The Automation Core

Electromechanical Brakes (EMB) Explained: How Brake-by-Wire Stops an EV Without Brake Fluid

· 48V architecture, brake-by-wire, Chery EXEED EX7, clamp force sensor, dry brake-by-wire, electromechanical brake, EMB, GB 21670-2025, Orient Motion, Sensata brake force sensor, WBTL,

 


Bottom line: In our regen-versus-calipers video we showed that most everyday EV deceleration comes from the motor, and the friction brakes only handle the last part. Now that last part is going electric too. Electromechanical braking (EMB) removes the hydraulic system entirely and lets a motor at each wheel clamp the disc, and it reached series production in China this year. Four engineering questions follow: where the speed comes from, how you control clamping without hydraulic pressure, where the power comes from, and how you guarantee a stop with no hydraulic fallback. Most performance figures are manufacturer claims; distance and current figures are my own illustrative arithmetic.

What happened

  • Oct 8, BASF × Chery × Orient Motion: the partners announced they would show the production EMB from the EXEED EX7 at FAKUMA 2026 (Oct 12–16, Friedrichshafen). PA and PBT engineering plastics are used in the pedal, the motor gear unit (MGU) and the domain control unit (DCU); the all-plastic pedal is said to be about 25% lighter, based on partner data.
  • Oct 14, Sensata: its caliper-integrated sensor that measures clamping force directly is now enabling EMB systems in production EVs (models not named).
  • Sep 29, WBTL (Bethel): four EMB production programs, more than 50,000 EMB units delivered by the end of June 2026, a response-time target of 100 ms or less, and TÜV NORD ASIL D certification. Brembo’s fluid-free Sensify platform also entered series production in May.
  • Regulation: China’s mandatory passenger-car braking standard GB 21670-2025 took effect on Jan 1, 2026 and covers electrical transmission braking systems (ETBS), giving EMB a legal path to type approval.

Three brake architectures: Conventional hydraulic runs pedal, vacuum booster, master cylinder, lines, wheel cylinders. EHB (today’s mainstream one-box units) replaces the vacuum booster with an electric one but keeps the fluid and lines. Full-dry EMB has no brake fluid at all: each wheel carries a motor and a reduction mechanism that presses the pads onto the disc. In between sits “semi-dry”: EMB at the rear, hydraulics retained at the front.

Engineering point 1: what is 60 ms actually worth?

Industry figures compiled by GGAI put conventional hydraulic braking at 200–300 ms, EHB at about 150 ms and EMB at 80–100 ms; Chery claims 90 ms and a 100-to-0 km/h stop in the 33 m class for the EX7. Run the numbers: at 100 km/h the car covers 27.8 m every second, so cutting the delay from 150 ms to 90 ms saves roughly 1.7 m of travel before braking even starts. That is the same order as Chery’s claimed 1.5 m shorter stopping distance (my arithmetic). Allegro’s EMB white paper adds a warning: vendors draw the measurement boundaries differently, so these figures are not directly comparable, and real automatic-emergency-braking latency also includes sensing, decision and communication time.

Engineering point 2: no hydraulic pressure, so how hard is it clamping?

Hydraulic brakes are controlled by measuring pressure. With no fluid, EMB has to control clamping force. Sensata puts a micro strain gauge in the caliper to measure force directly and stream it to the controller at high rate, turning each wheel into its own closed loop. The hardest case is the gentle one: the controller has to find the exact point where the pad first touches the disc, or light braking feels jerky. The motor can also actively retract the pads when you are not braking, cutting drag; Chery claims about a 2.5% range gain, including regen optimization (manufacturer figure). This ties straight back to regenerative braking: friction force can be trimmed precisely at each wheel, which smooths the hand-off between regen and the calipers. WBTL lists regen coordination as a design goal.

Engineering point 3: where does the power come from, 12 V or 48 V?

A 2025 SAE paper sizes an EMB concept for a 2.8-tonne SUV at a 0.7 g target deceleration: about 11 kN of front-axle braking force, with a specification of 48 V supply, at most 1.5 kW electrical per corner, and a dual-motor layout for redundancy. At 48 V, 1.5 kW is about 31 A; at 12 V it is 125 A. On the same wire, four times the current means sixteen times the I²R loss (my arithmetic). Allegro notes that hard stops shift load forward, so the front axle is the hungriest, which is why several programs start with semi-dry layouts, and why 12 V and 48 V EMB designs will coexist for a while. It is the same open question we raised in our 48 V architecture piece: once the auxiliary battery is gone, where does backup brake power come from?

Engineering point 4: no hydraulic backup, so how do you guarantee a stop?

Hydraulic-era designs are fail-safe: if the electronics fail, the fluid path still works when you push the pedal. Full-dry EMB removes that path, so it must be fail-operational: enough braking must survive the fault. Common practice is dual power supplies, dual controllers, dual communication links and dual-winding motors. At vehicle level, the four corners share the load: if one actuator drops out, the other three redistribute braking force while holding the car straight. GB 21670-2025 also requires the parking brake to be locked by a purely mechanical device, and requires emergency braking to stop the car within a reasonable distance if a single part of the service brake fails. Cost is the other hurdle: a system runs about RMB 3,000–4,000, noticeably more than EHB, and wheel-end hardware must survive heat, water, mud and constant vibration. Forecasts diverge widely, from about 15% EMB share by 2030 (the chairman of supplier Tongyu) to over 50% of new cars by 2029 including semi-dry systems (GGAI research). My read: through 2026 and 2027, EMB shows up first on premium models that lean on advanced driver assistance, and mass adoption waits on cost and durability data.

Open questions

  • The 90 ms, 33 m and +2.5% range figures are Chery’s own; the CATARC tests BASF cites have no published numbers.
  • Response-time measurement boundaries differ by vendor, so cross-comparisons are shaky, and Sensata has not named the production models.
  • No public data yet on long-term wheel-end durability (heat, wading, salt spray) or how EMB will be serviced.
  • How regulators outside China will approve full-dry EMB is still evolving.
  • The 1.7 m and 31 A / 125 A figures are illustrative arithmetic, not vendor data.

Related videos

Quick poll: if EMB were a paid option on your next car, would you tick the box, or is EHB plus regen already good enough? Tell me why in the comments.

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