Not all electric vehicles (EV) are made equally, some of which are of the hybrid powertrain and fully-electric variety. One of these EV advancements can be attributed to the development of belt starter generators (BSGs) or integrated starter generators (ISGs). That being said, this blog will provide a brief overview of BSGs/ISGs, allowing you to better understand how they have transformed the functionality of electric vehicles.
The combination of ISGs/BSGs with the internal combustion engine has set the foundation for the development of the Mild Hybrid Electric Vehicle (MHEV), creating new opportunities for electronic modules and electric motors. As such, BSGs replaced starter and alternator functional modules, while also augmenting the internal combustion engine’s functionality. This construction consists of two batteries, one traditional 12V battery, and a 48V lithium-ion battery. To begin, the 48V lithium-ion battery provides higher power loads in the same way that an inverter powers the electric motor of a BSG. The 12V battery, on the other hand, remains on the MHEV to power electronic modules and serves as a backup in the case that the 48V systems require alternate low voltage power. Located on the MHEV, the 12V battery also powers the legacy electronic control modules in the vehicle. In most cases, the MHEV provides OEMs with an intermediate step between traditional combustion engine propulsion and fully electric propulsion found in Battery Electric Vehicles (BEVs).
With concerns over CO2 emissions rising, environmental legislation dictates that automotive fleets reduce their CO2 output. By taking existing vehicle types and modifying them, OEMs can provide MHEV variants to fleet offerings. MHEVs significantly reduce CO2 outputs by providing mechanisms that lower the quantity of fuel used by the combustion engine. These mechanisms consist of the BSG’s start-stop functionally, energy recovery when coasting or braking, energy generation when the engine is running, and electric drive. When the vehicle is in energy recovery or generation mode, the BSG operates as a generator that provides reverse power flow back to the 48V battery. As a result, a DCDC module converts 48V to 12V to charge the legacy 12V battery.
MHEVs are only now making headway in the EV realm as many car owners do not notice any perceived differences in performance or functionality from traditional ICE vehicles. Furthermore, MHEVs do not need any form of charging, can be refueled with ease, and reduce driver range anxiety when compared to some BEV variants. That being said, the only time a driver may notice functional differences is when the ICE shuts down under certain driving scenarios. Nonetheless, there are specific conditions one should monitor to determine the usage of the ICE or BSG. These conditions include engine temperature, time between shutoffs, battery voltage levels, state of charge, electrical loads, minimum speed, and more.
With regard to the placement of the BSG, P0-P4 are the currently designated positions, each of which provide varying levels of capability and design challenges for the entire system. These designations are the topologies for MHEVs wherein P0 represents simplistic, low cost, and reduced emission BSGs, and P4 represents complex, high cost, and increased emission BSGs. Drivers typically notice subtle differences between each position. For example, if their vehicle has a BSG unit in P2-P4, the ICE may not immediately restart due to the electric drive attempting to move the vehicle from a full stop. For this reason, among others, engineers are continually making advancements in the field of MHEVs. In fact, by 2026, MHEVs are predicted to make up ? of all EVs produced.
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