referring first to fig1 to 5 , there may be seen a pen - type injector in accordance with the present invention in a number of positions . the pen - type injector comprises a housing having a first cartridge retaining part 2 , and second main housing part 4 . a first end of the cartridge retaining means 2 and a second end of the main housing 4 are secured together by retaining features 6 . in the illustrated embodiment , the cartridge retaining means 2 is secured within the second end of the main housing 4 . a cartridge 8 from which a number of doses of medicinal product may be dispensed is provided in the cartridge retaining part 2 . a piston 10 is retained in a first end of the cartridge 8 . a removable cap 12 is releasably retained over a second end of the cartridge retaining part 2 . in use the removable cap 12 can be replaced by a user with a suitable needle unit ( not shown ). a replacable cap 14 is used to cover the cartridge retaining part 2 extending from the main housing 4 . preferably , the outer dimensions of the replaceable cap 14 are similar or identical to the outer dimensions of the main housing 4 to provide the impression of a unitary whole when the replaceable cap 14 is in position covering the cartridge retaining part 2 . in the illustrated embodiment , an insert 16 is provided at a first end of the main housing 4 . the insert 16 is secured against rotational or longitudinal motion . the insert 16 is provided with a threaded circular opening 18 extending therethrough . alternatively , the insert may be formed integrally with the main housing 4 the form of a radially inwardly directed flange having an internal thread . a first thread 19 extends from a first end of a piston rod 20 . the piston rod 20 is of generally circular section . the first end of the piston rod 20 extends through the threaded opening 18 in the insert 16 . a pressure foot 22 is located at the first end of the piston rod 20 . the pressure foot 22 is disposed to abut a second end of the cartridge piston 10 . a second thread 24 extends from a second end of the piston rod 20 . in the illustrated embodiment the second thread 24 comprises a series of part threads rather than a complete thread . the illustrated embodiment is easier to manufacture and helps reduce the overall force required for a user to cause medicinal product to be dispensed . the first thread 19 and the second thread 24 are oppositely disposed . the second end of the piston rod 20 is provided with a receiving recess 26 . a drive sleeve 30 extends about the piston rod 20 . the drive sleeve 30 is generally cylindrical . the drive sleeve 30 is provided at a first end with a first radially extending flange 32 . a second radially extending flange 34 is provided spaced a distance along the drive sleeve 30 from the first flange 32 . an intermediate thread 36 is provided on an outer part of the drive sleeve 30 extending between the first flange 32 and the second flange 34 . a helical groove 38 extends along the internal surface of the drive sleeve 30 . the second thread 24 of the piston rod 20 is adapted to work within the helical groove 38 . a first end of the first flange 32 is adapted to conform to a second side of the insert 16 . a nut 40 is located between the drive sleeve 30 and the main housing 2 , disposed between the first flange 32 and the second flange 34 . in the illustrated embodiment the nut 40 is a half - nut . this assists in the assembly of the injector . the nut 40 has an internal thread matching the intermediate thread 36 . the outer surface of the nut 40 and an internal surface of the main housing 4 are keyed together by splines 42 ( see fig1 , 11 , 15 and 16 ) to prevent relative rotation between the nut 40 and the main housing 4 , while allowing relative longitudinal movement therebetween . a shoulder 37 is formed between a second end of the drive sleeve 30 and an extension 38 provided at the second end of the drive sleeve 30 . the extension 38 has reduced inner and outer diameters in comparison to the remainder of the drive sleeve 30 . a second end of the extension 38 is provided with a radially outwardly directed flange 39 . a clicker 50 and a clutch 60 are disposed about the drive sleeve 30 , between the drive sleeve 30 and a dose dial sleeve 70 ( to be described below ). the clicker 50 is located adjacent the second flange 34 of the drive sleeve 30 . the clicker 50 is generally cylindrical and is provided at a first end with a flexible helically extending arm 52 ( shown most clearly in fig6 ). a free end of the arm 52 is provided with a radially directed toothed member 54 . a second end of the clicker 50 is provided with a series of circumferentially directed saw teeth 56 ( cf fig7 ). each saw tooth comprises a longitudinally directed surface and an inclined surface . in an alternative embodiment ( not shown ) the clicker means further includes at least one spring member . the at least one spring member assists in the resetting of the clutch means 60 following dispense . the clutch means 60 is located adjacent the second end of the drive sleeve 30 . the clutch means 60 is generally cylindrical and is provided at a first end with a series of circumferentially directed saw teeth 66 ( see fig7 ). each saw tooth comprises a longitudinally directed surface and an inclined surface . towards the second end 64 of the clutch means 60 there is located a radially inwardly directed flange 62 . the flange 62 of the clutch means 60 is disposed between the shoulder 37 of the drive sleeve 30 and the radially outwardly directed flange 39 of the extension 38 . the second end of the clutch means 60 is provided with a plurality of dog teeth 65 ( fig8 ). the clutch 60 is keyed to the drive sleeve 30 by way of splines ( not shown ) to prevent relative rotation between the clutch 60 and the drive sleeve 30 . in the illustrated embodiment , the clicker 50 and the clutch 60 each extend approximately half the length of the drive sleeve 30 . however , it will be understood that other arrangements regarding the relative lengths of these parts are possible . the clicker 50 and the clutch means 60 are normally engaged , that is as shown in fig7 . a dose dial sleeve 70 is provided outside of the clicker 50 and clutch means 60 and radially inward of the main housing 4 . a helical groove 74 is provided about an outer surface of the dose dial sleeve 70 . the main housing 4 is provided with a window 44 through which a part of the outer surface of the dose dial sleeve may be seen . the main housing 4 is further provided with a helical rib 46 , adapted to be seated in the helical groove 74 on the outer surface of the dose dial sleeve 70 . the helical rib 46 extends for a single sweep of the inner surface of the main housing 4 . a first stop 100 is provided between the splines 42 and the helical rib 46 ( fig1 ). a second stop 102 , disposed at an angle of 180 ° to the first stop 100 is formed by a frame surrounding the window 44 in the main housing 4 ( fig1 ). conveniently , a visual indication of the dose that may be dialed , for example reference numerals ( not shown ), is provided on the outer surface of the dose dial sleeve 70 . the window 44 conveniently only allows to be viewed a visual indication of the dose currently dialed . a second end of the dose dial sleeve 70 is provided with an inwardly directed flange in the form of number of radially extending members 75 . a dose dial grip 76 is disposed about an outer surface of the second end of the dose dial sleeve 70 . an outer diameter of the dose dial grip 76 preferably corresponds to the outer diameter of the main housing 4 . the dose dial grip 76 is secured to the dose dial sleeve 70 to prevent relative movement therebetween . the dose dial grip 76 is provided with a central opening 78 . an annular recess 80 located in the second end of the dose dial grip 76 extends around the opening 78 . a button 82 of generally ‘ t ’ section is provided at a second end of the pen - type injector . a stem 84 of the button 82 may extend through the opening 78 in the dose dial grip 76 , through the inner diameter of the extension 38 of the drive sleeve 30 and into the receiving recess 26 of the piston rod 20 . the stem 84 is retained for limited axial movement in the drive sleeve 30 and against rotation with respect thereto . a head 85 of the button 82 is generally circular . a skirt 86 depends from a periphery of the head 85 . the skirt 86 is adapted to be seated in the annular recess 80 of the dose dial grip 76 . operation of the pen - type injector in accordance with the present invention will now be described . in fig9 , 10 and 11 arrows a , b , c , d , e , f and g represent the respective movements of the button 82 , the dose dial grip 76 , the dose dial sleeve 70 , the drive sleeve 30 , the clutch means 60 , the clicker 50 and the nut 40 . to dial a dose ( fig9 ) a user rotates the dose dial grip 76 ( arrow a ). with the clicker 50 and clutch means 60 engaged , the drive sleeve 30 , the clicker 50 , the clutch means 60 and the dose dial sleeve 70 rotate with the dose dial grip 76 . audible and tactile feedback of the dose being dialed is provided by the clicker 50 and the clutch means 60 . torque is transmitted through the saw teeth 56 , 66 between the clicker 50 and the clutch means 60 . the flexible arm 52 deforms and drags the toothed member 54 over the splines 42 to produce a click . preferably , the splines 42 are disposed such that each click corresponds to a unit dose . the helical groove 74 on the dose dial sleeve 70 and the helical groove 38 in the drive sleeve 30 have the same lead . this allows the dose dial sleeve 70 ( arrow c ) to extend from the main housing 4 and the drive sleeve 30 ( arrow d ) to climb the piston rod 20 at the same rate . at the limit of travel , a radial stop 104 on the dose dial sleeve 70 engages either the first stop 100 or the second stop 102 provided on the main housing 4 to prevent further movement . rotation of the piston rod 20 is prevented due to the opposing directions of the overhauled and driven threads on the piston rod 20 . the nut 40 , keyed to the main housing 4 , is advanced along the intermediate thread 36 by the rotation of the drive sleeve 30 ( arrow d ). when the final dose dispensed position ( fig4 , 5 and 13 ) is reached , a radial stop 106 formed on a second surface of the nut 40 abuts a radial stop 108 on a first surface of the second flange 34 of the drive sleeve 30 , preventing both the nut 40 and the drive sleeve 30 from rotating further . in an alternative embodiment ( not shown ) a first surface of the nut 40 is provided with a radial stop for abutment with a radial stop provided on a second surface of the first flange 32 . this aids location of the nut 40 at the cartridge full position during assembly of the pen - type injector . should a user inadvertently dial beyond the desired dosage , the pen - type injector allows the dosage to be dialed down without dispense of medicinal product from the cartridge ( fig1 ). the dose dial grip 76 is counter rotated . this causes the system to act in reverse . the flexible arm 52 now acts as a ratchet preventing the clicker from rotating . the torque transmitted through the clutch means 60 causes the saw teeth 56 , 66 to ride over one another to create the clicks corresponding to dialed dose reduction . preferable the saw teeth 56 , 66 are so disposed that the circumferential extent of each saw tooth corresponds to a unit dose . when the desired dose has been dialed , the user may then dispense this dose by depressing the button 82 ( fig1 ). this displaces the clutch means 60 axially with respect to the dose dial sleeve 70 causing the dog teeth 65 to disengage . however the clutch means 60 remains keyed in rotation to the drive sleeve 30 . the dose dial sleeve 70 and associated dose dial grip 76 are now free to rotate ( guided by the helical rib 46 located in helical groove 74 ). the axial movement deforms the flexible arm 52 of the clicker 50 to ensure the saw teeth 56 , 66 cannot be overhauled during dispense . this prevents the drive sleeve 30 from rotating with respect to the main housing 4 though it is still free to move axially with respect thereto . this deformation is subsequently used to urge the clicker 50 , and the clutch 60 , back along the drive sleeve 30 to restore the connection between the clutch 60 and the dose dial sleeve 70 when pressure is removed from the button 82 . the longitudinal axial movement of the drive sleeve 30 causes the piston rod 20 to rotate though the opening 18 in the insert 16 , thereby to advance the piston 10 in the cartridge 8 . once the dialed dose has been dispensed , the dose dial sleeve 70 is prevented from further rotation by contact of a plurality of members 110 ( fig1 ) extending from the dose dial grip 76 with a corresponding plurality of stops 112 formed in the main housing 4 ( fig1 and 16 ). in the illustrated embodiment , the members 110 extend axially from the dose dial grip 76 and have an inclined end surface . the zero dose position is determined by the abutment of one of the axially extending edges of the members 110 with a corresponding stop 112 .
a housing for a dispensing apparatus . the housing comprising a main housing and a dose dial sleeve . the dose dial sleeve comprising a helical groove configured to engage a threading provided by the housing . a dose knob is disposed near a proximal end of the dose dial sleeve and a piston rod is provided within the housing . the piston rod is non - rotatable during a dose setting step . a driver comprises an internal threading near a distal portion of the driver and is adapted to engage an external thread of the piston rod . a tubular clutch is located adjacent a distal end of the dose knob and operatively coupled to the dose knob . the dose dial sleeve may extend circumferentially around at least a portion of the tubular clutch .