WO2001031176A1

WO2001031176A1 - Vehicle exhaust assemblies

Info

Publication number: WO2001031176A1
Application number: PCT/GB2000/003951
Authority: WO
Inventors: Timothy Simon Lyons
Original assignee: Timothy Simon Lyons
Priority date: 1999-10-26
Filing date: 2000-10-13
Publication date: 2001-05-03
Also published as: AU7806100A; GB9925337D0

Abstract

An assembly mountable on a vehicle which is powered by an internal combustion engine and connectable to its exhaust system (5), comprising an aerofoil section (1) with internal ducting and an external slot (2), which, when subjected to the airflow generated by the vehicle's forward motion, generates an area of low pressure (12) in the vicinity of the slot (2), the area of low pressure (12) generating a partial vacuum and acting so as to assist the extraction of exhaust gases from the combustion chambers of the engine by sucking them out.

Description

VEHICLE EXHAUST ASSEMBLIES

The present invention relates to vehicle exhaust assemblies.

In a normally configured four-stroke internal combustion engine, exhaust gases are removed from combustion chambers by a combination of two forces. First, the piston, on its fourth upward stroke pushes these gases out of the cylinder through the exhaust ports and second, the gases themselves possess considerable kinetic energy, being under compression, and rapidly expand outward through the exhaust port and exhaust system. It is largely the second of these which causes the loud exhaust report to deal with which exhaust silencers were originally developed.

Vehicle silencers typically consist of a series of acoustic baffles which conspire to trap the offensive sound, while allowing the escaping exhaust gases the least resistance on their journey to reach normal atmospheric pressure. Inevitably, these baffles introduce some resistance - known as back-pressure - thereby reducing the ability of the exhaust gases to reach the outside world completely unimpeded.

Current legislation in most countries requires that all new petrol-driven vehicles must be fitted with a catalytic converter. The purpose of this apparatus is to cause the conversion of certain gases present in the exhaust mixture into less harmful gases.

Most catalytic converters operate by passing the exhaust gases through a honeycomb made of special compounds or metals which react with the gases to effect the conversion. By its nature, a catalytic converter introduces additional back-pressure to the escaping gases.

Finally, it is commonplace nowadays to find turbochargers fitted to vehicles. These boost engine power by using the pressure of the escaping exhaust gases to turn a turbine which in turn compresses incoming air entering the engine through the induction ports. Some of the kinetic energy of the exhaust gases is used in turning the turbine, once again introducing back-pressure and reducing exhaust system efficiency. According to the present invention, there is provided an assembly mountable on a vehicle which is powered by an internal combustion engine and connectable to its exhaust system, the assembly comprising an aerofoil section with internal ducting and an external slot, which, when subjected to the airflow generated by the vehicle's forward motion, generates an area of low pressure in the vicinity of the slot, the area of low pressure generating a partial vacuum and acting so as to assist the extraction of exhaust gases from the combustion chambers of the engine by sucking them out.

The present invention will now be described, by way of example, with reference to the accompanying drawings, in which:-

Figure 1 shows an aerofoil assembly in cross-section;

Figure 2 shows the assembly from the front;

Figure 3 shows the assembly from the underneath;

Figure 4 is a diagram for use in explaining operation of the assembly;

Figure 5 is a diagram for use in explaining the various parameters of the assembly;

Figures 6A and 6B show how the assembly may be mounted on a vehicle; and

Figure 7 shows an alternative design of aerofoil assembly.

Referring to Figure 1, a "wing-shaped" aerofoil 1 is shown in cross-section. There is an extractor slot 2 in its underside, connected via a hollow manifold 3 to a hollow expansion tube 4. The expansion tube in turn is connected to an exhaust inlet tube 5, which conveys exhaust gases from the engine. Although only one exhaust inlet tube is shown, there may be more than one, depending on the configuration of the engine and performance requirements. The assembly is mounted at a suitable place on the host vehicle using flanges 6, at least two in number, mounted at suitable places such as the extreme ends of the aerofoil 1 and in arrangement so as to allow the assembly to be mounted where required (Figure 1 shows flanges suitable for mounting beneath a vehicle). Additional flanges may be required to secure the assembly to the vehicle, depending upon the width of the vehicle, and the normal range of speeds at which it travels. This is because, owing to the forces created by air-flow over the surface of the aerofoil, as forward velocity increases, so does downward force on the aerofoil, thus necessitating additional flanges 6 to secure the assembly to the vehicle. The leading edge 7 of the aerofoil 1 faces the normal direction of travel of the vehicle, and the trailing edge 8 faces away from the normal direction of travel.

Figure 2 shows the assembly viewed from the front, showing axis A of Figure 1. The aerofoil 1 is shown in its full width as is the general arrangement of the expansion tube 4 and the exhaust inlet tube 5. Flanges 6 are shown at opposite ends of the aerofoil.

Figure 3 shows the assembly viewed from its underside, and shows the components and their general arrangement as detailed above. In particular, Figure 3 illustrates the lateral extent of the extractor slot 2.

Operation is as follows. Figure 4 shows the assembly functioning within an air- flow. The forward motion of the vehicle causes air to flow over the surfaces of the aerofoil, from its leading edge 7 towards its trailing edge 8. An aerofoil within such an airflow reacts with the airflow thus. Air flows (see 11 and 12) over the upper surface 9 and the lower surface 10. The latter has greater curvature and therefore a larger surface area than the upper surface 9, causing air pressure to drop adjacent to the lower surface. It is the pressure differential between the two surfaces of an aerofoil which produces a lifting force in a normally configured application. In the embodiment described here, the aerofoil is inverted, and the zone of lower pressure is created along the lower surface.

As shown in Figure 4, the extractor slot 2 is situated on the lower surface 10 at a location calculated to produce the lowest pressure at its opening over a given range of operating speeds. Since the extractor slot 2, the manifold 3 and the expansion tube 4 and exhaust inlet tube(s) 5 are in close proximity, the air pressure at all four is almost equal, this being lower than normal atmospheric pressure owing to the effect of the aerofoil described above. This lower pressure assists in the extraction of exhaust gases from the engine by combating back pressure and encouraging these gases to flow more freely.

It is noted that a single aerofoil would normally be mounted horizontally on a vehicle. This is because if it were mounted vertically, it would produce in operation an unbalanced lateral force which could adversely affect the vehicle's handling. It would be perfectly possible to utilise two (or any even number of) vertical 'opposed' aerofoils, thus cancelling out any lateral forces. However, the additional wind- loading imposed by vertically mounted aerofoils on a low vehicle such as a modern car might cause instability in high winds. Conversely, for a vehicle with substantial height, for example the tractor unit of a lorry or truck, vertically mounted aerofoils would contribute little additional wind-loading, and so may be a practical arrangement.

In summary, a primary effect is that the resultant effect of the motion of air past the aerofoil is to reduce the air pressure in the exhaust inlet tube(s) 5 to a value lower than normal atmospheric pressure. In turn this produces a suction effect which combats the back-pressure described above and assists in efficient extraction of the exhaust gases. This produces the benefit of increased efficiency of the engine.

A secondary affect of the suction produced by the aerofoil is as follows. Most modern vehicles provide some form of servo-assisted braking. This works generally by using the partial vacuum created under certain conditions at the inlet manifold of an internal combustion engine as a force to assist the pressure applied to the brakes, when the brake pedal is depressed. The conditions under which this effect takes place are generally when the accelerator is not depressed (commonly known as a 'trailing throttle'), but the brake pedal is - in other words the car is being slowed by the driver. Removal of pressure on the accelerator pedal causes the throttle butterfly valves to close, partially sealing the inlet manifold from atmospheric pressure. Meanwhile, the car's momentum continues to turn the engine. Under normal i.e. non-braking conditions, the first (or induction) stroke of the piston - a downward stroke - sucks air or fuel/air mixture into the cylinder from the inlet manifold. Under trailing throttle conditions, the piston's induction stroke sucks against the now-sealed inlet manifold, once the inlet valves are open. This action creates the useful vacuum which is used as a force to assist the braking process.

The aerofoil assembly described here assists this process since the additional suction produced at the exhaust manifold still has its effect during the inlet stroke, effectively decreasing the initial pressure in the cylinder, which in turn increases the evacuating effect on the inlet manifold. This delivers the benefit of an increased mechanical assistance available to the braking system.

An alternative arrangement and a tertiary effect will now be described.

By its nature, the silencer for an internal combustion engine has to be relatively bulky, certainly larger in cross-section than that of the exhaust pipes, which feed gases in and out of it. Additionally, as stated, new cars are fitted with catalytic converters, which are not small. As shown in Figures 6A and 6B, when a silencer 19 on a car is mounted underneath the body of the car 18, either it protrudes below the 'floor-line', which can act as an impediment to the smooth airstream 20 beneath the car, leading to turbulence 21 and thus drag (and in addition can be prone to damage), or else the floor-line is relieved upward at 22 in order to create a space for the silencer to be mounted away from the airstream. In the latter design, this can reduce the interior space available for passengers, luggage etc.

An alternative design for the aerofoil is shown in Figure 7, where the active elements of the silencer and/or catalytic converter 23 are contained within the body of the aerofoil 1. Since the aerofoil is deliberately placed in the airstream in order to have its primary effect, mounting the active elements of the silencer and catalytic converter inside the aerofoil will not increase resistance to the airstream and, indeed, will effectively relocate the silence to the rear of the vehicle, placing it inside a streamlined container. The tertiary effect is therefore to simplify the exhaust system by combining the silencer with the aerofoil, while removing the intrusion of a separate silencer into either the airstream beneath the vehicle, or the interior space of the vehicle. The tertiary effect also brings an additional benefit in that servicing or replacement of the silencer or catalytic converter is made simpler owing to the elimination of the requirement to raise the vehicle on a jack or ramp in order to gain access to its underside.

Careful design of the arrangement of the active catalytic and sound-absorbing elements of the silencer are necessary in order not to hinder the primary effect, and this will depend upon the specification of the exhaust system and the vehicle for which it has been designed.

It should be noted that the tertiary effect has more benefit for a small passenger vehicle such as a car, but would not be a major benefit to say a truck cab unit, as these are generally far from aerodynamic, and airflow around the vehicle is of less importance, while interior space is rarely at a premium.

A further by-product is that when mounted horizontally on a vehicle, the action of air-flow over the upper and lower surfaces results in a downward force on the aerofoil. This is transmitted through the flanges to the body of the vehicle. It is generally considered that some additional downward force aids the handling, stability and traction of a vehicle by pressing its tyres more firmly against the road surface.

It is for this reason that 'spoilers' are often fitted to the rear of some cars.

Referring to Figure 5, the major design parameters which will govern the effectiveness of the embodiments are:

The distance 13 from the leading edge 7 to the forward edge of the slot 2.

The width 14 of the slot 2.

The distance 15 of the rear edge of the slot 2 from the trailing edge 8.

The length of the slot 2 measured along the longest dimension of the aerofoil 1. The forward velocity 16 of the vehicle.

The angle of attack 17 which the aerofoil 1 presents to the air stream.

The internal dimensions of the manifold 3 and expansion tube 4. The nature of the materials used for each of the components.

The physical orientation of the assembly and its position on the vehicle. The proximity of the assembly to adjacent surfaces. Prevailing atmospheric conditions.

The design parameters of the internal combustion engine attached to the assembly. The shape of the vehicle to which the assembly is fitted.

It is likely that assemblies such as those described will be specifically designed for particular types of vehicles so as to take account of the design parameters mentioned above.

Claims

1. An assembly mountable on a vehicle which is powered by an internal combustion engine and connectable to its exhaust system, the assembly comprising an aerofoil section with internal ducting and an external slot, which, when subjected to the airflow generated by the vehicle's forward motion, generates an area of low pressure in the vicinity of the slot, the area of low pressure generating a partial vacuum and acting so as to assist the extraction of exhaust gases from the combustion chambers of the engine by sucking them out.

2. An assembly according to claim 1 , wherein the partial vacuum generated by the assembly and imparted to combustion chambers of the engine during over-run conditions acts as to enhance the operation of a servo assisted braking system by increasing the servo vacuum.

3. An assembly according to claim 1 or 2, wherein active elements of the vehicle's silencer or catalytic converter system are inside the assembly.

4. An assembly according to any preceding claim, or a plurality of such assemblies, mounted upon a vehicle.

5. An assembly or aplurality of assemblies according to claim 4, mounted upon a vehicle in the horizontal plane.

6. An assembly or a plurality of assemblies according to claim 4, mounted upon a vehicle in the vertical plane.