GB2284446A

GB2284446A - Variable length i.c. engine exhaust system

Info

Publication number: GB2284446A
Application number: GB9324661A
Authority: GB
Inventors: Michael John Stockbridge
Original assignee: Individual
Current assignee: Individual
Priority date: 1993-12-01
Filing date: 1993-12-01
Publication date: 1995-06-07
Also published as: GB9324661D0

Abstract

The length is variable in dependence on engine speed by rotating an element 5 or by axial movement of exhaust pipe sections (2, 3, Fig. 1). <IMAGE>

Description

VARIABLE LENGTH EXHAUST SYSTEM This invention relates to exhaust systems for internal combustion engines.

In operation an internal combustion engine relies on the flow of air, fuel and exhaust gases through the engine, and in a reciprocating engine these gases pulsate within the passageways of the engine according to engine speed. This pulsation occurs with both the air/fuel mixture entering the intake and with the exhaust gases in the exhaust system. For optimum efficiency, the pulsations within the passageways should be naturally resonant at the engine operating speed.

Within a normal engine, where the length of the intake and exhaust passageways are fixed, this optimum is achieved at only one engine speed, which is normally selected by the manufacturer to be the speed at which maximum power is achieved.

Some engine types, and notably two stroke engines with crank case primary compression, are very sensitive to passage length and in particular to the lengths of the different sections of a tuned exhaust system. In normal useage however, a two stroke engine powering an automotive or marine vehicle will be operated at a much lower speed than its design optimum. Thus any tuned exhaust system will be ineffective at this lower speed because the tuned lengths will have been fixed for a higher speed.

This invention describes an engine exhaust system in which the length of the tuned sections may be varied according to engine speed or other engine parameters.

According to the present invention the exhaust system length may be varied in a linear manner with the exhaust system forming a generally coaxial tube with slidable sections. A second embodiment is also described in which the variable lengths form the anulii within a cylindrical housing.

The invention will now be described by way of example for a two stroke engine, with reference to the accompanying drawings.

Figure 1 shows in cross section the exhaust system in its linear form, as a series of of coaxial tubes.

Figure 2 shows a sectioned pictorial view of the exhaust system in its rotatable anular form.

In its linear form the exhaust would consist of three coaxial tubular sections: the front pipe 1, the expansion section 2, and the reverse cone and tail pipe section 3. The three sections are connected by slip joints and seals 4.

In use, the sections are made tc slide within each other, in a ratio according to the rotational speed of the engine. This ratio is predetermimned to suit the particular engine to which the device is connected, such that the exhaust system presents a longer path to the exhaust gases at lower engine speeds.

In its rotatable form, the exhaust unit comprises a rotatable element 5, contained within a housing 6 and mounted on a spindle 7. The housing has an inlet pipe 8 and an outlet pipe 9, which direct the gas in and out of the housing. The rotatable element can be rotated within the housing by rotation of the spindle, using an external drive mechanics..

The rotatable element is fashioned such that in combination with the housing it forms the front pipe, expansion sezticn and reverse cone section of an equivalent concentric tubular system. The rotating element is sealed fro gas bypass within the housing by a mid point seal 10. The exhause gases pass through the unit as shown by the dotted line 10.

In use the rotating element is turned through a predetermined angle, according to the rotational speed of the engine, such that at lower engine speeds the exhaust gas has a longer path through both the front pipe and expansion sections.

The method of adjusting the tuned section lengths, for either embodiment of the invention may be by the use cf lead screws, racks or rams, these being electricall, hydraulically or pnumaticallv a-tuated.

Claims

1 An engine exhaust system in which the length of the tuned sections may be varied according to engine speed or other engine parameters.

2 An engine exhaust system as claimed in claim 1 wherein the length may be varied in a linear manner with the exhaust system forming a generally coaxial tube with slidable sections.

3 An engine exhaust system as claimed in claim 1 wherein the variable lengths form anulii within a cy'indr.cal housing.

4 An engine exhaust system as claimed in claim 1 and 2 wherein the exhaust would consist of two or more coaxial tubular sections connected by slip joints and seals.

5 An engine exhaust system as claimed in claim 1 and 3 wherein the exhaust unit comprises a rotatable element, contained within a housing and mounted on a spindle.

6 An engine exhaust system as claimed in any preceding claim wherein the actuation method is by the use of lead screws, racks or rams, these being electrically, hydraulica'ly or pnuratically powered.

7..... An engine exhaust system substantiaslly as described herein with reference to Figures 1 and 2 of the accompanying drawing.