JP2011047319A - Diagnostic device for egr system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a diagnostic device for an EGR system, specifying the portion of an EGR system and specifying the condition of the portion, even if there is a temporal change caused by adhesion of PM (soot). <P>SOLUTION: This diagnostic device for the EGR system includes: an EGR flow passage allowing an exhaust pipe to communicate with an intake pipe; a flow rate measurement device attached to the EGR flow passage and measuring an EGR gas flow rate; an EGR temperature measurement device attached to the inside or the vicinity of the flow rate measurement device and measuring the temperature of the EGR gas; and an EGR gas flow rate control valve controlling the EGR gas flow rate. The diagnostic device includes: a profile measurement means measuring the temperature profile of the EGR gas temperature changed according to a change in the valve opening of the EGR gas flow rate control valve and the flow rate profile of the EGR gas flow rate; and a diagnostic means specifying the portion of the EGR system, and diagnosing the condition of each position, based on the temperature profile and flow rate profile. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a diagnostic apparatus for an EGR system of an internal combustion engine, and more particularly to a diagnostic apparatus suitable for an EGR system that controls an EGR flow rate for NOx reduction in exhaust gas and engine output control.

  In recent years, diesel engines and lean burn engines are considered promising among the engines for improving the fuel efficiency of internal combustion engines. However, diesel engines and lean burn engines tend to contain more NOx in the exhaust gas than other engines. In order to reduce NOx contained in the exhaust gas, it is effective to reduce the combustion temperature of the fuel. A part of the exhaust gas is brought to the intake side via the EGR flow path that connects the exhaust pipe and the intake pipe. Conventionally, exhaust gas recirculation (EGR) control for returning and performing combustion control has been performed.

  As a diagnostic device for diagnosing a failure of the EGR system for performing EGR control, a diagnostic device for determining that the EGR system including the piping is defective based on the correlation between the target EGR flow rate and the EGR flow rate detected by the flow rate sensor has been proposed. (For example, refer to Patent Document 1).

  In addition to this, when the operation state determination means determines that the operation state is a predetermined steady operation state, the calculated target EGR flow rate is compared with the EGR flow rate measured by the EGR flow rate sensor to diagnose the contamination of the EGR flow rate sensor. (For example, refer to Patent Document 2), and the actual EGR rate and the target EGR rate are calculated, and when the two values do not match, there is proposed that the EGR control device is diagnosed as malfunctioning. (For example, see Patent Document 3).

JP 2006-316709 A JP 2008-069690 A Japanese Patent Laid-Open No. 05-018324

  However, even when the apparatus described in the above-mentioned patent document is used, there is a case where a failure cannot be diagnosed accurately. The EGR flow path (EGR pipe) is a gas flow path that connects the exhaust passage and the intake passage, and the exhaust gas in the EGR flow path corresponds to the pressure difference between the exhaust pressure and the intake (intake) manifold pressure. It flows from the exhaust side to the intake side. As a result, the flow rate of the exhaust gas that actually flows through the EGR flow path (EGR flow rate) fluctuates due to the influence of the fluctuations in the exhaust pressure and the intake manifold pressure.

  For this reason, the above-mentioned method, which does not take into account the exhaust gas pressure pulsation change accompanying the explosion for each cylinder of the engine and the temporal phase change of the intake manifold pressure pulsation fluctuation caused by the opening of the intake valve, accurately sets the EGR flow rate. It was difficult to measure. From such a viewpoint, it is preferable to use an EGR mass flow sensor in order to measure an EGR flow rate more accurate than a pressure sensor.

  However, when measuring the EGR mass flow rate of the EGR channel (EGR pipe) using the EGR mass flow rate sensor, the EGR mass flow rate sensor and the EGR cooler are used for the PM (soot) contained in the exhaust gas in the EGR channel. Since it is exposed to an atmosphere containing a fouling substance, its ability may change over time due to adhesion of the fouling substance. For this reason, in order to appropriately control the EGR system, it is important to identify and diagnose a site that changes (deteriorates) over time. However, the conventional techniques make such diagnosis accurate. The current situation is that it is not possible.

  The present invention has been made in view of the problems to be solved, and the object of the present invention is to provide a part of the EGR system even when it changes over time due to adhesion of PM (soot) or the like. It is an object of the present invention to provide a diagnostic apparatus for an EGR system that can specify the status of the system.

  In view of the above-mentioned problems, the inventors have conducted intensive studies, and as a result, when the valve opening degree of the EGR gas flow rate control valve constituting the EGR system changes to a predetermined opening degree, the EGR changes accordingly. If the temperature profile and flow rate profile of the gas could be captured, new knowledge was obtained that the degraded part of the EGR system could be identified and the state of degradation could be diagnosed.

  The present invention is based on the above-mentioned new knowledge, and an EGR system diagnosis apparatus according to the present invention is provided with an EGR flow path that connects an exhaust pipe and an intake pipe, and an EGR gas that is attached to the EGR flow path. A flow rate measuring device that measures the flow rate of the EGR gas, a temperature measurement device that is mounted in or near the flow rate measuring device and that measures the temperature of the EGR gas, and an EGR gas flow rate control valve that controls the EGR gas flow rate A diagnostic device for an EGR system comprising: a temperature profile of the EGR gas temperature that changes according to a change in a valve opening of the EGR gas flow rate control valve; and a flow rate of the EGR gas flow rate. A profile measuring means for measuring a profile, and identifying a part of the EGR system based on the temperature profile and the flow rate profile, Characterized in that it comprises a diagnostic means for diagnosing the condition, the.

  According to the present invention, the delay time of the EGR gas temperature, the initial EGR gas temperature when the valve opening degree changes, the time change amount of the EGR gas temperature, and the like can be captured from the temperature profile, and the EGR gas flow rate from the flow rate profile. Thus, it is possible to capture the delay time, and it is possible to identify a portion that has deteriorated over time and accurately diagnose the state.

1 is an overall configuration diagram of a diesel engine to which an EGR mass flow sensor according to an embodiment is applied. The schematic block diagram of the control apparatus containing the diagnostic apparatus of the engine EGR system shown in FIG. The block diagram for controlling the fuel injection-EGR flow volume by the microcomputer unit shown in FIG. The block diagram of the EGR mass flow sensor shown in FIG. The electric control circuit diagram of an EGR mass flow sensor. The block diagram for demonstrating the calculation of EGR flow volume from an EGR mass flow sensor. Explanatory drawing of a time change of an EGR gas temperature sensor. The flowchart which shows the contamination diagnosis routine (1) of an EGR mass flow sensor. The typical perspective view which shows attachment of an EGR mass flow sensor. Explanatory drawing which shows the backflow detection by an EGR mass flow sensor, and the frequency component of a pulsation. (A), (b) is a graph which shows the output characteristic of the contamination of an EGR mass flow sensor. The flowchart which shows the contamination diagnosis routine (2) of an EGR mass flow sensor. The timing chart of the contamination diagnosis of an EGR mass flow sensor. The flowchart which shows the correction | amendment calculation routine at the time of the contamination diagnosis of an EGR mass flow sensor. The block diagram which shows the procedure of the grilling of the EGR mass flow sensor. The flowchart of the starting delay of an EGR mass flow sensor. The figure which attached the some sensor in the bypass channel. Explanatory drawing of each signal of an EGR mass flow sensor signal output. Example of ropeless EGR. EGR mass flow sensor signal variation example.

[First embodiment]
An embodiment in which an EGR mass flow sensor is applied to a diesel engine in an EGR system diagnostic apparatus according to the present invention will be described. FIG. 1 is an overall configuration diagram of a diesel engine to which an EGR mass flow sensor according to this embodiment is applied.

  As shown in FIG. 1, the air taken in by the diesel engine 1 (hereinafter referred to as the engine 1) is taken in from an air cleaner (not shown), the mass flow rate is measured by the air flow meter 2, and the compressor 3 </ b> A of the turbocharger 3. Supercharged by. The supercharged air is cooled by the intercooler 4, and the flow rate is measured by the throttle valve 5. The supercharged air is distributed to each cylinder by the intake manifold 6, and is combusted from the intake port 7 of the engine 1 through the combustion chamber. 8 is inhaled.

  A fuel injection valve 9 for injecting fuel into the combustion chamber 8 is attached to the engine 1. The fuel injection valve 9 injects fuel corresponding to the intake air amount into the combustion chamber 8. The fuel injected into the combustion chamber 8 generates an air-fuel mixture with the intake air in the combustion chamber 8 and burns in the combustion chamber 8.

  The already burned gas discharged from the combustion chamber 8 by the engine 1, that is, the exhaust gas, is discharged from the exhaust port 10 to the exhaust pipe 11 to drive the turbine 3B of the turbocharger 3 and purify the exhaust gas by a de-NOx catalyst, an SCR catalyst or the like. The catalyst 12, the DPF (diesel particulate filter) 13, and the exhaust silencer 14 are discharged into the atmosphere.

  On the other hand, an EGR flow path that connects the exhaust pipe and the intake pipe is provided, and an EGR intake 15 is formed in the middle of the exhaust pipe 11 on the exhaust port 10 side from the turbine 3B of the turbocharger 3. Part of the exhaust gas flowing through the exhaust pipe 11 flows from the EGR intake port 15 through the EGR pipe 16 to the EGR cooler 19 and the EGR gas flow rate control valve (EGR valve) 17, and the flow rate is quantitatively controlled by the EGR valve 17. Then, it passes through the EGR mass flow sensor (flow rate measuring device) 18 and the EGR pipe 20, reaches the EGR outlet 21 formed in the intake manifold 6, and returns to the intake manifold 6 from the EGR outlet 21. Here, the flow rate measuring device 18 is attached to the EGR flow path and can measure the flow rate of the EGR gas.

  Although not shown in FIG. 1, the engine 1 includes a crank angle sensor 23 that measures the engine speed and crank angle position, a cam angle sensor 24 that performs cylinder discrimination, and a coolant temperature of the engine 1. A water temperature sensor 25 to be measured is attached (see FIG. 2).

  FIG. 2 is a schematic configuration diagram of a control device including a diagnostic device for the EGR system of the engine 1 shown in FIG. 1 according to the present embodiment. The control device of the engine 1 is of an electronic control type, and includes a digital input circuit 31 for inputting an on / off signal from the ignition switch 22 of the engine 1, a sensor signal (pulse signal) from the crank angle sensor 23 and the cam angle sensor 24. ), An analog signal input circuit 33 for inputting a sensor signal (analog signal) from the air flow meter 2 including the intake air temperature sensor, the water temperature sensor 25, or the EGR mass flow sensor 18, a CPU 34, and a ROM 35. And a microcomputer unit 37 including a RAM 36, a digital output circuit 38 that outputs a command signal to the EGR valve 17, the EGR cooler bypass valve 26, or the wastegate valve 27 of the turbocharger 3, and a drive pulse to the fuel injection valve 9. A timer setting output circuit 39 for outputting, and A S71, a the GPS 72, or a communication circuit 40 for communicating with GST73, the.

  The microcomputer unit 37 determines the operating state of the engine 1 based on the sensor signals input to the input circuits 31, 32, 33, calculates the fuel injection amount according to the operating state, and outputs the data to the output circuits 38, 39. Forward. In addition, the microcomputer unit 37 performs arithmetic processing for EGR flow rate control, EGR cooler control, and turbocharger 3 supercharging control in accordance with the operating state of the engine 1.

  FIG. 3 shows an example of an embodiment of a block diagram for controlling the fuel injection-EGR flow rate by the microcomputer unit 37 shown in FIG. The control device 37 includes an engine speed calculation unit 51 that calculates the engine speed from the crank angle signal output from the crank angle sensor 23.

  The basic fuel injection amount calculation unit 52 inputs the intake air amount signal output from the air flow meter 2 and the engine rotation number signal calculated and output by the engine rotation number calculation unit 51, and performs one combustion stroke. Each basic fuel injection amount (Tp) is calculated. In the fuel injection control, an output correction term (KMR) for the basic fuel injection amount is searched or calculated based on the engine speed and the basic fuel injection amount, and the basic corrected by the output correction term is performed. The fuel injection valve 9 injects the fuel of the fuel injection amount.

  Alternatively, as another aspect, the required target engine torque is calculated based on the accelerator pedal sensor signal and the rotational speed, and the fuel injection amount corresponding to the required target engine torque is calculated. The fuel injection valve 9 may inject a fuel injection amount of fuel.

  On the other hand, the target EGR rate calculating unit 54 calculates the target EGR rate η based on the engine speed calculated by the engine speed calculating unit 51 and the basic fuel injection amount Tp calculated by the basic fuel injection amount calculating unit 52. Set by map search or calculation. Further, the target EGR flow rate calculation unit 54 calculates the EGR flow rate that flows through the EGR flow path (EGR path) by the EGR pipes 16 and 20 from the target EGR rate η calculated by the target EGR rate calculation unit 54 and the intake air amount. To calculate a target EGR flow rate EGRTGT.

  The EGR valve opening degree control unit 55 compares the EGR flow rate measurement value measured by the EGR mass flow rate sensor 18 and corrected by the output characteristic correction unit 56, which is a gas flow rate correction unit, with the target EGR flow rate EGRTGT, and the control deviation is zero. The valve opening (valve passage area) of the EGR valve 17 is feedback-controlled so that Note that, based on the engine speed and the basic fuel injection amount, preset control valve opening information may be mapped, and the control valve opening information may be sent to the controller of the EGR valve 17.

Further, the target EGR flow rate EGRTGT of the target EGR flow rate calculation unit 54 described above can be obtained as follows. When the intake air amount measured by the air flow meter 2 is Qnew and the EGR flow rate is Qegr, the relationship between the intake air amount Qin entering the combustion chamber 8 and the exhaust gas flow rate Qex after combustion is expressed by the following equations (1) and (2 ).
Qnew + Qegr = Qin = Qex (1)
Qegr = Qex × η (2)

Therefore, in a steady state, Qex = Qnew / (1-η), and the EGR flow rate Qegr is expressed by the following equation (3).
Qegr = Qnew × η / (1-η) (3)

  The target EGR flow rate EGRTGT (control value) in steady operation and the EGR gas actual amount flow rate Qreal calculated based on the output signal of the EGR mass flow rate sensor 18 are compared, and the EGR valve is set so that they match. The EGR flow rate can be controlled by feedback control of the valve opening degree of 17.

Conventionally, the EGR flow rate is calculated based on the sensor signals of the intake pipe pressure sensor and the intake air temperature sensor. That is, if the new air amount before turbo charging is Qair, the temperature of the new air is Tair, the EGR flow rate is Qegr, and the temperature of the EGR flow is Tegr, based on the gas equation of state, Can be represented.
Qair × Tair + Qegr × Tegr = Qim × Tim∝Pim (4)

  Here, Qim is the mass of air sucked into the combustion chamber, Tim is the intake manifold internal temperature (intake manifold internal temperature), and Pim is the intake manifold pressure (intake manifold pressure).

From this relationship, the intake manifold pressure Pim and the intake manifold internal temperature Tim are obtained by a sensor or an estimated value, and Qim is a value corresponding to the engine speed,
Qair × Tair + Qegr × Tegr = Q (Tim, Pim) (5)
There is a relationship
To organize Qegr,
Qegr = {Q (Tim, Pim) −Qair × Tair} / Tegr (6)
Therefore, the estimated value Qegr of the EGR flow rate was calculated by obtaining the intake manifold temperature, intake manifold pressure, mass and temperature of new air, and EGR flow temperature. The temperature of the EGR cooler was substituted for the EGR flow temperature (the temperature of the new air).

  Thus, since the estimated value Qegr of the EGR flow rate is calculated based on the plurality of sensor signals, the respective sensor measurement errors are accumulated, and the measured flow rate error becomes large. Further, since the response of the sensor is slow, particularly the response of the EGR temperature sensor is slow, the EGR valve control cannot be performed using the estimated value of the flow rate in a transient state such as when the engine is accelerating or decelerating.

  On the other hand, it is necessary to realize PCI combustion that suppresses NOx generation and soot generation by controlling the combustion temperature and the air-fuel ratio in the engine, and the engine control device controls the air-fuel ratio for each explosion. In this case, the air-fuel ratio can be controlled by accurately detecting the EGR flow rate for each explosion.

  In particular, in a transient operation state such as during acceleration or deceleration, the estimated value of the EGR flow rate differs from the actual EGR amount, so that the exhaust gas level has deteriorated. That is, in the transient operation state, even if the opening degree of the EGR valve changes in accordance with the operation state, the inflowing EGR gas is a gas in a state before starting the transient operation, and thus the estimated value of the air-fuel ratio is different. End up. Further, since it takes time to diffuse the EGR gas into the intake manifold, the temperature in the intake manifold is difficult to be uniform with the delay of the gas diffusion. As a result, gas temperature unevenness occurs, and the estimated value of the EGR rate may differ from the actual value of the EGR rate.

  On the other hand, in the present embodiment, the target EGR flow rate EGRTGT, which is a control target value, is an average value of combustion and does not consider gas pulsation. For this reason, if the EGR valve is controlled based on the actually measured value, the control target value is likely to be hunted according to the pulsation of the gas, and the frequency response may be reduced. For this reason, the valve opening degree of the EGR valve is controlled by comparing the average value of the EGR mass flow sensor output signal with the target value that is the target EGR flow rate.

  However, there are further problems in calculating the conventional estimated value Qegr. First, when each combustion chamber is in the intake stroke, the intake pipe pressure decreases (closes to vacuum), and when the intake valve closes and enters the compression stroke, the intake pipe pressure increases (closes to the turbo charging pressure). Further, when the exhaust stroke is in progress, the exhaust gas flows out into the exhaust pipe, the exhaust pipe pressure rises, and when the exhaust valve closes and the next intake stroke starts, the exhaust pipe pressure decreases.

  Since the EGR flow flows according to the difference between the exhaust pipe pressure and the intake pipe pressure, the EGR flow includes a pressure fluctuation (pulsation). In particular, when the EGR flow rate is relatively small, the pulsation component reaches several times the average even if the average value of the EGR flow rate is almost zero.

  When the opening degree of the EGR valve is close to zero, the EGR flow begins to flow from the narrow gap of the EGR valve and diffuses into the intake manifold. For this reason, since the EGR flow is adiabatically expanded in the intake manifold after passing through the EGR valve, the EGR gas temperature is lowered. Therefore, the EGR gas temperature is lower than the temperature of the EGR cooler, and the EGR gas temperature Tegr in the intake manifold. Cannot be substituted with the EGR cooler temperature.

  Thus, the above-described conventional estimated value Qegr has a limit, and it is necessary to directly measure the EGR flow rate by the sensor (EGR mass flow rate sensor). By placing the EGR mass flow sensor downstream of the EGR valve, it is possible to improve the time delay of the EGR gas amount measurement and eliminate the influence of the error between the temperature sensor and the pressure sensor that has been conventionally required for estimating the EGR rate. it can.

  FIG. 4 is a block diagram of the EGR mass flow sensor shown in FIG. 1, and the EGR mass flow sensor (flow rate measuring device) 18 is a hot-wire type flow rate detecting means. As shown in FIG. In a sensor passage (EGR flow path) 61 through which gas flows, a heating resistor 62a which is a flow rate measuring element, and a temperature measuring resistor which is a gas temperature measuring element disposed upstream or downstream of the heating resistor 62a At least two resistors 62b are exposed, and an electrical signal corresponding to the flow rate is output from the connector 63 to the ECU (microcomputer unit 37).

  A microcomputer (microcomputer) is attached to the EGR mass flow sensor 18 to make the EGR mass flow sensor 18 intelligent, and A / D conversion is performed by the A / D input circuit of the microcomputer inside the EGR mass flow sensor, and EGR is performed inside the microcomputer. It is also possible to perform data conversion processing for linearizing the mass flow sensor output, and output the data through a microcomputer communication output, such as a serial port output, parallel port output, or CAN.

  FIG. 5 shows an electrical control circuit diagram of the EGR mass flow sensor 18. The EGR mass flow sensor 18 is connected to the power supply 101 and outputs a sensor signal Vout corresponding to the gas flow rate. The EGR mass flow sensor 18 is a sensor in which a heating resistor 62a and a temperature measuring resistor 62b are combined.

On the basis of the gas temperature (Tw) when there is no gas flow, when the voltage of the heating resistor 62a that decreases when there is a gas flow is V, and the gas temperature at that time is Tg,
Flow rate Q ∝ (μ ^ 0.26)
× (λ ^ -1.26)
× (Cp ^ -0.74)
× V ^ 4 / ((Tw−Tg) ^ 2) (7)
Here, μ = viscosity coefficient of EGR gas λ = thermal conductivity Cp = specific heat, and in particular, the viscosity coefficient μ, thermal conductivity λ, and specific heat Cp of EGR gas depend on temperature. For this reason, when the terms of viscosity coefficient μ, thermal conductivity λ, and specific heat Cp are collected and combined as a physical property correction term KSSP (Tg) with respect to gas temperature, flow rate Q ∝ KSSP (Tg) × V ^ 4 / ((Tw−Tg ) ^ 2) ... (8)
It becomes the physical property correction term KSSP with respect to the gas temperature.

  The heating resistor 62a is included in a part of the Wheatstone bridge circuit, and the flowing current value is feedback-controlled so that the resistance value is always equivalent to 600 ° C. When there is an EGR flow, heat is taken away from the heating resistor 62a to the EGR gas, so that the current from the power source 101 increases so as to increase the amount of heat generated by the heating resistor 62a. MAINAD corresponding to the gas flow rate is taken in by the A / D converter with the current flowing through the heating resistor 62a as the voltage flowing through the predetermined resistor.

  On the other hand, the resistance value of the resistance temperature detector (temperature measuring device) 62b changes according to the gas temperature. When a small constant current is passed through the resistance temperature detector 62b, a voltage corresponding to the gas temperature of the EGR gas is generated. As described above, the resistance temperature detector 62b is used as the EGR gas temperature sensor, and the voltage value CWAD corresponding to the gas temperature of the EGR gas is captured by the A / D converter as the voltage detected by the resistance temperature detector 62b. In addition, 600 degreeC is below the exhaust-gas temperature of a normal diesel engine, and is set as the temperature which soot burns in a short time, even if soot contained in EGR gas adheres to an EGR mass flow sensor. In this embodiment, the EGR gas temperature sensor is provided inside the flow rate measuring device, but may be provided separately in the vicinity of the device.

  Based on the flow rate and the voltage value corresponding to the gas temperature thus taken in, the actual EGR flow rate is calculated as follows. FIG. 6 is a block diagram for explaining the calculation of the EGR flow rate from the EGR mass flow sensor.

  In block 601, the microcomputer converts the voltage value MAINAD corresponding to the gas flow rate into a table using the VQ table, and calculates a flow rate value EGRQA at a predetermined gas temperature set in advance. Next, at block 602, the gas temperature Tg is calculated by converting the voltage value CWAD corresponding to the gas temperature into a table using the VT table. In this way, the flow value EGRQA and the gas temperature Tg are calculated, and using these as inputs, the final substantial flow rate Qreal of the EGR gas is calculated. More specifically, a correction amount corresponding to the difference ΔTh between 600 ° C. and the gas temperature Tg is calculated using the ΔTh correction table at block 603, and the gas temperature Tg using the temperature correction table at block 604. The correction terms according to the above are calculated, and these correction terms are multiplied by the flow rate value EGRQA, respectively, to determine the actual flow rate Qreal of the EGR gas.

  If the engine operating state is steady, the actual EGR flow rate (EGR mass flow rate) obtained in this way is compared with the target EGR flow rate EGRTGT as a target, and the EGR valve opening is controlled according to the difference. By doing so, EGR flow rate control is possible.

  If the engine speed, engine load, water temperature, and exhaust air / fuel ratio are within a predetermined range, and each change amount within a predetermined time is within a predetermined range, the engine operating state can be regarded as being constant. If the target EGR flow rate EGRTGT and the actual EGR flow rate Qegr do not match when the operation state is constant, a failure in the EGR valve opening degree control is diagnosed. Alternatively, the EGR valve opening degree control failure is diagnosed even when the EGR valve opening degree is outside the predetermined range.

  However, in the conventional case, when controlling the flow rate in the steady state, since the reference flow rate is an estimated value based on a plurality of sensor signals, the EGR mass flow sensor signal is set to a true value, or It becomes difficult to determine whether another sensor value is a true value. In addition, there is a problem that a drift (offset) of sensor signal output due to aging of each sensor occurs.

  Therefore, the EGR system diagnosis apparatus according to the present embodiment has a timing of a change in the EGR gas temperature accompanying a change in the opening degree of the EGR valve (when the second opening degree is reached from the first opening degree) or a change in the operating state. Measure the flow rate profile such as the temperature profile of EGR gas flow and the timing of EGR gas flow change (profile measurement means), and not only the EGR mass flow sensor that constitutes the EGR system shown below, but also other components that constitute the EGR system A (part) is specified, and a state including a state such as failure deterioration of the component is diagnosed (diagnostic means). As a result, there is an advantage that it is difficult to be influenced by other sensors.

  For example, when the engine is started at a low water temperature, the EGR valve is closed to increase the combustion temperature. At this time, if the output value of the EGR mass flow sensor (measured EGR gas flow rate) exceeds a predetermined value, the EGR valve is not fully closed. With this, the failure state of the EGR valve is diagnosed. can do.

  Thereafter, when the water temperature rises and the warm-up is completed, when the EGR valve is opened to a predetermined opening, the EGR gas flows and the output value of the EGR mass flow sensor (measured EGR gas flow rate) increases. If it takes longer than a predetermined time (predetermined time according to the operating state), since the valve is stuck or the passage area of the valve is insufficient, the failure state of the EGR valve can be diagnosed.

  At the same time, when the change in the gas temperature Tg is captured, as shown in FIG. 7, the temperature when the valve is closed in each case is the temperature Tair of the intake air. Next, immediately after the valve is opened, the temperature of the EGR gas accumulated in the EGR cooler and the EGR pipe is shown. Thereafter, the exhaust gas rises to a temperature cooled by the EGR cooler.

The time required for the EGR valve to reach the temperature of the open state is the sum of the volume of the EGR through which the EGR passes and the volume of the EGR pipe, and the EGR gas corresponding to the EGR valve opening (valve opening). The time corresponds to the time divided by the flow rate. A timing chart (standard temperature profile) in an initial state where the engine is new is a case A in FIG.
When the valve opening degree of the EGR valve is relatively narrow, the EGR valve becomes an orifice and the EGR gas is adiabatically expanded. For this reason, the gas temperature Tg may be further lowered than the temperature that has passed through the EGR cooler.

  In particular, when the temperature is further lowered than the cooling water temperature, soot adheres to the surface of the EGR valve and the passage area of the EGR valve is reduced, so that the adiabatic expansion is performed, and this effect is diagnosed as remarkable. That is, in this case, it corresponds to the temperature profile shown in Case B of FIG. 7, and by measuring this temperature profile, it is diagnosed that the EGR valve is deteriorating in performance.

  Furthermore, when the soot adheres to the inner surface of the EGR cooler, the volume in the EGR cooler pipe decreases. Thereby, heat exchange between the cooling water of the EGR cooler and the EGR gas is reduced. Due to the deterioration of the cooling capacity of the EGR cooler, the cooling efficiency of the EGR gas is lowered. Therefore, the EGR gas temperature starts to rise earlier after the EGR valve is opened than in the case A initial product. In this case, it corresponds to the temperature profile shown in case C of FIG. 7, and by measuring this temperature profile, it is diagnosed that there is a possibility that the EGR cooler has a reduced cooler capacity due to contamination or the like.

  In addition, if soot adheres to the temperature sensor (resistance temperature detector) of the EGR mass flow sensor, the contact with the EGR gas deteriorates, so the start of temperature rise does not change, but the temperature rise per unit time thereafter Slower (time change amount (temperature gradient) of EGR gas temperature becomes smaller). In this case, it corresponds to the temperature profile shown in case D of FIG. 7. By measuring this temperature profile, if the degree of temperature rise is slow, it is diagnosed that the EGR mass flow sensor is fouled.

At this time, the output signal of the heating resistor is a value corresponding to the EGR gas flow rate, but ΔTh (Tw−Tg) is larger than that in the normal state.
ΔTh correction = 1 / (Tw−Tg) ^ 2 (9)
Becomes smaller, and the real amount flow rate Qreal of the EGR gas becomes a value smaller than that in the normal state.

  Conventionally, the EGR mass flow sensor is diagnosed for fouling even when the EGR mass flow rate is small compared to values estimated by the temperature and pressure in the intake manifold.

  The EGR cooler has a cooler bypass valve that temporarily stops cooling of the EGR gas. When the engine cooling water is relatively low, in order to promote warm-up of the engine, the EGR cooler is bypassed and the EGR gas is not cooled and directly returned to the intake manifold. In this case, if the bypass valve of the EGR cooler is fixed in the state where the bypass valve is open to the cooler side, the gas is cooled by the amount of passage through the EGR cooler due to the fixation of the bypass valve. Become. Therefore, when the timing of starting the temperature rise is late after the engine is started at a relatively low water temperature and the EGR valve is opened, it corresponds to the temperature profile shown in Case E of FIG. 7, and this temperature profile is measured. It is diagnosed that the bypass valve of the EGR cooler is stuck.

  Alternatively, the same temperature profile can be obtained when condensation occurs in the following EGR cooler. Specifically, when the cooling water temperature is lower than the dew point temperature in the EGR cooler, the dew condensation water adheres in the EGR cooler. Until the dew condensation water in the EGR cooler evaporates to become water vapor, even if the temperature of the cooling water rises, the temperature of the EGR cooler surface is kept substantially constant, so the cooling period of the EGR gas becomes longer. Even in such a case, it corresponds to the temperature profile shown in case E of FIG. 7, and by measuring this temperature profile, it is diagnosed that condensation has occurred in the EGR cooler.

  FIG. 8 shows a flowchart of the diagnostic stain diagnosis routine (1). The EGR sensor diagnostic program (1) is a subroutine called by interruption at predetermined time intervals or predetermined crank angles.

  When the diagnosis condition is satisfied, the following operation is performed (S800). As diagnostic conditions, the engine speed is within a predetermined range, the fuel injection amount or the engine load is within a predetermined range, the air-fuel ratio is within a predetermined range, and It is a necessary condition that the condition that the DPF is not burned out and the condition that the air-fuel ratio remains within a predetermined range is satisfied. .

  Next, in S801, the EGR gas temperature Tegr is calculated by table conversion based on the voltage value (A / D value) CWAD of the temperature sensor (temperature measuring resistor). If the state in which the valve opening of the EGR is closed is established in S802, the process proceeds to S803, where Tegr is substituted for the initial temperature Tstart, and at the same time, the diagnostic counters Ccount and Dcount are cleared (S804, S805).

In the state where the EGR valve opening is open, the process proceeds to S811, where a difference Tdiff between the EGR gas temperature Tegr and the initial temperature Tstart is calculated as shown in the following equation, and the diagnostic counter Ccount is incremented in S812.
Tdiff = Tegr−Tstart (10)
Ccount = Ccount (n−1) +1 (11)

  Further, in S813, an estimated value (EGR reached temperature rise threshold) Tend of the EGR gas temperature rise degree is set in advance according to parameters such as the rotational speed, fuel injection amount, EGR valve opening, and supercharging pressure. Calculate using the appropriate map value.

  Similarly, a delay time (EGR cooler delay estimated value) Tdelay in which the EGR gas temperature rises by the capacity of the EGR cooler and a temperature estimated value (EGR cooler temperature estimated value) Tcool in the EGR cooler are set to the number of revolutions, fuel injection It is calculated from map values that have been adapted in advance according to parameters such as the amount, EGR valve opening, supercharging pressure, and water temperature.

  In S816, the temperature rise Tdiff (in this case, the initial gas temperature) at the start of the operation that operates from the first opening to the second opening is compared with the estimated temperature value Tcool, and the temperature rise Tdiff ( When the initial gas temperature) is lower than the estimated temperature (temperature estimated value) Tcool of the EGR cooler, the process proceeds to S817. In S817, when the EGR gas temperature Tegr is lower than the threshold value as compared with the threshold value corresponding to the EGR gas temperature Tegr and the water temperature, it corresponds to case B in FIG. 7 and passes through the EGR valve. It can be diagnosed that a temperature drop due to adiabatic expansion occurs.

  That is, in this step, the initial EGR gas temperature at the start of the operation that operates from the first opening to the second opening is measured, and the EGR valve has a performance deterioration based on the initial EGR gas temperature. Can be diagnosed.

  On the other hand, when the temperature increase Tdiff (initial gas temperature) becomes higher than the estimated temperature of the EGR cooler in S816, the process proceeds to S818. In S818, it is determined whether or not Ccount has reached the delay time Tdelay in which the EGR gas temperature rises by the amount of the EGR cooler. If it is determined that Ccount has not been reached, it corresponds to case C in FIG. It is diagnosed that there is a possibility that the cooler capacity has decreased from an early rise in the EGR gas temperature.

  If it is determined in S818 that Ccount has passed Tdelay or more and the preset maximum time has been reached, it is determined to be case E in FIG. 7, and condensation in the EGR cooler and EGR valve sticking are diagnosed. The

  That is, in these series of steps, as a temperature profile, the temperature change amount of the EGR gas temperature when the first opening degree is reached to the second opening degree is measured, and the temperature change amount is determined as the operation of the internal combustion engine. The delay time until reaching a predetermined temperature change amount set in accordance with the state is measured, and the diagnostic means determines whether the capacity of the cooler has decreased, condensation in the EGR cooler or EGR based on the delay time. Valve sticking can be diagnosed.

On the other hand, if it is less than the maximum time, the process proceeds to S820, and Dcount is incremented.
Dcount = Dcount (n−1) +1 (12)
At the same time, the process proceeds to S821, the temperature rise degree dT is calculated, and the process proceeds to S821 in order to perform the calculation shown in Expression (13).
dT = (Tdiff−offset) / Dcount (13)

  The process proceeds to S822, where the temperature rise degree (temperature gradient) dT is compared with a predetermined estimated value Tend. If the temperature rise degree Tend is larger than dT, this corresponds to case D in FIG. 7, and the EGR gas temperature sensor Diagnose that sensitivity is reduced due to adhesion of wrinkles.

  That is, in this step, as a temperature profile, a time change amount (temperature gradient) of the EGR gas temperature when the first opening degree is reached to the second opening degree is measured, and based on the time change amount. In addition, it is possible to diagnose a decrease in sensitivity due to fouling or the like of the EGR temperature sensor.

  On the other hand, in S822, when the temperature rise degree dT is smaller than dT compared with the predetermined estimated value Tend, a normal range is diagnosed (S822 → case A).

  In this way, when the EGR valve is opened from the closed state (in the flow rate time change amount), the degree of increase in the EGR gas temperature with respect to time (temperature time change amount) is large compared to a predetermined value. Diagnose a failure of the EGR system.

  Incidentally, the gas flowing through the EGR mass flow sensor 18 is a gas flowing through the bypass passage 70 provided in the EGR passage, as shown in FIG. The bypass passage 70 forms a spiral passage, and has a passage structure in which gas flows from an inlet 71 on the upstream side of the flow is rotated (turned), and gas is released from an outlet 72 opened on a side surface. . A mesh member 73 and a honeycomb member 74 are sequentially provided on the upstream side of the bypass passage 70. Thereby, the flow of EGR gas is rectified, and the drift is improved.

  When the EGR valve is controlled so that the engine speed and load are constant and the EGR rate η is constant, the EGR valve opening should be within the predetermined opening according to the operating condition. Therefore, it can be determined that valve control is normal. Further, when the opening is outside the predetermined range, if the opening is larger than the normal valve opening, it is assumed that the flow rate is insufficient due to clogging in the EGR passage. If the opening is smaller than the normal valve opening, the opening of the EGR valve may be too open and the fully closed position may be shifted.

  Alternatively, based on the intake manifold temperature and the intake manifold pressure, the calculated target EGR flow rate calculation value EGRRTGT and the EGR mass flow rate sensor output EGR gas actual amount flow rate Qreal are compared, and if they are within a predetermined range It can be determined that the EGR mass flow sensor is normal. When the target EGR flow rate calculation value EGRTGT is larger than the actual amount flow rate Qreal of the EGR gas when it is outside the predetermined range, the flow rate detection decreases due to changes in the elements of the EGR mass flow rate sensor, adhesion of soot, etc. There is a possibility.

  When the target EGR flow rate calculation value EGRTGT is smaller than the real amount flow rate Qreal of the EGR gas, the temperature difference between the heating resistor of the EGR mass flow sensor and the temperature measurement element is larger than normal, and the temperature measurement element There is a possibility that wrinkles are attached to only.

  Further, since the space for the EGR flow to flow out of the EGR valve and diffuse to the EGR pipe is not secured, the EGR gas distribution in the pipe is not uniform, and the EGR mass flow sensor does not hit the EGR flow. The flow may not be detected, resulting in an error in measurement accuracy.

  The EGR flow rate also depends on the negative pressure in the intake manifold. For this reason, a correction amount is calculated from an appropriate value between the opening of the throttle valve 5 that generates the negative pressure in the intake manifold and the engine speed, and is corrected with respect to the average value of the EGR flow rate at the EGR flow rate sensor unit. Is also possible. A throttle opening sensor is used for the negative pressure or the throttle opening in the intake manifold.

  FIG. 10 is an explanatory diagram showing frequency components of backflow detection and pulsation by the EGR mass flow sensor. As shown in FIG. 10, in a low flow rate region, a reverse flow exists even if the gas flow is zero, and a bidirectional flow detection sensor that cannot distinguish the flow direction generates a component that is an integral multiple of the reference frequency. To do. In particular, when there is a reverse flow, the bidirectional flow detection sensor output signal has a folded waveform, and therefore a higher-order frequency appears with respect to the fundamental frequency. When higher-order frequencies appear, it indicates that there is a backflow.

  Therefore, it can be determined that the EGR mass flow sensor has sufficient response when a high-order frequency component appears with the engine speed as the fundamental frequency in the low flow rate region. If higher-order frequency components do not appear, there is a possibility of responsiveness degradation of the EGR mass flow sensor.

  Furthermore, the pulsation width is relatively large with respect to the average flow rate in the low flow rate region. Furthermore, since the EGR flow rate sensor 18 cannot distinguish between forward flow and reverse flow due to pulsation, there is a large variation in the correction rate Qerror with respect to the pulsation rate. In such a region, the minimum value associated with the pulsation becomes the node of the pulsation, and the minimum value is set as the real amount flow rate Qreal of the EGR gas.

  Further, the time until the exhaust gas passes through the EGR cooler and reaches the EGR valve depends on the flow rate of the EGR gas flow. For this reason, there is a moment when the center value (average value) of the pulsation width flows when the intake manifold pressure and the exhaust pressure are balanced at an EGR predetermined crank angle corresponding to the rotation speed and the valve opening.

  Therefore, if the signal output of the EGR mass flow sensor is sampled at every predetermined crank angle and the value at the crank angle position corresponding to the rotation speed and the valve opening is the EGR mass flow, the measurement is performed while avoiding the pulsation of EGR gas. Is possible.

  By comparing the EGR mass flow sensor output with the target EGR flow rate and controlling the EGR valve opening degree control for controlling the EGR valve 17 so as to match the comparison result, and controlling the EGR valve 17, the EGR cooler 19 and the flow rate drop due to the increase in the EGR flow path resistance due to adhesion of soot on the surface of the EGR valve 17 can be corrected.

  FIGS. 11A and 11B show output examples when the EGR mass flow sensor is soiled. In the case of high pressure type EGR gas recirculation, the exhaust gas contains a large amount of soot. Soot contains not only carbon components but also unburned fuel components and incompletely burned hydrocarbon components. Such soot is also contained in the EGR gas and adheres to the sensor element of the EGR mass flow sensor 18 and its surroundings.

  If soot adheres to the sensor element, the EGR gas is less likely to touch the sensor element, and therefore, as shown in FIG. 11 (a), a value smaller than the actual flow rate of EGR is output. The

  On the other hand, when the soot adheres to the gas temperature measuring element, the gas temperature measuring element is insulated, so that it is less affected by the EGR gas temperature. For this reason, especially when the EGR flow rate is a large flow rate, the temperature difference between the gas temperature measuring element and the sensor element becomes large, and as shown in FIG. 11B, the sensor output is larger than the actual flowing amount. A small value is output. The deviation increases as the endurance time elapses.

  Further, if wrinkles adhere to the element mottle, the temperature distribution of the element becomes non-uniform, and the temperature of the part where the wrinkles adhere particularly increases, which may deteriorate the durability of the element. Thus, as shown in FIGS. 11 (a) and 11 (b), by measuring the flow rate profile of the EGR gas flow rate that changes according to the change in the valve opening degree of the EGR gas flow rate control valve, the flow rate profile can be used. Thus, it is possible to diagnose the adhesion state of the soot of the sensor element for measuring the flow rate and the gas temperature measuring element.

  FIG. 12 is a flowchart of a diagnostic program for diagnosing a decrease in output due to contamination of the EGR mass flow sensor 18. In the present embodiment, the target EGR flow rate obtained based on the rotation speed, the intake air amount per combustion determined from the intake air amount and the rotation speed, and the EGR mass flow sensor output are compared, and A feedback loop for controlling the EGR valve is configured so that there is no difference. First, in S12, it is determined whether the feedback control amount is hunting. When it is determined that hunting is being performed, the settling time of the feedback control amount is compared with a predetermined time as a threshold in S13, and when the settling time is longer than the predetermined time, the process proceeds to S14. The EGR flow sensor 18 determines that the responsiveness is reduced due to contamination.

  That is, in this step, for example, the flow rate change amount of the EGR gas flow rate when the first opening degree is reached to the second opening degree is measured, and the flow rate change amount is set according to the operating state of the internal combustion engine. The delay time until the predetermined flow rate change amount is reached is measured, and based on the delay time, the EGR flow sensor 18 diagnoses that the responsiveness decreases due to contamination.

  If these conditions are not satisfied in S12 and S13, the process proceeds to S15. Here, it is determined whether the opening degree of the EGR valve 17 is 0, that is, whether it is fully closed. If it is fully closed, it is determined whether the output value of the EGR mass flow sensor is equal to or greater than a threshold value. If it is equal to or greater than the threshold value, the process proceeds to S17, and it is determined that the EGR mass flow sensor is shifted by 0 point. As described above, when the operating state changes, for example, when acceleration is performed, if the EGR mass flow sensor output is a predetermined value or more even if the EGR valve 17 is closed, the EGR mass flow sensor 18 is It can be determined that the output zero point has shifted due to contamination.

  Further, if these conditions are not satisfied in S15 and S16, the process proceeds to S18. Here, first, it is determined whether or not the EGR valve control amount is constant, that is, in a steady operation state. If it is determined to be constant, it is determined whether the output value of the EGR mass flow sensor 18 has reached the target EGR flow rate. If it is determined that it has not reached, the process proceeds to S20, and it is determined whether the time during which the opening degree of the EGR valve is opened to a predetermined value or more is a predetermined time or more. If it is equal to or greater than the predetermined value, the process proceeds to S21, and it is determined that the EGR sensor has deteriorated. In this way, when the EGR valve 17 is opened and EGR gas is allowed to flow after acceleration after the acceleration, the output of the EGR mass flow sensor 18 does not reach the target EGR flow rate or takes a long time to reach. If the EGR valve opening is longer than the predetermined value, the sensor output value is lower than the actual value due to contamination of the EGR mass flow sensor. Thus, it is possible to perform the deterioration deterioration determination.

  In summary, the measured value of the gas flow rate flowing through the EGR flow path, that is, (1) the feedback control amount is hunting when the gas flow rate flowing through the EGR flow path is feedback controlled using the output signal of the EGR mass flow sensor 18. When the control amount stabilization time is longer than the predetermined time, (2) When the EGR mass flow sensor 18 outputs an output signal indicating a flow rate equal to or higher than the predetermined value when the EGR valve is stopped (closed). (3) The time until the EGR mass flow sensor 18 does not output an output signal indicating a flow rate higher than a predetermined value or an output signal indicating a flow rate higher than a predetermined value after the EGR valve control is started (opened). Is longer than the predetermined time, it is diagnosed that the EGR mass flow sensor 18 is contaminated.

  Further, even in a certain operating state, when the valve opening degree of the EGR valve 17 exceeds the predetermined range, there is a possibility that the output signal of the EGR mass flow sensor 18 outputs a value different from the actual flow rate. is there. The determination threshold value can be changed according to the integrated value of the engine operating time or the integrated value of the travel distance of the vehicle.

  FIG. 13 is a timing chart for estimating a decrease in output due to contamination. The target EGR flow rate is calculated by inputting the intake air amount and the rotation speed at predetermined time intervals. Then, when the operating state is within a predetermined range, it is determined as a steady operating state, and a diagnosis permission flag is set.

  For example, the engine speed is within a predetermined upper / lower limit, the intake air amount is within a predetermined upper / lower limit, the vehicle speed is within a predetermined upper / lower limit, the accelerator pedal request value is within a predetermined upper / lower limit, and the engine speed, intake When the time change ratio of the air amount, the vehicle speed, the accelerator pedal, and the like is below a predetermined value, the steady operation state is set.

  During the steady operation state, the output value of the EGR mass flow rate sensor 18 is always taken and compared with the target EGR flow rate. Here, when the diagnosis permission flag is set, the following diagnosis is performed. When the absolute value of the difference between the output value of the EGR mass flow sensor 18 and the target EGR flow rate is equal to or greater than the threshold value, the diagnostic counter is incremented and the OK counter is reset. When the diagnostic counter exceeds the threshold value, a flag indicating the possibility of contamination of the EGR mass flow sensor is set.

  When the absolute value of the difference between the output value of the EGR mass flow sensor 18 and the target EGR flow rate falls below the threshold value, the diagnostic counter is reset. At the same time, the OK counter is incremented. When the OK counter reaches a predetermined value or more, a flag indicating the possibility of contamination of the EGR mass flow sensor 18 is reset.

  In the fouling diagnosis, when the output value of the EGR mass flow sensor 18 becomes a value that is always far from the target EGR flow rate, it can be diagnosed that the soot is stuck, but the output of the EGR mass flow sensor 18 If pulsations are superimposed, neither OK nor fouling status can be determined.

  In this case, the number of periods within which the absolute value of the difference between the output value of the EGR mass flow sensor 18 and the target EGR flow rate is greater than a predetermined threshold is within a predetermined time, and is equal to or greater than a predetermined ratio. If it is off, a flag is set to indicate that there may be significant fouling or pulsation. The predetermined ratio as the threshold value is a function of the EGR mass flow rate and the opening degree of the EGR valve 17 or a preset map value.

  Further, the output of the EGR mass flow sensor 18 may be monitored by changing the opening of the EGR valve 17 to determine whether the relationship between the EGR valve opening and the sensor output, for example, the ratio is within a predetermined range.

  FIG. 14 shows an example in which the calculation result of the correction amount due to sensor contamination is reflected in the engine control. If there is a possibility that the output of the EGR mass flow sensor 18 shows fouling or pulsation based on the diagnosis result of the EGR mass flow sensor contamination or the pulsation diagnosis result shown above (step S31), the EGR mass flow sensor 18 A predetermined correction amount or another preset fail-safe value is calculated based on the output value of the EGR and replaced with the output value of the EGR mass flow sensor 18 for use (steps S32 to S36).

  When there is no possibility of sensor fouling or pulsation, or in an operation region where the possibility is low, the output value itself of the EGR mass flow sensor 18 is used (steps S37 and S36).

  Alternatively, the EGR flow rate in the preset or measured standard state and the output value of the EGR flow rate sensor 18 are compared with the intake air amount and the rotational speed in a predetermined operation state with the EGR valve 17 being a predetermined opening degree. Then, the ratio or difference between the EGR flow rate in the standard state and the output value of the EGR mass flow sensor 18 is obtained and learned as a correction amount, so that the learned value is changed to the output value of the EGR mass flow sensor 18 to another operating region. The reflection can be corrected.

  For example, when correcting the ratio, the output value of the EGR mass flow sensor 18 is multiplied by the correction value. Alternatively, when the difference is corrected, the correction value is added to the output value of the EGR mass flow sensor 18. In this case, if the result of addition is negative, the corrected value is set to zero.

  Further, when the engine output is zero using the exhaust brake, the output value of the EGR mass flow sensor 18 is calibrated so that the exhaust gas returns to the intake side of the engine by fully opening the EGR valve 17. It is possible. In this case, while the exhaust brake is used and the fuel injection amount is set to zero, a value proportional to the engine displacement x the number of revolutions flows through the EGR pipe. Therefore, the target EGR flow rate is calculated by setting the reflux rate η to 1.0. Is possible. The ratio or difference between the output value of the EGR mass flow sensor 18 and the target EGR flow rate at this time can be used as the correction amount.

  When the electric supercharger is used, if the electric supercharger is turned while the engine is stopped with the exhaust brake applied, the EGR gas flows with the reflux rate η = 1.0. Therefore, the correction amount can be calculated even when the engine is stopped.

FIG. 15 illustrates the fouling recovery of the EGR mass flow sensor 18.
The soot adheres not only to the EGR mass flow sensor 18 but also to the inside of the EGR cooler 19, the EGR valve 17, and the EGR passage, and narrows the cross-sectional area of the passage as compared with a new one. In this case, since the EGR flow rate in the standard operation state decreases, the output value of the EGR mass flow rate sensor 18 decreases. Therefore, it is expected that the sensor output value is recovered by removing the wrinkles.

  For example, if the correction value for the output value of the EGR mass flow sensor 18 is outside the predetermined range (step S41), the exhaust gas temperature is raised to the temperature at which the DPF soot is burnt in the operation region where the EGR flow rate is large (step S42). ). Thereby, not only the soot in the DPF but also the soot in the EGR passage can be baked (step S43). It is also possible to collect dust electrically by charging the soot.

  By providing a soot filter upstream of the EGR mass flow sensor 18 and hitting the soot against the filter with ultrasonic waves, it is possible to prevent soot from adhering to the EGR mass flow sensor 18. Alternatively, an ultrasonic sensor is provided in the EGR passage, and the reflected wave of the ultrasonic wave emitted from the ultrasonic sensor toward the inner surface of the EGR tube is measured to measure the amount of soot accumulated by measuring the reflectance. It is possible. If the amount of accumulated soot exceeds a predetermined threshold, a transition is made to an operation state where the soot in the EGR passage is burned, or a flag is set to notify the driver of replacement of the EGR pipe. Display on the engine warning light in the driver's seat. Or, it is obliged to periodically replace the EGR pipe every predetermined traveling distance.

  By applying a catalyst that easily decomposes soot on the surface inside the EGR passage, soot may be decomposed at a relatively low temperature. Further, a coating agent may be applied to the surface inside the EGR passage to prevent soot from adhering.

  The temperature is set higher than the gas temperature so that no soot adheres to the measurement element used for the EGR mass flow sensor 18. By setting the temperature to 600 ° C. or higher, it was confirmed that no soot was attached. When the EGR mass flow sensor 18 is energized from the start of the engine, the EGR mass flow sensor output signal may output a different value until the measurement element reaches 600 ° C.

  Therefore, the time required to reach a predetermined temperature is defined as a measurement start delay. For example, the heating period until the temperature difference between the sensor element temperature and the gas temperature reaches a predetermined temperature depends on the initial temperature of the sensor element.

  Therefore, as shown in FIG. 16, until the temperature Tg output from the EGR gas temperature sensor reaches a temperature corresponding to the operating state of the engine 1, the gas temperature response or elapsed time prohibiting the flow measurement by the EGR mass flow sensor 18. Corresponding delays are provided (steps S51 to S54). The delay value (threshold value) is set to an appropriate value according to the starting gas temperature sensor value (step S53). After the engine is started, if the gas temperature Tg is equal to or higher than the threshold value or the elapsed time is equal to or higher than the threshold value, flow measurement by the EGR mass flow sensor 18 is permitted (steps S54 and S55).

  A correction amount for the output of the EGR mass flow sensor 18 is prepared as a table value according to the elapsed time from the start of the engine, and EGR control using the output of the EGR mass flow sensor 18 from the start is also possible. is there.

[Second Embodiment]
In the second embodiment, as shown in FIG. 17, a sensor in which the direction of the bypass passage of the EGR mass flow sensor is reversed is added, and the EGR gas flow is diagnosed using two sensor signals.

  In this case, since the gas temperature sensor may be common, the sensor A that detects the forward flow (flow from the exhaust pipe to the intake pipe) from the exhaust side to the intake manifold side, and the sensor A that detects the forward flow from the exhaust pipe to the intake manifold side. Sensor B that detects reverse flow (flow from the intake pipe to the exhaust pipe) and a common gas temperature sensor are combined. The bypass passage is a spiral passage, and a sensor is attached to the back of the spiral.

  EGR gas entering from the entrance of the bypass passage enters the spiral passage, and the passage resistance flows out as pressure loss. Since the outlet has a direction different from the flow direction of the gas flow, it is difficult for the gas flow to enter from the outlet.

  A heating resistor of the EGR mass flow sensor is installed in the bypass passage to detect a gas flow in only one direction. The EGR flow rate is measured by A / D-converting the signal outputs from the two heating resistors installed at opposite sides of the bypass passage and the temperature sensors placed outside the bypass passage.

  FIG. 18 shows two EGR mass flow sensor signal outputs in a state where a backflow occurs. The EGR mass flow sensor signal output that detects only forward flow is substantially zero during reverse flow. The mass flow sensor signal output for detecting only the reverse flow is substantially zero during the forward flow. Therefore, the waveform of the EGR gas flow can be reproduced by combining the forward flow signal and the reverse flow signal.

  At this time, when the time difference between the forward flow signal and the peak value of the EGR gas flow rate of the reverse flow is measured and does not become the time difference according to the engine speed, there is a possibility of leakage of the EGR pipe. The flow may be diagnosed from the intake pipe along the exhaust pipe using not only the time difference but also, for example, a flow rate change amount (differential value) every predetermined time.

  A NOx sensor is provided in the exhaust passage to measure the NOx concentration CNOx contained in the exhaust gas, and at the same time, it is multiplied by the fresh air intake air amount Qair by the air flow meter to pass through the exhaust gas processing catalyst in the high pressure EGR. The amount of gas can be calculated.

Since the exhaust gas contains carbon dioxide CO ₂ and water vapor H ₂ O corresponding to the fuel mass, the exhaust gas mass is heavier than the intake air amount Qair. This deviation can be corrected by the air-fuel ratio sensor output signal A / F. However, in the lean region where the air-fuel ratio is high, the A / F measurement error is large, and the exhaust gas mass error is large.

  If an EGR mass flow sensor is also attached to the exhaust pipe and the exhaust gas mass flow rate is measured, the exhaust gas mass flow rate can be measured without depending on the air-fuel ratio sensor, so that the exhaust gas mass Qegr can be obtained.

In addition, in the ropeless EGR shown in FIG. 19, since the sum of the fresh air intake air amount Qair and the real amount flow rate Qreal of EGR gas flows into the combustion chamber, the amount of gas passing through the exhaust gas treatment catalyst is
Qegr = Qair + Qreal + fuel.

  By multiplying the exhaust gas mass flow thus obtained by the NOx concentration CNOx, a more accurate NOx mass can be measured. By performing the exhaust treatment corresponding to the NOx mass, the rich spike and urea injection amount necessary for the exhaust gas treatment can be accurately calculated.

When accelerating or decelerating, the EGR rate is shifted by the amount of EGR gas recirculation delay. This increases NOx emissions and soot emissions during acceleration. In order to keep the EGR rate within a predetermined range, the throttle is temporarily closed at the initial stage of acceleration, and at the same time, the EGR valve is largely opened to secure the EGR gas amount, and then the throttle is opened.
At the time of deceleration, the EGR valve is closed and simultaneously the throttle is opened to suppress fluctuations in the EGR rate.

  Conventionally, the degree to which the EGR valve and the throttle are changed at the same time is set to an appropriate value corresponding to the accelerator pedal and the rotational speed. This time, by confirming that the EGR gas flow can be recirculated by using the EGR mass flow sensor, it is possible to set the throttle and EGR valve to the target opening so that an accurate EGR rate can be obtained even during transient operation. Can be secured.

  Further, the rotation of the motor shaft that changes the lift amount of the EGR valve is transmitted to the nut, and converted to the valve lift by the shaft where the screw is cut. A slight gap is required between the screw and the nut, and even if the motor stops and the nut stops, the screw shaft may rattle.

  In particular, when the EGR valve opening degree is almost fully closed, the change in the EGR valve opening degree is emphasized with the deviation of the valve lift amount due to the backlash. As shown in FIG. 19, a change in EGR mass flow rate was observed.

  The conventional method of estimating the EGR flow rate based on the pressure and temperature in the intake manifold was not accurate enough to detect the EGR flow rate due to the deviation of the valve lift, but the EGR mass flow sensor directly measures the EGR mass flow rate. Therefore, even when the lift amount is almost fully closed, the change in the EGR flow rate can be accurately captured. Therefore, the EGR rate can be controlled for each explosion, and the stability of the engine output can be improved.

  Using the diagnostic results, the actual flow rate of exhaust gas flowing through the EGR flow path can be measured accurately, so the EGR rate of diesel engines and lean burn engines can be controlled more accurately than before, and the effect of reducing exhaust gas levels is high. Become.

  The present invention relates to internal combustion engine control, and is applicable not only to automobiles but also to marine engines, construction machine engines, and semi-fixed generator engines.

1 Diesel Engine 8 Combustion Chamber 9 Fuel Injection Valve 17 EGR Valve (EGR Gas Flow Control Valve)
18 EGR Mass Flow Sensor 53 Target EGR Rate Calculation Unit 54 Target EGR Flow Rate Calculation Unit 55 EGR Valve Opening Control Unit 56 Output Characteristic Correction Unit 62b Resistance Temperature Sensor (EGR Temperature Measurement Device)
70 Bypass passage

Claims (9)

An EGR flow path communicating with the exhaust pipe and the intake pipe, a flow rate measuring device attached to the EGR flow path to measure the flow rate of EGR gas, and attached to or in the vicinity of the flow rate measuring device, A diagnostic apparatus for an EGR system, comprising: a temperature measuring device that measures the temperature of EGR gas; and an EGR gas flow rate control valve that controls the EGR gas flow rate,
The diagnostic apparatus comprises: profile measuring means for measuring a temperature profile of the EGR gas temperature that changes according to a change in a valve opening degree of the EGR gas flow rate control valve; and a flow rate profile of the EGR gas flow rate;
A diagnostic device for an EGR system comprising: diagnostic means for identifying a part of the EGR system based on the temperature profile and the flow rate profile and diagnosing the state of the part.   2. The EGR system according to claim 1, wherein the profile measuring unit measures a temperature profile and a flow rate profile when the EGR gas flow rate control valve reaches from a first opening to a second opening. Diagnostic equipment. The temperature profile measuring means measures, as the temperature profile, a temperature change amount of the EGR gas temperature when the first opening degree reaches the second opening degree, and the temperature change amount is determined as an internal combustion engine. Measure the delay time to reach the predetermined temperature change amount set according to the operating state of
The diagnosis apparatus for an EGR system according to claim 2, wherein the diagnosis unit performs the diagnosis based on the delay time. The temperature profile measuring means measures an initial EGR gas temperature at the start of an operation that operates from the first opening to the second opening as the temperature profile,
The diagnostic apparatus for an EGR system according to claim 2 or 3, wherein the diagnostic means performs the diagnosis based on the initial EGR gas temperature. The temperature profile measuring means measures the time change amount of the EGR gas temperature when the temperature profile reaches from the first opening to the second opening,
The diagnostic apparatus for an EGR system according to any one of claims 2 to 4, wherein the diagnosis unit performs the diagnosis based on the amount of change with time.   6. The EGR system diagnosis apparatus according to claim 2, wherein the first opening is an opening when the EGR gas flow rate control valve is closed. The flow rate profile measuring means measures, as the flow rate profile, a flow rate change amount of the EGR gas flow rate when the first opening degree reaches the second opening degree. Measure the delay time to reach the predetermined flow rate change amount set according to the operating state of
The diagnosis apparatus for an EGR system according to claim 2, wherein the diagnosis unit performs the diagnosis based on the delay time.   The flow rate measuring device includes: a first flow rate measuring unit that measures an EGR gas flow rate that flows from the exhaust pipe along the intake pipe; and a second flow rate that converts the EGR gas flow rate that flows from the intake pipe along the exhaust pipe to the second flow rate. 8. A measurement unit according to claim 5, wherein the diagnosis unit performs the diagnosis based on the EGR gas flow rate measured by the first and second flow rate measurement units. The diagnostic apparatus of the EGR system described.   The diagnosis of the EGR system according to claim 8, wherein the diagnosis is performed based on a time difference between peak values of the EGR gas flow rate measured by the first and second flow rate measurement units and an engine speed. apparatus.

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