DEPARTMENT OF FOREST WORK SCIENCE AND ENGINEERING GEORG-AUGUST-UNIVERSITY GÖTTINGEN CONTACT PRESSURE ALLOCATION UNDER BOGIE AXLES

Transcription

1 DEPARTMENT OF FOREST WORK SCIENCE AND ENGINEERING GEORG-AUGUST-UNIVERSITY GÖTTINGEN CONTACT PRESSURE ALLOCATION UNDER BOGIE AXLES Dr. JÖRG HITTENBECK TEL /

2 Established characteristics? Tires increased ground pressure reduced traction deep ruts Tracks increased contact area reduced ground pressure increased traction Source: _Tracks_Brochure_LR.pdf ( ) FORMEC 2016 Contact Pressure Allocation under Bogie Axles 2

3 Concepts on contact pressure under tracks Nominal Ground Pressure (Mikkonen and Wuolijoki, 1975) p FN ( 1,25* r l)* B p = pressure F N = axle load (kn) Matthies (2008) FN p 0,2* l * B r l B = wheel radius = distance between wheels = width of tracks results differ with the factor 10 (0,2 bar vs. 2,2 bar) FORMEC 2016 Contact Pressure Allocation under Bogie Axles 3

4 PrAllCon Test design 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) Measurement system tekscan foil sensor resolution of 0.7 cm² Bildquelle: EBEL (2006) FORMEC 2016 Contact Pressure Allocation under Bogie Axles 4

5 PrAllCon - Results hard soft Bildquelle: EBEL (2006) -> Sidewall effect at lower inflation pressures -> pressure distributes bell-shaped Factors of influence: wheel load, tyre inflation pressure, tyre width, and tyre diameter vgl. JACKE (2008) FORMEC 2016 Contact Pressure Allocation under Bogie Axles 5

6 PrAllCon-Track: Requirements Bildquelle: EBEL (2006) replication of a bogie axle different wheel bases possible wheel loads of up to 70 kn comparability to PrAllCon (for single tires) FORMEC 2016 Contact Pressure Allocation under Bogie Axles 6

7 PrAllCon-Track: Experimental design Parameter Variants Values (tire-) Width mm Tread pattern (type) 1 Soft Rim diameter inch Inflation pressure 1 4,5 bar Wheel load kn Wheel base mm Track (type) 3 3, 4 4 OF TRACK MAGNUM EVO 5 Track tension 2 Centre sag acc. to manufacturer advice (4-8 cm) reduced tension (+ 50 %) Replications 3 Source: Manufacturer Nokian 1 only for rim diameter 22.5 inch 3 only for 600 mm (tire-) width only for rim diameter 26.5 inch, 4, 5 only for 710 mm (tire-) width 7

8 Pressure allocation under track No track 70 kn (710 mm) Magnum 70 kn (710 mm) FORMEC 2016 Contact Pressure Allocation under Bogie Axles 8

9 Pressure allocation under track (Video) FORMEC 2016 Contact Pressure Allocation under Bogie Axles 9

10 What determines the average contact pressure Effect compared to tires (4,5 bar) Step Regressor R² ΔR² 1 Wheel Auflast load 79,0 % 79,0 % 2 Nennbreite Tire width 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) FORMEC 2016 Contact Pressure Allocation under Bogie Axles 10

11 A comparsion of effects Tracks Tire-width 600 mm 710 mm Wheel load [kn] No track [bar] 1,199 1,559 1,919 1,078 1,438 1,798 Magnum Of Track Reduction of tire inflation (PrAllCon old ) The Tire-width pressure reduction 600 mm does / Rim not 22.5 change 710 much mm with / Rim the 26.5 tire width The relative effect decreases with increasing wheel load Wheel load [kn] ,5 bar (Reference) 1,3 1,8 2,3 1,2 1,7 2,2 2,0 bar ,5 bar ,0 bar FORMEC 2016 Contact Pressure Allocation under Bogie Axles 11

12 Differences between track types 600 mm tire width Step Regressor R² ΔR² 1 Wheel load 90,7 % 90,7 % 2 Track 92,0 % 1,3 % 3 OF 93,6 % 1,6 % X 710 mm tire width Track tension Step Regressor R² ΔR² 1 Wheel load 90,2 % 90,2 % X X X X Evo Track OF 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 FORMEC 2016 Contact Pressure Allocation under Bogie Axles 12

13 Some assumptions from PrAllCon-Track (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 FORMEC 2016 Contact Pressure Allocation under Bogie Axles 13