Simple and efficient design means the automotive driveshaft has remained fundamentally unchanged since its invention around a century ago.
But that has all changed with the development by US company Dana of a new shaft that collapses in an accident. This means that, unlike a rigid shaft, energy is absorbed, which helps prevent crash forces from being transmitted through the vehicle, which in turn helps minimise damage and injury.
Geoff Dutkiewicz, director of engineering at Dana explained: ‘We developed the technology because we felt our customers have a need for displacing or collapsing the shaft in a frontal crash.’ This was not as simple as it sounds. Dutkiewicz stressed the importance of ensuring that the shaft collapsed upon collision and did not shear off into two pieces, which might happen as a result of it continuing to rotate following a crash.
By using an electromagnetic forming process, similar to magnetic-pulse welding, Dana is developing collapsible designs for both steel and aluminium
driveshaft applications. These use low carbon steel and aluminium 6061 – traditionally used in heavy-duty structures and ship-building due to its good corrosive resistance and weldability.
The goal is to make motoring safer without increasing weight, cost or noise, vibration and harshness (NVH) characteristics, by being able to direct the collapse in a controlled manner.
Dutkiewicz claimed that concern over alterations to the integral design of a car are unfounded, adding that the driveshaft can be tailored according to a manufacturers’ specifications. ‘I don’t feel it will have any impact on the design of the vehicle,’ he said. ‘we take the requirements of the car makers and ask them what amount of force they are looking for and how much they want it to collapse by.’ He explained that there are a number or approaches available for the design of the shaft, depending on the force specified. ‘If the force is very low then a sliding spline can be used. In other cases wecreate a bulged tube through hydro-forming the shape into the tube, putting it into a die and setting the tube to the shape of the die.’
Dana has also been working on electronic smart systems in the development of new intelligent shaft technologies.
One such programme utilises magneto-rheological (MR) fluid to optimise parameters such as damping, deflection and stiffness. MR fluid is a thick substance made up of very small iron particles that goes from liquid to solid in the presence of a magnetic field. Dutkiewicz said that the company has developed a driveshaft mounting bracket based on this technology which, rather than absorbing the energy like the collapsible shaft uses MR fluids to control the displacement and radial direction of the shaft and to change the stiffness of the mount.
This allows for immediate adjustments to the stiffness of the bracket within the driveline suspension system while the vehicle is in motion. Such advances in tuning, claimed Dutkiewicz, mean that it is no longer necessary to sacrifice high-speed NVH for low-speed rigidity and strength.
He said that there are many other potential automotive applications for MR fluid. For example, used in tandem with ABS, a lock axle with MR fluid could provide both conventional speed differentiation and wheel traction selection using a computer algorithm. If wheel slip occurs, the fluid shear would be channelled to one or more wheels within one 20th of second with no mechanical actuation.
From a simple, functional piece of engineering, the driveshaft’s future is looking distinctly complex – but hopefully we will be all the safer for it.