An injection device with a gearbox

ES 2 249 442 T3

DESCRIPTION

Injection device with gearbox.

The invention relates to syringes by which a dose can be set by turning a dosing element and by which an injection button is raised from one end of the syringe at a distance proportional to the prepared dose and where the prepared dose can be injected by pressing the injection button to its non-raised position.

A more or less classical pen of this type is described in EP 327 910.

When setting a dose in this pen, a tubular element forming an injection button is screwed along a threaded piston rod at a distance corresponding to the distance that said piston rod must be moved to inject the prepared dose. The tubular element simply forms a nut that during dosing is screwed away from a stop and that during injection is pressed until it hits the stop again and the force exerted on the button is directly transmitted to one end of the piston closure of a ampoule in the syringe, ampoule containing the medicine to be injected. When the piston is pressed into the vial the drug is pressed out through a needle mounted through a closure at the other end of the vial.

It has long been desired to store a larger quantity in ampoules, usually 3 ml instead of 1.5 ml. As it has not been considered appropriate to make the syringe longer, instead the ampoule has been provided with a larger diameter, that is, the area of ​​the piston in front of the drug in the ampoule has been doubled and consequently the force there has been doubled. to be exerted on the piston to provide the same pressure as before within the ampoule. Furthermore, the distance that the piston has to be moved to inject one unit of the drug has been reduced by half.

This development is not very favorable, since especially users with little finger force have their difficulties in pressing the injection button, a problem that is further increased when even finer needles are used to reduce the pain produced by the injection. Furthermore, with fairly small movements of the button it is difficult to perceive whether the button has moved somewhat and by injection of a unit of a 3 ml ampoule, the piston and consequently the injection button have to be moved only about 0.1 mm.

Consequently there is a demand for a gear between the injection button and the piston so that the button has a greater travel than the piston. By means of such a gear the movement of the injection button is made greater and the force to be exerted on the injection button is correspondingly reduced.

In EP 608343 a gear is obtained by the fact that a dosing element is screwed along a spindle with a coarse thread. When said dosing element is pressed again in its axial direction, the thread will cause a rotation of said dosing element, which rotation is transmitted by means of a coupling to an actuating nut with a fine pitch, which actuating nut will make it pass towards front a non-rotatable threaded piston rod.

A similar gear is provided in WO 99/38554 where the coarse thread is cut on the outer surface of a dosing drum and is engaged by a mating thread on the inner side of the cylindrical housing. However, with this type of gear the relatively large surfaces slide over each other so that most of the transformed force is lost due to friction between the sliding surfaces. Consequently, a traditional gearing using mutually meshing sprockets and spur gears is preferred.

From WO 96/26754 an injection device is known where two integrated gear wheels mesh with a rectilinear gear in the housing and a rectilinear gear within a piston, respectively. When the plunger is moved axially in the housing the spur gear within this piston can drive the first gear wheel to cause the other integral gear wheel to follow along the spur gear fixed in the housing. In this way the gear wheel is moved in the direction of movement of the piston but at a shorter distance than this piston and this axial movement of the integrated gear wheels is transmitted by means of a housing that surrounds said gear wheels to a piston rod that presses the piston of a vial further into this vial. However, the spur gear within the plunger is one of a number of axial spur gears provided within the plunger. These rectilinear gears alternate with toothless recesses, which allow axial movement of the plunger without the first gear wheel in engagement with a rectilinear gear on this plunger. This arrangement is provided to allow the plunger to be moved in a direction away from the housing when preparing a dose. When the plunger rotates to prepare a dose it is moved outward a distance corresponding to one unit during the part of the rotation in which the first gear wheel passes through the toothless recess, then the first gear wheel receives one of the gears rectilinear so that the prepared unit can be injected, or the rotation can be continued to pass the first gear wheel through the next recess, passing which the prepared dose is increased by one more unit and so on until a dose with the desired number of units is prepared.

A disadvantage of this construction is that the teeth of the spur gears and the gear wheels have to be alternately brought in and out of engagement with each other with the inherent danger of colliding. Since only a few spur gears separated by recesses with no intermediate teeth can be placed along the inner surface of the plunger, only a few increments can be made during a 36θ ° turn.

It is an object of the invention to provide an injection device that combines the advantages of the devices according to the prior art without adopting their disadvantages and to provide a device where a direct gear is established, that is, a gear by which further transformations of rotary movement in linear movement and linear movement in rotary movement, between the injection button and the piston rod.

This can be obtained by an injection device2

ES 2 249 442 T3 tion comprising a housing where a piston rod threaded with a first passage is not rotatably guided but longitudinally movable with a nut engaging the thread of the piston rod, nut that can be threaded along the threaded piston rod out of a defined position in the housing to set a dose and can be pressed back into said defined position bringing the piston rod with it when the prepared dose is injected, a dosing drum being able to be threaded outwardly into the housing along a thread with a second step for lifting an injection button with it from the proximal end of the housing, the injection device of which according to the invention is characterized by the fact that a gearbox is provided that provides an engagement between the axial movements of the injection button and the nut with respect to the housing, gear having a gear ratio corresponding to the ratio of said second and first steps.

In a preferred embodiment, the engagement between the movements of the injection button and the nut is obtained by the gearbox comprising at least one gear wheel carried by a connector protruding from the gearbox longitudinally movable but not rotatable with respect to to said gearbox and forms a single piece with the nut, a first rectilinear one-piece gear with a first element of the gearbox, element that is rotatable but not longitudinally displaceable with respect to the housing, and a second element that carries a second rectilinear gear projecting from said longitudinally displaceable gearbox but that does not rotate with respect to said first element and being coupled to the injection button to continue longitudinal movements of said button, at least one gear wheel engaging the first and second rectilinear gears, respectively, and being dimensioned to provide a gear whereby a longitudinal movement of the second rectilinear gear is transformed into a longitudinal movement of the connector with a gear ratio for said longitudinal movements of the second rectilinear gear and the connector with respect to the housing, gear ratio which corresponds to the ratio of said second to said first step.

In such a device only the forces necessary to drive the dosing drum are transformed by a coarse thread, while the forces necessary to move the piston for injection are transmitted to said piston through a conventional gear with gear mechanisms and constantly meshed straight gears.

The piston rod is provided with a stop for movement of the nut along the thread of said piston rod. In this way a dosage limiter is provided in the classical way, which does not involve any additional element to prevent a dosage from exceeding the amount of liquid remaining in the ampoule.

The invention will now be described in greater detail with reference to the drawing, where

Figure 1 schematically shows a cross-sectional view of an injection device according to the invention, and

Figure 2 schematically shows a cross-sectional view of the gearbox along line II of figure 1,

Figure 3 shows a longitudinal cross-sectional view in the dosing part of another embodiment of an injection device according to the invention,

Figure 4 shows a longitudinal cross-section perpendicular to the view of figure 3, and

Figure 5 shows a defragmented image of the device shown in Figures 3 and 4.

In the device shown in figure 1 an elongated cylindrical housing 1 has a subdivision wall 2 that divides the housing into a compartment containing a dosing mechanism and a compartment 3 designed for receiving an ampoule not shown. A threaded piston rod 4 has a non-round cross section through which it is inserted through a central opening in wall 2 so that the piston rod 4 can be longitudinally displaced through the central opening in wall 2 but not rotated relative to this wall.

Concentric to the housing 1, the wall 2 carries on its side opposite the compartment 3 a tubular element 5 which is in a part adjacent to the wall 2 provided with an external thread 6 and which has a circumferential recess at its free end 7. A Ring-shaped coupling element 8 in a gearbox 9 engages recess 7. By this coupling the gearbox is fixed in the housing 1 in a way that allows the gearbox 9 to rotate in the housing but not axially displaced with respect to said housing.

In gearbox 9 a gear wheel assembly comprising two one-piece gear wheels is bolted on a shaft 11, which extends perpendicular to the longitudinal axis of the device between two axial connecting rods 12. The connecting rods 12 protrude of the gearbox towards the dividing wall 2 and are connected to a nut 13 which, adjacent to the wall 2, meshes the thread of the piston rod 4. The gear wheel assembly comprises a gear wheel 14 with a large diameter meshing the teeth of a spur gear 15 which is guided in the gearbox to be displaced in the longitudinal direction of the device, and a gear wheel 16 with a small diameter meshing a spur gear 10 in figure 2 extending in the longitudinal direction of the device on the inner wall of gearbox 9. The gear wheel 16 with the small diameter can be divided into two gear wheels placed on each side of the gear wheel 14, and the spur gear on the inner wall of the gear box 9 can have a longitudinal recess without any teeth. leaving a space for the gear wheel 14.

A tubular dosing drum 17 mounted on the housing 2 is provided at one end with an internal thread engaging and engaging the external thread 6 of the tubular element 5 and has at its other end a part of a larger diameter forming a dosing knob 18. Due Upon engagement with the thread 6 the dosing drum 17 can be screwed and unscrewed from the housing to display a number on a helical scale not shown on its surface

ES 2 249 442 T3 external in a window not shown in the housing

1.

A bottom 19 in a deep cup-shaped element, having a tubular part 20 mounted on the dosing drum 17 and surrounding the gearbox 9, forms an injection button. A coupling means between the dosing drum 17 and the cup-shaped element ensures that the rotation of the dosing drum 17 is transmitted to the cup-shaped element. Furthermore, the inner wall of the tubular part 20 has longitudinal recesses 22 engaged by the protrusions 23 in the gearbox 9 so that the rotation of the dosing drum 17 by means of the cup-shaped element is transmitted to the gearbox 9 .

Provided at the edge of the open end of the cup-shaped element is a rosette with "V" teeth, the teeth of which mesh a corresponding rosette with "V" teeth 24 in a ring 25 which is pressed against the edge of a cup-shaped element by a spring 26 which is compressed between a non-serrated side of the ring 25 and a rounded shoulder 27 on the internal wall of the dosing drum 17 at an internal end of the internal thread of this drum. The ring is provided with an internal recess which is engaged by a longitudinal rib 28 in the tubular element 5, so that the ring 25 can be displaced in the axial direction of the device but cannot be rotated with respect to the housing 1. Thereby a ratcheting engagement is established which clicks when the "V" shaped teeth on the edge of the cup element by rotation of this element run over the "V" shaped teeth of the ring 25.

A head 29 at the projecting end of the spur gear 15 is fixed with a clearance at the bottom of the cup-shaped element between the bottom 19 forming the injection button and an internal wall 30 near this bottom. The rectilinear gear is fixed in a position with its head pressed against the wall 30 by a spring 31 between the bottom 19 and the head 29.

To prepare a dose the dose knob 18 rotates to screw the dose adjustment drum 17 along the thread 6. Due to the coupling 21 the cup-shaped element will follow the rotation of the dose drum 17 and will be raised with it. housing end drum 1. Due to the rotation of the cup-shaped element, the “V” shaped teeth on the edge of its open end will run over the “V” shaped teeth of the non-rotating ring to make a click for each unit the dose is changed. . Too high a dose can be reduced by turning the dose knob 18 in the opposite direction to the direction to increase the dose. When the dosing drum is screwed along the thread 6 in the tubular element 5 the ring 25 follows the dosing drum in its axial movement since the spring 26 is supported on the shoulder 27. The spring will keep the "V" shaped teeth of the ring 25 and the cup-shaped element in engagement and will keep the coupling 21 in engagement, which may comprise the Δ-shaped protrusions 32 on the cup-shaped element engaging the elements. Λ-shaped recesses in an inner ring 33 in dose knob 18.

The rotation of the dosage knob 18 and the cup-shaped element is subsequently transmitted to the gearbox 9 through the protrusions 23 in this gearbox engaging the longitudinal recesses 22 in the inner wall of the tubular part 20 of said cup-shaped element. The rotation of the gearbox is transmitted through the connecting rods 12 to the nut 13, which is in this way screwed along the thread of the piston rod 4 and raised from its support with the wall 2 when a dose is ready. As the dose is prepared by moving the nut 13 on the piston rod that actuates the piston in the ampoule not shown in compartment 3, a dosage limiter, which ensures that the size of the prepared dose does not exceed the amount of the medicine to be has remained in the blister, it can easily be established by providing the piston rod 4 with a stop 35 that limits the movement of the nut 13 along the piston rod 4.

Due to the confinement of the head 29 in the space between the bottom 19 and the wall 30 of the cup-shaped element, the spur gear 15 is driven out with the injection button. Also the axial movement of the nut 13 with respect to the housing 1 will be transmitted to the gear wheel assembly through the connecting bars 12 and this movement through the gear box will determine an external movement of the rectilinear gear 15. This induced external movement has to be the same as the external movement induced by the external movement of the injection button. This is obtained by sizing the gear wheels of the gearbox 9 so that the gear ratio for the movements of the connecting rods 12 and the spur gear 15 with respect to the housing corresponds to the ratio of the pitches for the thread in the piston rod and for the thread 6 for the longitudinal movement of the dosing drum 17.

To inject a prepared dose, the injection button is pressed by pressing the bottom 19. In the initial phase of pressing, the spring 31 is compressed, after which the pressure force is directly transmitted to the head 29 of the rectilinear gear 15 and from this way to the spur gear itself 15. Through the gearbox 9 the force is transformed and transmitted through the connecting rods 12 to the nut 13 which will compress the piston rod 4 in the compartment 3 until the dosing drum 17 is adjacent to the wall two.

During the initial phase of the injection button movement the Δ-shaped protrusions 32 on the cup-shaped element will be pulled out of engagement with the Λ-shaped recesses in the ring 33. The dosing drum 17 can now rotate with relative to the injection button and will do so when the Δ-shaped protrusions 32 press against a shoulder 34 at the bottom of the dose button 18. Only a force sufficient to rotate the dosing drum to screw down along the thread 6 is necessary as the force necessary to cause the injection to be transmitted to the piston rod 4 through the gearbox 9. A helical restoration spring 36 concentric to the dosing drum can be mounted on the lower end of this drum and can have one end anchored in the dosing drum 17 and the other end anchored in the wall 2. During the preparation of a dose this spring can be wound more tightly so that on the drum

ES 2 249 442 T3 dosing exerts a rotary impulse approximately corresponding to the rotary impulse necessary to overcome the friction in the movement of the dosing drum along the thread 6, so that the force that the user must exert on the injection button be only the force necessary to actuate the piston rod in an ampoule to inject the prepared dose.

It should be noted that the use of only one size of meshing gear wheel as well as the spur gear 15, which is movable with respect to the gearbox 9, as well as the spur gear 10, which cannot be moved with respect to The gearbox provides a 2: 1 gear ratio for longitudinal movement with respect to the syringe housing 1 for the movable spur gear 15 and the connector 12, which carries the gear wheel shaft 11.

Figures 3 and 4 show a preferred embodiment where only one gear wheel size is used and where the elements corresponding to the elements of figures 1 and 2 are given the same references as those elements with a prefix "1 ”.

For production reasons minor changes are made. Thus the dividing wall 102 and the tubular element 105 are made as two parts that are, by assembling the device, connected to each other so that the assembled parts act as an integral part. Likewise the dosing drum 117 and the dosing knob 118 have been made as two parts which are firmly fixed together.

A circumferential recess 107 is provided as an external recess in the free end of the tubular part 105 and a ring-shaped coupling element is provided as an internal flange 108 on the gearbox element 109, which flange meshes with the recess 107 to provide an about but not axially movable connection between the tubular portion 105 and the gearbox.

A tubular element 120 having serrations 122 engaging the recesses 123 in the gearbox is closed at its head by a button 119 from where a force provided by pressing this button is transmitted to the tubular element 120.

The gearbox is made up of two housings, which together form a cylinder mounted on the tubular element where the housings are guided by the engagement between splines 122 and recesses 123. Spur gears 110 and 115 are provided along the edges of the housings opposite each other. One housing forming the gearbox part 109 is provided with the internal flange 108, which meshes the circumferential recess 107 at the end of the central tubular part 105 and carries the rectilinear gear 110. The other housing is axially movable in the tubular element 120 and forms spur gear 115. At its outer end, projecting from the gearbox, the housing that carries the rectilinear gear 115 is provided with a flange 140 that is located in a cutout 141 at the end of the tubular element 120 carrying the button 119 so that this button and the tubular element 120 can be moved so far into the device that the engagement of teeth 132 and 133 can be released before button 119 hits shoulder 140.

A tubular connecting member 112 connects the threaded piston rod 104 to the gearbox. The connecting element has, at the end that engages the piston rod 104, a nut 113 with an internal thread engaging the external thread of the piston rod. The connecting element is provided, at the end that meshes the gearbox, with two shafts 111 projecting perpendicular to the longitudinal axis of the connecting element 112 on each side of this element. Each shaft 111 carries a gear wheel 114 that is placed in the middle and receives the two rectilinear gears 110 and 115. In this way the connecting element 112 will be rotated with the gearbox but can be axially displaced with respect to said gearbox. when the spur gears 110 and 115 move relative to each other. In practice it will be the rectilinear gear 115 that moves with respect to the gearbox element 109 and the housing and will result, due to the construction shown, a movement of the connecting element 112 with respect to the housing a distance which is half the distance that the spur gear 115 moves. A ring 125 which is provided on its periphery with a tooth rosette 124 and has a central hole, fits over the central tube in the housing 101 so that this ring 125 can be axially displaced along said central tube 105, but the internal splines 128 in the center hole of the ring 125 engage the longitudinal recesses 137 in the center tube to make the ring non-rotating in the housing, such that a rosette of teeth on the edge of the tubular member 120 can click on the teeth 124 of the ring when said tubular member rotates with the dosing drum 117. A spring 126 that operates between the ring 125 and an internal shoulder 127 provided in the dosing drum 117 causes the ring to follow the tubular element 120 when this element with the dosing drum is moved longitudinally in the housing. To easily rotate the dosing drum, especially when the dosing drum is pressed into the housing, a roller bearing is provided with an outer ring 142 supported by shoulder 127 and an inner ring 143 supporting a pressure bearing 144 that supports the spring 126. By providing this smooth running support only very small axial forces are needed to rotate the dosing drum 117 back to its zero position when a ready dose is injected. This solution replaces the provision of a reset spring such as spring 36 in Figure 1. The bearing is shown as a radial bearing but can be replaced by an axial bearing.