Transcript Trucks and Loaders - Supplemental Teaching Resources

Next Part of Step II
Determining Peak Speed
©Dr. B. C. Paul 2000 revised 2008
Note – The methods outlined here are typical of widely known
published engineering practices. The slides contain
information taken specifically from the Caterpillar Performance
Handbook and screen shots taken from the FPC computer
program developed by Caterpillar Equipment Company.
Identify Peak Vehicle
Speeds
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Peak Vehicle Speeds are a
function of power a gearing and
the resistance to vehicle travel
Resistances are
• Grade resistance - overcoming (or
benefiting from gravity)
• Rolling Resistance - from flexure
of tires and road
• Wind Resistance
Review of Resistance
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Wind Resistance not normally
an issue for haul trucks common practice to ignore
Grade Resistance
• Good old physics problem where
break forces into components
2000 * sin (pheta)
Simplifying Grade
Resistance
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Tan (θ) = Rise / Run
At Slopes less than about 20%
Tan (θ) = Sin(θ)
Adjusting for Percentage Grade
instead of rise over run
• 20 lbs/ton * % Grade = Grade Res.

We just took the Trig out of
Grade Resistance Calculations
Rolling Resistance
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Tires Sink into Ground - softer
ground sink more
Tires Flatten
Driving uphill out of a rut on a
flat tire spot
Need to Know Underfoot
conditions and Type of Tire
(Radial or Bias Ply)
Data Comes From an All
Knowing Table
Reading the Table
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Note that Table Gives either
lbs/ton or % Grade
One way to treat rolling
resistance is as a equivalent
grade
• Puts in the same units as grade
resistance so they are additive
Two Ways of Totaling
Resistance

Equivalent Grade Method
• Take Grade in %
• Add Equivalent Grade for Rolling
Resistance
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Lbs Resistance method
• Tons Weight * 20 * % Grade
• Plus Tons Weight * lbs/ton rolling

Note That with Down Hill both
can be negative
Converting Between

To Convert Total Resistance in%
Grade to lbs
• Weight in tons * 20 * % eqiuv
Grade - lbs Resistance

To Convert Total lbs Resistance
to % Grade
• lbs / 20 / Weight in tons = % Grade

I’ll leave you in suspense
wondering why we care
Getting Rolling Resistance
for our FPC Example

FPC Uses the %
Grade System
Assume I have a firm smooth
Road with tires not sinking in
About 2.5% for bias ply tires
Entering into FPC
I had my grade
Resistance from my
Haulage profile
Description.
I added my rolling
Resistance of 2.5%
Peak Speed the Manual
Way

Cat 773B 58 ton Mechanical
Hauling Dolomite
• 77 foot Turning Radius so it can make
the 85 foot switch back
• 44.6 yards heaped capacity * 2600
lbs/yd3 = 57.8 tons Good match

For the level Run
• Grade Resistance is 0%
• For hard pack earth 4.25%
• Total is 4.25% Grade
Expressed as Lbs
Resistance
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Calculated as Lbs Resistance
43.5 tons Empty (from Cat Book)
* 20 lbs/ton
* 0% Grade
0 lbs Grade Resistance
43.5 tons * 85lbs/ton = 3697.5
lbs
Total 3697.5 lbs Resistance
Peak Speed Established
by Gradability Chart
Read Down the Grade Line
To the Intersection With the
Weight Line
Read Over to Gear Curve
Read Down to the Speed
Speed is 40 mph in 7th
Gear
By the Rimpull or Lbs
Resistance Method
Take Calculated Rimpull
Requirements (3698 lbs)
and go to Rimpull Scale on
Chart
Read over to Gear Line
Read down to Speed
Conclude Peak Speed is
40 mph in 7th Gear
Checking Other Peak
Speeds

Ramp -10% grade
• -10% Grade
• + 4.25% Rolling Resistance
• Total = - 5.75%
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Convert to lbs
• -5.75% * 20 * 87000/2000 = -5002.4
lbs
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Time to Go to the Chart
Holly Marshmellowed Jelly
Beans! Theres no Scale for a
negative Grade!
Enter the Retarder Chart
(No I didn’t Say Retarded)
Read Down the Net Favorable
Grade to the Truck Weight Line
Read Over to Gear Curve
Read Down to the Speed
Conclude 40 mph in 7th Gear
Things to Note About
Chart Reading

Some Charts Allow Either Grade
or Rimpull Method
• Cat Gradability Chart Allows Either

Some Allow Only One of the
Two Methods
• Cat Retarder Chart Allows Only
Favorable Grade

Since it Varies by Manufacture,
you must know both methods
More Notes
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For the Grade Method we read
down either the empty or full
weight line
• For a volume limited truck the
loaded truck may not weigh full
gross weight so you can’t use preprinted line - you must use actual
loaded weight
• Some bed liners alter empty
weight
Manufactures Also Have
Brake Performance Charts
Note That the Charts Differ in Braking Distance
Looking at the Total Negative Grade Distance in a cycle to
determine length - Not just grade for the chosen haul segment
How Does FPC do This
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All the curves are programmed
into FPC for Caterpillar
Equipment
You have to input the curves for
non-Caterpillar equipment.