A Mechanical Speedometer

Comsats Institute Of Information Technology

Islamabad

Presented by:

M Saif Ul Islam

SP13-BCE-031

In The Name Of Allah The Most Beneficient The Most Merciful

OutLine:

1. Defination

2. History

3. Invention

4. Working

5. Effect of changing diameter

defination:

What is speedometer…!!

A speedometer is the device in a vehicle that measures and displays the speed.

HISTORY:

How early people measure speed…!!

Early Romans marked the wheels of their chariots

and counted the revolutions, estimating distance

traveled and average daily speed.

In the eleventh century, Chinese inventors came

up with a mechanism involving a gear train and a

moving arm that would strike a drum after a

certain distance

INVENTION:

Josip Belusic invented speedometer in 1888.

1. When the engine turns over, the driveshaft turns to make the wheels spin round.

2. The speedometer cable, powered by the driveshaft, turns as well.

3. This cable is directly attached to a permanent magnet in the speedometer assembly, which spins at a rate proportional to the speed of the vehicle.

4. As the magnet rotates, it manipulates an aluminum ring, pulling it in the same direction as the revolving magnetic field. The ring's movement, however, is countered by a spiral spring.

5. The pointer is attached to the aluminum ring , which indicates the speed of the vehicle by making the balance between these two forces.

6. As the vehicle slows, the magnetic force on the aluminum ring lessens, and the spring pulls the speedometer's pointer back to zero

WORKING:

Inside a speedometer…

EFFECT OF CHANGE IN DIAMETER:

What if we change the diameter of wheel..!!

Nearly all tires have their standard size

which is shown as "T/A_W" on the side

of every tire.

Diameter in mm=2*T*A/100+W*25.4

Percentage error=100*(1-new diameter/standard diameter)

EFFECT OF CHANGE IN DIAMETER:

Lets take an example:

A standard tire is "185/70R14"

Its diameter = 2*185*(70/100)+(14*25.4) = 614.6 mm

Another is "195/50R15“

with diameter = 2*195*(50/100)+(15*25.4) = 576.0 mm

Replacing the first tire (and wheels) with the second.

Then the error = 100 * (1-(576/614.6)) = 6.28%

So at an actual speed of 100 km/h (60 mph), the speedometer will indicate

100 x 1.0628 = 106.28 km/h (60 * 1.0628 = 63.77 mph), approximately.

THANKS…!!

Hopefullly you will get a rough idea

of a speedometer……

Questions are welcomed..