Understanding Brake System Components and Operation
Brake System Components and Operation
Phases of Braking
Pressure Rise Phase
During the pressure rise phase, the hydraulic solenoid valves are not activated. Pressure is created by the effort exerted on the brake pedal. The braking force increases, the wheel slows down, and consequently, the vehicle’s speed reduces. Acceleration and velocity are reduced to values such that the adhesion of the vehicle to the ground is compromised. Therefore, we must reduce the braking force to allow the wheels to increase their speed and regain grip.
Pressure Drop Phase
In the pressure drop phase, the electronic control unit detects the tendency of the wheel to lock and activates the anti-lock device. The solenoid is activated with a current of 4.6 to 6 amps, closing communication between the pump and the caliper while opening communication between the brake caliper and the pump return. Thus, brake fluid is withdrawn from the calipers. This intermittent hydraulic action can be felt on the brake pedal during braking.
Pressure Maintenance Phase
During the pressure maintenance phase, the wheel’s speed and acceleration increase. The solenoid is activated with a current between 1.9 and 2.3 amperes. Communication between the pump and the brake caliper is cut off. Caliper pressure remains constant due to the force exerted on the brake pedal.
Key Components
Hydraulic Power Unit
The hydraulic power unit consists of a pump, accumulator chamber, feedback for each brake circuit, and solenoid valves.
Pump Feedback
The pump feedback is responsible for driving the fluid leaving the cylinder to reduce pressure. It leads to the accumulator, returning it to the brake master cylinder. This valve is activated by an electric motor.
Accumulators
Accumulators collect the brake fluid, suddenly decreasing the pressure.
Solenoid Valves
Solenoid valves modulate the pressure in the brake cylinders through three phases: rise, drop, and maintenance.
Working Positions of Solenoid Valves
- Sleep: The master cylinder is in communication with the actuator.
- Maintenance: Communication is cut off by a current of two amps that excites the coil and moves the piston, closing the master cylinder pressure.
- Reduction: A current of 5 amps excites the coil and moves the piston further, opening the path between the actuator and pump, releasing excess pressure.
Amplifier Tube Operation
The signal from valve T enters the amplifier tube, lifting the piston and diaphragm assembly. It moves from its seat at the double-cone valve, allowing air from the reservoir to brake the car. When the pedal or handbrake is released, the signal exits. The membrane piston is released by the spring force, closing the double-cone valve. The air then exits through the center hole of the plunger, causing the car to decelerate.
Two-Way T Valve
When the foot brake is applied, air pressure enters the T valve. The piston moves, closing communication with the manual brake. Compressed air then passes into the amplifier tube to stop the car. When the handbrake is applied, communication to the brake pedal is closed, and only compressed air is used to stop the car.
Overflow Valve Operation
Air from the primary circuit enters the valve and acts on the membrane. If it exceeds 4.5 kg/cm², the membrane rises from its seat. Air passes to the auxiliary circuit, balancing pressures up to 7 kg. If a failure occurs in the primary circuit and pressure drops to 0, the vehicle cannot be braked. In this case, the auxiliary circuit returns the air pressure, slowing the vehicle via a one-way valve.
Brake Pedal Valve Operation
When the brake pedal is pressed, force is transmitted to the rod or plate spring. The stepped piston moves from its seat at the pressure valve, allowing air into the chambers, stopping the vehicle. When the brake pedal is released, the stepped piston closes the pressure valve, cutting off the air. The air in the chambers then exits through the piston hole, decelerating the vehicle.
Safety Valve
If the pressure relief valve fails and pressure exceeds 7 kg, reaching 9 kg, the safety valve opens, venting at the top to prevent overpressure from destroying the system. If the throttle works correctly, the safety valve will never activate.
Regulator Debugger
Primary Function
The primary function is debugging or cleaning. Air from the compressor enters the debugger, passing through a narrow flame disc. This increases the air speed, producing a vortex. Centrifugal force separates impurities like water, oil, and charcoal, which are deposited in the filter.
Secondary Function
The secondary function is regulating pressure. The tank is connected to a flexible air valve. When the pressure rises above 7 kg, the membrane opens. Air passes into the stepped piston, opening communication with the outside and dragging impurities out.