Piezo Actuator
WARNING: This page does not describe the selected car, but rather 8 other vehicles, including the 2016 Ford Transit-350 HD, 2016 Ford Transit-350, 2016 Ford Transit-250, 2016 Ford Transit-150, and 2016 Ford F-550 Super Duty. However, it is still accessible from the selected car via links, so may be relevant.
The piezo actuator consists of a series of small disks. When the piezo actuator is electrically energized, it causes the disks to deform which results in an expansion. The expansion generates a longitudinal motion which pushes down against the valve piston. The piezo actuator returns to its non-energized state by fuel and spring pressure during engine operation, and by the spring pressure from the fuel injector valve return spring when the engine is shut down.