In this article, the hybrid drive is discussed of the combination of conventional
tractors with electrified trailers, usually referred to as E-trailer. We
demonstrate that this approach offers the possibility of achieving fuel savings
exceeding 20%. For regional trips, about half of this reduction is achieved
without offline charging, i.e., without applying electric energy from the
E-trailer battery. For motorway dominant trips, more use is required of the
battery energy.
A new control strategy is proposed, validated through simulations, in which only
three control parameters are required, which can be tuned effectively to achieve
maximum fuel reduction under certain trip and loading conditions. This control
strategy adjusts the E-trailer torque request, based on the requested power for
the tractor diesel engine, being estimated through a smart kingpin sensor. It
ensures that the E-trailer supports the tractor propulsion when significant
power is required, and recovers energy when the demand for power is low. The
control parameters consist of the maximum torque request for the E-trailer
during support, the maximum negative torque request during regeneration, and the
transition power between regeneration and support.
Semitrailers are generally not linked to a specific tractor. The control strategy
is unique in that it does not need access to the tractor data network, thus
achieving optimum interchangeability. The sensitivity with respect to driving
resistance parameters appears to be low and may be counteracted by tuning the
control parameters. More care is needed for the assessment of the trailer mass
and trailer center of gravity.
Finally, the total fuel reduction is discussed in comparison to the charging
costs for the E-trailer battery (cost–benefit analysis), for realistic cost
levels for fuel and kWh.
