Abstract:
Provided is a sensor structure capable of improving the reliability of connecting parts of electronic components and achieving excellent productivity and reduction in size and weight, for example, when electronic components are externally mounted on input/output terminals of a sensor. A relationship between a linear expansion coefficient for a housing serving as a base of a structure and a linear expansion coefficient of a resin material for a sensor casing of a sensor to be mounted is set to satisfy “sensor casing&lt;linear expansion coefficient a&lt;housing”. When electronic components are externally mounted, the electric components are mounted on input/output terminals which are integrally formed on the side of a component having a small linear expansion coefficient, i.e., on the side of the sensor casing.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a sensor integrated structure suitable for physical quantity measurement relating to intake air in an internal combustion engine, and an internal combustion engine control device that uses the sensor integrated structure 
         [0003]    2. Background Art 
         [0004]    A heating resistor type mass air flow measurement device relating to a flow measuring technique, for example, is known as a physical quantity measuring technique relating to intake air for internal combustion engines (see JP Patent No. 3523022). The heating resistor type mass air flow measurement device utilizes the correlation of the quantity of heat taken from a heating resistor with inflow discharge. The heating resistor type mass air flow measurement device is capable of directly measuring mass flow required to control combustion in an engine and is thus widely used as a flowmeter for air-fuel ratio control particularly in an automobile. 
         [0005]    As another physical quantity measuring technique relating to intake air for internal combustion engines, there is known a sensor including a flow measurement device, a pressure measurement device, a humidity sensing device, and the like which are integrated together, the sensor having a function of measuring a plurality of physical quantities. For example, JP Patent Publication (Kokai) No. 2008-304232A discloses an example in which an air flow sensor and a pressure sensor are integrated together. 
       SUMMARY OF THE INVENTION 
       [0006]    Automobiles that use an electronically-controlled fuel injection system have been common and become more sophisticated in performance and function in recent years. In this case, an engine room is internally crammed with various sensors and control instruments. Furthermore, a wire harness that interconnects various sensors and control instruments as well as a control unit configured to control the sensors and control instruments, for example, is complicatedly intricate. 
         [0007]    In such circumstances, there has been a demand to reduce the number of components and improve the appearance of the interior of the engine room by integrating the plurality of sensors and control instruments together. For example, in a certain measure, the above-described flow measurement device is integrated with a temperature sensing device and even a semiconductor pressure measurement device, a humidity sensing device, and the like to allow connectors to be shared. This enables a reduction in the number of steps required to assemble components together into a vehicle and simplification of the wire harness. 
         [0008]    In conventionally mainstream structures, the heating resistor type mass air flow measurement device is integrated with a temperature sensing device. However, as heating resistor type mass air flow measurement devices are integrated with the above-described pressure measurement device and humidity sensing device in the future, various technical problems are expected to occur. 
         [0009]    In particular, in order to promote multifunction of the sensor, the sensor is inevitably formed of a larger number of components compared to the conventional type. This raises concerns about a problem of mounting space, complicacy of manufacturing processes, and even an increase in the number of nodes in the multiple component configuration, i.e., the reliability in connecting parts and the like. 
         [0010]    For example, when a flow measurement device and a pressure measurement device are integrated and a chip capacitor is externally mounted and connected so as to improve the electromagnetic interference preventing function of the pressure measurement device, a distance between connector terminals of the chip capacitor or the like is displaced due to expansion/contraction of a resin, for example, which is caused by a change in environmental temperature, depending on a resin material for holding counterpart terminals to be mounted. As a result, for example, connecting parts between the chip capacitor and each terminal fatigue due to a solder, a conductive adhesive, or the like, which may finally lead to break. In this case, the pressure measurement device contributes to engine control in the state of being considerably deteriorated in the intended electromagnetic interference preventing function. Thus, when a signal from the pressure measurement device is used for throttle opening control, for example, a malfunction may occur in the pressure measurement device. 
         [0011]    In view of the foregoing, it is an object of the present invention to provide a sensor structure that is excellent in reliability and productivity and achieves reduction in size and weight, for example, when a pressure measurement device, a humidity sensing device, and the like are integrated with a flow measurement device. 
         [0012]    To deal with the above-mentioned problems, the following means is provided. 
         [0013]    A relationship between a linear expansion coefficient for a housing serving as a base of a structure and a linear expansion coefficient for a resin material used for a sensor casing of a sensor to be mounted is set to satisfy “sensor casing&lt;linear expansion coefficient a&lt;housing”. In the case of externally mounting electronic components, the electric components are mounted on input/output terminals which are integrated on the side of the component having a small linear expansion coefficient, i.e., on the side of the sensor casing. 
         [0014]    In this structure, the expansion/contraction of the resin material of the sensor casing (e.g. PPS) itself associated with an ambient temperature change is extremely small. Therefore, the reliability of connecting parts of the electronic components can be ensured even when the electronic components are connected to bridge input/output interface terminals. 
         [0015]    According to the present invention, it is possible to externally mount electronic components in order to improve performances such as the electromagnetic interference preventing function of a sensor to be mounted. Consequently, the reliability of connection between electronic components can be ensured for a long period of time, and simple external mounting can be applied. This achieves an improvement in productivity and a reduction in cost. 
         [0016]    Moreover, it is possible to provide a multifunction sensor that is excellent in performance and quality for automobiles and is capable of simultaneously detecting various physical quantities such as an air flow and an intake pressure. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]      FIG. 1  is a diagram of a sensor structure showing an embodiment of the present invention and a sectional view of the sensor structure taken along the line A-A. 
           [0018]      FIG. 2  is a diagram of a sensor structure showing an embodiment of the present invention. 
           [0019]      FIG. 3  is a diagram of a sensor structure showing another embodiment of the present invention. 
           [0020]      FIG. 4  is a diagram of a sensor structure showing still another embodiment of the present invention. 
           [0021]      FIG. 5  shows an embodiment in which the present invention is applied to an electronic fuel injection type internal combustion engine. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0022]    An embodiment of the present invention will be described with reference to  FIG. 1 . A main air flow passage component (intake air passage structural part)  2  constituting a main air flow passage (hereinafter also referred to as an intake line or simply an intake tube)  1  includes a sensor installation hole  4  formed in a part of the main air flow passage component  2 . A multifunction sensor  6  integrating a heating resistor type mass air flow measurement device  3  and a pressure measurement device  5  is inserted through the sensor installation hole  4 . 
         [0023]    The heating resistor type mass air flow measurement device  3  includes a housing  7  as well as a base plate  8 , a cover  10  for protecting an electronic circuit board  9 , a heating resistor  11  for measuring an air flow, an air temp compensation resistor  12  for use in measurement of an air flow, an intake air temperature sensor  13  used on a vehicle side, a bypass air passage  14  for packaging the heating resistor  11 , the air temp compensation resistor  12 , and the like, a bypass air passage structural part  15  for constituting the bypass air passage  14 , a seal material  16  for sealing the main air flow passage  1  and the outside, and the like. The heating resistor  11 , the air temp compensation resistor  12 , and the intake air temperature sensor  13 , which detect an intake air flow and an intake air temperature, are connected to the electronic circuit board  9  through a wire bonding material  17 . Further, the electronic circuit board  9  is electrically connected to connector terminals  18  through the wire bonding material  17  in a similar manner, to thereby input and output signals to and from the outside through a connector  25 . 
         [0024]    The pressure measurement device  5  mounted on the housing  7  of the heating resistor type mass air flow measurement device  3  has a structure in which a pressure sensing chip  19  including a pressure sensing part and an electronic circuit, input/output interface terminals  20 , and the wire bonding material  17  for electrically connecting the pressure sensing chip  19  and the input/output interface terminals  20  are integrated with a sensor casing (Pressure sensor housing)  21 . The input/output interface terminals  20  are provided so as to project from the sensor casing  21 . The input/output interface terminals  20  are electrically connected to pressure sensor connector terminals  24 , which are arranged in parallel on the same plane as the connector terminals  18 , by welding or the like, to thereby input and output signals to and from the outside through the connector  25 . 
         [0025]    Fixation between the pressure measurement device  5  and the housing  7  is completed by pouring a cast resin (filling material)  26  into a cavity formed in the housing  7 . A pressure within the main air flow passage  1  can be measured by allowing communication with the location, at which the pressure sensing chip  19  is placed, through the sensor installation hole  4  and a pressure intake hole  27 . 
         [0026]    In the case of integrating the pressure measurement device  5  with the heating resistor type mass air flow measurement device  3 , it is essential for the housing  7  of the heating resistor type mass air flow measurement device  3  to ensure robustness with respect to a temperature environment, a mechanical vibration environment, a shock environment, and the like which are required when the housing is used in an intake system of an automobile as a structure. Accordingly, a resin material that is excellent in ductility and toughness and has a required mechanical strength as well as a resistance to deterioration due to a temperature change and a humidity change is suitably used. For example, a PBT resin reinforced with fiberglass or the like is used and molded. 
         [0027]    As a material of the sensor casing  21  of the pressure measurement device  5 , a material having a small linear expansion coefficient, such as PPS, is selected. That is, the resin forming the sensor casing  21  has a linear expansion coefficient smaller than a linear expansion coefficient of the resin forming the housing  7  (the linear expansion coefficient has a relationship satisfying “sensor casing  21  &lt;linear expansion coefficient a &lt;housing  7 ”). 
         [0028]    In this case, the pressure measurement device  5  needs to have a structure in which electronic components  22 , such as a chip capacitor, are externally mounted in order to improve the electromagnetic interference preventing function. In this embodiment, the electronic components  22  are mounted on the input/output interface terminals  20 , i.e., on the side of the pressure measurement device  5 , through a connection paste material  23  such as a solder or a conductive adhesive. In other words, a structure is employed in which the electronic components  22  are mounted on the side of the component packaged with a resin having a small linear expansion coefficient. 
         [0029]    In this structure, since the sensor casing  21  is formed of a resin material having a small linear expansion coefficient, the sensor casing  21  hardly expands or contracts even when the ambient temperature changes. Therefore, a variation in a distance between the terminals on the input/output interface terminals  20  is minimized. Furthermore, the reliability of connecting parts can be ensured even when the electronic components are connected to bridge the input/output interface terminals. Consequently, the mounting of the electronic components  22  at such a position enables improvement in the reliability of connecting parts of the electronic components  22  and the input/output interface terminals  20 . 
         [0030]    If the electronic components are mounted on the side of the PBT resin (the housing  7 ), the connector terminals integrally formed with the thermal expansion/contraction of the PBT resin are also displaced, so that the connecting parts of the electronic components are affected by a repeated stress. 
         [0031]      FIG. 2  is a partial sectional view of the pressure measurement device  5 . Fixation between the pressure measurement device  5  and the housing  7  is completed by pouring the cast resin  26  into the cavity formed in the housing  7 . Meanwhile, it is necessary to ensure the fixation of the electronic components  22  connected onto the input/output interface terminals  20  through the connection paste material  23 , and to ensure a sufficient reliability in connection of the electronic components  22  under an assumed environment within an engine room of an automobile. In this case, it is effective to cover the entirety of the electronic components  22  and the input/output interface terminals  20  with the cast resin  26 . 
         [0032]    In order to completely coat the cast resin  26  over the periphery of the electronic components  22  and the input/output interface terminals  20 , it is necessary to improve flow-in or routing of the cast resin  26 . For this reason, no structure is disposed below the input/output interface terminals  20  in the region where the electronic components  22  are mounted, and an interspace  28  is provided below the input/output interface terminals  20 . The interspace  28  preferably has a thickness as twice or more thick as the thickness of the input/output interface terminals  20 . This structure makes it possible to cover the entire periphery of the electronic components  22  and the input/output interface terminals  20  with one type of cast resin  26 , which results in improvement in the reliability of connecting parts of the electronic components  22 . 
         [0033]      FIG. 3  is a diagram showing another embodiment relating to a method of mounting the electronic components  22 . 
         [0034]    In the case where two or more electronic components, such as a capacitor, are mounted on the input/output interface terminals  20  in order to improve the electromagnetic interference preventing function of the pressure measurement device  5 , the electronic components  22  are mounted in a staggered manner. In the case where electrodes of two components are connected on one terminal, it is preferable to prevent the connection paste materials  23  from being in contact with each other. If the connection paste materials  23  are in contact with each other, the connection paste materials  23  adhere with each other. This causes a failure in the connecting parts, such as a crack due to a residual stress, after heat curing of a paste. The mounting of the electronic components  22  in a staggered manner allows the distance between the adjacent connection paste materials  23  to be sufficiently ensured. 
         [0035]      FIG. 4  is a diagram showing still another embodiment relating to the method of mounting the electronic components  22 . 
         [0036]    In the case where electronic components, such as a capacitor, are mounted on the input/output interface terminals  20  in order to improve the electromagnetic interference preventing function of the pressure measurement device  5 , the electronic components  22  are disposed at a location close to the sensor casing  21  of the pressure measurement device  5 . The sensor casing  21  is formed of a resin material having a small linear expansion coefficient, such as PPS. Accordingly, even when the ambient temperature changes, the sensor casing  21  hardly expands or contracts, so that a variation in the distance between the terminals on the input/output interface terminals  20  is minimized at a location closest to the sensor casing  21 . The mounting of the electronic components  22  at such a location improves the reliability in connecting parts. 
         [0037]    Further, welding parts  29  are preferably provided at positions as far away as possible from the electronic components  22 . Assuming that the width of the input/output interface terminals  20  is represented by W, a distance of 2W or more between the electronic components  22  and the welding parts  29  is ensured. In  FIG. 4  the distance between the electronic components  22  and the welding parts  29  is represented by L. When the distance between the electronic components  22  and the welding parts  29  is ensured in this manner, a stress which is generated during or after welding and is applied to the input/output interface terminals  20  can be alleviated. This is effective for improvement in reliability of connecting parts of the electronic components  22 . 
         [0038]    Lastly, an embodiment in which the multifunction sensor  6  is applied to an electronic fuel injection type internal combustion engine will be described with reference to  FIG. 5 . 
         [0039]    An intake air  51  taken from an air cleaner  50  is introduced into an engine cylinder  56  through an intake manifold  55 . The intake manifold  55  includes the main air flow passage component  2  into which the multifunction sensor  6  is inserted, an intake air duct  52 , a throttle body  53 , and a fuel injector  54  supplied with fuel. On the other hand, an exhaust gas  57  generated in the engine cylinder  56  is discharged through an exhaust manifold  58 . 
         [0040]    An engine control unit  62  receives an air flow signal, a humidity signal, a pressure signal, and a temperature signal, which are output from the multifunction sensor  6 , a throttle valve angle signal output from a throttle angle sensor  59 , an oxygen concentration signal output from an oxygen meter  60 , which is provided in the exhaust manifold  58 , and an engine speed signal output from an engine speed meter  61 , for example. The engine control unit  62  sequentially calculates these signals to obtain an optimum amount of fuel injection and an optimum output torque. The engine control unit  52  uses these values to control the fuel injector  54  and the throttle valve  63 . 
       DESCRIPTION OF SYMBOLS 
       [0041]      1  Main air flow passage 
         [0042]      2  Main air passage component (Airflow tube) 
         [0043]      3  Heating resistor type mass air flow measurement device 
         [0044]      4  Sensor installation hole 
         [0045]      5  Pressure measurement device 
         [0046]      6  Multifunction sensor 
         [0047]      7  Housing 
         [0048]      8  Base plate 
         [0049]      9  Electronic circuit board 
         [0050]      10  Cover 
         [0051]      11  Heating resistor 
         [0052]      12  Air temp compensation resistor 
         [0053]      13  Intake air temperature sensor 
         [0054]      14  Bypass air passage 
         [0055]      15  Bypass air passage structural part 
         [0056]      16  Seal material 
         [0057]      17  Wire bonding material 
         [0058]      18  Connector terminals 
         [0059]      19  Pressure sensing chip 
         [0060]      20  Input/output interface terminals 
         [0061]      21  Sensor casing (Pressure sensor housing) 
         [0062]      22  Electronic component 
         [0063]      23  Connection paste material 
         [0064]      24  Pressure sensor connector terminals 
         [0065]      25  Connector 
         [0066]      26  Cast resin 
         [0067]      27  Pressure intake hole 
         [0068]      28  Interspace 
         [0069]      29  Welding part 
         [0070]      50  Air cleaner 
         [0071]      51  Intake air 
         [0072]      52  Intake air duct 
         [0073]      53  Throttle body 
         [0074]      54  Fuel injector 
         [0075]      55  Intake manifold 
         [0076]      56  Engine cylinder 
         [0077]      57  Exhaust gas 
         [0078]      58  Exhaust manifold 
         [0079]      59  Throttle angle sensor 
         [0080]      60  Oxygen meter 
         [0081]      61  Engine speed meter 
         [0082]      62  Engine control unit 
         [0083]      63  Throttle valve