| Abstract |
The ELFA® (= Electrical Low Floor Axle) hybrid drive system was developed for serial production.
It has been in serial use since summer 1999. The goal was to offer a flexible and modular system to
the city-bus market, allowing bus manufacturers to design individual solutions for their customers.
The system (figure 1) includes one or two drive motors and at least one generator which is connected
to the diesel engine (ICE = Internal Combustion Engine). These electric machines are controlled by
different DC/AC-converters and are connected to a DC-intermediate bus circuit (IBC). Moreover, a
DC/DC-converter is connected to either a lower voltage battery or an ultra-capacitor for the purpose
of energy storage. This DC/DC-inverter adapts the fluctuating battery voltage to the intermediate bus
circuit voltage, which is determined by the drive motors and generator speed. The system may
include a braking resistor with a converter unit, which is needed when the SOC (State of Charge) is
too high for further energy dissipation. The diesel engine may also be used to dissipate energy, but
the power is limited by the accepted noise level.
For an emission-free system, one or two auxiliary motors are needed to run the auxiliary devices, e.g.
steering pump or air pressure pump, which are normally run by the diesel engine. In the hybrid mode,
the diesel engine may be switched off when the SOC of the energy storage is high enough and no
further charge is expected. |
