JP2014098721A - Thermal air meter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thermal air meter that secures size precision by suppressing deformation during molding of a base member, and measures an air flow rate with high precision by reducing an influence of size variation on measurement precision.SOLUTION: A thermal air meter 200 includes a housing member 211 arranged in an intake passage of an internal combustion engine, and a base member 230 having a sub air passage 202 which is fixed to the housing member 211 and in which part of air passing through the intake passage flows. The base member 230 is composed of a plate-like resin molding made of a synthetic resin material, and has a reinforcing structure 231 for improving the strength of the base member 230, formed integrally between a substrate fixation part 301 to which a circuit board 205 is fixed, and a sub-passage constitution part 302 formed at a tip part of the substrate fixation part 301. Consequently, the strength of the base member 230 molded out of the resin is secured, and warpage deformation of the base member 230 during molding is suppressed.

Description

  The present invention relates to a thermal air flow meter that measures the flow rate of air, for example, a thermal air flow meter that is attached to an intake pipe of an internal combustion engine and measures the flow rate of intake air supplied to the engine.

  A thermal air flow meter that measures the flow rate of intake air supplied to an internal combustion engine is used by being attached to a part of the intake system of the internal combustion engine. The thermal air flowmeter has a structure in which, for example, a flow rate detection element such as a heating resistor is heated to measure the flow rate of passing air from the amount of heat released to the air. Therefore, it is necessary to consider the protection of the flow rate detection element from contaminated materials and the like in long-term use and ensuring the flow rate measurement accuracy. Further, in the intake pipe of an internal combustion engine, the intake air flow rate is arranged under a pulsating flow as the intake and exhaust valves of the engine are opened and closed, and it is also necessary to consider intake pulsation such as a backflow that occurs when the intake pipe resonates. .

  For this reason, in a conventional thermal air flow meter used for an internal combustion engine, as described in Patent Document 1, a flow rate detection element is disposed in a sub air passage, and a flow rate detection element from a pollutant, a reverse flow, or the like. It has been done to protect. Furthermore, in recent years, high-precision measurement of intake air flow rate has been demanded from the viewpoint of cleaner exhaust gas and improved fuel efficiency, and a thermal air flow meter that accurately measures the backflow generated in the intake pipe is required. ing.

  Further, as a thermal air flow meter having a rib structure described in the present invention, a structure in which a rib is provided on the back surface of an element for seismic reinforcement of a cantilever structure element is disclosed in Japanese Patent Application Laid-Open No. Hei 5- Proposed in 302839. Furthermore, JP 2002-107201 A as disclosed in Patent Document 3 can be cited as an example of measures against deformation against sink marks during injection molding. This is to reduce sink marks generated during injection molding by providing ribs, thereby improving the flatness of the opposing surface, thereby preventing air from leaking from the insertion portion of the flow meter into the intake system. .

Japanese Patent No. 3530222 Japanese Patent Laid-Open No. 5-302839 Japanese Patent Laid-Open No. 2002-107201

  The thermal air flow meter measures the reverse flow with the detection element placed in the secondary air passage, so the secondary air passage of the thermal air flow meter requires a complicated structure such as a bent passage and a throttle shape. Is done. On the other hand, the cost reduction of the thermal air flow meter is also demanded at the same time. In other words, it is necessary to overcome the conflicting problem of requiring a complicated structure while simultaneously reducing the cost.

  When the auxiliary air passage becomes complicated, there is a proposal to increase the number of components and combine them to configure the auxiliary air passage. However, increasing the number of parts leads to an increase in cost, and it is necessary to construct a complex structure without increasing the number of parts in order to achieve a reduction in cost. By doing so, it is possible to reduce the assembly man-hours in addition to reducing the parts cost, and it is possible to reduce the cost or increase the cost of the thermal air flow meter.

  Taking the structure shown in Patent Document 1 as an example, the main components of a thermal air flow meter are: 1) flow rate detection element 2) housing 3) circuit board 4) metal base 5) secondary air passage member 6 ) Cover is composed of a total of 6 parts.

  Of these, the parts mainly constituting the sub air passage are two parts, a part of the metal base and the sub air passage member. Since the auxiliary air passage member is manufactured by resin molding, a complicated passage structure can be easily formed.

  However, in the metal base, a part forms a secondary air passage, while in the other part, the part has a function of bonding and fixing a circuit board, a housing, and the like. Further, since the metal base is formed from a flat metal material by pressing, it is advantageous for maintaining a flat surface for adhesion or the like, but is not suitable for forming a complicated sub air passage.

  Therefore, it is conceivable that only the sub air passage portion constituted by the metal base member is formed of resin in the same manner as the sub air passage member. However, in order to arrange the flow rate detecting element in the sub air passage, this portion is used. As a result, the number of parts and the number of assembly steps must be increased, resulting in an increase in the cost of the thermal air flow meter.

  To cope with these problems, it is conceivable to use a metal base as a resin base by resin molding. However, the sub air passage portion having a complicated structure tends to be thick in resin, and circuit boards, housings, etc. The part to be bonded and fixed is preferably thin.

  Therefore, if the thick part and the thin part are formed as the same molded part, the heat shrinkage difference between the thick part and the thin part becomes non-uniform during molding, and a warp phenomenon may occur at the boundary between the thick part and the thin part. . This warpage deformation not only causes problems in the adhesion of the housing and circuit board, but also causes variations in the amount of warpage, resulting in variations in the shape of the flow measurement unit, resulting in variations in flow measurement accuracy. Produce.

  The present invention has been made in view of the above points, and the object of the present invention is to suppress deformation during molding of the base member to ensure dimensional accuracy and to reduce the influence on measurement accuracy due to dimensional change. An object of the present invention is to provide a thermal air flow meter capable of measuring an air flow rate with high accuracy.

  A thermal air flow meter of the present invention that solves the above-described problems has a housing member disposed in an intake passage of an internal combustion engine, and a sub-passage through which a part of air that is fixed to the housing member and passes through the intake passage flows. A plate-like base member, a flow rate detecting element disposed in the sub-passage, and a circuit board that is electrically connected to the flow rate detecting element, inputs a heat radiation amount of the flow rate detecting element, and outputs a signal corresponding to the air flow rate The base member is made of a synthetic resin material, and is formed integrally with a substrate fixing portion to which the circuit board is fixed and a tip portion of the substrate fixing portion. And a reinforcing structure that is provided in at least a connecting portion between the substrate fixing part and the auxiliary path constituent part to improve the strength of the base member. Features

  According to the thermal air flow meter of the present invention, the base member is made of a synthetic resin material, and is formed integrally with the substrate fixing portion to which the circuit board is fixed and the front end portion of the substrate fixing portion so as to be integrally formed. And a reinforcing structure for improving the strength of the base member provided at least at the connecting portion between the substrate fixing part and the auxiliary path constituent part. The strength of the flat base member is improved by the reinforcing structure.

  Therefore, when forming a base member having a substrate fixing portion composed of a thin portion having a substantially constant resin thickness and a sub-passage component in which a thick portion exists to form a sub-passage, the thin-wall portion and the thick-wall portion are formed. Even when a state in which the heat shrinkage difference is non-uniform occurs, warping deformation of the base member occurring at the boundary between the thick part and the thin part can be suppressed.

  Therefore, it is possible to prevent problems in mounting to the housing member and circuit board due to warp deformation, and also prevent variations in flow rate measurement accuracy.

Sectional drawing which shows a thermal type air flowmeter. FIG. It is a figure which shows the conventional base member, (a) is the figure which showed the base member from the joint surface side with a housing member, (b) is the sectional view on the AA line of (a). It is a figure explaining the difference of the cooling time of a thin part and a thick part, (a) is sectional drawing equivalent to FIG.3 (b), (b) expands the principal part of (a), respectively. FIG. It is a figure which shows an example of the curvature deformation | transformation which generate | occur | produces in a base member, (a) is sectional drawing equivalent to FIG.3 (b), (b) is a figure which expands and shows the principal part of (a). It is a figure which shows one Example, (a) is the front view which looked at the base member from the joint surface side with a housing member, (b) is the side view seen from the upstream in the forward flow direction, (c) is a top view. It is a figure which shows another Example, (a) is the front view which looked at the base member from the joint surface side with a housing member, (b) is the side view seen from the upstream in the forward flow direction, (c) is a top view (D) is the BB sectional view taken on the line of (a). It is a figure which shows another Example, (a) is the front view which looked at the base member from the joint surface side with a housing member, (b) is the side view seen from the upstream in the forward flow direction, (c) is a plane The figure, (d) is CC sectional view taken on the line of (a). It is a figure which shows another Example, (a) is the front view which looked at the base member from the joint surface side with a housing member, (b) is the side view seen from the upstream in the forward flow direction, (c) is a plane Figure. It is a figure which shows another Example, (a) is the front view which looked at the base member from the joint surface side with a housing member, (b) is the side view seen from the upstream in the forward flow direction, (c) is a plane Figure. The figure which shows the operation | movement principle of a thermal type air flowmeter. The figure which shows the control system of an internal combustion engine.

  Embodiments of the present invention will be described in detail with reference to the following drawings.

  First, the operation principle of a typical thermal air flow meter using a heating resistor will be described as an example of an intake air measuring device.

  FIG. 11 is a schematic circuit diagram showing the operation principle of the thermal air flow meter.

  The drive circuit of the thermal air flow meter is roughly divided into a bridge circuit and a feedback circuit. The heating resistor RH for measuring the intake air flow rate, the temperature sensing resistors RC and R10, R11 for compensating the intake air temperature are combined with a bridge circuit, and the operational resistor OP1 is used to apply feedback to the heating resistor RH. A heating current Ih is passed through the heating resistor RH so as to maintain a constant temperature difference between the temperature sensitive resistors RC, and an output signal V2 corresponding to the air flow rate is output. That is, when the flow rate is high, a large amount of heat is taken from the heating resistor RH, so that a large amount of heating current Ih is passed. On the other hand, when the flow rate is slow, the amount of heat taken away from the heating resistor RH is small, so that the heating current Ih can be reduced.

Next, the configuration of the thermal air flow meter of the present invention will be described with reference to FIG.
The main air passage 250 constituted by the intake pipe constituting member 251 has an air cleaner side (not shown) on the left side in the drawing and an engine side (not shown) on the right side. As the air flow direction, the air flow from the left side of the figure to the right side of the figure is the forward air flow, which is generally called the forward flow 252 and is the air flow normally taken into the engine.

  On the other hand, the air flow from the right side to the left side in the figure is a reverse flow, and is generally an air flow called a reverse flow 253. Such a reverse flow 253 is unlikely to occur under normal engine operating conditions, but the intake air pulsates due to the opening and closing of the intake and exhaust valves of the engine, and the throttle valve (not shown) is largely opened in a high load state, and further the engine rotation It is generally known that when several cycles and the nth order wave of the natural frequency of the intake pipe are synchronized, the pulsation amplitude of the intake pulsation increases and a backflow 253 is generated.

  In recent years, it has been required to measure the intake air flow rate with high accuracy for exhaust gas regulations and fuel efficiency reduction. In the thermal air flow meter, the intake air flow rate that also measures the air flow rate of the reverse flow 253 is required. There is a high demand for high-precision measurement.

  Also in the thermal air flow meter 200 shown in FIG. 1, the flow rate detecting element 201 not only measures the intake air flow rate but also detects the flow direction, and the air flow rate of the forward flow 252 and the air flow of the reverse flow 253 are detected. The one with the function to measure the flow rate is used. In addition, regarding the measuring method of the forward flow 252 and the backflow 253, a well-known technique is used and description is abbreviate | omitted in this invention.

  The flow rate detecting element 201 is installed in a sub air passage (sub passage) 202. The sub air passage 202 has a passage structure in which the passage inlet 203 is opened facing the forward flow direction and the passage outlet 204 is opened facing the reverse flow direction so that each air flow can be easily introduced into the sub air passage 202. It has become. The flow rate detecting element 201 is mechanically fixed and electrically connected to the circuit board 205 constituting the drive circuit of the thermal air flow meter 200 in the same manner as the electronic circuit component 206 such as an IC chip. .

  The circuit board 205 is electrically connected to the connector terminal 208 via an aluminum wire 207, and has a configuration in which an air flow rate signal is output to the outside at the same time that power and ground inputs are obtained. The thermal air flow meter 200 is mechanically connected to the intake pipe constituting member 251 by a fixing member such as a screw 209.

FIG. 2 is a part development view showing a part structure of the thermal air flow meter shown in FIG.
The thermal air flow meter 200 includes a total of four components including a housing member 211, a cover member 220, a circuit board 205, and a base member 230 as main components.

  The housing member 211 is made of a synthetic resin mold part such as plastic or a metal casting part, and is configured by a substantially rectangular plate-like member having a predetermined plate thickness. The housing member 211 is attached in the intake pipe constituent member 251 so as to extend in a direction orthogonal to the air flow so that both planar portions are in a posture state along the air flow. A flange portion for fixing to 251 and a connector terminal 208 for electrically connecting the circuit board 205 and an external device are provided.

  In the housing member 211, the base member 230 is attached to one base member attachment surface, and the cover member 220 is attached to the other cover member attachment surface. An opening hole 212 into which the electronic circuit component 206 of the circuit board 205 fixed to the base member 230 can be inserted and accommodated is formed on the base end side of the housing member 211, and on the distal end side and the cover member mounting surface side A housing groove portion 213 that forms the second passage portion 202 </ b> B of the sub air passage 202 in cooperation with the cover member 220 is recessed.

  The housing groove 213 is formed so as to extend in the forward flow direction from one side in the short direction disposed on the upstream side in the forward flow direction toward the other side in the short direction disposed on the downstream side in the forward flow direction. Is formed so as to penetrate through to the base member mounting surface side and the downstream end is continuous to the end portion on the other side in the lateral direction. Then, the cover member 220 is joined and combined with the cover member mounting surface of the housing member 211 to cover the open portion of the housing groove portion 213, and the second passage portion 202B and the passage outlet 204, which are part of the auxiliary air passage 202. Is configured.

  The cover member 220 is made of a plate-like member formed of resin or the like, and has a size that covers the open portion of the housing groove 213.

  The circuit board 205 is electrically connected to the flow rate detection element 201 and has a configuration for inputting a heat radiation amount of the flow rate detection element 201 and outputting a signal corresponding to the air flow rate. Various electronic circuit components 206 and conductor wiring (without symbols) are arranged on the circuit board 205, and the flow rate detection element 201 is also mechanically and electrically connected to the circuit board 205. In this structure, the flow rate detecting element 201 is exposed.

  The base member 230 is a plate-like resin molded product made of a synthetic resin material, and includes a flat plate-like substrate fixing portion 301 to which the circuit board 205 is bonded and fixed, and a first passage portion 202A that is a part of the sub air passage 202. Has a sub-passage component 302 that forms

  The board fixing portion 301 has a size that closes the opening hole 212 of the housing member 211 when attached to the base member mounting surface of the housing member 211, and sandwiches the circuit board 205 between the housing member 211. , To accommodate.

  The sub-passage component 302 is joined to the base member mounting surface of the housing member 211 in combination with the base member 230, so that the first passage portion 202 </ b> A that is a part of the sub-air passage 202 is cooperated with the housing member 211. The base groove part 214 which forms is recessed.

  The base groove portion 214 includes a passage portion 214a that is disposed so as to extend from the upstream side toward the downstream side in the forward flow direction, and a passage portion 214b that is bent toward the substrate fixing portion 301 at the end of the passage portion 214a. And a passage portion 214c which is bent at the end of the passage portion 214b and extends from the downstream side in the forward flow direction toward the upstream side along the passage portion 214a. The base groove portion 214 is formed such that the end portion of the passage portion 214c is disposed at a position facing and communicating with the upstream end of the housing groove portion 213 that opens through the housing member 211.

  3-5 is a figure explaining the factor by which curvature deformation generate | occur | produces in a base member. FIG. 3 is a view showing only a state in which the circuit board 205 is mounted on the base member 230, and FIG. 3A is a view showing the base member 230 from the joint surface side with the housing member 211. 3 (b) is a cross-sectional view taken along line AA in FIG. 3 (a). FIG. 4 is a diagram for explaining a difference in cooling time between the thin wall portion and the thick wall portion, and FIG. 5 is a diagram illustrating an example of warpage deformation occurring in the base member. ) Is a cross-sectional view corresponding to FIG. 3B, and FIGS. 4B and 5B are enlarged views of the main part of FIG. 4A and the main part of FIG. FIG.

  The base member 230 is a resin component in which the substrate fixing portion 301 and the sub passage constituting portion 302 are integrated, and is molded by, for example, injection molding. When the thermal air flow meter 200 is used in an automobile engine, the usage environment is harsh, and therefore, it is common to use PBT (polybutylene terephthalate) resin or the like called engineering plastics and perform molding by injection molding or the like.

  This injection molding is a processing method in which a resin material is melted at a high temperature of 250 ° C. or higher, injected under pressure, filled in a mold, and molded. After the molding, the resin temperature is cooled and taken out. It is completed as a part.

  In general, in a flat portion 401 that extends in a flat plate shape with a constant plate thickness such as the substrate fixing portion 301, when the resin thickness is increased, slight irregularities called sink marks after molding occur. Therefore, in such a flat portion 401, the resin thickness is generally formed as a thin wall.

  On the other hand, in the sub passage structure 302, it is necessary to form not only the flat portion 401 but also the vertical wall 402 standing upright from the flat portion 401, and the shape becomes complicated. Therefore, in the sub-passage constituting part 302, the resin thickness is not constant, and the resin thickness is thicker (t2) than the thin (t1) flat portion 401 (t2> t1). That is, as shown in FIG. 4, a thin part 411 and a thick part 412 having different resin thicknesses are mixed in one resin component (base member).

  In FIG. 4, the wall portion (vertical wall 402) perpendicular to the bonding surface of the circuit board 205 is described as the thick portion 412 for easy explanation, but this wall portion is not necessarily described. The thick portion 412 is not necessarily obtained.

  As described above, in the case of injection molding, a resin melted at a high temperature is injected into a mold for molding. Therefore, if there is a portion having a different resin thickness, a time difference occurs until the resin temperature cools after molding. That is, as shown in FIG. 4, even if the resin temperature is cooled in the thin wall portion 411, the temperature of the resin surface in the thick wall portion 412 is cooled, but the resin temperature is not completely cooled in the resin. And a portion 413 where cooling is delayed occurs.

  Thus, if a time difference occurs between the thin wall portion 411 and the thick wall portion 412 until the resin temperature cools, residual stress remains in the resin even when the resin wall is completely cooled. If this residual stress remains, for example, as shown in FIG. 5, the shape of the base member 230 undergoes deformation called warpage.

  For example, in the case of the configuration shown in FIG. 5A, the left side of the sub-passage configuration portion 302 of the base member 230 is a resin wall, which is a restrained state 501 that is structurally restrained. On the other hand, the right side of the auxiliary passage constituting portion 302 in the drawing is an open state 502 that is structurally open by the base groove portion 214 constituting the auxiliary air passage 202.

  For this reason, due to the influence of the residual stress, it is fixed on the constrained side and the residual stress is released in the open direction, so that the shape opens to the open side, resulting in a constrained state as shown in FIG. The shape is inclined to the bent side (the left side in the figure), causing deformation called warpage.

  When this warpage deformation occurs and the amount of warpage varies for each base member 230, the flow area of the sub air passage 202 and the distance between the inner wall of the sub air passage 202 and the flow rate detection element 201 vary, May affect the measurement accuracy of the flow rate. Further, the warp deformation of the base member 230 may affect the bonding to the housing member 211 and the adhesion of the circuit board 205. Therefore, it is necessary to minimize the warp deformation of the base member 230 during molding.

  6A and 6B are diagrams showing an embodiment of the base member. FIG. 6A is a front view of the base member as seen from the joint surface side with the housing member, and FIG. 6B is a view as seen from the upstream side in the forward flow direction. FIG. 6C is a plan view.

  The base member 230 is provided with ribs 231 as a reinforcing structure that improves the strength of the base member 230. The rib 231 is molded simultaneously with the base member 230 by a mold using the same resin material by the same molding method as the base member 230.

  The circuit board 205 (shown by a dotted line) on which the flow rate detecting element 201 is arranged and the base member 230 are bonded and fixed (the adhesive is not shown), but the rib 231 has a back-to-back direction with the bonding surface of the circuit board 205. Is provided on the surface. That is, the rib 231 protrudes from the outer surface disposed on the side away from the housing member 211 of the substrate fixing portion 301, and the thin substrate fixing portion 301 to which the circuit board 205 is bonded, and the first passage portion 202A. It is installed so as to connect the connecting portion with the thick sub-passage constituting portion 302 that constitutes the wall surface.

  In this embodiment, the rib 231 is formed so as to protrude from the outer surface of the substrate fixing portion 301 at the center position in the short direction of the base member 230 and to extend from the base end portion to the distal end portion of the substrate fixing portion 301. ing. Therefore, for example, when a residual stress that generates a warp as shown in FIG. 5A acts, the rib 231 acts like a refilling rod, and the warp of the base member 230 can be suppressed.

  FIG. 7 is a view showing another embodiment of the base member, FIG. 7 (a) is a front view of the base member as seen from the joint surface side with the housing member, and FIG. 7 (b) is from the upstream side in the forward flow direction. FIG. 7C is a plan view, and FIG. 7D is a cross-sectional view taken along line BB in FIG. 7A.

  What is characteristic in the present embodiment is that a rib 232 extending from the substrate fixing portion 301 to a position in the vicinity of the flow rate measuring portion of the sub passage constituting portion 302 is provided as the reinforcing structure. Note that the same components as those in the above-described embodiment are denoted by the same reference numerals, and detailed description thereof is omitted. In FIG. 7, the circuit board 205 and the flow rate detection element 201 are not shown.

  When the flow rate detection element 201 of the thermal air flow meter 200 is disposed in the sub air passage 202, it is necessary to measure a stable flow of the measurement fluid. For this reason, the narrowest portion where the cross-sectional area in the sub air passage 202 is the narrowest is used as the flow measuring unit, and the flow rate detecting element 201 is disposed in the flow measuring unit. A method of temporarily narrowing the flow is provided by providing a narrowing portion 215.

  FIG. 7 shows an embodiment in which the throttle portion 215 is provided in the sub air passage 202. As shown in FIG. 7D, the throttle portion 215 forms a convex shape that protrudes into the sub air passage 202 at a substantially central position of the passage portion 214c of the base groove portion 214, and the flow area of the sub air passage 202 is increased. It has a configuration that narrows in the width direction.

  Therefore, the outer wall portion of the sub-passage constituting portion 302 that becomes the back surface of the throttle portion 215 has a concave shape. In the present embodiment, the rib 232 extends to the outer wall portion. According to such a configuration, the single connected rib 232 passes from the substrate fixing unit 301 to the position near the flow rate measuring unit. Therefore, the strength of the base member 230 can be further improved simultaneously with the stabilization of the measurement fluid in the auxiliary air passage 202.

  According to the above configuration, since the rib 232 extends to a position in the vicinity of the flow rate measurement unit, variations in flow rate measurement accuracy can be suppressed. A dimensional change such as a cross-sectional area in the flow rate measurement unit in the auxiliary air passage 202 or a distance between the flow path wall and the flow rate detection element 201 has a sensitive effect on the flow rate measurement accuracy. The flow rate detecting element 201 is preferably measured in a state where the air flow is stabilized, and is installed at a position where the cross-sectional area in the sub air passage 202 becomes the narrowest. In the vicinity of the passage inlet 203 and the passage outlet 204 of the auxiliary air passage 202, the cross-sectional area is wider than that of the flow rate measurement unit, so that the change in the cross-sectional area of the passage is small even if there is a dimensional variation of ± 0.1 mm. On the other hand, in the flow rate measurement unit where the cross-sectional area of the passage is the narrowest, even if the dimensional change is the same ± 0.1 mm, the cross-sectional area is relatively larger than the passage inlet 203 of the secondary air passage 202 and the like. The change in the flow rate increases, and the flow measurement error increases accordingly. Of course, if the flow vector changes due to the influence of warpage in the flow rate measurement unit, it becomes a direct flow measurement error. Therefore, reducing the dimensional change in the vicinity of the flow rate detection element 201 leads to an improvement in flow rate measurement accuracy. . In the thermal air flow meter 200 of the present invention, since the rib 232 extends to a position near the flow rate measurement unit in the sub air passage 202, the rigidity of the flow rate measurement unit is high, and the dimensional shape of the flow rate measurement unit changes. Can be reduced, and variations in flow rate measurement accuracy can be suppressed.

  FIG. 8 is a view showing still another embodiment of the base member. FIG. 8A is a front view of the base member as seen from the joint surface side with the housing member, and FIG. 8B is the upstream side in the forward flow direction. 8C is a plan view, and FIG. 8D is a cross-sectional view taken along the line CC of FIG. 8A.

  What is characteristic in the present embodiment is that the ribs 233 are provided on the ribs 233 to make the resin thickness of the base member 230 uniform, and the thicknesses 234 are provided at a plurality of locations. In the figure, there are six places in total, five places in the substrate fixing part 301 and one place in the sub passage constituting part 302, but this number is not particularly limited.

  The rib 233 is configured to extend to the back surface of the throttle portion 215, similarly to the rib 232 of FIG. By providing the base member 230 with the thinning 234, the thick portion by the rib 233 is eliminated, the resin thickness of the entire base member 230 is made uniform, the time difference until the resin cools from high temperature is eliminated, and the dimensional accuracy is ensured. Can do.

  Further, providing the ribs 234 on the ribs 233 further works to improve the dimensional accuracy of the base member 230.

  Providing the base member 230 with the rib 233 is useful for improving the strength of the base member 230, but it will partially create a thick portion on the base member 230, until the resin cools from high temperature after molding, There may be a difference in cooling time between the thick part and the thin part, and the base member 230 may be distorted.

  This distortion causes the deterioration of the dimensional accuracy of the base member 230 as well as the warp. Therefore, in this embodiment, by providing the ribs 233 with the thinning 234, the base member 230 is free from thick portions, and the time difference until the resin cools from high temperature can be eliminated, thereby ensuring dimensional accuracy.

  FIG. 9 is a view showing still another embodiment of the base member. FIG. 9A is a front view of the base member as viewed from the joint surface side with the housing member, and FIG. 9B is the upstream side in the forward flow direction. FIG. 9C is a side view seen from above.

  What is characteristic in the present embodiment is that the rib 233 and the lightening 234 shown in FIG. 8 are arranged on the entire outer surface of the substrate fixing portion 301. In the present embodiment, a configuration in which a plurality of ribs 233 and a thinning 234 are provided only on the outer surface of the substrate fixing portion 301 is described. May be arranged.

  In particular, in this embodiment, the ribs 233 are installed so as to have a lattice shape, so that the dimensional accuracy of the base member 230 can be further improved. As in the other embodiments described above, for example, even if the dimensional change is ± 0.1 mm, the influence is large in the flow measurement unit, and the influence is small in the passage inlet 203 and the passage outlet 204 of the auxiliary air passage 202. did.

  However, even in the passage inlet 203 and the passage outlet 204 that are less affected, the flow rate measurement accuracy is further improved if the dimensional change is reduced. Therefore, as shown in FIG. 9, the flow rate measurement accuracy of the thermal air flow meter 200 can be further improved by installing the ribs 233 in a lattice shape and improving the dimensional accuracy of the entire base member 230.

  10A and 10B are views showing still another embodiment of the base member 230. FIG. 10A is a front view of the base member as viewed from the joint surface side with the housing member, and FIG. 10B is an upstream in the forward flow direction. A side view seen from the side, FIG. 10C is a plan view.

  What is characteristic in the present embodiment is that ribs 235 that are reinforcing structures are partially provided at the connection portion between the substrate fixing portion 301 and the sub-passage constituting portion 302 of the base member 230. The rib 235 is provided so as to be interposed between the outer surface of the substrate fixing unit 301 and the vertical surface of the sub-passage component 302 standing at the end of the substrate fixing unit 301. It has a right triangle shape that is inclined so as to gradually approach the sub-passage component 302 as it moves away from the outer surface. A plurality of base members 230, which are in the forward flow direction, are provided at predetermined intervals in the short direction. In this embodiment, the base member 230 is provided at a total of three locations.

  Even with such a simple rib 235, the effect of suppressing warping deformation of the base member 230 is sufficiently recognized. In the present embodiment, the number of the ribs 235 is three. However, the number of ribs 235 is not limited to this as long as the effect is recognized.

  FIG. 12 is a view showing an embodiment in which the product of the present invention is applied to an electronic fuel injection type internal combustion engine. The intake air 67 sucked from the air cleaner 54 passes through an intake manifold 59 including an intake pipe component 251 of the thermal air flow meter 200, a suction duct 55, a throttle body 58, and an injector 60 to which fuel is supplied, and then an engine cylinder. 62 is inhaled. On the other hand, the exhaust gas 63 generated in the engine cylinder 62 is discharged through the exhaust manifold 64.

  Air flow signal and pressure signal output from circuit board 205 of thermal air flow meter 200, intake air temperature signal from temperature sensor, throttle valve angle signal output from throttle angle sensor 57, exhaust manifold 64 The control unit 66 that inputs the oxygen concentration signal output from the oxygen concentration meter 65 and the engine rotation speed signal output from the tachometer 61 sequentially calculates these signals to obtain the optimum fuel injection amount and idle speed. The air control valve opening is obtained, and the value is used to control the injector 60 and the idle control valve.

  According to the thermal air flow meter 200 of the present invention, the plate-like base member 230 is formed by molding with a synthetic resin material, and is the same as the base member 230 on the outer surface of the board fixing portion 301 to which the circuit board 205 is bonded and fixed. Since one or more ribs 231 integrally formed of a resin material are provided, the strength of the base member 230 is improved, and the thin portion 411 and the thick portion 412 are mixed in the base member 230 formed of one component during molding. Even when the difference in thermal shrinkage is not uniform, it is possible to suppress warping deformation of the base member 230 that occurs at the boundary between the thick portion 412 and the thin portion 411.

  The present invention is not limited to the configurations of the above-described embodiments, and various modifications can be made without departing from the spirit of the present invention. For example, an element capable of measuring the direction of air flow at the same time as measuring the intake air flow rate may be used as the flow rate detection element 201. Originally, if it is a thermal air flow meter having a function of only measuring a flow rate from one direction, it is not necessary to have a complicated sub air passage structure. For example, a sub air passage structure as shown in Patent Document 1 is used. Even if it exists, it plays a role as a secondary air passage. The effect of the present invention is advantageous in the case of a thermal air flow meter that measures the direction of air flow at the same time as measuring the intake air flow rate.

  At present, attention is focused on the global environment such as global warming. Accurate measurement of the intake air flow rate means optimal fuel control of the vehicle, which not only cleans the exhaust gas for environmental protection represented by global warming but also realizes low fuel consumption. It is possible to make maximum use of fossil fuels that are considered to be limited reserves. According to the internal combustion engine using the thermal air flow meter of the present invention, a flow rate with high measurement accuracy can be obtained, and optimal fuel control can be performed.

51 ... Intake temperature sensor, 54 ... Air cleaner, 55 ... Duct, 56 ... Idle air control valve, 57 ... Throttle angle sensor, 58 ... Throttle body, 59 ... Intake manifold, 60 ... Injector, 61 ... Tachometer, 62 ... Engine Cylinder, 63 ... Gas, 64 ... Exhaust manifold, 65 ... Oxygen concentration meter, 66 ... Control unit, 67 ... Intake air, 200 ... Thermal air flow meter, 201 ... Flow detection element, 202 ... Sub Air passage, 203 ... passage entrance, 204 ... passage exit, 205 ... circuit board, 206 ... electronic circuit component, 207 ... aluminum wire, 208 ... connector terminal, 209 ... Fixing screw 210 ... Air flow in the sub air passage 211 ... Housing member 220 ... Cover member 23 ... resin base member, 231 ... rib, 233 ... rib, 234 ... thinning, 235 ... rib, 250 ... main air passage, 251 ... intake pipe component, 252 ... forward flow in main air passage, 253 ... reverse flow in main air passage.

Claims (5)

A plate-like first resin molded body having a board fixing part to which the circuit board is fixed, and a sub-passage constituting part constituting a part of the sub-passage;
A plate-like second resin molded body that forms a sub-passage that takes in part of the fluid flowing through the intake passage of the internal combustion engine in cooperation with the first resin molded body by being attached to the first resin molded body. When,
A flow rate detecting element provided in the sub-passage, and a thermal air flow meter comprising:
The first air molded body has a grid-like rib on an outer surface of the substrate fixing portion disposed on a side away from the second resin molded body.   2. The thermal air flow meter according to claim 1, wherein the rib extends in a direction away from the auxiliary passage constituting portion along an outer surface of the substrate fixing portion.   The thermal air flow meter according to claim 1, wherein the rib is provided on the entire outer surface of the substrate fixing portion. A plate-like first resin molded body having a board fixing part to which the circuit board is fixed, and a sub-passage constituting part constituting a part of the sub-passage;
A plate-like second resin molded body that forms a sub-passage that takes in part of the fluid flowing through the intake passage of the internal combustion engine in cooperation with the first resin molded body by being attached to the first resin molded body. When,
A flow rate detecting element provided in the sub-passage, and a thermal air flow meter comprising:
The first resin molded body is characterized in that a plurality of lightenings are provided on the outer surface of the substrate fixing portion disposed on the side away from the second resin molded body, and the outer surface has a lattice shape. Type air flow meter. The thermal air flow meter according to claim 4, wherein the lightening is provided on the entire outer surface of the substrate fixing portion.

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