JP2009031014A - Thermal gas mass flow meter - Google Patents

Abstract

A pulse gas modulation control type thermal gas mass flow meter capable of always measuring an accurate gas temperature and gas mass flow rate even when a battery voltage is fluctuating is realized.
Both end voltages V1 and V2 of the heat generation sensor element 5 are simultaneously measured, a current value flowing through the heat generation sensor element 5 is detected, and a resistance value is calculated by a resistance value calculation means 33. Thereby, even when the voltage of the battery power supply 1 fluctuates, the resistance value of the heat generation sensor element 5 can be accurately known. Since the temperature of the heat generation sensor element 5 can be accurately calculated from the accurate resistance value of the heat generation sensor element 5, the accurate gas temperature and gas mass flow are always measured even when the voltage of the battery power supply 1 is fluctuating. A thermal gas mass flow meter with pulse width modulation control can be realized.
[Selection] Figure 1

Description

  The present invention relates to a thermal gas mass flow meter for measuring a mass flow rate of a gas.

  For example, a thermal gas mass flow meter as described in Patent Document 1 is widely used as a gas flow meter for measuring the intake air amount of an engine. In this thermal gas mass flowmeter, a hot wire and a fluid temperature sensing element are installed inside the body, and a bridge circuit is configured by the hot wire, the fluid temperature sensing element, and a resistor.

  In addition, in the feedback circuit composed of an operational amplifier or the like, the temperature (Th) of the hot wire is kept higher by a certain temperature difference (fixed delta Th method) than the gas temperature (Te) determined by the change in resistance value of the fluid temperature sensing element. Thus, the heating current flowing through the hot wire is controlled by a bridge circuit and fed back in an analog manner through a power transistor.

  When the gas flow rate is fast, a large amount of heat is taken away from the hot wire, so that a large amount of heating current flows. On the other hand, when the flow rate is slow, the amount of heat taken away from the hot wire is small, so the heating current is also low. Since the flow rate is small, the mass flow rate of the gas can be measured by measuring the heating current.

  In addition, the electric power that is not used for heating the hot wire with respect to the battery voltage is mainly generated as heat by the power transistor.

  That is, when the heating current of the hot wire is large, the power transistor generates less heat, and when the heating current is small, the power transistor generates more heat.

  There is also a thermal gas mass flow meter that uses a MOS field effect transistor (MOS-FET) and is controlled by pulse width modulation.

  In a conventional thermal gas mass flowmeter, when measuring intake air, there is almost no deposit on the hot wire or fluid temperature sensing element to measure the air after passing through the air cleaner, but when measuring exhaust gas The problem is the adhesion of soot and oil contained in the exhaust gas.

  When these adhere to the hot wire or fluid temperature sensing element, the flow of exhaust gas or the like does not directly touch the hot wire or fluid temperature sensing element. As a result, the temperature of the exhaust gas or the like is not easily transmitted to the fluid temperature sensing element, and heat dissipation from the hot wire is reduced, resulting in an error in measuring the mass flow rate of the gas.

  Therefore, in order to cope with this problem, as shown in Patent Document 2 and Patent Document 3, by increasing the heating temperature of the hot wire, the oil attached to the hot wire is volatilized and fouled. A method for preventing the object from adhering is considered.

JP 2004-205528 A JP 59-206714 JP 2006-170804 A

  By the way, when adopting the method described in Patent Document 3, it is necessary to set the hot wire temperature to 400 ° C. or higher even when the gas temperature is −40 ° C., and the thermal gas mass flow rate controlled by pulse width modulation is used. It is necessary to efficiently raise the temperature of the hot wire using a meter.

  Here, although the terminal voltage of the vehicle-mounted battery itself is relatively stable, the terminal voltage greatly fluctuates when the vehicle-mounted electronic device is connected to the battery and turned on / off. Another factor that causes the power supply voltage of the in-vehicle battery to fluctuate is a cold crank (cold crank) in which a large current flows through the starter motor when the engine starts and the terminal voltage drops temporarily.

  There is also a phenomenon called load dump that generates a high voltage when the alternator is disconnected from the battery. As described above, the vehicle-mounted battery includes many factors that cause voltage fluctuation.

  When the power voltage of the on-board battery fluctuates, the thermal gas mass flowmeter controlled by the pulse width modulation described above determines the hot wire temperature when the MOS-FET is turned on from the voltage value of the low voltage terminal of the hot wire. The value fluctuates and the wrong hot wire temperature is detected.

  Similarly, if the battery power supply voltage fluctuates, the constant current circuit generated from the battery power supply voltage will not be able to output a predetermined constant current, and the hot wire temperature measurement when the MOS-FET is turned off will The voltage value at the voltage terminal fluctuates and an incorrect hot wire temperature is detected.

  In addition, immediately after the MOS-FET is turned OFF, a leak current flows from the MOS-FET in addition to a constant current to the hot wire, and the current value increases. Therefore, voltage cannot be taken into the A / D converter for measuring the hot wire temperature while the leakage current is flowing into the hot wire.

  In this way, if an incorrect hot wire temperature is detected, an incorrect duty or gas temperature is calculated and an accurate gas mass flow rate cannot be measured. Even if the correct hot wire temperature can be detected, the relationship between the duty calculated in the state where the power supply voltage of the battery fluctuates and the gas flow rate is different from that of the predetermined battery power supply voltage, and the correct gas flow rate is obtained. I can't.

  An object of the present invention is to realize a thermal gas mass flow meter of a pulse width modulation control system that can always measure an accurate gas temperature and gas mass flow rate even when the battery voltage is fluctuating.

  In order to achieve the above object, the present invention is configured as follows.

  The thermal gas mass flow meter of the present invention is based on voltage detection means for detecting the voltage across the heat sensor element, the value of the current flowing through the heat sensor element, and the voltage value across the heat sensor element. A resistance value calculating means for calculating a resistance value; a heat sensor element temperature calculating means for calculating a temperature of the heat sensor element based on a resistance value of the heat sensor element; and a temperature of the heat sensor element based on the temperature of the heat sensor element. The heating sensor element is heated or unheated so that the temperature is constant, so that the current control means for controlling on / off of the current supply from the power source to the heating sensor element and the gas supply based on the current supply on / off period Gas flow rate calculating means for calculating the flow rate.

  The present invention can realize a thermal gas mass flow meter of a pulse width modulation control system that can always measure accurate gas temperature and gas mass flow rate even when the battery voltage is fluctuating.

  Embodiments of a thermal gas mass flowmeter according to the present invention will be described below with reference to the drawings.

  FIG. 1 is a schematic configuration diagram of an embodiment of a thermal gas mass flow meter according to the present invention, which is an example when applied to a thermal gas flow meter that measures engine intake air and exhaust gas of an automobile.

  In FIG. 1, reference numeral 1 denotes a power source, and an in-vehicle battery is used. The power source 1 applies a driving voltage to the hot wire 5 which is a heat generation sensor element to heat it, and supplies current to the hot wire 5 and the current detection resistor 6 through the constant current circuit 2 and the backflow prevention diode 4. The drive voltage applied to the hot wire 5 is turned on / off by the MOS-FET 3 which is a current control means, and the time ratio (hereinafter referred to as Duty) of the current supplied to the hot wire 5 is controlled. The temperature of the hot wire 5 is controlled to be higher by a predetermined temperature difference delta Th than the gas temperature Tg at which the flow rate is to be measured.

  Reference numeral 9 denotes a control device (CPU (arithmetic control means)) that controls on / off of the MOS-FET 3 and calculates the gas flow rate. The resistance value calculating means 33 of the hot wire 5, the hot wire temperature detecting means 34, The gas temperature calculation means 13, the drive duty calculation means 14, the flow rate duty calculation means 35, the target Th setting means 36, the gas flow rate calculation means 15, and the physical property correction table 16 are provided. Here, Th is the temperature of the hot wire 5.

  The gas flow upstream voltage V1 of the hot wire 5 is supplied from the A / D converter 30 to the resistance value calculating means 33 via the differential amplifier 28, and the voltage V2 downstream of the hot wire 5 is supplied via the differential amplifier 8. It is supplied from the A / D converter 19 to the resistance value calculating means 33. Then, the resistance value of the hot wire 5 during heating is calculated by the resistance value calculation means 33.

  Further, the voltage V 1 on the upstream side of the hot wire 5 is supplied from the A / D converter 18 to the resistance value calculating means 33 via the differential amplifier 7, and the voltage V 2 on the downstream side of the hot wire 5 is supplied via the differential amplifier 29. Then, it is supplied from the A / D converter 31 to the resistance value calculating means 33. Then, the resistance value of the hot wire 5 when not heated is calculated by the resistance value calculation means 33.

  Here, even if the driving voltage of the power source 1 fluctuates, the current value of the constant current circuit 2 fluctuates, or the current value of the constant current circuit 2 increases due to leakage current immediately after the MOS-FET 3 is turned off. All, the resistance value of the hot wire 5 can be obtained by the following equation (1).

_{R H / W = (V1-} V2) / (V2 / R1) ··· (1)
In the above equation (1), R _{H / W} is the resistance value of the hot wire 5, V 1 is the voltage upstream of the hot wire 5, V 2 is the voltage downstream of the hot wire 5, and R 1 is the resistance of the current detection resistor 6. Value.

  The duty required to change the current temperature of the hot wire 5 from the gas temperature to the target temperature Th determined by the target Th setting means 36 is calculated as drive duty by the drive duty calculation means 14 using PI control.

  The drive duty is multiplied by a value obtained by dividing the actual battery voltage by the predetermined battery voltage 12V in the flow rate duty calculation means 35, and becomes the flow rate duty used in the gas flow rate calculation means 15. On the other hand, the drive duty is supplied as a PWM signal 10 to the MOS-FET 3 to turn the MOS-FET 3 on and off.

  FIG. 2 is a process flowchart in the control device (CPU) 9 in the thermal gas mass flowmeter shown in FIG. With reference to the flowchart shown in FIG. 2 and FIG. 1, the flow measurement operation by the thermal gas mass flow meter will be described.

  When the power supply 1 is turned on, in step S1, the temperature Th of the hot wire 5 is set to be higher than the gas temperature Tg by a temperature difference delta Th (temperature difference between the hot wire 5 and the gas temperature Tg) determined by the gas temperature Tg. To do.

  In step S2A, the duty (driving duty) necessary for setting the temperature of the hot wire 5 at the time of non-heating to the temperature Th set above is calculated by PI control. The drive duty is output to the MOS-FET 3 as the PWM signal 10, the MOS-FET 3 is turned on for a time determined by the drive duty, and the drive voltage is applied to the hot wire 5.

  In step S3A, a voltage V1 on the upstream side of the hot wire 5 and a voltage V2 on the downstream side of the hot wire 5 are simultaneously measured in a non-heated state in which a minute constant current is flowing from the constant current circuit 2 to the hot wire 5. Calculate the resistance value.

  In step S3B, the MOS-FET 3 is turned on and the upstream side voltage V1 and the downstream side voltage V2 of the hot wire 5 are simultaneously measured in a heating state where the drive voltage is applied to the hot wire 5, and the resistance of the hot wire 5 is measured. Calculate the value.

  In step S4A, the temperature of the hot wire 5 at the time of non-heating is detected by the hot wire temperature detecting means 34 in step 4B. In step S5, the gas temperature Tg is calculated from the temperature Th of the two hot wires 5 detected in steps S4A and S4B and during heating, and the gas flow rate calculated one cycle before.

  On the other hand, in step S2B, the drive duty is converted into a duty (flow rate duty) used by the gas flow rate calculation means 15 using the current power supply voltage value, and in step S6, the duty-flow rate conversion table is selected according to the delta Th, and the selected duty is selected. -Calculate the gas flow rate based on the flow rate Duty using the flow rate conversion table.

  In step S7, the gas flow rate calculated in step S6 is calculated using the physical property correction table 16 and the final gas flow rate Q is output 17 based on the gas temperature. That is, it is possible to know the fluctuation value of the drive voltage in steps S2A, S2B, S6, and S7, correct the relationship between the drive duty and the gas flow rate, and always measure the accurate gas flow rate.

  As described above, according to the embodiment of the present invention, the voltages V1 and V2 at both ends of the heat generation sensor element 5 are simultaneously measured, the current value flowing through the heat generation sensor element 5 is detected, and the resistance value calculating unit 33 is detected. By calculating the resistance value by the above, it is possible to accurately know the resistance value of the heat generation sensor element even when the drive voltage varies. Since the temperature of the heat generation sensor element 5 can be accurately calculated from the accurate resistance value of the heat generation sensor element 5, the accurate gas temperature and gas mass flow are always measured even when the battery voltage varies. It is possible to realize a thermal gas mass flow meter of a pulse width modulation control system that can be used.

  Furthermore, the drive duty calculation means 14, the flow rate duty calculation means 35, and the gas flow rate calculation means 15 know the fluctuation value of the drive voltage, correct the relationship between the duty and the flow rate, and always measure the accurate gas flow rate. it can.

  FIG. 3 is a schematic configuration diagram of another embodiment of a thermal gas mass flowmeter according to the present invention. The difference between the example of FIG. 3 and the example of FIG. 1 is that the differential amplifier 29 and the A / D converter 31 in the example of FIG. 1 are omitted, and the output of the differential amplifier 8 is the A / D converter 19. The point of being supplied to the heating time input terminal and the non-heating time input terminal of the resistance value calculating means 33.

  The output signal of the D / A converter 32 is supplied to the inverting input terminal of the differential amplifier 8.

  That is, in the example of FIG. 3, when the CPU 9 takes in the voltage V2 on the downstream side of the hot wire 5, it supplies a digital signal so that the output (offset voltage) of the D / A converter 32 becomes a predetermined voltage during heating. And, when not heated, the output of the D / A converter 32 is set to 0V. Thereby, the differential amplifier and the A / D converter can be shared, and the differential amplifier 29 and the A / D converter 31 in the example of FIG. 1 can be deleted.

  Other configurations and operations are the same as those in the example of FIG.

  Also in the example shown in FIG. 3, the same effect as the example shown in FIG. 1 can be obtained.

  As shown in FIG. 4, the thermal gas mass flowmeter shown in FIGS. 1 and 3 includes all circuits except for the hot wire 5 as a one-chip LSI 20, and a single one-chip LSI 20 is used to form a plurality of hot wires. 5 can be controlled, a thermal gas mass flowmeter using a plurality of heat generation sensor elements can be manufactured in a small size and at low cost.

  FIG. 5 is an example in which the present invention is not applied and the resistance value calculating means 33, the drive duty calculating means 14, the flow rate duty calculating means 35, the target Th setting means 36, etc. in the present invention are not provided. It is a figure which shows a comparative example.

  In FIG. 5, when the MOS-FET 3 is ON, the drive voltage from the power source 1 is applied to the hot wire 5 with almost no loss in the MOS-FET 3, and the hot wire 5 is heated. On the other hand, when the MOS-FET 3 is OFF, a small constant current from the constant current circuit 2 is passed through the hot wire 5, but the hot wire 5 is not heated.

  When the MOS-FET 3 is ON, the heating temperature conversion table 12 can be used to know the temperature of the hot wire 5 from the V2 voltage determined by the value of the current flowing through the current detection resistor 6.

  Further, when the MOS-FET 3 is off, the temperature of the hot wire 5 can be known from the V2 voltage determined by the resistance value of the hot wire 5 using the non-heating temperature conversion table 11.

  The application time control means 14 calculates the ON / OFF time ratio (Duty) of the MOS-FET 3 required to make the current temperature of the hot wire 5 higher than the gas temperature by a predetermined temperature difference delta Th by PI control, and PWM Digital feedback is provided as signal 10. When the gas flow rate is high, the amount of heat taken away from the hot wire 5 is large, so the duty increases.

  On the other hand, when the flow rate is low, the amount of heat taken away from the hot wire 5 is small and the duty becomes small. Therefore, by measuring this duty, the mass flow rate of the gas can be measured.

  However, in the example shown in FIG. 5, as described above, when the power supply voltage of the battery fluctuates, in the thermal gas mass flowmeter controlled by pulse width modulation, the hot wire temperature when the MOS-FET is turned on is hot. Since the voltage value is obtained from the voltage value of the low voltage terminal of the wire, the voltage value fluctuates and an incorrect hot wire temperature is detected.

  On the other hand, according to the present invention, the resistance value is calculated by measuring the both-end voltage and current value of the hot wire 5, and the accurate temperature of the hot wire is calculated based on the accurate resistance value. An accurate gas flow rate can be measured regardless of fluctuations in the power supply voltage.

  In addition, although the example mentioned above is an example at the time of applying this invention to the thermal-type gas mass flowmeter which measures the engine intake air amount of a motor vehicle, and exhaust_gas | exhaustion amount, it is not restricted to this, For example, the gas flow measuring device of a plant The present invention is also applicable to the above.

It is a schematic block diagram of the control apparatus in one Embodiment of the thermal type gas mass flowmeter which concerns on this invention. It is a process flowchart of the control apparatus (CPU) in one Embodiment of this invention. It is a schematic block diagram of the control apparatus in other embodiment of the thermal type gas mass flowmeter which concerns on this invention. It is a conceptual diagram which operates the some hot wire in the thermal type gas mass flowmeter which concerns on this invention with one control apparatus. It is a different example from the present invention, and is a figure showing a comparative example with the control device in the present invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Power source, 2 ... Constant current circuit, 3 ... MOS-FET, 4 ... Backflow prevention diode, 5 ... Hot wire, 6 ... Current detection resistor, 7, 8 , 28, 29... Differential amplifier, 9... Controller (CPU), 10... PWM signal, 13... Gas temperature calculation means, 14. Gas flow rate calculation means, 16 ... Physical property correction table, 17 ... Final flow rate output, 18, 19, 30, 31 ... A / D converter, 20 ... 1-chip LSI, 32 ... D / A converters 32, 33 ... resistance value calculating means, 34 ... hot wire temperature detecting means, 35 ... flow rate duty calculating means, 36 ... target Th setting means

Claims (8)

In a thermal gas mass flowmeter that measures the gas flow rate based on the heat dissipation amount of the heat generation sensor element to which current is supplied from the power source,
The voltage across the heat sensor element is detected, the current flowing through the heat sensor element is calculated, and the resistance value of the heat sensor element is calculated based on the calculated current value and the voltage value across the heat sensor element. A thermal gas mass flowmeter comprising: an operation control means for calculating a temperature of the heat generation sensor element based on the calculated resistance value and calculating a gas flow rate based on the calculated heat generation sensor element temperature. In a thermal gas mass flowmeter that measures the gas flow rate based on the heat dissipation amount of the heat generation sensor element to which current is supplied from the power source,
Voltage detecting means for detecting the voltage across the heat sensor element;
A resistance value for calculating a current value flowing through the heat generation sensor element and calculating a resistance value of the heat generation sensor element based on the calculated current value and a voltage value at both ends of the heat generation sensor element detected by the voltage detection means. A calculation means;
Heat generation sensor element temperature calculation means for calculating the temperature of the heat generation sensor element based on the resistance value of the heat generation sensor element calculated by the resistance value calculation means,
Based on the temperature of the heat generation sensor element calculated by the heat generation sensor element temperature calculation means, the heat generation sensor element is heated or not heated so that the temperature of the heat generation sensor element becomes a constant temperature. Current control means for controlling on / off of current supply to the sensor element;
A gas flow rate calculation means for calculating a gas flow rate based on a current supply on / off period of the current control means;
A thermal gas mass flowmeter comprising: The thermal gas mass flow meter according to claim 2,
The resistance value calculation means calculates a resistance value based on a voltage value at both ends of the heat generation sensor element and a calculated current value in each state when the heat generation sensor element is in a heated state and when it is not heated. And a gas temperature calculation means for calculating the temperature of the gas based on the calculated resistance value, wherein the gas flow rate calculation means corrects the gas flow rate according to the calculated gas temperature. Flowmeter. The thermal gas mass flowmeter according to claim 2 or 3,
The voltage detection means includes
A differential amplifier for detecting one terminal voltage at the time of heating of the heat generation sensor element, an A / D converter for A / D converting an output signal of the differential amplifier, and one of the heat generation sensor element at the time of non-heating. A differential amplifier for detecting a terminal voltage of the A / D converter, an A / D converter for A / D converting an output signal of the differential amplifier, and
A differential amplifier for detecting the other terminal voltage at the time of heating of the heat generation sensor element, an A / D converter for A / D converting an output signal of the differential amplifier, and the other at the time of non-heating of the heat generation sensor element A differential amplifier for detecting a terminal voltage of the A / D converter, an A / D converter for A / D converting an output signal of the differential amplifier, and
The thermal gas mass flowmeter is characterized in that output signals from the four A / D converters are supplied to the resistance value calculation means. The thermal gas mass flowmeter according to claim 2 or 3,
The voltage detection means includes
A differential amplifier for detecting one terminal voltage during heating of the heat sensor element, a first A / D converter for A / D converting an output signal of the differential amplifier, and the non-heating of the heat sensor element A differential amplifier for detecting one terminal voltage at the time, and a second A / D converter for A / D converting an output signal of the differential amplifier;
A differential amplifier for detecting the other terminal voltage of the heat sensor element, a third A / D converter for A / D converting an output signal of the differential amplifier, and the third sensor during the heating of the heat sensor element Means for setting the offset voltage of the A / D converter to a constant value and setting the offset voltage of the third A / D converter to 0 at the time of non-heating;
The thermal gas mass flowmeter is characterized in that output signals from the three A / D converters are supplied to the resistance value calculating means. The thermal gas mass flowmeter according to claim 3,
The heat sensor element temperature calculation means includes a temperature conversion table showing a relationship between the resistance value of the heat sensor element and the temperature of the heat sensor element, and when the heat sensor element is in a heated state and in a non-heated state. The temperature of the heat generating sensor element is calculated by using the common temperature conversion table at the time of the above. The thermal gas mass flow meter according to claim 2,
A flow rate duty calculating means for converting a drive duty, which is a time ratio between on and off of the current control means, required to raise the temperature of the heat generation sensor element into a flow rate duty required for obtaining a gas flow rate; A thermal gas mass flowmeter comprising:   3. The thermal gas mass flow meter according to claim 2, wherein the voltage detection means, resistance value calculation means, heat generation sensor element temperature calculation means, current control means, and gas flow rate calculation means are configured by a one-chip LSI. A thermal gas mass flowmeter characterized by

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