BMW 3 Owners & Service Manuals

BMW 3: Emergency braking function

Regenerative braking with help of the drivetrain only effects the rear axle. The brake force on the rear axle must not exceed a specific value in proportion to that on the front axle. This would otherwise compromise driving stability. This is also why there is a limit to the maximum deceleration that can be achieved through brake energy regeneration (maximum 0.07 g).

The maximum permissible brake force by brake energy recovery is subject to stability monitoring of slip, lateral accelerations and stability control processes. In this way it is guaranteed that the vehicle constantly remains in a stable driving condition also during brake energy regeneration.

If the DSC control unit identifies an unstable driving condition, regenerative braking is cancelled and the DSC control unit intervenes with stabilizing measures.

When the driver operates the brake pedal, a direct mechanical connection is established to the brake booster and thus to the hydraulic brake system. Activation is therefore the same as in a conventional vehicle.

Distribution of hydraulically and regenerative brake force

The following diagram summarizes how the entire brake force is distributed into the hydraulic and regenerative shares. In the diagram it is presupposed that there is no unstable driving condition and the high-voltage battery unit is able to use electrical energy.

Regenerative braking
G20 PHEV, diagram for distributing the brake force

  1. Brake force at the wheels
  2. Brake pedal travel
  3. Accelerator pedal angle
  1. Total brake force
  2. Hydraulically generated brake force of the front axle
  3. Hydraulically generated brake force of the rear axle
  4. Regenerative generated brake force
  5. Free travel at the brake pedal
  6. Artificial extension of the brake pedal free travel by the DSC function

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