The Car de Luxe was an American automobile manufactured from 1906 until 1910. A sister marque to the Queen, the Car de Luze had overhead valves which were operated by one rocker per cylinder. The 40/50 hp, 6755 cc car was actuated by a "push-pull" rod and an unusual back axle; the load was further taken by an I-beam dead axle which carried a separate differential unit. This article or section does not cite its references or sources. ... An axle is a central shaft for a rotating wheel or gear. ... I-beams are beams with an I- or H-shaped cross-section. ... A differential can mean one of several things: Differential (mathematics) Differential (mechanics) Differential signaling is used to carry high speed digital signals. ...

Reference

David Burgess Wise, The New Illustrated Encyclopedia of Automobiles.