Starter Motor Protection
Starter motors are sensitive for overheating. By estimating the
temperature and preventing cranking in time, there is an option to
avoid the dangerous temper- atures. The truck manufacturer Scania CV
AB proposed a master thesis that should evaluate the need of an
overheating protection for the starter motor. The aim is to evaluate
any positive effects of implementing an algorithm that can
estimate the brush temperature instead of using the available time
constrain, which allows 35 seconds of cranking with a following 2
seconds delay, allowing the crank shaft to stop before a new start
attempt is allowed. To achieve high load on the starter motor and high
temperature in the brushes, tests were performed under -20 degrees
Celsius. Initial testing on truck, under normal temperatures, showed
that the batteries could not run the starter motor long enough to
reach high temperatures in the brushes. This is believed to be caused
by the voltage drop between the batteries and the starter motor,
causing the starter motor to run in an operating area it is not
optimized for. There are several other problems which gives a higher
load on the engine, for example oil viscosity, resulting in higher
currents, but those are not mentioned in this report. Three
different models are compared, Two State Model, Single State Model
and a Time Constrained Model. Tests and verifications show that
the Two State Model is superior when it comes to protecting the
starter motor from overheating and at the same time maximizing the
cranking time. The major difference between the Two State Model
and the Single State Model are the cooling characteristics. In the
Single State Model the brush temperature drops quickly to the outside
temperature while in the Two State Model the brush temperature drops
to a second state temperature instead of the outside temperature. With
the currently implemented time constrain it is possible to overheat
the starter motor. The algorithms are optimized under cold conditions,
due to problems in reaching high temperatures under warmer conditions.
Daniel Gerhardsson
2010
Informationsansvarig: webmaster
Senast uppdaterad: 2021-11-10
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