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Brakes, ABS


Information

The LEAF has conventional hydraulically operated friction brakes. Additionally, the LEAF's electric motor provides regenerative braking.

The hydraulic brakes is electrically assisted. [1] An internal motor operates a piston in the master cylinder to generate assist force. A brake pedal stroke sensor detects the amount of brake pedal operation and signals the "electrically-driven intelligent brake unit" (IBU). The IBU performs cooperative control of the regenerative brake and friction brake according to brake pedal travel and amount of cooperative regenerative brake control. A pressure sensor in the master cylinder informs the IBU which increases or decreases brake assist so pressure inside the master cylinder equals a "target pressure", derived from amount of brake pedal movement.

Cars with internal combustion engine use the engine intake manifold's vacuum to "power" the brake booster, Since the LEAF does not have an internal combustion engine, an electric pump provides additional hydraulic pressure and acts as the brake booster [2]. In the event of power loss, a large capacitor (called a "brake power supply backup unit") provides stored electricity to power the pump [3].
Here is a pic of the capacitor ("brake power supply backup unit"):
Brake capacitor ingineerix com.jpg
Here is a pic of the Toyota Prius' brake back-up power capacitor assembly:
Prius brake capacitor evseupgrade com.jpg


  Rotor Caliper
Type Diameter Thickness
Front Ventilated 283mm / 11.14" 28mm / 1.102" Two-piston single-action caliper[1]
Rear Ventilated 292mm / 11.5" 16mm / 0.63" Single-piston single-action caliper[1]


  • Diagram of the "electrically-driven intelligent brake unit", from the LEAD Service Manual, colorized:
    Electrically-driven intelligent brake unit.gif


Parking/ Emergency Brake

Operation

  • To apply the parking brake while stationery, step firmly on the brake pedal and pull up on the parking brake switch to engage the parking brake. Pull up twice to apply maximum parking brake force[4].
  • To apply the parking brake while moving, pull up and hold the parking brake switch; when you release the parking brake switch, the parking brake will be released [4].
  • The parking/emergency brake can be applied while driving: pull up and hold the electric parking brake switch (page 5-16 of the 2011 Owner's Manual). A chime will sound. When you release the parking brake switch, the parking brake will be released. While moving, the parking brake is applied at a lower force than when stationery[5].

How The Parking/ Emergency Brake Works


The parking/emergency brake system consists of two drum brakes, one on each rear hub[6]. The rear service brake's rotor resembles a hat (5). The "crown" of the hat serves as the drum brake's (2) housing. The drum brakes' shoes are actuated by cables.Rear hub-brake-parking brake assembly.gif



An "equalizer" (5) rides on a threaded shaft (4) and tensions both brake cables. An electric motor (1), operating from the 12V battery[7] drives the shaft via a reduction gear (2) and a clutch (3). The electric motor operates on signals from the parking brake control module, which receives signals from the parking brake button via the CAN bus. The emergency release (6) turns the reduction gear which turns the shaft which de-tensions the brake cables.
Emergency brake actuator.gif


Here are a couple of pics of the parking brake's cabling: pic 1 pic 2.

Problems/issues




  1. 1.0 1.1 1.2 Nissan LEAF Service Manual, BR-10 - BR-13
  2. Nissan LEAF Service Manual, section BR, page BR-11.
  3. The Nissan LEAF service manual, page BR-11. The brake power is described on page BR-11 under "Brake Power Supply Backup Unit". Its exploded view is on page BR-223.
  4. 4.0 4.1 Nissan LEAF Owner's Manual, page 5-16.
  5. LEAF Service Manual, page PB-20.
  6. The diagrams in the service manual (page PB-87) shows two cables, one going to each side.
  7. Nissan LEAF's Owner's Manual, page 5-16.