Trucks
The truck industry is conservative when it comes to new technology. For this reason, Volvo Trucks raised many eyebrows when it presented the first individual front suspension (IFS) for trucks.
Senior engineer Jan Zachrisson explains why the IFS created such a buzz when it was introduced in the autumn 2012. “Parts of today’s suspension systems are in principle based on the same technology that was used in the horse-drawn carriages of the 18th century. Separating the wheels in the front chassis, so that they can work independently, is a revolution in heavy-duty trucking.”
Before Jan Zachrisson started work on the IFS system, he was involved in upgrading the existing front chassis with air suspension for the new Volvo FH. With a background from Volvo Buses, he also had previous experience of working with individual suspension systems, as this technology has already been used for almost 30 years in the bus industry.
“Today’s front chassis with leaf and air suspension systems are so good that there isn’t that much scope for developing these techniques much further. With the introduction of IFS, we are writing the first chapters in a totally new book and changing the driver’s take on what it feels like to drive a truck.”
With the introduction of IFS, we are writing the opening chapters of a totally new book and changing the driver’s understanding of what it feels like to drive a truck.
The first draft of the book on IFS was presented by Volvo Trucks more than 10 years ago. At that point, the first prototypes of the system were drawn, but it was not until 2008 that the development work really began in earnest. For the past five years, Bror Lundgren has been leading a project team comprising some 15 people and together they have developed the new technology.
“We were tasked with producing a design that would make Volvo’s trucks best in the world when it comes to handling and comfort. As some of the work had already been done, we had a really good platform on which to base our work, but the most important development work – the transition from a concept to an industrial project – still lay ahead,” explains Bror Lundgren.
It is no coincidence that Bror Lundgren, with his experience of individual suspension systems in the car industry, was chosen to lead the development of Volvo Trucks’ IFS system.
The basic principle for the system is the same for both a car and a truck – suspending the wheels individually makes the vehicle more stable and predictable on the road.
When it comes to the design, however, the systems differ. The greatest challenge facing Volvo Trucks’ engineers was space and stiffness.
In a car, the stiffness in the system is created through the frame to which the axle is attached. This kind of solution is, however, impossible on a truck for two reasons. The first is that the engine is located in the same areas as the suspension. The second is that the frame structure to which the system is attached is higher in relation to the road surface. As a result, the natural stiffness in a car cannot be re-created in a truck.
The solution is a design in which the moving parts of the system are held together by two subframes which follow the underside of the engine.
“There must be no lateral movements so we focused very heavily on stiffening the IFS system frame structure as much as we possibly could,” explains Bror Lundgren.
“When we passed our rig tests and realised that the design was going to function as intended, it was a huge victory,” he adds.
Rig tests are an important series of tests that are conducted at the Volvo Trucks development department in Gothenburg, Sweden. The whole test facility smells slightly of oil and a constant beeping noise from the hydraulic system leading to the gigantic shake rig can be heard throughout the facility.
“We call it T-Rex. It is the world’s largest shake rig. Its total weight exceeds 1,200 tonnes,” says test engineer Emil Skoog, who works at the facility.
A system of pistons and cylinders shakes the axle at different intervals, subjecting the IFS system to extreme forces in the shake rig. The signals that control the shaking have been collected in the form of data from a test vehicle at the Volvo Trucks’ proving ground in Hällered outside Gothenburg.
“At the proving ground, the test vehicle is subjected to a number of gruelling road tests. On the axle, there are a number of sensors that register forces and movements during the tests,” explains Bror Lundgren.
In the shake rig the number of loads on the structure is much larger than it would ever be in real life in order to make sure that the system is strong enough.
By transferring this data and then using it in the shake rig, the conditions at the proving ground can be re-created. The data that is used only simulate the parts of the proving ground where the test vehicle is subjected to the heaviest loads. In this way, the tests are optimised in terms of time, as unnecessary driving and other kinds of downtime can be eliminated.
“In the shake rig the number of loads on the structure is much larger than it would ever be in real life in order to make sure that the system is strong enough.” explains Bror Lundgren.
The axle is tested hundreds of times in the shake rig during a test period lasting 10 weeks. Bror Lundgren looks up at the test axle in the rig and explains the importance of all the tests.
“We have a responsibility to our customers and that is to test and keep testing until we are sure that the system is ready for production. As we are going to use this new technology in the future, it is also important to verify how it works. We need to document the knowledge we acquire.”
The result of five years’ development work is the world’s first series-manufactured IFS for heavy-duty trucks. However, what are the greatest advantages of this new technology?
“Its handling properties are quite simply revolutionary. As a driver, you can relax in an entirely different way and this creates a totally different feeling of safety and stability compared with a conventional front suspension,” Jan Zachrisson explains.
Bror Lundgren agrees and makes a comparison between two beach balls.
“With an axle with leaf or air suspension, you sit on top of the beach ball and you are frequently forced to counter movements with your senses in order to maintain your balance. With an IFS, you are instead sitting inside the beach ball and have greater control of your situation. This creates an enhanced feeling of safety.”
As a driver, you can relax in an entirely new way and this creates a totally different feeling of safety and stability compared with
a conventional front suspension.
The improvement in steering wheel feedback, which is a result of the rack and pinion steering that is integrated in the system – a technology that is also totally unique in the truck industry – is a decisive factor when it comes to the fantastic driving characteristics.
In the shake rig, Emil Skoog starts the day’s test programme. The pistons start working and the text axle shakes up and down. The air-suspended floor on which the rig stands moves and the wave-like movements can be clearly felt.
“Compared with a conventional steering gear, rack and pinion steering is a more rigid steering system and this results in a more direct response. The time between thought and action is shorter and this further reinforces the feeling of control and safety,” adds Jan Zachrisson.
With the introduction of IFS, Bror Lundgren is convinced that a new chapter is being written in automotive engineering history when it comes to wheel suspension systems in the truck industry.
“We have succeeded in re-defining the feeling of driving a truck. Jan Zachrisson says that we have written the first chapter in the book entitled IFS. I am convinced that this book is going to contain many chapters.”
The challenge for the designers was to create a design with several moving components, which would function as a solid unit. This is their solution.
1. Rack and pinion power steering gear
The movements of the steering wheel are transferred to the rack and pinion power steering gear. The movement is then transferred to the tie rod and ball joints on each side and then to the steering arms. From the steering arm, the movement passes to the axle shaft whereupon the wheel of the truck turns.
2. Shock absorbers
Impact energy is absorbed by shock absorbers fitted to a bracket on the kingpost and the chassis frame on the top.
3. Kingpost
Upper and lower support arms, shock absorbers, axle shafts, air bellows and the steering system are all connected to the kingpost. To withstand the severe stress, the kingpost is produced in a single piece of high-strength material. Correct caster and kingpin inclination is integrated in the design and offers extraordinary handling performance and a minimum of tyre wear.
4. Subframe structure
The upper and lower support arms are mounted on a subframe structure that holds the entire construction in place. The subframe structure, which is made of cast iron, is attached to the chassis frame.
5. Double control arms
The front wheels are connected to a kingpost on each side, independently suspended in the chassis structure by one upper and one lower control arm. An air spring, positioned between the kingpost and the frame structure, carries the load and absorbs the dynamic movements generated by obstacles in the road surface during driving.