The Effect of a Suspension on Off-Road Traction - an Investigation Using a Single Wheel Tester

摘要

The paper reports the initial results of experiments investigating the effect of wheel vibration on traction using a 495/70 R24 XM47 radial tyre and coil spring and damper suspension as used on high mobility agricultural tractors. Traction and vibration data were collected using a single wheel tester operating on a compacted sandy loam soil in a ground level soil tank. The general approach to this investigation has been to consider the tyre and load (with suspension locked out) as a one degree of freedom vibration system and the tyre, unsuspended mass, suspension and suspended mass as a two degree of freedom vibration system. These vibration systems were subjected to a ground displacement sine wave input and the resulting vibration output and drawbar pull measured. A sine wave was cut into the soil surface. A track vibration input amplitude of ±5 mm to ±7 mm and a wavelength of 0.76 m were used. Tyre pressures of 1 bar and 2 bar were used. The range of forward speeds included input vibration at the tyre's natural frequency. A wheel static load of 2060 kg was compared with the control load of 1560 kg. The tyre characteristics of dynamic radial stiffness, damping, and vibration amplitude transmissibility were determined. Drawbar pull data were collected with the suspension active and locked out of use. For the sandy loam soil and tyre used, the main conclusions were that the greatest variation of drawbar pull was found at the tyre's natural frequency and at the higher tyre pressure of 2 bar, at a wheel load of 1560 kg with the suspension locked out of use. Increasing the wheel load to 2060 kg with the suspension locked out of use had a large effect in reducing the draw bar pull variation but not as large as reducing the tyre pressure to 1 bar. Reducing tyre pressure increased tyre damping and increasing the tyre load also increased tyre damping. The suspension had a large effect in reducing the variation in drawbar pull at the higher tyre pressure of 2 bar and the wheel load of 1560 kg but had little effect at a tyre pressure of 1 bar. As the input frequency reduced towards the natural frequency of the spring and sprung mass the draw bar pull variation increased to be comparable or greater than with the suspension locked out of use. The drawbar pull variation with the suspension active was found to be very similar over the input frequency range for all the combinations of tyre pressure and load used. The effect of longitudinal tyre stiffness and damping and longitudinal soil effects require further investigation as do wheel and vehicle inertia effects.