Deirdre Hegarty, Martin Poceiro, and Ayoub Sidhom all at Sensata Technologies
From electric vehicles including passenger cars and commercial vehicle fleets to 2- and 3-wheelers, the electrification trend in transportation is transforming the need for different systems and component technologies to ensure safety while speeding up charging times and vehicle time to market for vehicle OEMs.
Passenger Vehicles- Brake Pedal Sensing Technologies for Electromechanical Brake Systems
The automotive industry’s evolution towards electric vehicles and increased levels of autonomy are demanding higher degrees of safety and performance from every system on the vehicle. As a result, direct safety devices such as the brake system are rapidly changing. Conventional hydraulic braking systems are migrating to Brake-by-Wire to reduce vehicle weight and complexity. The elimination of hydraulic fluid in fully dry braking systems provides additional environmental and maintenance advantages.
As electronics replace legacy hydraulic components in brake-by-wire systems, there is a need for new sensing topologies in the pedal assemblies. This trend, combined with stricter demands for functional safety, is leading vehicle and brake system manufacturers to consider different brake sensing technologies that ensure electromechanical brakes (EMBs) maintain or exceed the performance and safety of legacy systems.
Typical approaches for brake pedal sensing in electro-hydraulic and fully dry, brake-by-wire braking systems include using position sensors, force sensors or a combination of the two.
While position sensors can provide comparable system inputs to today’s fully hydraulic braking systems, the faster response time of force sensors presents an opportunity to react quicker during braking events, shortening braking distance and enhancing safety systems, particularly in emergency situations when it matters most (Figure 1).
Developers of electro-hydraulic and EMB brake systems must decide how to utilize different sensing technologies in their brake designs while ensuring adherence to fail-safe and fail-operational requirements. To meet these requirements, redundancy remains critical, hence braking systems will continue to rely upon two or more sensors within brake pedals.
The case for using two force sensors within EMB brake pedal assemblies is that it facilitates providing a backup control loop with the all the advantages in terms of short response time and detection of mechanical failure. This supports a fully safe operational system, where no system performance degradation is noted, even with a complete failure of the primary control loop.
That being considered, reliance on one sensing topology could potentially leave the system vulnerable to common-mode failures of primary and redundant controls should an external issue occur that influences the technology, for example, an external Electro-magnetic compatibility event (emission of a certain electromagnetic field) or a component level failure. To achieve a fully redundant system that realizes the benefits of each and complies with safety standards such as ISO26262, brake systems could use a combination of both position and force sensing technologies.
Combining the reaction speed and sensitivity to the driver’s braking intent from the force sensor together with the highly accurate position sensing technology which controls brake lights in current systems, maximizes redundancy and enhances the functional safety aspects of the system.
In summary, to meet more demanding safety requirements in next generation cars, like hybrid and electric vehicles (EVs), braking systems must consider the best solutions to ensure system redundancy. With both force and position sensing technologies available, EMB brake pedal control has an opportunity to meet and exceed these standards by combining multiple sensors of either force, position, or both to take a best of both worlds approach.
Commercial Vehicles- Addressing Higher Power Charging Levels and Time to Market
Driven by the need for faster charging, commercial electric vehicle manufacturers are requiring systems that can handle higher charging power levels. As a result, safe and reliable protection and power distribution solutions now need to be able to support Megawatt charging systems for medium and heavy-duty electric trucks up to 850 Volts and 1300 Amps.
Leading vehicle OEMs are utilizing new custom power management solutions that combine components such as contactors, fuses, current sensing, insulation monitoring devices (IMDs), and controller technologies into a compact package. Commercial vehicle manufacturers are opting for suppliers that can design and manufacture all the safety-critical components of the solution in-house as it helps simplify the OEM’s production processes.
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Figure 2: Leading heavy-duty electric vehicle OEMs are utilizing new custom power management solutionsthat combine components like contactors, fuses, and controller technologies into compact packages that provide safe and reliable protection and power distribution while simplifying their production processes
Suppliers are leveraging custom designs and cross-functional engineering expertise to package a variety of components together to solve different system needs and meet specific vehicle requirements (Figure 2).For example, suppliers like Sensata Technologies are developing vertically integrated system solutions and can offer a variety of High Voltage Distribution Units, including the following:
· Charge Units to control and support charging up to megawatt power levels, including potential integration with Electric Vehicle Communication Controller (EVCC)
· Power Distribution Units to distribute battery power over vehicle actuators or auxiliaries
· Battery Disconnect Units to ensure electrical safety of the battery packs
Another component trend that is allowing electric vehicle OEMs, in addition to battery packers, to simplify their production processes and speed up time to market is off-the-shelf functional safety certified Battery Management Systems (BMS). With the growing use of high energy and current density batteries such as Lithium-Ion (Li-Ion) in these applications, Battery Management Systems (BMSs) are more critical than ever for ensuring system safety.
To meet the Automotive Functional Safety Integrity Levels (ASILs) required for vehicles to be considered road safe, electrical systems are expected to comply with the ISO 26262 safety standard. This standard aims to prevent and mitigate risks associated with systematic or hardware failures throughout the development process for automotive electronic systems. Due to the increasing technological maturity and growing market of electric buses and commercial trucks, a certified BMS according to this stringent level of functional safety is now mandatory to get the vehicle approval in many regions around the globe. While the demand for ISO 26262 certified components is on the rise as battery packers and electric commercial vehicle OEMs prioritize functional safety in their platforms, the ISO 26262 certification process is complex, costly and can take years to complete. An off-the-shelf, ASIL C certified BMS can reduce the time-to-market and associated costs.
One typical challenge for functional safety certified solutions, however, is maintaining end-user design flexibility, which can help provide battery packers with more options to configure the BMS and adapt it to a variety of application needs. New Battery Management System designs that feature unique, two-tier software architectures with open APIs help maintain ISO 26262 certification while enabling design flexibility and shorter time-to-market for the end user. This allows customers to develop their own software functions without the need to re-certify the BMS. While such BMSs are proving to save cost and time for battery packers and electric vehicle OEMs, the same benefits will apply to other applications where similar standards are applicable, such as in material handling equipment and Energy Storage Systems (ESS) (Figure 3).
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Figure 3: New Battery Management System designs, like the n3-BMS from Sensata Technologies, that feature unique, two-tier software architectures with open APIs help maintain ISO 26262 certification while enabling design flexibility and shorter time-to-market for battery makers and heavy electric vehicle OEMs
Low Voltage EVs like 2 and 3-wheelers - Battery Management Systems Enable Battery Hot Swapping to Minimize Charging Time
As vehicles like 2 and 3-wheelers move to electric, especially in countries like India where they are extremely popular, concerns around battery charging time can slow the rate of adoption. A solution to this challenge is hot swap functionality and parallel battery pack support to enable the quick exchange of depleted batteries with fully charged batteries. This can apply to other low voltage applications such as automated guided vehicles and robotics as well.
For example, for material handling vehicles, delivery vehicles and drones, when returning to base to pick up a new load, the vehicle’s depleted batteries can be quickly swapped for charged ones, allowing for continuous uptime. For electric motorbikes and three wheelers, instead of needing to recharge for several hours every evening, fully charged batteries can be rapidly installed in the field at battery swap stations, practically eliminating the need to wait and charge on the road and helping alleviate end-user’s concerns around charging time.
Parallel pack support allows the use of two or more battery packs in parallel. This functionality allows OEMs of 2- and 3-wheelers to have smaller battery modules, improving the safety and serviceability of the battery system. For example, if one battery cell fails while in use, the issue is isolated to that one faulty module which is easier to replace than the entire system and additional battery packs can continue to provide power.
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Figure 4: Battery Management Systems, like Sensata’s i-BMS, that can support hot swap functionality, and parallel battery packs, while being convenient and cost-efficient for mass production, are critical to enabling the adoption of low voltage EV applications like 2 and 3-wheelers.
The key to enabling hot swap functionality and parallel battery pack support in low voltage EV applications is implementing a BMS that is equipped with all hardware features to manage and maintain a battery without additional external components, making it a convenient and cost-efficient design for mass production (Figure 4). The BMS would ideally have all the critical components pre-integrated into the system, including a pre-charge circuit, on-board current measurement, MOSFET power switches for battery disconnect, and a DC/DC power supply.
The electrification megatrend is rapidly transforming the need for different system and component designs to ensure safety while speeding up charging times and vehicle time to market for electric vehicles ranging from passenger cars to commercial vehicles and low voltage applications like motorbikes, scooters and material handling equipment. New sensing and control technologies are enabling the shift to the next generation of EVs that will help enable a cleaner and less fossil-fuel dependent transportation industry across the globe.