JP2007138768A - Exhaust emission control device of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust emission control device of an internal combustion engine so improved that the purification performance during cold idling can be further enhanced. <P>SOLUTION: This exhaust emission control device of the internal combustion engine having a TWC 7 and a LNC 9 installed on the downstream side comprises an intake control valve 5 capable of changing the amount of a fresh flow fed into an intake passage 2, an EGR control valve 13 capable of changing the flow of a recirculating exhaust gases from a combustion chamber to the intake passage, a TWC temperature sensor 28 outputting the values on the temperature of a TWC, and an LNC temperature sensor 29 outputting the values on the temperature of an LNC. The control device changes an operation mode between a catalyst temperature increasing mode in which the flow can be relatively increased while increasing the temperature of the exhaust gases to the TWC by controlling the intake control valve and the EGR control valve according to the output values of both temperature output means and a catalyst heating mode in which the supplied amount of the reducer to the TWC can be relatively increased. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

The present invention relates to an exhaust purifying apparatus for an internal combustion engine, and particularly relates to an exhaust purification system of an internal combustion engine capable of realizing quick activation of the lean NO _X purification catalyst during cold start.

The exhaust passage of a diesel internal combustion engine may be provided with a lean NO _X purification catalyst (hereinafter abbreviated as LNC) for reducing and purifying nitrogen oxide (hereinafter abbreviated as NO _X ) in exhaust gas. . In this LNC, when the air-fuel ratio of exhaust gas (hereinafter referred to as exhaust A / F) is higher than a predetermined value (hereinafter referred to as lean), in other words, NO _X taken in when the oxygen concentration is high, When the exhaust A / F is lower than a predetermined value (hereinafter referred to as rich), in other words, when the oxygen concentration is reduced, the exhaust A / F is released and reduced to be harmless. In addition, since the absorption performance of LNC decreases as the NO _X absorption amount increases, the unburned fuel is supplied into the exhaust gas at an appropriate time to increase the HC concentration and reduce the oxygen concentration, thereby reducing the NO _X from the LNC. Release is promoted and reduced and purified sufficiently.

On the other hand, in an internal combustion engine that performs lean combustion at the time of cold start, such as a diesel internal combustion engine, the exhaust A / F at the time of cold idling is excessively lean, so that the LNC is activated early after the cold start. It is difficult. For this reason, it has been difficult to prevent NO _{X from} being temporarily released into the atmosphere until the LNC reaches the activation temperature.

In order to cope with such inconvenience, a three-way catalyst (hereinafter abbreviated as TWC) is disposed upstream of the LNC in the exhaust passage in order to achieve early activation of the LNC during cold idling. by enriching limiting the exhaust a / F at the time during idling, achieving reduction and promoting the oxidation reaction of TWC of the NO _X concentration, techniques that try to exploit the self-heating of the TWC to increase the temperature of the LNC it is proposed (See Patent Document 1).
JP 2004-285832 A

  However, according to the technique described in Document 1, even if the exhaust A / F is enriched during cold idling to increase the concentration of the reducing agent for LNC, a sufficient oxidation reaction is not achieved with TWC in the region before the temperature rise. Since it was not obtained, there was a possibility of exacerbating exhaust gas emissions (unburned HC, CO, etc.).

  The present invention has been devised to improve such disadvantages of the prior art, and its main object is to improve the internal combustion engine so that the purification performance during cold idling can be further enhanced. An object of the present invention is to provide an exhaust purification device.

  In order to solve such problems, the present invention provides a variable means (intake control valve 5) for the flow rate of fresh air supplied to the intake passage 2 in the exhaust gas purification apparatus 10 for an internal combustion engine having the TWC 7 and the LNC 9 provided downstream thereof. ), A means for varying the recirculation exhaust flow rate from the combustion chamber to the intake passage (EGR control valve 13), a TWC temperature sensor 28 that outputs a value related to the temperature of the TWC, and an LNC temperature that outputs a value related to the temperature of the LNC And a catalyst temperature increase mode in which the exhaust gas flow rate is relatively increased while the exhaust gas temperature to the TWC is increased by controlling the intake control valve and the EGR control valve in accordance with the output values of both temperature sensors. And a catalyst heat generation mode in which the reducing agent supply amount to the TWC is relatively increased. In particular, it also has fuel injection control means for controlling the amount of fuel injected into the combustion chamber and the injection timing, and the catalyst heat generation mode includes retard control of fuel injection timing and / or control of lowering injection pressure. It was supposed to be.

According to the present invention as described above, the catalyst temperature rising mode for increasing the temperature of the exhaust gas and increasing the flow rate and the catalyst heat generation mode for increasing the amount of the reducing agent in the exhaust gas are selected, and the TWC is low in temperature. Sometimes, the TWC temperature can be raised to the activation temperature early by flowing a large amount of high temperature exhaust gas. Thereby, unburned HC and CO discharged at the time of cold can be reduced. After the TWC reaches the activation temperature, the unburned HC or CO as a reducing agent is actively fed into the TWC to promote the exothermic reaction of the TWC. The temperature can be raised.
That the present invention, LNC after cold start is shortened the time to activation, it is possible to greatly contribute to the reduction of further reduction and fuel consumption of the NO _X when cold idling.

  Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

  FIG. 1 is a basic configuration diagram of an internal combustion engine E to which the present invention is applied. The internal combustion engine (diesel engine) E has a mechanical configuration that is not different from that of a known one, and includes a turbocharger 1 with a supercharging pressure variable mechanism. A passage 2 is connected, and an exhaust passage 3 is connected to the turbine side of the turbocharger 1. An air cleaner 4 is connected to the upstream end of the intake passage 2, and an intake control valve 5 for adjusting the flow rate of fresh air flowing into the combustion chamber at an appropriate position of the intake passage 2, and flows in a low rotation speed / low load operation region. A swirl control valve 6 is provided for reducing the cross-sectional area of the road and increasing the intake air flow velocity. Further, at the downstream end of the exhaust passage 3, a TWC 7, a filter (hereinafter abbreviated as DPF) 8 for removing particulate matter such as soot, and an LNC 9 are arranged in this order along the exhaust flow. An exhaust purification device 10 is connected.

  The swirl control valve 6 and the exhaust passage 3 immediately after the combustion chamber are connected to each other via an exhaust gas recirculation (hereinafter abbreviated as EGR) passage 11. The EGR passage 11 includes a cooler passage 11a and a bypass passage 11b branched via a switching valve 12, and an EGR control valve 13 for adjusting the EGR flow rate flowing into the combustion chamber is provided at the junction. .

  The cylinder head of the internal combustion engine E is provided with a fuel injection valve 14 with its tip facing the combustion chamber. The fuel injection valve 14 is connected to a common rail 15 that stores fuel in a predetermined high pressure state, and a fuel pump 17 that is driven by a crankshaft and pumps fuel from the fuel tank 16 is connected to the common rail 15.

  These turbocharger 1 supercharging pressure variable mechanism 19, intake control valve 5, EGR passage switching valve 12 and EGR control valve 13, fuel injection valve 14, fuel pump 17... (Referred to as “abbreviated”) 18 (see FIG. 2).

On the other hand, as shown in FIG. 2, the ECU 18 includes an intake valve opening sensor 20, a crankshaft rotation speed sensor 21, an intake flow rate sensor 22, a supercharging pressure sensor 23, and an EGR valve disposed at predetermined locations of the internal combustion engine E. Output signals from the opening sensor 24, the common rail pressure sensor 25, the accelerator pedal operation amount sensor 26, the O ₂ sensor 27, the TWC temperature sensor 28, the LNC temperature sensor 29, etc. are input.

  The memory of the ECU 18 stores a map in which control target values for each control object including the optimum fuel injection amount obtained in advance by experiments or the like according to the crankshaft rotation speed and the required torque (accelerator pedal operation amount) are set. Therefore, each part is controlled so that an optimal combustion state is obtained according to the load state of the internal combustion engine E.

  Next, the control procedure of the present invention will be described with reference to FIGS. In the following examples, only those using a three-way catalyst will be described, but the present invention is also applicable to an oxidation catalyst.

  After the cold start, the detected value of the TWC temperature sensor 28 (or the estimated value of the TWC temperature) is compared with a predetermined switching determination value (the active temperature at which the catalyst can oxidize) by the comparator 31, and the TWC temperature is determined to be switched. It is determined whether or not the value is equal to or less than the value (step 1). As a result, if the current state is the region below the switching determination value, the temperature increase mode is selected by the mode selector 32 (step 2), and the temperature increase control map 33 having the engine speed and the required torque as addresses. Is searched (step 3).

  Here, since the TWC temperature is always equal to or lower than the switching determination value at the first start, the temperature raising mode is selected immediately after the start. As a result, the target values for the temperature increase mode of the intake air flow rate, the intake control valve opening, the common rail pressure, and the supercharging pressure are obtained from the temperature increase control map 33, and the control target devices are controlled by the target values. (Step 4).

  In this temperature raising mode, the sum of the intake flow rates is increased as compared to the normal mode after warming up, but the opening degree of the intake control valve 5 is set to an intermediate opening degree that is smaller than that in the normal mode, and the boost pressure is set to normal. Set lower than the mode. As a result, the inflow amount of fresh air increases from that in the normal mode, and the EGR flow rate relatively decreases. As a result, the temperature of the exhaust gas flowing into the TWC 7 rises and the flow rate increases.

  At the same time, the common rail pressure is lowered from the normal mode to extend the fuel injection period. Thereby, the rise in the exhaust temperature is further promoted, and thereby an early temperature rise of the TWC 7 is achieved.

If it is determined by the comparator 31 in step 1 that the TWC temperature has exceeded the switching determination value, the detection value of the LNC temperature sensor 29 (or the estimated value of the LNC temperature) and a predetermined switching determination value (during exhaust) temperature) and which can absorb NO _X in comparison by the comparator 34, LNC temperature is equal to or less than the switching determination value (step 5). As a result, if the current state is the region below the switching determination value, the heat generation mode is selected by the mode selectors 32 and 35 (step 6), and the heat generation control map 36 having the engine rotational speed and the required torque as addresses. Search for. As a result, the target values for the heat generation modes of the intake air amount, the intake control valve opening degree, the common rail pressure, and the supercharging pressure are obtained from the heat generation control map 36, and the devices to be controlled are controlled by the target values (steps). 4).

  In this heat generation mode, the sum of the intake air flow is reduced compared to the normal mode after warming up, but the opening of the intake control valve 5 is set to a lower opening that is further reduced than in the temperature raising mode, and the boost pressure is raised. Lower than the mode. In addition, the fuel injection period is further extended by lowering the common rail pressure further than the temperature raising mode. By these processes, the inflow amount of fresh air is reduced compared to the normal mode, and the EGR flow rate is relatively increased. As a result, the exhaust A / F flowing into the TWC 7 becomes rich, and the reduction supplied to the TWC 7 The agent is increased and the self-heating of TWC7 is promoted.

  On the other hand, the comparator 31 determines whether or not the TWC temperature is equal to or lower than the switching determination value (step 11). When it is determined that the TWC temperature is equal to or lower than the switching determination value, the normal control map 38 is referred to. (Step 12) The fuel injection timing is controlled by the target value obtained from this (Step 13), and if the TWC temperature exceeds the switching determination value, the comparator 34 determines whether the LNC temperature is equal to or lower than the switching determination value. (Step 14), and when the comparator 34 determines that the LNC temperature is equal to or lower than the switching determination value, the fuel injection timing control map is displayed by the mode selectors 40 and 41 for the normal control map 38. Is switched to the retard angle control map 39 (step 15), and the fuel injection timing is retarded by this target value (step 13) to further increase the reducing agent supplied to the TWC 7. The increase in the exhaust temperature to accelerate (see FIG. 5,6).

  When the TWC 7 self-heats in this way, the temperature of the LNC 9 disposed downstream of the TWC 7 is raised by the high-temperature gas discharged from the TWC 7, so that it is detected that the temperature of the LNC 9 has reached a sufficient activation temperature. If so, the mode selector 35 is switched to the normal mode (step 8), and the normal control map 37 with the engine speed and the required torque as addresses is referred to (step 9). Control is performed (step 4).

The trend of each control parameter in each operation mode is summarized as follows (see FIG. 7).
A. Temperature rising mode Increase the intake flow rate more than the normal mode.
2. Set the intake control valve to a lower opening than in the normal mode.
3. Reduce the supercharging pressure from the normal mode.
As a result, the fresh air flow rate increases and the EGR flow rate relatively decreases, so that the exhaust flow rate increases.
4). Reduce the common rail pressure below the normal mode.
As a result, the fuel injection period is extended and the exhaust temperature rises.
5. Bypass the EGR cooler and keep the EGR temperature high.
As a result, the exhaust temperature rises.
B. Heat generation mode Reduce the intake air flow rate from the normal mode.
2. The intake control valve is further closed than in the temperature raising mode.
3. As a result of further lowering the supercharging pressure than in the temperature raising mode, the fresh air flow rate decreases and the EGR flow rate increases relatively, so that the exhaust temperature rises.
4). The common rail pressure is further lowered than in the temperature raising mode.
As a result, the fuel injection timing is further extended, so that the exhaust temperature rises.
5. Bypass the EGR cooler and keep the EGR temperature high.
As a result, the exhaust temperature rises.
6). The fuel injection timing is delayed from the temperature raising mode.
Thereby, the reducing agent in exhaust gas increases.

1 is an overall configuration diagram of an internal combustion engine to which the present invention is applied. It is a block diagram of a control device to which the present invention is applied. It is a block diagram in connection with mode switching control. It is a flowchart in connection with mode switching control. It is a block diagram in connection with switching control of fuel injection timing. It is a flowchart in connection with switching control of fuel injection timing. It is a chart which shows the relationship between each control parameter and each mode.

Explanation of symbols

2 Intake passage 5 Intake control valve 7 TWC
9 LNC
10 Exhaust Purification Device 13 EGR Control Valve 28 TWC Temperature Sensor 29 LNC Temperature Sensor

Claims (2)

Three-way catalyst or oxidation catalyst, and an exhaust gas purification device for an internal combustion engine having a lean NO _X purification catalyst provided in the downstream,
A three-way catalyst or oxidation catalyst temperature that outputs a value related to the temperature of the three-way catalyst or the oxidation catalyst, and a variable means for the fresh air flow rate supplied to the intake passage, a variable means for the circulating exhaust flow rate from the combustion chamber to the intake passage. and output means, and a lean NO _X purification catalyst temperature output means for outputting the value related to the temperature of the lean NO _X purification catalyst,
The exhaust gas flow rate to the three-way catalyst or the oxidation catalyst is relatively increased by controlling the fresh air flow rate variable means and the circulating exhaust flow rate variable means in accordance with the output values of the temperature output means. An exhaust gas purification apparatus for an internal combustion engine, wherein a first catalyst temperature control mode and a second catalyst temperature control mode for relatively increasing a reducing agent supply amount to the three-way catalyst or the oxidation catalyst are switched.   Fuel injection control means for controlling the amount of fuel injected into the combustion chamber and the injection timing is provided, and the second catalyst temperature control mode is at least one of delay control of fuel injection timing and control of lowering fuel injection pressure. The exhaust emission control device for an internal combustion engine according to claim 1, comprising:

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