JPH1030434A - Secondary air heating device in exhaust system of vehicular engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent temperature fall inside a muffler while heating secondary air with a simple structure in an exhaust system of a vehicular engine, and simultaneously provide an introduction passage for the secondary air and a muffler cover. SOLUTION: An exhaust system of a motorcycle has a exhaust pipe 14 connected to an exhaust port of an engine 12 and a muffler part 16 communicated with the exhaust pipe 14 and housing a catalyst 22 threinside. Secondary air is introduced into the exhaust pipe 14. An introduction pipe 24 for the secondary air is laid on an outer surface of the exhaust pipe 14 near the exhaust port. The secondary air is heated in the introduction pipe 24 by the heat of the exhaust pipe 14 and suctioned thereby for preventing the temperature inside the muffler 16 from lowering.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a secondary air heating device in an exhaust system of a vehicle engine.

[0002]

2. Description of the Related Art FIG. 7 shows a conventional example of a secondary air introducing device in an exhaust system of a motorcycle. This motorcycle is provided with a main frame b and a down tube c from the steering head pipe a toward the rear of the vehicle,
The main frame b and the down tube c as viewed from the side of the vehicle.
A two-cycle engine d is mounted between the two. An exhaust muffler e is connected to an exhaust port on the front surface of the engine d. The exhaust muffler e is connected to an exhaust port f on the exhaust port side.
And a muffler portion g extending rearward from the rear end of the exhaust portion f at the lower part of the vehicle and having a catalyst (not shown) therein. In FIG. 7, reference numeral h denotes a radiator, i denotes a clutch cable, and j denotes a wire harness.

[0003] The secondary air introduction device supplies secondary air to the exhaust pipe section f, and includes a secondary air air cleaner k.
After being purified by taking in outside air from the outlet, the hose is sequentially passed through a hose m, a reed valve n, and a hose p, and is introduced from an introduction pipe q provided in an exhaust pipe section f. Air cleaner k for secondary air, hose m, reed valve n and hose p are
It is arranged along the down tube c from the vicinity of the head pipe a to the exhaust pipe section f. The secondary air introduced into the exhaust pipe section f via the reed valve n is guided to the muffler section g to promote the reaction of the catalyst. In order to prevent heat damage due to the reaction of the catalyst, a muffler cover is provided outside the muffler portion g as necessary.

[0004]

In the above-mentioned conventional secondary air introduction device, air at normal temperature is taken in from the secondary air air cleaner k and then introduced into the exhaust pipe section f without being particularly heated. In addition, there is a possibility that the temperature in the muffler portion g decreases with the introduction of the secondary air. Therefore, a secondary air heating device capable of causing a catalyst to react at a high temperature is demanded.

In Japanese Utility Model Laid-Open No. 58-154814, an exhaust manifold is covered with a cover, an outer plate is provided on the outer surface of the cover, and a secondary air passage defined by the cover and the outer plate is provided in a secondary air passage. Although an apparatus for heating by passing air is disclosed, the secondary air heating apparatus has a complicated structure and is not suitable for a small vehicle such as a motorcycle.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned conventional problems, and has a simple structure for heating secondary air to prevent a temperature drop in a muffler portion and forming a secondary air introduction passage. At the same time, a muffler cover can be formed,
An object of the present invention is to provide a secondary air heating device in an exhaust system of a vehicle engine.

[0007]

The present invention has the following configuration to achieve the above object. That is, the invention according to claim 1 includes an exhaust pipe portion connected to the exhaust port of the engine, and a muffler portion communicating with the exhaust pipe portion and having a catalyst therein, so that secondary air is introduced into the exhaust pipe portion. An exhaust passage for introducing secondary air into the exhaust section along the outer surface of the exhaust section in the vicinity of the exhaust port. It is a secondary air heating device in the system.

According to a second aspect of the present invention, a peripheral wall of the muffler portion located outside the catalyst is formed in a double structure, and an inner space of the double structure is a muffler side introduction passage communicating with the introduction passage. The secondary air heating device according to claim 1, wherein the secondary air that has passed through the muffler side introduction passage is guided to the introduction passage.

According to the first aspect of the present invention, since the secondary air introduction passage is provided along the outer surface of the exhaust pipe near the exhaust port, the secondary air is introduced into the introduction passage by the hot exhaust pipe. After being heated at, it is sucked into the exhaust pipe section.
For this reason, it is possible to prevent the temperature inside the muffler from lowering due to the introduction of the secondary air, and it is possible to cause the catalyst to react at a high temperature.

According to the second aspect of the present invention, the secondary air can be more effectively heated by passing through the inner space of the double structure before passing through the introduction passage. Moreover, in this case, since the secondary air absorbs the heat in the muffler portion in the inner space, the outer wall of the double structure functions as a muffler cover for preventing heat damage of the catalyst.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. In the present embodiment, the secondary air heating device of the present invention is applied to a motorcycle. As shown in FIG. 1, the motorcycle includes a head pipe 2, a main frame 4 and a down tube 6 extending rearward and downward from the head pipe 2, and a front frame 8 and a rear wheel 10 between the main frame 4 and the rear wheel 10. An engine 12 supported by the down tube 6. The engine 12 is a two-stroke engine, and mainly includes a cylinder 12a and a crankcase 12b. The exhaust portion 14a (see FIG. 2) on the front surface of the cylinder 12a has an exhaust portion 14,
The front end of an exhaust muffler 20 composed of a muffler section (so-called expansion chamber) 16 and a second muffler section 18 is connected.

The exhaust pipe portion 14 is bent in a substantially C-shape so that its central axis extends forward and downward from the exhaust port 12a1 on the front surface of the cylinder 12a and curves downward and rearward, and its cross-sectional shape goes downstream. The tapered shape gradually becomes thicker as the pressure increases. The muffler section 16 is an exhaust pipe section 1
4 extends from the rear end to the upper part of the rear wheel 10 toward the rear of the vehicle below the engine 12 in a side view of the vehicle. Muffler part 1
A cylindrical catalyst 22 is attached to a large-diameter body portion 16b constituting a central portion of the 6 through a stay 22a (see FIG. 5) along the front-rear direction. A second muffler portion 18 serving as a rear end portion of the exhaust system is connected to a small-diameter tail pipe portion 16a constituting a rear end portion of the muffler portion 16.

In the exhaust system configured as described above, the catalyst 2
The secondary air supplied to the exhaust pipe 2 is introduced from the exhaust pipe section 14. In the secondary air heating device of the present embodiment, the introduction passage for introducing the secondary air into the exhaust pipe section 14 is provided near the exhaust port 12a1. Are provided along the outer surface of the exhaust portion 14 in FIG.

That is, as shown in FIG. 2, the introduction pipe 24 forming the introduction passage is formed in a substantially circular arc shape in accordance with the bending radius of the substantially C-shaped exhaust pipe portion 14, and the rear side of the exhaust pipe portion 14 is formed. (The crankcase 12b side). The introduction port 24 a of the introduction pipe 24 projects upward at the front end of the muffler section 16. The connecting portion 24b of the introduction pipe 24 communicating with the exhaust pipe portion 14 is located near the flange 14a of the exhaust pipe portion 14 connected to the exhaust port 12a1. The connecting portion 24b is connected to the exhaust portion 14 directly or indirectly via a connecting component.

As shown in FIG. 3, if the joining surface 24c of the introduction pipe 24 is formed into a curved surface having substantially the same curvature as the outer surface of the exhaust pipe portion 14, for example, the two joining states are brought into surface contact.
The heat transfer efficiency can be increased by securing a large contact area. In addition, the introduction pipe 24 having a circular cross section is connected to the exhaust pipe section 1.
4 or the introduction pipe 24 may be formed integrally with the exhaust pipe section 14. There is no particular limitation on the formation of the introduction pipe 24 on the outer surface of the exhaust pipe section 14.

As shown in FIG. 1, an air cleaner 25a for secondary air, a hose 25b, a reed valve (or pump) 25c, and a hose 25d are provided at the front of the down tube 6 in the same manner as in a conventional secondary air introduction device. The lower end of the hose 25d is connected to the inlet 24a of the inlet pipe 24. It should be noted that a resonator may be interposed, for example, in the hose 25b in order to obtain a silencing effect of the secondary air.

According to the secondary air heating apparatus of the present embodiment having the above configuration, the secondary air introduction pipe 24 is attached to the outer surface of the bent portion of the exhaust portion 14 near the exhaust port 12a1, which is a high temperature portion. Since the secondary air is provided, the secondary air is supplied with the secondary air air cleaner 25a, the hose 25b, and the reed valve 25c.
After being sucked into the introduction pipe 24 via the hose 25d and heated in the introduction pipe 24, it is sucked into the exhaust pipe section 14. For this reason, the temperature inside the muffler section 16 can be prevented from lowering due to the introduction of the secondary air, so that the catalyst 22 can be reacted at a high temperature. Further, in the present embodiment, the crankcase 12b side (exhaust portion 14
(Behind the bottom), there is almost no cooling effect on the secondary air, and the secondary air can be reliably heated from room temperature to a high temperature. The temperature at which the catalyst 22 reacts most efficiently is about 250 ° C. to 300 ° C., the surface temperature of the bent portion of the exhaust pipe section 14 is about 300 ° C. to 400 ° C., and the temperature of the secondary air passing through the introduction pipe 24 is , 150 ° C ~ 25
It is expected to be around 0 ° C.

Next, another embodiment in which a muffler side introduction passage is further added to the secondary air heating device of the above embodiment will be described. In another embodiment shown in FIG. 4, the peripheral wall of the muffler portion 16 located outside the catalyst 22 has a body 16 b serving as an inner wall, and a cylindrical shape fitted concentrically outside the body 16 b. The outer wall 16c forms a double-pipe structure, and an annular inner space S serving as the muffler-side introduction passage 26 is formed between the body 16b and the outer wall 16c. The inner space S is substantially closed by, for example, folding and welding the front and rear end edges of the outer wall 16c to the outer peripheral surface of the body 16b. The rear end of the introduction pipe 24 is formed as it is along the outer surface of the muffler section 16 and communicates with the front upper end of the inner space S. On the other hand, an inlet 28 protrudes rearward from the rear lower end of the inner space S, and the lower end of the hose 25d is connected to the inlet 28.

According to another embodiment configured as described above, the secondary air that has passed through the secondary air air cleaner 25a and the like is supplied to the inner space S (muffler side introduction passage 26) of the double pipe structure.
And passing through the introduction pipe 24 sequentially,
The secondary air can be heated more effectively. Moreover, in this case, since the peripheral wall of the muffler section 16 has a double structure, the secondary air passing through the inner space S takes heat inside the muffler section 16. Therefore, heat is not easily transmitted to the outer wall 16c of the double structure, and the outer wall 16c functions as a muffler cover for preventing heat damage. Therefore, the muffler cover can be formed simultaneously with the formation of the muffler side introduction passage 26.

Further, as in a modification of the other embodiment shown in FIG. 6, the secondary air passes through the inner space S along a longer introduction path while alternately turning and meandering at the front and rear ends of the inner space S. The meandering passage 30 may be formed by a plurality of partition walls 32. In this case, since the path of the secondary air is long and complicated, the sound deadening effect and the heat transfer effect of the secondary air system can be enhanced.

The present embodiment is a preferred embodiment of the present invention, and the technical scope of the present invention is not limited to this embodiment. For example, in the other embodiments and the modifications thereof, the peripheral wall of the muffler section 16 has a double structure. However, when a catalyst is incorporated in the second muffler section 18, the peripheral wall of the second muffler section 18 has a double structure. The inner space can be used as a muffler side introduction passage. Further, the muffler side introduction passage according to the present invention does not necessarily need to be formed in an annular shape,
A predetermined peripheral wall of the muffler portion is partially formed in a double structure, and an arc-shaped inner space formed thereby is also included in the muffler-side introduction passage within the technical scope of the present invention.

[0022]

As described above, according to the present invention, in the exhaust system of a vehicle engine, the secondary air can be heated with a simple structure and the temperature inside the muffler can be prevented from lowering.
Further, the muffler cover can be formed simultaneously with the formation of the muffler-side introduction passage for the secondary air.

[Brief description of the drawings]

FIG. 1 is a side view of a motorcycle according to an embodiment.

FIG. 2 is a side view of a structure around an exhaust pipe portion according to the embodiment.

FIG. 3 is a sectional view taken along the line III-III in FIG. 2;

FIG. 4 is a side view of an exhaust pipe section and a muffler section according to another embodiment.

FIG. 5 is a sectional view taken along line VV in FIG. 4;

FIG. 6 is a cross-sectional view showing a modified example of the double structure according to another embodiment.

FIG. 7 is a side view showing a structure around an engine according to a conventional secondary air introduction device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 12 Engine 12a1 Exhaust port 14 Exhaust part 16 Muffler part 16b Trunk part (inner wall) 16c Outer wall 22 Catalyst 24 Introducing pipe (corresponding to an introducing passage) 26 Muffler side introducing passage S Inner space

Claims (2)

[Claims] 1. A vehicle engine comprising: an exhaust pipe connected to an exhaust port of an engine; and a muffler section communicating with the exhaust pipe and having a catalyst therein, so that secondary air is introduced into the exhaust pipe section. An exhaust passage for introducing secondary air into the exhaust pipe portion along an outer surface of the exhaust pipe portion near the exhaust port. Air heating device. 2. A muffler portion peripheral wall located outside the catalyst is formed in a double structure, and an inner space of the double structure is a muffler side introduction passage communicating with the introduction passage. 2. The secondary air heating device in an exhaust system of a vehicle engine according to claim 1, wherein the secondary air that has passed is guided to the introduction passage.