A device for automatically injecting a dose of a medicinal product, comprising:
- a long narrow casing having a front wall (26) pierced by an orifice (27b), and formed of two parts, a front part (11) and a rear part (10) fitted one into the other and capable of sliding longitudinally in relation to each other over a short traverse so as to be able to undergo a relative movement between two positions:
- a retracted rest position, of the rear part (10) with respect to the front part (11) obtained naturally in the absence of an external force exerted on the said parts, and a forward injection position, of the rear part (10) with respect to the front part (11) obtained by means of a longitudinal force exerted on the said rear part,
- a syringe (1) disposed in the casing and including a syringe body housing a piston (6), provided with a finger rest ring (4) and carrying a needle (3),
- a piston rod (7) provided with a collar (9) and extending into the rear extension of the syringe (1),
- means (35) for supporting the collar (9) of the piston rod (7),
- a propulsion spring (50) extending between the means (35) for supporting the collar (9) of the piston rod (7) and the bottom of the rear part (10) of the casing,
- means (15, 18, 39) for locking in translation the means (35) for supporting the collar (9) of the piston rod (7), capable of supporting them inside the casing in a position where the propulsion spring (50) is compressed, and where the syringe (1) is entirely housed inside the said casing, and capable of allowing their movement towards a forward position at the end of injection, produced by the propulsion spring (50), after the parts (10, 11) of the casing are moved from their retracted position to their forward position,
- a device (27c) for stopping the syringe body (1) in a forward position of the latter where the needle (3) extends at least partially through the orifice (27b) of the casing,
- means (13) for triggering the means (35) for supporting the collar (9) of the piston rod (7), capable of freeing the said collar, in the forward position of the said supporting means, after the parts (10, 11) of the casing are moved from their forward position to their retracted position,
- and a return propulsion spring (51) with a force less than that of the propulsion spring (50), disposed around the syringe body (1) so as to be compressed by the finger rest ring (4) of the said syringe body when the latter is moved to its forward position,
- wherein the said injection device:
- includes means for viewing (28, 29) provided in the wall of the casing so as to enable the means (35) for supporting the collar (9) of the piston rod (7) in their forward position to be seen,
- means for supporting the collar (9) of the piston rod (7) comprising:
- an inner guide tube (13) extending into the rear part (10) of the casing so as to delimit a peripheral annular space (21) within the latter adapted so as to house the propulsion spring (50) in the compressed position of the said spring,
- a cage (35) with a form adapted so as to slide inside the guide tube (13), and to house the piston rod (7) and the collar (9) thereof, the said cage including towards one of its ends, the rear end, an internal device (41) for locking the collar (9) of the piston rod (7), capable of deforming radially and, towards its other forward end, a front wall (38) for stopping the propulsion spring (50) and for contacting the means (15, 18, 39) for locking in translation the said supporting means in the retracted position of the latter,
- the said guide tube and cage being adapted so that, in the forward position of the supporting means (35), the device (41) for locking the collar (9) of the piston rod (7) remains imprisoned in the guide tube (13) in the forward relative position of the parts (10, 11) of the casing, and is freed in the retracted relative position of the said parts of the casing.