Improving sideshaft durability in EVs

Taking the latest developments in powertrain engineering, how can manufacturers improve the durability of sideshafts in electric vehicles?

The global transition to electrification has brought a shift in the technical requirements for hardware which has, historically, been engineered and optimised for conventional powertrains. Now, driveline components must withstand higher vehicle mass, greater acceleration torques, and up to 1,200Nm of braking force to enable key technologies like regenerative braking.

However, fundamental differences in the hardware requirements for an electric vehicle (EV) can be accommodated by redefining certain driveline components, so that they are optimised for the electric era, serving to improve the overall performance and durability of our cars.

EVALUATING THE DIFFERENCES

The shift from front-wheel drive (FWD) to rear-wheel drive (RWD), favoured in EVs, and the increased weight of the battery packs have been two of the more significant differences we’ve seen in vehicle dynamics in recent years. Unlike ICE-powered vehicles, which typically carry the majority of their weight on the front axle, the mass and dimensions of the battery pack in an EV alter the load distribution. The central location means that EVs generally have a lower centre of gravity and are more often positioned towards the rear axle.

One of the major challenges of this extra weight, though, is that it results in increased inertia of the vehicle and therefore higher torques both in acceleration and braking or in recuperation. This necessitates a shift in how suppliers develop, test and manufacture parts.

SIDESHAFT REQUIREMENTS

As a direct result of e-drive units being larger than conventional ICE gearboxes, EV sideshafts are significantly shorter than those in ICE vehicles, requiring different mounting points and larger installation angles. As a result, we’re seeing increased plunge distances as well as changes to some basic requirements for the constant velocity (CV) joints.

Despite their shorter length, EV sideshafts must be stronger and more durable to withstand the vehicle’s increased torque demand, while avoiding a significant increase in size to remain as efficient and cost-effective as possible.

At the same time, suppliers must contend with differing dynamic characteristics, with electrified powertrains providing much higher torque and torque gradients than ICE-powered vehicles. Although the improved acceleration and near-instant torque availability is part of the appeal, it relies on more robust sideshafts to manage the higher torque across a wider power band.

OPTIMISING FOR EVS

To navigate these changes, it’s vital that suppliers look to deliver solutions that have been optimised for EVs and their different hardware requirements. This presents considerable opportunities to advance technologies that fulfil the new technical requirements for EV sideshafts.

To take an example, GKN Automotive’s Countertrack CV joints use opposed tracks that better balance the internal forces, resulting in efficiency improvements, while reducing friction and noise, vibration and harshness (NVH), to which EVs are particularly sensitive. The improved efficiency helps to increase the range of the vehicle, which presents a real advantage in the case of battery electric vehicles (BEVs).

By increasing the stiffness of an EV sideshaft, it is possible to reduce wheel spin and extreme vibrations, offering greater torque control in spite of the hard acceleration. In fact, there is great potential in this area, which is why GKN Automotive has developed a range of solutions with increased stiffness for better oscillation control.

Forecasts indicate that future electric vehicles will have a longer lifetime than today’s ICE vehicles as a result of the improved efficiency of the whole system. Reducing wear and heat generation – without compromising the set of other parameters – will improve not only the longevity, but also performance, which is essential for electric applications. Therefore, a balanced and efficient system design, with the lowest possible material consumption, is vital to manufacturing driveline components that are fit for the future.

Christian Carlando is Director of Customer Engineering in Europe at GKN Automotive