Regen Charging & Battery Size : BMW Patent
BMW has patented a suspension system that can harness the movement of the suspension during vehicle operation to generate electricity. Although there seems to be no short-term application for this suspension system, the idea of increasing electric efficiency by diversifying regenerative charging schemes is notable.
A simple overview can be found in the article below since I’d just like to discuss on regenerative charging schemes and their impact on the battery system. (https://insideevs.com/news/624798/bmw-suspension-makes-electricity-patent/)
The application of this novel suspension system would yield longer single-charge mileage as the additional charge energy will be essentially regenerative energy. This would translate into smaller real-life DOD usage under the same drive pattern.
Consider the case of a drive that drives 50 miles a day who purchased a xEV with a mileage of 100 miles from DOD100, without regenerative charging. And for simplicity’s sake let’s assume 1 miles/1% SOC efficiency (although the actual conversion should be based on energy). Based on these three facts, the driver must charge every two days, meaning that the xEV will undergo DOD100 charge/discharge every two days. Regardless of chemistry, DOD100 cycle will yield in poor life performance throughout the vehicle life.
If we assume that an additional 10 miles can be charged by enabling regenerative charging schemes throughout the two days, the total mileage of the vehicle becomes 110 miles. In other words, the xEV will still have SOC10% left over in the battery after the two days and essentially, only operate at ~DOD90. Therefore, regenerative charge enabled xEVs will exhibit better life performance of the vehicle.
Good for customers and good for warranty.
Now based on this fact, and the increase in effective driving mileage, it is logical to assume that the additional mileage can pave the way to implement smaller battery packs. Essentially, if the regenerative charging scheme can reliably guarantee an average of ~10 miles every 100 miles driven, it means that the battery pack does not have to deliver the full 100 miles on its own. It only has to return ~90 miles worth of energy on its own. Therefore, a more efficient system (be it in the form of aerodynamic design and/or regenerative charging schemes), will give rise to the possibility for implementing smaller battery packs to drive costs down and decrease vehicle weight.
Good for cost, but the battery will run at a larger DOD and will experience poorer battery life.
It will be ultimately, a strategic decision on the part of the vehicle OEMs depending on the vehicle segment under discussion. For premium segments, this technology will be implemented as a mode to increase mileage and battery life, while for en masse segments, it will serve as a tool to reduce battery pack size.
