Three-Cylinder Gasoline Engine With Direct Injection

Abstract

Market studies identified for this decade two segments that could be satisfied with a common base: : European volume segment around 74 to 92 kW : small car segments around 48 and 59 kW in Europe but also in rapidly expanding Asian and South American markets, with naturally aspirated 1.0-l engines. Initial engineering studies established that fuel economy and cost targets could best be met with a three-cylinder engine. Further studies then showed that a three-cylinder engine derived from existing architectures would not achieve the full functional potential and be more expensive than a dedicated small architecture. An all new small engine architecture was therefore developed with a 1.0-l in-line three-cylinder configuration as the basis. The challenge was to design an engine architecture that has excellent fuel economy using latest technologies in the turbo DI version, while offering an efficient but very low cost PFI engine for growth markets. One key element to achieving these conflicting goals is a cast iron block, with an unsurpassed combination of strength and low cost. To keep the weight competitive the engine block has to be designed as compact as possible. This requirement is largely met through the small displacement and three cylinders, and further supported by a long stroke configuration, which also improves combustion efficiency and knock resistance. Even in the highly charged turbo version (24 bar BMEP), the cast iron block enables cooling slots in the bore bridge, which is only 6.1 mm wide. Before this solution could be implemented, a compatible solution had to be found for the top end. Here the first challenge was to find an effective, low cost and compact solution for the valve train. By means of detailed friction breakdown studies and benchmarking, it was established that while the bucket tappet valve train in itself has higher friction than roller finger followers, this is only part of the losses. The primary drive also makes up a large part of the valve train friction, and here the belt-drive engines were typically much better. Hence a bucket tappet valve train was chosen, with a lifetime belt-in-oil drive. Through intensive development and implementation of polished tappets this valve train achieves friction levels similar to roller finger follower concepts, but at significantly lower cost. The small dimensions of the cylinder head created a packaging conflict between the tappets and the cylinder head bolts, which was solved by threaded steel inserts in the head, ❸. Open image in new window ❸ Requirements driving the concept choices Having settled the basic configuration of the engine, another major question was the configuration of intake, exhaust and accessory systems. Studies showed that keeping the accessories, turbocharger and catalyst on the same side of the engine offers significant advantages in crash performance and package. Putting them all on the front side provided easier thermal management as well as commonality with the diesel engines used in these vehicles. The thermal challenge of having the alternator close to the exhaust was substantially eased by the integrated exhaust manifold, which radiates significantly less heat versus a conventional manifold.