JP2008133779A - Diagnosis device for differential pressure sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a diagnosis device for a differential pressure sensor capable of easily and accurately diagnosing the differential pressure sensor. <P>SOLUTION: An exhaust emission control device for an internal combustion engine is provided with DPF 136 installed in an exhaust passage 122 of the internal combustion engine; and the differential pressure sensor 138 arranged so as to be communicated with an upstream side pressure leading passage 137 communicated with an upstream side of the DPF 136 and a downstream side pressure leading passage 139 communicated with a downstream side of the DPF 136 respectively. In this case, the device is provided with a communication switching valve 142 capable of switching the communication of the downstream side pressure leading passage 139 communicated with the differential pressure sensor 138 to the downstream side of the DPF 136 or an atmosphere; a pressure sensor 144 installed in the upstream side of the DPF 136; and a diagnosis means for switching the communication switching valve to the atmosphere communication side and diagnosing whether the differential pressure sensor 138 is abnormal or normal based on comparison of the detection pressure by the differential pressure sensor 138 at that time with the detection pressure by the pressure sensor 144. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a differential pressure sensor diagnostic device, and more particularly to a differential pressure sensor diagnostic device that detects a pressure difference between upstream and downstream of an exhaust purification filter provided in an exhaust system of an internal combustion engine.

  In general, in an internal combustion engine, particularly a diesel engine, removal of particulate matter (particulate matter, hereinafter referred to as PM) contained in exhaust gas is an important issue. For this reason, there is a technique for providing an exhaust purification filter (for example, diesel particulate filter, hereinafter also referred to as DPF) for collecting particulate matter in the exhaust system of the internal combustion engine so that particulate matter is not released into the atmosphere. .

  Further, a technique is known in which an exhaust throttle valve is provided in an exhaust passage of an internal combustion engine so that the flow rate of exhaust flowing through the exhaust passage is reduced as necessary. This is used to raise the exhaust gas temperature by reducing the flow rate of the exhaust gas and raising the back pressure. That is, for the purpose of early warming up of the exhaust gas purification catalyst provided in the exhaust system, regeneration of the DPF that collects PM, and the like.

  In this DPF, if the amount of accumulated PM is excessive, the filter is clogged, and there is a possibility that the fuel consumption is deteriorated due to the output reduction resulting from this, or the filter is damaged. Therefore, as a technique for determining such clogging, a technique for determining the presence or absence of clogging by detecting a pressure difference between upstream and downstream of the DPF with a differential pressure sensor is known.

  By the way, when the pressure difference between the upstream and downstream of the DPF is detected using such a differential pressure sensor, the pressure difference between the upstream and downstream of the DPF depends on the exhaust flow rate passing through the DPF even if the PM accumulation amount is the same. May change. For example, the exhaust flow rate is small during driving in an urban area where a car runs at a relatively low speed, and the pressure difference between the upstream and downstream of the DPF is also small. The pressure difference also increases.

  In addition, when the differential pressure sensor that detects the pressure difference between the upstream and downstream of the DPF outputs an abnormal output, for example, a differential pressure signal that is too large or too small relative to the actual pressure difference, the PM deposition amount is correctly determined. The regeneration process cannot be executed at an appropriate time for the DPF.

  In response to this, in Patent Document 1, a plurality of differential pressure sensors are provided, and the detected values are mutually evaluated to determine abnormality of the differential pressure sensors, or the DPF is determined based on the operating state of the internal combustion engine. The accumulated amount of accumulated PM is estimated, the pressure difference between the upstream and downstream of the DPF is estimated based on the estimated accumulated amount, and the actual measurement obtained based on the estimated pressure difference and the detection value of the differential pressure sensor. A technique for detecting an abnormality of a differential pressure sensor by comparing with a pressure difference is disclosed.

JP 2005-307880 A

  However, providing a plurality of differential pressure sensors causes a cost increase as pointed out in Patent Document 1. Further, the technique described in Patent Document 1 is based on the estimated accumulation amount of PM based on the operating state of the internal combustion engine, the estimated pressure difference between the upstream and downstream of the DPF based on the estimated accumulation amount, and the actually measured pressure difference of the differential pressure sensor. Therefore, in order to obtain the estimated accumulation amount of PM, it is necessary to acquire information that closely corresponds to changes in the operating state, and complicated control is performed. I need. Further, there is a problem that the diagnostic accuracy is not reliable, although a map based on a large amount of experimental data is required to obtain the estimated pressure difference corresponding to the estimated accumulation amount.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide a differential pressure sensor diagnosis apparatus that can easily and accurately diagnose a differential pressure sensor.

  An apparatus for diagnosing a differential pressure sensor according to an aspect of the present invention that achieves the above object includes an exhaust purification filter installed in an exhaust passage of an internal combustion engine, and an upstream pressure guiding path communicated upstream of the exhaust purification filter. And an exhaust gas purification apparatus for an internal combustion engine comprising differential pressure detection means including a differential pressure sensor arranged in communication with a downstream pressure guiding path communicated with a downstream side of the exhaust purification filter. A communication switching means capable of switching the communication of the downstream downstream pressure guiding path to the downstream side of the exhaust purification filter or the atmosphere; and a pressure detection means including a pressure sensor installed on the upstream side of the exhaust purification filter; The communication switching means is switched to the atmosphere communication side at a predetermined time, and the differential pressure sensor is different based on the comparison between the pressure detected by the differential pressure detection means and the pressure detected by the pressure detection means at that time. And diagnosis means for diagnosing whether normal, characterized in that it comprises a.

  Here, an exhaust throttle valve is provided upstream of the exhaust purification filter and downstream of the pressure sensor, and an exhaust throttle valve full opening means for fully opening the exhaust throttle valve is provided in the diagnosis by the diagnostic means. preferable.

  In the differential pressure sensor diagnostic device according to the aspect of the present invention, when the communication of the downstream pressure guide path communicated with the differential pressure sensor is switched to the atmosphere communication side by the communication switching means at a predetermined time, the differential pressure detection is performed. The pressure difference between the upstream pressure of the exhaust purification filter communicated with the upstream pressure guiding path by the means and the atmospheric pressure communicated with the downstream pressure guiding path, that is, the upstream pressure of the exhaust purification filter is the absolute pressure. Detected. At the same time, the pressure on the upstream side of the exhaust purification filter is detected by pressure detection means including a pressure sensor installed on the upstream side of the exhaust purification filter. Then, the pressure detected by these differential pressure detecting means and the pressure detected by the pressure detecting means are compared to diagnose whether the differential pressure sensor is abnormal or normal. Specifically, when the difference between the two is smaller than a predetermined value, it is diagnosed that the differential pressure sensor is functioning normally. Conversely, when the difference between the two is greater than a predetermined value, it is diagnosed that the differential pressure sensor is not functioning normally, that is, is abnormal. Therefore, according to the configuration of the above embodiment, since the diagnosis is performed by comparing the absolute pressures, the differential pressure sensor can be easily and accurately diagnosed.

  Here, an exhaust throttle valve is provided upstream of the exhaust purification filter and downstream of the pressure sensor, and an exhaust throttle valve full opening means for fully opening the exhaust throttle valve is provided in the diagnosis by the diagnostic means. Therefore, even if there is an exhaust throttle valve, it does not become an obstacle to pressure detection upstream and downstream.

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

  FIG. 1 is a schematic diagram illustrating a schematic configuration of an embodiment in which the present invention is applied to an automobile diesel engine.

  In FIG. 1, 100 is a diesel engine body, 102 is an intake passage of the engine 100, 104 is a surge tank provided in the intake passage 102, and 106 is an intake branch pipe connecting the surge tank 104 and the intake port of each cylinder. . In the present embodiment, the intake passage 102 is provided with an intake throttle valve 108 that restricts the flow rate of intake air flowing through the intake passage 102 and an intercooler 110 that cools intake air. The intake throttle valve 108 includes an actuator 108A of an appropriate type such as a solenoid or a vacuum actuator, and takes an opening degree according to a control signal from an electronic control unit (ECU) 200 described later. In the present embodiment, the intake throttle valve 108 reduces the intake pressure, for example, at the time of low engine rotation, and increases the amount of exhaust gas (EGR gas) that returns to the surge tank 104 through the EGR passage 152 described later. Used.

  In FIG. 1, an air flow meter 112 is provided near the intake inlet of the intake passage 102. In the present embodiment, the air flow meter 112 is of a type that can measure the mass flow rate of the intake air flowing through the intake passage 102, such as a hot-wire flow meter. After the air flowing into the intake passage 102 passes through the air flow meter 112, it is pressurized by the compressor 130C driven by the turbine 130T of the turbocharger 130, cooled by the intercooler 110 provided in the intake passage 102, and then the surge tank 104. Then, it is sucked into each cylinder through the branch pipe 106.

  Reference numeral 114 in FIG. 1 denotes a fuel injection valve that directly injects fuel into each cylinder. The fuel injection valve 114 is connected to a common pressure accumulation chamber (common rail) 116 that stores high-pressure fuel. The fuel of the engine 100 is boosted by a high-pressure fuel pump 118, supplied to the common rail 116, and injected directly into each cylinder from the common rail 116 via each fuel injection valve 114.

  Further, reference numeral 120 in FIG. 1 is an exhaust manifold that connects the exhaust port of each cylinder and the exhaust passage 122, and the turbocharger 130 described above is disposed downstream thereof. As described above, the turbocharger 130 includes the exhaust turbine 130T driven by the exhaust gas in the exhaust passage 122 and the intake compressor 130C driven by the exhaust turbine 130T.

  Further, in the present embodiment, a catalyst device (for example, an oxidation catalyst or a three-way catalyst) 132 is disposed in the exhaust passage 122 on the downstream side of the turbocharger 130 and the exhaust flow rate flowing through the exhaust passage 122 is controlled downstream thereof. An exhaust throttle valve 134 is provided for this purpose. The exhaust throttle valve 134 includes an actuator 134A similar to the intake throttle valve 108, and takes a fully open position and a closed position with a predetermined opening according to a control signal from the ECU 200. In the present embodiment, the exhaust throttle valve 134 is used when raising the exhaust temperature for early activation of the catalyst device 132 and regeneration of the DPF described later. In the present embodiment, the above-described DPF 136 is disposed downstream of the exhaust throttle valve 134.

  Further, in the present embodiment, the upstream side pressure guiding path 137 communicated with the downstream side of the DPF 136 and the upstream side pressure guiding path 137 communicated with the downstream side of the DPF 136 and the downstream side of the exhaust throttle valve 134 installed in the exhaust passage 122. 139 is provided with a differential pressure sensor 138 disposed in communication with each other. The downstream side pressure guiding path 139 communicates with the atmospheric communication path 140 branched in the middle thereof, and a first position for maintaining the differential pressure sensor 138 and the downstream side of the DPF 136 in a communicating state is connected to the branched portion. A switching valve 142 that can be switched by an actuator (not shown) is provided at a second position where the differential pressure sensor 138 communicates with the atmosphere communication path 140.

  A pressure sensor 144 is provided in the exhaust passage 122 upstream of the exhaust throttle valve 134.

  Further, in the present embodiment, an EGR device 150 that recirculates part of the engine exhaust to the intake system is provided. The EGR device 150 includes the EGR passage 152 that connects the exhaust manifold 120 and the intake surge tank 104, an EGR control valve (hereinafter referred to as an EGR valve) 154 disposed in the EGR passage 152, and an upstream side of the EGR valve 154. The EGR cooler 156 provided in the EGR passage 152 is provided. The EGR valve 154 includes actuators such as stepper motors and solenoid actuators (not shown), takes an opening degree according to a control signal from the ECU 200, and controls an EGR gas flow rate recirculated to the intake surge tank 104 through the EGR passage 152. . Since the EGR gas is a high-temperature exhaust gas discharged from the cylinder, when a large amount of EGR gas is recirculated to the intake air, the intake air temperature rises, and the intake volume efficiency of the engine decreases. In the present embodiment, in order to prevent this, a water-cooled or air-cooled EGR cooler 156 is provided in the EGR passage 152 upstream of the EGR valve 154. In the present embodiment, by using the EGR cooler 156 to reduce the temperature of the EGR gas recirculated to the intake system, it is possible to recirculate a relatively large amount of EGR gas while suppressing a decrease in the intake volume efficiency of the engine. ing.

  Further, an electronic control unit (ECU) of the engine 100 is indicated by 200 in FIG. The ECU 200 according to the present embodiment is configured as a microcomputer having a known configuration, and is configured such that a CPU, a RAM, a ROM, an input port, and an output port are connected to each other via a bidirectional bus. The ECU 200 performs basic control such as fuel injection control and rotation speed control of the engine 100, and in this embodiment, diagnoses whether or not the differential pressure sensor 138 is functioning normally, as will be described later.

  In order to perform these controls, a signal corresponding to the engine rotational speed NE is input to the input port of the ECU 200 from the rotational speed sensor 160 disposed in the vicinity of the crankshaft of the engine 100. A signal corresponding to the air amount Gn is also disposed in the EGR valve 154 and a signal corresponding to the accelerator pedal depression amount (accelerator opening) of the driver from an accelerator opening sensor 162 disposed in the vicinity of an unillustrated accelerator pedal. The EGR valve opening sensor 164 receives a signal representing the EGR valve opening, output signals from the differential pressure sensor 138 and the pressure sensor 144, and the like.

  The output port of the ECU 200 is connected to the fuel injection valve 114 of the engine 100 via a fuel injection circuit (not shown), and controls the fuel injection amount from the fuel injection valve 114 and the fuel injection timing. Further, the output port of the ECU 200 is connected to the actuators of the EGR valve 154, the intake throttle valve 108, the exhaust throttle valve 134, and the switching valve 142 via a drive circuit (not shown) to control the respective valve openings.

  As described above, PM in the exhaust gas during engine operation is collected in the DPF 136, and the amount of PM collected by the DPF 136 gradually increases. In the present embodiment, when an increase in the amount of PM trapped by the DPF 136 is detected by the differential pressure sensor 136, the exhaust throttle valve 134 is closed to decrease the engine intake amount, and the exhaust temperature is increased to increase the DPF 136. The playback operation is performed.

  By the way, the differential pressure sensor 136 is communicated with the upstream pressure guiding path 137 communicated with the downstream side of the DPF 136 and the downstream pressure guiding path 139 communicated with the downstream side of the exhaust throttle valve 134 and the upstream side of the DPF 136. Located in a closed system, the relative pressure difference between the upstream and downstream of the DPF 136 can be easily detected, but the absolute pressure cannot be detected, so it does not correctly reflect the degree of clogging due to PM accumulation on the DPF 136. There is a time. For this reason, it is important to reliably diagnose whether the differential pressure sensor 136 is functioning correctly without any deviation in characteristics, in other words, whether the laterality is ensured.

  Hereinafter, the diagnostic processing procedure of the differential pressure sensor 136 of the present embodiment having the above-described configuration will be described with reference to the flowchart of FIG. Note that this diagnosis is executed at least once in a so-called one trip from when the engine 100 is started to when it is stopped, for example, at a relatively early time after completion of warm-up of the engine 100 or several times at a predetermined cycle. It only has to be done. Therefore, when diagnosis is completed normally, useless diagnosis during one trip may be avoided by setting a diagnosis completion flag. The timing or number of times of the diagnosis can be set in advance in a program in the ECU 200.

  Therefore, when diagnosis starts at a time set in the ECU 200, the exhaust throttle valve 134 is fully opened in step S201 of this diagnosis routine. That is, when the predetermined opening degree is maintained in the normal traveling state, a drive command for forcibly opening it fully is sent to the actuator 134A when this diagnosis routine is executed.

  Furthermore, in the next step S202, the switching valve 142 provided at the branch portion of the downstream pressure guiding path 139 starts from the first position where the differential pressure sensor 138 and the downstream side of the DPF 136 are kept in communication with each other. A drive command is sent to an actuator (not shown) so as to be switched to the second position where the sensor 138 and the atmosphere communication path 140 communicate with each other.

  Then, in the next step S203, the output pressure (P1) on the upstream side of the DPF 136 is detected and acquired by the pressure sensor 144 as pressure detecting means. In step S204, the output pressure difference (P2) between the upstream pressure of the DPF 136 and the atmospheric pressure with which the downstream pressure guiding path 139 is communicated by the differential pressure sensor 138 as a differential pressure detecting means, that is, the DPF 136 The upstream pressure is detected and acquired as an absolute pressure.

  Further, in the next step S205, the difference between the output pressure (P1) from these pressure sensors 144 and the output differential pressure (P2) from the differential pressure sensor 138 is compared with a predetermined threshold value α, and the differential pressure sensor is abnormal or normal. Is diagnosed. Specifically, when the difference (P1−P2) between the two is larger than the predetermined threshold value α, the process proceeds to step S206, and it is diagnosed that the differential pressure sensor 138 is not functioning normally, that is, is abnormal. In the state where the switching valve 142 is switched to the second position, the pressure sensor 144 and the differential pressure sensor 138 are merely detecting the absolute pressure of the same part, and therefore, based on a predetermined threshold value α. A large difference is because the output is not correct. On the other hand, when the difference between the two (P1−P2) is smaller than the predetermined threshold value α, the process proceeds to step S207 and it is diagnosed that the differential pressure sensor 138 is functioning normally.

It is a schematic diagram which shows the outline of embodiment of the diagnostic apparatus of the differential pressure sensor which concerns on this invention. It is a flowchart which shows an example of the diagnostic processing procedure of embodiment of the diagnostic apparatus of the differential pressure sensor which concerns on this invention.

Explanation of symbols

100 Engine Body 122 Exhaust Passage 134 Exhaust Throttle Valve 136 Exhaust Purification Filter (DPF)
137 Upstream side pressure guiding path 138 Differential pressure sensor 139 Downstream side pressure guiding path 140 Atmospheric communication path 142 Switching valve 144 Pressure sensor 200 Electronic control unit (ECU)

Claims (2)

An exhaust purification filter installed in the exhaust passage of the internal combustion engine, an upstream pressure guiding path communicated with the upstream side of the exhaust purification filter, and a downstream pressure guiding path communicated with the downstream side of the exhaust purification filter An exhaust gas purification apparatus for an internal combustion engine, comprising: a differential pressure detecting means including a differential pressure sensor arranged in a
Communication switching means capable of switching the communication of the downstream pressure guiding path communicated with the differential pressure sensor to the downstream side of the exhaust purification filter or the atmosphere;
Pressure detecting means including a pressure sensor installed upstream of the exhaust purification filter;
At a predetermined time, the communication switching means is switched to the atmosphere communication side, and whether the differential pressure sensor is abnormal or normal is diagnosed based on a comparison between the detected pressure by the differential pressure detecting means and the detected pressure by the pressure detecting means at that time Diagnostic means to
A differential pressure sensor diagnostic apparatus comprising: An exhaust throttle valve upstream of the exhaust purification filter and downstream of the pressure sensor;
2. The differential pressure sensor diagnostic device according to claim 1, further comprising an exhaust throttle valve full opening means for fully opening the exhaust throttle valve when performing the diagnosis by the diagnostic means.

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