KR101558760B1 - Apparatus and method for diagnosing deterioration rate of selective catalytic reduction in vehicle - Google Patents

Abstract

The present invention relates to an apparatus for diagnosing deterioration of a catalyst for selective catalytic reduction and a method therefor. The present invention measures the temperature of a front end and a rear end of a catalyst for selective catalytic reduction to measure deterioration of the catalyst. According to the present invention, an inlet temperature sensor (21) and an outlet temperature sensor (22) are installed in an inlet and an outlet of the catalyst for selective catalytic reduction (13), respectively. The method for diagnosing deterioration of a catalyst for selective catalytic reduction comprises: a vehicle ignition step (S110) where a vehicle is started; a temperature measurement step (S130) measuring the inlet temperature (TSCR_in) and the outlet temperature (TSCR_out); a temperature accumulation step (S140) calculating temperature accumulation from temperature inversion time (ts) to temperature re-inversion time (tf); and a deterioration determination step (S150) determining that the catalyst for selective catalytic reduction (13) is deteriorated when the temperature accumulation does not reach the deterioration determination temperature accumulation (b).

Description

[0001] APPARATUS AND METHOD FOR DIAGNOSING DETERIORATION RATE OF SELECTIVE CATALYTIC REDUCTION IN VEHICLE [0002]

The present invention relates to a selective reduction catalyst for post-treating nitrogen oxides contained in exhaust gas of a vehicle, and more particularly, to a catalyst for reducing NOx contained in exhaust gas of a vehicle by measuring the temperatures of the front end and the rear end of the selective reduction catalyst and the selective reduction catalyst, And more particularly, to a deterioration diagnosis apparatus and method for a selective reduction catalyst for diagnosing degradation.

A selective catalytic reduction (SCR) is installed behind the lean NOx trap (LNT) to reduce nitrogen oxides (NOx) in the exhaust gas discharged from the engine mounted on the vehicle.

At this time, the SCR is installed in the rear of the LNT in the form of SDPF (SCR on DPF) formed integrally with DPF (Diesel Particulate Filter) or separately provided from the DPF, and is installed in the order of LNT-DPF-SCR, The NOx contained in the gas is reduced.

In order to measure the degree of deterioration of the SCR, the NOx sensor is installed on the inlet side and the outlet side of the SCR, and the NOx is measured directly at the inlet and the outlet of the SCR, It is determined whether or not the SCR deteriorates.

Even when the SDPF is applied, the NOx sensor is directly installed at the inlet and the outlet of the SDPF to directly measure the NOx at the inlet and the outlet of the SDPF to determine the deterioration of the SDPF.

The method of directly measuring the amount of NOx by the NOx sensor in order to determine the degree of deterioration of SCR or SDPF is highly accurate, but the expensive NOx sensor must be installed at the inlet and the outlet of the SCR or SDPF, respectively , The exhaust gas treatment system becomes expensive, which causes a rise in the production cost of the vehicle.

The following prior art document relates to a 'catalyst deterioration diagnosis apparatus' and a configuration for installing an exhaust sensor for detecting the concentration of nitrogen oxides in order to measure the degree of deterioration of a rear end oxidation catalyst provided at the rear end of the selective reduction catalyst It is individual.

JP2012-036858A

DISCLOSURE OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and it is an object of the present invention to provide a zeolite-selective selective reduction catalyst or zeolite whose temperature is raised when moisture is supplied from SDPF, And a method for diagnosing degradation of a selective reduction catalyst capable of diagnosing degradation of a reducing catalyst or SDPF.

In accordance with another aspect of the present invention, there is provided an apparatus for diagnosing deterioration of a selective reduction catalyst, comprising: a selective reduction catalyst device installed to post-treat an exhaust gas discharged from an engine, The selective reduction from the temperature inversion time at which the temperature of the outlet is higher than the temperature at the inlet of the selective reduction catalyst after the start of the vehicle to the temperature inversion time at which the temperature of the inlet is higher than the temperature of the outlet of the selective reduction catalyst, An inlet temperature sensor and an outlet temperature sensor are installed at the inlet and the outlet of the selective reduction catalyst, respectively, in order to diagnose the deterioration degree of the selective reduction catalyst by the temperature accumulation amount of the outlet of the catalyst.

An internal temperature sensor is installed inside the selective reduction catalyst in order to use the catalyst temperature of the selective reduction catalyst instead of the temperature of the outlet of the selective reduction catalyst.

Wherein the selective reduction catalyst is a zeolite catalyst.

The diesel selective reduction catalyst is characterized by being coated inside a diesel particulate filter (DPF).

And the temperature of the inlet and the outlet of the selective reduction catalyst is input from the inlet temperature sensor and the outlet temperature sensor to compare the temperature accumulation amount of the selective reduction catalyst with the predetermined deterioration determination temperature accumulation amount, And a control unit for determining whether or not the signal is transmitted.

The control unit may further include a warning lamp that is lit when the control unit determines that the selective reduction catalyst is deteriorated.

A temperature measuring step of measuring an inlet temperature which is the temperature of the exhaust gas flowing into the selective reduction catalyst and an outlet temperature which is a temperature of the exhaust gas discharged from the selective reduction catalyst, The temperature accumulation amount is calculated by accumulating the difference between the outlet temperature and the inlet temperature until the temperature inversion time, which is the first time when the inlet temperature exceeds the outlet temperature, from the temperature inversion time which is the time when the outlet temperature exceeds the inlet temperature And a deterioration determining step of determining that the selective reduction catalyst is deteriorated if the temperature accumulation amount does not reach a predetermined deterioration determination temperature accumulation amount that the selective reduction catalyst is deteriorated.

And a diagnosis start judgment step of judging whether or not the temperature of the coolant is lower than a predetermined diagnosis start coolant temperature before the temperature measurement step is performed.

And the diagnosis starting coolant temperature is set to 37 캜 to 43 캜.

And the temperature inversion time and the temperature inversion time are determined from the inlet temperature and the outlet temperature of the selective reduction catalyst which has not deteriorated.

And the deterioration judgment temperature accumulation amount is set to 470 ° C to 530 ° C.

A deterioration determination step of determining that the selective reduction catalyst is deteriorated if the temperature accumulation amount is smaller than the deterioration determination temperature accumulation amount in the deterioration determination step; and a warning light for indicating deterioration of the selective reduction catalyst in the vehicle interior Further comprising a deterioration warning step.

And determining that the selective reduction catalyst is not deteriorated and is normal if the temperature accumulation amount is not smaller than the deterioration determination temperature accumulation amount in the deterioration determination step.

The catalyst temperature inside the selective reduction catalyst is measured in the temperature measurement step and the temperature accumulation amount is calculated at the catalyst temperature instead of the outlet temperature in the temperature accumulation step.

Wherein the selective reduction catalyst is a zeolite catalyst.

The diesel selective reduction catalyst is characterized by being coated inside a diesel particulate filter (DPF).

According to the apparatus for deterioration diagnosis of a selective reduction catalyst according to the present invention and the method therefor, the temperature sensor, which is inexpensive compared to the NOx sensor, can be installed inside the DPF having the selective reduction catalyst or the selective reduction catalyst, The deterioration of the selective reduction catalyst can be diagnosed by monitoring the accumulated temperature difference.

By using an inexpensive temperature sensor in diagnosing the degree of deterioration of the selective reduction catalyst, it is possible to reduce the production cost of the exhaust gas treatment system and the vehicle to which the exhaust gas treatment system is applied.

1 is a block diagram illustrating an apparatus for diagnosing degradation of a selective reduction catalyst according to an embodiment of the present invention;
2 is a block diagram illustrating an apparatus for diagnosing degradation of a selective reduction catalyst according to another embodiment of the present invention.
3 is a graph showing the temperature at the inlet of the selective reduction catalyst and the temperature at the outlet of the selective reduction catalyst according to the degree of deterioration.
4 is a graph showing the difference between the outlet temperature and the inlet temperature from the temperature reversal time to the temperature reversion time.
5 is a flowchart illustrating a method for diagnosing deterioration of a selective reduction catalyst according to an embodiment of the present invention.
6 is a flowchart showing a method for diagnosing deterioration of a selective reduction catalyst according to another embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings.

Degradation diagnostic apparatus for the selective reduction catalyst according to the present invention, the selective reduction by each measuring the temperature of the inlet and outlet of the catalyst 13, and after the vehicle start-up temperature (T _{SCR _} of the inlet of the selective reduction catalyst 13 _in ) than the temperature of the outlet (t _{SCR _ out),} the temperature (t _{SCR _ in} the inlet than the higher temperature inversion time (t _s) back to the selective temperature (t _{SCR _ out} of the outlet of the reducing catalyst (13)) from) the the higher temperature material reversal time (t _f) the selective reduction catalyst the selective reduction catalyst 13, the temperature of the inlet in order to diagnose the deterioration degree of the selective reduction catalyst 13 in the temperature accumulation amount of the exit of the 13 to An inlet temperature sensor (21) and an outlet temperature sensor (22) are provided at an inlet and an outlet, respectively.

1, the exhaust gas discharged from the engine 10 includes an LNT (Lean NOx Trap) 11, a DPF (Diesel Particulate Filter) 12, a selective catalytic reduction (SCR) And then discharged to the outside in a purified state.

The selective reduction catalyst 13 purifies the NOx contained in the exhaust gas. The deterioration efficiency of the selective reduction catalyst 13 decreases as the deterioration progresses in the initial state. Therefore, the deterioration degree of the selective reduction catalyst 13 must be continuously monitored. As described above, the NOx sensor is installed at the inlet and the outlet of the selective reduction catalyst 13, respectively, The deterioration degree of the selective reduction catalyst 13 is measured by measuring the temperature of the inlet and the outlet of the selective reduction catalyst 13. The temperature of the inlet and the outlet of the selective reduction catalyst 13 are measured indirectly, Is measured.

The selective reduction catalyst 13 to which zeolite is applied in the selective reduction catalyst 13 has a characteristic of generating heat when water is supplied. That is, when moisture generated by the combustion in the engine 10 is adsorbed to the selective reduction catalyst 13, the moisture and the selective reduction catalyst 13 are separated by the zeolite constituting the selective reduction catalyst 13 Heat is generated.

In the selective reduction catalyst 13, the degree of exothermicity varies depending on the degree of deterioration. In the absence of degradation, the surface area is increased to increase the exothermic amount and the exothermic temperature. As the deterioration progresses, the surface area decreases and the exothermic amount and the exothermic temperature are lowered .

The present invention indirectly measures the degree of deterioration of the selective reduction catalyst 13 by using such a characteristic. That is, at the initial stage of startup, the temperature of the inlet of the selective reduction catalyst 13 is higher than the temperature of the outlet by the heat transfer by the exhaust gas discharged from the engine 10. However, the engine 10 is driving the selective reduction catalyst 13 is more than the exit temperature, while heating by absorption of moisture, the selective reduction catalyst 13. At one point the inlet temperature (T _{SCR _ in)} as (T the _{SCR _ out)} is high.

Also, as the exhaust gas is continuously introduced into the selective reduction catalyst 13, the temperature of the inlet of the selective reduction catalyst 13 heated by the exhaust gas becomes higher than the outlet.

In this way, the selective reduction catalyst 13, the top of the inlet temperature (T _{SCR _ in)} and an outlet temperature inversion and re-inversion the selective reduction catalyst 13 by the use of the (T _{SCR _ out)} operate on or not, i.e., The degree of deterioration is determined.

To this end, in an apparatus for diagnosing deterioration of selective reduction catalyst according to an embodiment of the present invention, an inlet temperature sensor 21 is installed on the inlet side to measure the temperatures of the inlet and the outlet of the selective reduction catalyst 13 , And an outlet temperature sensor (22) is provided at the outlet side. By using the inlet temperature sensor 21 and the outlet temperature sensor 22, the degree of deterioration of the selective reduction catalyst 13 can be indirectly determined.

On the other hand, the outlet temperature of the selective reduction catalyst 13 is directly affected by the temperature inside the selective reduction catalyst 13, so that it can be regarded as being substantially the same. Therefore, in order to determine the degree of deterioration, the internal temperature of the selective reduction catalyst 13 may be used in place of the outlet temperature of the selective reduction catalyst 13. To this end, (23) can be installed.

The control unit 30 receives the temperatures measured by the inlet temperature sensor 21 and the outlet temperature sensor 22 and determines the degree of deterioration of the selective reduction catalyst 13. [ The control unit 30 is the inlet temperature with time (T _{SCR _ in)} and outlet temperature (T _{SCR _ out)} for receiving input, the outlet temperature (T _{SCR _ out)} is the inlet temperature (T _{SCR _ in)} than the higher temperature reversed by accumulating the difference between the time (t _s) from time to be again the temperature is re-inverted (t _f) the outlet temperature (T _{SCR _ out)} and the inlet temperature (T _{SCR _ in)} up, the deterioration degree of the selective reduction catalyst .

The temperature reversal and the temperature reversal in the selective reduction catalyst 13 become higher as the deterioration progresses less and the time continues for a longer time. In FIG. 3, the 'fresh' state in which no deterioration occurs, Aged 'state, and' Damaged 'state in which the degradation is severely progressed.

The control unit 30 operates the warning means provided in the vehicle interior to allow the driver to recognize when the deterioration degree of the selective reduction catalyst 13 is equal to or higher than the reference value.

For example, when the deterioration of the selective reduction catalyst 13 exceeds the set reference, the warning lamp 31 on the instrument panel is turned on so that the driver recognizes that the selective reduction catalyst 13 is deteriorated.

FIG. 2 shows an apparatus for diagnosing deterioration of a selective reduction catalyst according to another embodiment of the present invention.

1, the selective reduction catalyst is not provided independently of the DPF 12, but a selective reduction catalyst component is coated in the DPF, and the DPF 12 and the selective reduction catalyst 13 And can be applied in the form of SDPF (SCR on DPF) which performs the functions simultaneously.

In the present embodiment, the temperature of the inlet and the outlet of the SDPF are measured to measure the deterioration of the selective reduction catalyst component coated inside the SDPF 15. The inlet and the outlet of the SDPF 15 are respectively connected to the inlet A temperature sensor 21 and an outlet temperature sensor 22 are provided.

An internal temperature sensor 23 may be provided in the SDPF 15 to measure the internal temperature of the SDPF 15 instead of the outlet temperature measured by the outlet temperature sensor 22 .

1 and 2, a reference numeral 24 denotes a DPF temperature sensor for measuring the temperature of the exhaust gas discharged from the LNT 11 and flowing into the DPF 12 or the SDPF 15.

Hereinafter, a method for diagnosing deterioration of the selective reduction catalyst according to an embodiment of the present invention will be described with reference to FIG.

Degradation diagnosis method of the selective reduction catalyst according to the invention, the temperature of the inlet temperature of the exhaust gas flowing into the selective reduction catalyst 13 (T _{SCR _ in)} and the temperature of the exhaust gas discharged from the selective reduction catalyst (13) the outlet temperature (T _{SCR _ out)} for measuring the temperature measuring step of (S130) and, first the outlet temperature after the vehicle start (T _{SCR _ out)} is a time exceeding the inlet temperature (T _{SCR _ in)} temperature inversion time (t _s) back to the inlet temperature from (t _{SCR _ in)} that the outlet temperature (t _{SCR _ out)} to beyond and the outlet temperature (t _{SCR _ out)} to the first time-temperature re-reversal time (t _f) and temperature accumulation step (S140) by accumulating the difference between the inlet temperature (T _{SCR _ in)} for calculating a temperature accumulation, the temperature accumulation deterioration judgment temperature accumulation previously set to be the selective reduction catalyst 13 is deteriorated (b ), The selective reduction catalyst (13) is deteriorated And a deterioration determining step (S150) determines that.

The diagnosis start determination step (S120) determines whether the condition for measuring the degree of deterioration of the selective reduction catalyst (13) is satisfied after the vehicle is started (S110) before determining the degree of deterioration of the selective reduction catalyst (13).

That is, since it is difficult to determine whether or not the catalyst deteriorates due to other factors during driving, the selective reduction catalyst 13 must be performed immediately after the vehicle is started. To this end, the cooling water temperature of the vehicle is set to a predetermined diagnosis start- a).

If the temperature of the cooling water is higher than the diagnosis starting cooling water temperature (a), it is difficult to judge the deterioration of the selective reduction catalyst 13 by other factors, so that the cooling water temperature is lower than the diagnosis starting cooling water temperature , The degree of deterioration of the selective reduction catalyst (13) is determined.

Here, the diagnosis start coolant temperature (a) may be set to 37 캜 to 43 캜, preferably 40 캜.

The temperature measurement step S130 is performed by using the inlet temperature sensor 21 and the outlet temperature sensor 22 provided at the inlet and the outlet of the selective reduction catalyst 13, and of the inlet temperature (T _{SCR _ in)} the temperature of the outlet temperature (T _{SCR _ out)} the temperature of the exhaust gas discharged from the selective reduction catalyst (13) are measured. The method for diagnosing deterioration of the selective reduction catalyst according to the present invention uses the characteristic that the selective reduction catalyst 13 generates heat when moisture is adsorbed to the selective reduction catalyst 13 to which the zeolite is applied, ) as the input value for determining whether the degradation of the selective reduction catalyst 13, and measures the inlet temperature (T _{SCR _ in)} and outlet temperature (T _{SCR _ out)} of the selective reduction catalyst (13).

Temperature Cumulative step (S140) will be the first to the outlet temperature (T _{SCR _ out)} is the inlet temperature (T _{SCR _ in)} to beyond the time the temperature inversion time (t _s) from said temperature inversion time (t after the start of the vehicle _s) after the inlet temperature first back on (T _{SCR _ in)} that the outlet temperature (T _{SCR _ out)} to beyond time and temperature re-reversal time (t _f) the outlet temperature (T _{SCR _ out)} to the above It accumulates the difference between the inlet temperature (T _{_ in SCR).}

For example, the difference between the outlet temperature (T _{SCR _ out)} and the inlet temperature (T _{SCR _ in)} is - can be represented by 'T _{SCR _ out} T _{SCR _ in',} since this temperature inversion time (t _s) bars, stacked material to a temperature reversal time (t _f), the temperature accumulation can be expressed by the following equation.

Referring to FIG. 3, as the selective reduction catalyst 13 deteriorates, the surface area of the selective reduction catalyst 13 decreases, so that the amount of heat generated and the temperature of heat generated by the selective reduction catalyst 13 decrease, (t _s ) increases from the vehicle start, and the temperature re-turning time (t _f ) approaches from the vehicle start (see arrows in Fig. 3).

Further, the difference between the As, said temperature inversion time (t _s) from temperature re-reversal time (t _f) the outlet temperature (T _{SCR _ out)} and the inlet temperature (T _{SCR _ in)} of up shown in Figure 4 , That is, the temperature accumulation amount.

On the other hand, determined from said temperature inversion time (t _s) and temperature re-reversal time (t _f) is the inlet temperature of the non-degraded selective reduction catalyst _{(13) (T SCR _ in} ) and outlet temperature (T _{SCR _ out)} It becomes.

The deterioration determination step S150 compares the temperature accumulation amount with the deterioration determination temperature accumulation amount b previously set to deteriorate the selective reduction catalyst 13 to determine whether the selective reduction catalyst 13 is deteriorated.

The selective reduction catalyst 13 is deteriorated and the selective reduction catalyst 13 is not sufficiently heated if the temperature accumulation amount obtained in the temperature accumulation step S140 does not reach the deterioration determination temperature accumulation amount b, It is determined that the selective reduction catalyst 13 is deteriorated.

If the temperature accumulation amount obtained in the temperature accumulation step S140 reaches or exceeds the deterioration determination temperature accumulation amount b, the selective reduction catalyst 13 is not deteriorated and the selective reduction catalyst 13 is sufficiently heated It is determined that the selective reduction catalyst 13 is not deteriorated.

For example, in FIG. 4, in the state where the selective reduction catalyst 13 is not deteriorated (fresh), the temperature accumulation amount is about 1000 ° C., while the temperature accumulation amount is about 670 ° C. , The temperature accumulation amount decreases as the deterioration progresses. The deterioration judgment temperature accumulation amount (b) may be set to 470 ° C to 530 ° C, preferably to 500 ° C. Therefore, it is judged that the temperature accumulation amount is degraded when the temperature accumulation amount is lower than 500 캜.

When determining whether the selective reduction catalyst 13 is deteriorated in the deterioration determination step S150, it is determined whether the selective reduction catalyst 13 is normal or the selective reduction catalyst 13 is deteriorated The deterioration determination step S170 is performed.

After the deterioration confirmation step S170 is performed, a deterioration warning step S180 is performed to allow the driver to easily recognize the deterioration of the selective reduction catalyst 13. In the deterioration warning step (S180), the warning means installed in the vehicle interior is operated so that the driver recognizes the deteriorated state of the selective reduction catalyst (13). For example, the warning lamp 31 installed on the instrument panel is turned on to allow the driver to recognize the deterioration of the selective reduction catalyst 13.

In the deterioration diagnosis method of the selective reduction catalyst of the present invention, the deterioration degree of the selective reduction catalyst is determined by using the temperatures of the inlet and outlet of the selective reduction catalyst 13. However, the selective reduction catalyst 13 and the DPF 12, The temperature of the inlet and the outlet of the SDPF 15 may be used.

Meanwhile, FIG. 6 shows a method for diagnosing deterioration of the selective reduction catalyst according to another embodiment of the present invention.

Instead of this embodiment, the same as the method for assessing deterioration of the selective reduction catalyst according to an embodiment of the present invention discussed above, by default, however, the outlet temperature (T _{SCR _ out)} in the selective reduction catalyst 13 or SDPF (15) And uses the catalyst temperature (T _SCR ) therein. That is, instead of the outlet temperature (T _{SCR _ out)} in the "the selective reduction catalyst 13 or SDPF measure the catalyst temperature of 15, and the temperature accumulation step (S140 in) temperature measuring step (S130), The temperature accumulation can be calculated using the catalyst temperature (T _SCR ). Thus, by using the catalyst temperature (T _SCR), a temperature reversal time (t _s) from temperature re-reversal time (t _f) the deterioration determination in the catalyst temperature step (S150 ') to (T _SCR) and the inlet temperature (T obtaining the sum of the difference between _{SCR _ in)} to determine whether the degradation of the selective reduction catalyst component coated on the inside of the selective reduction catalyst 13 or the SDPF (15).

10: Engine 11: LNT
12: DPF 13: SCR
15: SDPF 21: inlet temperature sensor
22: outlet temperature sensor 23: internal temperature sensor
24: DPF temperature sensor 30:
31: Warning light T _{SCR _ in} : Inlet temperature
T _{SCR _ out} : outlet temperature T _SCR : catalyst temperature
t _s : temperature inversion time t _f : temperature inversion time
S110: vehicle start-up step S120: diagnosis start judgment step
S130: Temperature measurement step S140: Temperature accumulation step
S150: deterioration determination step S160: normal determination step
S170: deterioration confirmation step S180: deterioration warning step

Claims (16)

A selective reduction catalyst device installed to post-treat an exhaust gas discharged from an engine,
The temperature of the inlet of the selective reduction catalyst is measured and the temperature of the inlet is again lower than the temperature of the outlet of the selective reduction catalyst from the temperature inversion time at which the temperature of the outlet becomes higher than the temperature of the inlet of the selective reduction catalyst after starting the vehicle An inlet temperature sensor and an outlet temperature sensor are provided at the inlet and the outlet of the selective reduction catalyst, respectively, in order to diagnose the deterioration degree of the selective reduction catalyst by the temperature accumulation amount of the outlet at the inlet of the selective reduction catalyst up to the temperature re- Wherein the deterioration diagnosis apparatus further comprises:
The method according to claim 1,
Wherein an internal temperature sensor is installed inside the selective reduction catalyst to use the catalyst temperature of the selective reduction catalyst instead of the temperature of the outlet of the selective reduction catalyst.
The method according to claim 1,
Wherein the selective reduction catalyst is a zeolite catalyst.
The method according to claim 1,
Wherein the desorption selective reduction catalyst is coated inside a DPF (Diesel Particulate Filter).
The method according to claim 1,
And the temperature of the inlet and the outlet of the selective reduction catalyst is input from the inlet temperature sensor and the outlet temperature sensor to compare the temperature accumulation amount of the selective reduction catalyst with the predetermined deterioration determination temperature accumulation amount, Wherein the deterioration diagnostic apparatus further comprises a control unit for determining whether or not the selective reduction catalyst is deteriorated.
6. The method of claim 5,
Wherein the control unit further includes a warning lamp that lights up when the control unit determines that the selective reduction catalyst is deteriorated.
A vehicle starting step in which the vehicle is started,
A temperature measuring step of measuring an inlet temperature which is a temperature of the exhaust gas flowing into the selective reduction catalyst and an outlet temperature which is a temperature of the exhaust gas discharged from the selective reduction catalyst,
The difference between the outlet temperature and the inlet temperature is accumulated until the temperature reversal time, which is the first time after the inlet temperature exceeds the outlet temperature, from the temperature reversal time which is the time when the outlet temperature exceeds the inlet temperature for the first time after the start of the vehicle A temperature accumulating step of calculating a temperature accumulation amount,
And a deterioration determining step of determining that the selective reduction catalyst is deteriorated if the temperature accumulation amount does not reach the predetermined deterioration determination temperature accumulation amount due to deterioration of the selective reduction catalyst.
8. The method of claim 7,
Further comprising a diagnosis start determination step of determining whether the temperature of the cooling water is lower than a predetermined diagnosis start cooling water temperature before the temperature measurement step is performed.
9. The method of claim 8,
Wherein the temperature measuring step is performed when the temperature of the cooling water is lower than a predetermined diagnosis starting cooling water temperature.
8. The method of claim 7,
The temperature inversion time and the temperature inversion time may be,
Wherein the temperature of the selective reduction catalyst is determined from the inlet temperature and the outlet temperature of the non-degraded selective reduction catalyst.
8. The method of claim 7,
Wherein the degradation determination temperature accumulation amount is set to 470 캜 to 530 캜.
8. The method of claim 7,
A deterioration determination step of determining that the selective reduction catalyst is deteriorated if the temperature accumulation amount is smaller than the deterioration determination temperature accumulation amount in the deterioration determination step;
Further comprising a deterioration warning step for causing a warning lamp for indicating deterioration of the selective reduction catalyst to light up in the vehicle interior.
8. The method of claim 7,
And determining that the selective reduction catalyst is not deteriorated and is normal if the temperature accumulation amount is not smaller than the deterioration determination temperature accumulation amount in the deterioration determination step.
8. The method of claim 7,
Measuring the catalyst temperature inside the selective reduction catalyst in the temperature measurement step,
Wherein the temperature accumulation step calculates a temperature accumulation amount at the catalyst temperature instead of the outlet temperature.
8. The method of claim 7,
Wherein the selective reduction catalyst is a zeolite catalyst.
8. The method of claim 7,
Wherein the oxidation selective reduction catalyst is coated inside DPF (Diesel Particulate Filter).

Images