Cold Weather Testing

The R1 journeys into the cold, cold north

By Rivian

February 26^th, 2021

Our engineers have been layered up, testing and refining R1 vehicle dynamics and battery performance in one of the most dependably cold places in the Lower 48.

We also kicked up a little snow while we were at it.

Baudette is a small town of 1,100 nestled up against the Rainy River, which winds its way along an 81-mile stretch of border between northern Minnesota’s “ice box region” and Ontario. Walleyes come here to snack on the abundant emerald shiners swimming upriver. Anglers come here to catch the walleye. And automotive engineers come here to eat the walleye between validation runs at North America's largest cold-weather test facility.

Just a few minutes outside of town, the test facility sprawls across thousands of acres of snow, ice and forest. This former United States Air Force radar base has been reimagined as an automotive engineer’s dream — it offers 25 courses, including a multitude of autocrosses, snow and ice test tracks, a litany of vertical grades, a slush pool and other surfaces designed to capture winter weather at its worst.

Batteries like being at nice, moderate temperatures. They typically don't like extremes. A lot of effort has gone into our thermal systems to ensure robust performance across all conditions.

In extremely cold temps, it's best to plug in overnight if you can — and that goes for any EV. It not only recharges the battery, but it provides the energy to warm the battery to maintain maximum range and performance. As for the R1, if it’s plugged in all night, you can hop in and drive with very little compromise to performance at even -40° F.

Laura has been to Minnesota nearly every summer of her life, but never this far north. Her work as a Control Integrations Engineer is focused on keeping the battery (and the driver) happy. She's refining the R1 thermal control software and developing self-heating strategies to maintain optimal battery performance in sub-optimal conditions.

Her day starts early as she cracks open the doors to a cold cell where an R1T test vehicle has been "cold soaking" overnight at -40° F.

"In extremely cold conditions we use some battery energy to keep the cells in our battery above 14°F to provide controlled vehicle performance. Some EVs have electrical heaters to heat the battery up, which is another component — more cost, more mass and a drain on electrical supply. Instead, we’re using our inverter and motor to generate heat — even while stationary our traction system can generate substantial heat for the battery. And we use that heat to warm the battery to the point where it can deliver full performance. Our battery is uniquely designed to operate in super cold conditions, all the way down to an ambient temp of -40°F."

Laura Controls Integration Engineer

Our batteries use an axial cooling method via a central cold plate — a unique design feature of our pack — which is a highly efficient way to both heat and cool the battery. This system uses the minimum amount of energy possible to keep the cells at their optimum temperature, which is particularly important if the vehicle has been unplugged in extremely cold conditions.

Our cold soak tests are designed to replicate an R1 parked outside overnight, which is when batteries can reach their coldest and need to be warmed. In ideal conditions, an R1 can add 25 miles of range per hour when plugged into a home AC charger. At 0° F, because you’re using some of the charge current to warm the battery, you’ll get less charge when you first plug in — the charge rate on a home AC charger is approximately halved for the first hour, then returns to its maximum charge rate of 25 miles per hour after that.

“Our vehicles have been designed to minimize any performance or range impact from extreme cold temperatures. If getting in the vehicle after a long cold soak at -40F, the vehicle will operate fine but will take about 20 minutes for the battery to warm itself up and be capable of delivering full power and battery performance. The vehicle range prediction displayed to the driver will take into account the temperature, driving conditions and cabin heating considerations to give an accurate display of vehicle range from the remaining battery energy.”

Richard VP Propulsion Powertrain

While the energy management team validates our traction system's ability to warm the battery, our dynamics team is focused on traction control. The team is working to ensure our vehicle state calculations are accurate across varying surface and slip conditions. The state estimation algorithms are critical for much of our traction control features as they must accurately determine movements of the vehicle, and serve as a core input to determine which of its many control knobs to turn. The inertia measurement unit and a gyroscope mounted to the roof provide the 'ground truth' needed to confirm the accuracy of our algorithms.

"We are simultaneously developing traction control, torque vectoring, regen slip control, anti-lock braking and electronic stability control with the goal to get them all to play nicely together — especially in the snow."

Max Director of Vehicle Dynamics

Thanks to ample on-site living quarters at the test facility, our team can perform testing over multiple days and nights, with work frequently continuing long after sundown.

Late one night, the team pushes the R1T hard as part of the meticulous process of refining our traction systems. Snow sprays across the track as we perform multiple high-speed turns.

This particular test track is unique in that concentric rings of snow and ice allow the engineers to simulate a real-life scenario in which one side of the car encounters slick ice while turning at high speed. This allows us to refine our traction control system and adjust torque to each wheel to maximize stability and ultimately, driver safety.

After multiple laps between the garage and test tracks, it’s time for another cold-weather charge. Despite the late hour, a mountain of data analysis is yet to come.

Light snow begins to fall as another day of driving comes to a close. The long hours can be intense, but spirits are high, in part because this work takes us places we might not get the chance to explore otherwise. Even way up here in The Walleye Capital of the World — among lakes leftover from the last ice age, vast fields gone fallow through the dark months, and an occasional "you betcha" from a friendly local — don't think for a moment that this isn't fun.

“I like winter a lot, so I really enjoy this. Once we’re heated and charged, we’re going to take the truck out and just drive.”

Some images shown may contain pre-production vehicles and vehicle specifications mentioned in this blog post may have changed. Please refer to our website or reach out to Customer Service for current vehicle information.