Depending on a vehicles drive cycle, an improvement of the overall drivetrain efficiency does not necessarily have to go along with an improvement of its mileage. In here the ratio of energy to overcome rolling resistance, aerodynamic drag, acceleration and energy wasted directly in wheel brakes is responsible for potentially differing trends.
A detailed knowledge of energy flows, sources and sinks makes up a substantial step into optimizing any drive train. Most fuel energy leaves the drivetrain via exhaust pipes. Next to usable mechanical energy, a big amount is spent to heat up the system directly or to overcome drive train friction, which is converted into heat to warm up the system additionally. An in depth quantification of the most important energy flows for an upper middle-sized class gasoline powered drive train is given as results of warm-up cycle simulations. Combustion engine heat losses are split into four paths to be compared with the heat of ten engine friction components. Total engine friction of engines, started at room temperature in low load cycles used for emission legislation, makes up about one third of the heat input of the thermal system.
Energy flow manipulation in terms of thermal management measures are quantified as well as secondary effects and benefits seen in a holistic approach covering all relevant paths from fuel to wheel. Investigated is the effect of a split cooling system, a map controlled thermostat, the use of an electric water pump and combinations of those for a cold started FTP75 test cycle. Split cooling yields a benefit of ∼ 2.2 - 2.4 % fuel reduction potential; the use of an electrical water pump shows ∼ 0.3 - 1.2 %. The benefit of a combination of both measures is simulated to∼ 2.3 - 2.5 %.
