granddaddylow:
I was sent out with an 18.65m trailer the other day. Went well enough once I worked out that there was a button to lock the rear steer axle for the purposes of reversing.But how does the rear steer axle decide on the angle to steer at? I’m sure it isn’t taking the steering angle from the unit because that wouldn’t be useful. Does it calculate it based on the angle of the 5th wheel to the trailer?
It is steered via the fifth wheel. The kingpin is fixed to a plate that spins in the neck, which is attached to either long bars or hydraulic rams, which steer the rear axle. There is a wedge behind the kingpin, which fits in the jaws of the fifth wheel, so when the fifth wheel turns relative to the trailer, so does the steering axle.
The bars tend to steer the whole rear axle, on a turn table, whilst the hydraulic system tends to steer the rear axle wheels, like the front steering of the truck.