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Power Transmission Elements
Published in Godfrey C. Onwubolu, Introduction to SOLIDWORKS, 2017
A rack is a toothed bar or rod that can be thought of as a sector gear with an infinitely large radius of curvature. Torque can be converted to linear force by meshing a rack with a pinion: the pinion turns; the rack moves in a straight line. Such a mechanism is used in automobiles to convert the rotation of the steering wheel into the left-to-right motion of the tie rod(s). Racks are also featured in the theory of gear geometry, where, for instance, the tooth shape of an interchangeable set of gears may be specified for the rack (infinite radius), and the tooth shapes for the gears of particular actual radii are then derived from that. The rack and the pinion gear type is employed in a rack railway.
Reliability of super-slope bridge-rack system on rack railway
Published in International Journal of Rail Transportation, 2023
Zhaowei Chen, Lang Wang, Shihui Li, Mi’ao Yuan, Qianhua Pu, Zhihui Chen, Jizhong Yang
At present, rack railway is the only rail transit system with large climbing capacity [1]. During the operation, strong interaction occurs between gear and rack, so the vehicle arouses large longitudinal force [2]. For ordinary railway vehicles, the maximum slope that the longitudinal force provided by wheel rail adhesion can climb is 40 ‰ − 60 ‰. When the slope exceeds the limit slope, the adhesion is insufficient due to the sliding of the wheel rail contact surface [3]. However, the maximum slope that rack vehicles climb by relying on gear-rack meshing can reach 480 ‰ [4], which provides an important means of transportation for the development of rail transit in a large number of mountainous areas in China. In 2019, Sichuan Province promulgated Sichuan Mountain (Rack) Rail Transit Plan, planning 23 rack transit lines, including a number of super-slope rack railways and super-slope bridge-rack structures. The structure is a viaduct with gaps formed by simply supported beams. The rail and rack are continuously laid on the sleepers, which is consolidated with the bridge (see Figure 1). Under temperature load, longitudinal deformations occur in rack and bridge [5–7]. However, the deformation of rack is small due to its structural continuity, hence the rack structure near the bridge gap does not adapt to the deformation of bridge, which may cause damage of rack and bolts of fasteners. At the same time, the gear-rack meshing and wheel-rail contact during vehicle operation can exacerbate the structural stresses generated in the rack system. This further leads to the structural performance of the bridge-rack system being affected and seriously threatens the driving reliability and comfort [8–10].