PIT Crew Design Concepts

By

Dan Chapman, Tim Wilson, and Jon Miller

December 11, 2002

Design Alternative 1

• Experimental Data– Air consumption for a given torque of lug nut

– Pressure vs. volume of tank assuming a constant mass of air

– Pressure and torque vs. breaking time

• Modification• Review

Air consumption and torque dataRegulator Pressure:

Breaking Time (seconds)

Volumetric Flow Rate:[SCFM]

Volume of air needed: ft^3

Lug Torque: [ft-lbf]

85 4.07 6.5 2.6455 8085 2.46 6.5 1.599 8085 4.60 6.5 2.99 8085 7.60 6.5 4.94 8085 2.23 6.5 1.4495 80

4.19 2.7248 Average

90 1.41 6.5 0.9165 8090 1.41 6.5 0.9165 8090 2.26 6.5 1.469 80

1.69 1.100666667 Average

95 7.57 6.5 4.9205 8095 2.48 6.5 1.612 8095 3.36 6.5 2.184 8095 2.37 6.5 1.5405 80

3.95 2.56425 Average

100 3.13 6.5 2.0345 80100 1.87 6.5 1.2155 80100 1.76 6.5 1.144 80100 1.59 6.5 1.0335 80

2.09 1.356875 Average

(cont’d)

Total amount of air required for 6 lug nuts

massair = 1.284 [lbm]massair = 1.284 [lbm] m = 0.07135 [lbm/s] P1 = 112 [psia]Q = 0.125 [ft3/s] = 0.5708 [lbm/ft3] T1 = 70 [F]time = 18 [s] Volume = 2.25 [ft3]

massair = 1.284 [lbm]massair = 1.284 [lbm] m = 0.07135 [lbm/s] P1 = 112 [psia]Q = 0.125 [ft3/s] = 0.5708 [lbm/ft3] T1 = 70 [F]time = 18 [s] Volume = 2.25 [ft3]

Solution:

Solving for total mass of air needed

for the impact wrench for 6 lug nuts

Air flow from experiment

assumes an average flow of 7.5 scfm

Q = 7.5

60[ft3/s]

= ('Air' , T=T1, P=P1)

T1 = 70 [F]

P1 = 112 [psig]

m = · Q [lbm/s]

Finding total mass of air required

assuming 3 seconds per lug and 6 lugs

time = 3 · 6 [s]

massair = m · time [lbm]

Pressure vs. Volume of Tank

Assumes constant mass of air (1.214 lbm found from previous slide, [100 ft*lb of torque])

0 1000 2000 3000 4000 5000 60000

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0.5

0.55

0.6

P [PSIA]

Vre

al,

Vid

eal [

ft^3]

Real Air Density Properties

Ideal Air Density PropertiesIdeal Air Density Properties

Pressure vs. Breaking torque

0.000.50

1.001.50

2.002.50

3.003.50

4.004.50

0 1 2 3 4 5 6 7 8

run number

brea

king

tim

e (s

)

breaking time at 105 psi and 80 ft-lb breaking time at 105 psi and 100 ft-lb

breaking time at 100 psi and 80 ft-lb breaking time at 100 psi and 100 ft-lb

Breaking time at 5 psi increments(constant torque of 80ft-lb)

psi

Modified Chicago Pneumatic Impact Wrench

Developed to experimentally determine the effect of changing the moment of inertia of the “Hammer” on wrench performance.

Review of Alternative 1

Strengths:

• Impact design requires very little strength by user

• Impacting mechanism has already been designed

Concerns:• Consumes a large

amount of air• Will need pressures

approaching 6000 psi to contain the needed amount of air in a standard bottle for 6 lug nuts

• Will need more air to remove bolts torqued higher than 100 ft*lb

Design Alternative 2

• Pressurized Air Canister

• Air Piston with spring return

• Moment Arm

• Ratchet

• Bracing Attachment

Features:

Pressurized Air Canister

• Could contain up to 2000 psi of air

• Would be able to push piston about 90 times

• Enough air for 6 lug nuts

• Already designed by Autoliv

• Would also incorporate a pressure regulating device

Air piston

• With a bore of 2.5 in and a pressure of 90 psi piston will deliver 400 lb of force

• It will also have a spring return that will force the air out and pull the piston arm back

Moment arm

• Will be about 5 in long

• Using the 400 lb force from the piston, it will deliver a 170 ft*lb torque on the lug nut

Ratchet

• Allows piston to return to starting position without retightening the lug nut

• Attaches to moment arm

Bracing attachment

• It will attach to another lug nut

• The whole tool will now be attached to two lug nuts

• This will allow the piston to apply a large torque to the tightened lug nut without the user having to hold on and resist the torque

Review of Alternative 2Strengths:• Requires very little

physical strength• With adjustable

attachment, user does not have to resist applied torque

• 3 step usage•Attach air canister•Attach to lug nut•Activate

Concerns:• Manufactured piston

is relatively expensive• Safety issues involved

with pressures of 2000 psi

Design Alternative 3

Components• Air canister• Valve• Piston• Rack &

pinion• Stand

Rack and pinion transmits about 160 ft-lbs torque to lug

Piston is 50mm diameter, outputs 441lbf at 145 psi Consumes about 55 in3 of air per stroke

Rack and piston• Piston will be 50mm bore with 100mm

stroke, and provide about 440lbf output.

Actuati

on d

irecti

on

F out =

440l

bf

Rack and pinion • Rack and pinion will provide a moment arm of

4.75” and deliver a torque of about 175 ft-lbs.• The output will be a 0.5” or 0.375” square drive

(like the impact wrench).Torque = 175ft*lb

Socket driver

Stand• Keeps components accurately positioned

(dimensions are in inches)• Eliminates need for customer to provide the necessary

resisting torque by an adjustable lug nut attachment

Review of Alternative 3

Strengths:

• No need for user applied resistant torque.

• 3 step usage: attach canister, lug nut, activate

Concerns:

• Removes 6 lugs per canister of air (if canister is at 3000 psig)

• Much larger than existing equipment

Design Alternative 4Pneumatic Torque Actuator

• Pressurized air canister

• Torque actuator

• Gearing to turn all lugs at once

double-acting cylinder

Internal rack and pinion

• Single piston would activate a rack and pinion

• At a regulated pressure of 75 psi, it will deliver about 200 ft*lb shaft torque*

• Displaced volume is about 365 in3

• At an initial bottle pressure of 1500 psi there would be just enough air to remove 1 lug nut

* = Calculations were performed with a single cylinder model similar to the annotated one above

Review of Alternative 4Strengths:• Could potentially turn all four to six lug

nuts at once (the actuator has very high torques but at cost of much higher pressure)

• Removal of all lug nuts at once would require an adapter that would only fit certain wheels—specialized product for each car manufacturer

• Simple design mainly uses existing components but could be redesigned for a limited use application

• Compact design• Current models available on the market

Concerns:

• Air consumption quite high (7” bore and a 9” stroke)

• Would require a starting pressure of about 11,000 psi to remove 6 lug nuts

• Safety issues involved with using pressures around 11,000 psi

• Larger than existing equipment

Appendix

• Current Market Concepts and Products– Geared Air Motors– Torque multipliers– Electric Impact Wrench– EZ-Lug

• Impact wrench modification and description• Energy required to remove a lug nut• Order numbers for air piston and torque

actuator

Geared Air Motors

Atlas Copco Air Motors

Model Min. starting torque [lbf. Ft]

Air consumption at max. power [scfm]

Weight [lb]

Free speed [rpm]

Direction Cost

LZB 33 AR0003-11 170 18 11 25Reversible Obs.

LZB 42 AR0006-11 125 28 10.7 55 Reversible $1,640.00LZB 42 AR0004-11 199 28 10.7 35 Reversible $1,640.00LZB 42 AV0008-11 200 28 10.7 75 Counter $1,640.00LZB 46 AR0006-11 140 30.7 10.8 62 Reversible $1,700.00LZB 46 AV0012-11 150 35 6 120 Counter $1,300.00LZB 54 AR0009-11 122 37 10.3 90 Reversible $1,680.00LZB 54 AV0012-11 180 53 10.3 125 Counter Obs.

Product data at air pressure 6.3 bar (91 psi)

WWW.ProductiveTool.Com

Cost data from: Productive Tool Products, Inc.

LZB 46 AV0012-11

LZB 42 AR0004-11

Other Torque Multipliers

Eliminator HG by etorque.com which uses gears

Square drive Hydraulic Torque Machine by TorcUp, which is attached to a hydraulic compressor

Industrial duty torque tools available.

Electric Impact Wrench

• Connects to cigarette lighter• Max. torque: 150 ft. lbs. • 10 to 20 impacts per minute • 3.8 amps at peak load• Reversible rotation• Socket sizes: 11/16'', 3/4'', 13/16''

and 7/8''. • $19.95 at Harbor Freight

EZ-LugMechanical Advantage using Gears

• Uses 32:1 Gearing

• Low Cost ($50 to $60)

• Light Weight (3 pounds)

• Very Compact

Assembly of existinghammer design

Hammer Dog

Socket Adaptor

Anvil

Hammer Cage

Assembly of Modified Hammer Design

Steel Collar (increases moment of inertia)

Assembly of Current Rotor (Gas Turbine)

Final Assembly as Shown in Design Alternative 1

Energy Required to Remove a Lug Nut

50 60 70 80 90 100 110 120 130 140 150100

200

300

400

500

600

700

800

900

1000

1100

1200

Theoretical Energy to Remove a Lug NutDimensions from a Typical Passenger Vehicle

Torque Applied to Nut [ft*lbf]

Ene

rgy

Req

uire

d to

Rem

ove

Nut

[Jo

ules

]

Component callouts

Piston cylinder for design alternative 3:

Bimba: A-50-100-D

Torque Actuator:

FLO-TORK: A-4000-184-OO-ET-MS1-X-CCW-SR

Piston cylinder for design alternative 2:

FESTO: 160655, (2½” bore)