[0001] This disclosure relates to the field of dose setting mechanisms for an injection device, preferably for reusable pen-type injection devices.

BACKGROUND

[0002] Certain injection devices have a dose setting member, or dose selector, via which the user can select a desired dose of medicament to be delivered from the injection device. The dose selector can commonly be actuated in one direction to increase the set dose ("dialling up") and actuated in another direction to decrease the set dose ("dialling down"). As the dose is dialled up or down, this correspondingly increases or decreases stored energy in the device (e.g. in a torsion spring). An example of this type of dose setting can be seen in WO2006/045528.

[0003] In WO2006/045528, a drive member is connected to a dose setting member via a self-tightening ratchet having saw-toothed teeth. The ratchet enables the dose setting member to be rotated in both directions so that a given dose may be set, whilst preventing the spring from unwinding from the currently selected dose.

[0004] Another example of an injection device having this type of ratchet is described in WO2015/032780. A ratchet interface 1 19 between a dose selector ("dial member 106") and a drive member 108 prevents the spring unwinding.

[0005] Such dose setting ratchets have the additional advantage of creating audible and tactile feedback for each dose unit dialled by the user.

[0006] In both of the above prior art examples, if the user continues to increase the selected dose until the maximum dose limit is reached, a component abuts a hard endstop on an inner surface of the injection device housing, thus preventing further dialling up of the dose. A disadvantage of this arrangement is that, should the user continue to attempt to increase the dose, damage to components of the injection device may occur.

[0007] This issue is mitigated in US8920383 which describes a toothed limiter 10 which has a stopping position in which the dose cannot be further increased. If the user continues to apply torque to the dose setting member, two torque paths are provided such that it is possible to provide a larger torque without breaking parts of the device. In this way, the risk of the user causing damage to the device is reduced. BRIEF SUMMARY OF THE DISCLOSURE

[0008] In accordance with an aspect of the present invention there is provided an injection device comprising:

a housing having a longitudinal axis;

a dose selector capable of being rotated about said longitudinal axis with respect to said housing by a user to set a dose of medicament to be ejected from the injection device; a spring capable of storing energy necessary for ejecting the dose from the injection device, wherein the spring is coupled to the dose selector such that a charging force can be transferred from the dose selector to the spring to increase the energy stored by the spring; and

a ratchet arrangement rotationally coupling a ratchet component and an internal surface of the housing;

wherein the injection device further comprises

an over-torque feature arranged between the dose selector and the spring, the over-torque feature being actuable, when the rotation of the dose selector causes the charging force to exceed a defined limit, to reduce the charging force transferred from the dose selector to the spring,

and in that the ratchet component and the over-torque feature are both provided on a single component.

[0009] The ratchet arrangement limits the spring from unwinding from the currently selected dose. By having both the ratchet component and the over-torque feature provided on a single component, the construction of the injection device may be simplified and potentially made more cost effective. Fewer components may increase the reliability and accuracy of the injection device.

[0010] In certain embodiments, the spring may be a torsion spring and the charging force transferred to the spring is a charging torque. The injection device may further comprise a drive assembly having a rotational to axial coupling, where the drive assembly is rotationally drivable by the torsion spring and is arranged to provide an axial force for ejecting the dose from the injection device.

[0011] Additionally, or alternatively, the injection device of any of the preceding paragraphs wherein the spring is directly coupled to the dose selector. Alternatively, the spring may be coupled to the dose selector via one or more intermediate components capable of transmitting the charging force.

[0012] The single component may be a unitary component. Alternatively, the single component may comprise at least two component parts fixed with respect to one another.

[0013] In an embodiment, the drive assembly includes a drive shaft and the single component is said drive shaft. The ratchet component may comprise one or more ratchet arms on said drive shaft, the drive shaft ratchet arms being couplable with said internal surface of the housing. Preferably, said over-torque feature comprises one or more rearwardly-extending splines on said drive shaft, the drive shaft splines being couplable with one or more pawls on said dose selector. Forward axial movement of said drive shaft may be capable of uncoupling said ratchet component from said internal surface of the housing and, preferably also may be capable of engaging said ratchet component with a haptic feedback track on a second internal surface of the housing. The haptic feedback track may be located at a rear portion of the injection device where the device is intended to be gripped by a user.

[0014] In another embodiment, the single component comprises a ratchet pawl or a selector pawl.

The ratchet component may comprise one or more radially-flexible ratchet arms couplable with said internal surface of the housing. Additionally, said ratchet arms may be moveable radially-inwardly, so as to decouple them from said internal surface of the housing, by an inwardly-directed tab on an internal surface of said dose selector. Alternatively, said ratchet arms may be moveable radially-inwardly, so as to decouple them from said internal surface of the housing, by a ratchet disengagement finger formed on a dose button.

[0015] The over-torque feature may comprise one or more rearwardly-extending ratchet fingers, the ratchet fingers being engageable with a dose indicator. Alternatively, the over- torque feature may comprise one or more radially-inwardly extending splines, the splines being moveable between a coupled position in which they are rotationally coupled with a drive shaft of said drive assembly and an uncoupled position in which they are disengaged from drive shaft by the splines moving radially-outwardly.

[0016] In an embodiment, said one or more radially-inwardly extending splines are arranged on an elastic bridge of pawl material. The elastic bridge of material may be built by recesses, in particular cutaways in the pawl behind the splines.

[0017] In an embodiment, the over-torque feature is capable of reducing the charging force transferred from the dose selector to the spring to substantially zero.

[0018] In an embodiment, the injection device may further comprise a medicament container where the medicament container may comprise a pre-filled syringe, or cartridge. The injection device may further comprise a medicament contained in the medicament container. In certain embodiments, the medicament may be selected from the group comprising: antipsychotic substances including risperidone, hormones, antitoxins, substances for the control of pain, immunosuppressives, substances for the control of thrombosis, substances for the control or elimination of infection, peptides, proteins, human insulin or a human insulin analogue or derivative, polysaccharide, DNA, RNA, enzymes, antibodies, oligonucleotide, antiallergics, antihistamines, anti-inflammatories, corticosteroids, disease modifying anti-rheumatic drugs, erythropoietin, or vaccines, for use in the treatment or prevention of rheumatoid arthritis, psoriatic arthritis, ankylosing spondylitis, ulcerative colitis, hormone deficiency, toxicity, pain, thrombosis, infection, diabetes mellitus, diabetic retinopathy, acute coronary syndrome, angina, myocardial infarction, atherosclerosis, cancer, macular degeneration, allergy, hay fever, inflammation, anaemia, or myelodysplasia, or in the expression of protective immunity.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Embodiments of the invention are further described hereinafter, by way of example only, with reference to the accompanying drawings, in which:

Figure 1 shows an injection device in accordance with an embodiment of the present invention;

Figure 2 is a schematic representation of a force path of an injection device according an embodiment of the present invention;

Figure 3 is a cross-sectional view of selected injection device components, in schematic form;

Figure 4 is a perspective view of another embodiment of the injection device;

Figure 5 is an exploded view of the injection device of Figure 4;

Figure 5A is a perspective view showing further detail of the dose limit nut;

Figure 5B is a perspective view showing further detail of part of the plunger rack;

Figure 6 is a cross-sectional view of the injection device of Figure 4;

Figures 7 and 7A - 7C illustrate incrementing the dose;

Figures 8, 8A and 8B illustrate decrementing the dose;

Figures 9, and 9A - 9D illustrate maximum/minimum dose limiting;

Figures 10 and 10a illustrate over-torque protection;

Figures 1 1 ,1 1 A— 1 1 C, 12 and 12a - 12B illustrate dose delivery;

Figures 13, 13A and 13B illustrate a haptic feedback feature; Figures 14 and 14A - 14E illustrate last dose protection;

Figure 15 is a diagrammatic summary of the key engagement points of the components of the injection device of Figure 4, at four stages of dose delivery;

Figure 16 summarises schematically the mechanical motion of the drive shaft 140, dose limit nut 141 , worm gear 142 and plunger rack 145 during dose setting

(incrementing the dose);

Figure 17 summarises schematically the mechanical motion of the drive shaft 140, dose limit nut 141 , worm gear 142 and plunger rack 145 during dose delivery;

Figures 18, 18a and 18B show how the units wheel is incremented;

Figures 19, 19A and 19B show how the tens wheel is incremented;

Figure 20 is a perspective view of another embodiment of the injection device;

Figure 21 is an exploded view of the injection device of Figure 20;

Figure 21 A is a perspective view of the ratchet pawl, drawn to a larger scale;

Figure 21 B is a perspective view of the drive clutch, drawn to a larger scale;

Figure 22 is a cross-sectional view of the injection device of Figure 20;

Figure 23 is a cross-sectional view, drawn to a larger scale, of the rear end of the injection device of Figure 20;

Figure 24 is a cross-sectional view, drawn to a larger scale, of the central portion of the injection device of Figure 20;

Figures 25 and 25A - 25C illustrate incrementing the dose;

Figures 26, 26A and 26B illustrate decrementing the dose;

Figures 27 and 27A - 27F illustrate dose delivery;

Figure 28 illustrates a haptic feedback feature;

Figures 29, 29A and 29B illustrate last dose protection;

Figure 30 is a perspective view of the odometer mechanism;

Figure 31 is a perspective view of the units wheel from the odometer mechanism;

Figure 32 is a perspective view of the tens wheel from the odometer mechanism;

Figure 33 is a perspective view of the shuttle lock from the odometer mechanism;

Figure 34 is a perspective view of housing features relevant to the odometer mechanism; Figures 35A - 35C show three stages of the odometer mechanism's operation;

Figures 36, 36A and 36B show further detail of the stage illustrated in Fig. 35A;

Figure 37 shows further detail of the stage illustrated in Fig. 35B;

Figure 38 shows further detail of the stage illustrated in Fig. 35C;

Figures 39A and 39B illustrate maximum/minimum dose limiting; and

Figure 40 is a diagrammatic summary of the key engagement points of the components of the injection device of Figure 20, at six stages of dose delivery.

Figure 41 is a perspective view of another embodiment of the injection device;

Figure 42 is an exploded view of the injection device of Figure 41 ;

Figure 43 is a cross-sectional view of the injection device of Figure 41 ;

Figure 44 shows the rear end of the injection device of Figure 43, drawn to a larger scale;

Figures 45A - 45C illustrate incrementing the dose;

Figures 46A - 46C illustrate decrementing the dose;

Figures 47A and 47B illustrate over-torque protection;

Figure 48 is a cross-sectional view of a central portion of the injection device, showing key components involved in dose delivery;

Figures 49A - 49C illustrate dose delivery;

Figure 50 is a diagrammatic summary of the key engagement points of the components of the injection device of Figure 41 , at four stages of dose delivery;

Figures 51 A and 51 B show how the lead screw is advanced during dose delivery;

Figure 52 is a cross-sectional view of a central portion of the injection device, showing key components involved in dose display;

Figures 53A and 53B illustrate dose display;

Figure 54 is a cross-sectional view of a central portion of the injection device, showing key components involved in last dose protection; and

Figures 55A - 55C illustrate last dose protection. DETAILED DESCRIPTION

[0020] In the present disclosure, the following terms may be understood in view of the below explanations:

[0021] The term "injection device" may refer to a device intended for the injection of a medicament to the body and includes devices configured for various delivery methods, such as intradermal, subcutaneous, intramuscular, intravenous, intraosseous,

intraperitoneal, intrathecal, epidural, intracardiac, intraarticular, intracavernous, and intravitreal, which may include via a cannula, catheter or similar device. Injection device includes syringes of all types, devices that contain said syringes such as auto-injectors, pen-injectors, patch injectors and other similar devices.

[0022] The term "pen -injector" may include any device configured to deliver a dose of a medicament from a cartridge.

[0023] The term "user" may refer to a medical practitioner, end user or other user associated therewith.

[0024] The term "coupling" may refer to a connection between components (not necessarily a direct connection; there may be intermediate components therebetween) that enables a force to be transmitted between the components.

[0025] The term "a rotational coupling" may refer to a coupling which enables a rotational force to be transmitted between the components.

[0026] The term "operatively connectable" may refer to at least two individual components which are releasably connectable together in such a way that the individual components can work together, for example wherein rotation of one of the individual components effects rotation of all of the operatively connected components.

[0027] The term "dose selector" may refer to a component or components which, when actuated by a user, enable a dose of medicament to be selected.

[0028] The term "dose indicator" may refer to a component or components which provide a display or indication to the user of the selected dose of medicament.

[0029] The term "splines" may refer to one or more ridges, ribs or other protrusions on one component which engage in corresponding grooves or the like on a second

component to connect the two components together.

[0030] The term "a splined connection" may refer to a connection effected by one or more splines. [0031] The term "forward" or "forwards" may refer to a direction towards the end of the injection device from which medicament is expelled.

[0032] The term "backward", "backwards", "rearwards" or "rearwardly" may refer to a direction away from the end of the injection device from which medicament is expelled.

[0033] The term "drive assembly" may refer to an assembly of components capable of using a driving force from, for example, a spring, to eject medicament from an injection device.

[0034] The term "backlash" may refer to a clearance caused by a gap between mechanical components.

[0035] The term "medicament" may include a substance in liquid or gas form. The medicament may be selected from the group comprising of: antipsychotic substances including risperidone, hormones, antitoxins, substances for the control of pain,

immunosuppressives, substances for the control of thrombosis, substances for the control or elimination of infection, peptides, proteins, human insulin or a human insulin analogue or derivative, polysaccharide, DNA, RNA, enzymes, antibodies, oligonucleotide, antiallergics, antihistamines, anti-inflammatories, corticosteroids, disease modifying antirheumatic drugs, erythropoietin, or vaccines, for use in the treatment or prevention of rheumatoid arthritis, psoriatic arthritis, ankylosing spondylitis, ulcerative colitis, hormone deficiency, toxicity, pain, thrombosis, infection, diabetes mellitus, diabetic retinopathy, acute coronary syndrome, angina, myocardial infarction, atherosclerosis, cancer, macular degeneration, allergy, hay fever, inflammation, anaemia, or myelodysplasia, or in the expression of protective immunity.

[0036] When referring to the injection device, the term "containing the medicament", may refer to the medicament being contained within a suitable medicament container, such as a pre-filled syringe or cartridge, within the injection device.

[0037] The terms "rotationally locked to" or "rotationally locked with respect to" may refer to a prevention of relative rotational movement between two rotationally locked components i.e. substantially no relative rotational movement between two rotationally locked components is possible.

[0038] The term "a force path" may refer to a path between two or more coupled components via which a force can be transmitted between the components. A force path may be "interrupted" if there is a gap between the two or more components, i.e. if they are no longer coupled. Transmission of force between coupled components may be "held back" for example by a ratchet arrangement, but in such a case the force path is not "interrupted". [0039] The term "a clutch" may refer to a component or feature suitable for operatively connecting two component parts either by a positive fit e.g. with teeth, splines, grooves or the like suitable for engaging and disengaging each other, or by a non-positive (frictional) connection or a combination thereof. Disengaging the clutch may interrupt a force path between two or more coupled components.

[0040] The term "ratchet arrangement" may refer to an arrangement of components comprising a set of teeth and a "ratchet component" which can engage in said teeth to permit one-way movement.

[0041] The term "over-torque feature" may refer to a feature located on a first component and capable of interacting with a second component so as to reduce a force being transferred along a force path from the first component to the second component, for example by changing the direction of the force path and/or creating an additional force path.

[0042] The term "single component" may refer to one component, an integrally-formed component, a unitary component, or at least two component parts fixed together or with respect to one another.

[0043] The term "haptic feedback track" may refer to a plurality of ridges, ribs, teeth, or other protrusions on an internal surface of the injection device and with which another component, moving rotationally with respect thereto, can engage to provide audible and/or tactile feedback to a user of the injection device.

[0044] The term "a dose button" may refer to a button or the like at the rear of the injection device which is actuated, for example by pressing axially-forwardly with respect to the device housing, in order to initiate dose delivery.

[0045] The term "arranged between two components" may refer to being located, situated or otherwise positioned between the two components, so as to be capable of influencing any coupling between the two components. The two components may have any number of components arranged between them.

[0046] Description of First Example Embodiment

[0047] An injection device 10 according to an embodiment of the present invention is shown in Figure 1. The injection device 10 is configured to deliver a dose of medicament and extends along a longitudinal axis L between a front end 10a and a rear end 10b of the injection device 10. The injection device 10 has a housing 12 and a needle 14 projecting from the housing 12 at the front end 10a. A dose selector 16 is provided at the rear end 10b and is arranged to permit the selection of a desired dose of medicament for delivery through the needle 14 into an injection site. The housing 12 includes an aperture 12a through which a dose indicator 18 is visible.

[0048] Figure 2 shows a schematic representation of a force path 26 within the injection device 10. In particular, the force path 26 extends between internal components of the injection device 10 that are arranged in series with one another. The internal components include the dose selector 16, a ratchet component and an over-torque feature provided on a single component 28, a spring 20, a drive assembly 22 and a medicament container 24. As described in further detail below, the spring 20 is configured to provide a drive force to the drive assembly 22 such that the drive assembly 22 may act to dispense medicament from the medicament container 24.

[0049] The dose selector 16 is coupled to the spring 20 such that a charging force can be transmitted from the dose selector 16 to the spring 20 in order to charge the spring 20. The spring 20 is charged when a force is applied to the spring 20 so as to elastically deform the spring 20, and the resulting elastic energy is stored by the spring 20 (i.e. it is prevented from elastically relaxing during a storage phase). Therefore, charging the spring 20 involves increasing the energy stored by the spring 20.

[0050] The spring 20 is coupled to the drive assembly 22 and is arranged to provide a driving force thereto when energy stored by the spring 20 is released. The drive assembly 22 acts to expel medicament from the medicament container 24. In certain embodiments, the medicament container 24 may be a syringe, vial or cartridge having a barrel and a stopper moveable in the barrel. In such embodiments, the drive assembly 22 may act to move the stopper so as to expel medicament through an opening in the barrel. In certain embodiments of the invention, the medicament cartridge may or may not be connected to a needle.

[0051] In embodiments where the spring 20 is a torsion spring, the spring 20 is charged by applying a torque to wind the spring 20 and elastic energy may be stored by the spring 20 and subsequently released as torque.

[0052] In embodiments where the spring 20 is a compression spring, the spring 20 may be charged by applying an axial force to compress the spring 20 and elastic energy may be stored by the spring 20 and subsequently released as an axial force.

[0053] In certain embodiments, the force path 26 may include one or more torque paths and/or one or more axial force paths, where one or more rotational to axial couplings are employed to switch between rotational and axial forces along the force path 26. Indeed, in certain embodiments, one or more intermediate components may be provided between any of the components shown in Figure 2.

[0054] Figure 3 shows the dose selector 16 located near the rear end 10b of the injection device. The dose selector 16 can be rotated with respect to the housing 12. A single component 28 comprises the ratchet component 25 and the over-torque feature 27.

[0055] As torque or axial force is applied to charge the spring 20, for example by rotating the dose selector 16, the ratchet component 25 periodically moves between a coupled state in which it is coupled to the housing 12 and an uncoupled state in which relative rotation between the ratchet component and the internal surface of the housing 12 is permitted.

[0056] If the torque or axial force applied to charge the spring 20 exceeds a defined limit, for example if the user continues to rotate the dose selector 16 past the maximum dose limit, the over-torque feature 27 is actuated to reduce the charging force transferred from the dose selector 16 to the spring 20. Both the ratchet component and the over-torque feature are provided on a single component 28.

[0057] Description of Second Example Embodiment

[0058] A further, non-limiting, embodiment of an injection device according to the present invention is illustrated in Figures 4-19B.

[0059] Referring to Figures 4 - 6, the injection device 100 includes a housing 112, a dose selector 116, a dose button 130 and dose button spring 131 , a units wheel 118, a tens wheel 119, a dose indicator spring 117, a drive shaft 140, a drive spring 120, a dose limit nut 141 , a worm gear 142, a worm gear support 143 and a worm gear rotational lock 144, all located concentrically about a common longitudinal axis L. The axis L extends between a front end 100a and a rear end 100b of the injection device 100.

[0060] The injection device 100 has a medicament cartridge 124 supported in a cartridge holder 125 at the front end 100a of the injection device 100. The cartridge 124 is sealed by an axially-moveable cartridge stopper 126 at its rear end. The cartridge and cartridge holder are located concentrically about a second longitudinal axis Lc, such that the cartridge is offset from the main housing 112, with L and Lc offset from one another as shown in Figure 6.

[0061] The dose button 130 is biased rearwardly by the dose button spring 131. The dose selector 116 is provided at the rear end 100b of the injection device 100 and is arranged to permit the selection of a desired dose of medicament for delivery from the medicament cartridge 124 into an injection site. The dose selector 116 is axially constrained with respect to the housing 112 but is rotatable with respect thereto, about axis L. The dose selector 116 is rotationally coupled to the drive shaft 140 via pawl features 115, visible in Figure 7A, which engage splines 149 on the drive shaft 140. The housing 112 is provided with teeth 113 (visible in Figure 7A) on an inside surface thereof for engaging ratchet arms 146 on the drive shaft 140. Tabs 114 on the dose selector 116 are capable of depressing the drive shaft ratchet arms 146 when required, as shown in Figure 8B. The housing 112 is also provided with ramp features 111 (visible in Figure 12A) which facilitate disengagement of the ratchet arms 146 from the inside surface of the housing 112 when required.

[0062] A dose indicator is disposed within the housing 112 and displays reference indicia, such as numbers or symbols, to indicate the level of dose selected by the dose selector 116. The housing 112 includes an aperture 112a through which the dose indicator is visible. The dose indicator comprises the units wheel 118 for displaying units and the tens wheel 119 for displaying tens. The units wheel 118 is selectively engageable with the tens wheel to increment the tens wheel each time the units wheel moves through units 0 to 9. The units wheel 118 is rotationally coupled to the drive shaft 140.

[0063] As with the first embodiment, described with reference to Figures 1 -3, biasing means in the form of dose indicator spring 117 biases the units wheel 118 and tens wheel 119 axially rearwardly in the housing.

[0064] The housing 112 has features on an inside surface thereof for engaging with the units wheel 118 and the tens wheel 119.

[0065] An internal surface of the housing 112 is provided with a tens housing feature 108 selectively engageable with the tens wheel 119 to prevent rotation thereof. The tens housing feature comprises one or more axially forwardly extending formations 108 which may be equally spaced around the internal circumference of the housing 112. The formations 108 engage with corresponding axially rearwardly extending formations 119b at the rear of the tens wheel 119. The tens housing feature formations 108 and the tens wheel formations 119b may be teeth, notches, castellations or any other shaped formations that, when engaged together, prevent relative rotation between the tens wheel 119 and the housing 112.

[0066] An internal surface of the housing 112 is provided with a units housing feature 107 capable of moving the units wheel axially-forward against said biasing means 117. The units housing feature is an axially forwardly extending formation 107 having a cam surface which can engage with an axially rearwardly extending formation 118b on the units wheel 118 in order to push the units wheel 118 axially forwards. [0067] Teeth 118a on the front end of the units wheel 118 are engageable with correspondingly shaped teeth 119a at the rear end of the tens wheel 119. On the tens wheel 119, the teeth 119a (for engaging the units wheel) and the tens wheel formations 119b (for engaging the housing) may be concentrically arranged around the longitudinal axis of the injection device, with the teeth 119a radially inward of the formations 119b.

[0068] The drive spring 120 is a torsion spring which is fixed at one end with respect to the housing 112 and rotationally coupled at its other end to the drive shaft 140 via the units wheel 118.

[0069] A worm gear arrangement is provided which comprises a worm gear 142 meshed with a toothed plunger rack 145 located within the housing 112. During dose delivery, the worm gear 142 drives the plunger rack 145 forward which, in turn, pushes against the cartridge stopper 126 to deliver a dose of medicament. A splined clutch 150 at the forward end of the drive shaft 140 enables the worm gear 142 and drive shaft 140 to be splined together during dose delivery but not during dose setting and this will be described in more detail later. In Figure 6, the worm gear rotational lock 144 is engaged in the forward end of the worm gear 142, preventing rotation thereof. The worm gear rotational lock 144 is capable of being pushed axially forward by the drive shaft 140 in order to disengage the lock from the worm gear 142.

[0070] The dose limit nut 141 is keyed to the drive shaft 140 so that they are rotationally coupled but not axially coupled. The dose limit nut 141 is engaged with the teeth of the plunger rack 145 and can travel axially forward and backward along the plunger rack 145 as the dose is incremented or decremented respectively. The axial range within which the dose limit nut 141 can travel along the plunger rack 145 is determined by dose limit nut endstop features 141 a, 141 b which can engage features on the plunger rack thread to serve as endstops for the travel of the dose limit nut 141. Figure 5A shows the maximum dose limit nut endstop feature 141 a and the minimum dose limit nut endstop feature 141 b in more detail. Endstops 141 a, 141 b are able to engage features 147, 148 respectively on the plunger rack 145 (Figure 5B). These features 147, 148 are preferably changes in the depth of or formations on the plunger rack thread, past which the dose limit nut 141 cannot travel. During dose delivery, the dose limit nut 141 rotates about axis L with the drive shaft 140 to which it is keyed, but it does not move axially with respect to the plunger rack 145 with which it is engaged, thus always keeping the dose limit nut 141 within the range defined by the max/min dose endstops.

[0071] The operation of the respective features of the injection device 100 will now be described in more detail below.

[0072] Dose setting - incrementing the dose [0073] With the injection device 100 in the configuration shown in Figure 7, the user grips the dose selector 116 and rotates it clockwise about axis L, with respect to the housing 112, in order to increment the dose and charge the drive spring 120. As the dose selector 116 is turned clockwise, the pawl features 115 engaging the splines 149 on the drive shaft 140 cause the drive shaft 140 to also be driven clockwise, as shown in Figure 7A.

[0074] While the dose is being incremented, the ratchet arms 146 on the drive shaft 140 engage with the teeth 113 on the inside surface of the housing 112 to prevent un-winding by the drive spring 120, as shown in Figure 7B.

[0075] As shown in figure 7C, the drive shaft 140 is splined to the units wheel 118 which charges or torques up the drive spring 120. In other words, torque is transferred from the dose selector 116 to the drive spring 120 directly through the dose indicator, i.e. the units wheel 118.

[0076] Dose setting - decrementing the dose

[0077] When it is desired to decrement the selected dose, the dose selector 116 is turned anti-clockwise. As shown in Figure 8A, as the dose selector 116 is turned anticlockwise, there is a small amount of backlash at point A such that the dose selector 116 can rotate slightly with respect to the drive shaft 140. This small relative movement is sufficient to allow the tabs 114 on the dose selector 116 to depress the drive shaft ratchet arms 146 so that they can click past the housing teeth 113, allowing the drive spring to unwind slightly before the ratchet arms 146 catch again on the next housing tooth 113.

This is represented in Figure 8B. Each decrement preferably equates to 1 1U ("international unit") of medicament.

[0078] Dose setting - maximum/minimum dose

[0079] As the drive shaft 140 is rotated during dose setting, the dose limit nut 141 , which is keyed to the drive shaft 140, is also rotated (Figure 9A). The dose limit nut 141 travels forwards when incrementing the dose and rearwards when decrementing the dose (Figure 9B). The dose limit nut 141 is engaged in the thread of the plunger rack 145. Endstop features 147, 148 are located on the plunger rack 145, past which the dose limit nut 141 cannot travel (Figure 9C). These endstop features 147, 148 may be changes in the depth of the thread. As shown in Figure 9D, when the dose limit nut 141 rotates into a position wherein the dose limit nut endstop feature 141a engages feature 147 on the plunger rack 145, a rotary endstop occurs, preventing further rotation of the dose limit nut 141 so that a dose of medicament greater than the desired maximum dose of medicament cannot be set. Limiting the travel of the dose limit nut 141 sets the maximum and minimum doses of medicament that can be set during dose setting, preferably 1001 U and 01 U respectively. [0080] Dose setting - over torque

[0081] As shown in Figure 10A, in the event the user applies too much force (over torque)to the dose selector 116 in either rotational direction, the dose selector pawl features 115 will flex radially outwardly to allow them to skip past splines 149 on the drive shaft 140. Preferably the interfacing surface areas of the pawl features 115 and/or splines 149 act as a cam lever, preferably having a matching angle and/or a defined static and dynamic surface friction at the interface surface. The over-torque for flexing out the dose pawl features 115 to skip past spline 149 is preferably at least 10% higher than the torque required for dialling up (incrementing) or dialling down (decrementing) the dose indicator 18, 118. The dialling up torque can be 30 to 80 Nmm, preferably less than 60 Nmm, more preferably 30 to 50 Nmm. The dialling down torque can be 20 to 60 Nmm, preferably less than 50 Nmm, more preferably 30 to 40 Nmm. The over-torque in the dialling up direction may be different to the over-torque in dialling down direction. The outward flexing force and/or strength of one flexible pawl arm 115 could be lower compared to a second flexible pawl arm.

[0082] Figure 16 summarises schematically the mechanical motion of the drive shaft 140, dose limit nut 141 , worm gear 142 and plunger rack 145 during dose setting

(incrementing the dose). The drive shaft 140 rotates clockwise. The dose limit nut 141 rotates clockwise and advances forwards with respect to the plunger rack 145.

[0083] Dose delivery

[0084] To initiate dose delivery, the user presses the dose button 130 against the bias of the dose button spring 131 as shown in Figure 1 1A. This pushes the drive shaft 140 axially forwards. Although the drive shaft 140 is splined to the units wheel 118, it is free to slide axially with respect thereto (Figure 1 1 B).

[0085] As the drive shaft 140 advances, at its forward end, the splined clutch 150 between the drive shaft and the worm gear 142 engages (Figure 1 1 C, Figure 15 - Worm Gear Clutch 150). Preferably the drive element, in particular the worm gear 142 and the drive shaft 140 engage after 0.5 mm to 1.5 mm advancement of the dose button 130, more preferably after 0.8 mm to 1 .2 mm advancement of the dose button 130. Once the clutch 150 has started to engage, the ratchet arms 146 on the drive shaft 140 begin to disengage from the inside surface of the housing 112 aided by ramp features 111 (Figure 12A, Figure 15 - Hold Ratchet). Preferably the hold ratchet, in particular the ratchet arms 146 on the drive shaft 140 start to disengage from the structured, in particular toothed surface of the housing 112 after 1 .5 mm to 2.5 mm advancement of the dose button 130, more preferably after 1 .6 mm to 1.9 mm advancement of the dose button 130. Also, as the drive shaft 140 moves forward, the splines 149 coupling the drive shaft 140 to the dose selector 116 disengage (Figure 12B, Figure 15 - Over torque ratchet). Preferably the over torque ratchet, in particular the drive shaft splines 149 on the drive shaft 140 start to disengage from the dose selector pawls 115 after 1.5 mm to 3.5 mm of advancement of the dose button 130, more preferably after 2 mm to 3 mm advancement of the dose button 130. The dose indicator and drive shaft 140 are now free to rotate about longitudinal axis L.

[0086] The drive spring 120 drives the units wheel 118 to rotate about longitudinal axis L. The units wheel 118 drives the drive shaft 140 which drives the worm gear 142.

[0087] Figure 17 summarises schematically the mechanical motion of the drive shaft 140, dose limit nut 141 , worm gear 142 and plunger rack 145 during dose delivery. The drive shaft 140, dose limit nut 141 and worm gear 142 all rotate anti-clockwise. Only the plunger rack 145 advances forwards. During dose delivery, the dose limit nut 141 rotates with the drive shaft 140 but does not move axially with the plunger rack 145. The dose limit nut 141 and the drive worm gear 142 preferably have the same thread pitch.

[0088] The worm gear 142 actuates the plunger rack 145 to move axially forwards causing the cartridge stopper 126 to be driven into the cartridge in order to expel medicament thus delivering the selected dose.

[0089] When the dose button 130 is released, the dose button spring 131 returns the dose button 130 and drive shaft 140 to their original starting positions. This axially rearward movement disengages the worm gear clutch 150 and re-engages the drive shaft ratchet arms 146 with the housing 112 thereby stopping dose delivery.

[0090] Dose delivery - haptic feedback

[0091] During dose delivery, the drive shaft ratchet arms 146 run (rotationally) on a relatively smooth track 110 on the inside surface of the housing 112 (Figure 13A).

Optionally, this track could be modified to include ridges 109 which would provide audible/haptic feedback to the user during dose delivery (Figure 13B). The ridges 109 are conveniently placed relatively close to the user's fingers.

[0092] Last dose protection

[0093] When the medicament cartridge 124 is relatively empty, after several doses have already been delivered therefrom, it is undesirable for the user to be able to select a dose that is larger than the available quantity of medicament remaining. Last dose protection is provided to deal with this situation. Conveniently, the last dose protection is provided by the same feature as the max/min dose limiting i.e. the dose limit nut 141. [0094] As shown in Figure 14, after several doses have been delivered, the plunger rack 145 and dose limit nut 141 have advanced axially forwards such that the dose limit nut 141 is approaching the worm gear 142. When there is less than a predetermined amount (e.g. 100IU) of medicament available, the worm gear 142 serves as an endstop, stopping the dose limit nut 141 from moving further forwards and before the maximum dose limit feature 147 on the plunger rack 145 is reached (Figure 14A). Preferably, it is the dose limit nut endstop feature for maximum dose limiting 141a which engages the worm gear 142. If the user tries to increment the dose further, torque is transmitted through the dose limit nut 141 into the worm gear 142, the torque being reacted to by the worm gear rotational lock 144 (Figure 14B). As such, the worm gear 142 is unable to rotate due to rotational engagement with the rotational lock 144.

[0095] During dose delivery, when the drive shaft 140 is moved axially forwards, the worm gear clutch 150 is engaged before the worm gear rotational lock 144 is disengaged (Figure 14C). The axially-forward movement of the drive shaft 140 causes its forward end to push the worm gear rotational lock 144 out of the front of the worm gear 142. With the worm gear rotational lock 144 disengaged, the worm gear 142 is free to rotate, driven by the drive shaft 140 (Figure 14D). Once dose delivery is finished, the drive shaft 140 moves rearwardly. The worm gear rotational lock 144 re-engages, before the worm gear clutch 150 is disengaged (Figure 14E).

[0096] Figure 15 is a diagrammatic summary of the key engagement points of the injection device components, at four stages of dose delivery.

[0097] Dose display

[0098] As already described above, during dose selection the user rotates the dose selector 116 which also drives the drive shaft 140 around. Ratchet arms 146 interact with teeth 113 in the housing 112 to prevent unwinding (Figure 18A). The drive shaft 140 is splined to the units wheel 118 which, as it turns, increments the displayed unit (Figure 18B).

[0099] The units wheel 118 and tens wheel 119 are biased rearwardly by dose indicator spring 117. Twice per revolution of the units wheel 118, the units wheel 118 is moved axially forwards by the cam surface of the units housing feature 107 engaging with the formation 118b on the units wheel 118. This axially forward movement causes the teeth 118a of the units wheel 118 to engage with the teeth 119a of the tens wheel 119 (Figure 19A). Continued forward axial movement of the units wheel 118 pushes the formations 119b of the tens wheel 119 away from the tens housing feature 108, so that the tens wheel 119 is free to rotate with respect to the housing 112, allowing the tens wheel 119 to be driven around by the units wheel 118 by one increment (Figure 19B). [00100] In a preferred embodiment, the selectable and settable dose range is 1 to 100 IU, with a minimum dose setting of 1 IU, wherein per 360 degree rotation of the dose selector 116, 20 to 30 I U may be set. As the units wheel 118 and tens wheel 119 arrangement permits indication of the set IU dose by two digits, a much larger font size for the indicated dose number is usable, thus the arrangement affords better readability of the set dose and usability of the injection device 10, 100.

[00101] As with the first embodiment, described with reference to Figures 1 -3, the ratchet component (ratchet arms 146) and over-torque feature (splines 149) are both located on a single component (drive shaft 140).

[00102] Description of Third Example Embodiment

[00103] A further, non-limiting, embodiment of an injection device according to the present invention is illustrated in Figures 20-40.

[00104] Referring to Figures 20-24, the injection device 200 includes a housing 212, a dose selector 216, a dose button 230 and dose button spring 231 , a units wheel 218, a tens wheel 219, a ratchet pawl 217, a housing top cap 221 , an odometer shuttle lock 222, a drive spring 220, a drive sleeve 240, a last dose nut 241 , a drive clutch 250, a drive clutch spring 251 , a leadscrew nut 252, a leadscrew 253 and a thrust bearing 254, all located concentrically about a common longitudinal axis L. The axis L extends between a front end 200a and a rear end 200b of the injection device 200.

[00105] The injection device 200 has a medicament cartridge 224 supported in a cartridge holder 225 at the front end 200a of the injection device. A needle or needle hub unit (not shown) can be connected to the cartridge holder. The cartridge is sealed by an axially- moveable cartridge stopper 226 at its rear end.

[00106] The dose button 230 is biased rearwardly by the effect of the dose button spring 231 between the housing 212 and front end of the drive sleeve 240 with which the dose button 230 is axially engaged. The dose selector 216 is provided at the rear end 200b of the injection device 200 and is arranged to permit the selection of a desired dose of medicament for delivery from the medicament cartridge 224 into an injection site. The dose selector 216 is axially constrained with respect to the housing 212 but is rotatable with respect thereto, about axis L. The dose selector 216 is used to set the dose by increasing the rotational preload of the drive spring 220 which is prevented from unwinding by the ratchet pawl 217 which engages between the housing 212 and the units wheel 218.

[00107] The ratchet pawl 217 (best seen in Figure 21 A) includes a plurality of ratchet fingers 217a which, in the assembled injection device 200, extend generally axially rearwardly to engage with the units wheel 218 as shown in Figure 25C. The ratchet pawl 217 also includes ratchet arms 217b which, in the assembled injection device 200, engage with teeth 213 on the inside surface of the housing 212 to prevent un-winding of the drive spring 220, as shown in Figure 25B, while the dose is being incremented.

[00108] A dose indicator is disposed within the housing 212 and displays reference indicia, such as numbers or symbols, to indicate the level of dose selected by the dose selector 216. The housing 212 includes an aperture 212a through which the dose indicator is visible. The dose indicator comprises the units wheel 218 for displaying units and the tens wheel 219 for displaying tens and the odometer shuttle lock 222. The units wheel 218 is intermittently coupled to the odometer shuttle lock 222 which is always rotationally coupled to the tens wheel 219. The tens wheel 219 has maximum and minimum dose limit features in the form of rotational endstops 271 , 272 respectively, which can engage a limiting rib 290 in the housing 212 to keep the selected dose within the range defined by the maximum and minimum doses. This max/min dose limiting will be described in more detail later.

[00109] With reference to Figures 30-34, the dose indicator is an odometer comprising a units wheel 218, a tens wheel 219 and an odometer shuttle lock 222. The units wheel 218 has units numbers 260 around the circumference thereof, comprising two consecutive series of the numbers 0 - 9. Two drive dogs 261 are located 180 degrees apart on the internal surface of the forward end of the units wheel 218 and two engagement splines 262 are also located 180 degrees apart from one another. The sets of drive dogs 261 and engagement splines 262 may be rotationally offset from one another by approximately 90 degrees. In an alternative embodiment the units wheel 218 may comprise one consecutive series of the numbers 0 - 9 around its circumferential surface, and one drive dog 261. The units wheel 218 may comprise one or more than two engagement splines 262, the engagement splines 262 rotationally arranged to be engageable with the shuttle lock rear teeth 283. The drive dogs 261 have angled faces which, when engaging corresponding angled faces 282 on the shuttle lock 222, cause a camming action that can move the shuttle lock 222 axially.

[00110] Tens wheel 219 has tens numbers 270 around the circumference thereof, comprising a series of the numbers 0 - 10. The forward end of the tens wheel 219 includes maximum and minimum dose limit features 271 , 272, in the form of rotary endstops which can each engage a max/min limit rib 290 on the internal surface of the housing 212. The internal surface of the tens wheel 219 includes a key 273 for engaging with the shuttle lock 222. [00111] The shuttle lock 222 is a generally cylindrical component having a forward section of largest diameter with double-ended peripheral teeth 280 at the forward end thereof having angled faces which can alternately engage dogs 291 and engagement ribs 292 on the interior of the housing 212. The angled faces cause a camming action that can move the shuttle lock 222 axially.

[00112] In general terms, the function of the housing dogs 291 , housing engagement ribs 292 and units wheel drive dogs 261 is to enable the shuttle lock 222 to move alternately between two axial positions, as will be explained in more detail later.

[00113] An axially-extending keyway 281 is provided for engaging the key 273 on the tens wheel 219 in order to rotationally lock the tens wheel 219 and shuttle lock 222 together whilst permitting axial movement therebetween. In alternative embodiments, the key may be provided on the shuttle lock 222 and the axially-extending keyway may be provided on the tens wheel 219.

[00114] The rear section of the shuttle lock 222 is of smaller diameter and includes dogs 282 at the rear end thereof, located 180 degrees apart from one another which can engage with the drive dogs 261 of the units wheel 218.

[00115] The rear surface of the shuttle lock 222 is provided with a series of axially- extending shuttle lock rear teeth 283. The number of teeth 283 corresponds with the number of units of medicament available per rotation of the units wheel 218 (in this case 20). Depending upon the relative axial positions of the units wheel 218 and the shuttle lock 222, the engagement splines 262 on the units wheel 218 can either be engaged with the shuttle lock rear teeth 283, or not engaged with the shuttle lock rear teeth 283.

[00116] Figure 34 shows the portion of the internal surface of the housing 212 which interacts with the odometer mechanism. The aperture 212a through which the dose is displayed can be seen. The illustrated portion of the housing includes an internally- projecting max/min limit rib 290, two dogs 291 for engaging the shuttle lock 222 and three engagement ribs 292 for engaging the shuttle lock 222. Figure 34 is shown partly in cross- section; the pointed ends of dogs 291 are at the same axial position and are located 180 degrees apart on the internal surface of the housing 212 (half of the housing 212 has been removed from Figure 34).

[00117] As illustrated in Figure 34, one of the dogs 291 for engaging the shuttle lock 222 may be located at one end of the max/min limit rib 290 such that both functions can be performed by the same component on the internal surface of the housing 212.

[00118] The drive spring 220 is a torsion spring which is fixed at one end with respect to the housing 212 and engaged at its other end to the units wheel 218. [00119] The drive clutch 250, best seen in Figure 21 B, is generally circular with formations (uppermost in Figure 21 B) which, in the assembled injection device 200, extend in a direction towards the rear of the device. The drive clutch spring 251 biases the

medicament cartridge 224. The housing 212 is provided with forward-facing clutch engaging features 215 which, in the position shown in Figure 25, engage the clutch 250 so that they are rotationally locked together. The clutch 250 can be disengaged from the clutch engaging features of the housing 215 by forward axial movement of the clutch 250, caused by forward movement of the drive sleeve 240. A haptic feedback arm 250a is provided on the front face of the drive clutch 250 (the underside in Figure 21 B).

[00120] The operation of the respective features of the injection device 200 will now be described in more detail below.

[00121] When the dose button 230 is depressed, firstly the drive clutch 250 is decoupled from the housing 212 and coupled to the drive sleeve 240. Secondly, the ratchet pawl 217 is decoupled from the units wheel 218. Decoupling of the ratchet pawl 217 from the units wheel 218 allows the drive spring 220 to rotate the units wheel 218 and drive sleeve 240, which are rotationally coupled together, about the longitudinal axis L.

[00122] Rotation of the drive sleeve 240 causes the drive clutch 250 to rotate which, in turn, rotates the leadscrew 253 to which the drive clutch 250 is splined.

[00123] Rotation of the leadscrew 253 causes it to advance axially forwards towards the front end 200a of the injection device 200 because of the engagement of the leadscrew thread with the thread of the leadscrew nut 252. The leadscrew nut 252 is rotationally and axially fixed with respect to the housing 212.

[00124] During dose setting, the last dose nut 241 is rotationally fixed with respect to the housing 212 via the leadscrew 253. The last dose nut 241 can translate axially up and down the thread inside the drive sleeve 240 due to rotation of the drive sleeve 240 when the dose is being set. Translation of the last dose nut 241 inside the drive sleeve 240 is limited by a rotational stop feature on the drive sleeve 240 which limits the travel of the last dose nut 241 to a position corresponding with the maximum dispense volume of the injection device 200.

[00125] During dose delivery, the drive sleeve 240, leadscrew 253 and last dose nut 241 all rotate together and there is no axial translation of the last dose nut 241 with respect to the drive sleeve 240.

[00126] Dose setting - incrementing the dose

[00127] With the injection device 200 in the configuration shown in Figure 25, the user grips the dose selector 216 and rotates it clockwise about axis L, with respect to the housing 212, in order to increment the dose and charge the drive spring 220. As the dose selector 216 is turned clockwise, the dose selector 216 is engaged with the ratchet pawl 217, causing it to rotate with the dose selector 216. The ratchet pawl 217 drives the units wheel 218 clockwise because of ratchet fingers 217a engaging ribs 218a of the units wheel 218, as shown in Figure 25A. The drive spring 220 is hooked into the back of the units wheel 218 and is therefore tightened as the units wheel 218 is rotated. In other words, torque is transferred from the dose selector 216 to the drive spring 220 directly through the dose indicator, i.e. the units wheel 218.

[00128] While the dose is being incremented, the ratchet arms 217b on the ratchet pawl 217 engage with teeth 213 on the inside surface of the housing 212 to prevent un-winding of the drive spring 220, as shown in Figure 25B.

[00129] When the dose selector 216 reaches a maximum, minimum or last dose limit, the ratchet fingers 217a flex radially outwardly and skip past the ribs 218a of the units wheel 218 (Figure 25C).

[00130] Dose setting - decrementing the dose

[00131] When it is desired to decrement the selected dose, the dose selector 216 is turned anti-clockwise. As shown in Figure 26A, as the dose selector 216 is turned anticlockwise, there is a small amount of backlash at point A such that the dose selector 216 can rotate slightly with respect to the ratchet pawl 217. This small relative movement is sufficient to allow tabs 214 on the dose selector 216 to depress the ratchet arms 217b so that they can click past the housing teeth 213, allowing the drive spring to unwind slightly before the ratchet arms 217b catch again on the next housing tooth 213. The tabs 214 may be tooth-shaped formations projecting radially-inwardly from an internal surface of the dose selector 216. This is represented in Figure 26B. Each decrement preferably equates to 11U ("international unit") of medicament.

[00132] Dose delivery

[00133] To initiate dose delivery, the user presses the dose button 230 against the bias of the dose button spring 231 as shown in Figure 27. This pushes the drive sleeve 240 axially forwards. Although the drive sleeve 240 is rotationally locked to the units wheel 218, it is free to slide axially with respect thereto (Figure 27B).

[00134] As the drive sleeve 240 advances, its forward end engages the rear surface of the drive clutch 250. The drive clutch 250 disengages from the clutch engaging features 215 on the inside surface of the housing 212 (Figure 27C). Once the drive clutch 250 is fully engaged with the drive sleeve 240, the dose button 230 disengages the ratchet pawl 217 from the units wheel 218 (Figure 27D). The units wheel 218 is now free to rotate the drive sleeve 240 and therefore also the drive clutch 250 about longitudinal axis L. The drive clutch 250 is splined to the leadscrew 253 (Figure 27E).

[00135] Therefore the leadscrew 253 now rotates and is caused to advance axially due to threaded engagement with the leadscrew nut 252. The thrust bearing 254 advances the cartridge stopper 226 into the cartridge, in order to expel medicament to deliver the selected dose (Figure 27F).

[00136] When the dose button 230 is released, the dose button spring 231 returns the dose button 230 and drive sleeve 240 to their original starting positions. This axially rearward movement disengages the drive clutch 250 and re-engages the ratchet arms 217b with the housing 212 thereby stopping dose delivery.

[00137] Dose delivery - haptic feedback

[00138] Referring to Figure 28, during dose delivery haptic feedback occurs between the drive clutch 250 and the leadscrew nut 252 when the drive clutch 250 is spinning, by virtue of the haptic feedback arm 250a on the drive clutch clicking over axially-rearwardly-facing teeth on the leadscrew nut 252.

[00139] Last dose protection

[00140] When the medicament cartridge 224 is relatively empty, after several doses have already been delivered therefrom, it is undesirable for the user to be able to select a dose that is larger than the available quantity of medicament remaining. Last dose protection is provided to deal with this situation. Last dose protection is provided by the last dose nut 241.

[00141] As shown in Figure 29A, the last dose nut 241 moves axially forwards and backwards on the thread inside the drive sleeve 240 during dose incrementing and decrementing. When there is less than a predetermined amount (e.g. 100IU) of medicament remaining in the cartridge 224, the last dose nut 241 stops against a rotary endstop 240a at the rear of the drive sleeve thread.

[00142] Engagement of the last dose nut 241 with the endstop 240a means that, should the user attempt to wind the dose selector 216 beyond the remaining dose, the over-torque protection is actuated, preventing the user from damaging the device (Figure 29B). The ratchet fingers 217a disengage from the units wheel 218 as previously described in relation to Figure 25C.

[00143] Dose display

[00144] Figures 35A - 35C show, in schematic form, the three stages of the odometer mechanism's operation. More detail of the respective stages is shown in Figures 36 - 38. [00145] In stage 1 (Figure 35A, 36, 36A and 36B) for dose 0 - 9, the units wheel 218 is free to turn. Rotation of the dose selector 216 causes the dose to increment through doses 0 - 9. For doses 0 - 9, there is no engagement between the units wheel drive dogs

261 and the shuttle lock dogs 282 (Figure 36B). The tens wheel 219 is rotationally locked but is axially moveable relative to the shuttle lock 222 because the key 273 is engaged in the keyway 281 (see Figure 30). The shuttle lock 222 is rotationally locked to the housing 212 because the housing engagement ribs 292 (Figure 36A) are engaged with three of the shuttle lock peripheral teeth 280 (Figure 33).

[00146] After the units wheel has reached dose "9", in stage 2 (Figure 35B and Figure 37), the drive dogs 261 of the units wheel 218 engage shuttle lock dogs 282 during dose "10". The engagement of the angled faces of the dogs 261 , 282, causes a camming action that moves the shuttle lock 222 axially rearwardly enough to disengage the shuttle lock peripheral teeth 280 from the housing engagement ribs 292. The shuttle lock 222 is therefore no longer rotationally locked to the housing 212. Since the key 273 is axially moveable in the keyway 281 , the shuttle lock 222 is able to move axially relative to the tens wheel 219. Consequently, the tens wheel 219 itself does not move axially and the tens numbers 270 remain in a position adjacent to the units numbers 260. The axially rearward movement of the shuttle lock 222 causes angled faces of the dogs 261 , 282 to reach the end of their sloping engagement, at which point the shuttle lock rear teeth 283 engage the axially-extending splines 262 on the units wheel 218. This rotationally locks the units wheel 218 and the shuttle lock 222 together.

[00147] The units wheel 218 is still able to turn. The tens wheel 219 is still rotationally locked to the shuttle lock 222 by virtue of the key 273 engaging in the keyway 281.

Because the shuttle lock 222 (and hence the tens wheel 219 rotationally locked thereto) is rotationally locked to the units wheel 218 by the engagement of the units wheel splines

262 with the shuttle rear teeth 283, further turning of the units wheel 218 causes the shuttle lock 222 and the tens wheel 219 to rotate together.

[00148] After 9° of rotation of the shuttle lock 222 and tens wheel 219 by the units wheel 218, stage 3 is reached (Figure 35C and Figure 38), in which two of the shuttle lock peripheral teeth 280 come into contact with the angled faces of the two housing dogs 291.

[00149] Then, for the next 9° of rotation, the camming action of the angled faces of the housing dogs 291 and those of the shuttle lock peripheral teeth 280 cause the shuttle lock 222 to revert axially to re-engage the housing engagement ribs 292 so that the shuttle lock 222 is once again rotationally locked to the housing 212. Axial reversion of the shuttle lock 222 to its stage 1 forward position also causes the shuttle lock rear teeth 283 to disengage from the splines 262 on the units wheel 218. In this example, for every 18° of rotation (9° + 9°), the shuttle lock completes a full cycle as described above. Other angles of rotation for each cycle are possible.

[00150] This completes the number change of the tens wheel 219. The mechanism functions in reverse if the dose is decremented.

[00151] Dose setting - maximum/minimum dose limit

[00152] Limiting the maximum/minimum dose that can be set by the dose selector 216 is realised by cut out features 271 , 272 on the tens wheel 219 which interact with a limit rib 290 on the housing. One side of the rib 290 limits the tens wheel at the minimum dose when feature 272 is rotated into abutment with the rib 290 (Figure 39A). The other side of the rib 290 limits the tens wheel at the maximum dose, typically 100IU, when feature 271 is rotated into abutment with the rib 290 (Figure 39B). As mentioned above, the rib 290 is an extended part of one of the housing dogs 291 for engaging the shuttle lock 222.

[00153] Figure 40 is a diagrammatic summary of the key engagement points of the injection device components, at six stages of dose delivery. Example distances of advancement of the dose button 230, starting at 0mm, are shown. For each distance, each of the hold splines (ratchet pawls 217), drive clutch 250 and drive sleeve 240/drive clutch 250 are indicated as being either not engaged (dotted box outline), partially engaged (dashed box outline) or fully engaged (solid box outline).

[00154] As with the first embodiment, described with reference to Figures 1 -3, the ratchet component (ratchet arms 217b) and over-torque feature (ratchet fingers 217a) are both provided on a single component (the ratchet pawl 217).

[00155] Description of Fourth Example Embodiment

[00156] A further, non-limiting, embodiment of an injection device according to the present invention is illustrated in Figures 41 -55C.

[00157] Referring to Figures 41 -44, the injection device 300 includes a housing 312, a dose selector 316, a dose button 330 and dose button spring 331 , a selector pawl 317, a spring lock 321 , a drive spring 320, a number sleeve 318, a drive shaft 340, a drive sleeve 342, a lead screw 353, a last dose nut 341 , a cap pawl 351 , and a body cap 352, all located concentrically about a common longitudinal axis L. The axis L extends between a front end 300a and a rear end 300b of the injection device 300.

[00158] The injection device 300 has a medicament cartridge 324 supported in a cartridge holder 325 at the front end 300a of the injection device. The cartridge is sealed by an axially-moveable cartridge stopper 326 at its rear end. [00159] The dose button 330 is biased rearwardly by the effect of the dose button spring 331 between the dose button 330 and the dose selector 316. The dose button 330 includes a ratchet disengagement finger 330a which can engage with the selector pawl 317.

[00160] The dose selector 316 is provided at the rear end 300b of the injection device 300 and is arranged to permit the selection of a desired dose of medicament for delivery from the medicament cartridge 324 into an injection site. The dose selector 316 is axially constrained with respect to the housing 312 but is rotatable with respect thereto, about axis L. The dose selector 316 is used to set the dose by increasing the rotational preload of the drive spring 320 which is prevented from unwinding by the selector pawl 317 which will be described in more detail below. A loose coupling between the dose selector 316 and the selector pawl 317 is provided via dose selector slots 316a (visible in Figure 45A).

[00161] The selector pawl 317 has at least one ratchet arm 317b which is engageable with teeth 313 in an internal surface of the housing 312. The selector pawl 317 is also provided with at least one (preferably three equally spaced) selector pawl splines 317a which engage with the drive shaft 340. The selector pawl 317 is designed to be stiff in torsion but to have some flexibility in radial flexion (for example because of cutaways 317c behind the splines 317a.

[00162] A dose indicator, comprising a number sleeve 318 is disposed within the housing 312 and displays reference indicia, such as numbers or symbols, to indicate the level of dose selected by the dose selector 316. The housing 312 includes an aperture 312a through which the dose indicator is visible.

[00163] The drive spring 320 is a torsion spring which is fixed at one end with respect to the housing 312 via spring lock 321 and engaged at its other end to the drive shaft 340.

[00164] The rear end of the drive shaft 340 is provided with axially-extending splines 349. The selector pawl 317 is provided with one or more inwardly-directed splines 317a which can engage with the drive shaft splines 349 (Figure 45B).

[00165] Figure 48 indicates the key components involved in delivery of a dose of medicament from the injection device 300. The drive spring 320 provides rotational energy for dose delivery. The drive shaft 340 couples the drive spring 320 to the drive sleeve 342, the last dose nut 341 and the number sleeve 318.

[00166] The drive sleeve 342 couples the drive shaft 340 to the lead screw 353 and also advances the last dose nut 341 during dose setting. [00167] The lead screw 353 converts the rotation of the drive sleeve 340 to linear motion which can be used to depress the cartridge stopper 326 (not shown) to deliver medicament from the medicament cartridge 324.

[00168] The cap pawl 351 retains the drive sleeve 340 and provides a one-way ratchet to prevent back-drive of the lead screw 353. The cap pawl 351 may also provide haptic feedback of dose delivery.

[00169] The body cap 352 is threaded to allow the lead screw 353 to advance

therethrough and serves as a thrust bearing for the drive sleeve 340.

[00170] Figure 52 gives an overview of the components involved in displaying the dose to the user. The spring lock 321 is engageable with the number sleeve 318 to provide a minimum dose end stop. The number sleeve 318 includes a spiral of numbers which display the selected dose through the aperture 312a in the housing.

[00171] The housing 312 is has an internal thread 312b to guide the number sleeve 318 as it rotates. A maximum dose end stop 312c for the number sleeve 318 is provided at the forward end of the housing 312.

[00172] The drive shaft 340 is rotationally coupled with the number sleeve 318 to communicate the rotational position of the drive spring 320 to the number sleeve 318. This coupling can be seen in Figure 53A wherein a splined connection 318a between the number sleeve 318 and drive shaft 340 is present. As the drive shaft 340 rotates, the number sleeve 318 travels along the internal thread in the housing 312b, causing the number displayed in the aperture of the housing 312a to increase or decrease.

[00173] Figure 54 gives an overview of the components involved in last dose protection. The last dose nut 341 has a screw-threaded engagement with the drive sleeve 342 on its inner circumference. On the outer surface of the last dose nut 341 is a splined

engagement with the inner surface of the drive shaft 340.

[00174] The operation of the respective features of the injection device 300 will now be described in more detail below.

[00175] Dose setting - incrementing the dose

[00176] With reference to Figure 45A, the user rotates the dose selector 316 in the anti- clockwise direction indicated. The dose selector 316 is tightly coupled to the dose button 330 which also turns. A loose coupling between the dose selector 316 and the selector pawl 317 (via dose selector slots 316a) causes the selector pawl 317 also to rotate anticlockwise. [00177] The selector pawl's inwardly-directed splines 317a can engage with the drive shaft splines 349 (Figure 45B). As the selector pawl 317 rotates, the drive shaft 340 is also caused to rotate, which charges the drive spring 320. The number sleeve 318 is incremented to indicate the selected dose (the spring and number sleeve are not visible in Figure 45B).

[00178] The selector pawl 317 has at least one ratchet arm 317b which engages with teeth 313 in an internal surface of the housing 312. This ratchet arrangement rotationally couples the selector pawl 317 and the housing 312 so that, in this coupled state, the spring 320 is prevented from unwinding when the dose selector 316 is released. Uncoupling of the ratchet arrangement allows relative rotation between the selector pawl 317 and the housing 312 so that, in this uncoupled state, the dose can be further incremented. Haptic feedback is provided per IU incremented as the ratchet arm 317b clicks over the housing teeth 313 (Figure 45C).

[00179] Dose setting - decrementing the dose

[00180] With reference to Figure 46A, the user rotates the dose selector 316 in the clockwise direction indicated. The ratchet disengagement finger 330a built into the dose button 330 also moves clockwise (as the dose button 330 and dose selector 316 are rotationally coupled).

[00181] The ratchet disengagement finger 330a engages with the selector pawl ratchet arm 317b, depressing it radially inwardly by a sufficient amount to reduce the force required to shift the ratchet arm 317b over to the previous tooth 313 in the housing (Figure 46B).

[00182] With the ratchet arm 317b partially disengaged, the selector pawl 317 engages the other end of dose selector slots 316a, turning the selector pawl 317 clockwise (Figure 46C). The selector pawl splines 317a and drive shaft splines 349 cause the drive shaft 340 to rotate, unloading the drive spring 320 in order to decrease the dose.

[00183] Over-torque Protection

[00184] As shown in Figure 47A, the dose selector 316 is connected to the drive shaft 340 via the selector pawl splines 317a. Owing to the angle of the splines 317a, a component of the torque between the selector pawl 317 and drive shaft 340 is resolved into a force radially outwards on the splines 317a. When the torque exceeds a defined limit, the radial component of the force causes the bridge of material holding the spline 317a to flex elastically into the position shown in dotted lines in Figure 47B. The spline 317a thus disengages from the drive shaft splines 349. This disconnects the dose selector 316 from the internal components of the device, preventing torque in the device from exceeding the defined limit and potentially preventing damage to the device. The over-torque for flexing out the spline 317a to flex past spline 349 is preferably at least 10% higher than the torque required for dialling up (incrementing) or dialling down (decrementing) the dose selector 316. The dialling up torque can be 30 to 80 Nmm, preferably less than 60 Nmm, more preferably 30 to 50 Nmm. The dialling down torque can be 20 to 60 Nmm, preferably less than 50 Nmm, more preferably 30 to 40 Nmm. The over-torque in the dialling up direction may be different to the over-torque in dialling down direction.

[00185] Dose delivery

[00186] When it is desired to deliver a dose of medicament, the user depresses the dose button 330 as shown in Figure 49A. Since the dose button 330 is axially coupled to the drive shaft 340, the drive shaft 340 moves axially forward, disengaging the drive shaft splines 349 from the selector pawl 317.

[00187] As the drive shaft 340 moves axially forward, the drive shaft splined clutch 350 engages with the drive sleeve splines 342a (Figure 49B). This clutch engagement occurs before the selector pawl 317 is fully disengaged from the drive shaft splines 349 so that the drive spring 320 is never free to unwind in an uncontrolled manner. The splined clutch 350 and/or the drive sleeve splines 342a may be tapered to correct any potential misalignment.

[00188] The ratchet disengagement finger 330a in the dose button 330 moves axially, exposing a wider section of the finger 330a which ensures the selector pawl ratchet arm 317b is disengaged from the housing teeth 313 during dose delivery (Figure 49C). This avoids any erroneous haptic feedback being provided, should the dose selector 316 be rotated during dose delivery.

[00189] Figure 50 is a diagrammatic summary of the key engagement points of the injection device components, at four stages of dose delivery.

[00190] Figures 51 A and 51 B show how the lead screw 353 is advanced during dose delivery. Referring to Figure 51A, once the dose selector 316 has been disengaged, the drive spring 320 drives the drive shaft 340 anti-clockwise. The drive shaft 340 turns the drive sleeve 342 via the drive shaft splined clutch 350. A keyed engagement between the drive sleeve 342 and the lead screw 353 turns the lead screw 353. As the lead screw 353 turns, it advances through a screw thread in the body cap 352, causing the cartridge stopper 326 to advance forward to deliver medicament.

[00191] Referring to Figure 51 B, the drive sleeve 342 is coupled to the cap pawl 351 which has pawls 351a which engage with a second set of housing teeth 314 to provide haptic feedback during dose delivery as well as preventing the lead screw 353 and drive sleeve 342 from being back-driven. [00192] Dose display and maximum/minimum dose end stops

[00193] Travel of the number sleeve 318 is limited by end stops which serve as maximum and minimum dose protection. The maximum dose end stop 312c is shown on the left side of Figure 53B, the dotted line showing the angle at which the number sleeve 318 approaches the end stop 312c. The minimum dose end stop is provided by the spring lock 321 , shown on the right side of Figure 53B, the dotted line showing the angle at which the number sleeve 318 approaches the spring lock 321. The minimum dose may be 0IU and the maximum dose may be 100IU. Once either of the end stops is engaged, further rotation of the number sleeve 318 is prevented which, in turn, prevents further rotation of the drive shaft 340. This prevents the user incrementing the dose beyond the maximum or decrementing the dose below the minimum. The minimum dose end stop on the spring lock 321 also prevents the drive spring 320 from unwinding below zero IU during dose delivery.

[00194] Last dose protection

[00195] As shown in Figure 55A, as the drive shaft 340 rotates during dose setting, the last dose nut 341 , which is splined thereto, also rotates. This enables the last dose nut 341 to travel left or right along the screw thread on the drive sleeve 342. As the dose is incremented, the last dose nut 341 moves right until, after a preset maximum number of doses have been delivered by the device, the last dose nut 341 is in the position illustrated in Figure 55C.

[00196] During dose delivery, the drive shaft 340 and drive sleeve 342 are rotationally coupled together via the drive shaft splined clutch 350 so that there is no relative rotation between them. Therefore, during dose delivery (Figure 55B), the last dose nut 341 cannot travel along the screw thread on the drive sleeve 342.

[00197] After the preset maximum number of doses has been delivered, a rotational endstop 341a on the last dose nut 341 engages with a rotational stop on the drive sleeve 342, as indicated by the dotted line and arrow in Figure 55C. This prevents any further relative rotation between the drive sleeve 342 and the drive shaft 340, meaning that the user can no longer increment the dose setting. Any remaining dose can be delivered as normal.

[00198] As with the first embodiment, described with reference to Figures 1 -3, the ratchet component (selector pawl ratchet arm 317b) and over-torque feature (selector pawl splines 317a) are both provided on a single component (the selector pawl 317).

[00199] Throughout the description and claims of this specification, the words "comprise" and "contain" and variations of them mean "including but not limited to", and they are not intended to (and do not) exclude other moieties, additives, components, integers or steps. Throughout the description and claims of this specification, the singular encompasses the plural unless the context otherwise requires. In particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise.

[00200] Features, integers, characteristics, compounds, chemical moieties or groups described in conjunction with a particular aspect, embodiment or example of the invention are to be understood to be applicable to any other aspect, embodiment or example described herein unless incompatible therewith. All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive. The invention is not restricted to the details of any foregoing embodiments. The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

[00201] The reader's attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

[00202] Reference numerals

10 injection device

L longitudinal axis

10a front end of the device

10b rear end of the device

12 housing

12a aperture in the housing

14 needle

16 dose selector

18 dose indicator

20 spring

20a first end of the spring

20b second end of the spring

22 drive assembly

24 medicament container 25 ratchet component

26 force path

27 over-torque feature

28 single component

100 injection device

L longitudinal axis (housing)

Lc second longitudinal axis (cartridge)

100a front end of the device

100b rear end of the device

107 units housing feature

108 tens housing feature

109 housing ridge features

1 10 housing smooth inside surface track

1 1 1 housing ramps for drive shaft ratchet arms

1 12 housing

1 12a aperture in the housing

1 13 housing teeth

1 14 tabs

1 15 dose selector pawl

1 16 dose selector

1 17 dose indicator spring

1 18 units wheel

1 18a teeth on units wheel (for engaging tens wheel)

1 18b formation on units wheel (for engaging units housing feature)

1 19 tens wheel

1 19a teeth on tens wheel (for engaging units wheel)

1 19b formations on tens wheel (for engaging tens housing feature)

120 drive spring

124 medicament cartridge

125 cartridge holder

126 cartridge stopper

130 dose button

131 dose button spring

140 drive shaft

141 dose limit nut

141 a dose limit nut endstop feature for max dose limiting and last dose limiting

141 b dose limit nut endstop feature for min dose limiting 142 worm gear

143 worm gear support

144 worm gear rotational lock

145 plunger rack

146 drive shaft ratchet arms

147 max dose endstop on plunger rack for dose limit nut

148 min dose endstop on plunger rack for dose limit nut

149 drive shaft splines

150 worm gear clutch

A backlash point for over-torque protection

200 injection device

200a front end of the device

200b rear end of the device

L longitudinal axis

212 housing

212a aperture in housing

213 housing teeth

214 tabs on housing

215 clutch engaging feature on housing

216 dose selector

217 ratchet pawl

217a ratchet fingers

217b ratchet arms

218 units wheel

218a units wheel ribs

219 tens wheel

220 drive spring

221 housing top cap

222 odometer shuttle lock

224 medicament cartridge

225 cartridge holder

226 cartridge stopper

230 dose button

231 dose button spring

240 drive sleeve 240a last dose nut endstop

241 last dose nut

250 drive clutch

250a haptic feedback arm

251 drive clutch spring

252 leadscrew nut

253 leadscrew

254 thrust bearing

260 units numbers

261 units wheel drive dogs

262 units wheel engagement splines

270 tens numbers

271 max dose limit feature

272 min dose limit feature

273 tens wheel key to engage shuttle lock

280 shuttle lock peripheral teeth

281 shuttle lock keyway

282 shuttle lock dogs

283 shuttle lock rear teeth

290 housing max/min limit rib

291 housing dogs for engaging shuttle lock

292 housing engagement ribs

A backlash point for dose decrementing

300 injection device

300a front end of the device

300b rear end of the device

L longitudinal axis

312 housing

312a aperture in housing

312b internal thread in housing to guide number sleeve 312c maximum dose end stop

313 housing teeth

314 second set of housing teeth (for cap pawl)

316 dose selector

316a dose selector slots

317 selector pawl

317a selector pawl splines 317b selector pawl ratchet arm

318 number sleeve

318a splined connection of number sleeve to drive shaft

320 drive spring

321 spring lock

324 medicament cartridge

325 cartridge holder

326 cartridge stopper

330 dose button

330a ratchet disengagement finger

331 dose button spring

340 drive shaft

341 last dose nut

341 a last dose nut rotational endstop

342 drive sleeve

342a drive sleeve splines

349 drive shaft splines

350 drive shaft splined clutch

351 cap pawl

351 a pawls

352 body cap

353 lead screw