Put to the test: the MAHLE downsizing engine
Stuttgart/Germany, September 2009—MAHLE is using a compact, highly turbocharged three-cylinder gasoline engine to demonstrate the potential that lies in its technologies. Tests on the 1.2-l engine are proving that downsizing rates of up to 50 percent are possible.
The gasoline engine, in particular, benefits from downsizing because smaller engines often operate at higher load ranges—where combustion is more efficient in gasoline engines than at lower loads. To demonstrate the potential benefit of downsizing in the short term and evaluate individual modifications in a complete system, MAHLE has developed a 1.2-l gasoline engine prototype. With a power output of up to 144 kW and a torque rating of 287 Nm, this engine has what it takes to replace an engine with twice its displacement. Yet the MAHLE engine is extremely fuel-efficient: Based on fuel consumption data, a simulation of the New European Driving Cycle (NEDC) in a vehicle weighing 1.6 metric tons indicated a potential improvement in fuel efficiency of greater than 30 percent compared to the 2.4-l reference engine.
For the development and production of the demonstrator engine, MAHLE drew upon the combined expertise of the entire Group. For example, the weight-optimized, intricate structures of the cylinder head, engine block, and oil pump were made to the required quality standards using the MAHLE COSCAST® aluminum casting method.
To mitigate the high thermal load brought about by exhaust gas turbocharging, a particularly efficient cooling concept involving crossflow cooling at the cylinder head was developed, and high-performance coatings and materials are used for a large number of components. The cooling system uses a thermal management system tailored to the specific needs of the application to optimize the overall efficiency of the engine.
Two key MAHLE technologies, in particular, make the engine powerful, clean, and fuel-efficient:
Variable valve train
The demonstrator engine design uses four-valve technology with two overhead camshafts. Phasers at the intake side and exhaust side allow independent adjustment of the valve timing. Low-friction roller-type cam followers increase the efficiency of the valve train, as do the low weight, small moving masses, and low wear of MAHLE lightweight valves cooled with a sodium filler.
Exhaust gas recirculation
The demonstrator engine is outfitted with a cooled exhaust gas recirculation system for EGR rates of up to 15 percent. This lowers the peak combustion temperature so the engine emits fewer nitrogen oides. Fuel consumption is reduced by eliminating full-load enrichment and dethrottling in the partial load. The engine is designed for compliance with EURO 5 emissions standards.
Exhaust gas turbocharging (EGT)
Today, the demonstrator engine is available in two versions: For the 100-kW-to-120-kW performance class, the design utilizes single-stage exhaust gas turbocharging. It is with the two-stage turbocharger design that the demonstrator engine achieves its peak performance. In this design, two exhaust gas turbochargers are configured sequentially.
The turbine housing of the high-pressure-stage EGT is integrated in the manifold. Here as well, exhaust gas is drawn into the turbine directly from an exhaust port. The high-pressure stage is activated at low rpms and continues to compress the exhaust gases up to an engine speed of 2,500 rpm. Once this limit has been reached, all of the exhaust flow is redirected to the low-pressure EGT by means of a bypass valve located between the exhaust manifold and the low-pressure EGT. At this point, the second turbocharger takes over the turbocharging function for the entire remaining rpm range up to a maximum engine speed of 7,000 rpm. The compressor casing of the high-pressure EGT (on the air side) features a pressure regulating valve.
Fast electrical wastegate actuator ready for serial production
An electrical wastegate actuator recently introduced by MAHLE—for the first time in a series production application—makes it possible to implement a fast control strategy for the turbocharger. This does away with "turbo lag," therefore resulting in enhanced responsiveness. Moreover, because the exhaust gas back pressure can always be kept to a minimum, fuel consumption is lowered.
With the pneumatic actuators used previously, the control speed was too slow for this, and the wastegate could only be controlled when sufficient charge air pressure was available. The new actuator passes through the entire range of adjustment in just 80 milliseconds.
For the first time, the MAHLE electrical wastegate actuator makes available a cost-effective, fast, and precise actuating mechanism that is capable of controlling the wastegate irrespective of the pressures occurring in the system. In addition, the actuator enables a reduction in the charge exchange work taking place, resulting in achievable fuel savings of up to four percent.
The MAHLE Group is one the top 30 automotive suppliers and the globally leading manufacturer of components and systems for the internal combustion engine and its peripherals. Around 45,000 employees work at over 100 production plants and eight research and development centers. In 2008, MAHLE generated sales in excess of EUR 5 billion (USD 7.3 billion).