Increased range at decreased cost is the holy grail of electric vehicle design. Consumers list range anxiety, cost and charge times as the main reasons for not considering EVs instead of traditional internal combustion powered vehicles. All three of those factors are directly connected to electric vehicle batteries, but what if we made the car more efficient by making it lighter? It would increase range and reduce charge times, but in the past at least, it certainly didn’t make them more affordable.
- A 12-month project funded by Innovate UK is looking at using lightweight materials in electric drive units to make EVs more efficient.
- Engineering specialist, Drive System Design (DSD) has been contracted to determine the weight savings to cost benefit of drive unit light-weighting.
- The project will focus on the use of carbon fiber, and maybe more importantly, advanced engineering in an effort to reduce mass to increase performance.
- Using composite materials can drop as much as 30 percent from the mass of the drive unit as well as allow the use of more efficient gears.
The electric drive unit is typically comprised of the motor, gear set, differential and may even contain the power inverter as one unit. (Image: Drive System Design)
Manufacturers’ priorities have changed with the switch to electrified vehicles. Overall vehicle weight is more important than ever, as weight vs battery capacity is a major factor in determining range. Adding battery capacity is not only expensive, it also increases charging times to achieve the longer range. With the high cost of adding more battery capacity to a vehicle, using exotic materials to reduce weight is looking more affordable.
Drive System Design (DSD), is working with the UK’s National Composites Centre (NCC), to determine if carbon fiber, typically reserved for aerospace and exotic cars, can be used in electrified vehicle powertrains to increase efficiency.
The powertrain or Electrical Drive Unit (EDU), consists of the electric motor, gear set and sometimes even a differential and power inverter, all in one component. The housings for EDUs are usually made from cast aluminum or even steel. While metals are affordable, they aren’t particularly light weight or good at damping noise and vibrations produced by the motor and gears. Carbon fiber is better at both tasks.
Using carbon fiber in the EDU housing will not only save weight, but may allow for the optimization of the gear set, adding to overall efficiency advantages. (Image: Drive System Design)
First, what is carbon fiber? Carbon fiber is threads of pure carbon, usually woven into cloth (but not always) which is then laminated with an epoxy, resin or plastic. While Thomas Edison is said to be its inventor, as early as 1879, it didn’t see use as a structural material, even sparingly, until the 1950s. It was 1977 before a patent was issued for a production method making it viable for mass use.
DSD is studying very specific applications of the material in EVs. Early estimates show that EDUs can lose up to 30% of their mass with carbon fiber compared to cast aluminum. The EDU is right behind the battery in terms of heaviest components, so weight loss here is significant.
The initial weight loss is the obvious benefit, but DSD is confident it will find further advantages. Noise, vibration and harshness are the things that keep automotive engineers awake at night.
EDUs must be optimized to minimize NVH, which means compromises in efficiency. Most people don’t realize the amount of NVH that comes from the gears inside transmissions. The gear set in an electric vehicle is no different. Since carbon fiber is better at damping vibrations, and has different natural frequencies than aluminum, the gear set can be designed to be more efficient. The same design would be too noisy when housed inside aluminum, making this a double win.
A typical EDU for EV. (Image: Drive System Design)
WHY THIS MATTERS
Battery prices cannot drop fast enough. Customers expect more range and shorter charging times and reducing mass in EVs is the quick answer. Carbon fiber EDU housings can provide the longer range through increased efficiency. DSD’s work has the potential to democratize the benefits of carbon fiber across the entire EV market, so it is no longer just for the benefit of exotics.