I have some glimpses of my childhood days when I used to play with a flying disc. I still remember that was the only perfect circular thing in my house(according to my baby thoughts). My interest towards automobile especially bikes spiked up each year I celebrated my birthday. My father had a grey color scooter BAJAJ SUPER CHETAK to be précised on which all four of us used to travel the city. I used to occupy the front leg room portion of the scooter where I used to stand while holding the handle of the scooter for support. Today I have grown into a well healthy tall man and my dad often shares my childhood days with me. He mentions one habit of mine where I used to lock my eyes on a vehicle to swing my head along the motion on that vehicle as it crossed us. I remember once I saw that similar thing which I really thought was a flying disc on the front wheel of a bike. Actually it was not that toy disc but a mechanical heavy steel disc brake disc. Of course it is so lame to describe a disc brake disc like this but the real feel of this topic would be incomplete without this way. It looked like this......

Present day.....

That flying disc type thing was a disc brake as mentioned earlier and I have already written a whole article on that. If you are interested in knowing more about disc brake discs then please do visit this link(https://typesofdiscs.blogspot.com/2020/10/brake-means-to-stop.html). Braking has improved its degree of effective with every passing year. Now nearly all bikes come with a modern type of braking technology known by the name ABS or anti-lock/anti-skid braking system. With the introduction of ABS, the risk of wheel getting locked on hard braking is now missing. This is integrated to the disc brake itself. It means that ABS is used to enhance disc brake effect. There are several parts that constitute in a perfect function of ABS. Without putting in efforts to search the label specifying ABS or brochure to know if a bike is equipped with ABS, a simple phonic disc bolted to the disc would indicate you easily. You could know whether the bike is equipped with ABS or not just by ca look at the disc. A phonic disc is a circular disc made of small grooved metallic disc that is bolted to the hub region of the disc. It was invented way back in 1894 by L.R. Wilberforce and then later was used in a physics apparatus Stroboscope. In ABS, phonic disc indicates ECU about the rotation of the wheel as the disc is fixed on the wheel and rotates with the motion of the wheel.

There is a set of notches on the phonic disc. A speed sensor is attached close enough to the phonic disc so that it could sense every notch crossing the speed probe. This data is detected by the speed sensor and sent to the ECU(electronic control unit) which is connected to the ABS modulator or hydraulic control unit and controls it simultaneously. The data is continuously getting sent to ECU at whatever speed the wheel may be rotating at. ECU is a small computer which acts like a brain of the system and controls the flow of the brake fluid though the lines from the master cylinder. The fluid pressurizes the friction pads and pushes it against the disc on hard braking. This induces friction between the pads and the disc which initiates the braking action. Often the wheel loses grip or traction when the wheel locks itself on hard braking and the whole effect is detected by the sensor and rapid action of releasing the brake initiates which helps to gain back the necessary traction and avoid any crash or serious situation from happening.

This is detected by the difference in the speed of the number of times each notch crosses the speed sensor probe. The oil supply from the master cylinder is cut when the ECU detects any wheel lock. This release the pressure from the disc and the wheel again starts rotating freely at a slower speed. ECU again detects that the wheel is moving and so it again resumes the oil supply from the master cylinder. This initiates braking and the method keeps on repeating itself till the time the rider keeps the brake lever pulled. The cycle of brake release and resume occurs in less than 1 second and is a very quick cycle and that is why the rider would not come to know even when the whole process is going on at the time of braking. This brake release and reapplying keeps on happening fast as 100 times in a second. Yes there are chances that in some bikes, the rider may feel the lever swing which is the sign that ABS is in active mode. The system comes to life the moment the keys are inserted and turned once. An ABS sign flashes post key turning which looks somewhat like this.

Basically, ABS is not about reducing the braking distance but to maintain the control of the bike while braking. The bike could be steered even after the brakes are applied and so the rider could change the direction of the vehicle in order to dodge the obstacle in the way. Braking distance is the distance covered by a vehicle from that particular speed to a total halt as soon as the brakes are fully applied. A bike has brakes on both front and rear wheel. Front brake is controlled by a hand lever provided on the handle whereas the rear one is controlled by a foot pedal located on the right of the rider. The contrast in the braking distance is shown below based on which and how the brakes are applied.

The primary stage of ABS operation is detection where the speed probe sensor monitors the wheel speed and continuously sends the signals to the ECU. This is why phonic wheel becomes a crucial part of automobile in terms of safety. Phonic wheel also assists the engine control unit to detect the rotation speed and timing of the engine. Many of you might have seen a disc brake but never came to realize about the purpose and other tiny parts on it. I hope now after getting a small idea about a phonic wheel, you could now read and understand a practical disc brake ABS better the next time you take a walk around the bike.

 

by AutoVogue