JPH06212966A - Exhaust device of transverse v-engine - Google Patents

Abstract

PURPOSE:To prevent lowering of exhaust air purifying performance of a catalyst due to cooling caused by running wind of a front side exhaust manifold after warming-up while maintaining a high warming-up efficiency of the catalyst. CONSTITUTION:Exhaust manifolds 3, 4 of a transverse V-engine are formed as a double wall structure, the inner wall is made thinner so as to reduce the heat capacity, and the warming-up efficiency of start catalysts 3, 4 is kept high. The exhaust gas heat retaining property of the front side exhaust manifold 3 is kept higher than that of the rear side exhaust manifold, so that even if the strong vehicle running wind is blowing against the exhaust manifold 3, the temperature of exhaust gas flowing through the exhaust manifold is kept from dropping. Thus, it is possible to prevent the lowering of exhaust air purifying performance due to the temperature drop of the catalyst.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an engine having a V-shape when viewed from the front (V-type engine) which is mounted on a vehicle with its longitudinal direction orthogonal to the vehicle longitudinal direction (horizontal engine). Of the exhaust system including an exhaust manifold.

[0002]

2. Description of the Related Art Japanese Utility Model Laid-Open No. 4-69623 discloses an exhaust manifold for a horizontal V-type engine in which the front side is made of stainless steel and the rear side is made of cast iron. This solves the problem of durability of the exhaust manifold, but as described below, it does not solve the problem of deterioration of the exhaust gas heat retention after warm-up and deterioration of the activity of the catalyst which is affected thereby.

In order to purify the exhaust gas, a main catalyst is placed under the vehicle floor of the exhaust pipe, and the exhaust gas is purified until the main catalyst is warmed up to an activation temperature (about 250 ° C.) when the engine is started. In addition, a start catalyst whose warm-up property is improved by arranging it with a small capacity is arranged immediately below the exhaust manifold. In order to remove as much HC as possible from the start of the engine, which occupies a major part of the amount of HC (hydrocarbons) emitted, with the start catalyst, the heat capacity of the exhaust pipe system (mainly the exhaust manifold) on the upstream side of the start catalyst is reduced to start the engine. It is desired to suppress the exhaust gas heat quantity at the time of consumption on the upstream side of the start catalyst and quickly warm up the start catalyst. In order to satisfy this demand, it is effective to make the exhaust pipe system on the upstream side of the start catalyst a double wall structure and thin the inner wall to reduce the heat capacity.

[0004]

However, when the double-walled exhaust system structure is applied to a horizontal V-type engine, the following problems occur after warming up even if the start catalyst can be warmed up quickly. . That is, since the exhaust manifold on the front side of the vehicle is affected by the cooling by the traveling wind, the heat retention of the exhaust gas after warming up may be deteriorated, which may deteriorate the catalyst purification performance of the start catalyst and the main catalyst. Further, in the exhaust manifold on the rear side of the vehicle, since the traveling wind does not flow so much to the surroundings, in addition to the exhaust gas temperature being originally kept high in the double wall configuration, the exhaust gas temperature is kept too high, There is a possibility that the durability problem of the exhaust pipe system member, the thermal deterioration of the catalyst, and the like may occur. Among them, the problem of durability of the exhaust pipe system member of the vehicle rear side exhaust manifold is that the rear side is durable by changing the material of the member between the front side and the rear side as in the above Japanese Utility Model Laid-Open No. 4-69623. Can be solved, but the problems of the exhaust gas heat retention after warming up in the vehicle front side exhaust manifold and the deterioration of the exhaust purification performance of the catalyst cannot be solved.

It is an object of the present invention to maintain a high warm-up property of the catalyst, and to keep the exhaust gas heat-retaining property of the front side exhaust manifold high without being strongly influenced by the cooling of the running wind even after warm-up. To provide an exhaust system for a type engine.

[0006]

To achieve the above object, an exhaust system for a horizontal V-type engine according to the present invention comprises the following devices. That is, among the exhaust manifolds on the vehicle front side and the rear side of the horizontal V-type engine, the exhaust gas heat retention of the exhaust manifold on the vehicle front side is set higher than the exhaust gas heat retention of the exhaust manifold on the vehicle rear side. Type engine exhaust system.

[0007]

In the above-mentioned device of the present invention, due to the double wall construction,
The inner wall of the exhaust manifold has a low heat capacity. Therefore, when starting the engine, a large amount of heat is not consumed to raise the temperature of the inner wall, and the temperature of the start catalyst rises rapidly. Also,
After warming up, the exhaust manifold on the front side of the vehicle has been set to have a high degree of heat retention in the exhaust gas, so even if the outer wall is cooled by the running wind, the heat transfer from the inner wall to the outer wall is small and the exhaust gas is kept at a high temperature. There is no possibility that the temperature of the start catalyst and the main catalyst will drastically drop and the exhaust purification performance will deteriorate. On the other hand, the vehicle rear exhaust manifold tends to have a problem that the exhaust gas temperature becomes too high after warming up. However, since the heat transfer from the inner wall to the outer wall in the vehicle rear side exhaust manifold is not as small as that in the vehicle front side exhaust manifold, the heat transfer from the inner wall to the outer wall increases when the inner wall becomes hot, and the exhaust gas temperature level increases. Be properly maintained.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows a common configuration applicable to all the embodiments of the present invention, FIG. 2 shows the first embodiment of the present invention, and FIG. 3 shows the second embodiment of the present invention. First, the common configuration will be described with reference to FIG. In FIG. 1, reference numeral 1 denotes the front part of the vehicle. Reference numeral 2 is a V-type engine which is horizontally installed in the vehicle. The V-type engine has a V-shaped cylinder block when viewed from the front and has cylinder heads 10 and 10 '. Reference numeral 10 denotes a cylinder head of the vehicle front side bank, and 10 'denotes a cylinder head of the vehicle rear side bank.

An exhaust system is connected to the engine 2. The exhaust device includes exhaust manifolds 3, 4 and an exhaust pipe 6. An exhaust manifold 3 on the front side of the vehicle is connected to the cylinder head 10. An exhaust manifold 4 on the rear side of the vehicle is connected to the cylinder head 10 '. Exhaust pipe 6
Guides the flow from the exhaust manifolds 3 and 4 into one pipe and guides it to the rear part of the vehicle.

A main catalyst 7 is disposed downstream of the confluence of the exhaust pipes 6 and under the vehicle floor. The main catalyst 7 is, for example, a three-way catalyst, and contains HC contained in the exhaust gas,
It oxidizes CO, reduces NOx, and purifies exhaust gas. The catalyst capacity of the main catalyst 7 is large, and therefore the heat capacity is also large. The activation temperature in the case of a three-way catalyst is about 250 ° C., and the exhaust gas is not purified by the main catalyst 7 until the catalyst 7 reaches the activation temperature immediately after the engine starts. Since the main catalyst 7 is located far away from the engine, the temperature of the exhaust gas decreases until it reaches the catalyst, the catalyst capacity is large, and it takes time to raise the temperature. Not active for a few minutes. However, regarding HC, the HC discharged within a few minutes after the engine is started accounts for a major portion of the total amount of HC discharged into the atmosphere.

Exhaust H for a few minutes immediately after engine start
In order to reduce the amount of C as much as possible, the start catalysts 5 and 5'are arranged immediately below the exhaust manifolds 3 and 4, respectively. The start catalysts 5 and 5'constitute a three-way catalyst or an oxidation catalyst. The start catalysts 5 and 5'are arranged as close to the engine as possible and have a small catalyst capacity in order to quickly warm them up.

The start catalyst 5 is restrained by suppressing the heat of the exhaust gas from being consumed to raise the temperature of the pipe wall until reaching the start catalyst.
In order to quickly warm up the 5 ', the exhaust manifold 3,
Reference numeral 4 denotes a double wall structure, and the inner walls 8 and 8'are thinned within a range that does not hinder the strength and the rigidity, thereby reducing the heat capacity of the inner wall. The outer walls 9 and 9'of the exhaust manifolds 3 and 4 are thick enough to secure the strength and rigidity necessary to support the catalytic converter of the start catalysts 5 and 5'and the exhaust pipe 6, and the heat capacity determines the thickness. Not subject to restrictions.

The inner walls 8 and 8'and the outer walls 9 and 9'of the exhaust manifolds 3 and 4 are separated from each other in the thickness direction. The exhaust manifolds 3 and 4 have a flange 12 at the end portion on the side connected to the engine 2, and the inner walls 8 and 8'and the outer walls 9 and 9'are fixed to the flange 12. Exhaust manifold 3,4
Has a flange 13 at the end of the start catalyst 5, 5 ', which is connected to the catalytic converter, and the flange 13 is fixed to the outer wall 9, 9'. At the ends of the exhaust manifolds 3 and 4 on the flange 13 side, a wire mesh 11 is provided between the inner walls 8 and 8'and the outer walls 9 and 9 ', and the inner walls 8 and 8'slide to form inner walls. The difference in thermal expansion between the outer walls can be escaped.

The exhaust gas heat retention of the exhaust manifold 3 on the vehicle front side is set higher than the exhaust gas heat retention of the exhaust manifold 4 on the vehicle rear side. In other words, the heat transfer from the inner wall 8 of the vehicle-side exhaust manifold 3 to the outer wall 9 is lower than the heat transfer from the inner wall 8'of the vehicle-side exhaust manifold 4 to the outer wall 9 '. For heat transfer,
There are three types of radiation heat transfer, convection heat transfer, and heat transfer, but the inner walls 8 and 8'and the outer walls 9 and 9'are connected only through the flanges 12 and 12 'and the wire mesh 11,
The heat conduction is negligibly small. Therefore, heat transfer between the inner and outer walls occurs due to radiative heat transfer and convective heat transfer. Both the radiant heat transfer and the convective heat transfer become larger as the inner wall temperature is higher and the inner and outer wall temperature difference is larger, and the radiant heat transfer becomes effective in the high inner wall temperature region.

Next, the structure peculiar to each embodiment will be described. The first embodiment will be described with reference to FIG. As shown in FIG. 2, in the vehicle front side exhaust manifold 3, the inner wall 8
A heat insulating material 14 such as ceramic wool is inserted between the outer wall 9 and the outer wall 9. The insertion of the heat insulating material 14 blocks radiation, suppresses air flow, and suppresses convective heat transfer. As a result, the exhaust gas heat retention property of the vehicle front side exhaust manifold 3 is secured.

In the vehicle rear side exhaust manifold 4, the emissivity of the inner surface of the outer wall 9'is made relatively larger than the emissivity of the outer surface of the inner wall 8 ', and heat transfer by radiation from the outer surface of the inner wall to the outer wall 9'is performed. Is increased. For example, the inner wall 8'is SUS410 (stainless steel) having an emissivity of about 0.6, and the outer wall 9'is ordinary steel having an emissivity of about 0.8 or emissivity of about 0.
9 of 25Cr-20Ni stainless steel or the like. The material composition of the vehicle front side exhaust manifold 3 need not be limited to the emissivity. Therefore, the material composition of the front side manifold 3 may be made the same as the material composition of the rear side manifold 4, and the heat insulating material 11 may be inserted between the inner and outer walls.

Next, a second embodiment will be described with reference to FIG. As shown in FIG. 3, in the vehicle front side exhaust manifold 3, the emissivity of the inner surface of the outer wall 9 is made smaller than the emissivity of the outer surface of the inner wall 8 to reduce heat transfer due to radiation from the inner wall 8 to the outer wall 9. Therefore, the exhaust gas heat retention is enhanced.
As a concrete material composition, the inner wall 8 is made of SUS410 or the like having an emissivity of about 0.6, and the outer wall 9 is made of 1 having an emissivity of about 0.4.
It is made of 8Cr-8Ni stainless steel or the like, or the inner surface of the outer wall 9 is plated with a metal having a low emissivity (about 0.1) such as Ni or Cr.

In the rear side exhaust manifold 4, as shown in FIG. 3, contrary to the front side exhaust manifold 3, the emissivity of the inner surface of the outer wall 9'is more relative to that of the outer surface of the inner wall 8 '. The heat transfer by radiation from the inner wall 8'to the outer wall 9'is increased. As a concrete material constitution, the inner wall 8'is made of SUS410 having an emissivity of about 0.6, and the outer wall 9'is made of ordinary steel having an emissivity of about 0.8, or about 0.9 of 25Cr-20Ni stainless steel.

Next, the operation of the present invention will be described. When the engine is warmed up, since the exhaust manifolds 3 and 4 have a double-wall structure and the inner walls 8 and 8'are made thin to reduce the heat capacity, the temperature rise of the inner walls 8 and 8'on the upstream side of the exhaust manifolds 3 and 4. The amount of heat of exhaust gas consumed is reduced, and the temperature of exhaust gas at the inlets of the start catalysts 5 and 5'becomes faster. Therefore, the start catalysts 5 and 5'are quickly warmed up, and once warmed up, the heat of the HC oxidation reaction by the catalyst further raises the catalyst temperature, and the catalyst purification performance immediately after the engine start is improved, especially the HC emission. Will be reduced.

After the engine is warmed up, even if the outer wall 9 of the vehicle front side exhaust manifold is cooled by the running wind, the exhaust gas temperature is kept high so that the temperature of the exhaust gas does not drop significantly. Therefore, the occurrence of a case where the exhaust purification performance of the start catalyst 5 and the main catalyst 7 is reduced is reduced.

After the engine is warmed up, the radiant heat is smoothly transferred from the inner wall 8'to the outer wall 9'in the vehicle rear side exhaust manifold 4, so that the outer wall 9'is.
Therefore, the temperature rise of the exhaust gas flowing through the inner wall 8'and the inside thereof can be suppressed appropriately only by removing the heat from the outside air by the convection heat transfer close to the natural convection heat transfer. As a result, heat damage to the inner wall 8'and heat deterioration of the start catalyst 5'can be suppressed.

[0022]

According to the present invention, in the exhaust system for a horizontal V-type engine, the exhaust gas heat retention of the vehicle front side exhaust manifold is set higher than the exhaust gas heat retention of the vehicle rear side exhaust manifold. Even if the front-side exhaust manifold is strongly cooled by the vehicle running air after that, it is possible to prevent the exhaust purification performance of the start catalyst and the main catalyst from being significantly deteriorated.

[Brief description of drawings]

FIG. 1 is a side view of an exhaust system for a horizontal V-type engine according to the present invention as viewed from the side of a vehicle.

FIG. 2 is a cross-sectional view of an exhaust system for a horizontal V-type engine according to a first embodiment of the present invention in the vicinity of an exhaust manifold.

FIG. 3 is a cross-sectional view of an exhaust device for a horizontal V-type engine according to a second embodiment of the present invention in the vicinity of an exhaust manifold.

[Explanation of symbols]

 1 vehicle 2 horizontal V-type engine 3 vehicle front side exhaust manifold 4 vehicle rear side exhaust manifold 5 vehicle front side start catalyst 5'vehicle rear side start catalyst 6 exhaust pipe 7 main catalyst 8 (vehicle front side exhaust manifold) Inner wall 8 '(in the vehicle rear side exhaust manifold) 9 outer wall (in the vehicle front side exhaust manifold) 9' (outside vehicle rear side exhaust manifold) 10 cylinder head 10 'cylinder head 11 wire mesh 12 flange 13 flange

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI technical display location F02B 75/22 C 7541-3G

Claims (1)

[Claims] 1. The exhaust gas heat retention of the exhaust manifold on the vehicle front side of the exhaust manifolds on the vehicle front side and the rear side of a horizontal V-type engine is set to be higher than the exhaust gas heat retention of the exhaust manifold on the vehicle rear side. An exhaust system for a horizontal V-type engine, which is characterized in that