Honda has filed a patent application for an active diffuser that would deploy only when needed, keeping a vehicle's styling clean and uncluttered when it's not in use.

Rear diffusers are typically fixed in place, Honda notes in its patent application published by the United States Patent and Trademark Office (USPTO) on Feb. 6, but originally filed on Aug. 24, 2021. That creates a conflict between the need to design an effective diffuser and other considerations like styling, departure angles, and potentially even government regulations, according to Honda.

The solution proposed in the patent application is a rear diffuser that would slide out from a car's rear bumper using an actuator. When deployed, the diffuser would generate an upward flow of air from underneath the car, balancing the downward flow of air spilling off the roof and helping to reduce rear-end lift, the application says. Unlike a conventional diffuser, it would be stowed when not needed, so cars wouldn't have appendages sticking out past their rear bumpers.

While some production cars have active rear spoilers, it seems automakers are looking to apply a similar concept to other aerodynamic aids. In addition to Honda's rear diffuser patent, Ford has filed a patent application for deployable dive planes. But it's unclear if either of these features will reach production.

Honda active rear diffuser patent image

Honda active rear diffuser patent image

Drawings in the patent application show the active rear diffuser on what looks like  previous-generation versions of the Honda Civic and Acura MDX, hinting that Honda is considering this feature for ordinary sedans and SUVs. As the automaker notes in the application, a deployable rear diffuser could help increase performance in sportier versions of these vehicles while preserving practicality.

Sedan and SUV buyers will likely be less tolerant of a vehicle that has trouble negotiating steep driveways due to low-hanging bodywork than buyers of sports cars.

Honda does reportedly have an electric sports car in development as well, although such a vehicle has been rumored for some time with no confirmation of production plans from the automaker. Honda will begin launching a line of EVs developed in-house in 2026, starting with a passenger car for North America.