A patent application turned up at the USPTO last month that shows a new dual stage turbo system being developed by GM. This system appears to allow for isolation of either the low or high-pressure side of the turbo, with the ECU controlling which side is in use.
The idea is to make the turbo as efficient down low as it is at higher RPMs. Current turbo tech tends to lend to lag on the low end, that hurts off the line performance. A two-stage system such as this would let the engineers tune the car for ideal low-end performance and still get high-end performance. As with all patent applications, there is no guarantee that this tech will ever turn up in a vehicle that we can purchase.
Here’s the patent abstract for those of you who like to geek out on this kind of stuff:
In an internal combustion engine, a two stage turbocharger is disclosed including a low pressure turbine and the high pressure turbine are arranged in series. The high pressure turbine is connected to an exhaust manifold of the engine through a high pressure turbine inlet duct. The low pressure turbine is connected to the high pressure turbine through a low pressure turbine inlet duct and to the high pressure turbine inlet duct through a connecting channel. The two stage turbocharger is provided with a bypass system including a high pressure turbine valve arranged in the high pressure turbine inlet duct, and a low pressure turbine valve arranged in the connecting channel. An actuator is configured to operate the high pressure turbine valve and the low pressure turbine valve to alternatively close the high pressure turbine inlet duct or the connecting channel.
Source:: 95 Octane