Abstract:
The present disclosure relates to an injection device for setting and dispensing of a dose of a medicament, the device including an elongated housing to accommodate a cartridge filled with the medicament and sealed with a piston, a piston rod extending along a first axis and being threadedly or slidingly engaged with the housing to apply a distally directed thrust to the piston of the cartridge, a drive member rotationally or threadedly engaged with the piston rod and having a wheel section or geared section, and a drive sleeve extending along a second axis at a radial distance from the first axis and having a geared section to mesh with the wheel section or geared section of the drive member, wherein a first radial distance between first and second axes at a distal end of the drive sleeve differs from a second radial distance between first and second axes at a proximal end of the drive sleeve.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a U.S. national stage application under 35 USC §371 of International Application No. PCT/EP2015/079141, filed on Dec. 9, 2015, which claims priority to European Patent Application No. 14306995.3, filed on Dec. 10, 2014, the entire contents of which are incorporated herein by reference. 
     
    
     TECHNICAL FIELD 
       [0002]    The present disclosure relates to a drive mechanism of a drug delivery device and to a drive mechanism of an injection device, such like an injection pen. In particular the disclosure relates to a drive mechanism of a disposable injection device that allows and enables a user of the device to select or to set a dose of a medicament of variable size and to dispense or to inject the dose. 
       BACKGROUND 
       [0003]    Injection devices for setting and dispensing a single dose or multiple doses of a liquid medicament are as such well-known in the art. Generally, such devices have substantially a similar purpose to that of an ordinary syringe. 
         [0004]    Injection devices, in particular pen-type injectors have to meet a number of user-specific requirements. For instance, with patients suffering chronic diseases, such like diabetes, the patient may be physically infirm and may also have impaired vision. Suitable injection devices especially intended for home medication therefore need to be robust in construction and should be easy to use. Furthermore, manipulation and general handling of the device and its components should be intelligible and easy understandable. Moreover, a dose setting as well as a dose dispensing procedure must be easy to operate and has to be unambiguous. 
         [0005]    Typically, such devices comprise a housing or a particular cartridge holder, adapted to receive a cartridge at least partially filled with the medicament to be dispensed. The device further comprises a drive mechanism, usually having a displaceable piston rod which is adapted to operably engage with a piston of the cartridge. By means of the drive mechanism and its piston rod, the piston of the cartridge is displaceable in a distal or dispensing direction and may therefore expel a predefined amount of the medicament via a piercing assembly, which is to be releasably coupled with a distal end section of the housing of the injection device. 
         [0006]    The medicament to be dispensed by the injection device is provided and contained in a multi-dose cartridge. Such cartridges typically comprise a vitreous tubular shaped barrel sealed in distal direction by means of a pierceable seal and being further sealed in the proximal direction by the piston. With reusable injection devices an empty cartridge is replaceable by a new one. In contrast to that, injection devices of disposable type are to be entirely discarded when the medicament in the cartridge has been dispensed or used-up. 
         [0007]    Many injection devices, of e.g. pen-injector type, provide multiple and frequent dispensing and injection of the liquid medicament. For this, the piston rod of the drive mechanisms of such devices advances in discrete steps in a distal direction during repeated dose dispensing procedures until an end-of-content configuration has been reached, in which the piston of the cartridge reaches a distal stop or end configuration. In order to provide a safe and convenient handling of such devices it is a general aim, that the device provides audible, visual as well as tactile feedback during dose setting as well as during dose dispensing procedures. Moreover, with non-electrical and purely mechanically implemented injection devices it is a further aim that the device itself provides or generates a driving force or driving torque during dose dispensing so that the user is no longer obliged to exert a particular driving force for dose dispensing. This is generally achievable by making use of mechanical energy storing means, e.g. implemented as a spring element, which has to be arranged inside the device in a rather space saving way. 
         [0008]    It is a general aim for both, reusable as well as for disposable injection devices, to limit the total number of parts and to optimize the space inside the device in order to provide a rather compact and cost-attractive design. From WO 2013/156224 A1 an injection device for setting and injecting set doses from drug cartridge is known. There, a drive nut and a drive member are arranged at a radial distance. They are arranged along two longitudinally and parallel extending axes that are spaced from each other in radial direction. The radial separation of mutually engaging components of a drive mechanism of such an injection device is governed for instance by the size, in particular by the diameter of a tubular cartridge, by the diameter of sleeve-shaped elements, such like a dose indicating sleeve and the geometric package of mutually engaging components of the drive mechanism that might be engaged in a manifold of different ways. 
       SUMMARY 
       [0009]    The present disclosure provides a space optimized injection device for setting and for dispensing of a dose of a medicament. The injection device can reduce the overall number of movable components of the injection device. The present disclosure further provides a rather simple and user-friendly handling of the injection device and of its drive mechanism. The injection device can further provide a visual, tactile and audible feedback during both dose setting and dose dispensing. 
         [0010]    In a first aspect an injection device for setting and dispensing of at least a single, typically of multiple doses of a medicament, especially of a liquid medicament includes an elongated housing to accommodate a cartridge filled with the medicament. The cartridge is typically sealed with a piston or bung towards its proximal direction. The elongated housing defines an axial direction that coincides with the distal and with the proximal direction. The housing therefore comprises a distal end facing towards biological tissue and further comprises an oppositely located proximal end facing away from biological tissue, into which the medicament is to be injected. 
         [0011]    The injection device comprises a drive mechanism comprising numerous mechanically interacting or inter-engaging components that are rotatable and/or axially displaceable relative to each other as well as relative to the housing in order to set a dose of variable size and for subsequently dispensing the set dose of the medicament. The injection device comprises a piston rod extending along a first axis and being radially or slidingly engaged with the housing to apply a distally directed thrust to the piston of the cartridge. The piston rod is adapted to advance in distal direction so as to exert distally directed pressure to the piston of the cartridge. In this way, a fluid pressure inside the cartridge can be increased to expel a predefined amount of the medicament from the cartridge. For the purpose of injecting the medicament into biological tissue the cartridge is typically connected with a piercing assembly having a double-tipped injection needle, which needle being in fluid communication with the interior of the cartridge. 
         [0012]    Due to its threaded or sliding engagement with the housing the piston rod is displaceable in the distal direction relative to the housing. In a sliding engagement the piston rod is keyed or splined to a correspondingly-shaped structure to the housing. In this context, a sliding, splined or a keyed engagement means that the piston rod is rotatably locked to the housing but is free to slide in an axial direction relative to the housing. This is typically obtained by at least one radial protrusion of the housing or piston rod engaging with a correspondingly shaped radial groove of the piston rod or the housing. 
         [0013]    The injection device further comprises a drive member rotatably or threadedly engaged with the piston rod. When rotationally engaged with the piston rod, drive member and piston rod are typically splined or keyed so that the drive member being axially fixed to the housing, is rotatable in order to induce a corresponding rotation of the piston rod. In this embodiment the piston rod is typically threadedly engaged with the housing so that a rotation of the piston rod induced by a rotation of the drive member leads to a distally directed displacement of the piston rod relative to the housing and relative to a barrel of the cartridge, thereby displacing the piston of the cartridge relative to the barrel for expelling a predefined amount of the medicament from the cartridge. 
         [0014]    According to an alternative embodiment the drive member is threadedly engaged with the piston rod so that the piston rod experiences a distally directed displacement relative to the housing while being splined or keyed to the housing. 
         [0015]    The drive member further comprises a wheel section, typically at its outer circumference. The wheel section may have the shape of a geared wheel or resembles a gear wheel that is integrally formed with the drive member. The injection device and the drive mechanism further comprise a drive sleeve extending along a second axis, which second axis is located at a radial distance from the first axis. The drive sleeve further comprises a wheel section to engage or to mesh with the geared section of the drive member. Drive sleeve and drive member may be permanently rotationally engaged via their wheel sections or geared sections or through respective gear wheels. Via the mutually engaged wheel sections or mutually meshed geared sections a rotation of the drive sleeve induces a rotation of the drive member according to the gear ratio of the wheel sections or geared sections, respectively. 
         [0016]    The wheel sections may each comprise a geared profile at their outer circumference. Alternatively, they may each comprise a rather even and smooth shaped outer shape, wherein the two wheel sections of the drive member and the drive sleeve are engaged in a torque transferring way by means of a band or tape. So, any mentioning of mutually engaged geared sections of drive sleeve and drive member may therefore equally relate to a torque transfer between rather even and smooth shaped wheel sections in general. 
         [0017]    A first radial distance between first and second axes at a distal end of the drive sleeve differs from a second radial distance between first and second axes at a proximal end of the drive sleeve. The radial distance is measured perpendicular to the extension of the second axis. Since the radial distance between first and second axes differs in an axial direction it follows, that first and second axes are strictly speaking non-parallel. However, the offset from a parallel alignment of first and second axes is rather small, so that first and second axes are aligned substantially or almost parallel with respect to each other. 
         [0018]    By varying first and second radial distances between first and second axes the overall radial extension of the arrangement of drive sleeve and drive member in particular in the axial region of their wheel sections or geared sections can be modified. In this way, the diameter of the wheel section or geared sections, in particular of gear wheel sections of drive member or drive sleeve can be modified. The diameter of wheel sections or geared sections of at least one of drive member and drive sleeve can be reduced so that the overall radial dimensions of the arrangement of drive sleeve and drive member can be reduced accordingly in order to optimize the available space inside the housing of the injection device, and in particular to reduce the outer dimensions of the housing of the injection device. 
         [0019]    The drive member may also comprise a tubular and elongated shape. It may be axially intersected by or at least axially receive the proximal end of the piston rod. The drive member typically comprises a center axis coinciding with the first axis. Hence, at least in an initial configuration of the injection device drive member and piston rod are arranged concentrically and both extend along and align along the first axis. 
         [0020]    According to a further embodiment the first radial distance is larger than the second radial distance. Since the radial center of the drive sleeve coincides with the second axis and since the radial center of the drive member, which may also be of tubular or sleeve-like shape coincides with the first axis at least the diameter of one of the wheel sections or geared sections of drive member and drive sleeve is reducible or is actually reduced compared to a parallel arrangement of first and second axes to enable and to support a rather compact design of the housing. Typically and according to a further embodiment the difference between first and second radial distances is larger than 0 mm but is less than 3 mm, less than 2 mm or less than 1 mm. Depending of the difference between first and second radial distances also the radial dimensions of wheel sections or geared sections of at least one of drive member and drive sleeve can be reduced. Accordingly, also a number of teeth of a size-reduced geared section can be reduced, thereby also realizing a different gear ratio between drive sleeve and drive member. A modification of the gear ratio may be compensated or counteracted by a corresponding modification of the threaded engagement of the piston rod either with the housing or with the drive member. 
         [0021]    According to a further embodiment the injection device comprises a substantially tubular-shaped cartridge assembled inside the housing and extending along a third axis that is located at a radial distance from the second axis but which is oriented parallel to the second axis. Since the first and second axes extend at a small but distinct angle with respect to each other also the third axis extends at a non-zero angle with respect to the first axis. 
         [0022]    The piston rod coinciding with its radial center with the first axis is hence slightly slanted or angled with regard to the longitudinal extension of the tubular-shaped cartridge. However, the piston rod typically comprising or made of a thermoplastic material exhibits a certain flexibility so that the piston rod may flex in radial direction as it advances in the distal direction so that at least its distal tip it co-aligns with the third axis and hence with the longitudinal extension of the cartridge. 
         [0023]    According to a further embodiment the first and the third axes substantially overlap in a virtual crossing point. Due to the non-zero difference between first and second radial distances first and third axes extend at a relative offset angle equal to or smaller than 3°, equal to or smaller than 2° or equal to or smaller than 1° but larger than 0°. The virtual crossing point of first and third axes is typically located inside the injection device, hence, first and third axes virtually overlap inside the injection device. Consequently, first and third axes almost or substantially overlap but exhibit a small but distinct angular offset. 
         [0024]    According to a further embodiment the virtual crossing point of first and third axes is located distally from a distal end of the piston rod. Typically and with the cartridge assembled inside the injection device the virtual crossing point is located inside the cartridge. It may be located inside the piston of the cartridge. Moreover, it is conceivable that the virtual crossing point is located in an axial midsection of the cartridge. Consequently and in an initial configuration of the injection device, i.e. before an initial dose of the medicament is dispensed the distal end of the piston rod may be located radially offset from the third axis. As the piston rod advances in the distal direction it approaches with its distal end to the crossing point and may then with a further distally directed displacement co-align with the third axis due to its inherent elasticity. An elastic bending or deflection of the piston rod is easily attainable as the piston rod advances in the distal direction. Since the piston rod is axially guided either in threaded or splined engagement with a radially inward facing flange portion of the housing it starts to protrude more and more in the axial distal direction from such a flange portion as it is subject to repeated dose dispensing procedures. As the piston rod advances in the distal direction it forms a cantilevered beam being easily deformable to re-align to the third axis and hence to the center axis of the cartridge. 
         [0025]    It is to be mentioned that the angled or slightly slanted orientation of first and second axes is particularly present in an initial configuration of the injection device, i.e. prior to a first or initial dose setting or dose dispensing. As subsequent doses of the medicament have been dispensed and after the piston rod has advanced a substantial path in the distal direction, the piston rod may continuously approach an orientation of the second axis. The drive member however will remain oriented along the first axis. 
         [0026]    In an alternative embodiment it is also conceivable, that the distal end of the piston rod is allowed to move in radial direction relative to the position of the cartridge&#39;s piston. 
         [0027]    In another embodiment at least one of the geared sections of drive sleeve and drive member comprises a beveled gear profile. Such a beveled gear profile is beneficial when the geared sections of drive sleeve and drive member are subject to axial displacement relative to each other. It is in particular conceivable that one of drive member and drive sleeve is axially fixed or axially constrained in the housing while the other one of drive member and drive sleeve is axially displaceable relative to the housing, e.g. in order to switch the injection device from a dose setting mode to a dose dispensing mode and vice versa. 
         [0028]    It is particularly intended, that the wheel sections or geared sections of drive sleeve and drive member remain permanently engaged. Hence, during dose setting as well as during dose dispensing the geared sections of drive member and drive sleeve mutually mesh. The axial extension of at least one of the geared sections of drive member and drive sleeve is larger than a relative axial displacement of drive member and drive sleeve. In this way, an axial displacement of the drive sleeve relative to the drive member has substantially no effect on the geared engagement of their respective geared sections. 
         [0029]    It is of further benefit when at least one or when even both geared sections of drive sleeve and drive member comprise at least a small non-zero shaft angle, such like less than 3°, less than 2° or less than 1°. With beveled gear sections a drafted gear teeth geometry can be realized, which is beneficial when the drive sleeve or the drive member are manufactured as injection molded components. A drafted gear teeth geometry inherently supports and coincides with a beveled gear profile, which therefore maintains a full contact across the thickness or axial width of the mutually meshing geared sections. In this way, the mutual contact surface of meshed geared sections of drive member and drive sleeve can be improved with a realization of a drafted geometry of the gear teeth. 
         [0030]    According to a further embodiment the wheel section or geared section of the drive sleeve is located near or at the proximal end of the drive sleeve. Accordingly, also the wheel section or geared section of the drive member might be located near or at the proximal end of the drive member. Moreover, the proximal end of at least one of drive member and drive sleeve may be located at or near a proximal end section of the injection device and hence in or near a proximal end section of the housing. The intended tilt of first and second axis supporting a reduced diameter of at least one of the wheel sections or geared sections of drive sleeve and drive member therefore enables a reduction of the overall radial size of a proximal housing portion. 
         [0031]    According to another embodiment the injection device, in particular its drive mechanism further comprises a dispensing member aligned along the second axis with a shaft portion. The distal shaft portion further extends through the drive sleeve, which is hollow. The distal shaft portion is further displaceable in the distal direction relative to the drive sleeve and relative to the housing against the action of a spring member to switch the device and the drive mechanism from a dose setting mode (S) into a dose dispensing mode (D). Typically, the dispensing member further comprises a proximal button portion. The button portion serves as a proximally located dose button that is typically depressible in the distal direction by the thumb of a user in order to induce and to control a dispensing action of the injection device. 
         [0032]    As long as the dispensing member is depressed in the distal direction the drive mechanism is in dose dispensing mode. Releasing of the dispensing member leads to a proximally directed displacement of the dispensing member under the action of the spring member, thereby transferring and returning the drug delivery device and the drive mechanism from the dose dispensing mode into the dose setting mode. Hence, a dose dispensing operation can be immediately interrupted simply by releasing the dispensing member. 
         [0033]    According to a further embodiment the spring member comprises a distal tip overlapping with the second axis and being an axial abutment with an abutment member of the housing. The abutment member typically comprises an axially extending beam, which at its proximal end features a receptacle to receive the distal tip of the spring member. The spring member may comprise a conventional spring. Alternatively the spring member is made of an injection molded material. The spring member may therefore comprise an arbitrary shape and geometry. Furthermore, by having a distal tip, e.g. at a tapered distal end, the size of a mutual abutment area of abutment member and spring member can be minimized. In this way, frictional torque to rotate the spring member, e.g. for dose setting or for dose dispensing can be minimized. A respective driving torque, e.g. to be provided by a user, as well as inevitable wear can be minimized. 
         [0034]    Moreover, by the mutual axial abutment between the distal and pointed or tapered tip of the spring member with a correspondingly-shaped abutment portion of the housing&#39;s abutment member also a quality of a tactile feedback to be provided by or to be transferred by the spring member can be improved. 
         [0035]    In another embodiment the injection device and its drive mechanism further comprise a ratchet member aligned along the second axis and having a ratchet profile at a proximal end to selectively engage with a correspondingly-shaped ratchet profile at the distal end of the drive sleeve. Typically, the ratchet member is permanently axially and permanently rotationally locked to the dispensing member. Moreover, the ratchet member may be attached to a distal end of the dispensing member axially extending through and axially protruding from the distal end of the drive sleeve. The ratchet member is configured to provide an audible and/or tactile feedback signal during dose setting, in particular when the dispensing member is subject to a dose incrementing or dose decrementing rotation relative to the housing and/or relative to the drive sleeve. 
         [0036]    Typically, during dose setting, hence when the device is in dose setting mode the drive sleeve is rotationally locked to the housing and is prevented from rotating relative to the housing. The ratchet member, in particular its ratchet profile comprises numerous ratchet teeth that sequentially engage with correspondingly-shaped ratchet teeth of the ratchet profile of the drive sleeve. During dose setting the ratchet member and the dispensing member are both subject to rotation relative to the drive sleeve. Due to the ratchet engagement obtained through the axial bias of the spring member regular click sounds or respective tactile signals are generated indicating to the user, that a dose is incremented or decremented in discrete steps. During dose setting the ratchet member and hence the dispensing member are subject to an axially directed shuttling motion, which is not only audible but which is also visible at the proximal end of the device, namely when the proximally located button portion of the dispensing member shuttles back and forth in an axial direction relative to the housing. This axial displacement due to the mutual engagement of the teeth may be only slightly larger than a clearance between the dispensing member and the ratchet member. 
         [0037]    According to a further embodiment the spring member and the ratchet member are integrally formed. The ratchet member is axially displaceable relative to the housing and relative to the drive sleeve against the action of the spring member to switch from the dose setting mode into the dose dispensing mode. Integrally forming the ratchet member and the spring member is beneficial to reduce the overall number of components of the drive mechanism and the injection device. Moreover it may be of further benefit, when a distal end of the spring member is initially integrally connected to the ratchet member. It is then due to and during the assembly of the injection device and e.g. due to a comparatively large axial force acting on the ratchet member, that at least one or several predetermined breaking points between the distal end of the spring member and a distal end of the ratchet member break, so as to liberate and to activate the spring member. 
         [0038]    This frangible initial connection of at least the spring member&#39;s distal end with the ratchet member is beneficial in that the spring member is deactivated until it is actually assembled inside the injection device. In this way, the rather fragile or sensitive spring member can be protected against environmental influences and can be protected against unintended damage, e.g. during transportation before getting assembled inside the injection device. Moreover, the initially integral but frangible connection of spring member and ratchet member is beneficial during assembly since the spring member is radially and/or axially confined by the ratchet member thereby facilitating the assembly of spring member and ratchet member inside the injection device. 
         [0039]    According to another embodiment the injection device and the drive mechanism thereof further comprise a dose indicator rotationally supported on the second axis and having consecutive numbers or symbols showing up in a window of the housing when subject to a dose incrementing rotation or dose decrementing rotation with regard to the second axis during dose setting or dose dispensing. Typically, the dose indicator comprises a dose indicator sleeve or a number sleeve, wherein consecutive numbers representing the size of a dose are arranged on the outer circumference along a helical path. The dose indicator is typically axially constrained in the housing. It may be axially fixed inside the housing and is rotatable relative to the housing in this fixed axial position. Moreover, the dose indicator is selectively rotationally engageable or rotationally lockable to one of the drive sleeve and ratchet member. Typically, during dose setting or in dose setting mode the dose indicator is rotationally engaged with the ratchet member but is rotationally disengaged from the drive member. Upon switching the device into the dose dispensing mode, hence during dose dispensing the dose indicator is rotationally engaged or rotationally connected to the drive sleeve while it is decoupled or disconnected from the ratchet member. 
         [0040]    In this way, the dose indicator is either rotationally engaged with one of drive member and ratchet member while it is disengaged from the other one of drive member and ratchet member. Switching of the device between dose setting mode and dose dispensing mode leads to a respective switching of the coupling of the dose indicator with only one of drive sleeve and ratchet member. 
         [0041]    According to a further embodiment the injection device further comprises a gauge element that is radially sandwiched between the dose indicator and the interior of the main housing. The gauge element is typically rotationally locked to the housing but is free to move in an axial direction relative to the housing. Hence, the gauge element is splined or keyed to the housing by means of at least one radially extending protrusion of the housing or gauge element and a corresponding groove of the gauge element or housing. Due to its permanent threaded engagement with the dose indicator the gauge element travels in an axial direction as the dose indicator is subject to a rotation relative to the housing, either in dose incrementing or dose decrementing direction. 
         [0042]    Typically, the gauge element is non-transparent and opaque to cover most numbers or symbols of the dose indicator that would otherwise show up in the window of the main housing. The gauge element further comprises at least one recess or a window through which one number or symbol of the dose indicator is visible. 
         [0043]    The dose indicator and the gauge element further comprise mutually corresponding stop elements by way of which a maximum rotation of the dose indicator can be limited, thereby acting as a single dose limiting mechanism. The gauge element and the dose indicator may each comprise two mutually corresponding stop elements in order to limit a dose decrementing rotation of the dose indicator at the end of a dose dispensing procedure. The mutually corresponding stop elements of gauge element and dose indicator therefore provide a zero dose stop and a maximum dose stop for the drive mechanism. 
         [0044]    The zero dose stop is operable to prevent dialling of a negative dose as well as to provide a well-defined end of a dispensing process. The maximum dose stop serves to limit the maximum amount of a dose to be set by the device. 
         [0045]    According to a further embodiment the dose indicator is axially constrained to the housing and is threadedly engaged with the gauge element that is rotationally locked to the housing but which is axially slidably supported in the housing. Furthermore, the dose indicator comprises a click element extending in an axial direction and being located radially inside the hollow-shaped dose indicator. The click element is radially deflectable to protrude with a free end radially outwardly from the outer circumference of the dose indicator. The click element is particularly configured and adapted to provide a so called end of dose click. When mutually corresponding zero dose stops of the gauge element and the dose indicator get in abutment and engage so as to limit a further dose decrementing rotation of the dose indicator at the end of a dose dispensing procedure the click element of the dose indicator is configured to generate a well defined and distinct audible click sound to indicate to a user that the end of a dose dispensing procedure has been reached and that the process of dose injection or dose dispensing just terminated or is about to terminate. 
         [0046]    Axial alignment as well as axial elongation of the click element is of particular benefit to reduce the sensitivity to axial tolerances of the position of the click element relative to a further component of the injection device and its drive mechanism that serves to deflect the click element radially outwardly exclusively during and/or at the beginning of the process of dose dispensing. The click element may be of arched shape and may at least partially protrude into the interior of the hollow dose indicator. Inside the hollow dose indicator at least one further component of the drive mechanism is axially guided so as to engage with the radially inwardly protruding portion of the click element and to deflect the click element, in particular its free end radially outwardly so that the outwardly deflected click element generates a well-defined and distinct clicking noise when the injection device arrives at the end of dose configuration. 
         [0047]    According to a further embodiment the ratchet member is arranged radially inside the dose indicator and comprises a distal rim that is displaceable in the distal direction relative to the dose indicator for switching from the dose setting mode into the dose dispensing mode. During a distally directed displacement of the ratchet member during switching of the device from dose setting mode to the dose dispensing mode the distal rim of the dose indicator axially and radially engages with the click element, thereby deflecting or pivoting the free end of the click element radially outwardly in order to audibly engage with a corresponding click element of the gauge element when reaching an end of dose configuration. 
         [0048]    Typically, the ratchet member is displaceable in the distal direction relative to the dose indicator by means of the dispensing member rigidly attached thereto. When reaching the end of dose configuration the dispensing member is to be released, so that the arrangement of dispensing member and ratchet member returns into its initial position in the proximal direction. Due to this proximally directed motion of the ratchet member relative to the dose indicator the distal rim of the ratchet member and the click element of the dose indicator disengage so that the click element returns into its radially inwardly located undeflected state, thereby disengaging from the click element of the gauge element substantially without producing any audible noise. 
         [0049]    The axial alignment and elongation of the dose indicator click element is of particular benefit since this alignment tolerates slight deviations in the mutual alignment and arrangement of ratchet member, its distal rim and the dose indicator. 
         [0050]    The dispensing member may be further permanently rotationally engaged with a dose dial located at a proximal end of the housing of the injection device. Hence, the dispensing member is axially slidably supported inside the main housing and may be rotatable for at least setting of a dose. The dispensing member with its distal shaft portion may be selectively rotationally lockable to the dose indicator in order to set a dose of variable size when the device is in dose setting mode. In dose dispensing mode, the dispensing member is rotationally decoupled from the dose indicator so that the dose indicator is enabled to return into a zero dose position without inducing a rotation of the dispensing member. 
         [0051]    When in dose dispensing mode the dispensing member and hence the dose dial may be rotatable relative to the main housing. Since the dispensing member is rotationally disengaged from driving components of the drive mechanism during dose dispensing, any rotation of either the dose dial or the dispensing member has no measurable effect on the operation of the injection device. 
         [0052]    According to a further embodiment the drive sleeve is permanently rotationally coupled to the piston rod and is further rotationally biased by a mainspring. The drive sleeve is further rotationally locked to the housing when in dose setting mode and is rotationally released from the housing in dose dispensing mode. Hence, the drive sleeve is exclusively rotatable relative to the housing during dose dispensing for advancing the piston rod in the distal direction. The mainspring, acting as a driving spring and acting as a mechanical energy storage means is permanently engaged and coupled to the drive sleeve. It is typically pre-tensed or preloaded to such a degree, that the mechanical energy stored in the mainspring is sufficient to displace the piston rod from an initial proximal position into a final distally located position, in which the entirety of the medicament initially provided in the cartridge has been dispensed. 
         [0053]    The mainspring is therefore a preloaded spring. When the injection device is configured and designed as a reusable device the mainspring is rechargeable during a reset operation. The permanent coupling of the drive sleeve with the piston rod and with the mainspring and the selective coupling and rotational locking of drive sleeve and main housing is beneficial in terms of a user friendly handling of the injection device. Typically, the rotational lock between drive sleeve and main housing in dose setting mode allows a user-induced dose setting without acting against the preloaded mainspring. Dose setting is therefore rather easy and does not require biasing of the mainspring. It is only due to a distally directed displacement of the drive sleeve, typically by means of and through interaction with the dispensing member, that the drive sleeve rotationally disengages from the housing and is liberated to rotate under the action of the mainspring. 
         [0054]    In the course of a combined distally directed displacement of dispensing member and drive sleeve for dispensing of a dose, the dispensing member is rotationally decoupled from the dose indicator and the drive sleeve is rotationally coupled or rotationally locked to the dose indicator. In this way, the rotating drive sleeve induces a corresponding rotation of the dose indicator in a dose decrementing direction in order to return the dose indicator into an initial configuration. 
         [0055]    In another embodiment the ratchet member is rotationally locked to the dose indicator when in dose setting mode. The ratchet member is further rotationally released from the dose indicator when in dose dispensing mode. Switching of the injection device from the dose setting mode into the dose dispensing mode axially displaces the ratchet member relative to the dose indicator, thereby releasing a torque-proof clutch between ratchet member and dose indicator. 
         [0056]    The ratchet member is displaceable in the distal direction when switching the injection device in dose dispensing mode. This distally directed displacement is obtained through the permanent and axial coupling of ratchet member and dispensing member. Selective rotational interlocking or rotational engagement of ratchet member and dose indicator provides a dose incrementing rotation of the dose indicator during dose setting. A decoupling of ratchet member and dose indicator for dose dispensing and a rotational engagement of dose indicator and drive sleeve during dose dispensing provides a dose decrementing rotation of the dose indicator during dispensing of a dose, thereby returning to a zero dose configuration. 
         [0057]    According to a further embodiment the dispensing member is transferable in axial abutment with the drive sleeve to displace the drive sleeve into a distal dispense position, in which the drive sleeve is rotationally released from the main housing and from the dose indicator. The drive sleeve and the dispensing member comprise mutually corresponding radially extending shoulder portions that allow and support a rotation of the drive sleeve relative to the dispensing member when the injection device is in dose dispensing mode. Typically, the drive sleeve comprises a proximally facing abutment portion axially engaging with a distally facing abutment portion of the dispensing member. The abutment portions typically extending radially on the outer and inner circumference of drive sleeve and dispensing member, respectively. Distally displacing the dispensing member relative to the housing therefore advances the drive sleeve in the distal direction, thereby releasing the rotational interlock between the drive sleeve and the main housing. 
         [0058]    In dose setting mode there is an axial gap between the mutually corresponding shoulder portions of drive sleeve and dispensing member, in particular between the proximally facing abutment portion of the drive sleeve and the distally facing abutment portion of the dispensing member. In this way and in the course of depressing the dispensing member in the distal direction relative to the housing the ratchet engagement of ratchet member and drive sleeve is disengaged before the mutually corresponding abutment portions of drive sleeve and dispensing member get in axial abutment. In this way a coupling or a ratchet engagement between drive sleeve and ratchet member is disengaged before the torque-proof clutch between drive sleeve and housing is disengaged. 
         [0059]    Mutual engagement of dispensing member and drive sleeve is purely axial. While the drive sleeve is displaced in the distal direction by means of the abutment with the distally advancing dispensing member, the drive sleeve is free to rotate relative to the housing and relative to the dispensing member. 
         [0060]    Moreover, before the drive sleeve disengages from the housing it engages in a torque-proof way with the dose indicator. A selective engagement and disengagement of the drive sleeve and the dose indicator is obtained through the axial displacement of the drive sleeve relative to the housing and hence relative to the dose indicator which is axially constrained to and inside the housing. For this purpose, the drive sleeve intersecting or at least axially extending into a proximal end of the dose indicator comprises a geared, splined or keyed structure at its outer circumference to engage and to disengage with a correspondingly-shaped geared, splined or toothed structure at the inside facing sidewall portion of the dose indicator. The mutually corresponding toothed portions are arranged at such axial positions and comprise an axial elongation such that a torque-proof clutch formed by these toothed portions engages before a torque-proof clutch of housing and drive sleeve disengages. 
         [0061]    The injection device is particularly implemented as a so called auto-injector, wherein the mainspring serves as a mechanical energy storage, by way of which a driving or dispensing force or torque is provided for the injection of the medicament. The mainspring is typically preloaded to such an extent, that the mechanical energy stored therein is sufficient to expel the entirety of the medicament located inside the cartridge. Between consecutive dispensing actions a biasing or recharging of the mainspring is therefore not required. During dose setting a user does not have to provide a torque against the action of a spring element for eventually biasing the same. It is only during an optional reset operation that the mainspring or drive spring has to be charged and that the piston rod is retracted into its initial proximal position. 
         [0062]    In the present context, the distal direction points in the direction of the dispensing end of the device, where, preferably a needle assembly is provided having a double-tipped injection needle that is to be inserted into biological tissue or into the skin of a patient for delivery of the medicament. 
         [0063]    The proximal end or proximal direction denotes the end of the device or a component thereof, which is furthest away from the dispensing end. Typically, an actuating member is located at the proximal end of the injection device, which is directly operable by a user to be rotated for setting of a dose and which is operable to be depressed in the distal direction for dispensing of a dose. 
         [0064]    The term “drug” or “medicament”, as used herein, means a pharmaceutical formulation containing at least one pharmaceutically active compound, 
         [0000]    wherein in one embodiment the pharmaceutically active compound has a molecular weight up to 1500 Da and/or is a peptide, a proteine, a polysaccharide, a vaccine, a DNA, a RNA, an enzyme, an antibody or a fragment thereof, a hormone or an oligonucleotide, or a mixture of the above-mentioned pharmaceutically active compound,
 
wherein in a further embodiment the pharmaceutically active compound is useful for the treatment and/or prophylaxis of diabetes mellitus or complications associated with diabetes mellitus such as diabetic retinopathy, thromboembolism disorders such as deep vein or pulmonary thromboembolism, acute coronary syndrome (ACS), angina, myocardial infarction, cancer, macular degeneration, inflammation, hay fever, atherosclerosis and/or rheumatoid arthritis,
 
wherein in a further embodiment the pharmaceutically active compound comprises at least one peptide for the treatment and/or prophylaxis of diabetes mellitus or complications associated with diabetes mellitus such as diabetic retinopathy,
 
wherein in a further embodiment the pharmaceutically active compound comprises at least one human insulin or a human insulin analogue or derivative, glucagon-like peptide (GLP-1) or an analogue or derivative thereof, or exendin-3 or exendin-4 or an analogue or derivative of exendin-3 or exendin-4.
 
         [0065]    Insulin analogues are for example Gly(A21), Arg(B31), Arg(B32) human insulin; Lys(B3), Glu(B29) human insulin; Lys(B28), Pro(B29) human insulin; Asp(B28) human insulin; human insulin, wherein proline in position B28 is replaced by Asp, Lys, Leu, Val or Ala and wherein in position B29 Lys may be replaced by Pro; Ala(B26) human insulin; Des(B28-B30) human insulin; Des(B27) human insulin and Des(B30) human insulin. 
         [0066]    Insulin derivates are for example B29-N-myristoyl-des(B30) human insulin; B29-N-palmitoyl-des(B30) human insulin; B29-N-myristoyl human insulin; B29-N-palmitoyl human insulin; B28-N-myristoyl LysB28ProB29 human insulin; B28-N-palmitoyl-LysB28ProB29 human insulin; B30-N-myristoyl-ThrB29LysB30 human insulin; B30-N-palmitoyl-ThrB29LysB30 human insulin; B29-N—(N-palmitoyl-Y-glutamyl)-des(B30) human insulin; B29-N—(N-lithocholyl-Y-glutamyl)-des(B30) human insulin; B29-N-(ω-carboxyheptadecanoyl)-des(B30) human insulin and B29-N-(ω-carboxyheptadecanoyl) human insulin. 
         [0067]    Exendin-4 for example means Exendin-4(1-39), a peptide of the sequence H-His-Gly-Glu-Gly-Thr-Phe-Thr-Ser-Asp-Leu-Ser-Lys-Gln-Met-Glu-Glu-Glu-Ala-Val-Arg-Leu-Phe-Ile-Glu-Trp-Leu-Lys-Asn-Gly-Gly-Pro-Ser-Ser-Gly-Ala-Pro-Pro-Pro-Ser-NH2. 
         [0068]    Exendin-4 derivatives are for example selected from the following list of compounds: 
         [0000]                        H-(Lys)4-des Pro36, des Pro37 Exendin-4(1-39)-NH2,                    H-(Lys)5-des Pro36, des Pro37 Exendin-4(1-39)-NH2,                des Pro36 Exendin-4(1-39),                des Pro36 [Asp28] Exendin-4(1-39),                des Pro36 [IsoAsp28] Exendin-4(1-39),                des Pro36 [Met(O)14, Asp28] Exendin-4(1-39),                des Pro36 [Met(O)14, IsoAsp28] Exendin-4(1-39),                des Pro36 Asp28] Exendin-4(1-39),                des Pro36 IsoAsp28] Exendin-4(1-39),                des Pro36 [Met(O)14 Trp(O2)25, Asp28] Exendin-4(1-39),                des Pro36 [Met(O)14 Trp(O2)25, IsoAsp28] Exendin-4(1-39);        or                des Pro36 [Asp28] Exendin-4(1-39),                des Pro36 [IsoAsp28] Exendin-4(1-39),                des Pro36 [Met(O)14, Asp28] Exendin-4(1-39),                des Pro36 [Met(O)14, IsoAsp28] Exendin-4(1-39),                des Pro36 Asp28] Exendin-4(1-39),                des Pro36 IsoAsp28] Exendin-4(1-39),                des Pro36 [Met(O)14 Trp(O2)25, Asp28] Exendin-4(1-39),                des Pro36 [Met(O)14 Trp(O2)25, IsoAsp28] Exendin-4(1-39),             
wherein the group -Lys6-NH2 may be bound to the C-terminus of the Exendin-4 derivative;
 
or an Exendin-4 derivative of the sequence
 
         [0000]                        des Pro36 Exendin-4(1-39)-Lys6-NH2 (AVE0010),                    H-(Lys)6-des Pro36 [Asp28] Exendin-4(1-39)-Lys6-NH2,                des Asp28 Pro36, Pro37, Pro38Exendin-4(1-39)-NH2,                H-(Lys)6-des Pro36, Pro38 [Asp28] Exendin-4(1-39)-NH2,                H-Asn-(Glu)5des Pro36, Pro37, Pro38 [Asp28] Exendin-4(1-39)-NH2,                des Pro36, Pro37, Pro38 [Asp28] Exendin-4(1-39)-(Lys)6-NH2,                H-(Lys)6-des Pro36, Pro37, Pro38 [Asp28] Exendin-4(1-39)-(Lys)6-NH2,                H-Asn-(Glu)5-des Pro36, Pro37, Pro38 [Asp28] Exendin-4(1-39)-(Lys)6-NH2,                H-(Lys)6-des Pro36 Asp28] Exendin-4(1-39)-Lys6-NH2,                H-des Asp28 Pro36, Pro37, Pro38 [Trp(O2)25] Exendin-4(1-39)-NH2,                H-(Lys)6-des Pro36, Pro37, Pro38 [Trp(O2)25, Asp28] Exendin-4(1-39)-NH2,                H-Asn-(Glu)5-des Pro36, Pro37, Pro38 [Trp(O2)25, Asp28] Exendin-4(1-39)-NH2,                des Pro36, Pro37, Pro38 [Trp(O2)25], Asp28] Exendin-4(1-39)-(Lys)6-NH2,                H-(Lys)6-des Pro36, Pro37, Pro38 [Trp(O2)25, Asp28] Exendin-4(1-39)-               (Lys)6-NH2,                H-Asn-(Glu)5-des Pro36, Pro37, Pro38 [Trp(O2)25, Asp28] Exendin-4(1-39)-               (Lys)6-NH2,                H-(Lys)6-des Pro36 [Met(O)14, Asp28] Exendin-4(1-39)-Lys6-NH2,                des Met(O)14 Asp28 Pro36, Pro37, Pro38 Exendin-4(1-39)-NH2,                H-(Lys)6-desPro36, Pro37, Pro38 [Met(O)14, Asp28] Exendin-4(1-39)-NH2,                H-Asn-(Glu)5-des Pro36, Pro37, Pro38 [Met(O)14, Asp28] Exendin-4(1-39)-NH2,                des Pro36, Pro37, Pro38 [Met(O)14, Asp28] Exendin-4(1-39)-(Lys)6-NH2,                H-(Lys)6-des Pro36, Pro37, Pro38 [Met(O)14, Asp28] Exendin-4(1-39)-(Lys)6-NH2,               H-Asn-(Glu)5 des Pro36, Pro37, Pro38 [Met(O)14, Asp28] Exendin-4(1-39)-               (Lys)6-NH2,               H-Lys6-des Pro36 [Met(O)14, Trp(O2)25, Asp28] Exendin-4(1-39)-Lys6-NH2,                H-des Asp28 Pro36, Pro37, Pro38 [Met(O)14, Trp(O2)25] Exendin-4(1-39)-NH2,                H-(Lys)6-des Pro36, Pro37, Pro38 [Met(O)14, Asp28] Exendin-4(1-39)-NH2,                H-Asn-(Glu)5-des Pro36, Pro37, Pro38 [Met(O)14, Trp(O2)25, Asp28]                Exendin-4(1-39)-NH2,                des Pro36, Pro37, Pro38 [Met(O)14, Trp(O2)25, Asp28] Exendin-4(1-39)-               (Lys)6-NH2,               H-(Lys)6-des Pro36, Pro37, Pro38 [Met(O)14, Trp(O2)25, Asp28] Exendin-               4(S1-39)-(Lys)6-NH2,                H-Asn-(Glu)5-des Pro36, Pro37, Pro38 [Met(O)14,                Trp(O2)25, Asp28] Exendin-4(1-39)-(Lys)6-NH2;             
or a pharmaceutically acceptable salt or solvate of any one of the afore-mentioned Exendin-4 derivative.
 
         [0069]    Hormones are for example hypophysis hormones or hypothalamus hormones or regulatory active peptides and their antagonists as listed in Rote Liste, ed. 2008, Chapter 50, such as Gonadotropine (Follitropin, Lutropin, Choriongonadotropin, Menotropin), Somatropine (Somatropin), Desmopressin, Terlipressin, Gonadorelin, Triptorelin, Leuprorelin, Buserelin, Nafarelin, Goserelin. 
         [0070]    A polysaccharide is for example a glucosaminoglycane, a hyaluronic acid, a heparin, a low molecular weight heparin or an ultra low molecular weight heparin or a derivative thereof, or a sulphated, e.g. a poly-sulphated form of the above-mentioned polysaccharides, and/or a pharmaceutically acceptable salt thereof. An example of a pharmaceutically acceptable salt of a poly-sulphated low molecular weight heparin is enoxaparin sodium. 
         [0071]    Antibodies are globular plasma proteins (˜150 kDa) that are also known as immunoglobulins which share a basic structure. As they have sugar chains added to amino acid residues, they are glycoproteins. The basic functional unit of each antibody is an immunoglobulin (Ig) monomer (containing only one Ig unit); secreted antibodies can also be dimeric with two Ig units as with IgA, tetrameric with four Ig units like teleost fish IgM, or pentameric with five Ig units, like mammalian IgM. 
         [0072]    The Ig monomer is a “Y”-shaped molecule that consists of four polypeptide chains; two identical heavy chains and two identical light chains connected by disulfide bonds between cysteine residues. Each heavy chain is about 440 amino acids long; each light chain is about 220 amino acids long. Heavy and light chains each contain intrachain disulfide bonds which stabilize their folding. Each chain is composed of structural domains called Ig domains. These domains contain about 70-110 amino acids and are classified into different categories (for example, variable or V, and constant or C) according to their size and function. They have a characteristic immunoglobulin fold in which two β sheets create a “sandwich” shape, held together by interactions between conserved cysteines and other charged amino acids. 
         [0073]    There are five types of mammalian Ig heavy chain denoted by α, δ, ε, γ, and μ. The type of heavy chain present defines the isotype of antibody; these chains are found in IgA, IgD, IgE, IgG, and IgM antibodies, respectively. 
         [0074]    Distinct heavy chains differ in size and composition; α and γ contain approximately 450 amino acids and δ approximately 500 amino acids, while μ and ε have approximately 550 amino acids. Each heavy chain has two regions, the constant region (C H ) and the variable region (V H ). In one species, the constant region is essentially identical in all antibodies of the same isotype, but differs in antibodies of different isotypes. Heavy chains γ, α and δ have a constant region composed of three tandem Ig domains, and a hinge region for added flexibility; heavy chains μ and ε have a constant region composed of four immunoglobulin domains. The variable region of the heavy chain differs in antibodies produced by different B cells, but is the same for all antibodies produced by a single B cell or B cell clone. The variable region of each heavy chain is approximately 110 amino acids long and is composed of a single Ig domain. 
         [0075]    In mammals, there are two types of immunoglobulin light chain denoted by λ and κ. A light chain has two successive domains: one constant domain (CL) and one variable domain (VL). The approximate length of a light chain is 211 to 217 amino acids. Each antibody contains two light chains that are always identical; only one type of light chain, κ or λ, is present per antibody in mammals. 
         [0076]    Although the general structure of all antibodies is very similar, the unique property of a given antibody is determined by the variable (V) regions, as detailed above. More specifically, variable loops, three each the light (VL) and three on the heavy (VH) chain, are responsible for binding to the antigen, i.e. for its antigen specificity. These loops are referred to as the Complementarity Determining Regions (CDRs). Because CDRs from both VH and VL domains contribute to the antigen-binding site, it is the combination of the heavy and the light chains, and not either alone, that determines the final antigen specificity. 
         [0077]    An “antibody fragment” contains at least one antigen binding fragment as defined above, and exhibits essentially the same function and specificity as the complete antibody of which the fragment is derived from. Limited proteolytic digestion with papain cleaves the Ig prototype into three fragments. Two identical amino terminal fragments, each containing one entire L chain and about half an H chain, are the antigen binding fragments (Fab). The third fragment, similar in size but containing the carboxyl terminal half of both heavy chains with their interchain disulfide bond, is the crystalizable fragment (Fc). The Fc contains carbohydrates, complement-binding, and FcR-binding sites. Limited pepsin digestion yields a single F(ab′)2 fragment containing both Fab pieces and the hinge region, including the H—H interchain disulfide bond. F(ab′)2 is divalent for antigen binding. The disulfide bond of F(ab′)2 may be cleaved in order to obtain Fab′. Moreover, the variable regions of the heavy and light chains can be fused together to form a single chain variable fragment (scFv). 
         [0078]    Pharmaceutically acceptable salts are for example acid addition salts and basic salts. Acid addition salts are e.g. HCl or HBr salts. Basic salts are e.g. salts having a cation selected from alkali or alkaline, e.g. Na+, or K+, or Ca2+, or an ammonium ion N+(R1)(R2)(R3)(R4), wherein R1 to R4 independently of each other mean: hydrogen, an optionally substituted C1-C6-alkyl group, an optionally substituted C2-C6-alkenyl group, an optionally substituted C6-C10-aryl group, or an optionally substituted C6-C10-heteroaryl group. Further examples of pharmaceutically acceptable salts are described in “Remington&#39;s Pharmaceutical Sciences” 17. ed. Alfonso R. Gennaro (Ed.), Mark Publishing Company, Easton, Pa., U.S.A., 1985 and in Encyclopedia of Pharmaceutical Technology. 
         [0079]    Pharmaceutically acceptable solvates are for example hydrates. 
         [0080]    It will be further apparent to those skilled in the art that various modifications and variations can be made to the present disclosure without departing from the spirit and scope of the disclosure. Further, it is to be noted, that any reference numerals used in the appended claims are not to be construed as limiting the scope of the disclosure. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0081]    In the following, a non-limiting embodiment of the injection device with its drive mechanism is described in detail by making reference to the drawings, in which: 
           [0082]      FIG. 1  shows a partially transparent side view of the injection device, 
           [0083]      FIG. 2  shows an exploded and perspective view of the components of the injection device, 
           [0084]      FIG. 3  is a longitudinal cross-section through the injection device in dose setting mode, 
           [0085]      FIG. 4  shows an enlarged portion of the device according to  FIG. 3 , 
           [0086]      FIG. 5  shows the device according to  FIG. 3  in dose dispensing mode, 
           [0087]      FIG. 6  is an isolated side view of the ratchet member, 
           [0088]      FIG. 7  is a side view of the ratchet member in engagement with the dose indicator and the drive sleeve, 
           [0089]      FIG. 8  shows the mutually corresponding ratchet profiles at the proximal and distal end faces of the ratchet member and the drive sleeve, respectively, 
           [0090]      FIG. 9  shows a pre-assembly configuration of the ratchet member with integrated spring member, 
           [0091]      FIG. 10  shows the ratchet member according to  FIG. 9  in dose setting mode, 
           [0092]      FIG. 11  shows the configuration of the ratchet member and its integrated spring member in dose dispensing mode, 
           [0093]      FIG. 12  is a cross section through a proximal end section of a comparative injection device, wherein first and third axes are aligned parallel, 
           [0094]      FIG. 13  shows a cross section according to  FIG. 12  but of an embodiment, wherein first and third axes are slightly tilted, 
           [0095]      FIG. 14  shows the device according to  FIG. 3  in an end of content configuration with a slightly bended piston rod, 
           [0096]      FIG. 15  shows an isolated and perspective illustration of ratchet member, dose indicator and gauge element, 
           [0097]      FIG. 16  shows a cross section through a distal portion of the device in dose setting mode after setting of a dose, 
           [0098]      FIG. 17  shows the distal end of the device when in dose dispensing mode, 
           [0099]      FIG. 18  shows the section according to  FIGS. 16 and 17  when the dose indicator returns into the zero dose configuration at the end of a dose dispensing procedure and 
           [0100]      FIG. 19  is indicative of the end of dose configuration, in which the free end of the deflected click element of the dose indicator reaches a recess in the inside facing sidewall portion of the gauge element, 
           [0101]      FIG. 20  is a perspective illustration of the configuration according to  FIG. 16 , 
           [0102]      FIG. 21  is a perspective illustration of the configuration of the device according to  FIG. 17 , 
           [0103]      FIG. 22  is a perspective illustration of the configuration of  FIG. 18  and 
           [0104]      FIG. 23  is a perspective illustration of the configuration of  FIG. 19 . 
       
    
    
     DETAILED DESCRIPTION 
       [0105]    The injection device  5  as illustrated in  FIG. 1  is configured as an all mechanically implemented auto-injector. It comprises a housing  10  featuring a main housing  11  of elongated shape and extending in an axial direction. The main housing  11  comprises a distal end facing in a distal direction  1  and further comprising a proximal end facing in a distal direction  2 . The housing  10  comprises a proximal housing portion  12  that is connectable with a proximal end of the main housing  11 . The proximal housing portion  12  serves as a kind of a lid closing the tubular-shaped main housing  11  in proximal direction  2 . As shown in  FIG. 2 , the proximal housing portion  12  comprises a proximally extending socket portion  12   a  that serves as a support and a bearing for a dose dial  20  rotationally supported on the housing  10  and axially fixed thereto by means of at least one snap member  21  as shown in  FIG. 5 . 
         [0106]    In distal direction  1  the main housing  11  terminates with a distal front face from which a cartridge holder  14  axially protrudes. As it is apparent from  FIG. 1 , the cartridge holder  14  comprises a threaded socket  14   a  to threadedly engage with a needle hub  142  of a piercing assembly  140  that comprises a double-tipped injection needle  141 . The cartridge holder  14  comprises a through opening at its distal front face to receive the proximal end of the injection needle  141 . When not in use the distal end of the injection device  5 , in particular the cartridge holder  14  is covered by a detachable protective cap  13 . 
         [0107]    As it is apparent from  FIGS. 1-5  there are provided two principal axes  3 ,  4  along which almost all mechanical components of the injection device  5  are aligned. Almost all mechanical components of the injection device  5  are located concentrically about one of the two principal axes  3 ,  4 . The first and second axes  3 ,  4  are separated by a radial distance. They extend substantially parallel with respect to each other with a slight angular offset as shown in  FIG. 3 . Along the first axis  3  there are aligned the elongated piston rod  130  that is rotationally engaged with a co-aligned sleeve-shaped drive member  110 . Typically, the piston rod  130  is keyed or splined with the drive member  110 . The drive member  110  typically comprises a radially inwardly extending protrusion that is engaged with an axially extending groove on the outer circumference of the piston rod  130 . Furthermore, the piston rod  130  comprises an outer thread  133  by way of which it is threadedly engaged with a threaded through opening of a radially inwardly extending flange portion  9  of the main housing  11 . A rotation of the drive member  110  therefore leads to a corresponding rotation of the piston rod  130  relative to the housing  10 , which due to the threaded engagement of piston rod  130  and housing  10  or main housing  11  leads to a distally directed displacement of the piston rod  130  thereby exerting a distally directed pressure to the piston  7  of the cartridge  6 . 
         [0108]    In an alternative embodiment it is also conceivable, that the piston rod  130  is in splined engagement with the main housing  11 , i.e. the piston rod  130  is free to be axially displaced relative to the main housing  11  but is for instance threadedly engaged with the hollow drive member  110 . 
         [0109]    The drive member  110  is in permanent rotational engagement with a drive sleeve  100  through a geared engagement. The drive sleeve  100  is arranged radially adjacent to the drive member  110 . The geared engagement of drive sleeve  100  and drive member  110  is even invariant to slight axial displacement of the drive sleeve  100  relative to the drive member  110 . As can be seen from  FIGS. 3, 5, and 13  the drive sleeve  100  is arranged along the second principal axis  4 . Concentrically arranged with this second axis  4  there is further provided a sleeve-shaped dispensing member  30 , a dose dial  20 , a gauge element  90 , a dose indicator  80  and a ratchet member  60 . 
         [0110]    The dose dial  20  is axially fixed to the housing  10 , in particular to the proximal housing portion  12 , e.g. by way of mutually engaging latch or clip members  21 , e.g. positively locked and positively engaged with a corresponding recess of the proximal housing portion  12 . In this way, the dose dial  20  is rotatable relative to the housing  10 . The dose dial  20  is permanently rotationally locked to the dispensing member  30  having a proximal button portion  32  at least slightly proximally protruding from the proximal end of the dose dial  20  when in dose setting mode (S). 
         [0111]    The dispensing member  30  further has a shaft portion  31  extending along the second axis  4 . The dispensing member  30  comprises at least one, typically several radially outwardly biased snap members  34  at its distal end to permanently axially engage with correspondingly shaped recesses of the ratchet member  60 . In this way, the dispensing member  30  and the ratchet member  60  are permanently axially and rotationally locked to each other. Axial displacement as well as a rotation of the dispensing member  30  equally transfers to the ratchet member  60 ; and vice versa. 
         [0112]    The drive sleeve  100  further has a detent structure  102  at a proximally facing socket portion or at a proximal end engaging with a correspondingly-shaped detent structure  18  of the housing  10  as shown in  FIG. 5 . The detent structures  18 ,  102  form a first clutch C 1  by way of which the drive sleeve  100  is rotationally locked to the housing  10  when in the proximal dose setting position (S). The drive sleeve  100  further comprises a geared section  103  near or at its proximal end as shown in  FIGS. 2 and 7 . 
         [0113]    The drive sleeve  100  is axially intersected by the shaft portion  31  of the dispensing member  30 . The drive sleeve  100  further comprises a threaded section  104  near its distal end which is threadedly engaged with a correspondingly threaded last dose limiting member  50  as shown in  FIG. 7 . The last dose limiting member  50  is furthermore in splined engagement with the inside facing portion of the dose indicator  80  through which the drive sleeve  100  axially extends. During dose setting the dose indicator  80  rotates relative to the rotationally locked drive sleeve  100 , thereby inducing a corresponding rotation of the last dose limiter  50 , which upon the threaded engagement with the drive sleeve  100  travels in an axial direction, e.g. in the proximal direction as a dose of increasing size is set. 
         [0114]    There are provided mutually corresponding stop features on the outer circumference of the drive sleeve  100  and the last dose limiter  50 . When reaching an end of content configuration, in which the dose to be set would exceed the amount of medicament left in the cartridge, the last dose limiter  50  is blocked from rotating further relative to the drive sleeve  100  thereby inhibiting any further dose incrementing rotation of the dose dial  20 . 
         [0115]    The dose indicator  80  is axially constrained and hence axially locked to the housing  10 . This is achieved by a radially inwardly extending protrusion  17  of the main housing  11  engaging with a correspondingly shaped annular and circumferential groove  89  of the dose indicator  80  as shown in  FIG. 4 . In this way, the dose indicator  80  and the housing  10  are permanently axially engaged and the dose indicator  80  is free to rotate relative to the housing with regard to the second axis  4 . 
         [0116]    As it is shown in detail in  FIG. 3  the first axis  3  extends at a slight offset angle A with respect to the second axis  4 . Hence, a first radial distance d 1  between first and second axes  3 ,  4  at a distal end  100   a  of the drive sleeve  100  differs from a second radial distance d 2  between first and second axes  3 ,  4  at a proximal end  100   b  of the drive sleeve  100 . In the present embodiment, the first radial distance d 1  is larger than the second radial distance d 2 . Hence, the radial distance between first and second axes  3 ,  4  is smaller at the proximal end of the injection device  5 , compared to a middle section of the injection device or compared to an axial position, where the distal end  100   a  of the drive sleeve  100  is located. This non-parallel but slightly converging alignment of first and second axes  3 ,  4  towards the proximal direction  2  has the beneficial effect, that the center distance d 2  between drive member  110  and drive sleeve  100  in the region of their mutually engaged geared sections  103 ,  113  is reduced compared to a radial center distance d 1  at the distal end  100   a  of the drive sleeve  100 . 
         [0117]    A comparison of the cross section according to  FIG. 13  with a parallel arrangement of first and second axes  3 ,  4  as illustrated in  FIG. 12 , reveals, that the radial extension of at least one of the geared sections  103 ,  113  of drive sleeve  100  and drive member  110  can be reduced. Especially a comparison of the geared sections  113  and  113 ′ of  FIGS. 13 and 12  shows that the number of teeth of the geared section  113  is reduced compared to the number of teeth of the geared section  113 ′ of a drive member  110 ′ that is arranged parallel to the second axis  4  as shown in  FIG. 12 . 
         [0118]    The smaller and size reduced radial dimension of at least one of the geared sections  103 ,  113  provides the possibility to reduce the overall radial dimensions of the housing  10  of the injection device  5 . Consequently, a rather compact design of an injection device  5  can be provided, especially at a proximal end thereof which is to be gripped and held in the hand of a user. 
         [0119]    To avoid increasing the radial dimensions near a distal end of the injection device  5  the cartridge is assembled inside the housing  10  in particular inside the cartridge holder  14  and extends along a third axis  3 ′ at a radial distance from the second axis  4  but parallel to the second axis  4 . Consequently, first axis  3  and third axis  3 ′ almost coincide but are oriented at the offset angle A as can be seen from  FIG. 3 . Consequently first and third axes  3 ,  3 ′ coincide or cross in a virtual crossing point X. The virtual crossing point X is located distally from a distal end of the piston rod  130 . It is typically located inside the cartridge  6  or inside the piston  7  of the cartridge  6 . As subsequent dispensing procedures take place the piston rod  130  with a bearing  132  or pressure piece advances in distal direction  1 . Then, the piston rod  130  extends along the first axis  3  and tends to cross the third axis  3 ′. 
         [0120]    However and since the piston rod  130 , in particular its bearing  132  is radially confined inside the tubular-shaped barrel of the cartridge  6  at least its distal end experiences a co-alignment with the third axis  3 ′ as the distally directed displacement of the piston rod continues. Moreover, as the piston rod  130  advances distally its distal end departs more and more from the threaded flange portion  9  and therefore resembles a cantilever arm the free and distal end of which being easily deflectable in radial direction so that the distal end of the piston rod  130  co-aligns and coincides with the third axis  3 ′ as illustrated in  FIG. 14 . 
         [0121]    The ratchet member  60  as separately shown in  FIG. 6  comprises a proximal rim  61  and a distal annular rim  62  that are interconnected by at least one axially extending bridging portion  63 . Typically, there are provided two radially oppositely located rod-like bridging portions  63  interconnecting the proximal and distal rims  61 ,  63 . The proximal rim  61  comprises a toothed profile  64  on its radially outwardly facing circumference to selectively engage with the correspondingly toothed profile  84  of the dose indicator  80  as shown in  FIG. 7 . In this way, ratchet member  60  and dose indicator  80  form a third torque-proof clutch C 3  that is releasable through a distally directed displacement of the ratchet member  60  relative to the housing  10  and hence relative to the dose indicator  80 . 
         [0122]    The proximally facing surface of the proximal rim  61  further comprises a ratchet profile  65  that is selectively engageable with a correspondingly-shaped ratchet profile  105  located at a distal end face of the drive sleeve  100  as shown in  FIGS. 7 and 8 . In addition, the ratchet member  60  is axially biased by a spring member  70  that is integrally formed with the ratchet member  60  and which axially extends between the proximal rim  61  and the distal rim  62 . The ratchet member  60  and the spring member  70  are manufactured by injection molding, in particular by an injection molded thermoplastic material. The thermoplastic and injection molded spring member  70  comprises a helical structure that is axially compressible to provide an axial spring force. As shown in detail in  FIG. 4 , the spring member  70  has a tapered distal end featuring a knob-shaped distal tip  71 . By means of this distal tip  71  coinciding with the second axis  4  the spring member  70  axially abuts with an abutment member  15  of the housing  10 . The abutment member resembling a post extending proximally from a distal front face of the housing features a bearing  15   a  to accommodate the knob-shaped distal tip  71  of the spring member  70 . 
         [0123]    The almost pointed abutment between abutment member  15  and distal tip  71  of the spring member  70  is beneficial in that a contact surface between spring member  70  and abutment member  15  is minimized. Moreover, the mutual abutment coincides with the second axis  4  the spring member  70  and hence the ratchet member  60  is easily rotatable relative to the housing  10  with a minimum of friction. This friction reduced abutment is of particular benefit during setting of a dose as well as to provide an improved audible and/or tactile feedback during dose setting. 
         [0124]    As shown in  FIG. 6  the spring member  70  is integrally formed with a proximal end section with the proximal rim  61  of the ratchet member  60 . In an initial configuration and prior to an assembly of the ratchet member  60  inside the injection device  5  also a distal end of the spring member  70  is integrally formed and integrally connected to the distal rim  62  of the ratchet member  60 . In this initial state as shown in  FIG. 9  the spring member  70  and in particular its distal end is substantially deactivated. It is hence hindered to move or to swing relative to the ratchet member  60 . This makes the arrangement of ratchet member  60  and spring member  70  rather robust against environmental influences, especially during transportation to an assembly line of the injection device  5 . 
         [0125]    During assembly a rather larger axial force above a predefined threshold is applied in the distal direction towards the ratchet member  60 . When the distal tip  71  of the spring member  70  is already in axial abutment with the abutment member  15  the frangible connection  72 , in particular radially outwardly extending lobes  73  of the spring member  70 , that are initially interconnected with the distal rim  62 , disconnect and break so as to liberate and to activate the spring member  70 . The spring member  70  then relaxes into the shape as shown in  FIG. 10  wherein the distal tip  71  is located proximally compared to the axial position of the distal rim  62 . 
         [0126]    When in dose setting mode and when the ratchet member  60  is subject to an axial and distal displacement relative to the housing the spring member  70  is compressed as shown in  FIG. 11  against a restoring force. 
         [0127]    As the dispensing member  30  is released it is due to the action and effect of the spring member  70 , that the proximal rim  61  and hence the ratchet member  60  returns into its initial dose setting position in proximal direction  2 . 
         [0128]    In  FIG. 15  there are shown the sleeve-shaped dose indicator  80  as well as the gauge element  90 . The gauge element  90  comprises an elongated and opaque structure with a dose indicating window  91  through which dose indicating numbers of the dose indicator  80  are visible from outside the injection device  5 . The gauge element  90  is splined to the interior of the main housing  11 . It is rotationally locked to the main housing  11  but is free to slide in the axial direction relative to the main housing  11 . A distal portion of the dose indicator  80  comprises a threaded or helical section  85  that mates and engages a helical section  95  on the inside facing surface portion of the gauge element  90 . A rotation of the dose indicator  80  therefore leads to an axial displacement of the gauge element  90 . 
         [0129]    The dose indicator  80  further comprises a zero dose stop as well as a maximum dose stop at axially opposite end sections of the helical section  85 . When reaching a minimum or maximum dose configuration the dose indicator  80  with its stops tangentially and/or axially abuts with correspondingly-shaped stop features of the gauge element  90 . In addition and as shown in  FIGS. 16-23  the dose indicator  80  comprises a click element  88  to audibly engage with a correspondingly-shaped click element  98  of the gauge element  90  when reaching an initial, hence a zero dose configuration at the end of a dispensing procedure, thereby audibly indicating to a user that the process of injection has terminated. 
         [0130]    The opaque gauge element  90  is radially sandwiched between the dose indicator  80  and a dose indicating window  16  of the main housing  11  as it is apparent from  FIGS. 1 and 15 . During a dose setting, in particular during a dose incrementing rotation of the dose indicator  80 , the gauge element  90  travels in proximal direction  2 , thereby displacing the window  91  to reveal consecutively increasing numbers of the rotating dose indicator  80 . At the same time also a distal portion  93  of the gauge element  90  travels in proximal direction  2  which is visible through another window  16   a  of the main housing  11  as indicated in  FIG. 2 . The distal portion  93  of the gauge element  90  provides an additional visual user feedback of the actual dose position of the device. This is of particular benefit during dose dispensing, namely when the gauge element  90  returns into its distal position. 
         [0131]    As the gauge element  90  moves in the proximal direction during setting of a dose it reveals a further surface underneath. The axial size of the windows  16 ,  16   a  is directly correlated to the maximum size of a dose to be set and dispensed. During the dose dispensing procedure, the progress of dose dispensing is immediately apparent through a comparison of the actual position of the gauge element window  91  within the window  16  or by the axial position of the distal edge of the distal portion  93  inside the window  16   a.    
         [0132]    A visible surface portion of the gauge element  90  visible in the widow  16   a  therefore provides an analogue indication or analogue gauge of the size of the dose dialled, which helps to improve overall handling of the device  5  and which helps to improve patient safety. 
         [0133]    The analogue gauge provided by the additional window  16   a  and the distal portion  93  of the gauge element  90  is of particular use during dispensing of a dose. The number digit display provided by the rotating dose indicator  80  may change too quickly for individual dose position markings to be legible. It may be therefore difficult for the user to estimate the rate at which the dose is actually dispensed and the amount of medicament still to be dispensed. 
         [0134]    In the following setting of a dose is described. For setting of a dose a user starts to rotate the dose dial  20  in a dose incrementing direction, e.g. clockwise relative to the housing  10 . This causes the dispensing member  30  to rotate since dose dial  20  and dispensing member  30  are in permanent rotational interlock. The rotation of the dispensing member  30  equally transfers to a rotation of the ratchet member  60 , which due to the ratchet engagement with the ratchet profile  105  of the drive sleeve  100  starts to shuttle axially every time correspondingly-shaped teeth of the ratchet profiles  65 ,  105  mutually engage. 
         [0135]    In this way dialling or setting of a dose is accompanied by an audible click sound as well as by the button portion  32  that eventually shuttles back and forth in an axial direction. Since the ratchet member  60  is also rotatably locked to the dose indicator  80  when the drive mechanism  8  is in dose setting mode S also the dose indicator  80  starts to rotate in a dose incrementing direction. In this way a sequence of increasing numbers shows up in the window  91  of the gauge element  90  travelling in the proximal direction. During dose setting the drive sleeve  100  is rotatably locked to the main housing  11  through the clutch C 1  as illustrated in  FIG. 3 . 
         [0136]    In this way, since the drive sleeve  100  is rotationally locked and since the dose indicator  80  rotates in a dose incrementing direction the last dose limiter  50  travels in an axial direction as the dose indicator  80  is rotated. In case that the amount of medicament left in the cartridge is smaller than the size of the dose to be set the last dose limiter  50  gets in abutment with a stop element on the outer surface of the drive sleeve  100 , thereby preventing any further dose incrementing rotation of the dose indicator  80 . 
         [0137]    The ratchet member  60  and the dispensing member  30  are biased in proximal direction  2  by means of the spring member  70  extending axially between the abutment portion  15  and a distal end face or abutment face of the ratchet member&#39;s  60  proximal rim  61 . The spring member  70  is designed to bias the ratchet member  60  towards and against the distal end face of the drive sleeve  100 . This axial load acts to maintain the mutually corresponding ratchet profiles  65 ,  105  in engagement. 
         [0138]    A torque required to overhaul this ratchet is governed by the axial load provided by the spring member  70 , the ramp angle of the ratchet and the friction coefficient between the mating surfaces and the mean radius of the ratchet profiles  65 ,  105 . As the user rotates the dose dial  20  in a dose incrementing direction, e.g. clockwise, the ratchet member  60  rotates relative to the drive sleeve  60  by consecutive ratchet teeth. Every time a ratchet tooth re-engages into a next detented position an audible click is generated by the mutually engaged ratchet profiles  65 ,  105 . At the same time a tactile feedback is given to the user by the change in torque input required for rotating the dose dial  20 . 
         [0139]    For increasing a selected dose, the dose dial  20  is simply rotated further, e.g. in clockwise direction. Every time the dose is incremented by a discrete step the re-engagement of the ratchet profiles  65 ,  105  provides audible and tactile feedback to the user. If the user continues to increase the dose until a maximum dose limit is reached the dose indicator  80  engages with its maximum dose stop with the gauge element  90  thereby preventing any further rotation of the dose indicator  80  and hence any further rotation of the ratchet member  60 , the dispensing member  30  and the dose dial  20 . 
         [0140]    Once a dose of respective size has been set or selected the user is also able to de-select or to decrement the dose. De-selecting of a dose is achieved by the user rotating the dose dial  20  in a dose decrementing direction, e.g. counter-clockwise. The torque to be applied to the dose dial  20  is sufficient to overhaul the ratchet between the ratchet member  60  and the drive sleeve  100  in the dose decrementing direction. When the ratchet is overhauled counter-clockwise also the dose indicator rotates in the opposite direction, thereby consecutively illustrating a sequence of decreasing numbers in the window  91 . Also the last dose limiter  50  travels in the opposite axial direction towards its initial position. 
         [0141]    Once a dose of required size has been set the drive mechanism  8  may be switched into a dose dispensing mode D by depressing the dispensing member  30  in distal direction  1 . When the button portion  32  of the dispensing member  30  is depressed as illustrated for instance in  FIG. 5 , the ratchet member  60  advances in distal direction  1  against the action of the spring member  70 . The ratchet engagement of the ratchet profiles  65 ,  105  is disengaged. In addition the clutch C 3  between the ratchet member  60  and the dose indicator  80  is disengaged since the ratchet member  60  is displaced axially relative to the dose indicator  80 . 
         [0142]    Moreover and due to the axial abutment of dispensing member  30  and drive sleeve  100  also the drive sleeve  100  is displaced in distal direction  1  so that the clutch C 1  between drive sleeve  100  and main housing  11  is disengaged or released. Upon axial displacement of the dispensing member  30  a radially widened shoulder portion  35  thereof axially abuts against a correspondingly-shaped shoulder portion  106  of the drive sleeve  100  thereby disengaging the detent structure  102  from the detent structure  18  of the main housing  11  as illustrated in  FIG. 5 . Consequently, the drive sleeve  100  is free to rotate under the action of a mainspring  126 . Before the clutch C 1  disengages in the course of depressing the dispensing member  30  the clutch C 2  engages. 
         [0143]    The shoulder portion  106  faces in proximal direction  2  and is located on the inside facing sidewall of the hollow drive sleeve  100 . The shoulder portion  106  comprises a stepped down portion. This stepped portion is substantially even-shaped to provide reduced friction when in axial abutment with a correspondingly-shaped stepped shoulder portion  35  of the dispensing member  30 . The shoulder portion  35  of the dispensing member  30  faces in the distal direction. 
         [0144]    In dose setting mode S as shown in  FIG. 3  there exists at least a small axial gap between these shoulder portions  35 ,  106 . Consequently the axial abutment of dispensing member  30  and drive sleeve  100  is only obtained after the dispensing member  30  has been displaced a certain distance in distal direction  1  so that the ratchet engagement of ratchet member  60  and drive sleeve  100  is disengaged before the drive sleeve  100  advances in unison with the dispensing member  30  and with the ratchet member  60  in distal direction  1  to arrive in the distal dose dispensing position that defines the dose dispensing mode D. 
         [0145]    With the distally directed displacement of the drive sleeve  100  also a clutch C 2  between drive sleeve  100  and dose indicator  80  is engaged. This clutch C 2  is shown in  FIG. 7  in its disengaged state. Hence, the drive sleeve  100  axially extending through the hollow and sleeve-shaped dose indicator  80  comprises a toothed profile  101  to selectively engage with a correspondingly toothed profile  86  located at an inside facing sidewall section at the proximal end of the dose indicator  80 . When displacing the drive sleeve  100  in distal direction  1  to arrive at the dose dispensing position the toothed profile  101  engages with the toothed profile  86  in a torque-proof way. Moreover, as shown in  FIG. 7  the toothed profile  101  extends in the distal direction from a radially outwardly extending flange portion  108  of the drive sleeve  100 . 
         [0146]    During the combined distally directed displacement of dispensing member  30 , ratchet member  60  and drive sleeve  100  the second clutch C 2  engages before the clutch C 1  disengages. Moreover, the clutch C 2  also engages before the clutch C 3  disengages. The clutch C 1  disengages after the clutch C 3  has disengaged. This is to avoid any uncontrolled rotation of the drive sleeve and to make sure that the dose actually set and dispensed exactly corresponds to the dose size as indicated by the dose indicator  80 . When returning into the dose setting mode, the clutches C 1 , C 2  and C 3  engage and disengage in an inverted order. 
         [0147]    As the clutch C 2  engages the drive sleeve  100  is further in axial abutment with the proximal end of the dose indicator  80 . Consequently, the dose indicator  80  axially fixed to the housing  10  also serves as a distal stop for the combined distally directed displacement of drive sleeve  100  and dispensing member  30 . 
         [0148]    During dose dispensing the drive sleeve  100  then rotates in a dose decrementing direction, e.g. counter-clockwise under the action of the mainspring  126 . This rotation is equally transferred to a dose decrementing rotation of the dose indicator  80 . Hence, during dose dispensing the dose indicator  80  returns into its initial position and the gauge element  90  returns into its initial position as illustrated in  FIG. 1 . The process of dose dispensing is terminated when the zero dose stop of the dose indicator  80  abuts with a correspondingly-shaped stop of the gauge element  90 . 
         [0149]    There are further provided mutually engaging click elements  88  and  98  on the dose indicator  80  and the gauge element  90  that audibly engage when the zero dose configuration has been reached. The click element  88  comprises a flexible arm which is to be radially outwardly biased by the axial and distal displacement of the ratchet member  60 , in particular of its distal rim  62 . In this way, the click element  88  of the dose indicator  80  may be radially outwardly biased by the ratchet member  60  when switched into the dose dispensing mode D. In this way, a rather loud and distinct click noise is generated directly indicating to a user, that dose dispensing has terminated. 
         [0150]    As it is apparent from the sequence of  FIGS. 16-19  and the corresponding sequence of  FIGS. 20-23  the axially aligned click element  88  integrally formed with the dose indicator  80  extends at least slightly radially inwardly into the hollow-shaped dose indicator  80 . In the dose setting mode as shown in  FIGS. 16 and 20  the radially inwardly extending portion of the click element  88  is located distally from the distal rim  62  of the ratchet member  60 . The click element  88  extends in an axial direction and its free end  82  forms a distal end thereof. During a dose setting procedure the gauge element  90  is subject to a proximally directed displacement relative to the dose indicator  80  and hence also relative to the click element  88 . 
         [0151]    Since the click element is in its unbiased state it is substantially disengaged from the correspondingly-shaped click element  98  of the gauge element  90  that comprises a radially outwardly extending recess in the inside facing sidewall portion of the gauge element  90 . As a dose dispensing is triggered through the distally directed displacement of the dispensing member  30  and the ratchet member  60  also the distal rim  62  of the ratchet member  60  advances in distal direction  1 . Then and as illustrated in  FIGS. 17 and 21  the click element  88  is deflected radially outwardly. 
         [0152]    Consequently, this radially outwardly directed displacement is largest at the free end  82  of the click element  88 . It is particularly located radially outwardly compared to the outer circumference of the helical section  85  of the dose indicator  80 . As shown in  FIGS. 18 and 22  as the gauge element  90  returns into its initial zero dose position the click element  88 , in particular its free end  82  is deflected radially inwardly. Since the click element  88  is still biased by the distal rim  62  of the ratchet member  60  radially outwardly a rather loud and distinct click noise is generated when the recessed click element  98  of the gauge element  90  engages and axially overlaps with the free end  82  of the dose indicator&#39;s  80  click element  88 . 
         [0153]    When the dispensing member  30  is released, the spring member  70  induces a proximally directed return motion to the ratchet member  60 , thereby disengaging the click element  88  and the ratchet member&#39;s  60  distal rim  62 . In a subsequent dose setting procedure the gauge element  90  is displaceable in the proximal direction relative to the dose indicator  80  without producing any noise. 
         [0154]    The drive sleeve  100  is permanently rotatably engaged via the geared section  103  with the drive member  110 . As already explained a rotation of the drive member  110  in dose decrementing direction leads to a distally directed displacement of the piston rod  130 . In addition the drive member  110  comprises a radially outwardly protruding click element  112 , indicated in  FIG. 2 , engaging with a correspondingly-shaped toothed profile on the interior surface of the main housing  11 . In this way, delivery of a dose and hence a rotation of the drive member  110  is also accompanied by an audible click sound with each dose increment delivered. 
         [0155]    Delivery and dispensing of a dose continues as described above while the user keeps the dispensing member  30  in a depressed position. If the user releases the dispensing member  30 , the dispensing member  30  immediately returns into its initial and proximal dose setting position under the effect of the spring member  70 . Consequently, also the ratchet member  60  and the drive sleeve  100  return into their dose setting positions, thereby engaging the clutches C 1 , C 3  but releasing the clutch C 2 . 
         [0156]    During dose dispensing the dose indicator  80  and the drive sleeve  100  rotate together. Since there is no relative rotation between the drive sleeve  100  and the dose indicator  80  the last dose limiter  50  remains in its axial position relative to the drive sleeve  100  and the dose indicator  80 . 
         [0157]    Once the dispensing procedure is stopped by the dose indicator  80  getting in rotational abutment with the gauge element  90  the mainspring-driven rotation of the drive sleeve  100  stops. When the user releases the dispensing member  30 , in particular its button portion  32  the drive sleeve  100  will re-engage with the main housing  11  and the ratchet member  60  will re-engage with the dose indicator  80 . 
         [0158]    The mainspring  126  providing a mechanical energy storage and providing sufficient torque to expel the amount of medicament contained in the cartridge  6  comprises an elongated strip of material that has been rolled or coiled such that its natural state is to form a tightly wound spiral with a comparatively small inner diameter. One end of the elongated material strip is engaged and connected to the drive sleeve  100 . The drive sleeve  100  comprises a respective coil portion  107  axially constrained by flange portions  108  as shown in  FIGS. 1 and 7  that allows for a smooth and well-defined coiling of the elongated material strip of the mainspring  126 . 
         [0159]    There is further provided a storage spool  120  radially adjacent to the coil portion  107  of the drive sleeve  100 . The storage spool  120  is axially intersected by the drive member  110  and is free to rotate on the outer circumference of the drive member  110 . Also the storage spool comprises a distal and a proximal flange portion  122  in order to axially constrain the mainspring  126 . The mainspring  126 , hence the elongated strip of material, tends to coil itself onto the storage spool  120 . Since one end of the mainspring  126  is anchored to the drive sleeve  100  the mainspring  126  is chargeable by rotating the drive sleeve  100  in a dose incrementing direction thereby coiling up the elongated strip of material onto the coil portion  107  of the drive sleeve  100 . Once charged the majority of material of the mainspring  126  is wrapped around the drive sleeve  100 . During consecutive dispense procedures the elongated strip of material transfers back to the storage spool  120  thereby inducing a number of dose decrementing rotations of the drive sleeve  100 . 
         [0160]    As shown in  FIG. 3  the flange portions  108 ,  122  of the drive sleeve  100  and the drive member  110  are axially engaged. In this way the storage spool  120  is axially slaved or restrained by the drive sleeve  100 . The storage spool  120  is axially intersected by the sleeve shaped drive member  110  and is free to slide along the drive member  110  in an axial direction. In this way, the storage spool  120  is axially displaceable in unison with the drive sleeve when switching between dose dispensing and dose setting modes, thereby keeping any axial load away from the mainspring  126 . 
       LIST OF REFERENCE NUMERALS 
       [0000]    
       
           1  distal direction 
           2  proximal direction 
           3  axis 
           3 ′ axis 
           4  axis 
           5  injection device 
           6  cartridge 
           7  piston 
           8  drive mechanism 
           9  flange 
           10  housing 
           11  main housing 
           12  proximal housing portion 
           12   a  socket portion 
           13  protective cap 
           14  cartridge holder 
           14   a  threaded socket 
           15  abutment member 
           15   a  bearing 
           16  window 
           16   a  window 
           17  protrusion 
           18  detent structure 
           20  dose dial 
           21  clip member 
           30  dispensing member 
           31  shaft portion 
           32  button portion 
           34  snap member 
           35  shoulder portion 
           50  last dose limiter 
           60  ratchet member 
           61  proximal rim 
           62  distal rim 
           63  bridging portion 
           64  toothed profile 
           65  ratchet profile 
           70  spring member 
           71  distal tip 
           72  frangible connection 
           73  lobe 
           80  dose indicator 
           82  free end 
           84  toothed profile 
           85  helical section 
           86  toothed profile 
           88  click element 
           89  groove 
           90  gauge element 
           91  window 
           9   f   3  distal portion 
           95  helical section 
           98  click element 
           100  drive sleeve 
           100   a  distal end 
           100   b  proximal end 
           101  toothed profile 
           102  detent structure 
           103  geared section 
           104  threaded section 
           105  ratchet profile 
           106  shoulder portion 
           107  coil portion 
           108  flange portion 
           110  drive member 
           110 ′ drive member 
           112  click element 
           113  geared section 
           113 ′ geared section 
           120  storage spool 
           122  flange portion 
           126  mainspring 
           130  piston rod 
           132  bearing 
           133  outer thread 
           140  piercing assembly 
           141  injection needle 
           142  needle hub