Volvo‘s decision to offer independent front suspension (IFS) on selected models of its new-generation FH range of heavy chassis being unveiled in September is set to further the OEM’s standing as a driver of trends in the industry.
On virtually all passenger cars and vans up to 3.5 tonnes gvw, IFS is now taken for granted. It unquestionably confers a superior ride. The effect of road surface irregularities, including potholes and other symptoms of wear and tear, was greatly minimised in the 1950s and 60s as solid front axles, usually located by multi-leaf ‘cart’ springs, gave way to double-wishbone or Macpherson strut IFS, typically in conjunction with coil springs and concentric dampers.
Sneak preview pictures issued by Volvo ahead of the official launch of its new IFS package indicate wishbone/radius-arm geometry designed to keep the wheels vertical under varying loads
For heavier vehicles, IFS has long been discussed as a means of improving ride and handling. Coaches with rear-mounted or underfloor engines led the way. The relatively long front overhang of a coach and of many large buses allows the use of a correspondingly long horizontal A-frame, with its ‘apex’ just behind the front bumper/fender, to locate the wheel-hubs without upsetting the steering geometry.
Considerations of front-rear weight distribution obviate such generous overhangs on a heavy truck. The maximum weight which can be imposed on a front axle within most public highway regulations around the world is about eight tonnes, a limit determined effectively by tyre weight ratings and fail-safe power-steering considerations. Extending the front overhang of a front-engined truck to accommodate coach-style A-frame IFS geometry – that is by moving the front wheels rearwards – would cause overloading.
Limited-production heavy truck makers such as Ginaf in the Netherlands and Tatra in the Czech Republic have employed IFS in the past, but only for special applications where a beam front axle would have interferred with ancillary components on the chassis.
But for sustained on-highway use, IFS has – until now – been regarded as impractical for heavy trucks. ‘Too heavy and too expensive’ were the usual disclaimers, with uneven tyre wear across the tread width also sometimes cited as a practical impediment.
Volvo has a reputation as an innovator in truck technology…its IFS project can be expected to set another trend
Sneak preview pictures issued by Volvo ahead of the official launch of its new IFS package indicate wishbone/radius-arm geometry designed to keep the wheels vertical under varying loads. In any case, air bags rather than steel springs are the suspension medium, ensuring a constant ride height. It is apparent that any improvement in ground clearance under the centre of the vehicle – sometimes a motivation for eliminating a traditional axle beam – has not been a design influence for Volvo. The underslung ‘bridge’ structure straddling the chassis frame, from which the IFS radius arms are pivoted, sits as low as an axle beam.
Volvo has a reputation as an innovator in truck technology. It was the first diesel engine maker in Europe to adopt electronic unit injectors. It also took the lead in clutch-pedal-less automated mechanical transmissions as well as in full-air disc brakes. All those pioneering developments had their teething troubles, but they came right in the end, with many competitors following suit. Volvo’s IFS project can be expected to set another trend.
The opinions expressed here are those of the author and do not necessarily reflect the positions of Automotive World Ltd.
Alan Bunting has a background in engineering, and has been writing on commercial vehicle and powertrain related topics since the 1960s. He has been an Automotive World contributor since 1996.
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