As we all know, motorbike's engine capacity above 150cc should be equipped at least with a single channel ABS system and below 150cc must consist a combi braking system or linked braking system. Disc braking system is much efficient compared to the drum braking system as the braking action is very sharp. This is a major advantage and helps very much in reducing the stopping distance. But there's a problem in this braking system which is none other than a wheel lock. Many of us may experienced this including me which led me to an accident in my childhood. To avoid the problem of a wheel lock, Anti-lock Braking System is developed and in this article, let's see something basic about the system and how it works.
To begin with, firstly let's see some basics about the working of disc brake system. When we pull the brake lever, due to the leverage action, piston inside the master cylinder compress the brake fluid present inside it and directs it to the caliper which is clamped to the front disc rotor. Based on the Pascal's law, the fluid pushes the piston present inside the caliper in which it forces the brake pad or friction pad against the disc rotor. Due to the friction, the motorbike decelerates and enormous amount of heat will be produced. That's why we can able to see disc rotors with holes and there's also a petal type disc rotors which helps in cooling it down. This is the process happening in the disc brake system.
In the ABS function, there comes additional components such as Wheel Speed Sensor (WSS), Hydraulic Control Module and the ECU. For understanding, let's see about the single channel system which is meant only for front wheel. Wheel Speed Sensor regularly monitors the wheel speed and sends signal to the ECU. ECU, brain of the motorbike calculates the wheel speed automatically. In the normal disc brake system, brake fluid from the master cylinder is directed to the caliper. But here in the ABS function, brake fluid is first sent to the hydraulic control module and then only sent to the brake caliper.
In the Hydraulic Control Module (HCM), there are two valves with two solenoid actuators, a motor and pump, Low Pressure Accumulator (LPA) and a Non Return Valve (NRV). When we pull the brake lever, fluid in the master cylinder is compressed due to the leverage action and flows to the HCM via fluid lines. At the normal condition, isolation valve will be in the open position and the dump valve will be in the closed position. So, the brake fluid flows through the isolation valve and enters the caliper thereby initiating the braking action. Now if there's no wheel lock, then the HCM remains silent and allows the braking action to continue.
WSS constantly monitors the wheel speed and if the ECU detects the sudden drop in wheel speed or if the wheel locks suddenly, then it initiates the ABS function. To avoid the slippage, pressure inside the fluid line should be reduced to allow the wheel to spin freely, thereby avoiding the lock. To achieve this, here comes the action of the solenoid actuators. Firstly, ECU actuates the solenoid valve connected to the isolation valve and close it thereby the fluid line from the master cylinder is isolated from the caliper and prevents the further increase in pressure. ECU checks whether this action is sufficient for unlocking the brake.
If not, it further opens the dump valve thereby releasing some more pressure inside the fluid line and the excess brake fluid is stored inside the LPA. Now the braking action should be initiated to decelerate further. But by simply opening the isolation valve again, braking action will not be effective as there's less pressure. In this situation, ECU actuates the ABS motor which pumps the brake fluid from the LPA to the braking line via NRV valve. NRV valve helps in maintaining the pressure and doesn't allow the brake fluid to flow back to the LPA. After this, ECU closes the dump valve and opens the isolation valve as there's enough pressure in the braking line. Again the fluid flows to the caliper reinitiating the braking action and if there's a wheel lock again, then these steps will be repeated until the bike stops or until the brake lever is released.
I hope you'll understand the basic function of a ABS system and if you didn't got it, follow the diagram deeply and go through the working again. If you have any suggestions or corrections or if I conveyed anything wrong, please let me know in the comment section below.
Image courtesy : YouTube/Ajith Buddy
To begin with, firstly let's see some basics about the working of disc brake system. When we pull the brake lever, due to the leverage action, piston inside the master cylinder compress the brake fluid present inside it and directs it to the caliper which is clamped to the front disc rotor. Based on the Pascal's law, the fluid pushes the piston present inside the caliper in which it forces the brake pad or friction pad against the disc rotor. Due to the friction, the motorbike decelerates and enormous amount of heat will be produced. That's why we can able to see disc rotors with holes and there's also a petal type disc rotors which helps in cooling it down. This is the process happening in the disc brake system.
WSS constantly monitors the wheel speed and if the ECU detects the sudden drop in wheel speed or if the wheel locks suddenly, then it initiates the ABS function. To avoid the slippage, pressure inside the fluid line should be reduced to allow the wheel to spin freely, thereby avoiding the lock. To achieve this, here comes the action of the solenoid actuators. Firstly, ECU actuates the solenoid valve connected to the isolation valve and close it thereby the fluid line from the master cylinder is isolated from the caliper and prevents the further increase in pressure. ECU checks whether this action is sufficient for unlocking the brake.
If not, it further opens the dump valve thereby releasing some more pressure inside the fluid line and the excess brake fluid is stored inside the LPA. Now the braking action should be initiated to decelerate further. But by simply opening the isolation valve again, braking action will not be effective as there's less pressure. In this situation, ECU actuates the ABS motor which pumps the brake fluid from the LPA to the braking line via NRV valve. NRV valve helps in maintaining the pressure and doesn't allow the brake fluid to flow back to the LPA. After this, ECU closes the dump valve and opens the isolation valve as there's enough pressure in the braking line. Again the fluid flows to the caliper reinitiating the braking action and if there's a wheel lock again, then these steps will be repeated until the bike stops or until the brake lever is released.
I hope you'll understand the basic function of a ABS system and if you didn't got it, follow the diagram deeply and go through the working again. If you have any suggestions or corrections or if I conveyed anything wrong, please let me know in the comment section below.
Image courtesy : YouTube/Ajith Buddy
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