Trucks
The way in which vehicles are steered has changed as automotive history has evolved. What began life as a single lever developed during the 19th century to become a steering wheel fairly like the one that is used in present-day vehicles. The other major development was hydraulic power-assisted “servo” steering, a support system that became increasingly important as vehicles became larger and heavier. The next stage in this development process has now arrived – Volvo Dynamic Steering.
“At low speeds, a heavily loaded vehicle is so easy to manoeuvre that it can be steered with just one finger and, when driving on the highway, this dynamic steering system offers unbeatable directional stability,” explains Jan-Inge Svensson, one of the people responsible for the system software at Volvo Trucks.
The system is based on a classical mechanical steering arrangement in which the steering rod runs down from the steering wheel to the steering gear. A hydraulic servo system creates the power that helps the driver to turn the truck's wheels. The principal difference when it comes to Volvo Dynamic Steering compared to conventional steering is an electrically controlled electric motor that is fitted on top of the steering gear.
This electric motor works with the steering gear. At low speeds, the electric motor provides additional power assistance, making the truck incredibly easy to manoeuvre. At higher speeds, the electric motor controls the steering, automatically eliminating jags when steering.
I said from the start that it was completely impossible, that it wouldn’t work, but, with the assistance of our skilled colleagues at the cab development department, we succeeded.
The electric motor is controlled via signals from a management unit which contains what is known as an angle-reference generator. This is the brain of Volvo Dynamic Steering. Via sensors located in different parts of the truck, this management system collects information relating to the vehicle.
“These sensors are located in a wide range of different places and they combine to produce a complete picture of what is happening to the truck. Among other things, they measure the speed of the truck, what gear – forward or reverse – that has been selected,” explains Sten Ragnhult, the person responsible for developing the system hardware.
One important component in the system is the sensor in the electric motor. It has been fitted to a torsion rod and it measures the force the driver uses to turn the steering wheel and its steering angle. This data then forms the basis when it comes to determining how the system functions act to create the perfect steering response.
The information that reaches the management unit is analysed by the system software. Control signals are then sent from the system to the electric motor, which helps the truck compensate for the disruptions the sensors register. All this takes place in less than a millisecond and results in the optimal steering response.
One important function when it comes to the management unit is its straight-ahead compensation function. The straight-ahead engine position is continuously compensated for and, as a result, the driver rarely needs to adjust the steering wheel to accommodate an uneven road surface or continuous side winds.
“One example of the kind of situation that can occur is braking, when the friction on the right and left sides varies. The truck then attempts to pull to one side and the steering wheel turns as a result of the asymmetrical forces between the tyre and the road surface.
In simple terms, Volvo Dynamic Steering can be compared to a filter that improves the real-life situation the driver experiences via the truck steering wheel. It goes without saying that a system of this kind cannot be produced over- night. Volvo Trucks started the development work eight years ago.
“We have encountered a number of major challenges along the way. Finding room for the electric motor in purely physical terms in the cab has been a huge challenge for those of us involved with mechanical systems. I said from the start that it was completely impossible, that it wouldn’t work, but, with the assistance of our skilled colleagues at the cab development department, we succeeded,” says Sten Ragnhult with a smile.
Otherwise, most of the work has focused on developing the advanced software in the system. Working together, the development team have succeeded with the calculations that were needed to make the management unit function correctly.
It’s fantastic to suddenly be able to steer the truck with just one finger in situations in which I was previously forced to use both hands to control the steering wheel.
The team has been assisted by a number of different test drivers who have helped to make the project a success. These drivers have conducted a raft of different tests in which the developers have accompanied them to find out how the drivers would like the steering to respond.
“We have quite simply allowed the drivers to test a wide range of scenarios in which the steering response has been varied in many different ways. By collating the data that has been collected, we have succeeded in recreating the optimal steering response in the management unit software,” explains Jan-Inge Svensson.
One of the drivers who has played a leading role in the development work is timber truck driver, Henrik Gustafsson. Every day, he works deep in the Swedish forests in a new Volvo FH. The narrow, often muddy forest roads impose enormous demands both on Henrik’s professional skills and on the truck.
“I have been driving this test truck for a year. It has been exciting and incredibly enjoyable to be part of the development work. I know, for example, that the things I discover and point out will actually make the truck better for everyone.”
Fully loaded, Henrik’s timber truck weighs 60 tonnes. Manoeuvring a truck like this on the narrow, often poor-quality roads is physically demanding work. The smallest stone or root makes its presence felt and the constant steering-wheel adjustments this necessitates are a significant strain, not least in the driver’s shoulders, back and neck.
“I spent some time driving trucks in Norway, where the roads are often narrow and winding. As a result, I injured my left shoulder and the pain radiated from my shoulder blade.”
Since Henrik started driving the truck with Volvo Dynamic Steering, he tells us that the pain has totally disappeared.
“I can now drive and stay completely relaxed, even on poor roads. It’s fantastic to suddenly be able to steer the truck with just one finger in situations in which I was previously forced to use both hands to control the steering wheel. I don’t even feel potholes in the road, because the system compensates in such a way that they don’t exist.”
However, the narrow forest roads are not the only place Henrik experiences a real difference. A fully-loaded timber vehicle combination has a high centre of gravity and is particularly sensitive to rutted road surfaces and wind. However, as the system also compensates for these irregularities, Henrik can drive in a totally relaxed manner, even on larger roads.
“In the forest, where you drive slowly, you want the least possible steering-wheel resistance, whereas you want more resistance on highways. This system adjusts the steering-wheel resistance to match my speed,” he says. “I have already said that the next truck we buy must have Volvo Dynamic Steering!” he concludes with a smile.
