Driver response at tyre blow-out in heavy vehicles & the importance of scrub radius

Abstract

Front tyre blow-outs lead to several fatal accidents involving heavy vehicles. Common for most heavy vehicles is a positive scrub radius. This can result in a destabilising steering wheel torque at front tyre blow-out. In this study the safety improvement achieved when reducing scrub radius is quantified. By using a heavy truck equipped with a modified electric power steering system it was possible to change the scrub radius virtually. Brakes were configured to emulate front tyre blow-out which appeared as a sudden disturbance on one of the front tyres. In total 20 drivers took part in the study which was run on a test track at 50 km/h. Results show that the produced average lateral deviation from the original direction was 23 cm, when scrub radius was 12 cm, compared to 16 cm, when scrub radius was 0 cm. The main cause of the observed difference was a small, yet significant, initial overshoot in steering wheel angle which can be derived from the destabilising steering wheel torque.

Advanced emergency braking under split friction conditions and the influence of a destabilising steering wheel torque

“…The steering wheel angle response is of course central when considering a steering wheel disturbance, so it deserves some more attention. In [16] where a similar comparison was performed, but instead considering front tyre blow out producing 3 Nm of disturbance and including roughly the same number of subjects, a small overshot was seen caused by the disturbance after 0.3-0.5 s. This is also what could be expected from a destabilising steering wheel disturbance arising from an emergency braking event on a split-µ surface where asymmetric braking force act on the two front wheels. In fact this can be dimly seen also here.…”

“…The tractor unit was configured to perform emulated automatic split-µ braking and the kingpin offset at ground was varied virtually. The test was run in connection with the automatic brake test described in [8] and the tyre blow out test described in [16]. This section will describe the set-up of the test and also what precautions were taken in order to guarantee safety.…”

“…As the drivers were less surprised in the following runs speeds up to 70 km/h were considered as safe. As seen in Table 3 some exposures of emulated front tyre blow out were also incorporated into the experiment; this part has been reported in [16] and will not be treated herein. Group A Group B Figure 3.…”

“…This is the case for example under split-µ braking and also front tyre blow out. In [16] a study was performed to quantify the importance of r k during tyre blow out. An experiment was run with a solo tractor on a test track including 20 drivers.…”

“…• Measure experimentally the lateral path deviation of a tractor unit subjected to unexpected and repeated AEBS split-µ events, for a wider range of drivers (24) than previously investigated [8]; • Deduce the influence of positive kingpin offset on the lateral path deviation of the tractor unit during the AEBS split-µ events. The effect of kingpin offset was previously only investigated for a tyre blow out scenario [16]; • Use a driver-vehicle model [18] incorporating neuromuscular dynamics to aid deeper explanation of the observed behaviour of the driver and vehicle. Such a model has not been used previously for the scenario of a heavy truck in AEBS split-µ events.…”