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DEPARTMENT OF FOREST WORK SCIENCE AND ENGINEERING GEORG-AUGUST-UNIVERSITY GÖTTINGEN
Dr. JÖRG HITTENBECK – TEL +49-551/39-33578 – E-MAIL [email protected]
CONTACT PRESSURE ALLOCATION UNDER BOGIE AXLES
„Established“ characteristics?
• Tires
– increased ground pressure
– reduced traction
– deep ruts
• Tracks
– increased contact area
– reduced ground pressure
– increased traction
18.09.2016 FORMEC 2016 – Contact Pressure Allocation under Bogie Axles 2
Source: www.clarktracks.com/assets/files/brochures/product1/de_Clark _Tracks_Brochure_LR.pdf (28.08.2012)
Concepts on contact pressure under tracks
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Nominal Ground Pressure (Mikkonen and Wuolijoki, 1975)
Matthies (2008)
Blr
Fp N
*)*25,1(
Bl
Fp N
**2,0
results differ with the factor 10 (0,2 bar vs. 2,2 bar)
p = pressure
FN = axle load (kN)
r = wheel radius
l = distance between wheels
B = width of tracks
PrAllCon – Test design
Bildquelle: EBEL (2006)
Test design
70 tires (forestry) from 5 manufacturers
5 wheel loads (10 - 50 kN) 7 inflation pressures
(0,5|1,0|1,5|2,0 - 5,0 bar) different „undergrounds“
(„hard“ | „soft“) additional test series
(filled with water; brush cover)
18.09.2016 FORMEC 2016 – Contact Pressure Allocation under Bogie Axles 4
Measurement system
tekscan foil sensor resolution of 0.7 cm²
-> pressure distributes bell-shaped Factors of influence: wheel load, tyre inflation pressure, tyre width, and tyre diameter
PrAllCon - Results
Bildquelle: EBEL (2006)
„hard“
-> „Sidewall effect“ at lower inflation pressures
„soft“
vgl. JACKE (2008) 18.09.2016 FORMEC 2016 – Contact Pressure Allocation under Bogie Axles 5
PrAllCon-Track: Requirements
replication of a bogie axle different wheel bases possible wheel loads of up to 70 kN comparability to PrAllCon (for single tires)
Bildquelle: EBEL (2006)
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PrAllCon-Track: Experimental design
1 only for rim diameter 22.5 inch 3 only for 600 mm (tire-) width 2 only for rim diameter 26.5 inch, 4, 5 only for 710 mm (tire-) width
Parameter Variants “Values”
(tire-) Width 2 600 | 710 mm
Tread pattern (type) 1 Soft
Rim diameter 2 22.5 | 26.5 inch
Inflation pressure 1 4,5 bar
Wheel load 3 30 | 50 | 70 kN
Wheel base 2 1.3001 | 1.500 | 1.7002 mm
Track (type) 33, 44 OF | TRACK | MAGNUM | EVO5
Track tension 2 Centre sag acc. to manufacturer advice (4 - 8 cm) | reduced tension (+ 50 %)
Replications 3
Source: Manufacturer
Nokian
18.09.2016 7
Pressure allocation under track
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Magnum 70 kN (710 mm)
No track 70 kN (710 mm)
Pressure allocation under track (Video)
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What determines the average contact pressure
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Step Regressor R² ΔR²
1 Auflast 79,0 % 79,0 %
2 Nennbreite 82,3 % 3,3 %
3 Magnum 84,6 % 2,2 %
4 OF 85,8 % 1,3 %
5 Track 90,8 % 4,9 %
Method: Autoselective regression (stepwise) with covariant analytic regressors for all track types. Filter: 22.5-rim with wheel distance 1,3 m, 26.5-rim with wheel distance 1,5 m. EVO-track is not taken into analysis, as he tire width 710 mm would have been overrepresented (EVO was tested only for wider tires)
Effect compared to tires (4,5 bar)
Step Regressor R² ΔR²
1 Wheel load 79,0 % 79,0 %
2 Tire width 82,3 % 3,3 %
3 Magnum 84,6 % 2,2 %
4 OF 85,8 % 1,3 %
5 Track 90,8 % 4,9 %
Step Regressor R² ΔR²
1 Wheel load 79,0 % 79,0 %
2 Tire width 82,3 % 3,3 %
3 Magnum 84,6 % 2,2 %
4 OF 85,8 % 1,3 %
5 Track 90,8 % 4,9 %
• The pressure reduction does not change much with the tire width
• The relative effect decreases with increasing wheel load
A comparsion of effects
18.09.2016 FORMEC 2016 – Contact Pressure Allocation under Bogie Axles 11
Tracks
Tire-width 600 mm 710 mm Wheel load [kN] 30 50 70 30 50 70
No track [bar] 1,199 1,559 1,919 1,078 1,438 1,798
Magnum 26 20 16 28 21 17
Of 21 16 13 23 17 14
Track 20 15 13 22 17 13
Tire-width 600 mm / Rim 22.5 710 mm / Rim 26.5 Wheel load [kN] 30 50 70 30 50 70
4,5 bar (Reference) 1,3 1,8 2,3 1,2 1,7 2,2
2,0 bar 23 17 13 17 12 14
1,5 bar 23 22 17 25 18 14
1,0 bar 38 28 22 33 24 23
Reduction of tire inflation (PrAllCon „old“)
Differences between track types
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Step Regressor R² ΔR²
1 Wheel load 90,7 % 90,7 %
2 Track 92,0 % 1,3 %
3 OF 93,6 % 1,6 %
X Track tension
Method: Autoselective regression (stepwise) with covariant analytic regressors for track types TRACK and OF (at 700 mm including EVO) Filter: 22.5-rim with wheel distance 1,3 m, 26.5-rim with wheel distance 1,5 m, only tests with tracks.
600 mm tire width
Step Regressor R² ΔR²
1 Wheel load 90,2 % 90,2 %
X Evo
X Track
X OF
X Track tension
710 mm tire width
(Especially flotation) Tracks lead to a reduction of the measurable contact pressure. The pressure reduction effect of tracks decreases with increasing wheel load. The advantage of flotation tracks can not be verified for tires with 710 mm width. A comparable effect (to tracks) on contact pressure can also be achieved by reduction of tire inflation pressure. This is valid for the measured pressure in static conditions. According to the creation of rutting only the vertical load is taken into account – not the (horizontal) shear stress.
Some assumptions from PrAllCon-Track
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