KR20200129899A - Exaust system of vehicle and control method thereof - Google Patents

Abstract

The present invention relates to an exhaust system for a vehicle that reduces deterioration of a warm-up catalytic converter (WCC) catalyst due to high-speed driving or high-load driving of an engine. According to the present invention, the exhaust system for a vehicle comprises: a WCC and an underbody catalytic converter (UCC) arranged in series in an engine exhaust pipe; a bypass pipe connected from an upstream of the WCC to an upstream of the UCC to bypass the WCC; a first valve provided to control the opening and closing state of the bypass pipe; and a controller which adjusts the opening and closing state of the bypass pipe by adjusting the first valve according to a driving condition of the vehicle.

Description

Vehicle exhaust system and its control method {EXAUST SYSTEM OF VEHICLE AND CONTROL METHOD THEREOF}

The present invention relates to a vehicle exhaust system, and relates to a technology for properly purifying exhaust gas emitted from an engine and discharging it into the atmosphere.

WCC (Warm-up Catalytic Converter) and UCC (Underbody Catalytic Converter) are connected in series to the exhaust line in order to purify harmful substances contained in the exhaust gas before discharging the exhaust gas generated from the conventional vehicle engine into the atmosphere. The deployed configuration is commonly used.

The WCC is advantageous in purifying exhaust gas at the beginning of the engine cold start by rapidly warming up by heat provided from the engine at a location adjacent to the engine when the engine is cold starting, while the catalyst is liable to deteriorate due to excessive heat under high load conditions of the engine. Countermeasures such as catalyst deterioration prevention logic are required.

On the contrary, since the UCC is installed in the lower part of the vehicle body at a location relatively far from the engine, it is difficult to expect the exhaust gas purification performance at the initial cold start of the engine, but it has relatively strong durability against heat from the engine, and in the WCC after the engine warm-up. It further purifies harmful substances that could not be purified.

Meanwhile, the WCC has a tendency to gradually increase the cell density of the catalyst due to the recently strengthened exhaust regulation, which causes an increase in the back pressure of the engine, which negatively affects the fuel economy of the vehicle.

In addition, since the WCC is oxidized in the FUEL CUT situation, there is a problem that the NOx purification performance is greatly reduced by oxygen accumulated in the WCC immediately after the end of the FUEL CUT.

The matters described as the background technology of the present invention are only for enhancing an understanding of the background of the present invention, and should not be taken as acknowledging that they correspond to the prior art already known to those of ordinary skill in the art. Will be

KR 1020180123917 A

The present invention reduces deterioration of the WCC catalyst due to high-speed operation or high-load operation of the engine, improves fuel economy by improving the engine back pressure in the high-load section, and reduces the rich driving area by the operation of the catalyst protection logic in the high-load section. The purpose of this is to provide an exhaust system and a control method for the vehicle that reduces fuel economy deterioration and prevents oxidation of WCC in the FUEL CUT section to sufficiently secure NOx purification performance immediately after the FUEL CUT.

The exhaust system of the vehicle of the present invention for achieving the object as described above,

WCC and UCC arranged in series in the engine exhaust pipe;

A bypass pipe connected from an upstream of the WCC to an upstream of the UCC to bypass the WCC;

A first valve provided to control an open/close state of the bypass pipe;

A controller configured to adjust the opening and closing state of the bypass pipe by adjusting the first valve according to the driving condition of the vehicle;

It characterized in that it is configured to include.

A front oxygen sensor is installed upstream of the WCC;

A first rear oxygen sensor is installed between the WCC and the UCC;

A second rear oxygen sensor may be installed downstream of the UCC.

A second valve is further provided between the WCC and the UCC to block exhaust gas flowing from the WCC to the UCC;

The controller may be configured to close the second valve when opening the first valve and to open the second valve when closing the first valve.

In addition, the method of controlling the exhaust system of a vehicle according to the present invention,

When the temperature of the UCC is higher than the UCC activation temperature, the engine intake flow rate is higher than the predetermined reference flow rate, and the engine speed is higher than the predetermined reference speed, the controller is configured to allow the exhaust gas of the engine to flow through the bypass pipe. It characterized in that opening the first valve so as to.

When the first valve is opened, the controller may control the air-fuel ratio of the engine using an oxygen sensor installed downstream of the UCC.

In addition, the method of controlling the exhaust system of a vehicle according to the present invention,

The controller is characterized in that the first valve is opened so that the exhaust gas of the engine flows through the bypass pipe when the APS signal is determined to be a general acceleration situation because the APS signal is equal to or greater than a predetermined acceleration minimum value and less than a predetermined intermediate acceleration value.

The controller may close the first valve when it is determined that the APS signal is a sudden acceleration situation exceeding the intermediate acceleration value.

In addition, the method of controlling the exhaust system of a vehicle according to the present invention,

When the FUEL CUT is operated, the controller opens the first valve so that the exhaust gas of the engine flows through the bypass pipe.

When the FUEL CUT ends, the controller may close the first valve so that the exhaust gas of the engine flows through the WCC.

When the FUEL CUT ends, the controller may determine the end point of the oxygen purge action by an oxygen sensor installed downstream of the UCC.

In addition, the exhaust system of a vehicle according to the present invention,

A front oxygen sensor is installed upstream of the WCC;

A first rear oxygen sensor is installed between the WCC and the UCC;

In the UCC, at least two or more catalysts are arranged in series along the flow direction of the exhaust gas therein;

A second rear oxygen sensor may be installed between the catalysts of the UCC.

In addition, in the method for controlling the exhaust system of a vehicle according to the present invention,

When the temperature of the UCC is higher than the UCC activation temperature, the engine intake flow rate is higher than the predetermined reference flow rate, and the engine speed is higher than the predetermined reference speed, the controller is configured to allow the exhaust gas of the engine to flow through the bypass pipe. The first valve may be opened so as to be performed.

When the first valve is opened, the controller may control the air-fuel ratio of the engine using the second rear oxygen sensor.

In addition, in the method for controlling the exhaust system of a vehicle according to the present invention,

The controller may open the first valve so that the exhaust gas of the engine flows through the bypass pipe when the APS signal is greater than or equal to a predetermined minimum acceleration value and less than or equal to a predetermined intermediate acceleration value and thus is determined as a general acceleration situation.

The controller may close the first valve when it is determined that the APS signal is a sudden acceleration situation exceeding the intermediate acceleration value.

In addition, in the method for controlling the exhaust system of a vehicle according to the present invention,

When the FUEL CUT is operated, the controller may open the first valve so that the exhaust gas of the engine flows through the bypass pipe.

When the FUEL CUT ends, the controller may close the first valve so that the exhaust gas of the engine flows through the WCC.

When the FUEL CUT ends, the controller may determine the end point of the oxygen purge action by the second rear oxygen sensor.

The present invention reduces deterioration of the WCC catalyst due to high-speed operation or high-load operation of the engine, improves fuel economy by improving the engine back pressure in the high-load section, and reduces the rich driving area by the operation of the catalyst protection logic in the high-load section. It reduces fuel efficiency deterioration, and prevents oxidation of WCC in the FUEL CUT section to ensure sufficient NOx purification performance immediately after FUEL CUT.

1 is a view showing a first embodiment of a vehicle exhaust system according to the present invention;
2 is a view showing a second embodiment of the vehicle exhaust system according to the present invention;
3 is a flow chart showing an embodiment of a vehicle exhaust system control method according to the present invention;
4 is a view showing a third embodiment of the vehicle exhaust system according to the present invention;
5 is a view showing a fourth embodiment of the vehicle exhaust system according to the present invention.

1 and 2, the first and second embodiments of the vehicle exhaust system according to the present invention, in common, include WCC and UCC arranged in series in the engine exhaust pipe; A bypass pipe (1) connected from an upstream of the WCC to an upstream of the UCC to bypass the WCC; A first valve (3) provided to adjust the open/close state of the bypass pipe; It is configured to include a controller 5 for controlling the opening and closing state of the bypass pipe 1 by adjusting the first valve 3 according to the driving condition of the vehicle.

In addition, a front oxygen sensor 7 is installed upstream of the WCC; A first rear oxygen sensor 9 is installed between the WCC and UCC; A second rear oxygen sensor 11 is installed downstream of the UCC.

On the other hand, the second embodiment of FIG. 2 has the same configuration as the first embodiment of FIG. 1, and a second valve 13 capable of blocking exhaust gas flowing from the WCC to the UCC is provided between the WCC and the UCC. Further provided, accordingly, the controller 5 closes the second valve 13 when opening the first valve 3, and the second valve when closing the first valve 3 ( It is different that it is configured to open 13).

That is, in the second embodiment of FIG. 2, the second valve 13 is further provided, and when the exhaust gas flows through the bypass pipe 1, the exhaust gas flowing from the WCC to the UCC is blocked. This is to be able to block the exhaust gas flow more reliably.

Of course, in the first embodiment of FIG. 1, when the first valve 3 is opened, exhaust gas hardly flows to the WCC due to the difference in the relative flow resistance caused by the WCC, and only to the UCC through the bypass pipe. The exhaust gas flows.

3 is a flow chart showing an embodiment of a method for controlling the exhaust system as described above.

For reference, "flow A" in FIG. 3 means that the exhaust gas from the engine passes through the WCC by closing the first valve, and then flows to the UCC, and "flow B" means that the first valve is opened. , It means that the exhaust gas does not flow to the WCC, but flows directly to the UCC through the bypass pipe.

In addition, R1S is the first rear oxygen sensor, R2S is the second rear oxygen sensor, Twcc is the WCC temperature, Tucc is the UCC temperature, the activation temperature is the temperature at which the catalyst performs a normal purification function, and the deterioration temperature is the risk of catalyst deterioration. Means temperature.

In addition, ON and OFF of R1S and R2S can turn on or off the oxygen sensor itself, but ON means the case of using the signal of the oxygen sensor for control, and OFF means the signal of the oxygen sensor is used for control. It can mean not to do.

Referring to FIG. 3, when the engine is started, it basically starts with flow A, and the exhaust gas purification is started more quickly with a quick warm-up of the WCC at the initial stage of the cold start (S10).

While such flow A is implemented, the first rear oxygen sensor together with the front oxygen sensor is used to control the air-fuel ratio of the engine, and the second rear oxygen sensor may not use or turn off the signal ( S20).

When the FUEL CUT is operated, the controller opens the first valve so that the exhaust gas of the engine flows through the bypass pipe so that the flow B is formed (S30).

Accordingly, air discharged from the engine does not pass through the WCC, but only passes through the UCC through the bypass pipe, so that oxygen does not accumulate in the WCC.

When the FUEL CUT ends, the controller closes the first valve to allow the exhaust gas of the engine to flow through the WCC, thereby implementing the flow A (S40).

Accordingly, the WCC without oxygen accumulation during the FUEL CUT immediately exerts a normal and smooth purification function, so that the immediate purification of NOx can be performed.

On the other hand, when the FUEL CUT ends, the controller performs an oxygen purge action to purify the oxygen accumulated in the catalyst. In this case, the controller performs an oxygen purge action by an oxygen sensor installed downstream of the UCC, that is, a second rear oxygen sensor. To determine the end point of the UCC, when the oxygen purge of the UCC is completed, the oxygen purge action is terminated (S50).

In addition, the controller is in the heavy load situation of the engine where the temperature of the WCC is above the WCC activation temperature, the temperature of the UCC is above the UCC activation temperature, the engine intake flow rate is less than the predetermined reference flow rate, and the engine speed is less than the predetermined reference speed. , Flow B is implemented by opening the first valve so that the exhaust gas of the engine flows through the bypass pipe (S60).

In other words, when UCC is activated and the engine is under heavy load, there is a risk of WCC deterioration, and in a situation where the exhaust gas can be sufficiently purged with only UCC, flow B is implemented to prevent the deterioration of WCC more stably.

In this case, the engine back pressure is reduced, so that the fuel economy of the vehicle can be improved.

For reference, here, the engine load refers to the load above the heavy load, not the low load, divided into three stages: heavy load, heavy load, and high load, and the risk of WCC deterioration is small in the heavy load condition smaller than the heavy load. It is desirable to implement flow A and protect the WCC through catalytic protection logic because there is a risk of WCC deterioration under high load conditions, but UCC alone lacks purification performance.

The engine load can be determined by the engine intake flow rate as illustrated in FIG. 3, and the engine speed may be considered together, and the reference flow rate and the reference speed are values that can distinguish between a heavy load and a high load. By analysis, it can be determined in a design suitable for the engine and vehicle.

Meanwhile, when the first valve is opened, the controller controls the air-fuel ratio of the engine using the second rear oxygen sensor, which is an oxygen sensor installed downstream of the UCC (S70).

On the other hand, when the APS (Accelerator Position Sensor) signal is equal to or greater than a predetermined acceleration minimum value and less than a predetermined intermediate acceleration value, the controller opens the first valve so that the exhaust gas of the engine flows through the bypass pipe. When it is opened to realize the flow B, and when it is determined that the APS signal exceeds the intermediate acceleration value, the first valve may be closed to realize the flow A.

That is, in the general acceleration situation, there is a risk of WCC deterioration, and since the UCC can sufficiently purify, the flow B is implemented to reliably prevent the risk of WCC deterioration, while reducing the back pressure of the engine to improve fuel economy, Although there is a risk of WCC deterioration in the above rapid acceleration situation, it is difficult to expect sufficient purification with UCC alone, so flow A is implemented so that both WCC and UCC can purify, and the catalyst of WCC can be protected by catalytic protection logic. will be.

Of course, the minimum acceleration value is preferably set to a level that can be regarded as being substantially accelerated, and the intermediate acceleration value is preferably set to a level that can be distinguished from the rapid acceleration. It may be determined by design through a number of experiments and analysis, for example, the minimum acceleration value may be set to about 10% of the APS signal, and the intermediate acceleration value may be set to about 60% of the APS signal. That is, in this case, if the APS signal is 60% or more and 100% or less, it is determined as a sudden acceleration.

Meanwhile, FIGS. 4 and 5 respectively show a third and fourth embodiments of the exhaust system of a vehicle according to the present invention, and these embodiments are common to the first and second embodiments described above. WCC and UCC arranged in series in the engine exhaust pipe; A bypass pipe (1) connected from an upstream of the WCC to an upstream of the UCC to bypass the WCC; A first valve (3) provided to adjust the open/close state of the bypass pipe (1); A controller (5) for adjusting the opening and closing state of the bypass pipe (1) by adjusting the first valve (3) according to the driving condition of the vehicle; A front oxygen sensor 7 installed upstream of the WCC; It is configured to include a first rear oxygen sensor 9 installed between the WCC and UCC.

In the third and fourth embodiments, at least two catalysts are arranged in series along the flow direction of the exhaust gas inside the UCC, and the second rear oxygen sensor 11 is disposed between the catalysts of the UCC. The point installed in is different from the first and second embodiments.

For reference, in FIGS. 4 and 5, two catalysts are arranged in series inside the UCC, and the second rear oxygen sensor 11 is installed between these two catalysts, but there are three catalysts inside the UCC. It goes without saying that it may consist of the above.

Here, the meaning that the second rear oxygen sensor 11 is installed between the catalysts of the UCC means that the catalyst is also located upstream of the second rear oxygen sensor 11 in the UCC, and once after the WCC, the catalyst of the UCC The second rear oxygen sensor 11 measures the oxygen concentration of the exhaust gas that has been further purified by this, and a catalyst is located downstream of the second rear oxygen sensor 11 so that the second rear oxygen sensor 11 ) Means that it is possible to further purify the exhaust gas after the oxygen concentration is measured.

This is, even if the rich injection operation is terminated based on the signal of the second rear oxygen sensor 11 during the rich injection operation of the engine to desorb oxygen adsorbed on the UCC during the FUEL CUT period as described above, At the end of the exhaust gas path from the engine to the UCC, exhaust gas from the rich injection operation so far remains, so the catalyst located downstream of the second rear oxygen sensor 11 in the UCC is at the end of the rich injection operation. It is to purify the residual exhaust gas.

The method of controlling the exhaust system of a vehicle according to the third and fourth embodiments is in view of the method of controlling the exhaust system of the first and second embodiments, the second rear oxygen sensor 11 There is a difference only in that the location is not located downstream of the UCC, but between the catalysts of the UCC, and the remaining technical ideas are all the same, so a detailed description is omitted.

Although the present invention has been illustrated and described with reference to specific embodiments, it is understood in the art that the present invention can be variously improved and changed within the scope of the technical spirit of the present invention provided by the following claims. It will be obvious to a person of ordinary knowledge.

One; Bypass pipe
3; 1st valve
5; controller
7; Front oxygen sensor
9; 1st rear oxygen sensor
11; 2nd rear oxygen sensor
13; 2nd valve

Claims (18)

WCC and UCC arranged in series in the engine exhaust pipe;
A bypass pipe connected from an upstream of the WCC to an upstream of the UCC to bypass the WCC;
A first valve provided to control an open/close state of the bypass pipe;
A controller configured to control the opening and closing state of the bypass pipe by adjusting the first valve according to the driving condition of the vehicle;
Exhaust system of a vehicle, characterized in that configured to include. The method according to claim 1,
A front oxygen sensor is installed upstream of the WCC;
A first rear oxygen sensor is installed between the WCC and the UCC;
A second rear oxygen sensor is installed downstream of the UCC
Exhaust system of a vehicle, characterized in that. The method according to claim 1,
A second valve is further provided between the WCC and the UCC to block exhaust gas flowing from the WCC to the UCC;
The controller is configured to close the second valve when opening the first valve and to open the second valve when closing the first valve
Exhaust system of a vehicle, characterized in that. In the method of controlling the exhaust system of any one of claims 1 to 3,
When the temperature of the UCC is higher than the UCC activation temperature, the engine intake flow rate is higher than the predetermined reference flow rate, and the engine speed is higher than the predetermined reference speed, the controller is configured to allow the exhaust gas of the engine to flow through the bypass pipe. Opening the first valve so as to be
Exhaust system control method of a vehicle, characterized in that. The method of claim 4,
The controller controls the air-fuel ratio of the engine using an oxygen sensor installed downstream of the UCC when the first valve is opened.
Exhaust system control method of a vehicle, characterized in that. In the method of controlling the exhaust system of any one of claims 1 to 3,
The controller opens the first valve so that the exhaust gas of the engine flows through the bypass pipe when it is determined as a general acceleration situation because the APS signal is above a predetermined minimum acceleration value and below a predetermined intermediate acceleration value.
Exhaust system control method of a vehicle, characterized in that. The method of claim 6,
The controller closes the first valve when it is determined that the APS signal is a sudden acceleration situation exceeding the intermediate acceleration value.
Exhaust system control method of a vehicle, characterized in that. In the method of controlling the exhaust system of any one of claims 1 to 3,
The controller opens the first valve so that the exhaust gas of the engine flows through the bypass pipe when the FUEL CUT is operated.
Exhaust system control method of a vehicle, characterized in that. The method of claim 8,
When the FUEL CUT ends, the controller closes the first valve so that the exhaust gas of the engine flows through the WCC.
Exhaust system control method of a vehicle, characterized in that. The method of claim 9,
At the end of the FUEL CUT, the controller determines the end point of the oxygen purge action by an oxygen sensor installed downstream of the UCC.
Exhaust system control method of a vehicle, characterized in that. The method according to claim 1,
A front oxygen sensor is installed upstream of the WCC;
A first rear oxygen sensor is installed between the WCC and the UCC;
In the UCC, at least two or more catalysts are arranged in series along the flow direction of the exhaust gas therein;
A second rear oxygen sensor is installed between the catalysts of the UCC
Exhaust system of a vehicle, characterized in that. In the method of controlling the exhaust system of claim 11,
When the temperature of the UCC is higher than the UCC activation temperature, the engine intake flow rate is higher than the predetermined reference flow rate, and the engine speed is higher than the predetermined reference speed, the controller is configured to allow the exhaust gas of the engine to flow through the bypass pipe. Opening the first valve so as to be
Exhaust system control method of a vehicle, characterized in that. The method of claim 12,
The controller controls the air-fuel ratio of the engine using the second rear oxygen sensor when the first valve is opened.
Exhaust system control method of a vehicle, characterized in that. In the method of controlling the exhaust system of claim 11,
The controller opens the first valve so that the exhaust gas of the engine flows through the bypass pipe when it is determined as a general acceleration situation because the APS signal is above a predetermined minimum acceleration value and below a predetermined intermediate acceleration value.
Exhaust system control method of a vehicle, characterized in that. The method of claim 14,
The controller closes the first valve when it is determined that the APS signal is a sudden acceleration situation exceeding the intermediate acceleration value.
Exhaust system control method of a vehicle, characterized in that. In the method of controlling the exhaust system of claim 11,
The controller opens the first valve so that the exhaust gas of the engine flows through the bypass pipe when the FUEL CUT is operated.
Exhaust system control method of a vehicle, characterized in that. The method of claim 16,
When the FUEL CUT ends, the controller closes the first valve so that the exhaust gas of the engine flows through the WCC.
Exhaust system control method of a vehicle, characterized in that. The method of claim 17,
When the FUEL CUT ends, the controller determines the end point of the oxygen purge action by the second rear oxygen sensor.
Exhaust system control method of a vehicle, characterized in that.

Images