Trailing axle suspension system

A trailing axle suspension system for suspending a trailing axle with steerable wheels from a motor vehicle having a vehicle frame that is normally supported by primary axles with wheels and in turn supports a vehicle body with a tailgate wherein the vehicle frame is supported by the primary axles for rolling movement relative to a vehicle frame roll axis, and the maximum allowed load supported by the vehicle body has a center of gravity located below the vertical height of the vehicle body and at or substantially above the vertical mid-height thereof, said suspension system comprising

• a carriage from which the trailing axle is directly suspended wherein the carriage is pivotally connected to the vehicle body at locations outboard thereof and is adapted to locate the trailing axle in a stowed condition on the vehicle and in an active condition wherein the trailing axle is located at a substantial distance behind the vehicle with the steerable wheels engaging a road surface and the trailing axle is supported by the carriage for rolling movement relative to a trailing axle roll axis,
• a pair of hydraulically operated actuators pivotally connected at one end to the carriage and pivotally connected at an opposite end to the vehicle body adapted to establish the trailing axle in the stowed condition and in the active condition wherein the actuators apply force on the trailing axle to help support the vehicle frame,
• gas springs adapted with the trailing axle in the active condition to allow a prescribed range of swinging movement of the trailing axle relative to the vehicle frame to accommodate differences in road grade between the trailing axle wheels and the wheels of the primary axles, and
• the pivotal connections of the actuators with the vehicle body located forward of the tailgate and at a vertical height substantially above the center of gravity of the maximum allowed load supported by the vehicle body so that the minimum possible distance in height between the trailing axle roll axis and the pivotal connections of the actuators with the vehicle body is always greater than the maximum distance in height between the roll axis of the vehicle frame and the center of gravity of the maximum allowed load supported by the vehicle body within the prescribed range of trailing axle swinging movement allowed by the gas springs.