In unibody cars, what is used to provide constant velocity?

In unibody vehicles, a constant velocity (CV) joint is specifically designed to maintain a constant rotational velocity through varied angles, making it ideal for connecting the drive shafts to the wheels. This is especially crucial in unibody cars, which often have more complex suspension systems and steering geometry compared to traditional body-on-frame vehicles. The CV joint allows the wheels to turn and move up and down in response to the vehicle’s suspension while still transmitting power from the engine.

The other options do not provide the same functionality. A universal joint, while also transmitting torque and allowing for some flexibility in angles, does not maintain a constant rotational speed as effectively as a CV joint. Piston rods relate to engine components and aren’t relevant to the drivetrain function in terms of providing constant velocity. An axle assembly typically encompasses different components including the drive shaft and gears, but it doesn't directly serve the purpose of ensuring constant velocity through varying angles as the CV joint does.