September 15, 2015
Pierburg
Series-production contract for compact bypass valve
Pierburg GmbH has presented an especially compact bypass valve to fit even the tightestspace conditions. It is already going into series production this year, initially on the sporting models of a major German premium class auto manufacturer.
The new compressor bypass valve weighs about twothirds less than standard ones and hence takes up much less space inside the engine compartment. It can be fitted directly to the charge-air duct behind the turbocharger and works according to the principle of indirect action.
Pierburg ranks as world-market leader in bypass valves for turbochargers. Since 2004, the valves have been manufactured on now five automatic production lines at the German location in Neuss. There are three other assembly lines in China and the USA. In 2014, some 7.5 million units were produced in all and the numbers are rising. So far, as many as around 25 million have been sold—to almost all the important OEMs as well as manufacturers of turbochargers.
The bypass valve is a solenoid-type unit with built-in pressure compensation to allow the valve to largely work independently of the turbocharger pressure. This allows the magnetic force to be kept low in relation to pressure conditions which, in turn, translates into cost savings. In future, there may also be variable bypass valvethat can regulate the pressure/air volume ratio in diesel engines.
Turbocharger or charge air duct with bypass valve
The electric bypass valve goes into operation whenever the driver takes his foot off the accelerator and the throttle flap is closed. But for this regulating function, backpressure could cause damage to the turbocharger. With the flap closed, there is a sharp rise in pressure, and if thisis not diverted via a valve, the air will flow through the compressor, resulting in a “surging” action in the turbocharger. That means the air flow is released from the compressor blades and the pumping process is interrupted. The air flows backward through the compressor until the pressure stabilizes and the air flow reverts to positive. The pressure builds up again and the sequence of events is repeated in rapid succession.
It is from the noise generated in the course of this procedure that the term "surging" has been derived. To avoid pumping, the electric bypass valve opens up a bypass around the compressor wheel. This must be big enough to allow the pressure in the intake manifold to drop quickly enough so as to keep the turbocharger away from the surge line at lower RPMs. The turbocharger can then continue to rotate freely, renewed pressure buildup is shorter and the outcome is faster acceleration of the turbocharger in favor of improved response after gear change.