Abstract:
The present invention utilizes self-heating of electronic components to improve a humidity sensing part with low environment resistance, such as a condensation problem and the like, and also to enhance the heat radiation efficiency of electronic components. The humidity sensing part is used in an intake tube of an automobile by integrating, for example, with a heating resister type mass air flow measurement device. A humidity sensing element is mounted on an electronic circuit board in a mass air flow measurement device with the temperature thereof starting to increase immediately after a sensor has been actuated. This urges the temperature of the humidity sensing element to start increasing (being heated) immediately after the sensor has been actuated. To urge the humidity sensing element to be further heated, a base plate is composed of two types of materials, resin and metal. A part of the base plate holding an area of the electronic circuit board generating a large quantity of heat is composed of the metal. A part of the base plate corresponding to the periphery of the humidity sensing part which is to be heated is composed of the resin.

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 measurements 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 is known as a flow measuring technique 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]    In connection with a sensor including a flow measurement device, a pressure sensing device, a humidity sensing device, and the like for internal combustion engines which are integrated together, the sensor being capable of measuring a plurality of physical quantities, JP Patent Publication (Kokai) No. 2008-304232A discloses, as a well-known technique, an example in which an air flow sensor, a humidity sensor, and a pressure sensor are integrated together. 
       SUMMARY OF THE INVENTION 
       [0006]    In recent years, cars that use an electronically-controlled fuel injection system have been common. In this case, an engine room is internally crammed with various sensors and control devices. Furthermore, in that case a wire harness that interconnects various sensors and control devices as well as a control unit configured to control the sensors and control instruments is complicatedly intricate. 
         [0007]    Thus, 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 heating resistor type mass air flow measurement device is integrated with a temperature sensing device and even a semiconductor pressure sensing 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 sensing device and humidity sensing device in the future, various technical problems are expected to occur. 
         [0009]    In particular, the humidity sensing device described above has not been utilized for fuel control applications yet but has mainly been used to control air conditioning in the vehicle interior. Applications to the vehicle interior involve no demand for high durability based on an envisioned harsh environment. However, when integrated with, for example, the heating resistor type mass air flow measurement device or other sensors in order to control the engine, the humidity sensing device needs to offer environment resistance equivalent to that of the heating resistor type mass air flow measurement device. An environment particularly unfavorable to the humidity sensing device is condensation in a sensing element part thereof. Thus, a definite technical solution to this problem is essential. 
         [0010]    For example, if condensation occurs in the humidity sensing element, the humidity sensing element may output a signal value indicative of the maximum or minimum humidity depending on the configuration of the sensor or a peripheral circuit therefor, temporarily preventing the humidity sensing device from fulfilling its functions as a humidity sensing device until the sensing element part is dried. In this case, during the period in which the humidity sensing device is prevented from fulfilling its functions, the engine control system may be affected. On the other hand, the multiplexed sensor may disadvantageously increase the total current consumption of the sensor. 
         [0011]    An object of the present invention is to provide a sensor structure suitable for integration of the humidity sensing device and even the pressure sensing device with the mass air flow measurement device. 
         [0012]    To deal with the above-described problem, the present inventors have focused on the heat generation and radiation structure of the sensor itself in the mass air flow measurement device, which consumes the largest amount of current among the integrated sensors. A power transistor or the like which controls the quantity of heat applied to the mass air flow sensing element generates a large quantity of heat. If heat is not efficiently radiated from the power transistor, the temperature of the device as a whole increases. Then, electronic components and resistors with different temperature characteristics may contribute to reducing the accuracy at which the mass air flow is detected. This thermal effect may further affect, for example, the durability of the electronic components. Accordingly, an efficient heat radiation structure for the mass air flow measurement device has been sought. Thus, a base plate on which an electronic circuit board is adhesively held is preferably composed of metal. This configuration enables heat radiation based on the transfer of heat from the base plate to air flowing through a main air flow passage. 
         [0013]    On the other hand, the humidity sensing device needs to deal with the above-described condensation. The humidity sensing device requires, for example, means for drying the humidity sensing element subjected to condensation in a short time and means for keeping the surface of the humidity sensing element dry in wet air. To achieve this, the humidity sensing element itself may be maintained at high temperature. It is effective to heat the humidity sensing element part and the periphery thereof and to store heat in the humidity sensing element part and the periphery thereof. 
         [0014]    The heat radiation function and the heating function, which are contradictory to each other, are achieved by one device. 
         [0015]    A possible condensation environment corresponds to the cold start of an engine in a time zone from night till morning when the temperature is low. Hence, it is important to remove condensed dew in an environment in which the mass air flow in an intake tube is very low during engine start, particularly during idling. To achieve this, the humility sensing element is mounted on the electronic circuit board in the mass air flow measurement device with the temperature thereof starting to increase immediately after the sensor has been actuated. This facilitates an increase of the temperature of the humidity sensing element immediately after the sensor has been actuated. 
         [0016]    The humidity sensing element and a part of the circuit board surrounding the humidity sensing element are exposed to air flowing through a second bypass channel and thus radiate a slight quantity of heat. However, an intended idle flow rate offers a low flow velocity, and a “received heat&gt;radiated heat” relationship is thus established in the humidity sensing element part. This effect is higher when the relationship between the flow velocity of air flowing through a bypass air passage and the flow velocity of air flowing through the second bypass channel is such that the flow velocity in the bypass air passage is greater than the flow velocity in the second bypass channel. 
         [0017]    Furthermore, to facilitate heating of the humidity sensing element, the base plate is composed of two types of materials, resin and metal. The material of the base plate holding an area where the electronic circuit board generates a large quantity of heat is composed of the metal. A part of the base plate holding the periphery of the second bypass channel, which is to be heated, is composed of the resin. This further facilitates heating of the humidity sensing element. 
         [0018]    In contrast, in an environment in which the sensors are unlikely to be affected by condensation, at least a given amount of air flows through the humidity sensing element part. This corresponds to, for example, an operational environment in which the flow rate in the intake tube reaches a medium or high flow rate zone. In this case, condensed dew does not need to be removed but heat radiation from the electronic circuit board is preferably enhanced. In this operational environment, a sufficient airflow is generated in the second bypass channel, enabling heat to be radiated from the electronic circuit board through the second bypass channel part. Accordingly, the heat radiation effect of the electronic circuit board, in combination with heat radiation effect from the base plate is enhanced. 
         [0019]    The above-described configuration allows the device to provide both the heat generation function and the heat radiation function, which are contradictory to each other. 
         [0020]    Heat generated by the mass air flow measurement device is effectively utilized to remove condensed dew in the humidity sensing part. This eliminates the need to additionally provide a heater function around the humidity sensing part. Alternatively, condensed dew can be removed without the use of the heater function of the humidity sensing element. This enables accurate sensing of the humidity and a reduction in the total power consumption of the sensor. 
         [0021]    Moreover, the improved efficiency of heat radiation, which is a capability contradictory to heat generation, serves to suppress the self-heating of the sensor, thus improving the durability of electronic components. This also reduces the adverse effects of the temperature characteristics of the electronic components or print resistors, thereby enabling other physical quantities to be accurately measured. 
         [0022]    According to the present invention, the vehicle can be provided, over a long period, with accurate fuel control that is essential for dealing with both exhaust gas and fuel consumption regulations. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0023]      FIG. 1  is a diagram of a sensor structure showing an embodiment of the present invention. 
           [0024]      FIG. 2  is a diagram of the sensor structure in  FIG. 1  as seen from the front of the structure. 
           [0025]      FIG. 3  is a diagram of a sensor structure showing another embodiment of the present invention. 
           [0026]      FIG. 4  is a diagram of a sensor structure showing yet another embodiment of the present invention. 
           [0027]      FIG. 5  is a diagram of a sensor structure showing still another embodiment of the present invention. 
           [0028]      FIG. 6  is a sectional view taken along line A-A in  FIG. 4 . 
           [0029]      FIG. 7  is a diagram of a sensor structure showing further another embodiment of the present invention. 
           [0030]      FIG. 8  is a diagram of a sensor structure showing further another embodiment of the present invention. 
           [0031]      FIG. 9  is a schematic diagram of the system configuration of an internal combustion engine in which the present invention is used. 
       
    
    
     DESCRIPTION OF SYMBOLS 
       [0000]    
       
           1  Heating resistor 
           2  Air temp compensation resistor 
           3  Intake air temperature sensor 
           50  Air cleaner 
           51  Intake air 
           52  Flow tube mass air flow sensor installed 
           53  Intake air duct 
           54  Throttle body 
           55  Fuel injector 
           56  Intake manifold 
           57  Engine cylinder 
           58  Exhaust gas 
           59  Exhaust manifold 
           60  Integrated bypass channel type mass air flow sensor module 
           61  Throttle angle sensor 
           62  Oxygen meter 
           63  Engine speed meter 
           64  Engine control unit 
           65  Idle air control valve 
           100  Main air flow passage 
           101  Air flow tube 
           102  Sensor installation opening 
           200  Heating resistor type mass air flow measurement device 
           201  Housing structural part 
           202  Base plate 
           203  Electronic circuit board 
           204  Cover 
           205  Bypass air passage 
           206  Bypass channel 
           207  Seal material 
           208  Bonding material 
           209  Connector terminal 
           210  Air induction opening 
           211  Second bypass channel 
           212  Second bypass inlet 
           213  Second bypass outlet 
           500  Humidity sensing part 
           600  Pressure sensing part 
           601  Pressure intake hole 
           602  Pressure measurement I/O terminals 
       
     
       DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0072]    A specific example of a configuration according to the present invention will be described with reference to  FIG. 1 .  FIG. 2  is a diagram of the configuration in  FIG. 1  as seen from the front of the configuration. 
         [0073]    An air flow tube (intake line structural part)  101  forming a main air flow passage (hereinafter also referred to as an intake line or simply an intake tube)  100  includes a sensor installation opening  102  formed in a part of the air flow tube  101  and through which a part of a heating resistor type mass air flow measurement device  200  is inserted. The heating resistor type mass air flow measurement device  200  into which a humidity sensing part  500  is integrated is installed in the air flow tube  101 . 
         [0074]    The heating resistor type mass air flow measurement device  200  includes not only a housing structural part  201  but also a base plate  202 , a cover  204  configured to protect, an electronic circuit board  203 , a heating resistor  1  configured to measure mass air flow, an air temp compensation resistor  2  used to measure the mass air flow, an intake air temperature sensor  3  used on the vehicle side, a bypass air passage  205  in which the heating resistor  1 , the air temp compensation resistor  2 , and the like are installed, a bypass channel  206  for forming the bypass air passage  205 , and a seal material  207  configured to seal the main air flow passage  101  from the exterior. The heating resistor  1 , air temp compensation resistor  2 , and intake air temperature sensor  3 , each configured to sense intake mass air flow or intake air temperature, are connected to the electronic circuit board  203  via a bonding material  208 . Moreover, the electronic circuit board  203  is similarly electrically connected to a connector terminal  209  via the bonding material  208  so as to receive and output data from and to an external device via the connector terminal  209 . 
         [0075]    A humidity sensing part  500  is installed on the electronic circuit board  203  configured to drive the heating resistor type mass air flow measurement device  200 . The housing structural part  201  includes an air induction opening  210  so as to allow the humidity sensing part  500  to directly contact intake air. A humidity signal sensed by the humidity sensing part  500  is transmitted to the external device using the connector terminal  209 . 
         [0076]    In this configuration, when the heating resistor type mass air flow measurement device  200  is actuated, the electronic circuit board  203  starts generating heat without delay. The resultant thermal effect propagates to the humidity sensing part  500 . As a result, even if the humidity sensing part  500  has disadvantageously been subjected to condensation at the time of the actuation thereof, the humidity sensing part  500  can be recovered to a normal condition in a short time. 
         [0077]    Furthermore, for example, provided that the humidity sensing part  500  has the function of detecting relative humidity and temperature, the resultant humidity signal can be processed and utilized as an absolute humidity to accomplish the purpose while preventing heat received from the electronic circuit board  203  from affecting measurement results. 
         [0078]      FIG. 3  shows an example in which the humidity sensing part  500  is mounted inside a second bypass channel  211 . 
         [0079]    In this configuration, besides the bypass air passage  205  used for the heating resistor type mass air flow measurement device  200 , the second bypass channel  211  is installed to take in part of air flowing through the main air flow passage  100 . 
         [0080]    In this configuration, when the heating resistor type mass air flow measurement device  200  is actuated, the electronic circuit board  203  starts generating heat without delay. The resultant thermal effect propagates to the humidity sensing part  500 . As a result, even if the humidity sensing part  500  has disadvantageously been subjected to condensation at the time of the actuation thereof, the humidity sensing part  500  can be recovered to a normal condition in a short time. This is effective for removing condensed dew in an environment in which only a small amount of air can be taken in during the cold start of the engine, when condensation is likely to occur, particularly during idling. 
         [0081]    In contrast, in an environment in which the sensor is unlikely to be affected by condensation, the heat radiation efficiency of the electronic circuit board  203  is preferably enhanced. Thus, in the present configuration, in a high flow rate zone in which the electronic circuit board  203  generates the largest quantity of heat, a sufficient airflow is also generated in the second bypass channel. This enables heat to be radiated from the electronic circuit board  203  through the second bypass channel  211 . The heat radiation from the electronic circuit board  203 , in combination with heat radiation from the base plate  202 , enhances the heat radiation effect. The above-described configuration allows the device to provide both the heat generation function and the heat radiation function, which are contradictory to each other. 
         [0082]      FIG. 4  shows an example in which the second bypass channel  211  is rearranged. The second bypass channel  211  is configured to bypass the bypass air passage  205 . The humidity sensing part  500  is mounted in the second bypass channel  211 . A second bypass inlet  212  and a second bypass outlet  213  are open in a bypass air passage  205  in a horizontal direction with respect to the direction in which air flows through the bypass air passage  205 . This configuration allows contaminants such as dust and oil which float in the intake air not to be easily taken into the second bypass channel  211  with the humidity sensing part  500  mounted therein. Thus, the possible contamination of the humidity sensing part  500  can be avoided. 
         [0083]      FIG. 5  shows an example in which the second bypass channel  211  is shaped to enhance the effect of heating the humidity sensing part  500 . 
         [0084]    The second bypass channel  211  is configured such that when the flow velocity Ub of air flowing through the bypass air passage  205  is compared with the flow velocity Ub of air flowing through the second bypass channel  211 , a “Ub&gt;Usb” relationship is established. In the present example, the second bypass inlet  212  and the second bypass outlet  213  are open in the bypass air passage  205  in the horizontal direction with respect to the direction in which air flows through the bypass air passage  205 . This configuration suppresses heat radiation from the electronic circuit board  203  due to the air flowing through the second bypass channel  211 . This enables an increase in the quantity of heat applied to the periphery of the humidity sensing part  500 , thus allowing a “radiated heat&lt;received heat” tendency to be enhanced. This is an advantageous solution for a situation in which removal of condensed dew from around the humidity sensing part  500  is given top priority. 
         [0085]      FIG. 6  is a sectional view taken along line A-A in  FIG. 5 . 
         [0086]    The second bypass channel  211  is constructed as follows: the electronic circuit board  203  is fixed on the base plate  202  by adhesion or the like, and the base plate  202  is assembled with a housing structural part  201  and a bypass channel  206  by adhesion or the like. A part of a wall forming the cross section of the second bypass channel  211  is formed using the electronic circuit board  203 . Thus, air flowing through the second bypass channel  211  directly contacts the surfaces of the humidity sensing part  500  and the electronic circuit board  203 . 
         [0087]      FIG. 7  shows an example corresponding to the structure in  FIG. 6  in which the base plate  202  is composed of two types of materials. 
         [0088]    The base plate  202  is composed of a metal material and a resin material. The metal material is used in a drive circuit side of the heating resistor type mass air flow measurement device  200  which involves a large quantity of self-heating. The resin material is used in areas in which the humidity sensing part  500  and the second bypass channel  211  are installed. Heat generated on the drive circuit side of the heating resistor type mass air flow measurement device  200  is radiated, from the metal material side, to the air flowing through the main air flow passage  100 . The thermal effect is also transmitted from the drive circuit side of the heating resistor type mass air flow measurement device  200  through the electronic circuit substrate  203 , and reaches the periphery of the humidity sensing part  500 . Then, since the corresponding part of the base plate  202  is composed of the resin material, the radiation of the heat to the air is suppressed. This configuration enables the condensation in the humidity sensing part  500  to be recovered to normal environment in a short time. The configuration is advantageous if in connection with the balance between the heat radiation and the heating of the humidity sensing part  500 , higher emphasis is placed on the heating. 
         [0089]    However, even in this configuration, the velocity of air flowing through the bypass air passage  205  and the second bypass channel  211  also increases as the velocity of air flowing through the main air flow passage  100  increases. Thus, at a high flow velocity at which condensation is unlikely to occur, heat is expected to be radiated from the circuit board through the second bypass channel  211 . At a high flow rate, efficient heat radiation can be achieved. 
         [0090]      FIG. 8  shows an example in which the present invention is applied to a configuration in which a heating resistor type mass air flow measurement device  200 , an intake air temperature sensor  3 , and a humidity sensing part  500  as well as a pressure sensing part  600  are integrated together. 
         [0091]    An air flow tube (intake line structural part)  101  included in a main air flow passage (hereinafter also referred to as an intake line or simply an intake tube)  100  includes a sensor installation opening  102  formed in a part of the air flow tube  101  and through which a part of the heating resistor type mass air flow measurement device  200  is inserted. The heating resistor type mass air flow measurement device  200  into which the humidity sensing part  500  is integrated is installed in the air flow tube  101 . 
         [0092]    The heating resistor type mass air flow measurement device  200  includes not only a housing structural part  201  but also a base plate  202 , a cover  204  configured to protect an electronic circuit board  203 , a heating resistor  1  to measure mass air flow, an air temp compensation resistor  2  used to measure the mass air flow, the intake air temperature sensor  3  used at a vehicle side, a bypass air passage  205  in which the heating resistor  1 , the air temp compensation resistor  2 , and the like are installed, a bypass channel  206  forming the bypass air passage  205 , and a seal material  207  to seal the main air flow passage  101  from the exterior. Moreover, the pressure sensing part  600  is mounted on a part of the housing structural part  201  positioned outside the air flow tube  101 . The pressure sensing part  600  measures the pressure inside the main air flow passage  100  via a pressure intake hole  601  formed in the housing structural part  201 . 
         [0093]    The heating resistor  1 , air temp compensation resistor  2 , and intake air temperature sensor  3  which are configured to sense intake mass air flow or intake air temperature are connected to the electronic circuit board  203  via a bonding material  208 . Moreover, the electronic circuit board  203  is similarly electrically connected to a connector terminal  209  via the bonding material  208  so as to receive and output data from and to an external device via the connector terminal  209 . 
         [0094]    The humidity sensing part  500  is electrically connected to the connector terminal  209  from the electronic circuit board  203  via the bonding material  208  so as to receive and output data from and to the external device via the connector terminal  209 . 
         [0095]    The pressure sensing part  600  receives and outputs data to and from the external device via pressure measurement I/O terminals  602  and the connector terminal  209  by, for example, welding. 
         [0096]    The humidity sensing part  500  is installed on the electronic circuit board  203  configured to drive the heating resistor type mass air flow measurement device  200 , and is further mounted in the second bypass channel  211 . The second bypass channel  211  is configured to bypass the bypass air passage  205 . A second bypass inlet  212  and a second bypass outlet  213  are open in the bypass air passage  205  in the horizontal direction with respect to the direction in which air flows through the bypass air passage  205 . Furthermore, a part of a wall forming the cross section of the second bypass channel  211  is formed using the electronic circuit board  203 . Thus, air flowing through the second bypass channel  211  directly contacts the surfaces of the humidity sensing part  500  and the electronic circuit board  203 . 
         [0097]    Moreover, the base plate  202  is composed of a metal material and a resin material. The metal material is used on a drive circuit side of the heating resistor type mass air flow measurement device  200  which involves a large quantity of self-heating. The resin material is used in areas in which the humidity sensing part  500  and the second bypass channel  211  are installed. Heat generated on the drive circuit side of the heating resistor type mass air flow measurement device  200  is radiated, from the metal material side, to the air flowing through the main air flow passage  100 . The thermal effect is also transmitted from the drive circuit side of the heating resistor type mass air flow measurement device  200  through the electronic circuit substrate  203 , and reaches the periphery of the humidity sensing part  500 . Then, since the corresponding part of the base plate  202  is composed of the resin material, the radiation of the heat to the air is suppressed. 
         [0098]    The above-described configuration allows the heating resistor type mass air flow measurement device  200 , the intake air temperature sensor  3 , the pressure sensing part  600 , and the humidity sensing part  500  to be integrated together. The resultant structure is unsusceptible to condensation and excellent in heat radiation from the electronic components, particularly in connection with humidity sensing. 
         [0099]    Finally, an example in which the article of the present invention is applied to an internal combustion engine based on an electronic fuel injection system will be described with reference to  FIG. 9   
         [0100]    Intake air  51  is sucked through an air cleaner  50  passes through a flow tube mass air flow sensor installed  52  into which the heating resistor type mass air flow measurement device  200  is inserted, an intake air duct  53 , a throttle body  54 , and an intake manifold  56  with an injector  55  to which fuel is supplied, and then enters an engine cylinder  57 . On the other hand, exhaust gas  58  generated in the engine cylinder  57  is discharged via an exhaust manifold  59 . 
         [0101]    A control unit  64  receives a mass air flow signal, a humidity signal, a pressure signal, and a temperature signal output by an integrated bypass channel type mass air flow sensor module  60  of the heating resistor type mass air flow measurement device  200 , a throttle valve angle signal output by a throttle angle sensor  61 , an oxygen concentration signal output by an oxygen meter  62  provided in the exhaust manifold  59 , an engine rotation speed signal output by an engine speed meter  63 , and the like. The control unit  64  sequentially calculates these signals to determine the optimum fuel injection amount and idle air control valve opening degree. The control unit  64  then uses these values to control the injector  55  and an idle air control valve  65 .