How the blend is actually computed
The VCU converts one deceleration request into two torque targets, updated many times a second.
- Explain how the blend is actually computed at engineering level
- Read the numbers that define the behaviour
- Apply the idea to a real braking system
Overview
At the heart of blended braking is a control loop that takes the driver's requested deceleration, subtracts whatever regen torque is currently available, and sends the remainder to the friction brakes as a pressure target — all recomputed every few milliseconds as conditions change.
In depth
The friction brake target is always the shortfall left after regen has taken as much of the request as the battery, motor and stability system allow.
- 1Read the pedal
Two redundant sensors report travel and force; the VCU converts this to a total deceleration request.
- 2Query regen availability
Battery SOC/temperature limits and motor torque limits set the maximum regen torque available right now.
- 3Check stability limits
ABS/ESP can trim or veto regen torque instantly if a driven wheel is near slip.
- 4Command friction shortfall
The e-booster is told to make up exactly the difference, continuously, as regen availability changes mid-stop.
Why the blend must be seamless
If the handover between regen and friction torque were not perfectly torque-continuous, the driver would feel a lurch or a dip in deceleration mid-stop — a classic and easily detected calibration defect. Production programmes spend enormous effort tuning this transition so that total deceleration output never wavers even as the underlying split changes dramatically.
Regenerative Energy Calculator
Kinetic energy available in a stop and how much reaches the battery.
E = ½ m v² × η_chainA moving vehicle stores kinetic energy proportional to the square of its speed. Regeneration recovers what the driveline, inverter and cells do not lose as heat — typically 60–70% of it.
Example: A 2,000 kg car at 100 km/h holds 772 kJ; at 65% recovery that is 0.14 kWh back in the pack.
- Doubling speed quadruples recoverable energy.
- Regeneration is capped by pack state of charge, cell temperature and motor limits.
- Descending a long grade recovers far more energy than city stop-start.
Blending logic check
- 1
What determines the friction brake torque target in a blended system?
Key takeaways
- Friction torque is computed as the shortfall after regen torque is subtracted from the total request.
- The blend recalculates continuously as SOC, temperature and stability limits change mid-stop.
- A torque-continuous handover is essential so the driver never feels the transition.
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