performed, the air containing the pollutant collides with the surface of the flow rate measuring element. Therefore, the possibility of destroying the thin film portion 16 of the flow rate measuring element 1 is higher than that in the configuration of FIG. Therefore, by applying to the sub-passage 40 having the effect of inertia separation as shown in the present invention, it is possible to provide the flow sensor module 100 that is reliable and has a small variation in characteristics during mass production.

Further, in the flow sensor module 100, the influence of the drift generated in the main passage 25 can be reduced by arranging the thin film portion 16 of the flow measurement element 1 at a position where the flow velocity in the sub passage 40 is large. In the sub-passage 40 employed in the present invention, the pollutant is separated into the outer periphery of the sub-passage, so it is more effective to arrange the flow rate measuring element 1 inside the sub-passage.

Here, in the sub-passage, the flow velocity in the inner peripheral portion is larger than that in the outer peripheral portion. Further, in the shape of the diaphragm 43 of the present invention, as shown in FIG. 14, even when the height of the diaphragm 43 is the same on the inner periphery and the outer periphery, the inclination to the throttle portion apex 44 is steeper on the inner periphery. Become. Since the flow rate measuring element 1 is disposed in the vicinity of the inner periphery, there is an effect of further increasing the flow velocity of the inner periphery, and therefore, the influence of drift can be reduced. Further, since the flow is more directed toward the flow rate measuring element 1 in the inner peripheral portion, variation can be reduced.

  On the other hand, as shown in FIGS. 1 and 2, the configuration in which the flow is directed toward the flow rate measuring element 1 is effective even when the backflow 27 is generated. When the backflow 27 is generated, the flow passes through a state where the flow rate is zero, and the flow is reversed. Therefore, as shown in FIG. 10, if there is a mounting variation near the flow rate measuring element 1, a flow rate error is likely to occur. In particular, in the state in which the reverse flow 27 starts to occur, the minimum flow rate at the time of pulsation is close to zero, but the flow becomes unstable due to variations, so that the flow rate measuring element 1 cannot follow the flow and a flow rate error is likely to occur. .

  However, in the configuration of the present invention, stability against variations is improved, so that the flow rate error can be reduced even during pulsation including backflow. Here, if the throttle portion apex 44 exists on the flow rate measuring element, it causes variation. Since the occurrence frequency of the backflow 27 is lower than the occurrence frequency of the forward flow 26, a configuration in which the apex of the restriction exists on the downstream side of the flow rate measuring element 1 is effective.

  FIG. 17 shows a system diagram of an internal combustion engine such as a gasoline engine. The intake air flow into the engine is applied to the air cleaner 102, the intake passage 12, the throttle angle sensor 103, the idle speed control valve 104, and the throttle body 105 in the course of flowing through the intake passage 12 formed integrally with the intake manifold 106. The flow rate and the flow direction are detected by the measuring device 100, and the detected signal is taken into the vehicle control unit 107 by voltage or frequency.

  The flow rate signal is used for control of the combustion section structure and subsystem composed of the injector 108, the rotation speed meter 109, the engine cylinder 110, the exhaust manifold 111, and the oxygen concentration meter 112.

  Although not shown, the basic configuration of a diesel engine system is almost the same as that of a gasoline system, and the flow rate measuring device of the present invention can be applied.

The figure which shows the subchannel | throttle restrictor shape of the flow measuring device by this invention. Sectional drawing of the subchannel | throttle restricting part of the flow measuring device by this invention. The top view of the flow measuring element of this invention. Sectional drawing of the flow volume measuring element of this invention. The figure which has arrange | positioned the flow sensor module of this invention in the intake pipe. Sectional drawing of the flow sensor module of this invention. The drive circuit diagram of the flow sensor of this invention. The schematic diagram which shows the inertia effect of the subchannel | path of this invention. The figure which shows the example of mounting to the support body of the flow volume measuring element of this invention. The figure which shows the example of mounting to the support body of the flow volume measuring element of this invention. The figure which shows the example of mounting to the support body of the flow volume measuring element of this invention. The figure which shows the example of mounting to the support body of the flow volume measuring element of this invention. Flow characteristic diagram. The figure which shows the aperture shape of this invention. Sectional drawing which shows the aperture shape of this invention. Sectional drawing which shows the aperture shape of this invention. The control system figure of an internal-combustion engine using the flow measuring device of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Flow measuring element, 2 ... Single crystal silicon substrate, 3 ... Insulating layer, 4 ... Heating resistor, 5 ... Intake temperature detection resistor, 6, 7 ... Upstream temperature sensing resistor, 8, 9 ... Downstream feeling Thermal resistor, 10, 11 ... resistor, 13 ... protective layer, 14a to 14k ... electrode, 15 ... hollow portion, 44 ... vertical portion apex.

Claims (2)

A flow rate measuring element having means for detecting a fluid flow direction; a support for mounting the flow rate measuring element; and a sub-passage in which the flow rate measuring element is arranged, wherein the sub-passage is the flow rate measuring device. In the flow sensor having a bent portion upstream and downstream of the element, and the support constitutes a part of the wall of the sub passage,
The flow of air flowing from the air cleaner to the engine in the sub-passage (forward flow) is deflected in the direction toward the surface of the flow rate measuring element, and the flow of air from the engine to the air cleaner in the sub-passage (reverse flow) In order to deflect the flow of air in the direction toward the surface of the flow rate measuring element, a throttle portion is formed on the surface of the sub-passage that faces the flow rate measuring element,
The position where the distance between the surface facing the support and the flow rate measuring element is the smallest is downstream from the center position of the flow rate measuring element in the direction (forward flow) from the air cleaner to the engine in the sub-passage of the flow rate measuring element. On the side,
The constriction part swells the surface facing the flow meter element in a substantially fan shape, and the slope to the position where the distance of the surface facing the flow measuring element is the smallest is steeply inclined on the inner peripheral side than the outer periphery of the sub-passage. A flow sensor characterized by that. 2. The flow sensor according to claim 1, wherein the throttle part has a deflection angle to the flow measuring element on the reverse flow side larger than a deflection angle to the flow measuring element on the forward flow side.

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