Patent Application
20080029655
Explanation will now be given of a vehicle exhaust system structure 10 to which the support structure of an exhaust system heat exchanger according to an exemplary embodiment of the present invention has been applied, with reference to
(Overall Configuration)
In
The downstream end of the exhaust pipe 18A is connected to the upstream side of the catalytic converter 12, and the upstream end of the exhaust pipe 18A is connected to the exhaust manifold of an internal combustion engine, which not illustrated in the figure, in such a manner that exhaust gas from the internal combustion engine is introduced therein. Further, the longitudinal directions of each of the catalytic converter 12 and the exhaust system heat exchanger 14 substantially correspond to the vehicle body front-rear direction, and the catalytic converter 12 and the exhaust system heat exchanger 14 are connected to each other substantially in a straight line, when seen in plan view, by an exhaust pipe 18B. In this exemplary embodiment, the exhaust pipe 18A, the catalytic converter 12, the exhaust pipe 18B and the exhaust system heat exchanger 14 are disposed substantially in a straight line when seen in plan view. However, an exhaust pipe 18C, which serves as an exhaust gas outflow pipe portion, and whose upstream end is connected to the downstream end of the exhaust system heat exchanger 14, is inclined with respect to the vehicle body front-rear direction when seen in plan view. As a result, the vehicle exhaust system structure 10 avoids a fuel tank 20 disposed to the rear of the exhaust system heat exchanger 14.
The length direction of the muffler 16 substantially corresponds to the vehicle body front-rear direction, and the muffler 16 is disposed in parallel with the fuel tank 20 in the vehicle width direction. The downstream end of the exhaust pipe 18C is connected to the upstream end of a muffler inlet pipe 22. An upstream portion 22A of the muffler inlet pipe 22 is inclined with respect to the vehicle body front-rear direction so as to form a substantially straight line with the exhaust pipe 18C. A downstream portion 22B of the muffler inlet pipe 22 is disposed mainly within the muffler 16, and the length direction thereof is along the vehicle body front-rear direction. An intermediate portion 22C of the muffler inlet pipe 22 is bent so as to couple the upstream portion 22A and the downstream portion 22B. Furthermore, a muffler outlet pipe 24 that has an upstream portion 24A disposed within the muffler 16 is integrated with an exhaust pipe 18E whose downstream end serves as an exhaust gas atmosphere release portion 18D.
A layout of the vehicle exhaust system structure 10 such as explained above is applied, for example, to a small, front engine, front-wheel drive (FF) vehicle.
(Configuration of Exhaust System Heat Exchanger)
The exhaust system heat exchanger 14 is configured to recover heat from the exhaust gas to engine cooling water serving as a cooling medium, and as shown in
An inner pipe 28 serving as a bypass pipe portion formed in a substantially cylindrical shape is disposed coaxially at the inner side of the partition wall pipe 26. The space formed between the partition wall pipe 26 and the inner pipe 28 is the exhaust gas flow path 30 of the exhaust system heat exchanger 14. Furthermore, the partition wall pipe 26 is covered from the outer circumferential side thereof by an outer pipe 32 that is formed in a substantially cylindrical shape and disposed coaxially with the partitioning wall pipe 26. The space between the partition wall pipe 26 and the outer pipe 32 is the engine cooling water flow path 34 of the exhaust system heat exchanger 14.
In the exhaust system heat exchanger 14, the region in which the engine cooling water flow path 34 is formed in the exhaust gas flow direction is the heat exchange portion 14A in which heat exchange between the exhaust gas and the engine cooling water is carried out, and the inner pipe 28 projects out further at the upstream side and at the downstream side than the heat exchange portion 14A. The space in the inner pipe 28 in the exhaust system heat exchanger 14 is a bypass flow path 36 serving as an upstream gas flow path for bypassing the heat exchange portion 14A in the exhaust system heat exchanger 14.
More specifically, as shown in
At the portion in the inner pipe 28 that is positioned inside of the exhaust gas introduction portion 26C of the partition wall pipe 26, through holes 42 that communicate the bypass flow path 36, which is a space inside the inner pipe 28, with the exhaust gas flow path 30 of the exhaust system heat exchanger 14 are provided. That is to say, the through holes 42 configure a branch portion between the exhaust gas flow path 30 and the bypass flow path 36. Meanwhile, through holes 44 that communicate the inside and the outside of the exhaust gas flow path 30 are provided in the end pipe 40. The through holes 44 and a downstream side opening end 38B of the exhaust gas guide pipe 38 respectively open to an exhaust gas exit header 48, which is a space inside a heat exchanger rear portion shell 46, and an upstream side opening end 46A thereof is connected in a gastight state to the end pipe 40.
Accordingly, in the exhaust system heat exchanger 14, a configuration is provided in which the exhaust gas that bypasses the heat exchange portion 14A and passes through the bypass flow path 36 reaches the exhaust gas exit header 48 inside the heat exchanger rear portion shell 46 via the inner side of the exhaust gas guide pipe 38, while the exhaust gas that passes through the exhaust gas flow path 30 via the through holes 42 reaches the exhaust gas exit header 48 inside the heat exchanger rear portion shell 46 via the through holes 44 which are at the outer side of the exhaust gas guide pipe 38.
Furthermore, the exhaust system heat exchanger 14 is provided with a valve device 50 for opening and closing the downstream side opening end 38B of the exhaust gas guide pipe 38. As is also shown in
As shown in
One end 68A of a return spring 68 serving as a biasing member is locked at the heat exchanger rear portion shell 46 (refer to
Furthermore, in this exemplary embodiment, the valve device 50 is configured such that when the temperature of the engine cooling water carrying out heat exchange with the exhaust gas is equal to or greater than a predetermined temperature, the valve 54 is mandatorily retained in the open position, regardless of the pressure of the exhaust gas. Specifically, a first cooling water inlet pipe 70, the interior of which is communicated with the engine cooling water flow path 34, is connected to the outer pipe 32 at the downstream side thereof in the exhaust gas flow direction. A thermo-actuator 72 is disposed at an end portion of the first cooling water inlet pipe 70, and the thermo-actuator 72 comprises a pressure rod 72A which increases a protruding amount with respect to the first cooling water inlet pipe 70 by the thermal expansion of wax that is filled inside the thermo-actuator 72. The pressure rod 72A is configured such that, when the engine cooling water temperature is 80° C. or higher, the pressure rod 72A pushes the lever 64 so that the valve 54 assumes a fully open position in which the degree of opening is greater than that of the above-mentioned open position obtained by the exhaust gas pressure (the fully open position is maintained). As shown by the dashed-single dotted lines in
As shown in
Due to the foregoing, the exhaust system heat exchanger 14 is a countercurrent heat exchanger in which the direction of flow of the exhaust gas and the direction of flow of the engine cooling water are in opposite directions, and in this exemplary embodiment, the exhaust system heat exchanger 14 has a configuration that is compact and has high heat exchange efficiency, due to the exhaust gas generating a spiral-shaped flow along the spiral groove 26A and the engine cooling water generating a spiral-shaped flow in the opposite direction to that of the exhaust gas along the spiral groove 26B. Furthermore, the exhaust system heat exchanger 14 is configured such that the pressure loss (back pressure) of the exhaust gas due to passing through the bypass flow path 36 is sufficiently small relative to the pressure loss of the exhaust gas due to passing through the exhaust gas flow path 30, and the exhaust gas mainly flows through the bypass flow path 36 when the valve 54 assumes an open position.
(Support Structure of Exhaust System Heat Exchanger)
As shown in
The support rod 78 is formed in a substantial L-shape when seen in plan view and is configured to include a projecting portion 80, which is fixed by one end 80A thereof being welded to the outer surface of the exhaust gas exhaust portion 26D of the partition wall pipe 26, and which projects in a substantially orthogonal direction to the axial direction (vehicle body front-rear direction) of the exhaust system heat exchanger 14, and a supported portion 82, which extends from the projecting end side of the projecting portion 80 along the axial direction of the exhaust system heat exchanger 14. At the distal end of the supported portion 82, an expanded diameter portion 82A for retention of a support rubber 84, which will be described below, is formed.
In this exemplary embodiment, the supported portion 82 extends toward the upstream side from the projecting portion 80, and as shown in
Meanwhile, as shown in
The supported portion 82 of the support rod 78 described above is inserted into the support rubber 84 serving as an elastic member, such that relative displacement (heat elongation absorption) in the longitudinal direction is possible. As shown in
Further, in the vehicle exhaust system structure 10 as shown in
Next, operation of this exemplary embodiment will be explained.
In the vehicle exhaust system structure 10 of the configuration described above, when the engine cooling water temperature is low, the valve 54 is made to be free with respect to the thermo-actuator 72, and the valve device 50 operates as a self-pressure valve. For this reason, under driving conditions in which the pressure of the exhaust gas is low, the exhaust gas guide pipe 38, that is, the bypass flow path 36, is closed off due to the biasing force of the return spring 68, exhaust gas flows through the exhaust gas flow path 30 of the heat exchange portion 14A, and heat exchange with the engine cooling water flowing through the engine cooling water flow path 34 is carried out. As a result, promotion of warm-up of the internal combustion engine and heating maintenance during low-temperature start-up is achieved.
When the pressure of the exhaust gas increases under driving conditions, such as, for example, acceleration or hill-climbing, in which the output of the internal combustion engine increases, the valve 54 which receives the pressure of this exhaust gas undergoes rotational movement against the biasing force of the return spring 68 in the arrow A direction to reach an open position. As a result, the exhaust gas flows mainly through the bypass flow path 36, and compared with the case where the exhaust gas flows through the exhaust gas flow path 30, the back pressure is reduced. That is to say, in the vehicle exhaust system structure 10 equipped with the valve device 50 functioning as a self-pressure valve, in a case where back pressure reduction for securing output takes priority over exhaust heat recovery for warm-up of the internal combustion engine or the like, reduction of back pressure is automatically achieved due to the exhaust gas bypassing the heat exchange portion 14A and flowing through the bypass flow path 36. Further, in the event that the internal combustion engine generates maximum output, the valve 54 assumes an induction position (maximum degree of opening by the pressure of the exhaust gas) shown in
Further, in the vehicle exhaust system structure 10, when the engine cooling water temperature becomes equal to or greater than 80° C., the pressure rod 72A of the thermo-actuator 72 presses the lever 64 of the rotational shaft 52 to retain the valve 54 in the fully open position. As a result, the exhaust gas flows mainly through the bypass flow path 36 and is exhausted from the exhaust pipe 18C via the exhaust gas guide pipe 38 and the exhaust gas exit header 48 of the heat exchanger rear portion shell 46. In other words, in a driving state in which recovery of exhaust heat is unnecessary, the exhaust gas flow path is automatically switched to the bypass flow path 36.
In the vehicle exhaust system structure 10, since the one end 80A of the projecting portion 80 in the support rod 78 for supporting the exhaust system heat exchanger 14 with respect to the vehicle body is welding connected to the exhaust gas exhaust portion 26D of the partition wall pipe 26 in the exhaust system heat exchanger 14, the welding portion does not contact the engine cooling water. For this reason, the outer contour of the exhaust system heat exchanger 14 has a configuration in which rust induced by the welding hardly occurs. Accordingly, growth of rust resulting in water leakage due to long-term use is prevented.
Further, since the support rod 78 is not welded at (a portion of) the outer pipe 32 constituting the engine cooling water flow path 34 in the outer contour of the exhaust system heat exchanger 14, the formation of rear beads accompanying the welding within the engine cooling water flow path 34 is prevented. For this reason, the flow of the engine cooling water, which has a higher flow resistance compared with the exhaust gas, is not inhibited by such rear beads, and excellent heat exchange performance can be obtained.
Furthermore, in the vehicle exhaust system structure 10, since heat transmission to the support rod 78 fixed at the exhaust gas exhaust portion 26D of the partition wall pipe 26 is transmitted from exhaust gas that has been cooled by heat exchange with the engine cooling water in the heat exchange portion 14A, or transmitted via the exhaust gas flow path 30 (in this case, functioning as an insulating layer) from exhaust gas mainly flowing through the bypass flow path 36, the support rod 78 hardly reaches a high temperature. Meanwhile, since the support rubber 84 is disposed to the side of the heat exchange portion 14A, that is, the engine cooling water flow path 34, the amount of heat emitted (radiated) from the vehicle exhaust system structure 10 is small. As a result, the amount of heat received by the support rubber 84 due to both transmission and radiation is small.
Due to these features, the support rubber 84 can be disposed in close proximity to the exhaust system heat exchanger 14, or in other words, the support rod 78 (in particular, the projecting portion 80) can be configured to be shorter, and the resonance frequency of the support system of the exhaust system heat exchanger 14 can be made higher. Further, since the clearance between the heat exchange portion 14A of the exhaust system heat exchanger 14 and the vehicle body (tunnel wall) can be made smaller, the support rod 86 can be configured to be shorter, and the resonance frequency of the support system of the exhaust system heat exchanger 14 can be made even higher. As a result, the noise vibration performance (NV performance) of the vehicle can be improved.
Further, in the vehicle exhaust system structure 10, since contacting of the fixing portion (exhaust gas exhaust portion 26D of the partition wall pipe 26) of the support rod 78 in the exhaust system heat exchanger 14 with high-temperature exhaust gas is suppressed as discussed above, energy (pulsational energy and the like) of the exhaust gas that is transmitted to the vehicle body via the support rod 78, the support rubber 84, and the support rod 86 is reduced. As a result, vehicle body floor vibration is suppressed. In particular, in a structure in which the support rod 86 is fixed to the tunnel wall of the floor tunnel positioned in the vicinity of a seat for occupant seating as in the present exemplary embodiment, the effect of suppressing transmission of exhaust gas energy via the support rod 78 is great.
It should be noted that, although an example has been shown in which the exhaust system heat exchanger 14 is supported at the vehicle body by the vehicle exhaust system structure 10 according to the exemplary embodiment of the present invention, the present invention is not limited thereto and can be applied to the exhaust system heat exchanger 14 with various forms.
Further, in the exemplary embodiment described above, although an example has been shown in which the support rod 78 is fixed to the exhaust gas exhaust portion 26D of the partition wall pipe 26, which is a portion other than the heat exchange portion 14A in the exhaust system heat exchanger 14, the present invention is not limited thereto, and for example, in a configuration in which the support rubber 84 overlaps with the heat exchange portion 14A when seen in side view, the support rod 78 may be fixed at the exhaust pipe 18 disposed in front or to the rear (upstream or downstream in the exhaust gas flow direction) of the exhaust system heat exchanger 14, or at the outer pipe 32 configuring the heat exchange portion 14A.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2006-213003 | Aug 2006 | JP | national |
