How does Anti-Lock Braking System (ABS) function in two wheeler?

:Anti-Lock Braking System (ABS):

ABS means anti lock breaking system,which is use to avoid skidding during hard braking on all types of surface. ABS is equipped on a bike with single channel and dual channel.On a motorcycle,an anti-lock brake system prevents the wheels of a powered two wheeler from locking during braking situations.

In another way you can say that ABS on motorcycles prevents wheel locking and increases stability. Motorcycles are, by nature, less stable than four-wheeled vehicles. Braking too hard can destabilize a motorcycle and lead to either the front or rear wheel locking, causing the bike to overturn or slide.

ABS bike could not be seen before so much.As per the government of India's rule, all new two-wheeler launches after April 2020, will have to include ABS or CBS in their vehicles.Vehicles below or equal 125 cc will require combined braking system (CBS),while bikes more than capacity 125 cc will must have anti lock braking system (ABS). However nowadays almost all four wheeler cars have ABS.

Types of braking :

So you have heard many types of braking system used in automobile system nowadays in market for two wheeler,like drum brake,disc brake and ABS. Before gone through ABS system,first of all we will understand function of Disc brake.

Disc Brake : The disc brake is a mechanism for slowing or stopping the rotation of a wheel from its motion.A disc brake is normally made of cast iron, but in some cases, it is also made of composites such as carbon-carbon or ceramic -matrix composites.Primarily its uses braking power to transmit hydraulic fluid to braking power.

Mainly it has two piston,one is smaller and other one is bigger,as shown below picture.Also have hydraulic fluid reservoir. Primarily its uses braking power to transmit hydraulic fluid to caliper. When we applied the brake it pusses in small piston through a small cylinder and it pushes hydraulic fluid to brake caliper through a small hose. Greater piston in brake caliper pushed against the brake disc with greater force than at the brake lever,to stop the vehicle.

Now we will understand how ABS is work on two wheeler.ABS works to prevent a motorcycle's wheel, or wheels, from locking during braking.ABS uses speed sensors on both wheels to accurately determine wheel speed as well as sensors to determine when a wheel is about to lock.

In a simple way we have considered single channel ABS as an example. Important main part of the unit called hydraulic control unit (HCU), which is driven by ECU (Electronic control unit).ECU is type of small computer which constantly detect vehicle speed. Whenever a tendency of brake locking occur, it's activate HCU. There is a speed sensor of wheel is called toner ring.

Toner Ring

Toner rings are also used in anti-lock brake systems (ABS) to detect wheel rotation rate. As the name implies its senses speed from wheel and passing it to ECU. The toner ring rotate with the wheel and sensor produce electric pulse and it passing through the each teeth of toner ring for sense it and forward signal to ECU. Then ECU calculate the wheel speed,rotation from frequency of the electric pulses. As you know ECU is the brain of the system and HCU is execute the same as per instruction given by ECU.

ABS system in two wheeler

HCU is consist of two electrically valve ie. isolation valve and dump valve, expandable chamber called low pressure accumulator (LPA),hydraulic piston pump and its motor and Non-return valve (NRV).The ABS system is connected to the braking system in series,between the brake lever and brake.That means hydraulic hose from brake lever will first comes into HCU & then comes into brake system through a small hose mounted in two wheeler.

The ABS system comes to live when ignition on in two wheeler,it will display in dashboard as shown below picture.

But ABS light still pop up until bike speed reaches 10 km/hr,ie. ABS braking system will work only at 10 km/hr or more.

The ECU monitors wheels speed,which is normally the vehicle speed.Now we are applying the brake and hydraulic fluid pressurized by the lever and this way brake is applied.

In normal braking HCU do nothing and normal braking is applied on the wheel.But in case brake lock the wheel,ECU detect and try to sudden stop the vehicle and in faster way decrease the wheel speed,through a no of activities in the system. Activities occur in the braking system are as follows-

First it will activate the isolation valve by closing it.By doing this fluid line is isolate to deliver and prevent anymore pressure rise in the system.
Then ECU check that the whether action taken is sufficient for unlock the brake or not. If not then ECU take necessary next course of action by doing opening of dump valve. As the name implies dump valve,dump the fluids in brake line and fluid goes into low pressure accumulator(LPA).
Now brake starts free spin as it has low pressure in caliper.
Now ECU turn the pump with motor.This piston pump extract fluid from LPA supplied to input line brake line through NRV. This NRV keeps the fluid in pressurized condition in input line.
In the mean time dump valve close.
As enough pressure in reserve ECU open the isolation valve.Then fluid flow in brake line and brake is activated again.

If brake lock again,then this step repeated again.This cycle is go on,until vehicle is stop or brake lever releases. All this activities happens very fast,it will repeat 10 times per second.

Whatever I discussed regarding single channel ABS for better understanding,which means ABS is working on front wheel only,whether rear wheel is not in control. But in dual channel ABS there will be a two sets of same system in a single unit and both the wheels are control independently.

Most of two wheeler have only single channel ABS facility.I thing reason behind is due to 70% brake effort occur in front wheel only and other reason is for minimize vehicle cost. However safety point of view double channel ABS is very much required.

Benefits of ABS in two wheeler:

One renowned UK based company place a report, that ABS could reduce the rate of death and severe injury from motorcycle crashes by 31%.

ABS system also work on slippery surface also.It will provides equal distribution of braking force on each wheel and provides straight line stopping of vehicle.

ABS Bike in India,BS6 :

Some of renowned ABS bike available in market,mention below-

If you are planning to buy a motorcycle to ride on-road, it is recommended that you buy one with ABS. However, ABS may not be appropriate for off-road riding conditions. If you are planning to use an ABS-equipped motorcycle off-road, you can switch ABS on and off as required.

In next topic we will discuss in detail single channel ABS vs Dual Channel ABS.

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