Twincharger

From Wikipedia, the free encyclopedia

A twincharger is the denomination by the Volkswagen Group of a combination of a turbocharger and a supercharger in an engine. The 1.4 L TSI engine used in some current automobiles like the Volkswagen Golf, Touran employs both methods of forced induction, with the supercharger boosting low-end power while the turbocharger takes over at the high end. VW family of TSI engines also employs Fuel Stratified Injection.

The concept of a twincharger was pioneered by Lancia in the 1980s on the Delta S4 rally car and picked up by Nissan in the March compact car. In addition multiple aftermarket companies have made twincharger kits for cars like the Subaru Impreza WRX, Mini Cooper Type S, Skyline GT-R, Toyota MR-2, etc.

The most common type of twincharging system is a Roots type supercharger paired up with a medium-large sized turbocharger. The supercharger will give better power at low RPM while the turbocharger will give better power at medium-high RPMs. The main drawback of this configuration is that at high speeds, the supercharger (as it is driven by belts) will increase drag upon the engine, limiting the top end power. The Volkswagen Twincharging System overcomes this by locating the supercharger's pulley on a clutch system, which is automatically engaged and disengaged by the computer. This allows the car to keep its top-end performance and automatically switch to supercharging at low RPM.

Drawbacks

There are several drawbacks to this setup, such as the supercharger still creates drag in the airflow system, even when the clutch is off and the turbocharger is on. It can also cause excessive pulley/belt wear as the clutch engages/disengages at usually very high engine speeds. The transition from the supercharger engaging/disengaging can also be quite rough as well. Lastly, as turbos continue to flow more air as engine speed rises, the turbocharger will eventually outflow more air than it is receiving from the supercharger unless complex piping is used to bypass which can be quite costly and inefficient in a small engine bay.

Solution

The solution to these problems is quite simple, switch the places of both force induction units. By having a turbocharger feed air into a supercharger you gain several benefits as well as minimize any drawbacks from a conventional twincharger setup. The benefits are quite obvious, the supercharger will generate a set amount of boost (determined by pulley size) almost instantly, thus causing the engine to create more exhaust flow and spin the larger turbo quicker. As engine speeds start reaching past the superchargers efficiency under normal circumstances, the turbocharger is providing increasing amounts of air to the supercharger where it would normally run out. All pressure the supercharger receives from the turbocharger is further compressed by whatever the supercharger pulley is rated for. This helps reduce drag on the engine and top speed restrictions isn't as limited.

Simply put, the twincharger concept is a cheaper alternative to the high cost of Nitrous used in many race cars as it provides the instant power without excessive re-filling cost. The twincharger concept itself has not been used on many production cars simply due to the complexity and cost of implementing this system on a vehicle. Another reason simply put is the concept itself is really only viable on sports cars with relatively small displacement engines with high revving capabilities. The main purpose of twincharging is to provide a broad power band, in which the vehicle would perform in just about any RPM speed. This concept is relatively pointless on V8 engines or any vehicles with high torque in stock form as they already posess broad power bands.

Twincharger Vs. Anti-Lag System

Twincharging's biggest benefit over Anti-Lag Systems now being employed in quite a few race cars is the amount of power and reliability it provides. Anti-Lag Systems depend on excessive engine misfiring to keep the turbochargers spooled and thus to maintain the vehicles optimal powerband. Excessive misfiring will cause excessive heat and damage to the turbo manifolds, turbochargers as well as damaging the engine. Anti-Lag Systems make passing Emissions testing next to impossible due to the excessive heat damaging the catalytic converters as well, the Twincharger system does not rely on misfiring at all thus increasing longevity. There are several things such as fuel economy, etc. that are severely compromised.