VS - Electrical Systems From Stop-Start to Hybridization

Engine working conditions The aim of Stop-Start systems is to consume less in order to pollute less, nevertheless this could be detrimental to engines combustion quality and pollution levels if the engine has not reached some appropriate working conditions. The graph below illustrates one real case of engine stopping authorisation and prohibition conditions according to the engine coolant temperature and the intake air temperature.

Battery State Of Health (SoH)

The State of Charge level depends on the whole charging chain and particularly on the battery health. The S tate o f H ealth (SoH) is related to the aging of the battery; it has to be defined against a given parameter, Eg. The battery internal resistance, but the choice of parameter depends on the application. It can be assessed in several manners: looking at the maximum SoC reached after consecutive full charge cycles; counting the number of charge/ discharge cycles and their depth and comparing it to manufacturer data, or measuring another parameter that is well correlated with SoH and assessed during validation phases. Whatever the considered State Of Health parameter, it highly varies with manufacturer and battery model. State of Function (SoF) The State of Function is the ability of a battery to perform a function. The SoF can be defined by analysing several parameters, the basic ones being the SoC and SoH of the battery. Considering the start of the engine, the State of Function is an indication to the start-stop system of whether the battery will be able to crank the vehicle after the next shutdown. Based on the analysis, the system will decide whether it has to enable or disable the mode. One good way of processing the “cranking State of Function” is to analyze the most recent engine cranks events (voltage and current when the starter is engaged), the remaining battery charge (as a function of SoC and SoH), and the battery temperature. During cranking, the value of the internal resistance of the battery (Ri) can be calculated and recorded from voltage and current sampling. The internal resistance is quite constant over battery lifetime and can vary notably before battery failure occurs, so its average value needs to be below a defined level to assure a safe cranking. Engine too hot for Stop-Start mode Water circulation required, engine stop forbidden! Intake air temperature (°C) Engine too hot f r Stop-Start mode Water circulation required, engine stop forbidden! Engine too co d fo Stop-Star mode Engine stop forbidden, warm-up ongoing!

Engine coolant temperature (°C)

Gasoline

120

Diesel

Engine hot

100

Gasoline

Engine coolant temperature (°C)

Diesel

60

Engine normal

Gasoline

120

20 10 100 60

Diesel

Engine hot

Engine too hot for Stop-Start mode Water circulation required, engine stop forbidden! Engine too hot for Stop-Start mode Water circulation required, engine stop forbidden! Engine too cold for Stop-Start mode Engine stop forbidden, warm-up ongoing!

Gasoline

Engine cold

Diesel

-5

0 20 10

Engine normal

erature

Engine cold

Intake air temperature (°C)

-5

0

hot

Engine too hot for Stop-Start mode Water circulation required, engine stop forbidden! Engine too hot for Stop-Start mode Water circulation required, engine stop forbidden! Engine too cold for Stop-Start mode Engine stop forbidden, warm-up ongoing!

Gasoline

Diesel

Intake air temperature (°C)

68