JP5471832B2 - SCR system - Google Patents

Description

  The present invention relates to an SCR system for reducing NOx in exhaust gas of an engine using urea water.

  As an exhaust gas purification system for purifying NOx in exhaust gas of a diesel engine, 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 SCR system, the injection amount of urea water is controlled based on the storage amount of ammonia stored in the SCR catalyst and the NOx concentration in the exhaust gas.

  Further, a DPF (Diesel Particulate Filter) for collecting PM (Particulate Matter) in the exhaust gas is provided in the exhaust pipe of the engine. The SCR device is provided in the exhaust pipe downstream of the DPF.

  In a vehicle equipped with a DPF, in order to prevent clogging of the DPF, DPF regeneration is performed in which PM collected in the DPF is burned to regenerate the DPF. When the DPF is regenerated, the exhaust gas is heated to a high temperature (for example, about 500 to 600 ° C.) to burn the PM by fuel injection control or the like. Therefore, the high temperature exhaust gas also flows into the SCR device during the DPF regeneration.

  By the way, the SCR catalyst has a characteristic that the storage amount of ammonia that can be stored in the SCR catalyst (hereinafter referred to as storage capacity) decreases as the temperature of the SCR catalyst increases, and the temperature of the SCR catalyst exceeds 350 ° C. As a result, the storage capacity becomes almost zero.

  Therefore, when DPF regeneration is performed in a state where a large amount of ammonia is stored in the SCR catalyst, the temperature of the SCR catalyst suddenly rises and the storage capacity of the SCR catalyst decreases, and the ammonia stored in the SCR catalyst is reduced. A so-called ammonia slip phenomenon occurs that flows downstream from the apparatus and is released into the atmosphere.

  In order to prevent this ammonia slip, in the conventional SCR system, when performing DPF regeneration, prior to DPF regeneration, cooperative control that stops the injection of urea water and reduces the storage amount of ammonia stored in the SCR catalyst. Is done.

  In cooperative control, when a calculated value of the storage amount of ammonia stored in the SCR catalyst (hereinafter referred to as “calculated storage amount”) is obtained, and this calculated storage amount falls below a predetermined threshold (hereinafter referred to as “cooperative control threshold”). Then, DPF regeneration is started.

  The cooperative control threshold used for the cooperative control is determined by the exhaust gas temperature (SCR inlet temperature) at the inlet of the SCR device and the cooperative control threshold map referred to by the exhaust gas flow rate.

  The calculated storage amount is calculated by calculating the balance between the amount of ammonia stored in the SCR catalyst by the injection of urea water and the amount of ammonia used to purify NOx. , The temperature of the SCR catalyst, the exhaust gas flow rate, the NOx concentration in the exhaust gas upstream of the SCR device, the engine parameters, and the like.

  As for the temperature of the SCR catalyst used when calculating the calculated storage amount, it is not economical to provide a temperature sensor in the SCR device only for cooperative control, so the exhaust gas temperature at the inlet of the SCR device (SCR inlet temperature) I try to approximate it.

JP 2000-303826 A

  However, even when DPF regeneration is performed after performing the above-described cooperative control, it has been found that ammonia slip may occur during DPF regeneration depending on environmental conditions.

  More specifically, the present inventors do not generate ammonia slip when the outside air temperature is high (for example, 20 ° C.), but do not generate ammonia slip when the outside air temperature is low (for example, −18 ° C.). Has been found to occur.

  As a result of examining this cause, the present inventors have found that when the outside air temperature is low, the difference between the SCR inlet temperature used to calculate the calculated storage amount and the actual SCR catalyst temperature increases, It was found that DPF regeneration was performed even though ammonia remained in the SCR catalyst, and as a result, ammonia remaining in the SCR catalyst was released and ammonia slip occurred.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide an SCR system capable of preventing ammonia slip during DPF regeneration.

  The present invention was devised to achieve the above object, and is mounted on a vehicle provided with a DPF (diesel particulate filter) that collects particulate matter in exhaust gas in an exhaust pipe of an engine. SCR (selective reduction catalyst) device provided in the exhaust pipe upstream or downstream of the DPF, urea water injection means for injecting urea water upstream of the SCR device, and NOx provided in the exhaust pipe A sensor, an exhaust temperature sensor that is provided upstream of the SCR device and detects an SCR inlet temperature that is an exhaust gas temperature at the inlet of the SCR device, and an SCR inlet temperature detected by the exhaust temperature sensor, A calculation storage amount calculation unit that calculates a calculation storage amount that is the storage amount of ammonia stored in the SCR device; and the calculation storage amount calculation unit. The urea water injection control unit that controls the urea water injection amount according to the calculated storage amount and the NOx concentration detected by the NOx sensor, and when performing the DPF regeneration, the urea water injection is performed prior to the DPF regeneration. And a cooperative control unit that performs cooperative control to start DPF regeneration when the calculated storage amount becomes equal to or less than the cooperative control threshold, and a cooperative control threshold map that is referred to by the SCR inlet temperature and the exhaust gas flow rate. The SCR system includes an outside air temperature detecting means, and a cooperative control threshold value correcting unit that corrects the cooperative control threshold value obtained by the cooperative control threshold value map based on the exhaust temperature sensor and the outside air temperature detecting means, The cooperative control unit is an SCR system configured to start DPF regeneration when a calculated storage amount becomes equal to or less than a corrected cooperative control threshold.

  The cooperative control threshold value correcting unit may correct the cooperative control threshold value obtained by the cooperative control threshold value map so that the cooperative control threshold value decreases as the outside air temperature decreases.

  ADVANTAGE OF THE INVENTION According to this invention, the SCR system which can prevent the ammonia slip at the time of DPF reproduction | regeneration can be provided.

(A), (b) is a schematic block diagram of the SCR system based on this Embodiment. It is an input-output block diagram of DCU in the SCR system of FIG. In this invention, it is a flowchart which shows the control flow of a cooperation control part.

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

  First, an SCR system mounted on a vehicle will be described.

  As shown in FIG. 1A, an SCR system 100 includes an SCR device 103 provided in an exhaust pipe 102 of an engine E, and urea that injects urea water upstream of the SCR device 103 (upstream side of exhaust gas). Dosing valve (urea injection device, dosing module) 104 as water injection means, urea tank 105 for storing urea water, supply module 106 for supplying urea water stored in urea tank 105 to dosing valve 104, and dosing It mainly includes a DCU (Dosing Control Unit) 126 that controls the valve 104, the supply module 106, and the like.

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 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.

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

  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. Although not shown in FIG. 1A, the cooling line 123 is disposed along the liquid feed line 116, the pressure feed line 117, and the recovery line 118 through which the urea water passes.

  FIG. 2 shows an input / output configuration diagram of the DCU 126.

  As shown in FIG. 2, 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), exhaust temperature sensor 109, and SM of the supply module 106. The temperature sensor 113, the urea water pressure sensor 114, and an input signal line from an ECM (Engine Control Module) 125 that controls the engine E are connected. From the ECM 125, signals of outside air temperature and engine parameters (engine speed, etc.) are input.

  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).

  As shown in FIG. 1B, the DCU 126 uses a SCR inlet temperature detected by the exhaust temperature sensor 109 to calculate a calculation storage amount that is a storage amount of ammonia stored in the SCR device 103. An amount calculation unit 127 and a target storage amount calculation unit 128 for obtaining a target storage amount that is a target value of the storage amount of ammonia stored in the SCR device 103 are mounted.

  The calculated storage amount calculation unit 127 includes the urea water injection amount, the SCR catalyst temperature (here, the SCR inlet temperature is used), the exhaust gas flow rate, the NOx concentration detected by the upstream NOx sensor 110 and the downstream NOx sensor 111, and the engine. The calculation storage amount is calculated based on parameters and the like.

  The target storage amount calculation unit 128 is configured to obtain a target storage amount by referring to a target storage amount map (not shown) based on the exhaust gas temperature (here, the SCR inlet temperature is used) and the exhaust gas flow rate. As the exhaust gas flow rate, an intake flow rate measured by a flow sensor (MAF sensor) provided in the intake pipe of the engine may be used.

  Further, the DCU 126 includes a urea water injection control unit 129 that controls the urea water injection amount according to the calculated storage amount calculated by the calculated storage amount calculation unit 127 and the detected value of the NOx concentration detected by the upstream NOx sensor 110. Installed. The urea water injection control unit 129 controls the urea water amount to be injected so that the calculated storage amount approaches the target storage amount, and based on the engine parameter signal from the ECM 125 and the exhaust gas temperature from the exhaust temperature sensor 109. In addition, the amount of NOx in the exhaust gas is estimated, and the amount of urea water injected from the dosing valve 104 is determined based on the estimated amount of NOx in the exhaust gas.

  Further, when performing DPF regeneration, the DCU 126 stops cooperative injection of urea water prior to DPF regeneration, and performs cooperative control for starting DPF regeneration when the calculated storage amount falls below the cooperative control threshold. And a cooperative control threshold map 131 referred to by the SCR inlet temperature and the exhaust gas flow rate.

  When the cooperative control unit 130 receives the DPF regeneration request signal output from the ECM 125 during the DPF regeneration, the cooperative control unit 130 stops the urea water injection and starts the cooperative control. When the value is equal to or lower than the threshold value, a signal permitting the start of DPF regeneration is output to the ECM 125 to start DPF regeneration. The cooperative control threshold map 131 is conventionally used.

  In the SCR system 100 according to the present embodiment, the correction coefficient map 132 obtained from the correction coefficient map 132 referred to by the SCR inlet temperature and the outside air temperature and the cooperative control threshold map 131 is obtained by the correction coefficient map 132. And a cooperative control threshold value correcting unit 133 that corrects the cooperative control threshold value used for cooperative control by multiplying the correction coefficients. The correction coefficient map 132 and the cooperative control threshold value correction unit 133 are mounted on the DCU 126. An outside air temperature signal is input from the ECM 125 to the DCU 126 via the CAN. As the outside air temperature signal, a MAF sensor or an intake manifold temperature (intake air temperature) signal may be used.

  The cooperative control threshold value correcting unit 133 obtains the cooperative control threshold value by referring to the cooperative control threshold value map 131 with the SCR inlet temperature and the exhaust gas flow rate, and for correction with reference to the correction coefficient map 132 with the SCR inlet temperature and the outside air temperature. The cooperative control threshold value is corrected by obtaining a coefficient and multiplying these coefficients. The cooperative control unit 130 uses the corrected cooperative control threshold obtained by the cooperative control threshold correction unit 133 and starts DPF regeneration when the calculated storage amount becomes equal to or less than the corrected cooperative control threshold. .

  The correction coefficient map 132 is set such that the value of the correction coefficient becomes smaller as the outside air temperature is lower. Thereby, the lower the outside air temperature, the smaller the corrected cooperative control threshold value, and the longer the time during which the cooperative control is performed (the start of DPF regeneration is delayed). As a result, even if the ammonia stored in the SCR catalyst is consumed before starting the DPF regeneration, even if the SCR catalyst becomes hot during the regeneration of the DPF, ammonia slip can be suppressed. The correction coefficient is set to a numerical value of 1 or less (0 to 1).

  Here, the control flow of the cooperative control unit 130 will be described with reference to FIG. The cooperative control unit 130 is configured to repeatedly execute the control flow shown in FIG.

  As shown in FIG. 3, first, the cooperative control unit 130 determines whether a DPF regeneration request signal has been received from the ECM 125 (step S1). If it is determined NO in step S1, there is no need to perform cooperative control, so the control is terminated as it is.

  If YES is determined in step S1, the cooperative control unit 130 stops the urea water injection (step S2) and proceeds to step S3.

  In step S3, the cooperative control threshold value correcting unit 133 obtains the cooperative control threshold value by referring to the cooperative control threshold value map 131 with the SCR inlet temperature and the exhaust gas flow rate, and refers to the correction coefficient map 132 with the SCR inlet temperature and the outside air temperature. Then, a correction coefficient is obtained and multiplied to calculate a corrected cooperative control threshold value. After calculating the corrected cooperative control threshold, the process proceeds to step S4.

  In step S4, the cooperative control unit 130 determines whether or not the calculated storage amount obtained by the calculated storage amount calculation unit 127 is equal to or less than the corrected cooperative control threshold obtained in step S3. If NO is determined in step S4, the process returns to step S3.

  If YES is determined in step S4, the calculated storage amount is equal to or less than the corrected cooperative control threshold value, so the cooperative control unit 130 outputs a signal permitting the start of DPF regeneration to the ECM 125 to perform DPF regeneration. Is started, the urea water injection is restarted, and the cooperative control is terminated.

  As described above, in the SCR system 100 according to the present embodiment, the correction control value obtained from the correction coefficient map 132 referred to by the SCR inlet temperature and the outside air temperature is added to the cooperation control threshold value obtained from the cooperation control threshold map 131. By multiplying the coefficients, the cooperative control threshold value used for cooperative control is corrected, and when the amount of calculated storage becomes equal to or less than the corrected cooperative control threshold value, the cooperative control unit 130 starts DPF regeneration. Yes.

  When the outside air temperature is low, the difference between the SCR inlet temperature and the actual SCR catalyst temperature becomes large, and an error occurs in the calculated storage amount. However, according to the present invention, the cooperative control threshold value depends on the outside air temperature. The correction coefficient map 132 is set so that the value of the correction coefficient becomes smaller as the outside air temperature is lower, so that the corrected cooperative control threshold is reduced, and the cooperative control is performed. It is possible to lengthen the waiting time (slow start of DPF regeneration).

  As a result, when starting DPF regeneration, the amount of ammonia stored in the SCR catalyst can be reduced, and even when the SCR catalyst becomes hot during DPF regeneration, ammonia is prevented from being released into the atmosphere. In addition, ammonia slip at the time of DPF regeneration can be prevented.

  Further, in the SCR system 100, it is possible to prevent ammonia slip at the time of DPF regeneration with a simple configuration in which a correction coefficient map 132 and a cooperative control threshold value correction unit 133 are added to the conventional system, and a temperature sensor is provided. There is no need to add or make significant changes to the conventional system, so it is low cost.

  In the above embodiment, the case where the SCR device 103 is provided in the exhaust pipe 102 on the downstream side of the DPF 108 has been described. However, the present invention is not limited to this, and the SCR device 103 may be provided in the exhaust pipe 102 on the upstream side of the DPF 108. .

100 SCR system 102 exhaust pipe 103 SCR device 104 dosing valve (urea water injection means)
105 Urea tank 106 Supply module 110 Upstream NOx sensor 111 Downstream NOx sensor 125 ECM
126 DCU
127 Calculated storage amount calculation unit 128 Target storage amount calculation unit 129 Urea water injection control unit 130 Cooperation control unit 131 Cooperation control threshold map 132 Correction coefficient map 133 Cooperation control threshold correction unit E Engine

Claims (2)

It is mounted on a vehicle equipped with a DPF (diesel particulate filter) that collects particulate matter in the exhaust gas in the exhaust pipe of the engine.
An SCR (selective reduction catalyst) device provided in the exhaust pipe upstream or downstream of the DPF;
Urea water injection means for injecting urea water upstream of the SCR device;
A NOx sensor provided in the exhaust pipe;
An exhaust gas temperature sensor that is provided upstream of the SCR device and detects an SCR inlet temperature that is an exhaust gas temperature at the inlet of the SCR device;
A calculated storage amount calculation unit that calculates a calculated storage amount that is a storage amount of ammonia stored in the SCR device, using the SCR inlet temperature detected by the exhaust temperature sensor;
A urea water injection control unit that controls the urea water injection amount according to the calculated storage amount calculated by the calculated storage amount calculation unit and the NOx concentration detected by the NOx sensor;
When performing DPF regeneration, stop the injection of urea water prior to DPF regeneration, and when the calculated storage amount becomes equal to or less than the cooperative control threshold, a cooperative control unit that performs cooperative control to start DPF regeneration;
In a SCR system comprising a cooperative control threshold map referred to by an SCR inlet temperature and an exhaust gas flow rate,
Outside temperature detection means;
A cooperative control threshold correction unit that corrects the cooperative control threshold obtained in the cooperative control threshold map based on the exhaust temperature sensor and the outside air temperature detecting means;
The SCR system, wherein the cooperative control unit is configured to start DPF regeneration when the calculated storage amount becomes equal to or less than the corrected cooperative control threshold.   The SCR system according to claim 1, wherein the cooperative control threshold correction unit corrects the cooperative control threshold obtained by the cooperative control threshold map so that the cooperative control threshold decreases as the outside air temperature decreases.

Images