Dosing Unit for an Ambulatory Infusion Device

A dosing unit for an infusion pump device, the dosing unit comprising:

• a piston pump with a pump cylinder;
• a plunger arranged within the pump cylinder, the pump cylinder and the plunger coaxially arranged along a longitudinal axis;
• and
• a separate bias force element;
• wherein the plunger has a plunger shaft with a plunger thread and the pump cylinder has a threaded sleeve part with a cylinder thread;
• wherein one of the plunger thread or cylinder thread is an outer thread and the other one is an inner thread, the inner thread and outer thread engaging with each other in such a way that a rotational movement of the plunger around the longitudinal axis results in a linear displacement of the plunger along the longitudinal axis;
• and
• wherein the separate bias force element that biases the two threads in regard to each other along the longitudinal axis, such that the threaded engagement of the inner thread and the outer thread is free of play independent of a direction of a rotational movement and linear displacement of the plunger in regard to the cylinder.