Building a Scania V8 R500 - Part 2. Suspension, drive axle

I`m building a Scania R500 - from a 1:24 scale kit produced by ITALERI.

I`ll be discussing aspects of truck construction as I go along, hopefully highlighting some basic truck technology.  It`s easy to think that modern vehicles bear no resemblance to those of the past, but that`s not true.  Suspension and steering; engine, transmission and final drive; and tyres are all there to maximise the laws of physics, and have retained the same configuration since diesel replaced steam.  Cost and natural performance limits have meant that the chassis abandoned long ago in car design is still used in truck manufacture.   Yes, your truck is computer controlled and a modern marvel;  but so is the modern cruise liner - which is still a Titanic underneath.   




Building a Scania  R500    Part 2. Suspension (drive axle)



The live beam (non-independent suspension) drive axle is fitted with trailing arm 1/4 leaf springs and air springs.  The leaf springs are clamped to the axle with substantial fixings to prevent movement (the system has to absorb all drive and braking torques, and deal with uneven bump and body roll).  



The 1/4 leaf springs work with the axle to deal with uneven bump and body roll - they replace an anti-roll bar (stabilizer bar) in this set up.  Some drive axle systems use four air springs an anti-roll bars (e.g. 6x2 DAF 85).

How the 1/4 leaf spring system works - see both the above diagrams 

Dampers dampen the oscillations of the road spring.  Dampers provide ride comfort and have an effect on handling.  Springs store energy and are displacement dependent for the force they provide.  Dampers convert kinetic energy, the energy of motion, to heat.  They are speed dependent for the force they give.  In the simplified diagram above, the damper shows how it provides a greater force on rebound than it does on bump (bounce) by using different sized ports through which oil has to pass.  In reality, the innards are far more complex but the theory of area, force and pressure still apply. 

Next -  Part 3.  Suspension (front axle)