阅读说明：本技术 具有输送阶段速度调节器的注入设备 (Injection device with delivery phase speed regulator ) 是由 马修·D·法莫尔 于 2018-03-15 设计创作，主要内容包括：一种用于输送来自注射器的药剂的注入设备,该注射器在使用过程中被包含在所述设备的壳体内部,所述设备被配置成移动注射器通过所述壳体,以使注射器的注射针插入使用者皮肤,以及随后移动注射器的塞子通过注射器主体,以便通过注射针来输送药剂。该设备包括用于与塞子啮合的柱塞,围绕柱塞的套筒,相对于壳体偏置套筒的插入弹簧,以及相对于套筒偏置柱塞的输送弹簧。该设备进一步包括释放机制,用于通过从壳体上释放套筒而开始插入,并且在插入之后,通过从套筒上释放柱塞而开始输送药剂,以及速度调节器,用于在从套筒上释放柱塞的时候调节柱塞的速度以及在输送过程中脱离柱塞,所述速度调节器包括与套筒和柱塞中的一个相关联的螺纹以及在套筒和柱塞中的另一个上形成的一个或多个螺纹啮合构件。(An injection device for delivering medicament from a syringe contained, in use, inside a housing of the device, the device being configured to move the syringe through the housing to insert an injection needle of the syringe into a user's skin and subsequently move a bung of the syringe through the syringe body to deliver medicament through the injection needle. The device includes a plunger for engaging the stopper, a sleeve surrounding the plunger, an insertion spring biasing the sleeve relative to the housing, and a delivery spring biasing the plunger relative to the sleeve. The device further comprises a release mechanism for initiating insertion by releasing the sleeve from the housing and, after insertion, initiating delivery of the medicament by releasing the plunger from the sleeve, and a speed adjuster for adjusting the speed of the plunger when the plunger is released from the sleeve and disengaging the plunger during delivery, the speed adjuster comprising threads associated with one of the sleeve and the plunger and one or more thread engaging members formed on the other of the sleeve and the plunger.)

1. An injection device for delivering medicament from a syringe contained, in use, inside a housing of the device, the device being configured to move the syringe through the housing to insert an injection needle of the syringe into a user's skin and subsequently move a bung of the syringe through a syringe body to deliver medicament through the injection needle, the device comprising:

a plunger for engaging the stopper;

a sleeve surrounding the plunger;

an insertion spring biasing the sleeve relative to the housing;

a delivery spring biasing the plunger relative to the sleeve;

a release mechanism for initiating insertion by releasing the sleeve from the housing and, after insertion, initiating delivery of the medicament by releasing the plunger from the sleeve, and

a speed adjuster for adjusting the speed of the plunger when the plunger is released from the sleeve and disengaging the plunger during delivery, the speed adjuster comprising threads associated with one of the sleeve and the plunger and one or more thread engaging members formed on the other of the sleeve and the plunger.

2. The injection apparatus of claim 1, comprising a latching mechanism for latching the sleeve after insertion to prevent rearward movement of the sleeve.

3. An infusion device as claimed in claim 1 or claim 2, wherein the release mechanism comprises providing a feature on the hub for engagement directly or indirectly with a feature on a locking shroud of the device, whereby axial movement of the hub inside the housing is prevented by engagement and movement of the hub under the force applied by the insertion spring is permitted by disengagement.

4. An infusion device as claimed in any preceding claim, wherein the release mechanism comprises a feature which is fixed relative to the housing, which engages with the screw thread before and during insertion and which disengages from the screw thread after insertion.

5. The infusion device of any preceding claim, the speed adjuster being configured to cause disengagement of the one or more engagement features from the thread after a predefined axial movement of the plunger, thereby allowing axial travel of the plunger.

6. An injection device according to any preceding claim, comprising a sleeve surrounding the plunger, the sleeve being axially movable with the plunger during insertion so as to transfer force from the plunger or sleeve to the syringe body, and being disengageable from the piston after insertion so as to allow the piston to move axially through the sleeve and into the syringe body.

Technical Field

The present invention relates to an injection device for delivering a dose of a medicament from a syringe. The invention is particularly, but not necessarily, directed to a device of the type that facilitates self-injector with powered or power-assisted needle sticks and drug delivery.

Background

The injection device may be used for convenient administration of the medicament. For example, an infusion device, which may typically take the form of a pen-type infuser, may be used to provide both a single metered dose of medicament (e.g., epinephrine in an emergency) and a conventional metered dose of medicament (e.g., insulin). Such devices may be either single use "disposable" devices, which are typically equipped with a syringe that is installed and cannot be replaced by the user, or "reusable" devices that allow the user to replace the syringe after the medicament has been used.

It should be noted that although the term "syringe" is used herein for the sake of clarity and consistency, this term is not intended to be limiting. In some arrangements, the syringe may be, for example, a cartridge (which may be arranged to receive a disposable injection needle, as an example) or other medicament container. In some arrangements, the syringe/cartridge/medicament container may be formed integrally with (or as part of) the injection device.

The injection device may be provided in the form of a "self-injector" device, wherein in addition to automating the drug delivery process, the device is arranged to automate the process of inserting the injection needle into the skin prior to delivery of the drug.

The injection device typically comprises a delivery means arranged to automatically deliver a dose from a syringe and, optionally (for a self-injector), to first displace the syringe inside the housing to cause the needle to penetrate. Such delivery devices typically function by means of a plunger (also referred to as a bung) containing or engaging a piston slidably provided within the syringe. For a self-injector. Initial static friction or "stiction" between the stopper and the syringe will prevent forward movement of the plunger relative to the syringe, whereby the delivery device will initially move the syringe and plunger forward to the needle insertion position. Here, further movement of the syringe will be prevented and the delivery device will continue to move forward, thereby overcoming the static resistance and moving the plunger and stopper through the syringe.

Common forms of delivery devices include an automatic mechanism that biases the plunger forward, and a trigger mechanism that holds the plunger against the force of the (direct or indirect) actuation mechanism before it is released. By way of example, the actuation mechanism may include a drive spring (e.g., a compression spring) that remains in a charged (or primed) position until triggered by the trigger mechanism.

In WO2016/189286 a self-injector type injection device is described. The actuation mechanism of the device comprises two springs, a first, relatively weak insertion spring for moving the syringe through the device housing to insert the injection needle into the skin, and a second, relatively strong delivery spring for driving the plunger and piston through the syringe body.

WO2016/189286 solves a known problem with self-injectors in that the force exerted by the insertion spring during the needle insertion phase may be sufficiently great to damage the syringe at the end of its stroke by bottoming out against the housing. This problem is alleviated by the introduction of a speed regulator that limits the speed of the injector before it bottoms out.

Disclosure of Invention

According to the present invention, there is provided an injection device for delivering medicament from a syringe contained, in use, within a housing of the device, the device being configured to move the syringe through the housing to insert an injection needle of the syringe into a user's skin and subsequently move a bung of the syringe through a body of the syringe to deliver medicament through the injection needle. The device includes a plunger for engaging the stopper, a sleeve surrounding the plunger, an insertion spring biasing the sleeve relative to the housing, and a delivery spring biasing the plunger relative to the sleeve. The device further comprises a release mechanism for initiating insertion by releasing the sleeve from the housing and, after insertion, initiating delivery of the medicament by releasing the plunger from the sleeve, and a speed adjuster for adjusting the speed of the plunger when the plunger is released from the sleeve and disengaging the plunger during delivery, the speed adjuster comprising threads associated with one of the sleeve and the plunger and one or more thread engaging members formed on the other of the sleeve and the plunger.

Drawings

Fig. 1 is a cross-sectional view of a prior art self-injector;

fig. 2 is an exploded view of the rear portion of the self-injector of fig. 1;

fig. 3 is a cross-sectional and partial end view of an actuation mechanism including the speed regulator of the self-injector of fig. 1 in a pre-firing state;

fig. 4-6 are sequential views corresponding to fig. 3 during start-up of the self-injector of fig. 1;

FIG. 7 is a cross-sectional view of the injection device in a pre-firing state; and

fig. 8A-8C are sequential views corresponding to fig. 7 during start-up of the self-injection device.

Detailed Description

In the following embodiments, the terms "forward" and "front" refer to the end of the infusion device or part thereof facing the patient. In other words, during use, the front end of the injection device is the end close to the injection site. Likewise, the term "rear" refers to the non-patient end of the infusion apparatus fitting or component thereof. In other words, the term "posterior" refers to a distance or distance from the injection site during use.

Axial, radial and circumferential are used herein to conveniently refer to a general direction opposite to the longitudinal direction of the injection device (or elements thereof). However, those skilled in the art will appreciate that these terms should not be construed in a narrow sense (and that the injection device may be non-circular and/or irregular in form, as an example). Generally, regardless of the outer profile of the injection device selected, the syringe or cartridge has a convenient and generally cylindrical elongate form and will contain or be associated with an injection needle extending longitudinally from its forward end. Thus, the longitudinal axis of the injection device will typically be substantially coincident with (or parallel to) the axial direction of the syringe or cartridge.

Fig. 1 shows a cross-sectional view of a prior art self-injector 1 as disclosed in WO 2016/189286. The self-injector comprises a housing 10 inside which a medicament injector 5 is provided. The housing 10 has a generally elongate tubular shape and its cross-sectional profile is generally elliptical (and has a longitudinal axis passing through the centre of the syringe).

The syringe 5 is a conventional syringe having a stopper 7 inside its body and a needle 6 at its forward end, which needle may be initially protected (thereby remaining sterile) by a removable needle shield or "needle sheath" 8. The illustrated self-injector 1 should generally be a single-use device, and thus fig. 1 may generally represent a fully assembled, ready-to-use device provided to an end user. Before use, a cap 20 is provided near the front end of the autoinjector 1. The cap 20 comprises internal structure comprising a rearwardly extending member 21 arranged to engage with the removable needle shroud 8 of the syringe 5, so as to remove the cap 20 from the housing 10 and the removable needle shroud 8 from the syringe 5 during use.

The self-injector 1 comprises a front sub-assembly located at the front of the housing 10, and a rear sub-assembly located at the rear of the housing 10. During assembly, the two housing portions may be snapped together around the syringe. The front subassembly comprises elements surrounding the syringe 5 and/or initially located in front of the syringe 5. The rear subassembly comprises the elements initially located behind the syringe 5.

The front of the housing 10 includes a syringe carrier 30 for removably mounting a syringe inside the housing 10 to enable automatic needle penetration. It should be noted that the rearwardly extending member 21 of the cap 20 is located below the spring fingers 31 of the syringe carrier 30 prior to moving the cap 20. This arrangement will thereby prevent the spring clips 31 from moving inwardly prior to removal of the cover 20 and thereby prevent the spring clips 30 from tripping and moving relative to the housing 20.

A needle shield 35 will also be provided and arranged to cover the injection needle after use (when the syringe 5 and the syringe carrier 30 are in the forward position) in order to prevent needle stick injuries. The shield 35 is actuated by a pair of side-by-side shield springs 36a, 36b carried on respective spring guides 37a, 37 b. The operation of the shroud 35 and the carriage 30 is not described in any detail herein. It should be noted, however, that this arrangement corresponds substantially to the arrangement described in WO 2012/085580.

The rear of the housing 10 includes a trigger button 40 that is inserted into the rear of the housing 10 from the rear end, thereby substantially closing the rear end of the housing 10. The trigger button 40 has a cup-shaped profile with a side wall arranged to fit inside (and substantially concentric with) the rear housing 30, and an end wall closing the rear end of the housing. The trigger button 40 comprises a pair of forwardly extending resilient arms 41a and 41b arranged to provide engagement between the trigger button 40 and the injector 1.

The rear of the housing 10 also includes a drive mechanism 100 which can best be seen in fig. 2. The drive mechanism 100 comprises a plunger 110 arranged to engage, in use, the bung 7 of the syringe 5. In use, the plunger 110 will be driven forward by a pair of concentric drive springs 120 and 122 (although it will be appreciated that a single spring may be used in other embodiments). An intermediate drive member in the form of a sleeve 150 (which also acts as part of a speed regulator as described below) is provided between the first drive spring 120 and the second drive spring 122. A pair of thrust washers 121, 123 are provided between the first and second springs 120, 122 and the drive member/sleeve 150, respectively. The latch 130 is arranged to surround the drive springs 120, 122, the intermediate member/sleeve 150 and the plunger 110 in a concentric manner. The latch 130 is arranged to hold the plunger 110 against the bias of the springs 120, 122 until the latch is released by means of the trigger button 40. The latch member 130 includes a rear body portion 132 having a split cylindrical configuration and defining a latch aperture at a rear end, and a front connecting body portion 134. As an example, the basic functional operation of the drive mechanism 100 is substantially the same as described in WO2012/049484 and WO 2015/011488.

The actuation mechanism will now be described in more detail with particular reference to fig. 2 and 3-6.

Fig. 2 shows an exploded view of the rear subassembly of the self-injector device 1 (where it can be noted that the housing 10 comprises a separate rear housing element 12). The housing is omitted from fig. 3A for clarity, and only the elements directly associated with the speed regulator are shown in fig. 3B and 3C for greater clarity. As described above, the actuation mechanism includes the latch member 130, which is removably secured to the housing 10 (by a snap-fit arrangement) and initially retains the plunger 110 against the forward biasing force of the actuation springs 120 and 122 (which act through the intermediate member 150). A trigger button 40 is provided at the rear of the injection device 1, which trigger button 40 is initially held in place by a pair of arms 41a, 41 b. A forwardly extending boss 44 is provided at a central portion of the inner surface of the rearward facing face of the button 40 for forcing the plunger 110 out of engagement with the latch member 130 during actuation (e.g., in the manner described in the previously referenced applicant's prior patent application).

The boss 44 includes means for splined engagement with the rearward facing head end 112 of the plunger 110. It can be seen that the rear end of the plunger 110 is provided with a pair of axially extending radial slots which extend forwardly from the head end 112 and boss 33 which contain the corresponding projection pair. As explained in more detail below, this arrangement ensures that the plunger 110 is rotatably fixed relative to the trigger button 40. The trigger button 40, in turn, is non-rotatably engaged with the housing 10 (e.g., due to the non-circular shape of the housing 10 and the trigger button 40 and/or the engagement between the posts 41a, 41b of the trigger button 40 and the latch 130).

The actuation mechanism 100 of the self-injector apparatus 1 further comprises a speed regulator arranged to control or limit the initial speed of the plunger 110 when the actuation mechanism is released. The speed regulator uses a cam member 152, the cam member 152 traveling along a cam surface 162, the cam surface 162 providing an inclined plane along which the cam member 152 travels during actuation.

The cam surface 162 is conveniently provided on the cam body 160, wherein the cam body 160 engages the front portion 134 of the latch 130 via a snap-fit arrangement (illustratively, including at least one latch member 166). To ensure proper alignment between the cam body 160 and the latch member 130, an alignment flange 167 may also be provided on the cam body 160 to abut against a corresponding shoulder 135 in the latch 130. The cam body 160 may comprise a generally annular body with an outer profile that matches the requisite inner profile of the latch 130. A pair of helical cam surfaces 162a, 162b are defined at the rear end of the cam body and are inclined forwardly to define a pair of parallel cam paths which extend circumferentially around the interior of the injection device 1 whilst being inclined forwardly in a partial screw-thread manner. A correspondingly contoured shoulder may be provided on the inner surface of the latch 130 rearward of the cam surface 162 to define the slot or track 138 (and be configured to receive the cam member 152) when the cam body is assembled with the latch 130. A stop 163 is provided at the rear end of each cam surface 162 (which separates the individual cam paths defined by the cam body 160), and each cam surface 162 terminates in a cutout or aperture 164 at the forward-most end of the cam surface 162.

The sleeve 150 acts as an intermediate drive member between the first compression spring 120 and the second compression spring 122. Accordingly, the sleeve 150 includes an outer radial flange 151 at its forward end for seating the first compression spring 120 and an inner radial flange 154 at its rearward end for seating the second compression spring 122. Thrust washers 121, 123 are disposed on the seats between the radial flanges 151, 154 of the sleeve and the springs 120, 122. The sleeve 150 is a generally cylindrical body and is provided with a pair of radially oppositely outwardly extending ears 152a, 152 b. The ears 152a, 152b are provided on the radially outer surface of the outwardly extending flange 151 (so that they do not interfere with either compression spring 120, 122). The internal flange 154 at the rear of the sleeve 150 includes an aperture 155, wherein the head end 112 of the plunger passes through the aperture 155 when the actuation mechanism 100 is in the pre-firing state shown in fig. 3.

The aperture 155 is provided with a keyed profile defined by a cylindrical central aperture portion 155a and a pair of opposing radial slots 156. The cylindrical sidewall of the sleeve 150 extends rearwardly slightly beyond the flange 154, thereby defining a cylindrical cup surrounding the flange 154 and the aperture 155. The stopper members 157a, 157b extending radially inward may be provided at positions continuous with one side of the radial grooves 156a, 156 b.

In the pre-firing configuration, the rear portion of the plunger 110 axially rearward of the aperture 155 is provided with a profiled (profiled) profile for engaging the keyway defined by the aperture 155. This profiled portion is immediately forward of the head end 112 of the plunger configured to be engaged by the latch 130. The profiled portion is defined by a pair of radially outwardly extending projections 116a, 116b which provide a forwardly facing shoulder 117 which initially engages the rearwardly facing surface of the flange 154. The radial projections 116a, 116b are configured such that they can pass through the radial slots 156a, 156b when the radial slots 156 are aligned with the projections 116.

The sequence of actuation of the mechanism 100 and the speed adjusters will now be described with reference to fig. 3-6. The pre-firing configuration of actuation mechanism 100 is shown in fig. 3. In this configuration, the head end 112 of the plunger 110 is held within the aperture of the latch 130. As such, the first compression spring 120 and the second compression spring 122 are both in a compressed charging state. The trigger button 40 is splined to the rear end of the plunger 110 by means of a boss 44 located within a slot 114 in the rear of the plunger 110. Since a portion of the trigger button abuts the outer surface of the rear section of the latch 132, the rear portion 132 of the latch 130 cannot expand to release the head end 112 of the plunger 110.

In this position, the radial protrusion 116 of the plunger 110 is rearward with respect to the aperture 155 of the sleeve 150, and during assembly, the relative rotational position of the plunger 110 and sleeve 150 is set, whereby the protrusion 116 is not aligned with the slot 114. And in fact it should be noted that the protrusion 156 abuts against the stop 157 of the sleeve 150. In this initial position, the cam member 152 is positioned at the rearward end of the cam surface 162 and essentially abuts the stop 163 at the rearward most end of the cam surface 162.

To activate the device, the user pushes the trigger button 40 forward relative to the housing 10 of the autoinjector device 1 (any necessary initial steps have been performed in advance, such as removing the cap from the front end of the autoinjector 1 and/or releasing any safety mechanisms, such as an interlock). Forward movement of the trigger button 40 misaligns the closure means of the cover 20 with the rear section 132 of the latch 130 and also directly transfers forward thrust to the rear of the plunger 110 by virtue of the engagement of the boss 44 with the head end 112 of the plunger 110. As a result of the triggering action, the head end 112 of the plunger 110 will be released from the trigger 130, thereby releasing the rear spring 120 to advance the plunger in the direction of arrow a via the outer flange 151 or the sleeve 150.

This forward movement causes the cam members 152a, 152b to travel along the inclined path of the cam surfaces 162a, 162 b. When the first spring 120 expands, its axial force is transmitted by the sleeve 150 through the fully compressed second compression spring 122 to the forward end of the plunger 110. However, because the radial projections 116 engage the internal flange 154 at the rearward end of the sleeve 150, the plunger 110 cannot initially travel over the sleeve 150.

Due to the splined engagement between the trigger button 40 and the plunger 110, the sleeve 150 must rotate in the direction of arrow B relative to the plunger 110 as the cam members 152a, 152B travel along the cam surfaces 162a, 162B. The thrust washers 121, 123 prevent or reduce any frictional resistance caused by the springs 120, 122 to rotation of the sleeve 150. As best seen in the end view of fig. 4C, the resulting relative rotation of the sleeve 150 will cause the aperture 155 to rotate relative to the radial projections 116a, 116b, thereby causing the projections to move away from the stop surfaces 157 and toward the radial slots 156a, 156 b.

As the plunger 110 and sleeve 150 continue to move forward, the sleeve 150 will reach its fully rotated position, as shown in FIG. 5. In the illustrated example, the fully rotated position corresponds to approximately one-half turn of the sleeve 150 (although the skilled person will appreciate that the particular configuration may vary in anticipation of the profile of the cam surface and the required sequencing of the actuation mechanism 100). In this position, the radial slots 156a, 156b have rotated into alignment with the radial projections 116a, 116b, and the cam members 152a, 152b have also reached the ends of the cam surfaces 162a, 162b and have moved into alignment with the cutouts/apertures 164 at the ends of the cam paths.

Accordingly, as shown in fig. 6, the speed regulator may now be deactivated to allow the plunger to continue to advance freely (continue to advance in the direction of arrow a). In this forward movement, this forward movement of the plunger 110 will move forward relative to the sleeve 150 as the radial projections 116a, 116b pass through the radial slots 156a, 156b, and will also allow the sleeve 150 to pass forward through the cam body 160 as the cam members 152a, 152b pass through the cutout 164. In other words, the sleeve 150 will be disengaged from the plunger 110 and the sleeve 150 will be disengaged from the cam body 160. In the illustrated embodiment, the disengagement occurs in a substantially simultaneous manner (however, the skilled artisan will appreciate that this depends on the particular ordering desired). Once the radial protrusions 116a, 116b pass through the radial slots 156a, 156b, the second drive spring 122 is free to expand and push the sleeve 150 and the plunger 110. The sleeve 150 will likewise be free of the speed adjusters and the first drive spring 120 and the second drive spring 122 will act on the plunger.

Once the speed adjuster is released, the forward movement of the plunger 110 will no longer be adjusted (however the skilled person will appreciate that the plunger can now squeeze the medicament inside the syringe 5 so as to inhibit its movement in a natural manner). The force that the springs 120, 122 exert on the plunger and the cannula depends on the relative strengths of the first spring 120 and the second spring 122 and the damping force provided by the medicament through the plunger 110. Thus, once the sleeve 150 has passed through the speed adjusters, the axial movement of the sleeve 150 will depend on the application.

Although the apparatus has been described above with reference to one embodiment, it should be understood that various changes or modifications are possible. For example, the skilled person will appreciate that the timing of inter-element disengagement in the speed regulator may depend on the specific configuration of the device. For example, the speed regulator may only intentionally slow/control the movement of the plunger 110 during the initial movement of the plunger 110 into contact with the bung 7 of the syringe 5 (due to manufacturing tolerances it is often necessary for the front end of the plunger 110 to be initially spaced from the rear end of the bung 7) in order to reduce the effect thereon. Alternatively or additionally, the speed regulator may be configured to control the speed of movement of the actuation mechanism until the end of the needle insertion step of the actuation sequence. Although the illustrated example includes two opposing surfaces, the skilled person will appreciate that more or fewer features may be used.

In the illustrated device, the cam surface defines a substantially constant helical cam path, however, the skilled person will appreciate that the surface may have other slope profiles (e.g. variable slope angles) in accordance with the required speed profile for forward movement of the plunger 110. While providing two compression springs is highly advantageous in providing a compact actuation mechanism, the skilled person will appreciate that in some embodiments only a single compression spring may be used. For example, in a single spring arrangement, the cam member may be formed on a portion of the plunger, and the plunger may be allowed to rotate relative to the housing.

An alternative injection apparatus or self-injector 200 will now be described. Although the device may incorporate the features of the device of fig. 1-6, this is not required. Nevertheless, the description of the prior art devices will assist the skilled person in understanding the structure and operation of the replacement device. As will be described in more detail, a principal feature of the alternative apparatus is the provision of a speed regulator that adjusts the speed on the plunger at the beginning of the delivery phase. This speed adjustment allows the plunger tip to close any gap that initially exists between itself and the stopper inside the syringe body at a controlled rate, thereby preventing damage that would otherwise result from the plunger tip striking the stopper at high speed. Thereafter, the speed regulator will disengage from the plunger, thereby allowing the full force of the delivery spring to be applied to the plunger, and thus to the stopper. It is noted that this speed regulator is different from the speed regulator which regulates the speed during the insertion phase as described above. The speed regulator described below may be used in conjunction with speed regulators of the prior art, but this is not necessarily so.

Figure 7 shows an infusion device 200 having this feature. Although not all features are described herein, a number of elements are indicated in the figures, including a housing 201, a cover 202, a locking shroud 203, a plunger 204, an insertion spring 206, a delivery spring 207, and a sleeve 208. The device comprises a syringe having a syringe body 300, an injection needle 301 and a stopper 302 inside the syringe body 300. Figure 8 shows the upper part of the device in a different operating configuration in more detail.

Considering still further the construction of the upper part of the apparatus, the plunger 204 has the general form of a hollow cylinder with an elongate pin 205 depending into the plunger 204 from the top of the sleeve 208 and being axially movable with the sleeve 208. A delivery spring 207 is located inside the plunger 204 and surrounds the pin 205.

An insertion spring 206 abuts the top end of the sleeve 208 at its upper end so that it biases the sleeve 208 relative to the cap 202. Threads 209 are provided on the inside of the upper end of the sleeve 208. A pair of protrusions 210 are provided on the outer surface of the plunger 204, and the protrusions 210 engage with the threads 209. The cover 202 is fixed relative to the housing and is non-rotatable, and includes a pair of opposed depending legs 211. These struts 211 extend along axial slots provided in the sleeve such that the struts 211 intersect the threads 209, thereby initially preventing rotation of the plunger 204 within the sleeve 208. The sleeve 208 cannot rotate inside the housing, but it can move axially as will be described. The delivery spring 207 will bias the plunger 204 forward against the sleeve 208. In order for the plunger 204 to travel axially, it must rotate the speed adjuster thread 209 downward. The position of the cover post 211 resists such rotation and thereby maintains the plunger 204 in its stored state.

A sleeve 216 surrounds the plunger and contains spring fingers 217 at its upper end which initially engage corresponding recesses in the outer surface of the plunger 204. During insertion, features inside the housing will prevent the spring clip 217 from flexing outward. Thus, during insertion, the sleeve 216 will move axially with the plunger 204. The bottom of the sleeve 216 is provided with a flange 218 which abuts against the flange 304 of the syringe body 300.

In fig. 7, the device is shown in four different operating configurations. The left configuration shows the device prior to use with both the insertion spring 206 and the delivery spring 207 in a compressed state (also shown in fig. 8A). In this configuration, the injection needle 301 of the syringe is protected by a rubber sheath 303. Prior to performing an injection, the user removes the rubber sheath 303. As can be seen in fig. 8A, in this state a pair of posts 212 associated with the housing will engage with corresponding detents provided in the outer surface of the sleeve 208. The locking shield 203 (or some element secured to the locking shield) prevents the legs from moving outward. In this manner, the insertion spring 206 will be held in compression and the sleeve 208 will be locked in place. The user may then press the end of the locking shield 203 against the skin. Once the locking shield 203 is pushed far enough in the device housing, the legs 203 will be free to flex outwardly, thereby releasing the sleeve 208 from the housing. This configuration is shown in the second diagram of fig. 7.

The insertion spring 206 is now able to expand, thereby pushing the sleeve 208 and plunger 204 (and the delivery spring 207, which is still compressed), through the housing. At this stage, since the sleeve 216 is still fixed to the plunger 204, the sleeve 216 pushes the syringe body 300 in front of it, thereby causing the injection needle 301 to pierce the skin of the user. This movement will continue until the syringe bottoms out on the stop feature formed in the housing. After the stop 214 extending outwardly from the collar snaps under a pair of flexible posts 215 associated with the housing, the syringe will bottom out. This can best be seen in fig. 8C. This will prevent any rearward movement of the sleeve 208 within the housing.

At this stage, the housing features that prevent the spring clips 217 from flexing outward from the sleeve 216 will no longer engage, thereby allowing the spring clips 217 to flex outward and release the sleeve 216 from the plunger 204. It will also be seen in figure 8C that the sleeve 208 is also moved relative to the cap 202 so that the legs 211 no longer engage the projections 210, thereby releasing the plunger 204 to rotate within the sleeve 208 under the force exerted by the delivery spring 208. The plunger 204 will begin to rotate down the threads 209. As shown in the third of fig. 7, the bottom of the plunger 204 will move downward and through the syringe body, thereby closing any gap between the end of the plunger 204 and the stopper 302 until the plunger 204 contacts the stopper 302. This process is performed while the speed of the plunger 204 is controlled by the translation through the threads 209. The plunger 204 will then begin to push the bung 302 through the syringe body 300, thereby ejecting the medicament through the tip of the injection needle 301. Shortly thereafter, the plunger 204 will move sufficiently in the axial direction to disengage from the threads 209 in the sleeve 208. At this point, the threads 209 will cease inhibiting movement of the plunger 204 and the full force of the delivery spring 207 will be released, thereby acting on the stopper 302.

It will be appreciated that various modifications can be made to the embodiments described above without departing from the scope of the present invention. For example, rather than the plunger 204 rotating relative to the sleeve 208, the opposite is true. The positions of the threads 209 and the protrusions 210 may be reversed.