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<p>Modern heavy trucks tend to get more and more equipment demanding electric power. As a result, the electric power left for startingbecome more and more limited. If a complete view of the entire starting system-battery, starter and the combustion engine - is used, the total system can be investigated and optimized. This thesis is a study of the starting system and its components. Theories for each component are presented and models are derived for a complete starting system. Focus lies on the battery and starter motor. The purpose of the modelling work is to gain knowledge of the starting system. Some results can also be obtained from the simulations - it is very important to keep the electrical resistance as low as possible and the differences between battery types are surprisingly big.</p>

Modern heavy trucks tend to get more and more equipment demanding electric power. As a result, the electric power left for startingbecome more and more limited. If a complete view of the entire starting system-battery, starter and the combustion engine - is used, the total system can be investigated and optimized. This thesis is a study of the starting system and its components. Theories for each component are presented and models are derived for a complete starting system. Focus lies on the battery and starter motor. The purpose of the modelling work is to gain knowledge of the starting system. Some results can also be obtained from the simulations - it is very important to keep the electrical resistance as low as possible and the differences between battery types are surprisingly big.

In commercial vehicles, where the driver overnights with the engine turned off whilestill consuming electricity, it is important to know how much the battery can bedischarged before reliable engine starting is at risk. The vehicle’s ability to crank theengine, i.e. startability, changes with the vehicle’s ambient temperature and thebatteries state of charge. The aim of this project is therefore to test the startability ofa commercial vehicle and its cranking system’s behaviour at different ambienttemperatures and battery state of charge. Physical startability tests were planned andperformed on a commercial vehicle at different temperatures inside a climatechamber. The results of these tests show the torque of the vehicle’s powertrainincreasing with lowering temperature while the cranking system’s performancedecreases. This decrease in the cranking system’s performance is a result of thebattery’s lowering ability to supply power at lower temperatures. / I tunga fordon, där chauffören spenderar natten med avstängd motor men fortsätteratt förbruka el, är det viktigt att veta hur mycket batterierna kan urladdas innanmotorn inte kan startas. Fordonets förmåga att starta motorn, det vill säga dessstartbarhet, ändras med omgivningstemperaturen och batteriernas laddnivå. Syftetmed projektet var därför att undersöka startbarheten på ett tungt fordon samt dessstartsystems beteende vid olika omgivningstemperaturer och laddningsnivåer påbatterierna. Under projektets gång planerades samt genomfördes provstarter meddet tunga fordonet vid olika omgivningstemperaturer i en klimatkammare.Provstarterna påvisade att släpmomentet på fordonets drivlina ökade med enfallande temperatur medan startsystemets prestanda försämrades. Startsystemetsförsämrade prestanda beror huvudsakligen på batteriernas försämrade förmåga attavge effekt vid lägre temperaturer.