Exhaust control systems

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Exhaust control systems

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Exhaust control systems

Exhaust control systems
Exhaust control systems

Exhaust control systems should increase the torque and thus the power in the lower and middle speed range in two-stroke engines, as well as reduce the emission of unburned fresh gases and thus the fuel consumption.

02/25/2003

Exhaust control systems should increase the torque and thus the power in the lower and middle speed range in two-stroke engines, as well as reduce the emission of unburned fresh gases and thus the fuel consumption.

Especially in high-performance two-stroke engines, the long exhaust control times cause considerable fresh gas losses at low speeds. At the same time, the pressure in the outlet drops sharply, with the result that the compression and thus the efficiency decrease. Therefore one tries to make the timing variable through constructive measures.

Yamaha, for example, developed the YPVS (Yamaha Power Valve System) back in 1977. A roller with a segment-shaped cutout sits on the upper edge of the outlet channel. By turning the roller, the height of the outlet channel changes and thus the control time. The roller is controlled either mechanically via centrifugal actuation or via a servomotor and Bowden cables. This system causes an increase in torque in the lower and middle speed range.

Suzuki also uses the variation of the exhaust valve timing in the new two-stroke engine of the RGV 250. A servomotor moves two cylindrical segments and thus the upper edge of the outlet channel via a linkage.

Rotax developed a system in which the height of the upper edge of the outlet and thus the timing is changed by means of a flat slide. In contrast to the systems mentioned above, it is actuated pneumatically. As the speed increases, the increasing pressure in the exhaust is used to move the slide valve via a membrane.

In addition to the exhaust control times, the gas oscillations in the exhaust have a decisive influence on the pressure conditions in the exhaust port and thus on the performance characteristics of a two-stroke engine. The exhaust length, which is decisive for the pressure conditions at the outlet, can only be adjusted for a narrow speed range. For this reason, systems have been developed which, on the one hand, help to achieve variable control times and, on the other hand, additionally influence the vibration conditions of the exhaust system via switchable chambers. As a result, the compression and ultimately the power output at low speeds was increased again.

Honda first used the ATAC (Auto Control Torque Amplification Chamber) system in 1983. Here a chamber attached to the outlet is switched on and off depending on the speed. By influencing the pressure fluctuations in the exhaust, the usable speed range is wider and the torque curve is improved at low and medium speed.

The KIPS system (Kawasaki Integrated Power Valve System) from Kawasaki works in a similar way. Here, two auxiliary outlets are controlled by rollers depending on the speed. At low speeds, one of the secondary outlets is closed, the second opening into an additional volume. At high speeds, a roller closes the chamber, and at the same time both auxiliary outlets are opened parallel to the main outlet.

Suzuki developed a similar system called SAEC (Suzuki Automatic Exhaust Chamber). A roller with a breakthrough sits above the outlet channel and, when rotated, gives way to an expansion chamber.

With the ATAC system from Honda, an additional volume is switched on in the exhaust system via a flap.


Exhaust control systems

Kawasaki’s Keim KIPS system controls two roller segments, two secondary outlets and an additional volume at the same time.
Left picture: lower speed range
Right picture: Upper speed range.


Exhaust control systems

With the Suzuki SAEC system, an additional volume is opened in the lower speed range by turning a roller via a servo motor and Bowden cables.


Exhaust control systems

With the YVPS from Yamaha, the upper edge of the outlet is adjusted depending on the speed via roller segments.


Exhaust control systems

Suzuki varies the height of the exhaust ports on the RGV 250 by means of speed-dependent controlled slides.


Exhaust control systems

The exhaust control at Rotax works with a flat slide, which is pneumatically controlled via the pressure in the exhaust system.

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