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Rivian Patents Low-Range Gearbox Attachment for Extreme Off-Roading

Rivian was busy filing patents for the past year, and the USPTO granted dozens in the past month alone. One of them is really interesting, as it depicts a modular low-range gearbox attachment that would vastly expand a truck’s off-road capabilities. This would be a first on an electric vehicle.
Rivian patents a low-range gearbox attachment for extreme off-roading 10 photos
Photo: Rivian | Edited
Rivian R1 platform in quad-motor configurationRivian shares more details about the upcoming Dual-Motor configurationsRivian shares more details about the upcoming Dual-Motor configurationsRivian shares more details about the upcoming Dual-Motor configurationsRivian patents a low-range gearbox attachment for extreme off-roadingRivian patents a low-range gearbox attachment for extreme off-roadingRivian patents a low-range gearbox attachment for extreme off-roadingRivian patents a low-range gearbox attachment for extreme off-roadingRivian patents a low-range gearbox attachment for extreme off-roading
Electric vehicles can do away with having a gearbox because their electric motors can cover a wider rpm range while maintaining a consistent performance level. Nevertheless, some carmakers, like Porsche, still use gearboxes on their EVs. Taycan, for instance, features a two-speed transmission on the rear axle to offer brisk acceleration from the start and also improved efficiency at high speeds. Nevertheless, Rivian didn’t go that way and instead copied Tesla in providing a direct drive system.

This works well in most use-case scenarios and is also very convenient with Rivian’s quad-motor configurations. Despite that, Rivian wants its vehicles to be true adventure trucks and sees them used in more difficult conditions. The EV maker is concerned with the thermal limitations of its electric drive units in high-torque scenarios. These can range from rock crawling to heavy-duty towing and might cause the drive units to overheat if operated for extended periods.

Rivian mentions that the limit lies not with the electric motors, but with the controlling electronics. More specifically, the inverter’s insulated-gate bipolar transistors would reach their operating limits, causing the whole drive unit to enter protective mode with reduced torque output. As this could ruin all the fun in an off-road adventure, Rivian figured it needed to find a solution. And given that not many people would push their trucks to their absolute limits, the answer was a bolt-on device, which could be sold as an accessory to those who need it.

According to the patent granted by the USPTO, Rivian designed a bolt-on mini-gearbox that attaches directly to every drive unit. Conveniently, it replaces the inner CV joints of the stock axles. You would need four such gearboxes for a quad-motor configuration, so don’t expect this to be cheap if it ever enters production. Think of them as portal axles, only removable and with a variable ratio between 1.5:1 and 5.0:1. To offer such a high range, Rivian uses a planetary gearset and an actuator to engage or disengage the low range.

The low-range gearboxes would allow the electric motors to function in a more favorable rpm range, preventing overheating. The cases are also designed for improved cooling, further increasing their reliability. Nevertheless, considering the huge power and torque available, these mini-gearboxes must be sturdy. The quad-motor configuration of the Rivian R1T produces 835 horsepower and 908 lb-ft (1,230 Nm) of torque, and it has to move a heavy chunk of metal at almost 7,000 lb (3,150 kg).

Even if Rivian was granted the patent, this doesn’t necessarily mean it will be put into production anytime soon. If anything, Rivian might integrate it into some of its vehicles or offer it as aftermarket accessories to off-road professionals. As far as we know, this is a unique design for an electric vehicle, although reduction gears are common on ICE off-roaders.
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 Download: Modular high-low range gearbox attachment (PDF)

About the author: Cristian Agatie
Cristian Agatie profile photo

After his childhood dream of becoming a "tractor operator" didn't pan out, Cristian turned to journalism, first in print and later moving to online media. His top interests are electric vehicles and new energy solutions.
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