- Subaru has filed a patent application for a hollow camshaft that could help its engines operate more smoothly and with less vibration.
- Hollow camshafts are often used in racing engines to cut weight. Subaru’s engineers also add a balance weight in the shaft to curb vibration caused by the exterior cams.
- The patent is based on use in a four-cylinder horizontally opposed engine, Subaru style, but it could also be used with a V or inline engine design.
The idea for the first camshaft, it’s said, dates all the way back to Mesopotamia, where it was found in inventor Ismail al-Jazari’s writings from 1206. Now, 800 years later, engineers are still hard at work on improving it. Case in point: Subaru has filed a new patent for a hollow camshaft with a lockable balance weight meant to reduce vibrations.
“Restraining the resonation” is how patent lawyers say it, but if this technology makes it to production, we’re sure it’ll be referred to as “smooth.”
The patent, first spotted by CarBuzz, evolves the camshaft — at its most basic level, a rod in the engine with bumpy cams on it that help control when a valve opens or closes — by making it hollow and adding a balance weight that locks and unlocks its position relative to the shaft depending on the engine’s speed.
USPTO
Today, hollow camshafts are often used in racing engines to provide important, if minimal, weight savings, and most “solid” camshafts have an oil passage inside for lubrication purposes. What the eight Subaru engineers named on the patent are talking about here is having a balance weight — a specially machined smaller hollow cylinder — inserted into the shaft to reduce vibrations caused by the exterior cams. This weight would be locked in position, relative to the movement of the camshaft, at lower speeds, to cancel out some of the vibrations. At higher speeds, lock pins would release the weight so that it can rotate freely inside the shaft. When this happens, the shaft’s natural frequency rises and the result is supposed to be less noticeable vibrations to vehicle occupants.
The patent (application number 19/638,324) was filed in April 2026 and was published earlier this month. It describes a system by which the lock pins would shift from locked to unlocked positions by centrifugal force when the rotation speed of the camshaft body crosses a predefined threshold. The patent says the lock pins could also be activated by oil pressure, hydraulic controls, or electric actuators. Subaru also noted that while the patent uses a four-cylinder horizontally opposed engine as an example, the new camshaft could also be used in an inline engine or a V-engine.
USPTO
Subaru did not respond to requests for more information on the patent and its potential applications, but automakers often file patents for technologies that do not end up in production vehicles. Automakers frequently experiment with camshaft design and theory. Honda started working on its Variable Timing and lift Electronic Control (VTEC) system in the 1980s, which changes the cam profile at high rpm, and that helped trigger a wave of new variable-timing systems in internal-combustion engines across the industry. In 2016, Koenigsegg displayed a camshaftless engine called Freevalve. For a look at the human side of camshafts, a 2024 documentary featuring Isky Racing Cams, one of the first performance camshaft companies, is now available for streaming. Whether or not Subaru’s hollow camshaft ever reaches a production engine, the patent signals that the company’s engineers see room for improvement in one of the internal-combustion engine’s oldest components.
