JP2008231951A - Engine exhaust emission temperature estimation device and engine exhaust emission control device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To detect the temperature of the exhaust emission of an engine even if an exhaust emission temperature sensor fails. <P>SOLUTION: In the engine 1 having a turbocharger 12, an intake air pressure (boost pressure Pbst) on the downstream side of the compressor 12a of the turbocharger 12 is detected, and the rotational speed of the turbine 12b of the turbocharger 12 (number of rotations Nt of the turbine) and the flow of the fuel supplied to the engine 1 (fuel flow Gf) is detected. Based on the boost pressure Pbst, the number of rotations Nt of the turbine, and the fuel flow Gf thus detected, the exhaust emission temperature Test of the engine 1 is calculated. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an engine exhaust temperature estimation device and an engine exhaust purification device, and more particularly, to a technology that makes it possible to grasp an exhaust temperature without using a direct detection means such as a temperature sensor. In particular, in an engine equipped with a particulate filter for collecting particulates in exhaust gas, the exhaust temperature can be grasped and the particulate filter can be regenerated accurately even when the exhaust temperature sensor fails. It is related to technology.

  A diesel particulate filter (hereinafter referred to as “DPF”) is a device generally known to remove particulate matter (hereinafter referred to as “particulate”) discharged from a diesel engine. The DPF includes a filter carrier made of ceramic or the like, and collects particulates in the exhaust gas by the filter carrier and removes them.

  A DPF having an oxidation catalyst upstream of a filter carrier is known as a continuous regeneration type DPF. In this continuous regeneration type DPF, nitrogen monoxide in the exhaust gas is converted into nitrogen dioxide having high oxidation reactivity by an oxidation catalyst, and the particulates deposited on the filter carrier are oxidized and processed by this nitrogen dioxide. The A continuous regeneration type DPF and a urea reduction type NOx catalyst were used together for the purpose of simultaneously reducing particulates and nitrogen oxides (hereinafter referred to as “NOx”), which are air pollutants discharged from a diesel engine. Development of an exhaust purification system is underway.

  In an exhaust gas purification apparatus equipped with a DPF, it is necessary to detect the exhaust temperature of the engine and control the actual exhaust gas temperature based on this in order to satisfactorily perform the regeneration function of the DPF. Under operating conditions where the temperature in the DPF decreases due to a decrease in the exhaust temperature, such as during low-speed driving, and the particulates do not reach the ignition temperature, the particulates cannot be burned or burnt. Even if it is possible to do so, this is slow and the particulate processing does not proceed well.

Therefore, in order to control the inside of the DPF to a temperature range suitable for particulate processing, a temperature sensor for detecting the exhaust temperature is installed upstream or downstream of the DPF, and based on the exhaust temperature detected thereby, The fuel supply to the engine is controlled (Patent Document 1).
JP 2003-314249 A (paragraph number 0020)

  However, in such an exhaust purification device, there is a problem that when the temperature sensor fails, it is impossible to compensate for a decrease in exhaust temperature by controlling fuel supply or the like. If the exhaust temperature drop cannot be compensated for, the DPF regeneration function cannot be fully exerted, and excessive pressure build-up of the particulates increases pressure loss in the DPF, thereby deteriorating fuel consumption or excessive accumulation. The sudden burning of the particulates may cause an excessive heat load on the filter carrier and damage the filter carrier.

Therefore, it is desirable to provide a backup function for the failure of the temperature sensor so that the exhaust temperature can be grasped and the DPF regeneration function can be maintained even if the temperature sensor fails.
The present invention provides an engine exhaust temperature estimation device and an engine exhaust purification device that take the above problems into consideration.

  The engine exhaust temperature estimation device according to the present invention is configured as a device for estimating the exhaust temperature of an engine equipped with a turbocharger. Based on the detected intake pressure, turbine rotational speed, and fuel flow rate, while detecting the intake pressure downstream of the compressor of the turbocharger, and detecting the rotational speed of the turbine of the turbocharger and the flow rate of fuel supplied to the engine. Thus, the exhaust temperature of the engine is calculated.

  An exhaust emission control device for an engine according to the present invention is configured to include the exhaust temperature estimation device described above and a particulate filter that collects particulates in exhaust gas as a device for purifying exhaust gas of an engine equipped with a turbocharger. The temperature of the exhaust gas flowing into the particulate filter is controlled based on the exhaust gas temperature calculated by the exhaust gas temperature estimating device.

  According to the present invention, the exhaust gas temperature of the engine is calculated based on the intake pressure downstream of the compressor of the turbocharger, the rotational speed of the turbine, and the flow rate of the fuel supplied to the engine. The exhaust temperature can be ascertained without using direct detection means. And in an engine equipped with a particulate filter, it is possible to grasp the exhaust temperature without using a temperature sensor or the like, so that the regeneration function of the particulate filter is maintained even when the exhaust temperature sensor fails, While avoiding deterioration of fuel consumption due to excessive accumulation of particulates, it is possible to suppress the thermal load on the filter carrier.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 shows a configuration of an engine 1 including an exhaust temperature estimation device according to an embodiment of the present invention. In the present embodiment, the functions of the “arithmetic unit” of the exhaust gas temperature estimation device and the “control unit” of the exhaust gas purification device are combined with the control unit 101 of the engine 1. The engine 1 is a diesel engine and constitutes a drive source for a vehicle such as a truck.

  An air cleaner (not shown) is attached to the introduction portion of the intake passage 11, and dust in the intake air is removed by the air cleaner. A compressor 12a of a turbocharger 12 is installed in the intake passage 11, and the intake air is compressed and sent out by the compressor 12a. The compressed intake air is cooled by an intercooler (not shown), then flows into the surge tank 13, and is distributed to each cylinder at the manifold portion.

In the engine body, a fuel supply injector 21 is installed in the cylinder head for each cylinder. The injector 21 is actuated by a signal from the ECU 101. Fuel delivered by a fuel pump (not shown) is supplied to each injector 21 via a fuel supply pipe 22 and a common rail 23, and is injected into the combustion chamber of each cylinder.
A turbine 12b of the turbocharger 12 is installed in the exhaust passage 31 downstream of the manifold portion. When the turbine 12b is driven by exhaust, the compressor wheel is connected via a shaft (shown by a dotted line in the figure). It rotates and the compressor 12a operates. A DPF (diesel particulate filter) 32 is interposed downstream of the turbine 12b. The DPF 32 includes a honeycomb filter carrier (hereinafter simply referred to as “filter carrier”) 321 made of ceramic, and the particulate matter in the exhaust gas is collected by the filter carrier 321. As the accumulation of particulates in the filter carrier 321 progresses, the effective passage area of the exhaust gas decreases and the pressure loss increases. Therefore, it is necessary to regenerate the DPF 32 by burning the accumulated particulates. . In the present embodiment, an oxidation catalyst 322 is installed upstream of the filter carrier 321, the nitric oxide in the exhaust gas is converted into nitrogen dioxide by the oxidation catalyst 322, and nitrogen dioxide is supplied to the filter carrier 321. Nitrogen dioxide is known to have high oxidation reactivity, and can burn particulates even under relatively low temperature conditions. In this embodiment, the filter carrier 321 and the oxidation catalyst 322 are built in one housing, and a so-called continuous regeneration type DPF 32 is configured. The DPF is not limited to the continuous regeneration type, but may be an intermittent regeneration type. This intermittent regeneration type DPF estimates the amount of particulate accumulation, and performs control for burning the particulate when the amount of accumulation reaches a certain amount. For example, it is possible to burn the accumulated particulates while suppressing the heat load by reducing the excess air ratio compared to during normal operation and performing exhaust gas temperature raising control such as post injection.

  The exhaust passage 31 is connected to the intake passage 11 by an EGR pipe 33. A part of the exhaust gas is recirculated to the intake passage 11 through the EGR pipe 33. In the present embodiment, the EGR pipe 33 connects the exhaust passage 31 upstream of the turbine 12 b of the turbocharger 12 and the surge tank 13 interposed in the intake passage 11. An EGR control valve 34 is interposed in the EGR pipe 33, and the flow rate of exhaust gas recirculated by the EGR control valve 34 is controlled. The EGR control valve 34 is actuated by a signal from the ECU 101.

  In the exhaust passage 31, a temperature sensor (hereinafter referred to as “exhaust temperature sensor”) 41 for detecting the temperature of the exhaust before flowing into the DPF 32 is installed upstream of the DPF 32. The exhaust temperature sensor 41 corresponds to a “second temperature sensor”. In the intake passage 11, a pressure sensor 42 and a temperature sensor 43 for detecting the pressure and temperature of the intake air before supercharging are installed upstream of the compressor 12a, while supercharging is performed downstream of the compressor 12a. A pressure sensor 44 is installed for detecting the pressure of the intake air. Among the pressure sensors 42 and 44, the upstream one (hereinafter referred to as “intake pressure sensor”) 42 corresponds to the “second pressure sensor”, and the downstream one (hereinafter referred to as “boost pressure sensor”). 44) corresponds to the “first pressure sensor”. In the engine 1 according to the present embodiment including the intercooler, the boost pressure sensor 44 is installed upstream of the intercooler. The boost pressure sensor 44 may be installed downstream of the intercooler. However, it is necessary to consider the pressure loss when passing through the intercooler and the influence of state changes due to cooling. The temperature sensor (hereinafter referred to as “intake air temperature sensor”) 43 corresponds to a “first temperature sensor”. Furthermore, a rotational speed sensor 45 for detecting the rotational speed of the shaft of the turbocharger 12 (hereinafter referred to as “turbine rotational speed”) is provided. The temperature sensors 41 and 43, the pressure sensors 42 and 44, and the detection signals of the rotation speed sensor 45 are all output to the ECU 101. ECU 101 receives a signal from a crank angle sensor 151 that generates a signal for each unit crank angle and reference crank angle, and a signal from an accelerator sensor 152 that detects a depression amount of an accelerator pedal by a driver, and an ignition switch (not shown). Signals from the start switch and the coolant temperature sensor are input.

  As described above, the ECU 101 has both a function as an “arithmetic unit” of the exhaust gas temperature estimation device and a function as a “control unit” of the exhaust gas purification device. The ECU 101 monitors the regeneration state of the DPF 32 based on the input signal and detects the exhaust temperature sensor 41 when it is determined that the temperature in the DPF 32 is excessively lowered, such as during low-speed driving. Based on the temperature (hereinafter referred to as “detected exhaust temperature”) Texh, the exhaust temperature is raised by control such as post injection, and the regeneration function of the DPF 32 is maintained. Further, the ECU 101 determines whether or not the temperature sensor 41 has failed. When the ECU 101 detects the failure, the ECU 101 detects the pressure Tint and Tbst detected by the intake pressure sensor 42 and the boost pressure sensor 44 and the rotation speed sensor 45. The exhaust temperature (hereinafter, the estimated exhaust temperature is referred to as “estimated exhaust temperature”) Test is estimated based on the detected turbine speed Nt, and the exhaust temperature is increased using this as basic information for control such as post injection. The regeneration function of the DPF 32 is maintained. Hereinafter, the operation of the ECU 101 according to the present embodiment including the estimation of the exhaust gas temperature will be described with reference to a flowchart.

  FIG. 2 is a flowchart of a basic routine related to fuel supply control of the engine 1. This routine is executed every predetermined time while the ignition switch is on. By this routine, the fuel injection amount Qf for the engine 1 is calculated and set, and exhaust gas temperature raising control for maintaining the regeneration function of the DPF 32 is performed. In the present embodiment, the exhaust gas temperature raising control is performed by post-injection that is delayed from the main injection for injecting fuel of the amount Qf.

In S101, various operating state parameters required for fuel supply control such as the engine speed (which can be calculated based on the signal generation period for each reference crank angle) and the accelerator pedal depression amount are read.
In S102, a fuel supply amount Qf by main injection to the engine 1 is calculated based on the read operation state parameter.

  In S103, it is determined whether or not the failure determination flag Fdgn is zero. When it is 0, it progresses to S104, and when it is not 0, it progresses to S105. The failure determination flag Fdgn is for indicating that the exhaust temperature sensor 41 has failed, and is normally set to 0. In a failure diagnosis routine described later, it is determined that the exhaust temperature sensor 41 has failed. In the case of a change, it is switched to 1.

In S104, the temperature (detected exhaust gas temperature) Texh of the exhaust gas before flowing into the DPF 32 detected by the exhaust gas temperature sensor 41 is read.
In S105, the exhaust gas temperature Test is estimated. The estimation of the exhaust temperature is calculated based on the boost pressure Pbst, the intake pressure Pint, and the turbine speed Nt in the exhaust temperature estimation routine (FIG. 4) configured as a subroutine of S105. The exhaust temperature estimation routine will be described later.

In S106, the calculated estimated exhaust temperature Test is set to the exhaust temperature Texh.
In S107, it is determined whether or not the exhaust temperature Texh (the detected exhaust temperature Texh or the estimated exhaust temperature Test depending on the result of the failure determination) is equal to or higher than a preset threshold value Trgn for determining whether regeneration is possible. When it is equal to or greater than Trgn, the process proceeds to S110, and when it is less than Trgn, the process proceeds to S108 in order to increase the temperature in the DPF 32 by post injection.

In S108, the fuel supply amount Qp by post injection is calculated. The post injection amount Qp is set to a larger value based on the exhaust temperature Texh as the difference between the threshold value Trgn and the exhaust temperature Texh1 (= Trgn−Texh) is larger.
In S109, the calculated post injection amount Qp is set in the drive circuit of the injector 21 for post injection.

In S110, the main injection amount Qf is set in the drive circuit of the injector 21, and the fuel supply control in this routine is terminated.
FIG. 3 is a flowchart of a failure diagnosis routine according to the present embodiment. This routine is executed every predetermined time on condition that a certain time has elapsed after the engine 1 is started. By this routine, the function as “failure detection means” is realized, and the failure determination flag Fdgn is set.

In S201, it is determined whether or not the engine 1 is in steady operation. When the steady operation is being performed, the process proceeds to S202 in order to diagnose the failure through the following steps. When the steady operation is not being performed, this routine is terminated.
In S202, the output voltage E from the exhaust temperature sensor 41 is read.
In S203, it is determined whether or not the read output voltage E is in a normal determination region having predetermined values Esll and Eslh as lower and upper limits, respectively. If it is in the normal determination area, the exhaust temperature sensor 41 is assumed to be normal, and the process proceeds to S204. If it is not in the normal determination area, the process proceeds to S206 in order to make a definitive determination as to whether or not a failure has occurred.

In S204, a value CNT of a determination confirmation counter described later is reset to zero.
In S205, it is assumed that the exhaust temperature sensor 41 is normal, and the failure determination flag Fdgn is set to 0.
In S206, the value CNT of the determination confirmation counter is incremented by one.
In S207, it is determined whether or not the counter value CNT after the increase has reached a predetermined value CNTsl. If it has reached, the process proceeds to S208, and if not reached, this routine is terminated and the determination regarding the diagnosis is suspended.

In S208, the failure determination flag Fdgn is set to 1 to determine the determination that there is a failure.
FIG. 4 is a flowchart of the exhaust gas temperature estimation routine according to the present embodiment. As described above, this routine is configured as a subroutine of S105 in the basic routine (FIG. 2). By this routine, the estimated exhaust gas temperature Test is calculated.

In S301, the pressure (boost pressure) Pbst of the supercharged intake air detected by the boost pressure sensor 44 is read.
In S302, the pressure (intake pressure) Pint of the intake air before supercharging detected by the intake pressure sensor 42 is read.
In S303, the turbine rotational speed Nt detected by the rotational speed sensor 45 is read.

In S304, the flow rate Ge of intake air is calculated based on the read boost pressure Pbst, intake pressure Pint, and turbine rotational speed Nt. The calculation of the intake air flow rate Ge is performed by searching from a map stored in advance in the memory of the ECU 101. The boost pressure Pbst is used as a pressure at the outlet of the compressor 12a, and the intake pressure Pint is used as a pressure at the inlet of the compressor 12a. For the compressor 12a, the ratio of the pressures at the inlet and outlet (hereinafter referred to as "compressor pressure ratio") π _T = Pbst / Pint and the intake air flow rate Ge and the intake air flow rate Ge according to the turbine rotational speed Nt in FIG. It has the following characteristics. From this, by creating a map of the intake air flow rate Ge having this characteristic, by searching this map by the compressor pressure ratio π _T and the turbine rotational speed Nt in actual operation, the intake air flow rate Ge is obtained. Can be calculated. Intake air flow rate Ge is large as when the compressor pressure ratio [pi _T is low under certain turbine speed Nt, also has a characteristic that increases as at high turbine speed Nt.

  In S305, the combustion flow rate Gf is calculated. The fuel flow rate Gf can be calculated as a supply amount per unit time based on the fuel supply amount Qf by main injection and the engine speed Ne. For example, the fuel flow rate Gf is made to correspond to the accelerator pedal depression amount and the engine speed Ne. It is possible to calculate by searching from the map to which each value is assigned. By this S305, the function as “flow rate detecting means” is realized.

  In S306, the estimated exhaust gas temperature Test is calculated based on the intake air flow rate Ge and fuel flow rate Gf calculated as described above and the engine speed Ne. The estimated exhaust gas temperature Test is calculated by searching from a map created in advance with a tendency as shown in FIG. The estimated exhaust gas temperature Test is calculated as a higher temperature as the ratio of the fuel flow rate Gf to the intake air flow rate Ge (= Gf / Ge) is larger, and as the engine speed Ne is higher.

The estimated exhaust gas temperature Test calculated as described above is used for the exhaust gas temperature raising control as the exhaust gas temperature Texh when a failure of the exhaust gas temperature sensor 41 is detected in the basic routine shown in FIG.
In the present embodiment, the period during which the exhaust temperature sensor 41 is operating normally and the failure determination flag Fdgn is set to 0 corresponds to the “first operation period”. During this period, the exhaust temperature increase control is performed. The detected exhaust temperature Texh is used. On the other hand, when the failure of the exhaust temperature sensor 41 is detected and the failure determination flag Fdgn is set to 1, this corresponds to the “second operation period”. During this period, the estimated exhaust temperature Test is used for the exhaust gas temperature increase control. Used.

According to this embodiment, the following effects can be obtained.
In the present embodiment, the engine is based on the boost pressure Pbst, which is the intake pressure downstream of the compressor 12a of the turbocharger 12, the turbine speed Nt, which is the rotational speed of the turbine 12b, and the flow rate Gf of the fuel supplied to the engine 1. Since the exhaust gas temperature Texh (= Test) of 1 is calculated, when the exhaust gas temperature sensor 41 fails, the exhaust gas temperature is controlled based on the calculated estimated exhaust gas temperature Test, and the regeneration function of the DPF 32 can be maintained. In addition, it is possible to avoid deterioration of fuel consumption due to excessive accumulation of particulates and to suppress a thermal load on the filter carrier 321.

Further, according to the present embodiment, the intake pressure Pint upstream of the compressor 12a is detected and used for calculating the intake air flow rate Ge. Therefore, an accurate exhaust temperature is always obtained regardless of the atmospheric state. Can be calculated. However, the calculation may be simplified by approximating the intake pressure Pint to the atmospheric pressure (simply, the standard atmospheric pressure). In this case, the intake air flow rate calculation map (Fig. 5), as a parameter in place of the compressor pressure ratio [pi _T, employing the boost pressure Pbst. In an engine having an atmospheric pressure sensor, atmospheric pressure as an output can be used instead of the intake pressure Pint.

  Further, the intake air temperature Tint may be further taken into account in the calculation of the intake air flow rate Ge. The detection of the intake air temperature Tint may be provided with a dedicated temperature sensor, but the temperature of the engine cooling water before the engine 1 is started may be used instead of the cooling water temperature sensor. The intake air density changes according to the intake air temperature Tint, and the operating characteristics of the compressor shown in FIG. 5 change. For example, by correcting the basic flow rate calculated based on the tendency shown in FIG. 5 according to the intake air temperature Tint, it is possible to cancel the flow rate calculation error caused by the change in the intake air density. As the intake air temperature Tint, any of the outside air, the temperature of the compressed air downstream of the compressor, and the temperature of the compressed air after cooling downstream of the intercooler may be adopted.

  Further, the present invention can be applied not only to a diesel engine but also to a gasoline engine.

Configuration of diesel engine according to first embodiment of the present invention Flow chart of basic routine of fuel supply control according to the embodiment Flow chart of failure diagnosis routine according to the embodiment Flow chart of exhaust temperature estimation routine according to the embodiment Explanatory drawing showing the operating characteristics of the compressor Map for calculating the estimated exhaust temperature

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Diesel engine, 11 ... Intake passage, 12 ... Turbocharger, 12a ... Turbocharger compressor, 12b ... Turbocharger turbine, 13 ... Surge tank, 21 ... Injector, 23 ... Common rail, 31 ... Exhaust passage, 32 ... Diesel Particulate filter, 321 ... Filter carrier, 322 ... Oxidation catalyst, 33 ... EGR pipe, 34 ... EGR control valve, 41 ... Exhaust temperature sensor as "second temperature sensor", 42 ... as "second pressure sensor" , 43 ... Intake temperature sensor as "first temperature sensor", 44 ... Boost pressure sensor as "first pressure sensor", 45 ... Rotational speed sensor, 101 ... Engine control unit, 151 ... Crank Angle sensor, 152 ... accelerator sensor.

Claims (8)

An apparatus for estimating the exhaust temperature of an engine equipped with a turbocharger,
A first pressure sensor that detects an intake pressure downstream from the compressor of the turbocharger as a first intake pressure;
A rotational speed sensor for detecting a rotational speed of a turbine of the turbocharger;
Means for detecting the flow rate of fuel supplied to the engine;
The engine exhaust temperature is calculated based on the first intake pressure detected by the first pressure sensor, the rotational speed of the turbine detected by the rotational speed sensor, and the fuel flow rate detected by the flow rate detecting means. An exhaust temperature estimating device for an engine including an arithmetic unit for performing the processing.   The arithmetic unit has a storage unit in which a relationship between the first intake pressure and the flow rate of the intake air according to the rotational speed of the turbine is stored in advance, and the detected first intake pressure and The exhaust gas temperature is calculated based on the detected fuel flow rate and the calculated intake air flow rate, and the exhaust gas temperature is calculated based on the detected fuel flow rate and the calculated intake air flow rate based on the detected turbine rotation speed. Engine exhaust temperature estimation device. A second pressure sensor for detecting an intake pressure upstream of the compressor as a second intake pressure;
The arithmetic unit calculates the exhaust temperature based on the second intake pressure detected by the second pressure sensor in addition to the detected first intake pressure, turbine rotational speed, and fuel flow rate. The engine exhaust gas temperature estimation device according to claim 1 or 2. A first temperature sensor configured to detect the temperature of the intake air;
The arithmetic unit calculates the exhaust gas temperature based on an intake air temperature detected by the first temperature sensor in addition to the detected first intake air pressure, turbine rotation speed, and fuel flow rate. The engine exhaust gas temperature estimation apparatus according to any one of? An apparatus for estimating the exhaust temperature of an engine equipped with a turbocharger,
First flow rate detection means for detecting the flow rate of intake air;
Second flow rate detection means for detecting the flow rate of fuel supplied to the engine;
A rotational speed detecting means for detecting the rotational speed of the engine;
Based on the intake air flow rate detected by the first flow rate detection means, the fuel flow rate detected by the second flow rate detection means, and the engine rotational speed detected by the rotational speed detection means, the exhaust of the engine An exhaust temperature estimating device for an engine, comprising exhaust temperature estimating means for calculating a temperature. A device for purifying exhaust of an engine equipped with a turbocharger,
A particulate filter that collects particulates in the exhaust,
The exhaust gas temperature estimating device according to any one of claims 1 to 5,
A control unit for controlling the temperature of the exhaust gas flowing into the particulate filter based on the exhaust gas temperature calculated by the exhaust gas temperature estimating device. A second temperature sensor for detecting the exhaust temperature of the engine;
Based on the exhaust temperature detected by the second temperature sensor in the first operation period, the control unit sets the calculated exhaust temperature in the second operation period other than the first operation period. The exhaust emission control device for an engine according to claim 6, wherein the temperature of the exhaust gas flowing into the particulate filter is controlled based on the temperature. And further comprising means for detecting a failure of the second temperature sensor,
The engine exhaust gas purification apparatus according to claim 7, wherein the second operation period is a period determined in response to detection of a failure by the failure detection means.

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