BENDIX MC-12 MODULATOR CONTROLLER ASSY Instrukcja Naprawy Pobierz pdf (Strona 51)

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FIGURE 3 - EFFECT OF WEIGHT AND SPEED ON BRAKING FORCE REQUIRED

(Note: For illustration the Figure above shows horses; however in this case we are illustrating the effect of forces, not horsepower amounts, as in Figure 2.)

Braking Force

resistance which play a part in all stops, the brakes

must develop the same energy in six seconds as the

engine develops in 60 seconds; in other words, the

brakes do the same amount of work as the engine in

one-tenth the time and must develop approximately

1,000 horsepower during the stop.

Effect of Weight and Speed

Other factors to be considered are the effects on

braking when the weight and speed of a vehicle are

increased. If the weight of the vehicle is doubled, the

energy of motion to be changed into heat energy is

also doubled. If the brake cannot properly dissipate

and absorb the increased heat caused by the vehicle

FIGURE 4 - EFFECT OF SPEED ON STOPPING DISTANCES

weight (in excess of the vehicle design spec’s), poor

braking performance will result. Brake systems are

designed to properly control a vehicle loaded up to

its gross vehicle weight (GVW). Never exceed the

GVW for a vehicle.

The effect of higher speeds on braking is much more

signiﬁ cant. Comparing stops from a speed of 20 miles

per hour with stops from a speed of 40 miles per hour,

engineering calculations show there is actually four

times as much energy of motion to be changed to

heat energy during a stop from 40 miles per hour as

there is during a stop from 20 miles per hour. Thus,

if the speed is doubled, four times as much stopping

power must be developed, and the brakes must absorb

or dissipate four times as much heat. If the speed is

three times higher, the stopping power needed is nine

times higher.

It naturally follows that if both the weight and speed

of a vehicle are doubled, the stopping power must

be increased eight times and the brakes must absorb

or dissipate eight times as much heat.

Another way of illustrating the effect of speed on

stopping ability is to compare the stopping distance if

the speed is increased without increasing the weight.

In Figure 4, the vehicle shown stops from 20 miles per

hour in 30 feet. At 40 miles per hour it would typically

require 120 feet to stop, and 60 miles per hour it would

typically need 270 feet to stop.

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BENDIX MC-12 MODULATOR CONTROLLER ASSY Instrukcja Naprawy Strona 51

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