The invention relates to a method and means for increas¬ ing the output of an internal combustion engine by inter¬ mittently generating low pressure pulses in the exhaust- -silencer system of the engine.

Internal combustion engines have undergone numerous development phases during their lifetime but the basic design remains in principle unchanged. Several develop¬ ments to increase output have been proposed, in all of which various changes have been proposed in the engine design. These changes have resulted in more and more complicated engines which are sensitive to disturbances, require high-oσtane fuel, are difficult to repair, expensive, and so on. Examples of such developments are the use of superjacent cam shafts, half-spherical combus- tion chambers, compressor feeds and turbo-units driven by the exhaust gases.

As is known, the turbo-units function by the exhaust gas pressure driving a turbine wheel which in turn is used to compress the fuel-air mixture in the suction phase. However, this results in an increase in exhaust gas reaction-pressure, which has a negative influence on the running of the engine. Furthermore, turbo-units are extremely expensive and the costs are hardly justified by the extra power gained, at least not for an ordinary motorist. Besides, the turbo usually only gives extra power at an already high power, and entails greatly in¬ creased fuel consumption.

The object of the present invention, therefore is to achieve a method permitting increased output for a

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normal internal combustion engine, without intervention in the engine itself and which can also be used to save fuel. The invention also relates to a means for perform¬ ing the method according to the invention, said means being suitable for sale as a spare part and/or accessory and is thus fitted to engines already in use.

These objects are achieved according to the invention, with the methoddescribed in the introduction, substan¬ tially in that the exhaust gases are accelerated in a turbulence unit arranged at a certain minimum distance from the engine, in which unit a turbulent and a laminar flow are imparted to the exhaust gases, the laminarly flowing gases being caused to flow close to the inner defining surface of the turbulence unit in order to eliminate almost all friction for the turbulently flowing exhaust gases.

The invention also relates to a means for performing the method according to the invention, comprising a cylind¬ rical pipe with connections at each end for fitting into a conventional exhaust-silencer system, as well as a spiral element arranged in the pipe, the gap being arranged between the edges of the spiral element and the inner surface of the pipe.

According to a preferred embodiment of the invention, the means also comprises a pipe provided with counter¬ weight-loaded flap, by-passing a rear silencer, if any.

The pipe with the spiral element and the gap surrounding it form a turbulence unit and this turbulence unit is intended to replace the conventional front silencer in an exhaust-silencer system.

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The turbulence unit is preferably arranged at a certain minimum distance from the branch pipe of the engine. This distance is preferably ca. 2 meter.

The area of the gap is 5 - 10 % of the total through- -flow area for the exhaust gases in the turbulence unit.

Additional advantages and features of the invention will be revealed in the following detailed description with reference to the accompanying drawings, in which

Fig. 1 shows an exhaust-silencer system of conventional type with the arrangement according to the invention fitted,

Fig. 2 shows a longitudinal section along the line II - II in Fig. 3,

Fig. 3 shows a cross section along the line III - III in Fig. 2,

Fig. 4 shows a schematic cross-sectional view in a conventional cylinderpiston arrangement in an internal combustion engine, and

Fig. 5 shows a power-speed diagram, the unbroken lines indicating the output of an internal combustion engine with conventional exhaust system and the broken line the output of an engine with an exhaust system comprising a turbulence unit and by-pass pipe.

Fig. 1 shows an exhaust-silencer system of conventional type with branch pipe 1 , front silencer 2 and rear

silencer 3. The front silencer consists of a turbulence unit according to the invention, there being no direct external differences. The turbulence unit preferably has the same external dimensions as a conventional silencer, so that it can easily be fitted into a standard system.

The lenght of the pipe 4 between the branch pipe 1 and the turbulence unit is significant to the function of the device, as will be explained further in the follow¬ ing.

A pipe 5 is arranged to by-pass the rear silencer 3, the end of this pipe being partially closed by a counter¬ weight-loaded flap 6. The function of the flap will also be described below.

The construction of the turbulence unit can be seen in Figs. 2 and 3. It consists of a cylindrical pipe 11 with connections 12, 13 at each end. A helically twisted sheet-metal element is arranged centrally in the pipe 14, secured by point welding, for instance. The helical element is preferably turned two revolutions. A gap 15 is arranged between the inner surface of the pipe 11 and the edges of the spiral element 14.

The function of the invention will be described in connection with an ordinary piston-engine running on petrol (gasoline) , with suction and exhaust valves operating in the combustion chamber itself. The inven¬ tion of course functions together with other types of internal combustion engines. Fig. 4 shows a schematical cross section through the cylinderpiston arrangement of an ordinary petrol-fueled internal combustion engine with cylinder 21, piston 22, combustion chamber 23,

sparking plugs 24, branch pipe 25, suction valve 26 and exhaust valve 27.

The function of the turbulence unit is thus to extremely quickly accelerate the exhaust gases and then utilize the vacuum or partial vaacum occurring when the exhaust valve closes after the gases have been released from this cylinder. Once the engine is running, what is termed a standing wave of alternating high and ^' low pressure which be formed.

When a cylinder starts its suction and compression cycle or subsequent ignition and explosion of the fuel-air mixture, both suction valve 26 and exhaust gas valve 27 will be open for an instant. In this position, the previously performed exhaustion of gases will already have created a turbulent movement on its passage through the turbulence unit. This movement in the exhaust system forms a vacuum in the branch pipe when the exhaust valve closes.

The flow of exhaust gas which is given a turbulent move¬ ment upon its passage through the turbulence unit is subjected to minimal friction in view of the laminar flow in the gap along the inner cylinder surface. This laminarly flowing layer in principle lubricates the pipe and this lubrication effect remains right out into the by-pass pipe. Since the gases are subjected to extremely little friction, they are able to retain considerable acceleration. When this acceleration has reached its zenith, the flow of exhaust gas if abruptly cut off when the valves is closed. This rapid closing, combined with the swift movement of the gases, enables the creation of a strong momentary vacuum in the branch pipe. This strong vacuum is then utilized for the introduction of

the fuel-air mixture in the subsequent suction and ex¬ plosion phase. (This should be compared with forcing the same air-fuel mixture under high pressure into the combustion chamber of the cylinder, which is what happens in compressor-fed engines and in an exhaust-

-driven turbo-unit.) The process described above is thus entirely dependent on the speed of the engine and the vacuum effect is thus completely in phase with the power curve of the engine.

Fig. 5 is a diagram showing the output in kilowatt as a function of the motor speed, stated in rpm for a four- -cylinder petrol engine. The unbroken line represents the standard version and the broken line the use of an exhaust system with turbulence unit and by-pass pipe. As shown in the diagram, a power increase in the order of 20 % is obtained with the turbulence unit connected in an ordinary system. Even higher outputs are feasible depending on the technical construction of the engine used.

To more clearly describe the regular movement it has, as mentioned above, been likened"to a standing wave pro¬ duced in the exhaust system of the engine. This standing wave of exhaust gases with alternating high and low pressure is sinus-shaped. The frequency of the wave is dependent on the speed of the motor, higher frequency at higher speed.

No extra loads appear on an engine with a turbulence unit connected. However, it may be advisable to fit a speed limiter. This has been found with experiments performed on an old car with a turbulence unit fitted in the standard exhaust system. No complications whatsoever could- be observed during 10,000 km driving.

In this experiment a turbulence unit was inserted in the exhaust system where the ordinary front silencer had been and replaced this. The distance between the branch pipe and turbulence should preferably be at least ca. 2 m to enable the standing wave to be fully formed. After the turbulence unit the system was identi¬ cal to the original except that the by-pass pipe was fitted past the rear silencer.

The turbulence unit used for the experiment, also used in drawing up the curves shown in Fig. 5, consisted of a steel pipe about 400 mm long, with a diameter of 65 mm and a wall thickness of ca. 4 mm. A piece of helically twisted flat steel was fitted centrally with great accuracy in the pipe, leaving a gap of ca. 2 - 3 mm between the inner surface of the pipe and the edges of the flat steel. This created conditions suitable for a laminar gas flow necessary for the function of the whole system.

The by-pass pipe was provided with a counterweight-loaded flap with a smaller gap-opening in closed position. The object of the flap is to decrease the high effect of the turbulence unit at low-load. The gap-opening is necessary to provide a sufficient vacuum at low speed.

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