Chapter 2 Heavy Vehicle Braking Flashcards
What is Heat and its relation to an engine
Heat is a form of energy produced in the engine and this energy is converted into the energy of motion through the moving parts of the engine and drive train turning the wheels.
What role does traction play in moving a vehicle
if there is no traction Between the tires and the road surface the vehicle will not move anywhere
How does the vehicle stop using scientific explination
in stopping a vehicle energy of motion is converted to the energy of heat through friction between the lining/pad and drum/rotor surfaces of the vehicles breaks
What is the final factor in stopping the vehicle
The final factor is in the contact between the vehicle and the road through the tire
bald or defective tires may degrade braking performance.
What is reaction time
is the time it takes between recognizing a hazard ahead and applying the brakes
An average drivers reaction time is 3/4 a second
What happens If one of the brakes aren’t adjusted properly on a tire
It would cause the other brakes to work harder. Excessive use could result in buildup of more heat than the brake can absorb and dissipate. too much heat can result in brake damage and possible failure.
What is see-think-do
see-a hazard
think-decide to stop
do-place your foot on the brake pedal until you stop
What equals to total stopping time
Drivers perception time + reaction time + brake lag time + braking time = total stopping time
how long does it take to perceive a hazard
3/4 of a second
how long does it take to react to a hazard after percieving it
3/4 of a second
What is brake lag time
Brake lag time is the time between when you press the brakes to when they actually apply is 4/10 of a second
How many seconds behind should you follow a vehicle if you’re in a heavy vehicle
never be less then 5 seconds (stay even further back if in bad conditions)
What happens if your brakes aren’t correctly adjusted
or your vehicles on a downgrade while braking
total stopping time will increase
What is the most common air brake defect found during commercial vehicle inspections
brakes out of adjustment
What does the total stopping distance or time depend on
The ability of the brake linings or pads to produce friction the brake drums to dissipate heat and the tires to grip the road
what 2 factors are mostly in play involved in police reported casualty crashes
Driving without due care and attention and unsafe speeds are the 2 factors in casualty related crashes
if a vehicle is going double the speed and it needs to brake how much more stopping power is required to stop it
4 times the stopping power
If a vehicle is double the weight and it needs to brake how much more stopping power is required to stop it
2 times the stopping power
If a vehicle is going double the speed and double the weight how much stopping power is required to stop it
8 times the stopping power
What is Stopping power
stopping power is the distance required to stop
Going down hill does what to braking
increases brake time
going up hill does what to braking
decreases braking time
What is Brake fade
Brake fade occurs when your brakes stop working properly because they’re overheating your vehicle takes longer to stop or may not stop at all if you haven’t properly controlled the speed
In normal stopping what is the heat the brake component heats up to?
120 degrees Celsius or 250 Fahrenheit
What is the maximum heat the brakes are meant to with stand under hard braking circumstances
250 degrees Celsius
What happens when the brake drums heat up to much
to much heat causes the brake to expand away from the brake lining causing in the end brake fade, brake damage and or brake failure. (may catch on fire)
When braking what happens
Heat builds up with excessive hard braking until it exceeds the capability of the brake components to absorb and dissipate the heat
What is a Retarder
Reatrders provide an auxiliary slowing effect and assist the main brake system to slow the vehicle. good for controlling speed on long downgrades of hill. Many retarders can absorb as much or more horse power as the engine can develop
What are the 4 main type of rearders
- Engine retarder
- Exhaust Retarder
- Hydraulic drive line retarders
- electric driveline retarder
When is an engine retarder more efficient
at a higher rpm and a lower vehicle speed, Selecting the right gear before going down hill is important
What should you be cautious of when using a retarder/engine brake
On slippery surfaces some can actually cause the drive wheels to lock up, stalling the engine and can result to loss of control of even the tractor trailer to jack knife
When are retarders restricted
Watch for signs restricting the use of retarders and engine brakes
What does R.P.M. stand for
Revolutions per minuter refers to the number of complete turns the crankshaft make in one minute
How should you normally brake
Gradually squeezing the brake and before you stop reduce the pressure so your vehicle wont jerk
How to ensure a smooth controlled stop every time
- travel at a speed allows you to see a safe distance ahead
- maintain a safe following time or distance
- Use good braking skills
How to stop safely
Brakes properly adjusted your load is balanced and your tires are in good condition. be sure your tires are inflated
How do you stop on icy roads
to stop on icy roads use extremly light pressure on the brake to control vehicle speed. this will help prevent the wheel from locking up. a slow spinning wheels had mor stopping power then a locked up wheel
When should you put chains on
When you’re going to drive in bad conditions or potentially going to best be prepared. Its harder to mount chains on a hill.
When do the brakes get the hottest
going highway speeds while on a long downgrades. or from repeated use of the brakes without enough cooling time between application.
whats the causes the majority of all brake failures and downhill runaway crashes
they’re caused by over driving the ability of brakes to deal with heat. in other words poor speed control
in heavy vehicles when going on a downgrade
go slow you should be in a low gear never switch into a higher gear unless it can be controlled by a retarder
What does it mean by saving your brakes
on a hill use a retarder and save your breaks for emergency stops
If you fail to go slow enough on a downgrade what should you do
apply the brakes to go down 10 to 15 km/h
downshift to a lower main gear(don’t use the splitter valve when going down hill)
Repeat this process if it happens again
be careful when using this process in icy conditions
When should you obey brake check signs
Always
In town
In town you should select and appropriate low gear that holds speed and so you can safely stop in an emergency
Why should you avoid water on road ways
cause it can reduce braking efficiency.
why should you apply a slight drag on the brakes
so it reduces the amount of water entering the brake drums and shoes.
What are runaway lanes for
these are lanes located on some downgrading hills. These lanes are there to help slow and stop vehicles if their brakes fail as they are going down hill. Runaway lanes should be used to control speed or stop
why should you be cautious when braking
wheels can lock up causing them to slide when theres no ABS
What is an ABS
anti-lock braking system. It prevents wheel lock up or skids caused by overbraking on slippery surfaces
Whats bad when your wheels lock up
You cant steer
`What is a Jack knife and what causes it
Jackknife is when a tractor and the trailer form and angle of 90 degrees or less. relative to one another
Happens because of poor braking techniques and improper use of retarders
How to emergency stop with abs
- Apply firm hard continuous pressure
- don’t pump the brakes
- Don’t be alarmed by brake noise, pedal movement or shudder. this is normal keep applying firm pressure
- Be cautious about steering around obstacles
- make sure you know if your trailer has abs or not if it doesn’t brake as if you didn’t have abs
What is an ATC
Automatic Traction Control is an optional addition to the abs system. It uses a pulsating signal from the speed sensors to select loss of drive wheel traction on slippery roads.
If a wheel doesn’t gain traction the sensor will stop the wheel from spinning to gain traction
How is heat dissipated in the brake
its absorbed or dissipated in the brake components
