Abstract:
A door-closing device for a domestic electrical appliance comprises a frame with an aperture for the introduction of a keeper. A closing unit is arranged on the frame such that when in a closing position, the closing unit holds the keeper for the purposed of keeping the door closed and, in an open position, releases said keeper for the purposed of opening the door, said closing unit, in the course of its transfer from the open position into the closing position, draws the keeper along with it. A closing spring arrangement acts upon the closing unit to draw the keeper along with said unit. A blocking element that is movable relative to the frame to block and unblock the movement of the closing unit.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of German Patent Application No. DE 10 2007 044 577.8, filed Sep. 19, 2007, in the German Patent Office. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a door-closing device for a domestic electrical appliance. Particularly, the present invention relates to a door-closing device comprising a frame with an aperture for the introduction of a keeper or the like, a closing unit which is arranged on the frame so as to be movable, relative to the latter, and which, in a closing position, holds the keeper fast for the purpose of keeping the door closed and, in an open position, releases the keeper for the purpose of opening the door, the closing unit, in the course of its transfer from the open position into the closing position, drawing the keeper along with it along part of the keeper&#39;s path of movement, relative to the frame, a closing spring arrangement which acts upon the closing unit and which supplies the force necessary for drawing the keeper along with the unit, and a blocking system by which the closing unit can be blocked from moving out of the open position and into the closing position, it being possible to set aside the blocking of the closing unit by relative movement of said blocking system and closing unit. 
     2. Description of the Prior Art 
     A door-closing device of this kind with a pulling-shut function, that is to say spring-assisted pulling-shut of the door, is known, for example, from US 2005/0194795 A1. In this known solution, a blocking pin is provided which is arranged so as to be integral with the frame. The closing unit comprises a linearly movable carriage on which a rotary member is held so as to be movable about an axis of rotation. An arrangement of a number of helical compression springs is inserted between the carriage and a framework belonging to the door-closing device. The force of the helical compression springs pretensions the rotary member towards the blocking pin. The rotary member possesses a slot which is open in the radially outward direction and into which, when the closing unit is in the open position, the keeper moves on closure of the door. In the process, the keeper strikes against one of the flanks of the slot. This action of the keeper upon the rotary member leads to rotation of the latter about the axis of rotation, the outer peripheral face of said rotary member sliding along the blocking pin. Under these circumstances, considerable frictional forces can operate between the blocking pin and the rotary member, depending upon the firmness of the helical compression springs. While the keeper which has been introduced is rotating the rotary member, that part of said rotary member which adjoins the other flank of the slot engages in a clearance in the keeper. As soon as an edge at which the outer peripheral face of the rotary member bends away in the radially inward direction slips past the blocking pin, the helical compression springs are able to expand and thrust the carriage away. In the course of this displacement of the carriage, the keeper is drawn along with the rotary member by the latter, which now presses, with the other flank of its slot, against said keeper. 
     Another door fastener with a pulling-shut function, which door fastener is not a generic one however, is known from EP 1 344 486 A2. In this door fastener, a rotary member, to which a helical compression spring which supplies the pulling-shut force is attached by one of its ends, serves as the closing unit. When the fastener is in an open state, the straight line of force extending between the points at which the helical compression spring is attached lies on one side of the axis of rotation of the rotary member and pretensions the latter in the direction of an open position. When the fastener is closed, the straight line of force of the helical compression spring moves away over the axis of rotation of the rotary member and comes to rest on the other side of said axis of rotation. The pretensioning action of the helical compression spring is then in the direction of the closing position of the rotary member. In order to close the door, it is therefore first necessary to operate against the force of the helical compression spring. This comes about through the fact that a keeper which has been introduced strikes against one of the flanks of a slot constructed in the rotary member and thereby moves the latter away over the dead centre at which the straight line of force of the helical compression spring passes precisely through the axis of rotation. As soon as the dead centre has been crossed, the spring expands and drives the rotary member into its closing position. In the process, the keeper which is now trapped in the slot in the rotary member is drawn along with it. What is problematic about the fastener according to EP 1 344 486 A2 is that, for a low initial force of resistance when the door is being closed, the straight line of force of the helical compression spring is supposed to be removed only a little way from the dead-centre position, but this at the same time entails an increased susceptibility to unwanted automatic closing of the catch if vibration or jolting occurs. 
     German Laying-Open Specification DE 10 2006 037 494 A1, which was published subsequently, indicates a door-closing device with a pulling-shut function in which, on closure of the door, a closing body with a projecting nose plunges into a closing trough formed on the door and then snaps back under the action of an expanding closing spring, as a result of which the door is pulled shut. Said door first of all strikes against a control lever which is separated from the closing body and which is set in motion as a result. The rotating control lever in turn presses the closing body down against a blocking face formed by a base frame of the closing device. As soon as the closing body passes the blocking face, the closing spring is able to expand. 
     German Laying-Open Specification DE 10 2007 025 295 A1, which was likewise published subsequently, indicates a door fastener having a closing member which is guided, via two spindles, so as to be movable within a guide groove in a fastener housing and which, on closure of the door, grasps a closing catch arranged on the door and then moves, under the action of an expanding closing spring, in such a way that the door catch is pulled into the fastener. The course of the guide groove exhibits an inflexion which has to be overcome by one of the spindles of the closing member so that the closing spring is able to expand for the purpose of deploying its pulling-shut action. 
     SUMMARY OF THE INVENTION 
     The object of the invention is to provide a door-closing device of the type initially referred to, which can be closed with high functional reliability and little expenditure of force and which, in addition, can preferably provide high holding power when in the closed state. 
     In order to achieve this object, a door-closing device of generic type is characterised, according to the invention, in that the blocking system is formed by a blocking element which is arranged so as to be movable, relative to the frame, between a blocking position and a releasing position and which, in the blocking position, prevents a movement of the closing unit out of the open position and into the closing position and, in the releasing position, permits such a movement of the closing unit, and that the blocking element is constructed and arranged in such a way that it can be lifted by the keeper out of its blocking position and into its releasing position, against the action of a restoring force, on closure of the door. 
     The door-closing device according to the invention can be used, for example, in washing machines, dishwashers or tumble driers. When it is introduced into the aperture in the frame, the keeper, which is constructed, for example, with a leading transverse stud, lateral cheeks adjoining the latter and a gripping recess, which lies behind said transverse stud and between the lateral cheeks, for a gripping section of the closing unit, impinges upon the blocking element and lifts the latter out of its blocking position and into the releasing position. As a result of this, the closing unit becomes free and is able to move into the closing position under the action of the closing spring arrangement. It is thus possible, with simple means, to guarantee high stability of the blocking arrangement which is not susceptible to shaking or vibrating influences. At the same time, a design which permits unblocking of the closing unit with comparatively little expenditure of force is also possible. 
     According to one further development of the invention, the closing unit may, when the door-closing device is in a state preparatory to closing, prior to the introduction of the keeper into the aperture in the frame, be in blocking abutting contact with the blocking element, said closing unit being constructed and arranged in such a way that, on closure of the door, said unit is initially lifted by the keeper out of blocking abutting contact with said blocking element in the direction away from the closing position, before said keeper forces the blocking element into its releasing position. In this configuration, the blocking element is first of all relieved of load through the fact that the keeper which has been introduced drives the closing unit out of the open position and slightly in the direction away from the closing position, and therefore out of abutment against the blocking element. In its open position, the closing unit accordingly possesses a certain degree of mobility in the direction away from its closing position. In this context, “open position” means that position of the closing unit which it normally assumes when the door is open. The relieving of the load on the blocking element as a result of deflection of the closing unit by the incoming keeper then facilitates the lifting-out of the blocking element and thus the closing operation as a whole. 
     The provision of a blocking element which can be moved separately and the actuation of said element by the keeper also permit reliable identification of the state of the door (i.e. open or closed). An electrical switch, which interacts with the blocking element and the switching state of which depends upon the position of said element, may be provided for this purpose. Under these circumstances, the closing unit and blocking element are advantageously constructed and arranged in such a way that, when the closing unit is in the closing position with the keeper absent, the blocking element at least approximately assumes its blocking position. 
     If, in this configuration, the blocking element is lifted, when the door is open, out of its blocking position either inadvertently or intentionally, for instance by a playing child who penetrates the frame with an object through the aperture in said frame, the closing unit which has now been released admittedly turns over into its closing position. However the blocking element is able, when the playing child lets go of it again, to return to its blocking position in which the electrical switch assumes the same switching state as when the door-closing device is in the normal, open state. Although, therefore, the closing unit has passed over into its closing position, the electrical switch nevertheless continues—correctly—to indicate an open door. Only when the door has actually been closed and the keeper has been introduced into the aperture in the frame is the blocking element held in its releasing position by the keeper. The switch then correctly indicates the closed state of the door. 
     The blocking element is preferably formed by a blocking lever which is mounted so as to be pivotable, relative to the frame. Alternatively, said blocking element may be formed, for example, by a blocking slide which is guided so as to be movable in a linear manner, relative to said frame. In these cases, a separate pretensioning element which generates the restoring force is expediently associated with the blocking element. 
     The blocking element may also alternatively be formed, according to one variation, by a flexible blocking body. In this case, it is possible to dispense with an additional pretensioning element for generating the restoring force; the restoring force may be generated by the blocking body itself in the course of its elastic deflection. Said blocking body may, for example, be produced from spring steel sheet. 
     The closing unit may be formed by a rotary member which is rotatable about an axis of rotation which is stationary, relative to the frame, and the axis of rotation of which member extends at a radial distance from the path of movement of the keeper, relative to the frame. Under these circumstances, the rotary member preferably has a radially protruding gripping section which grasps the keeper, on closure of the door, and draws said keeper along with itself while rotating the rotary member, the movement of the gripping section after the grasping of the keeper possessing a substantial, in particular predominant, component in the direction of the path of movement of the keeper. In this way, a major tractive force can be exerted on said keeper by the rotary member. 
     The closing spring arrangement may comprise at least one spiral spring which acts upon the rotary member and is loaded in tension or compression and the straight line of force of which, observed in a section normal to the axis, always lies on the same side of the axis of rotation, but is at a smaller radial distance from said axis of rotation in the open position than in the closing position. This is advantageous in so far as the radial distance of the straight line of force from the axis of rotation, which distance is becoming increasingly greater, permits great closing force when the door is being closed. This is favourable for leakproof and secure closing of the door. 
     As an alternative to a spiral spring which is loaded in tension or compression, the closing spring arrangement may comprise, for example, at least one torsion spring that acts upon the rotary member. 
     Irrespective of its actual mobility (whether rotatable or of another kind) in relation to the frame, the closing unit is preferably formed by a single closing body, the said closing body having a gripping section which grasps the keeper, on closure of the door, and draws said keeper along with itself while moving the closing body. Under these circumstances, the movement of the gripping section after the grasping of the keeper possesses an at least predominant component in the direction of the path of movement of said keeper, a fact which—as has already been alluded to above—is favourable for a high tractive force upon the keeper. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be explained in greater detail below with the aid of the appended drawings, in which: 
         FIGS. 1 and 2  represent perspective views of a door-closing device according to a first exemplified embodiment; 
         FIG. 3  represents a sectional view of the door-closing device in  FIGS. 1 and 2 , in a state preparatory to closing; 
         FIG. 4  represents a sectional view of the door-closing device in  FIGS. 1 and 2 , during a closing operation; 
         FIG. 5  represents a sectional view of the door-closing device in  FIGS. 1 and 2 , after the door has been closed; 
         FIG. 6  represents a sectional view of the door-closing device in  FIGS. 1 and 2 , in a closing state without the keeper introduced; 
         FIGS. 7 and 8  represent partially cut-away perspective views of the door-closing device in  FIGS. 1 and 2  for the purpose of illustrating the dependence of the switching state of an electrical switch upon the position of a blocking element belonging to the door-closing device; 
         FIGS. 9 and 10  represent perspective views of a door-closing device according to a second exemplified embodiment; 
         FIG. 11  represents a sectional view of the door-closing device in figures  9  and  10 , in a state preparatory to closing; 
         FIG. 12  represents a sectional view of the door-closing device in figures  9  and  10 , during a closing operation; and 
         FIG. 13  represents a sectional view of the door-closing device in  FIGS. 9 and 10 , with the door closed. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     For the purpose of explaining the first exemplified embodiment, reference will initially be made, in particular, to  FIGS. 1 to 3 . A door-closing device, which is designated generally by  10 , is shown therein in a state preparatory to closing, in which it is being prepared for closing the door of a domestic electrical appliance, for instance a washing machine or a dishwasher. The door-closing device  10  comprises a framework  12  on which various other components of said device are mounted and which, according to one variant, is intended and constructed for installation in the main housing of the domestic appliance. Said framework  12  possesses an aperture  14  into which a keeper (door catch)  16 , which in this variant is located on the door, moves on closure of the door of the domestic appliance. The keeper  16  possesses a point  18  behind which a gripping clearance  20  is located. In the sectional representation in  FIG. 3 , it can be seen that the point  18  of the keeper possesses lateral flanks that run towards one another obliquely. 
     In another variant, the framework  12  is mounted, by means of its installing components, on the door of the domestic appliance, while the keeper  16  is fitted to the main housing of said appliance. The door serves to occlude an aperture through which a working space provided in the main housing of the appliance is accessible for the purpose of receiving dishes, washing or the like. In many cases, a so-called “door seal”, which is compressed to a greater or lesser extent when the door is closed, will extend around the access aperture. This door seal may be fitted to the door or to the main housing of the appliance. For the purpose of compressing the door seal, a force is necessary which is applied, at least partially, by the door-closing device  10  itself, namely by spring means which will be described in greater detail later on and which expand on closure of the door and, in the process, pull said door towards the main housing of the appliance. 
     A rotary member  22  which serves as the closing unit is held on the framework  12  so at to be rotationally movable about an axis of rotation  24  which is integral with the frame. In the state preparatory to closing according to  FIG. 3 , the rotary member  22  is in a so-called “open position”, from which it can be rotated in the clockwise direction into a closing position which is shown in  FIG. 5 . In addition to this, the rotary member  22  can be deflected out of the open position in  FIG. 3  in the anticlockwise direction by a small amount and into the rotational position shown in  FIG. 4 . In each rotational position, the rotary member  22  is pretensioned by a closing spring  26  in the direction of the closing position according to  FIG. 5 . In the exemplified embodiment in  FIGS. 1 to 8 , said closing spring  26  is formed by a spiral spring which acts as a leg spring, i.e. is loaded in rotation, and the axis of which substantially coincides with the axis of rotation  24  of the rotary member  22 . 
     Rotary member  22  possesses a radially protruding gripping or entraining section  28  which, in the open position according to  FIG. 3 , projects slightly into the path of movement of the keeper  16 , namely in such a way that said keeper  16 , when it moves into the frame aperture  14  (i.e. on closure of the door), impinges upon the gripping section  28  with the lower oblique flank of its point  18 . This brings about the aforementioned slight deflection of the rotary member  22  into the rotational position according to  FIG. 4 . 
     The path of movement of the keeper  16 , relative to the frame  12  and therefore relative to the rotary member  22  which is held in said frame  12 , is indicated by an arrow  29  in  FIG. 3 . Although the door will normally be fitted to the main housing of the appliance in a pivotingly movable manner, the relative path of movement of the keeper  16  can be regarded as being approximately rectilinear on a small scale, i.e. over short distances, even if, on the whole, it follows a circular path. That is why the arrow  29  is drawn in as a straight arrow in  FIG. 3 . 
     The path of movement of the keeper  16 , relative to the frame  12 , extends at a radial distance from the axis of rotation  24  of the rotary member  22 . This becomes clear if the arrow  29  in  FIG. 3  is imagined as being prolonged; it then runs past said axis of rotation  24  at a radial distance above the latter. 
     In the open position according to  FIG. 3 , the rotary member  22  is prevented by a blocking lever  30  from rotating into the closing position according to  FIG. 5 . Said blocking lever  30  is held on the framework  12  so as to be pivotingly movable about an axis of pivoting  32  extending parallel to the axis of rotation  24 . It possesses a blocking shoulder  34  with which a radially projecting nose  36  on the rotary member  22  interacts. Said blocking lever  30  possesses axially, on either side of the blocking shoulder  34 , extensions  38  with which the keeper  16  interacts on closure of the door. The nose  36  on the rotary member  22  moves freely between said extensions  38  on the blocking lever  30 . 
     The blocking lever  30  is pivotingly movable between a blocking position which is shown in  FIG. 3  and a releasing position which is shown in  FIG. 5 . A pretensioning element  40  which is constructed, in this case, as a leg spring pretensions the blocking lever  30  in the direction of its blocking position according to  FIG. 3 . The end faces of its extensions  38  form contact surfaces for the keeper  16  which, on moving into the aperture  14  in the frame, strikes against the said end faces with its point  18 , as is shown in  FIG. 4 . If the keeper  16  is then advanced further, it presses the blocking lever  30  upwards out of the blocking position and in the direction of the releasing position against the force of the pretensioning spring  40 . This state is shown in  FIG. 5 . 
     In the releasing position, the blocking shoulder  34  is moved radially out of the range of the nose  36  on the rotary member  22 , so that the latter is able to rotate unhindered into its closing position. However said rotary member  22  moves into its closing position only when the keeper  16  has moved into the aperture  14  in the frame sufficiently far for the gripping section  28  of the rotary member  22  to be able to plunge into the gripping clearance  20  in the keeper  16 . As soon as the gripping section  28  engages in the gripping clearance  20 , the rotary member  22 , in the course of its rotation into the closing position, pulls the keeper  16  deeper into the aperture  14  in the frame. The force needed for this pulling-shut movement is applied by the closing spring  26 , which expands as the rotary member  22  moves from the open position into the closing position. 
     When the rotary member  22  rotates, the gripping section  28  follows a circular path. During the phase in which the gripping section  28  is in entraining engagement with the keeper  16 , said gripping section  28  moves along one such part of the said circular path, on which part it has a substantial, in particular predominant, component in the direction of the path of movement of the keeper  16 , that is to say in the direction of the arrow  29 . As a result of this, the rotary member  22  is able to exert a comparatively high entraining force upon the keeper  16  in the direction of the arrow  29 . This force may, at the same time, bring about, or at least assist in, the compression of a door seal which may optionally be present on the domestic appliance. 
     In the closing state according to  FIG. 5 , the blocking lever  30  continues to be held in its releasing position by the keeper  16 . Under these circumstances, the extensions  38  on the blocking lever  30  are supported, in a manner of which no further details are represented, against side walls which laterally delimit the gripping clearance  20  in the keeper  16 . 
     On closure of the door, there first of all takes place the deflection of the rotary member  22  into the position according to  FIG. 4 , as a result of which the abutting contact between the nose  36  and the blocking shoulder  34  is set aside. This relieves the load on the blocking lever  30 , a fact which facilitates the subsequent lifting-out of the latter by the keeper  16 . It should be pointed out, of course, that it is possible, according to one variation, to dispense with prior deflection of the rotary member  22  for the purpose of terminating the abutting contact with the blocking lever  30 . In this variation, the keeper  16  moves past the gripping section  28  on being introduced into the aperture  14  in the frame, without coming into deflecting contact with said gripping section and pressing it downwards. The lifting-out of the blocking lever  30  by means of the keeper  16  which is moving in then takes place, without any change, in the manner which has been described so far, although of course the abutting contact that continues to exist between the nose  36  and the blocking shoulder  34  leads, under certain circumstances, to increased, friction-induced resistance. 
     Situations can be conceived of in which the rotary member  22  passes into its closing position without closing the door in the process. This can happen, for example, if a child is playing with the door-closing device and sticks an object into the aperture  14  in the frame. If the child strikes against the blocking lever  30  sufficiently hard, the possibility of the rotary member  22  being released and rotating into its closing position cannot be ruled out. In such an event, the blocking lever  30  can return, after the playing child has let go of it again, to its blocking position without colliding with the rotary member  22 . As can be clearly seen in  FIG. 6 , after the return of the blocking lever  30  into the blocking position, the gripping section  28  of the rotary member  22  is located in the clear space formed between the extensions  38  on said blocking lever  30 . Reciprocal obstruction of the rotary member  22  and blocking lever  30  does not take place in this state. 
     The ability of the blocking lever  30  to still return substantially into its blocking position after irregular actuation of the rotary member  22  (in this case, “irregular” means: without the introduction of the keeper  16 ) can advantageously be utilised in conjunction with an electrical switch that indicates the closing state of the door-closing device. A switch of this kind is shown at  42  in  FIG. 2 . In addition, it can be seen, in  FIGS. 7 and 8 , that the blocking lever  30  possesses an actuating section  44  which is constructed here as an arm which projects away laterally and which serves to actuate a mechanical sensor  46  belonging to the electrical switch  42 . In the state according to  FIG. 7 , the blocking lever  30  assumes its blocking position. In this state, the actuating section  44  presses the sensor  46  down, a fact which corresponds to a first switching state of the electrical switch  42 . In  FIG. 8 , on the other hand, the blocking lever  30  is located in its releasing position in which it is held by the keeper  16  which has been introduced. In this state, the actuating section  44  no longer presses on the sensor  46 , a fact which corresponds to a second switching state of the electrical switch  42 . The switching state of said electrical switch  42  accordingly gives reliable information as to whether the door is closed or open. For only when the door is actually closed does the blocking lever  30  remain in its releasing position; without the keeper  16  introduced, it returns at least approximately to its blocking position, at any rate after the door-closing device has been left alone again. 
     As an alternative to an inherently rigid blocking element, the blocking element may conceivably be manufactured from a flexible material, say from a piece of spring steel sheet. In such a case, it is possible to dispense with a separate pretensioning spring for said blocking element. 
     For the purpose of explaining the second exemplified embodiment, reference will now be made to  FIGS. 9 to 13 . In said second exemplified embodiment, components which are identical or which have an identical action are provided with the same reference symbols as before, but with the addition of a lower-case letter. In order to avoid unnecessary repetitions, the reader is referred to the above description of the first exemplified embodiment, provided that nothing to the contrary arises below. 
     The exemplified embodiment in  FIGS. 9 to 13  differs from the first exemplified embodiment substantially as a result of a different way of generating the spring pretensioning for the rotary member  22   a.  In concrete terms, two helical draw springs  26   a  serve to generate the said pretensioning. The rotary member  22   a,  which is of disc-like design, is designed, on each of its axial sides, with an axially protruding peg  48   a  which is arranged eccentrically to the axis of rotation  24   a  and to which one of the helical draw springs  26   a  is attached, in each case, by one of its ends. At their other ends, the two helical draw springs  26   a  are attached to the framework  12   a  in each case, as is indicated at  50   a  in  FIGS. 11 to 13 . The drawing action of each of the helical draw springs  26   a  extends along a straight line which connects the two points of attachment of the helical draw spring  26   a  in question to the framework  12   a  and to the rotary member  22   a.  In  FIGS. 11 and 13 , a straight line of this kind is indicated at  52   a.  It will also be referred to below as the “straight line of force” of the helical draw spring  26   a  in question. 
     The location of the straight line of force  52   a  of each helical draw spring  26   a  varies with respect to the axis of rotation  24   a  on account of the variable rotational position of the rotary member  22   a  when the door is opened and closed, and the eccentricity of the attachment pegs  48   a.  In concrete terms, the straight line of force  52   a  moves within a plane which extends transversely, and in particular normally, to the axis of rotation  24   a,  said straight line of force always lying on the same side of the axis of rotation  24   a  and always being at a radial distance from the latter. In the state preparatory to closing according to  FIG. 11  (which corresponds to the open position of the rotary member  22   a ), this radial distance is comparatively small, whereas in the closing state according to  FIG. 13  (which corresponds to the closing position of said rotary member  22   a ), the radial distance between the straight line of force  52   a  and the axis of rotation  24   a  is substantially greater. Although the helical draw springs  26   a  are tensioned more weakly when the door-closing device is in the closing state than when it is in the state preparatory to closing, a comparatively large closing momentum, which guarantees reliable, leakproof closing of the door, is nevertheless operative because of the larger radial distance of the straight line of force  52   a  from the axis of rotation  24   a.  On the other hand, the operative torque exerted by the helical draw springs  26   a  on the rotary member  22   a  is comparatively small, when the door-closing device is in the state preparatory to closing, on account of the smaller radial distance of the straight line of force  52   a  from the axis of rotation  24   a,  although the helical draw springs  26   a  are under stronger tension than in the closing state. This is advantageous, among other things, for gentle opening of the door. 
     In the second exemplified embodiment too, as in the first, the keeper  16   a  can initially, on moving into the aperture  14   a  in the frame, easily deflect the rotary member  22   a  out of its open position and in the direction away from the closing position, in order to thus set aside the abutting contact between the nose  36   a  on the rotary member  22   a  and the blocking shoulder  34   a  on the blocking lever  30   a,  before the keeper  16   a  presses said blocking lever  30   a  up into its releasing position. Even in the case of such prior deflection of the rotary member  22   a,  the straight line of force  52   a  of each helical draw spring  26   a  remains at a certain radial distance from the axis of rotation  24   a,  so that pretensioning in the direction of the closing position is operative in any rotational position of said rotary member  22   a.  It is obviously possible, of course, even in the case of the second exemplified embodiment, to dispense with the prior slight deflection of the rotary member  22   a  if desired. 
     Although the preferred embodiments of the present invention have been described herein, the above description is merely illustrative. Further modification of the invention herein disclosed will occur to those skilled in the respective arts and all such modifications are deemed to be within the scope of the invention as defined by the appended claims.