Two-Cylinder Gasoline Engine Concept for Highly Integrated Range Extender and Hybrid Powertrain Applications 2010-32-0130

The demand for improved fuel economy and the request for Zero Emission within cities require complex powertrains with an increasing level of electrification already in a short-termed timeframe until 2025. According to general expectations the demand for Mild-Hybrid powertrains will increase significantly within a broad range of implementation through all vehicle classes as well as on electric vehicles with integrated Range Extender (RE) mainly for use in urban areas.

Whereas Mild Hybrid Vehicles basically use downsized combustion engines at current technology level, vehicles with a high level of powertrain electrification allow significantly different internal combustion engine (ICE) concepts.

At AVL, various engine concepts have been investigated and evaluated with respect to the key criteria for a Range Extender application. A Wankel rotary engine concept as well as an inline 2 cylinder gasoline engine turned out to be most promising. The single rotor Wankel rotary engine was chosen for the Range Extender-ICE-concept of AVL's prototype vehicle for its extremely compact packaging and excellent NVH behavior.

For worldwide application however, an inline 2 cylinder gasoline engine concept shows considerable advantages compared to the Wankel rotary engine:

• Well known, proven engine technology
• Better fuel efficiency
• Low production cost (common technology with existing engines, use of existing manufacturing facilities, worldwide manufacturing options)

Consequently, the 2 cylinder gasoline engine concept was developed in parallel and is described in this paper.

Considering the given demands and requirements, a highly compact 4-stroke unit was realized. Since the range extender operation is limited to a few operation points, the system can be simplified, as comprehensive protection for overload, overspeed and complex transient operation conditions is not required. Crank train and valve train dimensions are optimized with regard to engine friction and weight. Roller bearings enable omission of the pressure lube oil pump and oil lines within the crank housing. Thermodynamically, valve timing, intake and exhaust geometries as well as resonance volumes are optimized for the operating points at low speed as well as idle speed operation can be disregarded. Additionally, the single-point operation allows optimization of acoustics via frequency and order.

The selected firing order and the integrated balancer shaft fully compensate first and second order inertia forces.

The RE-generator with starter function is directly mounted at the crankshaft rear end. The combination of crankcase and generator housing results in a fully integrated RE-core unit solution.

Beside the Range Extender application with few operating points of the internal combustion engine only, the modular concept is protected for use in serial hybrid concepts also with extended operating range of the ICE as well as a possible parallel hybrid concept with mechanical connection of the ICE to the drive shaft.