JP2008144645A - Exhaust emission control device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To always surely inhibit emission of unburned exhaust gas components during cold start of an engine by using activated oxygen component in a hybrid vehicle on which the engine is frequently started/stopped and cold start of the engine frequently occurs. <P>SOLUTION: The vehicle provided with two power sources of the engine 10 and a motor 20 is provided with an ozone supply passage 60 capable of supplying ozone to an upstream part of an exhaust gas conversion catalyst 40 in the exhaust gas passage 30, an air pump 61, and an ozone forming device 62. A second control unit 80 operates the ozone supply passage 60, the air pump 61 and the ozone forming device 62 when the engine is started, and raises temperature of the exhaust gas conversion catalyst 40 to second predetermined temperature higher than first predetermined temperature by using a heating heater 50 when stop conditions of the engine 10 are satisfied before temperature of the exhaust gas conversion catalyst 40 reaches the first predetermined temperature lower than catalyst activation temperature. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an exhaust gas purification device, and more particularly to an exhaust gas purification device in a vehicle equipped with two power sources, that is, an internal combustion engine and an electric motor, and belongs to a technical field for improving exhaust emission.

  In general, in a vehicle using fossil fuel such as gasoline as an energy source, the exhaust gas temperature is relatively low for several tens of seconds immediately after the engine is started. Therefore, in the exhaust gas purification catalyst disposed in the exhaust gas passage of the engine. It is known that catalytic metals such as platinum (Pt) and palladium (Pd) are not activated and it is difficult to purify hydrocarbons (HC) and carbon monoxide (CO), which are unburned exhaust gas components. Yes. As one method for improving this, conventionally, a manifold catalyst commonly referred to as “straight catalyzer” in which the catalyst is disposed directly under the exhaust manifold has been widely adopted. However, this method still has a problem that a sufficiently satisfactory purification performance cannot be obtained.

  Therefore, hydrocarbon adsorbents such as zeolite have been used as manifold catalyst materials. That is, when the exhaust gas temperature is relatively low, unburned hydrocarbons discharged from the engine are adsorbed in the pores of the hydrocarbon adsorbent, and when the exhaust gas temperature rises to about 200 ° C., the hydrocarbon adsorption Unburned hydrocarbons adsorbed on the material are released and reacted with a catalytic metal that provides a certain degree of catalytic activity at about 200 ° C. However, in this method, the aluminosilicate porous material such as zeolite has a property that its crystal structure is destroyed at a high temperature, so when used as a manifold catalyst material, the purification performance gradually increases over time. There is a problem of lowering.

Therefore, a method for oxidizing and purifying an unburned exhaust gas component with an active oxygen component without using a hydrocarbon adsorbent such as zeolite has been proposed. For example, Patent Document 1 discloses that ozone (O ₃ ), which is an active oxygen component, is generated by applying a high voltage to air, and this ozone is caused to flow upstream from the catalyst in the exhaust gas passage. Discloses a technique for converting a part of the HC component contained in CO into CO. Here, in general, ozone has a strong oxidizing power and has a long life from decomposition to decomposition at a relatively low temperature of about room temperature, so that the exhaust gas temperature is relatively low (for example, about 100 ° C.). This is considered to be an effective method for oxidizing and purifying unburned exhaust gas components such as HC and CO.

  On the other hand, a hybrid vehicle (HEV) equipped with two power sources of an engine and a motor has a low environmental load and can contribute to a reduction in fuel consumption. However, since the frequency of engine start / stop is high in the hybrid vehicle, the frequency of cold start of the engine is high, and as a result, the unburned exhaust gas components of HC and CO during a period where the exhaust gas temperature is relatively low. Suppressing emissions is an important issue. Therefore, for example, in Patent Document 2, a catalyst heater for activating the catalyst is provided in a hybrid vehicle, and at the start of running by the motor, the catalyst is heated by the catalyst heater so that the catalyst temperature is equal to or higher than a set temperature. A technique for starting the engine at a later stage is disclosed.

JP-A-2005-207316 (paragraphs 0046 to 0050) JP 2005-146910 (paragraph 0003)

  Under such circumstances, the inventors of the present invention oxidize unburned exhaust gas components such as HC and CO using active oxygen components such as ozone in a hybrid vehicle in which cold starting of the engine frequently occurs. As a result of intensive research and examination on purification technology, the following findings were obtained. That is, the engine is cold started and the active oxygen component is supplied to the upstream portion of the exhaust gas passage from the exhaust gas purification catalyst. Next, the engine is stopped and the supply of the active oxygen component is stopped. The engine was repeatedly started with a cold start, and the exhaust gas purification performance during the cold start of the engine was investigated. As a result, when the engine is stopped before the catalyst temperature rises to about 200 ° C., which is lower than the catalyst activation temperature, compared to when the engine is stopped after the catalyst temperature rises above the temperature, The exhaust gas purification performance at the time of cold start of the engine of this was low. The reason for this is not necessarily clear, but the active oxygen component supplied to the exhaust gas passage without excess or deficiency contacts and reacts with unburned exhaust gas components such as HC and CO in the exhaust gas passage with a probability of 100%. Therefore, the remaining active oxygen component reaches the catalyst that has not been fully activated, and an “oxygenated species” generated from unburned hydrocarbons is formed on the surface of the catalyst. It is thought that the catalyst is poisoned by the "oxygenated species" generated from the fuel hydrocarbons, and this state is thought to be partly due to the inhibition of the catalyst function during the cold start of the next engine. .

  The present invention has been made in view of the above-described situation in a hybrid vehicle in which engine start / stop frequently occurs, and therefore engine cold start frequently occurs. It is an object to always and reliably suppress the discharge of unburned exhaust gas components during cold start.

  In order to solve the above-described problem, an invention according to claim 1 is an exhaust gas purification apparatus for an internal combustion engine in a vehicle having two power sources, that is, an internal combustion engine and an electric motor. An disposed exhaust gas purification catalyst, active oxygen component supply means capable of supplying an active oxygen component to an upstream portion of the exhaust gas passage from the exhaust gas purification catalyst, and when the internal combustion engine is started Active oxygen component supply control means for operating the active oxygen component supply means and when the stop condition of the internal combustion engine is established before the temperature of the exhaust gas purification catalyst rises to a first predetermined temperature lower than the catalyst activation temperature Comprises catalyst temperature control means for raising the temperature of the exhaust gas purification catalyst to a second predetermined temperature higher than the first predetermined temperature.

  Next, the invention according to claim 2 is the exhaust gas purifying apparatus according to claim 1, wherein the first predetermined temperature is 150 to 250 ° C, and the second predetermined temperature is 450 to 550 ° C. It is characterized by being.

  Next, the invention according to claim 3 is the exhaust gas purifying apparatus according to claim 1 or 2, wherein the catalyst temperature control means is configured to continuously operate the internal combustion engine or to store electric energy stored in the vehicle. The temperature of the exhaust gas purification catalyst is raised to a second predetermined temperature by at least one of the heating used.

  First, according to the first aspect of the present invention, when the internal combustion engine is started, the active oxygen component is supplied to the upstream portion of the exhaust gas passage with respect to the exhaust gas purification catalyst, and the temperature of the exhaust gas purification catalyst is controlled by the catalyst. When the internal combustion engine stop condition is satisfied before the temperature rises to the first predetermined temperature lower than the activation temperature, the temperature of the exhaust gas purification catalyst is raised to a second predetermined temperature higher than the first predetermined temperature. From the "oxygenated species" generated from the remaining unburned hydrocarbons formed on the surface of the catalyst is removed at a high temperature, and the catalytic function during the cold start of the next engine is restored without being disturbed. The purification effect due to the contact between the unburned exhaust gas component and the catalyst that has not been fully activated does not deteriorate, and the emission of the unburned exhaust gas component during the cold start of the engine is always reliably suppressed. Can The ability.

  Next, according to the invention described in claim 2, in addition to the effect of claim 1, the first predetermined temperature is limited to 150 to 250 ° C and the second predetermined temperature is limited to 450 to 550 ° C. The

  Next, according to the third aspect of the invention, in addition to the effect of the first or second aspect, the continuous operation of the internal combustion engine and / or the electric energy stored in the vehicle (for example, a battery for driving the motor) is obtained. By the heating used, it becomes possible to reliably raise the temperature of the exhaust gas purification catalyst to the second predetermined temperature. Hereinafter, the present invention will be described in more detail through the best embodiment and experimental examples.

  FIG. 1 is a block diagram showing a configuration of a main part of a vehicle according to the present embodiment and a control system. This vehicle 1 is a so-called series / parallel type hybrid vehicle, and includes two power sources of an engine 10 and a motor 20. The driving force of the engine 10 and / or the motor 20 is transmitted to the left and right drive wheels via the transmission 11 and the differential device 12. The motor 20 also functions as a generator (generator) that is driven by the engine 10 to generate power. The motor 20 and the battery 22 are electrically connected via the inverter 21. When the motor 20 functions as a power source, electric power is supplied from the battery 22 to the motor 20, and when the motor 20 functions as a generator, the motor 20 Electric power is supplied to the battery 22.

  An exhaust gas purification catalyst 40 is disposed in the exhaust gas passage 30 of the engine 10. An ozone supply passage 60 joins upstream of the exhaust gas purification catalyst 40 in the exhaust gas passage 30. An air pump 61 and an ozone generator (ozonizer) 62 are disposed in the ozone supply passage 60 from the upstream side. By these 60 to 62, the active oxygen component is disposed upstream of the exhaust gas purification catalyst 40 in the upstream portion of the exhaust gas passage 30. An active oxygen component supply means capable of supplying ozone as a component is configured. Here, the ozone generator 62 generates ozone by silently discharging the air introduced by the air pump 61, for example.

  The first control unit 70 of this vehicle has a signal from the exhaust gas temperature sensor 31 that detects the temperature of the exhaust gas in the exhaust gas passage 30 and a signal from the catalyst temperature sensor 41 that detects the temperature of the exhaust gas purification catalyst 40. In addition to inputting a signal from an accelerator opening sensor 71 for detecting the amount of depression of an accelerator pedal (not shown), for example, means for detecting the operating state of the engine 10 based on, for example, the rotational speed of the engine 10 or the throttle opening Function as a means for controlling the engine 10 according to the detection result, function as a means for detecting the amount of electricity stored in the battery 22 based on power transfer between the inverter 21 and the battery 22, It functions as a means for controlling the motor 20 in accordance with the detection result, or adjusts the state of the exhaust gas purification catalyst 40. To function as.

  Further, the second control unit 80 of the vehicle receives the catalyst state adjustment signal from the first control unit 70 and outputs a control signal to the air pump 61 and the ozone generator 62, and also uses the power of the battery 22. The heater 50 is operated to increase the temperature of the exhaust gas purification catalyst 40.

  In this vehicle, for example, when starting and during low torque traveling, electric power is supplied from the battery 22 to the motor 20, and the vehicle travels with the driving force of the motor 20. During medium torque travel, the engine 10 is started and the vehicle travels with the driving force of the engine 10. During high torque traveling, the vehicle travels with the driving force of the engine 10 and the driving force of the motor 20. When the amount of power stored in the battery 22 decreases, the engine 10 is driven with a torque that is equal to or greater than the required torque during medium torque travel, and the battery 20 is charged with the generated power by driving the generator 20 with the surplus torque. Thus, in this vehicle, since the engine 10 is stopped when starting and running at a low torque, the frequency of start / stop of the engine 10 is increased, and therefore the frequency of cold start of the engine 10 is increased. As a result, it becomes an important issue to suppress the emission of unburned exhaust gas components of HC and CO during a period in which the exhaust gas temperature is relatively low.

  FIG. 2 is a flowchart showing an example of a specific control operation performed by the first and second control units 70 and 80 in order to solve the problem. First, when the engine 10 is started (step S1), it is determined whether or not the exhaust gas temperature is equal to or lower than a predetermined temperature based on the temperature detected by the exhaust gas temperature sensor 31 (step S2). Here, the predetermined temperature is 200 ° C., for example. As a result, when the exhaust gas temperature is equal to or higher than the predetermined temperature, the end is reached, but when the exhaust gas temperature is equal to or lower than the predetermined temperature, the active oxygen component supply means 60 to 62 are operated so Ozone is supplied to the upstream portion of the exhaust gas passage 30 (step S3). Thereby, when the engine 10 is cold started, unburned exhaust gas components such as HC and CO can be oxidized and purified using ozone.

  Next, it is determined whether or not a stop condition for the engine 10 is satisfied (step S4). Here, the stop condition of the engine 10 is, for example, the transition from the medium torque traveling or the high torque traveling to the low torque traveling as described above. Alternatively, the idle stop condition is satisfied during the temporary stop. As a result, when the stop condition of the engine 10 is not satisfied, the end is reached, but when the stop condition of the engine 10 is satisfied, the active oxygen component supply means 60 to 62 are deactivated and the exhaust gas purification is performed. The supply of ozone to the upstream portion of the exhaust gas passage 30 from the catalyst 40 is stopped, and the engine 10 is stopped (step S5).

  Next, based on the temperature detected by the catalyst temperature sensor 41, it is determined whether or not the temperature tmp of the exhaust gas purification catalyst 40 is equal to or lower than a first predetermined temperature tmp1 (step S6). Here, the first predetermined temperature tmp1 is, for example, 150 to 250 ° C. This first predetermined temperature tmp1 is a temperature lower than the activation temperature T of the exhaust gas purification catalyst 40 (for example, the temperature at which the exhaust gas purification rate is 50%, referred to as T50 or light-off temperature). As a result, when the catalyst temperature tmp is equal to or higher than the first predetermined temperature tmp1, the end is reached. 40 is heated (step S7). Thereby, when the stop condition of the engine 10 is satisfied before the temperature tmp of the exhaust gas purification catalyst 40 rises to the first predetermined temperature tmp1, the temperature tmp of the exhaust gas purification catalyst 40 is forcibly raised. become.

  Then, it is determined whether or not the temperature tmp of the exhaust gas purification catalyst 40 is equal to or higher than a second predetermined temperature tmp2 (step S8). Here, the second predetermined temperature tmp2 is a temperature higher than the first predetermined temperature tmp1, and is 450 to 550 ° C., for example. As a result, when the catalyst temperature tmp is equal to or higher than the second predetermined temperature tmp2, the end is reached, but when the catalyst temperature tmp is equal to or lower than the second predetermined temperature tmp2, heating of the exhaust gas purification catalyst 40 is continued. Thus, when the stop condition of the engine 10 is satisfied before the temperature tmp of the exhaust gas purification catalyst 40 rises to the first predetermined temperature tmp1, the temperature tmp of the exhaust gas purification catalyst 40 is forcibly set to the first predetermined temperature tmp1. The temperature is raised to a second predetermined temperature tmp2 higher than the temperature tmp1.

  As described above, in the present embodiment, when the engine 10 is started (step S1), ozone is supplied to the upstream portion of the exhaust gas passage 30 with respect to the exhaust gas purification catalyst 40 (step S3), and the exhaust gas purification is performed. When the stop condition of the engine 10 is satisfied before the temperature tmp of the catalyst 40 rises to the first predetermined temperature tmp1 lower than the catalyst activation temperature T (YES in step S4 to YES in step S6), the exhaust gas purification catalyst 40 Is increased to a second predetermined temperature tmp2 higher than the first predetermined temperature tmp1 (YES in steps S7 and S8), so that residual ozone is not yet fully activated in the catalyst 40. The “oxygenated species” generated from the remaining unburned hydrocarbons formed on the surface of the catalyst 40 by reaching the high temperature (second predetermined temperature tm 2), the catalyst function at the time of the cold start of the next engine 10 is restored without being disturbed, and as a result, the unburned exhaust gas component and the catalyst 40 which has not been fully activated come into contact with each other. Therefore, it is possible to always reliably suppress the discharge of unburned exhaust gas components when the engine 10 is cold-started.

  The above embodiment is the best embodiment of the present invention, but it goes without saying that various modifications and changes may be made without departing from the scope of the claims. For example, in the above-described embodiment, the temperature tmp of the exhaust gas purification catalyst 40 is raised to the second predetermined temperature tmp2 by heating the heater using the electric energy (battery 22) stored in the vehicle. In addition to this, even after the stop condition of the engine 10 is established (step S4), the temperature tmp of the exhaust gas purification catalyst 40 may be raised to the second predetermined temperature tmp2 by continuously operating the engine 1. .

Exhaust gas purification performance tests were conducted by passing simulated exhaust gas through an exhaust gas purification catalyst commonly used in gasoline engines. The composition of the simulated gas was 700 ppmC for propylene, 0.3 vol% for ozone (O ₃ ), 0.7 vol% for oxygen (O ₂ ), and the rest for nitrogen. The flow rate of the simulation gas was 10 L / min, and the temperature of the simulation gas was started from 70 ° C. (cold start), and the temperature was increased at 10 ° C./min. The ozone generation output of the ozone generator was 150 W. At this time, the amount of ozone generated was 30 cc / min when the air temperature was 70 ° C. Regarding the catalyst used, the total amount of the catalyst noble metal was 7.0 g / L, and the breakdown was Pt: Pd: Rh 1: 30: 2 by mass ratio. Further, Pd-supporting Al ₂ O ₃ was 100 g / L, Rh-supporting OSC material (oxygen storage material containing ceria) was 70 g / L, and Pt-supporting Al ₂ O ₃ was 60 g / L.

And in the Example, the catalyst was heated to 500 degreeC before the purification performance test of the said simulation gas. That is, an exhaust gas simulation gas of stoichiometric (A / F = 14.7) was circulated through the exhaust gas purification catalyst. Its composition, propylene 1400ppmC, 0.6vol% of CO, 1000 ppm of NO, the CO ₂ 13.9vol%, the _{H 2} 0.2 vol%, the _{O 2} 0.6vol%, 10vol% of _{H 2} O, The rest was nitrogen. The flow rate of the simulation gas was 10 L / min, and the temperature of the simulation gas was started at 70 ° C. and increased at 10 ° C./min. Until the temperature of the simulated gas reached 200 ° C., 0.3 vol% ozone (O ₃ ) and 0.7 vol% oxygen (O ₂ ) were further supplied to the stoichiometric exhaust gas having the above composition. When the temperature of the catalyst is 200 to 500 ° C., the supply of ozone (O ₃ ) 0.3 vol% and oxygen (O ₂ ) 0.7 vol% is stopped, and only the stoichiometric exhaust gas having the above composition is used as the catalyst. Circulated. That is, the temperature of the catalyst was raised to 500 ° C. by the temperature of the simulated gas.

On the other hand, in the comparative example, heating of the catalyst was not performed before the purification performance test of the simulated gas. That is, until the simulated gas temperature reaches 200 ° C., 0.3 vol% ozone (O ₃ ) and 0.7 vol% oxygen (O ₂ ) are further supplied to the stoichiometric exhaust gas having the above composition. Was passed through the catalyst, where the flow of simulated gas and ozone was stopped. Furthermore, as a reference example, the catalyst is not heated before the simulated gas purification performance test, and 1.0 vol% oxygen (without ozone (O ₃ ) is supplied during the simulated gas purification performance test. Only O ₂ ) was supplied.

  The results are shown in FIG. In the example in which the catalyst was forcibly heated to 500 ° C. before the simulated gas purification performance test, the propylene emission concentration decreased significantly from the early stage compared to the comparative examples and reference examples in which such heating was not performed. It was clear that the exhaust gas purification performance at the cold start was excellent.

  As described above in detail with reference to specific examples, the present invention uses an active oxygen component in a hybrid vehicle in which engine cold start frequently occurs, and uses an unburned exhaust gas component during engine cold start. Therefore, it is expected to have wide industrial applicability in the technical field of improving the exhaust emission of a hybrid vehicle in which the engine is frequently started and stopped.

1 is a block diagram showing a configuration of a main part of a vehicle and a control system according to a best embodiment of the present invention. It is a flowchart which shows an example of the concrete control operation | movement which the 1st, 2nd control unit of the said vehicle performs. It is a graph which shows the result of the exhaust gas purification performance test of the Example of this invention, a comparative example, and a reference example.

Explanation of symbols

1 Exhaust gas purification device 10 Engine (internal combustion engine)
20 Motor (electric motor)
22 battery 30 exhaust gas passage 31 exhaust gas temperature sensor 40 exhaust gas purification catalyst 41 catalyst temperature sensor 50 heater 60 ozone supply passage (active oxygen component supply means)
61 Air pump (active oxygen component supply means)
62 Ozone generator (active oxygen component supply means)
80 Second control unit (active oxygen component supply control means, catalyst temperature control means)

Claims (3)

An exhaust gas purifying device for an internal combustion engine in a vehicle having two power sources of an internal combustion engine and an electric motor,
An exhaust gas purification catalyst disposed in an exhaust gas passage of the internal combustion engine;
Active oxygen component supply means capable of supplying an active oxygen component to an upstream portion of the exhaust gas passage from the exhaust gas purification catalyst;
Active oxygen component supply control means for operating the active oxygen component supply means when the internal combustion engine is started;
When the stop condition of the internal combustion engine is satisfied before the temperature of the exhaust gas purification catalyst rises to a first predetermined temperature lower than the catalyst activation temperature, the temperature of the exhaust gas purification catalyst is higher than the first predetermined temperature. An exhaust gas purification device comprising catalyst temperature control means for raising the temperature to a second predetermined temperature. The exhaust gas purification device according to claim 1,
The exhaust gas purifying apparatus according to claim 1, wherein the first predetermined temperature is 150 to 250 ° C, and the second predetermined temperature is 450 to 550 ° C. The exhaust gas purification device according to claim 1 or 2,
The catalyst temperature control means raises the temperature of the exhaust gas purification catalyst to a second predetermined temperature by at least one of continuous operation of the internal combustion engine or heating using electric energy stored in the vehicle. Exhaust gas purifier.

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