For stopping the heavy vehicles, higher amount of braking force is required.Hence for increasing the braking force the driver has to apply more force on the brake pedal. During long distance travels the driver becomes tired due to the above problem. To avoid this difficulty
and help the drivers any one type of
brake is chosen and the brake system is coupled with the other brake system that enhances and converts the small power of the driver in to multiple times of the power for braking the vehicle.This type of brake system is called as the servo brake.
Generally, by using less amount of force getting more amount of power is called as servo action. In this way, using additional power from the high pressure air or from vacuum the hydraulic brakes are operated. This type of brake is called as servo brake or energized brake.Air servo brake or air assisted hydraulic brake In this type of brakes for increasing the force on a piston of the master cylinder,
compressed air is used. In this type of
braking system half of the pressure applied to the pedal from the simple hydraulic braking is sufficient to operate the system. Moreover, even in case of any leakage in the compressed air path, the brakes can be applied by the servo braking system. For operating the brake system
there are two air compressors and control valves used in this system. Apart from these, connecting pipes are present to connect the servo unit with the master cylinder to combine the air pressure with hydro power. When driver presses the brake pedal, the piston lever inside the servo unit is moved forward. At that time
the inlet valve in the master cylinder is opened and the compressed air is allowed to enter into the cylinder for increasing the pressure. Hence the brake fluid is sent out with high pressure to the wheel cylinder and operates the brakes. When
the driver releases the brake pedal, the outlet valve is opened and the compressed air is sent out through this valve. Hence the brake shoes are released from the brake drum and the drum is allowed to rotate which rotates the wheels.
Vacuum servo brake
The schematic view of the vacuum
servo brake is shown in the figure. This type of brake system utilizes the vacuum create at the inlet manifold of engine and increases the braking force. The vacuum reservoir
is connected to the inlet manifold of the engine with a non-return valve. Moreover,vacuum reservoir is connected on both sides of pistons inside the servo cylinder. In this
way the vacuum reservoir is attached to the right side of the piston in the Servo cylinder and the left side is attached with the control unit and the schematic of vacuum assisted
servo brake can be seen in Figure.
There is a piston in the control unit
that has two valves attached to it. These valves are arranged in a compressed state with the help of two springs. The valve at the top of the control unit controls the atmospheric pressure controls the connections in the left side of the piston in the servo cylinder. Similarly, valve at bottom of the control unit controls the
connections between the vacuum reservoir which is located in the right side of the control unit and servo cylinder. The piston inside the control unit is actuated by master cylinder. In the control unit valve at the top is in closed position and bottom will be in opened position when there is no any force applied to the brake pedal. Thus, the two sides of the piston inside servo cylinder are equally contacted
with the vacuum in the inlet manifold
When pressing the brake pedal the
pressure developed on the brake fluid
inside the master cylinder pushes the
piston inside the control unit in upward direction. Hence the valve in the bottom of the control unit gets closed and valve at the top get opened. Therefore right side of the piston inside the servo cylinder
contacted with atmospheric air. Hence the vacuum force completely spread over the right side of the piston in the servo cylinder and moves the piston lever in the same direction. This transfer in place
of piston actuates the braking system
with the path of connections. By this way the braking force got reducing while the driver presses the brake pedal.