Internal combustion engine variable tuned exhaust system

Details Internal combustion engine variable tuned exhaust system Internal combustion engine variable tuned exhaust system

1994-09-30

1997-10-21

Hart, Douglas

Power plants

Internal combustion engine with treatment or handling of...

Pulsed, timed, tuned or resonating exhaust

60324, F02B 2706

Patent

active

056784040

DESCRIPTION:

BRIEF SUMMARY
TECHNICAL FIELD

This invention relates to improvements in internal combustion engines. In particular, this invention relates to exhaust systems for internal combustion engines and to internal combustion engines incorporating such exhaust systems, as well as to a method of operating such exhaust systems.


BACKGROUND OF THE INVENTION AND PRIOR ART

A conventional internal combustion engine repeats a cycle of actions in either two or four movements of a piston. The cylinder in a two-stroke engine, for example, has a transfer port and an exhaust port, each of which is opened and closed by reciprocation of the piston. The cylinder in a four-stroke engine, for example, has, instead of the transfer port and the exhaust port, an inlet valve and an outlet valve, each of which is also opened and closed by reciprocation of the piston.
For the sake of simplicity, that stroke of the piston, which results in the exhaust products being scavenged from the cylinder, will hereinafter be referred to as the exhaust stroke. Further, those means through which the fuel mixture enters the cylinder, being the transfer port of a two-stroke engine or the inlet valve of a four-stroke engine, for example, will hereinafter be referred to as the transfer port.
Furthermore, those means through which the exhaust products leave the cylinder and enter the exhaust system, being the exhaust port of a two-stroke engine or the outlet valve of a four-stroke engine, for example, will hereinafter be referred to as the exhaust port. It should be noted that the exhaust port may further include one or more header pipes.
After the fuel mixture has entered the cylinder through the transfer port and has been compressed and ignited, the exhaust products are scavenged from the cylinder during the exhaust stroke, through the exhaust port.
It is known that the tuning or adjustment of the exhaust system of an engine can affect engine performance. It is possible to tune an exhaust system with regard to the opening of the exhaust port to enhance engine performance.
For example, Australian Patent No. 584087 describes the tuning of an exhaust system of a two-stroke engine in order to establish a low pressure at the exhaust port, when the exhaust port is open and before the transfer port is closed, and a higher pressure at the exhaust port, after the transfer port is closed and before the exhaust port is closed.
The purpose of establishing the low pressure at the exhaust port before the transfer port is closed is to enhance scavenging of the exhaust products from the cylinder. The purpose of establishing the higher pressure at the exhaust port after the transfer port is closed is to minimise loss of fresh fuel mixture from the cylinder. Tuning in this manner can produce a "super-charging" effect, giving both greater engine power and improved fuel economy.
In Australian Patent No. 584097, the tuning of the exhaust port is said to be achieved by controlling the temperature of the gas in the exhaust system.
In tuning the exhaust system of a four-stroke engine, a "super-charging" effect may be achieved during valve overlap time when scavenging of the exhaust products from the cylinder is enhanced by negative pressure created at the exhaust port.
It has now been found that excellent tuning of the exhaust system of an engine may be achieved by providing an exhaust chamber which is variable in effective length during use.


DISCLOSURE OF THE INVENTION

It is an object of the present invention to provide an improved exhaust system suitable for certain internal combustion engines.
Accordingly, the invention provides an exhaust system for a four stroke internal combustion engine having at least one cylinder and at least one header pipe receiving exhaust gases from the at least one cylinder, the exhaust system comprising:
an exhaust chamber communicating with the at least one header pipe and an exit port, whereby exhaust gases flow from the at least one header pipe, through the exhaust chamber and to the exit port; and
an inner member mounted at least partially within the

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patent: 4046219 (1977-09-01), Shaikh
patent: 4941319 (1990-07-01), Yamamoto
patent: 4999999 (1991-03-01), Takahashi

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