Minimum Vehicle–Guideway Clearances Based on a Contact Frequency Criterion

Abstract

An important consideration in the design of air cushion and magnetic suspensions is the power required to suspend or levitate the vehicle in equilibrium. Since this power level increases with an increase in the equilibrium clearance between the base of the suspension and the guideway, it is desirable to keep the design clearance as small as possible. Ideally, the base of the vehicle would never contact the guideway. Statistically, however, contact does occur and to establish a general criteria for defining minimum clearances based on the frequency of contact would be extremely difficult since the effects of contact, such as noise, vibration, wear, etc., vary with different design configurations and materials. The criteria of a very low average contact frequency (10−3 contacts/sec) is used in this paper to define the lower bound on vehicle-guideway clearance. Results are tabulated for an optimum suspension with heave dynamics and guideway irregularity inputs only. The sensitivity of the minimum clearance to guideway irregularity amplitude and wavelength characteristics and to RMS levels of primary suspension acceleration (force) levels is demonstrated. The results indicate that equilibrium clearances on the order of 0.03 in. are tolerable for operation over guideways as smooth as welded rail and that clearances on the order of 1.5 in. may be required for operation over guideways as rough as smooth highways.