Device for administering a fluid

A device for administering a fluid, comprising:

• a cylinder, including an open dispensing end;
• a piston, which is displaceable in the cylinder between a front end position and a rear end position, and is connected to a piston rod which, along a first direction, protrudes from a rear end of the cylinder opposite the open dispensing end;
• a nonreturn valve closing the open dispensing end;
• and
• a tensioning device connected to the piston rod, and including a ramp,
• wherein the tensioning device can move the piston rod along the first direction in a tensioning procedure until the piston is in the rear end position, thereby filling the cylinder with the fluid to be administered and to pretension the piston rod toward the open dispensing end, and
• wherein the tensioning device, when the piston is in the rear end position, releases the piston rod in a dispensing procedure such that, owing to the pretension which is present, the piston is moved counter to the first direction toward the open dispensing end and, in the process, the fluid in the cylinder is dispensed via the nonreturn valve for administration,
• wherein the ramp of the tensioning device is rotatable by a motor and includes a ramp track extending along a helical line,
• wherein the ramp track ascends from a first plateau along a region of inclination to a second plateau, and descends from the second plateau to the first plateau via a transition flank,
• wherein the ramp track includes a transfer region connecting the second plateau and the transition flank,
• wherein the tensioning device includes a roller which is in contact with the ramp track and which is mounted rotatably in a driver, the driver connected to the piston rod, and therefore, upon rotation of the ramp along a first rotation direction, the ramp track can run below the rotating roller,
• wherein, the ramp track is configured to be rotated in a tensioning procedure along the first rotation direction such that the roller runs on the region of inclination as far as the second plateau and the piston is thereby moved to the rear end position,
• wherein, the ramp track is configured such that in the dispensing procedure, starting from a contact of the roller with the second plateau, the ramp track can be rotated along the first rotation direction until the roller runs over the transfer region and, on account of the tensioning, is accelerated toward the first plateau, whereby the piston is moved toward the open dispensing end,
• wherein a dose setting unit is provided, the dose setting unit comprising a spacer and a movement unit,
• wherein the movement unit can move the spacer, when the piston is in the rear end position, from a neutral position, in which the spacer is not positioned between the driver and the cylinder, into an active position between the driver and the cylinder such that the driver, after the roller has run over the transfer region, is stopped by the spacer and therefore the piston stroke during the movement of the piston to the open dispensing end is shorter in comparison to the case in which the spacer is in the neutral position,
• wherein the spacer includes a through bore in which a spindle with a spindle thread is guided,
• wherein the spacer includes a pin which protrudes into the spindle thread,
• wherein the spindle thread has two ends, and
• wherein the spindle thread leads at least one of the two ends into an annular groove.