Energy Trade Offs and TIRESEnergy Trade Offs and TIRES10.17.0910.17.09

A presentation by:

Jason Greenblatt

B.S. in Mechanical EngineeringClean Transportation Analyst

Regional Utility Employed

Credit to

Shaw Lewisfor the initial presentation

Why Theorize Energy?Why Theorize Energy?

Energy is constantly lost while drivingAll parts of the car are constantly RESISTING motionEnergy loss and usage may be reduced

Where is this stuff called Energy?

Mechanical Energy• Bearings surfaces• Acceleration and Braking

Friction (non-regen) • Rolling Motion• Sidewall Flexion• Linear movement (driving)• Aerodynamic Drag

Tires have 5 out of 6!

Electrical Energy• High Voltage• Low Voltage• Resistance

Material property (i.e. copper)Mechanical connections (i.e.

bolted lugs, crimped cables, terminal blocks, plugs)

Chemical property (corrosion)Heat anywhere

What does Energy Look Like?Mechanical• Rotational Energy = (½)*Inertia*angular velocity2

• Linear Travel Energy = (½)*Mass*Velocity2

• Side wall Spring Energy = (1/2)*K spring constant *X2

(distance compressed)

Exponent means speed contributes more then mass!!Judge if smaller, shorter or narrower tires would suit your needs

Electrical• Energy = Volts*Amps*Time

Low Voltage, half hour driving, running the head lamps12 volts* 10amps* (1/2) Hour = 60 Watt Hours

High Voltage, 1 minute, 1 mile, 60mph, 120volts, 200amps120*200*(1/60 of an Hour)=

Lets compare some Driving

You can follow your amp guage to maintain constant current

  Volts Amps Time energy  

head lights for 20 minutes 12 10 .33 hour 40 Watt hours

1 mile at 45 mph, 1 minute 120 200 .022 hours 530 Watt hours

5 miles at 45 mph, 7 minutes 120 200 .1 hour 2400 Watt hours

15 consecutive miles at 45 mph 120 200 .3 hour 7200 Watt hours

Single 0-40mph acceleration 120 350 .003 hours 117 Watt hours

5 0-40mph accelerations 120 350 .015 hours 583 Watt hours

Watching your Energy Flow

Gauges are IMPORTANT; only if you need them

Use your gauge as an economy dial

Driving in lower gears will consume less energy

Watch the Amp Gauge in any gear

Cruising may should low amps (150-200amps)

Know vehicles limits, don’t push too hard up hills

The heavy EV may just not want to go faster uphill

Don’t waste juice trying to push it harder

Amp Guage relates to Controller

• Curtis Controller has following limits:

• Watching the Amp gauge to prolong Controller life

Curtis Controller 1231C-86xx  

Rating 2 Min 5 Min 1 Hour

Continuous Amps 500 375 225

LOW ROLLING RESITANCE TIRESLOW ROLLING RESITANCE TIRESShaw Lewis - EV Enthusiast, and Jason Greenblatt, Engineer

Take Stock of You’re Rolling Stock

Tires do the following:

Elevate a vehicle wheels from the ground

Support vehicle payload

Provide modest suspension damping

Accelerate and decelerate a vehicle

Provide cornering forces to steer a vehicle

Each vehicle has its own characteristics and drive cycle with unique needs

This will affect the choice of tire required or possible

Low Rolling Resistance tires are designed to improve fuel efficiency of a car (especially electrics) by minimizing the energy wasted as the tire rolls down the road.

A tire may not be marketed as LRR but may still qualify. Consider the following LRR attributes:

•Manufactured for higher pressures, 40-45 psi or above

•Additional sidewall construction plys (layers) will be stiffer

(light truck tires denoted as LT on tire sidewall)

•Higher Tread wear rating (harder rubber compound)

•Stable tread lug design, large lugs, more continuous shoulder

•Some vehicles may be able to use a narrower section width tire to put less material on the road surface and less drag through the air

General Definition

Air Pressure

• Based on vehicle curb weight– EV’s are typically heavy!

• Do not over inflate tire– Uneven tire wear

• Higher pressure resists sidewall deflection– Eats up energy, think of rubber bands

• Low Pressure increases road contact– Think of a mountain bike versus a road bike

• Increases cornering ability, maintaining speed

TREAD DESIGNS AND PATTERNSTREAD DESIGNS AND PATTERNS• Larger blocks are stable, avoid flexing and heat generation• Larger blocks can enhance handling, preserve cornering speed

• All weather tires may have more voids– Open areas create air drag

The more detailed the tread design, the more likely it will grip the road better. But this also creates the opportunity to trap air in each of the pockets when touching the road surface.

When trapping the air/water/dirt/snow in these pockets, the tire is compressing the material that is in the pocket. Therefore, the engine has to do more work to compress these pockets. This makes the tire less efficient to turn, and reduces the mileage of the vehicle.

It boils down to personal preference. For a sporty ride you might want softer rubber with better road adhesion. If you’re a fanatic for mileage and a very mellow driver, then you may want the lowest resistance tire you can find on the market.

Economy and Sport Traction can some times go hand in hand

Show models of tires with tread design

BFGoodrich g-Force T/A KDW 2

50psiI

Dunlop Direzza DZ101

50psi

TREAD DESIGNS AND PATTERNSTREAD DESIGNS AND PATTERNS

TIRE PRESSURETIRE PRESSURELRR tires make an important difference, but they will not

be as important as having your tires properly inflated.

KEY INFORMATION FOUND ON TIRESKEY INFORMATION FOUND ON TIRES

Don’t forget your wheelsThese guys rotate, translate and spin

Tirerack.com is awesome for details

Average Weight of Wheel Size

10

12

14

16

18

20

22

24

16x7.5 16x7 16x6.5 15x7 15x6.5 14x6

lbs

CAUTIONCAUTIONA tire with stronger LRR characteristics may be less safe in adverse weather conditions

orsafer in good driving conditions.

If the tire is over inflated (too round), the tire-patch (the area of tire that is in contact with the ground) will be too small to grip the road surface effectively. This in turn will allow the wheel to skid easier when trying to stop or allow the wheel to slip and spin when accelerating from a stop.

If using Stock tires pay attention to recommended tire pressure on your vehicle

Pay particular attention to ratings displayed directly on the tire itself

For typical EV conversion tires, consider these characteristics:•Manufactured for higher pressures, 45 psi or above •Additional sidewall construction plys (layers) will be stiffer

(light truck tires denoted as LT on tire sidewall)•Higher Tread wear rating (harder rubber compound)•Low Rolling Resistance tires are designed to improve fuel efficiency of a car (especially electrics) by minimizing the energy wasted as friction as the tire rolls down the road.

Some vehicles may be able to use a narrower section width tire to put less material on the road surface

•Pay attention to how heavy your car is and the load capacity of each tire.•The weight balance front to rear of the car needs to be considered when choosing tires as well so as not to underrate a tire.

CONCLUSIONCONCLUSION

Appendix

• Moment of Inertia I=Mass* Radius2

• Radius is taken as the CENTER of Mass

• Average Radius can be estimated for tread section

Sidewall section

Vehicular PhenomenaVehicular PhenomenaTransportation in California represents nearly 40% of Carbon Dioxide emissions

Combustion engines are typically less then 25% efficient

referencesCombustion engine efficiency picture

http://ffden-2.phys.uaf.edu/102spring2002_Web_projects/Z.Yates/Zach%27s%20Web%20Project%20Folder/EICE%20-%20power%20losses.htm