This application claims the priority of German Patent Document DE 100 54 006.6, filed in Germany on Nov. 1, 2000, the disclosure of which is expressly incorporated by reference herein.
The invention relates to an air gap insulated exhaust manifold for an internal combustion engine of a motor vehicle having a catalytic converter. The air gap insulated exhaust manifold includes an inner pipe and an outer pipe surrounding the inner pipe at a defined distance with a connecting flange on the side of the cylinder head.
German Patent Document DE 196 28 797 C1 discloses an air gap insulated exhaust manifold having an inner pipe which is surrounded by an outer pipe at a distance.
Air gap insulated exhaust manifolds are widely used in practice because relatively little thermal energy is released to the surroundings from the exhaust gas due to the insulating air gap. For quick catalytic converter heating, it is beneficial if the exhaust gas releases little thermal energy.
Similar embodiments of air gap insulated exhaust manifolds contain a fastening flange to the cylinder head, to which the exhaust pipes are fastened. The exhaust pipes lead from the manifold to the exhaust collecting pipe. Air gap insulation through an outer metal shell starts close to the connecting flange, however the exhaust pipe is not insulated directly on the connecting flange, but rather firmly connected.
This has the disadvantage that in the area of the connecting flange heat transmission to the surroundings occurs.
The invention is based on the goal of fastening an air gap insulated exhaust manifold having an outer pipe and an inner pipe to the cylinder head of an internal combustion engine in an optimal way.
At least this goal is achieved by arranging the inner pipe such that it protrudes into the cylinder head with its pipe end in a guided fashion and that only the outer pipe can be fastened to the cylinder head through a connecting flange.
Motor vehicles with internal combustion engines are equipped with catalytic converters so as to reduce the amount of pollutants in the exhaust gas. Conventional catalytic converters work only within a certain temperature range. In the case of low exhaust gas temperatures, the catalytic effect does not occur. In the case of high temperatures, the catalytic converter is destroyed. In order to achieve prompt starting of the catalytic converter, it is important that as little thermal energy as possible is lost between the combustion chamber in the cylinder head and the catalytic converter.
The distance between the cylinder head and the catalytic converter is bridged by the exhaust manifold, which is generally screwed to the cylinder head. The exhaust manifold has a connecting pipe for each cylinder, which joins into a common collecting pipe. The collecting pipe extends away from the cylinder head area and joins into the catalytic converter.
Good thermal insulation is accomplished by designing the exhaust manifolds with double walls, with an insulating air gap between the inner pipe and the outer pipe. The inner pipe is usually welded from several pipe sections. The outer pipe is formed by several preformed metal shells, which are joined, placed around the inner pipe and kept at a distance to the inner pipe with specialized spacers.
In the cylinder head, the exhaust port can be insulated with a so-called port liner. Such a solution, however, is complex.
It is advantageous when no or few heat bridges exist from the hot exhaust gas to the surroundings of the exhaust pipe between the exhaust port in the cylinder head and the end of the exhaust manifold on the catalytic converter side.
In a preferred embodiment of the cylinder head and the exhaust manifold, this requirement is fulfilled with the fact that the exhaust gas port contains an insulating air gap from the inside of the cylinder head to the end of the exhaust manifold on the catalytic converter side, without containing a heat bridge in the area of the cylinder head flange of the exhaust manifold.
The outer pipe of the exhaust manifold is fastened to the cylinder head with a continuous or with several individual flanges on the cylinder head. In order to better insulate against noise transmission, it is beneficial if a specialized spacer is arranged between the connecting flange and the cylinder head.
Since the outer pipe serves as a supporting pipe for the inner pipe, and does not come into contact with the hot exhaust gas but only with the air layer in the air gap insulation, it is not absolutely necessary to fasten the flange of the outer pipe to the cylinder head in a gas-tight manner. This opens up a multitude of opportunities for fastening the flange with specialized spacers to the cylinder head in such a way that no or little motor vibration is transmitted to the exhaust pipe. Since the insulating air gap encloses the inner pipe all the way into the cylinder head, large amounts of heat are not applied to the flange by the hot exhaust gas in the flange area, permitting also materials that are not heat-resistant to be used as specialized spacers.
Apart from the catalytic converter side end, the outer pipe is connected with the inner pipe only by support elements. These support elements have designs as they do in conventional air gap insulated exhaust manifolds, such as simple sheet metal parts that keep the inner pipe at a distance from the outer pipe, but at the same time permit minimal movement in the pipe direction caused by differences in thermal expansion.
Hot exhaust gas flows through the inner pipe, and the outer pipe is separated from it by an air gap and exposed to the cooler surrounding air. This results in considerable temperature differences between the two pipes. In order to prevent the pipes from deforming due to thermal expansion within the exhaust manifold, it is necessary to allow the inner pipe to be moved within the outer pipe.
Referring again to German Patent Document DE 196 28 797 C1, the inner and outer pipes are united on the catalytic converter side end of the exhaust manifold on a flange with simple insulation and connected in a conventional manner with the catalytic converter.
Here, as well, improved thermal insulation is achieved in a manner similar to the one on the cylinder head side end of the exhaust manifold. This means that the outer pipe of the exhaust manifold is connected with the catalytic converter housing e.g. through a conventional flange, and that the inner pipe protrudes into the catalytic converter housing beyond the flange area. In order to accomplish this, the inner pipe is held at a distance to the outer pipe, the flange and the catalytic converter intake across its entire length by way of specialized spacers.
The inner pipe protrudes into the exhaust port of the cylinder head as far as possible. For simple assembly of the exhaust manifold to the cylinder head, it is beneficial if the pipe section of the inner pipe that protrudes into the cylinder head is substantially straight. This means that the inner pipe protrudes into the cylinder head along a length equal to that of the exhaust port, with no or only a small bend.
The inner pipe has a continuous cross-section to the exhaust port section that is located downstream in front of it. In order to avoid an abrupt change of the cross-section in the transition from the exhaust port to the inner pipe of the exhaust manifold, the exhaust port exhibits a port expansion in the cylinder head, into which the inner pipe is slid from the cylinder head flange. The port expansion has such a design that an insulating air gap is created between the inner pipe and the expanded port.
The sealing elements that keep the inner pipe in the cylinder head and simultaneously seal it can be made of various materials, such as thermoplastic, rubber with high temperature stability or a metallic material. Fastening of the synthetic sealing elements occurs in a fashion similar to that of an O-ring.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.