Brake System Introduction
A vehicle’s brakes cause the vehicle to decelerate or stop by converting the vehicle’s kinetic (motion) energy into heat energy through friction. The heat is dissipated to the atmosphere.
Brakes can be classified into disc brakes and drum brakes. In a disc brake, pads squeeze a disc that rotates together with the wheel, thereby slowing the disc and wheel. In a drum brake, shoes expand onto the inside surface of a drum that rotates together with the wheel, thereby slowing the drum and wheel. Honda vehicles use disc brakes on front wheels, and disc or drum brakes on rear wheels.
Brake discs and drums are made from cast iron. The friction materials applied to them in the form of brake shoes and pads were originally made from asbestos but for health-related reasons are now usually made from sintered alloy substances.
A vehicle’s brake system consists of service brake and parking brake. The service brakes are activated hydraulically by the brake pedal and are used while the vehicle is moving. The parking brake is activated mechanically by a parking brake lever or pedal, and it is used to hold the vehicle in position while stationary.
Brake System Construction
Major component parts of brake system are as follows:
- Brake pedal
- Rear brake caliper
- Rear brake disc
- Parking brake lever
- Front brake disc
- Front brake caliper
- Proportioning valve
- Master cylinder
- Brake booster
Service Brake
Master Cylinder
The master cylinder of a brake system converts pedal force into hydraulic pressure. When the brake pedal is depressed, pistons in the master cylinder are activated, causing pressure to act on the brake fluid. When the brake pedal is released, return springs move the pistons back to their original positions.
Honda vehicles utilize tandem master cylinders. This type of master cylinder serves two independent hydraulic lines. Since both hydraulic lines are independent, fluid loss or other abnormalities in one line do not cause all the brakes to fail.
The master cylinder is fitted with a brake fluid reservoir. Fluid in the reservoir compensates for variations in the fluid level that accompany movement of the pistons and for permanent changes in the quantity of fluid in the brake lines that occur as the brake pads become worn. (When the brake pads are worn, the caliper piston must stroke longer to contact the pads to the disc. Thus more fluid is required in the brake line).
- Reservoir cap
- Reservoir
- Master cylinder
- Secondary piston
- Return spring
- Rear right brake
- Front left brake
- Rear left brake
- Front right brake
- Return spring
- Primary piston
Disc Brake
A disc brake consists of a brake disc, brake caliper and two brake pads. The brake disc is sandwiched by the brake pads and the pads are held inside the brake caliper. The brake hydraulic pressure created by the master cylinder is sent to the brake caliper and the caliper presses the pads against the disc.
Most brake discs are solid, but some vehicle models utilize ventilated discs (each of which contains radial vanes between its rubbing surfaces for optimum cooling performance) on their front brakes. (The front brakes are subjected to relatively heavy loading.) On certain models, ventilated discs are also used on the rear brakes.
Drum Brake
A drum brake consists of a brake drum, wheel cylinder, two brake shoes and a backing plate. The wheel cylinder and the brake shoes are mounted on the backing plate, which is fixed on the trailing arm and the brake drum is mounted on the rear hub and covering over them. The brake hydraulic pressure created by the master cylinder is sent to the wheel cylinder and the cylinder expands the shoes against the drum.
Proportioning Control Valve (PCV)
When a vehicle’s brake pedal is depressed, the vehicle undergoes a nosedive. At this time, the increased load on the front wheels makes the front brakes less prone to locking. On the other hand, the rear brakes become more prone to locking since the load on the rear wheels is simultaneously reduced.
Locking of the rear wheels would cause instability and could cause the vehicle to spin, so a proportioning control valve (PCV) is incorporated to adjust the brake pressure supplied to the front and rear brakes. When the brake hydraulic pressure exceeds a predetermined level, the PCV limits the amount of pressure supplied to the rear brakes, thus making them less likely to lock. Honda vehicles utilize dual PCVs, which are designed for operation with divided-line brake circuits. On some models, this function is built in the ABS hydraulic unit.
- Valve piston
- To rear wheel cylinder
- To rear wheel cylinder
- Valve piston
- From master cylinder
- From master cylinder
The brake booster reduces the amount of force required to depress the brake pedal. The type used in Honda vehicles is a diaphragm-type vacuum servo brake booster. This type boosts the force applied to the brake pedal utilizing the pressure differential between the atmospheric pressure and the vacuum pressure in the engine’s intake manifold. The boosted force is applied to the pistons in the master cylinder.
Metal pipes are used to connect brake system components that are fixed to a vehicle’s
chassis. Rubber hoses are used to connect components that move vertically due to
operation of the suspension system. Honda uses an X-split divided-line connection
arrangement to prevent a single abnormality from causing all the brakes to fail. In this
arrangement, one line serves the front-right and rear-left brakes and the other line serves the
front-left and rear-right brakes.
Parking Brake
Activation Mechanism
Every Honda vehicle utilizes a mechanical parking brake arrangement in which the rear-wheel parking brake mechanism is activated from the cockpit via cables. Parking brake arrangements can be lever-activated or pedal-activated.
Lever-Activated Parking Brake
In a lever-activated arrangement, the parking brake cables are connected to a lever between
the driver’s seat and front passenger seat. To activate the mechanism, the driver pulls the
lever upward. The lever is then held by a ratchet. To release the mechanism, the driver
depresses a release button at the end of the lever and returns the lever to its original
position.
The mechanical parking brake system consists of a parking brake lever (or pedal), parking
brake cable, and rear wheel brakes.
Pedal-Activated Parking Brake
- Parking brake lever
- Adjusting nut
- Parking brake cable
- Rear wheel brake
- Equalizer
Pedal-activated parking brake arrangements are used on certain vehicles with automatic
transmissions. In this type of arrangement, the parking brake cables are connected to a
pedal near the driver’s feet. To activate the mechanism, the driver depresses the pedal. To
unlock the pedal and release the mechanism, the driver pulls a lever on the dashboard.
A parking brake arrangement can be either a combined type, in which the rear service
brakes are used by the parking brake mechanism, or an independent type, in which
dedicated parking brakes are fitted independently of the service brakes.
As mentioned earlier, an independent parking brake arrangement utilizes dedicated parking
drum brakes that are fitted inside the disc hubs of the vehicle’s rear disc brakes.
Parking Brake Operation Flow
Service Brake
When the brake pedal is depressed, a push rod transmits the pedal force to the brake booster. It boosts the force and transmits the boosted force to the pistons in the master cylinder. From the master cylinder, pressure is transmitted to the wheel brakes via fluid-filled brake lines. In a disc brake arrangement, this pressure acts upon pistons in the brake calipers, causing the pistons to press pads against the discs.
Parking Brake
- Master cylinder
- Brake booster
- Brake pedal
- Rear brake caliper
- Rear brake disc
- Parking brake lever
- Front brake disc
- Front brake caliper
- Proportioning control valve
When the parking brake lever is pulled in a vehicle with disc brakes, cables transmit the
pulling force to the rear brake calipers mechanically, causing the pistons to press the pads
against the discs.
