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Micro and Mild Hybrid Systems is a bracket term, which covers functions like Engine Stop/Start (ESS), Intelligent Alternator Control (IAC), and many others, which collectively aim at optimizing the fuel consumption by preventing the wasteful running of the engine. Engine Stop/Start system is the prominent part of the Micro/Mild hybrid systems and is the most significant contributor while reducing the fuel consumption and greenhouse gas emissions. In the previous work of the Authors, various issues related to ESS were discussed in detail. ESS is not so popular among the customers, due to the complexities of the system operation and poor integration of the system design with the customer behavior. In addition, due to various functional safety conditions, and the traffic conditions, the actual benefits of ESS are negatively impacted. Therefore, it becomes necessary to have a different approach to the design of the systems like ESS.

Micro Hybrid Systems are essentially first step towards the electrification of the powertrains. They are aimed at improving the fuel efficiency of the conventional gasoline and diesel power trains with conventional 12 V electrical system, and thus reduce the CO2 emissions as well. Various technologies like Engine Stop-Start, Intelligent Alternator Control, and Electrical Energy Management Systems are included in the bracket of micro hybrid systems. These system functions demand a totally different approach for managing the SLI battery, which is a total departure from the conventional approach. Particularly, the Alternator Shutdown function of Intelligent Alternator Control maintains a calibrated average level of State of Charge, which is typically around 80%, to ensure that the battery can accept more current, during the energy recuperation, which indirectly improves fuel economy.

Micro hybrid Systems are emerging as a promising solution to reduce the fuel consumption and greenhouse gas emissions in emerging markets, where the strict emission requirements are being enforced gradually. Micro hybrid Systems reduce the fuel consumption and greenhouse gas emissions in a conventional vehicle with 12 V electrical system, by optimizing the electrical energy generation, storage, and distribution, with functions like Intelligent Alternator Control, Engine Stop/Start, and Load Management. With the advent of Connected Car Systems, information about the vehicle is seamlessly provided to the customer not just through the Human Machine Interface systems within the vehicle, but to other mobile devices used by the customers.

Engine Stop/Start System (ESS) is a prominent subsystem in the Micro Hybrid Systems, and helps to reduce greenhouse gas emissions and fuel consumption. Fundamentally, ESS detects the idle running of the engine, and shuts it down autonomously, and allows the driver to restart the engine, with a routine action like pressing or releasing the clutch or brake pedal. When an engineer designs a system like ESS, typical approach to trigger the system functions is by establishing a sequence of events, detecting it, and enabling the triggers. Influence of the functions on other vehicle systems or vice versa is also considered, and system design is revised to achieve the functional safety. This results in a set of hard rules to be followed for the system functions to work.

Engine starting torque requirement at extreme cold and hot conditions is not possible to evaluate by transient dynamometer. Due to this, starting system design may not meet the engine starting requirements under all operating environments. Starter motor can be used to overcome this problem. This paper deals with how to evaluate engine starting torque at all temperatures through starter motor. Conventionally, engine cold startability and hot startability are evaluated by using a starter motor of bigger rating. A new methodology found to circumvent this issue and it is, by evaluating the strain experienced by the pinion and drive mechanism, engine starting torque demand can be evaluated at any temperature. By this process, starting system design can be made to suit the correct requirements of the engine starting.