Abstract:
An injection device including a housing with a reservoir for an injectable product, a plunger axially movable in a direction of propulsion in the reservoir, a dosing and propulsion mechanism provided for the plunger and arranged in an axial continuation of the reservoir, with a dosing or display member moveable in one axial direction relative to the plunger when setting a product dose and moveable in the opposite direction when the dose is dispensed, and, optionally, a force-imparting member which forces the dosing or display member in the direction of an axial end position, wherein at least one of the dosing or display member and optional force-imparting member axially overlap the reservoir, at least when the dosing or display member is in the end position.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation of International Patent Application No. PCT/CH2006/000673 filed Nov. 30, 2006, which claims priority to German Patent Application No. DE 10 2005 060 928.7 filed Dec. 20, 2005, the contents of both of which are herein incorporated by reference. 
     
    
     BACKGROUND 
       [0002]    The present invention relates to devices for delivering, injecting, administering, infusing or dispensing a substance, and to methods of making and using such devices. In some embodiments, the present invention relates to an injection device for an injectable product, e.g. a liquid medicament such as insulin, a growth hormone, an osteoporosis preparation, etc. 
         [0003]    Patent specification EP 1 351 732 B1 discloses an injection device with a housing, in which a reservoir for an injectable product and, accommodated in the reservoir, a dose setting and forward drive unit for a conveyor plunger are disposed. The dose setting and forward drive unit comprises a dose setting element which can be rotated and axially displaced in a thread engagement with the housing to set a product dose. The dose setting element engages a plunger rod in a rotational lock, which permits relative axial movements between the plunger rod and the dose setting element. The dose setting and forward drive unit also has a force transmitting element in the form of a compression spring, which biases the dose setting element axially by an elastic force. The force transmitting element is tensed when the product dose is increased during the setting operation. The plunger rod sits in a thread engagement with the housing and is retained so that it can not rotate relative to the housing when the product dose is being set. The dose setting element simultaneously also serves as a display element for displaying the set dose. The threads of the dose setting element and housing forming part of the thread engagement have a thread pitch which is large enough so that when axial pressure is applied to the dose setting element, it rotates in said thread engagement and is not retained by self-locking. Due to the correspondingly long axial setting path, the markings of the dose scale can likewise be distributed across a correspondingly long length, which is beneficial to enabling a reading to be taken. The disadvantage, however, is that the known injection device is of a correspondingly long length. A trigger for activating the dispensing of the set dose is disposed in an axially central region of the housing. This makes it more difficult to manipulate the injection device during the injection, namely to trigger the dispensing operation. 
         [0004]    In another injection device known from patent specification DE 198 21 934 C1, a dose setting element is disposed in the reservoir so that it is not able to move, thereby enabling the installation-length to be reduced. The dose setting element is provided with several stops, each one of which restricts the stroke of a plunger rod during dispensing operations which can be effected one after the other and thus defines the dose which can be administered with each dispensing operation. However, the individual doses can not be freely selected as is the case with the dose setting and display element disclosed in EP 1 351 732. 
       SUMMARY 
       [0005]    One object of the present invention is to provide an injection device with an axially displaceable dose setting and/or display element of an ergonomically conducive design with as long as possible an axial displacement path. 
         [0006]    In one embodiment, the present invention comprises an injection device comprising a housing with a reservoir for an injectable product, a plunger axially movable in a direction of propulsion in the reservoir, a dosing and propulsion mechanism for the plunger and arranged in an axial continuation of the reservoir, a dosing and/or display member moveable in one axial direction relative to the plunger when setting a product dose and moveable in the opposite direction when the dose is dispensed, and, optionally, a force-imparting member which forces the dosing and/or display member in the direction of an axial end position, wherein at least one of the dosing and/or display member and optional force-imparting member axially overlap the reservoir at least when the dosing or display member is in the end position. 
         [0007]    In one embodiment, the present invention comprises an injection device comprising a housing with a reservoir for an injectable product, a plunger axially movable in the reservoir in a direction of propulsion, a dosing and propulsion driver provided for the plunger and arranged in an axial continuation of the reservoir, an element, comprising at least one of a dosing member and display member, said element moveable in one axial direction relative to the plunger when setting a product dose and in the opposite direction when the dose is dispensed, and a force-imparting member which forces the element in the direction of an axial end position, wherein at least one of the element and force-imparting member axially overlaps the reservoir, at least when the element is in the end position. In one embodiment, the injection device further comprises a manually operable operating knob which can be moved, by a rotating movement, backward and forward relative to the housing for setting the dose, the knob being kinematically coupled to the element to be prevented from rotating. 
         [0008]    In one embodiment, the present invention comprises an injection device comprising a housing with a reservoir for an injectable product, a plunger which is axially movable in a direction of propulsion in the reservoir, a dosing and propulsion means provided for the plunger and arranged in an axial continuation of the reservoir, with a dosing or display member which is moved in one axial direction relative to the plunger when setting a product dose and is moved in the opposite direction when the dose is dispensed, and, optionally, a force-imparting member which forces the dosing or display member in the direction of an axial end position, wherein at least one out of the dosing or display member and optional force-imparting member axially overlaps the reservoir, at least with the dosing or display member in the end position. 
         [0009]    In one embodiment, the present invention comprises an injection device comprising a housing with a reservoir for an injectable product, a plunger axially displaceable in the reservoir in a forward drive direction and a dose setting and forward drive unit, which is disposed in an axial extension of the reservoir, i.e. along a displacement axis of the plunger adjacent to the reservoir. The housing may serve directly as the reservoir but, in some embodiments, the housing merely constitutes a holder for a product container, which may be an ampoule with the plunger accommodated in it. The dose setting and forward drive unit has a dose setting or display element, which may assume the function of only dose setting element, only display element, or a dose setting and display element in combination. (The word “or” is used in the sense of “and/or,” i.e. in the logical sense with reference to the dose setting or display element and otherwise, unless otherwise stated in the respective context.) The dose setting or display element can be moved backward and forward axially relative to the plunger and reservoir, and moves in an axial direction relative to the plunger when a product dose to be administered is being set, and moves back in the opposite direction as the dose is being dispensed. In some preferred embodiments, the ability to move axially is restricted by a stop predefining an axial end position as far as which the display element can be moved for at least one of the two axial directions. In some preferred embodiments, an axial end position is predefined by a contact with a stop contact in both directions of the axial movement so that the dose setting or display element can be moved in a defined manner up to a stop in one direction as far as a maximum dose position and in the other direction as far as a minimum dose position, e.g. the zero dose position. 
         [0010]    In some embodiments, the injection device may have a force transmitting element, which biases the dose setting or display element with a force in one of the two axial directions. Although the injection device may be equipped with a force transmitting element, such a force transmitting element need not necessarily be provided, i.e. it is an optional force transmitting element. In some embodiments, the optional force transmitting element may generate the force needed to dispense a set or selected dose. 
         [0011]    If no force transmitting element is provided, the user must apply the force needed to drive the plunger during the dispensing operation. In embodiments of this type, the dose setting or display unit may be extracted from the housing in the proximal direction when setting the dose and pushed backed deeper into the housing by the user during the dispensing operation. Optionally, an operating element moving out of the housing may act on the dose setting element by a gear during the dispensing operation. 
         [0012]    In some preferred embodiments, when setting the dose, the dose setting or display element moves in the proximal direction and accordingly moves in the distal direction toward the injection site during the dispensing operation. This applies to embodiments which are not provided with a force transmitting element, namely if the dispensing operation is effected by applying axial pressure to the dose setting or display element or an operating element coupled with it by a gear mechanism. Although this operating sequence may be preferred for the dose setting or display element, the direction of movement for the setting operation and dispensing operation may just as easily be reversed if the force transmitting element is provided. 
         [0013]    In accordance with some embodiments of the present invention, the dose setting or display element overlaps the reservoir, at least on assuming the at least one axial end position. If the injection device is provided with the optional force transmitting element, at least one of the dose setting or display element and the optional force transmitting element overlap the reservoir, at least when the dose setting or display element assumes the at least one axial end position. If the force transmitting element is provided, only the dose setting or display element overlaps the reservoir in such embodiments. In alternative embodiments, however, it is also possible for only the force transmitting element to be disposed in a position axially overlapping the reservoir. In yet another alternative, it is also possible for both the dose setting or display element and the force transmitting element be positioned axially overlapping the reservoir. If the force transmitting element overlaps, it may be axially supported on the housing, either directly or via an intermediate element, e.g. in the region of the overlap, in every axial position of the dose setting or display element. If, as in some preferred embodiments, the dose setting or display element overlaps, it does so in the axial end position assumed after dispensing the set dose. 
         [0014]    In the at least one end position, the dose setting or display element or the optional force transmitting element overlaps or overlap not only a rear portion of the reservoir in relation to the forward drive direction, but advantageously also axially overlap the plunger. In some preferred embodiments, the dose setting or display element or the optional force transmitting element extend beyond the plunger in the forward drive direction, and in some preferred embodiments, at least do not locate behind the front end of the plunger. 
         [0015]    Due to the overlap in the direction in which the dose setting or display element moves, the length of the injection device can be kept within ergonomically conducive limits, even in situations where the dose setting or display element is to be enabled to cover an axially long displacement path when setting the dose. From a tactile point of view, long displacement paths are beneficial for setting an exact dose if the dose is set by moving the dose setting or display element. Long displacement paths also offer an advantage on a purely display element because the dose scale can be distributed across a long distance corresponding to the displacement path. 
         [0016]    If the dose setting or display element is a combined dose setting and display element in one, or if it constitutes a display element of the injection device and a pure or dedicated dose setting element is provided in addition, and the position it assumes after setting the dose defines the conveying stroke of the plunger, e.g. by a stop on reaching the minimum dose position, the dose setting and display element or the display element may serve as a support for the dose scale. The dose scale may alternatively be applied to or incorporated in the housing and the pure display element or the dose setting and display element serve as a support for a marking which migrates along the dose scale, for example in the form of a reading strip. In some preferred embodiments, the dose setting or display element combines the functions of setting the dose and providing a display, in which case the injection device of the present invention offers said advantages of the two functions in combination. 
         [0017]    The dose setting or display element may move solely in translation, i.e. only axially. Advantageously, however, it can also be rotated about a rotation axis pointing in the axial direction. In some preferred embodiments, the translating and rotating movements are forcibly superimposed on one another, to which end the dose setting or display element forms a link element of a screw joint, the other link element of which may be formed by the housing. The two link elements sit in a threaded engagement with a thread pitch which is large enough so that an axial force applied to the dose setting or display element, e.g. a pressing force, when in the thread engagement causes a rotation of the dose setting and display element with a superimposed translating movement. The two engaged threads are therefore not self-locking. The dose setting or display element advantageously sits in a direct threaded engagement with the housing. Optionally, it is not coupled with the housing directly, but instead is coupled with it kinematically via one or more intermediate elements which can be displaced relative to the housing, i.e. slip-free. During the movement of the dose setting or display element, intermediate elements fixedly connected to the housing may be regarded as belonging to the housing as far as the movement of the dose setting or display element is concerned. 
         [0018]    If the at least one end position is defined by a stop, as in some preferred embodiments, the stop maybe an axial stop against which the dose setting or display element presses in the axial direction on reaching the end position. If a rotating movement is superimposed on the axial movement, the stop may also be an axial stop or alternatively a radial or rotation stop, with which the dose setting or display element makes an abutting contact during the rotation in the circumferential direction about the rotation axis when it has reached the at least one end position. 
         [0019]    In some embodiments, to provide a defined displacement of the dose setting or display element during the setting operation and also during the dispensing operation, the dose setting and display element is provided with a mating region in the form of a thread as described above, for example in the form of a linear guide with catch elements disposed axially adjacent to one another. In preferred embodiments wherein the dose setting or display element can be moved in an axially overlapping arrangement with the plunger, the mating region of the dose setting or display element also overlaps the plunger, advantageously up to at least its front end. 
         [0020]    The force transmitting element, if provided, in some embodiments may be a spring element, which biases the dose setting element with an elastic force. This being the case, it may be a pneumatic or a mechanical spring element. In embodiments involving a spring element, the latter releases the elastic energy stored previously during the operation of setting the product dose during the dispensing operation and thus supplies the energy needed to drive the plunger forwards. The user only has to operate a trigger. Irrespective of the type of force transmitting element used, the end position in which the dose setting and display element overlaps the reservoir just or to the farthest point is the minimum dose position or the maximum dose position. If the force transmitting element is a compression spring, it acts on the dose setting or display element in the direction toward the minimum dose position (this direction coincides with the distal direction). If the compression spring is disposed distally of the dose setting or display element, its elastic force acts in the proximal direction. If the force transmitting element is a tension spring, for example, the directional relationship can be reversed. A situation where the actual force transmitting element has practically no relevant elasticity should also not be ruled out, and instead it may be formed by an electric motor, for example, which permits or also effects a dose setting movement of the dose setting element when the dose is being set or alternatively causes it by a motor driving action after a separately effected setting operation depending on the setting and also causes a dispensing movement of the dose setting element by a motor driving action when manually triggered. 
         [0021]    In fulfilling the function of a dose setting element, the dose setting or display element may extend out of the housing so that it forms a manually operable dose setting knob itself, in which case the portion extending out of the housing may be formed integrally with the remaining part of the dose setting element or may be fixedly connected to it. In this case, the dose setting or display element moves out of the housing during the operation of setting the dose and is moved back into the housing in the direction toward the minimum dose position again during the dispensing operation, this advantageously being done by the user pushing on the dose setting or display element in the distal direction. 
         [0022]    In some embodiments, if a force transmitting element is provided, the dose setting or display element does not move out of the housing and instead moves backward and forward inside the housing during setting and dispensing the dose. 
         [0023]    In embodiments incorporating a force transmitting element, the dose setting or display element may be provided in the form of a dose setting coupling retained in the respective dose setting position relative to the housing against the force of the force transmitting element. The dose setting coupling comprises coupling elements, which are in a coupled engagement with one another when the dose is being set. The coupled engagement is released for the dispensing operation so that the dose setting or display element is able to move in the direction toward the end position under the force of the force transmitting element. If the dose setting or display element does not itself extend out of the housing or is fixedly connected to a dose setting knob which can gripped and held, the dose setting coupling provides a coupling between the dose setting or display element and a dose setting knob which is accessible to the user and can therefore be manually operated to set the dose. To dispense the set dose, the dose setting coupling is released and the dose setting or display element is uncoupled from the externally accessible dose setting knob as a result. To release the coupled engagement, the injection device has an operating knob serving as a trigger. In some preferred embodiments, the operating knob is disposed on a proximal end of the injection device and may advantageously be operated with the thumb of the same hand as that with which the user holds the injection device during the injection. 
         [0024]    In some preferred embodiments the operating knob constitutes the proximal end of the injection device. It is also of advantage if the operating knob also serves as the dose setting knob and thus fulfils a dual function. In embodiments both without and with the force transmitting element, the same manually operable operating knob acts both as the dose setting knob and the trigger, operation of which causes the dispensing operation. 
         [0025]    In some preferred embodiments, the injection device has a dispensing coupling, which provides a kinematic coupling between the dose setting or display element and a plunger for the dispensing operation, i.e. slip-free. During the operation of setting the dose, the coupled engagement of the coupling elements constituting the dispensing coupling is released so that the dose setting or display element is uncoupled from the plunger rod. In embodiments in which the injection device has a dose setting coupling for providing a coupling between the dose setting or display element and said dose setting knob during the operation of setting the dose and a dispensing coupling for providing a coupling between the dose setting or display element and the plunger rod during the dispensing operation, the two couplings are “switched” so that when triggered by operating said operating knob, the dose setting coupling is automatically released and the dispensing coupling closed. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0026]      FIG. 1  is a view of one embodiment of an injection device in accordance with the present invention; 
           [0027]      FIG. 2  shows the injection device in longitudinal section; 
           [0028]      FIG. 3  shows the proximal portion of the injection device in longitudinal section; 
           [0029]      FIG. 4  shows an embodiment of a dose setting coupling in a coupled engagement; 
           [0030]      FIG. 5  shows an embodiment of a housing portion and an operating knob; and 
           [0031]      FIG. 6  shows an embodiment of a dispensing coupling out of engagement. 
       
    
    
     DETAILED DESCRIPTION 
       [0032]    With regard to fastening, mounting, attaching or connecting components of the present invention, unless specifically described as otherwise, conventional mechanical fasteners and methods may be used. Other appropriate fastening or attachment methods include adhesives, welding and soldering, the latter particularly with regard to the electrical system of the invention, if any. In embodiments with electrical features or components, suitable electrical components and circuitry, wires, wireless components, chips, boards, microprocessors, inputs, outputs, displays, control components, etc. may be used. Generally, unless otherwise indicated, the materials for making the invention and/or its components may be selected from appropriate materials such as metal, metallic alloys, ceramics, plastics, etc. 
         [0033]      FIG. 1  shows a side view of an embodiment of an injection device in accordance with the present invention. The injection device is a longitudinally extending, slim injection pen. It comprises a housing with a distal (or front) housing portion  1  and a proximal (or rear) housing portion made up of two housing portions  2  and  3  fixedly connected to one another. The injection device is used to administer a liquid medicament, for example insulin. The medicament is contained in a reservoir, which can be replaced by inserting it in the housing portion  1 . The medicament can be administered through an outlet  1   a  provided at the distal end of the housing portion  1 . By reference to a central longitudinal axis RT, the injection device is essentially rotationally symmetrical. The housing portions  1 - 3  are each made from a non-transparent plastic material. To make it possible to see through to the reservoir, housing portion  1  has a window  1   b , which extends up to or close to the proximal end of housing portion  1  and close to the outlet  1   a , but is relatively slim in the circumferential direction about the axis RT. Housing portion  2  likewise has a window  2   b , which overlaps the window  1   b  when housing portions  1  and  2  are connected, providing a free view through to the reservoir in the connecting region of housing portions  1  and  2 . The windows  1   b  and  2   b  are of the same width in the circumferential direction, but could conceivably be of different dimensions in the circumferential direction, provided the function of providing a view through to the reservoir can be fulfilled. Another window  4  in the form of a magnifying glass is also provided in housing portion  3 . An operating knob  27  forms the proximal end of the injection device. The operating knob  27  fulfils the function of a manually operable dose setting knob, which enables a dose to be selected or set for a medicament to be administered when operated and also serves as a trigger button enabling the set dose to be dispensed when operated. The set dose can be read through the window  4  on a dose scale extending continuously below the window  4  during the setting operation. 
         [0034]      FIGS. 2 and 3  each illustrate the injection device in a longitudinal section containing the longitudinal axis RT,  FIG. 2  showing it as a whole and  FIG. 3  illustrating the proximal portion on a larger scale. 
         [0035]    The reservoir R is an ampoule made from glass or transparent plastic. Disposed in the reservoir R is a plunger  10  which can be moved axially in a forward drive direction V toward the outlet  1   a . In the initial state illustrated in  FIGS. 2 and 3 , the reservoir R is completely full and the plunger  10  closing off the reservoir R at the proximal end assumes its most proximal position. Basically, the housing portion  1  merely serves as a reservoir holder. It is fixedly connected to the housing portion  2  but can be released by screwing, for example, to enable the reservoir  1  to be replaced. 
         [0036]    Portions  2  and  3  constituting the proximal housing portion are likewise fixedly connected to one another, e.g. by a material join, and may be regarded as a single housing portion in terms of their function. The housing portion formed by the two portions  2 ,  3  provides a mount for or carries a dose setting and forward drive mechanism, by which a dose of medicament can be set or selected for dispensing with each injection and the set dose can be dispensed by the forward driving action of the plunger  10 . The operating knob  27  is coupled with the dose setting and forward drive mechanism for setting the dose by a dose setting coupling. 
         [0037]    The dose setting and forward drive mechanism comprises several elements, which are coupled with one another in different ways by the dose setting coupling and a dispensing coupling when the dose is being set and dispensed. A plunger rod  11  is one of these elements. During the dispensing operation, the plunger rod  11  pushes against the rear face of the plunger  10  so that it moves in the forward drive direction V and dispenses medicament through the outlet  1   a . The plunger rod  11  sits in a threaded engagement with the housing portion  2 , for which purpose it is provided with a thread across the major part of its length. Housing portion  2  constitutes the co-operating thread on a retaining mechanism  2   a  ( FIG. 3 ) projecting radially inward toward the plunger rod  11 . The forward driving movement of the plunger rod  11  is a rotating movement about the longitudinal axis RT with a translating movement in the forward drive direction V superimposed on it. The thread of the plunger rod  11  is not continuous but is interrupted by an axially flat face or groove. However, this does not cause any interruption to the thread engagement with the retaining mechanism  2   a  and the plunger rod  11  retained in the thread engagement. 
         [0038]    The dose setting and forward drive mechanism also has a first coupling element  12 , a second coupling element  16  and a third coupling element  22 . Coupling element  12  is able to move axially with the plunger rod  11  along its flat face or groove in a guiding engagement but is connected so that it is prevented from rotating. The coupling element  12  is disposed proximally of the retaining mechanism  2   a  and pushes against the retaining mechanism  2   a  in the forward drive direction V. The coupling element  12  surrounds the plunger rod  11 . The coupling element  12  comprises a distal portion which sits in contact with the retaining mechanism  2   a  and a proximal portion which extends as far as the operating knob  27 . A spring  13  is provided between the two portions. Another spring  14  is provided on the distal end of the coupling element  12 , which has several resilient lugs which project in the direction toward the retaining mechanism  2   a  and are elastically biased. The resilient lugs of the spring  14  act as catch elements, which latch with catch elements of the retaining mechanism  2   a , thereby providing an anti-rotation slip coupling between the coupling element  12  and the retaining mechanism  2   a  and hence housing portion  2 , which prevents the plunger rod  11  from rotating relative to the housing  1 - 3  during dispensing operations. However, the force which can be transmitted when the catch elements and co-operating catch elements of the anti-rotation coupling is not so strong that it prevents the rotating movement of the plunger rod  11  needed to dispense the set dose or prevents it to only a practically relevant degree. In the portion of the spring  13 , the coupling element  12  may flex axially. The coupling element  12  incorporating the two springs  13  and  14  is made integrally from plastic, for example by an injection moulding process. 
         [0039]    The coupling element  16  is mounted so that it can rotate about the axis RT. It is a generally cylindrical, sleeve-shaped body and surrounds the coupling element  12 . Integrally formed on the distal end of the coupling element  16  is a spring  17 , which in the embodiment illustrated as an example is an axially short helical spring. The coupling element  16  is supported by its spring  17  on the coupling element  12  in the distal direction and pushes it against the retaining mechanism  2   a . Formed on the proximal end of the coupling element  16  are mating elements  20 , which sit in a releasable coupled engagement with co-operating mating elements  24  of the coupling element  22  when the injection device is in the state illustrated. The mating elements  20  and co-operating mating elements  24  may be teeth projecting axially out from the coupling element  16  or  22  in the direction toward the other ones, which form two toothed rings locating with one another in the coupled engagement concentric with the axis RT, e.g. with a uniform tooth distribution, as illustrated by way of example in  FIG. 4 . In the state illustrated, in which the user is able to set the dose to be administered, the mating elements  20  and co-operating mating elements  24  of the two coupling elements  16  and  22  locate in one another. The coupling elements  16  and  22  constitute the dose setting coupling and are connected to one another so that they can not rotate in the coupled engagement. 
         [0040]      FIG. 4  illustrates the coupling halves of the dose setting coupling, namely the coupling elements  16  and  22 , in the coupled engagement and removed from the overall context so that their functional elements  17 - 20  on the one hand and  23 - 25  on the other hand are more readily visible. 
         [0041]    The coupling element  22  is likewise sleeve-shaped and has a flange projecting radially outward at its proximal end. Formed on the external circumference of the flange are mating elements  25 , which connect the coupling element  22  to the operating knob  27  so that it can not rotate. The coupling element  22  is axially supported on the operating knob  27  by a spring  23 . The spring  23  is an integrated part of the coupling element  22  insofar as the coupling element  22  is made from plastic in one piece incorporating the spring  23 . Like spring  14 , spring  23  comprises several resilient lugs projecting axially out and bent about the axis RT. In conjunction with the spring  17 , it ensures that the coupling elements  16  and  22  are elastically retained axially in the coupled engagement. The spring  17  pushes the coupling element  16  and the spring  23  pushes the coupling element  22  axially in each case into contact with the housing portion  3 . 
         [0042]    The coupling element  22  is in a threaded engagement with a stop element  26 . To this end, the coupling element  22  is provided with a thread  22   a  ( FIG. 4 ) on its external circumference before the flange. The housing portion  3  acts an axial guide  7  for the stop element  26  lying radially outward opposite the thread  22   a  so that the stop element  26  is moved axially in the threaded engagement when the coupling element  22  is moved in rotation. The axial displacement path of the stop element  26  corresponds to the quantity of medicament which is available as a maximum and can be administered in several injections, i.e. when the reservoir R is full. When the coupling element  22  is moved in rotation, the stop element  26  migrates, guided by the axial guide  7  along the external thread  22   a  of the coupling element  22 , in the axial direction, which is the forward drive direction V in the embodiment illustrated as an example. Once the stop element  26  reaches an axial stop formed by the inner sleeve  6  in this direction of movement, it means that the reservoir R has been completely emptied. The inner sleeve  6  acts as the axial guide  7  and is not able to move axially relative to the housing portion  3 , and, in the embodiment illustrated as an example, is formed on the housing portion  3  by a radial connecting web, i.e. is an integral part of the housing portion  3 . 
         [0043]    The dose setting and forward drive mechanism also has a dose setting and display element  30 , which is in a threaded engagement with the housing portion  3 . To provide this engagement, the housing portion  3  is provided with an internal thread  3   a . Housing portion  2  is smooth in the contact region with the dose setting and display element  30 . The thread  3   a  is disposed directly on the internal surface of the circular cylindrical sleeve shell of the housing portion  2 ,  3 . The dose setting and display element  30  is essentially a simple circular cylindrical sleeve with an external thread  30   a  of complementary shape. The threads  3   a  and  30   a  have a significantly bigger, or larger or higher, thread pitch than the threads of the plunger rod  11  and retaining mechanism  2   a . The thread pitch is large enough to prevent retention in the thread engagement by friction and the dose setting and display element  30  is rotated and moved axially under the effect of a purely axial force relative to the housing portion made up of two parts in the threaded engagement. 
         [0044]    The dose setting and display element  30  may be moved axially but is coupled with the coupling element  16  so that it is prevented from rotating. In the embodiment illustrated as an example, the dose setting and display element  30  and the coupling element  16  sit directly in an appropriate guided engagement with one another. To this end, the coupling element  16  forms an axial guide  18  at its external circumference. A mating element  31  projects out from the internal face of the dose setting and display element  30 , by which the dose setting and display element  30  is in a guided engagement with the coupling element  16 , i.e. with its guide  18 . The guide  18  extends across the major part of the length of the coupling element  16  and the dose setting and display element  30  travels through the major part of its length when setting the maximum dose. The guide  18  is formed by axial grooves in the external surface of the coupling element  16  ( FIG. 4 ). At their distal ends, the grooves each serve as a stop  19  for the mating element  31 . 
         [0045]    The dose setting and forward drive mechanism comprises a spring element  32 , which applies a force to the dose setting and display element  30  in the distal direction. The spring element  32 , in the embodiment illustrated as an example, is a helical spring and acts as a compression spring. The spring element  32  is supported on the housing portion  3  in the proximal direction. In the distal direction, the spring element  32  is supported on an annular sliding disc  33 , inserted between the coupling element  16  and the dose setting and display element  30  and is in turn supported on the mating element  31 . By the sliding disc  33 , the spring element  32  is largely uncoupled from any rotating movements of the dose setting and display element  30 . 
         [0046]    The dose setting and display element  30  is able to move backward and forward relative to the plunger  10  and the plunger rod  11  and relative to the coupling elements  12 ,  16  and  22  between axial end positions. The two end positions are a zero dose position and a maximum dose position. The two end positions are each predefined by a stop. The stop for the zero dose position is formed by a shoulder  2   c  at the distal end of the housing portion  2  and serves as an axial stop. The stop for the maximum position is formed by the housing portion  3 . In the zero dose position, a distal portion of the dose setting and display element  30  overlaps the reservoir R in the forward drive direction V to beyond the plunger  10  when the plunger  10  assumes a rearmost position in the reservoir R as illustrated in  FIGS. 2 and 3 . The plunger  10  assumes this position when the reservoir R is completely full. The thread  30   a  extends as far as the distal end or at least close to the distal end of the dose setting and display element  30  so that the thread  30   a  also axially overlaps the reservoir R and the plunger  10  when the dose setting and display element  30  assumes the zero dose position. The thread  30   a  terminates before the distal end of the dose setting element  30  and in conjunction with the thread  3   a  of the housing portion  3  forms an anti-rotation stop, which defines the maximum dose position of the dose setting and display element. Alternatively, the thread  30   a  could also terminate at the distal end of the dose setting and display element  30 ; the stop defining the maximum dose position would then be of a different design in the event of such a modification. 
         [0047]    At its distal end, the dose setting and display element  30  is not circumferentially completely cylindrical but part-cylindrical so that, in spite of the axial overlap, the view onto the plunger is exposed if the dose setting and display element  30  is not made from a transparent plastic material, although this is preferred, but is made from a non-transparent or opaque plastic material or some other material. The distal edge of the dose setting and display element  30  extends in a spiral shape about the axis RT so that the dose setting and display element  30  stands out axially by its distal end in a circumferential region, even beyond the plunger  10 , as may be seen from  FIGS. 2 and 3 , and sits back behind the plunger  10  in another circumferential region overlapping the window in the zero dose position so that the plunger  10  can be observed through the windows  1   b  and  2   b . Instead of a spiral-shaped edge, the dose setting and display element  30  may extend circumferentially up to the same axial height all round with the exception of an interrupted region, for example, and thus extends across the plunger  10  in the forward drive direction V with the exception of the interrupted region, in which case the interruption would overlap with the window  2   b  in the zero dose position. The shoulder  2   c  of the housing portion  2  likewise winds about the axis RT following the spiral path of the distal edge of the dose setting and display element  30 , likewise winding about the axis RT. The winding course of the shoulder  2   c  may also be seen in  FIG. 1 . The housing portion  2  has an outer sleeve, which encloses the dose setting and forward drive mechanism in conjunction with the housing portion  3 , and an inner sleeve which is connected to the outer sleeve at its distal end by a web forming the shoulder  2   c , and the proximal end of which projects radially inward toward the retaining mechanism  2   a . An annular gap is left free between the outer and the inner sleeve, through which the dose setting and display element  30  extends across the greater part of its length in the zero dose position, and the greater part in the region of the longest circumferential segment of the dose setting and display element  30  amounts to approximately 50% of the total length of the dose setting and display element  30 . 
         [0048]    The dose setting and display element  30  provides a support for a dose scale, which extends round in a spiral on the external circumference of the dose setting and display element  30  with a pitch which corresponds to the pitch of the thread  30   a  as measured by reference to the axis RT. The dose scale is made up of markings and numbers, each of the markings corresponding to a smallest dose unit which can be set. During the operation of setting the dose to be administered, the dose scale can be read through the window  4  of the housing portion  3  ( FIG. 1 ). 
         [0049]    The operating knob  27  forms the proximal end of the injection device. It clips onto the housing portion  3  by a shoulder  5  provided on the proximal end of the housing portion  3 , which grips behind the operating knob  27 . The operating knob  27  is able to rotate relative to the housing  1 - 3  about the axis RT in a dose setting direction and a correction direction. When setting the dose, the dose is increased by rotating the operating knob  27  in the dose setting direction and reduced in a rotating movement in the correction direction, thereby enabling a dose that has been accidentally set too high to be corrected. The operating knob  27  is also axially displaceable with the coupling element  22  but is connected so that it is prevented from rotating by the mating elements  25 . 
         [0050]      FIG. 5  illustrates the housing portion  3  and the operating knob  27  in the coupled engagement, with part of the operating knob cut away to illustrate the engagement. 
         [0051]    Due to the anti-rotation lock with the coupling element  22 , the operating knob  27  forms a slip coupling, in the embodiment illustrated as an example, an anti-rotation slip coupling, with the housing portion  3 . Several catch elements  28  are disposed on the operating knob  27 , uniformly distributed about the axis RT forming the slip coupling, which sit in a coupled engagement with co-operating complementary catch elements  8  preferably congruently disposed on the distal end of the housing portion  3 . The number of complementary catch elements  8  is lower than the number of catch elements  28 . When the coupled engagement is established between the catch elements  28  and complementary catch elements  8 , the operating knob  27  can be rotated relative to the housing portion  3  about the axis RT, and the catch elements  28  and complementary catch elements  8  are able to latch with one another in a releasable arrangement in pairs distributed discretely about the circumference. The pitch of the catch elements  28  and hence the distance as measured in the angle or arc dimension between the respective adjacently disposed catch elements  28  in the circumferential direction corresponds to the smallest dose unit which can be set and the pitch of the complementary catch elements corresponds to a whole number multiple of the same dose unit. The slip coupling need not necessarily be disposed directly between the housing  1 - 3  and the operating knob  27 . Instead of providing the catch elements  28  on the operating knob  27 , they could also be disposed on the coupling element  22 . Modified catch elements and complementary catch elements could also locate in one another axially rather than radially in both embodiments. 
         [0052]    The catch elements  28  and accordingly the complementary catch elements  8  are of an asymmetrical shape with reference to the direction of rotation so that the force needed to release the catch engagement in a coupling dose setting direction is stronger than in the opposite direction of rotation, namely the coupling correction direction. Since the catch elements  28  are disposed directly on the operating knob  27  in the exemplary embodiment, the dose setting direction of the operating knob  27  is simultaneously the coupling dose setting direction, and the correction direction is the coupling correction direction. The complementary catch elements  8  are catch cams projecting radially outward from the external surface of housing portion  3 . Accordingly, the catch elements  28  are provided in the form of co-operating recesses or tooth gaps of internal teeth on the facing, opposite internal surface of the operating knob  27 . To obtain the asymmetry for the two directions of rotation, the leading edges of the catch elements  28  pointing in the coupling dose setting direction as the catch elements move  28  are flatter than the trailing edges pointing in the opposite direction of rotation. The two edges of the complementary catch elements  8  are likewise shaped accordingly. 
         [0053]    The asymmetry of the slip coupling by reference to the two rotation directions of the operating knob  27  is adapted to the direction of the force expended by the force transmitting element  32  on the dose setting and display element  30 . As the operating knob  27  is moved in the direction for increasing the dose, the dose setting and display element  30  is rotated in the thread engagement due to the dose setting coupling formed at  20 ,  24  and the guide coupling formed at  18  and  31 , and moves in the proximal direction. During the course of the translating movement in the proximal direction, the spring element  32  is tensed to an increasing degree. The elastic force of the spring element  32  produces a resistance countering the movement of the dose setting and display element  30  in the proximal direction, which acts on the slip coupling due to the coupling described above, and an additional frictional resistance which increases as the dose is increased counteracts the rotating movement of the operating knob  27  in the dose setting direction, in which the flatter edges of the catch elements  28  and complementary catch elements  8  point. Conversely, the force expended by the spring element  32  assists the rotating movement in the direction of a dose correction. 
         [0054]      FIG. 5  illustrates the housing portion  3  and its complementary catch elements  8  for the slip coupling. The housing portion  3  forms coupling springs  9  which are radially elastically flexible in a proximal sleeve portion, namely one coupling spring  9  per complementary catch element  8 . The complementary catch elements  8  respectively project radially outward from the coupling springs  9 . The coupling springs  9  are circle segments. The sleeve portion comprises the coupling springs  9  extending about the axis RT, alternating with circle segments which are stiffer than them. The coupling springs  9  respectively act as bending beams extending in the circumferential direction which are biased on both sides, namely on the two respective stiffer circle segments disposed closest. Extending in the circumferential direction along the coupling springs  9  is a respective recess, thereby increasing the flexibility of the respective coupling spring  9 . The sleeve portion incorporating the coupling springs  9  forms the proximal end of the housing portion  3 . 
         [0055]    The operating knob  27  is pot-shaped with a base constituting the distal end of the injection device and a wall projecting out from the base extending about the axis RT, on the internal face of which the catch elements  8  are uniformly distributed about the circumference and each shaped as an axially extending recess. In the assembled state, the catch elements  28  engage with both the complementary catch elements  8  and the mating elements  25  ( FIG. 3 ) of the coupling element  22 , as a result of which both the catch engagement with the complementary catch elements  8  and the anti-rotation engagement with the mating elements  25  are maintained in every axial position of the operating knob  27 . 
         [0056]    The dose setting and forward drive mechanism contains a second coupling due to the dose setting coupling formed by the coupling elements  16  and  22 , namely the dispensing coupling already mentioned above, which is illustrated in  FIG. 6 . The dispensing coupling comprises the coupling elements  12  and  16 , which are provided with mating elements which engage with one another in the coupled engagement for this purpose. These are mating elements  15   a  and  15   b  on the side of the coupling element  12 . The coupling element  16  is provided with mating elements  21 . The mating elements  15   a  are axial ribs which project radially outward from an internal surface of the coupling element  12  at the proximal end. The mating elements  21  are provided in the form of co-operating axially blind grooves on an internal surface at the proximal end of the coupling element  16 . The mating elements  21  form an axial guide for the mating elements  15   a . The mating elements  15   a  constitute a sort of external teeth or toothing about the axis RT. The external teeth are interrupted at one point at least and, in the embodiment illustrated as an example, at two points lying diametrically opposite one another. Disposed in each interrupted circumferential region is one of the mating elements  15   b . Like the mating elements  15   a , the mating elements  15   b  project radially outward but are wider than the mating elements  15   a  in the circumferential direction so that they are not able to move into the mating elements  21  formed by blind grooves. Instead, the rib webs left between the mating elements  21  form an axial stop for the mating elements  15   b  when the coupling element  12  is moved in the distal direction relative to the coupling element  16 . 
         [0057]    The coupling element  16  is moved selectively with the coupling element  22  or coupling element  12  in the coupled engagement, i.e. in the coupled engagement with the coupling element  22  when the dispensing coupling is released and in the coupled engagement with the coupling element  12  when the dose setting coupling is released. To set the dose, the dose setting coupling is closed, i.e. the mating elements  15   a  and  15   b  axially overlap only the coupling element  22 , the internal surface of which is circumferentially smooth so that the coupling element  22  is able to rotate relative to the coupling element  12  as the dose is being set. To dispense the set dose, the coupling element  12  moves into the coupled engagement with the dose setting and display element  16 , the dose setting coupling is released as a result and the dispensing coupling is closed so that the dispensing operation can start.  FIG. 6  illustrates the coupling elements  12 ,  16  and  22  in the state in which the dose setting coupling is closed. 
         [0058]    The user holds the injection device in one hand and places a cannula unit on the outlet  1   a  and screws it tight with the other hand. Otherwise, the injection device is in the state illustrated in  FIGS. 1 to 3 . Due to the windows  1   b  and  2   b , the user is able to see how full the reservoir R is and check the position of the plunger  10 . It is assumed the reservoir has been primed and that the user would like to inject a specific dose of medicament in the next step. The desired dose is set by turning the operating knob  27 . During the setting operation, the user can take a reading of the dose corresponding to the axial position of the dose setting and display element  30  at any time through the window  4 . If a dose is accidentally set too high during the process of increasing the dose, the user can correct the overdose by turning the operating knob  27  in the correction direction. During the process of setting the dose, the rotating movement of the operating knob  27  is transmitted to the coupling element  22  via the extant anti-rotation lock at  25  and to the coupling element  16  via the closed dose setting coupling at  20 ,  24  and to the dose setting and display element  30  in the guide engagement between  18  and  31 . With the threads  3   a  and  30   a  in the engaged state, the dose setting and display element  30  moves in rotation about the axis RT and in translation in the proximal direction. As the dose is being increased, the spring element  32  becomes increasingly elastically tensed and assists any dose correction which might be needed. Both when increasing the dose and also correcting the dose, the catch engagement of the slip coupling between the housing portion  3  and the operating knob  27  makes a clearly perceptible clicking noise. Due to the steepness of the threads  3   a  and  30   a , the dose setting and display element  30  travels a correspondingly long displacement path in the axial direction. The distances between the dose marks of the dose scale of the dose setting and display element  30  are equally long in the axial direction, thereby providing a clear reading of the dose marks extending below the window  4 , even for users with a impaired sight. 
         [0059]    The plunger rod  11  is uncoupled from the dose setting movement which, in the embodiment illustrated as an example, is the dose rotating movement, and is additionally prevented from effecting any rotating movements due to the surrounding coupling element  12 , which is likewise uncoupled. As explained above, the lock established by the slip coupling produced between the coupling element  12  and retaining mechanism  2   a  and the anti-rotation engagement of the coupling element  12  with the plunger rod  11  are maintained. 
         [0060]    When the desired dose has been set, the user pierces the desired injection site with the piercing cannula and moves it into the subcutaneous tissue below the skin. With the same hand which he is using to hold the injection device during piercing, he then triggers dispensing of the set dose. 
         [0061]    The operating knob  27 , which fulfils the function of a dose setting knob whilst the dose is being set, serves a dual function and is also the trigger knob. When the dose is being set, the dose setting and display element  30  is retained depending on the dose catch positions of the catch elements  28  and complementary catch elements  8  of the slip coupling, i.e. the slip coupling prevents the dose setting and display element  30  from being able to move under the action of the spring element  32 . For the dispensing operation, therefore, the coupling between the housing portion  3  and the dose setting and display element  30  established via the slip coupling at  8 ,  28  must be released. This is done by releasing the dose setting coupling established at  20 ,  24 , for which purpose the user presses the operating knob  27  in the distal direction with the thumb. When an appropriate pressing force is applied, the operating knob  27  moves relative to the housing portion  3  and coupling element  22  against the force of the spring  23  in the distal direction and during this movement pushes against the coupling element  12 . The coupling element  12  flexes axially inwards in the region of its integrated spring  13  so that its mating elements  15   a  move into engagement with the mating elements  21  of the coupling element  16  preventing any rotation. In a transition phase of the axial movement, the dose setting coupling between the coupling element  22  and the coupling element  16  is still closed, whilst the coupled engagement of the dispensing coupling between the coupling element  12  and coupling element  16  is also already being established. As soon as the mating elements  15   b  make contact with the axial stop of the coupling element  12  in the distal direction, however, continuing pressure on the operating knob  27  causes the coupling element  16  to move against the force of its spring  17  in the distal direction, and thus lift out of the coupled engagement with the coupling element  22 . 
         [0062]    As soon as the dose setting coupling has been released, the dose setting and display element  30  is screwed in the distal direction due to the elastic force of the spring element  32 . The rotating element of the movement effected by the dose setting and display element  30  is transmitted to the coupling element  16  in the coupled engagement between the guide  18  and mating element  31 . Since the dispensing coupling is closed, the coupling element  16  transmits the rotating movement to the coupling element  12 , which in turn is connected to the plunger rod  11  so as to rotate in unison with it, so that the plunger rod  11  rotates in the thread engagement with the retaining mechanism  2   a  and pushes the plunger  10  in the forward drive direction V. The dispensing movement of the components involved in this operation is terminated when the dose setting and display element  30  makes contact with the shoulder  2   c . The stroke or axial element of the displacement path of the dose setting and display element  30  therefore determines the stroke of the plunger  10  and hence the dispensed dose. Due to the fact that the thread pitch of the threads  3   a  and  30   a  is bigger than the threads of the plunger rod  11  and retaining mechanism  2   a , the stroke of the dose setting and display element  30  is reduced to the stroke of the plunger  10  in accordance with the reduction ratio. During the dispensing movement, the slip coupling between the spring  14  and retaining mechanism  2   a  generates a clearly perceptible clicking noise, providing an acoustic indication to the user that medicament is being dispensed. The dispensing operation can also be at least generally checked through the windows  1   b  and  2   b  on the basis of the axial position of the plunger  10 . 
         [0063]    When the dose is being set, the stop element  26  in the thread engagement with coupling element  22  likewise moves as a function of the set dose. When the quantity of medicament predefined by the maximum stroke of the stop element  26  has been totally administered, which will not be the case until after several injections if the reservoir R was completely full, the user replaces the empty reservoir R with a new, full reservoir R. To this end, she merely has to separate housing portion  1  from the proximal housing portion (made up of portions  2 ,  3 ), insert the new reservoir R with the plunger  10  already accommodated in it and connect the front and rear housing portions to one another again. 
         [0064]    In the exemplary embodiment, all the springs with the exception of the force transmitting element  32  are an integral part of a respective coupling element comprising a coupling part and spring part. Alternatively, however, one or more springs may also be provided separately from the respective coupling element in a conventional manner in the form of steel springs. This being the case, springs  13 ,  17  and  23  may just as easily be replaced by steel springs because they fulfil exclusively a spring function. To replace the spring  14 , a replacement spring and catch elements on the distal end of the coupling element  12  could be provided. 
         [0065]    As far as the disposition of the dose setting and display element  30  and spring element  32  is concerned, it should be pointed out that, instead of the dose setting and display element  30 , the spring element  32  may be disposed axially overlapping the reservoir R as an alternative, in which case it could be supported on a thrust bearing, for example the shoulder  2   c . If the fittings were reversed in this manner, the dose setting and display element  30  would be moved in the proximal direction until it made contact with a stop during the dispensing operation. In yet another alternative, the spring element  32  could be provided in the form of a tension spring, although a fitting incorporating a compression spring is more particularly preferred. Yet another alternative is described in German patent applications No. 10 2005 043 806.7 and 10 2005 043 807.5. As described in these applications, the spring element adapted to the slip coupling is provided in the form of a torsion spring. The older applications are incorporated herein by reference in connection with the adapted arrangement comprising the slip coupling and spring element. 
         [0066]    Embodiments of the present invention, including preferred embodiments, have been presented for the purpose of illustration and description. They are not intended to be exhaustive or to limit the invention to the precise forms and steps disclosed. The embodiments were chosen and described to provide the best illustration of the principles of the invention and the practical application thereof, and to enable one of ordinary skill in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. All such modifications and variations are within the scope of the invention as determined by the appended claims when interpreted in accordance with the breadth they are fairly, legally, and equitably entitled.