GB2254883A

GB2254883A - I.c. engine exhaust system.

Info

Publication number: GB2254883A
Application number: GB9107960A
Authority: GB
Inventors: Thomas Tsoi-Hei Ma
Original assignee: Ford Motor Co
Current assignee: Ford Motor Co
Priority date: 1991-04-15
Filing date: 1991-04-15
Publication date: 1992-10-21
Also published as: EP0580664A1; GB9107960D0; EP0580664B1; DE69206410D1; WO1992018755A1; DE69206410T2

Abstract

An exhaust system is described for an internal combustion engine, which comprises a first catalytic converter (34) arranged in the exhaust downpipe in close proximity to the engine, and a second catalytic converter (42) arranged further from the engine in series with the first catalytic converter (34). A by-pass pipe (32) is connected in parallel with the section of the exhaust downpipe containing the first catalytic converter (34), a shut-off valve (40) is arranged in the by-pass pipe (32) for closing the by-pass pipe (32) when the engine is cold so that the exhaust gases flow through the first catalytic converter (34) and a pressure relief valve (38) is arranged in series with the first catalytic converter (34) for increasing the exhaust back pressure when the shut-off valve (40) is closed and the exhaust gases flow through the first catalytic converter (34).

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 presence of an exhaust system results in a back pressure in the combustion chamber of an internal combustion engine, which affects engine performance. The design of exhaust systems is usually a compromise between, on the one hand, noise and emission control, which increase back pressure because silencers and catalytic converters present obstructions to the gas flow and, on the other hand, engine performance and fuel economy, both of which benefit from a low back pressure.

Though under normal running conditions one aims to minimise back pressure, it is known that warm-up times can be reduced by increasing back pressure and the total emissions during the statutory drive cycle over which engines are calibrated can be reduced by increasing back pressure during the warm-up phase.

Description of the Prior Art GB 1 043 865 and 1 063 091 describe systems which include a variable throttle in the exhaust system to vary the back pressure as a function of engine operating conditions. In these proposals, the throttle causes an increase in back pressure throughout the load and speed range of engine operation. Therefore the back pressure during normal operation is impaired.

This problem is recognised in by GB 2 181 182 which describes an exhaust system comprising a regulating valve to increase back pressure under certain operating conditions and an actuator for moving the regulating valve to an inoperative position to permit the path in which it is situated to be fully opened.

This design of regulating valve is however costly to implement and its reliability of operation is suspect having regard to the hostile environment in which it has to operate.

Object of the invention The present invention therefore seeks to provide a less complex and potentially more reliable exhaust system in which a valve is provided to permit the back pressure to be increased during warm-up but in which the presence of the valve is not the cause of an increase in back pressure under normal operating conditions.

Sununarv of the invention According to the present invention, there is provided an internal combustion engine exhaust system having an intake end for connection to an engine exhaust manifold and an outlet end for discharging the exhaust gases to atmosphere, wherein at least along part of its length, the exhaust system is formed of two parallel paths both connected for conducting the exhaust gases from the intake end of the exhaust system to the outlet end, a first of the two parallel paths including a shut-off valve which when operated obstructs the first path and thereby causes an increase in exhaust back pressure and the second path including a relief valve for regulating the back pressure when the shut-off valve in the first path is closed, the relief valve being fully closed when the shut-off valve is open.

The shut-off valve is normally open to allow all the exhaust gases to pass unimpeded through the first path, and, in order to reduce warm-up time, an actuating mechanism is provided for closing the shut-off valve during the engine start-up and warm-up phase.

Conveniently, the actuating mechanism may be a thermostatic valve responsive to the temperature of the exhaust gases. Alternatively, the actuating mechanism may be pneumatically or electrically operated under the control of an engine management system.

The relief valve serves as a regulating valve when the shut-off valve is closed and maintains a constant back pressure by varying its opening as a function of gas flow rate. The relief valve may conveniently be constructed in the same manner as a non-return valve or flap valve having a valve closure member biased by a spring into a position where it seats against a stationary valve seat and which lifts off the valve seat under the action of the exhaust pressure.

In a preferred embodiment of the invention, the exhaust system includes a down pipe, a catalytic converter and a silencer arranged, in that order, between the intake and outlet ends of the exhaust system, and the shut-off valve and the relief valve are arranged downstream of the catalytic converter.

It is particularly advantageous for the shut-off valve and relief valve to be arranged downstream of the silencer as they can then operate in a colder and less hostile environment. Furthermore, if arranged beyond the silencer leakage to atmosphere is less significant.

In an alternative embodiment of the invention, the exhaust system includes a down pipe assembly, a catalytic converter and a silencer arranged, in that order, between the intake and outlet ends of the exhaust system, and the downpipe assembly constitutes the two parallel paths, the shut-off valve and the relief valve being disposed between the downpipe assembly and the catalytic converter. In this case, a supplementary catalytic converter may be arranged in the second of the parallel paths constituted by the downpipe assembly.

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 shows a silencer of an exhaust system in accordance with one embodiment of the invention, including a shut-off valve and a relief valve connected in parallel paths, the shut-off valve being shown in its closed position for fast warm-up, Figure 2 shown the silencer of Figure 1 with the shut off valve in its open position for normal operation, and Figure 3 shows a second embodiment of the invention in which the shut-off valve and the relief valve are arranged at the lower end of a downpipe assembly.

Detailed description of the preferred embodiments Figures 1 and 2 show a silencer 10 which in most respects is of conventional design. The silencer 10 has an inlet pipe 12 for connection to the exhaust manifold through the engine downpipe assembly and, if present, a catalytic converter. Gases in the inlet pipe 12 can enter into a resonance chamber 16 through apertures in the wall of the pipe 12 in order to muffle pressure pulses and cut down on noise.

Thereafter the gases passes through a convoluted path taking them first to a chamber 18, then back to an absorption chamber 20 containing baffles before they reach an exit pipe 22 which in a conventional silencer would be connected directly to the tail pipe.

In the present embodiment, the exit pipe 22 of the silencer proper enters a further chamber 24 by way of a pipe section 23 which is closed off at its end by a shutoff butterfly valve 26 and having in its side wall a spring biased flap valve 28 which acts as a relief valve regulating the exhaust back pressure when the shut off valve 26 is closed. The exhaust gases find their way into the chamber 24 through one or other of the shut-off valve 26 and the relief valve 28 and are finally discharged to atmosphere through the outlet pipe 14.

When the engine is operating normally, the shut-off butterfly valve is fully open as shown in Figure 2.

No significant obstruction is presented to the exhaust gases which pass straight through the chamber 24 from the pipe section 23 to the outlet pipe 14. The regulating valve 28 is fully closed as it is pressure operated and the by-pass presented by the open shut-off valve 26 will ensure that there will be no pressure across it.

In the position illustrated in Figure 1, however, the shut-off valve 26 is closed and prevents exhaust gases from escaping altogether. While the regulating valve 26 is initially closed, this will result in an increase in back pressure and will cause the regulating valve 28 to open. The extent to which the valve 28 will open will vary with the pressure and gas flow rate with the result that the back pressure as sensed at the engine will be increased to the desired level to enhance engine warm-up and will be maintained at this regulated level by the valve 28 varying its open cross section automatically.

This embodiment of the invention has the advantage that the valves 26 and 28 are contained in a sealed box at the cold end of the exhaust system and are therefore away from any hostile environment. They can therefore be made simply and inexpensively. Furthermore, any existing exhaust system may be modified by installing no more than a new silencer. Indeed, it will be seen that the novel elements of the invention may be housed entirely in a separate box installed in the tail pipe.

The valve 26 in this case is preferably thermostically controlled so as not to require any external control. For example, the valve 26 may be actuated by a bi-metallic element or a memory metal sensing the exhaust temperature.

In the embodiment of Figure 3, a downpipe assembly connects a plenum chamber 30 at the end of the exhaust manifold to a main catalytic converter (not shown). The downpipe assembly comprises two separate paths, the first formed of two individual pipes 32 arranged in parallel and the second comprising a supplementary catalytic converter 34. Both paths open at their lower ends in a chamber 36 which is analogous to the chamber 24 in the embodiment of Figures 1 and 2 and which is in turn connected to the main catalytic converter. The path formed by the pipes 32 terminates in a shut off valve 40 while the path comprising the supplementary converter 34 terminates in a relief valve 38.

The operation of this embodiment is essentially the same as the previous embodiment. In normal operation, the shut-off valve 40 is open and gases flow through the pipes 32 to the main catalytic converter and the back pressure is at its minimum level. During warm-up, the valve 40 is closed and the gases flow through the second path containing the supplementary converter 34 and the back pressure is regulated at a higher level by the relief valve 38.

In this embodiment, the supplementary converter operates only during warm-up and as it is positioned nearer to the engine it will run hotter than the main converter and will reach its light off temperature sooner. The back pressure being higher while this converter 34 is functioning assists its operation further by reducing the space velocity through the converter giving more time for heat exchange as well as for the catalytic conversion reaction to take place.

It is not advisable to move the main converter into such close proximity with the engine as it would tend to run too hot under full load. However, the present invention permits the supplementary converter to be positioned in this manner because under full load, the exhaust gases do not pass through it and it does not risk damaged to its catalyst by overheating.

If desired, the supplementary converter can be heated from the other downpipes 32 to maintain it-above the light off temperature at all times so that it may be brought into operation as desired, for example under idle and low load conditions, by external actuation of the shut-off valve 40 by the engine management system.

It will be noted that in both embodiments off the invention, the shut-off valve and the relief or regulating valve provided alternative parallel paths for the exhaust gases and that the shut-off valve prevents the relief valve from increasing the back-pressure when the engine is warm by by-passing the flow entirely around the relief valve.

Claims

1. An internal combustion engine exhaust system having an intake end for connection to an engine exhaust manifold and an outlet end for discharging the exhaust gases to atmosphere, wherein at least along part of its length, the exhaust system is formed of two parallel paths both connected for conducting the exhaust gases from the intake end of the exhaust system to the outlet end, a first of the two parallel paths including a shut-off valve which when operated obstructs the first path and thereby causes an increase in exhaust back pressure and the second path including a relief valve for regulating the back pressure when the shut-off valve in the first path is closed, the relief valve being fully closed when the shut-off valve is open.

2. An exhaust system as claimed in claim 1, wherein the shut-off valve is controlled to be closed during engine warm-up and open during normal engine operation.

3. An exhaust system as claimed in claim 2, wherein the shut-off valve includes an actuating mechanism for closing the valve during the engine start-up and warm-up phase.

4. An exhaust system as claimed in claim 3, wherein the actuating mechanism is a thermostatic valve responsive to the temperature of the exhaust gases.

5. An exhaust system as claimed in any preceding claim, wherein the exhaust system includes a down pipe, a catalytic converter and a silencer arranged, in that order, between the intake and outlet ends of the exhaust system, and wherein the shut-off valve and the relief valve are arranged downstream of the catalytic converter.

6. An exhaust system as claimed in claim 5, wherein the shut-off valve and the relief valve are both arranged downstream of the silencer.

7. An exhaust system as claimed in any of claims 1 to 4, wherein the exhaust system includes a down pipe assembly, a catalytic converter and a silencer arranged, in that order, between the intake and outlet ends of the exhaust system, and wherein the downpipe assembly constitutes the two parallel paths, the shut-off valve and the relief valve being disposed between the downpipe assembly and the catalytic converter.

8. An exhaust system as claimed in claim 7, wherein a supplementary catalytic converter is arranged in the second of the parallel paths constituted by the downpipe assembly.

9. An internal combustion engine exhaust system constructed arranged and adapted to operate substantially as herein described with reference to and as illustrated in the accompanying drawings.