Name: 了解ABS防鎖死煞車系統Anti-lock Braking System（Understanding Anti-lock Braking System (ABS) !）
Uploaded: 2022-05-23T14:04:52.000Z
Duration: 6 min 48 s
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基礎被動語態

Nowadays an anti-lock braking system is used in almost all modern vehicles.

This system prevents accidents like this,

where you lose control of the steering as you apply the brakes.

With ABS, you will be able  to steer the vehicle properly

and it also reduces the braking distance.

How is it able to prevent  accidents due to the braking?

We will explore these  questions in this video.

we first need to understand  the principles of steering and braking.

the brake pads on the wheel disks will  be activated and press against the disks,

and this will stop the rotation  of the wheels.

this causes slippage between the road and wheels,

and the vehicle stops due to this friction.

Now let's understand the steering mechanism.

The whole steering mechanism is dependent on

the simple principle of the wheels rolling.

The wheels will always try to avoid slipping on the road.

So this means that the velocity of the wheel at the contact point

They rotate on their axis and also they move along the direction of the car.

Due to these two kinds of motion,  they have two kinds of velocity:

the sum of the translational and rotational velocities

and you will very easily be able  to understand the steering mechanism.

all four wheels should be rolling at  all times to avoid the vehicle slipping.

In fact, this simple rolling principle is the reason why

your car turns when you turn the front wheels.

Assume a hypothetical condition in which,

even after turning the wheels,  the car carries straight on.

In this case, the rolling velocity  will be inclined as shown,

and the translation velocity remains straight.

Therefore, if you add up  these two velocities,

The only way to avoid this is by making the translation velocity also inclined.

This is possible only when the whole  car makes a turn as shown.

When the car makes a turn at  the instantaneous center shown,

all four wheels can satisfy  the condition of rolling.

From this snapshot, you can  clearly see how the velocity

at the contact point of all four wheels becomes zero.

Now, let's analyze the steering  mechanism at the time of braking.

Due to the brake pads being activated,  the wheels stop spinning.

Even though the wheels are turned, since they are not rotating,

there will be no rotational velocity at all.

In this case, the vehicle  does not need to turn

as this has become like  a normal case of braking.

The vehicle will no longer react to the driver's changes to the steering

and will slide in a straight line  which can cause an accident.

Apart from losing control of the steering,

braking on surfaces with  different levels of traction.

When the left and right wheels  are on different traction surfaces,

applying the brakes will generate different frictional forces on the wheels.

This will produce torque, and the car will go into an uncontrollable spin.

An anti-lock braking system is very simple.

What ABS does is to prevent the wheels from completely locking up.

The ABS system includes speed sensors attached to all of the wheels.

When the sensors detect that a wheel is about to lock up,

a modulator unit partially releases the brake pad on that wheel.

This way, the wheels will be allowed  to spin intermittently during braking.

this intermittent wheel rotation on steering.

Here, the wheels will have  a rotational velocity component.

This will definitely allow  the steering to function,

and driver will be able to steer  the vehicle even during the braking.

How does the action of intermittently releasing the brakes

we first need to understand how the coefficient of friction

between the tire and the road  varies with respect to slip.

the value of the frictional  coefficient is nearly zero.

However, when the wheel is 100% slipping, sliding friction comes into play.

You can expect the frictional values for other levels of slippage to vary like this.

which has strange behaviors during braking,

the frictional coefficient between the tire and the road varies as shown

It has a peak value at  around 12% of slip ratio.

And below and above this,  the frictional coefficient reduces.

the frictional coefficient  which comes into effect

the clever algorithm adjusts the break pressure

where the frictional value  is at the maximum.

This significantly reduces  the braking distance.

Now back to the huge  instability issue of the cars.

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了解ABS防鎖死煞車系統Anti-lock Braking System（Understanding Anti-lock Braking System (ABS) !）

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