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Larry’s New truck. Larry’s Truck Improvements. Larry put a 6” lift kit on his Ford F-150 and a set of 33’s Super Swamper Thornbird Tires The Suspension System has been modified but the Brake System has not. Do You See Any Problems?. GIT-R-DONE. Master Cylinder Brake Hoses/Lines
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Larry’s Truck Improvements • Larry put a 6” lift kit on his Ford F-150 and a set of 33’s Super Swamper Thornbird Tires • The Suspension System has been modified but the Brake System has not. • Do You See Any Problems? GIT-R-DONE
Master Cylinder Brake Hoses/Lines Wheel Cylinders Brake Calipers What Parts Control the Stopping of the Truck?
Larry has a Problem! • What changes could you make to fix the problem? • Bigger parts • Such as: Master Cylinder, Brake lines, Wheel Cylinders, and/or Brake Calipers
Pascal’s LawUnlock the mechanics of the Hydraulic Braking System
Before we apply Pascal’s Law We must first review and be familiar with… • Diameter of a Piston • Radius of the Piston • Area of the top surface of the Piston Mathematically speaking… Diameter: The width of a circular or cylindrical object. Radius: The radius of a circle is half the diameter Area: Any particular extent of space or surface
Math – Hands on Practice • Measure across the top of the piston, through the center and record the diameter (inches) • Calculate the radius of the piston • Calculate the area of the top of the piston A = π · r · r orA = πr2
Area Example • Diameter = 7 inches • Radius = 3 1/2 inches • Area = ? A= π·r2 3.14 · (3 ½ in)2 = 38.465 in2 Area = 38.465 in2
Homework • Practice skill work • Read article: Effect of Oversize Tires on Braking Characteristics • www.aamva.org/Documents/ vehStudyEffectOfOversizedTiresOnAlteredHeightVehicles.pdf -
Pascal’s Law • In the 1600's, the French scientist Blaise Pascal discovered a fact now known as Pascal's Law. It states that pressure at any point in a body of fluid is the same in every direction, exerting equal force on equal areas. This works for gases and liquids (both are fluids).
Pascal’s Formula • This brings us to a very important formula: • P = Pressure, F = Force and A = Area This expresses that Pressure is Force per Unit Area. This is why pressure is usually expressed in pounds per square inch (psi).
Variations of Pascal’s Law • Pressure = Force divided by area • Force = Pressure times area • Area = Force divided by pressure
F =Force F PA P = Pressure A = Area
Have you used formulas like Pascal’s Law? Where are they used? • Generic Inverse Variation Problem used in Algebra • Time = Distance / Rate • Ohm’s Law used in science class with electrical components
Using Pascal’s Law Pascal's Law - gives us the mechanics to do a great deal of work with hydraulics. The drawing on the left shows that we can lift a large amount of weight with a small amount of effort. We can lift 100 pounds by applying just 10 pounds of force to the piston measuring 1 square inch
50 lbs force .5 sq in area of top of piston 50 lbs divided by .5 = 100 psi
Where might Pascal’s Law be used? • A twenty ton floor jack has a hydraulic piston with a 7 in diameter. • 60 pounds of force is being applied to the piston. • Calculate the line pressure being exerted on the piston.
Solving a Pascal’s Law problem • Which version of Pascal’s Law will you use? Pressure = Force divided by area • Recall from earlier….. A= π·r2 3.14 · (3 ½ in)2 = 38.465 in2 Area = 38.465 in2 • P = (60pounds) / (38.465 in2) P = 1.56 pounds/ in2 P = 1.56 psi
Using Pascal’s Law • A caliper piston has a diameter = 1.5 in • The Master cylinder has 50 pounds per square inch (psi) line pressure applied to it. • Determine the force exerted on the caliper piston.
Solving a Pascal’s Law problem • Which version of Pascal’s Law will you use? Force = Pressure times area • Recall how to find area….. A= π·r2 3.14 · (3/4 in)2 = 1.77 in2 Area = 1.77 in2 • F = (50pounds/ in2) (1.77 in2) F = 88.5 pounds
Remember Larry’s Truck …….. • The truck has a major braking problem. • You suggested earlier that we replace it with bigger brake parts… • What do we need to know about the original braking system? GIT-R-DONE
Facts about Larry’s Truck • ¼ in brake lines • ½ in bore master cylinder • 7/8 in bore wheel cylinders • 2 in caliper pistons
Can you fix Larry’s truck? • Devise a plan to fix Larry’s truck based on Pascal’s Law and your knowledge of automotive systems that will remedy Larry’s braking problems. • Be sure to show all calculations and justify your solution plan in a written paragraph. Remember Larry doubled the size of the original tire size…..
Be thorough..Larry is depending on you… • How would you • “Git-R-Done”? GIT-R-DONE