Page 147 - How It Works - Book of Amazing Answers To Curious Questions, 12

Q�
Transport _______________

What do anti-loci< bral<es do?

ABS is standard on nearly every new car; behind the little
yellow light lies a highly advanced system
Fast communication
tis very easy to lock a wheel under braking in a car, CANbus allows fast communications between the engine control unit
and sensors. A microprocessor processes this data and converts the
particularly when it is raining. A locked wheel Advanced braking signals. The hydraulic control unit and ECU are positioned close
I provides minimal braking force, though -peak brake components together, so the valves are controlled by the ECU.
ABS is made up of four key
efficiency is found at the point just before the wheel locks. components - wheel speed
Anti-lock braking systems (ABS) avoid the pitfalls of locked sensors, booster pump,
valves and a controller.
wheels while maximising the benefits ofbeingable to get
near this point.
ABS applies a computer algorithm to the mechanical
action of braking. The system uses feeds from wheel speed
sensors. A locked wheel decelerates fast compared to the
other three-such an incident instructs the computer to
release brake pressure on that wheel. The wheel accelerates
again; once it is in sync with the other three, brake pressure
is regained until the wheel just starts to lock again-and Speed sensor science
Speed sensors comprise a magnet
once more it is released. Sensing the lock Valves enclosed within a coil. They give off
High-tech valves can run this cycle many times a second, Inputs for ABS come These solenoid valves a magnetic field that interacts with
maintaining the wheel just on the point oflocking (that's the from wheel speed modulate the pressure from contact on the toothed ring, creating
sensors. These read inputs the brake master cylinder to a signal. The controller converts the
characteristic 'judder' of ABS operation). This maximises
from toothed wheels ensure 'too much' cannot be number of pulses into a digital signal,
braking effect while avoiding dangerous lock-ups where the mounted to the driveshaft. sent to the brake, locking it. and processes this.
driver's control is lessened.
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How do traffic jams start?

Ever wondered why traffic grinds to
a halt for seemingly no reason? r,...==:='===::i!:"!.::!!!��
The offending vehicle A has now
completed its manoeuvre and left
the motorway. However,
�����;r}=�is�SiiiJl�i;--;�!![!! ii�[5!;;:;;=;;;JI acceleration is still hindered and
slowed by traffic density and
':
:
;:
vehicle limitations.
This braking effect is then transferred to each
following vehicle, the total speed of the cars
decreasing the further back in the chain they are, until
standstill is reached. Often the shock wave travels
over 2km (lmi) to the rear, leaving drivers completely
unaware of the cause of their deceleration.

The immediate impact of the error is that
The traffic shock wave the vehicles behind cars A and B must
begins when a vehicle, break suddenly to 72km/h (45mph) to
travelling at the road's stated avoid crashing into them from the rear as
speed of 96km/h (60mph). they brake. This applies to vehicles in all
manoeuvres at the last three lanes, as car A crosses each of
minute. In this example, car them to exit the motorway.
A swerves across car B,
causing the latter to brake to
SOkm/h (50 mph) in order to
remain at a safe distance.
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