JP2011241722A - Exhaust emission control system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an exhaust emission control system capable of performing urea water supply control even in failure of an SCR inlet temperature sensor without a large difference as compared with the time of sound operation thereof.SOLUTION: The system includes: an SCR inlet temperature sensor 109 installed at an inlet of an SCR device 103 to detect SCR inlet temperature; a urea water supply controller 1 for controlling urea water supply into exhaust gas upstream of the SCR device 103 on the basis of the SCR inlet temperature detected with the SCR inlet temperature sensor 109; and a substitute temperature supply section 4 for supplying DFP inlet temperature detected with a DPF inlet temperature sensor 2 to the urea water supply controller 1 as substitute temperature for the SCR inlet temperature with respect to the urea water supply controller 1, when the SCR inlet temperature sensor 109 is in failure.

Description

  The present invention relates to an exhaust gas purification system for purifying exhaust gas by supplying urea water to exhaust gas of a diesel vehicle and collecting particulate matter, and even when the SCR inlet temperature sensor fails, urea is not much different from when it is healthy. The present invention relates to an exhaust gas purification system capable of performing water supply control.

  As one of exhaust gas purification systems for purifying NOx in exhaust gas of diesel engines, an SCR system using an SCR (Selective Catalytic Reduction) device has been developed.

  This SCR system supplies urea water upstream of the exhaust gas of the SCR device, generates ammonia by the heat of the exhaust gas, and reduces and purifies NOx on the SCR catalyst by this ammonia (for example, patents) Reference 1).

  In the exhaust gas purification system, a DPF (Diesel Particulate Filter) is provided in order to collect particulate matter (Particurate Matter) such as SOF and SOOT contained in the exhaust gas. For example, the DPF is installed upstream of the SCR device.

JP 2000-303826 A

  The SCR catalyst has a temperature range to be activated, and urea has a temperature range in which ammonia is likely to be generated. Therefore, in the SCR system, a temperature range in which NOx removal is positively performed by supplying urea water is not performed. There is a temperature range. In addition, urea has a temperature range in which crystallization and solidification are likely to occur, so it is not intended to remove NOx, but to prevent crystallization by blowing off urea water adhering to the nozzle of a dosing valve that injects urea water. In some cases, urea water is injected. Alternatively, in a temperature range where NOx removal is not performed, urea water may be injected to cool the dosing valve in order to prevent malfunction of the solenoid of the dosing valve. Furthermore, since the amount of ammonia that can be accumulated in the SCR device varies depending on the temperature, the supply amount of urea water is adjusted according to the temperature.

  Therefore, in order to control the timing and amount of supplying urea water to the exhaust pipe upstream of the SCR device, it is important to know the temperature of the SCR device. For this purpose, an SCR inlet temperature sensor is provided at the inlet of the SCR device. The SCR inlet temperature sensor detects the SCR inlet temperature, which is the exhaust gas temperature at the inlet of the SCR device, and performs urea water supply control using this as the temperature of the SCR device.

  However, if the SCR inlet temperature sensor fails, the temperature and the amount of urea water cannot be accurately determined because the temperature of the SCR device becomes unknown. If the timing and amount of urea water supply are wrong, NOx discharged to the outside air is increased, and excess ammonia is discharged to the outside air, which is not preferable.

  As a countermeasure, for example, when the SCR inlet temperature sensor fails, there is a method of stopping the supply of urea water. However, the stoppage of urea water supply means the stop of control of the SCR system, which makes it impossible to perform exhaust gas purification according to the basic performance of the vehicle. Driving such a vehicle is not preferable in terms of environmental measures and is legally prohibited in some countries. Therefore, if a failure of the SCR inlet temperature sensor occurs on the road, it is not possible to go to the repair shop on its own.

  In addition, a fixed value of the SCR device temperature is set in advance for the failure of the SCR inlet temperature sensor, and when the failure of the SCR inlet temperature sensor occurs, the fixed value is controlled as the temperature of the SCR device. There is also a way to do it. However, the fixed value often has a large deviation from the temperature of the true SCR device, and if control is performed based on the fixed value, problems such as increased NOx emissions and ammonia emissions cannot be avoided.

  Therefore, an object of the present invention is to provide an exhaust gas purification system that can solve the above-mentioned problems and can perform urea water supply control without much difference from the normal state even when the SCR inlet temperature sensor fails.

  In order to achieve the above object, the present invention provides a selective reduction catalyst device provided in an exhaust pipe of an engine, and an exhaust gas temperature provided at the inlet of the selective reduction catalyst device, which is provided at the inlet of the selective reduction catalyst device. SCR inlet temperature sensor that controls the urea water supply into the exhaust gas upstream of the selective reduction catalyst device based on the temperature of the exhaust gas at the inlet of the selective reduction catalyst device detected by the SCR inlet temperature sensor A water supply control unit; a diesel particulate filter provided upstream of the selective reduction catalyst device of the exhaust pipe; and an exhaust gas temperature at an inlet of the diesel particulate filter provided at an inlet of the diesel particulate filter. A DPF inlet temperature sensor for detecting the DPF, and when the SCR inlet temperature sensor fails, the DPF A surrogate temperature providing unit that provides the exhaust gas temperature at the inlet of the diesel particulate filter detected by the mouth temperature sensor to the urea water supply control unit as a surrogate temperature of the exhaust gas temperature at the inlet of the selective catalytic reduction device. It is equipped with.

  When the output voltage of the SCR inlet temperature sensor is within a predetermined voltage difference range with respect to the power supply voltage or within a predetermined voltage difference range with respect to the ground voltage, it is determined that the SCR inlet temperature sensor is defective. A failure determination unit may be provided.

  When the coolant temperature is below a predetermined value when the vehicle is turned on, and the temperature detected by the SCR inlet temperature sensor is outside the predetermined temperature difference range with respect to the outside air temperature, the SCR inlet temperature sensor is in failure. A failure determination unit for determining may be provided.

  The present invention exhibits the following excellent effects.

  (1) Even when the SCR inlet temperature sensor fails, urea water supply control can be executed without much difference from the normal state.

It is a principal part block diagram of the exhaust gas purification system which shows one Embodiment of this invention. It is the block diagram which showed in detail the exhaust gas purification system which shows one Embodiment of this invention. It is an input-output block diagram of the exhaust gas purification system of FIG. It is an image figure which performs a failure determination based on the output voltage of an SCR inlet temperature sensor.

  Preferred embodiments of the present invention will be described below with reference to the accompanying drawings.

  As shown in FIGS. 1 and 2, an exhaust gas purification system 100 according to the present invention is provided with an SCR device 103 provided in an exhaust pipe 102 of an engine E, an inlet of the SCR device 103, and an inlet of the SCR device 103. SCR inlet temperature sensor 109 for detecting the temperature of the exhaust gas (SCR inlet temperature) and urea water supply into the exhaust gas upstream of the SCR device 103 based on the SCR inlet temperature detected by the SCR inlet temperature sensor 109 The urea water supply control unit 1 that performs the above operation, the DPF 108 provided upstream of the SCR device 103 of the exhaust pipe 102, and the DPF inlet provided at the inlet of the DPF 108 for detecting the temperature of the exhaust gas at the inlet of the DPF 108 (DPF inlet temperature) The temperature sensor 2, the failure determination unit 3 for determining the failure of the SCR inlet temperature sensor 109, and the SCR inlet temperature sensor. When failure of Sa 109, and a substitute temperature providing unit 4 provided as a substitute temperature of the SCR inlet temperature DPF inlet temperature DPF inlet temperature sensor 2 is detected for the urea water supply control unit 1.

  The SCR inlet temperature sensor 109 is a platinum resistance sensor, for example.

  The DPF inlet temperature sensor 2 is a thermistor, for example.

  When the output voltage of the SCR inlet temperature sensor 109 is within a predetermined voltage difference range with respect to the power supply voltage or within a predetermined voltage difference range with respect to the ground voltage, the failure determination unit 3 performs the SCR inlet temperature sensor 109. Is determined to be a failure. Further, the failure determination unit 3 determines whether the SCR inlet temperature sensor 109 detects that the temperature detected by the SCR inlet temperature sensor 109 is outside the predetermined temperature difference range with respect to the outside air temperature when the coolant temperature is equal to or lower than a predetermined value when the vehicle is turned on. It is determined that the temperature sensor 109 has failed.

  Specifically, as shown in FIG. 2, the exhaust gas purification system 100 injects urea water on the SCR device 103 provided in the exhaust pipe 102 of the engine E and on the upstream side (upstream side of the exhaust gas) of the SCR device 103. Dosing valve (urea injector, dosing module) 104, urea tank 105 for storing urea water, supply module 106 for supplying urea water stored in urea tank 105 to dosing valve 104, dosing valve 104 and supply module It mainly includes a DCU (Dosing Control Unit) 126 for controlling 106 and the like.

  The urea water supply control unit 1, the failure determination unit 3, and the substitute temperature providing unit 4 may be provided in the DCU 126.

In the exhaust pipe 102 of the engine E, a DOC (Diesel Oxidation Catalyst) 107, a DPF (Diesel Particulate Filter) 108, and an SCR device 103 are sequentially arranged from the upstream side to the downstream side of the exhaust gas. The DOC 107 is for oxidizing NO in the exhaust gas exhausted from the engine E into NO ₂ and controlling the ratio of NO and NO ₂ in the exhaust gas to increase the denitration efficiency in the SCR device 103. The DPF 108 is for collecting PM (Particulate Matter) in the exhaust gas.

  A dosing valve 104 is provided in the exhaust pipe 102 on the upstream side of the SCR device 103. The dosing valve 104 has a structure in which an injection hole is provided in a cylinder filled with high-pressure urea water, and a valve body that closes the injection hole is attached to the plunger, and the valve is pulled up by energizing the coil to raise the plunger. The body is separated from the nozzle and the urea water is injected. When energization of the coil is stopped, the plunger is pulled down by the internal spring force and the valve body closes the injection port, so that the urea water injection is stopped.

  The exhaust pipe 102 upstream of the dosing valve 104 is provided with an SCR inlet temperature sensor 109 that measures the temperature of the exhaust gas at the inlet of the SCR device 103 (SCR inlet temperature). An upstream NOx sensor 110 that detects the NOx concentration upstream of the SCR device 103 is provided upstream of the SCR device 103 (here, upstream of the SCR inlet temperature sensor 109), and downstream of the SCR device 103. On the side, a downstream NOx sensor 111 that detects the NOx concentration on the downstream side of the SCR device 103 is provided.

  The supply module 106 includes an SM pump 112 that pumps urea water, an SM temperature sensor 113 that measures the temperature of the supply module 106 (the temperature of urea water flowing through the supply module 106), and the pressure of urea water in the supply module 106 ( The urea water pressure sensor 114 for measuring the pressure on the discharge side of the SM pump 112 and the urea water flow path are switched to supply urea water from the urea tank 105 to the dosing valve 104 or within the dosing valve 104. And a reverting valve 115 for switching whether to return the urea water to the urea tank 105. Here, when the reverting valve 115 is ON, the urea water from the urea tank 105 is supplied to the dosing valve 104, and when the reverting valve 115 is OFF, the urea water in the dosing valve 104 is supplied to the urea tank 105. I tried to return it.

  When the reverting valve 115 is switched to supply urea water to the dosing valve 104, the supply module 106 uses the SM pump 112 to supply the urea water in the urea tank 105 to a liquid supply line (suction line) 116. And the excess urea water is returned to the urea tank 105 through a recovery line (back line) 118.

  The urea tank 105 is provided with an SCR sensor 119. The SCR sensor 119 includes a level sensor 120 that measures the level (level) of urea water in the urea tank 105, a temperature sensor 121 that measures the temperature of urea water in the urea tank 105, and a sensor in the urea tank 105. And a quality sensor 122 for measuring the quality of the urea water. The quality sensor 122 detects the quality of the urea water in the urea tank 105 by detecting, for example, the concentration of urea water and whether or not a different mixture is mixed in the urea water from the propagation speed and electrical conductivity of the ultrasonic waves. To do.

  A cooling line 123 for circulating cooling water for cooling the engine E is connected to the urea tank 105 and the supply module 106. The cooling line 123 is configured to exchange heat between the cooling water passing through the urea tank 105 and flowing through the cooling line 123 and the urea water in the urea tank 105. Similarly, the cooling line 123 passes through the supply module 106 and exchanges heat between the cooling water flowing through the cooling line 123 and the urea water in the supply module 106.

  The cooling line 123 is provided with a tank heater valve (coolant valve) 124 for switching whether or not to supply cooling water to the urea tank 105 and the supply module 106. Although the cooling line 123 is also connected to the dosing valve 104, the dosing valve 104 is configured to be supplied with cooling water regardless of whether the tank heater valve 124 is opened or closed. In FIG. 2, the drawing is simplified and not shown, but the cooling line 123 is disposed along the liquid feeding line 116, the pressure feeding line 117, and the recovery line 118 through which the urea water passes.

  FIG. 3 shows an input / output configuration diagram of the DCU 126.

  As shown in FIG. 3, the DCU 126 includes an upstream NOx sensor 110, a downstream NOx sensor 111, an SCR sensor 119 (level sensor 120, temperature sensor 121, quality sensor 122), SCR inlet temperature sensor 109, and supply module 106. The SM temperature sensor 113, urea water pressure sensor 114, and an input signal line from an ECM (Engine Control Module) 125 that controls the engine E are connected. Engine parameter signals such as DPF inlet temperature, cooling water temperature, and outside air temperature are input from ECM 125 to DCU 126. A key-on signal is input from the ignition switch 131 to the DCU 126.

  The DCU 126 also has output signal lines to the tank heater valve 124, the SM pump 112 and the reverting valve 115 of the supply module 106, the dosing valve 104, the heater of the upstream NOx sensor 110, and the heater of the downstream NOx sensor 111. Connected. Note that the input / output of signals between the DCU 126 and each member may be input / output via individual signal lines or input / output via a CAN (Controller Area Network).

  The DCU 126 estimates the amount of NOx in the exhaust gas based on the engine parameter signal from the ECM 125 and the exhaust gas temperature from the SCR inlet temperature sensor 109, and based on the estimated amount of NOx in the exhaust gas. The amount of urea water injected from the dosing valve 104 is determined, and when the urea water amount injected by the dosing valve 104 is injected, the dosing valve 104 is controlled based on the detection value of the upstream NOx sensor 110. The amount of urea water injected from the dosing valve 104 is adjusted.

  Hereinafter, the operation of the exhaust gas purification system 100 of the present invention will be described.

  When the SCR inlet temperature sensor 109 is healthy, the urea water supply controller 1 controls the urea water supply into the exhaust gas upstream of the SCR device 103 based on the SCR inlet temperature detected by the SCR inlet temperature sensor 109. . For example, when the SCR inlet temperature is 190 ° C. or more, which is the activation temperature of the SCR catalyst, control is performed to inject an amount of urea water from the dosing valve 104 according to the amount of NOx in the exhaust gas. When the SCR inlet temperature is lower than 190 ° C., a small amount of urea water injection is performed at a predetermined time for the purpose of protecting the dosing valve 104 and not for the purpose of removing NOx.

  When the SCR inlet temperature sensor 109 fails, the substitute temperature providing unit 4 provides the DPF inlet temperature detected by the DPF inlet temperature sensor 2 to the urea water supply control unit 1 as a substitute temperature of the SCR inlet temperature.

  The SCR inlet temperature and the DPF inlet temperature are the same exhaust gas temperature although the positions of the exhaust pipe 102 in the exhaust flow direction are different. Therefore, the DPF inlet temperature can be used as a substitute temperature for the SCR inlet temperature.

  The DPF inlet temperature may be input directly from the output signal of the DPF inlet temperature sensor 2 to the DCU 126, but the DPF inlet temperature is conventionally known by the ECM 125 for engine control and input from the ECM 125 to the DCU 126. This may be referred to because it is included in the engine parameter signal.

  In addition, the SCR inlet temperature sensor 109 is a high-precision platinum resistance sensor, whereas the DPF inlet temperature sensor 2 is a thermistor with a lower precision. However, the DPF inlet temperature sensor 2 is sufficient to substitute for the failure of the SCR inlet temperature sensor 109. For example, the deviation from the temperature of the true SCR device compared to using a fixed value of the SCR device temperature. Is small.

  Next, the failure determination of the SCR inlet temperature sensor 109 will be described.

  As shown in FIG. 4, since the power supply for the SCR inlet temperature sensor 109 is supplied with a power supply for a control circuit, for example, 5V DC, the output voltage of the SCR inlet temperature sensor 109 is supplied from the ground voltage 0V. The voltage is within the range of 5V. However, if the SCR inlet temperature sensor 109 is functioning correctly, the output voltage falls within a predetermined range in the middle of 0 to 5V and does not become 0V or 5V. On the other hand, when disconnection or short circuit occurs, the output voltage becomes 0V or 5V.

  Therefore, the failure determination unit 3 determines that the SCR inlet temperature sensor 109 has failed when the output voltage of the SCR inlet temperature sensor 109 is within a predetermined voltage difference range with respect to the power supply voltage, specifically, the upper limit value shown in the figure. Judge that there is. Further, when the output voltage of the SCR inlet temperature sensor 109 is within a predetermined voltage difference range with respect to the ground voltage, specifically, is equal to or lower than the lower limit shown in the drawing, it is determined that the SCR inlet temperature sensor 109 has failed.

  Further, the failure determination unit 3 determines whether the SCR inlet temperature sensor 109 detects that the temperature detected by the SCR inlet temperature sensor 109 is outside the predetermined temperature difference range with respect to the outside air temperature when the coolant temperature is equal to or lower than a predetermined value when the vehicle is turned on. It is determined that the temperature sensor 109 has failed. As the predetermined value for comparing the cooling water temperature, a value indicating that the engine is started at the same temperature as the outside air temperature, that is, a so-called cold start is used. That is, the fact that the cooling water temperature is below a predetermined value at the time of key-on means a cold start, and of course, the temperature of the SCR inlet temperature sensor 109 should be the same as the outside air temperature. At this time, if the temperature detected by the SCR inlet temperature sensor 109 is outside the predetermined temperature difference range with respect to the outside air temperature, that is, abnormally higher or abnormally lower than the outside air temperature, it is determined that there is a failure. If the temperature detected by the SCR inlet temperature sensor 109 is within a predetermined temperature difference range with respect to the outside air temperature, it is determined that the sound is healthy. As a result, even if the output voltage of the SCR inlet temperature sensor 109 is between the upper limit value and the lower limit value in FIG. 4, it is understood that a failure occurs when the temperature detection is not correct.

  As described above, according to the exhaust gas purification system 100 of the present invention, when the SCR inlet temperature sensor 109 fails, the DPF inlet temperature detected by the DPF inlet temperature sensor 2 is supplied to the urea water supply controller 1 by the SCR inlet. Since the substitute temperature providing unit 4 provided as a substitute temperature of the temperature is provided, the urea water supply control can be performed at a substitute temperature with a small deviation from the temperature of the true SCR device without much difference from the normal time. For this reason, even if a failure of the SCR inlet temperature sensor 109 occurs on the road, it is possible to go to the repair shop by self-propelling while performing exhaust gas purification.

DESCRIPTION OF SYMBOLS 1 Urea water supply control part 2 DPF inlet temperature sensor 3 Failure determination part 4 Substitute temperature provision part 100 Exhaust gas purification system 102 Exhaust pipe 103 SCR apparatus 108 DPF
109 SCR inlet temperature sensor 131 Ignition switch

Claims (3)

A selective catalytic reduction device provided in the exhaust pipe of the engine;
An SCR inlet temperature sensor that is provided at the inlet of the selective catalytic reduction device and detects the temperature of exhaust gas at the inlet of the selective catalytic reduction device;
A urea water supply control unit that controls the supply of urea water into the exhaust gas upstream of the selective reduction catalyst device based on the temperature of the exhaust gas at the inlet of the selective reduction catalyst device detected by the SCR inlet temperature sensor;
A diesel particulate filter provided upstream of the selective reduction catalyst device of the exhaust pipe;
A DPF inlet temperature sensor that is provided at the inlet of the diesel particulate filter and detects the temperature of exhaust gas at the inlet of the diesel particulate filter;
When the SCR inlet temperature sensor fails, the exhaust gas temperature at the inlet of the diesel particulate filter detected by the DPF inlet temperature sensor is set to the exhaust gas at the inlet of the selective catalytic reduction device with respect to the urea water supply control unit. An exhaust gas purification system comprising a substitute temperature providing unit that provides a substitute temperature for the temperature of   When the output voltage of the SCR inlet temperature sensor is within a predetermined voltage difference range with respect to the power supply voltage or within a predetermined voltage difference range with respect to the ground voltage, it is determined that the SCR inlet temperature sensor is defective The exhaust gas purification system according to claim 1, further comprising a failure determination unit configured to perform the failure determination.   When the coolant temperature is below a predetermined value when the vehicle is turned on, and the temperature detected by the SCR inlet temperature sensor is outside the predetermined temperature difference range with respect to the outside air temperature, the SCR inlet temperature sensor is in failure. The exhaust gas purification system according to claim 1, further comprising a failure determination unit for determining.

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