Faster Four: GM Patents a Better Two-Stage Turbocharger
General Motors wants better performance from its boosted engines, so it headed to the patent office with a design for a new two-stage turbocharger — one that eliminates the drawbacks of the existing setup.
According to a document published by GM Inside News, the General filed the patent on May 19. The design (mated to a four-cylinder engine) isolates the low-pressure and high-pressure turbines, calling on one or the other (but not both) at different engine speeds and loads.
In a conventional two-stage setup, both turbines operate simultaneously at low to mid engine speeds, with only the low-pressure turbine working at high engine speeds. The two sides are never fully isolated, which compromises low-end performance.
Like a parent dealing with squabbling kids, GM decided to separate the two. In its design, the high-pressure turbo connects to the exhaust manifold via a high-pressure inlet duct, with the low-pressure unit connected to that channel via a low-pressure inlet duct. Depending on engine speed, an ECU-guided actuator located in the exhaust manifold opens opens the high-pressure inlet duct while closing off connecting channel, or vice versa.
The design aims to lower pumping losses while boosting the efficiency of both turbines. According to the patent, “maximum available enthalpy is given to the LP stage (low pressure turbine) in full power operation and to the HP stage (high pressure turbine) in maximum torque operation.”
Expect to see the turbo lag-reducing technology added to GM’s four-cylinder engines in the future, with the high-output 2.0-liter being a likely starting candidate.
[Image: General Motors]
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I for one do NOT welcome our new four cylinder overlords. (at least not in "performance" vehicles)
Seems like a similar setup to what Mazda is doing in the new CX-9 2.5T. Not being an engineer, not sure what the distinctions are.