48-V Mild Hybrid System for Commercial Vehicles
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48-V Mild Hybrid System for Commercial Vehicles
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48-V mild hybrid systems offer a significant fuel saving potential in city bus application with a good cost-benefit ratio. MAN has therefore developed a crankshaft starter-alternator for the Lion’s City bus. This electric machine converts mechanical energy into electrical energy during braking and supports the combustion engine when starting off.
MOTIVATION
The reduction of greenhouse gas emissions is a major challenge for the automotive industry. Hybrid drivetrains contribute to reducing fuel consumption. In
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[1] it is described that 48-V mild hybrid systems in different topologies offer a very good cost-benefit ratio compared to high-voltage full hybrid systems. Also, for MAN this showed to be an effective measure in city bus application to fur-
Markus Lampalzer, M. Sc. is Team Leader Design Engine Mechatronics in the Division Engineering Powertrain at MAN Truck & Bus SE in Nuremberg (Germany).
Dipl.-Ing. (FH) Michael Lechner is Team Leader Testing Inverter & E-Machine in the Division Engineering Electric/Electronic Systems at MAN Truck & Bus SE in Munich (Germany).
ther improve fuel consumption of conventional powertrains based on diesel and gas engines. Due to the driving cycles with frequent braking, standstill and acceleration situations, city buses offer great potential for the recovery of braking energy, switching off in standstill situations and assisting during acceleration processes. For this purpose, a P1 mild hybrid (P1: parallel hybrid drive in which the electric motor is permanently connected to the crankshaft of the combustion engine), which is quickly amortized for the customer in real vehicle use, was developed. DESIGN AND FUNCTION OF THE 48-V MILD HYBRID SYSTEM
MTZ worldwide 12|2020
FIGURE 1 Components of the 48-V mild hybrid system (© MAN)
CRANKSHAFT STARTERALTERNATOR AND INVERTER
The CSA is passively cooled in the powertrain between the engine flywheel housing and the gearbox, and designed as a three-phase SRM. Due to the frequent number of cranking cycles, a wear-free concept was selected. In a comparison of different machine types for this application on a commercial vehicle engine, the SRM has been found to be particularly advantageous. The main reasons are the simple and robust
design as a disc-shaped electric motor without parts affected by mechanical wear, FIGURE 3. The rotor consists of a toothed laminated core made of soft iron only, which is mounted to the engine flywheel. Due to the open installation at the flywheel, temperatures and vibrations, the machine is designed without permanent magnets. This reduces the costs, and simplifies the assembly in the plants and the service in the workshops. The stator is designed with inserted single tooth coils. The pulsating torque of the SRM is smoothed by the 30/20 tooth
50 Speed [km/h]
In addition to the conventional design of the powertrain, additional components are required for the selected system, FIGURE 1. The electric machine is installed between the combu
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