Injection device without a gearing

A dose delivery device comprising:

• a housing;
• a dose selector;
• a push-button;
• a piston rod threadably engaged to the housing, the piston rod not rotating during dose setting and rotating during injection;
• a driver threadedly engaged with the piston rod and having a flexible arm;
• and
• a numbered scale drum rotationally locked to the driver during dose setting and injection and axially moveable with respect to the driver, the scale drum having a slanted rib extending toward the driver;
• wherein when the driver and the scale drum are pressed together, axial movement of the scale drum toward the driver causes the slanted rib to engage the flexible arm and apply an axial force between the slanted rib of the scale drum and the flexible arm of the driver,
• wherein a dose can be set by rotating the dose selector, whereby the push-button is elevated from one end of the device a distance proportional to the set dose from a position fixed relative to the housing,
• wherein the set dose can be injected by pressing the push-button back to its non-elevated position, through which motion the piston rod and the driver will move the same distance, at least after an initial movement of the push-button, and
• wherein the driver follows a helical path in one direction when setting a dose and the driver follows the same helical path in an opposite direction and together with the piston rod when injecting the set dose.