(19)
(11)EP 3 346 240 B1

(12)EUROPEAN PATENT SPECIFICATION

(45)Mention of the grant of the patent:
24.06.2020 Bulletin 2020/26

(21)Application number: 16841344.1

(22)Date of filing:  27.07.2016
(51)International Patent Classification (IPC): 
G01F 1/696(2006.01)
G01F 1/68(2006.01)
G01F 15/04(2006.01)
G01F 1/00(2006.01)
G01F 1/698(2006.01)
(86)International application number:
PCT/JP2016/071944
(87)International publication number:
WO 2017/038312 (09.03.2017 Gazette  2017/10)

(54)

AIRFLOW METER

LUFTDURCHFLUSSMESSER

DÉBITMÈTRE D'AIR


(84)Designated Contracting States:
AL AT BE BG CH CY CZ DE DK EE ES FI FR GB GR HR HU IE IS IT LI LT LU LV MC MK MT NL NO PL PT RO RS SE SI SK SM TR

(30)Priority: 31.08.2015 JP 2015169972

(43)Date of publication of application:
11.07.2018 Bulletin 2018/28

(73)Proprietor: Hitachi Automotive Systems, Ltd.
Hitachinaka-shi, Ibaraki 312-8503 (JP)

(72)Inventors:
  • SATO Ryo
    Hitachinaka-shi Ibaraki 312-8503 (JP)
  • MATSUMOTO Masahiro
    Tokyo 100-8280 (JP)
  • ASANO Satoshi
    Tokyo 100-8280 (JP)
  • KOTABE Akira
    Hitachinaka-shi Ibaraki 312-8503 (JP)
  • SUZUKI Kazunori
    Hitachinaka-shi Ibaraki 312-8503 (JP)

(74)Representative: MERH-IP Matias Erny Reichl Hoffmann Patentanwälte PartG mbB 
Paul-Heyse-Strasse 29
80336 München
80336 München (DE)


(56)References cited: : 
EP-A1- 1 316 781
JP-A- H02 281 108
JP-A- 2010 216 906
JP-U- S6 218 708
WO-A1-2014/136468
JP-A- H02 281 108
JP-A- 2010 216 906
  
      
    Note: Within nine months from the publication of the mention of the grant of the European patent, any person may give notice to the European Patent Office of opposition to the European patent granted. Notice of opposition shall be filed in a written reasoned statement. It shall not be deemed to have been filed until the opposition fee has been paid. (Art. 99(1) European Patent Convention).


    Description

    Technical Field



    [0001] The present invention relates to an apparatus for measuring a flow rate of a gas to be measured, and more particularly to an air flow meter for measuring the flow rate of intake air of an internal combustion engine of an automobile.

    Background Art



    [0002] A method for correcting a temperature characteristic of an air flow meter for an automobile includes a technique described in JP 2010-216906 A (PTL 1). This publication includes a description that "air temperature and sensor module temperature are incorporated as adjustment factors of output characteristics and perform temperature correction of the output characteristics according to a difference between the air temperature and the sensor module temperature".

    Citation List


    Patent Literatures



    [0003] PTL 1: JP 2010-216906 A

    [0004] In WO 2014/136468 A1 a hot type fluid measurement device is described, comprising a sensor element that is disposed in a passage section and a circuit element that is disposed in the circuited chamber wherein the circuit element includes a correction section that corrects the flow rate information detected by the sensor element from temperature difference information of a temperature of a fluid and a temperature of the module.

    Summary of Invention


    Technical Problem



    [0005]  While PTL 1 describes that the air temperature and the sensor module temperature are individually detected by two temperature sensors, and correction is performed according to a difference between the detected temperatures, there is no contemplation of an influence of a temperature difference due to a difference in a degree of deterioration by aging between the two temperature sensors and the influence of a temperature difference due to individual characteristic variations in the temperature sensors. This would cause generation of an error in the output of the air flow meter in a case where two different temperature sensors output mutually different temperatures for a same temperature due to the difference in the degree of deterioration by aging and the characteristic variations.

    [0006] An object of the present invention is to provide a highly accurate air flow meter.

    Solution to Problem



    [0007] In order to solve the above-described problem, the features of the independent claims are suggested. A representative air flow meter of the present invention includes an arithmetic circuit that corrects an output, in which the arithmetic circuit incorporates an air temperature and a sensor module temperature as adjustment factors for an output characteristic of the air flow meter, the output characteristic is corrected in accordance with a temperature difference between the air temperature and the sensor module temperature, and a correction amount is decreased when an absolute value of the difference between the air temperature and the sensor module temperature is small.

    Advantageous Effects of Invention



    [0008] According to the present invention, it is possible to provide a highly accurate air flow meter.

    Brief Description of Drawings



    [0009] 

    [FIG. 1] FIG. 1 is a circuit configuration diagram of an air flow meter for an automobile according to the present invention.

    [FIG. 2] FIG. 2 is a block diagram of an arithmetic system mounted inside a DSP in FIG. 1.

    [FIG. 3] FIG. 3 is a correction characteristic diagram of a wall temperature correction unit according to a first exemplary embodiment.

    [FIG. 4] FIG. 4 is a characteristic diagram of region setting of a wall temperature correction characteristic according to the first exemplary embodiment.

    [FIG. 5] FIG. 5 is a correction characteristic diagram of a wall temperature correction unit according to a second exemplary embodiment.

    [FIG. 6] FIG. 6 is a characteristic diagram of a region setting of a wall temperature correction characteristic according to the second exemplary embodiment.

    [FIG. 7] FIG. 7 is a correction characteristic diagram of a wall temperature correction unit according to a third exemplary embodiment.

    [FIG. 8] FIG. 8 is a characteristic diagram of region setting of a wall temperature correction characteristic according to the third exemplary embodiment.

    [FIG. 9] FIG. 9 is a correction characteristic diagram of a wall temperature correction unit according to a fourth exemplary embodiment.

    [FIG. 10] FIG. 10 is a characteristic diagram of region setting of a wall temperature correction characteristic according to the fourth exemplary embodiment.


    Description of Embodiments



    [0010] Exemplary embodiments of the present invention will now be described with reference to the accompanying drawings. First exemplary embodiment

    [0011] FIG. 1 is a circuit configuration of an air flow meter according to the present invention. A constant temperature control bridge 1 is constituted with a heating resistor 4, a bridge circuit temperature measurement resistance temperature detector 5, an intake air temperature compensating resistance temperature detector 6, and fixed resistors 7 and 8. A heater control circuit 23 controls a current flowing to the heating resistor 4 so as to achieve a constant temperature difference between the bridge circuit temperature measurement resistance temperature detector 5 and the intake air temperature compensating resistance temperature detector 6.

    [0012] A temperature difference bridge 2 that detects the amount of heat emitted from the heating resistor 4 is arranged around the heating resistor 4 of the constant temperature control bridge 1. The temperature difference bridge 2 is constituted with resistance temperature detectors 9 to 12, and capable of detecting an air flow rate and a direction.

    [0013] An intake air temperature sensor 3 that measures an air temperature is constituted with a fixed resistor 13 and a temperature sensitive resistor 14 having a resistance value changing in accordance with the temperature.

    [0014] A flow rate signal detected by the temperature difference bridge 2 has variations among individual circuits, and thus needs to be adjusted to a target output characteristic. The output of the intake air temperature sensor 3 also needs to be adjusted to a target characteristic.

    [0015] Examples of a method of adjusting to the target output characteristic includes adjustment by a polynomial of second order or higher and adjustment by a correction map. Adjustment is performed in a state of being connecting with an external computer.

    [0016] An output characteristic adjustment circuit 27 is an LSI circuit integrating a heater control circuit and an arithmetic function, and includes an oscillator (hereinafter referred to as OSC) 20 for driving the whole circuit, a heater control circuit 23 that controls the constant temperature control bridge 1, the constant temperature control bridge 1, the temperature difference bridge 2, a constant voltage circuit 15 as a power source for driving the intake air temperature sensor 3 and the output characteristic adjustment circuit 27, a circuit temperature sensor 19 that detects the temperature of the circuit, an A/D converter 16 that converts an air flow rate signal, an A/D converter 17 that converts an output signal of the intake air temperature sensor 3, an A/D converter 18 that converts an output signal of the circuit temperature sensor 19, an arithmetic circuit (digital signal processor, hereinafter referred to as DSP) 22 that corrects an air flow rate signal and an intake air temperature sensor signal, D/A converters 25 and 26 that convert a digital output value calculated by the DSP 22 to a voltage value, free running counters (hereinafter, referred to as FRC) 30 and 31 that perform conversion to frequency, an SENT 32 as a digital output, a communication circuit (serial communication interface, hereinafter referred to as an SCI) 24 that communicates with an external computer for performing output adjustment, multiplexers (hereinafter referred to as MUX) 33 and 34 that switch an output mode, a storage circuit (EPROM, for example) 21 to which adjustment data is written, a ROM 29 that stores a program that controls the DSP 22, a RAM 28 that temporarily stores intermediate data in calculation by the DSP 22, and a protection circuit 35 that protects the circuit when an excessive surge is applied to a power supply VCC.

    [0017] FIG. 2 is a circuit block diagram illustrating an output adjustment function executed by the DSP 22.

    [0018] An output of the temperature difference bridge 2, an output of the circuit temperature sensor 19, and an output of the intake air temperature sensor 3 as input signals are incorporated as adjustment factors of an output characteristic. Adjustment is initially performed such that the output of the circuit temperature sensor 19 is adjusted by linear correction 38, and the output of the intake air temperature sensor 3 is adjusted by linear correction 39 so as to achieve a same target value. The value used for adjustment can be arbitrarily set, and it is desirable to set the temperature and the target value in a linear relationship. Next, zero point adjustment and span adjustment are applied to the output of the temperature difference bridge 2 in a zero span correction 40.

    [0019] Next, characteristic correction in a state where there is a difference between the circuit temperature and intake air temperature (wall temperature state) is performed in wall temperature correction 36. The wall temperature correction 36 multiplies a difference (TA-TLSI) between the corrected output (TLSI) of the circuit temperature sensor 19 and the corrected output (TA) of the intake air temperature sensor 3 by an optimum constant (K1) 42 different for each of flow rates. Furthermore, a wall temperature correction amount (ΔY) is obtained by multiplying K1 by a gain (K2) 41 corresponding to TA-TLSI and added to a zero span adjusted flow rate signal (QA) of the output of the temperature difference bridge 2. The calculation formula executed by the wall temperature correction 36 is illustrated in (1).

    Finally, the correction according to the corrected output (TLSI) of the circuit temperature sensor 19 is performed using data of an output correction map 37 so as to correct a flow rate signal (QA1) after correction of the wall temperature, and adjusts the flow rate signal to the target value. At the same time, the corrected output (TA) of the intake air temperature sensor 3 is output as a temperature signal. Moreover, this correction can be compatible not only with correction by a map but also with correction by polynomial. The merit of performing correction by polynomial is that it is sufficient to prepare a small capacity for the storage circuit 21 and the ROM 29. With small capacity, it is possible to reduce the chip size and the cost. The merit of performing correction by a map is its capability of coping with a sharp change of the correction amount with respect to the input and its capability of achieving high accuracy.

    [0020] FIG. 3 illustrates a characteristic diagram of the correction amount ΔY output from the wall temperature correction 36. ΔY indicates zero until an absolute value (|TA-TLSI|) of the difference (TA-TLSI) between the corrected output (TLSI) of the circuit temperature sensor 19 and the corrected output (TA) of the intake air temperature sensor 3 reaches a threshold, and indicates a primary characteristic of a gradient K1 with the threshold as a boundary.

    [0021] FIG. 4 illustrates a characteristic diagram of the gain (K2) 41. The diagram illustrates a characteristic of a step response of zero (0) and one with the threshold as a boundary. This threshold can be arbitrarily set, and is desirably set in consideration of the degree of deterioration by aging and characteristic variation in the circuit temperature sensor and the intake air temperature sensor.

    Second exemplary embodiment



    [0022] The present embodiment is applied to a case of a circuit configuration described in the first exemplary embodiment having a different correction characteristic, implemented in the wall temperature correction 36.

    [0023] FIG. 5 illustrates a characteristic diagram of the correction amount ΔY output from the wall temperature correction 36. ΔY indicates zero until an absolute value (|TA-TLSI|) of the difference (TA-TLSI) between the corrected output (TLSI) of the circuit temperature sensor 19 and the corrected output (TA) of the intake air temperature sensor 3 reaches a threshold, and indicates the primary characteristic approaching the gradient K1 with the threshold as a boundary.

    [0024]  FIG. 6 illustrates a characteristic diagram of the gain (K2) 41. The gain is zero until threshold, and illustrates a primary characteristic on and after the threshold.

    [0025] This configuration has an advantage of suppressing characteristic variation at discontinuous points before and after the threshold.

    Third exemplary embodiment



    [0026] The present embodiment is applied to a case of a circuit configuration described in the first exemplary embodiment having a different correction characteristic, implemented in the wall temperature correction 36.

    [0027] FIG. 7 illustrates a characteristic diagram of the correction amount ΔY output from the wall temperature correction 36. ΔY indicates a secondary characteristic until the absolute value (|TA-TLSI|) of the difference (TA-TLSI) between the corrected output (TLSI) of the circuit temperature sensor 19 and the corrected output (TA) of the intake air temperature sensor 3 reaches a threshold, and indicates the primary characteristic with the threshold as a boundary.

    [0028] FIG. 8 illustrates a characteristic diagram of the gain (K2) 41. The gain indicates the primary characteristic until the threshold, and indicates a characteristic of K2 = 1 with the threshold as a boundary.

    [0029]  This configuration has an advantage of suppressing characteristic variation before/after the threshold and achieving the primary characteristic with the gradient K1 on and after the threshold.

    Fourth exemplary embodiment



    [0030] The present embodiment is applied to a case of a circuit configuration according to the first exemplary embodiment having a different correction characteristic, implemented in the wall temperature correction 36.

    [0031] FIG. 9 illustrates a characteristic diagram of the correction amount ΔY output from the wall temperature correction 36. ΔY indicates zero until the absolute value (|TA-TLSI|) of the difference (TA-TLSI) between the corrected output (TLSI) of the circuit temperature sensor 19 and the corrected output (TA) of the intake air temperature sensor 3 reaches a threshold 1, indicates the secondary characteristic from the threshold 1 until a threshold 2, and indicates the primary characteristic on and after the threshold 2.

    [0032] FIG. 10 illustrates a characteristic diagram of the gain (K2) 41. The gain indicates zero until the threshold 1, indicates the primary characteristics from the threshold 1 until the threshold 2, and indicates characteristic of K2 = 1 on and after the threshold 2.

    [0033] This configuration has an advantage of suppressing characteristic variation before/after the threshold 1 and threshold 2 and achieving the primary characteristic with the gradient K1 on and after the threshold 2.

    [0034] The present invention is not limited to the above-described exemplary embodiments, but may include various types of modification. For example, the above-described exemplary embodiments give detailed explanation just to allow the present invention to be clearly understood. Therefore, the present invention is not limited to the case having all of components in the configuration. In addition, a portion of configuration of an exemplary embodiment can be replaced with a portion of configuration of another exemplary embodiment. A portion or the configuration of another exemplary embodiment can be added to a certain exemplary embodiment. Moreover, regarding the portions of the configuration of each of the exemplary embodiments, addition, deletion, and replacement from another configuration would be possible. Moreover, the above configurations, functions, processing units, processing means, or the like, may be implemented by hardware by designing a portion or all with an integrated circuit, for example. Moreover, each of the above-described configurations, functions, or the like, may be implemented with software by a processor by interpreting and executing a program designed to realize individual functions. Information such as programs, maps, correction values that realize individual functions can be stored in a storage apparatus such as a memory, a ROM, an EPROM, and a flash memory.

    Reference Signs List



    [0035] 
    1
    constant temperature control bridge
    2
    temperature difference bridge
    3
    intake air temperature sensor
    4
    heating resistor
    5 to 6
    resistance temperature detector
    7 to 8, 13
    fixed resistor
    9 to 12
    resistance temperature detector
    14
    temperature sensitive resistor
    15
    constant voltage circuit
    16 to 18
    A/D converter
    19
    circuit temperature sensor
    21
    storage circuit
    22
    DSP
    23
    heater control circuit
    24
    SCI
    25 to 26
    D/A converter
    27
    output characteristic adjustment circuit
    28
    RAM
    29
    ROM
    30 to 31
    FRC
    32
    SENT
    33 to 34
    MUX
    35
    protection circuit
    36
    wall temperature correction
    37
    output correction
    38 to 39
    linear correction
    40
    zero span correction



    Claims

    1. An air flow meter comprising an arithmetic circuit (22) that corrects an output, wherein the arithmetic circuit (22) incorporates an air temperature and a sensor module temperature as adjustment factors for an output characteristic of the air flow meter,
    the output characteristic is corrected in accordance with a temperature difference between the air temperature and the sensor module temperature;
    characterized in that
    a correction amount (ΔY) is decreased in comparison to a correction amount (ΔY) indicated by a primary characteristic when an absolute value of the difference between the air temperature and the sensor module temperature is smaller than a threshold.
     
    2. The air flow meter according to claim 1,
    wherein the correction amount (ΔY) of the output characteristic includes a first region and a second region having different change rates of the correction amount (ΔY)
     
    3. The air flow meter according to claim 2,
    wherein the first region has a change rate of the correction amount (ΔY) smaller than a change rate of the second region.
     
    4. The air flow meter according to claim 2 or 3,
    wherein the change rate of the correction amount (ΔY) with respect to the temperature difference between the air temperature and the sensor module temperature is zero in the first region, and
    the change rate in the second region has the primary characteristic.
     
    5. The air flow meter according to claim 2 or 3,
    wherein the change rate of the correction amount (ΔY) with respect to the temperature difference between the air temperature and the sensor module temperature indicates a secondary characteristic in the first region, and
    the change rate in the second region has the primary characteristic.
     
    6. The air flow meter according to claim 2 or 3,
    wherein the change rate of the correction amount (ΔY) with respect to the temperature difference between the air temperature and the sensor module temperature is zero in the first region until the absolute value of the difference between the air temperature and the sensor module temperature reaches a first threshold, and
    the change rate in the second region has a secondary characteristic until the absolute value of the difference between the air temperature and the sensor module temperature reaches a second threshold.
     


    Ansprüche

    1. Luftdurchflussmesser, der eine Arithmetikschaltung (22) enthält, die einen Ausgang korrigiert, wobei die Arithmetikschaltung (22) eine Lufttemperatur und eine Sensormodultemperatur als Einstellfaktoren für eine Ausgangskennlinie des Luftdurchflussmessers enthält und
    die Ausgangskennlinie in Übereinstimmung mit einer Temperaturdifferenz zwischen der Lufttemperatur und der Sensormodultemperatur korrigiert wird;
    dadurch gekennzeichnet, dass
    ein Korrekturbetrag (ΔY) im Vergleich zu einem Korrekturbetrag (ΔY), der durch eine primäre Kennlinie angegeben wird, erniedrigt wird, wenn ein Absolutwert der Differenz zwischen der Lufttemperatur und der Sensormodultemperatur kleiner als ein Schwellenwert ist.
     
    2. Luftdurchflussmesser nach Anspruch 1,
    wobei der Korrekturbetrag (ΔY) der Ausgangskennlinie einen ersten Bereich und einen zweiten Bereich mit unterschiedlichen Änderungsraten des Korrekturbetrags (ΔY) enthält.
     
    3. Luftdurchflussmesser nach Anspruch 2,
    wobei der erste Bereich eine Änderungsrate des Korrekturbetrags (ΔY) besitzt, die kleiner als eine Änderungsrate des zweiten Bereichs ist.
     
    4. Luftdurchflussmesser nach Anspruch 2 oder 3,
    wobei die Änderungsrate des Korrekturbetrags (ΔY) in Bezug auf die Temperaturdifferenz zwischen der Lufttemperatur und der Sensormodultemperatur in dem ersten Bereich gleich null ist, und
    die Änderungsrate in dem zweiten Bereich die primäre Kennlinie besitzt.
     
    5. Luftdurchflussmesser nach Anspruch 2 oder 3,
    wobei die Änderungsrate des Korrekturbetrags (ΔY) in Bezug auf die Temperaturdifferenz zwischen der Lufttemperatur und der Sensormodultemperatur eine sekundäre Kennlinie in dem ersten Bereich angibt und
    die Änderungsrate in dem zweiten Bereich die primäre Kennlinie besitzt.
     
    6. Luftdurchflussmesser nach Anspruch 2 oder 3,
    wobei die Änderungsrate des Korrekturbetrags (ΔY) in Bezug auf die Temperaturdifferenz zwischen der Lufttemperatur und der Sensormodultemperatur in dem ersten Bereich gleich null ist, bis der Absolutwert der Differenz zwischen der Lufttemperatur und der Sensormodultemperatur einen ersten Schwellenwert erreicht, und
    die Änderungsrate in dem zweiten Bereich eine sekundäre Kenntinie besitzt, bis der Absolutwert der Differenz zwischen der Lufttemperatur und der Sensormodultemperatur einen zweiten Schwellenwert erreicht.
     


    Revendications

    1. Débitmètre d'air comprenant un circuit arithmétique (22) qui corrige une sortie, dans lequel le circuit arithmétique (22) incorpore une température de l'air et une température d'un module capteur à titre de facteurs d'ajustement pour une caractéristique de sortie du débitmètre d'air,
    la caractéristique de sortie est corrigée en accord avec une différence de température entre la température de l'air et la température du module capteur ;
    caractérisé en ce que
    une correction quantitative (DY) est diminuée par comparaison à une correction quantitative (DY) indiquée par une caractéristique primaire quand une valeur absolue de la différence entre la température de l'air et la température du module capteur est inférieure à un seuil.
     
    2. Débitmètre d'air selon la revendication 1,
    dans lequel la correction quantitative (DY) de la caractéristique de sortie inclut une première région et une seconde région ayant des taux de changement différents de la correction quantitative (DY).
     
    3. Débitmètre d'air selon la revendication 2,
    dans lequel la première région a un taux de changement de la correction quantitative (DY) plus faible qu'un taux de changement de la seconde région.
     
    4. Débitmètre d'air selon la revendication 2 ou 3,
    dans lequel le taux de changement de la correction quantitative (DY) par rapport à la différence de température entre la température de l'air et la température du module capteur est nul dans la première région, et
    le taux de changement dans la seconde région a la caractéristique primaire.
     
    5. Débitmètre d'air selon la revendication 2 ou 3,
    dans lequel le taux de changement de la correction quantitative (DY) par rapport à la différence de température entre la température de l'air et la température du module capteur indique une caractéristique secondaire dans la première région, et
    le taux de changement dans la seconde région a la caractéristique primaire.
     
    6. Débitmètre d'air selon la revendication 2 ou 3,
    dans lequel le taux de changement de la correction quantitative (DY) par rapport à la différence de température entre la température de l'air et la température du module capteur est nulle dans la première région jusqu'à ce que la valeur absolue de la différence entre la température de l'air et la température du module capteur atteigne un premier seuil, et
    le taux de changement dans la seconde région a une caractéristique secondaire jusqu'à ce que la valeur absolue de la différence entre la température de l'air et la température du module capteur atteigne un second seuil.
     




    Drawing
































    Cited references

    REFERENCES CITED IN THE DESCRIPTION



    This list of references cited by the applicant is for the reader's convenience only. It does not form part of the European patent document. Even though great care has been taken in compiling the references, errors or omissions cannot be excluded and the EPO disclaims all liability in this regard.

    Patent documents cited in the description