WO2013187285A1

WO2013187285A1 - Exhaust device for internal combustion engine

Info

Publication number: WO2013187285A1
Application number: PCT/JP2013/065499
Authority: WO
Inventors: 徹深見; 智荻原
Original assignee: 日産自動車株式会社
Priority date: 2012-06-12
Filing date: 2013-06-04
Publication date: 2013-12-19
Also published as: JP2015165095A

Abstract

An exhaust device for an internal combustion engine is equipped with: a first catalyst (32) for purifying exhaust discharged from an internal combustion engine (1); a cooler (33) for cooling the first catalyst (32); and a second catalyst (34) for purifying the exhaust discharged from the first catalyst (32), and positioned near the first catalyst (32). Therein, the thermal capacity of the first catalyst (32) is smaller than that of the second catalyst (34).

Description

Exhaust device for internal combustion engine

The present invention relates to an exhaust device for an internal combustion engine.

In the conventional exhaust system of an internal combustion engine described in JP5-179942A, the exhaust gas discharged from the exhaust port is cooled by the cooling device after passing the catalyst provided in the exhaust manifold. Thereby, the exhaust performance at the time of engine start was improved.

However, the above-described conventional exhaust system for an internal combustion engine has a problem that the catalyst temperature may be excessively increased and the catalyst may be deteriorated at a high engine load when the exhaust gas is at a high temperature.

The present invention has been made paying attention to such a problem, and an object thereof is to suppress the deterioration of the catalyst at the time of high engine load while improving the exhaust performance at the time of starting the engine.

According to an aspect of the present invention, the first catalyst that purifies the exhaust discharged from the internal combustion engine, the cooler that cools the first catalyst, and the first catalyst are provided in the vicinity of the first catalyst and discharged from the first catalyst. And an exhaust device for an internal combustion engine having a heat capacity of the first catalyst smaller than that of the second catalyst.

Embodiments of the present invention and advantages of the present invention will be described in detail below with reference to the accompanying drawings.

FIG. 1 is a schematic configuration diagram of an engine according to an embodiment of the present invention. FIG. 2 is a perspective view of the first manifold catalyst and the cooler. 3 is a III-III cross-sectional view of the first manifold catalyst and the cooler of FIG. FIG. 4 is a view showing one end face of the first manifold catalyst in the axial direction. FIG. 5A is a cross-sectional view of a main part of the first manifold catalyst. FIG. 5B is a cross-sectional view of a main part of the second manifold catalyst. FIG. 6 is a diagram for explaining the operation and effect of the exhaust device according to the embodiment of the present invention. FIG. 7 is a schematic configuration diagram of an engine according to another embodiment of the present invention.

FIG. 1 is a schematic configuration diagram of an engine 1 according to an embodiment of the present invention.

The engine 1 includes a cylinder block 11 and a cylinder head 12, and is mounted in the engine room of the vehicle.

The cylinder block 11 includes a cylinder part 11a and a crankcase part 11b.

A plurality of cylinders 110 are formed in the cylinder part 11a. A piston 111 that receives combustion pressure and reciprocates inside the cylinder 110 is housed inside the cylinder 110.

The crankcase part 11b is formed below the cylinder part 11a. The crankcase part 11b supports the crankshaft 112 rotatably. The crankshaft 112 converts the reciprocating motion of the piston 111 into rotational motion via the connecting rod 113.

The cylinder head 12 is attached to the upper surface of the cylinder block 11 and forms a part of the combustion chamber 13 together with the cylinder 110 and the piston 111.

The cylinder head 12 is formed with an intake port 120 connected to the intake manifold 24 and opening to the top wall of the combustion chamber 13, and an exhaust port 121 connected to the exhaust manifold 31 and opening to the top wall of the combustion chamber 13. An ignition plug 122 is provided so as to face the center of the top wall of the combustion chamber 13. Further, the cylinder head 12 is provided with an intake valve 123 that opens and closes the opening between the combustion chamber 13 and the intake port 120, and an exhaust valve 124 that opens and closes the opening between the combustion chamber 13 and the exhaust port 121. Further, the cylinder head 12 is provided with an intake camshaft 125 that drives the intake valve 123 to open and close, and an exhaust camshaft 126 that drives the exhaust valve 124 to open and close.

The cylinder portion 11a and the cylinder head 12 of the cylinder block 11 are provided with

water jackets

114 and 127 through which cooling water for cooling around the cylinder 110 and the combustion chamber 13 circulates.

The intake device 2 of the engine 1 is a device that introduces a necessary amount of intake air into the engine 1, and includes an air cleaner 21, an air flow meter 22, an electronically controlled throttle valve 23, an intake manifold 24, and a fuel injection valve 25. And comprising.

The air cleaner 21 removes foreign matters such as sand contained in the intake air.

The air flow meter 22 detects the intake air amount.

The throttle valve 23 adjusts the intake air amount sucked into each cylinder 110 by changing the passage step area of the intake passage 20 continuously or stepwise. The throttle valve 23 is driven to open and close by a throttle actuator 26, and its opening (hereinafter referred to as “throttle opening”) is detected by a throttle sensor 27.

The intake manifold 24 is connected to the intake port 120 of the engine 1, and distributes and introduces the intake air flowing in through the throttle valve 23 to each cylinder 110 evenly.

The fuel injection valve 25 injects fuel toward the intake port 120 in accordance with the operating state of the engine 1.

The exhaust device 3 of the engine 1 is a device that converts harmful substances in the exhaust discharged from the engine 1 into innocuous substances and then discharges them to the outside air. The exhaust manifold 31, the first manifold catalyst 32, the cooling A vessel 33, a second manifold catalyst 34, and an underfloor catalyst 35.

The exhaust manifold 31 is connected to the exhaust port 121 of the engine 1, collects the exhaust discharged from each cylinder 110, and introduces it into the first manifold catalyst 32 disposed in the engine room of the vehicle.

The first manifold catalyst 32 and the cooler 33 will be further described with reference to FIGS.

FIG. 2 is a perspective view of the first manifold catalyst 32 and the cooler 33. 3 is a cross-sectional view taken along the line III-III in FIG. FIG. 4 is a view showing one end face of the first manifold catalyst 32 in the axial direction.

2 and 3, the first manifold catalyst 32 is integrated with a cooler 33 that cools the first manifold catalyst 32. As shown in FIG. As shown in FIG. 4, the first manifold catalyst 32 is partitioned by SiC (silicon carbide) partition walls 32a and penetrates in the axial direction from one end face to the other end face, and a plurality of cells through which exhaust flows. A three-way catalyst is supported on the surface of a carrier having 32b. The first manifold catalyst 32 converts harmful substances such as hydrocarbons, nitrogen oxides, and carbon monoxide in the exhaust into harmless substances by the three-way catalyst and discharges them. In addition, as a structure of the carrier, as shown in FIG. 4, the cells 32b may have a lattice shape, or may have a honeycomb shape, and the shape is not particularly limited.

In order for the first manifold catalyst 32 to obtain a high heat exchange rate with the cooler 33, it is preferable to use a material containing SiC having a high thermal conductivity as the material of the carrier.

The cooler 33 includes an accommodating portion 33a for accommodating the first manifold catalyst 32 therein, a water jacket 331 formed over the outer periphery of the accommodating portion 33a, and an inlet 33b for introducing cooling water into the water jacket 331. And a discharge port 33c for discharging cooling water from the water jacket 331. The cooler 33 cools the first manifold catalyst 32 with cooling water flowing through the water jacket 331.

The inlet 33b and the outlet 33c of the cooler 33 are formed so as to face the side surfaces of the cooler 33, respectively.

The inlet 33b of the cooler 33 communicates with the water jacket 114 of the cylinder block 11 on the cooling water inlet side by a cooling water introduction pipe 332. As a result, a part of the cooling water that is pumped by the water pump (not shown) and introduced into the water jacket 114 of the cylinder block 11 is introduced into the water jacket 331 through the introduction port 33b.

Further, the discharge port 33c of the cooler 33 communicates with the water jacket 127 of the cylinder head 12 on the cooling water outlet side through the cooling water discharge pipe 333. Thereby, the cooling water introduced into the water jacket 331 from the introduction port 33 b is discharged from the discharge port 33 c to the cooling water discharge pipe 333 and returned to the water jacket 127 of the cylinder head 12.

The second manifold catalyst 34 is provided close to the first manifold catalyst 32 and is disposed in the engine room of the vehicle. The second manifold catalyst 34 has a three-way catalyst supported on the surface of a lattice-shaped carrier, and removes harmful substances such as hydrocarbons, nitrogen oxides, and carbon monoxide in the exhaust gas from the three-way catalyst. To be discharged. The structure of the carrier of the second manifold catalyst 34 may be a honeycomb shape in addition to the lattice shape, and the shape is not particularly limited. Differences between the first manifold catalyst 32 and the second manifold catalyst 34 will be described later with reference to FIGS. 5A and 5B.

The underfloor catalyst 35 is provided under the floor of the vehicle. The underfloor catalyst 35 has a three-way catalyst supported on the surface of a lattice-like carrier, and converts harmful substances such as hydrocarbons, nitrogen oxides, and carbon monoxide in the exhaust into harmless substances by the three-way catalyst. Then discharge. The exhaust discharged from the underfloor catalyst 35 is discharged to the outside air through a muffler (not shown) that reduces exhaust noise.

The controller 4 includes a microcomputer having a central processing unit (CPU), a read only memory (ROM), a random access memory (RAM), and an input / output interface (I / O interface).

In addition to the detection signals from the air flow meter 22 and the throttle sensor 27, the controller 4 includes a water temperature sensor 41 for detecting the temperature of cooling water flowing through the water jacket 114 (hereinafter referred to as “engine water temperature”), and a crank angle. Detection from various sensors that detect the operating state of the engine 1, such as an engine speed sensor 42 that detects the engine speed and an accelerator stroke sensor 43 that detects the amount of depression of the accelerator pedal (hereinafter referred to as "accelerator operation amount"). A signal is input.

The controller 4 optimally controls the throttle opening, fuel injection amount, ignition timing and the like based on the detected operating state of the engine 1. For example, when a predetermined operating state such as when the vehicle is decelerated, fuel cut control for stopping fuel injection to each cylinder 110 is performed to improve fuel efficiency.

Further, the controller 4 automatically stops the engine 1 if a predetermined engine stop condition is satisfied, for example, when the vehicle stops due to a signal wait, and the engine 1 if a predetermined engine restart condition is satisfied thereafter. Implement idle stop control to restart

The engine stop condition includes an accelerator operation amount being smaller than a predetermined amount, a brake pedal being depressed, and a vehicle speed being smaller than a predetermined value. The engine restart condition includes that the accelerator operation amount is larger than a predetermined amount and that the brake pedal is not depressed.

FIG. 5A and FIG. 5B are diagrams for explaining the difference between the first manifold catalyst 32 and the second manifold catalyst 34. FIG. 5A is a cross-sectional view of the main part of the first manifold catalyst 32. FIG. 5B is a cross-sectional view of a main part of the second manifold catalyst 34.

As shown in FIGS. 5A and 5B, the first manifold catalyst 32 is formed such that the actual opening area of the carrier carrying the three-way catalyst is larger than the actual opening area of the second manifold catalyst 34. . That is, a coarse carrier is used for the first manifold catalyst 32, and a fine carrier is used for the second manifold catalyst 34. The actual opening area in the present embodiment is as follows when the number of lattices of the carrier supporting the three-way catalyst is n, the longitudinal length of the lattice is H, and the lateral length of the lattice is W: This is a value defined by equation (1).

Actual opening area = H x W x n (1)

The first manifold catalyst 32 is formed so that the surface area of the carrier carrying the three-way catalyst is smaller than the surface area of the second manifold catalyst 34. That is, the heat capacity of the first manifold catalyst 32 is made smaller than the heat capacity of the second manifold catalyst 34. In this embodiment, the surface area refers to the number of lattices of the carrier carrying the three-way catalyst is n, the longitudinal length of the lattice is H, the lateral length of the lattice is W, and the depth of the lattice (the length of the carrier). (S) is a value defined by the following equation (2), where D is D.

Surface area = 2 (H + W) × D × n (2)

By making the actual opening area of the first manifold catalyst 32 larger than the actual opening area of the second manifold catalyst 34, the exhaust resistance in the first manifold catalyst 32 is improved by suppressing the exhaust resistance of the first manifold catalyst 32. Can do. Since the exhaust resistance of the second manifold catalyst 34 is larger than the exhaust resistance of the first manifold catalyst 32, the exhaust discharged from the first manifold catalyst 32 is reflected at the inlet of the second manifold catalyst 34, and the exhaust is reflected. A wave is generated. For this reason, exhaust gas stays in the downstream area of the first manifold catalyst 32.

As described above, exhaust gas stays in the downstream area of the first manifold catalyst 32 while improving exhaust passage of the first manifold catalyst 32, so that the engine speed is relatively low at the time of engine start and the like. Even in the operation region where the flow rate is low, the first manifold catalyst 32 can be activated early.

Also, the early activation of the first manifold catalyst 32 can be further promoted by making the heat capacity of the first manifold catalyst 32 smaller than the heat capacity of the second manifold catalyst 34. Although the heat capacity of the first manifold catalyst 32 is reduced by reducing the surface area of the carrier of the first manifold catalyst 32, the initial catalyst activation time is short (about several seconds), and the surface area is small. The decrease in the total amount of heat received due to the small size is not a big problem, and the catalyst surface is sufficiently activated.

FIG. 6 is a diagram for explaining the operation and effect of the exhaust device 3 of the engine 1 according to the present embodiment.

When the engine 1 is started at time t1, the temperatures of the first manifold catalyst 32, the second manifold catalyst 34, and the underfloor catalyst 35 increase with the passage of time.

At this time, in this embodiment, since the heat capacity of the first manifold catalyst 32 is made smaller than the heat capacity of the second manifold catalyst 34, the temperature of the first manifold catalyst 32 is quickly raised as compared with the second manifold catalyst 34. Can be made. Further, in this embodiment, since the actual opening area of the first manifold catalyst 32 is larger than the actual opening area of the second manifold catalyst 34, the first manifold catalyst 32 is improved while the exhaust passage of the first manifold catalyst 32 is improved. The stagnation of the exhaust gas can be caused in the downstream area of 32. Therefore, the temperature of the first manifold catalyst 32 can be quickly raised even in an operation region where the engine rotational speed is relatively low and the exhaust flow rate is small, such as when the engine is started.

As a result, since the temperature of the first manifold catalyst 32 can be raised to the activation temperature (about 300 ° C. to 400 ° C.) very quickly after the engine is started, the exhaust performance at the time of starting the engine can be improved. . Further, the second manifold catalyst 34 is also provided in the vicinity of the first manifold catalyst 32 located upstream of the exhaust device 3 and is disposed in the engine room under a high temperature environment. Subsequently, the temperature can be raised rapidly.

On the other hand, when the vehicle starts running after the engine is started, the first manifold catalyst 32 located upstream of the exhaust device 3 is exposed to particularly high-temperature exhaust when the engine is heavily loaded. Therefore, if the heat capacity of the first manifold catalyst 32 is reduced in order to improve the exhaust performance at the time of starting the engine as described above, the temperature of the first manifold catalyst 32 may rise excessively and deteriorate when the engine is heavily loaded. .

On the other hand, in the present embodiment, since the cooler 33 is provided on the outer peripheral portion of the first manifold catalyst 32, it is possible to suppress the temperature of the first manifold catalyst 32 from rising excessively at a high engine load. Therefore, as shown after time t2, the temperature of the first manifold catalyst 32 can be maintained at a steady temperature (about 700 ° C.) even during vehicle travel, and deterioration of the first manifold catalyst 32 can be suppressed. .

Further, since the cooler 33 is provided on the outer peripheral portion of the first manifold catalyst 32, the exhaust flow is not hindered and the exhaust efficiency of the first manifold catalyst 32 is not lowered.

At time t3, if control for temporarily stopping combustion of the air-fuel mixture, such as idle stop control or fuel cut control, is performed while the vehicle is stopped or running, the combustion gas is not discharged from the engine. As the time elapses, the temperatures of the first manifold catalyst 32, the second manifold catalyst 34, and the underfloor catalyst 35 decrease.

At this time, the first manifold catalyst 32 has a smaller heat capacity than the second manifold catalyst 34 and is cooled by the cooler 33, so that the activation temperature falls below the activation temperature in a relatively short time.

On the other hand, the second manifold catalyst 34 has a larger heat capacity than the first manifold catalyst 32 and is provided in the engine room in a high temperature environment. Is slow. Therefore, even when idle stop control or fuel cut control is performed, the temperature of the second manifold catalyst 34 can be maintained at the activation temperature or higher for a relatively long time.

Therefore, until the temperature of the second manifold catalyst 34 falls below the activation temperature, the idle stop control and the fuel cut control can be continuously performed, so that the fuel consumption can be improved. Further, in the case of a vehicle that can run with the driving force of the motor with the engine stopped, such as a hybrid vehicle, the temperature of the second manifold catalyst 34 can be maintained above the activation temperature for a long time even after the engine is stopped. In addition, it is possible to suppress the deterioration of the exhaust performance at the time of restart.

Here, during the fuel cut, the crankshaft 112 of the engine 1 is driven by the drive wheels of the vehicle, so that the cooling water can be circulated by a water pump driven by the crankshaft 112 via a belt or the like. .

However, during idling stop (when the engine is stopped in the hybrid vehicle), the rotation of the crankshaft 112 of the engine 1 stops, so that the water pump cannot be driven and the cooling water cannot be circulated. Therefore, the cooling water in the water jacket 331 of the cooler 33 cannot be circulated.

During idle stop or fuel cut, the heat of the first manifold catalyst 32 is transferred to the cooling water in the water jacket 331 of the cooler 33. Then, during the idle stop where the cooling water is not circulated, the temperature of the cooling water in the water jacket 331 of the cooler 33 continues to rise due to the heat received from the first manifold catalyst 32 and may exceed the boiling point temperature. is there.

Here, the amount of heat Q1 required to raise the cooling water in the water jacket 331 of the cooler 33 to the boiling point temperature is C1 as the heat capacity of the cooling water in the water jacket 331 of the cooler 33, and the boiling point temperature of the cooling water. Assuming T1, it is expressed by the following equation (3).

Q1 = C1 × (T1-cooling water temperature at steady state (around 80 ° C.)) (3)

On the other hand, the heat quantity Q2 estimated to be possessed by the first manifold catalyst 32 at the time of idling stop is C2 as the heat capacity of the first manifold catalyst 32, and the expected temperature of the first manifold catalyst 32 at the time of idling stop (assuming a steady temperature of 700 ° C.). When a margin temperature (700 ° C. + α) obtained by adding a predetermined margin to T2 is T2, it is expressed by the following equation (4).

Q2 = C2 × (T2-cooling water temperature at steady state (around 80 ° C.)) (4)

Therefore, in the present embodiment, the amount of heat Q1 required to raise the cooling water in the water jacket 331 of the cooler 33 to the boiling point temperature is greater than the amount of heat Q2 estimated to be possessed by the first manifold catalyst 32 at the time of idling stop. The capacity of the water jacket 331 of the cooler 33 (heat capacity C1 of cooling water in the water jacket of the cooler 33) and the type of cooling water (boiling point boiling temperature T1) are set so as to increase.

Thereby, even if all the heat quantity of the first manifold catalyst 32 is transferred to the cooling water in the water jacket 331 of the cooler 33, the temperature of the cooling water does not exceed the boiling point temperature. Therefore, it is possible to prevent the cooling water in the water jacket 331 of the cooler 33 from boiling during idle stop.

The embodiment of the present invention has been described above. However, the above embodiment only shows a part of application examples of the present invention, and the technical scope of the present invention is limited to the specific configuration of the above embodiment. Absent.

For example, as shown in FIG. 7, a flow rate adjustment valve 334 may be provided in the cooling water discharge pipe 333 so that the flow rate of the cooling water circulating through the cooler 33 can be adjusted. When the engine is started, the cooling effect of the cooler 33 at the time of starting the engine can be reduced by closing the flow rate adjustment valve 334 until the temperature of the cooling water reaches a predetermined temperature or higher. Therefore, the temperature increase rate of the first manifold catalyst 32 when starting the engine can be further improved.

In the above embodiment, the cooling water introduction pipe 332 is configured such that a part of the cooling water introduced into the water jacket 114 of the cylinder block 11 is introduced into the water jacket 331 of the cooler 33, and the cooler 33 Although the cooling water discharge pipe 333 is configured such that the cooling water introduced into the water jacket 331 is returned to the water jacket 127 of the cylinder head 12, the invention is not limited to this. The both

pipes

332 and 333 are such that relatively low-temperature cooling water out of the cooling water circulating through the engine 1 is introduced into the water jacket 331 of the cooler 33 so that the respective pipe lengths are as short as possible. In addition, the cooling water may be configured to return to the water jacket of the engine 1 in which the relatively high-temperature cooling water circulates.

In the above embodiment, a part of the cooling water of the engine 1 is introduced into the water jacket 331 of the cooler 33, but the refrigerant (cooling water and cooling gas) is circulated through the water jacket 331 of the cooler 33. A cooling device may be provided separately. At that time, a radiator, a water pump, or the like that cools the cooling water of the engine may be shared.

In the above embodiment, a gasoline engine has been described as an example, but a diesel engine may be used.

This application claims priority based on Japanese Patent Application No. 2012-132716 filed with the Japan Patent Office on June 12, 2012, the entire contents of which are incorporated herein by reference.

Claims

An exhaust system for an internal combustion engine,
A first catalyst for purifying exhaust gas discharged from the internal combustion engine;
A cooler for cooling the first catalyst;
A second catalyst provided in the vicinity of the first catalyst and purifying exhaust gas discharged from the first catalyst;
With
The heat capacity of the first catalyst is smaller than the heat capacity of the second catalyst;
An exhaust system for an internal combustion engine.
An actual opening area of the carrier of the first catalyst is larger than an actual opening area of the carrier of the second catalyst;
The exhaust system for an internal combustion engine according to claim 1.
The cooler is provided on an outer periphery of the first catalyst;
An exhaust system for an internal combustion engine according to claim 1 or 2.
The internal combustion engine temporarily stops combustion in the cylinder according to the operating state of the vehicle.
The exhaust device for an internal combustion engine according to any one of claims 1 to 3.
The cooler includes therein a refrigerant passage through which a refrigerant circulates,
The amount of heat necessary to raise the refrigerant present in the refrigerant passage to the boiling point temperature is larger than the amount of heat of the first catalyst when combustion in the cylinder of the internal combustion engine is temporarily stopped. To set the capacity of the refrigerant passage and the type of refrigerant,
The exhaust device for an internal combustion engine according to claim 4.
The cooler includes therein a refrigerant passage through which the refrigerant circulates.
The exhaust device for an internal combustion engine according to any one of claims 1 to 4.
A flow regulator for adjusting the flow rate of the refrigerant circulating in the refrigerant passage;
The exhaust system for an internal combustion engine according to claim 5 or 6.