Exhaust purifier

Abstract

The present invention provides an exhaust gas purification device that can promote the heating (activation) of the outer periphery of the exhaust gas purification catalyst, thereby accelerating the activation of the entire exhaust gas purification catalyst (i.e., achieving a 100% purification rate of the exhaust gas purification catalyst at an earlier stage). [Solution] The exhaust gas purification device 1 includes an exhaust gas purification catalyst 20 installed in the exhaust pipe 18 of the engine 10 to purify the exhaust gas discharged from the engine 10, and a heat exchanger 60 that branches off a portion of the exhaust gas from the exhaust pipe 18 upstream of the exhaust gas purification catalyst 20 and guides it to the outer periphery of the exhaust gas purification catalyst 20, performs heat exchange between the exhaust gas and the outer periphery of the exhaust gas purification catalyst 20, and returns the exhaust gas after heat exchange to the exhaust pipe 18 upstream of the exhaust gas purification catalyst 20.

Description

Technical Field

[0001] The present invention relates to an exhaust gas purification device including an exhaust gas purification catalyst for purifying the exhaust gas of an engine.

Background Art

[0002] Conventionally, in order to activate the exhaust gas purification catalyst at an early stage and reduce the exhaust emissions after the engine is started (immediately after startup), early warm-up (temperature increase) control of the exhaust gas purification catalyst has been performed. In this early warm-up (temperature increase) control, for example, the temperature of the exhaust gas purification catalyst is increased by utilizing so-called afterburning generated by retarding the ignition timing (for example, see Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] By the way, the flow of exhaust gas in the exhaust pipe is not uniform. For example, the exhaust gas flow rate may be lower at the outer peripheral portion of the exhaust gas purification catalyst compared to the central portion (center portion). In such a case, the temperature increase at the outer peripheral portion of the exhaust gas purification catalyst may be slower than that at the central portion (center portion), and there is a risk of delay in activation. That is, there is a risk that the timing of activation of the entire exhaust gas purification catalyst (the purification rate reaches 100%) may be delayed.

[0005] The present invention has been made to solve the above problems, and it is an object of the present invention to provide an exhaust gas purification device capable of promoting the temperature increase (activation) of the outer peripheral portion of the exhaust gas purification catalyst, thereby accelerating the activation of the entire exhaust gas purification catalyst (that is, making the purification rate of the exhaust gas purification catalyst reach 100% earlier).

Means for Solving the Problems

[0006] An exhaust gas purification device according to one aspect of the present invention is characterized by comprising an exhaust gas purification catalyst provided in the exhaust pipe of an engine for purifying exhaust gas discharged from the engine, and a heat exchanger that branches off a portion of the exhaust gas from the exhaust pipe and guides it to the outer periphery of the exhaust gas purification catalyst, and performs heat exchange between the exhaust gas and the outer periphery of the exhaust gas purification catalyst.

[0007] According to one aspect of the present invention, an exhaust gas purification device is branched off from the exhaust pipe and guided to the outer periphery of the exhaust gas purification catalyst, and heat exchange takes place between the exhaust gas and the outer periphery of the exhaust gas purification catalyst. As a result, the temperature of the outer periphery of the exhaust gas purification catalyst can be increased, and the activation of the outer periphery of the exhaust gas purification catalyst can be accelerated. [Effects of the Invention]

[0008] According to the present invention, the temperature rise (activation) of the outer periphery of the exhaust gas purification catalyst can be promoted, thereby accelerating the activation of the entire exhaust gas purification catalyst (i.e., achieving a 100% purification rate of the exhaust gas purification catalyst at an earlier stage). [Brief explanation of the drawing]

[0009] [Figure 1] This diagram shows the configuration of an engine to which the exhaust gas purification device according to the embodiment is applied. [Figure 2] This is a diagram showing the configuration of an exhaust gas purification device according to an embodiment. [Figure 3] This is a diagram illustrating the operation of the exhaust gas purification device according to the embodiment. [Figure 4] This diagram shows the configuration of an exhaust gas purification device according to a modified example. [Modes for carrying out the invention]

[0010] Preferred embodiments of the present invention will be described in detail below with reference to the drawings. Unless otherwise necessary, the same reference numerals will be used for the same or corresponding parts in the drawings. Furthermore, in each drawing, the same reference numerals will be used for the same elements, and redundant descriptions will be omitted.

[0011] First, the configuration of the exhaust gas purification device 1 according to this embodiment will be described using Figures 1 and 2 together. Figure 1 is a diagram showing the configuration of an engine 10 to which the exhaust gas purification device 1 is applied. Figure 2 is a diagram showing the configuration of the exhaust gas purification device 1.

[0012] Engine 10 can be of any type, but for example, it is a horizontally opposed 4-cylinder gasoline engine. Also, engine 10 is an in-cylinder injection engine that directly injects fuel into the cylinder. In engine 10, air drawn in from the air cleaner 16 is restricted by an electronically controlled throttle valve (hereinafter also simply called "throttle valve") 13 provided in the intake manifold 15, passes through the intake manifold 11, and is drawn into each cylinder formed in engine 10.

[0013] Here, the amount of air drawn in from the air cleaner 16 is detected by an airflow meter 14 positioned between the air cleaner 16 and the throttle valve 13. In addition, a vacuum sensor 30 is installed inside the collector section (surge tank) that constitutes the intake manifold 11 to detect the pressure inside the intake manifold 11 (intake manifold pressure). Furthermore, a throttle opening sensor 31 is installed on the throttle valve 13 to detect the degree of opening of the throttle valve 13.

[0014] The cylinder head has an intake port 22 and an exhaust port 23 for each cylinder (only one bank is shown in Figure 1). Each intake port 22 and exhaust port 23 is provided with an intake valve 24 and an exhaust valve 25 that open and close the intake port 22 and exhaust port 23, respectively. Between the intake camshaft that drives the intake valve 24 and the intake cam pulley, a variable valve timing mechanism 26 is provided to advance or retard the valve timing (opening / closing timing) of the intake valve 24 by rotating the intake cam pulley and the intake camshaft relative to each other, thereby continuously changing the rotational phase (displacement angle) of the intake camshaft with respect to the crankshaft 10a. This variable valve timing mechanism 26 allows the opening and closing timing of the intake valve 24 to be variably set according to the engine operating conditions.

[0015] Similarly, a variable valve timing mechanism 27 is provided between the exhaust camshaft and the exhaust cam pulley. This mechanism rotates the exhaust cam pulley and the exhaust camshaft relative to each other, continuously changing the rotational phase (displacement angle) of the exhaust camshaft with respect to the crankshaft 10a, thereby advancing or retarding the valve timing (opening / closing timing) of the exhaust valve 25. This variable valve timing mechanism 27 allows the opening and closing timing of the exhaust valve 25 to be set variably according to the engine operating conditions.

[0016] Each cylinder of the engine 10 is fitted with an injector 12 that injects fuel into the cylinder. The injector 12 directly injects fuel pressurized by a high-pressure fuel pump (not shown) into the combustion chamber of each cylinder.

[0017] Furthermore, each cylinder head is fitted with a spark plug 17 for igniting the fuel-air mixture, and an igniter-integrated coil 21 for applying a high voltage to the spark plug 17. In each cylinder of the engine 10, the fuel-air mixture inhaled and injected by the injector 12 is ignited by the spark plug 17 and combusted. The exhaust gas after combustion is discharged through the exhaust pipe 18.

[0018] An air-fuel ratio sensor 19 is installed downstream of the manifold of the exhaust pipe 18 and upstream of the exhaust gas purification catalyst 20. The air-fuel ratio sensor 19 is a linear air-fuel ratio sensor (LAF sensor) that can output signals corresponding to the oxygen concentration and unburned gas concentration in the exhaust gas (i.e., signals corresponding to the air-fuel ratio of the mixture) and can linearly detect the air-fuel ratio.

[0019] Downstream of the LAF sensor 19, an exhaust gas purification catalyst 20 is disposed. The exhaust gas purification catalyst 20 is, for example, a three-way catalyst, which simultaneously oxidizes hydrocarbons (HC) and carbon monoxide (CO) in the exhaust gas and reduces nitrogen oxides (NOx), purifying the harmful gas components in the exhaust gas into harmless carbon dioxide (CO2), water vapor (H2O), and nitrogen (N2). Note that the exhaust gas purification catalyst 20 exhibits the catalyst function when the temperature reaches a predetermined activation temperature or higher. A muffler 43 for reducing exhaust noise is attached to the downstream side of the exhaust gas purification catalyst 20.

[0020] An exhaust gas recirculation device (hereinafter referred to as "EGR (Exhaust Gas Recirculation) device") 40 for recirculating a part of the exhaust gas discharged from the engine 10 to the intake manifold 11 of the engine 10 is provided in the exhaust pipe 18. The EGR device 40 has an EGR pipe 41 that connects the exhaust pipe 18 and the intake manifold 11 of the engine 10, and an EGR valve 42 that is interposed on the EGR pipe 41 and adjusts the exhaust gas recirculation amount (EGR flow rate). The opening degree (EGRSTP) of the EGR valve 42 is controlled by an electronic control unit 50 described later according to the operating state of the engine 10.

[0021] In addition to the air flow meter 14, LAF sensor 19, vacuum sensor 30, and throttle opening sensor 31 described above, a cam angle sensor 32 for discriminating the cylinders of the engine 10 is attached near the camshaft of the engine 10. Further, a crank angle sensor 33 for detecting the rotational position of the crankshaft 10a is attached near the crankshaft 10a of the engine 10. Here, a timing rotor 33a having, for example, 34 teeth with 2 teeth missing and formed at 10° intervals is attached to the end of the crankshaft 10a, and the crank angle sensor 33 detects the rotational position of the crankshaft 10a by detecting the presence or absence of the protrusions of the timing rotor 33a. As the cam angle sensor 32 and the crank angle sensor 33, for example, electromagnetic pickup type sensors are used.

[0022] These sensors are connected to an electronic control unit (hereinafter referred to as "ECU") 50. Further, various sensors such as a water temperature sensor 34 for detecting the temperature of the cooling water of the engine 10, an oil temperature sensor 35 for detecting the temperature of the lubricating oil, an accelerator sensor 36 for detecting the depression amount of the accelerator pedal, i.e., the operation amount of the accelerator, and a vehicle speed sensor 37 for detecting the speed of the vehicle are also connected to the ECU 50.

[0023] The ECU 50 includes a microprocessor that performs calculations, an EEPROM that stores programs for causing the microprocessor to execute each process, a RAM that stores various data such as calculation results, a backup RAM whose stored content is retained by a battery or the like, and an input / output I / F. Further, the ECU 50 includes an injector driver that drives the injector 12, an output circuit that outputs an ignition signal, and a motor driver that drives an electric motor 13a that opens and closes the electronically controlled throttle valve 13.

[0024] In the ECU 50, the cylinder is discriminated from the output of the cam angle sensor 32, and the rotational angular velocity and the engine speed are obtained from the output of the crank angle sensor 33. Further, in the ECU 50, based on the detection signals input from the various sensors described above, various information such as the intake air amount, the intake pipe negative pressure, the accelerator operation amount, the air-fuel ratio of the air-fuel mixture, and the water temperature and oil temperature of the engine 10 is acquired. Then, the ECU 50 comprehensively controls the engine 10 by controlling the fuel injection amount, the ignition timing, and various devices such as the throttle valve 13 and the EGR valve 42 based on the various information thus acquired.

[0025] Further, immediately after the engine is started, the ECU 50 performs early warm-up (temperature increase) of the exhaust purification catalyst 20 by using the so-called afterburning generated by delaying the ignition timing (IG retard) in order to activate the exhaust purification catalyst 20 early.

[0026] However, as mentioned above, the exhaust flow in the exhaust pipe 18 is not uniform. For example, the exhaust flow rate may be lower at the outer periphery of the exhaust catalyst 20 compared to the central part (see Figure 3). In such cases (if left as is), the heating of the exhaust catalyst 20 will be slower at the outer periphery compared to the central part, potentially delaying its activation. In other words, the time at which the exhaust catalyst 20 as a whole becomes activated (reaches 100% purification) may be delayed.

[0027] Therefore, the exhaust gas purification device 1 equipped with the exhaust gas purification catalyst 20 has the function of promoting the temperature rise (activation) of the outer periphery of the exhaust gas purification catalyst 20, thereby accelerating the activation of the entire exhaust gas purification catalyst 20 (i.e., achieving a 100% purification rate of the exhaust gas purification catalyst 20 at an earlier stage).

[0028] Therefore, the exhaust gas purification device 1 includes a heat exchanger (heat exchange means) 60 that branches off a portion of the exhaust gas from the exhaust pipe 18 and guides it to the outer periphery (outer surface) of the exhaust gas purification catalyst 20, and performs heat exchange between the exhaust gas and the outer periphery of the exhaust gas purification catalyst 20.

[0029] The heat exchanger 60 is configured such that, for example, a portion of the exhaust gas is branched from the exhaust pipe 18 upstream of the exhaust gas purification catalyst 20 and guided to the outer periphery of the exhaust gas purification catalyst 20, heat exchange takes place between the exhaust gas and the outer periphery of the exhaust gas purification catalyst 20, and the exhaust gas after heat exchange is returned to the exhaust pipe 18 upstream of the exhaust gas purification catalyst 20.

[0030] More specifically, as shown in Figure 2, the heat exchanger 60 is mainly arranged outside the exhaust gas purification catalyst 20 so as to cover the outer periphery of the exhaust gas purification catalyst 20 and comprises a heat exchange section 601 that performs heat exchange between the exhaust gas and the outer periphery of the exhaust gas purification catalyst 20, a supply pipe 602 that branches off from the exhaust pipe 18 upstream of the exhaust gas purification catalyst 20 and leads a portion of the exhaust gas to the heat exchange section 601, a return pipe 603 that returns the exhaust gas (after heat exchange) after heat exchange in the heat exchange section 601 back to the exhaust pipe 18 upstream of the exhaust gas purification catalyst 20, and a return pipe 604 that connects the heat exchange section 601 and the return pipe 603.

[0031] The heat exchange unit 601 is, for example, formed in a cylindrical shape and arranged on the outside of the exhaust gas purification catalyst 20, which is formed in a substantially cylindrical shape, so as to cover the outer periphery of the exhaust gas purification catalyst 20. The heat exchange unit 601 then performs heat exchange between the exhaust gas and the outer periphery of the exhaust gas purification catalyst 20.

[0032] The supply pipe 602 is formed, for example, in the shape (outer shape) of the exhaust pipe 18, in a hollow, bottomless, approximately truncated cone shape, and is arranged on the outside of the exhaust pipe 18 so as to cover the outer surface of the exhaust pipe 18. One end (open end) of the supply pipe 602 is connected to the exhaust pipe 18 upstream of the exhaust gas purification catalyst 20, and the other end (open end) is connected to one end (open end) of the heat exchange section 601. The supply pipe 602 then guides (takes in) a portion of the exhaust gas from the exhaust pipe 18 to the heat exchange section 601.

[0033] The return pipe 603 is formed, for example, to match the shape (outer shape) of the supply pipe 602 and the heat exchange section 601, and is arranged outside the supply pipe 602 and the heat exchange section 601 so as to cover the outer circumferential surface of the supply pipe 602 and the heat exchange section 601. One end (open end) of the return pipe 603 is connected to the exhaust pipe 18 upstream of the exhaust gas purification catalyst 20. The return pipe 603 then returns (recirculates) the exhaust gas after heat exchange to the exhaust pipe 18. Here, the exhaust gas after heat exchange is returned to the exhaust pipe 18 using, for example, the negative pressure generated by the Venturi effect.

[0034] The folded pipe 604, for example, has a roughly U-shaped cross-section along its axial direction, and connects the other end (open end) of the heat exchange section 601 with the other end (open end) of the return pipe 603. The folded pipe 604 then causes the exhaust gas after heat exchange to make a U-turn and send it to the return pipe 603.

[0035] The heat exchanger 60 described above is formed from, for example, the same SUS material as the exhaust pipe 18. The heat exchanger 60 is manufactured, for example, by first covering (joining) the outside of the exhaust pipe 18 and the exhaust gas purification catalyst 20 with the supply pipe 602 and the heat exchange section 601, and then covering (joining) the outside of the supply pipe 602 and the heat exchange section 601 with the return pipe 603 and the folded pipe 604, and then covering (joining) them with the outside of the supply pipe 602 and the heat exchange section 601. It is preferable (for strength reasons) to use, for example, a perforated mesh, at the connection point (inlet) between the supply pipe 602 and the exhaust pipe 18, and at the connection point (outlet) between the return pipe 603 and the exhaust pipe 18. Furthermore, it is preferable to set the cross-sectional area (passage area) of each pipe constituting the heat exchanger 60 considering, for example, the heating requirements of the exhaust gas purification catalyst 20 and the exhaust efficiency.

[0036] As described above, with this configuration, for example, as shown in Figure 3, a portion of the exhaust gas is branched from the exhaust pipe 18 upstream of the exhaust gas purification catalyst 20 and guided (taken in) to the outer circumference of the exhaust gas purification catalyst 20, and heat exchange takes place between the exhaust gas and the outer circumference of the exhaust gas purification catalyst 20. Therefore, the temperature rise (activation) of the outer circumference of the exhaust gas purification catalyst 20 is promoted when the engine is started (cold start).

[0037] The exhaust gas after heat exchange is then returned to the exhaust pipe 18 upstream of the exhaust gas purification catalyst 20. The exhaust gas returned to the exhaust pipe 18 after heat exchange is purified by the exhaust gas purification catalyst 20 before being discharged to the outside.

[0038] As described in detail above, according to this embodiment, a portion of the exhaust gas is branched from the exhaust pipe 18 and guided (taken into) the outer periphery of the exhaust gas purification catalyst 20, and heat exchange takes place between the exhaust gas and the outer periphery of the exhaust gas purification catalyst 20. Therefore, when the engine is started (cold start), the temperature of the outer periphery of the exhaust gas purification catalyst 20 can be promoted, and the activation of the outer periphery of the exhaust gas purification catalyst 20 can be accelerated.

[0039] As a result, the temperature rise (activation) of the outer periphery of the exhaust gas purification catalyst 20 can be promoted, thereby accelerating the activation of the entire exhaust gas purification catalyst 20 (i.e., achieving a 100% purification rate for the exhaust gas purification catalyst 20 at an earlier stage).

[0040] Furthermore, according to this embodiment, compared to adding a dedicated device such as an electrically heated catalyst (EHC), for example, it is possible to achieve a faster temperature rise of the exhaust gas purification catalyst 20 at a lower cost and with a simpler configuration.

[0041] Furthermore, according to this embodiment, a portion of the exhaust gas is branched off from the exhaust pipe 18 upstream of the exhaust gas purification catalyst 20 and guided to the outer periphery of the exhaust gas purification catalyst 20. Heat exchange takes place between the exhaust gas and the outer periphery of the exhaust gas purification catalyst 20, and the exhaust gas after heat exchange is returned to the exhaust pipe 18 upstream of the exhaust gas purification catalyst 20. Therefore, the exhaust gas after heat exchange can be returned to the exhaust pipe 18 using the negative pressure generated by the Venturi effect without requiring external power. In addition, the exhaust gas after heat exchange returned to the exhaust pipe 18 can be purified by the exhaust gas purification catalyst 20 before being discharged.

[0042] According to this embodiment, the heat exchange section 601 is formed in a cylindrical shape and is disposed on the outside of the exhaust gas purification catalyst 20, which is formed in a substantially cylindrical shape, so as to cover the outer circumference of the exhaust gas purification catalyst 20. The forward pipe 602 is formed in a hollow, bottomless, substantially frustoconical shape and is disposed on the outside of the exhaust pipe 18 so as to cover the outer circumference of the exhaust pipe 18, with one end communicating with the exhaust pipe 18 on the upstream side of the exhaust gas purification catalyst 20 and the other end communicating with one end of the heat exchange section 601. The return pipe 603 is disposed on the outside of the forward pipe 602 and the heat exchange section 601 so as to cover the outer circumference of the forward pipe 602 and the heat exchange section 601, with one end communicating with the exhaust pipe 18 on the upstream side of the exhaust gas purification catalyst 20. The return pipe 604 has a substantially U-shaped cross-section along the axial direction and is configured to communicate the other end of the heat exchange section 601 with the other end of the return pipe 603. Therefore, a portion of the exhaust gas can be branched from the exhaust pipe 18 upstream of the exhaust gas purification catalyst 20 and guided to the heat exchange section 601, where heat exchange can be performed between the exhaust gas and the outer periphery of the exhaust gas purification catalyst 20, and the exhaust gas after heat exchange can be returned to the exhaust pipe 18 upstream of the exhaust gas purification catalyst 20.

[0043] (modified version) In the above embodiment, a portion of the exhaust gas is branched (taken in) from the exhaust pipe 18 upstream of the exhaust gas purification catalyst 20, and the exhaust gas after heat exchange is returned to the exhaust pipe 18 upstream of the exhaust gas purification catalyst 20. However, a configuration in which a portion of the exhaust gas is branched (taken in) from the exhaust pipe 18 downstream of the exhaust gas purification catalyst 20, and the exhaust gas after heat exchange is returned to the exhaust pipe 18 downstream of the exhaust gas purification catalyst 20 is also possible.

[0044] Next, the configuration of the modified exhaust gas purification device 1B will be explained using Figure 4. Figure 4 is a diagram showing the configuration of the modified exhaust gas purification device 1B. In Figure 4, components that are the same as or equivalent to those in the above embodiment are denoted by the same reference numerals.

[0045] The heat exchanger 60B, which constitutes the exhaust gas purification device 1B, is configured such that, for example, a portion of the exhaust gas is branched from the exhaust pipe 18 downstream of the exhaust gas purification catalyst 20 and guided to the outer periphery of the exhaust gas purification catalyst 20, heat exchange takes place between the exhaust gas and the outer periphery of the exhaust gas purification catalyst 20, and the exhaust gas after heat exchange is returned to the exhaust pipe 18 downstream of the exhaust gas purification catalyst 20.

[0046] More specifically, the heat exchanger 60B is mainly configured to include a heat exchange section 601B which is arranged outside the exhaust gas purification catalyst 20 so as to cover the outer periphery of the exhaust gas purification catalyst 20 and performs heat exchange between the exhaust gas and the outer periphery of the exhaust gas purification catalyst 20, a supply pipe 602B which branches off from the exhaust pipe 18 downstream of the exhaust gas purification catalyst 20 and leads a portion of the exhaust gas to the heat exchange section 601B, a return pipe 603B which returns the exhaust gas (after heat exchange) after heat exchange in the heat exchange section 601B back to the exhaust pipe 18 downstream of the exhaust gas purification catalyst 20, and a return pipe 604B which connects the heat exchange section 601B and the return pipe 603B.

[0047] The heat exchange unit 601B is, for example, formed in a cylindrical shape and disposed on the outside of the exhaust gas purification catalyst 20, which is formed in a substantially cylindrical shape, so as to cover the outer periphery of the exhaust gas purification catalyst 20. The heat exchange unit 601B then performs heat exchange between the exhaust gas and the outer periphery of the exhaust gas purification catalyst 20.

[0048] The supply pipe 602B is formed, for example, in a hollow, bottomless, roughly truncated cone shape and is arranged outside the exhaust pipe 18 so as to cover the outer surface of the exhaust pipe 18. One end (open end) of the supply pipe 602B is connected to the exhaust pipe 18 downstream of the exhaust gas purification catalyst 20, and the other end (open end) is connected to one end (open end) of the heat exchange section 601B. The supply pipe 602B then guides (takes in) a portion of the exhaust gas from the exhaust pipe 18 to the heat exchange section 601B.

[0049] Furthermore, in order to change the direction of the exhaust flow, it is preferable to provide, for example, a return pipe 602Bb, that is, an annular projection or the like, when viewed from the axial direction, projecting radially inward from the connection point between the exhaust pipe 18 and the supply pipe 602B (the exhaust intake point).

[0050] The return pipe 603B is positioned outside the supply pipe 602B and the heat exchange section 601B, covering the outer surfaces of the supply pipe 602B and the heat exchange section 601B. One end (open end) of the return pipe 603B is connected to the exhaust pipe 18 downstream of the exhaust gas purification catalyst 20. The return pipe 603B then returns the exhaust gas after heat exchange to the exhaust pipe 18. Here, the exhaust gas after heat exchange is returned to the exhaust pipe 18, for example, by utilizing the negative pressure generated by the Venturi effect.

[0051] The folded pipe 604B, for example, has a roughly U-shaped cross-section along its axial direction, and connects the other end (open end) of the heat exchange section 601B to the other end (open end) of the return pipe 603B. The folded pipe 604B then sends the exhaust gas after heat exchange to the return pipe 603B.

[0052] The other components are the same as or similar to those of the embodiments described above, so a detailed explanation is omitted here.

[0053] According to this modified example, a portion of the exhaust gas is branched from the exhaust pipe 18 downstream of the exhaust catalyst 20 and guided (taken in) to the outer periphery of the exhaust catalyst 20, where heat exchange takes place between the exhaust gas and the outer periphery of the exhaust catalyst 20. The exhaust gas after heat exchange is then returned to the exhaust pipe 18 downstream of the exhaust catalyst 20. Therefore, similar to the above embodiment, the temperature rise of the outer periphery of the exhaust catalyst 20 can be promoted during engine startup (cold start), and the activation of the outer periphery of the exhaust catalyst 20 can be accelerated. As a result, the temperature rise (activation) of the outer periphery of the exhaust catalyst 20 can be promoted, thereby accelerating the activation of the entire exhaust catalyst 20 (i.e., achieving a 100% purification rate of the exhaust catalyst 20 earlier).

[0054] Furthermore, according to this modified version, it is possible to recover waste heat by using the exhaust gas (waste heat) after the exhaust gas purification catalyst 20 has been heated once to heat the outer periphery of the exhaust gas purification catalyst 20 again.

[0055] Although embodiments of the present invention have been described above, the present invention is not limited to the above embodiments and can be modified in various ways. For example, in the above embodiments, a three-way catalyst was used as an example for the exhaust gas purification catalyst 20, but the exhaust gas purification catalyst 20 is not limited to a three-way catalyst as long as it is a catalyst that requires heating for activation, and may be an oxidation catalyst (DOC: Diesel Oxidation Catalyst) or a NOx storage catalyst (LNT (Lean NOx Trap) catalyst), etc.

[0056] Furthermore, the dimensions, materials, and other specific numerical values ​​shown in the above embodiments are illustrative examples to facilitate understanding of the present invention and do not limit the present invention unless otherwise specified.

[0057] In the above embodiment, the present invention was described using the case where it is applied to a horizontally opposed engine 10 as an example. However, the present invention is not limited to horizontally opposed engines, but can also be applied to inline engines, V-type engines, and the like. Furthermore, the present invention can be applied not only to engine-powered vehicles that use only an engine as a driving force source, but also to hybrid electric vehicles (HEVs) that use both an engine and an electric motor as driving forces sources. [Explanation of Symbols]

[0058] 1.1B Exhaust purifying device 10 Engines 10a Crankshaft 11 Intake Manifold 13. Electronically controlled throttle valve 15 Intake pipe 18 Exhaust pipe 19. Air-fuel ratio sensor 20 Exhaust purifying catalyst 40 Exhaust gas recirculation system 43 Silencer 50 ECU 60, 60B heat exchanger 601, 601B Heat exchange section 602, 602B Outbound pipe 602Bb Reply 603, 603B return tube 604, 604B folded tube

Claims

1. An exhaust gas purification catalyst is installed in the exhaust pipe of an engine to purify the exhaust gas discharged from the engine, An exhaust gas purification device comprising: a heat exchanger that branches off a portion of the exhaust gas from the exhaust pipe and directs it to the outer periphery of the exhaust gas purification catalyst, and performs heat exchange between the exhaust gas and the outer periphery of the exhaust gas purification catalyst.

2. The exhaust gas purification device according to claim 1, characterized in that the heat exchanger branches off a portion of the exhaust gas from the exhaust pipe upstream of the exhaust gas purification catalyst and guides it to the outer periphery of the exhaust gas purification catalyst, performs heat exchange between the exhaust gas and the outer periphery of the exhaust gas purification catalyst, and returns the exhaust gas after heat exchange to the exhaust pipe upstream of the exhaust gas purification catalyst.

3. The heat exchanger is, A heat exchange unit is disposed on the outside of the exhaust gas purification catalyst so as to cover the outer periphery of the exhaust gas purification catalyst, and performs heat exchange between the exhaust gas and the outer periphery of the exhaust gas purification catalyst. A supply pipe that branches off from the exhaust pipe upstream of the exhaust purification catalyst and guides a portion of the exhaust to the heat exchange section, A return pipe that returns the exhaust gas, after heat exchange has been performed in the heat exchange section, to the exhaust pipe upstream of the exhaust gas purification catalyst, A return pipe connects the heat exchange section and the return pipe, and sends the exhaust gas after heat exchange to the return pipe, The exhaust gas purification device according to claim 2, characterized by having the following features.

4. The heat exchange section is formed in a cylindrical shape and is disposed on the outside of the exhaust gas purification catalyst, which is formed in a substantially cylindrical shape, so as to cover the outer circumference of the exhaust gas purification catalyst. The supply pipe is formed in a cylindrical or hollow, bottomless, substantially truncated cone shape, and is arranged outside the exhaust pipe so as to cover the outer surface of the exhaust pipe, with one end communicating with the exhaust pipe upstream of the exhaust gas purification catalyst, and the other end communicating with one end of the heat exchange section. The return pipe is arranged outside the supply pipe and the heat exchange section, covering the outer surfaces of the supply pipe and the heat exchange section, with one end connected to the exhaust pipe upstream of the exhaust gas purification catalyst. The exhaust gas purification device according to claim 3, characterized in that the folded pipe has a substantially U-shaped cross-section along the axial direction and connects the other end of the heat exchange section to the other end of the return pipe.

5. The exhaust gas purification device according to claim 1, characterized in that the heat exchanger branches off a portion of the exhaust gas from the exhaust pipe downstream of the exhaust gas purification catalyst and guides it to the outer periphery of the exhaust gas purification catalyst, performs heat exchange between the exhaust gas and the outer periphery of the exhaust gas purification catalyst, and returns the exhaust gas after heat exchange to the exhaust pipe downstream of the exhaust gas purification catalyst.

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