JP2024111756A - Exhaust purification equipment - Google Patents

Abstract

To reduce an emission amount of HC as much as possible and inhibit deterioration of a catalyst to extend the service life thereof.SOLUTION: An exhaust emission control apparatus 41 is configured to: be mounted in the exhaust passage 4 of an internal combustion engine 100; have an HC adsorption exhaust emission control device 411 capable of adsorbing HC, and another type of exhaust emission control device 412 capable of controlling emission of HC; and be accompanied by a cooling mechanism 413 capable of cooling the HC adsorption exhaust emission control device 411. The exhaust emission control device 41 is configured to suppress, by the cooling mechanism 413, the temperature of the HC adsorption exhaust emission control device 411 to a predetermined adsorption temperature or less when the temperature of the other type of exhaust emission control device 412 is below a predetermined activation temperature, and suppress the temperature of the HC adsorption exhaust emission control device 411 to a predetermined upper limit temperature or less, which is higher than the adsorption temperature, when the temperature of the other type of exhaust emission control device 412 is equal to or higher than the activation temperature.SELECTED DRAWING: Figure 2

Description

The present invention relates to an exhaust purification device that can be applied to an internal combustion engine mounted on a vehicle, etc.

In general, a three-way catalyst is installed in the exhaust passage of an internal combustion engine to purify harmful substances contained in the exhaust, such as hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides (NOx ₎ . A three-way catalyst is made by supporting a precious metal such as platinum (Pt), palladium (Pd), or rhodium (Rh) on a carrier. When exhaust gas passes through the three-way catalyst, HC and CO undergo an oxidation reaction and _NOx undergoes a reduction reaction, converting them into harmless water ( _H2O ), carbon dioxide ( _CO2) , and nitrogen ( _N2) (see, for example, the following patent document).

JP 2013-155699 A

Immediately after a cold start of an internal combustion engine, the temperature of both the internal combustion engine itself and the three-way catalyst used to purify the exhaust gas are low. HC is easily generated in the combustion chamber of the cylinder, and the three-way catalyst is not yet activated, so its purification efficiency is insufficient. As a result, there is a risk that HC will be emitted to the outside.

One possible solution is to place an adsorption catalyst that can adsorb HC upstream of the three-way catalyst, and hold the HC and stop it from flowing into the three-way catalyst until the three-way catalyst heats up and becomes activated.

However, the adsorption temperature of the HC adsorption catalyst is limited to approximately 200°C, and if the temperature is raised beyond that, the adsorbed HC will dissipate. In contrast, the activation temperature of a three-way catalyst is approximately 350°C or higher. This creates a problem in that HC will flow in from the HC adsorption catalyst before the three-way catalyst is activated.

On the other hand, after the internal combustion engine has finished warming up and the catalyst has sufficiently heated up, if the internal combustion engine is operated under high load, a large amount of high-temperature exhaust gas will flow through the exhaust passage, causing the catalyst temperature to rise excessively, which could lead to catalyst deterioration.

The intended purpose of the present invention is to reduce HC emissions as much as possible and to inhibit catalyst deterioration to extend its life.

In the present invention, an exhaust purification device is provided that is mounted in the exhaust passage of an internal combustion engine, has an HC adsorption catalyst capable of adsorbing HC, and another type of catalyst capable of purifying HC, and is provided with a cooling mechanism capable of cooling the HC adsorption catalyst, and the cooling mechanism suppresses the temperature of the HC adsorption catalyst below a predetermined adsorption temperature when the temperature of the other type of catalyst is below a predetermined activation temperature, and suppresses the temperature of the HC adsorption catalyst below a predetermined upper limit temperature higher than the adsorption temperature when the temperature of the other type of catalyst is equal to or higher than the activation temperature.

The HC adsorption catalyst and the other types of catalysts are preferably positioned in close proximity to the exhaust manifold of the internal combustion engine.

The present invention can further reduce HC emissions. It also makes it possible to suppress catalyst deterioration and extend the catalyst's life.

1 is a diagram showing a schematic configuration of an internal combustion engine according to an embodiment of the present invention; 2 is a side view showing the structure of the exhaust gas purification device according to the embodiment, with a part cut away; FIG. 2 is an enlarged cross-sectional view showing a main part of an HC adsorption catalyst provided in the exhaust purification device of the embodiment; FIG. FIG. 4 is a flow chart showing an example of processing executed by the control device according to a program of the embodiment.

An embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows an overview of an internal combustion engine 100 for a vehicle according to this embodiment. The internal combustion engine 100 is a spark-ignition four-stroke reciprocating engine having a plurality of cylinders 1 (one of which is shown in FIG. 1). An injector 11 that injects fuel toward the intake port is provided upstream of the intake valve of each cylinder 1 and near the intake port connected to each cylinder 1. An ignition plug 12 is attached to the ceiling of the combustion chamber of each cylinder 1. The ignition plug 12 generates a spark discharge between the center electrode and the ground electrode when an induced voltage generated by the ignition coil is applied to the ignition coil. The ignition coil is integrally built into the coil case together with an igniter, which is a semiconductor switching element.

The intake passage 3, which supplies intake air to the cylinders 1, takes in air from the outside and directs it to the intake port of each cylinder 1. An air cleaner 31, an electronic throttle valve 32, which is an intake throttle valve, a surge tank 33, and an intake manifold 34 are arranged in this order from upstream on the intake passage 3.

The exhaust passage 4, which discharges exhaust gas from the cylinders 1, guides gas generated by burning fuel inside the cylinders 1 to the outside through the exhaust port of each cylinder 1. An exhaust manifold 42 and an exhaust purification device 41 are arranged on the exhaust passage 4.

As shown in FIG. 2, the exhaust purification device 41 of this embodiment has a catalyst 412 other than the HC adsorption catalyst, specifically a three-way catalyst 412, arranged in series immediately downstream of the HC adsorption catalyst 411. The HC adsorption catalyst 411 temporarily adsorbs HC contained in the gas discharged from the cylinder 1. The HC adsorption catalyst 411 is formed by coating and supporting a material 4111 capable of adsorbing HC, such as zeolite, on a carrier 4110. The carrier 4110 is a honeycomb structure having numerous small holes penetrating the carrier 4110 along its extension direction, i.e., the direction in which the exhaust gas flows. The carrier 4110 of the HC adsorption catalyst 411 is preferably made of a metal or ceramic having a higher thermal conductivity than the carrier of the three-way catalyst 412, such as titania TiO ₂ or alumina Al ₂ O ₃ . As shown in FIG. 3, it is also possible to coat a carrier 4110 with an HC adsorption material 4111 and then coat the carrier with a precious metal material 4112 such as platinum (Pt), palladium (Pd), or rhodium (Rh) that functions as a three-way catalyst.

The three-way catalyst 412 induces an oxidation/reduction reaction of harmful substances HC, CO, and _NOx contained in the gas discharged from the cylinder 1, rendering them harmless. The three-way catalyst 412 is formed by coating and supporting a carrier with a precious metal such as Pt, Pd, or Rh. The carrier of the three-way catalyst 412 is also a honeycomb structure with countless small holes that penetrate the carrier in the extension direction, i.e., the direction in which the exhaust gas flows. The carrier of the three-way catalyst 412 is made of ceramics.

The carrier of the three-way catalyst 412 is in contact with or close to the carrier 4110 of the HC adsorption catalyst 411 from the downstream side. Both are then housed together in a single cylindrical casing 415. A known retaining material 414 is provided between the outer periphery of the carrier of the three-way catalyst 412 and the inner periphery of the casing 415. In contrast, a retaining material is not necessarily provided between the outer periphery of the carrier 4110 of the HC adsorption catalyst 411 and the inner periphery of the casing 415, and the carrier 4110 is directly in contact with or close to the casing 415. However, there is no prohibition on providing a retaining material between the carrier 4110 and the casing 415.

The exhaust purification device 41 (casing 415) containing the HC adsorption catalyst 411 and the three-way catalyst 412 is directly connected downstream of the exhaust manifold 42 in the exhaust passage 4 or is located as close as possible to the exhaust manifold 42. In addition, the exhaust purification device 41 is abutted against or located close to the side of the main body (cylinder block and/or cylinder head) of the internal combustion engine 100.

1 and 2, the HC adsorption catalyst 411 is provided with cooling mechanisms 413, 51, and 52. The cooling mechanism is a water-cooled type that has a water jacket 413 surrounding the HC adsorption catalyst 411 and cools the HC adsorption catalyst 411 with cooling water flowing through the water jacket 413 to appropriately suppress the temperature rise. The water jacket 413 does not necessarily surround the three-way catalyst 412 and does not directly cool the three-way catalyst 412. It is preferable to use the cooling water of the internal combustion engine 100. In other words, a portion of the cooling water flowing through each part of the internal combustion engine 100 is introduced from the main body of the internal combustion engine 100 into the water jacket 413, and the cooling water that has passed through the water jacket 413 is returned to the main body of the internal combustion engine 100. In this way, the water pump 51 of the internal combustion engine 100 can also be used as a pump for the water jacket 413. In the illustrated example, the water tucket 413 is arranged along the outer periphery of the casing 415, but the water jacket 413 may be arranged inside the casing 415, between the outer periphery of the carrier 4110 and the inner periphery of the casing 415.

A control valve 52 is installed on the cooling water flow path. When the control valve 52 is open, the cooling water flows through the water jacket 413. When the control valve 52 is closed, the cooling water does not flow through the water jacket 413 and stagnates. The control valve 52 is preferably one that can be controlled by an electronic control unit (ECU) 0. However, the control valve 52 may be a mechanical thermostat that uses wax, bimetal, shape memory alloy, etc. The control valve 52 may also be a flow control valve that can flexibly increase or decrease the flow rate of the cooling water by expanding or contracting the opening degree.

Air-fuel ratio sensors 43, 44 are installed upstream and downstream of the exhaust purification device 41 in the exhaust passage 4 to detect the air-fuel ratio of the gas flowing through the exhaust passage 4. The air-fuel ratio sensors 43, 44 may be _O2 sensors having nonlinear output characteristics with respect to the air-fuel ratio of the gas, or linear A/F sensors having output characteristics proportional to the air-fuel ratio of the gas, but in this embodiment, _O2 sensors are assumed. The _O2 sensors 43, 44 may be provided with heaters for heating them.

The exhaust gas recirculation device 2 includes an external EGR passage 21 that connects the exhaust passage 4 and the intake passage 3, an EGR cooler 22 provided on the EGR passage 21, and an EGR valve 23 that opens and closes the EGR passage 21 to control the flow rate of EGR gas flowing through the EGR passage 21. The inlet of the EGR passage 21 is connected to a predetermined location downstream of the exhaust purification device 41 in the exhaust passage 4. The outlet of the EGR passage 21 is connected to a predetermined location downstream of the throttle valve 32 in the intake passage 3, in particular the surge tank 33 or the intake manifold 34.

The ECU 0, which controls the operation of the internal combustion engine 100, is a microcomputer system having a processor, memory, an input interface, an output interface, etc. The ECU 0 may be configured by connecting multiple ECUs or controllers so that they can communicate with each other via an electrical communication line such as a CAN (Controller Area Network).

The input interface of the ECU0 receives inputs such as a vehicle speed signal a output from a vehicle speed sensor that detects the actual vehicle speed of the vehicle, a crank angle signal b output from a crank angle sensor that detects the rotation angle of the crankshaft of the internal combustion engine 100 and the engine speed, an accelerator opening signal c output from a sensor that detects the amount of depression of the accelerator pedal by the driver of the vehicle as the accelerator opening (in other words, the required engine load rate or engine torque), a cooling water temperature signal d output from a water temperature sensor that detects the temperature of the cooling water of the internal combustion engine 100, an intake air temperature/intake pressure signal e output from a sensor that detects the intake air temperature and intake pressure in the intake passage 3, particularly the surge tank 33 or the intake manifold 34, an air-fuel ratio signal f output from an air-fuel ratio sensor 43 that detects the air-fuel ratio of the gas upstream of the exhaust purification device 41 in the exhaust passage 4, an air-fuel ratio signal g output from an air-fuel ratio sensor 44 that detects the air-fuel ratio of the gas downstream of the exhaust purification device 41, and an atmospheric pressure signal h output from an atmospheric pressure sensor that detects the atmospheric pressure.

The output interface of ECU0 outputs an ignition signal i to an igniter associated with the spark plug 12, a fuel injection signal j to the injector 11, an opening operation signal k to the electronic throttle valve 32, an opening operation signal l to the EGR valve 23, an opening operation signal m to the control valve 52, etc.

The processor of ECU0 interprets and executes a program stored in memory in advance, calculates operating parameters, and controls the operation of internal combustion engine 100. ECU0 acquires various information a, b, c, d, e, f, g, and h required for controlling the operation of internal combustion engine 100 via an input interface, and determines various operating parameters such as the required fuel injection amount appropriate to the amount of air taken into cylinder 1, fuel injection timing (including the number of fuel injections per combustion), fuel injection pressure, ignition timing (including the number of spark ignitions per combustion), and required EGR rate (or EGR gas amount). ECU0 applies various control signals i, j, k, l, and m corresponding to the operating parameters via an output interface.

As shown in FIG. 4, in this embodiment, immediately after the cold start of the internal combustion engine 100, when the internal combustion engine 100 and the exhaust purification device 41 are at low temperatures, the temperature of the HC adsorption catalyst 411 is suppressed to a predetermined adsorption temperature, for example, about 200° C. or less (step S2) until the warm-up of the internal combustion engine 100 is completed and the temperature of the three-way catalyst 412 rises to a predetermined activation temperature, for example, about 350° C. or more (step S1). To achieve this, the ECU 0 performs feedback control by giving a control signal m to the control valve 52 to open and close it in order to maintain the current temperature of the HC adsorption catalyst 411 below the adsorption temperature until the current temperature of the three-way catalyst 412 reaches the activation temperature. The current temperatures of the HC adsorption catalyst 411 and the three-way catalyst 412 may be measured by a temperature sensor or may be estimated by a known method. Step S2 is intended to adsorb and stop HC in the adsorption catalyst 411 until the three-way catalyst 412 is activated and fully exerts the purification performance of the harmful substance HC.

If the temperature of the three-way catalyst 412 rises above the activation temperature, the temperature of the HC adsorption catalyst 411 is subsequently suppressed to a predetermined upper limit temperature, for example, about 800°C or less (step S3). At the same time, the temperature of the three-way catalyst 413 is suppressed to a temperature above the activation temperature and a predetermined upper limit temperature, for example, about 800°C or less. To achieve this, the ECU 0 performs feedback control by giving a control signal m to the control valve 52 to open and close it in order to maintain the current temperature of the HC adsorption catalyst 411 below the upper limit temperature and/or to maintain the current temperature of the three-way catalyst 412 below the upper limit temperature. Step S3 is intended to prevent deterioration of the HC adsorption catalyst 411 and the three-way catalyst 412 due to heat damage.

The actions of steps S2 and S3 may be achieved by setting the thermostat, which is the control valve 52.

In this embodiment, the exhaust purification device 41 is mounted in the exhaust passage 4 of the internal combustion engine 100, and has an HC adsorption exhaust purification device 411 capable of adsorbing HC and another type of exhaust purification device 412 capable of purifying HC. The exhaust purification device 41 is provided with cooling mechanisms 413, 51, and 52 capable of cooling the HC adsorption exhaust purification device 411. The cooling mechanisms 413, 51, and 52 suppress the temperature of the HC adsorption exhaust purification device 411 to a predetermined adsorption temperature or lower when the temperature of the other type of exhaust purification device 412 is below a predetermined activation temperature, and suppress the temperature of the HC adsorption exhaust purification device 411 to a predetermined upper limit temperature higher than the adsorption temperature when the temperature of the other type of exhaust purification device 412 is equal to or higher than the activation temperature.

According to this embodiment, the temperature rise of the HC adsorption catalyst 411 can be suppressed until the three-way catalyst 412 is activated, so that the adsorbed HC is prevented from being dispersed. After the three-way catalyst 412 is activated, the HC can be dispersed from the HC adsorption catalyst 411 and appropriately purified by the three-way catalyst 412. This can contribute to further reducing the amount of harmful HC emissions.

In addition, after the three-way catalyst 412 is activated, the HC adsorption catalyst 411 and the three-way catalyst 412 can be prevented from becoming excessively hot (the cooling mechanisms 413, 51, and 52 are used even in the high-load operating range after the internal combustion engine 100 has finished warming up). Therefore, deterioration of the catalysts 411 and 412 can be suppressed, and their lifespan can be extended.

The HC adsorption catalyst 411 and the three-way catalyst 412 are both housed inside a single casing 415, which is attached to the main body of the internal combustion engine 100, making the internal combustion engine 100 and the exhaust purification device 41 as a whole compact and allowing them to be housed inside the engine room (engine compartment) of the vehicle body. It is not necessary to place various catalysts in a location away from the internal combustion engine 100, in the exhaust pipe that extends forward and backward under the floor of the vehicle body. Placing the three-way catalyst 412 as close as possible to the main body of the internal combustion engine 100 promotes the temperature rise of the three-way catalyst 412 during cold start, leading to early activation.

It is also possible to perform deterioration diagnosis (diagnosis) of the catalysts 411, 412 by referring to the output signals f, g of the air-fuel ratio sensors 43, 44 installed upstream and downstream of the exhaust purification device 41.

The present invention is not limited to the embodiment described above. For example, a gasoline particulate filter that captures particulate matter may be provided in addition to the three-way catalyst at the location indicated by reference numeral 412 in FIG. 2.

In addition, the specific configuration of each part can be modified in various ways without departing from the spirit of the present invention.

100... internal combustion engine 0... control device (ECU)
4... Exhaust passage 41... Exhaust purification device 411... HC adsorption catalyst 412... Other type of catalyst (three-way catalyst)
413, 51, 52...cooling mechanism (water jacket, water pump, control valve)
415: Casing 42: Exhaust manifold 43, 44: Air-fuel ratio sensor m: Control valve opening operation signal

Claims (2)

An exhaust purification device that is installed in an exhaust passage of an internal combustion engine,
The present invention relates to an HC adsorption catalyst and a catalyst for purifying HC.
The exhaust purification device uses the cooling mechanism to suppress the temperature of the HC adsorption catalyst to below a predetermined adsorption temperature when the temperature of the other type of catalyst is below a predetermined activation temperature, and to suppress the temperature of the HC adsorption catalyst to below a predetermined upper limit temperature that is higher than the adsorption temperature when the temperature of the other type of catalyst is equal to or higher than the activation temperature. The exhaust purification device according to claim 1, in which the HC adsorption catalyst and the other type of catalyst are disposed in close proximity to the exhaust manifold of the internal combustion engine.

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