Connecting the Future of HEV/EV Powertrains

Takuya Fujimoto, Director, Automotive Segment at Hirose Electric


HEV/EV vehicle manufacturers still face many challenges to increase public acceptance worldwide.

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Figure 1. The floating contact system like the one found in Hirose’s FX26 Series board-to-board connector increases reliability by reducing the stress on solder joints caused by misaligned connectors. The floating design also enhances durability by preventing solder cracking.

The popularity of  hybrid vehicles (HEV) and electric vehicles (EV) continues to rapidly grow. This can be attributed to consumer demand for eco-friendly vehicles combined with increased confidence in the technology. Almost every automotive manufacturer has HEV and/or EV vehicles in future manufacturing plans. HEV and EV technology has made significant performance advancements in recent years, and offer many advantages over traditional internal combustion engines. However, HEV/EV vehicle manufacturers still face many challenges to increase public acceptance worldwide.

The most recent EV powertrain developments are aimed toincrease the length (time and mileage) a vehicle can travel, reduce charging time, and enhance power quality – all while reducing costs. More specifically, powertrain applications need high-power connectors in a smaller footprint, all while meeting the requirements of heat and vibration resistance. Advancements to rugged board-to-board connectors can help increase performance, while reducing design and assembly costs. High voltage connectors that feature a floating contact system not only simplify assembly, but also offer enhanced vibration resistance in HEV and EV powertrain applications.


Because they use less gasoline (HEV) or no gasoline (EV), these vehicles are much quieter, cleaner during operation, less costly to refuel, and typically require less maintenance due to fewer moving parts and subsequent wear and tear.Future projections for this market are bullish, with Markets and Markets forecasting upwards of 26 million electric vehicles on the road by 2030, up from some 3 million in 2019. Additional factors for increased HEV and EV sales include favorable government policies and support in terms of subsidies and grants, tax rebates and other non-financial benefits. Better charging infrastructure and proactive participation by automotive OEMs is also starting to drive the global electric vehicle sales. In addition, the increasing EV driving range enables consumers to make the green choice more often.

Powertrain Basics

The powertrain of an EV is a simpler and more efficient system compared to internal combustion engines (ICE). EVs can run solely on electric propulsion or they can have an internal combustion engine (ICE) working alongside it. Having only batteries as energy source constitutes the basic kind of EV, but there are kinds that can employ other energy source modes. These can be called hybrid EVs (HEVs).  An EV system has fewer parts by up to 60%, and even fewer moving parts. At its core, a standard EV system contains a charger, battery pack, converter, controller and motor.

·  The charger converts AC power received through the charge port to DC and controls the amount of current flowing into the battery pack

·  The battery pack  is made up of multiple Lithium-ion cells and stores the energy needed to run the vehicle. Battery packs provide direct current (DC) output.

·  The DC-AC converter transfers DC power from the battery pack to AC in order to power the electric motor

·  The electric vehicle controller is the electronics package that operates between the batteries and the motor to control the electric vehicle's speed and acceleration much like a carburetor does in a gasoline-powered vehicle

·  The electric motor converts electrical energy to mechanical energy to move the vehicle via a simple single speed transmission to reduce wheel speed and multiply torque.

Powertrain Connector Requirements

In all automotive applications, connectors must offerhigh reliability performance in terms of resistance to heat, shock, vibration and other environmental conditions.In addition, powertrain systems require rugged and reliable interconnect solutions that can handle higher currents. For example, an EV motor can run anywhere from 96 to 192 Volts DC. A three-phase AC motor is most likely operating at 240 V with a 300 V battery pack.

Powertrain Connector Trend: A Shift to Floating Board-to-Board

Previously, wire-to-board connectors were commonly used in HEV and EV drivetrain applications. This includes connectivity for motor controllers, inverters and more. However, wire-to-board connectors take up more real estate and can often be more taxing during the integration and assembly process. New board-to-board connectors that feature a floating contact system simplify assembly and reduce labor costs, all while offering space savings.

These versatile board-to-board connectors combine high voltage ratings up to 125V AC/DC in a small footprint with a 1mm pitch.  Offering high temperature resistance up to 140 degree C, new connector designs with a floating contact design provides superior vibration resistance for more reliable operation.

Floating contacts can compensate for alignment errors up to ± 0.7mm in both the X- and Y-axis direction, as well as ± 0.75mm tolerance between the boards the Z direction. This floating feature prevents misalignment during board installation and mounting. Because the spring portion of the terminal absorbs assembly errors, it reduces the need  for corrective re-work operations. The floating contact system is ideal for HEV and EV drivetrain systems that require multiple connectors to be used on the same board.

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Figure 2. An example of the FX26 Series used in a drivetrain motor controller


The development of HEV and EV is central to most car manufacturers’ future strategies. To meet the demand in this growth market, connector manufacturers continue to develop innovative interconnect solutions for HEV and EV powertrains. These connectors offer reliable and durable operation in small and light packages with increased functionality. Serving as a cost-effective alternative to wire-to-board connectors, innovative board-to-board connectors with a floating contact design simplify assembly and offer space savings in cramped powertrain applications. Floating contact designs improve reliability and durability for long life performance in HEV and EV powertrains – all while reducing labor costs.

Hirose Electric