GB2369092A

GB2369092A - Motorcycle exhaust system

Info

Publication number: GB2369092A
Application number: GB0126800A
Authority: GB
Inventors: Davide Mazzoni
Original assignee: Ducati Motor Holding SpA
Current assignee: Ducati Motor Holding SpA
Priority date: 2000-11-16
Filing date: 2001-11-07
Publication date: 2002-05-22
Also published as: IT250475Y1; GB0126800D0; ITMI20000653U1; DE20117024U1; FR2816657B3; FR2816657A3

Abstract

An asymmetric exhaust system comprises one exhaust pipe per cylinder. Where the motorcycle engine has two cylinders in a V arrangement, the second exhaust pipe joins the first exhaust pipe downstream of a reflective feature 16. This feature is an enlargement 16 of the first pipe's cross-section. When an exhaust valve opens, a compression wave travels towards this feature, which produces a reflective negative wave which travels back towards the valve to assist the removal of gases from the cylinder. The difference in pipe diameters at the junction 18 of the two pipes also acts as a reflective feature. The value for the length of each pipe 11,13 which is upstream of the relevant reflective feature 18,16 is designed to maximise the efficiency benefits from increased gas removal and improved cylinder charging. The system includes at least one silencer 22 and exit pipe 23.

Description

EXHAUST SYSTEM FOR A MULTI-CYLINDER MOTORCYCLE ENGINE The present invention relates to an exhaust system for a multi-cylinder motorcycle engine.

With reference by way of non-limiting example to a two-cylinder engine, this comprises two cylinders positioned in a V arrangement facing the travel direction.

Such an engine is of small overall dimensions and offers high performance.

It is well known that the exhaust system of an engine, and in particular of a high performance engine, must be designed to maximize dynamic effects in filling each cylinder and minimize pressure drops undergone by the gaseous combustion products. This is achieved by optimizing the lengths and diameters of the exhaust pipes characterizing the engine behaviour at the various rotational speeds.

The phenomenon utilized to obtain these filling effects is that of reflection: when a (positive) compression wave travelling along a pipe encounters an increase in cross-section, it is reflected to generate a depression wave which travels through the pipe in the opposite direction. In the case of an engine, when the exhaust valves of a cylinder open, a positive compression wave is generated in the corresponding exhaust duct and travels therethrough until it encounters an increase in the duct cross-section; at this point the compression wave is reflected to become a depression wave which travels through the duct towards the cylinder.

On reaching the cylinder slightly before closure of its usual exhaust valve or valves, this wave facilitates cylinder filling so maximizing engine efficiency. This effect is achieved by suitably dimensioning the exhaust system such that it exhausts at the speed for which the engine performance is to be optimized.

The cross-section of the exhaust duct can be enlarged in various ways. In one of these, a number of exhaust ducts converge into a pipe of larger cross-section ; in another solution, each duct presents two consecutive sections of different

diameter. The shape of each exhaust duct after the point in which reflection occurs is of little importance in achieving maximum power, hence beyond this point the ducts can converge into one or more pipes leading to a number of silencers.

By way of example, a known exhaust system of a two-cylinder engine comprises two exhaust ducts connected to the engine via a usual connection flange. These ducts converge at a point of the system known as the"junction"or"compensator" ; said ducts are known as the"primary exhaust ducts". The gases from the individual cylinders converge in the compensator. From the compensator two separate pipes can again extend from the compensator towards silencers, or alternatively one combined pipe can extend to a single silencer. A terminal pipe open at its end extends from each silencer.

In order for an engine to deliver maximum power, the individual cylinders must be optimized for the same rotational speed, this meaning that the primary exhaust ducts must have the same length and diameter. As the speed at which the engine is to be optimized increases, the diameter of the primary duct must be increased or its length decreased. Because of the fact that in a high performance motorcycle engine, space, weight and aerodynamic requirements set a limit to the diameter of each primary exhaust duct, it is its length which has to be varied. However in such a motorcycle, as its rotational speed increases, the primary ducts become of insufficient length for their connection to the rear silencer or silencers.

For this reason, the choice has been for a known exhaust system configuration in which the primary duct of the vertical cylinder (close to the rear of the vehicle) is shaped to descend towards the ground (or towards the plane of the horizontal cylinder). In this manner the two primaries are of equal length.

After the compensation point (compensator), one or more ducts extend upwards towards the front of the engine to then connect to the rear silencer or silencers.

This configuration is complicated, and involves a considerable use of material and components which negatively affect the weight (and hence the performance) of the engine.

An object of the present invention is to provide an exhaust system which represents an improvement over known systems.

A particular object of the invention is to provide an exhaust system which is of simple configuration, is easily mounted on the vehicle, and occupies little space thereon.

Another object is to provide an exhaust system of the stated type which provides easy access to the engine and to the other structural or mechanical parts of the motorcycle.

According to the invention there is provided an exhaust system for a multicylinder motorcycle engine, said engine comprising at least two cylinders disposed in V arrangement, said system comprising exhaust ducts of a number at least equal to the number of cylinders, each duct being connected to a corresponding cylinder, said system comprising at least a part in which there is reflection of the compression wave generated on opening at least one exhaust valve of each cylinder, said reflection part being individual to each exhaust duct or being common to several ducts, the system comprising at least one silencer member connected to an exhaust pipe for the off-gases leaving the engine, and wherein the exhaust ducts connected to the engine have a different shape and length, so defining an asymmetric exhaust system.

The present invention will be more apparent from the accompanying drawing, which is provided by way of non-limiting example and in which: Figure I is a schematic side view of the rear of a motorcycle provided with an exhaust system according to the invention; Figure 2 is a perspective view of the exhaust system of Figure 1 ;

Figure 3 is a schematic view of a variant of the system of Figure 1.

With reference to the said figures, a motorcycle 1 comprises an engine 2 with which an off-gas exhaust system 3 is associated. In the example this engine is a two-cylinder engine comprising a cylinder 4 of substantially horizontal longitudinal axis W parallel to a plane P in which the vehicle lies, and a cylinder 5 of substantially vertical longitudinal axis K. The engine is associated with a frame 7 supported by wheels 8, of which only the rear wheel is visible in Figure 1.

The system 3 comprises two exhaust ducts 10 and 11 connected respectively to the horizontal cylinder 4 and to the vertical cylinder 5. According to the invention, the system 3 is of the asymmetric type,. i. e. it comprises exhaust ducts 10 and 11 of different length and shape.

Specifically, the first duct 10 connected to the cylinder 4 is longer than the duct 11. This duct 10 comprises a first portion 13 (the primary exhaust duct) of constant cross-section; the duct 10 comprises a second portion 14 of greater crosssection than the primary exhaust duct or portion 13. Between the portion 13 and portion 14 there is a diameter variation region 16 defining the junction or compensator of the duct 10.

The second duct 11 connected to the cylinder 5 comprises instead a single portion 17 of constant cross-section; this portion 17 connects to the first duct 10 in its portion 14 of greater cross-section. The junction point or region 18 between the portions 17 and 14 acts as the junction or compensator of the duct 11. After the point at which the portions 14 and 17 of the ducts 10 and 11 join together, there extends a pipe portion 20 (which in the example of Figures 1 and 2 is a continuation of the portion 14 of the first duct 10) which terminates in a silencer 22 connected to an exhaust pipe 23 open at its end 24. Alternatively (Figure 3), two pipes 20A connect the ducts 10 and 11 to two different silencers 22A connected to corresponding exhaust pipes 23A opening at 24A.

At its free end, each duct 10 and 11 presents a flange 25 by which it is fixed to the engine.

It should be noted that the portions 13 and 17 (primaries of the ducts 10 and 11) preferably and advantageously have the same length ; the length of the exhaust primary 13 is unaffected by dimension problems and is independent of the position of the junction 16.

By virtue of the invention an exhaust system configuration is achieved which is much simpler than the configurations of known exhaust systems. This new configuration also has advantages in terms of accessibility of the engine members and of other mechanical parts of the motorcycle lying close to the rear wheel.

An embodiment of the invention applied to a two-cylinder engine has been described. The invention is however also applicable to engines with a different number of cylinders, for example four.

Claims

CLAIMS 1. An exhaust system for a multi-cylinder motorcycle engine, said engine comprising at least two cylinders disposed in V arrangement, said system comprising exhaust ducts of a number at least equal to the number of cylinders, each duct being connected to a corresponding cylinder, said system comprising at least a part in which there is reflection of the compression wave generated on opening at least one exhaust valve of each cylinder, said reflection part being individual to each exhaust duct or being common to several ducts, the system comprising at least one silencer member connected to an exhaust pipe for the offgases leaving the engine, and wherein the exhaust ducts connected to the engine have a different shape and length, so defining an asymmetric exhaust system.
2. An exhaust system as claimed in claim 1, wherein a first duct presents a first portion and a second portion having different cross-sections, the first portion being connected to the cylinder and having a smaller cross-section than the second portion, between said first portion and said second portion there being present the reflection part of said first duct, the second duct being connected to the second portion of said first duct.
3. An exhaust system as claimed in claim 2, wherein the second duct has a constant cross-section, which is less than that of the second portion of the first duct, the junction region between said second duct and said second portion defining the reflection part of the second duct.
4. An exhaust system as claimed in claim 1, comprising a single silencer connected to the second portion of the first duct downstream of its junction region with the second duct.
5. An exhaust system as claimed in claim 3, wherein from downstream of the junction region between the second duct and the first duct there extend two pipe portions each connected to a corresponding silencer member.
6. An exhaust system as claimed in claim 3, wherein the first portion of the first duct and the second duct have substantially identical lengths.
7. An exhaust system for a multi-cylinder motorcycle engine substantially as herein described and as illustrated in the accompanying drawings.