Brakes and Traction Control: Description and Operation

Brake System

The brake system has the following components:

- Brake master cylinder and fluid reservoir
- Cable actuated parking brake system
- Clevis pin
- Electric vacuum pump (hybrid vehicles)
- Fixed position brake pedal (non-hybrid vehicles)
- Fixed brake pedal with integrated brake-by-wire system (hybrid vehicles)
- Four-wheel ABS
- Front disc brake system
- Rear drum brake system
- Vacuum-assisted power brake booster (non-hybrid vehicles)
- Vacuum-assisted active booster (hybrid vehicles)

Conventional Brake System (non-hybrid vehicles)

The brake pedal is connected to the vacuum power brake booster, which is connected to the brake master cylinder. When the brake pedal is applied, brake fluid is pushed through the double-walled steel tubes and flexible hoses to the front disc brake calipers and rear drum brake wheel cylinders. The brake fluid enters the disc brake calipers and drum brake wheel cylinders, forcing the caliper and cylinder pistons, brake pads and brake shoes outward against the brake disc and drum friction surfaces, slowing or stopping wheel rotation. When the brake pedal is released, brake fluid pressure is relieved, returning the front disc brake and the rear drum brake systems to the unapplied position. The parking brake system uses the rear drum brakes and is self adjusting.

Regenerative Braking System (hybrid vehicles)

The regenerative brake system utilizes the electric motor portion of the hybrid electric power train as a generator to create electrical current. This recharges the High Voltage Traction Battery (HVTB) and delivers brake torque to be used in combination with the vehicle's conventional friction brakes to slow the vehicle. The amount of brake torque provided by the electric motor is dependent upon the state of charge of the HVTB. When the HVTB is almost fully charged, the amount of regenerative braking is limited to avoid overcharging, and the requested deceleration is produced by conventional friction braking alone.

For information on the following components:

- Rear drum brakes, refer to Drum Brake Description and Operation
- Front disc brakes, refer to Front Disc Brake Description and Operation
- Parking brake actuation, refer to Parking Brake and Actuation Description and Operation
- Hydraulic brake actuation, refer to Hydraulic Brake Actuation Description and Operation
- Vacuum-assisted power brake booster, refer to Power Brake Actuation Description and Operation
- ABS, refer to Vehicle Dynamic Systems Description and Operation
- Vacuum-assisted active brake booster, refer to Vehicle Dynamic Systems Description and Operation
- Electric vacuum pump, refer to Vehicle Dynamic Systems Description and Operation