- rivian has made a big deal out of the "tank turn" capability of its electric vehicles. the four motors, one powering each wheel, can basically spin the ev around in place by spinning the wheels on either side of the vehicle in opposite directions.
- but on soft surfaces, a tank turn brings with it the chance to get stuck, so the company is also trying to patent a "k-turn."
- using the same ability to control each wheel individually, the k-turn will hold one of the inside rear wheels and allow the vehicle to pivot around it, dramatically reducing its turning radius.
for a certain subset of star wars nerds, a k-turn (aka a koiogran turn) is a tricky way to escape a pursuing craft during a dogfight. but in the automobile world, "k-turn" could soon be associated with rivian, which filed a newly published patent application outlining a method for the company's electric vehicles to offer drivers a much tighter turn radius than other vehicles offer.
whether or not this k-turn will make an appearance on rivian's upcoming r1t and r1s evs is not directly specified in the patent application, but rivian has already promoted a different unusual turning method for these vehicles. called the "tank turn," this tech uses the ev's four motors (one connected to each wheel) to rotate the wheels on either side of the ev in opposite directions, kind of like moving the treads on a tank against each other, to basically spin the vehicle in place. it's a neat party trick, but it can't be used everywhere. as rivian notes in its patent application: "such a [tank] turn when employed on soft surfaces can cause the wheels to dig into the ground and sink rather than turning the vehicle."
rivian's k-turn builds off the tank turn, deploying its separate propulsion source at each of the four wheels in a slightly different way. instead of putting the center of the turning circle at the midpoint between all four wheels, a k-turn would instead happen only when there's substantial steering angle. forward torque is applied to those angled front wheels, while the inner back wheel is more or less held in place. this wheel then forms a pivot point for the car to turn left or right. think of it like an old-fashioned pencil compass, where the metal point represents the stationary rear wheel and the pencil side is the front of the car. the end result? "k-turn mode [allows] the vehicle to achieve a significantly reduced turn radius (e.g., the vehicle may pivot around a point under the chassis of the vehicle)," according to the patent application. this is similar to the ford bronco's trail-turn assist, where, at low speeds, it locks the inside rear wheel to pivot around it, shortening the turning radius by as much as 40 percent.
other parts of the patent filing talk about slightly different modes where the rear wheels would instead be spinning in reverse rather than the inside rear wheel held in place. rivian makes it sound like actually making one of its vehicles perform a k-turn will be a fairly simple process. the patent application mentions that "processing circuitry" could engage k-turn mode if the steering wheel is asking for the wheels to rotate beyond the standard turn threshold.
just because an automaker files a patent does not guarantee that the technology will ever make it to a production vehicle, but this is one that we expect to see on future rivian models. it uses the same components as the tank turn, something rivian has been happy to promote, and it provides a benefit in some situations where a tank turn would cause problems.
rivian filed the patent application on december 31, 2019.