Abstract:
To achieve a physical quantity detection device capable of obtaining a desired overall device accuracy without unnecessarily raising the tolerances of detection elements, the present invention is characterized by having a plurality of physical quantity detection units for respectively detecting plurality of physical quantities, a storage unit for storing the error characteristics of individual physical quantity detection units, a physical quantity calculation unit for using at least two physical quantities detected by at least two of the plurality of physical quantity detection units to calculate a separate physical quantity, and an error calculation unit for reading the error characteristics of the plurality of physical quantity detection units from the storage unit and calculating the error of the separate physical quantity.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to physical quantity detection device for detecting a physical quantity such as a temperature and a humidity of intake air taken by an internal combustion engine of an automobile. 
       BACKGROUND ART 
       [0002]    In PTL 1, a structure of a humidity detection device is disclosed. The humidity detection device includes a humidity sensing element, a temperature sensing element, and a ROM which has previously stored output characteristics and a temperature coefficient of the humidity sensing element arranged in a sensor probe, calculates a detection temperature by using a temperature detecting value of the temperature sensing element and referring to a storage table for managing the temperature in the ROM, and calculates a detection humidity by using the detection temperature and a humidity detecting value of the humidity sensing element and referring to a characteristics data storage table in the ROM. 
         [0003]    PTL 2 discloses a technique of a sensor device which includes an EPROM in which data to correct characteristics variation of the sensor and machine differences has been previously stored and transmits a signal in which the corrected data is added to collected physical information corresponding data to a sensor signal processing device. 
       CITATION LIST 
     Patent Literature 
       [0004]    PTL 1: JP 3-78650 A 
         [0005]    PTL 2: JP 9-113310 A 
       SUMMARY OF INVENTION 
     Technical Problem 
       [0006]    As the humidity detection device in PTL 1, an indirect physical quantity calculated by using detection values of a plurality of detection elements includes an error included in the detection value of the detection element. For example, even when the detection elements have the same tolerances, the single detection element has characteristics different from the other detection element. Therefore, the physical quantity to be calculated is different according to a combination of the detection elements. When a tolerance of each detection element is raised and an allowable error is reduced as possible to obtain a desired accuracy of the physical quantity to be calculated, a percent defective of the detection element and the cost are increased. 
         [0007]    Also, as the sensor device in PTL 2, when the physical quantity is corrected by outputting the correction data of the detection element to the sensor signal processing device, it is necessary to consider the characteristics of each sensor. It is necessary to perform a complicated error calculation by the sensor signal processing device. 
         [0008]    The present invention has been made to solve the above problems. A purpose of the present invention is to obtain a physical quantity detection device which can obtain a desired overall device accuracy without unnecessarily raising tolerances of detection elements. 
       Solution to Problem 
       [0009]    In order to solve the above problems, for example, a structure described in CLAIMS is employed. The present invention includes a plurality of solutions to solve the above problem. As an example, the present invention includes a plurality of physical quantity detection units which detects a plurality of physical quantities, a storage unit for storing error characteristics of the respective physical quantity detection units, a physical quantity calculation unit for calculating another physical quantity by using at least two physical quantities detected by at least two physical quantity detection units of the plurality of physical quantity detection units, and an error calculation unit for calculating an error of the another physical quantity by reading the error characteristics of the physical quantity detection units from the storage unit. 
       Advantageous Effects of Invention 
       [0010]    According to the present invention, a desired overall device accuracy can be obtained without unnecessarily increasing detection accuracy of each detection unit. A problem, a structure, and an effect other than those described above are described in the embodiment below. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0011]      FIG. 1  is a schematic diagram of an engine control system to which a physical quantity detection device according to the present invention is applied. 
           [0012]      FIG. 2  is a function block diagram to describe an embodiment of the physical quantity detection device according to the present invention. 
           [0013]      FIGS. 3( a ) and 3( b )  are diagrams of an exemplary structure of a humidity sensor. 
           [0014]      FIG. 4  is a diagram of an exemplary structure of a temperature sensor. 
           [0015]      FIG. 5  is an air diagram of a relation between a temperature of intake air, an absolute humidity, and a relative humidity. 
           [0016]      FIGS. 6( a ) and 6( b )  are diagrams to describe a relation of an absolute humidity error obtained from temperature characteristics of the humidity sensor and temperature characteristics of the temperature sensor. 
           [0017]      FIG. 7  is a function block diagram to describe another embodiment of a physical quantity detection device according to the present invention. 
           [0018]      FIG. 8  is a diagram to describe a problem of the related art. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0019]    Next, one embodiment of a physical quantity detection device according to the present invention is described below with reference to the drawings. 
         [0020]      FIG. 1  is a schematic diagram of an engine control system to which the physical quantity detection device according to the present invention is applied, and  FIG. 2  is a function block diagram to describe an embodiment of the physical quantity detection device according to the present invention. 
         [0021]    The physical quantity detection device is built into an engine control system  1  of an automobile. As illustrated in  FIG. 1 , the engine control system  1  includes an engine body  2  which is an internal combustion engine, an air intake passage  3  to supply intake air to the engine body  2 , and an exhaust passage  4  to exhaust exhaust gas from the engine body  2 . At the middle position of the air intake passage  3 , a compressor  12   a  of a turbocharger  12  is interposed, and an air flow sensor  11  is arranged at a position on the upstream side of the compressor  12   a.  An intercooler  13 , an electric control throttle valve  14 , a supercharging pressure sensor, and the like are arranged on the downstream side of the compressor  12   a.    
         [0022]    A turbine  12   b  of the turbocharger  12  is provided at the middle position of the exhaust passage  4 , and a catalyst  15  and a muffler  16  are arranged on the downstream side of the turbine  12   b.  A high pressure fuel injector  17  for injecting fuel in a combustion chamber and an ignition plug which is not shown are attached to the engine body  2 . Also, a crank angle sensor for detecting an engine speed, a water temperature sensor for detecting a cooling water temperature of the engine body, and the like are attached. 
         [0023]    The air flow sensor  11  includes a flow rate sensor to detect a flow rate which is one of physical quantities of the intake air. In addition, the air flow sensor  11  includes a humidity sensor  21  to detect a relative humidity of the intake air and a temperature sensor  31  (refer to  FIG. 2 ) to detect the temperature of the intake air. That is, in the present embodiment, the humidity sensor  21  and the temperature sensor  31  are provided in the air flow sensor  11 . 
         [0024]    Each sensor signal of the flow rate sensor, the humidity sensor  21 , the temperature sensor  31 , the crank angle sensor, the water temperature sensor, and the like of the air flow sensor  11  is input to an ECU  18  which is a control device of the engine control system  1 . Each sensor signal is used for various engine operation control such as ignition timing control and fuel injection control. 
         [0025]      FIGS. 3( a ) and 3( b )  are diagrams of an exemplary structure of the humidity sensor.  FIG. 3( a )  is a front view of the humidity sensor, and  FIG. 3( b )  is a cross-sectional diagram taken along a line A-A of  FIG. 3( a ) .  FIG. 4  is a diagram of an exemplary structure of the temperature sensor. A known humidity sensor  21  and a known temperature sensor  31  can be used. 
         [0026]    The humidity sensor  21  is an electrostatic capacitance type relative humidity sensor and includes a sensor element  22  for detecting the humidity. As illustrated in  FIGS. 3( a ) and 3( b ) , the sensor element  22  has structure in which a comb-shaped electrode pair  25 A and  253  is provided on the upper surface of a silicon substrate  23  and the comb-shaped electrode pair  25 A and  25 B is covered with a hygroscopic high-molecular polymer film  26 . The capacitance of the electrode pair  25 A and  25 B changes due to moisture absorption of the high-molecular polymer film  26 . The capacitance change has a high correlation with the relative humidity. When the capacitance is measured, the relative humidity can be detected. There are several types of electrode structures. In some of them, polymer is sandwiched between the upper and lower electrodes. A protection film  27  is provided on the upper surface of the high-molecular polymer film  26 , and the intake air passes through the outside of the protection film  27 . Then, water molecules  28  are absorbed by the high-molecular polymer film  26 . 
         [0027]    The temperature sensor  31  is provided near the humid it sensor  21  to measure the temperature near the humidity sensor  21 . For example, as an exemplary circuit structure is illustrated in  FIG. 4 , a band gap type semiconductor temperature sensor can be used as the temperature sensor  31 . 
         [0028]    As illustrated in  FIG. 2 , the air flow sensor  11  includes a signal processing unit  41 , a storage unit  42 , and a total error calculation unit  43  in addition to the humidity sensor  21  and the temperature sensor  31 . 
         [0029]    The signal processing unit  41  performs processing for generating humidity information which is information on the relative humidity of the intake air and temperature information which is information on the temperature of the intake air by processing signals of the humidity sensor  21  and the temperature sensor  31  and outputting them to the ECU  18 . 
         [0030]    The storage unit  42  stores error characteristics indicating a change of an error according to the temperature (refer to  FIG. 6 ) as specific information on the humidity sensor  21  and the temperature sensor  31 . The error characteristics of the respective sensors are different from each other, and the sensor having the error characteristics within a range of a pre-set tolerance is used. 
         [0031]    The total error calculation unit  43  calculates an error of the absolute humidity which is the total error by using the error characteristics of the relative humidity sensor  21  and the error characteristics of the temperature sensor  31  stored in the storage unit  42  and outputs the calculation result to the ECU  18 . The total error calculation unit  43  calculates the total error at the time of calculating the absolute humidity which is an indirect physical quantity by using a combination of the errors without using the respective errors of the humidity sensor  21  and the temperature sensor  31 . 
         [0032]    The total error calculation unit  43  calculates the total error by conducting a search by using the temperature information and the humidity information which are the two physical quantities or by conducting a search according to the axis corresponding to each physical quantity from a map arranged in a grid shape or a plurality of tables. 
         [0033]    The air flow sensor  11  is connected to the ECU  18  with a communication cable, and communication using digital signals is performed by using communication standards such as the SENT, the LIN, and the CAN. The sensor information output from the air flow sensor  11  to the ECU  18  is superimposed by digital communication by using a single or double communication cables and is output. The error information stored in the storage unit  42  is collectively output to the ECU  18  according to a request from outside or a time from power supply or the number of times to output the signals by the sensor. 
         [0034]    An absolute humidity calculation unit  61  of the ECU  18  calculates the absolute humidity based on the humidity information and the temperature information output from the air flow sensor  11  and corrects the absolute humidity based on the total error calculated by the total error calculation unit The corrected absolute humidity calculated by the absolute humidity calculation unit  61  is used for various engine operation control by a control unit  62  of the ECU  18 . Also, the ECU  18  can directly use the information on the total error for various engine operation control. 
         [0035]      FIG. 5  is an air diagram of a relation between a dry-bulb temperature, the absolute humidity, and the relative humidity of the intake air.  FIGS. 6( a ) and 6( b )  are diagrams to describe the total error of the absolute humidity obtained from the error characteristics of the humidity sensor and the temperature sensor. 
         [0036]    As described above, in the present embodiment, the absolute humidity is obtained from the two physical quantities, i.e., the temperature and the relative humidity. When the absolute humidity is calculated by using the temperature and the relative humidity, as illustrated in the air diagram in  FIG. 5 , the temperature has more effect than that of the humidity, and the absolute humidity to be obtained is largely different especially in the high temperature region even when the temperatures are slightly different. For example, when the temperature tolerances are the same, an absolute humidity error δ 2  at the time when a temperature error is generated on a high temperature side is larger than an absolute humidity error δ 1  at the time when a temperature error is generated on a low temperature side (δ 1 &lt;&lt;δ 2 ). 
         [0037]    Therefore, even when the humidity sensor  21  and the temperature sensor  31  have the same tolerances, the absolute humidity to be obtained is different according to the error characteristics of each sensor. For example, when a sensor  1  illustrated in  FIG. 6( a )  is compared with a sensor  2  illustrated in  FIG. 6( b ) , an error of the temperature sensor of the sensor  2  from the middle temperature region to the high temperature region is larger than that of the temperature sensor of the sensor  1 . Therefore, when the total error of the absolute humidity of the sensor  1  is compared with that of the sensor  2 , the error in the high temperature region of the sensor  2  is larger than that of the sensor  1 . Accordingly, the temperature sensor of the sensor  1  and the temperature sensor of the sensor  2  have the same tolerances, the total errors of the absolute humidities and the absolute humidities to be obtained are different from each other. 
         [0038]      FIG. 8  is a diagram to describe the related art and a function block diagram of a traditional physical quantity detection device. 
         [0039]    Generally, a traditional sensor  100  has measured physical quantities such as the humidity and the temperature by using a humidity sensor  101  and a temperature sensor  102  and has output them by modulating them to indirect physical phenomenon such as a voltage and a signal frequency. The above information is taken and processed by an ECU  110  and is combined with information on other sensor and the like by the absolute humidity calculation unit  111  and the error calculation unit  112  of the ECU  110 . Then, the information is used to perform correction to other physical quantity and the like and perform control. For example, the absolute humidity calculation unit  111  obtains the absolute humidity from the humidity information of the humidity sensor  101  and the temperature information of the temperature sensor  102 . Since both the humidity sensor  101  and the temperature sensor  102  have the tolerances and temperature characteristics, the total error is complicated. The error of the absolute humidity gets worse according to the temperature so that the information of the absolute humidity cannot be used. Therefore, in order to obtain and use the absolute humidity by the error calculation unit  112  of the ECU  110 , it is necessary to perform complicated error management. However, calculation processing to calculate the error is very complicated, and a development cost is needed. 
         [0040]    Whereas, as illustrated in  FIG. 2 , the physical quantity detection device according to the present invention has the storage unit  42  and the total error calculation unit  43  in the air flow sensor  11  on the sensor side. The total error calculation unit  43  calculates the total error at the time of calculating the absolute humidity which is the indirect physical quantity by combining the respective errors of the humidity sensor  21  and the temperature sensor  31  by using the error characteristics of the humidity sensor  21  and the temperature sensor  31  stored in the storage unit  42  and outputs it to the ECU  18 . 
         [0041]    In the present invention, the storage unit  42  stores the tolerance generated at the time of calculating the absolute humidity, and the absolute humidity error obtained from each error characteristics is transmitted separately from the sensor signal. Therefore, even when the tolerances of the humidity sensor  21  and the temperature sensor  31  are not unnecessarily raised, a desired overall device accuracy of the absolute humidity can be obtained. 
         [0042]      FIG. 7  is a function block diagram to describe another embodiment of a physical quantity detection device according to the present invention. The characteristics of the present embodiment are to provide an absolute humidity calculation unit  61  in an air flow sensor  11 . The place where the absolute humidity calculation unit  61  is provided is not limited to an ECU  18 , and the absolute humidity calculation unit  61  may be provided in the air flow sensor  11 . 
         [0043]    The embodiments of the present invention have been described in detail above. However, the present invention is not limited to the embodiments, and designs can be variously changed without departing from the spirit of the present invention described in CLAIMS. For example, the embodiments have been described in detail for easy understanding of the present invention. The embodiments are not limited to those including all the components described above. Also, a part of the components of the embodiment can be replaced with that of the other embodiment, and the components of the embodiment can be added to the other embodiment. In addition, a part of the components of each embodiment can be deleted, replaced with that of the other embodiment, and a part of the other embodiment can be added to the components of the embodiment. 
       REFERENCE SIGNS LIST 
       [0000]    
       
           1  engine control system 
           11  air flow sensor 
           21  humidity sensor (first physical quantity detection unit) 
           31  temperature sensor (second physical quantity detection unit) 
           41  signal outputting unit 
           42  storage unit 
           43  total error calculation unit 
           61  absolute humidity calculation unit (third physical quantity calculation unit)