GB2238004A

GB2238004A - Exhaust system.

Info

Publication number: GB2238004A
Application number: GB8925839A
Authority: GB
Inventors: Barry John Gale; Michael John Southwell
Original assignee: Ford Motor Co
Current assignee: Ford Motor Co
Priority date: 1989-11-15
Filing date: 1989-11-15
Publication date: 1991-05-22
Also published as: WO1991007575A1; GB8925839D0

Abstract

An exhaust system is described having a plurality of branches leading to different engine cylinders or groups of engine cylinders and a single catalytic converter (12) connected to the plurality branches in such a manner that gases from different branches of the manifold do not mix with one another prior to entering the converter nor during their passage through the converter.

Description

EXHAUST SYSTEM The present invention relates to an exhaust system incorporating a catalytic converter.

In exhaust systems using a single catalytic converter to purify the exhaust gases from several cylinders of an engine, the individual branches of the exhaust system have hitherto been joined to one another prior to their entering into the catalytic converter. As a result, the tuned lengths of the exhaust manifold extend only as far as the catalytic converter and this often is not sufficiently long for optimum performance.

It would be theoretically possible to use a separate catalytic converter in each branch of the manifold, but apart from the cost of such an arrangement, it would prove difficult to package within the space available in the engine compartment of a modern motor vehicle.

According to the present invention, there is provided an exhaust system having a plurality of branches leading to different engine cylinders or groups of engine cylinders and a single catalytic converter connected to the plurality branches in such a manner that gases from different branches of the manifold do not mix with one another prior to entering the converter nor during their passage through the converter.

A catalytic converter typically comprises a ceramic or metallic core in the form of a honeycomb structure which has axial passages for the exhaust gases. If such a core is positioned in the housing of the converter such that the inlet and outlet pipes abut, or terminate very close to, the core, then gases from the individual branches of the manifold can pass through the converter without mixing. The length of the branches of the manifold both upstream and downstream of the catalytic converter can now be tuned since the gases within the converter form part of the tuned gas columns.

The tuning of the exhaust manifold is now divorced from the positioning of the converter and it is preferred to connect the catalytic converter between the exhaust manifold and the exhaust down pipe. The converter can then be mounted directly onto the exhaust manifold, which is desirable having regard to its weight.

Furthermore, the operation of the converter is improved as the exhaust gases will be hotter while passing through the converter.

The invention will now be described further, by way of example, with reference to the accompanying drawing which is a schematic section through an exhaust system of the invention.

The flange 10 in the drawing is intended to be fitted directly to the exhaust manifold (not shown) of a four cylinder internal combustion. The manifold has two separate outlet conduits each leading to a pair of cylinders. The pairs of cylinders which are joined to one another in the manifold operate out of phase and therefore do not interfere with one another in so far as concerns the tuning of their manifold branches.

The conduits are semi-circular, or D-shaped, in cross section and when placed back to back form a complete circle divided into two by a partition wall extending along a diameter of the circle.

The flange 10 can be part of a flexible ball joint to be sealed against the circumference of the exhaust manifold by a collar having a part-spherical surface which can seal against a part-spherical seat under the action of a compression spring. This flexible joint is described in more detail in copending patent Application No.

filed on the same day as the present application (Agents reference P/ ). The purpose of the flexible joint is to accommodate rocking of the engine.

The converter 12 has a cylindrical housing 16 and a cylindrical honeycomb structure or core 14. At the upper end of the housing a partition wall 18 extends along a diameter and is aligned with the partition between the two conduits of the exhaust manifold. The partition wall 18 contacts the core 14 so that the gases from the individual branches of the manifold do not mix prior to passage through the core 14. Having regard to the manner in which such cores 14 are constructed, the gases pass through them without mixing.

At the lower end of the housing 12, where it joins down pipes 22 and 24, the housing includes a similar partition wall 20 so that gases do not mix before entering the two down pipes.

The down pipes 22 and 24 are joined to one another at a plenum 26 and the length of the pipes 22 and 24 from the converter 12 to the plenum 26 forms the tuned length of the manifold branches and is selected to optimise performance.

It can be seen from the foregoing description that the preferred embodiment of the invention provides a simple, inexpensive and robust solution to the positioning and mounting of a catalytic converter which affords considerable freedom in the design of the exhaust system with a view to optimising engine performance by improving engine scavenging.

Claims

CLAIM8

1. An exhaust system having a plurality of branches leading to different engine cylinders or groups of engine cylinders and a single catalytic converter connected to the plurality branches in such a manner that gases from different branches of the manifold do not mix with one another prior to entering the converter nor during their passage through the converter.

2. An exhaust system as claimed in claim 1, wherein the converter comprises a core positioned within a housing in such a manner that the inlet and outlet pipes abut, or terminate very close to, the core.

3. An exhaust system as claimed in claim 1 or 2, wherein the catalytic converter is connected between the exhaust manifold and the exhaust down pipe.

4. An exhaust system as claimed in claim 3, wherein the converter is mounted onto the exhaust manifold, by way of a flexible but gas tight ball joint.

5. An exhaust system constructed substantially as herein described with reference to and as illustrated in the accompanying drawing.