Efficient management of the energy resources in the vehicle requires a careful selection of the charging & starting system's electrical components namely alternator, battery and starter motor.
While deciding the system specifications, especially in the low cost / small car segment, the electrical engineer is confronted with conflicting requirements due to increasing electrical energy needs, demand for reduced alternator load on the engine, packaging size constraints, extreme operating temperatures, worsening urban traffic situations, the heavy wattages of electric radiator cooling fans especially in diesel engines, anticipation of user adding accessories in the field & last but not least is the cost of the components.
It is therefore prudent to avoid
Under designing of the system which leads to battery drainage, poor battery life, re-startability issues and
Over-designing which leads to weight, cost and mileage penalties. These make the charging system design more complex and challenging for system designers.
This paper describes the details of the simulation technique & validation methodology for the charging system design. The simulation is done by a computer program in which the input parameters like selection of city drive cycle (country/ weather specific), pulley ratio, gear ratios, tire size, alternator characteristic, load factors of intermittent loads in the vehicle can be varied & battery state of charge (SOC) can be monitored. This can be done iteratively for optimization of the charging system. Thereafter, validation should be carried out on
chassis dynamometer and/or
Actual field trials.
Once the measurements are available then the Δ(delta) factor can be established between simulation & validation results. This co-relation in turn helps in more accurate prediction & reduces the validation time considerably for future vehicle programs.
The methodology was evolved during a case study on TATA MOTORS hatchback car with 1.4 L diesel engine. The results have been successfully implemented in the new models under development.
Anand S. Sikchi, Randeep S. Khokar, U. Niranjan, G. S. Raju
TATA Motors Limited
SAE World Congress & Exhibition
Systems Engineering, 2007-SP-2130, SAE 2007 Transactions Journal of Passenger Cars: Electronic and Electrical Systems-V116-7, Automotive Systems Engineering - Approach and Verification-PT-145/4