Injection device with torsion spring and rotatable display

An injection device comprising:

• a housing (5) with an inner surface provided with threads (10),
• a dose setting member (1) adapted to set a dose to be ejected from the injection device,
• a piston rod (2) having a threaded outer surface with a track (7) arranged in a longitudinal direction of its outer surface,
• a rotatable drive member (6) that engages with the track (7) or with the threaded outer surface of the piston rod to drive the piston rod (2),
• a torsion spring (12) for accumulating energy that is releasable to rotate the drive member (6) whereby causing the piston rod (6) to move in a distal direction of the injection device to eject the set dose automatically,
• wherein,
• a rotatably mounted display member is operatively connected with the dose setting member (1) such that when the dose setting member (1) is rotated in order to set a dose,
• the display member rotates with the dose setting member (1) causing the display member to be axially displaced relative to the housing (5) and is adapted to display the dose to be ejected from the injection device in accordance with a setting of the dose setting member (1),
• a release button positioned in a distal half of the length of the injection pen,
• wherein when the release button is activated by the user, the release button causes the torsion spring to drive the set dose from the injection pen and the dose indicator barrel rotates during injection back to a zero position,
• the rotatably mounted display member is rotatable over an angle corresponding to at least one revolution, and the display member further returns to return to zero during ejection.