GB2280711A

GB2280711A - Two stroke i.c. engine with catalytic converters.

Info

Publication number: GB2280711A
Application number: GB9316249A
Authority: GB
Inventors: Timothy John Bowman
Original assignee: Ford Motor Co
Current assignee: Ford Motor Co
Priority date: 1993-08-05
Filing date: 1993-08-05
Publication date: 1995-02-08
Also published as: GB9316249D0

Abstract

Two exhaust port openings 15 supply respective exhaust flow paths 17, 19 and catalytic converters 20, 23 are arranged to receive the exhaust gases. The control valve 18 varies the distribution of gases between the two flow paths according to the speed and load conditions of the engine. The temperature of the converter 20 is thereby controlled to a restricted value below a limit at which the converter would be damaged. A butterfly valve may be provided in the path 17 in place of or in addition to the valve 18. When the engine is cold the path 17 is closed. <IMAGE>

Description

Two Stroke Internal Combustion Engine The present invention relates to a two stroke internal combustion engine having catalytic conversion of the exhaust gases.

In known forms of internal combustion engines, an exothermic catalytic converter is used to convert the exhaust gases prior to emission from the engine. The converter has to operate at a temperature such as to promote the desired catalytic reaction of the exhaust gases and is positioned within the engine exhaust to be heated as quickly as possible to its operating temperature. The time required to heat the converter to its operating temperature is important because exhaust gases will not be converted catalytically at start-up from cold until the converter is at an operating temperature, termed the light off temperature.

A catalytic converter positioned close to the exhaust manifold of an internal combustion-engine will be closely heat coupled to the engine with a consequent rapid rise to operating temperature. However under high load conditions and at high speeds, the catalyst could suffer from overheating. Under these conditions a catalyst positioned further from the exhaust manifold is desirable.

The invention seeks to obviate the problems of obtaining a rapid rise to operating temperature of a catalytic converter for a two stroke internal combustion engine while controlling the heating of the converter under high load conditions and at high speeds.

According to the present invention, there is now provided a two stroke internal combustion engine having exothermic catalytic converter means in the exhaust of the engine to convert the exhaust gases prior to being discharged into the atmosphere, wherein the engine has a cylinder, two exhaust port openings from the cylinder, a first converter to receive exhaust gases by way of a first flow path through the exhaust from a first of the exhaust port openings, a second converter to receive exhaust gases by way of a second flow path through the exhaust from the second of the exhaust port openings, the second flow path being parallel to at least a portion of the first flow path and the second converter being more closely heat coupled to the engine than the first, a control valve to control flow in the first exhaust port opening to vary the distribution of gases between the said flow paths, and control means to operate the control valve to so increase the flow of exhaust gases through the first flow path at the expense of the second flow path upon increase in the speed and load of the engine as to restrict the temperature of the second converter.

Preferably the engine exhaust port openings are formed by the provision of a wall dividing an exhaust port into first and second sections which constitute respectively the said first and second exhaust port openings.

The control valve is preferably a powered rotary control valve moveable between open and shut positions in one section only of the exhaust port. The second flow path may lead into the first flow path at a junction upstream of the first converter.

The invention will now be described, by way of example, with reference to the accompanying drawings in which: Figure 1 shows a two stroke internal combustion piston engine according to the present invention employing a rotary control valve and divided exhaust port the engine being shown as operating under a first set of speed and load conditions and, Figure 2 shows the engine of Figure 1 when operating under a second set of speed and load conditions.

Referring to Figs 1 and 2, there is shown diagrammatically a two stroke piston engine having a cylinder 10 and a piston 11. The cylinder 10 and piston 11 constitute one of a plurality of such cylinders and pistons in a multi-cylinder engine each piston being operated by means of a connecting rod 12 connecting to a crankshaft 13 as is well known in the art. The crankshaft 13 operates within bearings in a crankcase 14.

Each cylinder of the engine has inlet and exhaust ports and for the purposes of simplicity only the exhaust port 15 is shown in the accompanying drawings. The exhaust port is divided by a dividing wall 16 into an upper section and a lower section. The upper section of the exhaust port 15 of each cylinder feeds exhaust gases through a first branch 17 of the exhaust system under the control of a rotary power valve 18. The power valve 18 can be rotated to a shut position as shown diagrammatically in Fig. 1 or to an open position as shown diagrammatically in Fig. 2. The lower section of the exhaust port 15 of each cylinder feeds a second branch 19 of the exhaust system. The branch 19 incorporates a close coupled catalytic converter 20.

The first and second branches 17 and 19 of the exhaust system join at a junction 21 and feed a downstream section 22 of the exhaust system which incorporates a further catalytic converter 23. From the catalytic converter 23 the exhaust system emits exhaust gases through an exit tail pipe 24.

It will be apparent that the catalytic converter 23 receives gases by way of a first flow path through the exhaust system which includes the first branch 17 while the close coupled catalytic converter 20 receives exhaust gases by way of a second flow path which includes the second branch 19 in parallel with the first branch 17.

When the engine is running under conditions to produce high exhaust temperatures, the valve 18 is moved by a control means 25 to an open position as shown in Fig. 2. In this open position, the valve 18 allows exhaust gases to pass primarily through the branch 17 and on to the converter 23.

A minor proportion of the exhaust gases will pass through the parallel branch 19 and through the converter 20 to keep the converter 20 at its operating temperature.

When the engine is running under conditions to produce low exhaust temperatures, the valve 18 is moved by the control means 25 to shut off the branch 17 and thereby divert the exhaust gases to pass through the parallel branch 19.

These latter conditions are illustrated in Fig. 1.

The diversion of the exhaust gases through the branch 19 as shown in Fig. 1 causes the close coupled converter 20 to be heated rapidly to operating temperature at start-up of the engine and to be maintained at its operating temperature without overheating during low engine speed or during light loading of the engine.

In operation, the engine is started up from cold with the power valve 18 moved to a shut position to divert the exhaust gases through the close coupled converter 20. As a result the converter 20 rises rapidly to its operating temperature to activate the catalyst therein to clean the exhaust gases. If the valve 18 remains shut, the exhaust gases continue to pass through the converter 20 and subsequently pass on to the converter 23. As the engine operating conditions change and higher exhaust temperatures are produced by the engine, the power valve is in the open position to allow the passage of exhaust gases directly to the converter 23 and therefore a redistribution of the exhaust gas flow between the two flow paths. The effect on the close coupled converter 20 is a reduced flow of gas and a restriction of the temperature of that converter.

Whilst the engine shown and described with reference to Figs. 1 and 2 has a divided exhaust port, it will be apparent to those skilled in the art that two separate exhaust ports may be provided to feed respective ones of the exhaust branches 17 and 19. These separate ports could be positioned at different circumferential positions relative to one another to enable the potential loss of exhaust port area caused by the dividing wall 16 to be prevented. Another modification would be the use of a simple butterfly valve in place of the rotary valve 18 shown or in addition to the rotary valve 18. The butterfly valve may advantageously be positioned in the flow path branch 17 upstream from the junction 21.

Claims

1. A two stroke internal combustion engine having exothermic catalytic converter means in the exhaust of the engine to convert the exhaust gases prior to being discharged into the atmosphere, wherein the engine has a cylinder, two exhaust port openings from the cylinder, a first converter to receive exhaust gases by way of a first flow path through the exhaust from a first of the exhaust port openings, a second converter to receive exhaust gases by way of a second flow path through the exhaust from the second of the exhaust port openings, the second flow path being parallel to at least a portion of the first flow path and the second converter being more closely heat coupled to the engine than the first, a control valve to control flow in the first exhaust port opening to vary the distribution of gases between the said flow paths, and control means to operate the control valve to so increase the flow of exhaust gases through the first flow path at the expense of the second flow path upon increase in the speed and load of the engine as to restrict the temperature of the second converter.

2. An engine according to claim 1 wherein the said exhaust port openings are formed by the provision of a wall dividing an exhaust port into first and second sections which constitute respectively the said first and second exhaust port openings.

3. An engine according to claim 1 wherein the said exhaust port openings are formed by the provision of respective separate exhaust ports from the cylinder.

4. An engine according to claim 1, 2 or 3 wherein the second flow path is unobstructed by movement of the control valve between the open and shut positions.

5. An engine according to any one of the preceding claims wherein the second flow path leads into the first flow path at a junction upstream of the first converter.

6. An engine according to any one of the preceding claims wherein the control valve is a powered rotary valve.

7. An engine according to any one of claims 1 to 5 wherein the control valve is a butterfly valve.

8. A two stroke internal combustion engine substantially as hereinbefore described with reference to the accompanying drawings.