grease pot hung under axle of cart
輠 refers to a specific historical object: a grease pot hung under the axle of a cart. Its meaning is narrow and technical, centered on this single artifact.
輠 combines 車 (cart, vehicle) with 果, which likely contributes the sound. The character specifically denotes a grease container attached to a cart axle.
The left side is a cart 車, and the right side 果 looks like a container with something inside. Picture a pot of grease hanging under the cart's axle, ready to lubricate the wheels.
For カ, imagine a car mechanic hanging a grease pot under the axle: car -> カ, and the cart needs its grease.