EV Braking Systems in the Age of Electrification
Electric vehicles (EVs) are experiencing exponential growth, with over 4 million units sold globally in 2021. As battery capacities rise and driving ranges extend, automakers must holistically reassess vehicle systems designed for internal combustion engines and reengineer them for unique electric drivetrain demands. This transition shines a spotlight on brake system repurposing needs for contemporary EVs. Engineers must deliver safety and control expectations drivers and regulatory agencies rely on, balanced with efficiency gains harvesting vehicle motion to maximize EV range through regenerative braking integration. Examining the customer usage duties alongside functional system requirements illuminates focus areas for technologists to serve and advance zero-emissions mobility.
As electric motors replace engines, their innate torque decreases. Per Han Woong Hwang of Hyundai Mobis, “combustion engines provide 120-280 kW of power to assist vehicle stopping.” Without that supplemental braking torque transferring through the drivetrain, brake systems bear higher friction load duties. Today’s electric brake architects must rethink system specifications and componentry targeting heightened heat and wear capacities.
Additionally, electrification shifts the consumer driving experience. Studies indicate EV operators brake harder and more frequently than internal combustion engine (ICE) drivers due to vehicles’ near silent stirrings and instant torque. These behavioral shifts further press braking endurance limits. Combined stop energy loads directed solely to the friction brake system escalate component heat generation. Mitigating these thermal spikes has become a primary design challenge.
Further complicating matters, contemporary braking systems must orchestrate these friction elements seamlessly with regenerative braking. As James Holland, director of ErgonomX explains, “blending friction and regenerative braking enables recovering vehicle motion for efficiency while still achieving full vehicle control.” But amalgamating two deceleration systems with unique transient behaviors requires brake-blending algorithms of mounting intricacy.
As electrification trends flourish, solving these quandaries has become imperative to the function, efficiency, and durability of electric vehicle platforms globally. Examining the capabilities and limitations of leading friction brake architectures spotlights developmental pathways for tomorrow’s EVs.
In combustion vehicles, friction brakes historically include disc or drum varieties. As Paul Mitts, senior braking technologist with Consumer Reports explains, “Disc systems press brake pads against a rotor surface connected to the wheel. Drum systems wedge curved brake shoes outward into the inner wheel drum.”
Disc architectures deliver strengths like cooling capacity, self-drying wet surfaces, packaging space savings, and serviceability benefits that have made them the preferred option for over 97% of contemporary EV platforms. However, Mitts notes, “drum systems can still bring value through component cost savings and parking brake integration.”
As engineers reassess system specifications for electrified vehicles, most industry experts expect the reign of disc brakes to continue. But niche drum brake applications may still answer needs for specific regional markets or use cases.
Actuating any friction braking system relies on clamping loads between pads and rotors generated by hydraulic pressure in the brake fluid. Users step the brake pedal which pushes a plunger in the master cylinder, building hydraulic pressure. The pressurized fluid transfers through brake lines ultimately pressing caliper pistons and brake pads against the rotor.
Unlike pneumatic systems relying on engine vacuum or electric pumps, hydraulic architectures enable rapid pressure increases purely through human leg force for consistent pedal feels. As Sugimoto with Akebono states, “Drivers expect the same deceleration each time they hit the middle pedal.” Achieving those normalized sensations in varying situations requires refined pressure modulation only hydraulics provide.
Additionally, hydraulic circuitry reacts quickly to maintain clamping loads as pads erode and rotors warp through repetitive heating cycles. Holland says, “near instant pressure compensation ensures expected deceleration rates even as components wear.” Finally, separating fluid lines from bulky air compressors or motor-pump hardware unburdens packaging restraints. Given these virtues, hydraulic boosting satisfies EV braking demands from today’s most demanding drivers.
But hydraulic pressure only translates clamp loads to stop an EV effectively with capable friction materials attenuating motion. As Brakes India Chief Engineer Jeya Vikram explains, “friction material formulas blend chemical compositions with physical geometries targeting ideal wear, noise, and environmental performance.” However, elevated magnetism inside EV systems brings new considerations.
EV motors and batteries generate robust magnetic fields which can disturb friction pad compositions. Some formulas use metallic particles and fibers for durable heat resistance and noise dissipation. But their ferrous makeup risks magnetic “pickup” where pads attract to iron rotors without driver input. Alternatively, high copper content tunes wear smoothness but suffers worsening fade at high temperatures.
Material engineers continually tweak friction makeups with intricate metallurgy and binder varnishes to strike the best thermal, magnetic, and wear balance. Companies like TMD Friction and Util group now offer low-metallic and non-asbestos options specifically targeting EVs. As Vikram summarizes, “the ideal formula targets electric vehicle needs with just the right magnetic permeability.”
Integrating regenerative braking hardware introduces another layer of complexity for EV braking orchestration. Holland explains, “software modules monitor traction motor speeds, torque limits, battery state of charge and more to govern regen involvement.” Instantaneous optimization funnels only ideal amounts of regen current avoiding battery overcharge or driveline slip.
At the pedal, faithful brake blending seamlessly sums motor regen with hydraulic clamping into one stopper scoop. Yuto Suga, a senior Toyota engineer touts their blending algorithm: “our controller reacts within milliseconds using a custom map to replicate expected friction brake feel.” Such quick reactions prevent awkward transitions between motor and friction braking for imperceptible one-pedal driving.
Looking forward, machine learning and artificial intelligence hold the promise to unburden software complexities analyzing real-time vehicle sensors to refine blending. As sensors improve and computing power increases, smart brake controls grow ever brighter.
As global electric vehicle adoption accelerates, improving braking system efficiency and longevity remains imperative to advancement. Holland summarizes the path ahead, “braking technology must keep pace supporting larger battery packs and lengthening ranges.” Further friction material developments seek optimum magnetic and thermal behaviors for EV duty cycles. At the software level, smart regenerative blending strives for one-pedal driving imperceptibility. And holistic designs continue trimming component bulk while extending service lifecycles.
There’s little doubt electrification trends will continue redefining mobility for the foreseeable future. And while electric motors grab headlines, the stopping systems tuning kinetic motions into currents may play an unseen starring role enabling our zero-emission transportation future.