CN111350574A

CN111350574A - Automobile state 6 discharge post-treatment system

Info

Publication number: CN111350574A
Application number: CN201811655041.9A
Authority: CN
Inventors: 周浩明; 汤友志
Original assignee: Individual
Current assignee: Individual
Priority date: 2018-12-23
Filing date: 2018-12-23
Publication date: 2020-06-30

Abstract

A6 exhaust after-treatment system of automobile state, belong to the automotive exhaust treatment technical field, including exhaust pipe forepart, exhaust pipe back end, control system and connect in series exhaust gas temperature regulator, DOC, DPF, SCR, ASC ammonia escape catalyst and pyrolyzer between exhaust pipe forepart, exhaust pipe back end sequentially; the control system consists of a controller, a first temperature sensor arranged at the inlet end of the SCR, a second temperature sensor arranged at the inlet end of the DPF, a first pressure sensor arranged at the inlet end of the DPF, and a second pressure sensor arranged at the outlet end of the DPF; the exhaust temperature and airspeed of all working conditions can be controlled, high-temperature protection is carried out on the catalyst of each device, and the DPF minimum filter layer is controlled during continuous passive regeneration; the contact opportunity of the exhaust gas and the catalyst is increased, and the maximum efficiency maximization and the backpressure minimization can be realized at the same time; the catalyst of this patent starts fast cold, and each operating mode conversion efficiency is high, and exhaust resistance is little, the stable performance, long service life, it is with low costs.

Description

Automobile state 6 discharge post-treatment system

1. The technical field is as follows:

the patent relates to the technical field of automobile exhaust treatment, in particular to an automobile exhaust post-treatment system.

2. Background art:

with the progress of science and technology and the rapid development of economy, automobiles gradually enter more and more user families and become indispensable transportation tools for people to go out. With the popularization and increased use of automobiles, environmental pollution caused by automobile exhaust has become a considerable problem.

With the improvement of the whole world on the emission limit value of the automobile, the automobile exhaust system is gradually added with a corresponding post-treatment system, and higher challenges are provided for the structure, cost and calibration of the post-treatment of the exhaust system.

The existing diesel vehicles and GDI gasoline vehicles in China 5 and below can meet the standard requirements only by depending on a technical route, namely, the PM is reduced by optimizing combustion in the engine and reducing the NOx by SCR outside the engine, or the NOx is reduced by EGR in the engine and reducing the PM by DPF outside the engine.

Compared with the national standard 5, all indexes of the national standard 6 are basically reduced by 50%, so that the existing diesel vehicles and GDI gasoline vehicles can not reach the national standard 6 only by one technical route, and two routes are required to be adopted completely, namely, the internal combustion is optimized to reduce PM + EGR to reduce NOx) + the external combustion is performed (DOC + DPF + SCR + ASC).

The two indexes of NOx and NH3 escaped from the SCR under different working conditions are met simultaneously, and the SCR is very difficult to control by only depending on the SCR, so that the simplest method is that the SCR only controls the NOx, and the added post-ASC controls NH3 escaped from the SCR. In fact, the post-ASC can also assist the work of the front DOC, and the front DOC does not clean.

The method is a combined and discharged post-treatment technical route which is recognized worldwide, has the most mature technology and the best effect. However, the specific structure and control strategy for realizing the technical route are different due to different degrees of awareness of people on post-processing theory and devices, and the actual effects are different.

The fatal defect of the concrete structure and the control strategy of the existing diesel vehicle state 6 emission post-processing technical route:

although the national 6 emission standard has not been implemented, in practice, the post-treatment technical route of the national 6 emission is already applied, and only the control index is not so strict.

The existing post-treatment specific structures of

countries

4, 5 and 6 are only formed by simply connecting DOCs, DPFs or SCRs in series, and the design has the following important defects:

(1) in terms of post-treatment efficiency: the highest emission temperature working condition can be ensured, and the high efficiency under other emission temperature working conditions can not be ensured;

(2) in terms of post-treatment efficiency: the highest airspeed working condition can be guaranteed, and the high efficiency in other airspeed working conditions cannot be guaranteed;

(3) the catalyst of each device can not be protected at high temperature, so that the catalyst is easy to sinter, volatilize, deform and fall off, the efficiency is reduced, the service life is shortened, and secondary pollutants of N2O and NH3 are increased;

(4) the existence of the DPF minimum filter layer during continuous passive regeneration cannot be ensured, so that the emission of fine particulate matters is increased;

(5) during cold start, the catalyst has long start time and low conversion efficiency, so that pollutants are discharged in a large amount for a long time;

(6) in DOC or SCR, all molecules of relevant components of oxidation-reduction reaction need to be uniformly mixed before entering, and enough contact opportunities exist between the DOC or SCR and a catalyst after entering so as to maximize conversion efficiency; existing aftertreatment, under a selected design condition, if the airspeed is determined to be maximized at highest efficiency, i.e., in turbulent flow, the exhaust backpressure is very high, and if the airspeed is determined to be minimized at highest efficiency, i.e., in laminar flow, the highest efficiency is reduced; the prior post-processing structure can not realize maximum efficiency maximization and back pressure minimization at the same time;

(7) the active regeneration energy consumption is large.

3. The purpose of this patent:

the invention relates to a catalyst cold start-up post-treatment system with high conversion efficiency under various working conditions, small exhaust resistance, stable performance, long service life and low purchase cost, which is used for treating national 6 exhaust emission.

4. The content of the patent:

in order to achieve the purpose, the patent adopts the following technical route: the device comprises a temperature regulator, a DOC, a DPF, an SCR, an ASC and a pyrolyzer, and adopts the following technical scheme:

a6 exhaust after-treatment system of automobile country, including exhaust pipe forepart 2, exhaust pipe back end 13, control system and connect in series 23, DOC catalyst 4, DPF granule catcher 7, SCR catalyst 11, ASC ammonia escape catalyst 12 and pyrolyzer of exhaust gas cooler of exhaust pipe between forepart 2, exhaust pipe back end 13 sequentially from front to back; an air inlet pipe 24 of the waste gas cooler 23 is connected with the front section 2 of the exhaust pipe through the diverter valve 1, and an air outlet pipe 22 of the cooler 23 is fixedly connected to the front section 2 of the exhaust pipe behind the diverter valve 1; the DOC catalyst 4 is connected with a bypass pipe 20 in parallel, the front end of the bypass pipe 20 is connected with the inlet end of the DOC catalyst 4 through a reversing valve 3, and the rear end of the bypass pipe 20 is fixedly connected with the outlet end of the DOC catalyst 4; the SCR catalyst 11 and the ASC ammonia escape catalyst 12 are connected in parallel with a bypass pipe 19, the front end of the bypass pipe 19 is connected with the inlet end of the SCR catalyst 11 through a reversing valve 9, the rear end of the bypass pipe 19 is divided into two

branch pipes

18 and 16, and the two

branch pipes

18 and 16 are respectively and fixedly connected to the rear section 13 of the exhaust pipe at the front and the rear of the pyrolyzer.

In the exhaust gas post-treatment system of automobile country 6, the pyrolyzer is formed by fixedly connecting a urea liquid input pipe 15, a pyrolysis chamber 17 and an output pipe 14 of the pyrolyzer; a urea liquid input pipe 15 and an output pipe 14 of the pyrolyzer are fixedly connected on a pipe of the rear section 13 of the exhaust pipe; the pyrolysis chamber is arranged in the pipe of the exhaust pipe rear section 13, is isolated from the exhaust gas in the exhaust pipe rear section 13, and absorbs the heat of the exhaust gas in the exhaust pipe rear section 13 to heat the urea solution sprayed into the pyrolysis chamber 17 to be pyrolyzed into ammonia gas; a urea solution nozzle is installed in the inlet pipe 15.

In the automotive exhaust aftertreatment system of U.S. Pat. No. 6, the pyrolysis chamber 17 may be a section of a coil.

In the exhaust gas post-treatment system of the automobile country 6, the outlet end of the output pipe 14 of the pyrolyzer is fixedly connected to the inlet or outlet end of the DPF particle catcher 7.

In the automobile state 6 exhaust gas post-treatment system, the control system is composed of a controller, a first temperature sensor 10 arranged at the inlet end of an SCR catalyst 11, a second temperature sensor 5 arranged at the inlet end of a DPF particle catcher 7, a first pressure sensor 6 arranged at the inlet end of the DPF particle catcher and a second pressure sensor 8 arranged at the outlet end of the DPF particle catcher 7, and the sensors are connected with the controller through electric wires; when the pressure difference value detected by the first pressure sensor 6 and the second pressure sensor 8 exceeds the highest preset value of the working condition at that time, the temperature detected by the second temperature sensor 5 is lower than the lower limit value of the preset temperature range for DPF active regeneration, under the premise of closing the cooler 23, the controller takes a temperature-raising measure until the temperature entering the inlet end of the DPF particle catcher 7 is greater than the lower limit value, and when the temperature detected by the second temperature sensor 5 is higher than the upper limit value of the preset temperature range for DPF active regeneration, under the premise of closing the temperature-raising measure, the controller opens the cooler 23, the flow dividing valve 1 opens the air inlet pipe 24 of the exhaust gas cooler 23, reduces or even closes the exhaust gas flow directly leading to the DOC catalyst 4, the exhaust gas cooler 23 starts to work, cools the passing high-temperature exhaust gas until the temperature entering the inlet end of the DPF particle catcher 7 is less than the upper limit value, the DPF enters a normal active regeneration combustion state to rapidly reduce the thickness of a filter layer, meanwhile, the reversing valve 9 opens a bypass pipe 19 and closes a pipeline entering the SCR catalyst 11, the exhaust gas NOx treatment enters an SNCR mode until the controller stops active regeneration when the pressure difference value detected by the first pressure sensor 6 and the second pressure sensor 8 is smaller than a first low preset value of the working condition at that time, a temperature raising measure or a cooler 23 is closed, the DPF enters a passive regeneration combustion state to slowly reduce the thickness of the filter layer, meanwhile, the reversing valve 9 closes the bypass pipe 19 and opens the pipeline entering the SCR catalyst 11, and the exhaust gas NOx treatment is recovered to the SCR mode; when the pressure difference detected by the first pressure sensor 6 and the second pressure sensor 8 is smaller than the second low preset value of the working condition at that time, the reversing valve 3 opens the bypass pipe 20, closes the pipeline entering the DOC catalyst 4, the exhaust gas bypasses the DOC catalyst 4 and directly enters the DPF particle catcher 7, so that the filter layer in the DPF particle catcher 7 is rapidly thickened, and a large amount of tiny particles are prevented from being discharged, until the pressure difference detected by the first pressure sensor 6 and the second pressure sensor 8 is larger than the third low preset value of the working condition at that time, the reversing valve 3 closes the bypass pipe 20, opens the pipeline entering the DOC catalyst 4, and the exhaust gas enters the DPF particle catcher 7 through the DOC catalyst 4 again; after the exhaust gas NOx is treated and enters the SCR mode, when the temperature entering the SCR catalyst 11 and detected by the first temperature sensor 10 is lower than the low preset value of the SCR high-efficiency area, the controller takes a temperature rise measure on the premise of closing the cooler 23 until the temperature entering the SCR catalyst 11 is higher than the low preset value of the SCR high-efficiency area; after the exhaust gas NOx is treated and enters the SCR mode, when the temperature of the exhaust gas entering the SCR catalyst 11 and detected by the first temperature sensor 10 is higher than the high preset value of the SCR high-efficiency area, on the premise of closing a temperature rise measure, the controller starts the cooler 23, the air inlet pipe 24 of the exhaust gas cooler 23 is opened by the diverter valve 1, the flow of the exhaust gas directly leading to the DOC catalyst 4 is reduced or even closed, the exhaust gas cooler 23 starts to work, and the passing high-temperature exhaust gas is cooled until the temperature of the exhaust gas entering the SCR catalyst 11 is lower than the high preset value of the SCR high-efficiency area.

In the exhaust gas aftertreatment system of automotive country 6 according to the present patent, the temperature raising means may be performed in the engine 25, or a heating device may be provided outside the engine 25.

In the exhaust gas aftertreatment system of automobile country 6 in this patent, the heating device may be a fuel injector 21 controlled by a controller mounted on the exhaust pipe front section 2 in front of the reversing valve 3.

In the automobile state 6 exhaust aftertreatment system, the DOC catalyst 4, the SCR catalyst 11 and the ASC ammonia slip catalyst 12 can be composed of a plurality of segments along the axial direction, and the center lines of the honeycomb holes of the segments are parallel to each other or form a wave shape.

In the exhaust aftertreatment system of automobile country 6 described in this patent, the DOC catalytic converter 4, DPF particulate trap 7, SCR catalytic converter 11 and ASC ammonia slip catalytic converter 12, the structure of the carrier thereof may be composed of several pieces in the radial direction.

In the exhaust gas aftertreatment system of automobile country 6 described in this patent, each inlet of DOC catalytic converter 4, DPF particulate trap 7, SCR catalytic converter 11 and ASC ammonia slip catalytic converter 12 may be installed with a flow valve with adjustable carrier intake geometric cross section size, or for SCR catalytic converter 11 and ASC ammonia slip catalytic converter 12, only one flow valve with adjustable carrier intake geometric cross section size may be installed at the inlet of SCR catalytic converter 11; the controller adjusts the size of the geometric section of each flow valve according to the change of the displacement of the engine 25 so as to ensure that the time for the exhaust gas to flow through each device reaches a preset value.

In the exhaust gas after-treatment system of automobile country 6 stated in this patent, the flow valve of the geometric cross-sectional size of said adjustable carrier air inlet, its structure is such: two

valve plates

27, 28 rotating synchronously but in opposite directions are hinged on the exhaust pipe 26 at the inlet of the carrier 29, and an actuator is connected on a valve plate rotating shaft 30 and is controlled by a controller to adjust the section size allowing the exhaust gas to flow between the two valve plates.

In the exhaust gas after-treatment system of automobile country 6 described in this patent, the flow valve of the geometric cross-sectional size of the inlet air of said adjustable carrier, its structure can also be such that: several guide vanes 32 for distributing the exhaust gas uniformly to the whole inlet section of the carrier are fixed in the exhaust pipe 31 at the inlet of the carrier 35; a valve plate 33 is hinged in the flow passage 34 between every two guide vanes; all valve plates rotate synchronously; the rotating shaft 36 of each valve plate is hinged on the exhaust pipe 31; on the valve plate shafts 36, actuators are connected, which are controlled by a controller to adjust the cross-sectional size between each valve plate and one of the side deflectors to allow exhaust gas to flow through.

5. The effect that this patent has:

(1) in the aspect of post-treatment efficiency, the exhaust temperature of all working conditions is controlled, so that the efficiency of each catalyst is maximized as much as possible under all working conditions;

(2) in the aspect of post-treatment efficiency, the airspeeds of all working conditions are controlled, so that the efficiency of each catalyst is maximized as much as possible under all working conditions;

(3) the catalyst of each device is protected at high temperature to prevent the catalyst from sintering, volatilizing, deforming and falling off, so that the efficiency is not reduced, the service life is not shortened, and secondary pollutants of N2O and NH3 are increased;

(4) carrying out high-temperature protection on the DPF to prevent overheating and cause burning of the carrier;

(5) the existence of the DPF minimum filter layer during continuous passive regeneration is controlled to ensure that the emission of fine particulate matters is not greatly increased;

(6) during cold start, the catalyst start time is greatly shortened, so that the catalyst enters a high conversion efficiency state as soon as possible, and pollutants are prevented from being discharged in a large amount for a long time;

(7) all molecules of relevant components of the redox reaction, in the form of low-speed impingement mixing flow entering the DOC, SCR and ASC, have sufficient contact opportunities with the catalyst to achieve maximum efficiency maximization and backpressure minimization at the same time as much as possible;

(8) the urea pyrolysis fully utilizes the self heat of the post-treatment system, thereby not only saving the energy of the engine, but also reducing the temperature of the outlet of the exhaust pipe;

(9) the DOC is always in the high-efficiency temperature range of the reduction reaction and the high-efficiency temperature range of the NO oxidation reaction, and the thickness of a filter layer in the DPF can be continuously eliminated by a large amount of NO2, so that the number of times of active regeneration can be reduced, the energy consumption of the active regeneration can be saved, and the service life of each device can be prolonged.

6. Description of the drawings:

FIG. 1 is a schematic diagram of the automotive country 6 exhaust aftertreatment system of the present patent;

FIG. 2 is a schematic view of a flow valve with adjustable carrier inlet geometry cross-sectional size without flow deflectors;

fig. 3 is a schematic illustration of a flow valve with adjustable carrier inlet geometry cross-sectional size with flow deflectors.

7. The specific implementation mode is as follows:

the patent is further explained by combining the drawings and the embodiments.

As shown in fig. 1, an automobile state 6 exhaust gas post-treatment system comprises an exhaust pipe front section 2, an exhaust pipe rear section 13, a control system, and an exhaust gas cooler 23, a DOC catalytic converter 4, a DPF particle trap 7, an SCR catalytic converter 11, an ASC ammonia escape catalytic converter 12 and a pyrolyzer which are connected in series from front to back between the exhaust pipe front section 2 and the exhaust pipe rear section 13; an air inlet pipe 24 of the waste gas cooler 23 is connected with the front section 2 of the exhaust pipe through the diverter valve 1, and an air outlet pipe 22 of the cooler 23 is fixedly connected to the front section 2 of the exhaust pipe behind the diverter valve 1; the DOC catalyst 4 is connected with a bypass pipe 20 in parallel, the front end of the bypass pipe 20 is connected with the inlet end of the DOC catalyst 4 through a reversing valve 3, and the rear end of the bypass pipe 20 is fixedly connected with the outlet end of the DOC catalyst 4; the SCR catalyst 11 and the ASC ammonia escape catalyst 12 are connected in parallel with a bypass pipe 19, the front end of the bypass pipe 19 is connected with the inlet end of the SCR catalyst 11 through a reversing valve 9, the rear end of the bypass pipe 19 is divided into two

branch pipes

18 and 16, and the two

branch pipes

The pyrolyzer is formed by fixedly connecting a urea liquid input pipe 15, a pyrolysis chamber 17 and an output pipe 14 of the pyrolyzer; a urea liquid input pipe 15 and an output pipe 14 of the pyrolyzer are fixedly connected on a pipe of the rear section 13 of the exhaust pipe; the pyrolysis chamber is arranged in the pipe of the rear section 13 of the exhaust pipe, is isolated from the waste gas in the rear section 13 of the exhaust pipe, and absorbs the heat of the waste gas in the rear section 13 of the exhaust pipe so as to heat the urea solution sprayed into the pyrolysis chamber to be pyrolyzed into ammonia gas; a urea solution nozzle is installed in the inlet pipe 15.

The pyrolysis chamber is a section of spiral pipe.

The outlet end of the output pipe 14 of the pyrolyzer is fixedly connected to the inlet end of the DPF particle trap 7.

The control system comprises a controller, a first temperature sensor 10 arranged at the inlet end of an SCR catalyst 11, a second temperature sensor 5 arranged at the inlet end of a DPF particle catcher 7, a first pressure sensor 6 arranged at the inlet end of the DPF particle catcher and a second pressure sensor 8 arranged at the outlet end of the DPF particle catcher 7, wherein the sensors are connected with the controller through wires; when the pressure difference value detected by the first pressure sensor 6 and the second pressure sensor 8 exceeds the highest preset value 1kpa of the working condition at the time, the temperature detected by the second temperature sensor 5 is lower than the lower limit value 550 DEG of the preset temperature range of DPF active regeneration, the controller opens the fuel injector 21 to increase the temperature on the premise of closing the cooler 23 until the temperature entering the inlet end of the DPF particle catcher 7 is higher than the lower limit value, and when the temperature detected by the second temperature sensor 5 is higher than the upper limit value 600 DEG of the preset temperature range of DPF active regeneration, the controller opens the cooler 23 on the premise of closing the fuel injector 21, the diverter valve 1 opens the air inlet pipe 24 of the exhaust gas cooler 23 to reduce or even close the exhaust gas flow directly leading to the DOC catalyst 4, the exhaust gas cooler 23 starts to work to reduce the temperature of the passing high-temperature exhaust gas, until the temperature entering the inlet end of the DPF particle catcher 7 is smaller than the upper limit value, the DPF enters a normal active regeneration combustion state to rapidly reduce the thickness of a filter layer, meanwhile, the reversing valve 9 opens the bypass pipe 19 and closes a pipeline entering the SCR catalyst 11, the exhaust gas NOx treatment enters an SNCR mode until the controller stops active regeneration when the pressure difference value detected by the first pressure sensor 6 and the second pressure sensor 8 is smaller than a first low preset value 250pa of the current working condition, the fuel injector 21 and the cooler 23 are closed, the DPF enters a passive regeneration combustion state to slowly reduce the thickness of the filter layer, meanwhile, the reversing valve 9 closes the bypass pipe 19 and opens the pipeline entering the SCR catalyst 11, and the exhaust gas NOx treatment is recovered to the SCR mode again; when the pressure difference detected by the first pressure sensor 6 and the second pressure sensor 8 of the controller is smaller than the second low preset value 100pa of the current working condition, the reversing valve 3 opens the bypass pipe 20, closes the pipeline entering the DOC catalyst 4, the exhaust gas bypasses the DOC catalyst 4 and directly enters the DPF particle catcher 7, so that the filter layer in the DPF particle catcher 7 is rapidly thickened, and a large amount of tiny particles are prevented from being discharged, until the pressure difference detected by the first pressure sensor 6 and the second pressure sensor 8 of the controller is larger than the third low preset value 120pa of the current working condition, the reversing valve 3 closes the bypass pipe 20, opens the pipeline entering the DOC catalyst 4, and the exhaust gas enters the DPF particle catcher 7 through the DOC catalyst 4 again; after the exhaust gas NOx is treated and enters an SCR mode, when the temperature of the exhaust gas entering the SCR catalyst 11, which is detected by the first temperature sensor 10, is 280 degrees lower than the low preset value of an SCR high-efficiency area, the controller opens the fuel injector 21 on the premise of closing the cooler 23 until the temperature of the exhaust gas entering the SCR catalyst 11 is higher than the low preset value of the SCR high-efficiency area; after the exhaust gas NOx is treated and enters the SCR mode, when the temperature of the exhaust gas entering the SCR catalyst 11 and detected by the first temperature sensor 10 is 420 degrees higher than the high preset value of the SCR high-efficiency area, on the premise of closing the fuel injector 21, the controller opens the cooler 23, the air inlet pipe 24 of the exhaust gas cooler 23 is opened by the flow dividing valve 1, the flow of the exhaust gas directly leading to the DOC catalyst 4 is reduced or even closed, the exhaust gas cooler 23 starts to work, and the passing high-temperature exhaust gas is cooled until the temperature of the exhaust gas entering the SCR catalyst 11 is lower than the high preset value of the SCR high-efficiency area.

The fuel injector 21 controlled by the controller is arranged on the front section 2 of the exhaust pipe in front of the reversing valve 3.

The DOC catalyst 4, the SCR catalyst 11 and the ASC ammonia escape catalyst 12 are characterized in that the structure of a carrier of the DOC catalyst is composed of 4 sections along the axial direction, and the central lines of honeycomb holes of the sections mutually form a wave shape.

The DOC catalyst 4, the DPF particle catcher 7, the SCR catalyst 11 and the ASC ammonia slip catalyst 12 are arranged in a manner that the structure of the carrier is composed of 5 blocks along the radial direction.

Each inlet of the DOC catalyst 4, the DPF particle catcher 7 and the SCR catalyst 11 is provided with a flow valve which can adjust the geometric cross section of the carrier air inlet; the controller adjusts the size of the geometric section of each flow valve according to the change of the displacement of the engine 25 so as to ensure that the time for the exhaust gas to flow through each device reaches a preset value of 0.1 second.

The flow valve with the adjustable carrier air inlet geometric section size has the following structure: two

valve plates

Claims

1. The automobile state 6 exhaust aftertreatment system is characterized by comprising an exhaust pipe front section 2, an exhaust pipe rear section 13, a control system, and an exhaust gas cooler 23, a DOC (catalyst converter) 4, a DPF (diesel particulate filter) particle catcher 7, an SCR (selective catalytic reduction) catalyst 11, an ASC (ammonia slip catalyst) 12 and a pyrolyzer which are sequentially connected in series from front to back between the exhaust pipe front section 2 and the exhaust pipe rear section 13; an air inlet pipe 24 of the waste gas cooler 23 is connected with the front section 2 of the exhaust pipe through the diverter valve 1, and an air outlet pipe 22 of the cooler 23 is fixedly connected to the front section 2 of the exhaust pipe behind the diverter valve 1; the DOC catalyst 4 is connected with a bypass pipe 20 in parallel, the front end of the bypass pipe 20 is connected with the inlet end of the DOC catalyst 4 through a reversing valve 3, and the rear end of the bypass pipe 20 is fixedly connected with the outlet end of the DOC catalyst 4; the SCR catalyst 11 and the ASC ammonia escape catalyst 12 are connected in parallel with a bypass pipe 19, the front end of the bypass pipe 19 is connected with the inlet end of the SCR catalyst 11 through a reversing valve 9, the rear end of the bypass pipe 19 is divided into two branch pipes 18 and 16, and the two branch pipes 18 and 16 are respectively and fixedly connected to the rear section 13 of the exhaust pipe at the front and the rear of the pyrolyzer.

2. The automobile state 6 exhaust gas post-treatment system according to claim 1, wherein the pyrolyzer is formed by fixedly connecting a urea liquid input pipe 15, a pyrolysis chamber 17 and an output pipe 14 of the pyrolyzer; a urea liquid input pipe 15 and an output pipe 14 of the pyrolyzer are fixedly connected on a pipe of the rear section 13 of the exhaust pipe; the pyrolysis chamber is arranged in the pipe of the exhaust pipe rear section 13, is isolated from the exhaust gas in the exhaust pipe rear section 13, and absorbs the heat of the exhaust gas in the exhaust pipe rear section 13 to heat the urea solution sprayed into the pyrolysis chamber 17 to be pyrolyzed into ammonia gas; a urea solution nozzle is installed in the inlet pipe 15.

3. The automotive exhaust aftertreatment system of claim 2 wherein the pyrolysis chamber 17 comprises a section of coiled tubing.

4. The exhaust gas after-treatment system according to claim 2, wherein the outlet end of the outlet pipe 14 of the pyrolyzer is fixed to the inlet or outlet end of the DPF particulate trap 7.

5. The automotive exhaust gas post-treatment system according to claim 1, wherein the control system comprises a controller, a first temperature sensor 10 installed at an inlet end of the SCR catalyst 11, a second temperature sensor 5 installed at an inlet end of the DPF particulate trap 7, a first pressure sensor 6 installed at an inlet end of the DPF particulate trap 7, and a second pressure sensor 8 installed at an outlet end of the DPF particulate trap 7, and each sensor is connected to the controller by an electric wire; when the pressure difference value detected by the first pressure sensor 6 and the second pressure sensor 8 exceeds the highest preset value of the working condition at that time, the temperature detected by the second temperature sensor 5 is lower than the lower limit value of the preset temperature range for DPF active regeneration, under the premise of closing the cooler 23, the controller takes a temperature raising measure until the temperature entering the inlet end of the DPF particle catcher 7 is larger than the lower limit value, and when the temperature detected by the second temperature sensor 5 is higher than the upper limit value of the preset temperature range for DPF active regeneration, under the premise of closing the temperature raising measure, the controller opens the cooler 23, the diverter valve 1 opens the air inlet pipe 24 of the exhaust gas cooler 23, reduces or even closes the flow rate of the exhaust gas directly leading to the DOC catalyst 4, the exhaust gas cooler 23 starts to work, cools the passing high-temperature exhaust gas until the temperature entering the inlet end of the DPF particle catcher 7 is smaller than the upper limit value, the DPF enters a normal active regeneration combustion state to rapidly reduce the thickness of a filter layer, meanwhile, the reversing valve 9 opens a bypass pipe 19 and closes a pipeline entering the SCR catalyst 11, the exhaust gas NOx treatment enters an SNCR mode until the controller stops active regeneration when the pressure difference value detected by the first pressure sensor 6 and the second pressure sensor 8 is smaller than a first low preset value of the working condition at that time, a temperature raising measure or a cooler 23 is closed, the DPF enters a passive regeneration combustion state to slowly reduce the thickness of the filter layer, meanwhile, the reversing valve 9 closes the bypass pipe 19 and opens the pipeline entering the SCR catalyst 11, and the exhaust gas NOx treatment is recovered to the SCR mode; when the pressure difference detected by the first pressure sensor 6 and the second pressure sensor 8 is smaller than the second low preset value of the working condition at that time, the reversing valve 3 opens the bypass pipe 20, closes the pipeline entering the DOC catalyst 4, the exhaust gas bypasses the DOC catalyst 4 and directly enters the DPF particle catcher 7, so that the filter layer in the DPF particle catcher 7 is rapidly thickened, and a large amount of tiny particles are prevented from being discharged, until the pressure difference detected by the first pressure sensor 6 and the second pressure sensor 8 is larger than the third low preset value of the working condition at that time, the reversing valve 3 closes the bypass pipe 20, opens the pipeline entering the DOC catalyst 4, and the exhaust gas enters the DPF particle catcher 7 through the DOC catalyst 4 again; after the exhaust gas NOx is treated and enters the SCR mode, when the temperature entering the SCR catalyst 11 and detected by the first temperature sensor 10 is lower than the low preset value of the SCR high-efficiency area, the controller takes a temperature rise measure on the premise of closing the cooler 23 until the temperature entering the SCR catalyst 11 is higher than the low preset value of the SCR high-efficiency area; after the exhaust gas NOx is treated and enters the SCR mode, when the temperature of the exhaust gas entering the SCR catalyst 11 and detected by the first temperature sensor 10 is higher than the high preset value of the SCR high-efficiency area, on the premise of closing a temperature rise measure, the controller starts the cooler 23, the air inlet pipe 24 of the exhaust gas cooler 23 is opened by the diverter valve 1, the flow of the exhaust gas directly leading to the DOC catalyst 4 is reduced or even closed, the exhaust gas cooler 23 starts to work, and the passing high-temperature exhaust gas is cooled until the temperature of the exhaust gas entering the SCR catalyst 11 is lower than the high preset value of the SCR high-efficiency area.

6. The automotive 6 exhaust gas after-treatment system according to claim 5, wherein the warming means may be performed in the engine 25 or a heating device may be provided outside the engine 25.

7. The automobile 6 exhaust gas after-treatment system according to claim 6, wherein the heating device is a fuel injector 21 which is arranged on the exhaust pipe front section 2 in front of the reversing valve 3 and is controlled by a controller.

8. The automobile state 6 exhaust gas after-treatment system according to claim 1, wherein the DOC catalyst 4, the SCR catalyst 11 and the ASC ammonia slip catalyst 12 have a carrier structure which is composed of a plurality of segments along the axial direction, and the center lines of the honeycomb holes of the segments are parallel to each other or form a wave shape.

9. The automotive exhaust aftertreatment system of claim 1, wherein the DOC catalyst 4, DPF particulate trap 7, SCR catalyst 11 and ASC ammonia slip catalyst 12 are supported on a carrier structure consisting of several pieces in the radial direction.

10. The automotive exhaust aftertreatment system of claim 1, wherein each inlet of the DOC catalyst 4, the DPF particulate trap 7, the SCR catalyst 11 and the ASC ammonia slip catalyst 12 may be installed with a flow valve with adjustable carrier intake geometric cross section size, or for the SCR catalyst 11 and the ASC ammonia slip catalyst 12, only one flow valve with adjustable carrier intake geometric cross section size may be installed at the inlet of the SCR catalyst 11; the controller adjusts the size of the geometric section of each flow valve according to the change of the displacement of the engine 25 so as to ensure that the time for the exhaust gas to flow through each device reaches a preset value.

11. The automotive country 6 exhaust aftertreatment system of claim 10 wherein the flow valve of adjustable carrier inlet geometric cross-sectional size is configured such that: two valve plates 27, 28 rotating synchronously but in opposite directions are hinged on the exhaust pipe 26 at the inlet of the carrier 29, and an actuator is connected on a valve plate rotating shaft 30 and is controlled by a controller to adjust the section size allowing the exhaust gas to flow between the two valve plates.

12. The automotive exhaust aftertreatment system of claim 10 wherein the adjustable carrier inlet geometry cross-sectional size flow valve is further configured to: several guide vanes 32 for distributing the exhaust gas uniformly to the whole inlet section of the carrier are fixed in the exhaust pipe 31 at the inlet of the carrier 35; a valve plate 33 is hinged in the flow passage 34 between every two guide vanes; all valve plates rotate synchronously; the rotating shaft 36 of each valve plate is hinged on the exhaust pipe 31; on the valve plate shafts 36, actuators are connected, which are controlled by a controller to adjust the cross-sectional size between each valve plate and one of the side deflectors to allow exhaust gas to flow through.