As an automotive repair expert at obd2global.com, I’ve always been fascinated by the intricate workings of modern vehicle systems. Following my previous exploration into engine RPM using OBD2 data, I turned my attention to Dual Clutch Transmission (DCT) control logic in Electric Vehicles (EVs), specifically within the Hyundai Ioniq. Leveraging the power of Torque Pro and readily available OBD2 data, we can unravel the gear selection strategy and gain valuable insights into the programming of EVs in EV mode. For those with a penchant for automotive technology, the data revealed through this process is truly captivating. This analysis is based on a drive encompassing approximately 2.5 miles at a steady 60mph on the highway (I-90), followed by backroad driving around 40-50mph, and finally, urban Boston traffic averaging 15-20mph.
It’s important to preface this by stating that my background is in electrical engineering, specializing in circuits, signal processing, and controls. My foray into transmissions and electric motors is still in its early stages. Therefore, the interpretations presented here should be considered with a degree of caution, and corrections are welcome.
The data strongly suggests that the DCT in EVs offers a significant advantage: enhanced flexibility in optimizing the electric motor’s operating efficiency. While it’s commonly argued that EVs don’t require transmissions due to the broad efficiency range of electric motors, Hyundai seems to recognize the potential benefits of utilizing a DCT to further refine motor efficiency. By having the ability to select different gear ratios, the vehicle can ensure the electric motor consistently operates within its most efficient zone.
This principle of maintaining optimal motor efficiency extends even to regenerative braking. For an Interior Permanent Magnet Synchronous Motor (IPMSM), the most efficient operating range appears to be roughly between 1/4th and 1/3rd of its maximum RPM, and around 1/3rd of its maximum torque. The efficiency plot of a typical PMSM motor below illustrates this concept. While the specific values might differ for the Ioniq (~170Nm of torque and an estimated 9000-1000rpm max speed), the qualitative efficiency landscape remains similar.
The Hyundai Ioniq’s strategy appears to prioritize keeping the electric motor RPMs within the 1500-2500rpm range. This is evident in the plots below, which depict motor speed and car speed, both correlated with the calculated gear ratio over time.
To decipher the gear the car is operating in at any given moment, we can refer to the specifications provided in the Hyundai Newsroom:
IONIQ – Hyundai Newsroom
According to the specifications, the maximum theoretical gear ratio is 16.2 (calculated from 3.87 * 4.19). In my data plots, any gear ratio values exceeding this are likely due to data noise. The distinct levels observed in the plots align remarkably well with the gear ratios outlined in the Hyundai specifications.
An intriguing observation from the drive data is that the Ioniq never shifted into 6th gear. It consistently held 5th gear, maintaining around 2400rpm while cruising at 60mph. The lowest gear ratio recorded in the data was 2.99, which closely matches the calculated 5th gear ratio of 2.91 (0.956 * 3.045). As I transitioned to slower roads, the car favored 4th gear, and during urban driving, it primarily remained in 3rd gear, with occasional upshifts during acceleration or regenerative braking. Future experiments at higher speeds will be necessary to determine the conditions for upshifting to higher gears.
While concerns have been raised about EVs regenerating through a transmission, potentially introducing losses, the efficiency characteristics of electric motors suggest a different perspective. Electric motor efficiency tends to decrease under high torque and low RPM conditions. The DCT allows the vehicle to shift to a more favorable operating point for regenerative braking, optimizing energy recapture. A single-gear EV, lacking this flexibility, might not achieve the same level of regenerative efficiency. While transmissions inherently introduce some losses, dry clutch DCTs, like the one chosen for the Ioniq, are known for minimizing these losses, making them a suitable choice for maximizing overall efficiency in this application.
