GB2255027A

GB2255027A - Exhaust system

Info

Publication number: GB2255027A
Application number: GB9108818A
Authority: GB
Inventors: Thomas Tsoi-Hai Ma
Original assignee: Ford Motor Co
Current assignee: Ford Motor Co
Priority date: 1991-04-24
Filing date: 1991-04-24
Publication date: 1992-10-28
Also published as: GB9108818D0; DE69219485T2; WO1992019850A1; EP0678153B1; EP0678153A1; DE69219485D1

Abstract

An exhaust system for an internal combustion engine, comprises a down pipe (14) for connecting an exhaust manifold of the engine to a main catalytic converter and a supplementary catalytic converter arranged in a path connected in parallel with the down pipe (14). The supplementary converter has an annular passage defined between inner (18) and outer tubular (16) walls which contains a catalytic matrix (20) and communicates with the interior of the down pipe (14) at its upstream and downstream ends. A second passage (20) also communicates with the interior of the down pipe (14) at its upstream and downstream ends and an obstruction (34) obstructs the down pipe (14) between the upstream and down stream ends of both the first and the second passages. A flow control tube (32) is movable relative to the down pipe (14) between a first position in which exhaust gases can flow from the down pipe into the first annular passage and return to the down pipe downstream of the obstruction (34) after passing through the catalytic matrix (20) and a second position in which exhaust gases can flow from the down pipe (14) into the second passage (22) and return to the down pipe downstream of the obstruction without passing through the catalytic matrix (20).

Description

Title Exhaust System Field of the invention The present invention relates to an exhaust system for an internal combustion engine.

Background of the invention The positioning of a catalytic converter in relation to an internal combustion engine exhaust manifold is normally a compromise based on two conflicting requirements. The catalyst must be capable of reaching its light off temperature (typically 3500C) under all running conditions and it should preferably do so as quickly as possible.

These requirements dictate that the converter be placed as near as possible to the exhaust ports of the engine. On the other hand, the temperature should not exceed a certain threshold temperature (typically 8500C) beyond which the catalyst suffers damage. Placing a converter close to the exhaust manifold would for this reason endanger the catalyst under high load and high speed conditions when the gas temperature can exceed this limit.

Various proposals have been made in the prior art to mitigate the problems at both end of the temperature scale. To -avoid damage to the converter through overheating, it is common for the fuel mixture strength to be increased significantly at high load. This reduces the exhaust gas temperature but ruins fuel economy and aggravates the problem of hydrocarbon and carbon monoxide emissions.

Placing a converter next to the engine (close coupled) is not always easy to achieve on account of the lack of available space. For this reason, under floor converters have been used in the prior art but they have the disadvantage that the exhaust gases are cooled before they reach the converter and the light off time of the catalyst is therefore prolonged.

It has also been proposed to use two catalytic converters, one being a main under floor converter and the other being a smaller supplementary close coupled converter, the latter converter being by-passed under high load conditions. This however requires good isolation of the supplementary catalytic converter under high load conditions as any leakage of high temperature gases would cause it damage.

Object of the invention The present invention seeks to provide an exhaust system in which a supplementary close coupled catalytic converter is provided in a path extending in parallel with the down pipe and in which the flow can be fully diverted away from the catalytic converter when the engine is running under high load to avoid damage to the catalyst by overheating.

Summarv of the invention According to the present invention, there is provided an exhaust system for an internal combustion engine, comprising a down pipe for connecting an exhaust manifold of the engine to a main catalytic converter, a supplementary catalytic converter arranged in a path connected in parallel with the down pipe, the supplementary converter having an annular passage defined between inner and outer tubular walls which annular passage contains a catalytic matrix and communicates with the interior of the down pipe at its upstream and downstream ends, a second passage which also communicates with the interior of the down pipe at its upstream and downstream ends, an obstruction for obstructing the down pipe between the upstream and down stream ends of both the first and the second passages and a flow control tube movable relative to the down pipe between a first position in which exhaust gases can flow from the down pipe into the first annular passage and return to the down pipe downstream of the obstruction after passing through the catalytic matrix and a second position in which exhaust gases can flow from the down pipe into the second passage and return to the down pipe downstream of the obstruction without passing through the catalytic matrix.

Preferably, the inner tubular wall of the supplementary catalytic converter is spaced from the outer surface of the down pipe to define an annular passage constituting the second passage.

In the invention, the catalytic matrix is totally isolated from the down pipe under high load by the flow control tube. Because of the close coupling, heat can still be transferred from the exhaust gases to the catalytic matrix and this helps to maintain the latter above its light off temperature even in the stand-by mode. The catalytic converter will reach the temperature of the exhaust gases which under high load may be as high as 9500C. Even though this temperature is 1000C hotter than the maximum safe temperature for the converter when exposed to exhaust gases, it has been found that when suitably isolated from the exhaust stream, the converter can be raised to this temperature for prolonged periods of time without any long term ill effects.

The down pipe may conveniently be formed with apertures at its junctions with the first and second passages, which apertures are exposed and covered by suitable positioning of the flow control tube. In the preferred embodiment of the invention, the flow control tube is a straight tube disposed within the down pipe and formed with the obstruction.

For improved sealing, it is desirable for the control tube to be movable axially relative to the down pipe but it is alternatively possible for the flow control tube to be rotatable relative to the down pipe to form so-called hit and miss shutters at the connections between the down pipe and the first and second passages.

If the second passage has the same flow cross sectional area as the remainder of the down pipe, then the second passage may be arranged as part of the tuned length of the exhaust pipe.

The control tube in all embodiments need to be movable relative to down pipe and though it is preferred that the down pipe remain stationary relative to the engine and the the control tube move in relation to it, it is possible, alternatively, for the control tube to be fixed in relation to the engine and for the down pipe and catalytic converter to be movable relative to it.

Brief description of the drawings The invention will now be described further, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a vertical section through an exhaust system in accordance with a first embodiment of the invention, Figure 2 shows a section through a flow control tube for insertion into the exhaust system of Figure 1, Figure 3 is a vertical section through an exhaust system of a second embodiment of the invention, and Figure 4 is a vertical section through an exhaust system of a further embodiment of the invention.

Detailed description of the preferred embodiments In Figures 1 and 2, a section of an exhaust system is shown which comprises a down pipe 14 connectible by means of a first flange 10 to the exhaust manifold of the engine and by means of a second flange 12 to the remainder of the exhaust system comprising an under floor catalytic converter, a silencer and a tail pipe (not shown).

Mounted about the down pipe 14 is an annular supplementary catalytic converter which comprises an outer housing 16 welded to the down pipe 14 and an tubular inner wall 18 which is spaced from the down pipe 14 and defines therewith an annular passage 22 which is sealed at both ends. The catalytic matrix 20 of the converter is likewise annular and is situated between the housing 16 and the tubular wall 18.

Various apertures are formed in the down pipe 14. A first aperture 24 allows exhaust gases to enter the annular passage formed by the catalytic converter and an aperture 30 returns exhaust gases from the converter to the down pipe 14. Similarly, the apertures 26 and 28 act for the exchange of gases between the down pipe 14 and the annular second passage 22.

To control the flow of gases through the various apertures 24 to 30, a flow control tube 32 (see Figure 2) is inserted into the down pipe 14 from below. The flow control tube 32 has an obstruction 34 which, when the control tube 32 is in situ in the down pipe 14 lies between the aperture 26 and 28 and prevents direct passage of the exhaust gases along the down pipe. Depending on the axial position of the tube 32, the gases are forced to flow either through the converter matrix 20 or the second annular passage 22. To this end, the flow control tube has apertures 36, 38 and 40 which align with the apertures in the down pipe in different positions of the flow control tube 32 and ring seals 42 which prevent leakage through these apertures when they are closed.

Axial displacement of the flow control tube 32 is effected by means of a rod 44 pivotably connected to the obstruction 34 and a lever 46 which is mounted in a housing 48, which when assembled is disposed between the flange 12 and the under floor catalytic converter. The pin 50 on which the lever is mounted can be rotated externally by means of a suitable actuator.

When the aperture 36 of the control tube 32 overlies the aperture 24 of the down pipe 14, the aperture 40 will overlie the aperture 30. At the same time, the apertures 26 and 28 are closed off and sealed. The exhaust gases thus flow through the catalytic matrix 20 and this position is adopted during cold start, warm up and light load conditions to bring the supplementary converter on line into the exhaust stream.

During high load operation, the converter would be damaged if continued to remain on line and for this reason once the main under floor converter has reached its light off temperature, the actuator connected to the lever 46 raises the flow control tube 32 to align the apertures 26 and 38 and the apertures 28 and 40, respectively. At the same time, the apertures 24 and 30 are sealed off to prevent any gases from reaching the catalytic matrix 20. In this position, the entire exhaust flow passes through the annular passage 22 which is of approximately the same cross sectional area as the remainder of the down pipe 14 and does not therefore interfere with the gas flow.

The flow of exhaust gases being separated from the converter only by the wall 18 will mean that the matrix will run hot and may under full load reach a temperature as high as 9500C. Nevertheless, as the matrix 20 is not exposed to any reactive gases, this elevated temperature will not damage it. There is no need to take any further special precaution, such as over fuelling, to protect the catalyst from harm.

Under all but the lightest load conditions, the supplementary converter remains in a stand-by mode above its own light off temperature and should the main converter drop below its light off temperature, the supplementary converter can again be brought on line by lowering the flow control tube 32.

Figure 3 shows a generally similar embodiment and in order to avoid unnecessary repetition like elements have been allocated the same reference numerals and modified elements have been given like numerals but a prime has been added. The essential difference in this embodiment is that the obstruction 34' forms part of the down pipe 14' and instead of being located inside the down pipe 14, the flow control tube 32' is located between the down pipe 14' and the inner tubular wall 18' of the converter.

The tube 32 must in this case be controlled by a lever passing through the housing 16.

A different arrangement of apertures is required in this embodiment there being only three apertures 24', 26' and 28' in the down pipe 14' and two apertures 36' and 40' at the top and bottom of the flow control tube 32'. As illustrated to the left in the drawing, when the flow control tube 32' is in its lower position the exhaust stream passes entirely through the annular passage 22 and in its raised position the entire exhaust stream flows through the catalytic matrix 20.

Figure 4 is a modification of the embodiment of Figure 3 and the same rules for allocating reference numerals have been followed. The essential difference from Figure 3 is that the inner wall 18" of the converter now serves a dual function and replaces the control tube 32'. For this to be possible, it is necessary for the entire converter to be axially movable along the down pipe 14 and this is achieved without risk of leakage with the aid of bellows 60 and 62 at the opposite ends of the converter.

Claims

1. An exhaust system for an internal combustion engine, comprising a down pipe for connecting an exhaust manifold of the engine to a main catalytic converter, a supplementary catalytic converter arranged in a path connected in parallel with the down pipe, the supplementary converter having an annular passage defined between inner and outer tubular walls which annular passage contains a catalytic matrix and communicates with the interior of the down pipe at its upstream and downstream ends, a second passage which also communicates with the interior of the down pipe at its upstream and downstream ends, an obstruction for obstructing the down pipe between the upstream and down stream ends of both the first and the second passages and a flow control tube movable relative to the down pipe between a first position in which exhaust gases can flow from the down pipe into the first annular passage and return to the down pipe downstream of the obstruction after passing through the catalytic matrix and a second position in which exhaust gases can flow from the down pipe into the second passage and return to the down pipe downstream of the obstruction without passing through the catalytic matrix.

2. An exhaust system as claimed in claim 1, wherein the inner tubular wall of the supplementary catalytic converter is spaced from the outer surface of the down pipe to define an annular passage constituting the second passage.

3. An exhaust system as claimed in claim 1 or 2, wherein the down pipe is formed with apertures at its junctions with the first and second passages, which apertures are exposed and covered by the flow control tube in its different positions.

4. An exhaust system as claimed in any preceding claim, wherein the flow control tube is a straight tube disposed within the down pipe and formed with the obstruction.

5. An exhaust system as claimed in claim 4, wherein the control tube is movable axially relative to the down pipe.

6. An exhaust system as claimed in any preceding claim, wherein the second passage has the same flow cross sectional area as the remainder of the down pipe, and is arranged as part of the tuned length of the exhaust pipe.

7. An exhaust system for an internal combustion engine, constructed arranged and adapted to operate substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.