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Discussion Topics for Autoblog Podcast Episode #326
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GM patent reveals new two-stage turbocharger

Modern turbochargers may be some of the best ever made, but performance is something that engineers are always trying to improve. According to GM Inside News, General Motors (GM) is hoping to alleviate some of the negative aspects of a two-stage turbocharger setup with a newly-patented design. The patent, that was filed on May 19, 2016, reveals a clever bypass system that allows the engine, a four-cylinder unit, to optimize both the low-pressure and high-pressure inlets for its respective functions. According to the filing, a conventional two-stage turbocharger setup is engineered to allow both turbines to operate simultaneously at low and mid engine speeds. At high engine speeds, only the low-pressure turbine works. The setup can't isolate either the low or high pressure side, which can impair low-end performance. GM's new two-stage turbocharger setup looks to eliminate this by linking the high-pressure turbo to the exhaust manifold through the high-pressure inlet duct. The low-pressure turbo is attached to the high-pressure turbo by a low-pressure inlet duct, which is linked to a connecting channel. A single actuator that is housed in the exhaust manifold creates a bypass that can opens the high-pressure inlet or close the connecting channel. Depending on what the engine load and speed is, the ECU guides the actuator—a single rotating spindle with discs corresponding to flanges on the high and low pressure sides—to isolate one of the two turbos. Isolating the turbos allow the respective inlets to be engineered for the best possible fluid dynamic performance. The setup should increase performance and decrease lag. There's no word on what car this setup will make an appearance on, but it will most likely be used in premium vehicles before trickling down to the rest of GM's vehicles. Related Video: News Source: GM Inside News, AutoGuide via GM Authority Cadillac Chevrolet GM Technology Sedan turbo patent engine turbocharging

GM recalling 54k Cadillac SRX, HD pickup models

There are more recalls to report General Motors, but these latest actions pertain to newer examples of the Cadillac SRX, Chevrolet Silverado HD and GMC Sierra HD. With so much scrutiny on the company's recall strategy, GM is under increasing pressure to call in defective models more quickly, and it appears to be doing so here.
Here in the US, the automaker is recalling 50,571 Cadillac SRX crossovers from the 2013 model year fitted with the 3.6-liter V6 because the transmission control module programming can cause a three- or four-second lag in acceleration at low speeds. The explanation filed with the National Highway Traffic Safety Administration states, "if the following sequence occurs within two seconds: during an upshift from first to second gear (8-10 mph), the driver then brakes the vehicle to less than 5 mph, and then accelerates again," the delay can occur. According to Automotive News, the recall effects 56,400 vehicles worldwide, and the company is not aware of any crashes caused by the problem. The fix consists of a transmission control module (TCM) reflash.
In a separate recall, GM is repairing 51 Chevrolet Silverado HD and GMC Sierra HD pickups from the 2015 model year in the US. In vehicles with diesel engines and dual fuel tanks, the nuts that connect the fuel pipe to each side of the transfer pump between the tanks may be improperly torqued, which could cause a fuel leak. Obviously, this could be a fire hazard. The remedy is simply tightening the hardware. According to GM spokesperson Alan Adler, there have been no fires actually caused by the potential leak. "Only 21 of the trucks are in customer possession and they can be fixed anytime because there are no parts involved. The others are being fixed at dealerships," Adler said in an email to Autoblog.