JP5516072B2 - 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 NOx concentration in the exhaust gas. More specifically, in the SCR system, the NOx amount in the exhaust gas is calculated from the NOx concentration in the exhaust gas and the exhaust gas flow rate, and purification is performed by the SCR device based on the obtained NOx amount and the purification efficiency of the SCR catalyst. Control is performed to determine the possible amount of NOx and to inject urea water at an injection amount corresponding to the determined purifiable NOx amount.

  When the purification efficiency of the SCR catalyst is high, the amount of NOx that can be purified by the SCR device increases, so the injection amount of urea water increases. On the contrary, when the purification efficiency of the SCR catalyst is small, the amount of NOx that can be purified by the SCR device decreases, so the injection amount of urea water decreases.

  The purification efficiency of the SCR catalyst includes the temperature of the exhaust gas at the inlet of the SCR device (hereinafter referred to as SCR inlet temperature) and the calculated value of the storage amount of ammonia stored in the SCR catalyst (hereinafter referred to as calculated storage amount). And based on the exhaust gas flow rate.

  More specifically, the purification efficiency of the SCR catalyst uses a first efficiency map referred to by the SCR inlet temperature and the calculated storage amount, and a second efficiency map referred to by the SCR inlet temperature and the exhaust gas flow rate. It is calculated by multiplying the first efficiency obtained by the first efficiency map and the second efficiency obtained by the second efficiency map.

  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 and downstream of the SCR device, engine parameters, and the like.

  As for the temperature of the SCR catalyst used for calculating the calculated storage amount, it is not economical to add a temperature sensor to the SCR device, so it is approximated by the exhaust gas temperature (SCR inlet temperature) at the SCR device inlet. Yes.

  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.

JP 2000-303826 A

  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, if a large amount of urea water is injected during DPF regeneration when the SCR catalyst is at a high temperature, the supplied SCR catalyst cannot store the ammonia, and the ammonia flows out downstream of the SCR device and is released into the atmosphere. A so-called ammonia slip phenomenon occurs.

  As for this ammonia slip, the present inventors conducted an experiment and examined. When the outside air temperature is high (for example, 20 ° C.), ammonia slip does not occur, but when the outside air temperature is low (for example, −18 ° C.), It has been found that ammonia slip occurs during DPF regeneration.

  As a result of examining this cause, the present inventors found that when the outside air temperature is low, the difference between the SCR inlet temperature used when calculating the calculated storage amount and the actual SCR catalyst temperature becomes large. As a result, it was found that the urea water injection amount during DPF regeneration was not properly controlled, 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 for calculating a calculation storage amount that is a storage amount of ammonia stored in the SCR device; an SCR inlet temperature; The efficiency map includes the efficiency map in which the purification efficiency of the SCR device is given, the SCR inlet temperature, the calculated storage amount, the exhaust gas flow rate, and the outside air temperature for each of the air amount, the exhaust gas flow rate, and the outside air temperature. The urea water for controlling the urea water injection amount in accordance with the purification efficiency calculation unit for obtaining the purification efficiency of the SCR device, the purification efficiency obtained by the purification efficiency calculation unit, and the NOx concentration in the exhaust gas And an injection control unit.

  The efficiency map includes a first efficiency map referred to by an SCR inlet temperature, a calculated storage amount, and an outside air temperature, and a second efficiency map referred to by an SCR inlet temperature and an exhaust gas flow rate. The unit obtains the first efficiency by referring to the first efficiency map based on the SCR inlet temperature, the calculated storage amount, and the outside air temperature, and refers to the second efficiency map based on the SCR inlet temperature and the exhaust gas flow rate. The purification efficiency of the SCR device may be obtained by obtaining two efficiencies and multiplying the first efficiency and the second efficiency.

  The first efficiency map may be set so that the value of the first efficiency 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 figure explaining a 1st efficiency map. In this invention, it is a flowchart which shows the control flow at the time of determining the injection amount of urea water.

  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 OFF, the urea water from the urea tank 105 is supplied to the dosing valve 104, and when the reverting valve 115 is ON, 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 is equipped with a calculated storage amount calculation unit 127, an efficiency map 128, a purification efficiency calculation unit 129, and a urea water injection control unit 130.

  The calculated storage amount calculation unit 127 uses the SCR inlet temperature detected by the exhaust temperature sensor 109 to calculate a calculated storage amount that is a storage amount of ammonia stored in the SCR device 103. More specifically, 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 engine. The calculation storage amount is calculated based on parameters and the like.

  The efficiency map 128 is a map in which the purification efficiency of the SCR device 103 (SCR catalyst purification efficiency) is given for each SCR inlet temperature, calculated storage amount, exhaust gas flow rate, and outside air temperature. Since the purification efficiency of the SCR device 103 represents the purification performance of the SCR catalyst, the purification efficiency decreases as the SCR catalyst deteriorates. That is, the value of the purification efficiency differs between the state where the SCR catalyst is not deteriorated and the state where the SCR catalyst is deteriorated. In this embodiment, in order to make a judgment on the safety side, the value of the purification efficiency in a state where the SCR catalyst has deteriorated (for example, the state after traveling 200,000 km) is set as the value of the purification efficiency set in the efficiency map 128. We will use it.

  The efficiency map 128 includes a first efficiency map 128a referred to by the SCR inlet temperature, the calculated storage amount, and the outside air temperature, and a second efficiency map 128b referred to by the SCR inlet temperature and the exhaust gas flow rate.

  The first efficiency map 128a is a three-dimensional map referred to by the SCR inlet temperature, the calculated storage amount, and the outside air temperature. The first efficiency map 128a is set so that the value of the first efficiency decreases as the outside air temperature decreases.

  In the present embodiment, as shown in FIG. 3, the first efficiency map 128a includes three maps 133 referred to by the SCR inlet temperature and the calculated storage amount so as to correspond to the three different outside air temperatures. It consists of three maps.

  The first efficiency map 128a is used not only at the time of DPF regeneration, but also at the normal time when DPF regeneration is not performed. For this reason, when a significant change is made to the first efficiency map that has been used conventionally, the injection amount of urea water cannot be appropriately controlled during normal operation, and the exhaust gas may not be sufficiently purified. In order to solve this problem, in the present embodiment, at a temperature at which exhaust gas purification should be prioritized (for example, 25 ° C. or more), a conventional map is used and used at a low outside temperature where ammonia slip occurs. It is separated from the map.

  The purification efficiency calculation unit 129 obtains the first efficiency by referring to the first efficiency map 128a based on the SCR inlet temperature, the calculated storage amount, and the outside air temperature, and calculates the second efficiency map 128b based on the SCR inlet temperature and the exhaust gas flow rate. The purification efficiency of the SCR device 103 is obtained by referring to the second efficiency and multiplying the first efficiency and the second efficiency. In addition, when calculating | requiring 1st efficiency with the 1st efficiency map 128a, when outside temperature is the intermediate value (value different from the above-mentioned three different outside temperature) of the three maps 133, it is the same as a normal map. The first efficiency is obtained by linear interpolation. 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. 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.

  The urea water injection control unit 130 controls the urea water injection amount according to the purification efficiency obtained by the purification efficiency calculating unit 129 and the detected value of the NOx concentration detected by the upstream NOx sensor 110. More specifically, the urea water injection control unit 130 calculates the NOx amount in the exhaust gas from the NOx concentration detected by the upstream NOx sensor 110 and the exhaust gas flow rate, and the obtained NOx amount and the purification efficiency calculation unit Based on the purification efficiency obtained in 129, the amount of NOx that can be purified by the SCR device 103 is obtained, and control is performed so that urea water is injected at an injection amount that corresponds to the obtained amount of NOx that can be purified.

  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 132 referred to by the SCR inlet temperature and the exhaust gas flow rate.

  When the cooperative control unit 131 receives the DPF regeneration request signal output from the ECM 125 during the DPF regeneration, the cooperative control unit 131 stops the injection of urea water 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 132 is conventionally used.

  Here, the control flow at the time of determining the injection amount of urea water in the SCR system 100 will be described with reference to FIG. The SCR system 100 is configured to repeatedly execute the control flow of FIG.

  As shown in FIG. 4, first, the calculated storage amount calculation unit 127 calculates a calculated storage amount (step S1). After calculating the calculated storage amount, the process proceeds to step S2.

  In step S2, the purification efficiency calculation unit 129 obtains the first efficiency by referring to the first efficiency map 128a with the SCR inlet temperature, the calculated storage amount, and the outside air temperature, and the second with the SCR inlet temperature and the exhaust gas flow rate. The second efficiency is obtained with reference to the efficiency map 128b. After obtaining the first efficiency and the second efficiency, the process proceeds to step S3.

  In step S3, the purification efficiency calculation unit 129 obtains the purification efficiency of the SCR device 103 by multiplying the first efficiency obtained in step S2 and the second efficiency. After obtaining the purification efficiency, the process proceeds to step S4.

  In step S4, the urea water injection control unit 130 controls the urea water injection amount according to the calculated storage amount obtained in step S1 and the purification efficiency obtained in step S3.

  As described above, in the SCR system 100 according to the present embodiment, the efficiency map 128 in which the purification efficiency of the SCR device 103 is given for each SCR inlet temperature, calculated storage amount, exhaust gas flow rate, and outside air temperature. Is used to obtain the purification efficiency of the SCR device.

  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 outside air temperature is included in the parameter of the efficiency map 128. The purification efficiency can be set according to the outside air temperature, and the value of the purification efficiency (first efficiency) becomes smaller as the outside air temperature is lower in the efficiency map 128 (first efficiency map 128a). By setting in this way, it becomes possible to reduce the injection amount of the urea water to be injected.

  As a result, even if the SCR catalyst becomes hot during DPF regeneration, the supplied ammonia cannot be stored by the SCR catalyst and is not released into the atmosphere, and ammonia slip during DPF regeneration can be prevented. It becomes possible.

  In the SCR system 100, the first efficiency is obtained by referring to the first efficiency map 128a based on the SCR inlet temperature, the calculated storage amount, and the outside air temperature, and the second efficiency map 128b is determined based on the SCR inlet temperature and the exhaust gas flow rate. The second efficiency is obtained by reference, and the purification efficiency of the SCR device 103 is obtained by multiplying the first efficiency and the second efficiency.

  For example, the first efficiency may be changed according to the outside air temperature by multiplying the coefficient obtained by the coefficient map referred to by the outside air temperature with the first efficiency. In this case, all the SCR inlet temperatures are changed. And the calculated storage amount are multiplied by a coefficient, so that there is no risk of ammonia slip even when the outside air temperature is low and the DPF is regenerated (for example, the calculated storage amount is low and the SCR inlet temperature is high in purification efficiency). Even when the temperature is in a high temperature range, the amount of urea water injected may be reduced, and exhaust gas may not be sufficiently purified.

  In the present embodiment, the first efficiency map 128a is a three-dimensional map referred to by the SCR inlet temperature, the calculated storage amount, and the outside air temperature. It is possible to set the purification efficiency (first efficiency) of the water, and it is possible to reduce the injection amount of urea water only when ammonia slip may occur. Further, by making the first efficiency map 128a a three-dimensional map, a conventional map is used at a temperature at which exhaust gas purification should be prioritized (for example, 25 ° C. or higher), and ammonia slip is reduced. It can be separated from the map used at the outside temperature.

  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. .

  In the above-described embodiment, the calculation storage amount is calculated using the upstream NOx sensor 110. However, the downstream NOx sensor 111 may be used instead of the upstream NOx sensor 110.

  Furthermore, in the above embodiment, the first efficiency map 128a is configured by three maps corresponding to three different outside temperatures, but if there is a map that can be set to the conventional purification efficiency, three maps are provided. However, the present invention is not limited to this, and a plurality of maps can be configured.

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 Purification efficiency map 128a First efficiency map 128b Second efficiency map 129 Purification efficiency calculation unit 130 Urea water injection control unit 131 Cooperative control unit 132 Cooperative control threshold map 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;
An efficiency map in which the purification efficiency of the SCR device is given for each SCR inlet temperature, calculated storage amount, exhaust gas flow rate, and outside air temperature;
A purification efficiency calculation unit that obtains the purification efficiency of the SCR device by referring to the efficiency map with the SCR inlet temperature, the calculated storage amount, the exhaust gas flow rate, and the outside air temperature;
A urea water injection control unit that controls the urea water injection amount according to the purification efficiency obtained by the purification efficiency calculating unit and the NOx concentration in the exhaust gas ,
The efficiency map includes a first efficiency map referred to by an SCR inlet temperature, a calculated storage amount, and an outside air temperature, and a second efficiency map referred to by an SCR inlet temperature and an exhaust gas flow rate.
The purification efficiency calculation unit obtains the first efficiency by referring to the first efficiency map based on the SCR inlet temperature, the calculated storage amount, and the outside air temperature, and calculates the second efficiency map based on the SCR inlet temperature and the exhaust gas flow rate. A SCR system characterized in that a second efficiency is obtained by referring to the first efficiency and a second efficiency to obtain a purification efficiency of the SCR device . 2. The SCR system according to claim 1, wherein the first efficiency map is set such that the value of the first efficiency decreases as the outside air temperature decreases .

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