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Advanced Vehicle Technology Episode 2 Part 5

Tham khảo tài liệu 'advanced vehicle technology episode 2 part 5', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 8.1.2 Grip control Factors influencing the ability of a tyre to grip the road when being braked are a the vehicle speed b the amount of tyre wear c the nature of the road surface d the degree of surface wetness. Vehicle speed Fig. 8.4 Generally as the speed of the vehicle rises the time permitted for tread to ground retardation is reduced so that the grip or coefficient of adhesive friction declines Fig. 8.4 . Tyre wear Fig. 8.5 As the tyre depth is reduced the ability for the tread to drain off water being swept in front of the tread is reduced. Therefore with increased vehicle speed inadequate drainage will reduce the tyre grip when braking Fig. 8.5 . Road surface wetness Fig. 8.6 The reduction in tyre grip when braking from increased vehicle speed drops off at a much greater rate as the rainfall changes from light rain producing a surface water depth of 1 mm to a heavy rainstorm flooding the road to a water depth of about 2.5 mm Fig. 8.6 . Road surface texture Fig. 8.7 A new tyre braked from various speeds will generate a higher peak coefficient of adhesive friction with a smaller fall off at the higher speeds on wet rough surfaces compared to braking on wet smooth surfaces Fig. 8.7 . Fig. 8.5 Effect of speed on relative tyre grip with various tread depth when braking on a wet road Fig. 8.6 Effect of speed on relative tyre grip with various road surface water depths Fig. 8.7 Effect of speed on the coefficient of adhesive friction with both wet rough and smooth surfaces The reduction in the coefficient of adhesive friction when braking with worn tyres on both rough and particularly smooth wet surfaces will be considerably greater. 8.1.3 Road surface texture Fig. 8.8 A road surface finish may be classified by its texture which may be broadly divided in macrotexture 272 Fig. 8.8 Terminology and road surface texture which represents the surface section peak to valley ripple or roughness and microtexture which is a measure of the smoothness of the ripple contour Fig.