KR102529523B1 - Method for controlling urea supply of exhaust purification apparatus for vehicle - Google Patents

Abstract

The present invention relates to a method for controlling the supply of urea in an exhaust purification system for a vehicle, and more particularly, to improve the performance and efficiency of the exhaust purification system by precisely controlling the supply of urea used for purification of exhaust gas. It relates to a supply control method.

Description

Method for controlling urea supply of exhaust purification apparatus for vehicle {Method for controlling urea supply of exhaust purification apparatus for vehicle}

The present invention relates to a method for controlling the supply of urea in an exhaust purification system for a vehicle, and more particularly, to improve the performance and efficiency of the exhaust purification system by precisely controlling the supply of urea used for purification of exhaust gas. It relates to a supply control method.

In general, exhaust gas discharged from an engine through an exhaust manifold is guided to a catalytic converter connected to an exhaust pipe, purified, passes through a muffler, reduces noise, and then is released into the atmosphere through a tail exhaust pipe.

One of the catalyst types applied to the catalytic converter is a selective catalytic reduction (SCR). The selective catalytic reduction device catalyzes nitrogen oxides (NOx) contained in engine exhaust gas with a reducing agent, converts them into N2 and H2O, and discharges them through the exhaust pipe.

The selective catalytic reduction device (hereinafter, referred to as 'SCR converter') uses ammonia (NH3) as a reducing agent to purify NOx, and uses NH3 generated as urea (NH2CONH2) injected upstream thereof is decomposed to generate NOx. is selectively reduced.

Meanwhile, in the SCR converter, an injection amount of additional urea is determined based on the stored amount of ammonia stored in the SCR converter. The ammonia storage amount is calculated based on the amount of urea injected upstream of the SCR converter and the amount of ammonia consumed according to the amount of nitrogen oxide purification, and the amount of nitrogen oxide purification is calculated by the nitrogen oxide purification rate value determined by pre-established map data. do.

Further, the nitrogen oxide purification rate in an actual vehicle is different when urea is injected upstream of the SCR converter and when urea is not injected even though the amount of stored ammonia stored in the SCR converter is the same. Also, in a real vehicle, conditions in which urea is injected upstream of the SCR converter and conditions in which urea is not injected alternately occur.

However, since the currently used nitrogen oxide purification rate determination map was constructed by deriving the nitrogen oxide purification rate value when urea is injected upstream of the SCR converter through preliminary experiments and evaluation, the nitrogen oxide purification rate in the actual vehicle It is not appropriate to be used as a representative value, and thus results in a decrease in the accuracy of the nitrogen oxide purification rate.

When the accuracy of the nitrogen oxide purification rate is lowered, the accuracy of the injection amount of urea additionally injected upstream of the SCR converter is reduced, and the nitrogen oxide purification rate when urea is injected is lower than the nitrogen oxide purification rate when urea is not injected. Since the ratio is higher than the urea injection amount, the amount of ammonia slip discharged into the atmosphere increases due to the increase in the unnecessary amount of additional urea injection, resulting in an increase in the amount of urea consumption, and odor generation and additional environmental pollution due to the excessive generation of ammonia slip.

Therefore, it is necessary to separately apply the nitrogen oxide purification rate value when urea is not supplied upstream of the SCR converter, separately from the nitrogen oxide purification rate value when urea is supplied.

Registered Patent No. 10-1097492

The present invention was made in view of the above, and means for determining the nitrogen oxide purification rate when urea is supplied upstream of the SCR converter and means for determining the nitrogen oxide purification rate when urea is not supplied upstream of the SCR converter By separately constructing and using urea, the accuracy of the nitrogen oxide purification rate of the SCR converter is improved regardless of whether or not urea is supplied in real time, and as a result, the vehicle exhaust that can increase the nitrogen oxide removal efficiency of the SCR converter by precisely controlling the urea supply. It is an object of the present invention to provide a method for controlling urea supply of a purifier.

Accordingly, in the present invention, a method for controlling the supply of urea of an exhaust gas purification device using ammonia generated as urea injected upstream of an SCR converter installed in an engine exhaust line is decomposed is used to purify exhaust gas, and urea is supplied upstream of the SCR converter. A first step of determining whether or not it is running; a second step of calculating real-time storage of ammonia in the SCR converter using a first nitrogen oxide purification rate determination means when urea is being supplied upstream of the SCR converter; If urea is not supplied upstream of the SCR converter, a third step of calculating real-time storage of ammonia in the SCR converter using a second nitrogen oxide purification rate determining means; A fourth step of determining whether to supply urea upstream of the SCR converter based on the real-time stored amount of ammonia in the SCR converter;

Specifically, in the first step, it is determined that urea is being supplied if the rate of change of the ammonia storage amount over time is 0 or more, and if the rate of change is less than 0, it is determined that urea is not being supplied.

And in the second step, the real-time ammonia storage amount is calculated based on the previous ammonia storage amount of the SCR converter, the real-time ammonia supply amount according to the urea supply amount supplied upstream of the SCR converter, and the real-time ammonia consumption amount used to purify nitrogen oxide, , The real-time consumption of ammonia is calculated using the nitrogen oxide purification rate obtained by the first nitrogen oxide purification rate determining means.

In addition, in the third step, the real-time ammonia storage amount is calculated based on the previous ammonia storage amount of the SCR converter and the real-time ammonia consumption amount used for nitrogen oxide purification, and the real-time ammonia consumption amount is obtained by the second nitrogen oxide purification rate determining means. It is calculated using the calculated nitrogen oxide purification rate.

In the fourth step, when a value obtained by subtracting the real-time ammonia storage amount from the target ammonia storage amount exceeds a set threshold, urea supply upstream of the SCR converter is determined, and urea supply upstream of the SCR converter is continued or started.

In addition, in the fourth step, if the value obtained by subtracting the real-time ammonia storage amount from the target ammonia storage amount is less than the threshold value, it is determined that urea is not supplied and the real-time ammonia storage amount is recalculated.

Here, the nitrogen oxide purification rate value obtained by the first nitrogen oxide purification rate determining means has a higher value than the nitrogen oxide purification rate value obtained by the second nitrogen oxide purification rate determining means under the same conditions.

The first nitrogen oxide determining means may use a map built to determine the nitrogen oxide purification rate based on the exhaust flow rate and the exhaust temperature, and the second nitrogen oxide determining means may determine the nitrogen oxide based on the exhaust flow rate and the exhaust temperature. A built-in map can be used to determine the purification rate.

According to the urea supply control method of the vehicle exhaust purification system according to the present invention, it is possible to improve the accuracy of the nitrogen oxide purification rate according to the ammonia storage amount of the SCR converter, thereby reducing the ammonia slip amount of the SCR converter and minimizing the amount of urea consumption. As a result, it is possible to increase the nitrogen oxide removal efficiency of the SCR converter.

1 is a view showing the nitrogen oxide purification rate when urea is supplied and when urea is not supplied
Figure 2 is a flow chart for explaining the urea supply control method according to the present invention
3 is a schematic diagram showing a first nitrogen oxide purification rate determination map and a second nitrogen oxide purification rate determination map used for urea supply control according to the present invention.

As is known, the SCR converter installed in the engine exhaust line is part of a vehicle exhaust purification system that purifies exhaust gas by selectively reducing nitrogen oxides using ammonia (NH3) generated as urea injected upstream thereof is decomposed. .

The injection amount of urea additionally supplied to the upstream side of the SCR converter is determined based on the ammonia storage amount stored in the SCR converter, and the ammonia storage amount is based on the previously supplied urea injection amount and the nitrogen oxide purification amount purified by the SCR converter. is calculated as The nitrogen oxide purification amount may be determined based on a nitrogen oxide purification rate according to map data (a nitrogen oxide purification rate determination map) derived from prior experiments and evaluations.

However, since the conventional nitrogen oxide purification rate data is a value derived from conditions when urea is supplied upstream of the SCR converter, it is used when calculating the ammonia storage amount when urea is not supplied upstream of the SCR converter. not appropriate The reason for this is that the nitrogen oxide purification rate when urea is supplied is higher than the nitrogen oxide purification rate when urea is not supplied, based on the case where conditions such as exhaust temperature and exhaust flow rate are all the same in addition to the ammonia stored in the SCR converter. because it is high (see Fig. 1).

Therefore, when calculating the ammonia storage amount when urea is not supplied using the conventional nitrogen oxide purification rate determination map, it is misjudged that a large amount of ammonia is consumed for nitrogen oxide purification, and as a result, a larger amount of urea than actually needed is additionally supplied upstream of the SCR converter to increase the amount of ammonia slip (the amount of ammonia stored in the SCR converter that is not used for nitrogen oxide purification and discharged into the atmosphere). In particular, when ammonia is stored in a larger amount than the target ammonia storage amount and the exhaust gas temperature rises rapidly due to rapid acceleration of the vehicle, ammonia slip of the SCR converter easily occurs.

Therefore, it is necessary to accurately calculate the nitrogen oxide purification amount when urea is supplied and when urea is not supplied using a binary nitrogen oxide purification rate determination map.

Therefore, in the present invention, by separately constructing and using a nitrogen oxide purification rate determination means when urea is supplied upstream of the SCR converter and a nitrogen oxide purification rate determination means when urea is not supplied upstream of the SCR converter, urea Regardless of real-time supply of the SCR converter, the accuracy of the nitrogen oxide purification rate of the SCR converter is improved, and as a result, the nitrogen oxide removal efficiency of the SCR converter can be increased by precisely controlling the supply of urea.

Hereinafter, the present invention will be described so that those skilled in the art can easily practice it.

2 is a flowchart illustrating a method for controlling urea supply according to the present invention, and FIG. 3 is a first nitrogen oxide purification rate determination map and a second nitrogen oxide purification rate determination used for urea supply control according to the present invention. It is a schematic diagram showing the map.

The urea supply control method according to the present invention can be performed by an in-vehicle controller, specifically an engine controller, and as shown in FIG. 2, the first step of determining whether urea is being supplied upstream of the SCR converter. (S10); If urea is being supplied upstream of the SCR converter, a second step (S12) of calculating a real-time (current) ammonia storage amount of the SCR converter using a first nitrogen oxide purification rate determining means; If urea is not supplied upstream of the SCR converter, a third step (S14) of calculating a real-time (current) ammonia storage amount of the SCR converter using a second nitrogen oxide purification rate determining means; and a fourth step (S16, S18) of determining whether to additionally supply urea upstream of the SCR converter based on the real-time ammonia storage amount of the SCR converter.

First, in the first step, it is possible to determine whether urea is supplied based on the change rate (slope) of the ammonia storage amount in the SCR converter over time. If the change rate of the ammonia storage amount over time is 0 (ZERO) or more, it can be determined that urea is being supplied upstream of the SCR converter because the ammonia storage amount stored in the SCR converter is increasing or maintained. If the change rate of the ammonia storage amount over time is less than 0, it can be determined that urea is not supplied upstream of the SCR converter because the ammonia storage amount is decreasing.

In addition, whether or not the urea is supplied can be determined through the operation of a urea injector for injecting urea upstream of the SCR converter.

And, a means for determining the nitrogen oxide purification rate is selected and determined according to whether or not the urea is supplied. The nitrogen oxide purification rate determination means may apply a nitrogen oxide purification rate determination map for determining the nitrogen oxide purification rate according to real-time conditions, and may be stored in the engine controller as map data derived through prior experiments and evaluations. there is.

The nitrogen oxide purification rate determination means may be composed of a nitrogen oxide purification rate determination map for determining the nitrogen oxide purification rate based on driving conditions, and the first nitrogen oxide purification rate determination means and the second nitrogen oxide purification rate determining means depend on whether or not urea is supplied. It can be divided and used as a means for determining the oxide purification rate (see FIG. 3). As the driving condition, exhaust temperature (ie, ammonia temperature in the SCR converter), exhaust flow rate, nitrogen oxide concentration, and ammonia storage amount during driving may be used.

Specifically, the nitrogen oxide purification rate determining means includes a nitrogen oxide purification rate determination map for determining the nitrogen oxide purification rate according to the ammonia storage amount of the SCR converter and the ammonia temperature, and the nitrogen oxide purification rate according to the exhaust flow rate and the ammonia temperature in the SCR converter. Any one of the nitrogen oxide purification rate determination map for determining the nitrogen oxide purification rate determination map and the nitrogen oxide purification rate determination map for determining the nitrogen oxide purification rate according to the nitrogen oxide concentration measured at the front end of the SCR converter and the ammonia temperature in the SCR converter may be selected and used. .

The first nitrogen oxide purification rate determination means is used when determining the nitrogen oxide purification rate when urea is supplied upstream of the SCR converter, and the second nitrogen oxide purification rate determination means is used when urea is not supplied. It is used when determining the nitrogen oxide purification rate of

When the nitrogen oxide purification rate is determined using the first nitrogen oxide purification rate determination means, the real-time ammonia storage amount is calculated by "real-time ammonia storage amount = previous ammonia storage amount + real-time ammonia supply amount - real-time ammonia consumption amount".

In this case, the real-time ammonia supply amount is the ammonia supply amount currently supplied upstream of the SCR converter, the previous ammonia storage amount is the ammonia storage amount stored in the SCR converter before the real-time ammonia supply amount is input upstream of the SCR converter, and the real-time ammonia consumption amount is the amount of ammonia used to purify nitrogen oxides in the exhaust gas at present (when the real-time ammonia supply amount is input upstream of the SCR converter). And, the ammonia supply amount is calculated according to the urea supply amount DOSING upstream of the SCR converter, and the ammonia consumption amount is nitrogen oxide calculated based on the nitrogen oxide purification rate obtained by the first nitrogen oxide purification rate determining means. It is calculated according to the amount of purification. Here, the previous stored amount of ammonia can be detected and grasped by data stored in the engine controller.

When the nitrogen oxide purification rate is determined using the second nitrogen oxide purification rate determination means, the real-time ammonia storage amount is calculated by “real-time ammonia storage amount = previous ammonia storage amount - real-time ammonia consumption amount”. The previous ammonia storage amount is the ammonia storage amount before the real-time ammonia consumption occurs. The real-time ammonia consumption amount is the ammonia consumption amount used to purify nitrogen oxides in the exhaust gas at present (when urea is not dosed upstream of the SCR converter), and the nitrogen oxide purification obtained by the second nitrogen oxide purification rate determination means It is calculated according to the nitrogen oxide purification amount calculated on the basis of the rate.

Here, the nitrogen oxide purification rate value obtained by the first nitrogen oxide purification rate determining means is greater than the nitrogen oxide purification rate value obtained by the second nitrogen oxide purification rate determining means under the same conditions (see Fig. 3). ).

After calculating the real-time ammonia storage amount of the SCR converter as described above, as in the fourth step, whether to supply urea is determined based on the real-time ammonia storage amount (S16 and S18).

In order to determine whether to additionally supply urea upstream of the SCR converter, a target storage amount of ammonia is calculated. The target ammonia storage amount may be determined based on the exhaust flow rate and the exhaust temperature (ammonia temperature in the SCR converter). Specifically, the target ammonia storage amount can be obtained from a target ammonia storage amount determination map that determines the target ammonia storage amount based on the exhaust flow rate and ammonia temperature, and the target ammonia storage amount determination map is a map derived through preliminary experiments and evaluations. It can be built as data and stored in the engine controller. In addition, the target ammonia storage amount determination map may be equally applied regardless of whether urea is supplied or not.

Therefore, regardless of whether urea is supplied, if the value obtained by subtracting the real-time ammonia storage amount from the target ammonia storage amount exceeds the set threshold value α, it is determined to additionally supply urea upstream of the SCR converter. At this time, if urea is being supplied, urea is continuously supplied and additionally supplied, and if urea is not being supplied, urea is supplied and additionally supplied (S20). In addition, when the value obtained by subtracting the real-time ammonia storage amount from the target ammonia storage amount is less than the threshold value (α), urea supply is stopped or not started, and the real-time ammonia storage amount is recalculated. The threshold value α may be set as a difference value determined to require additional urea supply to increase the real-time ammonia storage amount to a target ammonia storage amount as ammonia is consumed to purify nitrogen oxides.

Since urea supply and non-supply conditions occur alternately in a real vehicle, the amount of ammonia used to purify nitrogen oxide is accurately calculated by using an appropriate means for determining the nitrogen oxide purification rate depending on whether urea is supplied or not, and accordingly, the SCR converter As a result, the amount of ammonia slip can be reduced and the amount of urea consumed can be minimized by precisely controlling the supply of urea added upstream of the.

Since the embodiments of the present invention have been described in detail above, the scope of the present invention is not limited to the above-described embodiments, and various modifications and modifications of those skilled in the art using the basic concept of the present invention defined in the following claims Improvements are also included in the scope of the present invention.

Claims (10)

A method for controlling the supply of urea of an exhaust purifier for purifying exhaust gas using ammonia generated as urea injected upstream of an SCR converter installed in an engine exhaust line is decomposed,
A first step of determining whether urea is being supplied upstream of the SCR converter;
a second step of calculating real-time storage of ammonia in the SCR converter using a first nitrogen oxide purification rate determination means when urea is being supplied upstream of the SCR converter;
If urea is not supplied upstream of the SCR converter, a third step of calculating real-time storage of ammonia in the SCR converter using a second nitrogen oxide purification rate determining means;
A fourth step of determining whether to supply urea upstream of the SCR converter based on the real-time stored amount of ammonia in the SCR converter;
Urea supply control method of a vehicle exhaust purification system comprising a.
The method of claim 1,
In the first step, if the change rate of the ammonia storage amount over time is 0 or more, it is determined that urea is being supplied, and if the change rate is less than 0, it is determined that urea is not being supplied. How to control urea supply.
The method of claim 1,
In the second step, the real-time ammonia storage amount is calculated based on the previous ammonia storage amount of the SCR converter, the real-time ammonia supply amount according to the urea supply amount supplied upstream of the SCR converter, and the real-time ammonia consumption amount used to purify nitrogen oxide, The urea supply control method of a vehicle exhaust purification apparatus, characterized in that the real-time consumption of ammonia is calculated using the nitrogen oxide purification rate acquired by the first nitrogen oxide purification rate determining means.
The method of claim 3,
In the second step, the real-time ammonia storage amount is calculated by "real-time ammonia storage amount = previous ammonia storage amount + real-time ammonia supply amount - real-time ammonia consumption amount".
The method of claim 1,
In the third step, the real-time ammonia storage amount is calculated based on the previous ammonia storage amount of the SCR converter and the real-time ammonia consumption amount used for nitrogen oxide purification, and the real-time ammonia consumption amount is obtained by the second nitrogen oxide purification rate determining means Urea supply control method of a vehicle exhaust purification system, characterized in that calculated using the nitrogen oxide purification rate.
The method of claim 5,
In the third step, the real-time ammonia storage amount is calculated by "real-time ammonia storage amount = previous ammonia storage amount - real-time ammonia consumption amount".
The method of claim 1,
In the fourth step, if a value obtained by subtracting the real-time ammonia storage amount from the target ammonia storage amount exceeds a set threshold value, urea supply to the upstream SCR converter is determined.
The method of claim 7,
In the fourth step, if the value obtained by subtracting the real-time ammonia storage amount from the target ammonia storage amount is equal to or less than the threshold value, urea supply control method of a vehicle exhaust purification apparatus, characterized in that urea non-supply is determined and real-time ammonia storage amount is recalculated. .
The method of claim 1,
The nitrogen oxide purification rate value obtained by the first nitrogen oxide purification rate determining means is greater than the nitrogen oxide purification rate value obtained by the second nitrogen oxide purification rate determining means under the same conditions. A method for controlling urea supply in a purifier.
The method of claim 1,
The urea supply control method of a vehicle exhaust purification apparatus, characterized in that the first and second nitrogen oxide determining means are maps built to determine a nitrogen oxide purification rate based on exhaust flow rate and exhaust temperature.

Images