Mechanical supercharging in combination with an expansion operation of the charger in part load range of the engine has proven to be an efficient method to reduce fuel consumption with simultaneous reduction of pollution. By reducing swept volume and maximal speed when compared to a naturally aspirated engine of similar power the operating conditions of the engine during driving may be shifted generally into ranges of more favourable specific fuel consumption. In a configuration particularly advantageous for application on Otto engines the charger is provided with a variable inlet control edge by means of which the charge of the engine during part load is influenced. The throttle loss of the engine is at least partly utilized as positive technical energy via the charger which is operating in this range as an expansion machine. The cooling of the inlet air due to the energy absorption results is a reduction of NOx emissions with simultaneous decrease of hydrocarbon emission. The influence on NOx emissions could be further increased considerably with additional use of an exhaust gas recirculation while maintaining the obtained.