JP2006317297A - Method for diagnosing degradation of thermal flowmeter and output correction method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem that fouling and degradations simultaneously occur in a heating resistor etc. to cause a substantial degradation in accuracy in a short time since especially diesel exhaust gases contain a large amount of fouling components such as carbon and oil in the case of measuring the quantity of flow of exhaust gases. <P>SOLUTION: A means for determining degradations of a flowmeter is provided for the inside of ECU or a flowmeter. Degradations of the flowmeter is determined by the degradation determination means before the engine is started or with an engine in a state of steady operation after it is started. Output of the flowmeter is corrected on the basis of determination results. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a deterioration diagnosis and output correction method for a gas flow meter that measures the flow rate of air or exhaust gas flowing in an automobile engine system.

  As a known example showing a conventional example, Patent Document 1 discloses that an exhaust gas recirculation passage extending from between a catalyst downstream side and a muffler upstream side of an exhaust pipe is provided with a flow meter and an intake air in the exhaust gas recirculation passage. A control valve is provided at the junction with the pipe, the valve opening of the control valve is controlled based on the signal from the flow meter, and feedback control is performed so that the flow rate of the exhaust gas flowing through the exhaust gas recirculation passage becomes a target value. Thus, means for accurately metering the actual flow rate is disclosed. In particular, the flow meter interposed in the exhaust gas recirculation passage is a thermal flow meter used for exhaust gas measurement, but does not have means for diagnosing deterioration of the flow meter caused by contamination or the like.

JP-A-6-74100

  EGR has long been adopted as a means for reducing NOx discharged from the engine. In particular, in recent years, more stringent regulations have been introduced for exhaust gas emitted from vehicles. On the other hand, lean burn engines such as gasoline engines and diesel engines that inject fuel directly into the cylinder are compared to ordinary engines. Therefore, the EGR limit has been greatly extended, and the lean limit of the air-fuel ratio for combustion has also been increased. Therefore, a large amount of EGR and further high accuracy of EGR control are required. Patent Document 1 aims to enable more accurate EGR gas metering and mixing when refluxing a large amount of EGR by directly measuring the EGR gas flow rate. In the case of an exhaust gas atmosphere, the problem of antifouling occurs. In particular, the exhaust gas of diesel contains many fouling components such as carbon and oil, so it cannot be technically established without taking antifouling measures. Patent Document 1 describes a means for removing a fouling component such as carbon or oil by newly installing a filter upstream of the flow meter in response to this problem. However, in the case of such a configuration, there is a demerit that the cost is increased by adding a new filter. In addition, while a small size is required due to the restriction of the installation space to be arranged, there is a problem that a large error occurs in the output of the flow meter in a short time due to the contamination unless the contamination component is completely removed. is there.

  The present invention has been made in view of the above circumstances, and in particular, a diagnosis method for an EGR gas flow meter that can maintain the measurement accuracy for a long period of time by always diagnosing and correcting deterioration of the flow meter caused by contamination or the like. It is an object to provide an output correction method.

  A diagnosis method and a correction method for an EGR gas flow meter according to the present invention include an EGR pipe that connects an exhaust pipe and an intake pipe, an EGR cooler that cools EGR gas, and an EGR valve that adjusts the amount of EGR gas, and a heating resistor. And a thermal flow meter that outputs a flow rate-related signal from a resistance temperature detector disposed upstream or downstream of the heating resistor on the EGR pipe, the engine is controlled in an integrated manner. The flow meter has a means for determining the deterioration of the flow meter in the unit or the flow meter, and the deterioration determination means determines the deterioration of the flow meter between the key ON and the start of engine start.

  A diagnosis method and a correction method for an EGR gas flow meter according to the present invention include an EGR pipe that connects an exhaust pipe and an intake pipe, an EGR cooler that cools EGR gas, and an EGR valve that adjusts the amount of EGR gas, and a heating resistor. And a thermal flow meter that outputs a flow rate-related signal from a resistance temperature detector disposed upstream or downstream of the heating resistor on the EGR pipe, the engine is controlled in an integrated manner. The unit or the flow meter has a means for determining the deterioration of the flow meter, and the deterioration determination means determines the deterioration of the flow meter in a steady operation state after the engine is started.

  A diagnosis method and a correction method for an EGR gas flow meter according to the present invention include an EGR pipe that connects an exhaust pipe and an intake pipe, an EGR cooler that cools EGR gas, and an EGR valve that adjusts the amount of EGR gas, and a heating resistor. And a thermal flow meter that outputs a flow rate-related signal from a resistance temperature detector disposed upstream or downstream of the heating resistor on the EGR pipe, the engine is controlled in an integrated manner. The unit or the flow meter has a means for determining the deterioration of the flow meter, and the output value of the thermal type flow meter is corrected based on the determination result by the deterioration determination means.

  A diagnosis method and a correction method for an EGR gas flow meter according to the present invention include an EGR pipe that connects an exhaust pipe and an intake pipe, an EGR cooler that cools EGR gas, and an EGR valve that adjusts the amount of EGR gas, and a heating resistor. And a thermal flow meter that outputs a flow rate-related signal from a resistance temperature detector disposed upstream or downstream of the heating resistor on the EGR pipe, the engine is controlled in an integrated manner. A unit or a flow meter for determining deterioration of the flow meter, wherein the deterioration determination unit stores an output value at the start of vehicle use in a memory, and thereafter an output value obtained at a predetermined condition Is performed by comparison with the memory value.

  In the diagnosis method and the correction method for an EGR gas flow meter according to the present invention, the deterioration determination means is a means for determining deterioration by comparing an output value of the flow meter with a voltage width A set in advance as a determination reference. Features.

  According to the EGR gas flow meter diagnosis method and correction method of the present invention, the deterioration determination means compares the output value of the flow meter with a voltage width A set in advance as a determination reference, and the amplitude of the output voltage of the flow meter. Is compared with a voltage width B set in advance as a determination criterion, and if either one of the two determination means is NG, it is determined that the deterioration has occurred.

  A diagnosis method and a correction method for an EGR gas flow meter according to the present invention include an EGR pipe that connects an exhaust pipe and an intake pipe, an EGR cooler that cools EGR gas, and an EGR valve that adjusts the amount of EGR gas, and a heating resistor. In the engine in which a thermal flow meter that outputs a signal related to the flow rate is provided on the EGR pipe from a resistance temperature detector arranged upstream or downstream of the heating resistor, two heating resistors are provided. And one is controlled by a circuit that maintains a constant temperature difference (ΔTh) with the resistance temperature detector, and the other is a circuit that always maintains a predetermined temperature regardless of the gas temperature to be measured. According to the control according to the above, a signal relating to the gas flow rate is simultaneously output, and the deterioration of the flowmeter is determined by comparing both output values under a predetermined condition.

  According to the present invention, it is possible to reliably determine the initial accuracy for a longer time by reliably determining the deterioration of the EGR gas mass flow meter over time and correcting the output based on the determination result. .

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 shows the configuration of the thermal flow meter of the present invention. In the thermal flow meter, the heating resistor 1 for detecting the gas flow rate and the temperature sensitive resistor 2 for detecting the gas temperature are configured in the passage inside the passage body 3. Signals detected by the heating resistor 1 and the temperature sensitive resistor 2 are processed in the module unit 4 having a drive circuit unit, and an electrical signal corresponding to the flow rate is sent to the ECU via the connector 5. With such a configuration, the flow rate of the gas to be measured is measured with high accuracy.

FIG. 2 shows actuator signals and operations at the time of activation. Usually the keys are ACC, ON,
Turn the engine in order of START to start the engine. In this series of operations, the power necessary for actuators around the engine is generally supplied from a battery by turning on a key. Further, when the key START, which is the next operation, is selected, the engine starts and gas starts to flow into the intake system and the exhaust system. Therefore, in the current control, in order to diagnose the flow meter according to the present invention, it is desirable to carry out from the key ON to the start of engine start by START. This is because, as described above, a gas flow is generated in the intake system and the exhaust system after the engine is started, and pulsation of the gas flow is necessarily accompanied in the intake pipe and the exhaust pipe. According to the present invention, it is possible to perform a more reliable diagnosis of the flowmeter in a stable environment without being affected by gas pulsation before the gas flow is generated. Further, in order to secure a sufficient time for performing the diagnosis, the flowmeter may be energized when the key is inserted or the ACC is turned on, and the diagnosis may be performed before the engine is started.

  In addition, even after the engine is started after the gas flow is generated, it is preferable that the engine is in a stable state as in steady operation. Therefore, the flow meter can be diagnosed with high accuracy. The steady operation is, for example, an idling operation state.

  Next, a control routine for correcting the output of the flowmeter based on the deterioration determination means will be briefly described using the flowchart shown in FIG. First, in step S101, the current flow meter output value Vout is read. Subsequently, it progresses to step S102 and determines deterioration of a flowmeter. The deterioration of the flowmeter is determined by comparing the previously read Vout with the determination reference value. If it is determined that the flowmeter is deteriorated, the process branches to step S103, the output of the flowmeter is corrected, and the process proceeds to step S101 again. On the other hand, if it is determined in step S102 that there is no deterioration, the present control routine is exited.

  In addition, the deterioration determination is performed by storing the output value at the start of vehicle use in a memory built in the ECU or the flow meter, and comparing the output value obtained at the predetermined condition described above with the memory value. Deterioration is judged.

  Next, a specific method for determining deterioration will be described with reference to FIGS. As shown in FIG. 4, basically, the deterioration determination method is effective from the change in the output voltage of the flow meter. A voltage upper limit value and a lower limit value are set as judgment criteria, and the output voltage after the elapse of time is compared with the set value as in the deterioration patterns A and B shown as examples in the figure, and within the reference voltage range. Deterioration is determined by whether or not there is. The determination criterion may be set in advance from a method of storing an output value at the start of vehicle use in a memory or an initial output characteristic of a flow meter as described in claim 4. Further, as shown in FIG. 5, the amplitude of the output voltage may increase with respect to the initial stage due to some factors such as contamination of the flow meter and the mounting duct. It is desirable to set an upper limit value of the amplitude for such a malfunction and determine the deterioration by comparing with the value after the elapse of time. For example, if these two determination methods are executed at the same time, the deterioration is further deteriorated. The accuracy of determination can be increased. Further, even if other than the specific determination method described with reference to FIGS. 4 and 5, there is no particular problem as long as it is a means for determining deterioration based on the output voltage of the flow meter.

  Next, a control flow in the case of having two deterioration determination means of voltage value and amplitude shown as the above example will be described with reference to FIG. First, in step S104, Vout, which is a flow meter output value, and Vmin and Vmax, which are upper and lower limit values of a voltage serving as a determination criterion, are read. Next, the process proceeds to step S105, and a comparison based on output values is performed as a first determination. If Vout exceeds the reference value such as Vmin or less or Vmax or more by comparing Vout with the determination reference value, it is determined that the deterioration has occurred and the process branches to step S106, the output of the flow meter is corrected, and the process proceeds to step S104 again. On the other hand, if there is no deterioration in step S105, that is, if it is determined that Vout is within the reference value, the process proceeds to step S107. In step S107, an amplitude reference voltage value Vref as a second determination criterion is read. Next, the process proceeds to step S108, and the comparison by the amplitude value is performed as the second determination. If Vout is greater than or equal to Vref by comparing Vout with the determination reference value, it is determined that the output has deteriorated, and the process branches to step S106, the output of the flow meter is corrected, and the process proceeds again to step S104. On the other hand, if it is determined in step S108 that there is no deterioration, the present control routine is exited.

  Next, as another means for determining deterioration using the output voltage of the flow meter, a method for determining deterioration based on the difference between two output voltages will be described.

  In this method, in order to obtain two output voltages, the structure has two heating resistors. FIG. 7 shows the configuration. The flow meter includes two heating resistors (hereinafter referred to as heating resistors A and B) and at least one resistance temperature detector, and includes two control circuits.

  Since the two control circuit configurations basically have the same configuration, the temperature difference constant control circuit shown in the upper part will be described here. A control circuit driven by a power source includes a Wheatstone bridge circuit including a heating resistor A, a resistance temperature detector, and other resistors. The middle point of the bridge is between the heating resistor A and the resistor arranged on the ground side, and the other midpoint of the bridge is between the resistance temperature detector and the resistor arranged on the ground side. To do. The Wheatstone bridge circuit is configured to adjust the current flowing through the heating resistor A by the differential amplifier and the transistor so that the potential difference at the midpoint becomes zero. This bridge circuit controls the heating current flowing through the heating resistor A so that the difference between the heating temperature of the heating resistor A and the gas temperature sensed by the resistance temperature detector becomes a predetermined temperature difference. In addition, the control circuit shown in the lower stage has a constant absolute temperature of the heating resistor B regardless of the change in gas temperature by disposing a fixed resistor instead of a resistance temperature detector with respect to a constant temperature difference control circuit. The heating current flowing through the heating resistor B is controlled so that

  Amplification is performed by an output adjustment circuit provided at the output of a differential amplifier provided in each control circuit, and respective output voltages Vout1 and Vout2 are obtained. Further, the difference between these Vout1 and Vout2 is calculated, and deterioration is determined by comparison with a reference value (initial value) of a voltage difference provided in advance. As this principle, for example, the difference between the output voltage before the initial deterioration and the deterioration due to the passage of time after the deterioration due to the difference in the control method, the difference in the voltage difference occurs. Even in this method, the deterioration of the flow meter can be determined.

The block diagram of the flowmeter which concerns on this embodiment. Operation until engine start according to the present embodiment. Flow meter output voltage correction control flow. An example of a deterioration diagnosis method according to the present embodiment. An example of a deterioration diagnosis method according to the present embodiment. Flow meter deterioration judgment control flow. Configuration for diagnosis of deterioration due to output voltage difference.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Heat generating resistor, 2 ... Temperature sensitive resistor, 3 ... Passage body, 4 ... Module part, 5 ... Connector, 6 ... Terminal.

Claims (7)

  An EGR pipe that connects the exhaust pipe and the intake pipe, an EGR cooler that cools the EGR gas, and an EGR valve that adjusts the amount of EGR gas, and a heating resistor and a measurement unit arranged upstream or downstream of the heating resistor In an engine in which a thermal flow meter that outputs a flow rate-related signal from a temperature resistor is arranged on the EGR pipe, the deterioration of the flow meter is determined in a unit that controls the engine or in the flow meter. And a deterioration diagnosis method for a thermal flow meter, wherein the deterioration determination unit determines deterioration of the flow meter between the key ON and the start of engine startup.   An EGR pipe that connects the exhaust pipe and the intake pipe, an EGR cooler that cools the EGR gas, and an EGR valve that adjusts the amount of EGR gas, and a heating resistor and a measurement unit arranged upstream or downstream of the heating resistor In an engine in which a thermal flow meter that outputs a signal related to the flow rate from the temperature resistor is arranged on the EGR pipe, a unit for controlling the engine or a unit for determining the deterioration of the flow meter is provided. A deterioration diagnosis method for a thermal flow meter, comprising: determining deterioration of the flow meter in a steady operation state after starting the engine by the deterioration determination means.   An EGR pipe that connects the exhaust pipe and the intake pipe, an EGR cooler that cools the EGR gas, and an EGR valve that adjusts the amount of EGR gas, and a heating resistor and a measurement unit arranged upstream or downstream of the heating resistor In an engine in which a thermal flow meter that outputs a signal related to the flow rate from the temperature resistor is arranged on the EGR pipe, a unit for controlling the engine or a unit for determining the deterioration of the flow meter is provided. And an output correction method for the thermal flow meter, wherein the output value of the thermal flow meter is corrected based on a determination result by the deterioration determination means.   An EGR pipe that connects the exhaust pipe and the intake pipe, an EGR cooler that cools the EGR gas, and an EGR valve that adjusts the amount of EGR gas, and a heating resistor and a measurement unit arranged upstream or downstream of the heating resistor In an engine in which a thermal flow meter that outputs a signal related to the flow rate from the temperature resistor is arranged on the EGR pipe, a unit for controlling the engine or a unit for determining the deterioration of the flow meter is provided. And the deterioration determining means stores an output value at the start of vehicle use in a memory, and thereafter performs an output value obtained at a predetermined condition by comparison with the memory value. Flow meter degradation diagnosis method.   4. The thermal type according to claim 1, wherein the deterioration determining means is means for determining deterioration by comparing an output value of a flow meter with a voltage upper limit value and a lower limit value set in advance as a determination criterion. Flow meter degradation diagnosis method.   The deterioration determining means compares the output value of the flow meter with the voltage upper limit value and the lower limit value set in advance as a determination reference, and the amplitude of the output voltage of the flow meter and the voltage amplitude upper limit value set as a determination reference in advance. The deterioration diagnosis method for a thermal type flow meter according to any one of claims 1 to 3, wherein the deterioration is determined when either of the two determination means is NG. An EGR pipe that connects the exhaust pipe and the intake pipe, an EGR cooler that cools the EGR gas, and an EGR valve that adjusts the amount of EGR gas are provided. In an engine in which a thermal flow meter for outputting a flow rate-related signal from the temperature resistor is arranged on the EGR pipe, the heating resistor has two heating resistors and each is controlled independently. The temperature difference (ΔTh) with the temperature resistor is controlled to be kept constant, and the other is controlled so as to always maintain the heating temperature of the heating resistor at a predetermined temperature regardless of the measured gas temperature. A method for diagnosing deterioration of a thermal flow meter, wherein a deterioration determination of a flow meter is performed by simultaneously outputting signals related to a flow rate and comparing both output values under a predetermined condition.

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