POWERTRAIN
acoustics across the entire RPM and load range. A low back pressure design with four tailpipe outlets enabled GM to meet its engine power and emissions targets, with and without cylinder deactivation. They also addressed how to
Space constraints mean tight curves The exhaust gas temperatures in
the 2020 Corvette far exceed the thermal limits of conventional coupled electronic valves, as Dmitri Konson, vice president, global engineering, Tenneco Clean Air, explains: “Typically, such electronic valves cannot operate reliably above 750°C exhaust gas temperatures. This isn’t an issue in the vast amount of applications, but in the scenario of a mid-engine, high-performance confi guration the exhaust gas temperatures can peak higher than the acceptable limit for conventional valves with electronic actuators.” Tenneco’s solution was to develop a
valve arrangement with the actuator decoupled from the valve body,
operating through a link arm, to greatly reduce heat conduction to the valve electronics. This arrangement represents a considerable step forward in actuated valve design, and when combined with Tenneco’s latest tribological developments in valve materials, enables their use on mid-engine vehicles and others with extremely high exhaust temperatures. The signature V8 sound that
epitomises the character of the Corvette was faithfully preserved in the new model as a result of co- operation between GM and Tenneco. The partnership resulted in a new approach to fl ow mixing between the left and right sections of the cold-end exhaust system, achieving optimum
Returning the CERV
Although this model is new, Chevrolet has been experimenting behind the scenes with a mid-engined layout for years. Designer Zora Arkus-
Duntov started at GM on May 1, 1953, after viewing the Corvette concept at the 1953 Motorama in New York City’s Waldorf Astoria. He became the model’s fi rst true chief engineer. He also liked mid-engines cars and was responsible for several concepts, including the Chevrolet Experimental Research Vehicles (CERVs).
10
www.engineerlive.com The fi rst iteration, CERV 1
came along in 1960. At the time Duntov described it as “a design without limit” and an “admirable tool” to instruct Chevy on “what to put in the Corvette.” It has served as the template for the 2020 model, with a small block and aluminium core. Arriving in 1964, CERV 2
was an interesting contraption, with torque converters fore and aft, it was a four-wheel drive for which Duntov held the patent. And in 1990, the fi nal version was a collaboration with
limit the unwanted transfer of high exhaust temperatures to the vehicle’s surrounding components. To eff ectively manage the thermal and packaging requirements of a mid-engine confi guration, Tenneco’s engineers developed special multi- layer heat shields, constructed from a sandwich of insulation between two thin stainless-steel layers. The use of the multi-layer shield technology minimises the weight and package size of the fi nished assembly, providing the minimum profi le to meet both the engineering and styling requirements. The emissions system was
a global eff ort led by Tenneco Clean Air’s Michigan, USA and Germany product and engineering teams. It is produced at the fi rm’s manufacturing facility in Tennessee, USA then shipped to the GM plant in New York, USA for fi nal assembly. Some 1,500 people work at the facility, producing this and also others ranging from the two-litre Malibu unit up to the small block V8 for the latest Silverado and Sierra. ●
Left to right: CERV I, CERV III, CERV II
Lotus powered by a 5.7L, 32-valve dual overhead cam Small Block V8 with twin turbochargers. It produced 650bhp and 655lb-ft of torque. Duntov fi nally retired from GM in 1975.
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